Small speed asymptotic stability study of induction motor sensorless vector control systems with extended Luemberger estimator

In this paper we analyze the asymptotic stability of a vector control system for a squirrel-cage induction motor that contains in its loop an extended Luemberger 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 both the continual and discrete cases. The mathematical model of the vector regulating system is made using a value d lambda(e) - q lambda(e) linked to stator current.