Synchronous motor observability study and an improved zero-speed position estimation design

This paper deals with the Permanent Magnet Synchronous Motor (PMSM) observability analysis for sensorless control design. The problem of loss of observability at low frequency range is always recognized in experimental settings. Nevertheless, there are no sufficient theoretical observability analyses for the PMSM. In the literature, only the sufficient observability condition has been presented. Therefore, the current work is aimed especially to the necessary observability condition analysis. Furthermore, an Estimator/Observer Swapping system is designed here for the surface Permanent Magnet SynchronousMotor (PMSM) to overcome position observability problems at zero speed which is an unobservable state point.