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CCS/BOOSTXL-DRV8301: Not achieving given speed in instaspin lab 5e

Abdul Rasheed28
Intellectual 480 points
Part Number: BOOSTXL-DRV8301

Tool/software: Code Composer Studio

After tuning bandwidth scale, when we set 'gMotorVars.SpeedRef_krpm' to maximum speed (for me it is 4000 rpm), the motor rotates in a speed of 2665 rpm. What should I do to get the actual speed?

  • 0
    TI__Expert 6065 points
    The expert for this part has been notified and will help you tomorrow when he is back in office.
  • 0 in reply to Sanmesh Udhayakumar
    Intellectual 480 points

    Hi Sanmesh,

    I didn't get any response yet.

  • 0 in reply to Abdul Rasheed28
    TI__Expert 6065 points
    I've sent an email to the assigned person to this question to try to answer it. Meanwhile, I can try to help, though I'm not an expert on this.

    1) There seems to be a factor of 1.5 between your set rpm and the actual rpm (4000/2665 =1.5). Is this relationship the same at other set speeds?
    2) Make sure the USER_MOTOR_NUM_POLE_PAIRS was identified correctly. Did you use instaspin to automatically find it or did you enter it yourself? You can try taking whatever current USER_MOTOR_NUM_POLE_PAIRS, and set the new value as USER_MOTOR_NUM_POLE_PAIRS*1.5. This is because RPM = Hz*60/#PolePairs. So if USER_MOTOR_NUM_POLE_PAIRS is 1.5x greater than actual, then the RPM will be 1.5 times less than desired.
    Sanmesh U.
  • 0 in reply to Sanmesh Udhayakumar
    TI__Guru** 115490 points
    Just have a couple of suggestions for you beside Sanmesh replied.
    1. Please ensure lab02b/c and lab05c have been run first to identify the motor parameters and inertia, and then set the identified data correctly in user.h.
    2. Increase the USER_MOTOR_MAX_CURRENT in user.h to check if the maximum torque current is too small to limit the speed.
  • 0 in reply to Sanmesh Udhayakumar
    Intellectual 480 points

    Hi Sanmesh,

    I tried your suggestion. For my motor value of 'USER_MOTOR_NUM_POLE_PAIR' was 2. Then I modified it to 2*1.5=3. Now when I set 'gMotorVars.SpeedRef_krpm' to 4.0, I got the actual RPM as 3863. Again shows the difference.

  • 0 in reply to Abdul Rasheed28
    TI__Guru** 115490 points
    1. Make sure that the motor parameters are identified as mentioned above.
    2. Please check the electrical frequency (fe) of the motor phase current to see if the pole pair is correct. You may calculate the feedback speed(rpm) = fe(Hz)*60/Pole-Pairs
    3. Ensure the maximum current is enough for high speed.
    4. Try to increase the dc bus voltage to see if the input voltage is not enough for high speed.