Structural diagnosability analysis of switched systems

Structural diagnosability analysis relies on determining over-constrained subsystems in the system model, which allow to detect and isolate faults. One way to find such subsystems is to decompose the structure graph of the system with the aim to select minimal structurally over-determined sets of equations. For hybrid systems that switch among different operation modes, the structure graph is changed by switching, which leads to different structure graphs for each mode. In this paper we derive graph-theoretical conditions, under which graph alterations do not affect the over-constrained subsystem of the model and the corresponding minimal structurally over-determined sets. On the other hand, conditions are given, under which switching augments the diagnosable part of a system. A case study shows that switching can change the diagnosability properties of a system and, hence, it is advisable for fault diagnosis to bring the system into one of its diagnosable modes.