INDIRECT FIELD-ORIENTED CONTROL OF INDUCTION-MOTORS IS ROBUSTLY GLOBALLY STABLE

Field orientation, in one of its many forms, is an established control method for high dynamic performance AC drives. In particular, for ind uction motors, indirect field-oriented control is a simple and highly reliable scheme which has become the de facto industry standard. In sp ite of its widespread popularity no rigorous stability proof for this controller was available in the literature. In a recent paper (Ortega et al, 1995) [Ortega, R., D. Taoutaou, R. Rabinovici and J. P. Vilain (1995). On field oriented and passivity-based control of induction mot ors: downward compatibility. In Proc. IFAC NOLCOS Conf., Tahoe City, C A.] we have shown that, in speed regulation tasks with constant load t orque and current-fed machines, indirect field-oriented control is glo bally asymptotically stable provided the motor rotor resistance is exa ctly known. It is well known that this parameter is subject to signifi cant changes during the machine operation, hence the question of the r obustness of this stability result remained to be established. In this paper we provide some answers to this question. First, we use basic i nput-output theory to derive sufficient conditions on the motor and co ntroller parameters for global boundedness of all solutions. Then, we give necessary and sufficient conditions for the uniqueness of the equ ilibrium point of the (nonlinear) closed loop, which interestingly eno ugh allows for a 200% error in the rotor resistance estimate. Finally, we give conditions on the motor and controller parameters, and the sp eed and rotor flux norm reference values that insure (global or local) asymptotic stability or instability of the equilibrium. This analysis is based on a nonlinear change of coordinates and classical Lyapunov stability theory. Copyright (C) 1996 Elsevier Science Ltd.