Fault detection and diagnosis from a hybrid system point of view

This paper gives an analysis of fault detection and diagnosis (FDD) from a hybrid system point of view. A simple RL circuit is used to illustrate detectability and modelling issues in traditional observer-based fault detection approaches. We show that traditional model-based FDD whereby a faulty model of the system is sought is not valid especially in the case of abrupt faults. We show that a more appropriate way to tackle the FDD problem is to derive a hybrid model of the system based on the fact that the occurrence of an abrupt fault will send the system from one mode (not necessarily safe) to another faulty mode. We also discuss the issue of fault sensitivity with respect to an output and show sits relation to fault detectability. Simulation results are presented to support all the arguments put forward.