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DRV10983EVM: open to closed-loop control issue

rac
Prodigy 10 points
Part Number: DRV10983EVM
Other Parts Discussed in Thread: DRV10975, DRV10983, MOTORSTUDIO, MCF8315C, , DRV10975EVM

Tool/software:

Hello,

I have been attempting to tune several BLDC motors with the DRV10983 and DRV10975 evaluation modules. The motors I am working with are within the specifications for both DRV10975 and DRV10983, however, they produce very low back-emf. I do not currently have the exact back-emf motor constant, Kt, since I do not have datasheets for the motors, but I know from testing that it is very low and I expect it to be on the low end of the acceptable range for these EVMs. When I follow the tuning guide I am able to get them spinning in open-loop, but see very poor performance transitioning to closed-loop control, after which they immediately lock up. Additionally, the RPMs reported in the GUI are much higher than the actual RPM, which is typically the error I get that resulted in the automatic shutdown or lockup. For example, the motor will be spinning around 2000 rpm according to a tachometer, but the GUI will report values in the range of 18,000-20,000 rpm. Is there any way you can help me isolate the issue here? I have been assuming it is due to the low back-emf produced by these motors, but there could be something else I am missing. For reference, these motors are able to spin up to 20,000 RPM or greater using commercially available drone ESCs, but I am hoping to get better performance and reliability out of the TI motor drivers.

Thank you!

  • 0
    TI__Mastermind 23572 points

    Hi,

    Have you verified lead time tuning?

    Can you share R, L, KE information if available.

    I also recommend to use MCF8315C/16C EVM, use MOTORSTUDIO with SmartTune feature to tune and spin the motor.

    Also, can you share the waveform (zoomed in and zoomed out waveform from open loop to closed loop).

    Thanks and Best regards

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    Prodigy 10 points

    Hello,

    No I have not verified the lead time tuning yet. Here are the parameters for the motor I am working with. They were all determined through testing since I do not have the datasheet:

    Poles: 12

    R (phase to center): 2.25 Ohms

    Kt: 300 mV/Hz (although the most successful open-loop behavior I have found is with a much lower Kt, around 6 mV/Hz)

    By L, do you mean the LR constant? If so, I don't have this for this motor yet. I am also struggling to get the current waveform with this motor. I am using an oscilloscope with a 1 ohm shunt resistor to capture current, but adding the shunt resistor seems to be preventing proper motor startup in open loop. If you have any advice on how to better capture current that would be helpful.

    Thank you!

  • 0 in reply to rac
    TI__Mastermind 23572 points

    Hi Rac,

    I suggest to use MCF8315C/16C EVM, use MOTORSTUDIO SmartTune feature to tune the motor.

    The parameters are aucto calculated by the GUI, and then verify the parameters used with DRV.

    Do not use any shunt resistor which affects the performance.

    MOTORSTUDIO support MCF8315C/16C.

    Introducing SmartTune: Automatically Tune your Motor Parameters | Video | TI.com

    Thanks and Best regards

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    Prodigy 10 points

    Hi Venkatadri,

    Thank you for the information. How reliable is the MOTORSTUDIO SmartTune feature at correctly determining the parameters and closed-loop control of motors with very low back-emf? I have not had much success with the DRV10983EVM or the DRV10975EVM, so I want to make sure this EVM has a good possibility of working before purchasing.

    Thank you

  • 0 in reply to rac
    TI__Mastermind 23572 points

    Hi Rac,

     MOTORSTUDIO SamrtTune is published couple of months now and we have got good feed back.

    I encourage you  to experience the SmartTune.

    Thanks and Best regards

    Venkatadri S