Experimental study of a doubly‐fed rotary frequency converter

Wind power generation using an unlimited, natural energy has been getting attention regarding environmental issues in recent years, and the installed capacity of wind power generation system is increasing at a rapid pace, resulting in deterioration of power quality especially in frequency and voltage. This fact will be a big problem in restricting large capacity of wind farms. This paper proposes a new frequency converter: rotary frequency converter (RFC) to moderate the electric output from wind generation, which is to be installed between a set of wind generators and a grid, providing a smoothed electric output, promoting the wind power generation introduction. This mainly consists of a synchronous machine and the adjustable‐speed machine. Independent controls of input/output voltage, active power, and reactive power offer electrical separation between the two networks. Experimental study of a prototype model and its characteristics, especially dynamic control, is discussed in this paper. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 26–34, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20922     

Study on output prediction system of wind power generation using complex‐valued neural network with multipoint GPV data

In recent years, wind power generation has seen rapid growth as a solution to the depletion of fossil fuels and to global warming. However, the output of the wind power generator fluctuates widely depending on the wind speed, which affects the power grid. In this paper, we propose a prediction system of wind power generation ahead of 24 h by using a complex‐valued neural network (CVNN). To predict the output of wind power generation, it is necessary to predict the wind speed accurately. Generally, wind data is expressed as a vector, which has both magnitude and direction. Therefore, it is also possible to treat wind data by a complex number and then use it as input information of the CVNN, which is very useful for operation of a complex number and nonlinear data. In computer simulations, we use multipoint numerical weather prediction data that surround the wind prediction point to realize long‐time prediction. Thereby, we expect that the CVNN can take into account wind dynamics in two‐dimensional space. Several simulation results and t‐tests demonstrate the effectiveness of the proposed prediction system. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Study of Low‐Voltage Ride‐Through Performance for Wind Power Generation with Doubly Fed Induction Generator

The introduction of wind power generation is increasing rapidly. The ratio of wind power generation to the total generation capacity is becoming higher and higher. When a phase‐to‐phase fault occurs in the power system, the frequency of the power system is lower due to disconnection of wind power generation with doubly fed induction generators (DFIG). Therefore, the power system might become unstable. This paper describes an LVRT (low‐voltage ride‐through) performance improvement scheme for wind power generation with DFIG. The wind power generator is disconnected from the grid in case of a power system fault. It is made to operate in isolation from the grid by controlling the inverters installed with the generators. After clearance of the power system fault, wind power generation is immediately reconnected to the grid. As a result, instability in the power system disappears. The performance of LVRT is confirmed by using the simulation software PSCAD/EMTDC. The simulation results show excellent results for the three‐phase short‐circuit fault with a voltage dip of 100%. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(1): 17–26, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22423     

Dynamic behavior of an island power system with variable‐pitch wind turbines under high renewable energy penetration and high wind speed

High penetration of renewable energy in a power system may cause the problem of power dispatching and stability. The detailed dynamic behavior analysis for such a system is therefore important to the planning and operation of the power system. This study discussed the dynamic characteristics of an island power system with variable‐pitch wind turbines under high wind speed and high small hydraulic output power. The system primarily consisted of three diesel engine power generation systems, three constant‐speed variable‐pitch wind turbines, a small hydraulic induction generation system, and lumped static loads. The maximum penetration of renewable energy in this system could reach almost 60%. Detailed models based on MATLAB/Simulink were developed to cater for the dynamic behavior of the system. The results suggested that this island power system can operate stably in this operational mode with the help of variable‐pitch wind turbines. This study can serve as an important reference for planning, operation, and further expansion of island power systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Reduction of power fluctuation by distributed generation in micro grid

Renewable forms of energy such as wind power or photovoltaic energy are environmentally focused, but the fluctuation of the output power of such renewable forms of energy may cause excessive variation of the voltage or frequency of the grid. Increasing the amount of renewable energy would degrade the quality of the grid. Micro grids, in which dispersed power sources compensate variations in the generation of renewable energy, can expand the limits of installation of renewable forms of energy by maintaining the quality of the interconnected grid. This paper discusses the use of gas turbines to absorb power variations from wind generation and the loads. In order to control the output power, gas turbines must run under partial load, which results in lower efficiency. An evaluation of the micro grids is made with consideration of their efficiency, the installed capacity of wind power generation systems, and frequency stability for islanded operation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 22–29, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20462     

A control method for small‐scale DC power systems including distributed generators

This paper describes a DC micro‐grid system interconnecting distributed power generators. The system consists of five generation and control units: a solar‐cell generation unit, a wind‐turbine generation unit, a battery energy‐storage unit, a flywheel power‐leveling unit, and an AC grid‐interconnecting power control unit. The control method is proposed for suppressing the circulating current by detecting only the DC grid voltage. This method brings high reliability, high flexibility, and maintenance‐free operation to the system. The method pays attention to DC output voltage performance of each unit. Each of the power control units and the energy‐storage unit is controlled to act as a voltage source with imaginary impedance. On the other hand, each of the two generation units is controlled to act as a current source. The power‐leveling unit is controlled to act as a current source having the function of frequency selectivity like a high‐pass filter. A 10‐kW prototype system verifies experimentally the validity and effectiveness of the proposed control method for the DC‐grid system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 86–93, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20603     

大规模风电并网对电力系统的影响

由于风能具有随机性、间歇性、不稳定性的特点,当风电装机容量占总电网容量的比例较大时会对电网的稳定和安全运行带来冲击。针对这一问题,阐述了大规模风电并网后对电力系统稳定性、电能质量、电网频率、发电计划与调度、系统备用容量等方面的影响,并提出改善风电并网影响的措施。     

Power smoothing and MPPT for grid‐connected wind power generation with doubly fed induction generator

Recently, doubly fed induction generators (DFIG) and synchronous generators have been applied mostly to wind power generation, and variable speed control and power factor control have been implemented for high efficiency of wind energy capture and for high quality of power system voltage. In variable speed control, the wind speed or generator speed is used for maximum power point tracking. However, the properties of wind generation power fluctuations due to wind speed variation have not yet been investigated for those forms of control. The authors discuss power smoothing by these forms of control for DFIG interconnected to a 6.6‐kV distribution line. The performance is verified by means of the power PSCAD/EMTDC system simulation software for actual wind speed data and is investigated by using an approximate equation for wind generation power fluctuations as a result of wind speed variation. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(2): 10–18, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.20958     

大规模风电并网系统控制问题综述

随着国家能源结构的调整,风电并网系统的规模迅速扩大,大规模风电并网对电网安全稳定运行会带来很大冲击。介绍了中国风电发展的整体概况,分析了风电并网对电力系统运行的影响因素,综述了风电并网系统控制技术的研究现状与发展方向。     

带储能的双馈风力发电系统控制策略

提出了一种将储能装置接入传统双馈风力发电系统背靠背变换器直流侧的新型双馈风力发电系统,通过对已有的背靠背变换器实施功率控制策略,可以有效地抑制风速随机化引起的风力发电系统并网点输出功率的波动。在分析系统构成及功能的基础上,提出了背靠背变换器相应的功率控制策略,并根据所建立的新型双馈风力发电系统的控制模型,在EMTDC/PSCAD仿真环境以及3kW双馈风力发电系统实验平台下进行了详细的研究和分析。研究结果表明,在风速波动的情况下该系统能够按照优化控制策略得到平滑的功率输出,实现风速的去随机化过程。     

基于D5000系统的风电优先调度工作方案设计与应用

近年来由于风电迅猛发展,大幅度超前电网建设和社会用电负荷增长,受网架约束和电网调峰问题影响,风电出力受阻的情况时有发生,风电消纳已成为困扰电网和风电场的共同问题。依据《风电优先调度工作规范》,基于智能调度技术支持系统建设,设计新疆电网风电优先调度工作方案,有利于在保证电网安全稳定运行的前提下,实现新能源消纳最大化的目标。     

同一控制区两级调度风电实时协调控制策略

新能源场站普遍存在点多面广、单场容量相对较小的特点,因此部分电网虽按同一控制区运行,但选择将新能源场站控制权下放,形成风电资源两级控制现状。为协调常规能源与风电运行,最大程度消纳风电,通过将下级调度风电整体等效为上级调度的自动发电控制(AGC)虚拟机组,提出同一控制区两级调度风电实时协调控制架构,并投入实际运行。上级调度根据电网当前运行状态、负荷超短期预测和风电实际出力及预测,每5min滚动计算得到电网内各个下级调度的风电发电指标,经余缺调剂后,下发给下级调度风电AGC执行。在大风季、供暖期的运行结果表明,采用所述的两级调度实时协调控制方案后,达到了京津唐地区风电增发的效果。     

Proposal and development of radial air‐gap coreless generator suitable for small wind turbine used in urban area

Independent distributed power generation using small wind turbines is becoming more widespread as wind power generation increases. Installation of small wind turbines in densely populated urban areas is not only useful from the viewpoint of extracting wind power sources in weak‐wind areas but also for making renewable energy easier to access when power supplies are closer to consumers. It is from this point of view that the authors proposed “urban wind power generation” using a collective system with a number of small vertical wind turbines, and have developed a suitable generator for low‐speed vertical wind turbines such as a Savonius windmill. Based on a standard coreless generator, the proposed generator is designed to make the direction of the magnetic flux radial in order to install the magnets and coils on the outer end of the generator. The change of magnet composition and flux direction maximizes the speed of the flux change and output voltage within a limited space. With the above configuration, the power of the proposed generator is independent of the diameter. In this report, the authors describe and evaluate the fundamental performance of a prototype of the proposed generator. Based on the experiments, a maximum output power of 283 W was obtained. The obtained starting torque is small enough to begin rotation under weak wind conditions of no more than 1 m/s. Therefore, it is clear that the proposed “radial” coreless generator is suitable for self‐starting and producing high power at low wind speed. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 26– 34, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20695     

3D FEM analysis,dynamic modeling,and performance assessment of transverse flux PMSG for small‐scale gearless wind energy conversion systems

The transverse flux permanent magnet synchronous generator has a great potential for use in direct‐drive wind energy conversion systems due to its large pole numbers, high torque, and power density. This research work develops dynamic model of a single‐side transverse flux permanent magnet synchronous generator for use in a small‐scale gearless wind energy conversion system. For acquiring the parameters of the considered generator, required for dynamic modeling, 3D finite element model of the machine is developed and analyzed in both magneto‐static and transient modes. Field‐oriented control approach is employed for tracking maximum power point from the variable wind speed. The simulation results illustrate an accurate response of the system to the wind speed variation and proper performance of the developed dynamic model and control approach of the system. Copyright © 2015 John Wiley & Sons, Ltd.     

Study on the ramp fluctuation suppression control of wind power generation output using optimization method

Recently, wind power generation are installed as a countermeasure for the environmental issue in Japan. However, wind power generation output is fluctuated due to wind condition. Moreover, it is some negative impact for system operation such as the economic load dispatching control and the load frequency control. In Japan, NEDO has started the project as a countermeasure for massive penetration of wind power generation in 2014, called “R&D Project on Grid Integration of Variable Renewable Energy.” In this paper, we proposed the output fluctuation suppression control method of wind power generation using the battery and forecast data of wind generation output. Specifically, the target value of wind power generation output is calculated to decrease the deviation output from fluctuation suppression code for ramp event using deterministic optimization method. The effectiveness of proposed method is evaluated through the computational simulation using forecast data and actual wind power generation output in Tohoku area.     

风力发电运行价值分析

不对风电并网产生的影响作深入的分析,就不能确定风力发电的实际效益。风力发电价值的计算需要综合考虑发电收益、发电成本、辅助服务成本、环保效益等各方面因素。文章采用可靠性评估的方法,分析了风电并网引起的电力系统辅助服务成本的变化,在此基础上,给出了风电运行价值的详细表达式,并讨论了风电穿透功率、风能预测误差、备用容量价格、风电场容量系数等因素对风电运行价值的影响。     

Compensation for harmonic currents and reactive power in wind power generation system using PWM inverter

In recent years, awareness of environmental problems is growing, and the price of electric power purchased by electric companies has been expensive for power plants utilizing natural energy. Thus, the introduction of wind power generation is being promoted in Japan. Generally, squirrel‐cage induction machines are widely used as generators in wind power generation systems because of their small size, light weight, and low cost. However, the induction machines do not have a source of excitation. Thus, inrush currents and instantaneous voltage drops occur when the generator is directly connected to a power grid. To reduce the inrush currents, an AC power regulator is used. Wind power generators are frequently connected to and disconnected from the power grid. However, when the inrush currents are reduced, harmonic currents are caused by phase control of the AC power regulator. And the phase control of the AC power regulator cannot control the power factor. Therefore, we propose the use of the AC power regulator to compensate for the harmonic currents and reactive power in a wind power generation system, and demonstrate the validity of this system by simulated and experimental results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(2): 58–67, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20254     

风电对电力系统运行的价值分析

从电力系统运行的角度，提出了基于随机模拟技术的定量分析计算风力发电对电力系统运行的价值的方法。定性地描述了风电并网引起的电力系统运行方式的变化和由此带来的发电变动情况。根据常规火电机组的边际发电成本曲线，分析了风电价值的构成。指出了风电价值与风电场所在地风资源特性、风电机组技术参数、风电负荷在电力系统负荷中所占比例以及配合风电运行的火电机组的耗量特性有关，给出院计算风电价值和灵敏度分析的数值实例。文中的概念性分析方法也适用于复杂电力系统。     

短期风电功率预测概念和模型与方法

随着并网风电容量的持续增加,风电强随机性给电力系统安全稳定运行带来了挑战,风电功率预测受到广泛的关注。文中较为全面地综述了国内外对风电功率预测的研究现状,着重从风电预测基本理论、风电预测方法和风电预测热点研究问题3个方面展开,主要介绍了确定性风电预测、概率性风电预测、风电爬坡事件预测、大数据和深度学习方法等方面的研究进展。     

含储能虚拟电厂接入配电网的联合优化调度

为解决不确定性能源发电给配电网带来的隐患和经济性问题,研究含间歇分布式能源的虚拟电厂(virtual pow er plant,VPP)接入配电网的联合优化调度对提高系统安全和促进新能源消纳具有十分重要的意义。综合考虑风电及储能的运行特性,提出一种改进的Buckets方法,建立了考虑风电不确定性和含储能的虚拟电厂参与配电网调度的优化机组组合模型,基于6节点系统研究了改进的Buckets方法对发电成本和机组组合的影响。与传统Buckets方法相比,采用所提方法使得模型的发电成本及开机时段减少,表明该方法能够实现发电成本最优、风电的充分消纳以及储能的灵活运用。