Global robust disturbance attenuation and almost disturbance decoupling for uncertain cascaded nonlinear systems (Q1301390)

The authors solve the problem of \(H_\infty\) disturbance rejection for a class of non-minimum phase nonlinear systems with triangular structure and subject to unknown but bounded uncertainties. The output is a nonlinear function of the state and is perturbed by the disturbance but not by the control input. A nonlinear state feedback controller is designed to ensure the input to state stability and \(L_2\) bounded effect of the disturbance input upon the controlled output with a bound that is independent of the parameter uncertainty. The design procedure is based on the recursive Lyapunov approach. Moreover, the authors present a solution to the problem of global robust \(H_\infty\) almost disturbance decoupling with the level of attenuation arbitrarily small for all admissible uncertainties.