Novel rotor-flux observer using observer characteristic function in complex vector space for field-oriented induction motor drives

This paper proposes a new strategy to estimate the rotor flux of an induction machine. The electrical model of the induction machine presents the basic idea based on an observer structure, which is composed of a voltage model and a current model. However, the former has the defects of sensitivity to machine parameters in the low-speed range, and the latter also has defects that are sensitive to the machine parameters in wide-speed range. In spite of these shortcomings, the closed-loop flux observer based on two models has been a prevalent estimation method for direct field-oriented control. In this paper, a generalized analysis method called the "observer characteristic function method" is proposed to analyze all kinds of the linear flux observers in an unified form. By the observer characteristic function being utilized, the estimated rotor-flux error involved in the classical methods can be easily clarified. Moreover, the novel rotor-flux observer based on this analysis is also presented. The proposed flux observer is robust to the offset voltage and to parameter variation. The effectiveness of the novel flux observer has been verified by the numerical analysis and experimental results.