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
.