Adaptive Non-Linear High Gain Observer Based Sensorless Speed Estimation of an Induction Motor

An efficient sensor-less speed estimator, based on an adaptive non-linear high gain observer (HGO) which uses only the measured stator currents and control voltages in the presence of measurement noise, is proposed to estimate the speed of an induction motor. The proposed observer is an improved version of the standard HGOs proposed in the literature. The observer gain, involving the use of a scalar time-varying design parameter governed by the Riccati differential equation, guarantees the best compromise between the fast convergence of the states and noise rejection; with such adaptation of gains that the internal states of the observer exert low influence during the transient period and, thus, prevent system peaking. The design methodology of the proposed observer is given, and its stability is studied. Results of simulations demonstrate that robustness and efficiency of the proposed observer are maintained under critical operating conditions, even where the efficiency of the fixed gain observer is decreased.