论文标题:考虑谐波影响的配电网电容器优化模型及相关算法研究
Study on Modeling and Solution Algorithms of Capacitor Optimization with Harmonic Consideration in Distribution Systems
论文作者 余欣梅
论文导师 尹项根；熊信艮,论文学位 博士,论文专业 电力系统及其自动化
论文单位 华中科技大学,点击次数 106,论文页数 146页File Size643k
2004-09-01论文网 http://www.lw23.com/lunwen_209501792/ 配电网; 电容器配置; 电容器投切; 微粒群优化算法(PSO); 潮流算法; 谐波畸变率(THD); 电抗率配置; 谐波放大
Distribution System; Capacitor Placement; Capacitor Switching; Particle Swarm Optimization (PSO); Power Flow Algorithm; Total Harmonic Distortion (THD); Reactance Rate Selection; Harmonic Amplification
配电网电容器优化是实现配电网安全和经济运行的重要手段,可有效改善配电网的电压水平、降低网损、提高功率因数和增强系统稳定。然而近年来由于配电网中非线性用电设备得到愈来愈广泛的应用,配电系统中的谐波污染日益加重,在谐波的作用下,一方面电容器受谐波影响而易遭损坏或无法正常运行,另一方面电容器有可能放大谐波而使系统的谐波污染更为严重。因此,研究谐波畸变条件下配电网电容器的合理配置和投切,既使电容器发挥对基波无功的最优补偿以达到最佳降损效果,又避免因发生谐波放大或谐振而破坏电容器和系统的安全运行,具有特别重要的意义。 本文对谐波畸变条件下配电网电容器优化的若干问题进行了深入的研究,主要内容涉及配电网基波潮流和谐波潮流的快速算法,优化算法及其改进研究,配电网电容器优化配置和优化投切问题的建模及其求解方法,集中补偿电容器组串联电抗率优化配置问题的建模及其求解方法等各个方面。 配电网基波潮流和谐波潮流计算是考虑谐波因素的配电网电容器优化的基本计算模块,潮流算法的性能是影响整体优化效率的关键因素之一。在基波潮流计算方面,本文提出了一种基于支路和节点分层的改进支路电流法,该算法通过对随意编号的支路和节点分层,逐层并行计算各层次的支路电流和节点电压,可避免繁琐的节点和支路编号,同时有效提高潮流计算效率。在谐波潮流计算方面,本文对现有的典型算法和谐波源模型进行了全面分析和评价,并借鉴辐射状配电网基波潮流的求解思路,提出了一种适用于辐射状配电网的前推回推谐波潮流算法,该算法能够快速、有效地计算配电网的谐波畸变指标,且所需计算时间不随网络规模的增大而显著增加。 微粒群优化算法(PSO)是目前备受关注的群集智能算法的代表性方法,也是本文研究工作的算法基础。本文全面分析了标准 PSO 算法的基本原理、主要参数、收敛性和优缺点,针对算法在收敛性能和搜索精度方面存在的缺陷,提出了 PSO 算法的改进思路:一方面根据所得到的收敛性结论,对算法关键参数的设置进行改进,以提高算法的收敛性能;另一方面在算法中引入非均匀变异机制,以增强算法的全局搜索能力。通过对典型函数优化问题和约束优化问题的测试,表明本文所提出的改进PSO 算法在收敛性能和搜索精度等方面较标准 PSO 算法有很大的改善。 I配电网电容器优化主要包括规划优化和运行优化两大类,本文将它们分别称为配电网电容器优化配置和配电网电容器优化投切。根据两者的优化目标和要求的不同,本文分别建立了计及谐波因素的电容器配置优化模型和电容器投切优化模型,并在约束条件中考虑了谐波潮流约束和谐波畸变率约束。电容器配置优化模型以电能损耗费用、最大有功网损费用和电容器费用三者之和的系统年总支出费用最小为目标函数,计算电容器费用时考虑了固定安装费用和购买费用,使模型在经济评价方面更加合理。电容器投切优化模型则以计及投切代价的方式在目标函数中考虑了电容器投切次数的限制,从而避免将投切次数的限制作为全局约束条件,使优化能够分时段独立地进行,满足在线优化计算的需要。针对所建立的电容器配置和投切优化模型,分别提出了基于改进 PSO 算法的求解方法,并通过算例验证了所提模型及算法的有效性。 随着谐波污染及其对电容器影响的加剧,如何选择变电站并联电容器组中串联电抗器的电抗率以有效避免谐波谐振或放大这一问题,目前正逐渐引起人们的关注。本文最后对该问题作了探讨,首次从系统全局的角度研究了集中补偿电容器组电抗率的全局优化配置问题,提出了该问题的内、外双层优化模型,该模型可保证优化方案在各种可能的运行组合方式下均满足谐波畸变率约束。针对该模型,提出了基于改进PSO 算法的电抗率全局优化算法。
Optimization of capacitor in distribution systems is an important measure to ensuresecurity and economy of system operation. Optimal capacitor placement and switching canresult in voltage profile improvement, system loss reduction, power factor correction, andfeeder capacity release. However, due to the wide-spread use of nonlinear loads indistribution networks, there is a significant amount of harmonic distortion in voltage andcurrent waveforms, which may cause capacitor failure or out of work. On the other hand,shunt capacitors may lead to harmonic amplification caused by resonance conditions.Therefore, it is of great significance to study on capacitor optimization in distributionsystems with harmonic consideration, aiming to achieve the maximum system lossreduction and prevent harmonic amplification as well. This dissertation devotes to the interrelated problems of capacitor optimization indistribution systems with harmonic consideration, including the research on efficientalgorithms of fundamental and harmonic power flow calculations for radial distributionsystems, the research on a practical optimization algorithm and its improvement, theresearch on problem formulations and solution algorithms of optimal capacitor placementand switching in distribution systems, and the research on problem formulation andsolution algorithm of optimal reactance rate selection of serial reactors in capacitor banksinstalled in substations. As essential calculations in capacitor optimization with harmonic consideration,fundamental and harmonic power flow calculations influence the efficiency of the wholeoptimization procedure to a great extent. In the aspect of fundamental power flowcalculation, an improved back/forward sweep algorithm based on branch and bus layeringis proposed. In this algorithm, the branches and buses are sorted by layers, and the branchcurrents and bus voltages in the same layer can be parallel computed, so as to improve thecalculation efficiency greatly. In the aspect of harmonic power flow calculations, byborrowing the solution method used in fundamental power flow calculation, a novel IIIback/forward sweep distribution harmonic flow algorithm is presented, which helps tocalculate harmonic currents, harmonic voltages and total harmonic distortion (THD)rapidly even for a large-scale distribution system. As a representative swarm-intelligence based optimization algorithm, Particle SwarmOptimization (PSO) algorithm is applied to capacitor optimization in the dissertation.Aiming to overcome the limitations of standard PSO algorithm, a modified PSO algorithmis proposed by adjusting key parameters to improve the convergence and introducingnon-uniform mutation mechanism to enhance the global search ability of the algorithm andhence achieve better-quality solutions. Test results on a typical function optimizationproblem and several constrained optimization problems show that the proposed modifiedPSO algorithm can achieve a significant improvement on the convergence and searchquality compared with the standard PSO algorithm. Optimal capacitor placement and optimal capacitor switching are formulated withharmonic distortion consideration respectively. In the problem formulation of optimalcapacitor placement, the objective function includes the energy loss cost, the cost of peakpower loss, and the total capacitor cost which comprises the installment cost and thepurchase cost. In the problem formulation of optimal capacitor switching, the switchingoperation cost is considered as one part of the objective function so as to avoid frequentswitchings which may shorten the capacitors’ life expectancies. In doing so, the large-scaleoptimization problem during a day can be decoupled into numbers of small-scaleoptimization problems at each hour, thus the computational complexity could besignificantly reduced. Mathematically, the two problems are both formulated as nonlinearinte
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