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TMS320F28027F: Motor driver w/ DRV8323S, motor stalls suddenly when torque is gradually increased

Michael Seeman
Prodigy 10 points
Part Number: TMS320F28027F
Other Parts Discussed in Thread: MOTORWARE,

I am running custom motor drive hardware using the TMS320F28027F and DRV8323S using firmware similar to motorware/instaspin lab5b.  The speed response feels pretty well tuned and stable.  

The test I'm running is to drive the motor at a constant speed, 1500 RPM or so, about midrange, and gradually increase load torque.

With the USER_MOTOR_MAX_CURRENT constant set to 8.0, as the command current reaches that value, the motor gradually and gracefully slows, as desired.

With USER_MOTOR_MAX_CURRENT  set to ~12.0, once the motor reaches 8-10A current consumption, it stops suddenly with a jolt.  The driver hardware used should be able to support over 50A of phase current.

I've attached a phase current waveform at the time of stall.

Any idea what's happening or what I should look for?

  • 0
    TI__Guru** 115480 points

    The maximum current of the hardware board is peak to peak current, that should be at least 4 times of the maximum torque current to avoid ADC sampling overflow. You might check if the peak current is close to half of the maximum current of the hardware, and make sure that the motor has enough torque output to support the adding load.

  • 0
    Prodigy 10 points

    The hardware uses 1 mohm current sense resistors and 20x CSA gain.  At 10A motor current, we are not anywhere close to overflowing the ADC.  With 7 mohm Rs and 10x gain, the motor stalled at the same current.  I'll take a look at the motor torque limits - but it was designed to do much more than this.

  • 0
    Prodigy 10 points

    Here's another recent scopeshot after trying a few things to fix the issue with no success.  It certainly appears that the current loop is becoming unstable at higher currents.  The labs manual does the analysis with a linear system - if it's stable at low currents, it should be stable at high currents.  There's clearly some nonlinearity coming into play - do you know where this is from and how to fix it?  I'm not sure if it's the current loop itself or the FAST estimator uncertainty. What's the best way to determine the FAST output stability and accuracy in the application setp?

  • 0 in reply to Michael Seeman
    TI__Guru** 115480 points

    It seems like the issue is not from the FAST estimator. Please make sure that the motor can generate enough output torque for this load.