A study of autonomous reactive power control method for distributed power generators to maintain power quality of the grid

Distributed power generators, such as cogenerators and renewable energy systems, have continued to advance and their penetration capacity is increasing. However, they may cause power quality problems in voltage regulation because of the reverse power flow. At present, when the distribution line voltage exceeds the limit value, distributed generators control reactive power to reduce the voltage, and if the reactive power output is not enough, they reduce the active power output. Therefore, an imbalance of active power output between distributed generators may occur because the voltage of generators varies by location and generators at lower voltage locations do not control the reactive power. A power control method for distributed generators needs to be established to solve these problems. In this study, an autonomous reactive power control method of sharing reactive power between distributed generators is proposed. The availability of this method is discussed experimentally and its applicability area is considered analytically by use of a model distribution system. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Optimal Control of Voltage in Distribution Systems by Voltage Reference Management

Recently, renewable energy technologies such as wind turbine generators and photovoltaic (PV) systems have been introduced as distributed generations (DGs). Connections of a large amount of distributed generations may cause voltage deviation beyond the statutory range in distribution systems. A reactive power control of DGs can be a solution of this problem, and it also has a possibility to reduce distribution loss. In this paper, we propose a control methodology of voltage profile in a distribution system using reactive power control of inverters interfaced with DGs and tap changing transformers. In the proposed method, a one-day schedule of voltage references for the control devices are determined by an optimization technique based on predicted values of load demand and PV power generation. Reactive power control of interfaced inverters is implemented within the inverter capacity without reducing active power output. The proposed method accomplishes voltage regulation within the acceptable range and reduction of distribution loss. The effectiveness of the proposed method is confirmed by simulations. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

One approach for reactive power control of capacitor banks in distribution and industrial networks

This paper presents an efficient solution for reactive power control of capacitor bank using changes in reactance of connected reactor. This solution ensures smooth control of reactive power of capacitor banks as important operational characteristic for maintaining the quality of supply. The proposed method works for a wide-range of reactive power variations in the system and is capable of injecting or absorbing reactive power when necessary. This control method can be successfully used in distribution and industrial networks where many loads vary their demand for reactive power. Other applications of this method are voltage regulation, power-factor correction and reactive power compensation. The effectiveness of the proposed method is demonstrated through the case studies in order to prove its feasibility for improvement of voltage profile and reduction of power losses.     

挖掘光伏无功能力的配电网无功电压协调控制策略

在高渗透光伏接入多电压等级配电网中,针对低压分布式光伏无功能力没有被充分利用和高/中/低压配电网无功电压未整体协调优化的问题,提出了一种充分挖掘光伏无功能力的多电压层级配电网无功电压协调控制策略。在低压配电网中,对于暂不具备通信网络,无法实现统一调度的光伏逆变器,采用3种就地自主电压控制模式进行实时无功电压控制;在多电压层级配电网无功电压协调控制模型中,考虑包括具备通信网络的光伏逆变器在内的各种无功源,建立电压分区和主导节点选择模型,设计上层全局优化和下层分区优化的双层协调控制策略,该策略充分挖掘了光伏无功对配电网电压的调节能力,实现对整个配电网的无功电压精准控制。将所提策略应用于江苏某220 kV主变区域实际系统,验证了其无功电压控制和消纳光伏发电的优势。     

考虑光伏集群无功贡献的配电网无功电压优化调节方法

为协调运用配电网各类调压资源,实现经济、灵活的电压控制,整合中高压配电网各类无功治理设备,提出考虑低压光伏无功集群贡献的配电网电压无功控制资源协调运行优化方法。针对配电网低压侧分布式小容量离线运行光伏电源,设计了3种光伏集群无功运行模式,使其按模式预设在线自律运行。提出低压光伏集群无功管控策略,建立配电网电压无功控制资源协调优化模型。采用最优分割联合优化方法对变压器分接头及电容器组的切换时间及切换状态进行优化,在此基础上得出光伏集群无功运行模式及其他治理设备无功输出优化结果。采用前推回代潮流计算嵌套粒子群优化的算法进行求解。仿真算例证明了所提方法的合理性及有效性。     

光伏并网系统参与电压调节的有功和无功协调控制策略研究

针对配电网线路阻抗大、分布式光伏并网系统无功调压能力有限,导致光伏电源在有功出力较大时并网点(PCC)电压越上限问题,在深入分析光伏系统PCC电压特性基础上,提出一种光伏逆变器有功和无功协调控制策略。在该控制策略下,光伏系统实时跟踪监测PCC电压变化,PCC电压不越限时,逆变器按最大功率点跟踪(MPPT)输出;PCC电压越上限时,优先利用逆变器剩余容量进行无功调压,若剩余容量不足,调节逆变器有功输出,并动态计算有功、无功最佳输出值,保证将PCC电压调节至满足要求的前提下,实现逆变器有功输出最大化、无功输出最佳化。算例结果验证了控制策略的有效性。     

特高压交流电网的无功电压控制

特高压交流电网是长距离大范围平衡能源供需、建设坚强智能电网和全球能源互联网的关键。特高压交流电网正在稳步发展中,无功电压控制是保证特高压交流电网安全可靠经济运行的重要手段。文中总结了特高压交流线路的无功、电压特性,指出了特高压交流电网在无功电压控制方面存在的困难;从独立控制、与近区电网协调控制、大电网全局优化三个方面综述了特高压交流电网的无功电压控制方法。最后,结合特高压电网的无功电压控制现状分析和发展趋势,指出了特高压交流电网在无功电压控制研究中的几个发展方向。     

主动配电网自动电压控制系统架构设计

针对配电网中引入大量分布式电源后运行特性和无功电压特性与传统配电网的显著差别,提出了基于配电自动化系统的主动配电网自动电压控制系统架构。以馈线实时拓扑连接为基础,提出以无功可调设备为控制对象的自治控制区域划分方法。设计了以自治控制区域作为控制单元的电压无功控制策略,包括电压控制分区策略、电压越限控制策略、馈线无功越限控制策略及与其他系统的协调控制策略和安全闭锁策略,并给出了主动配电网自动电压控制系统的整体流程。结合实际案例验证了文中所述主动配电网自动电压控制系统架构是一种在配电自动化系统层面进行电压无功控制的有益探索。     

Coordinated voltage control of transformer taps with provision for hierarchical structure in power system

Participation of distributed generators (DGs), such as wind turbines, cogeneration systems, etc., is a natural trend from an ecological point of view and will continue to increase. The outputs of these DGs mainly depend on weather conditions but do not correspond to the changes of electrical load demand necessarily. On the other hand, due to deregulation of the electric power market, the power flow in a power system will uncertainly vary with several power transactions. Thus, complex power flow by DGs or transactions will cause voltage deviation. It will be difficult to sustain the voltage quality by using conventional voltage/reactive power control in the near future. In this paper, in order to avoid such voltage deviation and to decrease the frequency of transformer tap operations, the coordinated voltage control scheme of transformer taps on account of hierarchical structure in the power system is proposed. In the proposed scheme, integral of voltage deviation at each layer bus is applied to decide the timing of each transformer tap operation. Numerical simulations confirm that the proposed scheme is able to respond to every condition on voltage deviation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 48–55, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20531     

动态无功补偿装置抑制风电汇集地区高电压问题的可行性研究

当大规模风电集中接入弱端电网对,短路故障后会出现高电压的问题,造成风电机组因不具备高电压穿越能力而脱网.运行经验表明高电压穿越问题已经成为风电机组脱网的主要原因.文章从上述问题出发,探索通过风电场普遍配置的动态无功补偿装置抑制高电压的问题,在BPA中搭建了不同动态响应时间的SVC/SVG模型,并对比分析了不同响应时间、不同容量、不同类型的无功补偿装置对抑制高电压的效果.仿真结果表明,适当容量满足标准要求的动态无功补偿装置可以很好地抑制短路故障后的高电压问题,对于提高风电汇集地区无功电压安全水平有明显效果.     

统一潮流控制器在风电机组并网运行中的应用

大规模风电并网改变了原来电网的潮流分布、线路传输功率以及电网故障时的暂态特性。将统一潮流控制器(UPFC)应用于异步风电机组并网的环形输电网络模型中,研究UPFC改善风电并网的性能。通过设计UPFC并联侧的双闭环反馈控制,设置风电输出线路三相短路故障来研究UPFC提高风电场低电压穿越能力。再建立UPFC串联侧有功与无功的独立控制系统,向输电线路输出补偿电压,研究其优化风电并网系统的潮流分布能力。在Matlab/Simulink软件中建立模型,仿真结果表明基于UPFC强大的无功补偿能力与潮流控制能力,UPFC能够显著提高风电并网的低电压穿越能力和优化潮流分布。     

A study on collaborative operation method for a new energy type dispersed power supply system by AC‐EMAP model

Application of a dispersed power supply system consisting of a large‐scale photovoltaic system (PV), a fuel cell (FC), and an electric double layer capacitor (EDLC) is studied in this paper. This system is operated in autonomous mode, taking account of time delay characteristics of FC. The modified Euler type Moving Average Prediction (EMAP) model is improved using short‐time fast Fourier transform (ST‐FFT). The Adaptive Control type EMAP (AC‐EMAP) model is introduced to reduce the capacity of EDLC. This system can meet the multi‐quality electric power requirements of customers, and improve voltage stability and uninterruptible power supply (UPS) function as well. Moreover, the required capacity of EDLC to compensate the fluctuation of both PV output and Load demand is clarified by a simulation based on collaborative operation method by a prediction model using software MATLAB/Simulink. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 13–24, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20262     

基于分布系数法的电磁环网潮流控制形式研究

电磁环网故障是威胁电网安全运行的一个重要因素,在实际运行中,需重点分析与监控。为解决传统电磁环网潮流控制形式存在安全隐患及不能充分发挥电磁环网的输送能力问题,研究了基于分布系数法的控制形式。该控制形式将高电压线路潮流乘以分布系数后叠加到低电压线路潮流上,以叠加后的潮流不超过稳定限值作为控制原则。以广西电网的一个电磁环网为例进行了对比研究,结果表明:该控制形式能较好地适应机组出力、负荷等工况的变化,能够在确保系统安全的前提下充分发挥电磁环网的输送能力,优于传统控制形式,可用于实际电磁环网的计算分析与调度监控。     

基于分层模型预测控制的风电场电压协调控制策略

针对弱连接并网风电场无功电压调节中电压支撑能力较弱且易受风功率波动影响的问题,提出一种基于多时间级垂直分层思想与模型预测控制(MPC)理论相结合的风电场无功电压分层协调控制策略。首先,在自适应调节层,依据风电场调节能力与并网点电压波动轨迹预测,提出一种并网点电压自适应调节策略。其次,在无功分配层,求解无功需求容量,并给出一种可考虑各机组无功调节裕度的改进比例分配策略。最后,在跟踪控制层,依据状态预测与参考、反馈信息实时修正控制误差。通过分层MPC,各层内不同时间级的预测信息可被高效利用,各层间不同时间尺度的控制亦可得到有效协调。基于PSCAD的仿真分析结果验证了所提方法的有效性。     

城市建筑配电系统中低压断路器选用问题的探讨

当前城市建筑配电系统中,在低压断路器的选用、上下级断路器之间的配合等方面存在一些问题,达不到选择性保护的要求,越级跳闸严重,影响电网供电的可靠性.就城市建筑配电系统中低压断路器的额定电流、脱扣动作特性及短路分断能力等技术参数的选择进行了分析和探讨,以提高电网供电的可靠性.     

10kV线路无功补偿技术在农网中的应用分析

无功补偿是节能降耗、改善电网电压质量、提高功率因数最方便、最经济有效的方法之一。随着农村用电负荷的迅速增长,部分供电半径大、负荷重的10 kV配电线路无法满足用户的需求,将线路无功补偿技术应用到10 kV农网线路中,是一种积极可行的手段。首先介绍了无功补偿的配置原则,然后介绍了10 kV线路无功补偿安装容量和安装位置的确定方法,最后介绍了10 kV线路无功补偿技术在德阳农网中的成功应用案例。     

一种分布控制系统24V直流电源的实现

在分析分散控制系统(DCS)供电电源需求的基础上,给出了一种实现方案。采用FAN4803的PFC功能和PWM功能,实现一种带功率因数校正的单相AC-DC变换器,输出直流电压385 V,并获得12 V工作和驱动电源。采用UC3844实现一种385 V~24 V的单端正激DC-DC变换器,最终连续负载能力为500 W。采用均载控制芯片UC3907实现2路N+1冗余设计,连续负载能力为500 W,总负荷能力可达750 W以上。     

新型正弦脉宽调制控制电压源型动态静止无功补偿器

提出了一种适用于低压配电系统的新型动态无功补偿电路拓扑。主电路采用三相四桥臂逆变器结构,可以对负荷不平衡进行有效补偿。逆变器控制采用正弦脉宽调制(sinusoidal pulse width modulation,SPWM)控制,保证电压电流失真度低,并通过调节逆变器的输出电压从而动态调节静态无功补偿器(static var compensator,SVC)补偿无功功率,最终实现系统无功补偿为零的目的。通过与固定补偿电容器相结合,它能以较小的逆变器容量来补偿动态无功,提高系统的功率因数和电压稳定性。利用PSCAD/EMTDC平台对该系统进行了仿真研究。仿真结果验证了控制策略的可行性和有效性。     

含分布式电源的配电网电压无功优化问题研究

本文根据分布式电源对配电网的有功损耗和电压稳定与分布等方面的影响,针对含分布式电源的配电网,构建以节点电压合格率最高为目标的电压无功优化模型,然后结合配电网负荷变化及太阳能容量的变化特点,选取一天中3个典型的负荷点,采用多种电压无功调节装置(OLTC、SVR、SC和SVC)组合优化的策略对配电网电压进行优化控制,并采用收敛性较好的遗传算法求解最优电压,最后通过算例仿真分析几种电压无功调节装置不同组合情况下的电压优化效果,验证了几种组合方法均能对配网电压起到优化作用的正确性。     

含扶贫式光伏农村配电网电能质量综合控制技术研究

针对含扶贫式光伏的农村配电网运行特点,提出在逆变器功率控制的基础上,光储联合发电分时协调控制技术。分析了扶贫式光伏电源接入农网后逆变器电压/无功控制原理,在某低压台区建立了光储联合发电系统。其中对逆变器设置死区控制环节保证无功调节优先性,同时分时对光伏电源和储能进行协调控制,平滑功率输出。最后结合Opendss软件对某低压台区进行验证,仿真结果表明所提控制策略能够有效提升农网电能质量运行水平。