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Collection Editor
Department of Energy Technology, Aalborg University, 9220 Aalborg, Denmark
Interests: power electronics and its applications in motor drives; wind turbines; PV systems; harmonics; reliability of power electronic systems
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Collection Editor
Department of Power Engineering and Mechatronics, Tallinn University of Technology, Tallinn, Estonia
Interests: Impedance-source power electronic converters; renewable energy; distributed generation

Topical Collection Information

Dear Colleagues,

This issue is a continuation of the previous successful Special Issue “Wind Turbines 2013”. Similarly, this issue also focuses on recent advances in the wind energy sector on a wide range of topics, including: wind resource mapping, wind intermittency issues, aerodynamics, foundations, aeroelasticity, wind turbine technologies, control of wind turbines, diagnostics, generator concepts including gearless concepts, power electronic converters, grid interconnection, ride-through operation, protection, wind farm layouts - optimization and control, reliability, operations and maintenance, effects of wind farms on local and global climate, wind power stations, smart-grid and micro-grid related to wind turbine operation.

Prof. Dr. Frede Blaabjerg
Collection Editor

Manuscript Submission Information

Manuscripts for the topical collection can be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on this website. The topical collection considers regular research articles, short communications and review articles. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page.

Please visit the Instructions for Authors page before submitting a manuscript. The article processing charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs).

Related Special Issues

Published Papers (98 papers)

2023

Jump to: 2022, 2021, 2020, 2019, 2018, 2017, 2016, 2015, 2014

22 pages, 3027 KiB  
Article
Wind Farm Power Prediction Considering Layout and Wake Effect: Case Study of Saudi Arabia
by Khadijah Barashid, Amr Munshi and Ahmad Alhindi
Energies 2023, 16(2), 938; https://doi.org/10.3390/en16020938 - 13 Jan 2023
Cited by 8 | Viewed by 2462
Abstract
The world’s technological and economic advancements have led to a sharp increase in the demand for electrical energy. Saudi Arabia is experiencing rapid economic and demographic growth, which is resulting in higher energy needs. The limits of fossil fuel reserves and their disruption [...] Read more.
The world’s technological and economic advancements have led to a sharp increase in the demand for electrical energy. Saudi Arabia is experiencing rapid economic and demographic growth, which is resulting in higher energy needs. The limits of fossil fuel reserves and their disruption to the environment have motivated the pursuit of alternative energy options such as wind energy. In order to regulate the power system to maintain safe and dependable operation, projections of current and daily power generation are crucial. Thus, this work focuses on wind power prediction and the statistical analysis of wind characteristics using wind data from a meteorological station in Makkah, Saudi Arabia. The data were collected over four years from January 2015 to July 2018. More than twelve thousand data points were collected and analyzed. Layout and wake effect studies were carried out. Furthermore, the near wake length downstream from the rotor disc between 1 and 5 rotor diameters (1D to 5D) was taken into account. Five robust machine learning algorithms were implemented to estimate the potential wind power production from a wind farm in Makkah, Saudi Arabia. The relationship between the wind speed and power produced for each season was carefully studied. Due to the variability in the wind speeds, the power production fluctuated much more in the winter. The higher the wind speed, the more significant the difference in energy production between the five farm layouts, and vice versa, whereas at a low wind speed, there was no significant difference in the power production in all of the near wake lengths of the 1D to 5D rotor diameters downstream from the rotor disc. Among the utilized prediction models, the decision tree regression was found to have the best accuracy values in all four utilized evaluation metrics, with 0.994 in R-squared, 0.025 in MAE, 0.273 in MSE, and 0.522 in RMSE. The obtained results were satisfactory and provide support for the construction of several wind farms, producing hundreds of megawatts, in Saudi Arabia, particularly in the Makkah Region. Full article
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2022

Jump to: 2023, 2021, 2020, 2019, 2018, 2017, 2016, 2015, 2014

19 pages, 3260 KiB  
Article
Detecting Wind Turbine Blade Icing with a Multiscale Long Short-Term Memory Network
by Xiao Wang, Zheng Zheng, Guoqian Jiang, Qun He and Ping Xie
Energies 2022, 15(8), 2864; https://doi.org/10.3390/en15082864 - 14 Apr 2022
Cited by 17 | Viewed by 2494
Abstract
Blade icing is one of the main problems of wind turbines installed in cold climate regions, resulting in increasing power generation loss and maintenance costs. Traditional blade icing detection methods greatly rely on dedicated sensors, such as vibration and acoustic emission sensors, which [...] Read more.
Blade icing is one of the main problems of wind turbines installed in cold climate regions, resulting in increasing power generation loss and maintenance costs. Traditional blade icing detection methods greatly rely on dedicated sensors, such as vibration and acoustic emission sensors, which require additional installation costs and even reduce reliability due to the degradation and failures of these sensors. To deal with this challenge, this paper aims to develop a cost-effective detection system based on the existing operation data collected from the supervisory control and data acquisition (SCADA) systems which are already equipped in large-scale wind turbines. Considering that SCADA data is essentially a multivariate time series with inherent non-stationary and multiscale temporal characteristics, a new wavelet-based multiscale long short-term memory network (WaveletLSTM) approach is proposed for wind turbine blade icing detection. The proposed method incorporates wavelet-based multiscale learning into the traditional LSTM architecture and can simultaneously learn global and local temporal features of multivariate SCADA signals, which improves fault detection ability. A real case study has shown that our proposed WaveletLSTM method achieved better detection performance than the existing methods. Full article
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2021

Jump to: 2023, 2022, 2020, 2019, 2018, 2017, 2016, 2015, 2014

19 pages, 3607 KiB  
Article
Design and Implementation of an Intelligent Blade Pitch Control System and Stability Analysis for a Small Darrieus Vertical-Axis Wind Turbine
by Gebreel Abdalrahman, Mohamed A. Daoud, William W. Melek, Fue-Sang Lien and Eugene Yee
Energies 2022, 15(1), 235; https://doi.org/10.3390/en15010235 - 30 Dec 2021
Cited by 7 | Viewed by 3552
Abstract
A few studies have been conducted recently in order to improve the aerodynamic performance of Darrieus vertical-axis wind turbines with straight blades (H-type VAWTs). The blade pitch angle control is proposed to enhance the performance of H-type VAWTs. This paper aims to investigate [...] Read more.
A few studies have been conducted recently in order to improve the aerodynamic performance of Darrieus vertical-axis wind turbines with straight blades (H-type VAWTs). The blade pitch angle control is proposed to enhance the performance of H-type VAWTs. This paper aims to investigate the performance of an H-type VAWT in terms of its power output and self-starting capability using an intelligent blade pitch control strategy based on a multi-layer perceptron artificial neural network (MLP-ANN) method. The performance of the proposed blade pitch controller is investigated by adding a conventional controller (PID) to the MLP-ANN controller (i.e., a hybrid controller). The dynamics of an H-type VAWT is mathematically modeled in a nonlinear state space for the stability analysis in the sense of Lyapunov. The effectiveness of the proposed pitch control system is validated by building an H-type VAWT prototype model that is extensively tested outdoors under different conditions for both fixed and variable pitch angle configurations. Results demonstrated that the blade-pitching technique enhanced the power output of an H-type VAWT by approximately 22%. The hybrid controller that used a high percentage of the MLP-ANN controller achieved a better control performance by reducing the overshoot of the control response at high rotor speeds. Full article
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29 pages, 13232 KiB  
Article
A Combined RMS Simulation Model for DFIG-Based and FSC-Based Wind Turbines and Its Initialization
by Farshid Goudarzi and Lutz Hofmann
Energies 2021, 14(23), 8048; https://doi.org/10.3390/en14238048 - 1 Dec 2021
Cited by 3 | Viewed by 2504
Abstract
Reconstructable dynamic simulation models of modern variable-speed wind turbines (WTs), which are integrable into any simulation software, are crucial to the scientists investigating the contribution of WTs to counteracting the current power system stability issues. The structural similarity between a doubly fed induction-generator-based [...] Read more.
Reconstructable dynamic simulation models of modern variable-speed wind turbines (WTs), which are integrable into any simulation software, are crucial to the scientists investigating the contribution of WTs to counteracting the current power system stability issues. The structural similarity between a doubly fed induction-generator-based (DFIG-based) WT model and a full-scale-convertor-based (FSC-based) WT model using induction generator offers the possibility of integrating them into a combined modular model with little effort and the same used parameter set. This article presents a combined root mean square (RMS) WT model, which contains a DFIG-based WT and a FSC-based WT using induction generator. The model is designed based on fundamental machine and converter equations and can be applied for classical network stability analyses. Furthermore, analogous well-performing initialization procedures for both DFIG-based and FSC-based WT models are also introduced. As an example, to demonstrate the performance of the WT model in frequency stability studies, the model is extended with a droop-based fast frequency response (FFR) controller and is implemented in a MATLAB-based RMS simulation tool. The results of the case studies confirmed a solid functionality of initialization procedures. Furthermore, they illustrate feasible and comparable general behavior of both WT models as well as their plausible responses in the event of a frequency drop in a 220 kV test system. Full article
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23 pages, 1851 KiB  
Article
A Review of Life Extension Strategies for Offshore Wind Farms Using Techno-Economic Assessments
by Benjamin Pakenham, Anna Ermakova and Ali Mehmanparast
Energies 2021, 14(7), 1936; https://doi.org/10.3390/en14071936 - 31 Mar 2021
Cited by 40 | Viewed by 5963
Abstract
The aim of this study is to look into the current information surrounding decommissioning and life extension strategies in the offshore wind sector and critically assess them to make informed decisions upon completion of the initial design life in offshore wind farms. This [...] Read more.
The aim of this study is to look into the current information surrounding decommissioning and life extension strategies in the offshore wind sector and critically assess them to make informed decisions upon completion of the initial design life in offshore wind farms. This was done through a two-pronged approach by looking into the technical aspects through comprehensive discussions with industrial specialists in the field and also looking into similar but more mature industries such as the Offshore Oil and Gas sector. For the financial side of the assessment, a financial model was constructed to help portray a possible outcome to extend the life for a current offshore wind farm, using the existing data. By employing a techno-economic approach for critical assessment of life extension strategies, this study demonstrates the advantages and disadvantages of each strategy and looks to inform the offshore wind industry the best course of action for current wind farms, depending on their size and age. Full article
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2020

Jump to: 2023, 2022, 2021, 2019, 2018, 2017, 2016, 2015, 2014

32 pages, 10258 KiB  
Article
Free and Forced Vibration Analysis of H-type and Hybrid Vertical-Axis Wind Turbines
by Minhui Tong, Weidong Zhu, Xiang Zhao, Meilin Yu, Kan Liu and Gang Li
Energies 2020, 13(24), 6747; https://doi.org/10.3390/en13246747 - 21 Dec 2020
Cited by 2 | Viewed by 2968
Abstract
Vertical-axis wind turbines (VAWTs) are compact and efficient and have become increasingly popular for wind energy harvesting. This paper mainly focuses on free and forced vibration analysis of two different types of VAWTs, i.e., an H-type VAWT and a new hybrid VAWT. The [...] Read more.
Vertical-axis wind turbines (VAWTs) are compact and efficient and have become increasingly popular for wind energy harvesting. This paper mainly focuses on free and forced vibration analysis of two different types of VAWTs, i.e., an H-type VAWT and a new hybrid VAWT. The H-type VAWT has a lower cost, while the hybrid VAWT has a better self-starting capability at a low wind velocity. Both of them can be used for wind energy harvesting. By using the assumed modes method, the two VAWTs are simplified by a single degree-of-freedom (SDOF) model. By utilizing the method of structural mechanics, a multi-degree-of-freedom (MDOF) model is developed for the two VAWTs and the turbines in them are reasonably simplified. Natural frequency analyses for the SDOF and MDOF models of the two VAWTs are conducted. A beam element model (BEM) of the two VAWTs is created to calculate their natural frequencies and mode shapes and to verify natural frequency results from the SDOF and MDOF models. By using the BEM of the two VAWTs, their amplitude-frequency responses are obtained from harmonic response analysis. To analyze forced vibrations of the two VAWTs, aerodynamic loads on the two VAWTs are obtained from computational fluid dynamics (CFD) simulation. By using solid element models of the two VAWTs, forced transient responses of the two VAWTs are calculated by using the aerodynamic loads from CFD simulation. Steady-state forced response amplitudes of the 1 m-mast hybrid VAWT are 23.8% and 20.5% smaller in X- and Y-directions than those of the 1 m-mast H-type VAWT, respectively. Frequency contents of the aerodynamic loads from CFD simulation are calculated, which confirm that they are periodic, and the power efficiency of the H-type VAWT is about 2.6% higher that of the hybrid VAWT. Full article
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20 pages, 2384 KiB  
Article
A Novel Analytical Wake Model with a Cosine-Shaped Velocity Deficit
by Ziyu Zhang, Peng Huang and Haocheng Sun
Energies 2020, 13(13), 3353; https://doi.org/10.3390/en13133353 - 30 Jun 2020
Cited by 21 | Viewed by 3918
Abstract
A novel analytical model is proposed and validated in this paper to predict the velocity deficit in the wake downwind of a wind turbine. The model is derived by employing mass and momentum conservation and assuming a cosine-shaped distribution for the velocity deficit. [...] Read more.
A novel analytical model is proposed and validated in this paper to predict the velocity deficit in the wake downwind of a wind turbine. The model is derived by employing mass and momentum conservation and assuming a cosine-shaped distribution for the velocity deficit. In this model, a modified wake growth rate rather than a constant one is chosen to take into account the effects of the ambient turbulence and the mechanical turbulence generated. The model was tested against field observations, wind-tunnel measurements in different thrust operations and high-resolution large-eddy simulations (LES) for two aerodynamic roughness lengths. It was found that the normalized velocity deficit predicted by the proposed model shows good agreement with experimental and numerical data in terms of shape and magnitude in the far wake region ( x / d 0 > 3 ). Based on the proposed model, predictions from multiple views and at different locations are demonstrated to show the spatial distribution of streamwise velocity downwind of a wind turbine. The result shows that the model is suitable for predicting streamwise velocity fields and thus could provide some references for the selection of wind turbine spacing. Full article
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18 pages, 3898 KiB  
Article
Application of the Feedback Linearization in Maximum Power Point Tracking Control for Hydraulic Wind Turbine
by Chao Ai, Wei Gao, Qinyu Hu, Yankang Zhang, Lijuan Chen, Jiawei Guo and Zengrui Han
Energies 2020, 13(6), 1529; https://doi.org/10.3390/en13061529 - 24 Mar 2020
Cited by 10 | Viewed by 3298
Abstract
Taking the hydraulic wind turbine as the research object, the method is studied to improve the utilization ratio of wind energy for hydraulic wind turbine, when the wind speed is lower than the rated wind speed. The hydraulic fixed displacement pump speed and [...] Read more.
Taking the hydraulic wind turbine as the research object, the method is studied to improve the utilization ratio of wind energy for hydraulic wind turbine, when the wind speed is lower than the rated wind speed. The hydraulic fixed displacement pump speed and generating power can be used as control output to realize the maximum power point tracking control. The characteristics of the maximum power point tracking control are analyzed for hydraulic wind turbine, and the hydraulic output power is taken as control output based on the comprehensive performance requirements. Because the hydraulic wind turbine is a strong multiplication nonlinear system, the system is globally linearized based the feedback linearization method, and the maximum power point tracking control law is obtained. The simulation and experiment results show that the system has good dynamic performance with the proposed control law. The control provides theoretical guidance for optimal power tracking control law application for hydraulic wind turbine. Full article
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2019

Jump to: 2023, 2022, 2021, 2020, 2018, 2017, 2016, 2015, 2014

19 pages, 3861 KiB  
Article
Analysis on the Force and Life of Gearbox in Double-Rotor Wind Turbine
by Yaru Yang, Hua Li, Jin Yao, Wenxiang Gao and Haiyan Peng
Energies 2019, 12(21), 4220; https://doi.org/10.3390/en12214220 - 5 Nov 2019
Cited by 5 | Viewed by 3526
Abstract
In order to study the force and life of the key components in the gearbox of an existing double-rotor wind turbine, the design and structural parameters of the gearbox in the traditional National Renewable Energy Laboratory (NREL) 5 MW single-rotor wind turbine are [...] Read more.
In order to study the force and life of the key components in the gearbox of an existing double-rotor wind turbine, the design and structural parameters of the gearbox in the traditional National Renewable Energy Laboratory (NREL) 5 MW single-rotor wind turbine are adopted, and the fixed ring gear of the first planetary stage transmission is released to form a differential gearbox suitable for a double-rotor wind turbine with two inputs. The double input is used to connect the double rotor. Subsequently, the characteristics of the gearbox in a double-rotor wind turbine are discussed. On the basis of the constant rated power of the whole wind turbine, the total power is divided into two parts, which are allocated to the double rotors, then two rotational speeds of the two inputs are given according to different power ratios by complying with the matching principle of force and moment. Furthermore, the force acting on the pitch circle of the planet gear, as well as the force and life of the planet bearing of the two-stage planetary transmission are calculated and compared with a single-rotor wind turbine. The results show that the structural advantages of a double-rotor wind turbine can reduce the stress of key components of the gearbox and increase the life span of the planet bearing, thereby the life of the whole gearbox is improved and the downtime of the whole wind turbine is reduced. Full article
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14 pages, 2619 KiB  
Article
AD/RANS Simulations of Wind Turbine Wake Flow Employing the RSM Turbulence Model: Impact of Isotropic and Anisotropic Inflow Conditions
by Linlin Tian, Yilei Song, Ning Zhao, Wenzhong Shen and Tongguang Wang
Energies 2019, 12(21), 4026; https://doi.org/10.3390/en12214026 - 23 Oct 2019
Cited by 6 | Viewed by 2669
Abstract
The Reynolds-averaged Navier–Stokes (RANS)-based generalized actuator disc method along with the Reynolds stress model (AD/RANS_RSM) is assessed for wind turbine wake simulation. The evaluation is based on validations with four sets of experiments for four horizontal-axis wind turbines with different geometrical characteristics operating [...] Read more.
The Reynolds-averaged Navier–Stokes (RANS)-based generalized actuator disc method along with the Reynolds stress model (AD/RANS_RSM) is assessed for wind turbine wake simulation. The evaluation is based on validations with four sets of experiments for four horizontal-axis wind turbines with different geometrical characteristics operating in a wide range of wind conditions. Additionally, sensitivity studies on inflow profiles (representing isotropic and anisotropic turbulence) for predicting wake effects are carried out. The focus is on the prediction of the evolution of wake flow in terms of wind velocity and turbulence intensity. Comparisons between the computational results and the measurements demonstrate that in the near and transition wake region with strong anisotropic turbulence, the AD/RANS_RSM methodology exhibits a reasonably good match with all the experimental data sets; however, in the far wake region that is characterized by isotropic turbulence, the AD/RANS_RSM predicts the wake velocity quite accurately but appears to over-estimate the wake turbulence level. While the introduction of the overall turbulence intensity is found to give an improved agreement with the experiments. The performed sensitivity study proves that the anisotropic inflow condition is recommended as the profile of choice to represent the incoming wind flow. Full article
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24 pages, 8124 KiB  
Article
Design Optimization of a Multi-Megawatt Wind Turbine Blade with the NPU-MWA Airfoil Family
by Jianhua Xu, Zhonghua Han, Xiaochao Yan and Wenping Song
Energies 2019, 12(17), 3330; https://doi.org/10.3390/en12173330 - 29 Aug 2019
Cited by 14 | Viewed by 5667
Abstract
A new airfoil family, called NPU-MWA (Northwestern Polytechnical University Multi-megawatt Wind-turbine A-series) airfoils, was designed to improve both aerodynamic and structural performance, with the outboard airfoils being designed at high design lift coefficient and high Reynolds number, and the inboard airfoils being designed [...] Read more.
A new airfoil family, called NPU-MWA (Northwestern Polytechnical University Multi-megawatt Wind-turbine A-series) airfoils, was designed to improve both aerodynamic and structural performance, with the outboard airfoils being designed at high design lift coefficient and high Reynolds number, and the inboard airfoils being designed as flat-back airfoils. This article aims to design a multi-megawatt wind turbine blade in order to demonstrate the advantages of the NPU-MWA airfoils in improving wind energy capturing and structural weight reduction. The distributions of chord length and twist angle for a 5 MW wind turbine blade are optimized by a Kriging surrogate model-based optimizer, with aerodynamic performance being evaluated by blade element-momentum theory. The Reynolds-averaged Navier–Stokes equations solver was used to validate the improvement in aerodynamic performance. Results show that compared with an existing NREL (National Renewable Energy Laboratory) 5 MW blade, the maximum power coefficient of the optimized NPU 5 MW blade is larger, and the chord lengths at all span-wise sections are dramatically smaller, resulting in a significant structural weight reduction (9%). It is shown that the NPU-MWA airfoils feature excellent aerodynamic and structural performance for the design of multi-megawatt wind turbine blades. Full article
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19 pages, 4043 KiB  
Article
Monitoring Wind Turbine Gearbox with Echo State Network Modeling and Dynamic Threshold Using SCADA Vibration Data
by Xin Wu, Hong Wang, Guoqian Jiang, Ping Xie and Xiaoli Li
Energies 2019, 12(6), 982; https://doi.org/10.3390/en12060982 - 13 Mar 2019
Cited by 14 | Viewed by 4108
Abstract
Health monitoring of wind turbine gearboxes has gained considerable attention as wind turbines become larger in size and move to more inaccessible locations. To improve the reliability, extend the lifetime of the turbines, and reduce the operation and maintenance cost caused by the [...] Read more.
Health monitoring of wind turbine gearboxes has gained considerable attention as wind turbines become larger in size and move to more inaccessible locations. To improve the reliability, extend the lifetime of the turbines, and reduce the operation and maintenance cost caused by the gearbox faults, data-driven condition motoring techniques have been widely investigated, where various sensor monitoring data (such as power, temperature, and pressure, etc.) have been modeled and analyzed. However, wind turbines often work in complex and dynamic operating conditions, such as variable speeds and loads, thus the traditional static monitoring method relying on a certain fixed threshold will lead to unsatisfactory monitoring performance, typically high false alarms and missed detections. To address this issue, this paper proposes a reliable monitoring model for wind turbine gearboxes based on echo state network (ESN) modeling and the dynamic threshold scheme, with a focus on supervisory control and data acquisition (SCADA) vibration data. The aim of the proposed approach is to build the turbine normal behavior model only using normal SCADA vibration data, and then to analyze the unseen SCADA vibration data to detect potential faults based on the model residual evaluation and the dynamic threshold setting. To better capture temporal information inherent in monitored sensor data, the echo state network (ESN) is used to model the complex vibration data due to its simple and fast training ability and powerful learning capability. Additionally, a dynamic threshold monitoring scheme with a sliding window technique is designed to determine dynamic control limits to address the issue of the low detection accuracy and poor adaptability caused by the traditional static monitoring methods. The effectiveness of the proposed monitoring method is verified using the collected SCADA vibration data from a wind farm located at Inner Mongolia in China. The results demonstrated that the proposed method can achieve improved detection accuracy and reliability compared with the traditional static threshold monitoring method. Full article
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31 pages, 14632 KiB  
Article
Intelligent Control of Wind-Assisted PHEVs Smart Charging Station
by Syed Zulqadar Hassan, Tariq Kamal, Muhammad Hussnain Riaz, Syed Aamir Hussain Shah, Hina Gohar Ali, Muhammad Tanveer Riaz, Muhammad Sarmad, Amir Zahoor, Muhammad Abbas Khan and Julio Pascual Miqueleiz
Energies 2019, 12(5), 909; https://doi.org/10.3390/en12050909 - 8 Mar 2019
Cited by 19 | Viewed by 3870
Abstract
Two technology opportunities, integration of renewable energy sources and the electrification of vehicles are being encouraged to reduce dependency on fossil fuels and pollution problems. Nevertheless, the huge increase of plug-in hybrid electric vehicles (PHEVs) on roads will cause an additional load in [...] Read more.
Two technology opportunities, integration of renewable energy sources and the electrification of vehicles are being encouraged to reduce dependency on fossil fuels and pollution problems. Nevertheless, the huge increase of plug-in hybrid electric vehicles (PHEVs) on roads will cause an additional load in demand, especially at rush hours, and therefore, threatens the stability of existing power grids. Considering PHEV stay for several hours in the workplace, (i.e., university), this may provide an inimitable framework to charge PHEV from wind in the workplace. This paper introduces the possibility of introducing intelligent control of wind power and battery storage units as supplementary power sources for future PHEV charging demands during rush hours. The operation of the proposed algorithm is based on the priority levels of PHEVs charging, and fluctuations in DC link voltage levels due to the variation in wind speed. The priorities of PHEVs charging are developed according to their power requirements, maximum rating of distribution transformer and park duration of PHEVs in the workplace during wind speed. Various non-isolated proportional–integral controllers and improved intelligent fuzzy control are used to keep a minimum critical DC link voltage to permit the power conditioning system to operate a charging station uninterruptedly, even at low wind speed. The improved intelligent fuzzy controller also contributes to minimizing the stress on the DC bus and ensures quality output power. The performance of the proposed charging station is verified for the real PHEV under real-world record of wind speed. All the energy sources, electric charging station and their controllers are designed in MATLAB/Simulink. Finally, the feasibility of proposed charging station is checked experimentally in the laboratory. Full article
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16 pages, 7300 KiB  
Article
Dynamic Behavior of Wind Turbine Generator Configurations during Ferroresonant Conditions
by Ajibola Akinrinde, Andrew Swanson and Remy Tiako
Energies 2019, 12(4), 639; https://doi.org/10.3390/en12040639 - 16 Feb 2019
Cited by 21 | Viewed by 4443
Abstract
In this paper the dynamic behavior of different wind turbine generator configurations including doubly fed induction generators (DFIG), squirrel cage induction generator (SCIG), wound rotor induction generator (WRIG), and permanent magnet synchronous generator (PMSG) under ferroresonant conditions of energization and de-energization was investigated [...] Read more.
In this paper the dynamic behavior of different wind turbine generator configurations including doubly fed induction generators (DFIG), squirrel cage induction generator (SCIG), wound rotor induction generator (WRIG), and permanent magnet synchronous generator (PMSG) under ferroresonant conditions of energization and de-energization was investigated using Simulink/MATLAB (version 2017B, MathWorks, Natick, MA, USA). The result showed that SCIG had the highest overvoltage of 10.1 PU during energization, followed by WRIG and PMSG, while the least was DFIG. During de-energization, PMSG had the highest overvoltage of 9.58 PU while WRIG had the least. Characterization of the ferroresonance was done using a phase plane diagram to identify the harmfulness of the ferroresonance existing in the system. It was observed that for most of the wind turbine configurations, a chaotic mode of ferroresonance exists for both energization and de-energization scenarios. Although overvoltage during energization for wind turbine generator configurations was higher than in the de-energization with an exception of PMSG, their phase plane diagrams showed that de-energization scenarios were more chaotic than energization scenarios. The study showed that WRIG was the least susceptible to ferroresonance while PMSG was the most susceptible to ferroresonance. Full article
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25 pages, 13470 KiB  
Article
Effect of Tailing-Edge Thickness on Aerodynamic Noise for Wind Turbine Airfoil
by Xinkai Li, Ke Yang, Hao Hu, Xiaodong Wang and Shun Kang
Energies 2019, 12(2), 270; https://doi.org/10.3390/en12020270 - 16 Jan 2019
Cited by 10 | Viewed by 3832
Abstract
The influence of wind turbine airfoil trailing edge thickness on aerodynamics and aerodynamic noise characteristics was studied using the computational fluid dynamics (CFD)/ Ffowcs Williams–Hawkings (FW–H) method in the present work. First, the airfoil of a DU97-W-300-flatback airfoil was chosen as the research [...] Read more.
The influence of wind turbine airfoil trailing edge thickness on aerodynamics and aerodynamic noise characteristics was studied using the computational fluid dynamics (CFD)/ Ffowcs Williams–Hawkings (FW–H) method in the present work. First, the airfoil of a DU97-W-300-flatback airfoil was chosen as the research object, and numerical method validation was performed. Three kinds of turbulence calculation methods (unsteady Reynolds average Navier-Stokes (URANS), detached eddy simulation (DES), and large eddy simulation (LES)) were investigated in detail, and three sets of grid scales were used to study the impact of the airfoil on the aerodynamic noise. Secondly, the airfoil trailing edge thickness was changed, and the impact of trailing edge thickness on aerodynamics and aerodynamic noise was investigated. Results show that three kinds of turbulence calculation methods yield the same sound pressure frequency, and the magnitude of the sound pressure level (SPL) corresponding to the mean frequency is almost the same. The calculation of the SPL of the peak value and the experimental results can match well with each other, but the calculated core frequency is slightly lower than the experimental frequency. The results of URANS and DES are closer to each other with a changing trend of SPL, and the consequences of the DES calculation are closer to the experimental results. From the comparison of two airfoils, the blunt trailing edge (BTE) airfoil has higher lift and drag coefficients than the original airfoil. The basic frequency of lift coefficients of the BTE airfoil is less than that of the original airfoil. It is demonstrated that the trailing vortex shedding frequency of the original airfoil is higher than that of the BTE airfoil. At a small angle of attack (AOA), the distribution of SPL for the original airfoil exhibits low frequency characteristics, while, at high AOA, the wide frequency characteristic is presented. For the BTE airfoil, the distribution of SPL exhibits low frequency characteristics for the range of the AOA. The maximum AOA of SPL is 4° and the minimum AOA of SPL is 15°, while, for the original airfoil, the maximum AOA of SPL is 19°, and the minimum AOA is 8°. For most AOAs, the SPL of the BTE airfoil is larger than that of the original airfoil. Full article
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2018

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14 pages, 4114 KiB  
Article
A Comparative Computational Fluid Dynamic Study on the Effects of Terrain Type on Hub-Height Wind Aerodynamic Properties
by Akintayo T. Abolude and Wen Zhou
Energies 2019, 12(1), 83; https://doi.org/10.3390/en12010083 - 28 Dec 2018
Cited by 5 | Viewed by 2952
Abstract
The increased adoption of wind power has generated global discourse in wind energy meteorology. Studies based on turbine performances show a deviation of actual output from power curve output, thereby yielding errors irrespective of the turbine site. Understanding the cause of these errors [...] Read more.
The increased adoption of wind power has generated global discourse in wind energy meteorology. Studies based on turbine performances show a deviation of actual output from power curve output, thereby yielding errors irrespective of the turbine site. Understanding the cause of these errors is essential for wind power optimization, thus necessitating investigation into site-specific effects on turbine performance and operation. Therefore, Computational Fluid Dynamics simulations of hub-height wind aerodynamic properties were conducted based on the k-ε turbulence closure model Reynolds Averaged Navier Stokes equations for three terrains. To isolate terrain-induced effects, the same 40 m above mean sea level wind climatology was imposed on all three terrains. For the four wind directions considered, turbulence intensity (TI) was least in the offshore terrain at about 5–7% but ranged considerably higher from 4–18% for the coastal and island terrain. TI on crests also increased significantly by up to 15% upstream of wind direction for the latter terrains. Inflow angle ranged from −15° to +15° in both coastal and island terrains but remained at <+1° in the offshore terrain. Hellman exponent increased from between factors of 2–4 in the other two terrains relative to that of the offshore terrain. Wind speed-up varied from about 1.06–1.13, accounting for a range of 17–30% difference in power output from a hypothetical operational 2 MW turbine output placed in the three different terrains. Turbine loading, fatigue, efficiency, and life cycle can also be impacted by the variations noted. While adopting a site-specific power curve may help minimize errors and losses, collecting these aerodynamic data alongside wind speed and direction is the future for wind power optimization under big data and machine learning. Full article
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18 pages, 9190 KiB  
Article
Application of an Eddy Current-Tuned Mass Damper to Vibration Mitigation of Offshore Wind Turbines
by Jijian Lian, Yue Zhao, Chong Lian, Haijun Wang, Xiaofeng Dong, Qi Jiang, Huan Zhou and Junni Jiang
Energies 2018, 11(12), 3319; https://doi.org/10.3390/en11123319 - 28 Nov 2018
Cited by 29 | Viewed by 4945
Abstract
Offshore wind turbine (OWT) structures are highly sensitive to complex ambient excitations, especially extreme winds. To mitigate the vibrations of OWT structures under windstorm or typhoon conditions, a new eddy current with tuned mass damper (EC-TMD) system that combines the advantages of the [...] Read more.
Offshore wind turbine (OWT) structures are highly sensitive to complex ambient excitations, especially extreme winds. To mitigate the vibrations of OWT structures under windstorm or typhoon conditions, a new eddy current with tuned mass damper (EC-TMD) system that combines the advantages of the eddy current damper and the tuned mass damper is proposed to install at the top of them. In the present study, the electromagnetic theory is applied to estimate the damping feature of the eddy current within the EC-TMD system. Then, the effectiveness of the EC-TMD system for vibration mitigation is demonstrated by small-scale tests. Furthermore, the EC-TMD system is used to alleviate structural vibrations of the OWT supported by composite bucket foundations (CBF) under extreme winds at the Xiangshui Wind Farm of China. It is found that the damping of the EC-TMD system can be ideally treated as having linear viscous damping characteristics, which are influenced by the gaps between the permanent magnets and the conductive materials as well as the permanent magnet layouts. Meanwhile, the RMS values of displacements of the OWT structure can be mitigated by 16% to 28%, and the acceleration can also be reduced significantly. Therefore, the excellent vibration-reducing performance of the EC-TMD system is confirmed, which provides meaningful guidance for application in the practical engineering of OWTs. Full article
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22 pages, 6123 KiB  
Article
Assessment of Wind Energy Potential as a Power Generation Source: A Case Study of Eight Selected Locations in Northern Cyprus
by Mohamad M. Alayat, Youssef Kassem and Hüseyin Çamur
Energies 2018, 11(10), 2697; https://doi.org/10.3390/en11102697 - 10 Oct 2018
Cited by 44 | Viewed by 5182
Abstract
This paper presents a techno-economic assessment of the wind power potential for eight locations distributed over the Northern part of Cyprus. The wind speed data were collected from the meteorological department located in Lefkoşa, Northern Cyprus.Ten distribution models were used to analyze the [...] Read more.
This paper presents a techno-economic assessment of the wind power potential for eight locations distributed over the Northern part of Cyprus. The wind speed data were collected from the meteorological department located in Lefkoşa, Northern Cyprus.Ten distribution models were used to analyze the wind speed characteristics and wind energy potential at the selected locations. The maximum-likelihood method was used for calculating the parameters of the distribution functions.The power law model is utilized to determine the mean wind speed at various heights. In addition, the wind power density for each location was estimated. Furthermore, the performances of different small-scale vertical axis 3–10 kW wind turbines were evaluated to find those that were suitable and efficient for power generation in the studied locations.The results showed that the annual mean wind speed in the regions is greater than 2 m/s at a height of 10 m. Moreover, it is indicated that Generalized Extreme Value distribution provided the best fit to the actual data for the regions of Lefkoşa, Ercan, Girne, Güzelyurt, and Dipkarpaz. However, the Log-Logistic, Weibull, and Gamma distributions gave a better fit to the actual data of Gazimağusa, YeniBoğaziçi, and Salamis, respectively. The Rayleigh distribution does not fit the actual data from all regions. Furthermore, the values of wind power densityat the areas studied ranged from 38.76 W/m2 to 134.29 W/m2 at a height of 50 m, which indicated that wind energy sources in these selected locations are classified as poor. Meanwhile, based on the wind analysis, small-scale wind turbine use can be suitable for generating electricity in the studied locations. Consequently, an Aeolos-V2 with a rating of 5 kW was found to be capable of producing the annual energy needs of an average household in Northern Cyprus. Full article
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18 pages, 6379 KiB  
Article
Combined Blade-Element Momentum—Lifting Line Model for Variable Loads on Downwind Turbine Towers
by Shigeo Yoshida
Energies 2018, 11(10), 2521; https://doi.org/10.3390/en11102521 - 21 Sep 2018
Cited by 5 | Viewed by 3397
Abstract
Downwind rotors are a promising concept for multi-megawatt scale large wind turbines due to their advantages in safety and cost reduction. However, they have risks from impulsive loads when one of the blades passes across the tower wake, where the wind speed is [...] Read more.
Downwind rotors are a promising concept for multi-megawatt scale large wind turbines due to their advantages in safety and cost reduction. However, they have risks from impulsive loads when one of the blades passes across the tower wake, where the wind speed is lower and locally turbulent. Although the tower shadow effects on the tower loads have been discussed in former studies, there is currently no appropriate model for the blade-element and momentum theory so far. This study formulates the tower shadow effects on the tower load variation induced by blades using the lifting line theory, which does not require any empirical parameters. The method is verified via computational fluid dynamics for a 2 MW(megawatt), 3-bladed downwind turbine. The amplitude and the phase of the variation are shown to be accurate in outboard sections, where the rotor-tower clearance is large (>3.0 times of the tower diameter) and the ratio of the blade chord length is small (<0.5 times of the tower diameter), in both of rated and cut-out conditions. Full article
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16 pages, 5144 KiB  
Article
Combined Pitch and Trailing Edge Flap Control for Load Mitigation of Wind Turbines
by Keshan He, Liangwen Qi, Liming Zheng and Yan Chen
Energies 2018, 11(10), 2519; https://doi.org/10.3390/en11102519 - 21 Sep 2018
Cited by 17 | Viewed by 3405
Abstract
Using active control methods for load mitigation in wind turbines could greatly reduce the cost of per kilowatt hour of wind power. In this work, the combined pitch and trailing edge flap control (CPFC) for load mitigation of wind turbines is investigated. The [...] Read more.
Using active control methods for load mitigation in wind turbines could greatly reduce the cost of per kilowatt hour of wind power. In this work, the combined pitch and trailing edge flap control (CPFC) for load mitigation of wind turbines is investigated. The CPFC includes an individual pitch control (IPC) loop and a trailing edge flap control (TEFC) loop, which are combined by a load frequency division control algorithm. The IPC loop is mainly used to mitigate the low frequency loads, and the TEFC loop is mainly used to mitigate the high frequency loads. The CPFC adopts both an azimuth angle feed-forward and a loads feedback control strategy. The azimuth angle feed-forward control strategy should mitigate the asymmetrical loads caused by observable disturbances. and the loads feedback control strategy should decrease asymmetrical loads by closed loop control. A simulation is carried out on the joint platform of FAST and MATLAB. The simulation results show that the damage equivalent load (DEL) of blade root out-of-plane bending moment is reduced by 53.7% while using CPFC, compared to collective pitch control (CPC); and the standard deviation of blade tip out-of-plane deflection is reduced by 50.2% while using CPFC, compared to CPC. The results demonstrate that the CPFC can mitigate the fatigue loads of wind turbines as anticipated. Full article
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13 pages, 2097 KiB  
Article
Using Multiple Fidelity Numerical Models for Floating Offshore Wind Turbine Advanced Control Design
by Joannes Olondriz, Wei Yu, Josu Jugo, Frank Lemmer, Iker Elorza, Santiago Alonso-Quesada and Aron Pujana-Arrese
Energies 2018, 11(9), 2484; https://doi.org/10.3390/en11092484 - 18 Sep 2018
Cited by 5 | Viewed by 4630
Abstract
This paper summarises the tuning process of the Aerodynamic Platform Stabiliser control loop and its performance with Floating Offshore Wind Turbine model. Simplified Low-Order Wind turbine numerical models have been used for the system identification and control tuning process. Denmark Technical University’s 10 [...] Read more.
This paper summarises the tuning process of the Aerodynamic Platform Stabiliser control loop and its performance with Floating Offshore Wind Turbine model. Simplified Low-Order Wind turbine numerical models have been used for the system identification and control tuning process. Denmark Technical University’s 10 MW wind turbine model mounted on the TripleSpar platform concept was used for this study. Time-domain simulations were carried out in a fully coupled non-linear aero-hydro-elastic simulation tool FAST, in which wind and wave disturbances were modelled. This testing yielded significant improvements in the overall Floating Offshore Wind Turbine performance and load reduction, validating the control technique presented in this work. Full article
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13 pages, 4198 KiB  
Article
Dimensional Analysis of Power Prediction of a Real-Scale Wind Turbine Based on Wind-Tunnel Torque Measurement of Small-Scaled Models
by Sutrisno, Sigit Iswahyudi and Setyawan Bekti Wibowo
Energies 2018, 11(9), 2374; https://doi.org/10.3390/en11092374 - 8 Sep 2018
Cited by 5 | Viewed by 4607
Abstract
A preliminary study of a horizontal-axis wind turbine (HAWT) design is carried out using a wind tunnel to obtain its aerodynamic characteristics. Utilization of data from the study to develop large-scale wind turbines requires further study. This paper aims to discuss the use [...] Read more.
A preliminary study of a horizontal-axis wind turbine (HAWT) design is carried out using a wind tunnel to obtain its aerodynamic characteristics. Utilization of data from the study to develop large-scale wind turbines requires further study. This paper aims to discuss the use of wind turbine data obtained the wind-tunnel measurements to estimate the characteristics of wind turbines that have field size. One should measure the torque of two small-scale turbines inside the wind tunnel. The first small-scale turbine has a radius of 0.14 m, and the radius of the second small turbine is 0.19 m. Torque measurement results from both turbines were analyzed using the Buckingham π theorem to obtain a correlation between torsion and diameter variations. The obtained correlation equation was used to estimate the field measurement of turbine power with a radius of 1.2 m. The resulting correlation equation can be applied to approximate the energy generated by the turbine using the size of the field well in the operating area and the tip-speed ratio (λ) of the turbine design. Full article
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33 pages, 7160 KiB  
Article
Conceptual Synthesis of Speed Increasers for Wind Turbine Conversion Systems
by Radu Saulescu, Mircea Neagoe and Codruta Jaliu
Energies 2018, 11(9), 2257; https://doi.org/10.3390/en11092257 - 27 Aug 2018
Cited by 14 | Viewed by 3524
Abstract
Most wind turbines (WT) are of the single-rotor type, which means they are simple, reliable and durable, but unlikely to convert more than 40% of the available wind energy. Different solutions are proposed to minimize WT energy loss and improve performance, such as [...] Read more.
Most wind turbines (WT) are of the single-rotor type, which means they are simple, reliable and durable, but unlikely to convert more than 40% of the available wind energy. Different solutions are proposed to minimize WT energy loss and improve performance, such as the use of speed increasers, counter-rotating wind rotors or counter-rotating electric generators. Downsizing the design, saving weight and reducing the cost of WT conversion systems, while increasing their efficiency, have posed constant challenges to WT designers. Nevertheless, very little research in the field is concerned with, and partially recommends, the design of conversion systems. Therefore, the aim of this paper is to propose a specific algorithm for the conceptual synthesis of speed increasers integrated in WT conversion systems, starting with an inventory of all combinations of the main components of a conversion system that prove compatible for efficient functioning. The algorithm is structured in two sections: the first one includes a four-step approach to WT system design, while the second one follows a three-step procedure for identifying the speed increaser concept. Twenty-two variants of speed increasers are further generated and analyzed, four of which are innovative solutions proposed by the authors. The paper also provides guidelines for identifying the WT conversion system concept according to the circumstances of its application. Full article
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6 pages, 219 KiB  
Article
An Analytical Model for the Regeneration of Wind after Exiting a Wind Farm
by Brian H. Fiedler
Energies 2018, 11(8), 2071; https://doi.org/10.3390/en11082071 - 8 Aug 2018
Viewed by 2999
Abstract
The simplest model for an atmospheric boundary layer assumes a uniform steady wind over a certain depth, of order 1 km, with the forces of friction, pressure gradient and Coriolis in balance. A linear model is here employed for the adjustment of wind [...] Read more.
The simplest model for an atmospheric boundary layer assumes a uniform steady wind over a certain depth, of order 1 km, with the forces of friction, pressure gradient and Coriolis in balance. A linear model is here employed for the adjustment of wind to this equilibrium, as the wake of a very wide wind farm. A length scale is predicted for the exponential adjustment to equilibrium. Calculation of this length scale is aided by knowledge of the angle for which the wind would normally cross the isobars in environmental conditions in the wake. Full article
15 pages, 1842 KiB  
Article
Assessment and Performance Evaluation of a Wind Turbine Power Output
by Akintayo Temiloluwa Abolude and Wen Zhou
Energies 2018, 11(8), 1992; https://doi.org/10.3390/en11081992 - 1 Aug 2018
Cited by 15 | Viewed by 4598
Abstract
Estimation errors have constantly been a technology bother for wind power management, often time with deviations of actual power curve (APC) from the turbine power curve (TPC). Power output dispersion for an operational 800 kW turbine was analyzed using three averaging tine steps [...] Read more.
Estimation errors have constantly been a technology bother for wind power management, often time with deviations of actual power curve (APC) from the turbine power curve (TPC). Power output dispersion for an operational 800 kW turbine was analyzed using three averaging tine steps of 1-min, 5-min, and 15-min. The error between the APC and TPC in kWh was about 25% on average, irrespective of the time of the day, although higher magnitudes of error were observed during low wind speeds and poor wind conditions. The 15-min averaged time series proved more suitable for grid management and energy load scheduling, but the error margin was still a major concern. An effective power curve (EPC) based on the polynomial parametric wind turbine power curve modeling technique was calibrated using turbine and site-specific performance data. The EPC reduced estimation error to about 3% in the aforementioned time series during very good wind conditions. By integrating statistical wind speed forecasting methods and site-specific EPCs, wind power forecasting and management can be significantly improved without compromising grid stability. Full article
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15 pages, 7628 KiB  
Article
Load Estimation of Offshore Wind Turbines
by Sang Lee, Matthew Churchfield, Frederick Driscoll, Senu Sirnivas, Jason Jonkman, Patrick Moriarty, Bjόrn Skaare, Finn Gunnar Nielsen and Erik Byklum
Energies 2018, 11(7), 1895; https://doi.org/10.3390/en11071895 - 20 Jul 2018
Cited by 16 | Viewed by 4887
Abstract
The influence of 3 MW Hywind-II wind turbine wakes from an upstream offshore floating wind turbine on a downstream turbine with a separation distance of seven rotor diameters was studied for a site in the Gulf of Maine. The turbines and the platforms [...] Read more.
The influence of 3 MW Hywind-II wind turbine wakes from an upstream offshore floating wind turbine on a downstream turbine with a separation distance of seven rotor diameters was studied for a site in the Gulf of Maine. The turbines and the platforms were subjected to atmospheric boundary layer flows. Various sensitivity studies on fatigue loads with respect to the positions of the downstream turbine were performed and validated with a large-eddy simulation tool. In particular, the effect of various lateral positions of the downstream turbine relative to the upstream turbine were considered using time-series turbine wake data generated from the large-eddy simulation tool which served as an input to an aero-elastic wind turbine model to assess the loads. The load response from the rotor, tower, and the floating platform for the downstream turbine were sensitive to the lateral offset positions where turbines that were partially exposed to upstream turbine wakes yielded significant increases in the cyclic load range. For the given set of lateral positions for the downstream turbine, the largest damage equivalent load occurred when the turbine was one rotor diameter to the left of the centerline, when looking upstream, which is the position of the turbine fully exposed to upstream turbine wake. On the other hand, the fatigue load on the downstream turbine placed on the right side of the position fully exposed to the upstream turbine wake, yielded lower stress due to the non-symmetric shape of the turbine wake. The configuration associated with the largest damage equivalent loads was further investigated in a large-eddy simulation, modeling both the upstream and downstream turbines. It was found that the energy spectra at the blade rotational frequency were a magnitude order higher for the downstream turbine, especially for surge, heave, pitch, and yaw motion of the platform. The increase of the damage equivalent load for the flapwise blade root moment was 45% compared to the upstream turbine, which can potentially reduce the turbine service life time. Full article
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14 pages, 6815 KiB  
Article
Computational Fluid Dynamics Approach to Predict the Actual Wind Speed over Complex Terrain
by Takanori Uchida
Energies 2018, 11(7), 1694; https://doi.org/10.3390/en11071694 - 29 Jun 2018
Cited by 11 | Viewed by 4273
Abstract
This paper proposes a procedure for predicting the actual wind speed for flow over complex terrain with CFD. It converts a time-series of wind speed data acquired from field observations into a time-series data of actual scalar wind speed by using non-dimensional wind [...] Read more.
This paper proposes a procedure for predicting the actual wind speed for flow over complex terrain with CFD. It converts a time-series of wind speed data acquired from field observations into a time-series data of actual scalar wind speed by using non-dimensional wind speed parameters, which are determined beforehand with the use of CFD output. The accuracy and reproducibility of the prediction procedure were investigated by simulating the flow with CFD with the use of high spatial resolution (5 m) surface elevation data for the Noma Wind Park in Kagoshima Prefecture, Japan. The errors of the predicted average monthly wind speeds relative to the observed values were less than approximately 20%. Full article
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15 pages, 30637 KiB  
Article
LES Investigation of Terrain-Induced Turbulence in Complex Terrain and Economic Effects of Wind Turbine Control
by Takanori Uchida
Energies 2018, 11(6), 1530; https://doi.org/10.3390/en11061530 - 12 Jun 2018
Cited by 14 | Viewed by 4059
Abstract
In the present study, numerical wind simulation was conducted by reproducing the realistic topography near wind turbine sites with high spatial resolutions and using the Large-Eddy Simulation (LES) technique. The topography near wind turbine sites serves as the origin of the terrain-induced turbulence. [...] Read more.
In the present study, numerical wind simulation was conducted by reproducing the realistic topography near wind turbine sites with high spatial resolutions and using the Large-Eddy Simulation (LES) technique. The topography near wind turbine sites serves as the origin of the terrain-induced turbulence. The obtained numerical simulation results showed that the terrain-induced turbulence is generated at a small terrain feature located upstream of the wind turbine. The generated terrain-induced turbulence affects the wind turbine directly. The wind speed and wind direction at the wind turbine site are significantly changed with time. In the present study, a combination of the series of wind simulation results and on-site operation experience led to a decision to adopt an “automatic shutdown program”. Here, an “automatic shutdown program” means the automatic suspension of wind turbine operation based on the wind speed and wind direction meeting the conditions associated with significant effects of terrain-induced turbulence at a wind turbine site. The adoption of the “automatic shutdown program” has successfully led to a large reduction in the number of occurrences of wind turbine damage, thus, creating major positive economic effects. Full article
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13 pages, 22838 KiB  
Article
Computational Fluid Dynamics (CFD) Investigation of Wind Turbine Nacelle Separation Accident over Complex Terrain in Japan
by Takanori Uchida
Energies 2018, 11(6), 1485; https://doi.org/10.3390/en11061485 - 7 Jun 2018
Cited by 11 | Viewed by 5157
Abstract
We have developed an unsteady and non-linear wind synopsis simulator called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain) to simulate the airflow on a micro scale, i.e., a few tens of km or less. In [...] Read more.
We have developed an unsteady and non-linear wind synopsis simulator called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain) to simulate the airflow on a micro scale, i.e., a few tens of km or less. In RIAM-COMPACT, the large-eddy simulation (LES) has been adopted for turbulence modeling. LES is a technique in which the structures of relatively large eddies are directly simulated and smaller eddies are modeled using a sub-grid scale model. In the present study, we conducted numerical wind diagnoses for the Taikoyama Wind Farm nacelle separation accident in Japan. The simulation results suggest that all six wind turbines at Taikoyama Wind Farm are subject to significant influence from separated flow (terrain-induced turbulence) which is generated due to the topographic irregularities in the vicinity of the wind turbines. A proposal was also made on reconstruction of the wind farm. Full article
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15 pages, 3954 KiB  
Article
Interaction of Wind Turbine Wakes under Various Atmospheric Conditions
by Sang Lee, Peter Vorobieff and Svetlana Poroseva
Energies 2018, 11(6), 1442; https://doi.org/10.3390/en11061442 - 4 Jun 2018
Cited by 7 | Viewed by 3706
Abstract
We present a numerical study of two utility-scale 5-MW turbines separated by seven rotor diameters. The effects of the atmospheric boundary layer flow on the turbine performance were assessed using large-eddy simulations. We found that the surface roughness and the atmospheric stability states [...] Read more.
We present a numerical study of two utility-scale 5-MW turbines separated by seven rotor diameters. The effects of the atmospheric boundary layer flow on the turbine performance were assessed using large-eddy simulations. We found that the surface roughness and the atmospheric stability states had a profound effect on the wake diffusion and the Reynolds stresses. In the upstream turbine case, high surface roughness increased the wind shear, accelerating the decay of the wake deficit and increasing the Reynolds stresses. Similarly, atmospheric instabilities significantly expedited the wake decay and the Reynolds stress increase due to updrafts of the thermal plumes. The turbulence from the upstream boundary layer flow combined with the turbine wake yielded higher Reynolds stresses for the downwind turbine, especially in the streamwise component. For the downstream turbine, diffusion of the wake deficits and the sharp peaks in the Reynolds stresses showed faster decay than the upwind case due to higher levels of turbulence. This provides a physical explanation for how turbine arrays or wind farms can operate more efficiently under unstable atmospheric conditions, as it is based on measurements collected in the field. Full article
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21 pages, 24785 KiB  
Article
Experimental Investigation of Static Stall Hysteresis and 3-Dimensional Flow Structures for an NREL S826 Wing Section of Finite Span
by Hamid Sarlak, Ariane Frère, Robert Mikkelsen and Jens N. Sørensen
Energies 2018, 11(6), 1418; https://doi.org/10.3390/en11061418 - 1 Jun 2018
Cited by 9 | Viewed by 4930
Abstract
Flow characteristics of an S826 airfoil at different Reynolds numbers, ranging from 40,000–400,000 (based on airfoil chord length) and angles of attack from −10–25 degrees are thoroughly investigated in a low-speed wind tunnel. The airfoil’s lift and drag polars are first measured, and [...] Read more.
Flow characteristics of an S826 airfoil at different Reynolds numbers, ranging from 40,000–400,000 (based on airfoil chord length) and angles of attack from −10–25 degrees are thoroughly investigated in a low-speed wind tunnel. The airfoil’s lift and drag polars are first measured, and with a focus on pitching the airfoil in upstroke and downstroke orders, static stall hysteresis is identified in selected experiments at Reynolds numbers below 100,000 near the stall angle and subsequently investigated. Experiments using wire-generated free stream turbulence are conducted, and the hysteresis effects are shown to disappear when introducing a free stream turbulence of less than 2.5%. Further, spanwise flow is detected by comparing lift and drag values measured using both surface pressure integration at one cross section as well as integral force gauge measurement, and the surface oil flow visualization technique is subsequently used to study the 3D flow topologies formed on the airfoil. The formation of distinct stall cells on the suction side of the airfoil is observed at Reynolds numbers above 100,000 near the stall angle. By repeating the experiments, stall cells are proven to be reproduceable, although the identical geometries are necessarily not retained in abscence of surface impurities such as tapes. The effect of disturbances on the stall cells is investigated by utilizing roughness elements on the airfoil surface, and it is found that while such disturbances tend to change the shape of the stall cells, they do not contribute to the creation, nor destruction of the cells. Polar and visualisation measurements are also used to study flow separation, and it is observed that the separation location, as well as the laminar separation bubble, moves towards the leading edge when increasing the angle of attack. Full article
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18 pages, 10427 KiB  
Article
Comparison of Shell and Solid Finite Element Models for the Static Certification Tests of a 43 m Wind Turbine Blade
by Mathijs Peeters, Gilberto Santo, Joris Degroote and Wim Van Paepegem
Energies 2018, 11(6), 1346; https://doi.org/10.3390/en11061346 - 25 May 2018
Cited by 28 | Viewed by 9417
Abstract
A commercial 43 m wind turbine blade was tested under static loads. During these tests, loads, displacements, and local strains were recorded. In this work, the blade was modeled using the finite element method. Both a segment of the spar structure and the [...] Read more.
A commercial 43 m wind turbine blade was tested under static loads. During these tests, loads, displacements, and local strains were recorded. In this work, the blade was modeled using the finite element method. Both a segment of the spar structure and the full-scale blade were modeled. In both cases, conventional outer mold layer shell and layered solid models were created by means of an in-house developed software tool. First, the boundary conditions and settings for modeling the tests were explored. Next, the behavior of a spar segment under different modeling methods was investigated. Finally, the full-scale blade tests were conducted. The resulting displacements and longitudinal and transverse strains were investigated. It was found that for the considered load case, the differences between the shell and solid models are limited. Thus, it is concluded that the shell representation is sufficiently accurate. Full article
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18 pages, 21558 KiB  
Article
Comparative Study of the Aerodynamic Performance of the New MEXICO Rotor under Yaw Conditions
by Yaoru Qian, Zhenyu Zhang and Tongguang Wang
Energies 2018, 11(4), 833; https://doi.org/10.3390/en11040833 - 4 Apr 2018
Cited by 22 | Viewed by 4204
Abstract
The influence of yaw misalignment on the aerodynamic performance of the New MEXICO rotor is investigated using blade-resolved Computational Fluid Dynamics (CFD) approaches with three wind speeds considered at a fixed yaw angle of 30 degrees. The air-load predictions and near wake characteristics [...] Read more.
The influence of yaw misalignment on the aerodynamic performance of the New MEXICO rotor is investigated using blade-resolved Computational Fluid Dynamics (CFD) approaches with three wind speeds considered at a fixed yaw angle of 30 degrees. The air-load predictions and near wake characteristics from the numerical results are compared and discussed against the most recent wind tunnel test data. The nacelle impact, dynamic stall phenomenon and wake characteristics are analyzed, demonstrating the yaw effects and numerical issues raised from Reynolds-Averaged Navier Stokes (RANS) and Detached Eddy Simulation (DES) computations. Full article
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19 pages, 592 KiB  
Article
Wind Turbine Condition Monitoring Strategy through Multiway PCA and Multivariate Inference
by Francesc Pozo, Yolanda Vidal and Óscar Salgado
Energies 2018, 11(4), 749; https://doi.org/10.3390/en11040749 - 26 Mar 2018
Cited by 45 | Viewed by 5063
Abstract
This article states a condition monitoring strategy for wind turbines using a statistical data-driven modeling approach by means of supervisory control and data acquisition (SCADA) data. Initially, a baseline data-based model is obtained from the healthy wind turbine by means of multiway principal [...] Read more.
This article states a condition monitoring strategy for wind turbines using a statistical data-driven modeling approach by means of supervisory control and data acquisition (SCADA) data. Initially, a baseline data-based model is obtained from the healthy wind turbine by means of multiway principal component analysis (MPCA). Then, when the wind turbine is monitorized, new data is acquired and projected into the baseline MPCA model space. The acquired SCADA data are treated as a random process given the random nature of the turbulent wind. The objective is to decide if the multivariate distribution that is obtained from the wind turbine to be analyzed (healthy or not) is related to the baseline one. To achieve this goal, a test for the equality of population means is performed. Finally, the results of the test can determine that the hypothesis is rejected (and the wind turbine is faulty) or that there is no evidence to suggest that the two means are different, so the wind turbine can be considered as healthy. The methodology is evaluated on a wind turbine fault detection benchmark that uses a 5 MW high-fidelity wind turbine model and a set of eight realistic fault scenarios. It is noteworthy that the results, for the presented methodology, show that for a wide range of significance, α [ 1 % , 13 % ] , the percentage of correct decisions is kept at 100%; thus it is a promising tool for real-time wind turbine condition monitoring. Full article
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24 pages, 6515 KiB  
Article
A New Analytical Wake Model for Yawed Wind Turbines
by Guo-Wei Qian and Takeshi Ishihara
Energies 2018, 11(3), 665; https://doi.org/10.3390/en11030665 - 15 Mar 2018
Cited by 105 | Viewed by 10243
Abstract
A new analytical wake model for wind turbines, considering ambient turbulence intensity, thrust coefficient and yaw angle effects, is proposed from numerical and analytical studies. First, eight simulations by the Reynolds Stress Model are conducted for different thrust coefficients, yaw angles and ambient [...] Read more.
A new analytical wake model for wind turbines, considering ambient turbulence intensity, thrust coefficient and yaw angle effects, is proposed from numerical and analytical studies. First, eight simulations by the Reynolds Stress Model are conducted for different thrust coefficients, yaw angles and ambient turbulence intensities. The wake deflection, mean velocity and turbulence intensity in the wakes are systematically investigated. A new wake deflection model is then proposed to analytically predict the wake center trajectory in the yawed condition. Finally, the effects of yaw angle are incorporated in the Gaussian-based wake model. The wake deflection, velocity deficit and added turbulence intensity in the wake predicted by the proposed model show good agreement with the numerical results. The model parameters are determined as the function of ambient turbulence intensity and thrust coefficient, which enables the model to have good applicability under various conditions. Full article
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26 pages, 3625 KiB  
Article
Flow Control over the Blunt Trailing Edge of Wind Turbine Airfoils Using Circulation Control
by He-Yong Xu, Qing-Li Dong, Chen-Liang Qiao and Zheng-Yin Ye
Energies 2018, 11(3), 619; https://doi.org/10.3390/en11030619 - 10 Mar 2018
Cited by 12 | Viewed by 5853
Abstract
A new partial circulation control (PCC) method is implemented on the blunt trailing edge DU97-Flatback airfoil, and compared with the traditional full circulation control (FCC) based on numerical analysis. When the Coanda jet is deactivated, PCC has an attractive advantage over FCC, since [...] Read more.
A new partial circulation control (PCC) method is implemented on the blunt trailing edge DU97-Flatback airfoil, and compared with the traditional full circulation control (FCC) based on numerical analysis. When the Coanda jet is deactivated, PCC has an attractive advantage over FCC, since the design of PCC doesn’t degrade aerodynamic characteristics of the baseline flatback section, in contrast to FCC, which is important in practical use in case of failure of the circulation control system. When the Coanda jet is activated, PCC also outperforms FCC in several respects. PCC can produce much higher lift coefficients than FCC over the entire range of angles of attack as well as the entire range of jet momentum coefficients under investigation, but with slightly higher drag coefficients. The flow field of PCC is less complex than that of FCC, indicating less energy dissipation in the main flow and hence less power expenditure for the Coanda jet. The aerodynamic figure of merit (AFM) and control efficiency for circulation control are defined, and results show that PCC has much higher AFM and control efficiency than FCC. It is demonstrated that PCC outperforms FCC in terms of effectiveness, efficiency and reliability for flow control in the blunt trailing edge wind turbine application. Full article
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11 pages, 1531 KiB  
Article
On the Evolution of the Integral Time Scale within Wind Farms
by Huiwen Liu, Imran Hayat, Yaqing Jin and Leonardo P. Chamorro
Energies 2018, 11(1), 93; https://doi.org/10.3390/en11010093 - 2 Jan 2018
Cited by 33 | Viewed by 5610
Abstract
A wind-tunnel investigation was carried out to characterize the spatial distribution of the integral time scale ( T u ) within, and in the vicinity of, two model wind farms. The turbine arrays were placed over a rough wall and operated under high [...] Read more.
A wind-tunnel investigation was carried out to characterize the spatial distribution of the integral time scale ( T u ) within, and in the vicinity of, two model wind farms. The turbine arrays were placed over a rough wall and operated under high turbulence. The two layouts consisted of aligned units distinguished only by the streamwise spacing ( Δ x T ) between the devices, set at five and ten rotor diameters d T (or S x = Δ x T / d T = 5 and 10). They shared the same spanwise spacing between turbines of 2.5 d T ; this resulted in arrays of 8 × 3 and 5 × 3 horizontal-axis turbines. Hotwire anemometry was used to characterize the instantaneous velocity at various vertical and transverse locations along the central column of the wind farms. Results show that T u was modulated by the wind farm layout. It was significantly reduced within the wind farms and right above them, where the internal boundary layer develops. The undisturbed levels above the wind farms were recovered only at ≈ d T / 2 above the top tip. This quantity appeared to reach adjusted values starting the fifth row of turbines in the S x = 5 wind farm, and earlier in the S x = 10 counterpart. Within the adjusted zone, the distribution of T u at hub height exhibited a negligible growth in the S x = 5 case; whereas it underwent a mild growth in the S x = 10 wind farm. In addition, the flow impinging the inner turbines exhibited T u / T i n c u < 1 , where T i n c u is the integral time scale of the overall incoming flow. Specifically, T u β T i n c u at z = z h u b , where β < 1 within standard layouts of wind farms, in particular β 0.5 and 0.7 for S x = 5 and 10. Full article
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2017

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2529 KiB  
Article
Machine Learning for Wind Turbine Blades Maintenance Management
by Alfredo Arcos Jiménez, Carlos Quiterio Gómez Muñoz and Fausto Pedro García Márquez
Energies 2018, 11(1), 13; https://doi.org/10.3390/en11010013 - 21 Dec 2017
Cited by 89 | Viewed by 9577
Abstract
Delamination in Wind Turbine Blades (WTB) is a common structural problem that can generate large costs. Delamination is the separation of layers of a composite material, which produces points of stress concentration. These points suffer greater traction and compression forces in working conditions, [...] Read more.
Delamination in Wind Turbine Blades (WTB) is a common structural problem that can generate large costs. Delamination is the separation of layers of a composite material, which produces points of stress concentration. These points suffer greater traction and compression forces in working conditions, and they can trigger cracks, and partial or total breakage of the blade. Early detection of delamination is crucial for the prevention of breakages and downtime. The main novelty presented in this paper has been to apply an approach for detecting and diagnosing the delamination WTB. The approach is based on signal processing of guided waves, and multiclass pattern recognition using machine learning. Delamination was induced in the WTB to check the accuracy of the approach. The signal is denoised by wavelet transform. The autoregressive Yule–Walker model is employed for feature extraction, and Akaike’s information criterion method for feature selection. The classifiers are quadratic discriminant analysis, k-nearest neighbors, decision trees, and neural network multilayer perceptron. The confusion matrix is employed to evaluate the classification, especially the receiver operating characteristic analysis by: recall, specificity, precision, and F-score. Full article
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23119 KiB  
Article
Flow Adjustment Inside and Around Large Finite-Size Wind Farms
by Ka Ling Wu and Fernando Porté-Agel
Energies 2017, 10(12), 2164; https://doi.org/10.3390/en10122164 - 18 Dec 2017
Cited by 73 | Viewed by 10448
Abstract
In this study, large-eddy simulations are performed to investigate the flow inside and around large finite-size wind farms in conventionally-neutral atmospheric boundary layers. Special emphasis is placed on characterizing the different farm-induced flow regions, including the induction, entrance and development, fully-developed, exit and [...] Read more.
In this study, large-eddy simulations are performed to investigate the flow inside and around large finite-size wind farms in conventionally-neutral atmospheric boundary layers. Special emphasis is placed on characterizing the different farm-induced flow regions, including the induction, entrance and development, fully-developed, exit and farm wake regions. The wind farms extend 20 km in the streamwise direction and comprise 36 wind turbine rows arranged in aligned and staggered configurations. Results show that, under weak free-atmosphere stratification ( Γ = 1 K/km), the flow inside and above both wind farms, and thus the turbine power, do not reach the fully-developed regime even though the farm length is two orders of magnitude larger than the boundary layer height. In that case, the wind farm induction region, affected by flow blockage, extends upwind about 0.8 km and leads to a power reduction of 1.3% and 3% at the first row of turbines for the aligned and staggered layouts, respectively. The wind farm wake leads to velocity deficits at hub height of around 3.5% at a downwind distance of 10 km for both farm layouts. Under stronger stratification ( Γ = 5 K/km), the vertical deflection of the subcritical flow induced by the wind farm at its entrance and exit regions triggers standing gravity waves whose effects propagate upwind. They, in turn, induce a large decelerating induction region upwind of the farm leading edge, and an accelerating exit region upwind of the trailing edge, both extending about 7 km. As a result, the turbine power output in the entrance region decreases more than 35% with respect to the weakly stratified case. It increases downwind as the flow adjusts, reaching the fully-developed regime only for the staggered layout at a distance of about 8.5 km from the farm edge. The flow acceleration in the exit region leads to an increase of the turbine power with downwind distance in that region, and a relatively fast (compared with the weakly stratified case) recovery of the farm wake, which attains its inflow hub height speed at a downwind distance of 5 km. Full article
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2406 KiB  
Review
Structural Reliability Analysis of Wind Turbines: A Review
by Zhiyu Jiang, Weifei Hu, Wenbin Dong, Zhen Gao and Zhengru Ren
Energies 2017, 10(12), 2099; https://doi.org/10.3390/en10122099 - 11 Dec 2017
Cited by 89 | Viewed by 14143
Abstract
The paper presents a detailed review of the state-of-the-art research activities on structural reliability analysis of wind turbines between the 1990s and 2017. We describe the reliability methods including the first- and second-order reliability methods and the simulation reliability methods and show the [...] Read more.
The paper presents a detailed review of the state-of-the-art research activities on structural reliability analysis of wind turbines between the 1990s and 2017. We describe the reliability methods including the first- and second-order reliability methods and the simulation reliability methods and show the procedure for and application areas of structural reliability analysis of wind turbines. Further, we critically review the various structural reliability studies on rotor blades, bottom-fixed support structures, floating systems and mechanical and electrical components. Finally, future applications of structural reliability methods to wind turbine designs are discussed. Full article
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1827 KiB  
Article
Force Measurements on a VAWT Blade in Parked Conditions
by Anders Goude and Morgan Rossander
Energies 2017, 10(12), 1954; https://doi.org/10.3390/en10121954 - 24 Nov 2017
Cited by 11 | Viewed by 4253
Abstract
The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured [...] Read more.
The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured on a 12 kW straight-bladed vertical axis wind turbine at an open site. Two cases are tested: one during electrical braking of the turbine, which allows it to rotate slowly, and one with the turbine mechanically fixed with the leading edge of the blade facing the main wind direction. The force variations with respect to wind direction are investigated, and it is seen that significant variations in forces depend on the wind direction. The measurements show that for the fixed case, when subjected to the same wind speed, the forces are lower when the blade faces the wind direction. The results also show that due to the lower forces at this particular wind direction, the average forces for the fixed blade are notably lower. Hence, it is possible to reduce the forces on a turbine blade, simply by taking the dominating wind direction into account when the turbine is parked. The measurements also show that a positive torque is generated from the blade for most wind directions, which causes the turbine to rotate in the electrically-braked case. These rotations will cause increased fatigue loads on the turbine blade. Full article
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17063 KiB  
Article
Numerical Investigation of the Tip Vortex of a Straight-Bladed Vertical Axis Wind Turbine with Double-Blades
by Yanzhao Yang, Zhiping Guo, Yanfeng Zhang, Ho Jinyama and Qingan Li
Energies 2017, 10(11), 1721; https://doi.org/10.3390/en10111721 - 27 Oct 2017
Cited by 34 | Viewed by 7941
Abstract
Wind velocity distribution and the vortex around the wind turbine present a significant challenge in the development of straight-bladed vertical axis wind turbines (VAWTs). This paper is intended to investigate influence of tip vortex on wind turbine wake by Computational Fluid Dynamics (CFD) [...] Read more.
Wind velocity distribution and the vortex around the wind turbine present a significant challenge in the development of straight-bladed vertical axis wind turbines (VAWTs). This paper is intended to investigate influence of tip vortex on wind turbine wake by Computational Fluid Dynamics (CFD) simulations. In this study, the number of blades is two and the airfoil is a NACA0021 with chord length of c = 0.265 m. To capture the tip vortex characteristics, the velocity fields are investigated by the Q-criterion iso-surface (Q = 100) with shear-stress transport (SST) k-ω turbulence model at different tip speed ratios (TSRs). Then, mean velocity, velocity deficit and torque coefficient acting on the blade in the different spanwise positions are compared. The wind velocities obtained by CFD simulations are also compared with the experimental data from wind tunnel experiments. As a result, we can state that the wind velocity curves calculated by CFD simulations are consistent with Laser Doppler Velocity (LDV) measurements. The distribution of the vortex structure along the spanwise direction is more complex at a lower TSR and the tip vortex has a longer dissipation distance at a high TSR. In addition, the mean wind velocity shows a large value near the blade tip and a small value near the blade due to the vortex effect. Full article
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10821 KiB  
Article
Sensitivity Analysis to Control the Far-Wake Unsteadiness Behind Turbines
by Esteban Ferrer, Oliver M.F. Browne and Eusebio Valero
Energies 2017, 10(10), 1599; https://doi.org/10.3390/en10101599 - 13 Oct 2017
Cited by 11 | Viewed by 4889
Abstract
We explore the stability of wakes arising from 2D flow actuators based on linear momentum actuator disc theory. We use stability and sensitivity analysis (using adjoints) to show that the wake stability is controlled by the Reynolds number and the thrust force (or [...] Read more.
We explore the stability of wakes arising from 2D flow actuators based on linear momentum actuator disc theory. We use stability and sensitivity analysis (using adjoints) to show that the wake stability is controlled by the Reynolds number and the thrust force (or flow resistance) applied through the turbine. First, we report that decreasing the thrust force has a comparable stabilising effect to a decrease in Reynolds numbers (based on the turbine diameter). Second, a discrete sensitivity analysis identifies two regions for suitable placement of flow control forcing, one close to the turbines and one far downstream. Third, we show that adding a localised control force, in the regions identified by the sensitivity analysis, stabilises the wake. Particularly, locating the control forcing close to the turbines results in an enhanced stabilisation such that the wake remains steady for significantly higher Reynolds numbers or turbine thrusts. The analysis of the controlled flow fields confirms that modifying the velocity gradient close to the turbine is more efficient to stabilise the wake than controlling the wake far downstream. The analysis is performed for the first flow bifurcation (at low Reynolds numbers) which serves as a foundation of the stabilization technique but the control strategy is tested at higher Reynolds numbers in the final section of the paper, showing enhanced stability for a turbulent flow case. Full article
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8029 KiB  
Article
Techno-Economic Assessment of Wind Energy Potential at Three Locations in South Korea Using Long-Term Measured Wind Data
by Sajid Ali, Sang-Moon Lee and Choon-Man Jang
Energies 2017, 10(9), 1442; https://doi.org/10.3390/en10091442 - 19 Sep 2017
Cited by 35 | Viewed by 8018
Abstract
The present study deals with wind energy analysis and the selection of an optimum type of wind turbine in terms of the feasibility of installing wind power system at three locations in South Korea: Deokjeok-do, Baengnyeong-do and Seo-San. The wind data measurements were [...] Read more.
The present study deals with wind energy analysis and the selection of an optimum type of wind turbine in terms of the feasibility of installing wind power system at three locations in South Korea: Deokjeok-do, Baengnyeong-do and Seo-San. The wind data measurements were conducted during 2005–2015 at Deokjeok-do, 2001–2016 at Baengnyeong-do and 1997–2016 at Seo-San. In the first part of this paper wind conditions, like mean wind speed, wind rose diagrams and Weibull shape and scale parameters are presented, so that the wind potential of all the locations could be assessed. It was found that the prevailing wind directions at all locations was either southeast or southwest in which the latter one being more dominant. After analyzing the wind conditions, 50-year and 1-year extreme wind speeds (EWS) were estimated using the graphical method of Gumbel distribution. Finally, according to the wind conditions at each site and international electro-technical commission (IEC) guidelines, a set of five different wind turbines best suited for each location were shortlisted. Each wind turbine was evaluated on the basis of technical parameters like monthly energy production, annual energy production (AEP) and capacity factors (CF). Similarly, economical parameters including net present value (NPV), internal rate of return (IRR), payback period (PBP) and levelized cost of electricity (LCOE) were considered. The analysis shows that a Doosan model WinDS134/3000 wind turbine is the most suitable for Deokjeok-do and Baengnyeong-do, whereas a Hanjin model HJWT 87/2000 is the most suitable wind turbine for Seo-San. Economic sensitivity analysis is also included and discussed in detail to analyze the impact on economics of wind power by varying turbine’s hub height. Full article
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5804 KiB  
Article
Analyses of the Extensible Blade in Improving Wind Energy Production at Sites with Low-Class Wind Resource
by Jiale Li and Xiong (Bill) Yu
Energies 2017, 10(9), 1295; https://doi.org/10.3390/en10091295 - 30 Aug 2017
Cited by 17 | Viewed by 5415
Abstract
This paper describes the feasibility analysis of an innovative, extensible blade technology. The blade aims to significantly improve the energy production of a wind turbine, particularly at locations with unfavorable wind conditions. The innovative ‘smart’ blade will be extended at low wind speed [...] Read more.
This paper describes the feasibility analysis of an innovative, extensible blade technology. The blade aims to significantly improve the energy production of a wind turbine, particularly at locations with unfavorable wind conditions. The innovative ‘smart’ blade will be extended at low wind speed to harvest more wind energy; on the other hand, it will be retracted to its original shape when the wind speed is above the rated wind speed to protect the blade from damages by high wind loads. An established aerodynamic model is implemented in this paper to evaluate and compare the power output of extensible blades versus a baseline conventional blade. The model was first validated with a monitored power production curve based on the wind energy production data of a conventional turbine blade, which is subsequently used to estimate the power production curve of extended blades. The load-on-blade structures are incorporated as the mechanical criteria to design the extension strategies. Wind speed monitoring data at three different onshore and offshore sites around Lake Erie are used to predict the annual wind energy output with different blades. The effects of extension on the dynamic characteristics of blade are analyzed. The results show that the extensive blade significantly increases the annual wind energy production (up to 20% to 30%) with different blade extension strategies. It, therefore, has the potential to significantly boost wind energy production for utility-scale wind turbines located at sites with low-class wind resource. Full article
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3818 KiB  
Article
Windbreak Effects Within Infinite Wind Farms
by Nicolas Tobin and Leonardo P. Chamorro
Energies 2017, 10(8), 1140; https://doi.org/10.3390/en10081140 - 3 Aug 2017
Cited by 9 | Viewed by 5748
Abstract
Building upon a recent study that showed windbreaks to be effective in increasing the power output of a wind turbine, the potential of windbreaks in a large wind farm is explored using simplified formulations. A top-down boundary layer approach is combined with methods [...] Read more.
Building upon a recent study that showed windbreaks to be effective in increasing the power output of a wind turbine, the potential of windbreaks in a large wind farm is explored using simplified formulations. A top-down boundary layer approach is combined with methods of estimating both the roughness effects of windbreaks and the induced inviscid speed-up for nearby turbines to investigate power production impact for several layouts of infinite wind farms. Results suggest that the negative impact of windbreak wakes for an infinite wind farm will outweigh the local inviscid speed-up for realistic inter-turbine spacings, with the break-even point expected at a spacing of ∼25 rotor diameters. However, the possibility that windbreaks may be applicable in finite and other wind farm configurations remains open. Inspection of the windbreak porosity reveals an impact on the magnitude of power perturbation, but not whether the change is positive or negative. Predictions from the boundary-layer approach are validated with power measurements from large-eddy simulations. Full article
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4429 KiB  
Article
A DC Microgrid Coordinated Control Strategy Based on Integrator Current-Sharing
by Liyuan Gao, Yao Liu, Huisong Ren and Josep M. Guerrero
Energies 2017, 10(8), 1116; https://doi.org/10.3390/en10081116 - 1 Aug 2017
Cited by 38 | Viewed by 7382
Abstract
The DC microgrid has become a new trend for microgrid study with the advantages of high reliability, simple control and low losses. With regard to the drawbacks of the traditional droop control strategies, an improved DC droop control strategy based on integrator current-sharing [...] Read more.
The DC microgrid has become a new trend for microgrid study with the advantages of high reliability, simple control and low losses. With regard to the drawbacks of the traditional droop control strategies, an improved DC droop control strategy based on integrator current-sharing is introduced. In the strategy, the principle of eliminating deviation through an integrator is used, constructing the current-sharing term in order to make the power-sharing between different distributed generation (DG) units uniform and reasonable, which can reduce the circulating current between DG units. Furthermore, at the system coordinated control level, a hierarchical/droop control strategy based on the DC bus voltage is proposed. In the strategy, the operation modes of the AC main network and micro-sources are determined through detecting the DC voltage variation, which can ensure the power balance of the DC microgrid under different operating conditions. Meanwhile, communication is not needed between different DG units, while each DG unit needs to sample the DC bus voltage, which retains the plug-and-play feature of the DC microgrid. The proposed control strategy is validated by simulation on a DC microgrid with permanent magnet synchronous generator-based wind turbines, solar arrays and energy storage batteries, which can be applied to small commercial or residential buildings. Full article
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3931 KiB  
Article
Optimal Dynamic Analysis of Electrical/Electronic Components in Wind Turbines
by Fausto Pedro García Márquez, Alberto Pliego Marugán, Jesús María Pinar Pérez, Stuart Hillmansen and Mayorkinos Papaelias
Energies 2017, 10(8), 1111; https://doi.org/10.3390/en10081111 - 31 Jul 2017
Cited by 63 | Viewed by 6144
Abstract
Electrical and electronic components are very important subcomponents in modern industrial wind turbines. Complex multimegawatt wind turbines are continuously being installed both onshore and offshore, continuously increasing the demand for sophisticated electronic and electrical components. In this work, most critical electrical and electronic [...] Read more.
Electrical and electronic components are very important subcomponents in modern industrial wind turbines. Complex multimegawatt wind turbines are continuously being installed both onshore and offshore, continuously increasing the demand for sophisticated electronic and electrical components. In this work, most critical electrical and electronic components in industrial wind turbines have been identified and the applicability of appropriate condition monitoring processes simulated. A fault tree dynamic analysis has been carried out by binary decision diagrams to obtain the system failure probability over time and using different time increments to evaluate the system. This analysis allows critical electrical and electronic components of the converters to be identified in different conditions. The results can be used to develop a scheduled maintenance that improves the decision making and reduces the maintenance costs. Full article
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2697 KiB  
Article
A New Miniature Wind Turbine for Wind Tunnel Experiments. Part II: Wake Structure and Flow Dynamics
by Majid Bastankhah and Fernando Porté-Agel
Energies 2017, 10(7), 923; https://doi.org/10.3390/en10070923 - 4 Jul 2017
Cited by 46 | Viewed by 7516
Abstract
An optimized three-bladed horizontal-axis miniature wind turbine, called WiRE-01, with the rotor diameter of 15 cm is designed and fully characterized in Part I of this study. In the current part of the study, we investigate the interaction of the turbine with a [...] Read more.
An optimized three-bladed horizontal-axis miniature wind turbine, called WiRE-01, with the rotor diameter of 15 cm is designed and fully characterized in Part I of this study. In the current part of the study, we investigate the interaction of the turbine with a turbulent boundary layer. The comparison of the spectral density of the thrust force and the one of the incoming velocity revealed new insights on the use of turbine characteristics to estimate incoming flow conditions. High-resolution stereoscopic particle image-velocimetry (S-PIV) measurements were also performed in the wake of the turbine operating at optimal conditions. Detailed information on the velocity and turbulence structure of the turbine wake is presented and discussed, which can serve as a complete dataset for the validation of numerical models. The PIV data are also used to better understand the underlying mechanisms leading to unsteady loads on a downstream turbine at different streamwise and spanwise positions. To achieve this goal, a new method is developed to quantify and compare the effect of both turbulence and mean shear on the moment of the incoming momentum flux for a hypothetical turbine placed downstream. The results show that moment fluctuations caused by turbulence are bigger under full-wake conditions, whereas those caused by mean shear are clearly dominant under partial-wake conditions. Especial emphasis is also placed on how the mean wake flow distribution is affected by wake meandering. Conditional averaging based on the instantaneous position of the wake center revealed that when the wake meanders laterally to one side, a high-speed region exists on the opposite side. The results show that, due to this high-speed region, large lateral meandering motions do not lead to the expansion of the mean wake cross-section in the lateral direction. Full article
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1423 KiB  
Article
A New Miniature Wind Turbine for Wind Tunnel Experiments. Part I: Design and Performance
by Majid Bastankhah and Fernando Porté-Agel
Energies 2017, 10(7), 908; https://doi.org/10.3390/en10070908 - 3 Jul 2017
Cited by 76 | Viewed by 12773
Abstract
Miniature wind turbines, employed in wind tunnel experiments to study the interaction of turbines with turbulent boundary layers, usually suffer from poor performance with respect to their large-scale counterparts in the field. Moreover, although wakes of wind turbines have been extensively examined in [...] Read more.
Miniature wind turbines, employed in wind tunnel experiments to study the interaction of turbines with turbulent boundary layers, usually suffer from poor performance with respect to their large-scale counterparts in the field. Moreover, although wakes of wind turbines have been extensively examined in wind tunnel studies, the proper characterization of the performance of wind turbines has received relatively less attention. In this regard, the present study concerns the design and the performance analysis of a new three-bladed horizontal-axis miniature wind turbine with a rotor diameter of 15 cm. Due to its small size, this turbine, called WiRE-01, is particularly suitable for studies of wind farm flows and the interaction of the turbine with an incoming boundary-layer flow. Especial emphasis was placed on the accurate measurement of the mechanical power extracted by the miniature turbine from the incoming wind. In order to do so, a new setup was developed to directly measure the torque of the rotor shaft. Moreover, to provide a better understanding on the connection between the mechanical and electrical aspects of miniature wind turbines, the performance of three different direct-current (DC) generators was studied. It is found that electrical outputs of the tested generators can be used to provide a rather acceptable estimation of the mechanical input power. Force and power measurements showed that the thrust and power coefficients of the miniature turbine can reach 0.8 and 0.4 , respectively, which are close to the ones of large-scale turbines in the field. In Part II of this study, the wake structure and dynamic flow characteristics are studied for the new miniature turbine immersed in a turbulent boundary-layer flow. Full article
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1696 KiB  
Article
Wind Turbine Synchronous Reset Pitch Control
by Yolanda Vidal, Leonardo Acho, Ignasi Cifre, Àlex Garcia, Francesc Pozo and José Rodellar
Energies 2017, 10(6), 770; https://doi.org/10.3390/en10060770 - 1 Jun 2017
Cited by 3 | Viewed by 4531
Abstract
Reset controllers are commonly used to smooth the transient response of systems. We use this technique to improve a standard baseline pitch controller for offshore wind turbines (WTs). The introduction of this strategy enhances the overall performance of the WT. In particular, the [...] Read more.
Reset controllers are commonly used to smooth the transient response of systems. We use this technique to improve a standard baseline pitch controller for offshore wind turbines (WTs). The introduction of this strategy enhances the overall performance of the WT. In particular, the fore-aft and side-to-side accelerations of the WT tower are significantly reduced, whilst a steadier power output is obtained, in comparison to the standard baseline pitch controller. Furthermore, our designed pitch control’s main advantage, with respect to the baseline, is its ease of implementation and reduced complexity as it does not require a gain-scheduling technique, nor pitch position measurement (thus, it is insensitive to pitch sensor faults). The proposed approach has been simulated on the NREL 5-MW prototype offshore turbine model, mounted on a jacket support. The simulations are carried out using the aero-hydro-servo-elastic simulator FAST, and key observations are thoroughly discussed. Full article
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657 KiB  
Article
Sliding Mode Control of a Variable- Speed Wind Energy Conversion System Using a Squirrel Cage Induction Generator
by Mohamed Zribi, Muthana Alrifai and Mohamed Rayan
Energies 2017, 10(5), 604; https://doi.org/10.3390/en10050604 - 1 May 2017
Cited by 50 | Viewed by 7685
Abstract
This paper deals with the control of a variable-speed wind energy conversion (WEC) system using a squirrel cage induction generator (SCIG) connected to the grid through a back-to-back three phase (AC-DC-AC) power converter. The sliding mode control technique is used to control the [...] Read more.
This paper deals with the control of a variable-speed wind energy conversion (WEC) system using a squirrel cage induction generator (SCIG) connected to the grid through a back-to-back three phase (AC-DC-AC) power converter. The sliding mode control technique is used to control the WEC system. The objective of the controllers is to force the states of the system to track their desired states. One controller is used to regulate the generator speed and the flux so that maximum power is extracted from the wind. Another controller is used to control the grid side converter, which controls the DC bus voltage and the active and reactive powers injected into the grid. The performance of the controlled wind energy conversion system is verified through MATLAB simulations, which show that the controlled system performs well. Full article
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4761 KiB  
Article
Automatic Tracking of the Modal Parameters of an Offshore Wind Turbine Drivetrain System
by Mahmoud El-Kafafy, Christof Devriendt, Patrick Guillaume and Jan Helsen
Energies 2017, 10(4), 574; https://doi.org/10.3390/en10040574 - 22 Apr 2017
Cited by 15 | Viewed by 5230
Abstract
An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important [...] Read more.
An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important design aspect. For tackling noise, vibration, and harshness (NVH) issues and validating complex simulation models, it is of high interest to continuously track the vibration levels and the evolution of the modal parameters (resonance frequencies, damping ratios, mode shapes) of the fundamental modes of the turbine. Wind turbines are multi-physical machines with significant interaction between their subcomponents. This paper will present the possibility of identifying and automatically tracking the structural vibration modes of the drivetrain system of an instrumented OWT by using signals (e.g., acceleration responses) measured on the drivetrain system. The experimental data has been obtained during a measurement campaign on an OWT in the Belgian North Sea where the OWT was in standstill condition. The drivetrain, more specifically the gearbox and generator, is instrumented with a dedicated measurement set-up consisting of 17 sensor channels with the aim to continuously track the vibration modes. The consistency of modal parameter estimates made at consequent 10-min intervals is validated, and the dominant drivetrain modal behavior is identified and automatically tracked. Full article
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1714 KiB  
Article
Fatigue Reliability Analysis of Wind Turbine Cast Components
by Hesam Mirzaei Rafsanjani, John Dalsgaard Sørensen, Søren Fæster and Asger Sturlason
Energies 2017, 10(4), 466; https://doi.org/10.3390/en10040466 - 2 Apr 2017
Cited by 3 | Viewed by 4433
Abstract
The fatigue life of wind turbine cast components, such as the main shaft in a drivetrain, is generally determined by defects from the casting process. These defects may reduce the fatigue life and they are generally distributed randomly in components. The foundries, cutting [...] Read more.
The fatigue life of wind turbine cast components, such as the main shaft in a drivetrain, is generally determined by defects from the casting process. These defects may reduce the fatigue life and they are generally distributed randomly in components. The foundries, cutting facilities and test facilities can affect the verification of properties by testing. Hence, it is important to have a tool to identify which foundry, cutting and/or test facility produces components which, based on the relevant uncertainties, have the largest expected fatigue life or, alternatively, have the largest reliability to be used for decision-making if additional cost considerations are added. In this paper, a statistical approach is presented based on statistical hypothesis testing and analysis of covariance (ANCOVA) which can be applied to compare different groups (manufacturers, suppliers, test facilities, etc.) and to quantify the relevant uncertainties using available fatigue tests. Illustrative results are presented as obtained by statistical analysis of a large set of fatigue data for casted test components typically used for wind turbines. Furthermore, the SN curves (fatigue life curves based on applied stress) for fatigue assessment are estimated based on the statistical analyses and by introduction of physical, model and statistical uncertainties used for the illustration of reliability assessment. Full article
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3115 KiB  
Article
Power Loss Analysis for Wind Power Grid Integration Based on Weibull Distribution
by Ahmed Al Ameri, Aouchenni Ounissa, Cristian Nichita and Aouzellag Djamal
Energies 2017, 10(4), 463; https://doi.org/10.3390/en10040463 - 2 Apr 2017
Cited by 19 | Viewed by 6606
Abstract
The growth of electrical demand increases the need of renewable energy sources, such as wind energy, to meet that need. Electrical power losses are an important factor when wind farm location and size are selected. The capitalized cost of constant power losses during [...] Read more.
The growth of electrical demand increases the need of renewable energy sources, such as wind energy, to meet that need. Electrical power losses are an important factor when wind farm location and size are selected. The capitalized cost of constant power losses during the life of a wind farm will continue to high levels. During the operation period, a method to determine if the losses meet the requirements of the design is significantly needed. This article presents a Simulink simulation of wind farm integration into the grid; the aim is to achieve a better understanding of wind variation impact on grid losses. The real power losses are set as a function of the annual variation, considering a Weibull distribution. An analytical method has been used to select the size and placement of a wind farm, taking into account active power loss reduction. It proposes a fast linear model estimation to find the optimal capacity of a wind farm based on DC power flow and graph theory. The results show that the analytical approach is capable of predicting the optimal size and location of wind turbines. Furthermore, it revealed that the annual variation of wind speed could have a strong effect on real power loss calculations. In addition to helping to improve utility efficiency, the proposed method can develop specific designs to speeding up integration of wind farms into grids. Full article
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10909 KiB  
Article
Wind Turbine Power Curve Design for Optimal Power Generation in Wind Farms Considering Wake Effect
by Jie Tian, Dao Zhou, Chi Su, Mohsen Soltani, Zhe Chen and Frede Blaabjerg
Energies 2017, 10(3), 395; https://doi.org/10.3390/en10030395 - 20 Mar 2017
Cited by 25 | Viewed by 7116
Abstract
In modern wind farms, maximum power point tracking (MPPT) is widely implemented. Using the MPPT method, each individual wind turbine is controlled by its pitch angle and tip speed ratio to generate the maximum active power. In a wind farm, the upstream wind [...] Read more.
In modern wind farms, maximum power point tracking (MPPT) is widely implemented. Using the MPPT method, each individual wind turbine is controlled by its pitch angle and tip speed ratio to generate the maximum active power. In a wind farm, the upstream wind turbine may cause power loss to its downstream wind turbines due to the wake effect. According to the wake model, downstream power loss is also determined by the pitch angle and tip speed ratio of the upstream wind turbine. By optimizing the pitch angle and tip speed ratio of each wind turbine, the total active power of the wind farm can be increased. In this paper, the optimal pitch angle and tip speed ratio are selected for each wind turbine by the exhausted search. Considering the estimation error of the wake model, a solution to implement the optimized pitch angle and tip speed ratio is proposed, which is to generate the optimal control curves for each individual wind turbine off-line. In typical wind farms with regular layout, based on the detailed analysis of the influence of pitch angle and tip speed ratio on the total active power of the wind farm by the exhausted search, the optimization is simplified with the reduced computation complexity. By using the optimized control curves, the annual energy production (AEP) is increased by 1.03% compared to using the MPPT method in a case-study of a typical eighty-turbine wind farm. Full article
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8722 KiB  
Article
Wind Farm Wake: The 2016 Horns Rev Photo Case
by Charlotte Bay Hasager, Nicolai Gayle Nygaard, Patrick J. H. Volker, Ioanna Karagali, Søren Juhl Andersen and Jake Badger
Energies 2017, 10(3), 317; https://doi.org/10.3390/en10030317 - 7 Mar 2017
Cited by 35 | Viewed by 26330
Abstract
Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake [...] Read more.
Offshore wind farm wakes were observed and photographed in foggy conditions at Horns Rev 2 on 25 January 2016 at 12:45 UTC. These new images show highly contrasting conditions regarding the wind speed, turbulence intensity, atmospheric stability, weather conditions and wind farm wake development as compared to the Horns Rev 1 photographs from 12 February 2008. The paper examines the atmospheric conditions from satellite images, radiosondes, lidar and wind turbine data and compares the observations to results from atmospheric meso-scale modelling and large eddy simulation. Key findings are that a humid and warm air mass was advected from the southwest over cold sea and the dew-point temperature was such that cold-water advection fog formed in a shallow layer. The flow was stably stratified and the freestream wind speed was 13 m/s at hub height, which means that most turbines produced at or near rated power. The wind direction was southwesterly and long, narrow wakes persisted several rotor diameters downwind of the wind turbines. Eventually mixing of warm air from aloft dispersed the fog in the far wake region of the wind farm. Full article
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2016

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5197 KiB  
Article
Experimental and Simulation Studies of Strength and Fracture Behaviors of Wind Turbine Bearing Steel Processed by High Pressure Torsion
by Ning Wang, Luis V. Wilches Peña, Ling Wang, B. G. Mellor and Yi Huang
Energies 2016, 9(12), 1033; https://doi.org/10.3390/en9121033 - 8 Dec 2016
Cited by 5 | Viewed by 5135
Abstract
White structure flaking (WSF) has been found to be one of the failure modes in bearing steels under rolling contacts through the formation of cracks associated with a microstructural change called white etching area (WEA). In the present research, the effects of the [...] Read more.
White structure flaking (WSF) has been found to be one of the failure modes in bearing steels under rolling contacts through the formation of cracks associated with a microstructural change called white etching area (WEA). In the present research, the effects of the high-pressure torsion (HPT) process on the microstructure and mechanical properties of an AISI 52100 alloy are studied. An annealed AISI 52100 was subjected to high-pressure torsion at room temperature under a pressure of up to ~6 GPa for up to three turns. Finite-element modeling (FEM) was used to simulate the process under high-pressure torsion and quasi-constrained conditions to reveal the material property changes occurring in HPT. Scanning electron microscopy and microhardness testing after processing were used to investigate the microstructural and mechanical property evolution of the steel. Strain induced microstructural transformations occur and affect the mechanical properties in a similar way to the well-known white etching area (WEA) found beneath the surface of wind turbine bearings. Here, HPT is used to study the feasibility of creating microstructural changes that are similar to WEA. This paper presents the preliminary results of using HPT to produce WEAs. Full article
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3691 KiB  
Article
Inverse Aerodynamic Optimization Considering Impacts of Design Tip Speed Ratio for Variable-Speed Wind Turbines
by Zhiqiang Yang, Minghui Yin, Yan Xu, Yun Zou, Zhao Yang Dong and Qian Zhou
Energies 2016, 9(12), 1023; https://doi.org/10.3390/en9121023 - 3 Dec 2016
Cited by 5 | Viewed by 5085
Abstract
Because of the slow dynamic behavior of the large-inertia wind turbine rotor, variable-speed wind turbines (VSWTs) are actually unable to keep operating at the design tip speed ratio (TSR) during the maximum power point tracking (MPPT) process. Moreover, it has been pointed out [...] Read more.
Because of the slow dynamic behavior of the large-inertia wind turbine rotor, variable-speed wind turbines (VSWTs) are actually unable to keep operating at the design tip speed ratio (TSR) during the maximum power point tracking (MPPT) process. Moreover, it has been pointed out that although a larger design TSR can increase the maximum power coefficient, it also greatly prolongs the MPPT process of VSWTs. Consequently, turbines spend more time operating at the off-design TSRs and the wind energy capture efficiency is decreased. Therefore, in the inverse aerodynamic design of VSWTs, the static aerodynamic performance (i.e., the maximum power coefficient) and the dynamic process of MPPT should be comprehensively modeled for determining an appropriate design TSR. In this paper, based on the inverse design method, an aerodynamic optimization method for VSWTs, fully considering the impacts of the design TSR on the static and dynamic behavior of wind turbines is proposed. In this method, to achieve higher wind energy production, the design TSR, chord length and twist angle are jointly optimized, which is structurally different from the conventional separated design procedure. Finally, the effectiveness of the proposed method is validated by simulation results based on the Bladed software. Full article
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6096 KiB  
Article
Numerical Investigation of Wind Conditions for Roof-Mounted Wind Turbines: Effects of Wind Direction and Horizontal Aspect Ratio of a High-Rise Cuboid Building
by Takaaki Kono, Tetsuya Kogaki and Takahiro Kiwata
Energies 2016, 9(11), 907; https://doi.org/10.3390/en9110907 - 3 Nov 2016
Cited by 32 | Viewed by 6106
Abstract
From the viewpoint of installing small wind turbines (SWTs) on rooftops, this study investigated the effects of wind direction and horizontal aspect ratio (HAR = width/length) of a high-rise cuboid building on wind conditions above the roof by conducting large eddy simulations (LESs). [...] Read more.
From the viewpoint of installing small wind turbines (SWTs) on rooftops, this study investigated the effects of wind direction and horizontal aspect ratio (HAR = width/length) of a high-rise cuboid building on wind conditions above the roof by conducting large eddy simulations (LESs). The LES results confirmed that as HAR decreases (i.e., as the building width decreases), the variation in wind velocity over the roof tends to decrease. This tendency is more prominent as the angle between the wind direction and the normal vector of the building’s leeward face with longer roof edge increases. Moreover, at windward corners of the roof, wind conditions are generally favorable at relatively low heights. In contrast, at the midpoint of the roof's windward edge, wind conditions are generally not favorable at relatively low heights. At leeward representative locations of the roof, the bottoms of the height range of favorable wind conditions are typically higher than those at the windward representative locations, but the favorable wind conditions are much better at the leeward representative locations. When there is no prevailing wind direction, the center of the roof is more favorable for installing SWTs than the corners or the edge midpoints of the roof. Full article
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5915 KiB  
Article
A Short-Term Outage Model of Wind Turbines with Doubly Fed Induction Generators Based on Supervisory Control and Data Acquisition Data
by Peng Sun, Jian Li, Junsheng Chen and Xiao Lei
Energies 2016, 9(11), 882; https://doi.org/10.3390/en9110882 - 28 Oct 2016
Cited by 3 | Viewed by 6098
Abstract
This paper presents a short-term wind turbine (WT) outage model based on the data collected from a wind farm supervisory control and data acquisition (SCADA) system. Neural networks (NNs) are used to establish prediction models of the WT condition parameters that are dependent [...] Read more.
This paper presents a short-term wind turbine (WT) outage model based on the data collected from a wind farm supervisory control and data acquisition (SCADA) system. Neural networks (NNs) are used to establish prediction models of the WT condition parameters that are dependent on environmental conditions such as ambient temperature and wind speed. The prediction error distributions are discussed and used to calculate probabilities of the operation of protection relays (POPRs) that were caused by the threshold exceedance of the environmentally sensitive parameters. The POPRs for other condition parameters are based on the setting time of the operation of protection relays. The union probability method is used to integrate the probabilities of operation of each protection relay to predict the WT short term outage probability. The proposed method has been used for real 1.5 MW WTs with doubly fed induction generators (DFIGs). The results show that the proposed method is more effective in WT outage probability prediction than traditional methods. Full article
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477 KiB  
Article
Fuzzy Logic Based Multi-Criteria Wind Turbine Selection Strategy—A Case Study of Qassim, Saudi Arabia
by Shafiqur Rehman and Salman A. Khan
Energies 2016, 9(11), 872; https://doi.org/10.3390/en9110872 - 26 Oct 2016
Cited by 39 | Viewed by 5817
Abstract
The emergence of wind energy as a potential alternative to traditional sources of fuel has prompted notable research in recent years. One primary factor contributing to efficient utilization of wind energy from a wind farm is the type of turbines used. However, selection [...] Read more.
The emergence of wind energy as a potential alternative to traditional sources of fuel has prompted notable research in recent years. One primary factor contributing to efficient utilization of wind energy from a wind farm is the type of turbines used. However, selection of a specific wind turbine type is a difficult task due to several criteria involved in the selection process. Important criteria include turbine’s power rating, height of tower, energy output, rotor diameter, cut-in wind speed, and rated wind speed. The complexity of this selection process is further amplified by the presence of conflicts between the decision criteria. Therefore, a decision is desired that provides the best balance between all selection criteria. Considering the complexities involved in the decision-making process, this paper proposes a two-level decision turbine selection strategy based on fuzzy logic and multi-criteria decision-making (MCDM) approach. More specifically, the fuzzy arithmetic mean operator is used in the decision process. The proposed approach is applied to wind data collected from the site of Qassim, Saudi Arabia. Results indicate that the proposed approach was effective in finding the optimal turbine from a set of 20 turbines of various capacities. Full article
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5086 KiB  
Article
A Vertical-Axis Off-Grid Squirrel-Cage Induction Generator Wind Power System
by Peifeng Xu, Kai Shi, Feifei Bu, Dean Zhao, Zhiming Fang, Rongke Liu and Yi Zhu
Energies 2016, 9(10), 822; https://doi.org/10.3390/en9100822 - 14 Oct 2016
Cited by 8 | Viewed by 8142
Abstract
In order to broaden the limited utilization range of wind power and improve the charging and discharging control performance of the storage battery in traditional small wind power generation systems, a wind power system based on a vertical-axis off-grid induction generator is proposed [...] Read more.
In order to broaden the limited utilization range of wind power and improve the charging and discharging control performance of the storage battery in traditional small wind power generation systems, a wind power system based on a vertical-axis off-grid induction generator is proposed in this paper. The induction generator not only can run in a wide wind speed range but can also assist the vertical-axis wind turbine to realize self-starting at low wind speed. Combined with the maximum power point tracking method, the slip frequency control strategy is employed to regulate the pulse width modulation (PWM) converter to control the output power of the proposed system when the wind speed and load change. The charge and discharge of the storage battery is realized by the segmented current-limiting control strategy by means of an electric power unloader device connected to the DC bus. All these implement a balanced and stable operation of the proposed power generation system. The experimental research on the 5.5 kW prototype system is developed, and the corresponding results verify the correctness and feasibility of the system design and control strategy. Some comparison experiments with a magnetic suspension permanent magnet synchronous generator (PMSG) demonstrate the application prospect of the proposed vertical-axis off-grid induction generator wind power system. Full article
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3937 KiB  
Article
A Novel Pitch Control System of a Large Wind Turbine Using Two-Degree-of-Freedom Motion Control with Feedback Linearization Control
by Ching-Sung Wang and Mao-Hsiung Chiang
Energies 2016, 9(10), 791; https://doi.org/10.3390/en9100791 - 29 Sep 2016
Cited by 25 | Viewed by 7979
Abstract
Pitch Control plays a significant role for a large wind turbine. This study investigates a novel robust hydraulic pitch control system of a large wind turbine. The novel hydraulic pitch control system is driven by a novel high efficiency and high response hydraulic [...] Read more.
Pitch Control plays a significant role for a large wind turbine. This study investigates a novel robust hydraulic pitch control system of a large wind turbine. The novel hydraulic pitch control system is driven by a novel high efficiency and high response hydraulic servo system. The pitch controller, designed by two degree-of-freedom (2-DOF) motion control with feedback linearization, is developed to enhance the controllability and stability of the pitch control system. Furthermore, the full-scale testbed of the hydraulic pitch control system of a large wind turbine is developed for practically experimental verification. Besides, the wind turbine simulation software FAST is used to analyze the motion of the blade which results are given to the testbed as the disturbance load command. The 2-DOF pitch controller contains a feedforward controller with feedback linearization theory to overcome the nonlinearities of the system and a feedback controller to improve the system robustness for achieving the disturbance rejection. Consequently, the novel hydraulic pitch control system shows excellent path tracking performance in the experiments. Moreover, the robustness test with a simulated disturbance load generated by FAST is performed to validate the reliability of the proposed pitch control system. Full article
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11388 KiB  
Article
Study on the Wake of a Miniature Wind Turbine Using the Reynolds Stress Model
by Jianxiao Hu, Qingshan Yang and Jian Zhang
Energies 2016, 9(10), 784; https://doi.org/10.3390/en9100784 - 28 Sep 2016
Cited by 7 | Viewed by 6009
Abstract
The Reynolds Stress Model (RSM) is adopted to simulate the wind turbine wake and the simulation results are compared with the wind tunnel test data, simulation results from the standard k-ε model and a modified k-ε model. RSM shows good performance in predicting [...] Read more.
The Reynolds Stress Model (RSM) is adopted to simulate the wind turbine wake and the simulation results are compared with the wind tunnel test data, simulation results from the standard k-ε model and a modified k-ε model. RSM shows good performance in predicting the turbine wakes velocity, turbulence intensity and the kinetic shear stress, while the k-ε based models fail to predict either wakes velocity or turbulence intensity. Simulation results show that the wake velocity will be recovered up to 90% at around 10 D downstream of the turbine (D denotes turbine rotor diameter) and it stops at 91% at around 16 D downstream. The wake turbulence intensity reaches a maximum at around 5 D downstream of turbine. Further investigation shows that the horizontal profile of the wakes velocity can be approximated by a Gaussian distribution, and the turbulence intensity can be approximated by a bimodal distribution. The influence of the wakes effect is limited to within ±D in the across-wind direction. The turbine wakes show clear anisotropy, which could explain the incorrect estimation on the turbulence intensity with the extended k-ε model. Full article
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6820 KiB  
Article
Coherence Effects on the Power and Tower Loads of a 7 × 2 MW Multi-Rotor Wind Turbine System
by Shigeo Yoshida, Uli Goltenbott, Yuji Ohya and Peter Jamieson
Energies 2016, 9(9), 742; https://doi.org/10.3390/en9090742 - 13 Sep 2016
Cited by 17 | Viewed by 5138
Abstract
A multi-rotor system (MRS), in which multiple wind turbines are placed on one tower, is a promising concept for super-large wind turbines at over 10 MW due to the cost and weight advantages. The coherence effects on an MRS were investigated in this [...] Read more.
A multi-rotor system (MRS), in which multiple wind turbines are placed on one tower, is a promising concept for super-large wind turbines at over 10 MW due to the cost and weight advantages. The coherence effects on an MRS were investigated in this study. Although a wide range of coherences were measured so far, a decay constant of C = 12 is recommended in the IEC61400-1 standard. Dynamic simulations were performed for a 14-MW MRS, which consists of seven 2-MW turbines and includes wind models with three different coherences. Although the results show that a larger coherence increases the output power and the collective loads due to tower base fore-aft bending, it reduces the differential loads due to tower-base torque and tower-top nodding. The most significant case is the fatigue damage due to tower base fore-aft bending, which was more than doubled between the decay constants of C = 6 and C = 12. The present results indicate that the coherence should be defined carefully in the design of large-scale MRSs because its effect on them is not straightforward. Full article
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1638 KiB  
Article
Axial Dynamic Stiffness of Tubular Piles in Viscoelastic Soil
by Mehdi Bayat, Lars Vabbersgaard Andersen and Lars Bo Ibsen
Energies 2016, 9(9), 734; https://doi.org/10.3390/en9090734 - 10 Sep 2016
Viewed by 6211
Abstract
Large offshore wind turbines are founded on jacket structures. In this study, an elastic full-space jacket structure foundation in an elastic and viscoelastic medium is investigated by using boundary integral equations. The jacket structure foundation is modeled as a hollow, long circular cylinder [...] Read more.
Large offshore wind turbines are founded on jacket structures. In this study, an elastic full-space jacket structure foundation in an elastic and viscoelastic medium is investigated by using boundary integral equations. The jacket structure foundation is modeled as a hollow, long circular cylinder when the dynamic vertical excitation is applied. The smooth surface along the entire interface is considered. The Betti reciprocal theorem along with Somigliana’s identity and Green’s function are employed to drive the dynamic stiffness of jacket structures. Modes of the resonance and anti-resonance are presented in series of Bessel’s function. Important responses, such as dynamic stiffness and phase angle, are compared for different values of the loss factor as the material damping, Young’s modulus and Poisson’s ratio in a viscoelastic soil. Results are verified with known results reported in the literature. It is observed that the dynamic stiffness fluctuates with the loss factor, and the turning point is independent of the loss factor while the turning point increases with load frequency. It is seen that the non-dimensional dynamic stiffness is dependent on Young’s modulus and Poisson’s ratio, whilst the phase angle is independent of the properties of the soil. It is shown that the non-dimensional dynamic stiffness changes linearly with high-frequency load. The conclusion from the results of this study is that the material properties of soil are significant parameters in the dynamic stiffness of jacket structures, and the presented approach can unfold the behavior of soil and give an approachable physical meaning for wave propagation. Full article
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5069 KiB  
Article
Modeling of Load Bearing Characteristics of Jacket Foundation Piles for Offshore Wind Turbines in Taiwan
by Cheng-Yu Ku and Lien-Kwei Chien
Energies 2016, 9(8), 625; https://doi.org/10.3390/en9080625 - 9 Aug 2016
Cited by 23 | Viewed by 8819
Abstract
This paper presents a pioneering study on numerical modeling of load bearing characteristics of the jacket foundation pile for offshore wind turbines on the west coast of Taiwan. Because Taiwan is located in an earthquake prone area, there is significant interest in improving [...] Read more.
This paper presents a pioneering study on numerical modeling of load bearing characteristics of the jacket foundation pile for offshore wind turbines on the west coast of Taiwan. Because Taiwan is located in an earthquake prone area, there is significant interest in improving the prediction of the behavior of wind turbine jacket foundations subjected to seismic loading. Investigation of the bearing capacity of the jacket foundation pile for the offshore wind farm using effective stress analysis, with consideration of pore pressure generation and soil/liquid coupled analysis, was conducted. A new procedure to evaluate the design of offshore wind turbine foundation piles in the sand and clay inter-layered soil was also proposed. Static and dynamic analyses of bearing capacity of the jacket foundation pile were conducted. Results obtained demonstrate that the design process for the jacket foundation pile proposed in this study can properly reflect the interaction behavior of the foundation and the soil. In addition, the pore pressure generation model can be used to simulate soil liquefaction. The proposed method is also very useful in the evaluation of the design capabilities of offshore wind turbine jacket foundations. Full article
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2657 KiB  
Review
A Review of Research on Large Scale Modern Vertical Axis Wind Turbines at Uppsala University
by Senad Apelfröjd, Sandra Eriksson and Hans Bernhoff
Energies 2016, 9(7), 570; https://doi.org/10.3390/en9070570 - 21 Jul 2016
Cited by 34 | Viewed by 14284
Abstract
This paper presents a review of over a decade of research on Vertical Axis Wind Turbines (VAWTs) conducted at Uppsala University. The paper presents, among others, an overview of the 200 kW VAWT located in Falkenberg, Sweden, as well as a description of [...] Read more.
This paper presents a review of over a decade of research on Vertical Axis Wind Turbines (VAWTs) conducted at Uppsala University. The paper presents, among others, an overview of the 200 kW VAWT located in Falkenberg, Sweden, as well as a description of the work done on the 12 kW prototype VAWT in Marsta, Sweden. Several key aspects have been tested and successfully demonstrated at our two experimental research sites. The effort of the VAWT research has been aimed at developing a robust large scale VAWT technology based on an electrical control system with a direct driven energy converter. This approach allows for a simplification where most or all of the control of the turbines can be managed by the electrical converter system, reducing investment cost and need for maintenance. The concept features an H-rotor that is omnidirectional in regards to wind direction, meaning that it can extract energy from all wind directions without the need for a yaw system. The turbine is connected to a direct driven permanent magnet synchronous generator (PMSG), located at ground level, that is specifically developed to control and extract power from the turbine. The research is ongoing and aims for a multi-megawatt VAWT in the near future. Full article
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1581 KiB  
Article
A Comparative Study of Multiple-Criteria Decision-Making Methods under Stochastic Inputs
by Athanasios Kolios, Varvara Mytilinou, Estivaliz Lozano-Minguez and Konstantinos Salonitis
Energies 2016, 9(7), 566; https://doi.org/10.3390/en9070566 - 21 Jul 2016
Cited by 224 | Viewed by 12508
Abstract
This paper presents an application and extension of multiple-criteria decision-making (MCDM) methods to account for stochastic input variables. More in particular, a comparative study is carried out among well-known and widely-applied methods in MCDM, when applied to the reference problem of the selection [...] Read more.
This paper presents an application and extension of multiple-criteria decision-making (MCDM) methods to account for stochastic input variables. More in particular, a comparative study is carried out among well-known and widely-applied methods in MCDM, when applied to the reference problem of the selection of wind turbine support structures for a given deployment location. Along with data from industrial experts, six deterministic MCDM methods are studied, so as to determine the best alternative among the available options, assessed against selected criteria with a view toward assigning confidence levels to each option. Following an overview of the literature around MCDM problems, the best practice implementation of each method is presented aiming to assist stakeholders and decision-makers to support decisions in real-world applications, where many and often conflicting criteria are present within uncertain environments. The outcomes of this research highlight that more sophisticated methods, such as technique for the order of preference by similarity to the ideal solution (TOPSIS) and Preference Ranking Organization method for enrichment evaluation (PROMETHEE), better predict the optimum design alternative. Full article
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482 KiB  
Article
On Real-Time Fault Detection in Wind Turbines: Sensor Selection Algorithm and Detection Time Reduction Analysis
by Francesc Pozo, Yolanda Vidal and Josep M. Serrahima
Energies 2016, 9(7), 520; https://doi.org/10.3390/en9070520 - 5 Jul 2016
Cited by 20 | Viewed by 5128
Abstract
In this paper, we address the problem of real-time fault detection in wind turbines. Starting from a data-driven fault detection method, the contribution of this paper is twofold. First, a sensor selection algorithm is proposed with the goal to reduce the computational effort [...] Read more.
In this paper, we address the problem of real-time fault detection in wind turbines. Starting from a data-driven fault detection method, the contribution of this paper is twofold. First, a sensor selection algorithm is proposed with the goal to reduce the computational effort of the fault detection method. Second, an analysis is performed to reduce the data acquisition time needed by the fault detection method, that is, with the goal of reducing the fault detection time. The proposed methods are tested in a benchmark wind turbine where different actuator and sensor failures are simulated. The results demonstrate the performance and effectiveness of the proposed algorithms that dramatically reduce the number of sensors and the fault detection time. Full article
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3344 KiB  
Article
Analysis and Solution for Operations of Overcurrent Relay in Wind Power System
by Yeonho Ok, Jaewon Lee and Jaeho Choi
Energies 2016, 9(6), 458; https://doi.org/10.3390/en9060458 - 16 Jun 2016
Cited by 8 | Viewed by 6615
Abstract
Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay’s malfunctions is essential to the [...] Read more.
Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay’s malfunctions is essential to the mitigation of power quality problems due to the frequent starts and stops of high capacity wind generators. In this study, the problem of frequent false operations of the protective relays are analyzed using real data as line voltages, line currents, and wind speed. A new re-coordination of the overcurrent relay (OCR) based on the wind speed is proposed to avoid frequent operations of relays and tested for a grid-connected wind farm. This study verifies that the false actions by the OCRs that are not accompanied by actual electrical faults in the power grid or wind power system can be solved by the appropriate re-coordination of the OCR. Full article
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3853 KiB  
Article
Application of a Heat Flux Sensor in Wind Power Electronics
by Elvira Baygildina, Liudmila Smirnova, Kirill Murashko, Raimo Juntunen, Andrey Mityakov, Mikko Kuisma, Olli Pyrhönen, Pasi Peltoniemi, Katja Hynynen, Vladimir Mityakov and Sergey Sapozhnikov
Energies 2016, 9(6), 456; https://doi.org/10.3390/en9060456 - 14 Jun 2016
Cited by 6 | Viewed by 6747
Abstract
This paper proposes and investigates the application of the gradient heat flux sensor (GHFS) for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has [...] Read more.
This paper proposes and investigates the application of the gradient heat flux sensor (GHFS) for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has high sensitivity and yields direct measurements without an interruption to the normal power device operation, which makes it attractive for power electronics applications. The development of systems for monitoring thermal loading and methods for online detection of degradation and failure of power electronic devices is a topical and crucial task. However, online condition monitoring (CM) methods, which include heat flux sensors, have received little research attention so far. In the current research, an insulated-gate bipolar transistor (IGBT) module-based test setup with the GHFS implemented on the base plate of one of the IGBTs is introduced. The heat flux experiments and the IGBT power losses obtained by simulations show similar results. The findings give clear evidence that the GHFS can provide an attractive condition monitoring method for the thermal loading of power devices. Full article
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6077 KiB  
Article
Wind Turbine Driving a PM Synchronous Generator Using Novel Recurrent Chebyshev Neural Network Control with the Ideal Learning Rate
by Chih-Hong Lin
Energies 2016, 9(6), 441; https://doi.org/10.3390/en9060441 - 9 Jun 2016
Cited by 4 | Viewed by 5104
Abstract
A permanent magnet (PM) synchronous generator system driven by wind turbine (WT), connected with smart grid via AC-DC converter and DC-AC converter, are controlled by the novel recurrent Chebyshev neural network (NN) and amended particle swarm optimization (PSO) to regulate output power and [...] Read more.
A permanent magnet (PM) synchronous generator system driven by wind turbine (WT), connected with smart grid via AC-DC converter and DC-AC converter, are controlled by the novel recurrent Chebyshev neural network (NN) and amended particle swarm optimization (PSO) to regulate output power and output voltage in two power converters in this study. Because a PM synchronous generator system driven by WT is an unknown non-linear and time-varying dynamic system, the on-line training novel recurrent Chebyshev NN control system is developed to regulate DC voltage of the AC-DC converter and AC voltage of the DC-AC converter connected with smart grid. Furthermore, the variable learning rate of the novel recurrent Chebyshev NN is regulated according to discrete-type Lyapunov function for improving the control performance and enhancing convergent speed. Finally, some experimental results are shown to verify the effectiveness of the proposed control method for a WT driving a PM synchronous generator system in smart grid. Full article
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3772 KiB  
Article
A Multi-Point Method Considering the Maximum Power Point Tracking Dynamic Process for Aerodynamic Optimization of Variable-Speed Wind Turbine Blades
by Zhiqiang Yang, Minghui Yin, Yan Xu, Zhengyang Zhang, Yun Zou and Zhao Yang Dong
Energies 2016, 9(6), 425; https://doi.org/10.3390/en9060425 - 31 May 2016
Cited by 11 | Viewed by 7186
Abstract
Due to the dynamic process of maximum power point tracking (MPPT) caused by turbulence and large rotor inertia, variable-speed wind turbines (VSWTs) cannot maintain the optimal tip speed ratio (TSR) from cut-in wind speed up to the rated speed. Therefore, in order to [...] Read more.
Due to the dynamic process of maximum power point tracking (MPPT) caused by turbulence and large rotor inertia, variable-speed wind turbines (VSWTs) cannot maintain the optimal tip speed ratio (TSR) from cut-in wind speed up to the rated speed. Therefore, in order to increase the total captured wind energy, the existing aerodynamic design for VSWT blades, which only focuses on performance improvement at a single TSR, needs to be improved to a multi-point design. In this paper, based on a closed-loop system of VSWTs, including turbulent wind, rotor, drive train and MPPT controller, the distribution of operational TSR and its description based on inflow wind energy are investigated. Moreover, a multi-point method considering the MPPT dynamic process for the aerodynamic optimization of VSWT blades is proposed. In the proposed method, the distribution of operational TSR is obtained through a dynamic simulation of the closed-loop system under a specific turbulent wind, and accordingly the multiple design TSRs and the corresponding weighting coefficients in the objective function are determined. Finally, using the blade of a National Renewable Energy Laboratory (NREL) 1.5 MW wind turbine as the baseline, the proposed method is compared with the conventional single-point optimization method using the commercial software Bladed. Simulation results verify the effectiveness of the proposed method. Full article
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6447 KiB  
Article
A Large-Eddy Simulation Study of Vertical Axis Wind Turbine Wakes in the Atmospheric Boundary Layer
by Sina Shamsoddin and Fernando Porté-Agel
Energies 2016, 9(5), 366; https://doi.org/10.3390/en9050366 - 13 May 2016
Cited by 66 | Viewed by 8919
Abstract
In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs) exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs). Nevertheless, there is currently a [...] Read more.
In a future sustainable energy vision, in which diversified conversion of renewable energies is essential, vertical axis wind turbines (VAWTs) exhibit some potential as a reliable means of wind energy extraction alongside conventional horizontal axis wind turbines (HAWTs). Nevertheless, there is currently a relative shortage of scientific, academic and technical investigations of VAWTs as compared to HAWTs. Having this in mind, in this work, we aim to, for the first time, study the wake of a single VAWT placed in the atmospheric boundary layer using large-eddy simulation (LES). To do this, we use a previously-validated LES framework in which an actuator line model (ALM) is incorporated. First, for a typical three- and straight-bladed 1-MW VAWT design, the variation of the power coefficient with both the chord length of the blades and the tip-speed ratio is analyzed by performing 117 simulations using LES-ALM. The optimum combination of solidity (defined as N c / R , where N is the number of blades, c is the chord length and R is the rotor radius) and tip-speed ratio is found to be 0.18 and 4.5, respectively. Subsequently, the wake of a VAWT with these optimum specifications is thoroughly examined by showing different relevant mean and turbulence wake flow statistics. It is found that for this case, the maximum velocity deficit at the equator height of the turbine occurs 2.7 rotor diameters downstream of the center of the turbine, and only after that point, the wake starts to recover. Moreover, it is observed that the maximum turbulence intensity (TI) at the equator height of the turbine occurs at a distance of about 3.8 rotor diameters downstream of the turbine. As we move towards the upper and lower edges of the turbine, the maximum TI (at a certain height) increases, and its location moves relatively closer to the turbine. Furthermore, whereas both TI and turbulent momentum flux fields show clear vertical asymmetries (with larger magnitudes at the upper wake edge compared to the ones at the lower edge), only slight lateral asymmetries were observed at the optimum tip-speed ratio for which the simulations were performed. Full article
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7484 KiB  
Article
Experiments on the Performance of Small Horizontal Axis Wind Turbine with Passive Pitch Control by Disk Pulley
by Yu-Jen Chen and Y. C. Shiah
Energies 2016, 9(5), 353; https://doi.org/10.3390/en9050353 - 7 May 2016
Cited by 19 | Viewed by 13300
Abstract
The present work is to design a passive pitch-control mechanism for small horizontal axis wind turbine (HAWT) to generate stable power at high wind speeds. The mechanism uses a disk pulley as an actuator to passively adjust the pitch angle of blades by [...] Read more.
The present work is to design a passive pitch-control mechanism for small horizontal axis wind turbine (HAWT) to generate stable power at high wind speeds. The mechanism uses a disk pulley as an actuator to passively adjust the pitch angle of blades by centrifugal force. For this design, aerodynamic braking is caused by the adjustment of pitch angles at high wind speeds. As a marked advantage, this does not require mechanical brakes that would incur electrical burn-out and structural failure under high speed rotation. This can ensure the survival of blades and generator in sever operation environments. In this paper, the analysis uses blade element momentum theory (BEMT) to develop graphical user interface software to facilitate the performance assessment of the small-scale HAWT using passive pitch control (PPC). For verification, the HAWT system was tested in a full-scale wind tunnel for its aerodynamic performance. At low wind speeds, this system performed the same as usual, yet at high wind speeds, the equipped PPC system can effectively reduce the rotational speed to generate stable power. Full article
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3689 KiB  
Article
Optimal Coordinated Control of Power Extraction in LES of a Wind Farm with Entrance Effects
by Jay P. Goit, Wim Munters and Johan Meyers
Energies 2016, 9(1), 29; https://doi.org/10.3390/en9010029 - 6 Jan 2016
Cited by 50 | Viewed by 6482
Abstract
We investigate the use of optimal coordinated control techniques in large eddy simulations of wind farm boundary layer interaction with the aim of increasing the total energy extraction in wind farms. The individual wind turbines are considered as flow actuators, and their energy [...] Read more.
We investigate the use of optimal coordinated control techniques in large eddy simulations of wind farm boundary layer interaction with the aim of increasing the total energy extraction in wind farms. The individual wind turbines are considered as flow actuators, and their energy extraction is dynamically regulated in time, so as to optimally influence the flow field. We extend earlier work on wind farm optimal control in the fully-developed regime (Goit and Meyers 2015, J. Fluid Mech. 768, 5–50) to a ‘finite’ wind farm case, in which entrance effects play an important role. For the optimal control, a receding horizon framework is employed in which turbine thrust coefficients are optimized in time and per turbine. Optimization is performed with a conjugate gradient method, where gradients of the cost functional are obtained using adjoint large eddy simulations. Overall, the energy extraction is increased 7% by the optimal control. This increase in energy extraction is related to faster wake recovery throughout the farm. For the first row of turbines, the optimal control increases turbulence levels and Reynolds stresses in the wake, leading to better wake mixing and an inflow velocity for the second row that is significantly higher than in the uncontrolled case. For downstream rows, the optimal control mainly enhances the sideways mean transport of momentum. This is different from earlier observations by Goit and Meyers (2015) in the fully-developed regime, where mainly vertical transport was enhanced. Full article
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945 KiB  
Article
Hybrid Intelligent Control Method to Improve the Frequency Support Capability of Wind Energy Conversion Systems
by Shin Young Heo, Mun Kyeom Kim and Jin Woo Choi
Energies 2015, 8(10), 11430-11451; https://doi.org/10.3390/en81011430 - 13 Oct 2015
Cited by 11 | Viewed by 5968
Abstract
This paper presents a hybrid intelligent control method that enables frequency support control for permanent magnet synchronous generators (PMSGs) wind turbines. The proposed method for a wind energy conversion system (WECS) is designed to have PMSG modeling and full-scale back-to-back insulated-gate bipolar transistor [...] Read more.
This paper presents a hybrid intelligent control method that enables frequency support control for permanent magnet synchronous generators (PMSGs) wind turbines. The proposed method for a wind energy conversion system (WECS) is designed to have PMSG modeling and full-scale back-to-back insulated-gate bipolar transistor (IGBT) converters comprising the machine and grid side. The controller of the machine side converter (MSC) and the grid side converter (GSC) are designed to achieve maximum power point tracking (MPPT) based on an improved hill climb searching (IHCS) control algorithm and de-loaded (DL) operation to obtain a power margin. Along with this comprehensive control of maximum power tracking mode based on the IHCS, a method for kinetic energy (KE) discharge control of the supporting primary frequency control scheme with DL operation is developed to regulate the short-term frequency response and maintain reliable operation of the power system. The effectiveness of the hybrid intelligent control method is verified by a numerical simulation in PSCAD/EMTDC. Simulation results show that the proposed approach can improve the frequency regulation capability in the power system. Full article
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397 KiB  
Article
Fault Current Characteristics of the DFIG under Asymmetrical Fault Conditions
by Fan Xiao, Zhe Zhang and Xianggen Yin
Energies 2015, 8(10), 10971-10992; https://doi.org/10.3390/en81010971 - 30 Sep 2015
Cited by 31 | Viewed by 6109
Abstract
During non-severe fault conditions, crowbar protection is not activated and the rotor windings of a doubly-fed induction generator (DFIG) are excited by the AC/DC/AC converter. Meanwhile, under asymmetrical fault conditions, the electrical variables oscillate at twice the grid frequency in synchronous dq frame. [...] Read more.
During non-severe fault conditions, crowbar protection is not activated and the rotor windings of a doubly-fed induction generator (DFIG) are excited by the AC/DC/AC converter. Meanwhile, under asymmetrical fault conditions, the electrical variables oscillate at twice the grid frequency in synchronous dq frame. In the engineering practice, notch filters are usually used to extract the positive and negative sequence components. In these cases, the dynamic response of a rotor-side converter (RSC) and the notch filters have a large influence on the fault current characteristics of the DFIG. In this paper, the influence of the notch filters on the proportional integral (PI) parameters is discussed and the simplified calculation models of the rotor current are established. Then, the dynamic performance of the stator flux linkage under asymmetrical fault conditions is also analyzed. Based on this, the fault characteristics of the stator current under asymmetrical fault conditions are studied and the corresponding analytical expressions of the stator fault current are obtained. Finally, digital simulation results validate the analytical results. The research results are helpful to meet the requirements of a practical short-circuit calculation and the construction of a relaying protection system for the power grid with penetration of DFIGs. Full article
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2278 KiB  
Article
Effect of Various Excitation Conditions on Vibrational Energy in a Multi-Degree-of-Freedom Torsional System with Piecewise-Type Nonlinearities
by Jong-Yun Yoon and Byeongil Kim
Energies 2015, 8(10), 10861-10882; https://doi.org/10.3390/en81010861 - 29 Sep 2015
Cited by 1 | Viewed by 5082
Abstract
Dynamic behaviors in practical driveline systems for wind turbines or vehicles are inherently affected by multiple nonlinearities such as piecewise-type torsional springs. However, various excitation conditions with different levels of magnitudes also show strong relationships to the dynamic behaviors when system responses are [...] Read more.
Dynamic behaviors in practical driveline systems for wind turbines or vehicles are inherently affected by multiple nonlinearities such as piecewise-type torsional springs. However, various excitation conditions with different levels of magnitudes also show strong relationships to the dynamic behaviors when system responses are examined in both frequency and time domains. This study investigated the nonlinear responses of torsional systems under various excitations by using the harmonic balance method and numerical analysis. In order to understand the effect of piecewise-type nonlinearities on vibrational energy with different excitations, the nonlinear responses were investigated with various comparisons. First, two different jumping phenomena with frequency up- and down-sweeping conditions were determined under severe excitation levels. Second, practical system analysis using the phase plane and Poincaré map was conducted in various ways. When the system responses were composed of quasi-periodic components, Poincaré map analysis clearly revealed the nonlinear dynamic characteristics and thus it is suggested to investigate complicated nonlinear dynamic responses in practical driveline systems. Full article
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3139 KiB  
Article
A Switched Capacitor Based AC/DC Resonant Converter for High Frequency AC Power Generation
by Cuidong Xu and Ka Wai Eric Cheng
Energies 2015, 8(10), 10842-10860; https://doi.org/10.3390/en81010842 - 29 Sep 2015
Cited by 4 | Viewed by 8267
Abstract
A switched capacitor based AC-DC resonant power converter is proposed for high frequency power generation output conversion. This converter is suitable for small scale, high frequency wind power generation. It has a high conversion ratio to provide a step down from high voltage [...] Read more.
A switched capacitor based AC-DC resonant power converter is proposed for high frequency power generation output conversion. This converter is suitable for small scale, high frequency wind power generation. It has a high conversion ratio to provide a step down from high voltage to low voltage for easy use. The voltage conversion ratio of conventional switched capacitor power converters is fixed to n, 1/n or −1/n (n is the switched capacitor cell). In this paper, A circuit which can provide n, 1/n and 2n/m of the voltage conversion ratio is presented (n is stepping up the switched capacitor cell, m is stepping down the switching capacitor cell). The conversion ratio can be changed greatly by using only two switches. A resonant tank is used to assist in zero current switching, and hence the current spike, which usually exists in a classical switching switched capacitor converter, can be eliminated. Both easy operation and efficiency are possible. Principles of operation, computer simulations and experimental results of the proposed circuit are presented. General analysis and design methods are given. The experimental result verifies the theoretical analysis of high frequency AC power generation. Full article
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3125 KiB  
Article
Vibro-Impact Energy Analysis of a Geared System with Piecewise-Type Nonlinearities Using Various Parameter Values
by Jong-Yun Yoon and Byeongil Kim
Energies 2015, 8(8), 8924-8944; https://doi.org/10.3390/en8088924 - 21 Aug 2015
Cited by 5 | Viewed by 5760
Abstract
Torsional systems with gear pairs such as the gearbox of wind turbines or vehicle driveline systems inherently show impact phenomena due to clearance-type nonlinearities when the system experiences sinusoidal excitation. This research investigates the vibro-impact energy of unloaded gears in geared systems using [...] Read more.
Torsional systems with gear pairs such as the gearbox of wind turbines or vehicle driveline systems inherently show impact phenomena due to clearance-type nonlinearities when the system experiences sinusoidal excitation. This research investigates the vibro-impact energy of unloaded gears in geared systems using the harmonic balance method (HBM) in both the frequency and time domains. To achieve accurate simulations, nonlinear models with piecewise and clearance-type nonlinearities and drag torques are defined and implemented in the HBM. Next, the nonlinear frequency responses are examined by focusing on the resonance areas where the impact phenomena occur, along with variations in key parameters such as clutch stiffness, drag torque, and inertias of the flywheel and the unloaded gear. Finally, the effects of the parameters on the vibro-impacts at a specific excitation frequency are explained using bifurcation diagrams. The results are correlated with prior research by defining the gear rattle criteria with key parameters. This article suggests a method to simulate the impact phenomena in torsional systems using the HBM and successfully assesses vibro-impact energy using bifurcation diagrams. Full article
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1922 KiB  
Article
Computational Fluid Dynamics Prediction of a Modified Savonius Wind Turbine with Novel Blade Shapes
by Wenlong Tian, Baowei Song, James H. VanZwieten and Parakram Pyakurel
Energies 2015, 8(8), 7915-7929; https://doi.org/10.3390/en8087915 - 30 Jul 2015
Cited by 99 | Viewed by 12649
Abstract
The Savonius wind turbine is a type of vertical axis wind turbine (VAWTs) that is simply composed of two or three arc-type blades which can generate power even under poor wind conditions. A modified Savonius wind turbine with novel blade shapes is introduced [...] Read more.
The Savonius wind turbine is a type of vertical axis wind turbine (VAWTs) that is simply composed of two or three arc-type blades which can generate power even under poor wind conditions. A modified Savonius wind turbine with novel blade shapes is introduced with the aim of increasing the power coefficient of the turbine. The effect of blade fullness, which is a main shape parameter of the blade, on the power production of a two-bladed Savonius wind turbine is investigated using transient computational fluid dynamics (CFD). Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations with a renormalization group turbulent model. This numerical method is validated with existing experimental data and then utilized to quantify the performance of design variants. Results quantify the relationship between blade fullness and turbine performance with a blade fullness of 1 resulting in the highest coefficient of power, 0.2573. This power coefficient is 10.98% higher than a conventional Savonius turbine. Full article
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898 KiB  
Article
Online Fault Identification Based on an Adaptive Observer for Modular Multilevel Converters Applied to Wind Power Generation Systems
by Hui Liu, Ke Ma, Poh Chiang Loh and Frede Blaabjerg
Energies 2015, 8(7), 7140-7160; https://doi.org/10.3390/en8077140 - 15 Jul 2015
Cited by 26 | Viewed by 6721
Abstract
Due to the possibility of putting a large number of modules consisting of switches and capacitors connected in series, the modular multilevel converter (MMC) can easily be scaled to high power and high voltage power conversion, which is an attractive feature for filter-less [...] Read more.
Due to the possibility of putting a large number of modules consisting of switches and capacitors connected in series, the modular multilevel converter (MMC) can easily be scaled to high power and high voltage power conversion, which is an attractive feature for filter-less and transformer-less design and helpful to achieve high efficiency. However, a significantly increased amount of sub-modules in a MMC may increase the requirements for sensors and also increase the risk of failures. As a result, fault detection and diagnosis of MMC sub-modules are of great importance for continuous operation and post-fault maintenance. Therefore, in this paper, an effective fault diagnosis technique for real-time diagnosis of the switching device faults covering both the open-circuit faults and the short-circuit faults in MMC sub-modules is proposed, in which the faulty phase and the fault type is detected by analyzing the difference among the three output load currents, while the localization of the faulty switches is achieved by comparing the estimation results by the adaptive observer. In contrast to other methods that use additional sensors or devices, the presented technique uses the measured phase currents only, which are already available for MMC control. In additional, its operation, effectiveness and robustness are confirmed by simulation results under different operating conditions and load conditions. Full article
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892 KiB  
Article
Improving Transient Stability in a Grid-Connected Squirrel-Cage Induction Generator Wind Turbine System Using a Fuzzy Logic Controller
by Minh Quan Duong, Francesco Grimaccia, Sonia Leva, Marco Mussetta and Kim Hung Le
Energies 2015, 8(7), 6328-6349; https://doi.org/10.3390/en8076328 - 25 Jun 2015
Cited by 51 | Viewed by 8023
Abstract
A common problem in wind power plants involves fixed-speed wind turbines. In fact, being equipped with a squirrel-cage induction generator (SCIG), they tend to drain a relevant amount of reactive power from the grid, potentially causing voltage drops and possible voltage instability. To [...] Read more.
A common problem in wind power plants involves fixed-speed wind turbines. In fact, being equipped with a squirrel-cage induction generator (SCIG), they tend to drain a relevant amount of reactive power from the grid, potentially causing voltage drops and possible voltage instability. To improve SCIG power quality and transient stability, this paper investigates a new control strategy for pitch angle control based on proportional-integral (PI) controller and a fuzzy logic controller (FLC), considering both normal and fault ride-through (FRT) schemes. In the literature, often, the mechanical torque output is assumed constant for a specific wind speed. This might not be accurate, because the mechanical torque-speed typical of a wind turbine depends also on the power coefficient or pitch angle. In this paper, an analytic model of transient stability is proposed using the equivalent circuit of the SCIG and using the concepts of stable and unstable electrical-mechanical equilibrium. The method has been evaluated by comparing the results obtained by the analytic method with the dynamic simulation. The results show that the proposed hybrid controller is effective at smoothing the output power and complying with FRT requirements for SCIG in the power system. Full article
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1049 KiB  
Article
Evaluation of a Blade Force Measurement System for a Vertical Axis Wind Turbine Using Load Cells
by Morgan Rossander, Eduard Dyachuk, Senad Apelfröjd, Kristian Trolin, Anders Goude, Hans Bernhoff and Sandra Eriksson
Energies 2015, 8(6), 5973-5996; https://doi.org/10.3390/en8065973 - 18 Jun 2015
Cited by 32 | Viewed by 8359
Abstract
Unique blade force measurements on an open site straight-bladed vertical axis wind turbine have been performed. This paper presents a method for measuring the tangential and normal forces on a 12-kW vertical axis wind turbine prototype with a three-bladed H-rotor. Four single-axis load [...] Read more.
Unique blade force measurements on an open site straight-bladed vertical axis wind turbine have been performed. This paper presents a method for measuring the tangential and normal forces on a 12-kW vertical axis wind turbine prototype with a three-bladed H-rotor. Four single-axis load cells were installed in-between the hub and the support arms on one of the blades. The experimental setup, the measurement principle, together with the necessary control and measurement system are described. The maximum errors of the forces and accompanying weather data that can be obtained with the system are carefully estimated. Measured forces from the four load cells are presented, as well as the normal and tangential forces derived from them and a comparison with theoretical data. The measured torque and bending moment are also provided. The influence of the load cells on the turbine dynamics has also been evaluated. For the aerodynamic normal force, the system provides periodic data in agreement with simulations. Unexpected mechanical oscillations are present in the tangential force, introduced by the turbine dynamics. The measurement errors are of an acceptable size and often depend on the measured variable. Equations are presented for the calculation of measurement errors. Full article
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2144 KiB  
Article
An Innovative Design of a Microtab Deployment Mechanism for Active Aerodynamic Load Control
by Kuo-Chang Tsai, Cheng-Tang Pan, Aubryn M. Cooperman, Scott J. Johnson and C. P. Van Dam
Energies 2015, 8(6), 5885-5897; https://doi.org/10.3390/en8065885 - 17 Jun 2015
Cited by 23 | Viewed by 8038
Abstract
This study presents an innovative design of a microtab system for aerodynamic load control on horizontal-axis wind-turbine rotors. Microtabs are small devices located near the trailing edge of the rotor blades and enable a rapid increase or decrease of the lift force through [...] Read more.
This study presents an innovative design of a microtab system for aerodynamic load control on horizontal-axis wind-turbine rotors. Microtabs are small devices located near the trailing edge of the rotor blades and enable a rapid increase or decrease of the lift force through deployment of the tabs on the pressure or suction side of the airfoil, respectively. The new system has been designed to replace an earlier linearly-actuated microtab mechanism whose performance was limited by space restrictions and stiction. The newly-designed microtab system is based on a four-bar linkage that overcomes the two drawbacks. Its improved kinematics allows for the tab height to increase from 1.0% to 1.7% of the airfoil chord when fully deployed, thereby making it more effective in terms of aerodynamic load control. Furthermore, the modified four-bar link mechanism provides a more robust and reliable mechanical structure. Full article
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3866 KiB  
Article
Upgrading a Shrouded Wind Turbine with a Self-Adaptive Flanged Diffuser
by Jun-Feng Hu and Wen-Xue Wang
Energies 2015, 8(6), 5319-5337; https://doi.org/10.3390/en8065319 - 3 Jun 2015
Cited by 26 | Viewed by 8122
Abstract
In this paper, a self-adaptive flange is proposed for the wind turbine shrouded by a flanged diffuser to reduce the wind loads acting on the flanged diffuser at high wind velocities. The self-adaptive flange can maintain the advantages of the flanged diffuser at [...] Read more.
In this paper, a self-adaptive flange is proposed for the wind turbine shrouded by a flanged diffuser to reduce the wind loads acting on the flanged diffuser at high wind velocities. The self-adaptive flange can maintain the advantages of the flanged diffuser at wind velocities lower than the rated velocity and reduce the wind loads acting on the diffuser and blades at higher wind velocities. Numerical analyses of fluid-structure interactions are carried out to investigate the flow field around the diffuser with a self-adaptive flange and the variation of wind load acting on the diffuser due to the reconfiguration of the self-adaptive flange at various wind velocities. Numerical results show that the wind load acting on the total flanged diffuser can be reduced by about 35% at 60 m/s due to the reconfiguration of the self-adaptive flange. Full article
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638 KiB  
Article
An Electro-Thermal Analysis of a Variable-Speed Doubly-Fed Induction Generator in a Wind Turbine
by Yingning Qiu, Wenxiu Zhang, Mengnan Cao, Yanhui Feng and David Infield
Energies 2015, 8(5), 3386-3402; https://doi.org/10.3390/en8053386 - 24 Apr 2015
Cited by 32 | Viewed by 9015
Abstract
This paper focuses on the electro-thermal analysis of a doubly-fed induction generator (DFIG) in a wind turbine (WT) with gear transmission configuration. The study of the thermal mechanism plays an important role in the development of cost-effective fault diagnostic techniques, design for reliability [...] Read more.
This paper focuses on the electro-thermal analysis of a doubly-fed induction generator (DFIG) in a wind turbine (WT) with gear transmission configuration. The study of the thermal mechanism plays an important role in the development of cost-effective fault diagnostic techniques, design for reliability and premature failure prevention. Starting from an analysis of the DFIG system control and its power losses mechanism, a model that synthesizes the thermal mechanism of the DFIG and a WT system principle is developed to study the thermodynamics of generator stator winding. The transient-state and steady-state temperature characteristics of stator winding under constant and step-cycle patterns of wind speed are studied to show an intrinsic thermal process within a variable-speed WT generator. Thermal behaviors of two failure modes, i.e., generator ventilation system failure and generator stator winding under electric voltage unbalance, are examined in details and validated by both simulation and data analysis. The effective approach presented in this paper for generator fault diagnosis using the acquired SCADA data shows the importance of simulation models in providing guidance for post-data analysis and interpretation. WT generator winding lifetime is finally estimated based on a thermal ageing model to investigate the impacts of wind speed and failure mode. Full article
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2310 KiB  
Article
Toward Isolation of Salient Features in Stable Boundary Layer Wind Fields that Influence Loads on Wind Turbines
by Jinkyoo Park, Lance Manuel and Sukanta Basu
Energies 2015, 8(4), 2977-3012; https://doi.org/10.3390/en8042977 - 17 Apr 2015
Cited by 14 | Viewed by 6674
Abstract
Neutral boundary layer (NBL) flow fields, commonly used in turbine load studies and design, are generated using spectral procedures in stochastic simulation. For large utility-scale turbines, stable boundary layer (SBL) flow fields are of great interest because they are often accompanied by enhanced [...] Read more.
Neutral boundary layer (NBL) flow fields, commonly used in turbine load studies and design, are generated using spectral procedures in stochastic simulation. For large utility-scale turbines, stable boundary layer (SBL) flow fields are of great interest because they are often accompanied by enhanced wind shear, wind veer, and even low-level jets (LLJs). The generation of SBL flow fields, in contrast to simpler stochastic simulation for NBL, requires computational fluid dynamics (CFD) procedures to capture the physics and noted characteristics—such as shear and veer—that are distinct from those seen in NBL flows. At present, large-eddy simulation (LES) is the most efficient CFD procedure for SBL flow field generation and related wind turbine loads studies. Design standards, such as from the International Electrotechnical Commission (IEC), provide guidance albeit with simplifying assumptions (one such deals with assuming constant variance of turbulence over the rotor) and recommend standard target turbulence power spectra and coherence functions to allow NBL flow field simulation. In contrast, a systematic SBL flow field simulation procedure has not been offered for design or for site assessment. It is instructive to compare LES-generated SBL flow fields with stochastic NBL flow fields and associated loads which we evaluate for a 5-MW turbine; in doing so, we seek to isolate distinguishing characteristics of wind shear, wind veer, and turbulence variation over the rotor plane in the alternative flow fields and in the turbine loads. Because of known differences in NBL-stochastic and SBL-LES wind fields but an industry preference for simpler stochastic simulation in design practice, this study investigates if one can reproduce stable atmospheric conditions using stochastic approaches with appropriate corrections for shear, veer, turbulence, etc. We find that such simple tuning cannot consistently match turbine target SBL load statistics, even though this is possible in some cases. As such, when there is a need to consider different stability regimes encountered by a wind turbine, easy solutions do not exist and large-eddy simulation at least for the stable boundary layer is needed. Full article
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388 KiB  
Article
Reliability Analysis of Fatigue Failure of Cast Components for Wind Turbines
by Hesam Mirzaei Rafsanjani and John Dalsgaard Sørensen
Energies 2015, 8(4), 2908-2923; https://doi.org/10.3390/en8042908 - 15 Apr 2015
Cited by 19 | Viewed by 9048
Abstract
Fatigue failure is one of the main failure modes for wind turbine drivetrain components made of cast iron. The wind turbine drivetrain consists of a variety of heavily loaded components, like the main shaft, the main bearings, the gearbox and the generator. The [...] Read more.
Fatigue failure is one of the main failure modes for wind turbine drivetrain components made of cast iron. The wind turbine drivetrain consists of a variety of heavily loaded components, like the main shaft, the main bearings, the gearbox and the generator. The failure of each component will lead to substantial economic losses such as cost of lost energy production and cost of repairs. During the design lifetime, the drivetrain components are exposed to variable loads from winds and waves and other sources of loads that are uncertain and have to be modeled as stochastic variables. The types of loads are different for offshore and onshore wind turbines. Moreover, uncertainties about the fatigue strength play an important role in modeling and assessment of the reliability of the components. In this paper, a generic stochastic model for fatigue failure of cast iron components based on fatigue test data and a limit state equation for fatigue failure based on the SN-curve approach and Miner’s rule is presented. The statistical analysis of the fatigue data is performed using the Maximum Likelihood Method which also gives an estimate of the statistical uncertainties. Finally, illustrative examples are presented with reliability analyses depending on various stochastic models and partial safety factors. Full article
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4324 KiB  
Article
High Step-Up 3-Phase Rectifier with Fly-Back Cells and Switched Capacitors for Small-Scaled Wind Generation Systems
by Yi-Feng Wang, Liang Yang, Cheng-Shan Wang, Wei Li, Wei Qie and Shi-Jie Tu
Energies 2015, 8(4), 2742-2768; https://doi.org/10.3390/en8042742 - 10 Apr 2015
Cited by 12 | Viewed by 9955
Abstract
This paper proposes and discusses a novel AC/DC converter suitable for small-scaled wind power generation system applications. By introducing flyback cells into the three-phase single-switch Boost circuit, the proposed converter is designed as single-stage and has both rectification and high step-up power conversion [...] Read more.
This paper proposes and discusses a novel AC/DC converter suitable for small-scaled wind power generation system applications. By introducing flyback cells into the three-phase single-switch Boost circuit, the proposed converter is designed as single-stage and has both rectification and high step-up power conversion functions. It is able to obtain high voltage gain at low input voltage level, and high efficiency, low total harmonic distortion (THD) at rated power. The inherent power factor correction (PFC) is also determined, and can reach 0.99. Besides, since no electrolytic capacitor is employed and high voltage gain is achieved, the converter can also collect weak power at low input voltage in combination with energy storage devices, and contribute to a better low-wind-speed/low-power performance. Finally, a 400 W prototype is built to verify the theoretical analysis, and its efficiency is 87.6%, while THD is 7.4% at rated power. Full article
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582 KiB  
Article
Forces and Moments on Flat Plates of Small Aspect Ratio with Application to PV Wind Loads and Small Wind Turbine Blades
by Xavier Ortiz, David Rival and David Wood
Energies 2015, 8(4), 2438-2453; https://doi.org/10.3390/en8042438 - 26 Mar 2015
Cited by 75 | Viewed by 11411
Abstract
To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin [...] Read more.
To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 104 to 2 × 105. Measurements were made for angles of attack between 0° and 90° both in the free stream and in wall proximity with increased turbulence and mean shear. The ratio of drag to lift closely follows the inverse tangent of the angle of incidence for virtually all measurements. This implies that the forces of interest are due largely to the instantaneous pressure distribution around the plate and are not significantly influenced by shear stresses. The instantaneous forces appear most complex for the smaller aspect ratios but the intensity of the normal force fluctuations is between 10% and 20% in the free-steam but can exceed 30% near the wall. As the wind tunnel floor is approached, the lift and drag reduce with increasing aspect ratio, and there is a reduction in the high frequency components of the forces. It is shown that the centre of pressure is closer to the centre of the plates than the quarter-chord position for nearly all cases. Full article
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663 KiB  
Article
Tuning of the PI Controller Parameters of a PMSG Wind Turbine to Improve Control Performance under Various Wind Speeds
by Yun-Su Kim, Il-Yop Chung and Seung-Il Moon
Energies 2015, 8(2), 1406-1425; https://doi.org/10.3390/en8021406 - 13 Feb 2015
Cited by 79 | Viewed by 12012
Abstract
This paper presents a method to seek the PI controller parameters of a PMSG wind turbine to improve control performance. Since operating conditions vary with the wind speed, therefore the PI controller parameters should be determined as a function of the wind speed. [...] Read more.
This paper presents a method to seek the PI controller parameters of a PMSG wind turbine to improve control performance. Since operating conditions vary with the wind speed, therefore the PI controller parameters should be determined as a function of the wind speed. Small-signal modeling of a PMSG WT is implemented to analyze the stability under various operating conditions and with eigenvalues obtained from the small-signal model of the PMSG WT, which are coordinated by adjusting the PI controller parameters. The parameters to be tuned are chosen by investigating participation factors of state variables, which simplifies the problem by reducing the number of parameters to be tuned. The process of adjusting these PI controller parameters is carried out using particle swarm optimization (PSO). To characterize the improvements in the control method due to the PSO method of tuning the PI controller parameters, the PMSG WT is modeled using the MATLAB/SimPowerSystems libraries with the obtained PI controller parameters. Full article
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315 KiB  
Article
Simulating Dynamic Stall Effects for Vertical Axis Wind Turbines Applying a Double Multiple Streamtube Model
by Eduard Dyachuk and Anders Goude
Energies 2015, 8(2), 1353-1372; https://doi.org/10.3390/en8021353 - 11 Feb 2015
Cited by 37 | Viewed by 8092
Abstract
The complex unsteady aerodynamics of vertical axis wind turbines (VAWT) poses significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions for VAWTs, and it is in the focus of the study. Two dynamic stall [...] Read more.
The complex unsteady aerodynamics of vertical axis wind turbines (VAWT) poses significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions for VAWTs, and it is in the focus of the study. Two dynamic stall models are compared: the widely-used Gormont model and a Leishman–Beddoes-type model. The models are included in a double multiple streamtube model. The effects of flow curvature and flow expansion are also considered. The model results are assessed against the measured data on a Darrieus turbine with curved blades. To study the dynamic stall effects, the comparison of force coefficients between the simulations and experiments is done at low tip speed ratios. Simulations show that the Leishman–Beddoes model outperforms the Gormont model for all tested conditions. Full article
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4252 KiB  
Article
Altering Kinetic Energy Entrainment in Large Eddy Simulations of Large Wind Farms Using Unconventional Wind Turbine Actuator Forcing
by Claire VerHulst and Charles Meneveau
Energies 2015, 8(1), 370-386; https://doi.org/10.3390/en8010370 - 6 Jan 2015
Cited by 34 | Viewed by 7815
Abstract
In this study, horizontally periodic large eddy simulations (LES) are utilized to study turbulent atmospheric boundary-layer flow over wind turbines in the far-downstream portion of a large wind farm where the wakes have merged and the flow is fully developed. In an attempt [...] Read more.
In this study, horizontally periodic large eddy simulations (LES) are utilized to study turbulent atmospheric boundary-layer flow over wind turbines in the far-downstream portion of a large wind farm where the wakes have merged and the flow is fully developed. In an attempt to increase power generation by enhancing the mean kinetic energy (MKE) entrainment to the wind turbines, hypothetical synthetic forcing is applied to the flow at the turbine rotor locations. The synthetic forcing is not meant to represent any existing devices or control schemes, but rather acts as a proof of concept to inform future designs. The turbines are modeled using traditional actuator disks, and the unconventional synthetic forcing is applied in the vertical direction with the magnitude and direction dependent on the instantaneous velocity fluctuation at the rotor disk; in one set of LES meant to enhance the vertical entrainment of MKE, a downward force is prescribed in conjunction with a positive axial velocity fluctuation, whereas a negative axial velocity fluctuation results in an upward force. The magnitude of the forcing is proportional to the instantaneous thrust force with prefactors ranging from 0.1 to 1. The synthetic vertical forcing is found to have a significant effect on the power generated by the wind farm. Consistent with previous findings, the MKE flux to the level of the turbines is found to vary along with the total power produced by the wind turbine array. The reverse strategy of downward forcing of slow axial velocity flow is found to have almost no effect on the power output or entrainment. Several of the scenarios tested, e.g., where the vertical force is of similar magnitude to the horizontal thrust, would be very difficult to implement in practice, but the simulations serve the purpose of identifying trends and bounds on possible power increases from flow modifications through action at the turbine rotor. Full article
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2014

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694 KiB  
Article
A Grid Voltage Measurement Method for Wind Power Systems during Grid Fault Conditions
by Cheol-Hee Yoo, Il-Yop Chung, Hyun-Jae Yoo and Sung-Soo Hong
Energies 2014, 7(11), 7732-7745; https://doi.org/10.3390/en7117732 - 20 Nov 2014
Cited by 7 | Viewed by 8183
Abstract
Grid codes in many countries require low-voltage ride-through (LVRT) capability to maintain power system stability and reliability during grid fault conditions. To meet the LVRT requirement, wind power systems must stay connected to the grid and also supply reactive currents to the grid [...] Read more.
Grid codes in many countries require low-voltage ride-through (LVRT) capability to maintain power system stability and reliability during grid fault conditions. To meet the LVRT requirement, wind power systems must stay connected to the grid and also supply reactive currents to the grid to support the recovery from fault voltages. This paper presents a new fault detection method and inverter control scheme to improve the LVRT capability for full-scale permanent magnet synchronous generator (PMSG) wind power systems. Fast fault detection can help the wind power systems maintain the DC-link voltage in a safe region. The proposed fault detection method is based on on-line adaptive parameter estimation. The performance of the proposed method is verified in comparison to the conventional voltage measurement method defined in the IEC 61400-21 standard. Full article
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