Observer-based residual design for nonlinear systems with unknown inputs

This paper presents unknown-input observer-based approach for robust fault detection and isolation of a class of nonlinear Lipschitz systems subject to unknown inputs or disturbances. Residual signals are generated by bank of observers to detect and isolate between actuator faults and sensor faults. The effect of unknown inputs or disturbances can be decoupled from the residual signals by using the generalized inverse method. Necessary and sufficient conditions for the existence and stability of low-order nonlinear unknown input functional observer are derived. A design procedure for the generation of residual signals to detect and isolate actuator and sensor faults is developed using the proposed unknown-input observer-based solution.