A nonlinear model for aerodynamic configuration of wake behind horizontal-axis wind turbine

Determination of the aerodynamic configuration of wake is the key to analysis and evaluation of the rotor aerodynamic characteristics of a horizontal-axis wind turbine. According to the aerodynamic configuration, the real magnitude and direction of the onflow velocity at the rotor blade can be determined, and subsequently, the aerodynamic force on the rotor can be determined. The commonly employed wake aerodynamic models are of the cylindrical form instead of the actual expanding one. This is because the influence of the radial component of the induced velocity on the wake configuration is neglected. Therefore, this model should be called a "linear model". Using this model means that the induced velocities at the rotor blades and aerodynamic loads on them would be inexact. An approximately accurate approach is proposed in this paper to determine the so-called "nonlinear" wake aerodynamic configuration by means of the potential theory, where the influence of all three coordinate components of the induced velocity on wake aerodynamic configuration is taken into account to obtain a kind of expanding wake that approximately looks like an actual one. First, the rotor aerodynamic model composed of axial (central), bound, and trailing vortexes is established with the help of the finite aspect wing theory. Then, the Biot-Savart formula for the potential flow theory is used to derive a set of integral equations to evaluate the three components of the induced velocity at any point within the wake. The numerical solution to the integral equations is found, and the loci of all elementary trailing vortex filaments behind the rotor are determined thereafter. Finally, to formulate an actual wind turbine rotor, using the nonlinear wake model, the induced velocity everywhere in the wake, especially that at the rotor blade, is obtained in the case of various tip speed ratios and compared with the wake boundary in a neutral atmospheric boundary layer. Hereby, some useful and referential conclusions are offered for the aerodynamic computation and design of the rotor of the horizontal-axis wind turbine.

Performance Investigation of Three Combined Airfoils Bladed Small Scale Horizontal Axis wind Turbine by BEM and CFD Analysis

The present work is based on the comparative study between “Blade-Element- Momentum” (BEM) analysis and “Computational-Fluid-Dynamics” (CFD) analysis of small-scale horizontal axis wind turbine blade. In this study, the pitch is considered as fixed and rotor speed is variable. Firstly, the aerodynamic characteristics of three different specialized airfoils were analyzed to get optimum design parameters of wind turbine blade. Then BEM was performed with the application of the open source wind turbine design and performance computation software Q-Blade v0.6. After that, CFD simulation was done by Ansys CFX software. Here, k-ω “Shear-Stress-Transport” (SST) model was conducted for three-dimensional visualization of turbine performance. However, the best coefficient of performance was observed at 6o angle of attack. At this angle of attack, in the case of BEM, the highest coefficient of performance was 0.47 whereby CFD analysis, it was 0.43. Both studies showed good performance prediction which was a positive step to accelerate the continuous revolution in wind energy sector.

Neural Network Predictive Control of Variable-pitch Wind Turbines Based on Small-world Optimization Algorithm

通过将混沌映射用于产生初始节点集和进行算子构造,提出一种新的基于实数编码的混沌小世界优化算法。采用4种算法对多例复杂函数的优化问题进行仿真试验,表明所提算法具有能够有效避免陷入局部极小值、快速搜索到最优值的能力。将上述方法应用于变桨距风电机组启动并网时的转速控制,提出一种基于混沌小世界优化算法的神经网络预测控制策略,其预测模型由基于现场数据的神经网络模型建立。仿真与实际测试结果表明,该系统可以根据风速扰动提前预测电机的转速变化,使控制器超前动作,保证系统输出跟踪参考轨迹的方向稳步改变,确保风电机组平稳并网。

An Experiment on Power Properties in a Small-Scaled Wind Turbine Generator

This study configures a simple wind tunnel using a blower for generating wind energy, which is equivalent to natural wind, and a test system that measures properties of power. Also, the mechanical and electrical power in a small-scaled wind turbine are empirically measured to analyze the relationship between the mechanical and electrical power.

Dynamic Simulation of Novel Small Wind Turbine Generation System with SynRG

This paper describes a small wind turbine generation system with SynRG （synchronous reluctance generator）. SynRGs are robust and inexpensive. In addition, SynRG has no cogging torque. Hence, wind turbine generation system with SynRG can achieve smooth start at low wind velocity. The rotor design of proposed SynRG is multi flux barrier type. With FEA （finite element analysis） software, the characteristics of SynRG are brought out, and the performance of wind turbine generation system with SynRG including copper loss and iron loss is simulated by FEA coupled with the motion equation of the wind turbine generation system under the maximum power point tracking control. In this paper, the constant wind test and the quasi-natural wind test are conducted. In conclusion, the results of these simulations indicate that the wind turbine generation system with SynRG has good performance, especially in starting phenomena.

Numerical Simulation of Wind Turbine Wake Characteristics in Uniform Inflow

Flow field around a two-bladed horizontal-axis wind turbine(HAWT)is simulated at various tip speed ratios to investigate its wake characteristics by analyzing the tip and root vortex trajectories in the nearwake,as well as the vertical profiles of the axial velocity.Results show that the pitch of the tip vortex varies inversely with the tip speed ratio.Radial expansion of the tip vortices becomes more obvious as the tip speed ratio increases.Tip vortices shed not exactly from the blade tip but from the blade span of 96.5%—99%radius of the rotor.The axial velocity profiles are transformed into V-shape from W-shape at the distance downstream of eight rotor diameters due to the momentum recovery.

CFD-Based Load Calculation Method for Monopile Support Configuration of Offshore Wind Turbine

An unsteady load calculation method for the support configuration of a monopile-supported offshore wind turbine is developed based on the Fluent software platform.Firstly,the water wave is generated by imposing the inlet boundary conditions according to the exact potential flow solution.Then the wave evolution is simulated by solving the unsteady incompressible Navier-Stokes(N-S)equations coupled with the volume of fluid method.For the small amplitude wave with reasonable wave parameters,the numerical wave result agrees well with that of the given wave model.Finally,a monopile support configuration is introduced and a CFD-based load calculation method is established to accurately calculate the unsteady load under the combined action of wave and wind.The computed unsteady wave load on a small-size monopile support located in the small amplitude wave flow coincides with that of the Morison formula.The load calculations are also performed on a large-size monopile support and a monopile-supported offshore wind turbine under the combined action of small amplitude wave and wind.

Increasing the Efficiency of Grid Tied Micro Wind Turbines in Low Wind Speed Regimes

Major problem with grid tied micro wind turbine is synchronization and wind variability. Due to this problem the stability of available grid gets reduced. The stability can be achieved by output power control of the turbine. Major part of many countries like India, the annual mean wind speed is not high. The rated wind speed of turbine remain around 11 m/s and cut in is around 3.5 m/s. Due to this problem we aimed to develop a sustainable wind energy system that can provide stable power supply even at the locations of low wind speed of 2 - 4 m/s. To address this issue, a momentary impulse or external torque to the rotor by external motor is one of the good options to maintain the momentum of blades and thus provide stability for sufficient time. Various theoretical calculations and experiments are conducted on the above method. This would increase the output power and also the efficiency of wind turbine. We show that Return-On-Investment will be high as compared with other grid connected turbines. Our proposed concept in the present study, if implemented properly, can help the installation of number of wind turbines even at domestic level. It also makes the consumers energy independent and promotes the use of wind as a source of energy and may enter as a rooftop energy supply system similar to solar.

Structural Design Optimization of a Vertical Axis Wind Turbine for Seismic Qualification and Lightweight

Recently, there is a growing interest in seismic qualification of ridges, buildings and mechanical equipment worldwide due to increase of accidents caused by earthquake. Severe earthquake can bring serious problems in the wind turbines and eventually lead to an interruption to their electric power supply. To overcome and prevent these undesirable problems, structural design optimization of a small vertical axis wind turbine has performed, in this study, for seismic qualification and lightweight by using a Genetic Algorithm (GA) subject to some design constraints such as the maximum stress limit, maximum deformation limit, and seismic acceleration gain limit. Also, the structural design optimizations were conducted for the four different initial design variable sets to confirm robustness of the optimization algorithm used. As a result, all the optimization results for the 4 different initial designs showed good agreement with each other properly. Thus the structural design optimization of a small vertical-axis wind turbine could be successfully accomplished.

NEAR WAKE OF A MODEL HORIZONTAL-AXIS WIND TURBINE

An experimental investigation on the properties of the near wake behind the rotor of a Horizontal-Axis Wind Turbine （HAWT） was carried out at model scale. Measurements were made with a stationary slanted hot-wire anemometer using the technique of phase-locked averaging. The primary aim is to study the formation and development of the three-dimensional wake. Five axial locations were chosen within four chord lengths of the blades over a range of tip speed ratios. The results show that during the downstream developmerit of the wake, the wake centre traces a helical curve with its rotation direction opposite to that of the rotor. The distribution of mean velocity behind the HAWT rotor reveals an expansion and a decay of the three-dimensional wake. The shapes of the mean velocity distribution are similar along the blades span at the same downstream axial location. It is shown that the turbulence levels in the wake are higher than those in the non-wake region. The circumferential component and the radial component of the turbulence intensity are higher than the axial component. Our study offers some food of thought for better understanding of the physical features of the flow field as well as the performance of HAWT.

Studies on a low Reynolds number airfoil for small wind turbine applications

In contrast to large horizontal axis wind turbines (HAWTs) that are located in areas dictated by optimum wind conditions, small wind turbines are required for producing power without necessarily the best wind conditions. A low Reynolds number airfoil was designed after testing a number of low Reynolds number airfoils and then making one of our own; it was tested for use in small HAWTs. Studies using XFOIL and wind tunnel experiments were performed on the new airfoil at various Reynolds numbers. The pressure distribution, C p , the lift and drag coefficients, C L and C D , were studied for varying angles of attack, α. It is found that the airfoil can achieve very good aerodynamic characteristics at different Reynolds numbers and can be used as an efficient airfoil in small HAWTs.

Portable Multi-Inputs Renewable Energy System for Small Scale Remote Application

This paper presents a potable renewable energy system. The portable renewable energy power unit is designed from a need. The need is for first response teams in remote natural disaster situations to have a reliable source of energy to power a small vaccine refrigerator or water purification system and a basic satellite communication system. It is important that such a need is explored as a practical solution has the potential to save the lives of people in remote areas, who would otherwise suffer from a lack of humanitarian aid. Currently diesel generators are the primary source of electricity generation for disaster responders and in most situations work very well and provide a sufficient amount of electricity to meet the power needs. However, in remote areas road infrastructure is often damaged. In this type of situation getting a constant supply of diesel to the area is an expensive or impractical operation. This is where the portable renewable energy power unit bridges the gap and allows a more practical solution to be implemented. The specific aim of the work is to design a compact, stand-alone, product that can be easily transported by people across uneven terrain. It can generate power from wind, solar and hydro energy sources. In this work a new non-isolated multiport DC-DC converter topology for a hybrid energy system in low power applications is proposed. The new topology assimilates multiple renewable energy sources and power up multiple loads with different output levels. A complete Solid works model and FEA analysis, on required components, is completed. The scope of the work encompasses both the electrical and mechanical design of the system.

风向变化下不同材料叶片动态应力试验研究

为了了解不同材料风力机叶片在风向变化过程中的应力变化规律,以木质、玻璃纤维和碳纤维材料的S型风力机叶片为研究对象,使用风洞及动态旋转平台模拟风向变化情况并通过试验方法进行研究.结果表明:在同风速、同尖速比条件下,弹性模量较大的碳纤维叶片叶根前缘处应力值远大于玻璃纤维叶片和木质叶片叶根前缘处应力值,重量较大的玻璃纤维叶片比碳纤维叶片和木质叶片叶根前缘处应变值大;不同材料叶片叶根及展向应力、应变分布有所不同,但总体基本呈现由前缘(0.25C)向后缘(0.90C)、由叶根(0.20R)向叶尖(0.90R)减小的趋势;风向变化开始后,刚度高的碳纤维叶片由于抵抗弹性变形的能力强,其各测点应力、应变值最先出现明显下降趋势,之后依次为玻璃纤维叶片和木质叶片,3种材料叶片各测点的应力、应变值均呈现反S型下降曲线;叶片材料不同会导致同翼型同一测点处受到拉伸或挤压作用的大小、最大主应力方位角出现较大差异.

双馈虚拟同步机快速励磁控制和功角补偿策略

针对以激磁电势为目标控制电压的双馈虚拟同步发电机策略下运行功角大而带来的功率耦合问题,提出采用快速励磁控制消除功角扰动对无功控制的影响,采用功角补偿消除激磁电势扰动对功角有功控制的影响的功率解耦方案。在分析双馈电机数学模型及双馈虚拟同步机整体控制策略的基础上,构建计及无功控制环节的双馈虚拟同步机小信号模型。通过分析无功环节PI控制器参数对功角稳定性的影响,设计快速励磁控制策略。通过分析无功扰动与功角变化的关系,确定功角补偿传递函数。设定风速扰动、电网频率扰动和电网电压扰动3种不同工况进行验证。结果表明:所提控制策略可有效避免双馈虚拟同步机大功角运行时有功功率控制和无功功率控制间的相互影响,实现功率解耦。

风电机组附加有功控制参数对系统低频振荡的影响

附加有功控制环节使风机参与至同步机的机电振荡模式中,这使得系统功率振荡特性机理更加复杂,不利于附加有功控制环节的参数设计。为了研究风机附加有功控制对系统稳定性的影响,首先建立了考虑锁相环特性的风机与同步机动态作用的小信号模型;然后基于该模型利用阻尼转矩法分析了风机附加有功控制对系统振荡稳定性的影响机理,并提出了综合考虑系统等效惯性时间常数和阻尼比的附加有功控制环节系数设计方法;最后通过“10机39节点系统”的仿真结果量化分析了各系数对系统低频振荡稳定性的影响规律。结果表明,合理设置风电机组附加有功功率控制系数、滤波时间系数和锁相环带宽均能提升系统频率稳定性;理论分析的正确性也得到了验证。

并联永磁同步风电机组小干扰稳定性分析

采用平均磁链定向控制多台永磁同步风电机组进而构造分频发电系统是未来陆上尤其是海上风电的汇集方案之一,但对该模式下多台风电机组间稳定性的研究鲜有文献涉及。针对此问题,基于特征值分析法,研究了平均磁链定向控制的永磁同步风电机组之间的小干扰稳定性。首先,基于高压大容量直驱式永磁同步风电机组的分频集电系统拓扑结构,建立了适用于小干扰稳定分析的风电系统的数学模型;其次,通过辨识振荡模态并分析模态参与因子确定了影响系统振荡的主控因素,通过绘制根轨迹分析了主控因素参数变化对系统振荡的影响,并发现系统振荡受发电机电感、电阻和直流电容参数的影响最大;最后,通过时域仿真验证了研究结论的正确性。

基于双流生成对抗网络数据增强的风电机组智能故障诊断

针对实际工况下风电机组故障数据难以获取,现有数据增强方法对1维数据特征提取效果不佳的问题,提出一种基于双流生成对抗网络(DSGAN)的小样本智能故障诊断方法。设计了一种新的双流网络,通过深度特征提取流与时间特征提取流对风电机组故障数据进行深度与时间双特征提取。提出一种全局特征引导的自适应加权融合(GFG-AWF)模块对提取的双特征进行融合,并通过引入对抗生成思想,设计DSGAN完成小样本数据的增强。构建基于增强数据集辅助的双流诊断网络实现故障分类识别。利用轴承试验台数据与实际风电机组运行数据对所提方法进行了验证,最终诊断准确率达到98%,表明所提方法可以有效解决小样本的故障诊断问题。

基于运行状态与功率特性引导的覆冰天气下风电机组功率预测

针对覆冰天气下风电机组功率预测精度不足的问题,提出一种基于运行状态与功率特性引导的覆冰天气下风电机组功率预测方法。针对覆冰天气下风电机组样本不平衡的问题,采用贝叶斯优化的改进轻量级梯度提升机模型对覆冰天气下的风电机组数据样本进行状态判别并建立运行状态特征标签;针对覆冰天气下非停机运行小样本的问题,构建基于功率特性引导的风电机组功率预测模型,降低功率预测模型对数据的依赖,提升在覆冰天气运行场景下的预测准确性。采用广西某风电场风电机组数据进行算例验证,结果表明,相较于典型预测方法,所提方法在覆冰天气下的预测性能显著提升。

包含串补的并网直驱风电场振荡稳定性及可行域分析

串补装置广泛存在于电力系统中,含串补的大规模直驱永磁同步发电机(PMSG)构成的风电场并网系统存在次同步振荡范畴的小干扰失稳风险。针对上述现象,该文首先构建包含PMSG网侧换流器控制模型、锁相环控制模型以及含有串补装置的线路动态模型的并网系统全阶模型及等效模型。然后在不同的时间尺度下对等效模型进行化简,运用劳斯-赫尔维茨判据求得各时间尺度场景下并网系统的稳定性判据,从机理上解释了并网系统中各运行参数和控制参数之间的联系及其对系统稳定性的影响。进一步通过一个包含15台PMSG风电机组的并网风电场验证了该文推导的稳定判据的正确性。最后基于可行域的分析,直观地讨论了串补线路和其他参数对系统稳定性的影响。

大型海上风电机组叶片故障图像识别方法

针对海上风电机组叶片故障诊断建模时缺乏大量实际故障图像训练样本的问题,文章提出了一种基于小数据集的海上风电机组叶片故障图像识别方法。该方法针对风机叶片图像的叶片及其故障的颜色与形状特征,改进K均值聚类算法以实现叶片分割,设计自适应算法调整Canny算子参数以实现叶片表面早期故障区域的分割,使用K均值聚类算法提取故障的颜色和形状特征并设计相应的分类器以实现故障分类。仿真算例表明,该方法对于叶片表面早期故障的识别是有效的,可以在少量故障样本的基础上为海上风电机组叶片故障识别提供准确的诊断模型,提高了海上风电场的运维效率。