PMLSM FOC Control: Chopper Resistor and PWM Control

Hi All,

Quick question.

I am modelling an FOC PMLSM drive model. I need to add a chopper resistor and switch (ideal semiconductor for now) to dissipate the excess power (so the DC bus hoovers around 550 to 600 V).

I am controlling the switch PWM signal, manually for the time being (pulse generator with a step inut for the duty period). Silly question, I am attempted to control the chopper duty cycle with a PI controller, as the model cannot be linearised how do I tune the PI gains? Also will the tuned PI controller always output a 0 to 1 value for the duty cycle?

Any pointers would be great.

Thanks,

Patrick

Answer 1

[Joel Van Sickel]

no, the value should be between 0 and 1, but usually not at the extremes if you've sized your resistor correctly. In general, for a system like this, you'd probably just tune the PI controller by hand (guess and check), but you could replace the switch with a variable resistor and make the resistance and input signal that would be linearizeable (you'd have to do some match to scale back to a 0 to 1 signal) OR, if you are really ambitious, you can use frequency response estimation to linearize the system around an operating point the frequency domain. https://www.mathworks.com/company/technical-articles/estimating-the-frequency-response-of-a-power-electronics-model.html

However, for this, I'd probably set up a more complex control scheme. As you are in control of the motor, you should know almost exactly how much current you will be regenerating, so you can use this as a feedforward signal to set the initial rate at which the chopper should run.