Design and stability study of an induction motor vector control system with extended rotor-flux and rotor-resistance Gopinath observer

The paper presents the synthesis of an extended Gopinath observer (EGO) and analyzes the asymptotic stability of a vector control system for a squirrel-cage induction motor that contains in its loop an EGO. The extended Gopinath observer proposed in this paper is designated to estimate the rotor flux components and the rotor resistance of the induction motor. This work presents a new strategy to assign the Gopinath matrix elements of the flux estimator in the EGO observer. The studied control system is based on the direct rotor flux orientation method (DFOC) and the stability study is based upon the linearization theorem around the equilibrium points of the control system, emphasizing the estimated variation domain of the rotor resistance for which the control system remains asymptotically stable when the prescribed speed of the control system is close to zero. The stability study is made in continual case. The mathematical model of the vector control system uses a value dlambda_e - dlambda_e linked to the stator current.