Improvement of dynamic characteristic for sensorless vector-controlled induction motor system with adaptive PI mechanism

This paper introduces a speed sensorless vector-controlled system for general-purpose induction motor, which is based on the flux observer and the model reference adaptive system method. According to the vector control theory of an induction motor, this system utilizes the q-axis flux converging on zero for speed estimation and speed control. In order to solve the problems of flux estimation by using only a voltage model, the flux-observer-based method is applied. As the mathematical model of this system is based on a synchronously flux-rotating reference frame, a linear model of the proposed system is easily derived to analyze the dynamic characteristic under the influence of the controller gain. For improving the system dynamic characteristic, an adaptive PI controller for speed estimation with variable gain is employed to change the proportional and integral gains on-line according to the q-axis flux. We present the choosing rule for Pl gains of speed estimation. Furthermore, a simplified linear function of this controller is proposed and the rule is modified considering the system being under the influence of noise. The new controller is compared with the conventional controller (constant gain) by experimental result. The validity of the proposed method is proven through experimentation.