Supervisor Localization of Discrete-Event Systems based on State Tree Structures

TL;DR

This paper extends supervisor localization to State Tree Structures, enabling efficient distributed control of large discrete-event systems with proven equivalence to global control and demonstrated on semiconductor manufacturing.

Contribution

It introduces a new localization theory within State Tree Structures, including novel concepts and an efficient BDD-based algorithm for large system control.

Findings

Localized control behavior matches global optimal control

Proposed algorithm improves computational efficiency

Validated on a complex semiconductor manufacturing system

Abstract

Recently we developed supervisor localization, a top-down approach to distributed control of discrete-event systems in the Ramadge-Wonham supervisory control framework. Its essence is the decomposition of monolithic (global) control action into local control strategies for the individual agents. In this paper, we establish a counterpart supervisor localization theory in the framework of State Tree Structures, known to be efficient for control design of very large systems. In the new framework, we introduce the new concepts of local state tracker, local control function, and state-based local-global control equivalence. As before, we prove that the collective localized control behavior is identical to the monolithic optimal (i.e. maximally permissive) and nonblocking controlled behavior. In addition, we propose a new and more efficient localization algorithm which exploits BDD computation. Finally we demonstrate our localization approach on a model for a complex semiconductor manufacturing system.