Robust stabilization of nonlinear systems via normalized coprime factor representations

A reasonably complete theory for the synthesis of robust controllers for a broad class of nonlinear systems is now available. We use this theory to ge neralize the linear theory of normalized coprime factor robustness optimiza tion to the case of affine input nonlinear systems. In particular, we show that the equilibrium controller may be characterized in terms of the stabil izing and destabilizing solutions of the Hamilton-Jacobi equation used to c alculate the normalized (right) coprime factors of the plant. We also show that the optimal robustness margin of ?(1 - parallel to[(M)(N)]parallel to(H)(2)) generalizes to the nonlinear case. In preparation for the nonlinear analysi s, we review the linear case in a way which motivates our approach to the n onlinear case and highlights the parallels with it. (C) 1998 Elsever Scienc e Ltd. All rights reserved.