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Accesse of Neutral point in 3 phase motors

Discussion in 'General Electronics Discussion' started by electronicsLearner77, Jan 23, 2021.

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  1. electronicsLearner77

    electronicsLearner77

    174
    1
    Jul 2, 2015
    When you are controlling the 3 phase motors using a micro controller using FOC or any other methodology, i assume that ,we can only control the phase-phase voltages of the motor and not the phase - neutral voltage, this is because the neutral is never accessible from the motor. Is my understanding correct?

    upload_2021-1-23_10-11-55.png
    So, i can control phases R,Y,B by generating the SVPWM / Sine wave using R,Y,B terminals that is phase-phase, but i cannot control the Phase - Neutral voltage, since the neutral is not exposed . Am i correct?
     
  2. Minder

    Minder

    3,182
    691
    Apr 24, 2015
    BLDC, PMAC and ECM (HVAC) motors are connected either Star or Delta arrangement.
    Why do you need access to the star point, if it has one?
    M.
     
  3. electronicsLearner77

    electronicsLearner77

    174
    1
    Jul 2, 2015
    No, i do not want access to the neutral point. It is only a clarification.

    Ok, always i get confused and i repeat the same question, i think my specific question is
    upload_2021-1-23_12-37-21.png
    I generate the micro controller R,Y,B with reference to ground of the micro and they are directly connected to the R, Y, B phases of the motor. There is no direct link between the grounds of the micro and the motor. Is it required or not? They are a kind of isolated am i correct?
     
  4. electronicsLearner77

    electronicsLearner77

    174
    1
    Jul 2, 2015
    From the reply, is my question relevant?
     
  5. Minder

    Minder

    3,182
    691
    Apr 24, 2015
    You don't normally drive a BLDC etc motor directly from a micro, there is usually a mosfet bridge or drivers or other means of driving the motor.
    The bridge or drivers common can be isolated or not from the micro in question.
    By 'ground' of the micro and 'neutral' ?? of the motor, I assume you mean circuit common?
    I prefer to use 'power common' it is less ambiguous, Ground is often used in the wrong context.
    M
     
  6. Minder

    Minder

    3,182
    691
    Apr 24, 2015
    Just to clarify, if the drives section is not isolated, opto's etc, then both power common's have to be connected.
    M.
     
  7. electronicsLearner77

    electronicsLearner77

    174
    1
    Jul 2, 2015
    If you can show me a rough sketch it will really help. For a motor i am not sure it has a separate power common, i am aware of R, Y, B connections coming out.
     
  8. Minder

    Minder

    3,182
    691
    Apr 24, 2015
    What are you using for a motor drive/power section?
    Usually the drive semi's have a power common to the motor supply.
    I can see if I have a diag somewhere.
    Also look up ST APP note AN1625. shows how the common is related to the motor
    M.
     
  9. electronicsLearner77

    electronicsLearner77

    174
    1
    Jul 2, 2015
    Thank you for support. I use MOSFET for drive section.
     
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