An integrated approach for optimal coordination of wind power and hydro pumping storage

The increasing wind power penetration in power systems represents a techno‐economic challenge for power producers and system operators. Because of the variability and uncertainty of wind power, system operators require new solutions to increase the controllability of wind farm output. On the other hand, producers that include wind farms in their portfolio need to find new ways to boost their profits in electricity markets. This can be done by optimizing the combination of wind farms and storage so as to make larger profits when selling power (trading) and reduce penalties from imbalances in the operation. The present work describes a new integrated approach for analysing wind‐storage solutions that make use of probabilistic forecasts and optimization techniques to aid decision making on operating such systems. The approach includes a set of three complementary functions suitable for use in current systems. A real‐life system is studied, comprising two wind farms and a large hydro station with pumping capacity. Economic profits and better operational features can be obtained from the proposed cooperation between the wind farms and storage. The revenues are function of the type of hydro storage used and the market characteristics, and several options are compared in this study. The results show that the use of a storage device can lead to a significant increase in revenue, up to 11% (2010 data, Iberian market). Also, the coordinated action improves the operational features of the integrated system. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimal integration of wind farms to isolated wind-Diesel energy system

Wind farms installed on isolated systems are subject to significant restrictions, affecting their expected energy yield and, hence, the feasibility of investments. As wind power penetrations increase in isolated power systems, it is very important to understand how variations in wind plant outputs affect the operation of the isolated system on a day to day basis and what the associated added costs are. In this paper, a wind-Diesel coordination generation scheduling (WCGS) software is developed for appropriate assessment of the added cost to cover the unpredictable wind generator output variations. The developed WCGS software is also a useful tool for the system planner to predict the energy cost and the fuel saving from the expected new wind-Diesel systems. Several technique constraints are applied to determine the optimal proportion of wind generator capacity that can be integrated into the existing system. A simple benefit cost ratio (BCR) is used in this study to evaluate the investment effectiveness of the installation of wind farms for an isolated hybrid system. Numerical experiments are included to understand the wind generator output variations in system operating cost analysis and to assess the impact and economic benefits of the installation of wind farms.     

西北电网风电调度运行管理研究

介绍了西北电网的风电场现状、规划容量及接入情况．阐述了大规模风电场接入对西北电网调频、调峰、稳定性及无功调节等各方面安全运行带来的影响,分析研究了大量风电场集中投运对发电计划编制、调度运行控制、电力市场交易模式、并网运行管理所提出的新要求,最后提出了加快750骨干网架建设、提高对风电的监控能力及调度技术支撑手段、探索电量交易模式及消纳机制、加强风电并网运行管理等解决方案和应对策略,确保西北风电与电网实现协调、有序的发展。     

理论发电量完成率在海上风电场评价中的应用

针对中国目前海上风电场起步较晚,技术不够完善,行业内对于海上风电场建设、机组选型和运营维护缺乏足够经验的特点,为完善海上风电场效能评价体系,提出理论发电量完成率的概念和相应的计算方法;同时,将理论发电量完成率这一指标代入实际案例进行计算分析。结果表明,理论发电量完成率能较好地反映风电机组和风电场的运行状态,能够将风资源状况和风电机组运行状态按照时间序列有机结合起来,是一个可操作性强且具有实际参考价值的指标,对海上风电场的评价和运行管理水平的提升有较好的指导意义。     

Development strategies for wind power industry in Jiangsu Province,China: Based on the evaluation of resource capacity

Jiangsu Province is one of the planned strategic areas for wind power development in China, but its current development of wind power industry is not so outstanding. Since, Jiangsu would encounter little market resistance, this paper focuses on the evaluation of resource capacity for wind power development in Jiangsu Province, including the wind energy capacity, land resources capacity and power grid capacity, in order to find their supportive or restrictive effects on the development of wind power industry. The results show that the wind energy resource in Jiangsu Province are sufficient to meet the needs of the development of wind farms; the extensive mudflat in the coastal areas also provides ideal site conditions for wind farms; but the power grid capacity is insufficient for the wind power development in Jiangsu. Therefore, from the aspect of enhancing the capacity of power grid for carrying wind power and from the other aspect of combining the non-grid-connected utilization and the large-scale storage of wind power, this paper suggests some strategies to overcome the constraints of grid capacity and promoting the wind power development in Jiangsu Province.     

Difference between grid connections of large-scale wind power and conventional synchronous generation

In China, regions with abundant wind energy resources are generally located at the end of power grids. The power grid architecture in these regions is typically not sufficiently strong, and the energy structure is relatively simple. Thus, connecting large-capacity wind power units complicates the peak load regulation and stable operation of the power grids in these regions. Most wind turbines use power electronic converter technology, which affects the safety and stability of the power grid differently compared with conventional synchronous generators. Furthermore, fluctuations in wind power cause fluctuations in the output of wind farms, making it difficult to create and implement suitable power generation plans for wind farms. The generation technology and grid connection scheme for wind power and conventional thermal power generation differ considerably. Moreover, the active and reactive power control abilities of wind turbines are weaker than those of thermal power units, necessitating additional equipment to control wind turbines. Hence, to address the aforementioned issues with large-scale wind power generation, this study analyzes the differences between the grid connection and collection strategies for wind power bases and thermal power plants. Based on this analysis, the differences in the power control modes of wind power and thermal power are further investigated. Finally, the stability of different control modes is analyzed through simulation. The findings can be beneficial for the planning and development of large-scale wind power generation farms.     

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.     

Hydrogen production from idle generation capacity of wind turbines

This paper is concerned with the hydrogen production from wind energy. It is motivated by the new regulations for wind farms that compel them to operate normally with idle generation capacity. The idea is to use the excess wind power to produce hydrogen. The operation of a proposed system configuration, which essentially consists in incorporating an electrolyzer between the electronic converters of a conventional wind turbine, is analyzed. In particular, the control requirements to simultaneously achieve the grid and electrolyzer specifications are investigated. In this context, a control strategy for the different operating modes of the system is developed.     

风电场风功率实时预测效果综合评价方法

超短期风电功率预测对含大规模风电的电力系统安全经济运行有着重要意义。但目前对预测结果的评价均停留在常规统计学指标上,缺乏合理的评价体系来评价某特定风电场所选取预测模型的优劣。简述了目前风电功率预测结果评价指标的不足,提出一种基于预测误差评价和预报考核等指标的风电场输出功率实时预测效果评估方法,为不同地区风电场根据其风电输出功率变化的特点,选择预测模型以及风电场输出功率预测效果的工程检验提供依据。最后,利用吉林省某风电场实测数据,采用该评估方法对不同预测模型的实时预测结果进行分析评价,实现了该风电场不同预测模型间的择优,验证了该评价方法的指导价值。     

风电场调度自动化系统的设计与应用

本文结合风电场及风电机组自身所具备的调节能力和运行特点,论述风电场调度自动化系统的设计思路,引入AVC(自动电压控制系统)、有功功率控制系统、风电功率预测系统及其他风力监测和报警等辅助系统,建立风电场与电网系统良好的调度方式,从而使风电场切实参与到电网调度和系统安全稳定的维护中。     

Reactive power control of wind farms for voltage control applications

In the last few years, there is a strong trend towards decentralised production and supply, leading to a situation where a growing number of small and medium size producers will be connected to energy networks. But at the same time, the power quality of the generation must be ensured and this means that the electrical parameters of the distribution network have to be maintained within their upper and lower limits. Therefore, new problems related to the management and operation of energy transfer and distribution and to the efficient distribution of renewable energy in the grids are actually arising. Hence, it is reasonable to think that dispersed generation (wind energy generation in this paper) should start to take part in the control of electric variables, and in particular, in reactive power control which is directly related to the voltage level control of distribution networks. This paper presents a control strategy developed for the reactive power regulation of wind farms made up with double fed induction generators, in order to contribute to the voltage regulation of the electrical grid to which farms are connected.     

考虑大规模风电接入的电力规划研究

由于风电出力的不确定性、反调峰性和风电场选址的限制等问题,大规模风电并网后要求电力系统留有更多的备用电源和调峰电源,且电网结构薄弱远距离输送能力有限,使得多数风电场出力无法被消纳,对系统的稳定运行、电源规划和电网规划等方面造成了很大的负面影响,阻碍了风电的规模化应用。分析了大规模风电接入对系统可靠性、系统备用以及运营成本等带来的挑战,从电力规划角度回顾和评述了国内外风电接入系统在电源规划、电网规划以及电源电网协调规划等领域的研究进展和研究现状,明确了该领域的研究重点和研究方向。     

Energy balance analysis of wind-based pumped hydro storage systems in remote island electrical networks

The introduction of pumped hydro storage (PHS) systems in isolated electrical grids, such as those found in island regions, appears to be a promising solution that is able to face both the high electricity production cost and the continuously increasing power demand encountered in these areas. In this context, the current work presents a methodology for the sizing of PHS systems that exploit the excess wind energy amounts produced by local wind farms, otherwise rejected due to imposed electrical grid limitations. The methodology is accordingly applied to the Greek island of Lesbos. Initially, a calculation of the wind power penetration ability to the local grid is carried out and the corresponding curtailments of existing and future wind farms are determined. An integrated computational algorithm is then presented which simulates the operation of the system during an entire year and gives in detail the hourly operational status as well as the various energy losses of the system main components. Based on the application results obtained, the ability of the wind energy to remarkably contribute to the electrification of the remote islands becomes evident.     

Impact of wind farms on a power system. An eigenvalue analysis approach

This paper analyzes the frequency dynamic behavior in a power system with a high wind power penetration. To this end, wind farms equipped with squirrel cage and doubly fed induction generators are compared. Aspects of the modeling of the different kinds of wind generation and power systems are cited. Then, it is shown, through an eigenvalue analysis, that wind farms equipped by doubly fed induction machines, adequately controlled, can contribute to improve the frequency dynamics. Simulations are presented which verify the theoretical results.     

Using nacelle‐based wind speed observations to improve power curve modeling for wind power forecasting

Wind power forecasting for projection times of 0–48 h can have a particular value in facilitating the integration of wind power into power systems. Accurate observations of the wind speed received by wind turbines are important inputs for some of the most useful methods for making such forecasts. In particular, they are used to derive power curves relating wind speeds to wind power production. By using power curve modeling, this paper compares two types of wind speed observations typically available at wind farms: the wind speed and wind direction measurements at the nacelles of the wind turbines and those at one or more on‐site meteorological masts (met masts). For the three Australian wind farms studied in this project, the results favor the nacelle‐based observations despite the inherent interference from the nacelle and the blades and despite calibration corrections to the met mast observations. This trend was found to be stronger for wind farm sites with more complex terrain. In addition, a numerical weather prediction (NWP) system was used to show that, for the wind farms studied, smaller single time‐series forecast errors can be achieved with the average wind speed from the nacelle‐based observations. This suggests that the nacelle‐average observations are more representative of the wind behavior predicted by an NWP system than the met mast observations. Also, when using an NWP system to predict wind farm power production, it suggests the use of a wind farm power curve based on nacelle‐average observations instead of met mast observations. Further, it suggests that historical and real‐time nacelle‐average observations should be calculated for large wind farms and used in wind power forecasting. Copyright © 2011 John Wiley & Sons, Ltd.     

基于电池储能系统和双重扩展卡尔曼滤波的风能发电智能调度技术研究

风能等新能源发电系统在供电体系中的占比越来越大,但其随机性和波动性问题,将风力发电厂输出的电力直接向电网调度会造成安全隐患。为了解决这一问题,基于电池储能系统提出了一种风能发电智能调度技术,该技术以风力发电动力学模型和电池储能系统状态模型为基础,利用双重扩展卡尔曼滤波算法实现了风能发电系统的稳定输出。以某地风速实测数据和电网需求功率为参考,对不同算法的输出功率预测值进行了仿真分析和实验对比。结果表明：提出的改进算法预测的风速值误差相比于传感器观测值平均误差降低了28%以上,可以更准确地提供发电系统输出功率;提出的智能调度技术可以使电压波动幅度降低60%以上,系统整体输出功率稳定在参考功率附近,误差不超过2%,有一定的实用意义。     

风电场接入电力系统最佳接入点选择

分析了风力发电的特性,建立了基于双馈感应风力发电机(Doubly-Fed Induction Generator,DFIG)的风力发电系统的动态数学模型。利用MATLAB/Simulink仿真软件,对风电场接入典型电力系统的接入点选择进行了仿真。仿真结果表明,通过合理选择风电场的接入点,可以减小风电场对电力系统的影响。     

Impact of wind power in autonomous power systems—power fluctuations—modelling and control issues

This paper describes a detailed modelling approach to study the impact of wind power fluctuations on the frequency control in a non‐interconnected system with large‐scale wind power. The approach includes models for wind speed fluctuations, wind farm technologies, conventional generation technologies, power system protection and load. Analytical models for wind farms with three different wind turbine technologies, namely Doubly Fed Induction Generator, Permanent Magnet Synchronous Generator and Active Stall Induction Generator‐based wind turbines, are included. Likewise, analytical models for diesel and steam generation plants are applied. The power grid, including speed governors, automatic voltage regulators, protection system and loads is modelled in the same platform. Results for different load and wind profile cases are being presented for the case study of the island Rhodes, in Greece. The scenarios studied correspond to reference year of study 2012. The effect of wind fluctuations in the system frequency is studied for the different load cases, and comments on the penetration limits are being made based on the results. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparative study on the performance of control systems for doubly fed induction generator (DFIG) wind turbines operating with power regulation

As a result of the increasing wind power penetration on power systems, the wind farms are today required to participate actively in grid operation by an appropriate generation control. This paper presents a comparative study on the performance of three control strategies for DFIG wind turbines. The study focuses on the regulation of the active and reactive power to a set point ordered by the wind farm control system. Two of them (control systems 1 and 2) are based on existing strategies, whereas the third control system (control system 3) presents a novel control strategy, which is actually a variation of the control system 2. The control strategies are evaluated through simulations of DFIG wind turbines, under normal operating conditions, integrated in a wind farm with centralized control system controlling the wind farm generation at the connection point and computing the power reference for each wind turbine according to a proportional distribution of the available power. The three control systems present similar performance when they operate with power optimization and power limitation strategies. However, the control system 3 with down power regulation presents a better response with respect to the reactive power production, achieving a higher available reactive power as compared with the other two. This is a very important aspect to maintain an appropriate voltage control at the wind farm bus.