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Current waveforms

Rajan Joshi
Expert 1020 points

Other Parts Discussed in Thread: DRV8301

Hello, 

My setup is DRV8301 and LAUNCHXL-20869M.

I am trying to see the current that is going into the three phases of my motor. 

I want to use the current patterns from all the three phases to control the position of the motor, as in get the total number of pulses from the motor and use that to set the position of my motor. 

Is there a way that I can monitor these currents? or which points can i probe to observe these waveform on a scope ?

Is there such a variable that I can monitor that shows me the current being drawn by the driver? I cannot seem to find one in lab 05b.

Regards,

Rajan

  • 0
    TI__Guru** 119680 points
    you would need to use the current samples from the shunts to produce a phase current waveform

    "I want to use the current patterns from all the three phases to control the position of the motor, as in get the total number of pulses from the motor and use that to set the position of my motor. "
    It doesn't work that way. Are you using a rotor sensor?

    "Is there such a variable that I can monitor that shows me the current being drawn by the driver? "
    No, for currents you are sampling 2-3 low side shunts and you are generating an Iq peak current command. That's all of the currents you are monitoring.
  • 0 in reply to ChrisClearman
    Expert 1020 points
    Hello Chris,

    I understand, thank you for the quick reply.

    What I was trying to get at is how does the motor get to the speed that I have specified using the SpeedRef variable? How does the motor actually attain that speed and how is that communicated to the controller by the motor.

    So, what I would like to do is to take the integral of speed to achieve the position of the motor.

    Is there a way I could go about doing this?

    Regards,

    Rajan
  • 0 in reply to Rajan Joshi
    TI__Guru** 119680 points
    " What I was trying to get at is how does the motor get to the speed that I have specified using the SpeedRef variable?"

    A PI controller is used to create an error signal for the desired speed (SpeedRef is passed through a TRAJ module which takes into account acceleration settings to generated a desired speed reference) minus the Speed_Est. The error signal creates an IqRef_A value for the Iq PI current control, which is effectively a torque command.

    So torque is increased to increase speed and decreased to decrease speed.

    "how is that communicated to the controller by the motor. "
    The FAST observer provides a Speed Estimate that is used by the speed controller as feedback.

    "So, what I would like to do is to take the integral of speed to achieve the position of the motor. "
    Well, I suppose you could, but to what end? At best you could probably count revolutions. You wouldn't be able to determine down revs plus degrees between revs. You also wouldn't be able to actually control the output to any of these specific positions.

    FOC is torque control
    With good speed estimates you can add a speed controller.
    With a position sensor you can add a position controller.