A state observer for minimum phase nonlinear systems

In this paper a local state observer for minimum phase nonlinear systems is presented. It is shown that if a nonlinear system has asymptotically stable zero dynamics, then there always exists a state observer for given nonlinear system. As a consequence, it is also shown that if a nonlinear system has exponentially stable zero dynamics, then there exists an output feedback tracking controller. An illustrative example to show the effectiveness of proposed method is included.