ADAPTIVE OUTPUT-FEEDBACK CONTROL OF CURRENT-FED INDUCTION-MOTORS WITHUNCERTAIN ROTOR RESISTANCE AND LOAD TORQUE

We present an adaptive nonlinear control algorithm for current-fed ind uction motors which is adaptive with respect to both load torque and r otor resistance. The eighth-order adaptive controller provides referen ce signals for stator currents on the basis of measurements of rotor s peed, 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 d ynamic controller guarantees speed tracking and bounded signals for ev ery initial condition of the motor. When persistency of excitation con ditions are satisfied, the rotor flux tracking error tends asymptotica lly to zero so that motor power efficiency may be improved. Moreover, in this case, the estimates of rotor fluxes, torque load and rotor res istance tend asymptotically to their true values. Simulations show tha t persistency of excitation conditions are satisfied in physical opera ting 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.