Back to back PMSM with parasitics IGBT converter

Question

Trying to simulate two mechanically coupled PMSMs each driven by an IGBT converter with parasitics. The problem is that both converters cannot be specified with a forward voltage drop on the IGBT/diode, or else Simulink throws a zero-crossing error on the circuit S-function (the error is not more specific than that). If one of the convertera are specified with a forward voltage drop equal to 0, then it works.

There is a way around this, I have found, which is to connect a three-phase resistor net in parallell with the machine. In turn, the problem now is that it only works if the resistance is sufficiently low (around 200 Ohm) or else the simulation time becomes unrealisticly long. This makes the current, beacuse of the reisance, a bit too high for my liking.

Any thoughts on this are highly appreciated.

Model and figure attached.

Answer 1

You are using the Rotor Reference Frame implementation of the PMSM which cannot interface to an arbitrary three-phase network.  Changing the "Model" setting of both PMSMs to "Voltage Behind Reactance" allows the simulation to proceed without a snubber.  Look at the PMSM component documentation for more information on the differences and usecases of the two model implementations.

The "Automatic" solver in Simulink chooses ode15s, but ode23tb is much faster in this case.

Part of the issue here is that your PWM signals may not be what you expect. In order to get your model running, I had to replace the Simscape components for abc<->dq0 transformations with generic implementations, which might have influenced things, but I suggest you take a closer look at your modulator outputs.

Comments

Thanks for taking your time and answering this, really appreciate it.

It very much did the trick to change the PMSM model and Simulink solver.

One thing I don't understand is your remark on the PWM signals, though. It's just a standard sinusoidal modulation and from what I can see the do behave as I expect them to. Do you mean something happens out of my control when the gate signals are propagated to the plecs circuit?

Anyhow, many thanks.

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Glad to hear my guidance helped.

I was seeing all the PWM modulators saturate.  The lower machine had all the upper switches on, then all the lower switches on, depending on the motor position.  As I said, I had to replace a few blocks that required an additional SimScape library, so I may have inadvertently made some other modification.  If you're seeing the expected signals, then you can disregard my comment.