Global robust output regulation for Lur´e systems

We consider the global output regulation problem for systems with an output depending nonlinearity. If the system model is known and the corresponding regulator equations are solvable, an observer-based controller solving the global output regulation problem is presented. Sufficient conditions for the existence of such a controller are formulated in terms of an LMI. If the system parameters are not exactly known and the nonlinearity can vary over a given class, we show that there exists a robust controller provided that the robust output regulation problem for the system without the nonlinearity is solvable and that there exists a suboptimal solution to a certain H_∞ optimization problem.