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DRV8301-69M-KIT: Problem at higher speeds with BLDC motor

Terry Harrison
Intellectual 615 points

Part Number: DRV8301-69M-KIT

I am using InstaSPIN FOC and I have gone through the labs and have used lab10a as the basis of our application. Our application has to work the motor from dead stop with full mechanical load to 6000 RPM with full load. The documents have suggestions on how to work the dead stop with full load and they have worked fairly well. I think I am close with the low end. The motor is a 258 kv unit running 36 volts, it has 11 pole pairs and we require approximately 1 Nm torque from the unit. I can run the motor with a minimum load all the way to 6000 RPM without issue. When I load the motor to require approximately 0.5 Nm it does fine until about 4500 RPM and then the motor simply cuts off. It then tries to restart and makes a grinding sound within the motor. If the load is reduced it operates fine. 

The voltage and current is well behaved from the power source so it does not appear it is hitting some limit of the power supply. The power supply have a 20 amp capacity and with the load described it is only using about 8 a. The motor current is rated much higher than these values.

Can you give me some pointers as to what is failing at this level and what values to look for please?

  • 0
    TI__Guru** 117160 points

    1. PLease use lab02c to identify the motor parameters, and use a higher PWM frequency as the settings below in the file of the user.h/user_j1.h

    #define USER_PWM_FREQ_kHz         ((float32_t)(45.0))

    #define USER_NUM_PWM_TICKS_PER_ISR_TICK       (3)

    2. Please try to use lab10a with overmodulation by setting USER_MAX_VS_MAG_PU  to 0.574 in user.h as below. To increase the dc bus voltage if the maximum speed can't be still achieved.

    #define USER_MAX_VS_MAG_PU        (0.5774)

    3. Make sure the USER_MOTOR_MAX_CURRENT and the dc bus voltage is set to enough value for high speed.

  • 0 in reply to Yanming Luo
    Intellectual 615 points

    Ok I have been working to try to be sure what is happening but it is still unclear. You have told me before regarding the PWM rate, the USER_MAX_VS_MAG_PU, and the PWM ticks. Those have been set to those values since the last suggestion from you. The max motor current is set to 25 amps and the bus voltage is 36. You mentioned was the DC bus voltage set high enough. The motor specs say so but to verify I also connected the motor to a simple triangle controller and ran it at full load, full speed with the 36 volt power supply. At this point the TI controller using InstaSPIN FOC seems to not be able to start the motor at full load, it can run it at full load from around 600 RPM until about 4000 RPM. At 4000 RPM the motor just stops and then it tries to restart but it has a grinding noise as though the SVM is simply out of sync.

    No other computing load is running on the processor so from what we can tell it is not being over taxed for computation. At this point we are simply out of ideas and are unable to achieve what seems should be attainable with the TI InstaSPIN. I am not sure where to go looking. Some suggestion would be very appreciated.

    Terry

  • 0 in reply to Terry Harrison
    TI__Guru** 117160 points

    You might take a look at chapter 14 in the InstaSPIN-FOC™ and InstaSPIN-MOTION™ User's Guide as the link below.

    http://www.ti.com/lit/ug/spruhj1h/spruhj1h.pdf 

  • 0 in reply to Yanming Luo
    Intellectual 615 points

    Yes we have spent quite a lot of time reading Chapter 14 for low speed start and I think with some more experimenting we will figure out the low speed factors. I am quite surprised that the high end is stopping - that doesn't seem to be addressed anywhere in the docs and if you don't have any suggestions we are not sure where to go. Hopefully we don't have to start looking at other products. We trusted TI to be able to help us here and in normal cases I would have expected to be able to talk with someone such as an application engineer directly for at least some direction. I am disappointed.

  • 0 in reply to Terry Harrison
    TI__Guru** 117160 points

    Can you post some current waveforms captured by the oscilloscope to show the issue you mentioned above?

    What speed range does the motor run with the full load? And what rated current and torque of the motor? 

    Did you try to use different Kp&Ki of the speed controller for running the motor at low speed and high speed?

    What do you mean "the high end is stopping"?