47 research outputs found
Supervisor Localization of Discrete-Event Systems based on State Tree Structures
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
Nonconflict check by using sequential automaton abstractions
In Ramadge-Wonham supervisory control theory we often need to check nonconflict of plants and corresponding synthesized supervisors. For a large system such a check imposes a great computational challenge because of the complexity incurred by composition of plants and supervisors. In this paper we present a novel procedure based on automaton abstractions, which removes internal transitions of relevant automata at each step, allowing the nonconflict check to be performed over relatively small automata, even though the original system can be fairly large
Model Properties for Efficient Synthesis of Nonblocking Modular Supervisors
Supervisory control theory provides means to synthesize supervisors for
systems with discrete-event behavior from models of the uncontrolled plant and
of the control requirements. The applicability of supervisory control theory
often fails due to a lack of scalability of the algorithms. We propose a format
for the requirements and a method to ensure that the crucial properties of
controllability and nonblockingness directly hold, thus avoiding the most
computationally expensive parts of synthesis. The method consists of creating a
control problem dependency graph and verifying whether it is acyclic. Vertices
of the graph are modular plant components, and edges are derived from the
requirements. In case of a cyclic graph, potential blocking issues can be
localized, so that the original control problem can be reduced to only
synthesizing supervisors for smaller partial control problems. The strength of
the method is illustrated on two case studies: a production line and a roadway
tunnel.Comment: Submitted to Journal of Control Engineering Practice, revision