Nonlinear Output Regulation Without Immersion

The main goal of this paper is to show that the so-called"immersion assumption" is not in principle needed in solving a problem of nonlinear output regulation by output feedback. Under the only assumption that the zero dynamics of the controlled system have bounded trajectories, it is shown that there exists a controller solving the problem. The design procedure illustrated in the paper is based on some recent results, developed in [1], on the theory of nonlinear state observers originally proposed in [16]. The internal model obtained in this way is a linear Hurwitz system with nonlinear output map.