Hierarchical robust supervisory control of discrete-event systems

The problem of Robust Supervisory Control (RSC) of Discrete-Event Systems (DES) is concerned with situations in which the DES plant model has dynamics uncertainty. A main challenge in the development of solutions for supervisory control problems (including RSC) is the issue of complexity of resulting solutions. Hierarchical approaches to supervision have been found to be effective in mitigating the above issue. In hierarchical control, a high-level supervisor designed based on a simplified high-level model of the plant, receives information about important events in the plant and issues high-level supervisory commands. In this thesis, the problem of hierarchical robust supervisory control under partial observation is studied. First, the setup of Zhong-Wonham for hierarchical control is extended to the case of control under partial observation. A Factorization property is derived that the reporting map must satisfy so that the reports sent to the high-level supervisor rely only on the low-level observable sequences. Furthermore, the three properties of Unobservable-and-Unique-Controllability (UUC), Unobservable-and-Uncontrollable-Prefixes-for-Observability (UUPO) and Partially-Observable-Strict-Output-Control-Consistency (PO-SOCC) are introduced and showed to ensure hierarchical consistency. Algorithms for modification of the plant model and reporting map (if necessary) to satisfy the Factorization, UUC, UUPO and PO-SOCC properties have also been developed. Next, the problem of robust supervisory control of a finite family of discrete-event plants is studied. Each plant has a separate closed specification language. A hierarchical solution is developed assuming full observation and then extended to the case of partial observation, following the approach in the thesis for hierarchical control under partial observation. Finally, a case study involving a flexible manufacturing system production line is studied where a machine is prone to failure. Following the approach developed in this thesis, a hierarchical robust supervisory control is designed to solve the control problem