Magnetizing inductance identification algorithm for operation of speed-sensorless induction motor drives in the field weakening region

Accurate speed estimation of sensorless induction motor drives in the field weakening region depends on the precise magnetizing inductance which varies due to rotor flux reference variation and consequently, the main flux saturation. Therefore, the structure of the speed observer should be modified in such a way that the variation of main flux saturation is recognized within the speed estimation algorithm. In this paper, the sliding mode observer (SMO) of a sensorless induction motor drive is modified for a wide speed range operation at speeds higher than the base speed. The online identification algorithm of magnetizing inductance to operate in the field weakening region is presented. The identification algorithm is based on measured stator voltages and currents and the magnetizing curve of the machine. Simulation and experimental results are presented on indirect field oriented controller of an induction motor drive with compensation of main flux saturation to demonstrate the effectiveness of the modified SMO to operate in the field weakening region.