ROBUST TRACKING FOR NONLINEAR-SYSTEMS VIA HYBRID CONTROL

In this paper, the problem of output tracking for single-input/single- output nonlinear systems in the presence of mismatched uncertainty is studied. In our problem, the so-called matching condition in the liter ature is further relaxed, and a more general condition on the uncertai nty is given. To attenuate the effects of uncertainties on the trackin g error, a design method which is referred to as the Stable Combined V ariable Perturbation Method (SCVPM) is presented. Based on this design method, a new robust tracking controller is derived using hybrid cont rol strategy. This controller, taken as a root-controller, is then use d to generate two other controllers. All these controllers guarantee r obustness of the closed-loop system, only with different tracking accu racies. The design method as well as the robust controllers is charact erized by a small robust design parameter, epsilon. The tracking error converges to an epsilon-neighbourhood of the origin, and, by letting epsilon go to zero, the accuracy of tracking can be improved to any de sired degree. Finally, an example is given and the simulation results confirm the theoretical analyses, thus show the effectiveness of the n ew design method and controllers.