A MRAS-based speed sensorless field oriented control of induction motor with on-line stator resistance tuning

This paper describes a model reference adaptive system (MRAS) for the speed estimation of induction motor from measured terminal voltages and currents. The estimated speed is used as feedback in a vector control system. The MRAS approach has the immediate advantage in that the model is simple, very easy to implement and has direct physical interpretation. This paper studies the influence of the stator resistance variation on MRAS speed estimation. It has been shown that when a motor is running at high speed, the effect of error in stator resistance is usually quite negligible. But as the frequency approaches zero, this becomes more serious because the voltage drop on stator resistance becomes relatively larger as the frequency decreases. In comparison with rotor resistance adaptation, the stator resistance adaptation has received less consideration. In this paper, a new reference scheme has been used for stator resistance estimation. Under this reference scheme, one component of flux can be decoupled from the corrupting effects of the stator resistance and the other quadrature component can provide a near-instantaneous estimate of the stator resistance. In the system, the output of the stator resistance identifier updates the value of the stator resistance used in the MRAS speed estimator. Simulation of rotor field oriented speed sensorless control of VSI-fed induction motor using stator circuit variables is performed incorporating the on-line stator resistance estimation technology.