A Modified Disturbance Rejection Mechanism in Sliding Mode State Observer for Sensorless Induction Motor Drive

This paper presents a modified sliding mode state observer for sensorless vector-controlled induction motor drive. The objective is to improve the dynamic performance of the sensorless drive subjected to parameter uncertainty, fault and disturbances. The sensorless drive along with the proposed observer is modeled and built in Simulink, and the dynamic behavior is obtained for different test cases such as flux-weakening region, variations in commanded speed and torque, low-speed operation and under faulty operation mode subjected to an electrical fault in the inverter. The conventional disturbance rejection mechanism is modified by constraining the estimated disturbance along with the stator current error in the sliding surface, thereby increasing the ability of the observer to reject the effect of the external load on the tracking performance. Extensive simulation results prove that the modified observer has a wide speed bandwidth compared to the conventional observer along with superior tracking, disturbance rejection characteristics and torque holding capability.