Robust nonlinear control of time-varying systems

For a class of SISO nonlinear time-varying systems, we present a robust output feedback control scheme. The control scheme removes some of the structural constraints so as to enlarge the class of systems that can be handled by recently developed nonlinear control schemes. The enlargement can be seen via four aspects: 1) all the unknown coefficients and parameters are assumed to be time-varying; 2) the linear parameterization condition is not required; 3) there is no limitation on how fast the uncertainties vary with respect to time; and 4) all of the unknown nonlinearities are not constrained to be in the span of the control. The robust control approach for linear time varying systems is a special case of the nonlinear control proposed in this paper. We first discuss a second order nonlinear system example to demonstrate the systematic design procedure, then a general class of system is described in which the systematic procedure discussed in the second order example can be applied