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DRV10983-Q1: Current limit when run close loop at low speed

Part Number: DRV10983-Q1
Other Parts Discussed in Thread: DRV10987, DRV10970, , DRV8308

hello experts,

I have own a DRV10983Q1EWM to evaluate my motor. From help from this forum, I can do open loop and close loop control very well.

https://e2e.ti.com/support/motor-drivers/f/38/t/773710

However, I got stuck at current limit alarm, and the driver will automatically shutdown the motor and restart gain when over current. Even the current is not high

I make a report file, but can not attach. So that I would like to past its content here:

I have some questions:

1. Speed motor report may not exactly. What should I do? may I ignore it?

2. why driver alarm Current limit while actual current is lower than its threshold?

Best regards,

My  report file as below:

Picture 1: motor speed report may not exactly, it is far from the true. Over current is happened always at speed setting 280Hz. If increase speed setting to 300Hz, motor will shutdown automatically.

 

Picture 2: driver configuration

Picture 3: driver configuration

Picture 4: current waveform at phase V of the motor using current sensor ACS712ELC-05B. Voltage output 0à5V corresponding linearly with current input -5A à 5A (zero ampere mean 2.5V output).

From the wave form, we can see that the current is under 1A (the external digital monitor is also show that the average current is 0.8A). But the driver alarm Limit current even driver can run at 2A RMS, 3A max.

  • 1. Speed motor report may not exactly. What should I do? may I ignore it?
    What speed isnt being reported properly, the "motor speed" in the display tab, Hz or RPM?

    2. why driver alarm Current limit while actual current is lower than its threshold?
    Please take scope capture of current when fault happens.

    Does this happen in open or closed loop?
  • Hello Sanmesh,

    1. from picture 1 of the first post, both Hz and RPM are wrong. Speed command at close loop are 280 Hz; but speed display are 1310.7 Hz and RPM = 153846. It is very far from the setting.

    2. Current waveform at phase V of the motor captured by current sensor ACS712ELC-05B. Voltage output from 0 to 5V corresponding linearly with current input from -5A to 5A (zero ampere mean 2.5V output).

    From the wave form, we can see that the "upper peak current" is 0.82A and the "under peak current" is -0.94 A; "peak to peak current" is 1.76 A.

    It is only happen in close loop when speed setting is reach to 280 Hz. If setting speed is 300 Hz, the motor will automatically shutdown. When 280 Hz speed setting, "current limit, lock code 0x1" happen and can not be cleared because "fault persist".

    Because open loop only setting maximum up to 204.8 Hz, under than 280 Hz. I don't know it can be happen in open loop or not

    Best regards,

  • 1) You cannot enter a speed command as a Hz. Speed is just translated as a duty cycle command, and this corresponds to some motor Hz depending on the particular motor torque load. According to the datasheet, "The speed command is used to determine the PWM duty cycle output". So if you enter "280" in the "speed" box in speed control on the display tab, this means apply a duty cycle of 280/511% or 54% duty cycle. This will associate with some speed in Hz of the motor according to the torque load.
  • Thank you very much for your explanation. I understand.

    since my motor has 8 poles, the rpm display may divide by 8 to get the actual RPM.

    How about over current? are there anything wrong on the current waveform? Do you have any idea?

    Thanks for your help

  • My only guess would be maybe there is a current spike when the fault happens.Please capture the currrent when the fault happens. Another recommendation is maybe increase the dead time.
  • Hello Sanmesh,

    your help is appreciated,

    Please watch the video recorded while turning the motor.

    https://youtu.be/tKK2w_-s3fE

    I did try to increase dead time but nothing improve. I had tried from 440ns to 800ns and get the same result. if dead time if over than 800ns, the motor seem hard to start.

    Best regards

  • Hey Bui,

    Let me get back to you in the middle of the week. I looked at the video briefly and my only comment is that I wish auto refresh was enabled on tje display tab, so I could see what is going on in real time in the GUI as you increase the speed.
  • Hello Sanmesh,

    I took another video with auto - fresh enable on display tab:

    https://youtu.be/CiPysALlCk8

    Thanks you very much,

  • Hey Bui, thanks a lot for the video.

    1) Assuming that voltage output from 0 to 5V corresponds linearly with current input from -5A to 5A (zero ampere mean 2.5V output), then the max peak currents we saw in the video were +-600mA.
    a)Please make sure that this voltage to current ratio is correct to make sure we are seeing the right current. An easy way to do this is to apply a voltage across a resistor, and then see if the current through the resistor on the oscilloscope matches what you expect (I = Vcc/R).
    b) If the current reading is correct, then that means for the specific current phase you are measuring should not trigger the current lock. The only thing I can suggest is to check the other motor phase currents in this lock condition to see if they exceed the current limit for some reason.
    c) Also, you can always disable the current limit lock, and let the overcurrent shutdown function instead protect the device.
    d) Also, I doubt this is the case, but maybe something is damaged on the dRV10987 causing the current limit to falsely trigger so maybe switch another unit in.
    2) Near the end when it keeps hitting lock and restarting, it looks like improper spinning of the motor keeps leading to the current limit happening, since the current waveform becomes not-sinusoidal. Maybe that is something to explore
    3) When using the autorefresh buttons, only enable 1 at a time. Otherwise both displays will freeze, as you saw in the video, and you will have to refresh it manually. What I was trying to see is if the measured kt value started to drop as you got to faster and faster speeds, indicating improper commutation. From your occasional manual refreshing, it looked like it wasnt, but you should just check yourself.
  • Hello Sanmesh,

    You had been very helpful. I appreciate your help,

    Best regards

  • Hello Sanmesh,
    In case of my motor, if I use hall sensor (Hall sensor is already integrated on the sample motor), does it become better?
  • Hall sensor will always lead to more reliable motor-spinning commutation than sensorless.

    DRV10983-q1 cannot spin motors based of halls, so I would recommend DRV10970.

  • Thank you Sanmesh,

    Since DRV10970 is low power. I have just picked up a DRV8308 EVM with external FET. Hope it will be a better solution.

    Best regards