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IS-MOTION zero speed for ACIM

Hello,

 

Sorry to bother you with a new question.

 

I meet a difficult problem, which I can hardly solve. I run the “lab5e” and follow the “Lab procedure”. When I set “gMotorVars.SpeedRef_krpm” to 0 to make the ACIM hold zero, the shaft begin to violently oscillate with a high current up to 20-30A. I find that decreasing  “gMotorVars.SpinTAC.VelCtlBwScale” makes this oscillation less violente, but it will lose the robustness of the system and the oscillation still exists.

 

And when I run the “lab6a” that problem comes again. I change “gMotorVars.SpeedRef_krpm” from “1” to “-1”, then from “-1” to “1”. The oscillation of the shaft will continue for a few seconds when the speed gets closed to “0”. But this zero-speed-oscillation does not happen every time. Sometimes it can make a smooth transition.

 

By the way, in my application, I want to use “SpinTAC Position Control” technology to make a steering system of a forklift. The ACIM needs to tightly hold zero after getting the reference position.

 

Could you give me some advice? Thank you for your time!

 

Best regards,

 

Brant Zheng

 

  • the root cause of your issues is that at zero speed the FAST observer does not have good enough inputs for it to produce good estimates. 

    you can look at turning off the PWM outputs at zero speed, or providing full PWM High or Low side for a "brake" function, but it will be challenging to make 0 speed control work well in your application. 

    do make sure that you have ForceAngle DISABLED if you are trying 0 speed, otherwise you will ALWAYS get a rotating angle estimate which will certainly cause issues.

    Brant Zheng said:
    And when I run the “lab6a” that problem comes again. I change “gMotorVars.SpeedRef_krpm” from “1” to “-1”, then from “-1” to “1”. The oscillation of the shaft will continue for a few seconds when the speed gets closed to “0”. But this zero-speed-oscillation does not happen every time. Sometimes it can make a smooth transition.

    sounds like you have ForceAngle enabled.

    If you have it disabled, just using FAST, and the speed controller is stiff enough, and there is some amount of load, and the acceleration is above some minimum (very low usually), you can drive through zero speed quite well. here is an example:

     

  • Brant,

    It seems like you have been trying to control your motor'a position without a position encoder. This would be the cause of your zero speed issues. SpinTAC Position Control will be able to hold a fixed position on an ACIM very well but it requires a rotor position sensor to do that. Typically you can use just a incremental encoder. There is an incremental encoder that come with the HVACIMTR from TI. 

  • Hello Adam,

     

    Thank you for your advice!

     

    I put an incremental encoder to my ACIM and it run perfectly without a zero problem.

     

    Best regards,

     

    Brant Zheng

  • Hi,
    I'm in the same (5e) lab with a motor without load and without encoder. Motor sheet information is very poor. I never reach true zero speed. The motor stops and makes short rotations to stop again, I cannot find the solution yet. I need some hints.
    Best regards.
    Andrés
  • disable ForceAngle
    stiffen your speed controller

    remember that the FAST estimator isn't giving reliable feedback at 0 speed, so it will not hold indefinitely. The rotor will move - FAST will lock on - control to zero speed, then it will drift again and the process continues.