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BLDC motor phase Current waveform's at high speed

vankayala krishna kanth
Prodigy 25 points

Dear sir/madam,

I have a small doubt in controlling BLDC motor, when motor is operated in 6-step commutation sequence using hall sensors as feedback, phase current shape should be in quasi-square wave. 

When i am simulating, Bldc motor logic in Matlab waveforms are generating correctly but in Realtime hardware the waveforms are not in correct shape.

I have tried at low speed also, at that time one commutation step signal is missing every time.Current waveforms are attached to this thread.

At high speed, it generating more spikes across the current sensor (ACS712).

I am using tms320c28069 micro controller.

Regards,
krishna kanth.

  • 0
    TI__Guru** 116920 points
    It seems like you didn't get the correct commutation point from hall sensor, there is some delay between hall sensor signal and drive commutation . You can monitor the current waveform and hall sensor output signal in the same time. And make sure that the installation of hall sensor is right, if no, you need to do calibration for hall sensor in your project.
  • 0 in reply to Yanming Luo
    Prodigy 25 points
    Thanks for the reply.
    As you mentioned, i have already checked current waveform and hall sensor output signal in the same time. The hall sensor signal is not coming correctly, because of that current is not generated as required.
    one thing i have noticed is hall sensor signal is in not 50% ON.
    How to calibrate hall sensor ?
  • 0 in reply to vankayala krishna kanth
    TI__Guru** 116920 points

    In general, the hall signal should be correct, and only has a very small error that is ok for motor control in most cases. You'd better to check with motor provider if there is a big error.
    And you may add a calibrated code to implement correct commutation, add a delay time to change commutation if the hall signal is ahead of right commutation point, the delay time need to be calculated based on current motor speed. Add also a delay time for commutation if the hall signal is back of right commutation point, but need to use the previous hall signal and delay time is also calculated based on current motor speed.