Stability Improvement Methods of the Adaptive Full-Order Observer for Sensorless Induction Motor Drive-Comparative Study

The adaptive full-order observer (AFO) is the most popular speed estimator for the induction motor (IM) drives. Therefore, due to its instability in the regenerating mode a few stabilization methods have been proposed in the literature. However, there is a lack of fair comparison of all advantages and drawbacks of these proposals. Thus, in this article, the classical AFO and its all known stabilization methods are compared with a recent new proposal, which is based on the introduction of an auxiliary adaptive variable in the observer state matrix. The stability analysis of this new proposal is presented in details in this article. The generalized AFO model containing all possible stabilization methods is formulated and stability analysis methods for each proposed solution are discussed and proved by simulation and experimental tests. Also the behavior of these modified AFOs in the open- and closed-loop sensorless IM vector control structure is presented and evaluated.