Robust output feedback control of incompletely observable nonlinear systems without input dynamic extension

We introduce a new output feedback controller for general MIMO nonlinear systems which are only observable on regions of the state and input spaces. Unlike previous approaches, we do not add integrators at the input side of the system, and thus avoid the need to design a stabilizing control law for a higher order system. Robustness with respect to a class of time-varying disturbances is guaranteed, and the performance of any state feedback controller designed to achieve closed-loop stability with respect to a set (e.g., a robust controller) is recovered