ONLINE ESTIMATION OF STATOR RESISTANCE OF AN INDUCTION-MOTOR FOR SPEED CONTROL APPLICATIONS

Speed control of induction motors requires the accurate estimation of the fluxes in the motor. But the flux estimate, when estimated from th e stator circuit variables, is dependent on the stator resistance of t he induction motor. As a consequence the flux estimate is prone to err ors due to variations in the stator resistance, especially at low stat or frequencies. A scheme is presented in this paper for an online esti mation of the stator resistance under steady state operating condition s, using variables that can be measured from the terminals of the moto r alone. The scheme is based on estimating the steady-state magnitudes of the stator and rotor flux space phasors using the reactive power. An analysis of the effect of the stator resistance variations on the f lux estimate is presented. A simulation of a rotor field oriented spee d control of a VSI-fed induction motor using stator circuit variables is performed incorporating the online stator resistance estimation str ategy.