Response to comments on "passivity-based control of saturated induction motors"

A review of the experimental evidence shows that passivitybased control of saturated induction motors does not provide superior performance over input–ouput linearization. Higher tracking errors can be observed and traced to the open-loop nature of the flux controller. In contrast, input–output linearization controllers achieve close tracking of flux, speed, and position references for the most demanding trajectories. In the above paper [1], the authors consider the use of a passivitybased controller for an induction motor that undergoes saturation in the main field flux. Despite the claimed advantages of the algorithm, significant problems can be observed. The results given in [1, Fig. 2(b)] show large tracking errors in the flux. The poor performance is due to Manuscript received November 19, 2001; revised February 12, 2003. Abstract published on the Internet May 26, 2003. R. T. Novotnak is with Aerotech, Inc., Pittsburgh PA 15238 USA (e-mail: [email protected]). J. Chiasson is with the Electrical and Computer Engineering Department, University of Tennessee, Knoxville, TN 37996 USA (e-mail: [email protected]). Digital Object Identifier 10.1109/TIE.2003.814994 0278-0046/03$17.00 © 2003 IEEE IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 50, NO. 4, AUGUST 2003 821 the fact that the flux controller is open loop, and cannot keep up with the time-varying flux reference (a time-varying flux reference is necessary to maximize the torque at high speed). In contrast, the approach of [2] and [3] estimates the flux and uses the estimate to drive the flux control loop through the direct stator current. Interestingly, the performance of the passivity-based controller of [1] and of the input–output linearization controller of [2], [3] can be compared without prejudice, because the two studies used the same hardware, and the study of [1] used the code developed earlier for [2] and [3], simply replacing the estimated flux ^ d by the flux reference d. (This is because the only difference between the passivity-based controller of [1] and the input–output linearization controller of [2] is this replacement.) The results of [2] and [3] show close tracking for a reference trajectory that is much more demanding than the one chosen by the authors of [1]. Tracking of the flux, speed, and position references is also demonstrated. As a matter of correction, it is worth noting that the flux saturation curve, the moment of inertia J , and the coefficient of mutual inductance M of [1] do not have the values given in [1, Ref. 6] as stated in the paper. Instead, [2] and [3] should be consulted for these values.