Selection of objectives in minimum loss power flow in hydrothermal electric power systems

Two formulations of the optimal minimum loss hydrothermal power flow problem in electric power systems are discussed. The formulations — one based on Kron's loss objective function and the other a network-based loss formulation — are treated in detail and the results of the two approaches are compared using two standard test systems. For the systems investigated, Kron's loss minimization schedules higher thermal generation than that required by the network loss minimization during lower demand. Kron's loss minimization involves lower active power transmission losses than those involved by the network-based loss minimization during low demand, and higher active power transmission losses than those required by the network-based loss minimization during higher demand. The total energy loss involved in the outcome of the Kron's loss minimization results is higher than that due to the network-based loss minimization schedule. There is a negligible difference in voltage magnitudes. Reactive power generation results favour the network-based loss approach. On the basis of the experiments, it is concluded that a network-based loss model is preferable in this application.     

Cost minimization in allocation of reactive power sources

A LP-based method for the optimization of the investment and operational costs of the reactive power generation in a large electric power network is presented. The optimal solution is based on the application of decomposition and linear programming approaches. The global problem is decomposed into investment and operation subproblems using the Benders decomposition method. The revised simplex method is proposed for the solution of the investment subproblem. However, the Dantzig-Wolfe decomposition method is used to solve the operation subproblem. The formulation of the operation subproblem has been discussed in our previous studies. The method has been generalized to represent and solve multiple load levels and contingencies simultaneously in the operation subproblem. The results of applying this approach to the IEEE 30-bus system, a 60-bus system and a 180-bus system verify its robustness in solving the operation subproblem and the capability to converge quickly.     

基于负荷预报的区域电网电压无功控制

电网电压无功优化运行自动控制过程中，由于负荷的波动会造成各变电所电容的投切和有载主变分接头调节振荡或者不必要操作。为避免设备不必要的操作，延长设备的运行寿命，在电网电压无功优化运行自动控制的基础上，引入短期和超短期负荷预报技术，在每日开始的时记得预测当日的负荷曲线，划分出高峰、低谷、腰荷时间段，并对每一个状态断面后若干时间(如15min)的电网负荷状况进行超短期预报，实现电网电压无功优化运行与调节设备动作次数的最佳组合，提高系统电压稳定性，降低网损，减少设备动作次数。     

Optimal active and reactive nodal power requirements towards loss minimization under reverse power flow constraint defining DG type

In this paper a novel approach regarding the optimal penetration of Distributed Generation (DG) in Distribution Networks (DNs) towards loss minimization is proposed. More specific, a Local Particle Swarm Optimization (PSO) variant algorithm is developed in order to define the optimal active and reactive power generation and/or consumption requirements for the optimal number and location of nodes that yield loss minimization. Thus, the proposed approach provides the optimal number, siting and sizing of DGs altogether. In addition, based on the optimal power requirements of the resulted nodes, a combination of potential DG types to be installed is recommended. The proposed objective function in this paper is also innovative since it embeds the constraint of reverse power flow to the slack bus by the formation of a new penalty term. The proposed methodology is applied to 30 and 33 bus systems. The results indicate the optimal number, locations, and capacity of DG units, which were calculated simultaneously. Finally, the impact of the predefined amount of permissible reverse power flow to the optimal solution is also examined through two scenarios: the first considers zero reverse power flow and the second unlimited reverse power flow.     

含电压源换流器的交直流混联电网无功优化模型

随着厦门柔性直流输电工程的建成投运,福建电网形成了以柔性直流输电通道与交流输电通道环网运行的交直流混联电网。为解决含柔性直流的交直流混联电网的无功优化控制问题,提出了一个含电压源换流器的无功优化模型,并采用分支定界法及原对偶内点法求解。所提模型及求解方法已在福建电网自动电压控制系统中进行了测试,实现了对辖区范围内机组、容抗器、有载调压抽头和电压源换流器等各类无功电压调节策略的在线实时优化计算,取得了较好的测试效果。     

中压配电网计及动态无功补偿装置的理论线损计算

结合无功补偿电容器在配电网中的实际应用情况以及配电网的一些自有特点,充分考虑动态无功补偿电容器的投切状态,提出计及动态无功补偿装置的新的理论线损计算方法。该方法根据电容器“投切”动作的时刻将理论线损计算划分为更多的时段,提出新的实时数据处理方式,并且考虑到各个配电变压器日负荷曲线的差异,不仅可以获得比旧有方法精确许多的线损计算结果,而且可以获得在计算时间内的各个细分的小时段内的详细线损情况,明确地表现出加装无功补偿装置对于配网理论线损的影响,有利于运行人员进行配网线损分析与计算。     

电压越限概率指标及其在含风电场电网无功优化控制的应用

针对间歇性风电使得基于实时无功优化的电压控制效果劣化问题,提出一种含风电场的无功优化控制模型,用以应对风电功率不确定性对电压控制的影响。根据变速恒频风机有功出力的概率分布,联合风电出力变化与电压变化的关系提出电压越限概率指标及其表达式,基于电压越限概率建立无功优化控制模型。以国内某电网为例,分别应用传统无功优化控制模型和文中所提出的模型进行无功优化控制,并对比其优劣性。结果表明,所提模型不仅能够有效地控制电压,还能降低风电接入下节点电压发生越限的概率。     

考虑静态电压稳定裕度的含UPFC最优潮流计算方法研究

提出一种考虑静态电压稳定裕度的含统一潮流控制器(UPFC)最优潮流计算模型及方法。模型中增加了局部电网的静态电压稳定裕度约束和UPFC运行约束条件,以及UPFC串联和并联侧等效电压源的幅值、相角等自变量。基于Benders分解法将模型分解为主模型和子模型,其中,主模型为典型的含UPFC最优潮流模型,子模型为静态电压稳定计算模型,通过Benders割建立主子模型间的协调优化,最终实现了整个模型的求解。以苏州南部500 k V为例进行仿真计算,结果验证了文中模型及算法的有效性。     

电压无功优化控制系统在地区电网中的应用

介绍了地区电网电压无功优化控制系统的结构、技术特点及功能。系统针对电力系统无功优化调度分层、分区的实际特点,按分层控制结构设计,其优化算法以网损最小为目标函数,考虑电压质量、控制代价等约束条件。系统在徐州地区电网的实际应用中达到降低运行劳动强度、提高电压合格率、降低网损等效果。     

有源电力滤波器直流侧电压优化控制研究

首先通过分析有源电力滤波器直流侧电压波动对系统补偿效果的影响,并且做了相应的实验,进一步证明了直流电压控制效果越好,对系统谐波补偿更有利。然后针对此问题,在直流侧采用两种电压控制方式,通过分析实验数据,得出优化的PI控制方式,系统电流补偿效果更好。     

基于动态无功电压灵敏度的有源配电网移动式储能优化调度

随着城市负荷尖峰以及分布式电源渗透率的持续攀升,有源配电网存在负荷峰谷差进一步增大以及电压越限的风险。移动式电池储能系统(MBESS)具备时间-空间灵活性和四象限输出能力,考虑其有功出力参与削峰填谷、无功出力参与电压调节,提出了一种基于电压灵敏度分析的有源配电网MBESS的优化调度方法。首先,针对MBESS出力与接入位置之间的耦合影响,推导定有功功率条件下满足仿射关系的无功电压修正灵敏度;其次,考虑不同网络结构下不同节点电压的调整需求,提出一种动态无功电压修正灵敏度的计算方法,旨在确定MBESS的时序最优接入方案;然后,构建充分考虑运行经济性与可靠性的MBESS双层优化调度模型;最后,以IEEE 33节点配电系统为例,采用增强烟花算法对所提模型进行求解,结果表明所提方法能够在保证MBESS具备较好经济效益的同时,有效减小负荷峰谷差以及提升配电系统的整体电压水平。     

Optimal VAR control for real power loss minimization using differential evolution algorithm

Differential evolution algorithm (DEA) is an efficient and powerful population-based stochastic search technique for solving optimization problems over continuous space, which has been proved to be a promising evolutionary algorithm for solving the ORPD problem and many engineering problems. However, the success of DEA in solving a specific problem crucially depends on appropriately choosing trial vector generation strategies (mutation strategies) and their associated control parameter values. This paper presents a differential evolution technique with various trial vector generation strategies based on optimal reactive power dispatch for real power loss minimization in power system. The proposed methodology determines control variable settings such as generator terminal voltages, tap positions and the number of shunts compensator to be switched, for real power loss minimization in the transmission systems. The DE method has been examined and tested on the IEEE 14-bus, 30-bus and the equivalent Algerian electric 114-bus power system. The obtained results are compared with two other methods, namely, interior point method (IPM), Particle Swarm Optimization (PSO) and other methods in the literature. The comparison study demonstrates the potential of the proposed approach and shows its effectiveness and robustness to solve the ORPD problem.     

基于可变容差法的电力系统最优潮流计算

介绍了电力系统中以发电费用最小为目标的最优潮流计算的可变容差法。该方法无需求解目标函数的导数，利用数值搜索优化机制，可较好地获得最优解。实例分析表明，与现有的模型求解方法相比，可变容差法具有较好的寻优效果。可以作为电力系统最优潮流计算的一种补充方法。     

考虑运行方式转移过程的无功优化控制

电力系统的运行方式是一个连续转移过程。将单点的无功优化控制扩展到考虑运行方式转移过程,从而使电压控制的可操作性和效率更符合实际需求。构建了包括变压器档位在内的非线性约束条件下的无功最优化目标函数,提出了优化和潮流计算相互迭代算法,两个实例分析说明了考虑转移过程的无功优化控制具有更好的鲁棒性和效率。     

Distributed power flow loss minimization control for future grid

In this paper, a novel decentralized algorithm is proposed to minimize power flow loss in a large‐scale future grid connecting with many real‐time‐distributed generation systems by which power flows bi‐directionally. The DC‐power loss at each link is defined as the product of resistance and the square of current that can be considered as a quadratic flow cost. We employ the notion of tie‐sets that reduces the complexity of the power flow loss problem by dividing a power network into a set of loops that forms a linear vector space on which the power loss problem can be formulated as a convex optimization problem. As finding a solution in each tie‐set enables global optimization, we realize parallel computing within a system of independent tie‐sets by integrating autonomous agents. Simulation results demonstrate the minimization of the power loss on every link by iteratively optimized power flows and show the superiority against the traditional centralized optimization scheme. Copyright © 2014 John Wiley & Sons, Ltd.     

基于分级分区的地区电网无功电压闭环控制系统

采用两级无功电压控制策略相结合的体系实现无功电压闭环控制。"区域级"无功电压控制将电网划分为若干具有辐射状结构的无功电压控制区域,以各分区为单位,采用等值递推和最优匹配注入流算法的交叉迭代方法来实现。"厂站级"无功电压控制利用改进的九区图法实现,并在"区域级"无功电压控制策略无法实施时启动。现场控制实例和仿真算例表明,算法实用、鲁棒性好,形成的控制策略合理有效,优化控制效果明显。     

计及可靠性和经济性的中压配电线路最佳运行效率计算方法

当前中压配电线路运行效率评价过程中采用“N-1”准则难以合理度量在不同负荷结构下线路最佳负载能力,未能充分考虑在不同负荷结构下线路运行经济性的问题,针对以上问题提出了计及可靠性和经济性的中压配电线路最佳运行效率计算方法。首先,结合安全性和经济性两个方面,对中压配电线路的运行效率进行了定义并提出了其计算方法;其次,基于可靠性指标与线路负载率关系解析,提出了不同负荷结构的中压配电线路可靠性评估流程;然后,以经济性最优为目标构建了中压配电线路最佳负载能力优化模型。最后通过算例分析,验证了本文所提方法的有效性和实用性。     

超高压电网无功平衡实用计算

介绍了以直流潮流为基础,结合最优无功补偿理论的超高压电网无功平衡计划实用计算方法.该方法根据电网有功日负荷预测值,按照实际的电网拓扑结构和运行方式,首先计算线路和变压器等电网元件的等值电、路参数,生成导纳矩阵,通过直流潮流计算支路有功潮流和无功损耗,然后按照无功分点在线路中点的优化理论,快速优化各节点无功补偿量.算例表明,该实用算法可避免重复迭代和潮流不收敛问题.     

A study of voltage and reactive power control methods for high‐efficiency operation of distribution networks

Transformers with on‐load tap changer and step voltage regulators are most often used for regulating the distribution network voltage. Their use, however, creates certain problems, namely, the voltage control is in discrete steps and the response time is not satisfactory enough. In addition, the power factor (p.f.) compensation relies on capacitors installed by electricity users which creates additional problems manifesting themselves in unexpected overvoltages during light load and increase of power losses. To solve these problems, the authors have proposed a new voltage and p.f. control system for distribution networks based on sophisticated power electronics technology. This paper describes our study on the operating theory of inverter‐controlled regulators and thyristor‐controlled reactors, which play important roles in this system, and the results of simulation through which the usefulness of these equipment has been ascertained. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 76–87, 2000     

Improved algorithm for optimum reactive power allocation

An improvised algorithm is presented for optimal VAr allocation in a large power system using a linear programming technique. The proposed method requires less computer memory than those algorithms currently available.