A DC-Offset Removed Sensorless Control Method for PMSM Based on SMO With an Improved Prefilter and a Speed Immune Position Error Compensation Strategy

The conventional sliding mode observer (SMO) based sensorless control methods for permanent magnet synchronous motor (PMSM) often have some key drawbacks, such as the strong coupling between the speed and rotor position estimation, and the sensitivity to unexpected dc-offset. To solve these demerits, an improved prefilter and a new speed immune position error compensation strategy are proposed to achieve sensorless control of PMSM based on SMO. First, the drawbacks of the traditional methods are summarized. Second, to overcome the effects of dc-offset, a new prefilter is proposed, which is composed of two low-pass filters with different cut-off frequencies. Theoretical analysis shows that the proposed prefilter not only can remove the effects of dc-offset, but also has two degrees of freedom, which allows to adjust the high-frequency and low-frequency characteristics severally, increasing the flexibility. Third, to compensate the position error caused by the designed prefilter without using the estimated speed, a new adaptive compensation phase-locked loop is proposed, which not only can remove the strong coupling between the speed and position estimation, but also can further suppress the high-frequency sliding mode chattering. Comparative analysis and experimental study are carried out, validating the effectiveness and superiority of the proposed techniques.