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FOC sensorless motor changes direction when closing speed loop.

Other Parts Discussed in Thread: DRV8301, CONTROLSUITE

Hello everyone,

I am operating a 30.000 RPM motor that I drive with sensorless and FOC. I use a F28335 with a 50KHz current / control loop and 5 KHz speed control loop. I am using the DRV8301 in 6 PWM mode like in various projects of ControlSUITE. I have tuned Iq and Id controllers and I have a nice response across RPM range of the motor and current consumption looks normal. My estimated rotor angle position follows correctly the forced angle generated by the ramp with a very little shift phase as described in your application notes. I actually adjust KSlide incrementally and slightly depending on the speed.   

In current loop, I set my target speed to 20%, the motor reaches it with no problem and my speed estimation is good within ~1%. In that configuration, my speed PID controller has for input feedback 20% and reference 20% and output is ~ 0.

When I switch to speed control, the motor stops and reverse direction all the time.

I try to wrap my head around the sequence of events which leads to that... any ideas ? Is this because the PID speed output (also Iqref in that case) is close to 0 when closing loop ? I have tried to transition from Iqref constant to PID output incrementally but it does not seem to help either.

Thanks.