Cascaded EMF and speed sliding mode observer for the nonsalient PMSM

The paper presents an EMF and speed estimator for the nonsalient permanent magnet synchronous motor (PMSM). The method uses two cascaded sliding mode (SM) observers and is realized using only the measured voltages and currents of the motor. A first SM observer estimates the EMFs of the machine in the stationary reference frame. These EMFs are passed as inputs to a second SM observer that estimates the motor speed and re-estimates the EMFs. The method is applicable in a sensorless PMSM speed control scheme where the estimated EMFs are used to obtain the rotor position and the estimated speed is used for speed feedback. The paper verifies the existence conditions of the sliding mode motion and proves the convergence of the observers. The theoretical findings are validated with simulation results that show that the estimated EMFs and speed are of good quality. The advantages of the proposed method compared to the state of the art are discussed.