A Study of Sensorless Control of PMSM Based on an Improved Sliding Mode Observer

The traditional sliding mode observer (SMO) for permanent magnet synchronous motor (PMSM) has low accuracy and poor sinusoidality in observing back-electromotive force (EMF), resulting in noticeable chattering and large errors of estimated rotor position and speed. To address these issues, this paper proposed an improved SMO based sensorless control strategy for PMSM. Firstly, a high-order SMO (HSMO) is analyzed, in which the back-EMF is introduced as a new state variable of the traditional SMO. Then, an improved SMO which contains a high pass filter-low pass filter (HPF-LPF) structure is proposed. In order to achieve good filtering effect, two HPF-LPFs are adopted and cascaded. The comparative analysis and experiments results show that the performance of the proposed two HPF-LPFs-based SMO is comparable to that of HSMO.