Nonlinear control of induction motors: torque tracking with unknown load disturbance

Ortega and Espinosa (1993) 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 exceed certain bounds which depend on the systems natural damping, and that the motor parameters are known. In the present contributions the authors extend these results in several directions. First, by “adding mechanical damping” to the closed-loop system the authors relax the upper bound condition on the desired torque. Second, the authors use a new controller structure that allows them to treat the case of time-varying desired torque. Finally, a new estimator is proposed to handle time-varying (linearly parameterized) unknown loads