Speed, EMF and Rotor Position Estimation of PMSM using Phase Locked Loop and Simple Sliding Mode Observer

The paper presents a simple method to estimate the quantities needed for implementation of sensorless control for the Permanent Magnet Synchronous Motor (PMSM). In sensorless control, the speed, EMFs and rotor position of the motor need to be estimated using the terminal quantities (measured voltages and currents). The paper proposes a sequential estimation approach: the speed is estimated first; then, it is used in the estimation of the EMFs and rotor position. The speed is obtained using a Phase Locked Loop (PLL) synchronized with the motor voltages. The PLL does not depend on the motor parameters and yields a speed estimate with guaranteed zero steady-state error. The availability of the motor speed allows to improve the estimation of the EMFs and rotor position using speed dependent gains and angle correction. The paper presents a simple sliding mode observer whose estimation accuracy is improved using the speed estimate. The results are validated with simulations. The method presented is simple and easy to implement. The estimators presented are reliable, accurate, depend on a minimal set of parameters and yield zero steady-state error.