GLOBAL APPROXIMATE OUTPUT TRACKING FOR NONLINEAR-SYSTEMS

This paper addresses the global output tracking problem for nonlinear systems with singular points. For nonlinear systems which satisfy a su itable observability condition, the authors identify a class of smooth output trajectories which the system can track using continuous open- loop controls. This class includes all output trajectories generated b y smooth state feedback. They then study the problem of approximate ou tput tracking using discontinuous time-varying feedback controllers. G iven a smooth output trajectory for which exact tracking is possible, the authors construct a discontinuous feedback controller which achiev es robust tracking of the desired output trajectory in the face of per turbations. Finally, it is shown that their results can be applied to the control of a chain system, and some numerical results are presente d to illustrate the performance of their controller.