Deadlock Avoidance Controller Design for Timed Petri Nets Using Stretching

The recently introduced method, which was called ldquostretching,rdquo is extended to timed Petri nets which may have both controllable and uncontrollable transitions. Using this method, a new Petri net, called ldquostretched Petri net,rdquo which has only unit firing durations, is obtained to represent a timed-transition Petri net. Using this net, the state of the original timed Petri net can be represented easily. This representation also makes it easy to design a supervisory controller for a timed Petri net for any purpose. In this paper, supervisory controller design to avoid deadlock is considered in particular. Using this method, a controller is first designed for the stretched Petri net. Then, using this controller, a controller for the original timed Petri net is obtained. Algorithms to construct the reachability sets of the stretched and original timed Petri nets, as well as algorithms to obtain the controller for the original timed Petri net are presented. These algorithms are implemented using Matlab. Examples are also presented to illustrate the introduced approach.     

基于加权模糊时序Petri网络的电网故障诊断模型

提出了一种基于加权模糊时序Petri网络(FTPN)的电网故障智能诊断模型,该模型主要包括停电区域识别、可能故障元件加权FTPN建模、故障元件集求解、保护/断路器动作情况判定4个部分。介绍了故障差错告警差错信息的分类以及故障告警信息时序特性,研究了断路器动作信息及网络拓扑关系,结合广度优先搜索,得到了停电区域识别方法。最后,以新英格兰10机39节点系统为例,建立了母线和线路加权FTPN故障诊断数学模型,并给出该系统的总体结构,结果表明该模型能够快速故障定位,准确提供保护和断路器动作评价信息。     

Petri网描述的继电保护动作逻辑时序建模

Petri网理论具有完善的理论证明依据,是离散动态系统建模的有效工具。该文基于Petri网理论,介绍了一种新的继电保护建模思路。保护装置可以看成一个离散动态系统。利用Petri网中并行、冲突、资源分享等特性,对继电保护中的动作逻辑演化及二次回路动态进行描述,建立了保护装置的PN模型。最后就RCS-901A/B超高压线路成套保护装置进行了工作原理分析和性能评估,证明了所提方法的有效性。     

Petri网络在变压器故障诊断中的应用

Petri网络理论以网络理论，代数理论等为数学基础，以图形化的方法直观地描述了离散事件系统的各种关系和行为，适用于描述异步并发现象的计算机系统模型和对并行及并发系统进行行为分析，在人工智能领域中正得到越来越广泛的应用。作者提出一种基于Petri网络的变压器故障诊断模型，论述了利用Petri网络进行知识表示及推理的矩阵运算算法。描述了故障征兆与故障的关系。使用了比传统系统更深的知识、简单，明确。与传统的专家系统相比，利用此理论及方法仅仅使用简单的矩阵计算，可以减少诊断时间，提高准确度。通过实例对此模型进行的测试表明该模型方法是快速、准确的。     

时间约束的改进分层模糊Petri网的配电网故障诊断方法

配电网发生故障后,迅速利用大量的告警信息判别出故障元件,能为调度中心的工作人员提供重要的决策支持。针对现有Petri网的故障诊断方法未应用在配电网中的问题,提出了一种时间约束的改进分层模糊Petri网的配电网故障诊断方法。对配电网中的可疑故障元件建立改进的分层模糊Petri网模型,能够适应网络拓扑结构的变换,利用获得的报警信息通过反向和正向时序推理对保护和断路器进行时序检查,对不满足时间约束的库所进行置信度修正。给出了改进分层模糊Petri网模型的推理流程及矩阵推理算法,在矩阵推理过程中引入高斯函数修正概率,使概率始终保持在0～1,最终得到故障元件的置信概率及其时间点约束。通过对配电网系统算例的比较、分析,验证了所提方法的正确性和合理性,能够有效地诊断出配电网的故障元件。     

Fault Section Estimation of Power System Using Colored and Timed Petri Nets

A correct and rapid inference is required for practical use of expert system for fault section estimation in power systems. This paper proposes a new model-based expert system for fault section estimation using colored and timed Petri nets. The Petri nets simplify the inference procedure greatly because it can represent the causalities among faults of power system components, protective actions of relays and circuit breakers. They can also represent the operating states of these protective devices explicitly, or, more precisely, whether a relay has been actuated correctly or falsely, etc. In addition, time sequence information on actuated relays and tripped circuit breakers can be handled by using the colored and timed Petri nets. Therefore, the operating states of relays and circuit breakers can be inferred more correctly. Petri nets are suited for parallel processing so well that there is a possibility of reducing the inference time considerably. In the proposed system, the inference is executed by setting the initial states in the Petri nets using the information on the actuated relays and the tripped circuit breakers and then operating the Petri nets. There have been several test cases which used a prototype system on the Macintosh computer employing Object Common Lisp, and good results have been obtained.     

多层Petri网应用于电网规划

Petri网应用于电网规划时,既要考虑实际的潮流,又要考虑负荷需求信息以及电力系统运行的限制,所以 不能按照传统的方法选择一个单一的Petri网来建模。把基本Petri网和一个改进的可变弧权Petri网通过一个“界面” 结合起来模拟规划过程,这个多层的Petri网模型能够很好地协调电力系统负荷需求和电力供应能力之间的关系。     

基于模糊时间Petri网的电网故障诊断方法

故障元件判别作为电网故障应急处置的首要环节,是在线调控运行的重点工作之一。针对现有基于Petri网的电网故障诊断方法未充分利用时序信息或者时序推理过程复杂的问题,提出一种基于模糊时间Petri网的电网故障诊断方法。为Petri网中库所及变迁引入时间属性以表征电力系统告警信息的时序约束关系,定义了置信概率与时序约束的关联推理运算,并从模型结构出发建立了模糊时间Petri网的分层推理过程,能够同时推理得到元件故障的置信概率及其时间点约束。算例仿真表明,所提方法能够快速判定故障元件,诊断结果正确且合理,具有较强的容错性,且能对告警信息做出正确评价。     

一种混和Petri网结构分析方法

混和Petri网可很好地描述由连续动态和离散动态相互混和、相互作用而形成的混和系统.其特点是,将位置和变迁区分为连续和离散两种类型,以表征连续变量过程和离散事件过程.Petri网是离散系统建模和分析的一种有效的图形和数学工具.在文中,基于图论提出一种分析Petri网结构特性的方法,然后介绍转换矩阵和Petri网的对应关系.其次,应用转换矩阵的特征多项式和方程分析Petri网的结构特性;最后,应用例子来说明该方法的应用.     

基于时序信息的模糊Petri网电网故障诊断方法

为提高电网故障诊断的准确性,充分利用报警信号的时序信息,研究一种基于时序信息的分层变迁模糊Petri网故障诊断方法。首先,建立分层变迁加权模糊Petri网(WFPN)故障诊断模型;其次,构建元件、保护和断路器之间的时间关联特性(TAC),进行时间关联一致性检查;最后,通过模糊推理进行故障诊断,并对保护和断路器异常行为进行评判。通过典型电网算例推理验证,结果证明该方法不仅能够提高故障诊断的准确性和容错性,还能够判断保护和断路器的异常行为并推出元件故障发生时刻。     

Modeling by petri net with place invariants for sequential control systems

It is more difficult to model a discrete system than a continuous system. Recently, a great number of applications of Petri nets to the design and the analysis of discrete systems has been reported. However, a common problem in its applications is that the required computer memories and the computation times increase explosively in accordance with the increase in the number of systems components. Some methods to divide or to reduce Petri nets have been proposed to solve this problem. Although the liveness and boundedness of Petri nets are held in the divided or reduced Petri nets, the reachability problem cannot be solved by these methods. This paper proposes another method to model discrete systems by Petri nets with place invariants. A sequential control system will be described as a typical kind of discrete system, and its structural characteristics will be used in modeling. Each component of a sequential control system will be modeled by a sub-Petri net with place invariants. There are many components in one sequential control system, but not each one is necessarily complicated. Most sub-Petri nets do not have so many places or transitions. It is also well known that a Petri net with place invariants is bounded and can be live by placing sufficient tokens into its initial marking. Besides, the reachability problem is not so difficult to solve in a small sub-Petri net. Further, an activating relation to combine two or more sub-Petri nets is defined, and some rules to reduce conflicts among enabled transitions will be described for simulations.     

汽轮发电机组振动故障诊断的Petri网模型

Petir网理论是以网络理论、代数理论等为数学基础的,可利用图形语言对故障诊断系统的结构、功能及流程进行系统的分析和描述,是异步并发诊断系统建模与分析的重要工具之一.作者在论述了Petri网矩阵描述方法的基础上,根据汽轮发电机组故障征兆与常见故障类型之间的关系,建立了一种基于Petri网的汽轮发电机组振动故障诊断模型.与传统的汽轮发电机组振动故障诊断方法相比,该模型仅使用简单的矩阵运算,诊断过程简单直观,速度快.实例分析表明,利用该模型可对汽轮发电机组的振动故障作出正确判断.     

Petri nets semantics of π-calculus

As π-calculus based on the interleaving semantics cannot depict the true concurrency and has few supporting tools, it is translated into Petri nets. π-calculus is divided into basic elements, sequence, concurrency, choice and recursive modules. These modules are translated into Petri nets to construct a complicated system. Petri nets semantics for π-calculus visualize system structure as well as system behaviors. The structural analysis techniques allow direct qualitative analysis of the system properties on the structure of the nets. Finally, Petri nets semantics for π-calculus are illustrated by applying them to mobile telephone systems.     

粗糙集结合Petri网的3/2接线变电站故障诊断研究

500kV及以上的变电站多采用3/2接线方式,其主接线结构和保护配置具有自身的特点.本文在分析了3/2接线系统保护动作策略的基础上,建立了故障诊断的初始决策表,并利用粗糙集的属性优选对该表进行最小约简,构建最优的Petri网模型,从而实现故障诊断.变电站故障诊断实例证明了该方法不仅能够准确诊断出3/2接线系统的故障元件,而且诊断速度快,容错性好.     

远程备用智能保护一体化中心动作逻辑时序建模

针对双重化智能站域保护在检修、故障退出、灾变恢复等多种场景下可靠性不充分的问题,提出远程备用智能保护一体化中心(Remote Duplicate Configuration Smart-Protection Center,RDCSPC)继电保护新架构,需研究RDCSPC的动作逻辑情况。根据其与双重化智能站域保护之间的配合关系,使用Hierarchical Petri net Simulator(Hi PS)软件分别建立RDCSPC在热备用、冷备用工作模式下的时序Petri网(PN)模型并对之进行动态仿真分析,同时,采用PN矩阵分析法对所建立的时序PN模型进行描述验证。模型验证结果表明:所建立的时序PN模型可以有效的描述RDCSPC的动作逻辑。     

A fuzzy Petri net based approach for fault diagnosis in power systems considering temporal constraints

The fuzzy Petri net is a promising and efficient approach that can tackle the complexities of power system fault diagnosis. In this work, the temporal constraint between event occurrences in power systems is investigated. Then, it is introduced to a fuzzy Petri net (FPN) for fault diagnosis. The temporal attributes are assigned to the propositions in the Petri net, so that temporal information can be taken into account, which makes the true hypothesis distinguishable from the false ones. The modified matrix execution algorithm can enhance computational efficiency, with a “weighted average” operation included to improve the fault-tolerance. The developed model possesses a modular structure, which is easy to adapt to topology changes, and to accommodate modern protection schemes. A preliminary evaluation of the operating performance of protective devices is also carried out after fault section identification. The testing results on the IEEE 14-bus power system and Zhejiang provincial power system in China demonstrate that the developed model is correct and efficient. Compared with three existing fault diagnosis methods, the proposed one has stronger fault-tolerance with lower computational cost, and is suitable for on-line fault diagnosis in large-scale power systems.     

基于改进Petri网技术的智能操作票系统的应用

在Petri网模型构建的操作票知识库的基础上,利用Petri网的动态行为设计相应推理机制,使推理过程形式化,实现推理过程与规则表示的完全分离,提高了电网调度操作票专家系统的通用性和灵活性;同时,改进后的推理方法通过改变Petri网的运行规则和引入抑制弧,并利用Petri网技术对操作任务进行分解,对子任务建立基本Petri网,简化了推理过程,提高了推理效率,解决了"状态组合爆炸"问题。实例表明,改进Petri网的推理机制可有效提高操作票专家系统的适应性。     

基于高级Petri网的继电保护建模方案研究

为提高继电保护建模的方便性和准确性,提出了基于高级Petri网的继电保护建模方案。针对继电保护建模的特点,构建了带有混杂特性的有色时间Petri网(H_TCPN),并基于H_TCPN建立了继电保护3层模型,该模型引入顺序变迁、空变迁、时延、时限等概念,丰富了对保护系统混杂性和时间参数的描述。开发了一套组态式继电保护建模仿真系统,利用分层和图形化的方式提高了建模的直观性,并给模型配置了完备的接口程序和开放的设置环境,为继电保护的分析研究提供了一个有效的建模工具和仿真手段。以11型装置距离保护部分为例,介绍了采用该方案建模的详细过程,并利用实际故障录波数据对继电保护模型进行回放检验,证明了基于高级Petri网的继电保护建模方案的可行性和有效性。     

基于冗余嵌入Petri网技术的变电站故障诊断

基于Petri网技术，利用电力系统实时离散事件（保护继电器和断路器）信息，探讨了一个具体变电站故障诊断的方法。主要讨论了变电站故障诊断的Petri网建模，计算冗余嵌入Petri网的错误伴随式矩阵等问题。仿真结果表明该方法计算简单，非常适合应用于在线实时监控系统。     

一种 Petri 网禁止状态控制器综合方法

针对含有不可控变迁Petri网的禁止状态问题,提出了一种基于整数线性规划的控制器综合方法,该方法适用于任意普通Petri网模型。首先,根据Petri网的结构特性构建所有不可控变迁应满足的约束条件集合,其次通过求解整数线性规划问题将给定的线性约束转换为允许线性约束;最后,利用库所不变量方法设计控制器将转换后的约束综合到Petri网中。以某零件加工系统为例进行实验,实验结果表明,提出的方法简单高效,对实际自动制造系统的禁止状态监控问题具有一定借鉴意义。