An adaptive speed sensor-less fourth order observer for on-line estimating rotor flux and speed in induction motor drives is presented in the paper. The synthesis procedure of the adaptive observer is based on the hyper-stability theory. Assuming the speed as unknown parameter of the rotor flux observer, the on-line identification process of its value has been set-up. The adaptation mechanism of the rotor speed and the gain matrix of the observer have been chosen so that stable operation is assured. The stability is tested using the hyperstability theory. The parameter (speed) convergence is assured thanks to the persistent exciting propriety of the input vector. Simulation tests conducted on the observer and on a field oriented controlled drive, using the proposed adaptive observer, show the convergent trajectories of the speed and of the state error vector under various significant steady state and transient operating condition and for different values of the adaptation gains. The results show the satisfactory behaviour of the proposed adaptive observer.
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