Torque and flux control of induction motors: a physically-based approach

We address the problem of torque and rotor flux control of induction motors perturbed by an unknown constant load torque. Our main contribution is the proof that this objective can be achieved without linearizing the motor dynamics. The design, which is presented as a variation of model matching, proceeds in two steps: 1) define a target closed loop dynamics compatible with the physical model of the motor that delivers the desired torque and operates in a balanced regime; and 2) propose a nonlinear dynamic output feedback controller that insures asymptotic model matching. A complete proof of global asymptotic stability is given under the assumption of known motor parameters. When the motor resistances are unknown, a globally convergent adaptive scheme is also presented. Two key features of our physically-based design are: 1) the control law does not require measurement of rotor variables; and 2) it does not rely on nonlinear dynamics cancellation. The controller is designed without considering the classical Park´s coordinate transformation of the motor model, therefore directly giving its implementable form