Disturbance observer based sensorless speed controller for PMSM with improved robustness against load torque variation

An improved sensorless operation scheme for permanent magnet synchronous machine (PMSM) is proposed. A sliding mode observer is employed to estimate the Back-EMF, with which the rotor position is estimated. To improve the robustness against the load torque variation, the disturbance observer (DOB) scheme is adopted so that it estimates the load torque and generates a compensating signal to approximately cancel it. Moreover, the transient response of the rotor speed has been improved in the sense that the settling time and maximum overshoot are reduced. Simulations and experiments show the effectiveness of the proposed scheme.