Supervisory Control Of Discrete Event Systems By Petri Nets

In discrete event systems,deadlocks occur due to the unreasonable allocation of resources.Deadlocks can reduce the efficiency of a system and even cause the system to stop.It is essential to solve the problem of deadlocks.Since a Petri net has a strong ability to model and control a system,it is widely used to solve the problem of deadlocks in discrete event systems.The main research work of this thesis is as follows:1)Based on the concepts of the enabling arcs and inhibitor arcs,some extended modules are analyzed,including the enabling modules and inhibitor modules.Some simple models in this thesis can prove that these modules are more general than the enabling arcs and the inhibitor arcs.Modulo-N Counter is an example of these modules.These modules can be used to segment analyze the dynamic behavior of a system,which can effectively analyze and control some complex systems.2)A new type of arcs is studied.The weight of such arcs is labeled by a function rather than an integer interval and a set of integers.The new type of arcs is more general compared with data decision arcs and interval inhibitor arcs.When a transition satisfies the enabling conditions and fires,the tokens in the corresponding place can be moved.Such arcs are not only used to solve the problem of conflicts in the resource allocation systems,but also improve the analysis and control capabilities of Petri nets.3)The incidence matrix and state equation of a Petri net are extended.The incidence matrix can be used to split the set of the reachable markings into multiple subsets.Then,these subsets are connected by the transitions that are obtained by solving the state equation.And it must be guaranteed that the number of the added transitions is minimal.Then,an asymptotically stable controlled system can be obtained.The new type of arcs not only extends the structure of Petri nets,but also improves its modeling capability.The extended incidence matrix and the corresponding state equations can make the system always run among subsets,which can accomplish some complicated processes.