Robust global stabilization of a class of uncertain feedforward nonlinear systems

The problem of global asymptotically stabilizing a certain class of uncerta in feedforward nonlinear systems is considered. The control law is obtained by nesting saturation functions whose amplitude can be rendered arbitraril y small. With respect to previous works on the subject the design procedure is able to deal with uncertain (possibly time-varying) parameters ranging within the prescribed compact sets which can affect also the linear approxi mation of the system. The small gain theorem for nonlinear systems which ar e input to state stable "with restrictions" is shown to be a key tool for d esigning a state feedback saturated control law. (C) 2000 Elsevier Science B.V. All rights reserved.