Fault Recovery in Discrete-Event Systems using Observer-Based Supervisors

In this paper, we study the synthesis of fault recovery procedures in discrete—event systems, following a state—based approach. It is assumed that the faults are unobservable but can be diagnosed within a bounded delay. A modular switching supervisory scheme is proposed to satisfy the system design specifications. The design consists of observer-based supervisor modules. One of the modules enforces design specifications during the normal mode of operation and after a fault occurs but before the fault is diagnosed. The rest of the modules are designed for recovery from faults — one module for each fault. When a fault is diagnosed, the corresponding recovery module takes sole control of the plant. The issue of the nonblocking property of the system under supervision is also studied.