Fault Modeling in Discrete Event Systems Using Petri Nets

Abstract

In this article a model-based controller reconfiguration method for fault-tolerant control of discrete event systems has been introduced. In this method, we model the fault conditions for each specified fault as a new model called fault model. The system then consists of three different models called process, specification and fault. The faulty parts of the system are not permitted to do any job and the controller tries to enforce the specifications by other parts of the system. With this method, the controller reconfiguration problem for fault- tolerant control of discrete event systems converts to the problem of synchronizing the process, specification and fault model. We must synthesize a supervisor that can enforce both specifications and faults status. If this supervisor can be determined, we can achieve a fault-tolerant controller. Implementing both specification and fault models in the system, may lead to a large number of forbidden states and constraints and so on a more complicated forbidden states problem must be solved. The application of constraints simplification methods is shown. By the existing methods for offline simplifying of constraints, we can arrive at a simplified fault tolerant controller.