Output feedback disturbance attenuation with robustness to nonlinear uncertain dynamics via state-dependent scaling

This paper presents a novel approach to output feedback stabilization with L-2 disturbance attenuation for nonlinear systems in the presence of dynamic uncertainties. A new method of state-dependent scaling unifies treatment of nonlinear and linear gains in the output feedback design. The effect of disturbance on the controlled output, which is allowed to be any function of output measurements, can be attenuated to an arbitrarily small level with global asymptotic stability if the plant belongs to a wide class of interconnected systems whose uncertain components unnecessarily have finite linear-gain. 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. The design procedure proposed in this paper consists of novel recursive calculation of robust observer gain as well as feedback gain.