Semiglobal output feedback control for uncertain minimum-phase nonlinear systems

Semiglobal practical output feedback stabilization is achieved for a class of uncertain minimum-phasenonlinear systems involving an unknown control gain, matched uncertainty, and unknown internal dynamics. Notably, neither boundedness conditions are imposed on the nonlinear model functions, nor are the input-to-state stability andbounded-input-to-bounded-state conditions imposed on the system's internal dynamics. Therefore, theproposed output feedback approach serves as a somewhat universal (model-free) controller because it exclusively requires the system output and structural information (e.g., the relative degree $r$). In addition, our results demonstrate that a (Byrnes-Isidori) minimum-phase normalform with $r\leq2$ is semiglobally practically stabilizableusing output feedback control.