减小风力机1P气动载荷和3P气动转矩脉动的独立变桨距控制策略研究

为研究风切变和塔影效应对三叶片风力机气动载荷、气动转矩以及输出功率的影响,根据风切变和塔影效应的风速模型,引入等效风速模型,推导分析风力机1P(P为风轮旋转频率)气动载荷和3P气动转矩脉动的形成机理,并基于GH Bladed仿真平台验证这2种脉动的存在性。为减小这2种脉动对风力机产生的影响,基于变桨控制,设计带通滤波器过滤出风力机输出功率的3P脉动分量,并结合方位角信号将其转换为每支叶片的桨距角调节信号,与统一变桨控制的桨距角参考信号叠加,实现基于输出功率和方位角联合反馈的独立变桨距控制。仿真结果表明,所提独立变桨距控制策略不仅能有效缓解风力机1P叶根挥舞载荷脉动,还能明显减小气动转矩和输出功率的3P分量,从而在减小风轮疲劳载荷的同时提高风电机组输出电能质量。     

关于风力机异步变桨的初步研究

由于存在风速的高度切变,使同步变桨距风力机风轮的各个叶片并非都处于最佳升阻比状态,影响了风力机功率的输出和减少了风力机的使用寿命。通过对风力机叶片的空气动力学分析,提出要使叶片始终处于最佳升阻比的基本原理以及实现这一目标时变桨系统所应达到的要求。     

新型变桨风力机结构设计与性能分析

为满足分布式电网发展要求,提高小型风力机风能利用率,防止大风条件损坏风力发电设备,文章设计了一种应用于小型风力机的新型主动统一变桨调节装置。文章介绍了装置的基本构造与工作原理,利用熔融沉积3D打印技术制作小比例模型验证了变桨装置的可行性,并通过数值模拟方法对功率输出性能及风轮载荷进行了模拟分析。模拟结果表明:通过适当调节桨距角大小,可有效控制风力机输出功率保持在额定功率值附近,且高转速条件下增大桨距角对功率输出性能有较强抑制作用;叶片应力集中区域主要在叶根及叶片中部靠近前缘部位,在功率调控过程中,随着桨距角与风速的增加,应力集中区域由叶中向叶根转移,最大应力值总体呈下降趋势。     

海上浮式水平轴风力机气动特性研究

以NREL-5 MW风力机为研究对象,基于叶素动量理论,考虑动态失速、风剪切及塔影效应等气动修正模型,开发Matlab非定常气动载荷计算程序,研究浮式水平轴风力机气动特性。结果表明:为保证风力机气动载荷模拟的正确性,气动修正模型必不可少;基础运动对风力机气动性能有显著影响,基础运动使风力机输出功率增大,但同时存在较大的振荡幅度,导致功率输出不稳定;叶片变桨失效导致功率输出更加不稳定。     

大型风力发电机组变桨距系统结构可靠性设计研究

随着风力发电技术的不断发展,大功率、长叶片已逐渐成为大型风力发电机组的主要特征和发展方向,以持续提升风能利用的经济性。风力发电机组大型化带来叶片长度和重量的显著增加,风轮每旋转一周,在低速轴上的受力和作用在叶片上的重力均会出现周期性变化,同时,在风轮旋转平面上,因风切变、塔影效应和湍流的作用而产生循环变化的载荷。风力发电机组大型化必然带来机组疲劳载荷的增加,疲劳载荷是风力发电机组在全风速范围内运行所产生的典型载荷循环,循环的数量正比于各种风速下机组发电运行的时间,决定着部件的设计使用寿命。为进一步研究风切变、塔影效应、叶片重力、叶片推力载荷对大风轮直径机组叶根疲劳载荷所产生的影响,文章通过对风轮运行载荷分析和系统仿真,对变桨传动系统结构有限元计算和分析,研讨影响变桨传动系统可靠运行的主要因素,为大型风力发电机组变桨传动系统可靠性设计提供参考。     

基于风剪切和塔影效应的风力机风速动态建模

在对三桨叶上风向水平轴风力机的风剪切和塔影效应深入分析的基础上,得到了整个风轮扫掠面上的风速动态模型.并考虑了轮毂高度、轮毂风速、风剪切系数、叶片半径、塔架半径、悬垂距离等参数对计算模型的影响,对一台2MW风力机进行了计算和对比分析,为深入研究风力机的独立变桨、功率控制、疲劳、动力稳定性等奠定了基础.     

低空急流条件下水平轴风力机风轮气动特性的研究

为阐明低空急流条件下风力机风轮的气动特性,基于工程化的边界层风速模型和Von Karman谱模型建立不同来流的脉动风场,对比研究低空急流条件下NREL 5 MW风力机风轮的输出功率和气动载荷的变化规律。结果表明:如果仅以轮毂高度处的风速作为风力机变桨控制的依据,与均匀来流和剪切来流相比较,低空急流条件下,虽然来流风功率明显增大,但风轮的输出功率在较高风速时反而减小;风轮所受的不平衡气动载荷,包括横向力、纵向力、偏航力矩和倾覆力矩在较高风速时小于剪切来流的结果;且仅以轮毂高度处的风速预测得到的风轮输出功率高于实际结果,其最大相对误差为89.4%。因此,低空急流条件下,为提高风能利用率和风轮输出功率的预测精度,应考虑不同高度位置处的风速大小对风力机进行变桨控制和功率预测。     

基于风轮气动特性的风力机变桨优化控制策略研究

当风速大于额定风速时,风电机组通过控制变桨机构调整桨距角来减小风能捕获,从而使机组的输出功率保持在额定功率附近。变桨系统一般采用PI(比例积分)控制算法,但由于风轮气动转矩与风速、风轮转速、桨距角呈高次复杂非线性关系,单一控制参数的变桨控制器难以满足风电机组在额定风速以上的运行性能要求。为了解决单一变桨控制性能不足的问题,提出一种基于风轮气动特性的风力机变桨优化控制策略,该策略通过测量桨距角当前值来动态调整变桨控制器参数,可有效提升变桨系统随风动作连续性,减小由变桨控制引起的转速与功率波动,削减机组由变桨动作引起的动态载荷。     

基于功率灵敏度因子的风力机变速变桨距控制研究

针对大型变速变桨风力机在高风速区的气动性能随桨距角变化而改变的特性,文章提出了一种功率-桨距角变化的灵敏度控制策略。通过设计功率灵敏度因子调节PID变桨距控制器,建立输出功率偏差与风轮转速偏差的闭环系统。将提出的策略应用到某5 MW风机的参数模型中,利用MATLAB平台进行仿真验证。结果表明,提出的控制策略抑制了高风速区的扰动风速对系统的影响,使输出功率和风轮转速保持在额定值附近且波动很小,提高了系统的动态性能和稳态性能,同时提高了发电质量,并为风电机组并网需求奠定了理论基础。     

新型变桨风力机关键部件载荷特性试验研究

以新型变桨距风力机为研究对象,针对其独特的变桨调节机构,通过风洞试验的方法,采用IMC载荷测试系统,对其关键部件进行载荷测试。试验结果显示：随着桨距角增大,叶根所受弯矩降低,但叶根挥舞弯矩较摆振弯矩减小更明显;塔筒俯仰方向的受力大于侧弯方向,当风轮转速约为243.5 r/min时,塔筒侧弯受力出现突增;不同桨距角下,变桨调节机构的齿条与齿条同步盘测点载荷大小随风速变化趋势一致,但随着桨距角的增加,表现为先增加后减小再增加的趋势。     

Simulation model of wind turbine 3p torque oscillations due to wind shear and tower shadow

To determine the control structures and possible power quality issues, the dynamic torque generated by the blades of a wind turbine must be represented. This paper presents an analytical formulation of the generated aerodynamic torque of a three-bladed wind turbine including the effects of wind shear and tower shadow. The comprehensive model includes turbine-specific parameters such as radius, height, and tower dimensions, as well as the site-specific parameter, the wind shear exponent. The model proves the existence of a 3p pulsation due to wind shear and explains why it cannot be easily identified in field measurements. The proportionality constant between the torque and the wind speed is determined allowing direct aerodynamic torque calculation from an equivalent wind speed. It is shown that the tower shadow effect is more dominant than the wind shear effect in determining the dynamic torque, although there is a small dc reduction in the torque oscillation due to wind shear. The model is suitable for real-time wind turbine simulation or other time domain simulation of wind turbines in power systems.     

Prediction of aerodynamic performance of NREL offshore 5-MW baseline wind turbine considering power loss at varying wind speeds

In this study, a computational fluid dynamics (CFD) model was developed to simulate the aerodynamic performance of the National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine with single rotor and full wind turbine. Using statistical methods, the relation between pitch angle and performance when the speed is above the rated wind speed was analyzed; furthermore, other published data were compiled to establish the functional equations of power, thrust with various inflow wind speeds, and pitch angles. In addition, according to shape optimization based on parametric modeling, the two-dimensional cross-section of the wind turbine blade can be defined through a metasurface approach, and the three-dimensional surface modeling of the wind turbine blade, nacelle, and tower is completed using the nonuniform rational B-splines (NURBS) interpolator. In terms of aerodynamic simulation, the unstructured polygon mesh was used herein to discretize the space and simulate the highly curved and twisted surfaces of the blade. In this study, the compact and accurate mesh form obtained through a grid independence test will be used to analyze the distribution of the pressure coefficient, shear stress coefficient, and limited streamline on the blade surface at various inflow wind speeds and pitch angles to understand the differences between different turbulence models and the causes of power and thrust attenuation at high inflow wind speeds. In addition, the phenomena of blade-tip vortices, dynamic stall, blade loading, and the interaction between nacelle and tower were collectively explored.     

A practical approach for selecting optimum wind rotors

The main objective of this paper is to categorize practical families of horizontal-axis wind turbine rotors, which are optimized to produce the largest possible power output. Refined blade geometry is obtained from the best approximation of the calculated theoretical optimum chord and twist distributions of the rotating blade. The mathematical formulation is based on dimensionless quantities so as to make the aerodynamic analysis valid for any arbitrary turbine models having different rotor sizes and operating at different wind regimes. The selected design parameters include the number of blades, type of airfoil section and the blade root offset from hub center. The effects of wind shear as well as tower shadow are also examined. A computer program has been developed to automate the overall analysis procedures, and several numerical examples are given showing the variation of the power and thrust coefficients with the design tip speed ratio for various rotor configurations.     

Load alleviation of wind turbines by yaw misalignment

Vertical wind shear is one of the dominating causes of load variations on the blades of a horizontal axis wind turbine. To alleviate the varying loads, wind turbine control systems have been augmented with sensors and actuators for individual pitch control. However, the loads caused by a vertical wind shear can also be affected through yaw misalignment. Recent studies of yaw control have been focused on improving the yaw alignment to increase the power capture at below rated wind speeds. In this study, the potential of alleviating blade load variations induced by the wind shear through yaw misalignment is assessed. The study is performed through simulations of a reference turbine. The study shows that optimal yaw misalignment angles for minimizing the blade load variations can be identified for both deterministic and turbulent inflows. It is shown that the optimal yaw misalignment angles can be applied without power loss for wind speeds above rated wind speed. In deterministic inflow, it is shown that the range of the steady‐state blade load variations can be reduced by up to 70%. For turbulent inflows, it is shown that the potential blade fatigue load reductions depend on the turbulence level. In inflows with high levels of turbulence, the observed blade fatigue load reductions are small, whereas the blade fatigue loads are reduced by 20% at low turbulence levels. For both deterministic and turbulent inflows, it is seen that the blade load reductions are penalized by increased load variations on the non‐rotating turbine parts. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of extreme wind shear on aeroelastic modal damping of wind turbines

Wind shear is an important contributor to fatigue loads on wind turbines. Because it causes an azimuthal variation in angle of attack, it can also affect aerodynamic damping. In this paper, a linearized model of a wind turbine, based on the non‐linear aeroelastic code BHawC, is used to investigate the effect of wind shear on the modal damping of the turbine. In isotropic conditions with a uniform wind field, the modal properties can be extracted from the system matrix transformed into the inertial frame using the Coleman transformation. In shear conditions, an implicit Floquet analysis, which reduces the computational burden associated with classical Floquet analysis, is used for modal analysis. The methods are applied to a 2.3 MW three‐bladed pitch‐regulated wind turbine showing a difference in damping between isotropic and extreme shear conditions at rated wind speed when the turbine is operating closest to stall. The first longitudinal tower mode decreases slightly in damping, whereas the first flapwise backward whirling and symmetric modes increase in damping. This change in damping is attributed to an interaction between the periodic blade mode shapes and the azimuth‐dependent local aerodynamic damping in the shear condition caused by a beginning separation of the flow. Copyright © 2012 John Wiley & Sons, Ltd.     

Wind turbine aerodynamics and loads control in wind shear flow

Wind turbine is subjected to some asymmetrical effects like wind shear, which will lead to unsteady blade airloads and performance. Fatigue loads can lead to damage of turbine components and eventually to failures. It is evident that the variation of the velocity over the rotor disc has an influence on the blade and introduces both flap-wise and edge-wise fatigue damage on the blade as a result of moment fluctuations in the two directions. The flap-wise moments on the blade are the origin of the rotor yaw and tilt moments which transmit to the turbine structure through the drive train to the yaw system and the tower. A lifting surface method with time marching free wake model is used to investigate the periodic unsteady nature in the wind shear. Individual pitch control (IPC) that is applied nowadays is the most advanced active control to reduce the fatigue. The blade airloads and performance of the turbine are also predicted under IPC control. It is found that IPC of the fluctuating blade root flap-wise moment can reduce the flap-wise fatigue damage remarkably while the blade root edge-wise moments are less sensitive to the varying blade pitch than the blade root flap-wise moments.     

Wind turbine load reduction by rejecting the periodic load disturbances

For the cost per kilowatt hour to be decreased, the trend in offshore wind turbines is to increase the rotor diameter as much as possible. The increasing dimensions have led to a relative increase of the loads on the wind turbine structure; thus, it is necessary to react to disturbances in a more detailed way, e.g. each blade separately. The disturbances acting on an individual wind turbine blade are to a large extent deterministic; for instance, tower shadow, wind shear, yawed error and gravity are depending on the rotational speed and azimuth angle and will change slowly over time. This paper aims to contribute to the development of individually pitch‐controlled blades by proposing a lifted repetitive controller that can reject these periodic load disturbances for modern fixed‐speed wind turbines and modern variable‐speed wind turbines operating above‐rated. The performance of the repetitive control method is evaluated on the UPWIND 5 MW wind turbine model and compared with typical individual pitch control. Simulation results indicate that for relatively slow changing periodic wind disturbances, this lifted repetitive control method can significantly reduce the vibrations in the wind turbine structure with considerably less high‐frequent control action. Copyright © 2012 John Wiley & Sons, Ltd.     

风剪切下塔影效应对水平轴风力机叶片及风轮气动载荷的影响

采用CFD方法,以NH1500三叶片大型水平轴风力机为研究对象,研究额定风速剪切来流下的塔影效应对水平轴风力机叶片和风轮非定常气动载荷的影响。结果表明：剪切来流下,叶片和风轮的气动载荷均呈余弦变化规律,塔影效应的主要影响叶片方位角范围为160°~210°,且该范围不随风剪切指数的变化而变化。相同风剪切指数下,塔影效应对叶片和风轮气动载荷的均方根影响较小,对其波动影响较大。当风剪切指数从0.12增至0.30时,塔影效应下,叶片气动载荷的均方根减小,推力和转矩的波动幅度增大,偏航力矩和倾覆力矩的波动幅度减小;风轮推力和转矩的均方根减小,波动幅度变化较小,而倾覆力矩和偏航力矩的均方根增大,且波动幅度也增大。     

基于流固耦合的风力机塔筒动态特性分析

塔筒动态特性分析对风力发电机的振动设计起着关键作用。文章以1.5 MW风力发电机塔筒为研究对象,将叶片旋转和随机风载荷作为载荷输入条件,建立风力机塔筒叶片旋转载荷模型、流固耦合风载荷模型、结构动力学方程,分析计算得到随机载荷下叶片旋转和风载共同作用时,风力机塔筒动态特性评估方法。     

变速风力机变桨距系统建模与仿真

变速风力发电机组一般采用变桨距控制来稳定输出功率,但是桨距角的改变会引起攻角的改变,从而引起叶片气动性能的改变,所以在变桨距控制过程中,必须保证合适的攻角,以确保风力机具有良好的气动性能。采用统一变桨距控制方法,在matlab/simulink环境下,通过预测攻角仿真研究了变速风力发电机组的变桨距控制过程,结果表明,该控制模型能正确模拟各种风速下风力发电机组变桨距的动态过程,为进一步研究变速风力发电机的功率控制奠定了基础。