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To develop a small scale solar powered
system that will power a DC load,
which incorporates power management
techniques, DC-DC conversion and a
user interface.
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Renewable energy source Non-polluting Reliable Can work anywhere sun is shining No major mechanical parts Relatively no maintenance Noise Free Last decades
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SolarPanel
DC-DC ConverterLoad
Controller Back-upBattery
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Silicon cells combined in series or parallel Converts solar energy into electricity Cell Technologies
› Copper Indium Selenide (CIS) and Amorphous› Monocrystalline and Polycrystalline
Current varies with cell size and light intensity
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Peak Power of 10 Watts
Vmpp = 15.6 V Impp = 0.64 A
Shell ST10
Voc = 22.9 V Isc = 0.77 A
The solar panel was tested withdifferent resistances under aconstant light source
+
-V
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Two MPPT algorithms were considered: Incremental Conductance Method
› By comparing incremental conductance with instantaneous conductance.
Perturb & Observe Method› By periodically perturbing the PV array
voltage and comparing the output power with that of the previous cycle. The operating point oscillates around the MPP since the system is continuously perturbed.
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Algorithm was implemented using LabVIEW
Solar panel read via a NI-USB 6009
The voltage was measured across a high power resistor to read current
Duty cycle output on NI USB 6009 digital output line
Start
Set Duty Out
Read V, I
P_new = V*I
P_new > P_old Duty = Duty(-)
Duty = Duty(+)
P_old P_new
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Used to implement P&O algorithm› ‘G’ programming
Also used to generate a user interface through the front panel› Waveforms showing voltage and current of
solar panel› Numeric indicator showing power› Duty cycle displayed› ‘Stop’ button to end program
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Data acquisition tool
Read data in, and generate digital signals out
Does not have a hardware counter, cannot generate digital outputs at high frequencies
Solution M series
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DC-DC converter needed for two reasons› To implement the MPPT algorithm› To bring the DC voltage to an acceptable
level to power the load
Buck converter was chosen and designed
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The most important components are the inductor and capacitor
Use Vo = DVi to deduce ideal duty cycle range (0.3 – 0.5)
Using both of these values for D, and the ΔI equation two values for the inductor were calculated (2.8 mH & 1.6 mH)
Using the ΔV equation the capacitor value was determined (21.3 μF)
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Vin
2.2 mH
22 uF
LOAD
+
-
+
-
D
PWM
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Solar panels only generate power when there sun available
Storage element is recommended Various rechargeable battery cell
chemistries› Lead Acid› Nickel-Cadmium› Nickel-Metal-Hydride› Lithium Ion
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Up to 99% efficiencies Highest weight to energy ratio Average voltage of one Li-ion cell is
3.6-3.7 Volts A Li-ion battery pack with a capacity of
4 AH would be enough to store all energy generated on the longest day of the year at maximum power
Safety issues
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Overvoltage Over discharging can
cause short circuit Battery packs usually
include protective circuit› Limits input voltage› Limits discharge
voltage Li-ion charger IC is
recommended to implement charging profile
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Initially it was thought a mobile phone charging algorithm would have to implemented
Research showed that the charging algorithm is employed on the phone
To prove this, a commercial Nokia car cigarette lighter charger was disassembled
A ‘ma34063a’ DC-DC converter was found To charge a mobile an appropriate
constant voltage is needed, along with some circuitry protection
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Solar cell equivalent circuit, characteristics and various cell technologies
Maximum power point tracking techniques LabVIEW – ‘G’ programming and user
interface DC-DC converter design including choosing
appropriate components and simulation in Pspice
Rechargeable Batteries