High Gain Observer Design for Induction Motor with Non Linear Magnetic Characteristic

State estimators for induction motors are generally designed based on standard simplified models, assuming linear magnetic characteristics. Since they are actually nonlinear, especially for high power machines, the mentioned state estimators are likely not able to achieve the estimation accuracy they have been designed for. In this paper, a new state estimator is developed for a (uniform air-gap) AC machine, based on a more accurate model that appropriately accounts for the saturation feature in the magnetic characteristics. The proposed estimator is a high-gain full-order nonlinear observer designed using Lyapunov stability tools. The resulting estimation errors are shown to asymptotically vanish, if their initial values belong to a well defined attraction region. Supremacy of the new observer over standard ones is illustrated by simulation using a 7.5 KW AC machine