State-dependent scaling approach to global control of interconnected nonlinear dynamic systems

This paper presents a novel approach to the problem of global stabilization with L₂ disturbance attenuation for a class of interconnected nonlinear systems. An innovative generalization of state-dependent scaling is newly accomplished, which allows one to deal with interconnection of nonlinear-gain bounded dynamic systems which unnecessarily have finite linear-gain. The effect of the disturbance on the controlled output can be attenuated to an arbitrarily small level with global asymptotic stability by partial-state feedback control if the nonlinear system is an interconnection of a strict-feedback system and a uncertain time-varying dynamics of unmeasurable state variables. The procedure of designing such partial-state feedback controllers is described in the form of recursive selection of state-dependent scaling functions. The state-dependent scaling approach offers flexibility to render the nonlinear controller identical with robust linear ℋ^∞ control at the equilibrium