Design of high-gain unknown input observer based on Riccati equation

For a class of Lipschitz nonlinear system, the reconstruction problems of state estimation, unknown input and measurement noise were studied. Regarding the measurement noise as an extended state, the original system can be transformed into a descriptor system. For the descriptor system, first, a high-gain observer which can estimate the states and the measurement noise of original system simultaneously was developed based on the solution of a Riccati equation. Second, a second-order high gain sliding mode observer was used to exactly estimate the derivatives of the system outputs in a finite time. Third, by using the estimates of the states and the output derivatives, an algebraic unknown input reconstruction method was proposed. It was pointed out that both the unknown input and measurement noise reconstruction methods are suitable for stronger time-varying signals. Finally, a numerical simulation of a practical model was given to illustrate the effectiveness of the proposed methods. ©, 2015, Beijing University of Aeronautics and Astronautics (BUAA). All right reserved.