Nonlinear Control of Induction Motors: Torque Tracking with Unknown Load Disturbance

In a recent paper (Ortega and Espinosa, 1991) presented a globally stable controller for torque regulation of a complete induction motor model with partial state feedback, i.e. no assumption of flux measurement. The result was established under the assumptions that both the desired and load torques are constant, that the former does not excede certain bounds which depend on the systems natural damping, and that the motor parameters are known. In the present contribution we extend these results in several directions. First, by "adding mechanical damping" to the closed-loop system we relax the upper bound condition on the desired torque. Second, we use a new controller strutcture that allows us to treat the case of time-varying desired torque. Finally, a new estimator is proposed to handle time-varying, but linearly parametrized unknown loads.