ROBUST OUTPUT TRACKING FOR NONLINEAR-SYSTEMS WITH WEAKLY NONMINIMUM-PHASE

This paper is concerned with the problem of designing a robust output tracking controller for MIMO nonlinear systems with weakly non-minimum phase. Based on our system formulation, control plants with uncertain ties and/or with actuator dynamics fall into the class under considera tion. The controller design here is divided into two phases: fast feed back control and slow feedback control, so that a final composite cont rol is obtained. The former is chosen to stabilize the boundary layer system, whereas the latter essentially handles the mismatched uncertai nties after the system is reformulated. Under some mild assumptions, i t is shown that the overall states are bounded and the tracking errors converge to a residual set whose size is a class k function of epsilo n. As epsilon --> 0, the residual set shrinks to the origin. An intere sting application to a simplified aircraft model with fast actuator dy namics, which turns out to be weakly non-minimum phase, is given. The computer simulation has verified the expected satisfactory performance .