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.