Dear all,
I am currently modellig a control structure for a synchronous machine. I’m using a discrete solver and every controller of mine is discretized and build according to the Tustin method. After starting the simulation, I get an error that says:
“The mechanical inputs are either infinite or uknown”
Does anyone have an idea how to solve this, or I should change also something within the synchronous machine model when switching to this discrete time simulation.
Can you please post a simple model that represents this behavior?
Unfortunately not. The model isn’t simple and I don’t know if I can even share it (because of the job). I’m just curious how the discrete time simulation affects the model of electric machines?
Ok, without a model it is difficult to comment on specifics. You should reach out to the team at support@plexim.com with your question and model if you would like a concrete answer.
There is nothing prohibiting a discrete simulation of an electric machine, so it is either something in the solver settings or how you have configured the model.
For solver settings, Tustin is only 2nd order and and can have poor damping. Therefore I would recommend testing with RADAU and/or revising the simulation time-step. Also, is there a particular reason why you are using a fixed-step solver? You can have a discrete time control system and a variable step solver.
For the model it could be something in your motor parameters (e.g. 0 inertia), mechanical model (e.g. infinite torque injection), or control model.
I using PLECS for only half of a year (but I’m of course not a totally beginner). So I have to ask, are You telling me I can use discrete block like delays z^(-1) with a variable-step solver?
Yes, that’s correct.
Thank you very much Bryan. 