A Framework for Global Robust Output Regulation of Nonlinear Lower Triangular Systems With Uncertain Exosystems

This technical note considers global robust output regulation for nonlinear lower triangular systems with uncertain exosystems. The problem, under standing minimum phase and solvability of regulator equations conditions, has not been well solved in the literature. It has attracted many researchers to contribute efforts to build solutions, however only partially from different aspects, mostly utilizing adaptive internal models. The bottleneck is that the usual adaptive approach is not suitable for recursive implementation due to the so-called "propagation of uncertainties" while recursion is usually indispensable for global control of lower triangular systems. This motivates the present development of an expanded and "nonadaptive" internal model based design framework. As a major consequence, we are able to avoid propagation of uncertainties and establish a constructive solution for the problem.