Sensorless control of permanent magnet synchronous motor based on two stage low pass filtering sliding mode observer

This paper proposes a sensorless control strategy of permanent magnet synchronous motor (PMSM) based on two stage low pass filtering sliding mode observer (SMO). Due to the switching characteristics of sliding mode control, traditional SMO has inherent chattering problem, and traditional SMO has disadvantages such as poor observer accuracy and poor adaptive ability. To suppress the system chattering problem caused by SMO, a new continuous function is used to replace the discontinuous sign function as the switching function. To improve the adaptive ability of the system, the boundary layer thickness of the proposed switching function is designed as a variable. The boundary layer thickness varies with the distance from the sliding surface to the system state. This paper also proposes a two stage low pass filter (LPF) to filter the noise and harmonics in the estimated back EMF more effectively, so as to improve the observation accuracy. The cut-off frequency of the two stage LPF can vary adaptively with the motor speed. Therefore, the proposed two stage LPF can achieve effective filtering when the motor speed changes. The back EMF signal will produce phase delay after being filtered by two stage LPF. To offset the phase delay, a two stage variable phase delay compensation is designed for the two stage variable cut-off frequency LPF. The effectiveness and feasibility of the proposed method are verified by simulation and experiment. The results of the traditional SMO and the proposed SMO on the speed and rotor position observation under different working conditions are compared. The simulation and experimental results show that compared with the traditional SMO, the proposed SMO effectively improves the observation performance and robustness.