Design of Regulatory Traffic Light Control Systems with Synchronized Timed Petri Nets

Fixing the phases is one of the common methods to control an urban traffic network. Once a road is filled with a high traffic flow approaching its capacity, the conventional traffic light controller is not able to handle this traffic congestion phenomenon well. In this paper, we propose a novel regulatory traffic light control system to handle such traffic congestion by using synchronized timed Petri nets (STPNs). Three kinds of intersections in an urban traffic network are defined and employed to demonstrate our new regulatory traffic light control system models. Finally, the liveness and reversibility of the proposed STPN models are proven through the reachability graph analysis method. To our knowledge, this is the first work that solves a traffic congestion problem with a regulatory traffic light control technique that is effective in preventing vehicles from entering traffic congestion zones.     

Liveness Problem of Petri Nets Supervisory Control Theory for Discrete Event Systems

A quite great progress of the supervisory control theory for discrete event systems (DES) has been made in the past nearly twenty years, and now, automata, formal language and Petri nets become the main research tools. This paper focus on the Petri nets based supervisory control theory of DES. Firstly, we review the research results in this field, and claim that there generally exists aproblem in Petri nets based supervisory control theory of DES, that is, the deadlock caused by the controller introduced to enforce the given specification occurs in the closed-loop systems, especiallythe deadlock occurs in the closed-loop system in which the original plant is live. Finally, a possible research direction is presented for the solution of this problem.     

基于混合随机Petri网的一类混合系统的模型及稳定性

混合动态系统是包含离散事件系统（ＤＥＳ）和连续变量系统（ＣＶＳ）的复杂系统。讨论了一类每个离散状态包含一个连续动态系统,且离散事件具有Ｍａｒｋｏｖ链性质的随机混合系统,在提出利用混合随机Ｐｅｔｒｉ网的建模方法的基础上,给出混合均方稳定的概念、稳定性和可镇定条件,最后以一个简单的例子做子说明和仿真。     

基于TCPN的交叉口信号控制模型与优化

针对城市路网中交叉口车辆通行效率低下,交通信号控制策略难于满足输入路段上车流变化的问题,本文提出了一种基于时延赋色Petri网的交叉口交通流优化控制模型。首先建立路段车流、交叉口车流和交通信号控制的TCPN模型,其次建立以交叉口输入路段车辆数最小为目标的车流优化方程。在假设信号周期固定的前提下,利用15个周期采集的交叉口输入、输出路段车辆数,求解满足优化目标的相位配时,确保交叉口输出车辆数最大,且输入路段上待通过车辆平均数最小。仿真结果表明,交叉口的通行能力显著提高,各输出路段上的车辆平均数分别增加了13.3%,9.7%,9.8%和4.3%。     

基于赋时Petri 网的化工批处理建模与控制优化

分析了化工批处理过程的特点,以过程设备为核心将整个过程操作划分为若干个子进程,用赋时Ｐｅｔｒｉ网来建立以子进程表示的批处理过程,并提出启发式动态 经自救对过程进行控制。仿真结果表明,基于赋时Ｐｅｔｒｉ网模型与启发式动态 经算法的Ｐｅｔｒｉ网控制器,不仅能准确描述批处理过程的同步、并发及资源工人享关系,而且Ｐｅｔｒｉ网的运行能给出过程生产的最优控制序列。     

基于平行Petri网的制造系统调度与控制一体化方法

为了消除制造系统调度层与控制层之间的隔阂, 实现对生产事件快速灵活响应, 本文提出了一种调度与控制一体化的方法. 首先, 定义了一种新型Petri网模型, 即平行Petri网, 从而集成地描述了传感器、执行器、任务和资源信息, 构建制造系统的信息物理系统模型; 其次, 提出了一种从平行Petri网到赋时Petri网的抽象简化方法, 大规模压缩优化调度所需搜索的状态空间; 再次, 定义了策略Petri网以描述最优调度策略. 最后, 给出了平行Petri网与策略Petri网同步执行算法, 使得平行Petri网与物理系统同步执行.     

混合动态系统的混合Petri网（HSPN）模型

针对混合动态系统,提出一种混合Ｐｅｔｒｉ网（ＨＳＰＮ）模型,分析了该模型具有的特点及其运行规则。以冶金加热炉为例,给出了该系统的ＨＳＰＮ模型。     

Comparison of Hybrid Systems and Fluid Stochastic Petri Nets

Hybrid Systems are modelsof interacting digital and continuous devices with applicationsin the control of aircraft, computers, or modern cars for instance.Concurrently, Fluid Stochastic Petri Nets (FSPNs) have been introducedas an extension of stochastic Petri nets to model physical systemsthat contain continuous fluid quantities controlled by discretelogic, as well as a means to deal with the possible state explosionof discrete models. Of course, an FSPN is by definition a hybridsystem but in this paper, we compare a general hybrid systemsformalism with FSPN formalism. The conclusion of this paper,suplemented by some examples, is that fluid stochastic Petrinets and hybrid system formalism can be converted from one tothe other. Although there is a price to pay for such a conversion,the conversion can transfer the solution methods from one tothe other and thus help the development of both formalisms.     

离散时间Petri网的模糊模型

离散时间Petri网是一种系统模拟和分析的有效工具，它可以结合图形和分析描述评估离散事件系统的动态执行．基于T—S模糊模型，提出用于描述离散时间Petri网的模糊模型，讨论该模型适应于TtPNs的情况，用以推广文章结论，并且给出用于TtPNs的线性模糊控制规则．同时，文章还给出TtPNs聚合的结论．     

Generalised Batches Petri Net: Hybrid Model For High Speed Systems With Variable Delays

Recently, the possibilityof associating both discrete events and continuous time behaviourin the same formalism has generated a considerable interest inthe Petri net paradigm. A central issue in this field is theconcept of Hybrid Petri net which consists in continuous transitionsand places holding non negative real number, and discrete transitionsand places holding integer tokens. By adding a new type of nodes,batch transitions and batch places, Batches Petri nets have beendefined. A batch node combines both a discrete event and a linearcontinuous dynamic behaviour in a single structure. Batches Petrinets can then be used in the control design and performance analysisof high-speed systems composed of continuous transfer elementswhich introduce variable delays on continuous flows. In thispaper, the complete formalism of Generalised Batches Petri netsis given through the definition of the model, the enabling andfiring rules, the time analysis methods, and two examples illustratethese notions.     

On Hybrid Petri Nets

Petrinets (PNs) are widely used to model discrete event dynamic systems(computer systems, manufacturing systems, communication systems,etc). Continuous Petri nets (in which the markings are real numbersand the transition firings are continuous) were defined morerecently; such a PN may model a continuous system or approximatea discrete system. A hybrid Petri net can be obtained if onepart is discrete and another part is continuous. This paper isbasically a survey of the work of the authors' team on hybridPNs (definition, properties, modeling). In addition, it containsnew material such as the definition of extended hybrid PNs andseveral applications, explanations and comments about the timingsin Petri nets, more on the conflict resolution in hybrid PNs,and connection between hybrid PNs and hybrid automata. The paperis illustrated by many examples.     

Invariants of Timed Petri Nets

A linear fundamental equation for a timed Petri net is constructed. Full and partial invariants of state and behavior of a timed Petri net are introduced. Properties of invariant nets are analyzed. Interrelations of full and partial invariants are shown. Examples of analysis of net models of production systems and processes are described.     

基于混合Petri网的一类混合系统的动态分析

利用混合Ｐｅｔｒｉ网对一类典型的混合系统－－模式切换系统进行建模和分析；提出模式切换系统动态平稳性的概念；给出了二模式切换系统的平稳条件以及求解平稳点的算法，并用实例进行了说明。     

基于时间Petri网的企业铁路作业系统模型的研究

由于企业自备铁路作业现场比较混乱,作业类型相当复杂,好多因素难以从数学模型的角度加以考虑,因此,寻找一种有效的建模方法来描述系统的数学模型是很有意义的。Petri网具有易于描述系统的并发、竞争、同步等特征,很好地满足了系统建模、验证及实现方面的众多需求。文中利用时间Petri网描述了企业铁路的作业系统的模型,并对产生的冲突提出了解决方案。     

Tutorial and Survey Articles: An introduction to Petri Nets

This paper describes the fundamental concepts and characteristics of Petri nets (PNs) that make them a significant tool for modeling and analyzing asynchronous systems with concurrent and parallel activities and follows the extensions that improved the implementation capabilities of the original PNs.

Their first and most relevant extension was time modeling, a vital aspect of system performances not considered in the original version. There are several possibilities for introducing time in PNs. Among them, a technique that associates time with places is presented in some detail. As PNs tend to become cumbersome and time consuming when large and complex systems are involved, a method for decomposing timed PNs of open queuing networks is reviewed here.

Though initially developed as an information/computer-based technique, PNs were immediately adopted in a variety of application areas, such as manufacturing, design, planning and control. Viewed through a more recently developed programming perspective, the ordinary PNs became “high level” PNs suitable for defining different data types and for applying hierarchical approaches.

It is expected that the robust theoretical basis of this tool coupled with its visual and flexibility features will continue to appeal to researchers and practitioners alike in a variety of domains and as a result will continue to evolve and expand.     

A Simulation Engine for Stochastic Timed Petri Nets and Application to Emergency Healthcare Systems

In many service delivery systems, the quantity of available resources is often a decisive factor of service quality. Resources can be personnel, offices, devices, supplies, and so on, depending on the nature of the services a system provides. Although service computing has been an active research topic for decades, general approaches that assess the impact of resource provisioning on service quality matrices in a rigorous way remain to be seen. Petri nets have been a popular formalism for modeling systems exhibiting behaviors of competition and concurrency for almost a half century. Stochastic timed Petri nets (STPN), an extension to regular Petri nets, are a powerful tool for system performance evaluation. However, we did not find any single existing STPN software tool that supports all timed transition firing policies and server types, not to mention resource provisioning and requirement analysis. This paper presents a generic and resource oriented STPN simulation engine that provides all critical features necessary for the analysis of service delivery system quality vs. resource provisioning. The power of the simulation system is illustrated by an application to emergency health care systems.      

流体随机Petri网与混合Petri网的比较分析

流体随机Petri网和混合Petri网作为传统Petri网的拓展,可以建模离散成分和连续成分并存的混合系统,也可用于解决离散模型的状态空间爆炸问题.由于这两种建模机制远未发展成熟,分析比较它们的异同点有助于机制本身的进一步发展完善,有助于为特定的应用选择合适的建模方法.本文讨论了流体随机Petri网和混合Petri网的定义、连续标识、分析方法、以及相互转换的可能性.结论是这两种建模机制是互补的,各自适合于特定的应用场合.     

Discrete Supervisory Control of Hybrid Systems Based on l-Complete Approximations

The topic of this paper is the synthesis of discrete supervisory control for hybrid systems with discrete external signals. Such systems are in general neither l-complete nor can they be represented by finite state machines. Our solution to the control problem is as follows: we find the strongest l-complete approximation (abstraction) _l for , represent it by a finite state machine, and investigate the control problem for the approximation. If a solution exists on the approximation level, we synthesize the maximally permissive supervisor for _l . We show that it also solves the control problem for the underlying hybrid system . If no solution exists, approximation accuracy can be increased by computing the strongest k-complete abstraction _k , k > l. The basic ideas regarding the approximation step are explained within the framework of Willems' behavioral systems theory. Implementation issues are treated in a state space framework, and the main results are interpreted from a traditional control engineering point of view.     

Petri网方法及其在制造系统研究中的应用

Petri网是描述、分析和控制离散事件动态系统最有效和应用最广泛的方法。本文先对Petri网的基础理论和重要性质加以介绍,然后对其在制造系统研究中的应用进行评述。