Analysis and detection of incipient faults in post-fault systems subject to adaptive fault-tolerant control

This paper presents an effective scheme for detecting incipient faults in post-fault systems (PFSs) subject to adaptive fault-tolerant control (AFTC). Through a survey of existing techniques, it is shown that the adaptivity of the AFTC counteracts the effect of an incipient fault in the PFS. This makes some of the conventional fault-detection strategies, such as Beard-Jones detection filters and adaptive observers, ineffective in this situation. It is shown that the unknown input observer (UIO) is an effective tool; hence, the UIO is designed to decouple the incipient fault from the AFTC such that the fault-detection residual is sensitive only to the incipient fault. Extensive simulation study is presented using an aircraft example to test three fault-detection approaches; it is demonstrated that the UIO is the most effective tool in detecting the incipient fault in a PFS subject to AFTC. Copyright (C) 2007 John Wiley & Sons, Ltd.