Identification of a nonlinear plant under nonlinear feedback using left coprime fractional based representations

It has been shown that the set of all nonlinear plants stabilised by a know n linear controller, which also stabilises a linear nominal model of the pl ant, can be parametrised by a stable operator known as the Youla-Kucera par ameter. By utilising this description it is possible to convert the closed- loop plant identification problem to one of open-loop identification. This paper extends previous work by allowing the model of the nominal plant and the controller in the above scenario to be nonlinear. The ideas rely on a c oncept of differential coprimeness for nonlinear fractional system descript ions. (C) 1999 Elsevier Science Ltd. All rights reserved.