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H bridge inverter output current increase not as expected

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Timothy TenCate
Timothy TenCate on 9 Aug 2019
Answered: Joel Van Sickel on 17 Aug 2021
I recently asked a question about my H bridge inverter that I modeled in Simscape and received a great answer. However, a day after I thought it was working I attached a load that has a higher iductance value than before. I am not sure if the output of the model is what I should be getting. I have attached four screenshots of the output and the model file. My questions are as follows:
1) In Current 1 I have the inverter attached to the load and in Current 2 I have an ideal voltage source attached and the inverter unattached to the load(which is just unattached to the circuit in the model file) and I do not understand why the current spikes up and then comes down to a steady state value after approximetly 1 second and why in Current 2 is begins right at the steady state value.
2) In Current 1 zoom I can see that the current begins at zero on the y-axis (this seems to be the case always) and in Current 2 zoom it begins at a value lower than zero. It almost appears that the current starts lower and then rises to its correct value when the ideal source is attached.
I am not sure if it has something to do with resonance between the capsitor on the output filter and the load inductance.
Any help would really be appreciated.
Thank you.
Tim
  3 Comments
Timothy TenCate
Timothy TenCate on 11 Aug 2019
Thank you for your response. It does steady out to a steady state sinusoidal current after around 1 second. The wierd part is that the sinusoidal current initially is the same amplitude as the whole time but it seems to be just shifted up by a specific amount. I did change the phase to the sinusoidal input to the PWM and the fluation went downs slightly.
Thank you again for your help.
Tim

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Answers (1)

Joel Van Sickel
Joel Van Sickel on 17 Aug 2021
Hello Timothy,
this actually looks mostly like an initial condition issue. Specialized Power Systems actually has an algorithm that tries to calculate good initial conditions for different components in your model, so you can get different initial results if these are specified explicitly. You can either try and have the system start in the off state and then start the system up, or specificy initial currents in your inductors to try and address this. You can also try using saved states to start the model from a true steady state setting.
Regards,
Joel

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