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Drag Brake with Torque Control

Asif Ahmed
Expert 1570 points
Other Parts Discussed in Thread: MOTORWARE

Hello -

I am designing for an application that requires active deceleration of the motor. With InstaSPIN, speed control provides this active deceleration when a lower speed is commanded. However, speed control is not an option for this application. Rather, I need torque control, but upon requesting a lower torque command (or even if zero torque is commanded suddenly), I want the motor to decelerate actively, rather than purely coasting.

Please advise on the best way to implement such a feature. I would prefer something that requires as little tuning as possible from motor to motor. Any assistance is much appreciated!

Best,

asifjahmed

  • 0
    TI__Guru** 119500 points
    active braking simply requires commanding an IqRef with the opposite polarity. If you are motoring with +IqRef_A then applying a -IqRef_A will actively brake the motor
  • 0 in reply to ChrisClearman
    Expert 1570 points
    Thanks Chris. I'm aware that commanding negative Iq will actively brake the motor. However, short of creating another PID loop to manage this, I'm not sure how to accomplish the desired effect here. In torque mode, during rapidly-lowering throttle inputs, is there a way to detect that the inertial torque being applied to the motor exceeds the current torque reference, and apply some proportion of negative Iq? Basically i want to change the coasting behavior (default) to something more active. Many off-the-shelf motor controllers have this feature and refer to it as "drag brake" or "dynamic braking". These aren't using FOC or torque control, though....

    Any further insight would be appreciated, Chris. I'm fairly well-versed in Motorware/InstaSPIN at this point, so am seeking some deeper knowledge.

    Best,
    -asifjahmed
  • 0 in reply to Asif Ahmed
    TI__Guru** 119500 points
    You could set your IqRef commands to be a default negative value instead of 0. And you apply this until the speed is near zero. You could have different settings for this -IqRef to give you different modes of braking. You could further modulate this to change the negative IqRef at different speed zones.

    or you can set-up a control loop for setting this negative IqRef. It could be based on speed, or deceleration, whatever you like.