Synthesis Of Petri Nets Controller For Discrete Event Systems

In essence, discrete event systems (DES) is a manmade system and the family of manmade systems that hold the characteristics of DES becomes larger and larger and the system itself also becomes more complex due to the rapid development of computer science and its extensively application in modem society. The manufacturing system (especially FMS and dM5), system scheduling, communication network, traffic control system, random service system, computer operating system and military C31 complexes and the other systems that are crucial to the modem civilization are the typical examples of DES. The scholars pursuing the researches of DES come from the fields of automatic control as well as computer, communication, manufacturing and management science and so on.The research of DES mainly consists of system performance analysis and control synthesis. The present dissertation uses Petri nets (PN) as tool to study the controller synthesis of DES with inequality constraint. The principal research results and contents can be outlined as following:Firstly, the FCP method of synthesizing PN controller for DES based on the concept of finite capacity places (FCP) is proposed for the first time in this dissertation. This method has the advantage of simpler computation and the advantage is more obvious especially when the system is large and complex. The FCP method is also applied to design a controller for DES with combined place marking and transition firing constraint. Compared with the reported methods, the obtained method is capable of dealing with more general system and constraint. In addition, the synthesis method has the advantage of indicating whether the constraint can be enforced due to the cause of deadlock.'-III-~: ?~±~{xL~)2Then, two dualistic PN controller synthesis methods are proposed by utilizing extended Petri nets. One is the weighted inhibitor arc (WIA) method, and the other is the weighted enabling arc (WEA) method. The WIA method has the advantage of avoiding searching the entire state space over the reported methods in which inhibitor arc is also used, thus the computation efficiency superiority of WIA method is unexampled. In addition, the application of the method has no restriction of PPIC (precedence path input constraint). The WEA method is a method of synthesizing controller for DES by using weighted enabling arc is applicable to enforce 'greater-than-or-equal-to' marking inequality constraint. The control concept of this method is plain and easy to be understood by the control engineers.Thirdly, combined PN controller for DES is proposed for the first time in this paper. The combined controller takes advantage of both of the compiled controllers and mapping controllers. It can automatically get the state information of the system and permit a real concurrency in the system.Fourthly, colored Petri nets are utilized for the first time to enforce OR logic in DES. One method of maximally permissive enforcing OR logic is obtained via implementing hierarchical control of DES by exploiting colored Petri nets. In the other method, the maximally permissive control is obtained via properly defining the guard function of colored Petri nets. Both of the two methods are able to enforce OR logic without adopting negative number of tokens.Finally, in order to enforce the given inequality constraint, a constraint transformation method for the marked graphs is proposed due to accounting for uncontrollable transitions in the net. This transformation is based on the transition enabling rule of Petri nets and the unique structure of marked graphs.There are not only detailed descriptions of control algorithms but also theory proof in this dissertation. Many examples are provided throughout the text to verify and illustrate the efficiency and feasibility of the various presented synthesis methods of Petri nets controller for DES.