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Cannot reach the rated power

Brant Zheng
Intellectual 415 points

Hello InstaSPIN community,

Here is my high current ACIM.

I am running the “lab12b” with DRV8301-69-KIT and making some load testing with a motor dynamometer.

 

First, I set “SpeedRef_krpm” to the rated speed(2.6krpm) with no load. Then I increase the torque of the shaft little by little. With the torque increasing, Iq increases little by little as well and the speed(2.6krpm) keeps steady. But when Iq increases to 30A, I put a little bit of torque increase, Iq directly jumps to the max current(41.25A). After that, if I keep increasing the torque, the speed will decline down and Iq maintains the saturation value.

 

I find that this situation is associated with “USER_IQ_FULL_SCALE_FREQ_Hz”. In that case, I set USER_IQ_FULL_SCALE_FREQ_Hz = 2600rpm * 4 poles /120 ≈ 100.And Iq exhibited good linearity within 0 to 30A, but suddenly jumps to the max current(41.25A) when it is just over 30A.

 

In another case，I set USER_IQ_FULL_SCALE_FREQ_Hz = 200. Iq exhibited good linearity within 0 to 20A, then suddenly jumps to the max current(41.25A) when it is just over 20A. It seems that Iq will lose control, jump to the max current and maintain the saturation value earlier if I set USER_IQ_FULL_SCALE_FREQ_Hz to a bigger value.

 

By the way, if I set “Flag_enablePowerWarp” to 0, Iq will directly jumps to the max current(41.25A) even with no load and the speed will never get the reference value. could you give me some advice?

 

Best regards,

 

Brant Zheng

  • 0
    Guru 12800 points

    Brant,

    When your speed loop is in saturation, iq ref is 41.25A, what is the maximum torque you are able to get from the motor before it cannot spin the motor any longer?  Is this torque the rated torque of the motor?

    Most motors are not able to run at rated speed and rated current.  They will get into a mode where the speed falls off in order to supply additional torque.  

    One thing you can try is to decrease the USER_MOTOR_MAGNETIZING_CURRENT.  This will allow you to put more current into the Q-axis of the motor.  

  • 0
    TI__Guru** 118090 points

    your motor parameters are incorrect.

    if you are using 40A for Id, that only leaves you sqrt((41.25)^2 - (40^2)) = 10A for Iq torque generation

    If 41.25A is really the max for this motor I'd try a magnetizing current of (29.0) as a better guess.

    Your Rr also looks a little high, it's typically smaller than Rs.

    And your Ls...that's just a guess to give Rs/Ls = 2x the rated frequency? 

    I assume you tried motor ID but it did not work correctly?

  • 0 in reply to ChrisClearman
    Intellectual 415 points

    Hello Chris and Adam,

     

    Thank you for your attention!

    1. There is an unsolved problem in my motor ID and I post it on “Critical error occurs when Using InstaSPIN-MOTION” before. Finally I asked my motor supplier for these parameters and only got “Rr” and “Rs”. So I took a guess to give Rs/Ls = 2x the rated frequency. Then I ran some labs smoothly but failed when I tested the load characteristics.

    2. I checked the “motor data graph”. It shows that the motor is able to run at rated torque and rated speed. But when the speed loop is in saturation, the torque gets just the half of the rated value. I tried to decrease the USER_MOTOR_MAGNETIZING_CURRENT to “29A”, and the result is the same(IqRef gets “34A” --> put a little bit of torque increase --> IqRef gets “41.25A”). Is this problem caused by my guessed motor ID or something else?

    Best regards,

    Brant Zheng

    Motor parameters:

     

    Model:                    ZPJ0.75-90S-4

    Rated Power:         750W

    Rated frequency:    90Hz

    Rated voltage:        16V

    Rated current:        43A

    Rated speed:         2600r/min

    Rated torque:         2.75N.m

    8080.user.h

  • 0 in reply to Brant Zheng
    TI__Guru** 118090 points

    you need about 40A of Iq to create that torque, so if you keep mag_current at (29) you should increase the MAX_CURRENT to (50)

    if you still can't get there for some reason leave the (50) and start decreasing the max_current amp by amp

  • 0 in reply to ChrisClearman
    Intellectual 415 points

    Hello Chris and Adam,

     

    You really helped me a lot. Thank you very much!

     

    Following the method you suggested, I tried a few times and found the suitable magnetizing current of my ACIM to provide enough torque.

     

    As I mentioned that there is an unsolved problem in my motor ID and I post it on “Critical error occurs when Using InstaSPIN-MOTION” before. Finally I asked my motor supplier for these parameters and only got “Rr” and “Rs”. And I took a guess to give Rs/Ls = 2x the rated frequency and used a magnetizing current which was gotten from load testing.

     

    With the guessed motor ID, I run from lab03a to lab13. It seems that the motor can run smoothly under control. And I’m going to preliminary achieve my position-control application (steering system on a forklift). I wonder what potential problems may be caused by using these guessed ID parameters? What motor indexes or performance may be adversely affected?

     

    Best regards,

     

    Brant Zheng

  • 0 in reply to Brant Zheng
    TI__Guru** 118090 points

    incorrect value of Rr will make the FAST speed/torque estimations incorrect.

    incorrect Ls will effect the FAST angle estimation, and can cause the current control loops to not be tuned as well as possible.

    incorrect magnetizing current reduces efficiency.