Optimal torque control for current-fed induction motors

This paper presents an optimal control design for current-fed induction motor drives. The problem to be considered is to find a feedback control that minimizes a generalized convex energy cost function including the stored magnetic energy and the coil losses, while satisfying torque tracking control objectives. Necessary and sufficient conditions for optimality are established. It is shown here that all the stationary solutions can be obtained analytically and are uniquely defined. It is also shown that closed-forms for dynamic suboptimal solutions can also be obtained. The optimal solutions turn out to imply nonstandard time-varying (reference depending) norm flux operations in opposition to well established field-oriented control that operates with constant flux norm.