Hierarchical control of DES based on colored Petri nets

In the reported literatures on the control of discrete event systems (DES) modeled by Petri nets with the constraint of a logical intersection of some linear inequalities or just a single one, the constraint usually has to be transformed into the form of logical union when there are some uncontrollable transitions in the net. In this paper, we propose a hierarchical control method for DES with logical union of constraints based on colored Petri nets though the plant (uncontrolled DES) is modeled as a noncolored Petri net. The low-level gets the state information from the plant and sends it to the high-level. The high-level plays the role of controller and ensures that there is at least one of the constraints is satisfied at any time for any system state. In addition, it is proved that the proposed hierarchical control is maximal control.