The paper presents a speed and EMF estimator for the non-salient permanent magnet synchronous motor (PMSM). The method uses only the measured motor voltages and currents of the motor; estimation is done with two sliding mode (SM) observers that run sequentially. A first SM observer estimates the EMFs of the motor in the stationary reference frame. These are passed as inputs to a second SM observer that estimates the speed and reestimates the EMFs. The method is applicable in a sensorless speed controlled PMSM drive where the EMFs are used to provide field orientation and the estimated speed is used for speed feedback. The paper proves the convergence of the observers and discusses the design of the gains. The theoretical development is supported with simulation results and experimental tests. The advantages of the proposed method compared to the state of the art are discussed.
Keywords: permanent magnet synchronous motor, PMSM, rotor position estimation, speed estimation, sliding mode, SM, observers, sensorless control