Asymptotic stabilization of minimum phase nonlinear systems using output feedback

Considers a single-input single-output (SISO) nonlinear system which has a well defined normal form with asymptotically stable zero dynamics. The authors allow the output and its derivatives to appear in the unobservable dynamics. The authors also allow uncertainities in the model which do not change the relative degree. The authors goal is to design a dynamic output feedback controller which stabilizes the origin. The authors consider regional as well as local analysis. In the regional analysis, the robust output feedback controller brings the state of the closed-loop system to a positively invariant set that includes the origin. Once inside this set, the authors rely on local growth conditions in the local analysis to show that the trajectories approach the origin. The authors give also semi-global results whereby, they do not require the nonlinearities to satisfy global Lipschitz conditions