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6 switch H bridge + 3 phase motor commutation

Discussion in 'Datasheets, Manuals and Component Identification' started by ecdowney, May 6, 2009.

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  1. ecdowney

    ecdowney

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    May 6, 2009
    Can anyone point me to docs or app notes that describe how to correctly commutate the six switches in an H bridge connected to a brushless 3 phase Y motor?

    My problem is that when the load is off balance and pulling the same way as the motor is already turning, the control loop tries to reverse power to control the fall, as it should. But just as the control loop sign crosses zero the motor suddenly jerks to a halt instead of slowing smoothly. It looks like when the control loop reverses the commutation cycle suddenly the back EMF is finding a path through the H bridge and causing a large increase in resistance to motion. I have a hunch there is a way to sequence the H bridge such that either 1) the back emf is always cut off or (more likely) 2) is always allowed to flow so the control loop just deals with it like any other disturbance.

    FWIW, I'm using an IR IRAMY20 H bridge with an Harmonic Drive FHA-25C-100-US250. I'm controlling the IRA from the PWM outputs of a TI F28335 DSP.

    Thanks in advance for any tips.
     
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