Global Asymptotic Position Research Articles

A Globally Stable Discrete-Time Controller for Current-Fed Induction Motors

In this short paper we present a discrete-time field oriented controller (FOC) for current-fed induction motors which insures global asymptotic rotor position (or velocity) tracking. To the best of our knowledge, this is the first time such a result is rigourously established for a controller implemented in discrete-time. As expected in a discrete-time controller, an unavoidable condition relating the sampling rate with the rate of change of the references is imposed. This condition disappears as the sampling rate goes to zero. Interestingly enough, the condition also reflects the well known fact that to avoid magnetic saturation the flux norm must be increased when the machine is requested to deliver large torques. One important feature of our scheme is that it is obtained via a slight -but essential- modification to a first difference approximation of the classical indirect FOC, hence its additional computational burden is negligible.