ADAPTIVE OUTPUT-FEEDBACK REGULATION OF A CLASS OF NONLINEAR-SYSTEMS -CONVERGENCE AND ROBUSTNESS

In this paper pie consider a minimum-phase, input-output linearizable system that is represented globally by an nth-order differential equat ion. The nonlinearities of the system depend linearly on unknown param eters which belong to a known convex set, We design a semiglobal adapt ive output feedback controller to ensure boundedness of ail state vari ables and regulation oi the output to zero (an open-loop equilibrium c ondition). It is shown that the adaptive controller is robust with res pect ta bounded disturbances in the sense that tile mean square regula tion error is of the order of the magnitude of the disturbance. Moreov er, if the disturbance vanishes when the input and output are identica lly zero and if its slope is sufficiently small, then :he adaptive con troller will ensure convergence of the regulation error.