Optimal Reconfiguration in Radial Distribution System Using Gravitational Search Algorithm

This article presents an innovative technique for solving network reconfiguration problems with an objective of minimizing network I²R losses for an explicit set of loads. Amid many performance standards considered for optimal network reconfiguration, voltage constraint is an important one. This problem calls for determining the best combination of feeders to be opened in the radial distribution system so it provides optimal performance in the preferred settings. In solving this problem, the gravitational search algorithm is used to reconfigure the radial distribution system; this algorithm practices an optimal pattern for sustaining the radial nature of the network at every stage of the solution, and it further allows proficient exploration of the solution space. The anticipated scheme minimizes the objective function, which has been given in the problem formulation to reduce I²R losses in addition to balancing loads in the feeders. The solution technique involves determination of the best switching combinations and calculation of power loss and voltage profile. The practicality of the anticipated technique is validated in two distribution networks, where attained results are compared by means of available literature. Correspondingly, it is seen from the results that network losses are reduced when voltage stability is enriched through network reconfiguration.     

Multi-Objective Approach for Reconfiguration of Distribution Systems with Distributed Generations

This paper presents a fuzzy multi-objective based heuristic algorithm for network reconfiguration of distribution systems considering distributed generations (DGs). The objectives of reduction of real power loss, branch current carrying capacity limit, maximum and minimum voltage constraints, and feeder load balancing are considered for performance enhancement of the distribution system. Since these objectives are non-commensurable and difficult to solve simultaneously using conventional approaches, they are converted into fuzzy domain and a fuzzy multi-objective function is formulated. A sensitivity analysis based on voltage profile improvement and real power loss reduction is used for obtaining optimal locations of DGs and genetic algorithm is used for optimal sizing of DGs. The proposed reconfiguration algorithm is implemented in two stages, initially in the first stage without incorporating DGs and in the second stage incorporating DGs for obtaining an optimal distribution system network reconfiguration. The advantage of the proposed method is demonstrated through a seventy node four feeders and a sixteen node three feeders distribution systems.     

基于模糊多目标协调优化的配电网络重构研究

配电网络重构通过改变开关的开合状态以提高供电的可靠性和经济性。建立以网损最小、馈线负载均衡指标最小、开关操作次数最少多个目标协调优化的配电网络重构的数学模型。引入模糊隶属度函数对各目标进行模糊化处理,根据模糊集理论的最大最小法则,将多目标优化问题转化为单目标非线性规划问题。应用禁忌算法对该配电网络重构模型进行优化求解。对某个69节点配电网络系统,比较分析了四种不同的优化方案,仿真结果验证了所提出模型和求解方法的正确有效。     

A new heuristic approach for optimal reconfiguration in distribution systems

This paper presents a novel approach for optimal reconfiguration of radial distribution systems. As an integral part of the distribution system configuration, a load flow algorithm based on graph theory is presented. The algorithm follows changes in system structure by traversing a directed graph of the system to find the depth-first search discovery order. For each switching-iteration, this discovery order generates down-stream-nodes vectors necessary for dynamic generation of two matrices: one is the branch node incidence matrix and the other the relationship between the bus current injection and branch currents. Thus avoiding creation of unconnected branches or forming closed loops. The developed load flow program is integrated with known heuristic techniques in a new heuristic search methodology for determining the minimum loss configuration of a radial distribution system. The technique consists of two parts; one is to determine the best switching combinations in all loops with minimum computational effort while the other is a power loss and voltage profile calculation of the best switching combination found in part one by load flows. Compared to other published articles, the efficient developed load flow reduces the switching combinations searched and gives the optimum solution in few number of load flow runs. To demonstrate the validity of the proposed algorithm, computer simulations are carried out on 33-bus system. The results show that the performance of the proposed method is better than that of the other methods.     

A new heuristic approach for distribution systems loss reduction

This paper presents a new approach to solve the reconfiguration problem by a switching operation in order to reduce the power loss of distribution systems. By using the proposed heuristic technique, based on the direction of the branch power flows, a better network configuration is obtained. This reconfiguration algorithm starts with a radial topologic by opening all tie switches. At each step, after a normally open switch is closed, the heuristic procedure establishes the switching-options significantly reducing (in most cases) the number of candidate branches to be opened within a loop. Finally, the choice of the most effective switching-option for loss minimization is obtained from the calculation of a few power flows. The solution procedure is illustrated on a simple example and several test systems used by others authors are included to demonstrate the effectiveness of the proposed method. The results obtained are satisfactory and show that the method is very robust, in spite of its simplicity.     

配电网络重构的改进支路交换法

根据配电系统中存在大量独立拓扑调整的特点,提出一次可以实施多个独立拓扑调整的配网重构方法,并通过节点流过的负荷电流值与理想转移负荷之间的距离确定打开的分段开关,进一步提高了处理效率,当降损效率小于给定值时不再进行网络重构;避免了无实际意义的拓扑调整。该算法考虑并非所有配网支路上都安装开关,更符合实际情况。给出的算例表明该方法是有效的。     

基于启发式规则与熵权理论的配电网故障恢复

为快速准确实现配电网故障恢复,提出了启发式规则与熵权理论相结合的两阶段配电网故障恢复算法。第1阶段,利用启发式规则生成故障恢复的候选方案集;第2阶段,考虑故障恢复的目标,引入负荷恢复量、负荷转移量、负荷容量裕度、负荷均衡率和开关操作次数5个评价指标,分别计算候选方案的各评价指标,利用熵权理论对方案进行评价,同时引入主客观权重对方案进行综合评价,得出优选和备选恢复方案。算例结果验证了该方法的有效性。     

配电网负荷均衡的网络分割算法

随着配电网规模的不断扩大 ,配电网网络重构算法的实时性越来越难以满足工程实用化的要求。而网络重构的结果其实是将一个配电网分割成几部分 ,各部分通过常开的联络开关相连。基于此 ,提出了配电网负荷均衡的新算法———网络分割算法。该算法将负荷均衡作为一个网络优化问题 ,利用配电网的一种新模型———分层拓扑模型 ,将全局最优问题转为多阶段分割问题 ;同时 ,充分利用配电网负荷均衡的特点 ,通过寻找源点分支负荷大于负荷平均值的下确界负荷和小于负荷平均值的上确界负荷的方法 ,实现了配电网的负荷全局最优均衡。算例的仿真结果说明了该算法的正确、有效和快速。     

TRANSIENT ANALYSIS OF CAPACITOR SWITCHING IN UNBALANCED DISTRIBUTION SYSTEM WITH HARMONIC DISTORTION

ABSTRACT

The wide application of shunt capacitor banks in distribution systems for economic reasons, have raised concern about over-voltage transients and harmonic magnification in unbalanced distribution systems. This paper introduces a new method for transient analysis during capacitor switching. Presence of harmonic sources, unbalance in feeder configuration, and combinations of single-and three-phase loads are accounted for. The new method is a frequency domain-based approach using a three-phase Z-Bus algorithm. The paper reviews the concepts of the building algorithm of a three-phase Z-bus matrix in the complex frequency domain. Untransposed feeders and different types of loads are considered. Finally, the boundary conditions for different capacitor switching cases and the results with harmonic distortion are reported.     

基于改进二进制粒子群优化算法的负荷均衡化配电网重构

提出了基于改进的二进制粒子群优化算法、以均衡负荷为目标的配电网重构方法。将配电网重构问题表示为以负荷均衡指标最小为目标函数的非线性优化问题,针对配电网开环运行的结构特点对配电网拓扑结构模型进行了简化,并对二进制粒子群优化算法加以改进,以保证配电网的辐射状结构,同时大大减少迭代次数。算例分析结果表明,该方法能够有效解决负荷均衡化的配电网重构问题,计算速度快,收敛性好。     

一种基于可靠性指标的复杂配电网络重构算法

以提高可靠性为目标,提出了一种简单、高效的复杂配电系统的网络重构算法。该算法将网络重构的优化过程分解成与动态变化的联络刀闸相对应的重构子问题。依次闭合每个联络开关,就可以得到具有不同网络拓扑结构的单环网,并分别对馈线内单环网和馈线间单环网提出了网络重构方法。通过一个实际的电力系统算例证实了本算法的有效性。     

配电网故障判断与负荷均衡化

提出一种配电网简化模型 :将馈线开关当做节点 ,将馈线当做弧 ,从负荷的角度描述配电网 ,并采用邻接表的数据结构加以描述。在此基础上发展了配电网故障区域判断方法 ,讨论了以最少的开关操作隔离故障区域的方法。提出一种以联络开关为核心的用于负荷均衡化的配电网络重构方法 ,将每个联络开关对应的两条馈线看做馈线偶 ,分别定义了馈线偶和配电网的负荷均衡率 ,并以此作为网络重构的评价函数 ,配电网络重构过程由若干馈线偶内负荷均衡化过程组成 ,这种方法具有迭代次数少和不需要量测馈线配电变压器参数等优点。文中给出了典型实例     

LOSS REDUCTION IN DISTRIBUTION NETWORKS USING NEW NETWORK RECONFIGURATION ALGORITHM

ABSTRACT

Network reconfiguration is an operation task, and consists in the determination of the switching operations such to reach the minimum loss conditions of the distribution networks. In this paper, a general formulation of the network reconfiguration for loss minimization is given for the optimization of distribution loss reduction and a solution approach is presented. The solution employs a search over different radial configurations, created by considering branch exchange type switches. The solution algorithm for loss minimization has been developed based on the two stage solution methodology. The first stage of this solution algorithm finds a loop which gives the maximum loss reduction in the network. For this purpose a simple-to-use formula, called loop loss reduction formula, has been developed. To find a branch exchange, which results in the maximum loss reduction in the loop, the second stage applies a proposed technique called distance-center technique. Therefore, the solution algorithm of the proposed method can identify the most effective branch exchange operations for loss reduction, with a minimum computational efforts. The solution algorithm of the proposed method has been tested, with very promising results, on a 69-bus radial distribution system. Test results prove that, via proposed network reconfiguration for loss minimization, real power loss is reduced significantly, and that the voltage profile of the network is considerably improved. As compared to the established methods the proposed method eliminates the need to run numerous load flows.     

基于柔性多状态开关的主动配电网双层负荷均衡方法

分布式电源(DG)的大量接入使得配电网源荷不确定性与随机性增大,而柔性多状态开关(FMS)的应用使得供区间互联不再受制于电压等级和相位,主动配电网(ADN)多供区联合优化运行将成为新常态,也为改善负荷不均衡现象、提高供电水平提供了基础.利用FMS灵活互联的特点,以供区层和馈线层负荷均衡指数加权最小为目标函数,建立了ADN双层嵌套负荷均衡模型,并采用改进粒子群和二阶锥规划的混合优化算法求解网络重构拓扑方案与FMS出力.整体算法外部对合环配电网进行简化和等效,减小网络重构的粒子群算法的粒子规模,加快计算速度;内部采用最佳等距分段线性逼近法(OEPLAA)对目标函数进行线性化,将FMS出力优化问题进行二阶锥转化.最后,通过某实际配电网对所提出的负荷均衡方法进行了分析和验证.     

Optimal switching sequence path for distribution network reconfiguration considering different types of distributed generation

Minimizing power losses in a distribution system is commonly realized through optimal network reconfiguration. In the past, network reconfiguration research was focused on planning, where the final configuration with the lowest power losses was the main goal. However, power losses during switching operations from the initial state to the final state of the configuration were not considered. This paper presents the optimal switching sequence path to minimize power losses during the network switching operation. Apart from this contribution, the simultaneous optimal network reconfiguration for variable load network and distributed generation (DG) output is also proposed. The proposed methodology involves the (i) optimal network reconfiguration with variable load and DG output simultaneously, and (ii) the optimal sequence of switching operations required to convert the network from the original configuration to the optimal configuration obtained from (i). The selected optimization technique in this work is the firefly algorithm. To assess the capabilities of the proposed method, simulations using MATLAB are carried out on IEEE 33‐bus radial distribution networks. The results demonstrate the effectiveness of the proposed strategy to determine the sequence path of switching operations, as well as the optimal network configuration and optimal output of DG units. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于混合算法的油田配电网负荷均衡化

提出了基于遗传算法和网络分割算法以均衡负荷为目标的配电网优化方法。将配电网优化问题表示为以负荷均衡指标最小为目标函数的非线性优化问题,针对配电网运行的结构特点对配电网拓扑结构模型进行了简化,然后再通过遗传算法对已分割的网络开关进行优化。算例分析结果表明能够有效解决配电网负荷均衡化的问题,计算速度快,并且收敛性好。     

Multi-objective feeder reconfiguration by distribution managementsystem

Feeder reconfiguration for use by distribution management systems is discussed in this paper. Multiple objectives are proposed to reflect realistic operating environments while achieving all benefits from feeder reconfiguration. The multiple objectives considered are minimization of power losses, load balancing among supply transformers, minimization of the worst voltage drop, minimization of service interruption frequency, and balanced service of important customers for enhanced service reliability. The objective function containing five different objectives are optimized subject to capacity and protection device constraints. The overall solution approach is a two-stage process. In the first stage, a suboptimal solution is found by analyzing the mesh distribution system in which all open switches are simulated to be closed. Applying special power flow analyses to this mesh network, a radial distribution system is determined as an intermediate solution. In the second stage, this solution is continuously improved by the branch exchange scheme. Special topology models are also developed to accelerate the search procedure. Use of the algorithm is illustrated by numerical examples     

A self adaptive hybrid differential evolution algorithm for phase balancing of unbalanced distribution system

Electrical power distribution systems are critical links between the utility and customer. In general, power distribution systems have unbalanced feeders due to the unbalanced loading. The devices that dependent on balanced three phase supply are affected by the unbalanced feeders. This necessitates the balancing of feeders. Phase swapping, the process of changing the loads amongst phases, has been practiced for feeder phase balancing. The primary objective of phase balancing is to balance the loads with the phases subject to constraints such as load flow equations, capacity and voltage constraints, while maintaining the radial structure. In this paper, a Self adaptive Hybrid Differential Evolution (SaHDE) technique has been employed to solve the phase balancing problem. The effectiveness of the proposed method is demonstrated through modified IEEE 34 node and IEEE 123 node distribution systems.     

Economic Evaluation of Distribution System Smart Grid Investments

This article investigates the economic benefits of smart grid automation investments. A system consisting of 7 substations and 14 feeders is used in the evaluation. Here benefits that can be quantified in terms of dollar savings are considered, termed “hard dollar” benefits. Smart grid investment evaluations to be considered include investments in improved efficiency, more cost effective use of existing system capacity with automated switches, and coordinated control of capacitor banks and voltage regulators. These smart grid evaluations are sequentially ordered, resulting in a series of incremental hard dollar benefits. Hard dollar benefits come from improved efficiency, delaying large capital equipment investments, shortened storm restoration times, and reduced customer energy use. Analyses used in the evaluation involve hourly power flow analysis over multiple years and Monte Carlo simulations of switching operations during storms using a reconfiguration for a restoration algorithm. The economic analysis uses the time-varying value of the locational marginal price. Algorithms used include reconfiguration for restoration involving either manual or automated switches and coordinated control involving two modes of control. Field validations of phase balancing and capacitor design results are presented. The evaluation shows that investments in automation can improve performance while simultaneously lowering costs.     

考虑多种负荷方式的配电网络重构

提出了考虑多种负荷方式的配电网络重构算法.用最大负荷、最小负荷和一般负荷方式模拟研究时段内负荷的变化,首先按照上述三种负荷方式,采用改进支路交换法对配电网络分别进行重构,得到每种负荷方式下的最优重构方案;然后计算出每种最优重构方案下考虑三种负荷方式的加权平均有功损耗;具有最小平均有功损耗的重构方案即为该研究时段内的最优重构方案.所提算法避免了只考虑单一负荷方式的片面性,算例结果表明了该算法的有效性和可行性.