Performance comparison of sliding mode observers for back EMFs based speed estimation in PMSM

This paper proposes a second-order high-speed sliding mode (SHSM) observer and compares the performance with the recent higher-order sliding mode (HOSM) observer for the problem of sensorless speed estimation in the permanent magnet synchronous motor (PMSM). In which, a sigmoid function is substituted for the signum function with a variable boundary layer. A SHSM observer is proposed to provide the estimation of back electro motive forces (EMFs) that are treated as unknown inputs in the PMSM model. An accurate speed estimate of PMSM can be algebraically computed with the estimated back EMFs. The chattering phenomenon, that is commonly found in the sliding mode observers is well-reduced by replacing signum function with the sigmoid function, in comparison to the HOSM observer. Simulation results show the effectiveness of the proposed SHSM speed estimation method in comparison to the earlier HOSM observer in terms of good accuracy and chattering phenomenon.