OBSERVER DESIGN AND DETECTION FOR NONLINEAR DESCRIPTOR SYSTEMS

A nonlinear observer is considered for a class of continuous nonlinear descriptor systems subject to unknown inputs and faults. This class i s partly characterized by globally Lipschitz nonlinearities, and a mem ber system may be singular and possibly non-causal. The observer struc ture chosen makes it useful for both state estimation for feedback con trols and residual generation for fault detection. Results on the exis tence of solutions are given and some useful bounds are derived which are important in the observer design, which is based on a transformed system and on the solution of a Riccati equation. The existence, conve rgence properties and robustness of the observer are investigated by t he use of a quadratic Lyapunov function. Conditions are given for a bo und to hold on the norm of the transfer function relating the residual error to the disturbance (linear case). A design algorithm is given a nd applied to the estimation of the states of a flexible joint robot.