Sensorless method for the compensation of cogging torque in PM synchronous machines

The cogging torque in PM syncrhonous machines can be reduced by taking measures in the design of the machine or by means of the control system of the drive. For compensating the cogging torque through control, it is required to accurately know the position of the rotor. Consequently, the implementation of such a method using a sensorless estimated position is very difficult. In the present paper, an encoderless method is proposed, which determines the compensating torque signal directly without resolving the estimated position. The proposal is developed for machines with concentrated windings and fractional slot pitch, where the cogging torque is of special concern. The compensating signal is synthesized from the inverse inductance matrix, which has components with 2 and 4 times the fundamental electric angular frequency. The proposed method is tested by using a simulation model. The parameters, including the position dependent inductance matrix, where obtained by the finite elements method.