Safety Control of Hierarchical Synchronous Discrete Event Systems: A State-Based Approach

In this paper, we discuss the control of a particular class of hierarchical discrete event systems and the state avoidance control problem is considered. A methodology is provided that locally computes on each component of the system the set of bad states (these are the states that may lead to the forbidden states via an uncontrollable trajectory). This is performed without computing the whole system. At this point, the supervisor is evaluated on the fly w.r.t. the bad states and thus requires an on-line evaluation in order to determine the set of events that has to be disabled by control. It is performed in such a way that the global partial transition function does not need to be built