Single Wind Turbine Research Articles

Application of the Townsend–George theory for free shear flows to single and double wind turbine wakes – a wind tunnel study

Abstract. The evolution of the mean velocity and the turbulence downstream of wind turbine wakes within the atmospheric boundary layer has been studied over the past decades, but an analytical description is still missing. One possibility to improve the comprehension of this is to look into the modeling of turbulent bluff body wakes. There, by means of the streamwise scaling of the centerline mean velocity deficit, the nature of the turbulence inside a wake can be classified. In this paper, we introduce the analytical model of classical wake theory as introduced by Albert Alan Townsend and William Kenneth George. To test the theories, data were obtained from wind tunnel experiments using hot-wire anemometry in the wakes of a single model wind turbine and a model wind turbine operating in the wake of an upstream model wind turbine. First, we test whether the requirements under which the Townsend–George theory is valid are fulfilled in the wake of a wind turbine. Based on this verification we apply the Townsend–George theory. Further, this framework allows for distinguishing between two types of turbulence, namely equilibrium and non-equilibrium turbulence. We find that the turbulence at the centerline is equilibrium turbulence and that non-equilibrium turbulence may be present at outer parts of the wake. Finally, we apply the Townsend–George theory to characterize the wind turbine wake, and we compare the results to the Jensen and the Bastankhah–Porté-Agel models. We find that the recent developments from the classical bluff body wake formalism can be used to further improve the wind turbine wake models. Particularly, the classical bluff body wake models perform better than the wind turbine wake models due to the presence of a virtual origin in the scalings, and we demonstrate the possibility of improving the wind turbine wake models by implementing this parameter. We also see how the dissipation changes across the wake, which is important to model wakes within wind farms correctly.

Turbine recommender: The selection of wind turbine type using one of a machine learning technique

This study aims to utilize the machine learning technique to build a model to recommend the suitable wind turbine type based on some variables, such as air speed and air density, as well as visualize the location of the recommended wind turbine selection on a 3D map. Particularly, we applied the K-nearest neighbor model (KNN) to determine the amount of energy produced by a single wind turbine. We applied it on 10 separate wind farms in Saudi Arabia. The results indicate that the model performs very well in predicting the best wind turbine type with the mean accuracy of 88%, where ten wind stations resulted from the optimized model with the suggested turbine type in each station. Adding more wind attributes and other factors may assist in increasing the model mean accuracy. The project’s findings will assist decision-makers in Saudi Arabia to make informed decisions as to what kind of wind turbine is suitable for a specific location. In the long run, this will help to make wind energy-a sustainable source of energy-one of the main goals of the 2030 vision, specifically under National Industrial Development and Logistics Program.

Optimizing of the installed capacity of hybrid renewable energy with a modified MPPT model

The lack of wind speed capacity and the emission of photons from sunlight are the problem in a hybrid system of photovoltaic (PV) panels and wind turbines. To overcome this shortcoming, the incremental conductance (IC) algorithm is applied that could control the converter work cycle and the switching of the buck boost therefore maximum efficiency of maximum power point tracking (MPPT) is reached. The operation of the PV-wind hybrid system, consisting of a 100 W PV array device and a 400 W wind subsystem, 12 V/100 Ah battery energy storage and LED, the PV-wind system requires a hybrid controller for battery charging and usage and load lamp and it’s conducted in experimental setup. The experimental has shown that an average increase in power generated was 38.8% compared to a single system of PV panels or a single wind turbine sub-system. Therefore, the potential opportunities for increasing power production in the tropics wheather could be carried out and applied with this model.

Evaluation of the impact of active wake control techniques on ultimate loads for a 10 MW wind turbine

Abstract. Wind farm control is one of the solutions recently proposed to increase the overall energy production of a wind power plant. A generic wind farm control is typically synthesized so as to optimize the energy production of the entire wind farm by reducing the detrimental effects due to wake–turbine interactions. As a matter of fact, the performance of a farm control is typically measured by looking at the increase in the power production, properly weighted through the wind statistics. Sometimes, fatigue loads are also considered in the control optimization problem. However, an aspect which is rather overlooked in the literature on this subject is the evaluation of the impact that a farm control law has on the individual wind turbine in terms of maximum loads and dynamic response under extreme conditions. In this work, two promising wind farm controls, based on wake redirection (WR) and dynamic induction control (DIC) strategy, are evaluated at the level of a single front-row wind turbine. To do so, a two-pronged analysis is performed. Firstly, the control techniques are evaluated in terms of the related impact on some specific key performance indicators, with special emphasis on ultimate loads and maximum blade deflection. Secondarily, an optimal blade redesign process is performed with the goal of quantifying the modification in the structure of the blade entailed by a possible increase in ultimate values due to the presence of wind farm control. Such an analysis provides for an important piece of information for assessing the impact of the farm control on the cost-of-energy model.

A Comparative Study of Dual Stator With Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

Compared with the single rotor wind turbine, a counter-rotating (CR) wind turbine with two rotor sets leads to twice power density. In this regard, dual stator CR (DSCR) permanent magnet flux switching generator (DSCR-PMFSG) is employed. However, in DSCR-PMFSG both rotor and armature parts are rotating and require slip rings for power transmission. These slip rings associate demerits of constant maintenance, poor speed regulation, increased cost, and additional slip ring losses, whereas DSCR-PMFSG offer lower flux and lesser power density. To overcome the demerits of DSCR-PMFSG as mentioned earlier, this paper proposed a novel dual rotor counter-rotating permanent magnet flux switching generator (DRCR-PMFSG) for wind turbine applications that eliminate the requirements of slip rings and retain brushless operation. The proposed DRCR-PMFSG share one stator connected back-to-back through a flux bridge that provides an alternate flux path between two mechanical ports associated with the inner rotor and outer rotor, contributing to the cumulative output. A detailed comparative analysis of DSCR-PMFSG and DRCR-PMFSG is performed under static characteristics, overload, and wide speed range to generate output power, voltage, current, power density, and efficiency. Quantitative comparative analysis under static analysis evident that proposed DRCR-PMFSG exhibits 33.29% higher flux, suppressed cogging torque and torque ripples up to 53.48% and 67.45%, respectively. Furthermore, a comprehensive quantitative analysis is performed under coupled overload and over-speed capability. Analysis exposes that in comparison with DSCRP-PMFSG, the proposed DRCR-PMFSG improves voltage regulation factor by 55.88%, output current enhanced by 67.9%, raise output voltage to 2.01 times, and power density to 1.72 times while maintaining the efficiency of 90.195% and achieving stable voltage profile with load variation. Finally, a detailed comparative analysis with conventional designs is performed and comprehensive mathematical modelling based on sub-domain model is developed accounting stator slot and rotor pole combinations, magnetic saturation, and winding configuration to validates finite element analysis (FEA) of JMAG Designer v.20.1.

Large Eddy Simulations for Offshore Wind Farms Based on the Lattice Boltzmann Method

This study developed a large-eddy simulation code for offshore wind farms based on the lattice Boltzmann method. We present simulation results for a mesh convergence study for a single wind turbine performance and turbine wake and simulation results for a portion of the wind farm (8 wind turbines) under different inflow turbulence conditions. For Vestas V80 wind turbine with a rotor diameter of 80 m, the actuator line model shows the mesh convergence on a 2 m grid. The mesh dependence was significant for the uniform inflow condition for the wind turbine wake. In contrast, the resolution dependence on the mean velocity was significantly smaller for the turbulence inflow winds. The wind farm calculations captured trends in the observed wind turbine performance. Still, the following wind turbine performances were smaller than the observation data, suggesting the need to introduce rotational speed and pitch control into the simulations.

Transferability of site-dependent wind turbine performance predictions using machine learning

Within this work, machine learning models of site-specific machine learning models of wind turbine power curves of the Beberibe Wind Farm in Brazil, which consists of 32 turbines and one met mast, were developed. Previous work already showed that machine learning models taking into account site-specific effects can increase power prediction accuracy of single wind turbines by a factor of three compared to the standard power curve binning method. The main goal was to investigate the transferability of these models through power output predictions of various turbines depending on the distance from the met mast. It was found that transferring models within a wind farm is possible, but a decrease of prediction accuracy by up to 30% in certain cases could be observed. Neither the combination of various turbine data, nor the incorporation of site-specific data had an apparent effect on the transferability performance. It was thus concluded that a further investigation is needed, where a larger and more distributed subset of turbines should be used.

Design and Performance Analysis of Composite Airfoil Wind Turbine Blade

Abstract
 Small horizontal axis wind turbine rotors with composite airfoil rotor blades were designed and investigated in the present study in order to improve its performance in low wind speed and low Reynolds number (Re) conditions for standalone system. The geometrical and aerodynamic nature of a single airfoil small horizontal axis wind turbine blade curtails efficient energy harnessing of the rotor blade. The use of composite airfoil rotor blade improves energy production but imposes uncertainty in determining an optimal design angle of attack and the off design aerodynamic behaviour of the rotor. This research investigated the effects of two airfoils used at different sections in a composite blade and determined the blade’s optimal design angle of attack for maximum power generation. The wind turbine rotor blades were designed using blade element momentum (BEM) method and modelled by SolidWorks software. The SG6042 and SG6043 airfoils were used for the composite airfoil blades. Five wind turbines were designed with rotor blades of design angles of attack from 3° to 7°. The five wind turbine blades were simulated in computational fluid dynamics to determine the optimal design angle of attack. The composite airfoil wind turbine blade showed improved performance, whereas, the wind power generated ranged from 4966 W to 5258 W and rotor power coefficients ranged from 0.443 to 0.457. The blade with design angle of attack of 6° showed highest performance.
 Keywords: composite airfoil, lift-to-drag ratio, pressure coefficient, Reynolds number, design angle of attack.

Performance optimization of a dual-rotor ducted wind turbine by using response surface method

• The effect of different dual-rotor wind turbine operating conditions on ducted wind turbines was studied. • ANOVA was used to model the effect of dual rotor design factors on extracted power. • Response Surface Method applied to experimental data in order to optimize the dual rotor wind turbine performance. • Key parameters were affecting the performance of the turbine investigated by RSM. • A suitable dual rotor wind turbine for ducted wind turbines was designed, and RSM was an excellent method to optimize DWTs. The presented study evaluates and optimizes the performance of dual-rotor wind turbines installed inside a developed duct. The effect of different operating conditions on the extracted power was compared between dual-rotor wind turbines (DRWT) and single rotor wind turbines (SRWT). These operating conditions include the type of dual-rotor wind turbines installed in the throat section of the duct, the distance between the two rotors of a turbine, and the flow velocity through the duct throat that were evaluated by the multivariate statistical method response surface methodology. The central composite design of the response surface method was utilized to fit the designed model based on the least-squares method. Also, the multiple regression method was applied for the empirical data to match variable operating conditions with the developed model by analysis of variance (ANOVA). Afterward, some experiments were carried on to validate this method. The results showed a maximum power ratio of about 55% at the optimized conditions for dual rotor wind turbines. Determined P-values for designed parameters of models were less than 0.05, which makes its effect on the model significant. Furthermore, the power ratio obtained from empirical data was compatible with the considered model.

An Assessment of Renewable Energies in a Seawater Desalination Plant with Reverse Osmosis Membranes.

The purpose of our study was to reduce the carbon footprint of seawater desalination plants that use reverse osmosis membranes by introducing on-site renewable energy sources. By using new-generation membranes with a low energy consumption and considering wind and photovoltaic energy sources, it is possible to greatly reduce the carbon footprint of reverse osmosis plants. The objective of this study was to add a renewable energy supply to a desalination plant that uses reverse osmosis technology. During the development of this research study, photovoltaic energy was discarded as a possible source of renewable energy due to the wind conditions in the area in which the reverse osmosis plant was located; hence, the installation of a wind turbine was considered to be the best option. As it was a large-capacity reverse osmosis plant, we decided to divide the entire desalination process into several stages for explanation purposes. The desalination process of the facility consists of several phases: First, the seawater capture process was performed by the intake tower. This water was then transported and stored, before going through a physical and chemical pre-treatment process, whereby the highest possible percentage of impurities and organic material was eliminated in order to prevent the plugging of the reverse osmosis modules. After carrying out the appraisals and calculating the amount of energy that the plant consumed, we determined that 15% of the plant’s energy supply should be renewable, corresponding to 1194 MWh/year. As there was already a wind power installation in the area, we decided to use one of the wind turbines that had already been installed—specifically, an Ecotecnia turbine (20–150) that produced an energy of 1920 MWh /year. This meant that only a single wind turbine was required for this project.

PMSM Wind Farm Aggregation Algorithm Based on Power Equivalence Principle

With the continuing increase of offshore wind farm power scale, it is urgent to propose a simplified wind farm model, which aggregates the entire wind farm into single or several aggregated wind turbine generators (WTGs), aiming to save computing resources and improve simulation speed. A novel aggregation algorithm that considers the power loss of offshore submarine cable is proposed, which is different from the traditional wind farm modeling method that adopts amplifying transformer as aggregation medium. Moreover, multi machine aggregation (MMA) algorithm is furtherly proposed to improve the aggregation accuracy. Simulation results verify that the proposed aggregation method can present the dynamic characteristics of wind farm with high accuracy, and can be popularized for other types of wind farm.

High Generalization in Anomaly Detection of Wind Turbine Generator Based on Voiceprint

The major research work of the paper is the anomaly diagnosis of wind turbine generator based on voiceprint. The research finds that the reference and comparison between the three blades of a single wind turbine can diagnose whether the wind turbine is faulty. On this base, the paper proposes a periodic audio cutting method based on clustering and median convergence, which effectively cuts the voiceprint, reduces the amount of calculation, and provides a basis for subsequent anomaly detection. The steady-state difference method between three blades of wind turbine is used to detect anomalies, which avoids the migration failure of algorithm caused by the changes of channels and objects to be checked. The paper provides an effective technical means for fan blade inspection.

Inertia and primary frequency modulation strategy for a doubly fed induction generator based on supercapacitor energy storage control

ABSTRACT Doubly fed wind turbines cannot respond to changes in grid frequency under maximum power point tracking control. The traditional deloading frequency control suffers from problems, such as low power generation efficiency, small speed adjustment range, and frequent starting of pitch angle control. An inertia and primary frequency modulation (FM) strategy for a doubly fed wind turbine based on supercapacitor energy storage control is proposed in this study. Virtual inertia and primary frequency adjustments are realized by supercapacitor control. Changing or increasing the additional control of the wind turbine is unnecessary. The proposed strategy can improve the disturbance resistance and self-stabilization of a single wind turbine. The capacity of the energy storage unit is optimally configured in accordance with the cost and charging/discharging efficiency of the actual supercapacitor module. Comparing and evaluating the economics of the primary FM scheme of an active power reserve provide a powerful economic advantage. Simulations and experiments show that inertial support, primary frequency adjustment capability, and power generation benefits are significantly improved compared with those in the conventional primary frequency control. This study provides new ideas for the modified inertia and primary FM function of a doubly fed wind turbine.

Maintenance optimization for a single wind turbine component under time-varying costs

In this paper, we introduce a new, single-component model for maintenance optimization under time-varying costs, specifically oriented at offshore wind turbine maintenance. We extend the standard age replacement policy (ARP), block replacement policy (BRP) and modified block replacement policy (MBRP) to address time-varying costs. We prove that an optimal maintenance policy under time-varying costs is a time-dependent ARP policy. Via a discretization of time, the optimal time-dependent ARP can be found using a linear programming formulation. We also present mixed integer linear programming models for parameter optimization of BRP and MBRP. We present a business case and apply our policies for maintenance planning of a wind turbine gearbox and show that we can achieve savings up-to 23%.

Extensive model validation for generic IEC 61400-27-1 wind turbine models

The aim of this paper is to demonstrate the usefulness, practical applicability, accuracy and reliability of Standard IEC 61400-27-1. The objective of this standard is to specify generic simulation models for the four main types of wind turbines, as well as procedures to validate them. Given that most of the works published and related to the validation of generic wind turbine models have applied a limited number of voltage dip tests to a single wind turbine, the present paper significantly widens the scope of these studies, conducting a total of 59 voltage dip field tests in 7 different wind turbines from 3 manufacturers. The Type 3 and Type 4 wind turbines, i.e., the doubly-fed and the full-scale converter wind turbines, respectively, are the two topologies analysed, since these comprise the vast majority of the market share for new wind turbines. The field measurements carried out on the actual wind turbines are compared to the simulation results of the corresponding IEC dynamic wind turbine models, and the IEC validation methodology is applied. Based on the results obtained, several comparative analyses are performed, and the reasons for differences in the accuracy of the behaviour of the wind turbine topologies considered are also analysed.

Numerical Study for HAWT Wake shape with different Angles of Attack

Increasing world demand for renewable energy resources as wind energy was one of the goals behind research optimization of energy production from wind farms. Wake is one of the important phenomena in this field. This paper focuses on understanding the effect of angle of attack (α) on wake characteristics behind single horizontal axis wind turbines (HAWT). This was done by design three rotors different from each other in value of α used in the rotor design process. Values of α were (4.8˚,9.5˚,19˚). The numerical simulations were conducted using Ansys Workbench 19- Fluent code; the used turbulence model was (k-ω SST). The results showed that best value for extracted wind energy was at α=19˚, spread distance of wake behind single HAWT was inversely proportional with α value. Highest turbulence intensity level was in small values of α =4.8֯ and 9.5֯, which explain presence of meandering phenomenon in these two cases on contrast of α=19֯, while symmetry in wake shape was more obvious in α=19֯ than other cases due to the moderate turbulence intensity which was found in this case, which indicates that lowest aerodynamics loads on rotor components was in α=19˚. So best distribution for turbines in farm could be achieved at use high values of α in comparison to low values.

A novel three-dimensional wake model based on anisotropic Gaussian distribution for wind turbine wakes

The development of a more advanced three-dimensional wake model for wind power generation is presented based on a multivariate Gaussian distribution. The newly-presented model is closer to reality as it truly depends on two independent dimensions (namely horizontal and vertical directions) rather than the radius of a circle. For this reason, the general expression of wake expansion rate in each dimension is specifically developed. In addition, by taking into account the inflow wind shear effect, this current model is able to accurately capture the asymmetric distribution of the vertical wake profile. Four cases including experimental data from wind tunnels and field observations as well as high-fidelity numerical simulation are used to validate the present model. Compared with conventional models, this new model is capable of predicting the wake distribution of a single wind turbine reasonably well. The proposed model is highly simple with a low computational cost. Before applying this model, no additional numerical calculation or trial calculation is required. Wake velocity at any given spatial position can be calculated in an accurate and fast manner. Because of its accuracy, universality and low cost, the present three-dimensional wake model is able to make contributions to farm-level applications such as layout optimization and control strategies and therefore benefit the power output of wind farms.

High-resolution numerical simulation of the performance of vertical axis wind turbines in urban area: Part II, array of vertical axis wind turbines between buildings

Vertical axis wind turbines can harvest wind energy from every direction, and they are suitable for the complex flow conditions in urban areas. The flow field around buildings consists some high speed regions, and the blockage effect can provide higher wind velocity. Meanwhile, they can be installed at a certain altitude with no interference to pedestrians and vehicles. In this paper, we investigate the characteristics of wind turbines in an array by arranging them between two buildings. For this aim, a high-resolution numerical simulation method is adopted to simulate the accurate flow field and force coefficients. The high-resolution numerical simulation method is composed of adaptive mesh refinement and overset grid techniques. Firstly, there are two array types with wind turbines uniformly arranged in a line, which is perpendicular to the free stream. The result shows that array type A with asymmetric wake achieves a greater mean power coefficient. It reveals that the wake matching phenomenon of array type B causes a loss of wind energy between each couple. Secondly, five column positions between the two buildings are arranged in different positions. The five positions correspond to different flow conditions, and they belong to three typical processes: contraction acceleration process, uniform velocity process, and expansion deceleration process. When mounting array type A in contraction acceleration or expansion deceleration regions, the velocity profile is non-uniform along with the array. The power coefficients of wind turbines in one array are significantly different from each other. The array in the contraction acceleration region reaches the maximum mean power coefficient. Thirdly, in order to evaluate the influence of wind directions in urban area, there are four cases with different wind directions. The simulation results show that the array at α∞=15∘ obtains the maximum mean power coefficient. In summary, the mean output power of the wind turbine array in urban areas is always greater than that of a single wind turbine.

Reliability and Economic Evaluation of Offshore Wind Power DC Collection Systems

One key directive to realize the global transition towards net-zero emission goals is to integrate more renewable energy resources into the generation mix. Due to higher and more consistent wind speeds, offshore wind farms (OWFs) have the potential to generate more energy at a steadier rate than their onshore counterpart. However, at the collection system level, all the OWFs use alternating current (AC) technology at present. Nonetheless, with an increasing capacity of the single wind turbine (WT) and larger distances to the shore, the use of direct current (DC) technology at the collection system level is beneficial. To select a suitable DC collection system topology, this paper proposes a comprehensive analytical reliability evaluation method, based on the Universal Generating Function technique, together with associated economic factors. Four candidates DC collection system options were evaluated with different WT capacities for a 400 MW OWF. The availability indices such as Generation Ratio Availability and Expected Energy Not Supplied were used to assess their reliability levels. The results show that the radial topology with a single platform DC/DC converter is more reliable and economical than the other candidate options.

Distributed placement of wind farms to minimize the impact of power fluctuations on the electric power system

The problem of the influence of power fluctuations of wind farms due to the variability of the wind speed on the electric power system is considered. With high wind energy penetration, an increase in the operating reserve in electric power systems is required to cover possible sudden power fluctuations. One of the ways to reduce the stochastic nature of the wind farms power generation is their geographically distributed location. A method is proposed for the selection of capacity and distributed placement of wind farms, taking into account the factor of the variability of the total generated power. In each of the prospective areas for wind farm placement, the simulation of electricity generation by a single wind turbine with hour-by-hour breakdown is carried out using the developed WindMCA software based on long-term ground-based weather stations data. Optimization of wind farms capacity and their distributed placement in areas is carried out using a genetic algorithm in the MATLAB environment. The target function is the coefficient of variation of the power generated by all wind farms in the areas under consideration, depending on the number of wind turbines therein. Power duration curves are used in the final comparison of wind farms siting options. The application of the method is carried out on the example of the wind farms placement in the Zabaykalsky Krai. A solution has been obtained that provides a minimum coefficient of variation of the wind farms generated power and a relatively high capacity utilization factor. With a distributed location of wind farms, the duration of the period with the maximum output is reduced, however, the duration of low power generation is significantly increased. With an increase in the number of wind farms connected to various nodes of the electric power system, a certain guaranteed level of power generation can be obtained, which, ultimately, will reduce the required amount of the reserve of generating capacities.