I have implemented the direct field oriented control of the three phase induction motor. The control algorithm exploits a speed sensor and machine model based on the Luenberger state observer.
The control structure is functional but during the tests I have found that at zero speed the machine doesn't produce its nominal torque. I have a suspicion that the reason for the error in the torque production is caused by the discrepancy between the actual stator voltage at the machine terminals and the stator voltage supplied as an input to the state observer. This discrepancy is in my opinion caused by the inverter nonlinearities - I would say mainly the dead-times. I have attempted to compensate them in the feedforward manner based on the stator current. But it seems to me that this method isn't sufficient because the error in torque production is smaller against the case without compensation but still exists.
I have been looking for some feedback based method. Does anybody know a robust method for compensation of the inverter nonlinearities?
The stator voltage at zero speed
The stator current at zero speed
The stator current provided by the Luenberger state observer at zero speed as a part of the state estimate