Robust Stabilization and Performance Recovery of Nonlinear Systems With Unmodeled Dynamics

In this technical note we present a time-scale separation redesign for stabilization and performance recovery of nonlinear systems with unmodeled dynamics. The unmodeled dynamics studied do not change the relative degree of the plant and are minimum phase. We design two sets of high gain filters-the first to estimate the uncertain input to the plant over a fast time-scale, and the second to force this estimate to converge to the nominal input on an intermediate time-scale. The control input then acts over the slow time-scale and guarantees that the closed-loop trajectories approach those of the nominal system.