Output feedback stabilization of a class of uncertain nonlinear systems

The problem of global output feedback stabilization for a class of nonlinear systems, whose zero dynamics are not necessarily stable, is addressed in this paper. It is shown that, using a novel observer design tool together with standard backstepping and small-gain techniques, it is possible to design a stabilizing output feedback controller, which ensures robustness with respect to dynamic uncertainties. The proposed stabilization method generalizes existing tools in several directions. Finally, the method is illustrated by means of a simple example.