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DRV10987: Motor fails to start with large initial speed of the reverse rotation

Part Number: DRV10987

Hi, team

My customer want to test the motor starup performance with spinning reversely state. Here some issues:when the initial speed of the reverse rotation of the motor is large, the motor fails to start. The motor keeps reversing, decelerating and accelerating, and it cannot rotate forward. The test result will show in below table, and the motor information are:

  • Phase to center tap resistance: RPH=1.7Ω;
  • BEMF constant kt=132mV/Hz;
  • Motor supply voltage: 24VDC/20W
  • Number of pole pairs of the motor: 4

Support needs:

  • What are the possible reasons for the failure of reversely start and what are the solutions?
  • Could u help confirm whether the parameter settings are reasonable?

Thanks a lot.

Test results: 

Parameters setting in GUI:

  • Hi Chester,

    Thanks for posting your question in MD forum. Can you try setting the ISD threshold to 0.8 Hz?  

    Regards,

    Vishnu.

  • Hi, Vishnu

    I have tried setting the ISD threshold to 0.8 Hz, the result has not improved.

    Thanks!

  • Hi, Vishnu

    Another test I have done:When the initial speed of reverse rotation is kept unchanged, changing the value of first order acceleration[A1] can affect whether the motor starts smoothly. When A>=9.2Hz, the motor can start normally; when A<=4.5Hz,the motor fails to start. Similarly, when the initial speed reaches a certain value, the motor fails to start.

    Thanks.

  • Can you check and tell me what fault is getting triggered when the motor fails to start?

  • Hi, Vishnu

    I have do some lab test, and get some test result as below:

    • Acceleration range / RevDr threshold / Op2cl threshold has the great impact on the starting reliability and starting time of the reverse drive;
    • IPD advance angle have some impact on the starting reliability of the reverse drive;
    • IPD current threshold / ISD initial speed detect have some impact on the starting reliability and starting time of the reverse drive;

    Based on these test, the optimal parameter settings are as follows. Under these parameter, the motor can start smoothly, but the start time[Ts=19.7s] is still unacceptable:

    • IPD current threshold: 0.8A
    • IPD Advance Angle: 90°
    • Acceleration: A1=1.2Hz/s, A2=0.22Hz/s2
    • Op2cl threshold: 12Hz
    • RevDr threshold: 51Hz

    Here some questions:

    1. Although the motor can start smoothly when the initial reverse speed is relatively high under the above parameters are set, its start time [Ts=19.7s] is still unacceptable. The test results show that increasing the acceleration will cause the motor to fail to start. Could u make some comment to optimize the star time?
    2. As shown in about parameter setting, the RevDr threshold is 51Hz. According to datasheet, the RevDr threshold needs to be reasonably low, if it is set too high, the current caused by the BEMF may damage the motor. So, how to optimize the RevDr threshold.
    3. In addition to these parameters, what other parameter settings can also affect the problem of reverse drive failure when the initial reverse speed is large? And how to balance the startup reliability and startup time?
    4. Under the premise of ensuring the smooth start of the motor and acceptable start time, what is the maximum initial reverse speed that DRV10987 can withstand?

     

    The test report is as below, please let me know if you have any question.

    Thanks a lot.

  • Hi, Vishnu

    Here adding a fault interface when the motor starts abnormally.

    Thanks.

  • Hi Chester,

    Thanks for proving the details. I understand that the motor startup failure has been resolved and now the goal is to minimize startup time correct? What is the rated current of the motor? Also, what is the estimated Kt that you read back from the display tab in GUI when in closed loop? How much is the phase current drawn by the motor in closed loop?

    Regards,

    Vishnu. 

  • Hi, Vishnu

    Yes,  the motor startup failure has been resolved and now the goal is to minimize startup time correct.

    The information is as below:

    • The rated current of the motor: 0.83A [24VDC/20W]
    • Kt in closed loop: 136.7mV/Hz
    • The phase current of the motor in closed loop: 2.8A [peak to peak phase current

    Some lab picture as below:

    Thanks 

  • Hi Chester,

    Thanks for the details. Is the IPD disabled? I see from the GUI that IPD is enabled but the phase current tells me that align and go is enabled. Device stays in open loop for longer time, so clearly, A1 and A2 should be increased. What fault is getting triggered when you increase A1 and A2? Alos, you can try increasing closed loop acceleration to 48Vcc/sec but this will not decrease the startup time much. 

    Regards,

    Vishnu.

  • Hi, Vishnu

    Thanks for your support. When I increase A1 and A2, the motor starts abnormally or fails to start. Please see the blow picture.

    Thanks.

  • What is the peak current drawn by the motor phases when you increase A1 and A2? 

  • Hi, Vishnu

    The peak phase current is 1.5A.

    Thanks.

  • Hi Chester,

    I think this is a tuning issue. Looking at the GUI screenshots and the fault code, the estimated BEMF constant is 33 mV/Hz while the actual value is 132 mV/Hz and the device is triggering Abnormal Kt fault. I would recommend you to tune the lead time till the device estimates 132 mV/Hz. 

    Regards,

    Vishnu