Nonlinear unknown input observer design for nonlinear systems

This paper provide new developments in the design of observers for a class of nonlinear systems with unknown inputs whose nonlinear functions satisfy Lipschitz condition. The proposed methods guarantee the error system stability without requiring the rank condition and also yield many additional degrees of freedom available to the designer. The algorithms for designing a nonlinear observer for the nonlinear systems with unknown inputs is precisely derived. The proposed observers may be used for the state estimation and fault diagnosis. A nonlinear mass-spring-damper model is given in order to highlight the efficiency of the proposed method.