Output Stabilization via Nonlinear Luenberger Observers
  The present paper addresses the problem of existence of an (output) feedback law to the purposes of asymptotically steering to zero a given controlled variable, while keeping all state variables bounded, for any initial conditions in a given compact set. The problem can be viewed as an extension of the classical problem of semi-globally stabilizing the trajectories of a controlled system to a compact set. The problem also encompasses a version of the classical problem of output regulation. Assuming only the existence of a feedback law that keeps the trajectories of the zero dynamics of the controlled plant bounded, it is shown that there exists a controller solving the problem at hand. The paper is deliberately focused on theoretical results regarding the existence of such controller. Practical aspects involving the design and the implementation of the controller are left to a forthcoming work. 
Lorenzo Marconi, Laurent Praly, Alberto Isidori