DRIVER CARD FOR SINGLE PHASE INVERTER

USING SKHI22BR

A PROJECT REPORT

Submitted by

HARI BABU (07241A0234)

A .NAVEEN KUMAR (07241A0239)

D.ANAND(08245A0210)

N.M.M.D.PRAVEEN (08245A0211)

In partial fulfillment for the award of the degree

of

Bachelor of Technology

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

GOKARAJU RANGARAJU INSTITUTES OF ENGINEERING AND

TECHNOLOGY

JNTU HYDERABAD : 500090

1

GOKARAJU RANGARAJU INSTITUTES OF

ENGINEERING AND TECHNOLOGY

BONAFIED CERTIFICATE

This is to certify that this project report DRIVER CARD FOR SINGLE PHASE

INVERTER USING SKHI22BR is the bonafide work of Hari babu ,

A.Naveen kumar, D.Anand ,N.M.M.D.Praveen who carried out the project

under my supervision.

HEAD OF THE DEPARTMENT SUPERVISOR

ASSOCIATE

PROFESSOR

ELECTRICAL AND ELECTRONICS ELECTRICAL AND ELECTRONICS

GRIET, GRIET,

BACHUPALLY, KUKATPALLY, BACHUPALLY, KUKATPALLY,

HYDERABAD-500 090. HYDERABAD-500 090.

2

ABSTRACT:-

This project presents the design of the driver card using SKHI22BR ic to trigger the igbts or mosfets of a inverter using TMS320F2812 which is a digital signal processor. The

DSP has inbuilt feature of generating the PWM signals by comparing with the sinusoidal

signal. The block diagram for generating the PWM signals is placed in matlab simulink and

the code is dumped in to the DSP using CODE COMPOSER STUDIO . The PWM signals

for various frequencies are obtained in the matlab by changing the wave form period and the

pwm signals obtained from the dsp is given to the driver card and is analyzed through the

simulation studies using MatlabR2006b under various switching frequencies and the results

are validated through the experimental setup based on TMS320 F2812 DSP board.

This project gives brief advantages of pulse width modulation technique used for

inverter design over normal switching techniques. These PWM pulses are generated using

DSP TMS320F2812 which plays a major role in the hardware design.

3

CONTENTS:-

CHAPTER No. TITLE

1. INTRODUCTION

1.1 INVERTERS

1.2 PULSE WIDTH MODULATION

2. IMPLEMENTATION OF DSP WITH MATLAB

2. 1 ABOUT DSP TMS320F2812

2.1.1 BLOCK DIAGRAM OF TMS320F2812

2.1.2 PWM GENERATION USING TMS320F2812

2.1.3 GENERATION OF PW SIGNALS THROUGH MATLAB

2.2 CODE COMPOSER STUDIO

2.2.1 INTERFACING DSP KIT TO PC

2.2.2 STEPS TO DUMP CODE IN DSP

3. INTERFACING DSP TO DRIVER CARD

3.1 MOSFET DRIVER CIRCUIT BOARD

4 . HARDWARE IMPLEMENTATION

5. OUTPUT WAVEFORMS

6. RESULTS AND DISCUSSIONS

6.1 RESULT

6.2 CONCLUSION

6.3 SCOPE FOR FURTHER WORK

4

7. REFERENCES

APPENDIX

5

1. INTRODUCTION Power electronics have revolutionized the concept of power conversion and for

control of electrical motor drives. Power electronics combine power, electronics and control.

Power deals with static and rotating power equipment for generation, transmission and

distribution of electric power. Electronics deals with solid-state devices and circuits for signal

processing to meet desired control objectives. Control deals with steady-state and dynamic

characteristics of the system. Power electronics may be defined as application of electronics

for control and conversion of electric power.

Power electronics is primarily based on switching of the power-semiconductor

devices. With developments of power-semiconductor technology, the power handling

capabilities and switching speed of the power devices have improved tremendously. Modern

power electronics equipment uses

1) Power semi-conductors that can be regarded as the muscle

2) micro-electronics that has the power and intelligence of brain.

1.1 INVERTERS:-

An inverter is a circuit that converts direct current (DC) power to alternating current

(AC) power at desired output voltage and frequency. The DC power input to the inverter may

be battery, fuel cell, solar cells and other dc sources. But in most industrial applications it is

fed by a rectifier.

The AC output voltage could be at a fixed or variable frequency. This conversion can

be achieved either by controlled turn-on and turn-off of power semi-conductor devices (eg:-

BJTs, IGBTs, MOSFETs ). The diagram shown below represents a single phase inverter

whose triggering pulses are having equal ON and OFF states. During one half cycle mosfets

1and 3 are turned ON and during another half cycle mosfets 2 and 4 are turned ON.

6

Block diagram Single Phase H-Bridge Inverter

21

3

4

Fig 1.1 Single phase inverter

Waveform for the single phase inverter:-

Fig 1.2 Simulated Waveform Using Pulse Generator.

The output frequency of an inverter is determined by the rate at which the semi-conductor

devices are switched on and off. The magnitude of output of the inverter can be controlled by

7

varying the dc link voltage due to which only magnitude can be varied but the frequency of

the output cannot be changed. In order to change the frequency of the output on and off times

of the semi-conductor device has to be changed. In this method the output of the inverter is a

square wave which contains 3rd and 5th harmonics of the fundamental frequency of 50Hz

which is deviated from the sine-waveform. The most of the electrical equipments are

designed to operate efficiently for sine-waveform. Hence the square wave output of the

inverter has to be converted into sine-waveform by using the filter circuit. As the square wave

consists of 3rd and 5th harmonics of the fundamental frequency (50Hz) which are very less

when compared to harmonic frequency of output waveform of inverter using pulse-width

modulated scheme. As the harmonic frequency of inverter using pulse-width modulated

scheme is very high due to which size of the filter components will be reduced (inductor and

capacitor) due to which efficiency increases and cost reduces.

To find out the output waveform using PWM for an H- bridge inverter shown below

using Matlab is shown below

Fig 1.3 Single Phase Inverter Using PWM Technique

Fig 1.4 Simulated Output Voltage Waveform Using PWM Technique

8

Fig 1.5 Simulated Output Current Waveform Using PWM Technique

THREE PHASE INVERTERS :-

Three phase inverters are generally used for high power applications. The switches of three

phase inverters can be controlled with 180 degrees or 120 degrees conductions. However,

180 degrees conduction has better utilization of the switches and is preferred.

180 degrees conduction :

Each transistor conducts for 180 degree. Three transistors remain on at any

instant of time. When transistor Q1 is switched on, terminal a is connected to the positive

terminal of the dc input voltage. When transistor Q4 is switched on, terminal a is brought to

the negative terminal of the dc source. There are six modes of operation in cycle and the

duration of each mode is 60degree. The transistors are numbered in the sequence of gating

the transistors (e.g.,123, 234, 345,456, 561, and612). The gating signals shown in the

figure2(b), are shifted from each other by 60degree to obtain three-phase balanced

(fundamental) voltages.

The load may be connected in Y or delta as shown in Figure 3. The switches

of any segment of the inverter (S1, and S4, S3 and S6, or S5 and S2) cannot be switched on

simultaneously; this would result in a short circuit across the dc link voltage supply.

9

Similarly, to avoid undefined states and thus undefined ac output line voltages, the switches

of any leg of the inverter cannot be switched off simultaneously; this can result in voltages

that depend on the respective line current polarity.

Three-phase bridge inverter:

Transistors Q1, Q6 in Figure 2(a) act as the switching devices S1, S6,

respectively. If two switches: one upper and one lower conduct at the same time such that the

output voltage is +Vs, the switch state is 1, whereas if these switches are off at the same time,

the switch state is 0. State 1 to 6 produces nonzero output voltages. States 7 and 8 produce

zero line voltages and the line currents freewheel through either the upper or the lower

freewheeling diodes. To generate a given voltage waveform, the inverter moves from one

state to another. Thus, the resulting ac output line voltages are built up of discrete values of

voltages of Vs, O, and Vs,

For a delta-connected load, the phase currents can be obtained directly from

the line-to-line voltages. Once the phase currents are known, the line currents can be

determined. For a Y-connected load, the line-to-neutral voltages must be determined to find

the line (or phase) currents. There are three modes of operation in a half-cycle and the

equivalent circuits are shown in Figure 2 a for Y-connected load.

During mode 1 for 0t< /3, transistor Q1, Q5, and Q6 conduct

2

3R 2R R Req =+=

3R2V

RV i s

eq

s1 ==

10

3V

2Ri v v s1cnan ===

32V- Ri- v s1bn ==

During mode 2 for /3t< 2/3, transistor Q1, Q2, and Q6 conduct

2

3R 2R R Req =+= 3R

2V RV i s

eq

s2 ==

3

2V Ri v s2an == 3

V-

2Ri- v v s2cnbn ===

Fig. 1.1 Three-Phase Bridge Inverter With Wave Forms

During mode 3 for 2/3t< , transistor Q1, Q2, and Q3 conduct

11

2

3R 2R R Req =+=

3R2V

RV

i seq

s3 ==

3

V

2Ri

v v s3bnan ===

3

2V- Ri v s3cn ==

The line-to-line rms voltage can be found from

ss

2/13/2

0

2sL 0.8165V V 3

2 )t(dV22 V ==

=

Fig. 1.2 Equivalent Circuits for Y connected Resistive Load

12

Fig. 1.3 Three-Phase Inverter With RL Load

120 degree conduction:

In this type of control, each transistor conducts for 120 degrees. Only two

transistors remain On at any instant of time. The control signals are shown in fig.5. The

conduction sequence of transistors is 61,12,23,34,45,56,61. There are three modes of

operation in one half cycle and the equivalent circuits for a star-connected load are shown in

fig.6.

During mode 1 for t/3, transistor 1 and 6 conduct

0 v 2

V- v

2V

v cns

bns

an ===

13

Fig. 1.4 Gating Signals for 1200 Conduction

During mode 2 for /3t2/3, transistor 1 and 2 conduct

2

V- v 0 v

2V

v scnbns

an ===

During mode 3 for 2/3t3/3, transistor 2 and 3 conduct

2

V- v

2V

v 0 v scns

bnan ===

14

Fig. 1.5 Equivalent Circuits For Y-connected Resistive Load

Table 2 : Switch States for Three-Phase Voltage-Source Inverter (VSI)

V0=00000008S4, S6 and S2 are ON and S1, S3 and S5 are OFF

V7=00001117S1, S3 and S5 are ON and S4, S6 and S2 are OFF

V6=1-j0.577= 2/3 33000-VSVS1016S6, S1 and S5 are ON and S3, S4 and S2 are OFF

V5=-j1.155= 2/3 2700VS-VS00015S5, S6 and S4 are ON and S3, S2 and S1 are OFF

V4=-1-j0.577= 2/3 2100VS0-VS0114S4, S5 and S3 are ON and S1, S2 and S6 are OFF

V3=-1+j0.577= 2/3 15000VS-VS0103S3, S4 and S2 are ON and S6, S1 and S5 are OFF

V2=j1.155= 2/3 900-VSVS01102S2, S3 and S1 are ON and S5, S6 and S4 are OFF

V1=1+j0.577= 2/3 300-VS0VS1001S1, S2 and S6 are ON and S4, S5 and S3 are OFF

Space Vector VcaVbcVabSwitch State

State No.State

There is a delay of /6 between the turning off Q1 and turning On Q4. Thus there should be no short circuit of the dc supply through one upper and one lower transistors.

At any time, two load terminals are connected to the dc supply and the third one remain open.

The potential of this open terminal depends on the load characteristics and would be

unpredictable. Because one transistor conducts for 120 degrees, the transistors are less

utilized as compared with those of 180 degree conduction for the same load condition. Thus,

180 degree conduction is preferred and it is generally used in three phase inverter.

15

1.2 PULSE WIDTH MODULATION :

VoltageControlofSinglephaseInverters

In many industrial applications, to control of the output voltage of inverters is often necessary

1. to cope with the variations of dc input voltage

2. to regulate voltage of inverters and

3. to satisfy the constant volts and frequency control equipment.

There are various pulse width modulation techniques to vary the inverter gain. The commonly used

techniques are:

1. Single-pulse-width modulation

2. Multiple-pulse-width modulation

3. Sinusoidal pulse-width modulation

4. Modified sinusoidal pulse-width modulation

5. Phase-displacement control

Single pulse width modulation:

In single pulse width modulation control, there is only one pulse per half-cycle and the width

of the pulse is varied to control the inverter output voltage. The generation of control signals and

inverter output voltage for single phase full bridge inverters is shown in fig. 8. The control signals are

generated by comparing a rectangular reference signal of amplitude Ar with a triangular carrier wave

of amplitude Ac. The frequency of the reference signal determines the fundamental frequency of

output voltage. The instantaneous output voltage is vo=Vs(g1-g4). The ratio of Ar to Ac is the

control variable and defined as the amplitude modulation index and given as

M = Ar/Ac

16

Fig.7Singlepulsewidthmodulation

The RMS output voltage can be found from

=

=

+

s

2/12/)(

2/)(

2so V t)d( V2

2 V

by varying Ar from 0 to Ac, the pulse width can be modified from 0 to 180 and the RMS output voltage Vo, from 0 to Vs.

Fig. 8 Harmonic profile of single pulse width modulation

17

Multiple pulse width modulation:

Fig. 9 Multiple Pulse Width Modulation

The harmonic content can be reduced by using several pulses in each half-cycle of output

voltage. The generation of control signals for turning on and off of transistors is shown in fig. 9 by

comparing a reference signal with a triangular carrier wave. The control signals are shown in fig.9.

The frequency of reference signal sets the output frequency fo, and the carrier frequency fc

determines the number of pulses per half-cycle p. The modulation index controls the output voltage.

This type of modulation is also known as uniform pulse width modulation (UPWM). The number of

pulses per half-cycle is found from

P = fc / 2fo = mf / 2

Where mf = fc / fo is defined as the frequency modulation ratio.

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The instantaneous output voltage is vo= Vs(g1-g4). The output voltage for single phase

bridge inverters are shown in fig. 9 .

If (delta) is the width of each pulse, the RMS output voltage can be found from

=

=

+

pV t)d( V22P V s

2/12/)p/(

2/)p/(

2so

The variation of the modulation index M from 0 to 1 varies the pulse width d from 0 to T/2p (

0 to /p) and RMS output voltage Vo from 0 to Vs. The harmonic profile of UPWM is shown in fig.10.

Fig. 10. Harmonic profile of multiple PWM

Sinusoidal pulse width modulation

Instead of maintaining the width of all pulses the same as in the case of multiple-pulse

modulation, the width of each pulse is varied in proportion to the amplitude of a sine wave evaluated

at the center of the same pulse. The distortion factor and lower order harmonics are reduces

significantly. The control signals are generated by comparing a sinusoidal reference signal with a

triangular carrier wave of frequency fc as shown in fig.11. This sinusoidal pulse width modulation is

commonly used in industrial applications. The frequency of reference signal fr determines the inverter

19

output frequency fo, and its peak amplitude Ar controls the modulation index m, and then in turn the

RMS output voltage Vo. Comparing the bi-directional carrier signal vcr with two sinusoidal reference

signals vr and vr, produces control signals gt1 and g4 respectively as shown in fig.11(b). The output

voltage is vo = Vs(g1-g4). However, g1 and g4 can not be released at the same time. The number of

pulses per half-cycle depends on the carrier frequency. Within the constraint that two transistors of the

same arm(Q1 andQ4) cannot conduct at the same time, the instantaneous output voltage is shown in

fig.11(c). The same control signals can be generated y using unidirectional triangular carrier wave as

in fig/ 11(d). It is easier to implement this method and is preferred. The generation of control signals

is similar to that for the UPWM, except the reference signal is a sine wave vr= Vr sin wt, instead of a

dc signal. The output voltage is vo = Vs(g1-g4).

Fig. 11 Sinusoidal PWM

The RMS output voltage can be varied by varying the modulation index M. it can be observed

that the area of each pulse corresponds approximately to the area under the sine wave between the

adjacent midpoints of off periods on the control signals. If ( m ) is the width of mth pulse, then the RMS output voltage is

20

2/1p2

1m

mso V V

=

=

Fig. 12 Harmonic profile of sinusoidal PWM

The harmonic profile of SPWM is shown in fig.13. The output voltage of an inverter contains

harmonics. The PWM pushes the harmonics into a high-fequency range around the switching

frequency fc and its multiples, that is , around harmonics mf, 2mf, 3mf and so on.

Modified Sinusoidal Pulse Width Modulation

Fig. 13 indicates that the widths of pulses nearer the peak of the sine wave do not change

significantly with the variation of modulation index. This is due to the characteristics of a sine wave ,

and the SPWM technique can be modified so that the carrier wave is applied during the first and last

60 degree intervals per half-cycle(e.g.,) to 60 and 120 to 180). This modified sinusoidal pulse width

modulation is shown in fig.--. The fundamental component is increased and its harmonic

characteristics are improved. It reduces the number of switching of power devices and also reduces

switching losses.

21

Fig. 13. Modified sinusoidal pulse width modulation

The number of pulses q in the 60 degree period is normally related to the frequency ratio,

particularly in three-phase inverters by fc / fo = 6q + 3.

Fig. 14 Harmonic profile of modified sinusoidal PWM

The instantaneous output voltage is vo= Vs(g1-g4). The algorithm for generating the control

signals is similar to that for sinusoidal PWM, except the reference signal is a sine wave from 600 to

1200 only.

Phase-Displacement Control

22

Voltage control can be obtained by using multiple inverters and summing the output voltage

of individual inverters. A single phase full bridge inverter in fig.16 can be perceived as the sum of

two-bridge inverters in fig.16. a 1800 phase displacement produces an output voltage as shown in

fig.16 whereas a delay or displacement angle of produces an output as shown in fig.16. The RMS output voltage,

= V V so

Fig. 15 Phase displacement control

The RMS value of fundamental output voltage is

2

sin 2

4V V s1o

=

4.2 ADVANCED MODULATION TECHNIQUES

The SPWM, which is most commonly used, suffers from drawbacks (e.g., low fundamental

output voltage).The other techniques that offer improved performances are

1. Trapezoidal modulation

23

2. Staircase modulation

3. Stepped modulation

4. Harmonic injection modulation

5. Delta modulation

4.2.1Trapezoidal modulation

The control signals are generated by comparing a triangular carrier wave with a modulating

trapezoidal wave as shown in fig.17. The trapezoidal wave can be obtained from a triangular wave by

limiting its magnitude to +_Ar, which is related to the peak value Ar(max) by

Ar = Ar(max) where is called the triangular factor, because the waveform becomes a triangular wave when =1.

The modulation index M is M = Ar/Ac = Ar(max)/Ac for 0< M

Fig. 16 Trapezoidal modulation

For fixed values of Ar(max) and Ac, M that varies with the output voltage can be varied by

changing the triangular factor . This type of modulation increases the peak fundamental output voltage up to 1.05Vs, but the output contains LOHs.

4.2.2 Staircase modulation :

Fig.17. Staircase Modulation

25

The modulating signal is a staircase wave, as shown in Fig.18. The staircase is not a sampled

approximation to the sine wave. The levels of the stairs are calculated to eliminate specific harmonics.

The modulation frequency ratio mf and the number of steps are chosen to obtain the desired quality of

output voltage. This is an optimized PWM and is not recommended for fewer than 15 pulses in one

cycle. It has been shown that for high fundamental output voltage and low DF, the optimum number

of pulses in one cycle is 15 for two levels, 21 for three levels, and 27 for four levels. This type of

control provides a high-quality output voltage with a fundamental value of up to 0.94Vs.

4.2.3 Stepped modulation :

Fig. 18 Stepped Modulation

The modulating signal is a stepped wave as shown in Fig. 19. The stepped wave is not a

sampled approximation to the sine wave. It is divided into specified intervals, say 200, with each

interval controlled individually to control the magnitude of the fundamental component and to

eliminate specific harmonics. This type of control gives low distortion, but a higher fundamental

amplitude compared with that of normal PWM control.

4.2.4 Harmonic injected modulation :

26

The modulating signal is generated by injecting selected harmonics to the sine wave. This

results in flat-topped waveform and reduces the amount of overmodulation. It provides a higher

fundamental amplitude and low distortion of the output voltage. The modulating signal is generally

composed of

vr = 1.15 sint + 0.27 sin 3t 0.029 sin 9t

Fig. 19. Selected harmonic injection modulation

The modulating signal with third and ninth harmonic injections is shown in Fig.19. It should

be noted that the injection of 3nth harmonics does not affect the quality of the output voltage, because

the output of a three phase inverter does not contain triplen harmonics. If only the third harmonics is

injected, vr is given by

vr = 1.15 sint + 0.19 sin 3t

27

Fig. 20 Harmonic injection modulation

The modulating signal can be generated from 2/3 segments of a sine wave as shown in Fig.20. This is the same as injecting 3nth harmonics to a sine wave. The line-to-line voltage is

sinusoidal PWM and the amplitude of the fundamental component is approximately 15% more than

that of a normal sinusoidal PWM. Because each arm is switched off for one-third of the period, the

heating of the switching devices is reduced.

4.2.5 Delta Modulation

In delta modulation, a triangular wave is allowed to oscillate within a defined window V above and below the reference sine wave vr. The inverter switching function, which is identical to the

output voltage vo is generated from the vertices of the triangular wave vc as shown in Fig.21 It is also

known as hysteresis modulation. If the frequency of the modulating wave is changed keeping the

slope of the triangular wave constant, the number of pulses and pulses widths of the modulated wave

would change.

28

Fig. 21 Delta Modulation

The fundamental output voltage can be up to 1Vs and is dependent on the peak amplitude Ar

and frequency fr of the reference voltage. The delta modulation can control the ratio of voltage to

frequency, which is a desirable feature, especially in ac motor control.

Due to these advantages now-a-days pulse-width modulation technique is most

preferred. Our project is to design single phase inverter using pulse-width modulation

technique. The pulse width modulated signals are generated using Digital signal processor

because it is less affected to noise. The code for the pwm signals is generated using Matlab

through Code Composer Studio. Digital signal processor used in this project is

TMS320F2812 which has the following features.

32 x 32 bit arithmetic logic unit (ALU)

Atomic read-modify-write instructions

8-stage fully protected pipeline

Fast interrupt response manager

Two event managers

12-bit ADC modules

12 PWM output signals

29

56 General purpose input output pins

Watchdog time

2. IMPLEMENTATION OF DSP WITH MATLAB

The software used for interfacing DSP TMS320F2812 is MATLAB R2006b through CODE

COMPOSER STUDIO V3.0.

2.1 ABOUT DSP TMS320F2812:-

TMS320F2812 belongs to Texas instruments C2000 family which is used for electrical

purposes. We are also having other type of DSP models such as C6000 family which is used

for communication purposes and so on. TMS320F2812 DSP is highly integrated, high

performance solutions for demanding control applications.

Fig 2.1 TMS320F2812 Board

2.1.1 BLOCK DIAGRAM OF TMS320F2812:- TMS320F2812 consists of 32 bit Data lines and 22 bit Address lines, 32 bit ALU, 2

Event Managers modules. The event-manager modules include general-purpose (GP) timers,

30

full-compare/PWM units, capture units, and quadrature-encoder pulse (QEP) circuits. EVA

and EVB timers work identically. The other peripherals present in the block diagram are used

for communication purpose only.

Fig 2.2 Block diagram of TMS320F28121

2.1.2 PWM Generation Using TMS320F2812

31

Fig 2.3 Block diagram of Analog to Digital Converter (12 bit ADC of TMS320F2812)

The 12-bit ADC of TMS320F2812 has 16 inputs so that 16 analog signals can be converted

simultaneously or sequentially. The 16 analog input signal pins are divided into two blocks

with each block having 8 analog input signals. Each block is connected to the analog MUX

which is connected to the 12-bit ADC module through Sample and Hold circuit. The analog

signal converted into digital form which is stored in the respective registers. The analog

signal is given to any one of the input pin of analog to digital converter. The analog to digital

conversion starts when the ADC SOC (Start of Conversion) is activated.

The analog signal considered here is a sine wave with peak 3.3V which will be the

reference signal for PWM generation. Internally a carrier signal (triangular wave) is

generated within the Event manager module through which pwm pulses can be obtained.

These pulses can be obtained from the General purpose input output module. The digital

value of the analog input is derived as follows

Digital value = 0 when input < 0V

Digital value = when 0V input 3.3V

Digital value = 4095 when input 3.3V

32

The above condition says that the Analog to Digital Converter block present in DSP works

only for voltage range 0V to 3.3V. If the input analog is of 0V the digital value will be all

zeros. If the input analog voltage is above 3.3V the digital value will be all ones.

The PWM signals can be generated using ADC block if and only if the analog input

(reference signal) is within the specified limits i.e. 0 to 3.3V. If it exceeds the specified limits

the DSP kit gets damaged.

2.1.3 Generation of PWM signals through Matlab:-

To overcome the above problem, the reference signal can be given to DSP using

Matlab r2006b through Code Composer Studio V3.0. The simulated waveform of 3.3V

obtained through Matlab is shown next

Fig 2.4 Reference signal waveform in Matlab

The above sine wave generated using Matlab is given to DSP block which in turn generates

pwm pulses. The below diagram shows Matlab simulink model reference signal interfaced

with the DSP block.

33

Fig 2.5 Interfacing of reference input signal with DSP block

In the above diagram the reference sine wave is given to the PWM block present in the Event

Module A. The reference signal is compared with ramp signal which is generated internally

and has a frequency of 75MHz.

Fig 2.6 Asymmetric PWM Waveform

Asymmetric PWM signal is generated by comparing the reference signal with ramp signal

having less retrace time.

Fig 2.7 Symmetric PWM Waveform

Symmetric waveform is generated by comparing the reference signal with ramp signal having

equal rise time and retrace time.

34

Though we represent the DSP block in Matlab the program generated has to be dumped into

the hardware DSP kit for which Code Composer Studio V3.0 software is required.

2.2 CODE COMPOSER STUDIO:-

Code Composer Studio (CCStudio) is the integrated development environment for TI's

DSPs, microcontrollers and application processors. CCStudio includes a suite of tools used to

develop and debug embedded applications. It includes compilers for each of TI's device

families, source code editor, project build environment, debugger, profiler, simulators and

many other features. CCStudio provides a single user interface taking users through each step

of the application development flow. Before interfacing the DSP kit to PC the drivers related

to TMS320F2812 has to be installed.

2.2.1 INTERFACING DSP KIT TO PC:-

Code Composer Studio plays a major role in interfacing DSP kit to PC because if the JTAG

of the DSP is connected to PC (which doesnt have Code Composer Software) it declares as

unknown hardware. The figure below shows the connection of DSP to PC

Fig 2.8 JTAG port is Connected to the Cable.

35

Fig 2.9 JTAG Controller of DSP is Connected to the Serial Port of PC

After connecting the DSPs JTAG to PC the below steps have to be followed

Step 1: Select the SD config on the screen

36

Fig 2.10 Selection of SD config

Step 2: Now open the SD config and click on the symbol as pointed by the arrow

Fig 2.11 Selection of Verify connection

Step 3: Now click on the symbol as pointed below which detects the emulator

37

Fig 2.12 Performing the Emulator test

Then the following picture appears at the bottom that an emulator has been detected as

pointed below

Fig 2.13 Result of the emulator test

Step 4: Now click on the button as pointed as shown by the pointer which is used for

resetting the emulator

38

Fig 2.14 Resetting the emulator

Step 5: Check the output of the emulator reset test which is shown by pointer

Fig 2.15 Result of the emulator reset

Step 6: Now select the option as shown in the figure

39

Fig 2.16 Selection of Code composer studio

Step 7: Now select the option as pointed by the pointer

Fig 2.17 Selection of the option Debug

Step 8: After selecting the DEBUG option select the option connect as shown by the pointer

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Fig 2.18 Selection of the option Connect

Step9: After clicking on the option we have the following message indicating that the DSP is

now successfully connected to the PC which is shown by the pointer

Fig 2.19 Indication of the DSP kit being connected to PC

2.2.2 STEPS TO DUMP THE PROGRAM IN DSP:-

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After successfully connecting the DSP kit to the PC to dump the required program the following steps have to be followed

Step 1: Construct the required model in simulink of Matlab (for more information refer to

section 2.1.3)

Fig 2.20 Construction of a simulink model in Matlab

Step 2: Click on the sine wave block as given below and change the parameters according to

the width of the PWM

Fig 2.21 Dialog Box for Changing the Reference Sine Wave parameters

Step 3: Double click on the PWM block and set the Timer specifications as given below

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Fig 2.22 Dialog box for Changing the Timer specifications

Step 4: Click on the outputs and select the desired PWM output pins.

Fig 2.23 Dialog box for changing PWM Output Ports

Step 5: Select the logic button in the same dialog box and change the PWM logic outputs in

such a way that PWM1 and PWM2 are complimentary and PWM3 and PWM4 are

complimentary.

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Fig 2.24 Dialog box for changing the Logics of the PWM Output

Step 6: Select the deadband option in the same dialog box and set it to desired value.

Fig 2.25 Dialog box for changing the Deadband Width of the PWM Pulses

Step 7: Select the ADC option in the dialog box and set it to none because the reference

signal is given through matlab itself.

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Fig 2.26 Dialog box for changing ADC control

Step 8: After completing the design in Matlab simulink as shown Figures 2.27, 2.28, 2.29,

Press the keys Ctrl+b (build). On pressing the keys we can see the building process in the

command window of the Matlab and at the same instant the code generated will be

automatically get dumped into DSP. The following pictures guides through the process

The linker files are being generated

Fig 2.27 Generation of Code for Matlab Simulink Model

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Fig 2.28 Generated code is being dumped into DSP kit

Finally the code generated for the matlab simulink model is dumped into the DSP kit which is

shown by the pointer

Fig 2.29 The Code Generated is Dumped into DSP

The DSP kit is successfully connected to the PC and the required code is dumped into the

DSP and the outputs can be checked which will be dealt in the next section

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3. INTERFACING DSP TO DRIVER CARD

The PWM signals generated in the previous section are given to the driver card to drive the

igbts. The below figure shows the pin location of the PWM pulses in TMS320F2812

Fig 3.1 Pin Location of PWM outputs in DSP Board.

IGBTs are voltage controlled devices and it requires a minimum gate threshold voltage of

about 15-V for turning ON. This requirement makes it difficult to directly interface IGBTs

to DSP. For proper operation of IGBTs, correct power levels are required (Vgs (th)=15V and

Id= 50 mA). Voltage and current levels of DSP are 3.3v and 2mA and hence output signals

fail to operate the IGBTs .The driver circuit amplifies DSP output signal to the required level

for triggering the IGBTs and isolates the DSP from the power circuit.

3.1 DRIVER CIRCUIT: From the above section it is seen that the PWM signals generated from the DSP cannot trigger the MOSFETs of the H-bridge inverter hence the driver will be prominent in

triggering the switches. The driver circuit consists of SKHI 22B/A ic and power supply

circuit to power the ic.

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3.1.1 SKHI 22A/B:-

This is driver ic . It has inbuilt separation circuit , buffer , short pulse

suppression, interlock deadtime circuit, Vce monitor , error memory, error

monitor circuits.

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4. HARDWARE IMPLEMENTATION

In the previous section the Code has been successfully generated and dumped into the DSP

TMS320F2812 which is used as the control circuit for the Single Phase Inverter Design. It

generates the required PWM pulse which has a voltage level of 3.3V.

Fig 4.1 DSP Board With PWM outputs

The PWM outputs from the DSP cannot be given directly to the H-bridge inverter circuit as

the PWM outputs from DSP cannot trigger the IGBTs used.

IGBTs have Gate to Emitter threshold voltage of 15V so an MOSFET driver circuit is used

which consists of SKHI 22 B/A. It has inbuilt separation circuit , buffer , short pulse

suppression, interlock deadtime circuit, Vce monitor , error memory, error monitor circuits.

It consists of an amplifier which amplifies the 3.3V PWM signal from the DS toP 15V so

that the IGBTs can be triggered easily.

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Fig 4.2 Driver Circuit Board

The output from the driver circuit board is given to the gate emitter of the IGBTs of the H-

bridge inverter as shown in fig

Fig 4.3 H-bridge Inverter Circuit

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Input voltage of 30V is given to the input pins as shown in Fig 4.3. During one half cycle

IGBTs 1 and 3 are turned ON and during another half cycle IGBTs 2 and 4 are turned on. A

load of 3.3K ohms is connected between the output pins and the output is measured across

the 3.3K ohm.

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5. OUTPUT WAVEFORMS

5.1 PWM SIGNALS FROM DSP KIT

Fig 5.1 PWM1 Signal from DSP

Fig 5.2 PWM2 signal from DSP

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Fig 5.3 PWM3 Signal from DSP

Fig 5.4 PWM4 Signal from DSP

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5.2 OUTPUT SIGNALS FROM MOSFET DRIVER CIRCUIT

Fig 5.5 PWM1 Signal from Diver Circuit Board

Fig 5.6 PWM2 Signal from Driver Circuit Board

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Fig 5.7 PWM3 Signal from Driver Circuit Board

Fig 5.8 PWM4 Signal form Driver Circuit Board

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6. RESULTS AND DISCUSSIONS

6.1 RESULT

In this project gate signals required to single phase inverter is designed.

6.2 CONCLUSION

The driver card to trigger the Single Phase Inverter is designed using DSP TMS320F2812 as

the control circuit and the required waveforms have been obtained.

6.3 SCOPE FOR FURTHER WORK

The scope of the project is to obtain the output waveform of Single Phase Inverter for

different values of width of PWM signals, different loads and conversion of the obtained

output into pure sine wave using a filter design.

7. REFERENCES

http://www.emo.org.tr/ekler/4c76e43c96a0124_ek.pdf

www.datasheetcatalog.com

POWER ELECTRONICS BY M.A RASHID

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4.2 ADVANCED MODULATION TECHNIQUES 4.2.1Trapezoidal modulation