High frequency injection method improved by flux observer for sensorless control of an induction motor

This paper presents a high frequency signal injection method (HFIM) improved by the flux observer for sensorless control of an induction motor. In order to reduce the chattering effect caused by the designed higher cut-off frequency of flux angle estimation to keep the high dynamics, the HFIM is combined with the flux observer, which has the filtering effect and keeps the dynamics. Furthermore, the hybrid speed estimator is proposed for smooth transition from low-speed to medium- and high-speed regions. Experimental results show that it improves the performance at ultra-low frequency including zero speed and stator frequency.