Semiglobal robust output regulation of a class of nonlinear systems via output feedback control

In this paper, we establish the solvability conditions of the semiglobal robust output regulation problem for a special class of nonlinear SISO systems in the normal form. We take three steps to deal with this problem based on a recently developed general framework for handling the robust output regulation problem. First, convert the robust output regulation problem of the given plant into a robust stabilization problem of an augmented system composed of the original plant and a well defined internal model. Second, solve the semiglobal robust stabilization problem of the augmented system via partial state feedback. Third, solve the semiglobal robust stabilization problem of the augmented system via output feedback. Taking advantage of the nonlinear internal model, we have obtained a result that does not rely on the polynomial assumption of the solution of the regulator equations needed in the existing literatures.