Design of the flux observer based vector control system of induction machines taking robust stability into consideration.

Abstract

In this paper, we describe the theoretical aspects of the flux feedback type vector control system based on the flux observer, giving emphasis on its robust stability to the secondary resistance variation.The main reason for our success in realization of this control system is the desensitization of the flux observer. Actually, robustness of this control system entirely depends upon that of the flux observer. First, we clarify a class of flux observers and derive its general structure and pole allocation to accomplish its desensitization to the secondary resistance variation. Then, we show that in our proposed vector control system, right half plane zeros (i.e., unstable zeros) may appear in the open loop system with changes of the secondary resistance; we, however, can avoid their occurrence by the pole allocation method of the flux observer. Furthermore, we establish the design criterion for the feedback gain and the pole allocation of the flux observer which guarantees robust stability of this control system, by exploring the influence of such zeros on the flux feedback control system.Finally, by theoretical and experimental approaches, it is shown that our proposed vector control system has an extremely low sensitivity to the secondary resistance variation in comparison with the slip frequency controlled type vector control system.