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TMS320F280025C-Q1: RPM Stuck at 200

Seongmin Oh
Prodigy 40 points

Part Number: TMS320F280025C-Q1

Tool/software:

Dear Whom It May Concern,

I am currently using the F280025C-Q1 microcontroller with the Single Shunt DC-SS library and have encountered an issue described below.

Problem Description
I observe specific behavior where the target RPM is set to 3500, but the actual RPM begins at 200 and decreases continuously until it reaches a specific value (between 0 and 100). After this, the system recovers and resumes normal operation. This behavior occurs in probability of 3.6%.

I would appreciate your insights on the following questions:

  1. Why does the RPM decrease from 200?
  2. Why does the system initially become stuck at 200 RPM?
  3. Why does the RPM recover after decreasing?

Additional Observations

  1. When USER_MOTOR_MAX_CURRENT_A is set to 11A, the RPM decrease lasts up to 40 seconds.
  2. When USER_MOTOR_MAX_CURRENT_A is set to 20A, the RPM decrease lasts approximately 3 seconds.
  3. When USER_MOTOR_MAX_CURRENT_A is set to 7A, the 200 RPM stuck behavior does not occur.
  4. When motorVars.accelerationMax_Hzps is set to 800, the 200 RPM stuck behavior happens consistently every 28 runs.
  5. When motorVars.accelerationMax_Hzps is set to 200, the 200 RPM stuck behavior does not occur.

Please let me know if additional information or data would assist in analyzing this issue.

Thank you for your support, and we look forward to your response.

Sincerely,
Min Oh

  • 0
    TI__Guru** 117270 points

    Any current waveforms to show this issue? Any load is adding on the motor in this case? Can you check the Id & Iq within CCS watch window?

    The sensing current is not correct when startup the motor, so the estimated angle and speed may be not correct. You can try to tune the maximum torque current and speed controller that could be suppress this issue.

  • 0 in reply to Yanming Luo
    Prodigy 40 points

    Thank you so much for your quick answer.

    Answer to your questions

    1. Here is the U phase current waveform

    2. Load to the motor does not take part into causing this problem. This happens with or without load to the motor.

    3. The Id & Iq are as such when 200 RPM stuck happens.

    Notes

    1. When I change USER_MOTOR_Rs_Ohm from 0.2 to 0.35, RPM stuck happens at 1000RPM instead of 200RPM. And the abnormal RPM stuck happens consistently.

    2. When I change USER_MOTOR_Rs_Ohm from 0.2 to 0.15, RPM stuck doesn't occur.

    Questions

    1. Why is this kind of behavior occur?

    2. What is causing this kind of behavior?

    3. What is the root cause and how to fix this?

    4. Would you be able to elaborate more with detail on "You can try to tune the maximum torque current and speed controller that could be suppress this issue."?

     - Did you mean try to tune the speed controller P gain, I gain and USER_MOTOR_MAX_CURRENT_A?

  • 0 in reply to Seongmin Oh
    TI__Guru** 117270 points

    Can you post the waveform to show the issue you mentioned above? Not the waveform under normal running.

    Seongmin Oh said:
    1. When I change USER_MOTOR_Rs_Ohm from 0.2 to 0.35

    You should use the exact Rs according to the motor, not any values.

    Seongmin Oh said:
    3. What is the root cause and how to fix this?

    Please monitor the output of the speed PI controller, and tune the speed PI controller as mentioned above.

    Seongmin Oh said:
     - Did you mean try to tune the speed controller P gain, I gain and USER_MOTOR_MAX_CURRENT_A?

    Yes.

  • 0 in reply to Yanming Luo
    Prodigy 40 points

    That is the waveform under abnormal running.

    When the motor is running at 200 RPM.

    It is abnormal because 200 RPM doesn't consume 10A to run the motor without load.

    You should use the exact Rs according to the motor, not any values.

    - Yes, I have used exact Rs according to the motor but 200 RPM stuck situation happened. I was trying to find the root cause by changing Rs value.

     

    Please monitor the output of the speed PI controller, and tune the speed PI controller as mentioned above.

    - Lowering the Kp and Ki will help reduce the abnormal situation. It seems to have same effect with changing Acceleration value.

    - Why do you think this problem is related to the Speed PI controller?

    Below is under normal running Speed PI Handle

    Below is under abnormal running Speed PI Handle

    Thank you for your help!

  • +1 in reply to Seongmin Oh
    TI__Guru** 117270 points
    Seongmin Oh said:
    That is the waveform under abnormal running.

    Can you show more electrical period? The waveform looks good.

    Seongmin Oh said:
    - Why do you think this problem is related to the Speed PI controller?

    Since the issue is related to the specific speed, please keep tuning the controller parameters for speed.