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Experiment 9 Single Phase Inverters

9.0 In-laboratory Experimentation 9.1 Developing a Unipolar and Bipolar PWM strategy for a Single phase H-bridge

a) Using SimPowerSystems toolbox of MATLAB/SIMULINK software, simulate the circuit of a

single phase H-Bridge inverter with Unipolar PWM. Connect the dc-side to a dc voltage source of Vdc=15V and the ac-side to an RL load with R=10Ω and L= 3mH. The desired ac voltage has a fundamental of 60 Hz. Select the triangle wave with a frequency of 2 kHz. i) Vary the modulation index from 0.2 to 1 (steps of 0.2) and record the voltage and current

waveforms. Confirm that the amplitude of the fundamental component of the load voltage has a linear relationship with the modulation index (you can confirm by measuring the amplitude of load current).

ii) For a fixed modulation index, e.g., m=0.7, decrease the fundamental frequency from 60Hz to 40Hz and comment on the results.

iii) For a fixed modulation index, e.g., m=0.7, decrease and increase the switching frequency

and comment on the results. Specifically pay attention to the current ripples. iv) In linear modulation region where the modulation index is below one, measure the

switching frequency of the MOSFETs. Increase the modulation index to m=1.2 and measure the switching frequency of the MOSFETs and provide a comparison.

Fig.1 Circuit of a Single phase H-bridge inverter with Unipolar PWM strategy

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Fig.2 Simulation results of Unipolar PWM strategy

b) Using SimPowerSystems toolbox of MATLAB/SIMULINK software, repeat part (a) with bipolar PWM.

Fig.3 Circuit of a Single phase H-bridge inverter with Bipolar PWM strategy

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Fig.4 Simulation results of Bipolar PWM strategy

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9.2 MATLAB GUI Interface:

Develop a MATLAB GUI interface program to implement the bipolar and unipolar PWM techniques for an H-Bridge inverter. In the developed programs, the control parameters would be modulation index, fundamental/desired frequency, and switching frequency (triangle waveform frequency).

9.2.1 Implementing Unipolar and Bipolar PWMS using Real Time Workshop of MATLAB/Simulink 1. Simulink model

a) Overall Diagram

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b) Under mask of PWM Control block

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2. Configuration of the blocks, parameters and components a) Fixed data point calculation setting (constant blocks)

b) Sampling time setting (Simulation---- >Configuration Parameters)

c) For all IQN x IQN block settings

d) For all IQNtrig blocks the function settings should be “_IQsin”

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e) ePWM1 block settings

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f) ePWM2 block setting

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3) Developing the Control Interface a) The GUI interface

b) Sample Matlab code for the above control interface

at line 64 global cc; cc=ticcs; configure(cc.rtdx,1024,4); open(cc.rtdx, 'sinefreq' , 'w' ); open(cc.rtdx, 'module' , 'w' ); enable(cc.rtdx, 'sinefreq' ); enable(cc.rtdx, 'module' ); enable(cc.rtdx); cc.rtdx;

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At line 132 or where ever you have the “executes on button press in xxxxx” comment % --- Executes on button press in menable. function menable_Callback(hObject, eventdata, handles) % hObject handle to menable (see GCBO) % eventdata reserved - to be defined in a future v ersion of MATLAB % handles structure with handles and user data ( see GUIDATA) global cc; mtemp = str2num(get(handles.mindex, 'string' )); writemsg(cc.rtdx, 'module' ,int32(mtemp)); % --- Executes on button press in ffenable. function ffenable_Callback(hObject, eventdata, handles) % hObject handle to ffenable (see GCBO) % eventdata reserved - to be defined in a future v ersion of MATLAB % handles structure with handles and user data ( see GUIDATA) global cc; ftemp = str2num(get(handles.frin, 'string' )); writemsg(cc.rtdx, 'sinefreq' ,int32(ftemp)); % --- Executes on button press in Run. function Run_Callback(hObject, eventdata, handles) % hObject handle to Run (see GCBO) % eventdata reserved - to be defined in a future v ersion of MATLAB % handles structure with handles and user data ( see GUIDATA)

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global cc; run(cc); % --- Executes on button press in Halt. function Halt_Callback(hObject, eventdata, handles) % hObject handle to Halt (see GCBO) % eventdata reserved - to be defined in a future v ersion of MATLAB % handles structure with handles and user data ( see GUIDATA) global cc; halt(cc);

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9.3 Implementation

1. Turn on the TI C2000 micro-controller You must turn on the TI C2000 micro-controller by selecting the USB side of toggle switch.

2. Check the connection between the Matlab and TI C2000 micro-controller Type “ticcs” in the Matlab command window to check the connection between the TI C2000 micro-controller and Matlab. If the connection is established, you will get the following message.

3. Build C code language from simulation model

Users can build the simulation model by clicking the build button in the simulation toolbar.

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And then, IDE link links to Code Composer Studio to generate C code. If build is completed, Code Composer Studio must be linked like below.

4. Loading C code on the target board

Since the build action is selected as ‘build’, use must load the C code on the target board manually by selecting ‘load program’ command in the ‘File’ option.

After that a window as shown in the below figure appears. Then select the .out file and press open.

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5. Run the m-file You can run the control interface by clicking RUN button of toolbar of m-file.

6. Connections on the DSP board To see the outputs generated connect the oscilloscope probes to pins GPIO 00 and 01(ePWM1) for first sine function and GPIO 02 and 03(ePWM2) for second sine function.