A Flux Observer Based Vector Control of a Controlled Current Source-Fed Induction Motor

The vector control of an induction motor is classified into direct and indirect types. Indirect vector control (slip frequency controlled type) is usually used because of its simplicity and superior characteristic at low speed operation. A defect of this type is sensitive influences by thermal variations of the secondary resistance. In order to improve the robustness against the parameter change, a flux observer based direct vector control has been proposed in the literature. In this paper, a flux observer based indirect vector control is proposed and the stability of the system is investigated.At first, a flux observer based direct vector control is constructed by using a controlled current source. By considering the observer in a fixed co-ordinate system located on its secondary flux, an indirect type is presented. An observer gain matrix which is invariable according to the co-ordinate transformation is derived. The poles of the observer and those of the observer based vector control system are calculated analytically by neglecting the machine parameter change. Furthermore, a linear model of the observer based vector control system is proposed by taking into account the change of primary and secondary resistances. By using this model, the trajectories of the poles and zeros of the torque transfer function are computed and discussed.