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?

  • \$\begingroup\$ In a BLDC motor drive, there are two switching frequencies: the commutation frequency, and in most drive methods, a higher frequency switching with the goal of effectively applying less than the full supply voltage to the windings. There is also a third possibility: some BLDC motors with an integrated controller receive a speed or torque input through a PWM signal. Which are you asking about? \$\endgroup\$ – Phil Frost Jan 9 '13 at 16:08

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.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.