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The 30 degree delay of sensorless trapezoidal communication compared to sensored one.

Aaron Chen (FAE)
Intellectual 1310 points

Hi Team,

I am asking because I don't know why there is a 30 degree delay of sensorless trapezoidal communication compared to sensored one?
I inferred that is because of it's the backemf, the waveform can't react immediately, but I am not sure.
Please refer to following Youtube link, it's from TI Precision Labs - Motor Drives: Trapezoidal Commutation

As the video, the six segment of sensorless are 30 degree delay than sensored one. 


The waveform of sensorless is below, it is located at top left.
https://youtu.be/xIORHY8Ii90?t=502

The waveform of sensored is below, it is located at bottom left.
https://youtu.be/xIORHY8Ii90?t=424

  • 0
    TI__Guru 71516 points

    Hello Aaron,

    Please provide some additional information such as motor driver IC used in the circuit.  

    Thank you,

    ~Leonard  

  • 0
    TI__Intellectual 1310 points

    Here are some supplement regarding the question.

    As the sensored and sensorless waveform below, the waveform are with respect to the same truth table.
    but the waveform of sensorless one has 30 degree delay than the waveform of sensored one.
    I am curious about the reason of it.  

    Any advice will be appreciated.

  • +1 in reply to Aaron Chen (FAE)
    TI__Mastermind 21805 points

    Hello Aaron,

    For a sensored approach, the Hall sensors are placed 60 degrees apart and ideally cause commutation to happen in the displayed sequence.

    For a sensorless approach, the Back-EMF zero crossing is ideally in the center of the Hi-Z window, but some lead angle adjustment may be required to set this time exactly. The lead angle adjusts the time from the back-EMF zero crossing to the actual commutation in sensorless approaches.

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    TI__Mastermind 24405 points

    Aaron,

    If your issue has been resolved, please help us out by clicking the green “This Resolved My Issue” button. If you have a related question, please use the orange "Ask a related question" in the top right corner of the page.

    Regards,

    Vishnu