微网并网与孤岛运行模式下的无功优化策略

高渗透率的间歇性分布式电源(DG)使微网在并网或孤岛模式的运行可靠性降低,而传统的无功优化方法往往因忽略微网可靠性导致优化效果较差。依据有功及无功功率充足和电压极限限制,以概率方式来评估微网的可靠性,提出了一种微网在并网及孤岛模式下的无功优化规划模型,以系统年电能损耗最小和微网可靠性最大为目标进行求解。最后,采用PGE 69节点进行算例分析,研究了优化系数的作用效果和算法的鲁棒性,并通过成本-效益分析来确定系统的电容器组的最优容量。结果表明,对微网进行分布式无功电源的优化配置能有效改善网损,并提高系统的可靠性。     

谐波影响下电力电容器的协调无功降损方法

传统采用退火—逐步优化算法对电力系统中的电容器,进行多形态高载荷负荷协调时,未综合考虑谐波影响下电容器的负荷状态,无法对总谐波畸变进行有效控制,降损效果差;因此提出新的谐波影响下电力电容器的协调无功降损方法,通过谐振影响下的电力电容器优化配置数学模型,综合考虑谐波影响下电力电容器电能消耗总金额和配置电容器所需的费用,获取谐波影响下电容器的电压总谐波畸变率;通过微粒群优化算法,确保各节点电压总谐波畸变率控制在规定限值以内,对电容器进行优化配置,实现电容器的无功降损控制。实验结果说明,采用所提方法优化配置后的电容器可有效抑制谐振发生,可降低约37%的电网损耗,具有节能高的优势。     

微电网孤岛模式下无功分配及电压优化分层控制策略

针对在微电网孤岛模式下并联运行的分布式电源采用传统下垂控制策略时存在无功功率受并网线路阻抗影响较大、电压偏离额定值等问题,提出了微电网孤岛模式下无功分配及电压优化分层控制策略,将微电网优化控制过程分为两层:初级控制层针对分布式电源无功功率受并网线路阻抗影响较大问题,提出变系数法下垂控制策略,根据下垂特性和线路特性约束方程调整下垂系数,实现无功功率精确分配;二级控制层应用多智能体一致性算法维持微电网电压稳定。仿真模型使用PSCAD/EMTDC搭建,结果表明,分层优化策略使无功功率合理分配的同时提高了微电网电压水平。     

基于改进最优覆盖法的变电站无功补偿不等容分组优化配置

针对变电站无功补偿不等容分组优化配置问题,提出一种基于改进最优覆盖法的优化分组方法,获取变电站典型日无功需求曲线,总补偿容量为无功需求最大值,并进行电容器补偿容量的最优覆盖。再利用蒙特卡洛抽样法计算无功失配面积,并转化成年损耗费用,且为协调电容器组无功调节能力与控制策略复杂度之间的矛盾,定义档位系数指标加入投资成本,建立年损耗费用与投资成本之和最小的无功优化数学模型。采用改进遗传算法进行求解,得到电容器组各类型容量及其对应组数,用以指导变电站无功优化配置。与最优覆盖法及分段-聚类法相比,所提方法有效可行。     

基于改进遗传算法的配电网无功优化

在传统无功优化模型的基础上,引入静态电压稳定裕度指标,建立了综合考虑系统有功网损最小、无功补偿容量最小和系统静态电压稳定裕度最大的配电网无功优化模型。根据节点无功2次电阻矩的大小,确定了待补偿节点以及各节点补偿容量的上下限。在基本遗传算法的基础上,对遗传操作进行了改进,提出了1种改进遗传算法。实例计算表明,采用该方法对配电网进行无功优化不仅可以降低有功网损,还能提高系统静态电压稳定性。     

Optimization of hybrid solar energy sources/wind turbine systems integrated to utility grids as microgrid (MG) under pool/bilateral/hybrid electricity market using PSO

This study presents an optimized design of microgrid (MG) in distribution systems with multiple distributed generation (DG) units under different market policies such as pool/hybrid electricity market.Proposed microgrid includes various energy sources such as photovoltaic array and wind turbine with energy storage devices such as battery bank.In this study, microgrid is considered as independent power producer company (IPP) in power system. Price of selling/buying power in on-peak or off-peak for MG, DG and upstream power system (DISCO) under pool/bilateral/hybrid electricity market are different. In this study, particle swarm optimization (PSO) algorithm has been implemented for the optimization of the microgrid cost. The costs include capital cost, replacement cost, operation and maintenance costs and production cost for microgrid and DGs. Then, an objective function to maximize total net present worth (NPW) is presented. PSO approach is employed to obtain the minimum cost of microgrid, during interconnected operation by optimizing the production of local DGs and power exchanges with the main distribution grid. The optimization algorithm is applied to a typical LV network operating under different market policies.     

变/配电无功集中优化与电压分布控制策略研究

根据负荷和无功电压控制装置的特点,通过引入小容量调压式动态无功补偿装置将变/配电系统的无功电压控制分为两级控制,一级控制针对负荷的较大变化,以集中优化为手段控制电容器组的投切;二级控制以就地分布控制为原则,按九域图模式控制变压器分接头及无功补偿装置的可调容量部分,即可实现变/配电系统的无功电压集中-分布协调控制,力求达到控制效果和效率的最优化.实例分析结果表明,本方法为变/配电系统无功电压控制的有效方式.     

基于等微增率法的混合微电网无功协调控制

在馈线潮流控制(FFC)和单元输出功率控制(UPC)两种控制模式下的混合微电网中,FFC模式下分布式电源(DG)的无功裕量不能满足增加的无功负载时,会引起微电网和大电网之间馈线无功潮流的变化,且馈线无功潮流值越大,脱网时公共连接点(PCC)电压偏差越大。为此,提出了一种考虑微电网内部节点电压稳定性的多台DG无功协调控制策略。该策略以FFC模式下DG为主要补偿设备,当不能满足负载需求时,采用等微增率法求解优化模型,从而确定UPC模式下DG无功输出参考值。算例结果表明,该控制策略能在维持微电网与大电网之间馈线无功潮流恒为最小值的同时,使得微电网内部节点电压更稳定。     

Hybrid renewable energy‐based distribution system for seasonal load variations

In recent scenario, there is abundant availability of renewable energy resources to satisfy the significant increase in residential, industrial, and commercial demand. This paper presents a novel framework to determine the preeminent size of renewable distributed generators (RDGs) by optimizing the system components such as area required for solar‐photovoltaic modules, swept area occupied by wind turbine blades, and area used by fuel cell. A microgrid with hybrid RDG (h‐RDG) is integrated in distribution system to minimize the distribution loss, substation energy requirement, and improve the voltage level of the load. The power loss minimization is formulated as a nonlinear problem and optimized by the proposed Hybrid Nelder Mead‐Particle Swarm Optimization algorithm. The microgrid location is identified by voltage stability index to improve the stability of system. Further, the system is analyzed for energy flow in different seasonal loading conditions with mixture of residential, industrial, and commercial load. The effective performance of the proposed technique is applied to standard 12‐bus, 69‐bus, and a practical Tamil Nadu (TN) 84‐bus radial distribution system (RDS) for different hybrid combinations of h‐RDG in microgrid. The result proves that the proposed method provides a simple and efficient tool for optimal and flexible use of h‐RDG in microgrid under different climatic changes by simultaneously reducing distribution energy loss and improving voltage profile.     

低压配电网不平衡和谐波问题的综合治理

针对低压配电网三相电流不平衡及谐波而导致三相电压不平衡、线损和变压器损耗增加、中性点电压偏移等问题,提出了基于晶闸管投切电容器和有源滤波器的综合治理方法,给出了利用晶闸管投切电容器进行“粗补”、有源滤波器进行“微补”的小容量综合治理装置及其拓扑结构和控制方法,并提出采用“变P法”和“限无功法”对有源滤波器进行保护。实例仿真结果表明,该综合治理方案行之有效。     

A comprehensive power loss,efficiency, reliability and cost calculation of a 1 MW/500 kWh battery based energy storage system for frequency regulation application

Battery based energy storage system (ESS) has tremendous diversity of application with an intense focus on frequency regulation market. An ESS typically comprised of a battery and a power conversion system. A calculation of performance parameters is performed in this research. The aim is to formulate an in-depth analysis of the ESS in terms of power losses of the semiconductor and electrical devices, efficiency, reliability and cost which would foster various research groups and industries around the globe to improve their future product. In view of this, a relation between the operating conditions and power losses is established to evaluate the efficiency of the system. The power loss calculation presented in this paper has taken into account the conduction and switching losses of the semiconductor devices. Afterwards, the Arrhenius Life Stress relation is adopted to calculate the reliability of the system by considering temperature as a covariate. And finally, a cost calculation is executed and presented as a percentage of total cost of the ESS. It has been found that the power loss and efficiency of the ESS at rated power is 146 kW and 85% respectively. Furthermore, the mean time between failures of the ESS is 8 years and reliability remains at 73% after a year. The major cost impact observed is for battery and PCS as 58% and 16% respectively. Finally, it has been determined that further research is necessary for higher efficient and lower cost system for high penetration of energy storage system in the market.     

含双馈感应风电机组的配电网无功优化

考虑传统无功调节设备调节次数限制和双馈感应电机无功容量限制等约束条件,提出一种基于双馈感应电机与传统无功调节设备协调控制的分时段分层无功优化策略。首先,该策略采用谱系聚类算法对预测等效负荷曲线进行分段;其次,在每个时段采用分层调控策略进行无功优化,建立以网损和平均电压偏离度之和为目标函数的无功优化模型,上层利用改进粒子群算法计算出包括双馈感应机组在内的各种无功调节设备的优化运行状态,并预先对变压器、电容器动作;在此基础上,下层利用双馈感应机组的无功调节能力对上层优化得出的并网点电压进行自动跟踪控制,由此实现了每个时段内接入点电压控制和全局无功优化相结合,最后以IEEE33节点配电系统为算例来验证上述策略的有效性。     

Analysis of reactive power strategies in HVDC‐connected wind power plant clusters

Offshore wind power plants (WPPs) built near each other but far from shore usually connect to the main grid by a common high‐voltage DC (HVDC) transmission system. In the resulting decoupled offshore grid, the wind turbine converters and the high‐voltage DC voltage‐source converter share the ability to inject or absorb reactive power. The overall reactive power control dispatch influences the power flows in the grid and hence the associated power losses. This paper evaluates the respective power losses in HVDC‐connected WPP clusters when applying 5 different reactive power control strategies. The case study is made for a 1.2‐GW–rated cluster comprising 3 WPP and is implemented in a combined load flow and converter loss model. A large set of feasible operating points for the system is analyzed for each strategy. The results show that a selection of simulations with equal wind speeds is sufficient for the annual energy production comparison. It is found that the continuous operation of the WPPs with unity power factor has a superior performance with low communication requirements compared with the other conventional strategies. The optimization‐based strategy, which is developed in this article, allows a further reduction of losses mainly because of the higher offshore grid voltage level imposed by the high‐voltage DC voltage‐source converter. Reactive power control in HVDC‐connected WPP clusters change significantly the overall power losses of the system, which depend rather on the total sum of the injected active power than on the variance of wind speeds inside the cluster.     

微网中储能系统的控制与分析

在微网系统中,大功率电力负荷的投切会导致电网电压幅值和频率产生波动。将储能装置应用于微网系统中,可以通过逆变控制单元,实时监控电网电压波动,即时调节配电网输送的有功、无功功率大小,从而达到平抑电网电压波动的效果。采用了电压频率环控制和有功、无功补偿控制相结合的控制算法,可以即时检测电网电压波动并进行快速补偿,具有较强的有功、无功调节能力。通过构建微网模拟环境,对比试验了不加储能装置和接入储能装置后微电网投入不同电力负荷时的电压波动情况,验证了控制策略的有效性和正确性。     

分散式风电多点接入协调优化控制策略

针对分散式风电机组并网导致的配电网网损增加、电压稳定性降低等问题,文章提出一种分散式风电并网多点协调双层控制策略。首先,分析了分散式风电多点接入特性,研究分散式风电多点接入后的网损、电压分布和功率因数的关系,并提出最小网损和电压偏差为目标的双层优化控制策略。最后,基于IEEE-33节点进行仿真计算,结果表明,所提多点协调控制策略能够有效降低配电网网损和提升母线电压水平,增加系统的稳定性。与超前功率因数相比,滞后的功率因数能够增大风能消纳能力,提高供电可靠性,减少电压偏移水平。     

Application of the fast Newton-Raphson economic dispatch andreactive power/voltage dispatch by sensitivity factors to optimal powerflow

This paper applies the sensitivity factor method to the reactive power/voltage dispatch problem and combines it with the fast Newton-Raphson economic dispatch to solve the optimal power flow problem. The advantage of this method is that it is fast and reliable. Firstly, the real power generalized generation shift distribution (GGSD) factors are used in economic dispatch to find the real power generation for every unit so that the fuel cost is minimum. During the process of solving the economic dispatch problem, the voltage magnitudes of load buses in a power system may be changed and may exceed the ranges of secure values. Therefore, reactive power sensitivity factors of bus voltage magnitudes are used to regulate the voltage magnitudes of load buses to the secure ranges. The process is repeated to find the optimal generation with all voltages staying within the secure ranges. Results show that the algorithm converges very fast     

Design and coordination of a capacitor and on‐load tap changer system for voltage control in a wind power plant of doubly fed induction generator wind turbines

Larger percentages of wind power penetration into the grid translate to more demanding requirements coming from grid codes; for example, voltage support at the point of connection has been introduced recently by several grid codes from around the world, thus making it important to analyse this control. Voltage control is actuated by reactive power injection, and for a wind power plant of doubly fed generator turbines, reactive power capability can be a challenge, which typically is overcome by installing reactive power compensators. The integration and the interaction between all these reactive power sources and the on‐load tap changer of the main substation transformer need to be analysed and taken into account in the control design. In this paper, a novel coordination and control strategy for capacitor banks and on‐load tap changer for a wind power plant is introduced. The capacitor banks are controlled in such way that the steady‐state usage of the converters for reactive power injection is driven below to a maximum desired value of 0.1 pu. Additionally, the control transients because of the capacitor bank switching are minimized by using a suitable control structure. The tap changer control is coordinated with the plant control to decrease the impact of the capacitors reactive power in the line drop calculation, thus reducing the amount of tap operations and improving the accuracy of the line drop voltage estimation. The coordination of the central controller with the plant components is analysed and tested through electromagnetic transient program simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

无功补偿在火电厂厂用电系统的应用及研究

充分保证火电厂厂用电系统安全性前提下,高低压厂用电系统中接入无功补偿装置。无功补偿优化的基本原则是:全面规划,合理布局,自动控制,降损与调压相结合,以降损为主兼顾调压。     

A review on distributed generation impacts on electric power system

In 2021, the world's total installed capacity of generation units based on renewable energy sources (not including hydropower) amounted to about 1674 GW: over 825 GW and 849 GW of wind and solar power plants were installed respectively. The growing of the installed capacity of these distributed generators is a response to the increasing the power consumption, global environmental issues and has also become possible due to the development of technology in field of power semiconductor devices. However, on the way of large-scale implementation of distributed generators based on renewable energy sources, traditional electric power system meets new challenges to ensure the reliability and sustainability of new electric power systems with renewable energy sources. In particular, distributed generators change processes in the electric power system, impact to the parameters and power balance, change the magnitude and direction of power flow and short-circuit current, which determines the need to update the settings of the relay protection and automation systems of traditional electric power system and to coordinate their operation with automatic control systems of installed distributed generators. The above-mentioned tasks form a number of scientific research directions, one of which is a task of determining optimal size and location of distributed generators. The main purpose of this optimization task is to reduce power losses, operating and total electricity cost, improve the voltage profile, etc. In addition, the correct and reasonable placement of distributed generators defines an effective planning of the operating modes of electric power system and power plants (especially based on renewable energy sources, the operating modes of which depend on weather conditions and can be sharply variable).The paper highlighted the impacts of distributed generators on power losses, the voltage level, maintaining the power balance and the possibility of participating in the frequency regulation, and short-circuit current in power system. The optimization criteria, the main limiting conditions, as well as methods for solving this optimization problem are considered. This review will help the System operators and investing companies, especially in Russia, to form the main aim, objective function and constraints that will aid to meet their load demand at minimum cost and to choose from the options available for optimization of location and capacity of distributed generators.     

基于自适应虚拟阻抗的分布式电源并联控制策略

当传统下垂控制策略应用于低电压微电网分布式电源并联系统时,其等效输出阻抗易受线路阻抗的影响而呈阻性,致使无功功率不能完成精准分配,破坏微电网系统的稳定性。因此,分析了低电压微电网系统的等效输出阻抗,并提出将自适应虚拟阻抗添加到电压电流双闭环控制方法,结合下垂特性可实现无功和有功功率的解耦,还能对产生的环流进行有效抑制;又利用CAN通讯技术通过引入电压补偿信号在线监测无功功率分配,以提高各分布式电源无功功率的分配精准度。最后通过在仿真平台建立两台逆变器并联运行模型,验证了该方法的可行性和稳定性。