基于HHT变换的微网电压闪变与谐波检测新技术

微网中大规模的分布式电源由于其自身特点及大量电力电子设备的使用,容易引起电网电压波动、电压闪变及谐波等电能质量问题,影响电力用户的供电要求。利用HHT(Hilbert-Huang transform)变换方法对微网中的电压闪变、谐波等电能质量扰动信号进行了EMD分解,得到各IMF分量,通过对IMF分量进行Hilbert谱分析和边际谱分析。仿真结果表明,该方法能快速有效地检测出微网中电压闪变信号的频率和幅值及谐波信号产生及终止的时刻。     

适用于双馈风机的并网电压波动与 闪变检测系统的研究

风电因电能质量问题影响使其发展受到制约,电压波动及闪变是其中之一。使用目前的闪变仪对风电机组并网引起电压闪变进行检测,发现在检测低频段波动引起的闪变时误差较大,而这也是风电并网产生闪变的主要频段。因此,如何使低频段检测误差减小是该文研究的意义。根据IEC标准,在Matlab平台建立数字闪变检测系统仿真模型,并利用双线性方法求得系统的参数。针对上述情况,分析其误差产生的原因,通过对检测的瞬时闪变视感度S（t）引入参数校正以减小低频检测误差,使其满足风电并网闪变值检测的要求。最后将修正系数后的检测系统运用在一个双馈风力发电系统实例中,证明该风电场满足我国电压闪变值要求。     

基于区间数逼近的微网电压暂降风险评估

当前微网的概念已逐渐深入到现代电网运行中,其中电能质量问题具有很强的随机性和不确定性。将风险评估理论引入到微网电能质量分析中,用区间数估计理论替代传统的定值估计方法,建立了基于区间数逼近的微网电压暂降风险评估模型。该模型还考虑了微网中各类分布式电源的权重优化问题,对合理配置分布式电源具有一定指导作用。算例结果表明,该方法可以较好地反映微网中电压暂降的随机性,并引入模糊理论对其风险值综合评估,能准确反映事实,客观科学,具有一定的推广和应用价值。     

浅析风力发电并网技术及电能质量控制

风能作为一种可再生的清洁能源,近年来获得了国家与社会各界的大力支持,规模日益增大,在我国电力事业中的地位日益提高。此外,由于风力发电一般都选择人烟稀少的地区,其所承受的冲击较大,加之风能的特殊性,其潜在的谐波污染或其他质量方面的风险也相对较大。文中主要针对风力发电并网技术及电能的质量控制进行探讨,首先介绍了风力发电并网技术,其次对风力发电机并网运行进行了试验,进而在此基础之上分析了并网对风力发电电能质量的影响,并提出了控制电能质量的策略与建议,旨在为风力发电电能质量控制提供一定的理论参考。     

基于MMC-PET的直流微电网综合控制策略

为提升智能配电网电能质量,提出一种基于模块化多电平型电力电子变压器的直流微网构架及其综合控制策略,对分布式电源并网方式进行简化,设计MMC-PET及风光储系统的控制器,对智能配电网中电压深度跌落、三相不平衡等电能质量问题进行治理。在PSCAD/EMTDC平台搭建基于MMC-PET的直流微网风光储系统仿真模型,进行仿真分析总结,结果表明该方法很大程度地提高了新能源接入适应性,具备更快的动态响应速度和更强的鲁棒性,能有效改善智能配电网电能质量。     

风电场并网对电力系统稳定性影响

稳定性是影响大电网区域互联的关键性因素。随着风电场规模的不断扩大,其接入电网会对电力系统的稳定性带来一定影响。介绍了风力发电系统建模方法及风力发电机模型,分析了风电场并网对电力系统无功电压、潮流分布、电能质量、系统短路容量、调峰调频等方面的影响,并对电力发电技术发展新动向作了展望。     

基于Hilbert-Huang变换的风电场闪变

随着风电场装机容量的增大,风电并网所带来的电压偏差、谐波污染、电压波动和闪变等电能质量问题日益严重,因此,需要对其进行评估和治理,而评估和治理的前提是参数的准确检测。将一种新的非平稳信号处理方法,即Hilbert-Huang变换用于风电场闪变的分析。该方法可以从频域和时域同时对信号进行分析,能够准确检测出非平稳电压闪变信号的时间、频率和幅值信息。仿真分析结果表明了该方法分析风电场闪变的有效性。     

基于模糊综合评判的风电并网系统电能质量研究

随着大规模风电并网和用户对电能质量要求的提高,现有评估方法并不能很好地应用于风电并网系统。文章首先提出一种基于模糊综合评判的风电并网系统电能质量评估方法,该方法在分析风力发电并网运行特点及风电并网后引起的电能质量问题的基础上,提出风电并网系统电能质量的评价指标;然后使用层次分析法和熵权法组合求取综合权重,使用模糊综合评判对风电并网系统电能质量进行量化评估;最后对所提的评价方法进行实例验证。结果表明,该方法合理有效,对提升风电并网系统电能质量具有一定指导意义和参考价值。     

微网中基于储能系统的动态电压恢复器研究

引入动态电压恢复器(DVR)来提高微网的电能质量,为给DVR提供工作时所需能量,采用DC-DC斩波器将蓄电池储能系统(BESS)接于DVR中,讨论BESS在微网中的作用,BESS不仅可作为DVR的组成部分,而且可在微网孤岛模式时维持电压、频率恒定和迅速响应波动的负荷,在微网并网时进行功率平滑和削峰填谷。此外,还分析储能系统直流斩波部分的控制,比较d-q变换法与双d-q变换的正负序检测法两种d-q变换法DVR的检测方法。最后,在PSCAD/EMTDC平台上对所提出的微网系统进行仿真分析,结果表明双d-q变换的正负序检测法能快速无延迟地检测出跌落电压,基于BESS的DVR能迅速有效补偿微网的电压暂降,从而维持敏感负荷的电压恒定。     

光伏并网逆变器入网检测平台实现方案研究

随着光伏发电在传统配电网中的大规模接入,对配电网的电压调节、潮流控制、继电保护和综合自动化等带来新的挑战,同时,光伏发电系统通过并网逆变器连接到电网,由此带来的电能质量问题也会给用户的设备安全带来隐患。文章结合光伏并网逆变器主要检测内容及相关标准,构建了光伏并网逆变器入网检测平台,利用该平台可开展光伏逆变器入网检测,实现包括电能质量、保护功能、逆变效率、低电压穿越和高电压穿越等功能的测试。     

风机并网对电能质量影响因子研究

为了给电网控制策略提供可靠的参考依据,对电网在接入风机后电能质量的变化进行了详尽的分析。风机作为电源同时也作为非线性负载接入配电网中使得电能质量的分析更加复杂。首先对国标中着重介绍的稳态电能质量：电压偏差,三相不平衡度,谐波以及电压波动进行理论介绍,然后在Matlab／Simulink上建立了配电系统与风机并网的模型,得到风机对电能质量不同方面的影响程度,最后采用先进电力电子设备为平稳电压电流输出提供一定的方法,并进行验证。研究结果表明,电力谐波和电压波动闪变是风机对电网的最主要的影响因素。     

基于改进型恒压控制与直流电压控制的交流微网协调控制方法研究

PQ控制、下垂控制与交流微网中光伏发电、风力发电等微电源之间存在协调性差问题,该文通过采用交流微网的直流电压控制策略,可使直流电压控制与光伏发电、风力发电之间的配合与协调更好,但当采用直流电压控制时,光伏发电、风力发电微电源的恒压控制策略就无法实现,为此改进恒压控制策略,提出基于改进型恒压控制与直流电压控制的交流微网的协调控制策略。Matlab/Simulink仿真结果验证了该文所提控制策略的有效性和可行性。     

短路故障清除时刻直驱风电机组机端暂态过电压研究

大规模风电汇集地区的配套火电机组少,属于交流弱电网,故障后暂态过电压问题严重。2011年至今,中国西北、东北、华北等多个区域电网已经发生了数十起风电暂态过电压脱网事件,且事故中,故障恢复过电压引发脱网的风力机占比很高,其过电压程度直接影响风电场的开机容量。针对该问题,该文基于典型低电压穿越策略建立永磁直驱风电机组（PMSG）并网模型,研究弱电网条件下送出线路短路故障清除时刻PMSG机端暂态过电压的影响因素。结果表明,PMSG暂态过电压与风电机组容量、电压跌落程度及锁相环动态特性等因素有关,根据某实际直驱风场搭建仿真系统模型验证了该结论。     

基于风电机组无功裕度预测的风电场无功分层控制策略

针对风电电压波动的问题,文章基于风电机组无功裕度预测,提出了一种风电场无功分层控制策略。该策略首先以并网点电压偏差和线路有功损耗最小为目标,使用二次规划算法在线实时求解最优并网电压,进而求解风电场无功参考值;其次,采用EWT-LSSVM预测算法进行风电功率预测,并提出预测功率校正方法实时修正预测功率,精确求解风电机组的无功裕度预测值;最后,以风电机组的出口电压波动最小和预测无功裕度最大为无功分配依据,实现风电场的无功电压闭环控制。仿真结果表明,所提控制策略能够提高风电功率预测的精确性和时效性,降低了风电机组出口电压波动性,同时为风电场预留出充足的无功裕度。     

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。     

基于二阶广义积分的风电系统电压跌落检测法

随着风力发电装机容量的不断增大,风电在电网中所占比重也越来越高,这就要求并网风电系统应具有低电压穿透能力。在电网电压发生跌落的情况下,为了使风电系统保持并网状态,对电网进行支撑并穿越故障,文章提出一种准确的、快速的电网故障电压检测方法——正序电压检测方法。该方法能在电网电压发生故障下做出快速的、精准的频率自适应响应。该电压检测系统包括正交信号发生器(QSG)、正序分量计算(PSC)和锁相环(PLL)3部分,系统中应用了二阶广义积分正交信号发生器。系统的输入为电网电压,输出为实时的相位角、正序电压分量和故障信号。通过对系统研究和仿真,表明该系统在电网发生故障时可有效地检测到故障信号。     

Field tests of wind turbines submitted to real voltage dips under the new Spanish grid code requirements

This paper adds the new Spanish grid code to the previously published works about the comparison of international regulations for connection of wind turbines to the network. All the electrical magnitudes—currents and active and reactive power—regulated in the Spanish grid code are studied when the wind turbines are submitted to real voltage dips. Because grid codes and, specifically, the Spanish grid code do not fix the reactive power definition to be applied, four definitions commonly used have also been studied. Taking advantage of the voltage dips field tests carried out to the Gamesa G80 wind turbines, the results obtained for two representative voltage dip tests are presented: a three‐phase and a phase‐to‐phase voltage dip. Copyright © 2007 John Wiley & Sons, Ltd.     

Applying power quality characteristics of wind turbines for assessing impact on voltage quality

Injection of wind power into an electric grid affects the voltage quality. As the voltage quality must be within certain limits to comply with utility requirements, the effect should be assessed prior to installation. To assess the effect, knowledge about the electrical characteristics of the wind turbines is needed or else the result could easily be an inappropriate design of the grid connection. The electrical characteristics of wind turbines are manufacturer‐specific but not site‐specific. This means that, having the actual parameter values for a specific wind turbine, the expected impact of the wind turbine type on voltage quality when deployed at a specific site, possibly as a group of wind turbines, can be calculated. The methodology for this is explained and illustrated by case studies considering a 5 × 750 kW wind farm on a 22 kV distribution feeder. The detailed analysis suggests that the wind farm capacity can be operated at the grid without causing unacceptable voltage quality. For comparison, a simplified design criterion is considered assuming that the wind farm is only allowed to cause a voltage increment of 1%. According to this criterion, only a very limited wind power capacity would be allowed. Measurements confirm, however, the suggestion of the detailed analysis, and it is concluded that a simplified design criterion such as the ‘1% rule’ should not be used for dimensioning the grid connection of wind farms. Rather, this article suggests a systematic approach including assessment of slow voltage variations, flicker, voltage dips and harmonics, possibly supported by more detailed analyses, e.g. system stability if the wind farm is large or the grid is very weak, and impact on grid frequency in systems where wind power covers a high fraction of the load, i.e. most relevant for isolated systems. Copyright © 2002 John Wiley & Sons, Ltd.     

Modelling of wind energy‐based microgrid system implementing MMC

Nowadays, renewable energy systems have come up with more potential in power generation so as to meet the power demand. Among all the renewable systems, the wind energy generating system is believed to be at the peak. However, the wind energy‐based microgrid system is associated with many problems such as fluctuations in output voltage due to the fluctuated wind speeds and harmonics generations in the system. To address these issues, this article proposes a new method in order to achieve harmonic mitigation across its output by maintaining constant voltage. Nevertheless, particular attention has been given to the form and function of modular multilevel converter with multi‐winding transformer connected to the grid. Modular multilevel converter has been implemented with an advanced voltage controller tuned to control the voltage at its output. Also, a new system topology has been introduced with two wind turbines that are interconnected to multi‐winding transformer through asynchronous generators. The proposed system has been implemented with constant and variable wind speeds, and their respective results have also been analysed. The proposed scheme shows its effectiveness by theoretical calculations, verified by simulation and experimental results. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessment of flicker limits compliance for wind energy conversion system in the frequency domain

Fixed-speed wind turbines produce voltage flicker during switching operations and they also produce flicker during continuous operation. In order to avoid power quality problems to consumers, it would be important to predict flicker emission from wind turbines at a certain site previously to installation. This paper focuses on a method to perform a fast flicker analysis caused by grid-connected fixed-speed wind turbines in continuous operation. The method has been developed completely in the frequency domain, including wind turbines. This method predicts the P_st value for each node system. Applying this method there would be no need to perform measurements in every node, which would be nearly impossible or to simulate the whole model in the time domain, demanding an enormous computational effort and storage capacity. The performance of the frequency domain method is applied to analyze different wind energy generation scenarios to assess their influence in a real power system.