Robust disturbance attenuation of nonlinear systems using output feedback and state-dependent scaling

This paper presents an approach to output feedback stabilization with L-2 disturbance attenuation for nonlinear systems in the presence of dynamic uncertainties. A new formulation of state-dependent scaling is introduced into the output feedback design, which unifies treatment of nonlinear and linear gains. The effect of disturbance on the controlled output, which is allowed to be any function of output measurements, can be always attenuated to an arbitrarily small level with global asymptotic stability if the plant belongs to a wide class of triangular systems whose uncertainties do not necessarily have finite linear-gains. The uncertain dynamics is not limited to input-to-state stable systems either. The approach is not only a natural extension of popular approaches in robust linear control, but also advantageous to numerical computation which is applicable to non-triangular systems as well as triangular systems. (C) 2004 Elsevier Ltd. All rights reserved.