Analysis on flutter performance of flexible photovoltaic support based on full-order method

Taking a three-cable flexible photovoltaic(PV)support structure as the research subject,a finite element model was established.Utilizing a full-order flutter analysis method,the flutter critical wind speed and flutter frequency of the flexible PV support structure at a tilt angle of 0°were calculated.The results showed good agreement with wind tunnel test data.Further analysis examined the pretension effects in the load-bearing and stabilizing cables on the natural frequency and flutter critical wind speed of the flexible PV support structure.The research findings indicate increasing the pretension in the load-bearing cables significantly raises the natural frequencies of the first four modes.Specifically,as the pretension in the load-bearing cables increases from 22 to 102 kN,the flutter critical wind speed rises from 17.1 to 21.6 m/s.By contrast,the pretension in the stabilizing cable has a smaller effect on the natural frequency and flutter critical wind speed of the flexible PV support structure.When the pretension in the stabilizing cable increased from 22 to 102 kN,the flutter critical wind speed increased from 17.1 to 17.7 m/s.For wind-resistant design of flexible PV support structures,it is recommended to prioritize increasing the pretension in the load-bearing cables to enhance the structural flutter performance.

Random vortex induced vibration response of suspended flexible cable to fluctuating wind

A popular dynamical model for the vortex induced vibration(VIV)of a suspended flexible cable consists of two coupled equations.The first equation is a partial differential equation governing the cable vibration.The second equation is a wake oscillator that models the lift coefficient acting on the cable.The incoming wind acting on the cable is usually assumed as the uniform wind with a constant velocity,which makes the VIV model be a deterministic one.In the real world,however,the wind velocity is randomly fluctuant and makes the VIV of a suspended flexible cable be treated as a random vibration.In the present paper,the deterministic VIV model of a suspended flexible cable is modified to a random one by introducing the fluctuating wind.Using the normal mode approach,the random VIV system is transformed into an infinite-dimensional modal vibration system.Depending on whether a modal frequency is close to the aeolian frequency or not,the corresponding modal vibration is characterized as a resonant vibration or a non-resonant vibration.By applying the stochastic averaging method of quasi Hamiltonian systems,the response of modal vibrations in the case of resonance or non-resonance can be analytically predicted.Then,the random VIV response of the whole cable can be approximately calculated by superimposing the response of the most influential modal vibrations.Some numerical simulation results confirm the obtained analytical results.It is found that the intensity of the resonant modal vibration is much higher than that of the non-resonant modal vibration.Thus,the analytical results of the resonant modal vibration can be used as a rough estimation for the whole response of a cable.

Interface Mechanical Behavior of Flexible Piles Under Lateral Loads in OWT Systems

This paper investigates the interface mechanical behavior of flexible piles with L_p/D>10 under lateral load and an overturning moment in monotonic loading conditions.To modify the beam-on-Winkler-foundation model of piles in offshore wind farms,the energy-based variational method is used.The soil is treated as a multi-layered elastic continuum with the assumption of three-dimensional displacements,the pile modeled as an Euler-Bernoulli beam.A series of cases using MATLAB programming was conducted to investigate the simplified equations of initial stiffness.The results indicated that the interaction between soil layers and the applied force position should be taken into account in calculating the horizontal soil resistance.Additionally,the distributed moment had a limiting effect on the lateral capacity of a flexible pile.Moreover,to account for the more realistic conditions of OWT systems,field data from the Donghai Bridge offshore wind farm were used.

Dynamic Analysis of a 10 MW Floating Offshore Wind Turbine Considering the Tower and Platform Flexibility

Recently,semisubmersible floating offshore wind turbine technologies have received considerable attention.For the coupled simulation of semisubmersible floating offshore wind energy,the platform is usually considered a rigid model,which could affect the calculation accuracy of the dynamic responses.The dynamic responses of a TripleSpar floating offshore wind turbine equipped with a 10 MW offshore wind turbine are discussed herein.The simulation of a floating offshore wind turbine under regular waves,white noise waves,and combined wind-wave conditions is conducted.The effects of the tower and platform flexibility on the motion and force responses of the TripleSpar semisubmersible floating offshore wind turbine are investigated.The results show that the flexibility of the tower and platform can influence the dynamic responses of a TripleSpar semisubmersible floating offshore wind turbine.Considering the flexibility of the tower and platform,the tower and platform pitch motions markedly increased compared with the fully rigid model.Moreover,the force responses,particularly for tower base loads,are considerably influenced by the flexibility of the tower and platform.Thus,the flexibility of the tower and platform for the coupled simulation of floating offshore wind turbines must be appropriately examined.

Stochastic Economic Dispatch Based Optimal Market Clearing Strategy Considering Flexible Ramping Products Under Wind Power Uncertainties

High penetration level of renewable energy has brought great challenges to operation of power systems,and use of flexible resources(FRs)is becoming increasingly important.Flexibility of power systems can be improved by changing generation arrangements,but the interests of some market participants may be harmed in the process.This study proposes a stochastic economic dispatch model with trading of flexible ramping products(FRPs).To calculate changes in revenue and reasonably compensate units that provide FRs,multisegmented marginal bidding for energy is simulated by linearizing generation cost,and an optimal market clearing strategy for FRPs is developed according to changes in clearing energy and marginal clearing price.Then,the correlation between prediction errors of wind speeds among different wind farms is determined based on a joint distribution function modeled by the copula function,and quasi-Monte Carlo simulation(QMC)is used to generate wind power scenarios.Finally,numerical simulations of modified IEEE-30 and IEEE-118 bus systems is performed with minimum comprehensive cost as the objective function.This verifies the proposed model could effectively deal with wind variability and uncertainty,stabilize the marginal clearing price of the electricity market,and ensure fairness in the market.

Effects of Flexibility and Suspension Configuration of Main Shaft on Dynamic Characteristics of Wind Turbine Drivetrain

The current research of wind turbine drivetrain is mainly concentrated in dynamic characteristics of gearbox with a specific suspension of main shaft, such as one-point and two-point suspension. However, little attention is paid to the e ects of these suspension configurations on the dynamic responses of wind turbine gearbox. This paper investigates the influences of suspension configurations of main shaft on the dynamic characteristics of drivetrain. For evaluating the dynamic behaviors of drivetrain with multi-stage transmission system more realistically, a dynamic modeling approach of drivetrain is proposed based on Timoshenko beam theory and Lagrange's equation. Considering the flexibility and di erent suspension configurations of main shaft, time-varying mesh sti ness excitation, time-varying transmission error excitation and gravity excitation, etc., a three-dimensional dynamic model of drivetrain is developed, and the dynamic responses of drivetrain are investigated. Results show that with the one-point suspension of main shaft, the resonance frequencies in gearbox, especially at the low-speed stage, obviously shift to the higher frequency range compared to the gearbox without main shaft, but this trend could be inversed by increasing main shaft length. Meanwhile, the loads in main shaft, main shaft bearing and carrier bearing are greatly sensitive to the main shaft length. Hence, the load sharing is further disrupted by main shaft, but this e ect could be alleviated by larger load torque. Comparing to the one-point suspension of main shaft, there occurs the obvious load reduction at the low-speed stage with two-point suspension of main shaft. However, those advantages greatly depend on the distance between two main bearings, and come at the expense of increased load in upwind main shaft unit and the corresponding main bearing. Finally, a wind field test is conducted to verify the proposed drivetrain model. This study develops a numerical model of drivetrain which is able to evaluate the e ects of di erent suspension configurations of main shaft on gearbox.

A simplified method for analyzing the fundamental frequency of monopile supported offshore wind turbine system design

Preliminary design of offshore wind turbines requires high precision simplified methods for the analysis of the system fundamental frequency. Based on the Rayleigh method and Lagrange’s Equation, this study establishes a simple formula for the analysis of system fundamental frequency in the preliminary design of an offshore wind turbine with a monopile foundation. This method takes into consideration the variation of cross-section geometry of the wind turbine tower along its length, with the inertia moment and distributed mass both changing with diameter. Also the rotational flexibility of the monopile foundation is mainly considered. The rigid pile and elastic middle long pile are calculated separately. The method is validated against both FEM analysis cases and field measurements, showing good agreement. The method is then used in a parametric study, showing that the tower length Lt, tower base diameter d0, tower wall thickness δt, pile diameter db and pile length Lb are the major factors influencing the fundamental frequency of the offshore wind turbine system. In the design of offshore wind turbine systems, these five parameters should be adjusted comprehensively. The seabed soil condition also needs to be carefully considered for soft clay and loose sand.

柔性光伏系统颤振性能的节段模型试验研究

柔性光伏支架的频率低、质量轻,极易在风荷载作用下发生大幅振动。以某实际柔性光伏项目为工程背景,借鉴桥梁抗风的研究经验,对该柔性光伏支架的颤振性能进行研究。首先,考虑严格的相似比关系,设计并制作了弹性悬挂节段模型系统,并对其动力特性进行了测试;然后,进行不同光伏组件倾角(-39°~+39°)下的弹性悬挂节段模型测振风洞试验,研究光伏组件风致响应随风速的变化规律,得到各倾角下柔性光伏节段模型的颤振临界风速值,探讨2种气动措施对提高柔性光伏支架颤振稳定性的效果。结果表明:在0°~39°的正倾角工况下,柔性光伏支架的颤振临界风速随光伏组件倾角的增大,呈现先减小后增大的趋势,最小颤振临界风速出现在12°~21°光伏组件倾角范围内,折算成实际风速为9.6m/s;在-39°~0°的负倾角工况下,颤振临界风速随光伏组件倾角的增大,也呈现先减小后增大的趋势,最小颤振临界风速出现在-21°~-12°光伏组件倾角范围内,折算成实际风速为10.1m/s;设置中央稳定板的气动措施难以有效提高柔性光伏支架的颤振临界风速。

Path to Coordinated Development of Wind Power and Power Grids in China

Based on an analysis of the misunderstandings and problems concerning wind power development, this paper summarizes the experiences of the coordinated development of wind power and power grids in foreign countries, and proposes principles and strategies for the coordinated development of wind power and power grids, and related measures and suggestions for large scale development of wind power in China.

Enhancing Wind Power Integration through Optimal Use of Flexibility in Multi-Carrier Energy Systems from the Danish Perspective

Denmark’ goal of being independent of fossil energy sources in 2050 puts forward great demands on all energy subsystems (electricity, heat, gas and transport, etc.) to be operated in a holistic manner. The Danish experience and challenges of wind power integration and the development of district heating systems are summarized in this paper. How to optimally use the cross-sectoral flexibility by intelligent control (model predictive control-based) of the key coupling components in an integrated heat and power system including electrical heat pumps in the demand side, and thermal storage applications in buildings is investigated.

考虑场间-场内风电机组疲劳载荷均衡的海上风氢系统灵活调度

为了降低海上风电场维护次数频繁所带来的高昂成本,提高海上风电的消纳率,提出一种考虑场间-场内风电机组疲劳载荷均衡的海上风氢系统灵活调度方法。首先,量化分析风电机组的疲劳载荷与风电出力、疲劳成本之间的关系,建立了场间-场内风电机组疲劳载荷均衡模型,协调风力发电与疲劳载荷之间的关系。然后,考虑海上天气因素的多变性,提出船舶自适应航行模型。进而,采用柔性直流输电,建立了电氢并举的能量流灵活外送模型。最后,以系统运行总成本最小为目标,提出考虑场间-场内风电机组疲劳载荷均衡的海上风氢系统灵活调度策略。仿真结果表明,相对于传统调度策略,所提的调度策略能够均衡场间疲劳载荷,同时有效地减小场内疲劳载荷差异,经济性提高了8.11%。

“双碳”目标下我国电力系统灵活性资源发展策略研究

大力发展新能源是实现“双碳”目标的重要途径,但新能源的随机性、波动性和间歇性特点给电力系统供需平衡及稳定性带来严峻挑战,亟需发展多元灵活性资源来保障系统的安全稳定运行。本文综述了我国碳中和目标下电力需求及电源结构发展路线的相关研究情况,深入分析了不同风光发电量比例下电力系统对灵活性调节的不同需求,并从高峰能力(充足性)、爬坡灵活性、稳定性、惯性4个方面阐述了未来所需要的“源网荷储”各类灵活性资源特性;结合国际经验,提出了保障安全、低碳发展、经济最优的灵活性资源发展原则,并在分析我国灵活性资源发展存在问题的基础上,提出了与我国电力行业减排目标和中长期电力结构变化趋势相一致的灵活性资源发展路线;最后从电源、电网、负荷、储能、市场机制5个方面提出了发展灵活性资源的重点举措。

多排大跨度光伏柔性索桁架结构设计的差异化

山地光伏电站建设的发展势头迅猛,光伏柔性索桁架结构应运而生。这种结构在原有单层悬索的柔性支架基础上增加了防风结构,能更好地适应复杂地形。但索桁架结构和受力更为复杂,目前缺少统一的设计规范,为研究光伏柔性索桁架两种典型结构的结构性能,采用有限元的方法对不同拱形矢高多排大跨度光伏柔性索桁架进行仿真分析,从结构模态、风振系数以及极限工况多角度开展研究。结果表明,增大防风索拱形的矢高,有利于抑制倒拱和正拱两种结构的风致振动;分析四种极限工况,矢高每增加100 mm,倒拱Z向位移平均减小率最小为10.07%,正拱最小为2.79%。同时倒拱结构的挠度变形和轴力等力学性能优于正拱结构,更具市场应用价值。

双层索系柔性光伏支架结构受力性能研究

目的研究双层索系柔性光伏支架结构在风荷载作用下的静力性能与动力响应。方法采用ABAQUS有限元软件开展双层索系柔性光伏支架结构的静力性能、动力特性、动力响应和风振系数分析,探究了跨度、横向连接系间距以及挠度限值等影响因素对支架结构受力性能的影响。结果结构的风振响应随着跨度的增加而增大;结构跨中挠度及上层索索力随横向连接系间距的增大而增大;增大上层索预应力可以减小结构的动力响应,而下层索预应力过大会导致结构的风振响应增大。结论通过研究给出了双层索系柔性光伏支架结构的风振系数取值范围以及上、下层索的初始预拉力设置建议,可以为其结构抗风设计提供参考。

基于二极管整流器的双极型复合式海上换流站及其控制策略

为提高海上换流站的紧凑型性并降低换流站一次性投入成本,西门子公司提出了基于二极管整流器(diode rectifier,DR)的高压直流输电技术,在此基础上,国内外学者对其控制策略及各种串并联拓扑进行了研究,但仍存在结构复杂、可行性差、运行灵活性低等问题。为此,提出了基于二极管整流器的双极型复合式海上换流站拓扑,正负极分别采用模块化多电平换流器(modularmultilevelconverter,MMC)和DR,以充分利用MMC灵活可控和DR体积小、成本低、可靠性高的优点。为降低直流电缆输电损耗,提出了复合式换流站正负极功率平衡控制,将接地极电流控制在零附近,提高了输电效率,可将高压直流电缆所产生的损耗降低67.7%。设计了限功率控制,在发生直流非对称故障期间通过低速通信,可主动对风电场发出功率进行限制,防止了换流站过电流风险,提高了系统可靠性。最后通过PSCAD/EMTDC仿真分析对所提拓扑及其控制策略进行了可行性验证。

基于变载工况的海上风电机组主轴轴承刚柔耦合动态响应分析

针对海上风电机组主轴用三排圆柱滚子轴承在恒载工况下的仿真结果存在局限性、片面性的问题,提出了一种变载工况下的仿真分析方法,建立了轴承接触力学模型和柔性体模型并对轴承内圈、外圈、保持架进行了刚柔耦合处理。基于变载工况,分析了刚性模型与刚柔耦合模型的理论速度、仿真速度以及加速度响应,并通过刚柔耦合模型研究了三排圆柱滚子轴承内部不同接触表面的接触力特性,结果表明:刚性模型的自转误差比刚柔耦合模型大3.67~22.6倍,刚柔耦合模型的加速度趋势更加平稳且速度波动更小;近风叶轮毂端的推力滚子受力约是远端推力滚子的1.85倍,保持架的平均受力是远端保持架的1.6倍。

光伏组件柔性拖曳结构与传统刚性结构风振响应对比

为准确探究柔性支撑体系下光伏组件振动特性,以某光伏工程为研究对象,考虑稳定结构及承重结构对整体的影响,分别建立传统刚性支撑体系与柔性支撑下的“系泊-光伏组件阵列结构”有限元模型,基于Davenport风谱采用AR自回归技术模拟脉动风荷载进行风振响应分析,对比两种支撑方式的经济性、风振特性及稳定结构对柔性支撑体系的振动影响。结果表明:1)刚性支撑主要以横向摆动为主,平均振幅约为0.5cm,其风振系数分布均匀,建议取值2.0;2)柔性支撑体系以竖向振动为主,平均振幅约为12.3 cm,比刚性体系振幅大,风振系数建议取值1.7~1.8;3)柔性支撑体系建造成本比传统刚性支撑高出约40%,但占地面积减少约32%。说明柔性支撑在抗风性能、经济性方面都不及传统刚性支撑,但其优势主要在于对地形的高适应性,具有跨度大、净空高、有效提高地面利用率等优点,可在劣势地貌下作为刚性支撑的替代;4)地锚拖曳结构对光伏组件振动有明显约束作用,因此在设计时,地锚拖曳结构的数量、分布调整可作为柔性支撑下光伏阵列的结构优化首选条件,以提高整体稳定性。

基于火电灵活性改造的可再生能源消纳系统成本优化

随着风电等可再生能源的大规模发展,带来了消纳难等新挑战,通过火电灵活性改造可以增强电力系统灵活调节能力、提升可再生能源消纳空间,同时需要考虑火电灵活性改造的经济性和对可再生能源消纳的影响。因此,综合考虑火电机组常规运行成本及灵活性改造后增加的各项成本,结合碳排放成本和弃风成本,建立以总成本最小为目标的火电灵活性改造前后优化调度模型,采用对比差值法计算基于火电灵活性改造的可再生能源消纳系统成本。通过算例,将所建模型应用于对比改造前后、不同碳排放强度、是否考虑弃风等不同方案下的机组运行状况及消纳系统成本大小,并拟合得到可再生能源渗透率和消纳系统成本的关系曲线,验证了模型的有效性。

多能互补发电系统故障识别与测距方法

随着大量新能源的接入,使得多端柔性直流系统(modular multilevel converter based multi-terminal direct current, MMC-MTDC)故障特征愈加复杂,快速准确的故障识别与测距是亟需解决的关键难题之一。为此,提出了一种风-光-储-蓄互补发电站经柔性直流输电外送系统故障识别与测距方法。首先,搭建风-光-储-蓄互补发电站经柔直外送系统,在此基础上,提出了一种Teager能量算子能量熵的新方法,利用测量点正负极Teager能量算子能量熵的比值构建故障选极及区段识别判据。接着,针对已识别的故障线路,提出变分模态分解(variational mode decomposition, VMD)与Teager能量算子(teager energy operator, TEO)相结合的故障测距方法。最后,利用PSCAD/EMTDC进行仿真,结果表明所提识别方法可以准确判断故障所在线路,所提测距方法能在故障发生2 ms时间窗内实现故障测距,误差率不超过2.55%,并具有较高的耐过渡电阻能力。

含规模氢能综合利用的高比例风光多能源系统低碳灵活调度

随着风光等间歇性可再生能源大规模增长和并网,可再生能源弃能率升高与系统备用灵活性问题日益突出,为解决高比例可再生能源科学消纳与能源系统灵活稳定运行问题,该文提出一种含规模氢能综合利用的高比例风光多能源系统低碳灵活调度方法。针对电制氢、氢燃料电池、甲烷反应器等组成的氢能综合利用单元进行机理分析并建模,研究该单元参与多能源系统运行的调度策略;对该单元各设备的备用能力进行分析,基于各设备的运行特性,提出氢能利用单元–火电联合承担备用的策略,并建立备用优化模型;最后在改进的IEEE39节点电网、20节点气网和6节点热网构成的多能源系统中进行对比仿真分析,验证所提调度方法促进高比例风光消纳和提供灵活性备用的能力。