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TMS320F28027: Not enough Torque being generated

Rajan Joshi
Expert 1020 points
Part Number: TMS320F28027

During identification my motor runs well and my header file is attached.

After identification however, when i try to run the motor in Lab3a, the motor is running very jerky. I tried to move onto to the torque controller lab4 which seems to be able to run the motor better. 

However, when I set:

gMotorVars.Flag_enableRsRecalc = true;
gMotorVars.Flag_enableForceAngle = false;
gMotorVars.Flag_enableOffsetcalc = true;

my motor seems to be very jerky and not run. 

When I leave :

gMotorVars.Flag_enableRsRecalc = false;
gMotorVars.Flag_enableForceAngle = true;
gMotorVars.Flag_enableOffsetcalc = true;

The motor does not run at low speed. I was able to provide enough torque before for the application that I am using this motor for. Now the motor seems to provide almost no torque even in the torque controller mode.

I know that this motor is capable of providing enough torque for my application since I have been able to do it several times before. 

I am also able to control the motor very well with my hall effect sensor feedback with position control using Lab 5b. However even increasing speed does not help increase the torque. I am able to stop the stator at high speed, but I can still hear the motor trying to spin out and the motor temperature get to almost 10 degrees below the overheat temp. 

What could be the issue?

I am using the 28027F with the 8305EVM motor driver. 

Regards,

Rajan Joshi5706.user.h

  • 0
    TI__Guru** 115450 points
    1. It seems the motor is a low inductance motor, use lab02c to identify the motor properly first.
    2. Adjust the Kp and Ki of speed PI regulator, reduce both value to 1/4 of original calculated value.
    3. Reduce the Kp and Ki of current PI regulators also.
  • 0 in reply to Yanming Luo
    Expert 1020 points
    Hello Yanming,

    I have performed all of that with no luck. I also monitored the Iq_A variable and i can see it shoot up to almost the rated current of the motor which is about 11 Amps and it is still producing no torque.

    I did identify the motor with lab2c.

    Is there some current limit that I am setting in my header file?

    Regards,

    Rajan
  • 0 in reply to Rajan Joshi
    TI__Guru** 115450 points
    You can check the output of speed PI if you are using speed close loop, to look whether the Ui (ctrl. pid_spd.Ui) of speed PI is equal to max current (_IQ(maxCurrent/iqFullScaleCurrent_A)). If yes, it means the max current is too small.
    If no, check whether the input voltage is enough for torque current, is gMotorVars.Vs equal to USER_MAX_VS_MAG_PU?
  • 0 in reply to Yanming Luo
    Expert 1020 points
    Hello Yanming,

    Thank you for your help!

    All those parameters looks okay.

    I am able to identify the motor but am not able to run the motor using the same parameters in lab2c when i set the run identify flag again. When I run lab 5b the motor starts up good, maintains the speed, I start applying some load with my hands to the shaft of the motor, as soon as i start to do that the motor freaks out and starts to jitter, this causes the motor to heat up. After which it jitters some more and then gets back to its normal speed.

    I am really frustrated that this motor is being identified but I am not able to run it correctly.

    Please send help.
  • 0 in reply to Rajan Joshi
    TI__Guru** 115450 points
    The process is right, use lab02c to identify motor parameters, and input them in user.h, and then use lab05b to run the motor.
    Can the lab05 run the motor smoothly from low speed to high speed without load or with a light weight? How much load was applied on motor will appear the issue? Percent of rated torque?
    Tune the speed controller so that the reaction of the speed controller is fast enough to avoid the motor stall, and tune the current controller to improve the response also.
  • 0 in reply to Yanming Luo
    Expert 1020 points

    "The process is right, use lab02c to identify motor parameters, and input them in user.h, and then use lab05b to run the motor."

    This is what I did.

    Can the lab05 run the motor smoothly from low speed to high speed without load or with a light weight?

    No, sometimes the motor jitters on startup, my motor heats up like crazy, then somehow it fixes it self and runs at the commanded speed. Maintains for a while and then freaks out again and starts jittering and heating up and repeats this cycle over and over again until the motor gets too hot.

    How much load was applied on motor will appear the issue? Percent of rated torque?

    its almost 5% of the rated torque.

    Tune the speed controller so that the reaction of the speed controller is fast enough to avoid the motor stall, and tune the current controller to improve the response also.

    I am tuning the speed controller and the current controller using lab 5b. I am unsure how to find the motor inertia needed to find the motor constant. 

    Also, I was wondering since this is a small hobby motor with low inductance, 12 poles with a max current of 15 amps, do I need to adjust the gains even further? I was reading this thread and it seems like i have to reduce the speed gains by a factor of 10. 

    Please advise.