Performance improvement of MRAS based speed sensorless field oriented controlled induction motor drives at low speed

Abstract

In this paper, improved rotor flux, a classical model command/reference adaptive control system (MRAS) based rotor speed observer is proposed for better performance of speed sensorless field oriented control (FOC) of induction motor drives in low and through zero speed regions. In conventional rotor flux MRAS speed estimator, rotor flux error used as tuning signal, drives the adequate adaptation mechanism which generates the estimated speed. However, this speed observer performance near zero speed region is poor and uncertain. In comparison to classical MRAS speed estimator, in proposed speed observer two state error vectors are used simultaneously. One between the rotor flux state and second between electromagnetic torque state. Also, adaptation mechanism in classic MRAS speed observer which is proportional-integral for the adjustment of rotor flux error vector is modified to new adaptation law by introducing the electromagnetic torque error vector filtered by low pass filter and added together with classic MRAS adaptation mechanism. The effectiveness of the proposed speed estimator is verified in SIMULINK using MATLAB for different speed and load torque profile.