Adaptive output feedback control of current-fed induction motors with uncertain rotor resistance and load torque

We present an adaptive nonlinear control algorithm for current-fed induction motors which is adaptive with respect to both load torque and rotor resistance. The eighth-order adaptive controller provides reference signals for stator currents on the basis of measurements of rotor speed, stator currents and stator voltages; estimates of rotor fluxes, which are the unmeasured state variables; estimates of torque load and rotor resistance which may vary considerably during operations. The dynamic controller guarantees speed tracking and bounded signals for every initial condition of the motor. When persistency of excitation conditions are satisfied, the rotor flux tracking error tends asymptotically to zero so that motor power efficiency may be improved. Moreover, in this case, the estimates of rotor fluxes, torque load and rotor resistance tend asymptotically to their true values. Simulations show that persistency of excitation conditions are satisfied in physical operating conditions and that all estimation errors tend quickly to zero so that high tracking performances are achieved both for speed and rotor flux. (C) 1998 Elsevier Science Ltd. All rights reserved.