Fault recovery in discrete event systems

In this paper, we study the synthesis of fault recovery procedures using discrete-event models. It is assumed that a diagnosis system is available that detects and isolates the faults with a bounded delay. Thus, the combination of the plant and the diagnosis system, as the system to be controlled, will have three modes: normal, transient and recovery. Initially, the plant and thus the system to be controlled, are in the normal mode. Once a fault occurs in the plant, the system enters the transient mode. After the fault is diagnosed by the diagnosis system, the system enters the recovery mode. We study the design of a nonblocking supervisor to enforce the design specifications of the system in all three modes. The solution is obtained by first transforming the problem into an equivalent robust nonblocking supervisory control problem under partial observation, and then (using our previous results on robust control) solving the resulting robust control problem and thus the fault recovery problem. As a result, we obtain a set of necessary and sufficient conditions for the existence of a solution for the fault recovery problem