A zero speed operation sensorless PMSM drive without additional test signal injection

The inherent back EMF and the saliency of AC machines can be utilized to identify the rotor/flux position. A novel technique, which takes both of these effects into account is proposed in this paper. No additional test signals are injected into the machine and the difficulties in sensing the machine terminal voltage at low speed is eased. Only three standard current transducers are used in the drive system. For the position/speed estimator only the machine current derivative during the relatively long (at low speed) zero voltage vectors is used as feedback. Practical results show the operation of the drive at several torque and speed conditions including stand still.