sun tracking system using micro controller
TRANSCRIPT
CHAPTER 1
INTRODUCTION
11 PROJECT BACKGROUND
As the range of applications for solar energy increases so it needs
for improved materials and methods used to harness this power source
There are several factors that affect the efficiency of the collection process
Major influences on overall efficiency include solar cell efficiency intensity
of source radiation and storage techniques The materials used in solar cell
manufacturing limit the efficiency of a solar cell This makes it particularly
difficult to make considerable improvements in the performance of the cell
and hence restricts the efficiency of the overall collection process
Therefore the most attainable method of improving the performance of solar
power collection is to increase the mean intensity of radiation received from
the source
12 JUSTIFICATION FOR THE PROJECT
There are three distinct methods of increasing the mean intensity of
solar radiation received by a solar array These include focusing the incident
rays tracking the path of the sun using fixed control algorithms and
dynamic tracking
The first method involves focusing incident rays onto a rigid array
this allows incident rays to reach the array normal to the array surface The
second method uses a controller device to determine the position of the sun
with reference to the current day month and year The dynamic tracking is
1
similar to this method however sensors are used to determine the current
position of the radiation source
Currently there are a number of variations on each of these methods
The research undertaken in this thesis is directed towards the design of a
dynamic tracking system The dynamic tracking system was chosen because
it proposed the most accurate method of maintaining maximum power
collection possible
13 DEFINITION OF PROJECT
The objective of this thesis is to design a Sun Tracking Solar Array
System The concise definition of this system is as follows A
microcontrolled solar array that actively tracks the sun so that maximum
power is received by the array at all times This is achieved by using sensors
to locate the suns position at any instance and aligning the array using the
microcontroller so that all incident rays are normal to the array surface
14 SCOPE OF PROJECT
The scope of this project only encompasses the design of the
tracking system There has been no formal consideration of optimizing
power used by the tracking device or the affect of heat on the performance
of the array
2
15 PROJECT OVERVIEW
The remaining chapters detail the research design and analysis
performed during the course of the thesis project
Chapter 2 discusses theory associated with solar cell technology and the
optimizing of power received by an array This incorporates a review of
relevant literature and current designs in the field of sun tracking
Chapter 3 explains the methodology used while forming a solution to the
problem and the design considerations undertaken in this process
Chapter 4 gives an analysis of the design and data obtained during testing
Chapter 5 concludes the report by discussing the effectiveness of the
tracking system and possible applications This chapter also suggests some
further research areas and future design proposals
3
CHAPTER 2
BACKGROUND THEORY
21 INTRODUCTION
Before beginning the design of the tracking system it was
necessary to obtain some background information on solar cells and methods
of energy collection It was equally important to research the various
tracking systems available To obtain this information a study of relevant
literature was conducted This study involved a review of solar cell theory
an investigation into the sources of loss in solar systems and an examination
of current tracking methods
22 SOLAR CELL THEORY
Nuclear fusion reactions on the suns surface supply earth with solar
energy This energy is primarily released in the form of electromagnetic
radiation in the ultraviolet infrared and radio spectral regions (wavelengths
from 02 to3microm)Presently the most efficient means of harnessing this
power source is the solar cell which converts solar radiation directly into
electricity Solar cells are fabricated from various semiconductor materials
using numerous device configurations and selecting single-crystal
polycrystal and amorphous thin-film structures To following theory
considers the silicon p-n junction cell because it acts as
1Reference device for all solar cells
2The solar cell has a single energy bandgap
4
When the cell is exposed to the solar spectrum a photon with
energy less than Eg makes no contribution to the cell output A photon with
energy greater than Eg contributes an energy Eg to the cell output and the
remaining energy is wasted as heat The idealized equivalent circuit of the
cell is shown in Figure 1(b) where a constant-current source is in parallel
with the junction The source IL results from the excitation of excess carriers
by solar radiation Rs is the diode saturation current and RL is the load
resistance
(b) Figure 1 (a) Energy-band diagram of a silicon p-n junction solar
cell under solar irradiation (b) Idealised equivalent circuit of a solar cell
5
A typical schematic representation of a solar cell is shown in Figure 2 It
consists of a shallow p-n junction formed on the surface (eg by diffusion)
a front ohmic contactstripe and fingers a back ohmic contact that covers the
entire back surface and an antireflection coating on the front surface
6
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
similar to this method however sensors are used to determine the current
position of the radiation source
Currently there are a number of variations on each of these methods
The research undertaken in this thesis is directed towards the design of a
dynamic tracking system The dynamic tracking system was chosen because
it proposed the most accurate method of maintaining maximum power
collection possible
13 DEFINITION OF PROJECT
The objective of this thesis is to design a Sun Tracking Solar Array
System The concise definition of this system is as follows A
microcontrolled solar array that actively tracks the sun so that maximum
power is received by the array at all times This is achieved by using sensors
to locate the suns position at any instance and aligning the array using the
microcontroller so that all incident rays are normal to the array surface
14 SCOPE OF PROJECT
The scope of this project only encompasses the design of the
tracking system There has been no formal consideration of optimizing
power used by the tracking device or the affect of heat on the performance
of the array
2
15 PROJECT OVERVIEW
The remaining chapters detail the research design and analysis
performed during the course of the thesis project
Chapter 2 discusses theory associated with solar cell technology and the
optimizing of power received by an array This incorporates a review of
relevant literature and current designs in the field of sun tracking
Chapter 3 explains the methodology used while forming a solution to the
problem and the design considerations undertaken in this process
Chapter 4 gives an analysis of the design and data obtained during testing
Chapter 5 concludes the report by discussing the effectiveness of the
tracking system and possible applications This chapter also suggests some
further research areas and future design proposals
3
CHAPTER 2
BACKGROUND THEORY
21 INTRODUCTION
Before beginning the design of the tracking system it was
necessary to obtain some background information on solar cells and methods
of energy collection It was equally important to research the various
tracking systems available To obtain this information a study of relevant
literature was conducted This study involved a review of solar cell theory
an investigation into the sources of loss in solar systems and an examination
of current tracking methods
22 SOLAR CELL THEORY
Nuclear fusion reactions on the suns surface supply earth with solar
energy This energy is primarily released in the form of electromagnetic
radiation in the ultraviolet infrared and radio spectral regions (wavelengths
from 02 to3microm)Presently the most efficient means of harnessing this
power source is the solar cell which converts solar radiation directly into
electricity Solar cells are fabricated from various semiconductor materials
using numerous device configurations and selecting single-crystal
polycrystal and amorphous thin-film structures To following theory
considers the silicon p-n junction cell because it acts as
1Reference device for all solar cells
2The solar cell has a single energy bandgap
4
When the cell is exposed to the solar spectrum a photon with
energy less than Eg makes no contribution to the cell output A photon with
energy greater than Eg contributes an energy Eg to the cell output and the
remaining energy is wasted as heat The idealized equivalent circuit of the
cell is shown in Figure 1(b) where a constant-current source is in parallel
with the junction The source IL results from the excitation of excess carriers
by solar radiation Rs is the diode saturation current and RL is the load
resistance
(b) Figure 1 (a) Energy-band diagram of a silicon p-n junction solar
cell under solar irradiation (b) Idealised equivalent circuit of a solar cell
5
A typical schematic representation of a solar cell is shown in Figure 2 It
consists of a shallow p-n junction formed on the surface (eg by diffusion)
a front ohmic contactstripe and fingers a back ohmic contact that covers the
entire back surface and an antireflection coating on the front surface
6
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
15 PROJECT OVERVIEW
The remaining chapters detail the research design and analysis
performed during the course of the thesis project
Chapter 2 discusses theory associated with solar cell technology and the
optimizing of power received by an array This incorporates a review of
relevant literature and current designs in the field of sun tracking
Chapter 3 explains the methodology used while forming a solution to the
problem and the design considerations undertaken in this process
Chapter 4 gives an analysis of the design and data obtained during testing
Chapter 5 concludes the report by discussing the effectiveness of the
tracking system and possible applications This chapter also suggests some
further research areas and future design proposals
3
CHAPTER 2
BACKGROUND THEORY
21 INTRODUCTION
Before beginning the design of the tracking system it was
necessary to obtain some background information on solar cells and methods
of energy collection It was equally important to research the various
tracking systems available To obtain this information a study of relevant
literature was conducted This study involved a review of solar cell theory
an investigation into the sources of loss in solar systems and an examination
of current tracking methods
22 SOLAR CELL THEORY
Nuclear fusion reactions on the suns surface supply earth with solar
energy This energy is primarily released in the form of electromagnetic
radiation in the ultraviolet infrared and radio spectral regions (wavelengths
from 02 to3microm)Presently the most efficient means of harnessing this
power source is the solar cell which converts solar radiation directly into
electricity Solar cells are fabricated from various semiconductor materials
using numerous device configurations and selecting single-crystal
polycrystal and amorphous thin-film structures To following theory
considers the silicon p-n junction cell because it acts as
1Reference device for all solar cells
2The solar cell has a single energy bandgap
4
When the cell is exposed to the solar spectrum a photon with
energy less than Eg makes no contribution to the cell output A photon with
energy greater than Eg contributes an energy Eg to the cell output and the
remaining energy is wasted as heat The idealized equivalent circuit of the
cell is shown in Figure 1(b) where a constant-current source is in parallel
with the junction The source IL results from the excitation of excess carriers
by solar radiation Rs is the diode saturation current and RL is the load
resistance
(b) Figure 1 (a) Energy-band diagram of a silicon p-n junction solar
cell under solar irradiation (b) Idealised equivalent circuit of a solar cell
5
A typical schematic representation of a solar cell is shown in Figure 2 It
consists of a shallow p-n junction formed on the surface (eg by diffusion)
a front ohmic contactstripe and fingers a back ohmic contact that covers the
entire back surface and an antireflection coating on the front surface
6
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
CHAPTER 2
BACKGROUND THEORY
21 INTRODUCTION
Before beginning the design of the tracking system it was
necessary to obtain some background information on solar cells and methods
of energy collection It was equally important to research the various
tracking systems available To obtain this information a study of relevant
literature was conducted This study involved a review of solar cell theory
an investigation into the sources of loss in solar systems and an examination
of current tracking methods
22 SOLAR CELL THEORY
Nuclear fusion reactions on the suns surface supply earth with solar
energy This energy is primarily released in the form of electromagnetic
radiation in the ultraviolet infrared and radio spectral regions (wavelengths
from 02 to3microm)Presently the most efficient means of harnessing this
power source is the solar cell which converts solar radiation directly into
electricity Solar cells are fabricated from various semiconductor materials
using numerous device configurations and selecting single-crystal
polycrystal and amorphous thin-film structures To following theory
considers the silicon p-n junction cell because it acts as
1Reference device for all solar cells
2The solar cell has a single energy bandgap
4
When the cell is exposed to the solar spectrum a photon with
energy less than Eg makes no contribution to the cell output A photon with
energy greater than Eg contributes an energy Eg to the cell output and the
remaining energy is wasted as heat The idealized equivalent circuit of the
cell is shown in Figure 1(b) where a constant-current source is in parallel
with the junction The source IL results from the excitation of excess carriers
by solar radiation Rs is the diode saturation current and RL is the load
resistance
(b) Figure 1 (a) Energy-band diagram of a silicon p-n junction solar
cell under solar irradiation (b) Idealised equivalent circuit of a solar cell
5
A typical schematic representation of a solar cell is shown in Figure 2 It
consists of a shallow p-n junction formed on the surface (eg by diffusion)
a front ohmic contactstripe and fingers a back ohmic contact that covers the
entire back surface and an antireflection coating on the front surface
6
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
When the cell is exposed to the solar spectrum a photon with
energy less than Eg makes no contribution to the cell output A photon with
energy greater than Eg contributes an energy Eg to the cell output and the
remaining energy is wasted as heat The idealized equivalent circuit of the
cell is shown in Figure 1(b) where a constant-current source is in parallel
with the junction The source IL results from the excitation of excess carriers
by solar radiation Rs is the diode saturation current and RL is the load
resistance
(b) Figure 1 (a) Energy-band diagram of a silicon p-n junction solar
cell under solar irradiation (b) Idealised equivalent circuit of a solar cell
5
A typical schematic representation of a solar cell is shown in Figure 2 It
consists of a shallow p-n junction formed on the surface (eg by diffusion)
a front ohmic contactstripe and fingers a back ohmic contact that covers the
entire back surface and an antireflection coating on the front surface
6
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
A typical schematic representation of a solar cell is shown in Figure 2 It
consists of a shallow p-n junction formed on the surface (eg by diffusion)
a front ohmic contactstripe and fingers a back ohmic contact that covers the
entire back surface and an antireflection coating on the front surface
6
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
23 CONVERTING PHOTONS TO ELECTRONS
The solar cells that you see on calculators and satellites are
photovoltaic cells or modules (modules are simply a group of cells
electrically connected and packaged in one frame) Photovoltaics as the
word implies (photo = light voltaic = electricity) convert sunlight directly
into electricity Once used almost exclusively in space photovoltaics are
used more and more in less exotic ways
They could even power your house How do these devices work
Photovoltaic (PV) cells are made of special materials called semiconductors
such as silicon which is currently the most commonly used Basically when
light strikes the cell a certain portion of it is absorbed within the
semiconductor material This means that the energy of the absorbed light is
transferred to the semiconductor The energy knocks electrons loose
allowing them to flow freely
PV cells also all have one or more electric fields that act to force
electrons freed by light absorption to flow in a certain direction This flow of
electrons is a current and by placing metal contacts on the top and bottom of
the PV cell we can draw that current off to use externally For example the
current can power a calculator This current together with the cells voltage
(which is a result of its built-in electric field or fields) defines the power (or
wattage) that the solar cell can produce Thats the basic process but theres
really much more to it Lets take a deeper look into one example of a PV
cell the single crystal silicon cell
7
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
24 WHEN LIGHT HITS THE CELL
When light in the form of photons hits our solar cell its energy frees
electron-hole pairs Each photon with enough energy will normally free
exactly one electron and result in a free hole as The effect of the electric
field in a PV cell If this happens close enough to the electric field or if free
electron and free hole happen to wander into its range of influence the field
will send the electron to the N side and the hole to the P side
This causes further disruption of electrical neutrality and if we
provide an external current path electrons will flow through the path to their
original side (the P side) to unite with holes that the electric field sent there
doing work for us along the way The electron flow provides the current and
the cells electric field causes a voltage With both current and voltage we
have power which is the product of the two How much sunlight energy
does our PV cell absorb Unfortunately the most that our simple cell could
absorb is around 25 percent and more likely is 15 percent or less
25 ENERGY LOSS
Solar cell absorbs only about 15 percents of the sunlights energy
Visible light is only part of the electromagnetic spectrum Electromagnetic
radiation is not monochromatic -- it is made up of a range of different
wavelengths and therefore energy levels (See How Special Relativity
Works for a good discussion of the electromagnetic spectrum) Light can be
separated into different wavelengths and we can see them in the form of a
rainbow Since the light that hits our cell has photons of a wide range of
energies it turns out that some of them wont have enough energy to form an
electron-hole pair
8
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Theyll simply pass through the cell as if it were transparent Still
other photons have too much energy Only a certain amount of energy
measured in electron volts (eV) and defined by our cell material (about 11
eV for crystalline silicon) is required to knock an electron loose We call
this the band gap energy of a material
If a photon has more energy than the required amount then the extra
energy is lost (unless a photon has twice the required energy and can create
more than one electron-hole pair but this effect is not significant) These
two effects alone account for the loss of around 70 percent of the radiation
energy incident on our cell Our band gap also determines the strength
(voltage) of our electric field and if its too low then what we make up in
extra current (by absorbing more photons) we lose by having a small
voltage Remember that power is voltage times current
The optimal band gap balancing these two effects is around 14 eV
for a cell made from a single material We have other losses as well Our
electrons have to flow from one side of the cell to the other through an
external circuit We can cover the bottom with a metal allowing for good
conduction but if we completely cover the top then photons cant get
through the opaque conductor and we lose all of our current (in some cells
transparent conductors are used on the top surface but not in all) If we put
our contacts only at the sides of our cell then the electrons have to travel an
extremely long distance
9
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
26 OPERATION OF A PV CELL
Silicon is a semiconductor -- its not nearly as good as a metal for
transporting current Its internal resistance (called series resistance) is fairly
high and high resistance means high losses To minimize these losses our
cell is covered by a metallic contact grid that shortens the distance that
electrons have to travel while covering only a small part of the cell surface
Even so some photons are blocked by the grid which cant be too small or
else its own resistance will be too high
27 MAXIMIZING POWER OBTAINED FROM SOLAR CELLS
Through experiments conducted during research it was concluded
that the current obtained from solar cells is influenced by the angle at which
incident rays strike the cell surface By using a stationary light source and
adjusting the angle at which the light rays strike the cell a plot of current
delivered vs angle of incidence can be created This property of solar cells is
confirmed by the data contained in Table 1 and illustrated by figure(3)
Table 1 current delivered for various incidence
10
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
After considering the experimental data obtained it can be stated that
to maintain maximum power output from a solar array the angle of
incidence must be held at zero degrees Hence the array must constantly face
the sun This requires a tracking system that can continuously align the array
into the desired position
11
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
28 SOLAR CELL TESTING PRINCIPLE
Measurement of solar cells and solar irradiance measurements are
closely linked Solar radiation on the ground is changing all the time this
change is not only reflected in the total irradiance but also its intrinsic
details of the spectral irradiance are also constantly changes this has brought
about the first solar cell measurements have been very great difficulties As
the solar cell is a spectrum selective components and its optical sensitivity
of the distribution of the solar spectrum changes with changes in the same
total irradiance and spectral irradiance of different light sources the solar
cells electrical properties of the output will be quite different
In order to achieve the unity of solar cell measurement value the
International Electro technical Commission first standard solar spectral
irradiation has been stipulated All the ground with solar standard conditions
of measurement is used AM15 standard solar spectral distribution the
spectral distribution of the data from specific meteorological conditions
atmospheric absorption of solar spectral distribution under the condition of
the measured values
The main technical parameters of solar cells is the spectral response of
solar cells short-circuit current and open circuit voltage and photoelectric
conversion efficiency of solar cells As a solar cell measuring the project
usually carried out the following two aspects of the test - the standard solar
cells under the conditions of the solar spectrum in the standard short-circuit
current in the solar simulator calibration and measurement of solar cells
under the V - A characteristics measurements
12
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Calculate the standard solar spectrum under the condition of the
photoelectric conversion efficiency of solar cells Unable to get with the
standard AM15 solar spectral distribution consistent with artificial light so
can not directly measure the solar cells under the conditions of solar
radiation in the standard short-circuit current
The solar cell measurement laboratories usually a very complicated
method to achieve the standard AM15 solar spectrum solar cells under
short-circuit current measurements and traceability to the international
benchmark measure light irradiation this process is known as solar
calibration
IV characteristics of solar cell measurement method is to first use of
solar cells with the measured spectral response similar to the standard solar
cell to set the sun simulator under standard test conditions of irradiance and
then measured in the sun simulator under test solar cells IV characteristic
curve as measured with the standard solar cell solar cell spectral response
similar to so this alternative measurement method can overcome the out due
to the spectral distribution of solar simulator
281 CHINArsquoS SOLAR CELL TECHNOLOGY DEVELOPMENT
TEST
The seventies of last century Tianjin Institute in solar power research
and development applications at the same time invested considerable human
and material resources the establishment of a solar cell measuring
laboratory began solar cell calibration and testing of technology research
13
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
The main testing equipment including domestic and imported A-
grade solar simulator for the measurement of electrical properties and the
development of phase-locked amplification technology based on solar
spectral response measurement system
The initial goal was to establish an accurate solar as a standard
industry-wide baseline measurement of solar cells In the meantime a
variety of solar cell calibration technique has been fully developed mainly
including mountain calibration ground spectral calibration spectral
calibration laboratories aircraft calibration calibration of the space shuttle
and many other calibration techniques have been developed and tried and
eventually the formation of Tianjin Institute of the standard solar power
system and Tianjin Institute of the standard solar power in mainland China
has been widely promoted and applied
The early eighties Chinas solar cell testing technology has gradually
matured As an emerging industry the importance of products measurement
of the standardization work so organized industry-wide testing experts has
established a national solar photovoltaic energy systems Standardization
Committee specializing in solar cell measuring testing and product quality
standards of the drafting of and development work The initial goal is to
achieve the solar value products industry-wide unity has formulated the
solar cell calibration method general norms mono crystalline silicon
solar cells space-solar temperature coefficient measurement method
single crystal general norms of silicon solar cells on the ground with the
solar components of the environment experimental methods on the
ground with standard solar cells space with standard solar cells
14
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
282 CHINArsquoS SOLAR CELL TECHNOLOGY INTERNATIONAL
ADVANCED LEVEL TEST
The early nineties the state investment fund special transformation
transformation of Tianjin Institute of solar power testing laboratory to
establish a set of a standard solar cell measuring device Include the
laboratory a standard solar cell calibration system and two standard solar
value transfer systems greatly improves the level of the labs solar cell
testing and capacity On this basis the establishment of a Ministry of
Information Industry E-205 metering stations specializing in solar testing
Dell LATITUDE D410 Battery for the Chinese solar industry to provide
accurate
Value of solar cells is also a unity in the world to be a difficult
problem To this end the international advanced solar testing laboratory
trying to achieve through international comparison of the solar value unity
throughout the world The most famous and most successful of an
international alignment is PEP `93 solar cells compared to international
standards it is the US Department of Energy project By the United States
Renewable Energy Laboratory led 10 countries around the world have 13
well-known solar testing laboratories to participate
Each laboratory provides two standard solar cell calibration data is not
standard sample all 23 standard solar cell through a variety of laboratory
calibration back to back to form after the international solar cell base WPVS
(world photovoltaic scale) Tianjin Power Research Institute (MII 205
metering stations) participated in this sub-standard solar activities in the
international comparison
15
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Through the screen near the end only four laboratories with the
average data is used as WPVS the value the four laboratories are NREL
(USA) JQA (Japan) PTB (Germany) and the Tianjin Institute of Power It
also has four laboratories in the world photovoltaic measurement for future
reference
Now this solar standard (WPVS) has become the worlds solar
industry widely used standards As the active promotion of Tianjin Institute
of Power Chinas solar industry is now widely used WPVS as a test The
value of a mention is that by this ratio of activities 205 solar cell testing
capacity metering station has been internationally peer recognition
Calibration of metering station already has 205 solar cells (production
standard) and transmission of solar standards 205 measuring stations are
also the Global Environment Facility China Renewable Energy
Development solar testing laboratory for the project is being carried out to
upgrade the capacity
283TIMES EQUIVALENT TO IEC STANDARD FOR USE
As an emerging industry solar product range and performance is
changing very fast corresponding solar cell testing technology has not been
able to keep up immediately For example the multi-junction solar cell
testing technology
In recent years China developed a new variety of multi-junction solar
cells for multi-junction solar cells solar cells if it is using the traditional test
equipment will produce incalculable test error
16
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Developing multi-junction solar cell is an urgent need testing
technology and development for multi-junction solar cell measurements
In addition with the expansion of industrial scale the entire industry
has with international standards and must therefore pay close attention to the
implementation of international standards as soon as tantamount to the
adoption of work Solar cells work is the standardization of the mainlands
solar industry to make greater sony vgp-bps9 laptop battery
29 TRACKING TECHNIQUES
There are several forms of tracking currently available these vary
mainly in the method of implementing the designs The two general forms of
tracking used are fixed control algorithms and dynamic tracking
The inherent difference between the two methods is the manner in
which the path of the sun is determined
In the fixed control algorithm systems the path of the sun is
determined by referencing an algorithm that calculates the position of the
sun for each time period That is the control system does not actively find
the suns position but works it out given the current time day month and
year The dynamic tracking system on the other hand actively searches for
the suns position at any time of day (or night)
Common to both forms of tracking is the control system This
system consists of some method of direction control such as DC motors
stepper motors and servo motors which are directed by a control circuit
either digital or Analog
17
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
210 FUTURE HIRING PLANS
When asked to forecast future hiring nearly half of those responding
worldwide report that they anticipate adding few or no staff members or full-
time contractors to their work groups over the next year The outlook for
hiring in Asia however is considerably more optimistic than in the world as
a whole with 72 from that region anticipating their organizations will
increase work group headcount by 5 or more These hiring forecasts are in
line with the Asian respondentsrsquo statements about gearing up for RampD
within the next year
211 THE FUTURE POINTS TO GROWTH IN SOLAR CELL
PRODUCTION
Although the percentage of those reporting engagement in full-scale
production is relatively low today the number of manufacturers seems
destined to grow substantially over the next few years with 43 reporting
plans to move into full scale production in the next 12ndash36 months In
Europe EU mandates to increase the use of alternative energy sources and
high energy costs will likely continue to drive investments in research there
In North America the energy research and development portion of the US
economic stimulus bill (the American Recovery and Reinvestment Act of
2009) is likely to provide a boost to the nationrsquos solar industry
The situation in China is similar in that the Chinese government
included solar subsidies as part of its ldquogreenrdquo stimulus package These
subsidies have the potential to improve the profitability of producing and
selling solar cells for Chinese solar companies
18
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Given the staggering array of device technologies now being explored
or developed the industry seems poised to become larger and increasingly
competitive with manufacturers making significant investments in finding
new ways to extract the maximum energy at the lowest possible cost from
every photon that reaches their products Asian manufacturers appear firmly
committed to playing a major role in the worldwide solar cell industry
212 SHORT-CIRCUIT CURRENT (ISC)
The point at which the I-V curve crosses the x axis at zero volts
When a solar cell is operated at short circuit (that is when a low-resistance
connection is established by accident or intention between two points in an
electric circuit so the current tends to flow through the area of low
resistance bypassing the rest of the circuit) V = 0 and the current (I)
through the terminals is defined as the short-circuit current
2121 OPEN-CIRCUIT VOLTAGE (VOC)
The cell voltage at which there is zero current flow When a cell is
operated at open circuit (that is an incomplete electrical circuit in which no
current flows so I = 0) the voltage across the output terminals is defined as
the open-circuit voltage
Assuming the shunt resistance is high enough to neglect the final term
of the characteristic equation the open-circuit voltage (VOC) is
19
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
2122 MAXIMUM POWER OUTPUT (PMAX)
The voltage and current point where the cell is generating its
maximum power The PMAX point on an I-V curve is often referred to as
the maximum power point (MPP)
2123 CURRENT AT MAXIMUM POWER (IMAX)
The cellrsquos current level at PMAX
2124 VOLTAGE AT MAXIMUM POWER (VMAX)
The cellrsquos voltage level at PMAX
2125 FILL FACTOR (FF)
PMAX divided by the VOC multiplied by ISC Fill factor is a popular
measurement because it indicates the cellrsquos efficiency under a specific
spectrum and intensity of light In essence it calculates the percentage of
performance of the real cell vs an ideal cell with no internal losses
2126 SHUNT RESISTANCE (RSHUNT)
RSHUNT can be thought of as leakage across the cell
20
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Any decrease in RSHUNT creates a more attractive leakage path
which allows more of the cell current and power to be lost This can be
caused by leakage in the interconnect but it is more often an effect of the
intrinsic cell design As the plot shows this percentage drop in current looks
like a change in slope on what should be the flat part of the I-V curve
2127 SERIES RESISTANCE (RSERIES)
An increase in series resistance will cause a cellrsquos efficiency to decrease
Intuitively one can think of RSERIES as taking voltage from the load as the
diode turns on Given that RSHUNT is much greater than RSERIES
RSERIES doesnrsquot normally affect the amount of current being delivered but
directly takes voltage from the load as it appears in series As RSERIES
increases cell efficiency decreases
2128 CONVERSION EFFICIENCY
The percentage of power converted (from absorbed light to electrical
energy) and collected when a solar cell is connected to an electrical circuit
This term is calculated by dividing Pmax by the input light irradiance (E in
Wm2 measured under standard test conditions) multiplied by the surface
area of the solar cell (AC in m2)
2129 DOPING DENSITY (N)
Doping density is an important property of any doped semiconductor
material Taken together information on doping density and resistivity
provide valuable information about the quality of a material By adding
assumptions about the consistency of the fabrication process itrsquos possible to
infer the electron mobility within the material Understanding the mobility
doping density and resistivity and eventually the changes over operating
temperatures can help you to refine your process
21
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
21210 CELL RESISTIVITY (VAN DER PAUW RESISTIVITY OR
SURFACE RESISTIVITY)
There are two common methods for resistivity measurements on
semiconductor materials four-point collinear probe measurements and van
der Pauw resistivity measurements These techniques can be used to find the
surface resistivity and conductivity of the material itself which are
important in optimizing fabrication techniques
21211 DEFECT DENSITY
Defect density is a measure of defects (electrons or holes) in the
active region of the semiconductor material Drive Level Capacitance
Profiling (DLCP) is a new measurement technique used to characterize this
material property Understanding when defects appear in a semiconductor
material is important to refining a fabrication process
21212 CURRENT DENSITY
A measurement used in comparing the outputs of cells of different
sizes Current density refers to the amps of current produced per square
centimeter of cell area
21213 QUANTUM EFFICIENCY (QE)
The quantum efficiency of a solar cell is a measure of efficiency over
wavelength Changes in quantum efficiency might indicate different
processes occurring at the junction that would affect the cellrsquos efficiency
213 CONCLUDING REMARKS
After careful consideration of the forms of tracking available and
the methods of implementing each it was decided that the preferred tracking
system involved a microcontroller based dynamic tracking system using
stepper motors for alignment
22
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
CHAPTER 3
P89V51RD2 MICROCONTROLLER
31 INTRODUCTION
It is a computer implemented on a single VLSI chip which contains
memory timer ADCDACDMA controllerparallel portserial portetc
Need for microcontroller is
Microprocessors require external memory
Microprocessors cannot interface directly with input or output devices
Glue logic such as address decoders and buffers is needed to interconnect
external memory and peripherals ICs with microprocessors
The differences between microcontroller and microprocessor is
Microprocessors have less bit handling instructions but microcontrollers
have many such instructions
Microprocessors are concerned with rapid movement of code and data
from external memory But microcontrollers is concerned with that of bits
within the chip
Of course Microprocessors needs additional chips for memory parallel
port timer etc and microcontrollers needs no such external ports
32 P89V51RD2 DESCRIPTION
The P89V51RD2 is an 80C51 microcontroller with 64 kB Flash and
1024 bytes of data RAM A key feature of the P89V51RD2 is its X2 mode
option The design engineer can choose to run the application with the
conventional 80C51 clock rate (12 clocks per machine cycle) or select the
X2 mode (6 clocks per machine cycle) to achieve twice the throughput at the
same clock frequency
23
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Another way to benefit from this feature is to keep the same
performance by reducing the clock frequency by half thus dramatically
reducing the EMI The Flash program memory supports both parallel
programming and in serial
In-System Programming (ISP) Parallel programming mode offers
gang-programming at high speed reducing programming costs and time to
market ISP allows a device to be reprogrammed in the end product under
software control The capability to fieldupdate the application firmware
makes a wide range of applications possible The P89V51RD2 is also In-
Application Programmable (IAP) allowing the Flash program memory to be
reconfigured even while the application is running
This device has the option of storing a 31-byte serial number along
with the length of the serial number (for a total of 32 bytes) in a non-volatile
memory space When ISP mode is entered the serial number length is
evaluated to determine if the serial number is in use If the length of the
serial number is programmed to either 00H or FFH the serial number is
considered not in use
If the serial number is in use reading programming or erasing of the
user code memory or the serial number is blocked until the user transmits a
lsquoverify serial numberrsquo record containing a serial number and length that
matches the serial number and length previously stored in the device The
user can reset the serial number to all zeros and set the length to zero by
sending the lsquoreset serial number record In addition the lsquoreset serial
numberrsquo record will also erase all user code
24
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
33 FEATURES
80C51 Central Processing Unit
5 V Operating voltage from 0 to 40 MHz
64 kB of on-chip Flash program memory with ISP (In-System
Programming) and IAP (In-Application Programming)
Supports 12-clock (default) or 6-clock mode selection via software
or ISP
SPI (Serial Peripheral Interface) and enhanced UART
PCA (Programmable Counter Array) with PWM and
CaptureCompare functions
Four 8-bit IO ports with three high-current Port 1 pins (16 mA
each)
Three 16-bit timerscounters
Programmable Watchdog timer (WDT)
Eight interrupt sources with four priority levels
Second DPTR register
Low EMI mode (ALE inhibit)
TTL- and CMOS-compatible logic levels
Brown-out detection
Low power modes
Power-down mode with external interrupt wake-up
25
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
34 BLOCK DIAGRAM OF P89V51RD2
26
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
35 PIN DIAGRAM
27
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
36 SPECIAL FUNCTION REGISTERS
Special Function Registers (SFRs) accesses are restricted in the
following ways
User must not attempt to access any SFR locations not defined
Accesses to any defined SFR locations must be strictly for the
functions for the SFRs
SFR bits labeled lsquo-rsquo lsquo0rsquo or lsquo1rsquo can only be written and read as
follows
Unless otherwise specified must be written with lsquo0rsquo but can
return any value when read (even if it was written with lsquo0rsquo) It
is a reserved bit and may be used in future derivatives
lsquo0rsquo must be written with lsquo0rsquo and will return a lsquo0rsquo when read
lsquo1rsquo must be written with lsquo1rsquo and will return a lsquo1rsquo when read
37 IN-SYSTEM PROGRAMMING (ISP)
In-System Programming is performed without removing the
microcontroller from the system The In-System Programming facility
consists of a series of internal hardware resources coupled with internal
firmware to facilitate remote programming of the P89V51RD2 through the
serial port This firmware is provided by Philips and embedded within each
P89V51RD2 device The Philips In-System Programming facility has made
in-circuit programming in an embedded application possible with a
minimum of additional expense in components and circuit board area The
ISP function uses five pins (VDDVSS TxD RxD and RST)
28
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
371 USING THE IN-SYSTEM PROGRAMMING
The ISP feature allows for a wide range of baud rates to be used in
your application independent of the oscillator frequency It is also
adaptable to a wide range of oscillator frequencies This is accomplished by
measuring the bit-time of a single bit in a received character This
information is then used to program the baud rate in terms of timer counts
based on the oscillator frequency The ISP feature requires that an initial
character (an uppercase U) be sent to the P89V51RD2 to establish the baud
rate The ISP firmware provides auto-echo of received characters Once
baud rate initialization has been performed the ISP firmware will only
accept Intel Hex-type records
In the Intel Hex record the lsquoNNrsquo represents the number of data bytes
in the record The P89V51RD2 will accept up to 32 data bytes The
lsquoAAAArsquo string represents the address of the first byte in the record If there
are zero bytes in the record this field is often set to 0000 The lsquoRRrsquo string
indicates the record type A record type of lsquo00rsquo is a data record A record
type of lsquo01rsquo indicates the end-of-file mark In this application additional
record types will be added to indicate either commands or data for the ISP
facility
The maximum number of data bytes in a record is limited to 32
(decimal) ISP commands are summarized As a record is received by the
P89V51RD2 the information in the record is stored internally and a
checksum calculation is performed
29
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
The operation indicated by the record type is not performed until the
entire record has been received Should an error occur in the checksum the
P89V51RD2 will send an lsquoXrsquo out the serial port indicating a checksum
error
38 FLASH ORGANIZATION
The P89V51RD2 program memory consists of a 64kB block An
InSystem Programming (ISP) capability in a second 8kB block is provided
to allow the user code to be programmed in-circuit through the serial port
There are three methods of erasing or programming of the Flash memory
that may be used
First the Flash may be programmed or erased in the end-user
application by calling low-level routines through a common entry point
(IAP) Second the on-chip ISP boot loader may be invoked This ISP boot
loader will in turn call low-level routines through the same common entry
point that can be used by the end-user application Third the Flash may be
programmed or erased using the parallel method by using a commercially
available EPROM programmer which supports this device
381 BOOT BLOCK
When the microcontroller programs its own Flash memory all of the
low level details are handled by code that is contained in a Boot block that
is separate from the user Flash memory A user program calls the common
entry point in the Boot block with appropriate parameters to accomplish the
desired operation Boot block operations include erase user code program
user code program security bits etc A Chip-Erase operation can be
performed using a commercially available parallel programer
30
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
382 POWER-ON RESET CODE EXECUTION
Following reset the P89V51RD2 will either enter the SoftICE mode
(if previously enabled via ISP command) or attempt to autobaud to the ISP
boot loader If this autobaud is not successful within about 400 ms the
device will begin execution of the user code
383 FLASH PROGRAM MEMORY
There are two internal ash memory blocks in the device Block 0 has
64kbytes and contains the userrsquos code Block 1 contains the Philips-
provided ISPIAP routines and may be enabled such that it overlays the first
8kbytes of the user code memory The 64kB Block 0 is organized as 512
sectors each sector consists of 128 bytes
384 DATA RAM MEMORY
The data RAM has 1024 bytes of internal memory The device can
also address up to 64kB for external data memory
385 EXPANDED DATA RAM ADDRESSING
The P89V51RD2 has 1kB of RAM ldquoInternal and external data
memory structurerdquo
The device has four sections of internal data memory
1 The lower 128 bytes of RAM (00H to 7FH) are directly and indirectly
addressable
2 The higher 128 bytes of RAM (80H to FFH) are indirectly addressable
3 The special function registers (80H to FFH) are directly addressable only
4 The expanded RAM of 768 bytes (00H to 2FFH) is indirectly addressable
by the move external instruction (MOVX) and clearing the EXTRAM bit
31
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
CHAPTER 4
METHODOLOGY AND DESIGN
41 INTRODUCTION
When beginning the design for the tracking system a TOPDOWN
approach was used to break the project into separate tasks Taking the
project as a whole it involves reading voltages from a sensor array then
comparing these voltages digitally to determine the direction the array must
move to align itself with the sun To perform this movement a motor circuit
is needed to receive output from the controller and step the motors
accordingly The following sections of this chapter outline the methods and
designs used to implement this system
42 METHOD OF ALIGNMENT
Before the design of the sensing circuit can be considered it is
necessary to choose an appropriate method of alignment There are two
feasible methods for aligning the array The first method involves tilting the
array in two axes to maintain the required position illustrated in Figure 4(a)
The second method involves rotating and tilting the array toachieve the same
result illustrated in Figure 4(b)
32
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
43 DRIVER CIRCUIT
In applications where absolute positioning is important the drive
electronics must calibrate the motor position
This is may be done by
Driving the motor all the way in one direction until it encounter a
mechanical stop
Driving the motor all the way in one direction until it triggers a
ldquolimit switchrdquo
Using some form of feed back such as the current track number on
a disk
431 DESCRIPTION OF ULN2003
The ULN2003 is a monolithic high voltage and high current
Darlington transistor arrays It consists of seven NPN darlington pairs that
features high-voltage outputs with common-cathode clamp diode for
switching inductive loads The collector-current rating of a single darlington
pair is 500mA The darlington pairs may be parrlleled for higher current
capability Applications include relay drivershammer drivers
33
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
lampdriversdisplay drivers(LED gas discharge)line drivers and logic
buffers The ULN2003 has a 27kW series base resistor for each darlington
pair for operation directly with TTL or 5V CMOS devices
432 FEATURES
500mA rated collector current(Single output)
High-voltage outputs 50V
Inputs compatibale with various types of logic
433LOGIC DIAGRAM OF ULN2003
34
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
44 STEPPER MOTOR
A stepper motor (or step motor) is a brushless synchronous electric
motor that can divide a full rotation into a large number of steps The
motors position can be controlled precisely without any feedback
mechanism Stepper motors are similar to switched reluctance motors
(which are very large stepping motors with a reduced pole count
441 FUNDAMENTALS OF OPERATION
Stepper motors operate differently from DC brush motors which
rotate when voltage is applied to their terminals Stepper motors on the
other hand effectively have multiple toothed electromagnets arranged
around a central gear-shaped piece of iron An external control circuit such
as a microcontroller energizes the electromagnets To make the motor shaft
turn first one electromagnet is given power which makes the gears teeth
magnetically attracted to the electromagnets teeth When the gears teeth are
thus aligned to the first electromagnet they are slightly offset from the next
electromagnet So when the next electromagnet is turned on and the first is
turned off the gear rotates slightly to align with the next one and from there
the process is repeated Each of those slight rotations is called a step with
35
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
an integer number of steps making a full rotation In that way the motor can
be turned by a precise angle
442 STEPPER MOTOR CHARACTERISTICS
1 Stepper motors are constant power devices
2 As motor speed increases torque decreases
3 The torque curve may be extended by using current limiting drivers and
increasing the driving voltage
4 Steppers exhibit more vibration than other motor types as the discrete
step tends to snap the rotor from one position to another
5 This vibration can become very bad at some speeds and can cause the
motor to lose torque
6 The effect can be mitigated by accelerating quickly through the problem
speeds range physically damping the system or using a micro-stepping
driver
7 Motors with a greater number of phases also exhibit smoother operation
than those with fewer phases
443 OPEN-LOOP VERSUS CLOSED-LOOP COMMUTATION
Steppers are generally commutated open loop ie the driver has no
feedback on where the rotor actually is Stepper motor systems must thus
generally be over engineered especially if the load inertia is high or there is
widely varying load so that there is no possibility that the motor will lose
steps This has often caused the system designer to consider the trade-offs
between a closely sized but expensive servomechanism system and an
oversized but relatively cheap stepper
36
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
A new development in stepper control is to incorporate a rotor
position feedback (eg an encoder or resolver) so that the commutation can
be made optimal for torque generation according to actual rotor position
This turns the stepper motor into a high pole count brushless servo motor
with exceptional low speed torque and position resolution An advance on
this technique is to normally run the motor in open loop mode and only
enter closed loop mode if the rotor position error becomes too large -- this
will allow the system to avoid hunting or oscillating a common servo
problem
444 THERE ARE THREE MAIN TYPES OF STEPPER MOTORS
Permanent Magnet Stepper
Hybrid Synchronous Stepper
Variable Reluctance Stepper
Permanent magnet motors use a permanent magnet (PM) in the rotor
and operate on the attraction or repulsion between the rotor PM and the
stator electromagnets Variable reluctance (VR) motors have a plain iron
rotor and operate based on the principle of that minimum reluctance occurs
with minimum gap hence the rotor points are attracted toward the stator
magnet poles Hybrid stepper motors are named because they use use a
combination of PM and VR techniques to achieve maximum power in a
small package size
445 TWO-PHASE STEPPER MOTORS
There are two basic winding arrangements for the electromagnetic
coils in a two phase stepper motor bipolar and unipolar
4451 UNIPOLAR MOTORS
37
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
A unipolar stepper motor has two windings per phase one for each
direction of magnetic field Since in this arrangement a magnetic pole can be
reversed without switching the direction of current the commutation circuit
can be made very simple (eg a single transistor) for each winding
Typically given a phase one end of each winding is made common giving
three leads per phase and six leads for a typical two phase motor Often
these two phase commons are internally joined so the motor has only five
leads
A microcontroller or stepper motor controller can be used to activate the
drive transistors in the right order and this ease of operation makes unipolar
motors popular with hobbyists they are probably the cheapest way to get
precise angular movements
Unipolar stepper motor coils
A quick way to determine if the stepper motor is working is to short
circuit every two pairs and try turning the shaft whenever a higher than
normal resistance is felt it indicates that the circuit to the particular winding
is closed and that the phase is working
4452 BIPOLAR MOTOR
38
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Bipolar motors have a single winding per phase The current in a
winding needs to be reversed in order to reverse a magnetic pole so the
driving circuit must be more complicated typically with an H-bridge
arrangement There are two leads per phase none are common
Static friction effects using an H-bridge have been observed with
certain drive topologies Because windings are better utilised they are more
powerful than a unipolar motor of the same weight
An 8 lead stepper is wound like a unipolar stepper but the leads are
not joined to common internally to the motor
Bipolar with series windings This gives higher inductance but lower
current per winding
Bipolar with parallel windings This requires higher current but can
perform better as the winding inductance is reduced
Bipolar with a single winding per phase This method will run the
motor on only half the available windings which will reduce the available
low speed torque but require less current
Multi-phase stepper motors with many phases tend to have much
lower levels of vibration although the cost of manufacture is higher
45 STEPPER MOTOR DRIVE CIRCUITS
Stepper motor performance is strongly dependent on the drive circuit
Torque curves may be extended to greater speeds if the stator poles can be
reversed more quickly the limiting factor being the winding inductance To
overcome the inductance and switch the windings quickly one must increase
the drive voltage This leads further to the necessity of limiting the current
that these high voltages may otherwise induce
39
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
451 LR DRIVE CIRCUITS
LR drive circuits are also referred to as constant voltage drives
because a constant positive or negative voltage is applied to each winding to
set the step positions However it is winding current not voltage that applies
torque to the stepper motor shaft The current I in each winding is related to
the applied voltage V by the winding inductance L and the winding
resistance R
The resistance R determines the maximum current according to
Ohms law I=VR The inductance L determines the maximum rate of
change of the current in the winding according to the formula for an Inductor
dIdt = VL Thus when controlled by an LR drive the maximum speed of a
stepper motor is limited by its inductance since at some speed the voltage V
will be changing faster than the current I can keep up
With an LR drive it is possible to control a low voltage resistive
motor with a higher voltage drive simply by adding an external resistor in
series with each winding This will waste power in the resistors and
generate heat It is therefore considered a low performing option albeit
simple and cheap
452 CHOPPER DRIVE CIRCUITS
Chopper drive circuits are also referred to as constant current drives
because they generate a somewhat constant current in each winding rather
than applying a constant voltage On each new step a very high voltage is
40
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
applied to the winding initially This causes the current in the winding to rise
quickly since dIdt = VL where V is very large The current in each winding
is monitored by the controller usually by measuring the voltage across a
small sense resistor in series with each winding
When the current exceeds a specified current limit the voltage is
turned off or chopped typically using power transistors When the
winding current drops below the specified limit the voltage is turned on
again In this way the current is held relatively constant for a particular step
position This requires additional electronics to sense winding currents and
control the switching but it allows stepper motors to be driven with higher
torque at higher speeds than LR drives Integrated electronics for this
purpose are widely available
A stepper motor is a polyphase AC synchronous motor and it is
ideally driven by sinusoidal current A full step waveform is a gross
approximation of a sinusoid and is the reason why the motor exhibits so
much vibration Various drive techniques have been developed to better
approximate a sinusoidal drive waveform these are half stepping and
microstepping
Full step drive is the usual method for full step driving the motor
Both phases are always on The motor will have full rated torque
453 WAVE DRIVE
In this drive method only a single phase is activated at a time It has
the same number of steps as the full step drive but the motor will have
significantly less than rated torque It is rarely used
41
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
454 HALF STEPPING
When half stepping the drive alternates between two phases on and a
single phase on This increases the angular resolution but the motor also has
less torque at the half step position (where only a single phase is on) This
may be mitigated by increasing the current in the active winding to
compensate The advantage of half stepping is that the drive electronics need
not change to support it
455 MICROSTEPPING
What is commonly referred to as microstepping is actual sine cosine
microstepping in which the winding current approximates a sinusoidal AC
waveform Sine cosine microstepping is the most common form but other
waveforms are used Regardless of the waveform used as the microsteps
become smaller motor operation becomes more smooth thereby greatly
reducing resonance in any parts the motor may be connected to as well as
the motor itself It should be noted that while microstepping appears to make
running at very high resolution possible this resolution is rarely achievable
in practice regardless of the controller due to mechanical stiction and other
sources of error between the specified and actual positions In professional
equipment gearheads are the preferred way to increase angular resolution
Step size repeatability is an important step motor feature and a
fundamental reason for their use in positioning Example many modern
hybrid step motors are rated such that the travel of every Full step (example
18 Degrees per Full step or 200 Full steps per revolution) will be within 3
42
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
or 5 of the travel of every other Full step as long as the motor is operated
with in its specified operating ranges Several manufacturers show that their
motors can easily maintain the 3 or 5 equality of step travel size as step
size is reduced from Full stepping down to 110th stepping Then as the
microstepping divisor number grows step size repeatability degrades At
large step size reductions it is possible to issue many microstep commands
before any motion occurs at all and then the motion can be a jump to a
new position
46 THEORY
A step motor can be viewed as a synchronous AC motor with the
number of poles (on both rotor and stator) increased taking care that they
have no common denominator Additionally soft magnetic material with
many teeth on the rotor and stator cheaply multiplies the number of poles
(reluctance motor) Modern steppers are of hybrid design having both
permanent magnets and soft iron cores
To achieve full rated torque the coils in a stepper motor must reach
their full rated current during each step Winding inductance and reverse
EMF generated by a moving rotor tend to resist changes in drive current so
that as the motor speeds up less and less time is spent at full current -- thus
reducing motor torque As speeds further increase the current will not reach
the rated value and eventually the motor will cease to produce torque
47 APPLICATIONS
Computer-controlled stepper motors are one of the most versatile
forms of positioning systems They are typically digitally controlled as part
43
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
of an open loop system and are simpler and more rugged than closed loop
servo systems
Industrial applications are in high speed pick and place equipment and
multi-axis machine CNC machines often directly driving lead screws or
ballscrews In the field of lasers and optics they are frequently used in
precision positioning equipment such as linear actuators linear stages
rotation stages goniometers and mirror mounts Other uses are in packaging
machinery and positioning of valve pilot stages for fluid control systems
Commercially stepper motors are used in floppy disk drives flatbed
scanners computer printers plotters slot machines and many more devices
48 SENSOR CIRCUIT
LIGHT DEPENDENT RESISTOR
A photoresistor or light dependent resistor or cadmium sulfide (CdS)
cell is a resistor whose resistance decreases with increasing incident light
intensity It can also be referenced as a photoconductor
A photoresistor very is made of a high resistance semiconductor If
light falling on the device is of high enough frequency photons absorbed by
the semiconductor give bound electrons enough energy to jump into the
conduction band The resulting free electron (and its hole partner) conduct
electricity thereby lowering resistance
44
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
A photoelectric device can be either intrinsic or extrinsic An intrinsic
semiconductor has its own charge carriers and is not an efficient
semiconductor eg silicon
In intrinsic devices the only available electrons are in the valence
band and hence the photon must have enough energy to excite the electron
across the entire bandgap Extrinsic devices have impurities also called
dopants added whose ground state energy is closer to the conduction band
since the electrons do not have as far to jump lower energy photons (ie
longer wavelengths and lower frequencies) are sufficient to trigger the
device If a sample of silicon has some of its atoms replaced by phosphorus
atoms (impurities) there will be extra electrons available for conduction
This is an example of an extrinsic semiconductor
A photoresistor is a sensor whose resistance varies with light
intensity Most decrease in resistance as the light intensity increases In a
typical microcontroller application this resistance must be converted to a
voltage so that an A2D converter can measure it The easiest way to do this
is with a voltage divider circuit
A voltage divider is just two resistors in series connected between a
voltage supply and ground
45
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
If R1 is connected to the voltage supply and R2 is connected to
ground then the voltage at the junction between the two resistors is
If R1 is the photoresistor the voltage will increase with increasing
light intensity If R2 is the photoresistor the voltage will decrease with
increasing light intensity
481 SENSOR DESIGN
To design the sensor circuit a suitable method for determining the
position of the sun was needed This involved a process of design and testing
to establish the most efficient and accurate method After testing several
designs the most effective design was found to be a simple opposites of
sensor
The sensors are arranged so that the voltage across each sensor is the
same when the LDR points at the sun This is possible because the sensors
are set at 45o to the base of the pyramid Hence when the LDR is not
pointing at the sun the voltage will increase on the side that is most exposed
to the sun This allows for a simple comparison to determine the direction in
which the array must move
To simplify the comparison even more two opposing sensors are
dedicated to rotating and two are dedicated to tilting Due to the fact that the
controller reads the voltage output from the sensors it is necessary to set the
operating range of the sensors to an appropriate voltage range To
accomplish this the output of the sensors must be sent to an amplifier circuit
that will deliver the required voltage range to the controller
46
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
482 APPLICATIONS
Photoresistors come in many different types Inexpensive cadmium
sulfide cells can be found in many consumer items such as camera light
meters street lights clock radios alarms and outdoor clocks
They are also used in some dynamic compressors together with a
small incandescent lamp or light emitting diode to control gain reduction
Lead sulfide (PbS) and indium antimonide (InSb) LDRs (light
dependent resistor) are used for the mid infrared spectral region GeCu
photoconductors are among the best far-infrared detectors available and are
used for infrared astronomy and infrared spectroscopy
49 TRACKING CONTROLLER
491 CHOICE OF CONTROL CHIP
When choosing a controller chip for the tracking system it was
important to consider the functions it would need to perform The controller
also needs the capacity to handle inputs from the user interface and the
outputs to the stepper motor control circuit These inputs and outputs need to
be clarified before the controller is chosen
After researching an appropriate control chip the P89V51RD2 micro-
controller was found to be the preferred choice as it can perform all required
functions using only a single chip The chip contains an adequate
programmable memory space ample input and output pins and a supply
voltage of five volts
492 READING SENSORS
The P89V51RD2 has an adjustable voltage reference range for the
LDR The amplifier circuit for the sensor voltage inputs was chosen to
supply between zero and five volts
47
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
After setting the required gain on the amplifiers the circuit outputs
five volts when the sensors are normal to the incident rays and outputs zero
volts when the sensors receive no light Refer to Appendix B for the
schematic diagram of the amplifier circuit
493 FLOWCHART
48
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
410 CONCLUDING REMARKS
For a detailed description of the controller program refer to Appendix
A The control circuit including the sensor voltage amplifier circuit the
P89V51RD2 and attachments circuit and the stepper motor driver circuit
has been implemented on a Printed Circuit Board (PCB) which is shown in
Appendix C The schematic diagram of this circuit is shown in Appendix B
CHAPTER 5
49
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
ANALYSIS OF DESIGN
51 INTRODUCTION
Testing the design of the Tracking system involved breaking the
project up into the same tasks as used when designing the system The
various sections of the design were first tested separately by writing two test
programs for the 68HC11A1 processor The first test was for the user
interface and stepper motors to test that the manual controls stepped the
motors correctly The second test checked that the AD converter was
correctly functioning After both test programs worked the final program
was then loaded and tested
52 CURRENT RECEIVED TRACKED VS STATIONARY ARRAY
To test the accuracy of the tracking system the amount of current
delivered by a single solar cell was measured during the course of a day A
50
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
set of measurements was taken for a stationary array set in the stowed
position (array surface horizontal) as well as for Sun Tracking System
Stationary
Here above table considered as differences of fixed solar panal and
variable solar amptook the reading between them Rotating solar panel of total
ampaverage value is greater than the fixed solar panel
53 CONCLUDING REMARKS
From Figure 8 it is apparent that the sun tracking system supplies
a greater average current supply that is almost constant throughout the day
The drop in intensity of the incident light can account for the slight drop in
readings at the beginning and end of the day
CHAPTER 6
LITERATURE REVIEW
51
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
In remote areas the sun is a cheap source of electricity because instead
of hydraulic generators it uses solar cells to produce electricity While the
output of solar cells depends on the intensity of sunlight and the angle of
incidence It means to get maximum efficiency the solar panels1 must
remain in front of sun during the whole day But due to rotation of earth
those panels canrsquot maintain their position always in front of sun This
problem results in decrease of their efficiency Thus to get a constant output
an automated system is required which should be capable to constantly
rotate the solar panel
The Automatic Sun Tracking System (ASTS) was made as a
prototype to solve the problem mentioned above It is completely automatic
and keeps the panel in front of sun until that is visible The unique feature of
this system is that instead of taking the earth as its reference it takes the sun
as a guiding source Its active sensors constantly monitor the sunlight and
rotate the panel towards the direction where the intensity of sunlight is
maximum In case the sun gets invisible eg in cloudy weather then without
tracking the sun the ASTS keeps rotating the solar panel in opposite
direction to the rotation of earth
Renewable energy is rapidly gaining importance as an energy
resource as fossil fuel prices fluctuate At the educational level it is
therefore critical for engineering and technology students to have an
understanding and appreciation of the technologies associated with
renewable energy
One of the most popular renewable energy sources is solar energy
Many researches were conducted to develop some methods to increase the
efficiency of Photo Voltaic systems (solar panels) One such method is to
employ a solar panel tracking system This project deals with a micro
52
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
controller based solar panel tracking system Solar tracking enables more
energy to be generated because the solar panel is always able to maintain a
perpendicular profile to the sunrsquos rays
Development of solar panel tracking systems has been ongoing for
several years now As the sun moves across the sky during the day it is
advantageous to have the solar panels track the location of the sun such that
the panels are always perpendicular to the solar energy radiated by the sun
This will tend to maximize the amount of power absorbed by PV systems
It has been estimated that the use of a tracking system over a fixed
system can increase the power output by 30 - 60 The increase is
significant enough to make tracking a viable preposition despite of the
enhancement in system cost It is possible to align the tracking heliostat
normal to sun using electronic control by a micro controller
Design requirements are
1 During the time that the sun is up the system must follow the sunrsquos
position in the sky
2 This must be done with an active control timed movements are
wasteful It should be totally automatic and simple to operate The
operator interference should be minimal and restricted to only when it
is actually required
EXISTING SYSTEM
In the existing system we used the solar panel as keep as stable
53
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Such solar panel is fixed on the roof tops and it did not rotate
If the light intensity is decreased in the environment solar battery went to
low energy state
At this state we lost the power
PROPOSED SYSTEM
In the proposed system we have to use the microcontroller based
stepper motor with multiple sensors
Sensors are fixed at the different angles such like that ldquo -180 to +180rdquo
degrees
The unique feature of this system is that instead of taking the earth as
its reference it takes the sun as a guiding source
Sensors(LDR) are connected with the stepper motor using
microcontroller
So if the intensity is decreased then sensor sense the maximum light
intensity in environment
Automatically it rotates at small angles as per the sensing
So at this state we cannot lose the power because of it is sensing
towards the sunrsquos position
CHAPTER 7
CONCLUSIONS AND SUGGESTIONS
54
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
71 CONCLUDING REMARKS ON THE TRACKING SYSTEM
After examining the information obtained in the data analysis
section it can be said that the proposed sun tracking solar array system is a
feasible method of maximizing the energy received from solar radiation The
controller circuit used to implement this system has been designed with a
minimal number of components and has been integrated onto a single PCB
for simple assembly The pyramid sensor design enables the device to be
attached to solar panels The use of stepper motors enables accurate tracking
of the sun while keeping track of the arrays current position in relation to its
initial position Manual control allows the user to set the arrays initial (or
reset) position as well as make it possible to easily service the array surface
for cleaning or replacing damaged cells
72 APPLICATIONS
The sun tracking solar array system can be used for any application
that currently uses solar energy It is ideal for hot water systems and other
domestic applications where long-term efficiency is preferred
73 FUTURE DESIGN PROPOSALS
Future design proposals include but are not limited to an auto-
battery supply that runs off the solar array and a heat management system to
cool solar cells for improved efficiency
731 SUGGESTED AREAS OF FURTHER RESEARCH
The research are that would prove most beneficial would be heat
management as it was found during the design stage and testing that the
efficiency of the cells varies considerably with varying heat conditions
8 BIBLIOGRAPHY
55
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
[1] Sze SM Physics of semiconductor devices 2nd Ed New York Wiley
1981 pp 791-835
[2] Chapin DM Fuller CS and Pearson GL A New Silicon p-n
Junction Photocel for Converting Solar Radiation into Electrical Power J
Appl Phys 1954 25 676
[3] Koyuncu b and Balasubramanian K A microprocessor controlled
automatic sun tracker
[5]Piao Z GPark J MA study on the tracking photovoltaic system by
programme type
[6]Yousef H ADesign and implementation of a Fuzzy Logic Computer-
Controlled Sun tracking system
[7]SaxenaA K DuttaA Versatile microcontroller based solar tracking
system
[8]Beckman William A and Duffie John A Solar Engineering of Thermal
Processes 2nd Ed John Wiley and Sons Inc 1991 pp768-793
[9]1048698 Zweibel Ken Harnessing Solar Power The Photovoltaics Challenge
Plenum Press New York and London 1990
56
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Appendix I
includereg52h
sbit sen1=P1^0
sbit sen2=P1^1
sfr stepmtr=0x80
sbit sen=P3^0
void stepfwd(void)
void Delay(unsigned int i)
void steprew(void)
void main()
P1=0xFF
P0=0xFF
P3=0xFF
while(1)
if(sen1==1ampampsen2==0)
stepfwd()
else if(sen1==0ampampsen2==1)
steprew()
72
57
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
else
P0=0x00
void stepfwd(void)
stepmtr=0x80
while(sen==1)
Delay(6500)
stepmtr=0x40
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x10
Delay(6500)
void steprew(void)
stepmtr=0x10
while(sen==1)
Delay(6500)
stepmtr=0x20
Delay(6500)
stepmtr=0x40
Delay(6500)
58
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
stepmtr=0x80
Delay(6500)
void Delay(unsigned int i)
while(i--)
59
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
Appendix II
SCHEMATIC DIAGRAM
60
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
61
LIST OF ABBREVIATIONSPVC Photo Voltaic CellsWPVS World Photo Voltaic ScaleISC Short Circuit CurrentVOC Open Circuit VoltageQE Quantum EfficiencyDPTR Data PointerALE Address Latch EnablePCA Programmable Counter ArrayVRM Variable Reluctance MotorPMM Permanent Magnet MotorMPP Maximum Power PointFF Fill FactorDLCP Drive Level Capacity ProfileISP In System ProgrammingIAP In Application ProgrammingSPI Serial Peripheral InterfacePCA Programmable Counter ArrayWDT Watch Dog TimerSFR Special Function RegistersLDR Light Dependent RegistersASTS Automatic Sun Tracking System
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