A globally-stable adaptive field-oriented controller for current-fed induction motors

We propose a procedure to adjust online the rotor time constant estimate of an indirect field-oriented control law for current-fed induction machines. The resulting scheme is shown to be globally exponentially stable provided the load torque on the motor is zero and the a priori uncertainty on the range of variation of the rotor time constant is smaller than 100%. The latter is a reasonable assumption in many practical cases. We also show that, when the load torque is different from zero, the speed error enters in finite time a residual set whose size is proportional to the load torque.