Robust output tracking for nonlinear systems with weakly non-minimum 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 uncertainties and/or with actuator dynamics fall into the class under consideration. The controller design here is divided into two phases: Fast feedback control and slow feedback control, so that a final composite control is obtained. The former is chosen to stabilize the boundary layer system, whereas the latter essentially handles the mismatched uncertainties after the system is reformulated. Under some mild assumptions, it 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 ϵ. As ϵ → 0, the residual set shrinks to the origin. An interesting application to a simplified aircraft model with fast actuator dynamics, which turns out to be weakly non-minimum phase, is given. The computer simulation has verified the expected satisfactory performance.