Internally stable nonlinear systems with disturbances: a parameterization

This paper deals with the control of a nonlinear system whose output is subjected to an additive disturbance. The main result is a simple parameterization of the set of all system responses that can be obtained through internally stable control of the given system. The parameterization provides a clear indication of the effects of the disturbance on the response of the stabilized closed loop system. The class of achievable responses is determined by the “numerator” of a right coprime fraction representation of the system being controlled