Choosing PWM frequency for brushless DC motor

I bought a DC motor from China to build a drone and it looks like this: DC motor.

It is a 2212 1000kV DC motor. I am trying to figure out the right PWM frequency to use and I was referring to here and here. I think to select the PWM frequency, the most important parameters to consider are the R and L of the motor. If I were to refer to the datasheet above (assuming that it is the same as the one that I bought as they look the same), the R value is provided. The L, however, is not provided and I do not have any equipment to measure that. In this case, how should I measure/estimate the value of L so that I can select the right PWM frequency?

Please correct me if my understanding in selecting a suitable PWM frequency is wrong. My ultimate goal is to decide on a right PWM frequency with some understanding in the theory behind it.

Thanks.

Edit: I am using ESC to drive the motor. Does that caused the PWM frequency to be fixed at 50Hz?

• Too low (below 20 kHz) and you can hear it whistling.
– user16324
Commented Jul 29, 2021 at 17:40

Basically the higher the better. Until hysteresis and switching losses become significant.

Small motors have been tested at up to 5MHz.

More normal frequencies with iron armature motors would be a few tens of kiloHertz. Coreless motors tend to have lower inductance so would need a higher frequency to avoid losses that would cause excessive heating.

The lower limit in frequency is such that the pulse width should be much less than the time constant of the motor inductance and armature resistance.

For best efficiency, the system should be the same as a buck converter with the armature current close to constant over the entire switching cycle.

Don't forget the flyback diode across the motor to carry the current when the switches are off. In the case of an H-bridge driver the diodes are not across the motor directly but are across the switches so that the energy in the motor inductance is returned the supply when the switches turn off.

• so I can't really do any rough calculation in my case but can only select any frequency starting from 10kHz?
– mike
Commented Jul 30, 2021 at 7:42