In this paper the stability problem of the stator current error based Model Reference Adaptive System (MRAS) speed estimator for induction motor (IM) drive is discussed. The MRASCC that is analyzed in this paper is created with a rotor flux simulator based on the stator current (first superscript C) and the stator current estimator (second superscript C), both adapted with the estimated rotor speed. As the original estimator is unstable in the regenerating mode, a simple stability extension solution is proposed based on the introduction of an auxiliary variable in the mathematical model of this estimator. The new adaptation rule is derived using the Lyapunov theory and stability range of a modified speed estimator is determined. This modification is compared with the existing solutions and analyzed in simulation and experimental tests under motoring and regenerating modes of the drive system, in open and closed-loop operation. It has been shown that the modified speed estimator with an additional variable adapted on-line is stable in the whole regenerating mode, contrary to the classical solution and does not require any modifications during the change from the regenerating to motoring mode and vice versa, as it is required in the existing solutions.

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 has been proposed in the literature. However, there is a lack of fair comparison of all advantages and drawbacks of these proposals. Thus, in this paper 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 paper. 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.

This paper deals with the stability problem of three stator current error-based estimators of induction motor speed, especially in the regenerating operation mode. The stability of the adaptive full-order observer (AFO) and two model reference adaptive systems (MRASs) based on a stator current error (MRAS^CCand MRAS^CV) is briefly analysed, and the stability borders are determined and compared. It is shown that MRAS^CVspeed estimator is stable in the whole operation range including the regenerating mode without any modifications. The stability enhancement method for AFO and MRAS^CCestimators is described, and the solution for their stability improvement is proposed. Torque-speed characteristics of the analysed MRAStype estimators in a wide range of drive speed and load torque changes are given, as well as the behaviour of estimators during transients is compared. The theoretical analysis and simulation test results are validated by experimental tests.

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In this article a comparison of stability ranges of speed estimators MRAS(CV) and MRAS(CC), as well estimator MRAS(CC) with application of stability extension method in regenerating mode was presented. Theoretical analysis was validate by simulation and experimental result.