Robust Stability of Induction Motor Control Systems under Torque Load

A nonlinear control method for induction motor drives has been proposed to guarantee robust stability in the large as an alternative of the vector control method. This paper examines the robust stability of the proposed nonlinear control system under the persistent torque load. A sufficient condition for the existence of locally stable equilibrium points is derived, which clarifies the relation between allowable torques and parameter variations. The local stability condition for vector control method is also derived. These two control methods are compared, from the robust stability view point, by means of a numerical example of 150 kW induction motor model.