Extended EMF observer for wide speed range sensorless control of salient-pole synchronous motor drives

This paper presents an observer-based position sensorless control method with signal injection. An extended electromotive force (EEMF) observer is suitable for salient-pole synchronous motors, because position information of EMF and saliency are both included. Signal injection is needed to make use of the position information of saliency at low speed. However, observer consists of a low-pass filter. Therefore, position information of saliency has not been used enough for the EEMF observer. In this paper, signal injection method without torque ripple is applied to make effective use of the EEMF observer at low speed. The signal frequency can be selected in a bandwidth of the observer. Then, position estimation method based on heterodyne detection with the filter of the EEMF observer is proposed. The proposed technique makes it possible to expand the operating range of the EEMF observer to lower speed. The validity of the proposed control is confirmed by experiments.