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Hierarchical fault diagnosis: application to an ozone plant

A framework for online passive fault diagnosis in hierarchical finite-state machines (HFSM) is presented and applied to an ozone generation plant. This approach takes advantage of system structure to reduce computational complexity. Here, the system model is broken into simpler substructures called D-holons. A diagnoser is constructed for each D-holon. At any given time, only a subset of the diagnosers are active, and as a result, instead of the entire model of the system, only the models of D-holons associated with active diagnosers are used for diagnosis. Furthermore, a set of sufficient conditions is provided under which the diagnosis process becomes semi-modular. The ozone generation plant under study, consisting of two units, is modeled as an HFSM. It is shown that a proper choice of sensors results in modular diagnosis (one diagnoser for each unit). Following the proposed framework, a hierarchical fault diagnosis system is designed for the plant. It is shown that the proposed approach significantly reduces the complexity of constructing and storing the diagnosis system.