Electronic – the mathematical relationship between MOSFET switching frequency (motor speed control) and motor speed in rpm

controlmotor

What is the mathematical relationship between the switching frequency of MOSFET in a three phase motor controller (induction motor and BLDC motor) and the speed in rpm of the motor shaft?

Best Answer

There isn't one really.

The switching frequency of the MOSFETs is a function of the inductance and resistance of the motor and is used to control current ripple (and therefore torque ripple).

The speed of the motor shaft is a function of how fast you change which of the three phases are being powered.

That being said, there are limits. For instance the switching losses incurred from a high switching frequency will limit the amount of power available to the motor and therefore limit the speed with which you can commutate the motor.