Sliding mode observer for sensorless control of permanent magnet synchronous motors

A number of estimation techniques have been developed to achieve speed and position sensorless permanent magnet synchronous motor (PMSM) drives. Most of them suffer from variation of motor parameters such as the stator resistance, stator inductance and torque constant. Also, it is known that conventional linear estimators are not adaptive to variations of the operating point in a nonlinear system. The sliding mode technique has shown promising results when estimating or controlling nonlinear systems. This paper presents a sliding mode observer (SMO) for estimating the position and speed of a permanent magnet synchronous motor (PMSM) to achieve sensorless drive system. The technique can be generalized to other motor drives and motion control systems. The effect of the variations of motor parameters such as torque constant, stator resistance and stator inductance on the position and/or speed estimations, over a wide speed range, have been studied. Compared to other methods, the observer is more robust to operating conditions and parameter uncertainties. Simulations show that the observer is robust to 200% parameter detuning.