Multi Wind Turbine Research Articles

Dynamic response strength of integrated foundation for multiple wind turbines

The focus of this paper is on the conceptual design of offshore multi wind turbine integrated floating foundation (MWF) and the strength analysis method of floating structures considering motion response. Firstly, the maximum environmental load and ultimate motion attitude of MWF were used as boundary conditions to solve the problem of imprecise constraint loads in traditional analysis methods. Then, a stress solving equation based on motion state and inertia release was established to solve the equivalent accuracy problem of floating body motion state. Finally, through theoretical analysis, numerical simulation, and experimental testing, it was found that the stress solution method considered the motion state of the floating body in this paper to be more accurate and reliable, with an error of less than 10% compared to the stress results of experimental testing. Improved calculation accuracy by 30%. These studies provide more accurate analytical methods and theoretical references for predicting the strength of floating structures in actual oceans.

Assessment of the azimuthal loads variation by a bi-rotor configuration

Multi wind turbine configurations are emerging in the offshore wind energy market. The modelling of the aerodynamics of these systems is challenging, due to the small lateral distance between rotors and the subsequent interaction between wakes. Previous analysis in the literature showed that, due to this interaction, multi wind turbine concepts present the advantage of an increment in power production, if the rotors are laterally aligned. However, the counterpart in the variation of the blade loads throughout the revolution, has yet to be analysed in depth. This study focuses on the differences observed in azimuthal cycles of blade aerodynamic loads in side-by-side bi-rotor configurations, as an initial analysis of their potential impact on fatigue loads. The analysis has been developed using two aerodynamic codes, with different levels of fidelity. These models are: a Free Vortex filament Method (FVM) combined with an unsteady Lifting Line (LL) model, and a URANS-blade resolved approach. The simulations show that the sectional blade loads are affected by the adjacent rotor, changing the shape of the aerodynamic load cycles along the azimuth. The load azimuthal distributions predicted by a FVM and a URANS models have been compared, showing agreement on the shape of the cycle with slight differences on maximum peak values, specially at the inner sections of the blade. The FVM model has predicted increments in the blade load cycles, with respect to a single rotor case, with a maximum amplitude of a 3% for out-of-plane forces, and a 8% for in-plane forces. The difference in the azimuthal position of both rotors (phase shift angle) mainly affects the azimuthal shape and not so much the characteristic amplitude of these cycles. Finally, including geometric angles as tilt or pre-cone, produces imbalances between the blade sectional forces of the different rotors.

Multi-Wind Turbine Wind Speed Prediction Based on Weighted Diffusion Graph Convolution and Gated Attention Network

The complex environmental impact makes it difficult to predict wind speed with high precision for multiple wind turbines. Most existing research methods model the temporal dependence of wind speeds, ignoring the spatial correlation between wind turbines. In this paper, we propose a multi-wind turbine wind speed prediction model based on Weighted Diffusion Graph Convolution and Gated Attention Network (WDGCGAN). To address the strong nonlinear correlation problem among multiple wind turbines, we use the maximal information coefficient (MIC) method to calculate the correlation weights between wind turbines and construct a weighted graph for multiple wind turbines. Next, by applying Diffusion Graph Convolution (DGC) transformation to the weight matrix of the weighted graph, we obtain the spatial graph diffusion matrix of the wind farm to aggregate the high-order neighborhood information of the graph nodes. Finally, by combining the DGC with the gated attention recurrent unit (GAU), we establish a spatio-temporal model for multi-turbine wind speed prediction. Experiments on the wind farm data in Massachusetts show that the proposed method can effectively aggregate the spatio-temporal information of wind turbine nodes and improve the prediction accuracy of multiple wind speeds. In the 1h prediction task, the average RMSE of the proposed model is 28% and 33.1% lower than that of the Long Short-Term Memory Network (LSTM) and Convolutional Neural Network (CNN), respectively.

Coordinated Power Smoothing Control Strategy of Multi-Wind Turbines and Energy Storage Systems in Wind Farm Based on MADRL

The randomness and volatility of wind power greatly affect the safety and economy of the power systems, and the wake effect of the wind farm aggravates the wind energy loss and the wind power fluctuation. Taking into consideration the wake effect of the wind farm, a new coordinated wind power smoothing control strategy for multi-wind turbines (M-WT) and energy storage systems (ESS) is proposed. The proposed method is based on a multi-agent deep reinforcement learning (MADRL), in which the relationship between output power and wake effect is firstly analyzed, and a power smoothing control model of the M-WT and ESS is established. MADRL is then introduced to optimize the power control of M-WT and ESS. In order to further increase the learning and training efficiency, an improved MADRL algorithm based on the partitioned experience buffer and prioritized experience replay is proposed, where the experience buffer is divided into positive, negative, and neutral experiences, and the experiences are sampled according to experience priority. The effectiveness of the proposed strategy is verified on the SimWindFarm platform. The results show that the proposed control strategy can maximize the economic benefits while further smoothing wind power fluctuations and increasing power generation.

Numerical Framework for the Coupled Analysis of Floating Offshore Multi-Wind Turbines

Floating offshore multi-wind turbines (FOMWTs) are an interesting alternative to the up-scaling of wind turbines. Since this is a novel concept, there are few numerical tools for its coupled dynamic assessment at the present time. In this work, a numerical framework is implemented for the simulation of multi-rotor systems under environmental excitations. It is capable of analyzing a platform using leaning towers that handle wind turbines with their own features and control systems. This tool is obtained by coupling the seakeeping hydrodynamics solver SeaFEM with the single wind turbine simulation tool OpenFAST. The coupling of SeaFEM provides a higher fidelity hydrodynamic solution, allowing the simulation of any structural design using the finite element method (FEM). Additionally, a methodology is proposed for the extension of the single wind solver, allowing for the analysis of multi-rotor configurations. To do so, the solutions of the wind turbines are computed independently using several OpenFAST instances, performing its dynamic interaction through the floater. This method is applied to the single turbine Hywind concept and the twin-turbine W2Power floating platform, supporting NREL 5-MW wind turbines. The rigid-body response amplitude operators (RAOs) are computed and compared with other numerical tools. The results showed consistency in the developed framework. An agreement was also obtained in simulations with aerodynamic loads. This resulting tool is a complete time-domain aero–hydro–servo–elastic solver that is able to compute the combined response and power generation performance of multi-rotor systems.

Design of an Innovative Point Array Offshore Floating Wind Turbine System and Analysis of Hydrodynamic Coupling Response Law

The new lattice floating wind turbine integrated system (also known as dot matrix floating wind turbine, and hereinafter referred to as DMF) is proposed as a new concept. More far reaching, it has obvious advantages over the traditional floating wind turbine scheme in terms of structural cost and motion stability, which provides a new idea for the development of offshore wind power energy. First, the structural parameters and mechanical model of DMF are analyzed to determine the feasibility and superiority of the overall scheme of the new lattice foundation. It is concluded that the stability of DMF in pitching motion is 70% higher than that of the traditional OC4 system. In order to further verify the feasibility of the DMF system and the accuracy of the theoretical model, based on the similarity theory, the research carried out the small‐scale prototype processing of DMF and the simulation experiment of wind wave flume. The test results are in good agreement with the simulation data. This study provides a reference and theoretical basis for the research and development of offshore multi wind turbine combined equipment and hydrodynamic stability optimization. It has certain theoretical guiding significance and economic development value.

Efficiency and Feasibility Analysis of Wind Turbines in Tandem in a Vortex Tube

Polar scientific research is of great importance for the human. The exploitable wind energy of the polar region accounts for more than 20% in the worldwide sense. However, the harsh polar storms, extreme wind speed (up to 100 m/s), ice crystals and sand in the wind all hinder the exploitation of wind resources. Therefore, in order to protect the power generation infrastructure and to maximize the power generation window, this paper proposes an innovative concept of power generation first. This concept, placing multi wind turbines in tandem in a vortex tube, is based on the Venturi principle which allows the wind in a funnel-shaped air inlet to accelerate. Meanwhile, the large-scale vortices and associated turbulent kinetic energy in the tube are diminished through the inlet honeycomb grid, thus driving the multi-turbines in tandem to generate more power. Second, to verify the efficiency of this concept, the CFD simulation technology is employed to investigate the wake characteristics in two distinct flow fields, namely the open space and the vortex tube space. The simulation results are then compared with prototype site tests. The comparison confirms the superior performance of this vortex tube scheme accommodating multi-turbines and the use of a honeycomb at the inlet.

Study on structural design and hydrodynamic response law of new floating wind power fishery integration

The new lattice floating wind turbine integrated system (also known as Dot Matrix Floating wind turbine, and hereinafter referred to as DMF) is proposed as a new concept. It is a design scheme that combines multiple wind turbines into a polygonal floating foundation in the form of a lattice arrangement, which can meet the research and development requirements of higher power generation equipment in the future. More far-reaching, it has obvious advantages over the traditional floating wind turbine scheme in terms of structural cost and motion stability, which provides a new idea for the development of offshore wind power energy. Firstly, the structural parameters and mechanical model of DMF are analyzed to determine the feasibility and superiority of the overall scheme of the new lattice foundation. Combined with the traditional OC4 semi-submersible wind turbine system, the hydrodynamic simulation under wind, wave, and current load is carried out, and the hydrodynamic response law of DMF under the different environmental factors is summarized and analyzed. It is concluded that the stability of DMF in pitching motion is 70% higher than that of traditional OC4 system. In order to further verify the feasibility of the DMF system and the accuracy of the theoretical model, based on the similarity theory, this study carried out the small-scale prototype processing of DMF and the simulation experiment of wind wave flume. The test results are in good agreement with the simulation data. Finally, aiming at the problem of the large amplitude of swaying motion response of DMF in the simulation results, a mooring optimization scheme suitable for the new DMF is proposed, which provides 47% stability compared with the traditional catenary mooring through comparative analysis. This study provides a reference and theoretical basis for the research and development of offshore multi-wind turbine combined equipment and hydrodynamic stability optimization. It has certain theoretical guiding significance and economic development value.

Influence of lateral rotor spacing on the benefits in power generated by multi-rotor configurations

In this work, an analysis of the rotor wakes interaction for different array configurations of onshore wind turbines, has been made using CENER’s in-house aerodynamic module, called AeroVIEW. The study focuses on how the distance between rotors affects the increases in power and thrust obtained by configurations with more than one laterally aligned rotor. Two configurations of laterally aligned multi wind turbines of NREL 5-MW type, operating at 8 m/s wind speed and 9.21 rpm, have been analyzed. The first one consists of 5 wind turbines and the second one consists of 2 wind turbines. These configurations have been studied for different separation distances between the rotors hubs, between 1.1 diameters and 3 diameters. The increases obtained in power with AeroVIEW are in line to the results of high fidelity tools found in the literature. The results show a higher increment of power with lower separation distances. Moreover, this beneficial effect on the power generated, has a counterpart in the average thrust, whose increase is around half of the power increase.

Design and Stability Analysis of an Offshore Floating Multi-Wind Turbine Platform

The multi-wind turbine platform technology has the potential to harness the significant source of offshore wind energy in deep waters. However, the wake interference between the turbines on the multi-wind turbine platform can cause a reduction in power production; hence, it is important to study the wake effects in the initial phase of the design. This paper studies the effects of wake interference between the wind turbines on three different platform configurations to find a suitable configuration for the wind turbines on a multi-turbine platform. The analytical Larsen wake model and computational fluid dynamics (CFD) simulations are used for evaluating the wake effects. The platform configuration required for the wind turbines is determined based on the results of wake effects, and then a novel platform is designed. The free-floating stability behavior of the multi-wind turbine platform is analyzed using the hydrostatic analysis of the modeled platform. The wave-body interaction between the platform and the waves is predicted using the hydrodynamic analysis. A preliminary cost analysis of the multi-turbine platform concept is evaluated and compared with a single wind turbine floating concept. The results showed that the presented design is a promising concept that can enhance the offshore wind industry.

Potential and Development of Horizontal Axis Wind Turbine Systems and Technologies: A Review

Wind energy has a potency of playing a vital role in the future of energy demand providing and environment freshening in many areas of the world. Utilizing wind turbine systems has become a competitive recourse among other renewable energy sources in terms of cost-effectiveness and the transition toward renewable energy usage. Researchers and developers are constantly dedicated to innovating to improve the technology of designing wind turbine systems. Wind energy depends mainly on the wind velocity and the area that swept them, increasing the wetted area. This is done by either upscaling the area of the wind rotor or constructing multi-wind turbines according to the type of designs that fit modern innovative systems. Though large wind turbine units do not fit with all sites, especially in cities, these turbines may be installed offshore and onshore. This paper aims to explore the relevant works technologies related to the wind energy potential, developments, design improvements, and multi-rotor horizontal axis wind turbine systems (HAWTs). This was achieved based on favorable characteristics such as economic viability and clean energy resources. Hence, these aspects reduce the environmental impacts and improve technological advantages and profitability. The results of this paper provide a recognizable system's facts and platforms that can be easily utilized. Wind Energy has the potency of hybridization with other renewable energy resources, which play an important role in urban planning, smart cities, and Buildings integration.

Reactive Voltage Control of Wind Farm Based on Tabu Algorithm

In view of the fact that current wind farms are mostly multi-wind turbines and it is difficult to accurately control a single wind turbine because of its high dimension in the optimization solution process, the article proposes a reactive power and voltage coordinated control strategy suitable for doubly-fed wind farms. The strategy is mainly divided into three layers. The first is the group layer, which can obtain the reactive power compensation task of the entire group according to the current voltage and voltage indicators of the group collection station. The second is the field layer, in which according to the reactive power compensation tasks issued by the group layer, the reactive power tasks are allocated to each field area based on the tabu search algorithm or the equal margin method. The third is the equipment layer, which allocates equal margins in the area according to the reactive power compensation tasks assigned by the field layer. At the field layer, this article divides 66 wind turbines into five different field areas to solve the reactive power compensation distribution task according to the voltage sensitivity characteristics of the wind turbines on different feeders.

Optimization study of control strategy for combined multi-wind turbines energy production and loads during wake effects

In order to increase the economic benefits of offshore wind farms, reducing the wake effect on the power and fatigue load of wind farms is one of the fundamental ways. In this study, the optimal method of combing yaw offset and pitch control (CYOPC) is put forward for wind farm power and fatigue loads below rated wind speed. To quantify potential power increase and fatigue loads decrease, three turbines in China’s Binhai offshore wind farm are investigated using FAST.Farm. The simulation studies are carried out in region 2 of turbine operation and compared with under yaw control only. Results indicate that the CYOPC method has the potential to increase power and reduce fatigue load.

RoCoF-Minimizing H₂ Norm Control Strategy for Multi-Wind Turbine Synthetic Inertia

The reduction in system inertia under the penetration of power electronic-interfaced generation has fostered various proposals on wind synthetic inertia. Several works in the state of the art propose control strategies to optimize synthetic inertia performance; however, most of the performance metrics indirectly represent frequency control adequacy indicators such as rate of change of frequency or frequency nadir. Also, control definitions assume that there is one variable speed wind turbine and one controller, which limits the applicability of the proposals as power systems normally count with various wind turbines/farms over extended geographical areas with different wind regimes. This work presents a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{2}$ </tex-math></inline-formula> optimal control approach for a variable speed wind turbine synthetic inertia controller. First, the objective of the formulation is to explicitly minimize the rate of change of power system frequency. Second, a stability proof for the multi-wind turbine case is proposed, allowing optimal controllers to be independently implemented for an arbitrary number of wind turbines and wind regimes. The effectiveness of the proposed control scheme is demonstrated with a numerical example, considering an empirically-validated, reduced-order model of the Electric Reliability Council of Texas frequency dynamics.

Effect of Pitch Control on the Performance of an Offshore Floating Multi-Wind-Turbine Platform

The extraction of wind energy from more reliable deep-water offshore wind resources can be advanced by using a multi-wind turbine platform that can reduce mooring and installation costs. This paper describes the results of research aimed at designing a novel semi-submersible platform for placing multiple wind turbines. The offshore floating multi-wind-turbine platform (OFMWTP) hosts five 8 MW wind turbines which is proposed for installing on the gulf coast of the United States. The principal problems that have been addressed here include analyzing the effects of blade pitch control on the performance of the OFMWTP in the above-rated wind speed operating conditions. In this process, the adaptive control techniques vary the blade pitch angle for generating optimum power production and reduce platform motions. The coupled dynamics of the wind turbines with the platform are formulated considering the aerodynamic, hydrostatic, hydrodynamic, and mooring forces. In this study, the adaptive control algorithm designed in previous work is used for the blade pitch control. The wind speed distribution with 15% turbulence intensity and irregular waves with zero degrees incident wave angle is used for simulating the operating conditions. The performance of the adaptive control is compared to a baseline proportional-integral (PI) controller. Simulation results showed that the adaptive controller significantly improves the rotor speed regulation and reduces the fluctuations in generated output power under varying operating conditions.

3-D Layout Optimization of Wind Turbines Considering Fatigue Distribution

As wind resources and land resources become increasingly strained with the rapid expansion of wind energy, the problem of getting a better micro-sitting of wind turbines has gained more and more concerns in the wind industry. A methodology of three-dimension layout of wind turbines (WTs) is proposed in this paper to optimize the horizontal layout and vertical hub height simultaneously. New development of low speed WT technology and influences of micro-sitting of WTs to their O&M costs are considered for the first time. A nested loop consisting of a harmony search algorithm-based layout optimization and a sorting genetic Algorithm-II (NSGA-II)-based turbine selection is also presented to deal with the multi-objective functions. In the optimization process, a polar coordinate transformation-based wake effect model is conducted to simplify the wake effect calculations among the multiwind turbines with different hub height and rotor diameters when the wind direction changes. A 100 MW wind farm case is discussed to illustrate the flexibility and performance improvements of the proposed methodology.

An optimal integrated production and maintenance strategy for a multi-wind turbines system

This paper presents an optimal integrated production and maintenance strategy for a wind farm. A cost model is developed in order to determine sequentially the optimal plan of energy production characterised by the number of working wind turbines and their production rates, and the optimal preventive maintenance policy to be adopted. We model the relationship between the variation of energy production rates and the failure rate of the wind turbines. A numerical example and a sensitivity analysis are presented and the obtained results are discussed.

Wake Management in Wind Farms: An Adaptive Control Approach

Advanced wind measuring systems like Light Detection and Ranging (LiDAR) is useful for wake management in wind farms. However, due to uncertainty in estimating the parameters involved, adaptive control of wake center is needed for a wind farm layout. LiDAR is used to track the wake center trajectory so as to perform wake control simulations, and the estimated effective wind speed is used to model wind farms in the form of transfer functions. A wake management strategy is proposed for multi-wind turbine system where the effect of upstream turbines is modeled in form of effective wind speed deficit on a downstream wind turbine. The uncertainties in the wake center model are handled by an adaptive PI controller which steers wake center to desired value. Yaw angle of upstream wind turbines is varied in order to redirect the wake and several performance parameters such as effective wind speed, velocity deficit and effective turbulence are evaluated for an effective assessment of the approach. The major contributions of this manuscript include transfer function based methodology where the wake center is estimated and controlled using LiDAR simulations at the downwind turbine and are validated for a 2-turbine and 5-turbine wind farm layouts.

Development of an Efficient Numerical Method for Wind Turbine Flow, Sound Generation, and Propagation under Multi-Wake Conditions

The propagation of aerodynamic noise from multi-wind turbines is studied. An efficient hybrid method is developed to jointly predict the aerodynamic and aeroacoustics performances of wind turbines, such as blade loading, rotor power, rotor aerodynamic noise sources, and propagation of noise. This numerical method combined the simulations of wind turbine flow, noise source and its propagation which is solved for long propagation path and under complex flow environment. The results from computational fluid dynamics (CFD) calculations not only provide wind turbine power and thrust information, but also provide detailed wake flow. The wake flow is computed with a 2D actuator disc (AD) method that is based on the axisymmetric flow assumption. The relative inflow velocity and angle of attack (AOA) of each blade element form input data to the noise source model. The noise source is also the initial condition for the wave equation that solves long distance noise propagation in frequency domain. Simulations were conducted under different atmospheric conditions which showed that wake flow is an important part that has to be included in wind turbine noise propagation.

Modeling and Stability Analysis of DC-Link Voltage Control in Multi-VSCs With Integrated to Weak Grid

This paper contributes to giving physical insights into stability of DC-link voltage control in multi-wind turbines integrated to weak grid. Wind farm stability operation will suffer from integrating to weak AC grid, due to strong coupling between the wind turbines control and grid dynamics. Multi-VSCs model is presented for DC-link voltage control stability analysis with effect of coupling among VSCs and grid strength. Based on the model, self-impact components and interaction-impact components are presented to study interactions among VSCs. Impacts of VSCs interactions on stability of DC-link voltage control are studied by investigating self-impact and interaction-impact components variations with considering grid strength, operating point and control loop bandwidth. It is found that interactions between VSC1 and VSC2 become more serious with decline of grid strength, decaying stability of VSCs. Theoretical analysis is verified with simulation of two parallel wind turbines connected to weak grid.