Direct vector control of induction motors based on rotor resistance-invariant rotor flux observer

A novel speed-flux tracking controller for induction motors has been developed and experimentally verified. Direct rotor flux field oriented controller is designed for current-fed induction motor model on the base of full order hybrid continuous time-sliding mode flux observer. Controller guarantees local asymptotic speed-flux tracking and asymptotic direct field-orientation under condition of unknown constant load torque. The flux subsystem is invariant with respect to limited rotor resistance variations due to special structure of the flux observer. The efficiency of the proposed solution is confirmed by the results of experimental studies, which demonstrate the improved robustness properties in all motor operating conditions including nearby zero speeds.