Low RPM motor

[manishsangram]

We are using S12ZVMC128 MCU

We are trying to drive a motor at a low RPM of 500. Motor stalls at anything below 900 or is unstable and then stalls. We have tried various motors from 850 to 1200 to 500 Kv and we are using 24Khz PWM. We are using the Minibrd and the BLDC code using back emf (not PMSM).

Is there any guidance on how to do low RPM

[pachamatej]

Hello,

In my opinion, there is no general guidance to that. It depends on if you are using sensorless or sensor-based algorithm, PMSM or BLDC motor. Please note that the PMSM/BLDC is not related to the application in the MCU. It is related to the back-EMF shape of the motor.

To make the sensorless application running well, the motor should provide a good back-EMF response, thus the motor itself should be of a low nominal RPM. If the nominal speed is higher than the operational speed, some of the advanced techniques should be used, such as published in http://ieeexplore.ieee.org/document/5618131/?arnumber=5618131.

I hope it helps.

Regards,

Matej

[manishsangram]

Hello Matej,

We understand and agree with what you are saying. Certainly lower nominal RPM would work better. 

The question was more about whether existing settings could be modified in any way, such as would having a longer period for PWM by reducing the frequency from 24Khz to 10Khz be better for slow speed?

Another possibility we have been considering for long was would integration based commutation logic work better than just back-emf detection logic at low speeds?