This paper presents the operating principle, results and conclusions for an FTC mechanical sensor that can guarantee continuity of operation on the whole speed range. This active FTC is based on analytical redundancy using three different estimators (an Extended Kalman Filter (EKF), a back electromotive force based observer (back-EMF observer) and a high frequency voltage injection (HFI). Thanks to this structure, the mechanical measurement is continuously monitored and at sensor fault occurrence the sensorless controller can be engaged using the best estimate. From numerical simulations and experimental results on a 1.1kW salient PMSM drive, the following conclusion has been drawn : at low and zero speed, the drive availability is obtained with the combination of the EKF and the HFI while for higher speeds EKF and back-EMF observer have better performance.

Keywords: Permanent-Magnet Synchronous Motor, Sensorless Control, Fault Tolerant Control (FTC), High Frequency Injection, Kalman Filter