Reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor drives

This paper deals with reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor drives. A general analytical solution for the stabilizing observer gain is given. The gain has two free positive parameters (which may depend on the operating point), whose selection significantly affects the damping, convergence rate, robustness, and other properties of the observer. The general stability conditions for the stator-resistance adaptation are derived. An observer design is proposed that yields a robust and well-damped system and requires a minimal amount of tuning work. The proposed observer design is experimentally tested using a 45-kW induction motor drive; stable operation at very low speeds under different loading conditions is demonstrated.