How to design three phase grid connected inverter in MATLAB Simulink?

Hello Everyone,

I am trying to simulate a three phase grid connected inverter with LCL filter as shown in picture. I am trying to complete the simulation in open loop condition first before going to close loop with DQ transformation. I am using a 2-level PWM generator to provide gate signals. The simulation is done in two steps

Step 1, Only load connected and Three Phase source(grid) commented out. The output is fairly good sinuosoidal as expected. V=400V, I=20A

Step 2, Grid is connected and simulation is run. The output is not how I wanted. Voltage waveform is pretty ok. But current waveform have higher magnitude and higher harmonics.

My question is what could be the reason for higher currents when inverter is grid connected and what could be the reason of such non sinuosiodal current waveform. Can anyone help me with getting this problem fixed or share their three phase grid connected model?

Answer 1

[Joel Van Sickel]

Hello Akhtar,

running open loop on a grid connected simulation would often not work since it won't by synchronized with the grid. It is possible in simulation but you'd need to often tweak a number of phase ofsets and frequencies to ensure it actually worked, which is probably more work than just synchronizing it to the gril with PLL and closed loop controller given the examples that are available. There are shipping examples of how this works grid connected:

https://www.mathworks.com/help/physmod/sps/ug/grid-tied-inverter.html

Regards,

Joel

[Akhtar Javed]

Hi Joel,

Thanks. I also feel that it is difficult to control grid connected inverter in open loop especially to provide the reference signal for frequency. I have implemented a closed loop controller and now it is working fairly well. Thanks for your answer.

Answer 2

[SOURABH GHOSH]

There exists a simulink model example: 250-kW Grid-Connected PV Array - MATLAB & Simulink - MathWorks India

You can derive some ideas from this example.

Thank you.

[Akhtar Javed]

Yes. Thank you.