Semiglobal robust output regulation of minimum-phase nonlinear systems

In this paper, we address the problem of semiglobal robust output regulation for a general class of single-input, single-output nonlinear systems. The proposed solution does not require the assumption of input-to-state stability of the zero-dynamics of the plant. The design method is based on a classical decomposition of the control law into a stabilizing feedback and a feedforward control, where the latter is asymptotically reconstructed by an internal model. The scheme exploits the passivity properties of the internal model, and combines small-gain and high-gain feedback. Simulation results for an illustrative example are included.