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DRV10975: Open To Closed Loop Transition

Joseph Lupton
Prodigy 20 points
Part Number: DRV10975
Other Parts Discussed in Thread: MCF8316A

Hello,

I have a Maxon EC20 Flat that I am attempting to run in closed loop using the DRV10975. So far I can run in seamlessly in open loop but it fails on the transition to closed loop.

Based on the motor spec sheet and some testing, I have come up with the values below:

Pole Pairs 2 Pairs
Motor Voltage 9 V
Speed Constant 1080 rpm/V
KT 55.55556 mV/Hz
R_Ph 3.54 Ohms
Time Constant 119.774 us
Closed Loop Speed 9430 rpm
Closed Loop Speed 314.3333 Hz
Nominal Current 0.954 A
Stall Current 2.54 A

I know the stall current is a little high but I am willing to risk it for now. Aside from that it looks like I should be able to use the motor with this driver.

In attempts to modify the eeprom values, I have made these changes:

Register Value Default? Reasoning
0x20 0x5F N Enable Half Frequency, Resistance = 3.52  (0x00|0x5F)
0x21 0xBA N Half Cycle Adjustment, KT = 15.3 (0x80|0x1B) Through Experimentation
0x22 0x2A Y
0x23 0x00 Y
0x24 0xD8 N Open Loop Current = 1.6, Tried to remove any limitations
0x25 0xFF N Change Accel to as Slow as Possible
0x26 0xC2 N Align Time 1.3s, Op2ClThresh = 115.2Hz
0x27 0xF0 N Disable Mechanical AVS
0x28 0xA9 N Software current Limit = 2.0A (Making sure this wasn’t the issue)
0x29 0xB8 Y
0x2A 0x0D N Disable IPD
0x2B 0x0C Y

Throughout the experiment I polled the registers to see what the driver is seeing. Please find this table at the at the end of the post. The resulting current waveform can also be seen below. 

I measured the electrical frequency to be about 109 Hz when it attempted to transition and about 1.52kHz after the transition. (Speed command was set to maximum, 511, but has also been tried much lower).

Please let me know if there is anything I need to change or what you think the issue may be!

Thank you!

Voltage Speed (Hz) Current (A) KT Fault Status
8.549999 1.1 0.1875 2.844097 OK OK
8.549999 1.1 0.1875 2.844097 OK OK
8.639062 1.1 0.1875 2.844097 OK OK
9.173437 1.1 0.1875 2.844097 OK OK
8.015625 1.1 0.1875 2.844097 OK OK
8.015625 1.1 1.335938 2.844097 OK OK
8.549999 1 1.335938 2.844097 OK OK
8.015625 7.5 1.335938 2.844097 OK OK
8.460938 2.3 1.189453 0.454167 OK OK
8.104688 1.3 1.341797 0.454167 OK OK
7.926562 12.9 1.341797 0.454167 OK OK
8.104688 4.3 1.171875 0.419792 OK OK
8.015625 18.2 1.324219 0.419792 OK OK
8.104688 2.4 1.324219 0.357986 OK OK
8.460938 10 1.166016 0.309722 OK OK
7.926562 12.2 1.166016 0.309722 OK OK
8.639062 3.1 1.318359 0.272569 OK OK
8.460938 3.5 1.318359 0.249653 OK OK
8.639062 6.3 1.318359 0.230208 OK OK
8.371875 4 1.330078 0.214236 OK OK
8.015625 5.6 1.154297 0.201389 OK OK
8.817187 5.9 1.148438 0.185417 OK OK
8.728125 5.2 1.335938 0.173264 OK OK
8.817187 45.2 1.160156 0.156597 OK OK
8.104688 51.2 1.330078 0.151736 OK OK
8.995312 6.6 1.330078 0.140625 OK OK
8.460938 7.2 1.330078 0.135069 OK OK
8.549999 7.7 1.318359 0.131597 OK OK
8.728125 8.3 1.324219 0.127083 OK OK
8.282812 72 1.324219 0.118403 OK OK
8.817187 75.3 1.148438 0.112847 OK OK
8.639062 64.7 1.318359 0.107292 OK OK
8.639062 10.4 1.318359 0.101389 OK OK
8.728125 87.40001 1.142578 0.097569 OK OK
8.639062 92.3 1.142578 0.093403 OK OK
8.639062 95 1.142578 0.088542 OK OK
8.728125 12.8 1.3125 0.086111 OK OK
8.104688 107.5 1.142578 0.085069 OK OK
8.728125 13.9 1.306641 0.082292 OK OK
8.460938 14.7 1.3125 0.080208 OK OK
8.371875 70.8 1.142578 0.077778 OK OK
8.460938 16.3 1.306641 0.075 OK OK
8.639062 26.3 1.300781 0.069792 OK OK
8.817187 139.4 1.136719 0.067361 OK OK
8.104688 145.6 1.136719 0.064931 OK OK
8.460938 85.9 1.289063 0.062153 OK OK
8.282812 159.8 1.289063 0.059375 OK OK
8.460938 168.1 1.142578 0.057986 OK OK
8.549999 21.3 1.294922 0.056944 OK OK
8.817187 182 1.136719 0.054167 OK OK
8.460938 192.8 1.142578 0.053125 OK OK
8.728125 192.8 1.130859 0.052431 OK OK
8.371875 19.8 1.283203 0.050694 OK OK
8.282812 39.7 1.136719 0.05 OK OK
8.371875 41.4 1.277344 0.048958 OK OK
8.460938 42.8 1.277344 0.047569 OK OK
8.193749 43.6 1.130859 0.046528 OK OK
8.371875 182 1.277344 0.045139 OK OK
8.639062 36.9 1.130859 0.044097 OK OK
8.460938 48.6 1.136719 0.043403 OK OK
8.460938 222.3 1.130859 0.042361 OK OK
8.549999 51.2 1.271484 0.039931 OK OK
8.460938 234.1 1.265625 0.038542 OK OK
8.549999 242.8 1.265625 0.038194 OK OK
8.639062 162.2 1.265625 0.036806 OK OK
8.460938 58.5 1.136719 0.036111 OK OK
8.193749 60.7 1.130859 0.035417 OK OK
8.193749 62.4 1.130859 0.034722 OK OK
8.728125 105.9 1.136719 0.034375 OK OK
8.371875 65.5 1.130859 0.033333 OK OK
8.639062 66.2 1.253906 0.032986 OK OK
8.193749 67.6 1.130859 0.032639 OK OK
8.549999 45.5 1.248047 0.031944 OK OK
8.460938 66.1 1.130859 0.031944 OK OK
8.639062 49.9 1.119141 0.031597 OK OK
8.639062 49.7 1.230469 0.03125 OK OK
8.728125 72.1 1.125 0.029514 OK OK
8.728125 59.5 1.125 0.029514 OK OK
8.460938 52.9 1.224609 0.029514 OK OK
8.460938 58 1.125 0.028472 OK OK
8.371875 59 1.119141 0.028472 OK OK
8.549999 56.5 1.224609 0.027778 OK OK
8.193749 61.8 1.113281 0.027431 OK OK
8.371875 63 1.113281 0.026389 OK OK
8.549999 63.5 1.113281 0.027083 OK OK
8.549999 64.3 1.212891 0.026389 OK OK
8.549999 66.9 1.212891 0.025694 OK OK
8.371875 69 1.107422 0.026042 OK OK
8.549999 67.4 1.212891 0.024653 OK OK
8.549999 72 1.201172 0.025 OK OK
8.549999 72.8 1.113281 0.023958 OK OK
8.282812 74.5 1.101563 0.023958 OK OK
8.371875 76.2 1.101563 0.023958 OK OK
8.549999 73.6 1.195313 0.023958 OK OK
8.549999 75.4 1.183594 0.023611 OK OK
8.639062 78.1 1.177734 0.023958 OK OK
8.549999 79.8 1.177734 0.023264 OK OK
8.549999 79.9 1.177734 0.021875 OK OK
8.549999 83.30001 1.189453 0.021528 OK OK
8.549999 82.9 1.171875 0.022222 OK OK
8.549999 89.40001 1.171875 0.021528 OK OK
8.549999 87.40001 1.183594 0.021181 OK OK
8.639062 89.1 1.171875 0.021181 OK OK
8.460938 93.6 1.101563 0.021181 OK OK
8.549999 92.5 1.166016 0.021181 OK OK
8.371875 95.5 1.078125 0.020486 OK OK
8.549999 95.4 1.154297 0.020139 OK OK
8.549999 98.4 1.148438 0.020486 OK OK
8.549999 102.4 1.078125 0.019792 OK OK
8.549999 101.8 1.066406 0.020139 OK OK
8.549999 100.8 1.136719 0.019097 OK OK
8.549999 105.1 1.136719 0.019444 OK OK
8.639062 107.7 1.125 0.019097 OK OK
8.460938 107.4 1.136719 0.01875 OK OK
8.549999 109.2 1.130859 0.01875 OK OK
8.371875 114.7 1.054688 0.01875 OK OK
8.193749 1310.7 5.958984 0.001736 OK OK
9.084374 1638.3 0 0 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0 0 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0 0 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0 0 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0 0 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0 0 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0 2.844097 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
9.084374 1638.3 0.005859375 2.844097 FAULT: Speed Abnormal ERROR:MOTORISLOCKED
  • 0
    TI__Mastermind 24415 points

    Hi Joseph,

    Thanks for providing all the details. I see 55.5 mV/Hz mentioned in the datasheet but you programmed 15.3 mV/Hz. Is there any reason for this difference? Device is failing to transition to closed loop because the estimated Kt at the handoff frequency (115.2 Hz) is very low (~1.05 mV/Hz). This can happen when the lead time/control advance angle is not tuned correctly. Estimated Kt should be close to the programmed Kt during the open to closed loop transition.

    You can check the below linked app note and use as a reference to tune the lead time.

    https://www.ti.com/lit/an/slaa561/slaa561.pdf

    Regards,

    Vishnu

  • 0 in reply to Vishnu Balaraj
    Prodigy 20 points

    Hi Vishnu,

    I think the 1.05 you are seeing is actually the phase current, correct? It looks like the handoff Kt seen by the motor at  handoff is around 18.7 mV/Hz. 

    I picked the 15.3 mV/Hz primarily to get closer to that handoff Kt. Also based on the motor tuning guide, section 4.8, I found that the 55 mV/Hz was too high. I will try sweeping the Kt upward and see if that works. 

    It looks as though that lead-time tuning is only applicable once in closed loop. Do the same principles apply for open loop? I will test all of this first thing on Monday. 

    Thank you!

    Joseph

  • 0 in reply to Vishnu Balaraj
    Prodigy 20 points

    Hi Vishnu,

    I updated the KT to match the motor specs. I still can't seem to get it to work. I tried roughly sweeping the advance angle for now and didn't have any luck there since the current is always the same in open loop. I also tried to increase to the maximum o2c loop transition speed but that didn't work either. Please let me know your thoughts!

    Thank you,

    Joseph

  • +1 in reply to Joseph Lupton
    TI__Mastermind 24415 points

    Joseph,

    Yes, 1.05 is the phase current. Still, if you look at KT at 114.7 Hz, it is 0.01875 mV/Hz which is too low. The way how you tune is that, you program the measured Kt and tune the lead time such that the estimated KT is close to programmed KT. Lead time is also used in open loop.  

    If you still see issues, I would recommend you to try MCF8316A which has several advanced features compared to DRV10975. 

    MCF8316A product page link: https://ti.com/mcf8316a

    Regards,

    Vishnu

  • 0 in reply to Joseph Lupton
    TI__Mastermind 18916 points

    Hi Joseph, 

    Can you let us know if the problem has been resolved? 

    Please let us know if further support is needed on this question. Thanks 

    Best Regards, 
    Andrew 

  • 0 in reply to Vishnu Balaraj
    Prodigy 20 points

    After doing a lead time sweep, I was able to get the motor to run in closed loop sometimes. Usually the first few runs pass to closed-loop but after trying again without changing settings, the motor will not enter closed-loop again. More than likely, the use of the MCF IC would fix the issue. I may just change my application slightly to utilize the open-loop for now! Thank you Vishnu.