基于PC测量仪器的风电机组电能质量测试系统

风电机组的电能质量测试不同于传统负荷的电能质量测试,需要排除电网特性和其他负荷的影响,并考虑不同风速对测试结果的影响．目前常规的电能质量测试仪器无法完成测试。风电机组电能质量测试系统选择高性能的PC测量仪器作为硬件采集平台．通过搭建虚拟电网排除电网结构及其他负荷产生的影响,采用适合风电机组的数字化闪变仪算法实现了风电机组的电能质量测试。测试系统通过对典型风电机组实际测试,证明测试系统完全能够满足风电机组电能质量测试标准IEC61400—21的要求。     

双馈风电机组电能质量特性联合仿真建模分析

建立双馈风电机组（DFIG）联合仿真精细化模型——GH Bladed-Matlab模型。在GH Bladed中搭建机组主要机械部件模型,在Matlab中搭建机组的主要电气部件。选取2.2 MW的双馈风电机组搭建模型,根据现场测试数据修正GH Bladed-Matlab模型,使仿真得到的机组闪变外特性、谐波外特性、功率控制外特性与其现场测试波形外特性基本保持一致,确保研究得到的联合仿真模型高精确性。所建立的模型在针对机组电能质量特性因素定性研究的基础上,结合数据进行定量分析,为同系列机组电能质量特性优化提供参考。     

Modeling and analysis of reactive power in grid‐connected onshore and offshore DFIG‐based wind farms

The analysis of reactive power for offshore and onshore wind farms connected to the grid through high‐voltage alternating‐current transmission systems is considered in this paper. The considered wind farm is made up with doubly fed induction generators (DFIGs). Modeling and improved analysis of the effective reactive power capability of DFIGs are provided. Particularly, the optimal power‐tracking constraints and other operational variables are considered in the modeling and analysis of the DFIG reactive power capability. Reactive power requirements for both overhead and cable transmission systems are modeled and compared with each other as well as with the reactive power capability of the wind farms. Possibility of unity power factor operation suggested by the German Electricity Association (VDEW) is investigated for both types of installations. Aggregate reactive power demands on both wind farms are assessed such that the bus voltages remain within an acceptable bandwidth considering various operational limits. The reactive power settings for both types of wind farm installations are determined. In addition, the minimum capacity and reactive power settings for reactive power compensation required for cable‐based installations are determined. Several numerical examples are given to illustrate the reactive power characteristics and capability of DFIGs, performance of transmission lines and reactive power analysis for DFIG‐based grid‐connected wind farms. A summary of the main outcomes of the work presented in this paper is provided in the conclusions section. Copyright © 2012 John Wiley & Sons, Ltd.     

Reactive power management and control of distant large-scale grid-connected offshore wind power farms

Reactive power management and control of distant large-scale offshore wind power farms connected to the grid through high-voltage alternating current (HVAC) transmission cable are presented in this paper. The choice of the transmission option is based on the capacity of the considered wind farm (WF) and the distance to the onshore grid connection point. The WF is made up of identical doubly-fed induction generators (DFIGs). Modelling and improved analysis of the effective reactive power capability of DFIGs as affected by various operational constraints are provided. In addition, modelling and analysis of the reactive power demands, balance, and control are presented. The minimum capacity and reactive power settings for reactive power compensation required for the system are determined. Possibility of unity power factor operation suggested by the German electricity association (VDEW) is investigated. A summary of the main outcomes of the work presented in this paper is provided in the conclusions section.     

Exploitation of wind-energy resources in proximity to weak electric grids

Many sites with favourable wind conditions exist in proximity to relatively weak electric grids. This may imply that the sites only to a limited degree can be exploited for wind farms producing electricity due to technical constraints related to the weak grid. The paper first describes these constraints and secondly a number of ways for connecting more wind power to a weak electric grid are presented. The methods and technologies presented are relevant for all projects involving exploitation of wind energy in proximity to weak electric grids.     

Wind model for low frequency power fluctuations in offshore wind farms

This paper investigates the correlation between the frequency components of the wind speed Power Spectral Density. The results extend an already existing power fluctuation model that can simulate power fluctuations of wind power on areas up to several kilometers and for time scales up to a couple of hours, taking into account the spectral correlation between different wind turbines. The modelling is supported by measurements from two large wind farms, namely Nysted and Horns Rev. Measurements from individual wind turbines and meteorological masts are used. Finally, the models are integrated into an aggregated model which is used for estimating some electrical parameters as power ramps and reserves requirements, showing a quite good agreement between simulations and measurement. The comparison with measurements generally show that the inclusion of the correlation between low frequency components is an improvement, but the effect is relatively small. The effect of including the low frequency components in the model is much more significant. Therefore, that aggregated model is useful in the power system planning and operation, e.g. regarding load following and regulation. Copyright © 2009 John Wiley & Sons, Ltd.     

Interconnector capacity allocation in offshore grids with variable wind generation

Different capacity allocation regimes have a strong impact on the economics of offshore wind farms and on interconnectors in offshore grids. Integrating offshore generation in offshore grids is currently a subject of discussion for different regions, e.g. the North Sea. A novel question is how the interconnector capacity should be allocated for wind generation and for international power trading. The main difficulty arises from the stochastic nature of wind generation: in a case with radial connections to the national coast, the wind park owner has the possibility of aggregating the offshore wind park with onshore installations to reduce balancing demand. This is not necessarily the case if the interconnector capacity is sold through implicit or explicit auctions. Different design options are discussed and quantified for a number of examples based on Danish, Dutch, German and Norwegian power markets. It is concluded that treating offshore generation as a single price zone within the interconnector reduces the wind operator's ability to pool it with other generation. Furthermore, a single offshore price zone between two markets will always receive the lower spot market price of the neighbouring zones, although its generation flows only to the high‐price market. Granting the high‐price market income for wind generation as the opposite design option reduces congestion rents. Otherwise, compensation measures through support schemes or different balancing responsibilities may be discussed. Copyright © 2012 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.     

浅谈变速恒频双馈风力发电机

阐述了双馈风力发电机实现变速恒频的工作原理,讨论了双馈电机的运行状态,推导了双馈电机功率传输方式与转差率的关系,指出了变速恒频风力发电系统的优点是拓宽了风速的可利用范围,对提高风电场发电能力具有重要意义。     

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.     

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.     

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。     

动态无功补偿装置在酒泉地区风电场的优化应用

通过对酒泉地区风电场动态无功补偿装置的测试及参数分析,结合风电大规模脱网事故的电气暂态过程特征,对风电场动态无功补偿装置的应用提出了优化思路。     

中国风电开发消纳及输送相关重大问题研究

分析了中国风电发展现状（风电装机容量快速增长;风电分布较为集中）及存在的问题（系统调峰能力不足;跨大区域互联规模小,不利于风电消纳）,提出了中国风电健康可持续发展的思路（优化电源结构以建设适度规模的调峰电源;建设坚强跨区域互联电网;合理的煤电布局和风火打捆输送：政策支持）和中国未来风电的合理开发规模及相关效益。     

An up to date review of continuously variable speed wind turbines with mechatronic variable transmissions

As a promising and potential alternative to conventional fixed or variable speed wind turbines, continuously variable speed wind turbines (CVSWTs) with variable transmissions offer improved power efficiency and enhanced power control capabilities. The CVSWTs can be generally achieved by adapting mechatronic variable transmissions in the turbine drive train for continuously variable speed operations for wind turbines. Therefore, this paper serves to provide an up to date and exhaustive review of the CVSWTs with mechatronic variable transmissions such as mechanical variable transmission, electrical variable transmission, and power splitting transmission. In this paper, the analysis of CVSWTs with different mechatronic transmission topologies is performed regarding basic configurations, dynamic characteristics, control principles, and experimental or simulation results. Review results indicate the feasibility of applying CVSWTs with such mechatronic transmissions and highlight superiorities of the CVSWTs with power splitting transmission. The CVSWT with power splitting transmission will be particularly suitable for megawatt‐scale turbine systems and will hence increase the economic competitiveness of these turbines due to its large power capacity and high reliability. The directions or challenges for future investigations of CVSWTs with such mechatronic transmissions are also presented to foster in‐depth understanding of such CVSWTs and their control strategies.     

Wind turbine performance decline in Sweden

We show that Swedish wind turbines constructed before 2007 lose 0.15 capacity factor percentage points per year, corresponding to a lifetime energy loss of 6%. A gradual increase of downtime accounts for around one third of the deterioration and worsened efficiency for the remaining. Although the performance loss in Sweden is considerably smaller than previously reported in the UK, it is statistically significant and calls for a revision of the industry practice for wind energy calculations. The study is based on two partly overlapping datasets, comprising 1,100 monthly and 1,300 hourly time series spanning 5–25 years each.     

Impact of Wind Power on the ATC Values in Hydro-Dominated Power System

The wind power generation is increasing in many countries as a result of decreasing technology costs, active government policies for renewable energy sources, environmental concerns, etc.. This paper investigates the impact of wind power generation on ATC （available transmission capacity） calculation. In order to determine the maximum incremental MW transfer possible between two parts of a power system without violating any specified limits, ATCs are calculated. When calculating ATC values, it is necessary to assume production and consumption pattern in power system. Production of wind power depends on the wind speed, which is a random variable and it is impossible to forecast exactly the production of wind power that is needed for the ATCs calculation. In order to investigate influence of the stochastic wind power production on the ATCs value, computer model of Croatian electric power system is made in Power World Simulator. ATCs are calculated for southern part of Croatian power system in which besides wind power, hydro power plants are only type of power generation. Available wind speed measurements are used as input data for wind power production. The results of the ATC calculation for different scenario of wind power production and location in the Southern Croatian power system are presented and discussed in the paper.     

Analysis of Short Circuit Faults in a System Fed by Wind Turbine

Short circuit and ground failures that are quite common in power transmission lines are investigated. These failures are designed considering a system that is supplied by this wind system, and analyses are interpreted. In the study, a system is set up and it is fed by the wind turbine. Furthermore, the mathematical model of wind turbine and generator is prepared and the results obtained from the simulation are evaluated. The short circuit and ground fault analyzes were performed separately for each of the three phases. ATP （alternative transient program）-EMTP （electromagnetic transients program） program is used in the analysis and the results obtained were found to be quite compatible.     

考虑抑制连锁脱网的风电汇集区域多无功源协调控制策略

风电汇集区域无功支撑能力较弱,电压问题日益突出,若配置的STATCOM动态无功储备不足,不能快速响应电压变化,易导致风电场发生连锁脱网事故。为此,基于风电汇集区域的电压状态,提出3种状态下不同无功源的协调控制策略,即正常状态下利用静态无功装置置换出动态无功装置的无功功率,提高动态无功储备、警戒状态下调整风电出力校正电压越限情况、紧急状态下利用STATCOM快速提供无功电压支撑。某实际风电汇集区域电网的仿真结果表明,该策略能够提高动态无功储备,有效抑制风电场连锁脱网。