Modular Supervisory Control with Equivalence-Based Abstraction and Covering-Based Conflict Resolution

A modular approach to control is one way to reduce the complexity of supervisory controller design for discrete-event systems (DES). A problem, however, is that modular supervisors can conflict with one another. This paper proposes requirements on coordinating filters that will resolve this conflict. Abstractions are employed to reduce the complexity of the filter construction. Our specific approach is unique in that it employs a conflict-equivalent abstraction that offers the potential for greater reduction in model size than those abstractions employed in previous works on conflict resolution. The resulting control implemented by the modular supervisors in conjunction with coordinating filters meeting the proposed requirements is shown to be safe and nonblocking. Approaches for constructing these filters are discussed and a methodology that implements deterministic coordinating filter control laws by nondeterministic automata is presented. The covering-based filter law construction methodology presented here is further demonstrated to provide less restrictive control than existing results on state-feedback supervisory control.