Semi-global robust stabilization of nonlinear systems by partial state and output feedback

We study the problem of semi-global robust stabilization for a class of multi-input multi-output uncertain nonlinear systems which cannot be transformed, via a change of coordinates and a state feedback, into a lower dimensional zero dynamics driven by a set of chains of integrators, but more complicated interconnected structures. Sufficient conditions are presented for the existence of a linear high-gain partial state controller and/or a nonlinear dynamic output feedback compensator, which achieves semi-global asymptotic stability, uniformly in unknown time-varying parameters ranging over a known compact set. Both the partial state and dynamic output controllers are explicitly constructed via the design tools such as semi-global backstepping and high-gain observer. We also show how the results obtained for affine systems can be extended to a more general class of MIMO non-affine systems.