Adaptive observer-based control of induction motors with unknown rotor resistance

An output feedback control for induction motors which is based on rotor speed and stator current measurements is presented. It is adaptive with respect to constant unknown torque load and rotor resistance. The main feature of this control is the incorporation of a novel adaptive flux observer which provides exponentially convergent estimates of rotor fluxes and rotor resistance under persistency-of-excitation conditions that are satisfied in physical operating conditions. Extensive simulations show that asymptotic convergence is achieved for the overall closed loop system; in particular, the true values of torque load and rotor resistance are obtained and the speed and flux level references are independently tracked.