Dynamic and Power Generation Features of A Wind-Wave Hybrid System Consisting of A Spar-Type Wind Turbine and An Annular Wave Energy Converter in Irregular Waves

Combining wave energy converters(WECs)with floating offshore wind turbines proves a potential strategy to achieve better use of marine renewable energy.The full coupling investigation on the dynamic and power generation features of the hybrid systems under operational sea states is necessary but limited by numerical simulation tools.Here an aero-hydro-servo-elastic coupling numerical tool is developed and applied to investigate the motion,mooring tension,and energy conversion performance of a hybrid system consisting of a spar-type floating wind turbine and an annular wave energy converter.Results show that the addition of the WEC has no significant negative effect on the dynamic performance of the platform and even enhances the rotational stability of the platform.For surge and pitch motion,the peak of the spectra is originated from the dominating wave component,whereas for the heave motion,the peak of the spectrum is the superposed effect of the dominating wave component and the resonance of the system.The addition of the annular WEC can slightly improve the wind power by making the rotor to be in a better position to face the incoming wind and provide considerable wave energy production,which can compensate for the downtime of the offshore wind.

Research of Power Take-off System for “Sharp Eagle Ⅱ” Wave Energy Converter

The " Sharp Eagle” device is a wave energy converter of a hinged double floating body. The wave-absorbing floating body hinges on the semi-submerged floating body structure. Under the action of wave, the wave-absorbing floating body rotates around the hinge point, and the wave energy can be converted into kinetic energy. In this paper, the power take-off system of " Sharp Eagle Ⅱ” wave energy converter (the second generation of " Sharp Eagle”) was studied, which adopts the hydraulic type power take-off system. The 0-1 power generation mode was applied in this system to make the " Sharp Eagle Ⅱ” operate under various wave conditions. The principle of power generation was introduced in detail, and the power take-off system was simulated. Three groups of different movement period inputs were used to simulate three kinds of wave conditions, and the simulation results were obtained under three different working conditions. In addition, the prototype of " Sharp Eagle Ⅱ” wave energy converter was tested on land and in real sea conditions. The experimental data have been collected, and the experimental data and simulation results were compared and validated. This work has laid a foundation for the design and application of the following " Sharp Eagle” series of devices.

Hydraulic Power Take-off and Buoy Geometries Charac-terisation for a Wave Energy Converter

In the past few decades, world energy consumption grew considerably. Regarding this fact, wave energy should not be discarded as a valid alternative for the production of electricity. Devices suitable to harness this kind of renewable energy source and turn it into electricity are not yet commercially competitive. The work described in this paper aims to contribute to this field of research. It is focused on the design and construction of robust, simple and affordable hydraulic Power Take-Off using hydraulic commercial components.

Experimental Study on Hydrodynamic Characteristics of Vertical-Axis Floating Tidal Current Energy Power Generation Device

To study the characteristics of attenuation, hydrostatic towage and wave response of the vertical-axis floating tidal current energy power generation device （VAFTCEPGD）, a prototype is designed and experiment is carried out in the towing tank. Free decay is conducted to obtain attenuation characteristics of the VAFTCEPGD, and characteristics of mooring forces and motion response, floating condition, especially the lateral displacement of the VAFTCEPGD are obtained from the towing in still water. Tension response of the #1 mooring line and vibration characteristics of the VAFTCEPGD in regular waves as well as in level 4 irregular wave sea state with the current velocity of 0.6 m/s. The results can be reference for theoretical study and engineering applications related to VAFTCEPGD.

Effect of Different Raft Shapes on Hydrodynamic Characteristics of the Attenuator-Type Wave Energy Converter

A numerical simulation method based on CFD has been established to simulate the fully coupled motion for an atten-uator-type wave energy converter(WEC).Based on this method,a detailed parametric analysis has been conducted to investigate the design of the rafts.The effects of different parameters(wave parameters,structural parameters and PTO parameters)on the hydrodynamic characteristics of the attenuator-type WEC were studied in detail.The results show that in terms of wave parameters,there is an optimal wave period,which makes the relative pitching angle amplitude of the WEC reach the maximum,and the increase of wave height is conducive to the relative pitching angle amplitude of wave energy.Under different wave conditions,the relative pitch angle of the parallelogram raft device is the maximum.In terms of structural parameters,the parallelogram attenuator-type device has the optimal values in different relative directions,different distances and different apex angle,which makes the relative motion amplitude of the device reach the maximum,and the spacing and the apex angle have influence on the motion frequency of the device,while the relative direction has almost no influence on it.In terms of PTO parameters,there is an optimal damping coefficient,which makes the power generation efficiency of the WEC reach the maximum.The research results provide a valuable reference for future research and design of the attenuator-type WEC.

Hydrodynamic Performance Study of Wave Energy-Type Floating Breakwaters

The integration of wave energy converters(WECs) with floating breakwaters has become common recently due to the benefits of both cost-sharing and providing offshore power supply. In this study, based on viscous computational fluid dynamics(CFD) theory, we investigated the hydrodynamic performances of the floating box and Berkeley Wedge breakwaters, both of which can also serve as WECs. A numerical wave flume model is constructed using Star-CCM+software and applied to investigate the interaction between waves and wave energy converters while completing the verification of the convergence study of time and space steps. The effects of wave length on motion response and transmission coefficient of the floating box breakwater model are studied. Comparisons of our numerical results and published experimental data indicate that Star-CCM+ is very capable of accurately modeling the nonlinear wave interaction of floating structures, while the analytical potential theory overrates the results especially around the resonant frequency. Optimal damping can be readily predicted using potential flow theory and can then be verified by CFD numerical results. Next, we investigated the relationship between wave frequencies and various coefficients using the CFD model under optimal damping, including the motion response, transmission coefficient, reflection coefficient,dissipation coefficient, and wave energy conversion efficiency. We then compared the power generation efficiencies and wave dissipation performances of the floating box and Berkeley Wedge breakwaters. The results show that the power generation efficiency of the Berkeley Wedge breakwater is always much higher than that of the floating box breakwater. Besides, the wave dissipation performance of the Berkeley Wedge breakwater is much better than that of the floating box breakwater at lower frequency.

Time Series-, Time-Frequency- and Spectral Analyses of Sensor Measurements in an Offshore Wave Energy Converter Based on Linear Generator Technology

Inside the second experimental wave energy converter (WEC) launched at the Lysekil research site on the Swedish west coast in March 2009 a number of sensor systems were installed for measuring the mechanical performance of the WEC and its mechanical subsystems. One of the measurement systems was a set-up of 7 laser triangulation sensors for measuring relative displacement of the piston rod mechanical lead-through transmission in the direct drive. Two measurement periods, separated by 2.5 month, are presented in this paper. One measurement is made two weeks after launch and another 3 months after launch. Comparisons and correlations are made between different sensors measuring simultaneously. Noise levels are investigated. Filtering is discussed for further refinement of the laser triangulation sensor signals in order to separate noise from actual physical displacement and vibration. Measurements are presented from the relative displacement of the piston rod mechanical lead-through, from magnetic flux in the air gap, mechanical strain in the WEC structure, translator position and piston rod axial displacement and active AC power. Investigation into the measurements in the time domain with close-ups, in the frequency domain with Fast Fourier transform (FFT) and with time-frequency analysis with short time Fourier transform (STFT) is carried out to map the spectral content in the measurements. End stop impact is clearly visible in the time-frequency analysis. The FFT magnitude spectra are investigated for identifying the cogging bandwidth among other vibrations. Generator cogging, fluctuations in the damping force and in the Lorenz forces in the stator are distinguished and varies depending on translator speed. Vibrations from cogging seem to be present in the early measurement period while not so prominent in the late measurement period. Vibration frequencies due to wear are recognized by comparing with the noise at generator standstill and the vibration sources in the generator. It is concluded that a moving average is a sufficient filter in the time domain for further analysis of the relative displacement of the piston rod mechanical lead-through transmission.

Power enhancement of pontoon-type wave energy convertor via hydroelastic response and variable power take-off system

Wave energy has gained its popularity in recent decades due to the vast amount of untapped wave energy resources.There are numerous types of wave energy convertor(WEC)being proposed and to be economically viable,various means to enhance the power generation from WECs have been studied and investigated.In this paper,a novel pontoon-type WEC,which is formed by multiple plate-like modules connected by hinges,are considered.The power enhancement of this pontoon-type WEC is achieved by allowing certain level of structural deformation and by utilizing a series of optimal variable power take-off(PTO)system.The wave energy is converted into useful electricity by attaching the PTO systems on the hinge connectors such that the mechanical movements of the hinges could produce electricity.In this paper,various structural rigidity of the interconnected modules are considered by changing the material Young’s modulus in order to investigate its impact on the power enhancement.In addition,the genetic algorithm optimization scheme is utilized to seek for the optimal PTO damping in the variable PTO system.It is observed that under certain condition,the flexible pontoon-type WEC with lesser connection joints is more effective in generating energy as compared to its rigid counterpart with higher connection joints.It is also found that the variable PTO system is able to generate greater energy as compared to the PTO system with constant/uniform PTO damping.

基于逆变器直流电压模式波能装置并网接入方法

针对采用蓄电池提供直流母线电压难于满足波能装置装机容量不断增长需求的问题,提出基于逆变器直流电压模式的多液压发电机组并网接入方法。逆变器为液压发电机组直接提供直流母线电压,组建成波能装置无蓄电池组支撑的直流纳电网。建立了逆变器直流电压模式电路拓扑和直流电压外环控制回路。通过多液压发电机组波能装置基于逆变器直流电压模式仿真试验,验证了无蓄电池组波能装置并网接入方法的可行性。该研究成果已应用到500 kW“长山号”波能装置中,为大功率波能装置并网系统研究奠定了基础。

波浪能液压发电系统灵活接入下的孤岛微电网细粒化调度

当前,波浪能液压发电系统一般采用最大效率转化的控制策略,然而由于波浪能装置的间歇式出力特性,直接通过电池消纳会导致电池容量损耗进一步增大。在这种背景下,是否追求波浪能的最大效率转化值得商榷。为此,该文针对波浪能灵活接入的孤岛微电网系统,深入分析波浪能装置的工作原理,搭建波浪能液压系统的数学模型;在此基础上,以调度周期内的经济性最优为目标,综合考虑电池容量损耗和寿命损耗的影响,建立波浪能灵活接入下的孤岛微电网细粒化调度模型。仿真结果表明,相对于常规的孤岛微电网调度策略而言,在不同的波浪能出力场景下,该文所提的方案具有更优的经济性,为含波浪能的孤岛微电网经济运行策略提供了一个新的思路。

液压式波浪能发电技术研究现状及展望

液压式波浪能发电技术因成熟度高、输出稳定,是目前发展较好的波浪能发电技术之一。介绍了液压式波浪能发电装置的三大元件和液压式波浪能发电系统最新的研究进展,提出了液压式波浪能发电系统现阶段存在的不足,展望了液压式波浪能发电技术未来的发展趋势。

液压蓄能式波浪能装置发电系统的特性

分析了液压蓄能式波浪能转换器(WEC)的工作原理和优势;根据液压马达和永磁同步发电机的数学方程推导出了发电系统的4个基本特性,分析了蓄能器压力和发电机负载对转速、电压和功率的影响;针对液压蓄能式WEC发电系统的两种工作模式——恒电阻模式和恒转速模式,建立了液压蓄能式WEC发电系统的Matlab/Simulink仿真模型,并进行了仿真实验,结果验证了关于液压蓄能式WEC发电系统特性推理的正确性.

基于液压传动的风浪互补发电系统的建模与仿真

针对海上风能和波浪能构建以液压传动为基础的风浪互补发电系统。以该系统的工作原理为依据,在Matlab/Simulink和AMESim环境下创建系统的联合仿真模型,对系统进行模拟仿真。通过系统仿真工作曲线可看出,风力机与波浪能装置输出功率存在一定的互补特性,在蓄能器的缓冲作用下,可实现液压马达的流量、转速和输出功率的基本稳定,进而验证了采用液压传动方案的风浪互补发电系统的可行性。

100 kW组合型振荡浮子式波浪发电装置能量转换系统研究

组合型振荡浮子式波浪发电装置由能量俘获系统与能量转换系统构成,其中能量转换系统直接决定整个装置的能量转换效率和发电功率。基于前期10 k W波浪发电装置的海试结果,对装置中的直驱型液压式能量转换系统进行结构优化,设计一种应用于100 k W波浪发电装置的蓄能型液压式能量转换系统,并研制"液压自调整控制系统",实现能量转换系统蓄能与放能过程的解耦控制。通过现场试验,验证优化后的能量转换系统在提高能量转换效率和维持过程平稳性上的有效性。基于该能量转换系统的能量输出特性,提出发电机带纯阻性负载时的"最大功率点跟踪"匹配负载计算方法,以及后续并网电力变换系统的拓扑结构设计,并通过Simulink仿真,验证方案的可靠性。

液压式波浪能装置能量转换系统研究

波浪能转换装置由能量俘获系统与能量转换系统构成,其中能量转换系统是提高波浪能利用效率的关键环节。以鸭式波浪能装置的能量转换系统为研究对象,介绍液压式能量转换系统组成,分析系统结构及工作原理,提出判断目前系统组成合理的依据,最后采用交叉组合试验对比,得出如何设计选择系统发电机及负载类型。试验现象及数据表明,采用永磁同步发电机(PSMG)及蓄电池组的液压能量转换系统较之其他组合的液压系统在效率和可靠性方面有了明显的改进,如发电品质优,系统稳定性高,对系统设备冲击性小,发电效率及电能利用率高,有利于降低维护成本,符合鸭式波浪能装置实海况试验要求,对波浪能实海况试验样机研发意义重大。

基于液压传动的浮力摆式波浪能发电系统稳压恒频控制

将液压传动应用于波浪能转换装置,并提高能量转换稳定性及转换效率是波浪能开发的热点。文中介绍了基于液压传动的独立浮力摆式波浪能发电系统的结构及工作原理,分析了通过蓄能器、负载控制及变量液压马达排量控制提高系统能量俘获效率及能量输出稳定性的原理。在联合仿真环境下建立了系统整机模型进行计算机仿真,然后进行了半物理试验仿真。计算机和半物理试验仿真的结果表明,基于所述调控原理的浮力摆式波浪能发电系统的能量转换效率及能量输出稳定性得到了提高,验证了调控原理的正确性。

波浪能发电装置中液压自治控制系统实海况试验

介绍一种具有自治功能的液压控制系统,并在鹰式装置"万山号"实海况运行过程中对其工作状况进行对比性试验,记录其对发电参数的影响。结果显示:带有自治控制模块的发电机组蓄能集中发电,输出电压、电流稳定,转换效率保持在80%以上,证明带有蓄能环节的液压自治控制发电系统具有较好的高效性、稳定性,同时可验证利用液压自治控制实现波能装置随来波功率大小自适应分级发电的可行性。

基于液压转换的共振波力发电装置提能系统

根据共振波力发电装置的原理特点及控制需求,设计了闭环阀控式液压提能系统,该提能系统可将波能捕获系统所俘获的波浪能稳定可控地转换为液压能,进而通过液压马达带动发电机发电。通过对比例调速阀和减压阀开度的调节可改变液压提能系统的流量和压力,实现自适应高效提取海洋波能。对液压提能系统进行了启停、变开度、变负载以及稳压变功率等整体性能实验,证明其原理可行。实验表明,该装置具有启停灵活、功率跟踪迅速、过渡过程较短、参数调节容易等较好的静态和动态特性,具备良好的开发应用前景。

波浪能装置中液压发电系统Boost变换机理及控制策略

根据液压发电系统特性可知,其工作转速由蓄能器压力和发电机负载决定,而蓄能器压力和发电机负载是实时变量,不加控制将无法实现液压发电系统始终工作在最佳转速曲线。特别是当液压发电系统整流后直接馈入海岛直流微电网时,转速由直流电网电压唯一确定。文中通过引入Boost变换电路,实现液压发电系统转速的实时控制。提出最高效率转换控制策略,实现液压发电系统始终工作在最佳转速曲线。推导了液压发电系统Boost变换机理,通过试验得到了最佳转速曲线,建立了液压发电系统经过交错并联Boost变换器馈入直流微电网的仿真模型。仿真结果表明,在Boost变换器控制下,液压发电系统始终工作在给定的最佳转速曲线,实现了液压发电系统最高效率转换控制策略。

波浪能装置液压式蓄能系统设计

蓄能系统是漂浮式波浪能装置液压式能量转换系统中的储能环节。以漂浮式波浪能装置液压式能量转换系统为研究对象,介绍了液压式能量系统中的蓄能系统的组成,分析了该系统在大浪下实现稳定发电和小浪时实现0-1发电的原理,建立了预充压力、最低工作压力和最高工作压力、蓄能量几个关键设计参数之间的数学模型,通过计算实例进行数值模拟,获得了大量试验数据。试验结果表明:最高工作压力与最低工作压力在数值上差越大,蓄能系统单个循环释放出的蓄能越多,蓄能系统的成本越低;设计的预充压力安全值为最低工作压力的80%;蓄能量与最高工作压力、最低工作压力、预充压力之间存在耦合关系。