Motor Driver and Sinusoidal Commutation Question

Discussion in 'General Electronics Chat' started by asabalon, Nov 10, 2010.

  1. asabalon

    Thread Starter New Member

    Nov 10, 2010
    I am working with a three phase AC servo motor with a rating of 84V, 1Amp. I built a motor driver using 3 PMOS for the high sides and 3 NMOS for the low sides. Shown below is the circuit I built for the servo motor and the input signal I used.



    The input signal was chopped and fed to the six mosfets.
    PMOS1 = from phase 0 to phase 180
    NMOS1 = from phase 180 to phase 360
    PMOS2 = from phase 120 to phase 300
    NMOS2 = from phase 300 to phase 120
    PMOS3 = from phase 240 to phase 60
    NMOS3 = from phase 60 to phase 240

    I tried to implement this design with these control signals but it does not work. I do not know what went wrong. If my understanding is wrong about sinusoidal commutation and designing of motor drivers, please enlighten me. Thank You.
  2. asabalon

    Thread Starter New Member

    Nov 10, 2010
    i really need help in debugging this circuit...
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    I see the PWM portion is working, But not sure I understand why you are keeping the negative going portion, below zero.

    and the connection to the motor seems to be rather convoluted and perhaps self defeating. Check that portion again, and be sure that your motor inputs are correctly phased.
  4. BillB3857

    Senior Member

    Feb 28, 2009
    Although the motor connections appear convoluted, it looks like it a standard Y configuration for a 3 phase motor. As for the voltage going to the motor leads, unless I'm looking at all wrong (a strong possibility), it seems to be equivalent to a full wave rectified AC, not a true bi-polar AC. Am I seeing it wrong? Please enlighten me.