A restoration aid expert system for distribution substations

This paper presents a practical restoration aid expert system for 154 kV distribution substations. The proposed expert system has a topology-based simple structure and utilizes basic rules suggested by the Korean electric power company including heuristic rules, topology identification rules and search rules to generate switching sequences for feasible restoration processes. In this paper, the general system structure as well as rules and data representations are discussed. The expert system is realized using an HP9000 workstation. X-window and Motif shells are used for the user-friendly GUI. The system has been tested in a practical sub-control center as a part of an intelligent fault diagnosis and restoration aid system to assist the decision making of SCADA operators     

A Petri net based protection monitoring system for distribution networks with distributed generation

Connection of distributed generation (DG) essentially changes distribution network operation and creates a range of well-documented effects varying voltage levels and short circuit currents. Among others, DG can alter protection system operations in distribution networks, leading to failure of reclosing, disconnection of healthy feeder or prevention of protection operation. This paper proposes a procedure, based on Petri nets and supported by a centralized monitoring architecture for monitoring failures of the protection systems in radial distribution networks. Some case studies applied to a real Italian distribution network proved the effectiveness of the proposed procedure that can therefore represent an effective solution to improve distribution systems reliability in presence of DG.     

Distribution system temperature adaptive load transfer using colored Petri net approach

This paper derives appropriate decisions for load transfer among distribution feeders by switching operations to improve system operating performance by combining the load characteristics and the variations among customers as a result of temperature increases using a switching operation decision inference mechanism based on a colored Petri net (CPN) approach. A practical distribution system with 19 feeders, daily load profiles, and corresponding data on temperature sensitivity (TS) is used to perform computer simulations to demonstrate the effectiveness of the proposed methodology. It is concluded that the proposed CPN inference mechanism can enhance the system operating performance with the proper switching operation by considering the TS of customer power consumption served in each service zone of distribution feeders.     

A Petri net algorithm for scheduling of generic restoration actions

This paper is concerned with scheduling of the restoration actions. Generic restoration actions (GRAs) have been identified in the authors' previous research based on a variety of restoration strategies used by electric utilities. This paper proposed a scheduling method using the Petri net (PN) techniques. The PN model incorporates the conditions that have to be met before an action can be taken. The time required to perform an action is also modeled in the net. A token passing and a backward search process are used to identify the sequence of restoration actions and their timing. The advantages of the proposed methods are: (1) the time required to restore a subsystem can be estimated; (2) a systematical method is obtained for identification of the sequence of actions. The BN method has been tested with simulation cases     

Using Petri nets to verify acyclic rule-based system

A series of Petri net-based definitions were formulated for describing four types of structural errors in a rule-based system (RBS), including inconsistency, incompleteness, redundancy and circularity. A marked ω-Petri net model of acyclic RBS was constructed. Then, its reachability tree was generated to record all reachable relations between propositions in RBS. Moreover, a backward reasoning forest of a reachable marking was generated for explicitly representing reachable paths in RBS. Finally, a set of theorems and algorithms were provided to analyze and check structural errors. The usability of the research results presented in this paper was illustrated by an example. __________ Translated from Journal of Tongji University (Natural Science), 2007, 35(2): 232–238 [译自: 同济大学学报(自然科学版)]     

An autosynthesizing non-linear control system using a rule-based expert system

An advanced non-linear control system is obtained by combining recent developments in non-linear control system synthesis with a rule-based system approach to real-time control. The basic problem to be addressed is the control of a non-linear plant which is sufficiently sensitive to both operating point and input amplitude that the desired control system performance can be obtained only with a non-linear controller that is ‘retuned’ or ‘resynthesized’ whenever the operating point changes significantly. (The term ‘changes significantly’ in this context signifies an operating point change that causes the non-linear control system input/output behaviour to change substantially in an undesirable way.) This is accomplished by a hierarchically organized intelligent control system with a conventional reprogrammable controller under the direction of a rule-based expert system. The function of the expert system is to (i) monitor the behaviour of the non-linear control system to determine when retuning or resynthesis is required; if the behaviour is satisfactory, then continue passive monitoring; else (ii) when retuning or resynthesis is required: set up and execute experiments to derive the model information required to tune or synthesize a new non-linear controller in terms of a given structure and parametrization; execute the retuning/resynthesis procedure; reprogramme the controller (download the parametrization); and recommission the updated non-linear control system and return to normal operation. In essence, the rule-based system provides supervisory control (‘meta-control’) for a conventional reprogrammable non-linear controller that will autotune or autosynthesize as required. Autosynthesis takes place to accommodate variability in plant behaviour due to operating point changes, and the nonlinear controller thus synthesized corrects for amplitude sensitivity. This concept represents one way to combine artificial intelligence with control; it will be discussed and illustrated by example below.     

A mathematical programming approach to service restoration for distribution systems

This paper aims to develop a suitable power system restoration method by using mathematical programming (MP). Generally, the problem of determining the target configuration can be formulated as a mixed integer programming (MIP) problem. Whether or not each branch is included in a target system is expressed as a 0–1 variable, while the other constraints such as the demand and supply balance conditions are formulated in terms of continuous variables. Although an MP‐based method can obtain an optimal solution under specified operational constraints, in the case of large‐scale problems the solution time often exceeds the computation time that is practically available due to combinatorial explosion. The object of this paper is to develop an efficient solution algorithm for service restoration in distribution systems. First, an MIP problem is solved to determine the sound network configuration that maximizes the available power to the out‐of‐service area, then an MIP problem is solved to determine the target configuration for the out‐of‐service network. The proposed method has been applied to distribution system restoration problems, and simulation results demonstrate its effectiveness. © 2001 Scripta Technica, Electr Eng Jpn, 135(4): 35–42, 2001     

A fault diagnosis expert system for distribution substations

This paper presents a practical expert system for the diagnosis of various faults which may occur in distribution substations. The backward inexact reasoning process is applied for the fault section estimation using the knowledge of topology, the operation rules of protective devices, heuristic knowledge of well-trained operators, and instantaneous alarms. In this paper, the overall structure, detailed knowledge-base and the efficiency of general methodology based on topology are discussed. The proposed system has been tested in a local control center in Korea as a part of an intelligent guidance system for the SCADA operators     

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。     

改进的油田配电调度工作流时间着色Petri网模型

针对由电网规模的日渐增加所引起的海量信息和数据的处理变得异常困难的问题,建立基于时间着色Petri网的配电调度工作系统.改进了电力审批工作流模型,给出其Petri网时间着色模型,利用可达图与状态方程对改进的时间着色Petri网的静态性能和动态性能进行分析,建立配电网规则信息库.在采油厂配电调度工作中的应用结果表明,改进的Petri网是有界的,避免了死锁和陷阱,变迁是“活的”,不存在冗余现象,可以顺利执行工作任务.利用时间着色Petri网对配电调度工作流进行分析建模,建立电网操作规则关系型数据库,实现操作中的信息共享是可行的.     

Deterministic and stochastic Petri net models of protection schemes

The authors establish the relevance of Petri net modeling to protection studies. They illustrate how the different Petri net models capture the information that is of importance to both qualitative and quantitative evaluation of protection schemes. The marked Petri nets allow one to evaluate the qualitative performance measures of conservativeness, safeness, and properness. Time Petri nets are able to represent the timing parameters of protection schemes, and serve as a tool for the establishment of relationships between these parameters, in order that the coordination between primary and backup protection is ensured. An alternative means of representing timing information is the timed Petri net, which is useful in the computation of the cycle times of the operational cycles of protection schemes. Stochastic Petri nets adequately represent the stochastic nature of protection. Their advantage over simulation techniques as a means of computing the mean sojourn time and the steady-state probability of occupancy of each state of the protection scheme is demonstrated     

基于Petri网的递归模型构造与分析

在软件的设计过程中,开发者通常会使用递归的方法来代替复杂的循环过程.虽然递归的方法相对简单,却比较难于理解和控制.本文使用Petri网工具,通过建模的方法针对递归过程进行分析和模拟.在以往的研究中,Petri网很少被用于构造递归模型.文中建立了一个递归模型,提供了形式化建模方法和验证,并通过Java程序对其进行了模拟验证,达到了对递归过程分析的目的.     

A heuristic method for feeder reconfiguration and service restoration in distribution networks

A sequential switch opening method is proposed for minimum loss feeder reconfiguration in this paper. The algorithm is further extended for service restoration. The method is based on the branch power flow rather than the current flow as reported in earlier methods. The final algorithm arrives at opening of a branch in a loop carrying minimum resistive power flow to make the network radial causing minimum loss. The test results reveal that the proposed method yields optimal configuration with reduced computation burden and better restoration plan.     

A learning Fuzzy Petri net model

Fuzzy Petri net (FPN) is a powerful modeling tool for the construction of knowledge systems. In this paper, we propose a new learning model tool—learning fuzzy Petri net (LFPN). In contrast with the existing FPN, there are three extensions in the new model: (i) the place can possess different tokens which represent different propositions; (ii) these propositions have different degrees of truth toward different transitions; and (iii) the truth degree of the proposition can be learned by adjusting the arc's weight function. The LFPN model obtains the capability of learning fuzzy production rules through truth degree updating. The LFPN learning algorithm which introduces network learning method into Petri net update is proposed and the convergence of algorithm is analyzed. Finally, for the purpose of certification of the effectiveness of the proposed model, LFPN is used to model the Web service discovery. The result of the simulation shows that the proposed LFPN is useful and effective. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A multiagent approach to distribution system restoration

This paper proposes a multiagent approach to decentralized power system restoration for a distribution system network. The proposed method consists of several feeder agents (FAGs) and load agents (LAGs). LAG corresponds to the customer load, while a FAG is developed to act as a manager for the decision process. From the simulation results, the proposed multiagent system was able to reach the right solution by making use of only local information. This means that the proposed multiagent restoration system is a promising approach to more large‐scale distribution networks. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(3): 21–28, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20065     

基于Petri Nets和遗传算法结合的配变变压器故障的恢复研究

在基于Petri Nets(PN)模型的配电变电站的在线故障恢复研究中,重点研究了变压器的PN恢复处理模型与优化策略模块的结合:PN模型依据配变运行模式、非故障变压器容量对转移负载和过载的承受力来考虑恢复策略的求解操作;在甩负荷操作时,则按供电可靠性的原则对负荷重要性排序,按尽量少的操作次数、按流过母联功率最小作约束,构造有序优化约束目标的全局优化GA算法来完成.该文的变压器故障恢复方法,不仅保证了PN模型数学求解的快速优势,而且可克服单一PN模型恢复中优化处理和刻画动态特性的局限性.仿真结果表明研究方法是可行、有效的,具有较高的实用价值.     

Petri网在信号控制系统中的应用

详细介绍了基于Petri网的自动售货机以及列车运行信号控制系统的建模及其工作原理。结果表明,Petri网能够清楚而简单地描述事件间的因果关系、时序关系以及并发系统中某些与时间有关的重要性质,如最终性和公平性。因此,Petri网可作为并发系统形式描述和分析的有力工具。     

Application of expert system to power system restoration insub-control center

An expert system is developed for emergency operation of power system restoration in a sub-control center. The proposed method restores the blackout area in a power system by using sensitivity analysis and heuristic rules. The rules are categorized into flow-control rules, energization rules, line switching rules, load shedding rules, and voltage correction rules. The switching (opening, closing) of transmission lines, transformers and shunt capacitors, and the load shedding are used for the emergency operations in this paper. For the real time recognition of the network topology, the power system components are represented in hierarchical data structure