A multiagent approach to power system normal operation

Recently, the electric utility industry worldwide has been facing pressure to be deregulated or restructured in order to increase its efficiency, to reduce operational cost, or to give consumers more alternatives. For this aspect, a great deal more research is needed to achieve a better, intelligent knowledge process. The present centralized system for power system control, operation, and planning must be remodeled to cope with these situations. With the promotion for the deregulation of the electric power system, the definition of the objective function for the optimization problem such as outage work operation for electric power systems is becoming critical. Currently, agents are an intense focus in many subfields of computer science and artificial intelligence. Agents are being used in an increasingly wide variety of applications. In this paper, we developed a power system normal operation application by multiagent architecture. Our multiagent system consists of several facilitator agents, equipment agents, and switch‐box agents. Facilitator agent acts as a manager for negotiation process between agents. Equipment agent corresponds to the element of the electric power system, such as bus, transformer, and transmission line, while switch‐box agent is the pseudo object which consists of neighboring current breakers and disconnecting switches. The proposed system realizes the appropriate switching operations by interacting with corresponding agents. The proposed approach is applied to a simple network, and the results show that the proposed multiagent system is an efficient decentralized approach for solving power system normal operations. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 26–33, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10227     

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     

Comparison of Centralized and Decentralized Systems in Power System Restoration

This paper proposes a multiagent approach to decentralized power system restoration for distribution system networks and presents a comparison of centralized and decentralized systems for power system restoration. Numerous studies have been conducted on power system restoration problems. From the viewpoint of system structures, this research can be divided into two categories: centralized systems and decentralized systems. In this study, we solve a power system restoration problem for a power distribution network by two different methods: mathematical programming (MIP) and the proposed multiagent‐based method (MAS). The proposed multiagent system consists of several distributing substation agents (DSAGs) and load agents (LAGs). An LAG corresponds to the customer load, and a DSAG supplies electricity to the LAG. From the simulation results, it can be seen that the proposed system can reach the right solution by making use of only local information and that the solution quality is better than that of the centralized system (MIP). This means that the proposed multiagent restoration system is a promising approach to larger scale distribution networks.     

一种配电网故障阶段式恢复方法

为快速确定配电网故障恢复的最优方案,提出了一种将启发式规则与优化算法相结合的故障阶段式恢复方法。各个阶段通过指标判定是否执行,不同故障的恢复阶段不同。第一阶段采用启发式搜索方法恢复网络连通性;第二阶段利用和声算法以电压不越限及线路不过载为目标进行重构;第三阶段基于深度优先搜索法及负荷优先级切负荷;第四阶段利用和声算法进行网损优化重构。为快速分析配电网的拓扑结构,提出单联络回路的概念,不仅可用于快速恢复故障后网络的连通性,而且可为优化算法避免拓扑不可行解编码提供理论基础,有效提高了运算效率。通过仿真验证了所提方法的可行性。     

Service restoration problem in distribution power system using improved GA

The service restoration problem in distribution power systems has already been addressed with regard to this issue, for purposes such as the minimization of unrecovered load and power supply loss, considerations of priority sections, and preparation of switching procedures. However, since this involves the application of a number of methods, the related algorithms are complex. In this paper, in order to resolve this issue we first apply GA as an optimization method for investigation purposes, to simplify the algorithms used. Next, to confirm this proposed method's effects in reducing computing time, we consider the efficacy of the proposed method by using smaller numbers of generations and individual sizes than have been used in the past. The effectiveness of the proposed method is shown by the system when failure occurs. It is clear that the proposed method, consisting of GA only, is superior in terms of average fitness values and the ability to reduce computation times. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(1): 10–19, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20752     

基于MAS的配电网复电系统设计

针对配电网负荷失电后的复电问题,基于多代理技术和JADE开发平台,设计了一个配电网主动复电系统,其中主要包含代表实际配电网支线的支线代理和代表配电网负荷的负荷代理。当配电网支线上发生故障时,失电的负荷代理向其所在的支线代理发送故障报告,请求为其恢复供电。故障支线的代理通过与网络中其他支线的协调,通过负荷开关将失电负荷转供到邻近正常支线上,从而恢复故障负荷的供电。在Matlab/Simulink仿真环境下搭建了一个简单配电网络模型,将所设计的多代理系统用于解决该配电网的负荷复电问题,验证了该多代理系统的可行性和有效性。     

考虑可控负荷的含分布式电源配电网短时故障供电恢复

通过支路数组元素的有效组合形成恢复方案,并利用负荷相对适应度和风险度指标引导恢复方案优化过程。通过合理投切可控负荷充分利用故障后剩余电源容量,在保障重要负荷供电的同时,尽可能恢复更多失电负荷。同时,将馈线间联络线和分布式电源在非故障失电区进行供电孤岛划分,并实现协调恢复。针对分布式电源和备用联络线在初始孤岛划分方案形成时存在的独立性和在优化过程中的关联性,引入包括信息层、执行层、设备层和协调层的多代理系统,进行并行计算、协调优化。采用69节点算例进行仿真,仿真结果验证了方法的正确性和有效性。     

一种快速启发式配电网故障恢复算法

提出一种基于网络拓扑分析快速有效的配电网故障恢复算法。该算法在满足系统电流、电压的约束条件下,充分考虑负荷的优先级别,使得在开关操作次数尽可能少的情况下,尽可能多的恢复对重要负荷的供电以及其他负荷的供电,尽可能减小全系统的停电损失。算例计算表明该算法是高效和可行的。     

遗传算法在配电网停电恢复中的应用

将遗传算法应用于配电网停电恢复中，给出了综合考虑开关操作次数最少，网损最小以及潮流分布合理等方面的停电恢复模型，采用遗虎法对停电区域进行重构，形成恢复方案，通过对实际配电网的测试分析表明，将遗传算法用于电网停电恢复中，能快速有效地提供若干个优化方案，为运行人员提供更多的参考。     

含分布式电源的复杂配电网故障恢复

考虑到实际配电网复杂多变及负荷等量测数据大量缺乏,建立基于等效负荷的配电网简化模型,减小了计算时间,并可以反映配电网的潮流分布。提出了一种针对含分布式电源的复杂配电网故障恢复方案,当配电网发生故障引起大面积停电时,首先在已知分布式电源容量的情况下确定各孤岛系统的最佳供电范围,转入孤岛运行模式以保证重要负荷的持续供电,然后依据启发式规则对剩余失电网络进行供电恢复并利用改进支路交换法对恢复后的网络进行重构优化,使得失电负荷和网损都尽可能少。算例表明,提出的方案能够有效地解决含分布式电源的配电网故障恢复问题。     

A distributed autonomous approach for bulk power system restoration by means of multi‐agent system

In recent years, the electric utility industry worldwide has been facing pressure to be deregulated. Also, the risk of blackout in large areas will increase. Actually, it is still vivid in our memory that the northeastern United States and southern Canada suffered the worst blackout in history. Consequently, a method to find the optimal solution rapidly is needed all the more. In this paper, we propose a new multi‐agent method for a bulk power system restoration. In order to demonstrate the capability of the proposed multi‐agent system, it has been applied to a model bulk power system, which consists of three local areas including 12 generating units and 12 loads, and three remote areas with 12 loads. A large number of simulations are carried out on this model network with changing conditions. The simulation results show that the proposed multi‐agent approach is effective and promising. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 69–76, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20485     

Power system restoration by joint usage of expert system and mathematical programming approach

When electric power supply interruption is caused by a fault, it is imperative to restore the power system promptly to an optimal target configuration after the fault. The problem of obtaining a target system is referred to as power system restoration. Both mathematical programming (MP) and expert systems (ES) have been used to solve restoration problems. However, existing approaches based on either MP and ES alone have inherent limitations stemming from their own paradigms. Mathematical progressing can obtain an optimal configuration under specified operational constraints, but requires a relatively long solution time. Although ES are effective in that they can utilize expert knowledge, maintenance of large-scale ES requires inordinate effort. This paper proposes a new approach to power system restoration that utilizes both methodologies so as to exploit both systems' advantages. That is, a system under study is decomposed into a set of subsystems based on the knowledge of restoration experts, which is realized as an expert system. Then, MP is applied to each decomposed subsystem to obtain an optimal target configuration. A feasible operation sequence leading to the target configuration is generated by ES. This approach reduces significantly the computation time required to obtain target systems and is far less than would be the case if the total system is solved (as a unity). Moreover, the number of rules in the knowledge-base are greatly decreased.     

Petri Nets算法在电力系统恢复中的应用

通过对电力系统恢复的不同恢复策略、方法和恢复阶段的研究，发现恢复过程中存在一系列的“普遍恢复动作”，而将这一系列的普遍恢复动作组织起来即可形成恢复方案。提出应用Peter Nets算法组织电力系统恢复过程中的普遍恢复动作。Peter Nets算法对系统恢复时各电力元件状态和恢复操作进行建模，可以在时域上直接仿真系统恢复的全过程。该算法考虑了不同恢复阶段的目标、每个操作措施的估计时间和操作员的经验，具有灵活的冲突处理机制和并行处理特性，形成的恢复方案准确而直观。对给定的一个电网算例进行了仿真计算。     

Application of parallel tabu search‐based hierarchical optimization to distribution system service restoration

This paper proposes a hybrid method of hierarchical optimization and parallel tabu search (PTS) for distribution system service restoration with distributed generators. The objective is to evaluate the optimal route to recover the service. The improvement of power quality makes the service restoration more important. Distribution system service restoration is one of the complicated combinational optimization problems that are expressed as nonlinear mixed integer programming. In this paper, an efficient method is proposed to restore the service in a hierarchical optimization with PTS. The proposed method is tested in a sample system. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 15–23, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20463     

基于网络等效的配电网快速供电恢复策略并行化实现

现代智能配电网在故障后可以调度需求侧的"灵活源"实现快速供电恢复。针对智能配电网的特点,提出了一种基于网络等效和并行化实现的快速供电恢复策略,能够灵活地利用电网资源以应对不同的失电情况。算法将支援线路等效为电源节点(称为等效源点),采用离线等效源点预存储与实时等效源点并行计算相结合的模式:保存并优先使用离线数据;在失电负荷较大时,调取实时数据对不同的调度可能进行并行计算。为进一步提升算法的时效性,利用改进邻接矩阵记录和维护电网拓扑结构,实现网络的高效重构。通过若干个算例,验证了该供电恢复策略在面对不同程度失电时均能合理高效地运用电网的各类支援资源,实现快速供电恢复。     

配电系统网络重构方法研究

网络重构是配电系统安全经济运行的一个重要环节，目前网络重构方法多种多样，在实际应用中如何选取适合不同的配电网络重构方法是研究的目的。对配电系统中网络重构技术的概念、作用、建模作了概述，对各种方法进行了比较分析，并在对网络重构的基本方法及其特点分析基础上，针对不同的网络规模和网络重构的目的，对网络重构方法的实际应用作了探讨。提出了在实际应用过程中，将现有的两种或是多种算法加以结合，形成新的复合方法的观点。随着计算机技术及网络通信技术的发展，复合算法将会得到不断的改进，并被有效地应用到配电网络规划及实时系统中去。     

A value-based probabilistic approach to designing urban distribution systems

Achieving high distribution reliability levels and concurrently minimizing capital costs can be viewed as a problem of optimization. Assuming given outage rates and repair times, distribution system design is the remaining factor in determining customer reliability. Including customer value of reliability in an economic analysis allows for optimization of the major components of distribution system design. Using mathematical models and simulations, a comparison of design concepts can be performed to compute the optimal feeder section length, feeder loading level, and distribution substation transformer loading level. The number of feeder ties and feeder tie placement are also optimized through the models. The overall outcome of this analysis is that capital costs can then be directed towards system improvements that will be most cost-effective in improving system reliability. This paper presents a value-based probabilistic approach to designing urban distribution systems. The value-based reliability methodology is illustrated using a practical urban distribution system of MidAmerican Energy Company.     

Optimizing service restoration in distribution systems based on scheduling of crews considering priorities of loads

The service restoration to sound sections within a short period as much as possible, performed after the permanent fault occurs in a distribution system, is significant for maintaining power supply reliability. This paper proposes an efficient method to find service restoration procedures based on fault searching and the optimal work scheduling of crews, considering the power supply priorities of loads and the probability of occurrence of faults. The proposed method is composed of two-stage problems to reduce the outage sections efficiently: (i) the problem to find a series of searching procedures for unknown fault locations in the first stage and (ii) the optimization problem of work schedules of crews in the second stage. In the first stage, the order of operation of switches opened for searching for the fault direction is determined, constituting the searching tree. After that, the proposed optimization method can efficiently solve the work scheduling problem by formulating it as a mixed-integer linear programming problem in the second stage. The computational experiments using a large-scale distribution system model with many remote and manual switches show that the proposed method can provide efficient service restoration procedures within a reasonable computational time.     

An innovative approach for solving the restoration problem in distribution networks

An effective heuristic graph-based approach is proposed in this paper for solving the service restoration problem in distribution networks. Minimisation of the de-energised consumers’ load and reduction of the number of switching operations were considered in this service restoration application. A suitable assignment of the weighting coefficient to all branches in a de-energised area was used to decrease the number of switching operations. Prim's algorithm for finding of the minimum spanning tree logic was used to realise this approach. Other applications necessary for the optimal performance of the service restoration application were also developed and tested in this study (e.g., load flow, load reallocation of overloaded network elements, generation of the sequence of switch actions, etc.).     

关于配电网自动化系统实施的建议

阐述了实施配电网自动化系统的目的.在分析配电自动化系统的内容和特点的基础上,提出应将配电网自动化系统的实施作为整个电力营销策略的环节之一,建立一个完整的、统一的自动化体系平台.