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can we do V/f control of a PMSM?

I am making a simulink model for PMSM control by V/f method. This model works for an induction motor but the speed output for PMSM coming oscillating, i think the fields are not synchronizing. Am i missing something?

Re: can we do V/f control of a PMSM?

Hello,

Indeed the fields may not be synchronizing properly. With an induction motor, the rotor slip induces currents in the rotor windings which produce a natural electro-magentic damping effect. Within a PMSM there is no slip, no induced rotor current like in an induction motor, therefore no inherent damping. The rotor PMs must lock exactly to the rotating stator field. The angle between rotor and stator fields behaves like an undamped pendulum resulting in any disturbance causes the rotor to oscillate around sync position.

Options to address this:

1. Add an active damping to your V/f model - you can inject the missing damping by modulating the output voltage or frequency based on estimated speed error:

estimate rotor speed using a sensor or a sensorless technique
feed d(w_error)/dt back to modulate the V/f output amplitude

This is the simplest fix if you want to stay with V/f method.

2. Other option would be to move to I/f control where you control the stator current magnitude at a commanded frequency. More information about I/f control on the following page I-F Controller

Hope this helps!

Best regards,

Stefan.