双馈风力发电机组系统接入与稳定运行仿真

分析了包含大量异步风力发电机组的风电场并网运行后对电力系统静态和动态稳定性的影响。从系统接入和稳定运行的角度研究了双馈风力发电机组及普遍采用的定子磁链定向矢量控制策略在提高风电系统稳定性方面的优势与不足。以实际机组为例在PSCAD/EMTDC平台上建立了仿真模型,结果表明双馈风力发电机组在风速发生变化时不仅能够以变速恒频方式运行并追踪最大风能,且电网电压也比传统鼠笼式风力发电机组更为稳定。在系统发生最严重的三相接地故障时,风电场具有更好的暂态稳定性。     

Development of trouble diagnosis technology of 50‐W‐grade micro wind turbine generator

The establishment of an early trouble diagnosis system is needed in order to prevent damage to wind turbine generators. Therefore, acoustic emission (AE) signals resulting from damage to a wind blade were detected with an AE sensor installed on the body of the wind turbine generator and on the mounting pole. In this study, the length of a blade of a micro wind turbine generator was varied to simulate trouble at constant wind velocity. The AE signals which occurred at this time were measured with an AE sensor. The signal was processed by FFT analysis, and the change of spectral strength was examined. A trouble diagnosis technology for 50‐W‐grade micro wind turbines generator was then developed. A method of counting the number of occurrences of above‐threshold AE signals was suggested by the wave pattern of the AE signals. It was found that the number of occurrences could be used as a standard to judge the normality or abnormality of 50‐W‐grade micro wind turbine generators. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 33–39, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21017     

A novel method to improve low‐voltage ride‐through capability of wind turbine generators

With increasing penetration of wind farms, power grids have responded by developing specific grid codes to maintain their stability. One of the main grid codes is the low‐voltage ride‐through (LVRT) capability, which requires the wind generator to remain connected when the grid voltage sags for a certain time period. A wind farm with squirrel cage induction generators suffers this LVRT problem the most because of their direct connection to the grid and reactive power consumption. In this paper, a new method is proposed to solve this problem by shunt‐connecting a motor‐driven mechanical load to the cage wind generator. For driving mechanical loads, the induction motor is most widely used in industries. This paper studies the terminal voltage holding effect of an induction machine during grid voltage sag due to the magnetic flux holding effect and the saturation characteristic. Taking advantage of this effect, the induction motor that is used for driving mechanical load is then proposed to improve the LVRT capability of wind turbine generators. Furthermore, the change of the rotating speed or slip of the induction machine is found to have a great impact on improving the LVRT. By adding some inertia to the motor‐driven mechanical load, an enhanced voltage holding effect, and therefore LVRT improvement, is expected for the wind farm. Both simulation and experimental results prove the effectiveness of the proposed method. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Transient stability simulation of wind generator expressed by two‐mass model

Recently, wind power generation is increasing worldwide. In wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as a one‐mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two‐mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 27–37, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20394     

Pitch control based on voltage dip detection for improving the LVRT of wind farm

For the stability of power systems including large‐scale generation of wind power, wind farms are expected to fulfill the requirement with the capability to remain connected to the systems during a momentary voltage dip occurring in power networks. This has prompted many utilities to adopt the low‐voltage ride‐through (LVRT) of wind turbine generators (WTGs) as one of the requirements in interconnection of large wind farms. This paper presents a new method of pitch angle control for fixed‐speed wind turbine (FSWT) to achieve LVRT capability improvement. The FSWT is equipped with directly grid‐coupled squirrel‐cage induction generator and the LVRT behavior of such wind turbine is closely related to the overspeeding of wind turbine rotor during voltage dip. If the turbine rotor speed can be reduced quickly during voltage dip so as not to rise over the maximum speed, then the sudden disconnection of WTG can be avoided. The proposed pitch control system can modify the pitch angle in the short response time by the coordination of protective relay. Then the pitch angle is adjusted by a feedback proportional integral controller based on the measurement of induction generator terminal voltage. Simulation study shows that the application of the proposed pitch control system can improve the LVRT performance of a wind farm equipped with FSWTs. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A study of AC link and DC link method for wind power generation connected to electric power system

In this paper, grid‐connection of wind power generators was evaluated from the viewpoint of frequency fluctuation. Wind power generation is a power generation method that depends on natural energy, and there is some concern that it may exert a negative influence on electric power quality. As a result, it is necessary to maintain high electric power quality when wind power generation is connected to the grid. The AC link method, the AC‐DC link method, and the DC link method are alternatives for grid connection of wind power generators. The model system was constructed with the use of a synchronous generator and an induction generator as wind power generator, and verification experiments were performed. Verification experiments using the various grid‐connection methods for each generator were conducted. The steadiest frequency characteristic was obtained in the DC link method. In particular, the stability level was highest in the wind power generation system using the DC link method with a wound‐rotor induction generator. Generally, induction generators are grid‐connected by the AC link method. Therefore, grid‐connection of induction generators by the DC link method appears effective from the viewpoint of frequency fluctuation. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(3): 21–30, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21196     

直驱风电机组次同步振荡阻尼控制方法及其适应性

由风电波动引发的次同步振荡具有振荡频率多变、涉及动态装置多、影响因素复杂等特点,现有的阻尼控制类装置难以实现有效抑制,需研究适用的附加阻尼控制方法。文中通过线性化方法推导了直驱风电机组并网系统的特征方程和传递函数,并获取了风电机组并网系统在不同工况下的频率响应特性。然后提出了基于奈奎斯特稳定判据的风电机组次同步振荡阻尼控制器的参数设计方法,以及基于粒子群优化算法的参数优化方法;结合特征值法及时域仿真法,分析了阻尼控制器对于次同步振荡的抑制作用。研究结果表明,依据前述方法设计的阻尼控制器在多种运行条件下均具有较好的适应性。     

A calculation method of the total efficiency of wind generators

The spread of wind energy converters is progressing in recent years and its capacity is becoming larger and larger. In order to capture more energy from the wind, it is important to analyze loss characteristics of wind generators for the operating speed which is determined dependent on the wind speed. This paper presents a method to evaluate various losses in a wind generator as a function of wind speed, which is based on steady‐state analysis and thus the calculations can be performed quickly. By using the proposed method, wind turbine power, generator output, various losses, and the total energy efficiency are calculated for three types of wind speed data which are represented by a Weibull function. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 52–62, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20426 Copyright © 2006 Wiley Periodicals, Inc.     

并网型双馈电机风力发电系统建模与仿真

双馈电机已成为变速恒频风力发电系统的主流电机.文中介绍了交流励磁变速恒频双馈电机运行的基本原理,推导了风力机模型和交流励磁双馈电机动态数学模型.交流励磁变速恒频双馈电机风力发电系统空载运行和发电运行由于涉及并网时刻状态转移导致建模复杂,故提出用S函数描述双馈电机的数学模型,结合MATLAB中Simulink环境建立完备的系统仿真模型.由仿真结果可看出,所提系统实现了最大风能追踪控制,且动态响应快,双馈电机可运行于不同转差频率下亚同步和超同步状态,同时稳态时转子侧和定子侧注入电网谐波基本为零.     

国外风力发电导则及动态模型简介

分析了美国、丹麦、德国、苏格兰以及爱尔兰等欧美国家输电网运行公司针对风力发电制定的电网导则及其对风力发电动态仿真提出的要求,讨论了四种典型风力发电机组的动态建模,并给出了恒速感应式风力发电机组和变速双馈风力发电机组的仿真实例.仿真结果表明风力发电机组具有很多不同于同步电机或马达类负荷的特性,应认真研究其对电力系统规划和运行的影响.电网导则的更新以及风机的动态建模是目前电力系统面临的重要课题.     

基于聚类算法的风电场动态等值

风电机组在实际运行时,受尾流效应等因素影响,运行状态并不相同。为提高风电场实际运行模型的精度,提出了一种适用于双馈式风力发电机的动态等值建模方法。它将风电机组的状态变量矩阵作为分群指标,利用聚类算法将矩阵中的数据进行分群,将同群的风电机组等值成为一台风力发电机,实现了风电场的动态等值。利用PSD/BPA平台,对系统侧故障与风速变化2种情况仿真,并与传统等值方法及风电场详细模型对比。仿真结果表明,采用仿真过程中的状态变量作为分群指标是合理的,该模型与详细模型的动态特性基本一致,可以用来描述风电场的实际运行状态。     

一种改进的虚拟永磁风力发电系统模拟平台

提出了一种包含风剪塔影效应的风力发电系统的改进型模拟方案。以背靠背三相变流器平台为基础,建立了考虑包含风剪塔影效应的虚拟永磁直驱风力发电系统的数学模型,进而搭建其控制系统;针对简化叶尖速比与转矩系数拟合的问题,提出了一种基于Kalman滤波的分段线性拟合的方法来简化拟合方程;利用MATLAB/Simulink仿真软件搭建虚拟风力发电系统模拟平台,对负载变化时的模拟平台输出以及有无风剪塔影效应时风力机的机械转矩变化进行仿真分析。仿真结果表明,该平台能够较好地模拟出风力机发电机组地运行特性。     

Controller saturation nonlinearity in doubly fed induction generator‐based wind turbines under unbalanced grid conditions

Doubly fed induction generator (DFIG) is widely used in wind energy generation systems due to its cost‐effective, partially rated back‐to‐back power converters, variable rotor speed operation, and maximum wind power capture. The conventional design assumes balanced grid voltage and utilizes power protection for the power converters. The DFIG wind turbine is naturally one of the major components in distributed generations of the smart grid system. However, newly developed smart grid system is rich in unbalanced loads. This paper summarizes the limiter settings of controllers and explores the nonlinear behaviors of the DFIG‐based wind power generation system with unbalanced loads. The generator rotor speed and an unbalanced load resistance are chosen as variation parameters. An emerging low‐frequency linear‐modulated oscillation at line second harmonic frequency with DC drifting is identified on the DC link voltage of the back‐to‐back power converters. In terms of second harmonic and the usually reported hazardous low‐frequency oscillation, the saturation nonlinearity and over‐modulation of the back‐to‐back power converter and its power flow are investigated and analyzed. The built‐in detailed model of the DFIG wind energy generation system in Matlab with SimPowerSystems library is used in this study. Copyright © 2015 John Wiley & Sons, Ltd.     

Wind turbine Generator modeling and Simulation where rotational speed is the controlled variable

To optimize the power produced in a wind turbine, the speed of the turbine should vary with the wind speed. A simple control method is proposed that will allow an induction machine to run a turbine at its maximum power coefficient. Various types of power control strategies have been suggested for application in variable speed wind turbines. The usual strategy is to control the power or the torque acting on the wind turbine shafts. This paper presents an alternative control strategy, where the rotational speed is the controlled variable. The paper describes a model, which is being developed to simulate the interaction between a wind turbine and the power system. The model is intended to simulate the behavior of the wind turbine using induction generators both during transient grid fault events and during normal operation. Sample simulation results for two induction generators (2/0.5 MW) validate the fundamental issues.     

Influence of quadrature‐axis reactance of large turbine generator on operation

Two‐pole large generators are extensively used in power utilities. Growing demand for electric power in recent years has led to substantial increases in the capacity of generators. In line with this trend, our company has manufactured two‐pole turbine generators in the 900,000‐kVA to 1,200,000‐kVA classes. As the capacity of generators becomes larger, equivalent circuits are increasingly expected to improve their precision in estimating operation characteristics. The Park model has been widely used as an equivalent circuit model. The Park model with quadrature axis transient reactance $x_{q}^{\prime}$ is claimed to be useful for accurately estimating the load rejection characteristics of turbine generators. However, it is difficult to measure $x_{q}^{\prime}$, few studies based on measured data have appeared. As one of the few examples, we have conducted a measured data on a 500,000‐kVA‐class generator. Recently, the authors obtained test data on $x_{q}^{\prime}$ of a 900,000‐kVA‐class generator. In this study, based on these data, we studied the effect of $x_{q}^{\prime}$ using the finite element method and a transient analysis program (EMTP‐ATP). © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(3): 17–27, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21099     

电力系统对并网风电机组承受低电压能力的要求

阐述了风电机组低电压穿越原理和相应的控制策略,在电力系统仿真分析软件DIgSILENT/Power Factory中建立了具有低电压穿越功能的双馈风电机组模型。以某地区电网为例进行仿真计算,并提出了一种确定风电机组低电压穿越参数与要求的方法。通过计算系统中所有母线依次发生短路时风电机组在短路瞬间的机端电压值,在地理接线图中标出了系统中不同母线短路时对风电机组端电压的影响程度,据此给出了风电场低电压穿越功能中的电压限制值。分析结果表明,在某些情况下要求风电机组具有很强的低电压穿越能力是不符合实际的;而在另外一些情况下则必须要求风电机组具有较好的低电压穿越能力,否则会对系统的稳定运行构成威胁。因此,应根据具体接入方案计算风电机组低电压穿越功能中的电压限值。     

Speed control of grid-connected switched reluctance generator driven by variable speed wind turbine using adaptive neural network controller

In wind energy conversion system, variable speed operation is becoming popular nowadays, where conventional synchronous generators, permanent magnet synchronous generators, and doubly fed induction generators are commercially used as wind generators. Along with the existing and classical solutions of the aforementioned machines used in wind power applications, the switched reluctance generator (SRG) can also be considered as a wind generator due to its inherent characteristics such as simple construction, robustness, low manufacturing cost, etc. This paper presents a novel speed control of switched reluctance generator by using adaptive neural network (ANN) controller. The SRG is driven by variable speed wind turbine and it is connected to the grid through an asymmetric half bridge converter, DC-link, and DC-AC inverter system. Speed control is very important for variable speed operation of SRG to ensure maximum power delivery to the grid for any particular wind speed. Detailed modeling and control strategies of SRG as well as other individual components including wind turbine, converter, and inverter systems are presented. The effectiveness of the proposed system is verified with simulation results using the real wind speed data measured at Hokkaido Island, Japan. The dynamic simulation study is carried out using PSCAD/EMTDC.     

含不同风电机组的风电电网仿真研究

为了研究包含恒速异步风力发电机和双馈异步风力发电机的风电场对电网的影响,应用Matlab 7.0建立了含不同风电机组的风电场动态模型。分析了风电场对电网暂态稳定性的影响,风电机组电压恢复情况,有功、无功变化情况,以及不同风电机组的低电压穿越能力。仿真结果表明：双馈异步风力发电机变速平稳、低电压穿越能力较强,有利于优化电能质量;当电网发生故障时,应针对不同的风电机组采取不同的控制策略以提高电力系统稳定性。     

Matching between straight‐wing nonarticulated vertical axis wind turbine and a new wind turbine generator

In the current wind turbine generation system, there are substantial problems such as the fact that the maximum power of the wind turbine cannot be obtained in the presence of fluctuating wind speed, as well as high cost and low annual net electricity production (due to mismatch between generators and wind turbines). A new wind turbine generator optimized for the wind turbine output is presented in order to solve such problems. This wind turbine generator consists of a permanent magnet generator, a reactor, and a rectifier, and uses neither a control circuit which requires standby electricity nor a PWM converter having a switching element. By selecting the most appropriate combination of a permanent magnet generator with multiple windings and a reactor connected in series with each winding, the maximum output of the wind turbine can be obtained without using a control circuit. The new wind turbine generator was directly coupled with a straight‐wing nonarticulated vertical‐axis wind turbine (SW‐VAWT), and matching of the generator with the wind turbine was examined in field tests. The test results and review confirm that the new wind turbine generator is highly matched with the wind turbine in the presence of fluctuating wind speed. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 26–35, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21036     

Research on individual pitch control below rated wind speed

The structure of the modern wind turbine is becoming larger and more complex, with the wind rotor exceeding hundreds of meters in diameter. The blade shear force is also becoming increasingly serious below the rated wind speed, which leads to structure fatigue loads and instability of the generator power. For improving the dynamic performance of large wind turbines, it was proposed that individual pitch control (IPC) method was operated below the rated wind speed. In this paper, we analyze the relationship between the aerodynamic characteristics of blades and the nonlinear time‐varying pitch control system based on wind shear and the tower shadow effect. The combination of IPC and torque control is used to optimize the control mode of the wind turbine. By fine‐tuning the pitch angle, the unbalanced force on the wind rotor was relieved to achieve the purpose of mitigating fatigue loads. Finally, our experimental results prove the validity of the proposed IPC method below the rated wind speed by showing that it can improve power quality and reduce fatigue loads of the key components without reducing the generator output power. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.