Robust tracking of a nonlinear system with parameter uncertainties

We discuss the problem of the robust output tracking of a class of nonlinear systems which has time varying, exogenous signal and slowly-varying parameter uncertainties. The approach is based on the equilibrium manifold, which depends upon continuously both the exogenous signal and the parameter uncertainties. In order to achieve the control objective, we propose a two loop control law. The nonlinear closed loop system achieves boundedness of state and robust output tracking within a prescribed level