A New Framework for Supervisory Control of Discrete Event Systems

Abstract

We propose a new framework for supervisory control design for discrete event systems. Some of the features of the proposed approach are: (i) By associating control and observation capabilities and limitations with the plant as well as the supervisor, it models reactive systems, and also treats plant and supervisory processes in a symmetric way. (ii) By introducing a single general interconnection operation, called masked composition, it permits open-loop as well as closed-loop control. (iii) By viewing the uncontrollability of events as corresponding to a projection-type control mask, and considering more general nonprojection-type control as well as observation masks, it treats the controllability and observability of events in a unified way. (iv) It applies to both deterministic and nondeterministic plant models and supervisory design. The sublanguages of a given language that are realizable under control are closed under union. Hence, the supremal realizable sublanguage always exists. In addition, it yields conditions under which existence of a non-deterministic supervisor implies existence of a deterministic supervisor. (v) By encapsulating control and observation masks with process logic to form process objects, and using a single type of interconnection operator to build complex process objects out of simpler component process objects, it provides a foundation for an object-oriented approach to discrete event control.