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No Holding Torque with FOC + Current Loop Appears Unresponsive

Isaac1
Associate II

Hello,
I am generating firmware using MCSDK 6.4.0 and testing my motor with Motor Pilot. I am using FOC with encoder feedback.

Under no-load conditions, the velocity control loop works perfectly with the default PI gains, the motor tracks speed very accurately. However, the motor produces no holding torque and can be stalled easily with just my fingers at all speeds.

I assumed this was due to a poorly tuned current loop, so I began increasing the proportional gain of the torque (Iq) PI controller in Motor Pilot while running in torque mode. During testing, I monitored the I_Q_MEAS and I_Q_REF registers while gradually increasing the torque current.

There is quite a bit of noise in the I_Q_MEAS signal, but it is still clear that it never steps anywhere near I_Q_REF. Increasing the torque gain has no noticeable effect, the motor still pulls only a small amount of current, and the holding torque remains nonexistent.

I have been searching for any hidden current limit or clamp that could explain this behavior, but I have not found anything yet.

I am using the EVLSERVO1 drive.

I would appreciate any insight or suggestions.

Thanks,
Isaac

3 REPLIES 3
GMA
ST Employee

Hello @Isaac1,

Max Modulation Index could also limit the current. Check MMI value:

GMA_0-1751634755517.png

If it is low, decrease the PWM frequency.


 

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Best regards.
GMA
Isaac1
Associate II

Thanks! That fixed my problem. How do you chose an optimal PWM frequency? I was at 16kHz, and went down to 12kHz and that fixed my issue. The SDK shows 100% modulation at 16kHz and it does not seem to update that percent when changing PWM frequency.

 

Hello @Isaac1 

You can consider the shot I provided

Regards