A new approach for the prediction and identification of generatedharmonics by induction generators in transient state

For the planning of future connection of wind generators to the public power system there is a need to specify the conditions when they can become sources of harmonic distortion. Induction generators have applications in wind power systems. Generators connected to the infinite bus are not sources for voltage harmonics. Autonomous generators are variable frequency variable voltage systems and their steady state voltage is distorted. In transient state the transient frequencies are superposed on the steady state waveform increasing the harmonic distortion. In this paper the transient model of the induction generator is extended and adapted for the prediction of the higher order transient harmonics in the generated voltage. Then, using experimental equipment a new numerical technique for their identification is implemented. A data acquisition system records the generated stator voltage during transients from various types of disturbances and the spectral analysis identifies the transient frequencies produced by the steady state fundamental and by its fractional and subfractional order harmonics. The identification of harmonics validates the predicted values by the analytical method     

考虑风资源影响的风电场电压波动和闪变评估

风电并网后引起的电压波动和闪变水平可能超出国家有关标准,造成严重的电能质量问题,因此,在风电并网之前需对这两者进行评估。采用了一种新的评估方法。区别于国际电工标准(IEC61400-21)中电压波动与闪变的评估,此方法考虑了风电场的风资源情况对这2个指标的影响。对风电场在不同出力下由阵风引起系统的电压波动进行计算,并用IEC闪变仪计算短时间闪变值Pst。用所提方法和IEC标准对我国某一新建的风电场进行评估。结果表明,所提方法不仅能有效地进行电压波动与闪变评估,而且能更好地考虑风速变化对风电场带来的潜在影响。     

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。     

Power limits of grid-connected modern wind energy systems

Wind energy is a prominent area of application of variable speed generators operating on the constant grid frequency. A modern wind energy system of this type consists of a surface mounted permanent-magnet generator with a frequency converter, which allows variable speed operation. The maximum power capability of the wind energy system is limited by the grid inverter. The theoretical formulation for active and reactive power limits is given. This formulation is used to set power reference limits to the inverter. Two different regions are distinguished depending on the tolerable Ac current harmonic distortion. Experimental results in a variable frequency wind energy generation system are shown.     

基于指标关联的分布式电源并网规划策略

为解决新能源并网时的电源规划与风光消纳问题,考虑风光能源功率波动特性并计及储能单元提出一种计及风光协调出力的电网规划策略。综合考虑电压波动、新能源消纳及新能源发电效益建立多指标规划模型,采用引入指标关联策略的粒子群优化方法对模型进行求解,确定分布式电源及储能的位置和容量。进一步分析优化方案在电能质量方面的规划效果,统计对比电压累计概率密度对规划方案进行评价。以某电网45节点配电系统为例,采用所提分布式电源并网规划策略进行仿真,决策风光储并网方案,并验证所提策略的合理性和可行性。     

A variable speed wind energy conversion scheme for connection toweak AC systems

A three level control system for a variable speed wind energy conversion scheme (VSWECS) supplying a weak AC power system is presented. The objective of the control strategy is to maximize energy capture and simultaneously to support the voltage of the bus where the VSWECS is connected. Using an insulated gate bipolar transistor (IGBT) inverter, both control of active and reactive power supplied to the grid and reduction of harmonic distortion can be achieved. The response of the proposed scheme has been tested and evaluated in a test system using a developed computer program simulating in detail the system operation     

基于电力系统分析软件ETAP的电网谐波分析

针对目前电力系统中由于非线性负荷的使用以及某些可再生能源发电系统的接入导致的谐波问题,首先介绍了电力系统仿真分析软件ETAP的主要功能和特点,然后在ETAP中建立算例模型并对其进行谐波仿真分析,同时也在另外两款仿真分析软件EMTDC和PSASP上对算例模型建模并导出谐波分析图谱,通过对照进一步说明ETAP在谐波分析中的优缺点。然后在原算例模型的基础上修改其中的高压网络短路容量、减少变压器投运数量、改变变压器阻抗以及增加电动机和无源负荷容量等参数,将仿真所得数据同理论计算结果对比,并分析这些参数的变化给系统并联谐振点的位置和幅值,以及谐波畸变程度造成的影响。结果表明,由于ETAP软件在谐波仿真方面的卓越性能,在面临大规模系统的规划和电能质量评估方面的问题时,利用ETAP进行预先的谐波仿真分析可以辅助建立有效的方案降低系统中的谐波畸变程度,并利用谐振分析可以有效地避开谐振位置,从而提高电力系统的电能质量。     

恒速风电机组对电网暂态电压稳定性的影响

基于恒速风电机组的结构,给出风电机组各部分的数学模型,利用仿真软件DIgSILENT/PowerFactory建立恒速风电机组的动态模型,并利用该模型在WSCC 3机9节点算例中仿真恒速风电机组并网运行时因风速变化引起的电网电压波动,通过极限切除时间分析恒速风电机组并网对电网暂态电压稳定性的影响,并与接入相同容量的同步机组进行比较。结果表明,恒速风电机组的接入降低了电网的暂态电压稳定性,且接入恒速风电机组装机容量越大,电网的暂态电压稳定性越差。由此提出改善恒速风电机组并网后电网暂态电压稳定性的建议。     

解决新疆风能资源大规模开发瓶颈的探讨

本文对如何解决新疆风能资源进行大规模开发时所遇到的瓶颈进行了探讨,提出了一种解决问题的新思路。用详细的数据介绍了新疆丰富的风能资源分布,讨论了在大规模开发时遇到的电网稳定性、有效负荷需求不足以及没有联网电网的支持等问题,最后,根据新疆拥有丰富的天然气资源,提出了采用一种新型的风电-燃气轮机互补发电系统来彻底解决风电场负荷的波动对电网稳定性不利的影响,为新疆的风能大规模开发提供了一种新的可能。     

Voltage and Frequency Controller for a Three-Phase Four-Wire Autonomous Wind Energy Conversion System

This paper deals with control of voltage and frequency of an autonomous wind energy conversion system (AWECS) based on capacitor-excited asynchronous generator and feeding three-phase four-wire loads. The proposed controller consists of three single-phase insulated gate bipolar junction transistor (IGBT)-based voltage source converters (VSCs) and a battery at dc link. These three single-phase VSCs are connected to each phase of the generator through three single-phase transformers. The proposed controller is having bidirectional flow capability of active and reactive powers by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind. VSCs along with transformer function as a voltage regulator, a harmonic eliminator, a load balancer, and a neutral current compensator while the battery is used to control the active power flow which, in turn, maintains the constant system frequency. The complete electromechanical system is modeled and simulated in the MATLAB using the Simulink and the power system blockset (PSB) toolboxes. The simulated results are presented to demonstrate the capability of the proposed controller as a voltage and frequency regulator, harmonic eliminator, load balancer, and neutral current compensator for different electrical (varying consumer loads) and mechanical (varying wind speed) dynamic conditions in an autonomous wind energy conversion system.     

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。     

Dynamic modeling and simulation of a small wind–fuel cell hybrid energy system

This paper describes dynamic modeling and simulation results of a small wind–fuel cell hybrid energy system. The system consists of a 400 W wind turbine, a proton exchange membrane fuel cell (PEMFC), ultracapacitors, an electrolyzer, and a power converter. The output fluctuation of the wind turbine due to wind speed variation is reduced using a fuel cell stack. The load is supplied from the wind turbine with a fuel cell working in parallel. Excess wind energy when available is converted to hydrogen using an electrolyzer for later use in the fuel cell. Ultracapacitors and a power converter unit are proposed to minimize voltage fluctuations in the system and generate AC voltage. Dynamic modeling of various components of this small isolated system is presented. Dynamic aspects of temperature variation and double layer capacitance of the fuel cell are also included. PID type controllers are used to control the fuel cell system. SIMULINK^TM is used for the simulation of this highly nonlinear hybrid energy system. System dynamics are studied to determine the voltage variation throughout the system. Transient responses of the system to step changes in the load current and wind speed in a number of possible situations are presented. Analysis of simulation results and limitations of the wind–fuel cell hybrid energy system are discussed. The voltage variation at the output was found to be within the acceptable range. The proposed system does not need conventional battery storage. It may be used for off-grid power generation in remote communities.     

A New Variable-Speed Wind Energy Conversion System Using Permanent-Magnet Synchronous Generator and $Z$-Source Inverter

With the growth of wind energy conversion systems (WECSs), various technologies are developed for them. Permanent-magnet synchronous generators (PMSGs) are used by these technologies due to special characteristics of PMSGs such as low weight and volume, high performance, and the elimination of the gearbox. In this paper, a new variable-speed WECS with a PMSG and $Z$-source inverter is proposed. Characteristics of $Z$-source inverter are used for maximum power tracking control and delivering power to the grid, simultaneously. Two control methods are proposed for delivering power to the grid: Capacitor voltage control and dc-link voltage control. Operation of system with these methods is compared from the viewpoint of power quality and total switching device power (TSDP). In addition, TSDP, current ripple of inductor, performance, and total harmonic distortion of grid current of proposed system is compared with traditional wind energy system with a boost converter.      

PSCAD/EMTDC-Based Modeling and Analysis of a Gearless Variable Speed Wind Turbine

This paper presents dynamic modeling and simulation of a grid connected variable speed wind turbine (VSWT) using PSCAD/EMTDC, a widely used power system transient analysis tool. The variable speed wind system with a direct-drive generator and power electronics interface is modeled for dynamic analysis. Component models and equations are addressed and their implementations into PSCAD/EMTDC are described. Controllable power inverter strategy is intended for capturing the maximum energy from varying wind speed and maintaining reactive power generation at a pre-determined level for constant power factor or voltage regulation. The component models and entire control scheme are constructed by user-defined function provided in the program. Simulation studies provide control performance and dynamic behavior of a gearless VSWT under varying wind speeds. In addition, the system responses to network fault conditions have been simulated. This modeling study can be employed to evaluate the control scheme, output performance and impacts of a VSWT on power grid at planning or designing stage.     

低风速分散式风电并入配电网的双层电压优化模型

从规划和运行2个角度出发,提出一种针对低风速风电机组并入配电网的双层电压优化模型。上层模型计及低风速的波动性、负荷的随机性与用户行为特性,求解以网损、电压偏差、电压稳定性指标和分散式风电总投资为目标函数的多目标规划问题,同时利用Q-V曲线法获得静止无功补偿器(SVC)的最佳接入位置;下层模型建立基于模糊逻辑的低风速风电机组与SVC协调调压的无功控制策略。最后通过仿真验证所提方法不仅能够实现电压优化控制,而且能显著改善配电网的整体电压分布。     

Wind farms connected to weak grids in India

This article describes the mutual influence between the wind turbines and the power quality in the Indian power systems. The Indian power systems are weak in general and the wind energy development has been very fast and concentrated in a few rural areas where the existing transmission and distribution grids are very weak. Therefore the mutual influence between wind turbines and power quality is particularly strong in India. The wind farms influence power quality aspects such as steady state voltage, power factor, flicker and harmonic and interharmonic distortion. The power quality of the grid influences the power performance and safety of the wind turbines and the lifetime of mechanical and electrical components. The findings presented are general for wind farms connected to weak grids, but the Indian case is pronounced concerning weakness of grid as well as wind energy penetration level. Copyright © 2001 John Wiley & Sons, Ltd.     

陕西靖边鲁能风电并网对电网的影响

风力发电机组由于风速的易变性和不可控性,给风电场的并网运行带来电能质量低、谐波污染严重、系统不稳定等问题。结合陕西靖边鲁能风电接入系统工程,提出了风电场接入系统方案:采用无功补偿措施和软并网方式。为抑制风电场带来的电压波动和闪变,一方面应尽可能将大型风电场接入与系统紧密联系的变电站,另一方面应增大风电场接入点的短路容量。     

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。     

风氢耦合系统能量管理策略研究

针对风力机出力的波动性和并网弃风问题,采用风力机/电解槽/燃料电池/超级电容的风氢耦合发电系统及其能量管理控制策略。针对风氢耦合发电系统的12种运行模式,提出一种能量管理控制策略,确保在各个控制单元的作用下,能量协调流动于各个子单元间。能量管理控制策略不仅使风氢耦合发电系统出力可控,而且平抑了直流母线电压波动,平滑了上网功率。通过Matlab/Simulink软件进行仿真研究,验证了风氢耦合发电系统的能量管理控制策略的有效性,提高了风电消纳能力。     

一种并网型风光互补发电系统的建模与仿真

分析了风光互补发电系统的技术优势,设计了基于固态变压器结构的并网型风光互补发电系统。分别建立了光伏系统,风力发电系统,超级电容和蓄电池的模型,并分析各环节的控制策略,提出了基于平均功率的储能设备容量配置方法。仿真结果表明,该系统能模拟风光互补系统在不同模式下的运行特性,可以有效降低功率波动和维持电压稳定,并能在低光照强度、低风速等情况下为系统提供短时能量支撑。