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Topical Collection "Wind Turbines"

Editor

Collection Editor
Prof. Dr. Frede Blaabjerg
Highly Cited - Clarivate Analytics (formerly Thomson Reuters)

Department of Energy Technology, Aalborg University, Aalborg 9220, Denmark
Website | E-Mail
Fax: +45 9815 1411
Interests: power electronics and its applications in motor drives; wind turbines; PV systems; harmonics; reliability of power electronic systems

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 1600 CHF (Swiss Francs).

Related Special Issues

Published Papers (66 papers)

2018

Jump to: 2017, 2016, 2015, 2014

Open AccessArticle Comparative Study of the Aerodynamic Performance of the New MEXICO Rotor under Yaw Conditions
Energies 2018, 11(4), 833; https://doi.org/10.3390/en11040833
Received: 12 February 2018 / Revised: 18 March 2018 / Accepted: 2 April 2018 / Published: 4 April 2018
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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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Open AccessArticle Wind Turbine Condition Monitoring Strategy through Multiway PCA and Multivariate Inference
Energies 2018, 11(4), 749; https://doi.org/10.3390/en11040749
Received: 20 February 2018 / Revised: 22 March 2018 / Accepted: 23 March 2018 / Published: 26 March 2018
Cited by 1 | PDF Full-text (592 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle A New Analytical Wake Model for Yawed Wind Turbines
Energies 2018, 11(3), 665; https://doi.org/10.3390/en11030665
Received: 26 January 2018 / Revised: 28 February 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
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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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Open AccessArticle Flow Control over the Blunt Trailing Edge of Wind Turbine Airfoils Using Circulation Control
Energies 2018, 11(3), 619; https://doi.org/10.3390/en11030619
Received: 16 February 2018 / Revised: 4 March 2018 / Accepted: 8 March 2018 / Published: 10 March 2018
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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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Open AccessArticle On the Evolution of the Integral Time Scale within Wind Farms
Energies 2018, 11(1), 93; https://doi.org/10.3390/en11010093
Received: 27 November 2017 / Revised: 19 December 2017 / Accepted: 28 December 2017 / Published: 2 January 2018
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Abstract
A wind-tunnel investigation was carried out to characterize the spatial distribution of the integral time scale (Tu) 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

Jump to: 2018, 2016, 2015, 2014

Open AccessArticle Machine Learning for Wind Turbine Blades Maintenance Management
Energies 2018, 11(1), 13; https://doi.org/10.3390/en11010013
Received: 28 October 2017 / Revised: 14 December 2017 / Accepted: 18 December 2017 / Published: 21 December 2017
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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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Open AccessArticle Flow Adjustment Inside and Around Large Finite-Size Wind Farms
Energies 2017, 10(12), 2164; https://doi.org/10.3390/en10122164
Received: 1 December 2017 / Revised: 13 December 2017 / Accepted: 14 December 2017 / Published: 18 December 2017
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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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Open AccessReview Structural Reliability Analysis of Wind Turbines: A Review
Energies 2017, 10(12), 2099; https://doi.org/10.3390/en10122099
Received: 7 November 2017 / Revised: 5 December 2017 / Accepted: 6 December 2017 / Published: 11 December 2017
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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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Open AccessArticle Force Measurements on a VAWT Blade in Parked Conditions
Energies 2017, 10(12), 1954; https://doi.org/10.3390/en10121954
Received: 24 October 2017 / Revised: 17 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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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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Open AccessArticle Numerical Investigation of the Tip Vortex of a Straight-Bladed Vertical Axis Wind Turbine with Double-Blades
Energies 2017, 10(11), 1721; https://doi.org/10.3390/en10111721
Received: 5 September 2017 / Revised: 23 October 2017 / Accepted: 23 October 2017 / Published: 27 October 2017
Cited by 1 | PDF Full-text (17063 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle Sensitivity Analysis to Control the Far-Wake Unsteadiness Behind Turbines
Energies 2017, 10(10), 1599; https://doi.org/10.3390/en10101599
Received: 19 August 2017 / Revised: 9 October 2017 / Accepted: 10 October 2017 / Published: 13 October 2017
Cited by 2 | PDF Full-text (10821 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle Techno-Economic Assessment of Wind Energy Potential at Three Locations in South Korea Using Long-Term Measured Wind Data
Energies 2017, 10(9), 1442; https://doi.org/10.3390/en10091442
Received: 25 August 2017 / Revised: 12 September 2017 / Accepted: 15 September 2017 / Published: 19 September 2017
Cited by 2 | PDF Full-text (8029 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle Analyses of the Extensible Blade in Improving Wind Energy Production at Sites with Low-Class Wind Resource
Energies 2017, 10(9), 1295; https://doi.org/10.3390/en10091295
Received: 24 July 2017 / Revised: 24 August 2017 / Accepted: 27 August 2017 / Published: 30 August 2017
Cited by 6 | PDF Full-text (5804 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle Windbreak Effects Within Infinite Wind Farms
Energies 2017, 10(8), 1140; https://doi.org/10.3390/en10081140
Received: 9 May 2017 / Revised: 14 July 2017 / Accepted: 27 July 2017 / Published: 3 August 2017
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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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Open AccessArticle A DC Microgrid Coordinated Control Strategy Based on Integrator Current-Sharing
Energies 2017, 10(8), 1116; https://doi.org/10.3390/en10081116
Received: 10 July 2017 / Revised: 23 July 2017 / Accepted: 25 July 2017 / Published: 1 August 2017
Cited by 3 | PDF Full-text (4429 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle Optimal Dynamic Analysis of Electrical/Electronic Components in Wind Turbines
Energies 2017, 10(8), 1111; https://doi.org/10.3390/en10081111
Received: 23 May 2017 / Revised: 28 June 2017 / Accepted: 18 July 2017 / Published: 31 July 2017
Cited by 2 | PDF Full-text (3931 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle A New Miniature Wind Turbine for Wind Tunnel Experiments. Part II: Wake Structure and Flow Dynamics
Energies 2017, 10(7), 923; https://doi.org/10.3390/en10070923
Received: 10 May 2017 / Revised: 24 June 2017 / Accepted: 29 June 2017 / Published: 4 July 2017
Cited by 1 | PDF Full-text (2697 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle A New Miniature Wind Turbine for Wind Tunnel Experiments. Part I: Design and Performance
Energies 2017, 10(7), 908; https://doi.org/10.3390/en10070908
Received: 10 May 2017 / Revised: 24 June 2017 / Accepted: 28 June 2017 / Published: 3 July 2017
Cited by 2 | PDF Full-text (1423 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
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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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Open AccessArticle Wind Turbine Synchronous Reset Pitch Control
Energies 2017, 10(6), 770; https://doi.org/10.3390/en10060770
Received: 6 April 2017 / Revised: 22 May 2017 / Accepted: 27 May 2017 / Published: 1 June 2017
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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
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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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Open AccessArticle Sliding Mode Control of a Variable- Speed Wind Energy Conversion System Using a Squirrel Cage Induction Generator
Energies 2017, 10(5), 604; https://doi.org/10.3390/en10050604
Received: 25 January 2017 / Revised: 19 April 2017 / Accepted: 19 April 2017 / Published: 1 May 2017
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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
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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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Open AccessArticle Automatic Tracking of the Modal Parameters of an Offshore Wind Turbine Drivetrain System
Energies 2017, 10(4), 574; https://doi.org/10.3390/en10040574
Received: 20 February 2017 / Revised: 13 April 2017 / Accepted: 19 April 2017 / Published: 22 April 2017
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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
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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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Open AccessArticle Fatigue Reliability Analysis of Wind Turbine Cast Components
Energies 2017, 10(4), 466; https://doi.org/10.3390/en10040466
Received: 14 December 2016 / Revised: 23 February 2017 / Accepted: 28 March 2017 / Published: 2 April 2017
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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
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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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Open AccessArticle Power Loss Analysis for Wind Power Grid Integration Based on Weibull Distribution
Energies 2017, 10(4), 463; https://doi.org/10.3390/en10040463
Received: 3 January 2017 / Revised: 28 March 2017 / Accepted: 29 March 2017 / Published: 2 April 2017
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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
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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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Open AccessFeature PaperArticle Wind Turbine Power Curve Design for Optimal Power Generation in Wind Farms Considering Wake Effect
Energies 2017, 10(3), 395; https://doi.org/10.3390/en10030395
Received: 2 December 2016 / Revised: 14 March 2017 / Accepted: 15 March 2017 / Published: 20 March 2017
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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
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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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Open AccessArticle Wind Farm Wake: The 2016 Horns Rev Photo Case
Energies 2017, 10(3), 317; https://doi.org/10.3390/en10030317
Received: 22 December 2016 / Revised: 24 February 2017 / Accepted: 27 February 2017 / Published: 7 March 2017
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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
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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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Open AccessArticle Experimental and Simulation Studies of Strength and Fracture Behaviors of Wind Turbine Bearing Steel Processed by High Pressure Torsion
Energies 2016, 9(12), 1033; https://doi.org/10.3390/en9121033
Received: 3 November 2016 / Revised: 30 November 2016 / Accepted: 2 December 2016 / Published: 8 December 2016
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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
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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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Open AccessArticle Inverse Aerodynamic Optimization Considering Impacts of Design Tip Speed Ratio for Variable-Speed Wind Turbines
Energies 2016, 9(12), 1023; https://doi.org/10.3390/en9121023
Received: 5 September 2016 / Revised: 23 November 2016 / Accepted: 28 November 2016 / Published: 3 December 2016
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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
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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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Open AccessArticle Numerical Investigation of Wind Conditions for Roof-Mounted Wind Turbines: Effects of Wind Direction and Horizontal Aspect Ratio of a High-Rise Cuboid Building
Energies 2016, 9(11), 907; https://doi.org/10.3390/en9110907
Received: 6 September 2016 / Revised: 23 October 2016 / Accepted: 25 October 2016 / Published: 3 November 2016
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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).
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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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Open AccessArticle A Short-Term Outage Model of Wind Turbines with Doubly Fed Induction Generators Based on Supervisory Control and Data Acquisition Data
Energies 2016, 9(11), 882; https://doi.org/10.3390/en9110882
Received: 21 July 2016 / Revised: 13 October 2016 / Accepted: 14 October 2016 / Published: 28 October 2016
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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
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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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Open AccessArticle Fuzzy Logic Based Multi-Criteria Wind Turbine Selection Strategy—A Case Study of Qassim, Saudi Arabia
Energies 2016, 9(11), 872; https://doi.org/10.3390/en9110872
Received: 20 July 2016 / Revised: 12 September 2016 / Accepted: 22 September 2016 / Published: 26 October 2016
Cited by 5 | PDF Full-text (477 KB) | HTML Full-text | XML Full-text
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
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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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Open AccessArticle A Vertical-Axis Off-Grid Squirrel-Cage Induction Generator Wind Power System
Energies 2016, 9(10), 822; https://doi.org/10.3390/en9100822
Received: 16 August 2016 / Revised: 3 October 2016 / Accepted: 9 October 2016 / Published: 14 October 2016
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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
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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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Open AccessArticle A Novel Pitch Control System of a Large Wind Turbine Using Two-Degree-of-Freedom Motion Control with Feedback Linearization Control
Energies 2016, 9(10), 791; https://doi.org/10.3390/en9100791
Received: 13 July 2016 / Revised: 9 September 2016 / Accepted: 20 September 2016 / Published: 29 September 2016
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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
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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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Open AccessArticle Study on the Wake of a Miniature Wind Turbine Using the Reynolds Stress Model
Energies 2016, 9(10), 784; https://doi.org/10.3390/en9100784
Received: 25 July 2016 / Revised: 8 September 2016 / Accepted: 13 September 2016 / Published: 28 September 2016
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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
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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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Open AccessArticle Coherence Effects on the Power and Tower Loads of a 7 × 2 MW Multi-Rotor Wind Turbine System
Energies 2016, 9(9), 742; https://doi.org/10.3390/en9090742
Received: 16 June 2016 / Revised: 23 August 2016 / Accepted: 30 August 2016 / Published: 13 September 2016
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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
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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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Open AccessArticle Axial Dynamic Stiffness of Tubular Piles in Viscoelastic Soil
Energies 2016, 9(9), 734; https://doi.org/10.3390/en9090734
Received: 22 June 2016 / Revised: 20 August 2016 / Accepted: 24 August 2016 / Published: 10 September 2016
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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
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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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Open AccessArticle Modeling of Load Bearing Characteristics of Jacket Foundation Piles for Offshore Wind Turbines in Taiwan
Energies 2016, 9(8), 625; https://doi.org/10.3390/en9080625
Received: 12 May 2016 / Revised: 18 July 2016 / Accepted: 1 August 2016 / Published: 9 August 2016
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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
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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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Open AccessReview A Review of Research on Large Scale Modern Vertical Axis Wind Turbines at Uppsala University
Energies 2016, 9(7), 570; https://doi.org/10.3390/en9070570
Received: 30 May 2016 / Revised: 6 July 2016 / Accepted: 11 July 2016 / Published: 21 July 2016
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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
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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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Open AccessArticle A Comparative Study of Multiple-Criteria Decision-Making Methods under Stochastic Inputs
Energies 2016, 9(7), 566; https://doi.org/10.3390/en9070566
Received: 21 April 2016 / Revised: 4 July 2016 / Accepted: 7 July 2016 / Published: 21 July 2016
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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
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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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Open AccessArticle On Real-Time Fault Detection in Wind Turbines: Sensor Selection Algorithm and Detection Time Reduction Analysis
Energies 2016, 9(7), 520; https://doi.org/10.3390/en9070520
Received: 10 May 2016 / Revised: 16 June 2016 / Accepted: 30 June 2016 / Published: 5 July 2016
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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
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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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Open AccessArticle Analysis and Solution for Operations of Overcurrent Relay in Wind Power System
Energies 2016, 9(6), 458; https://doi.org/10.3390/en9060458
Received: 1 February 2016 / Revised: 2 June 2016 / Accepted: 7 June 2016 / Published: 16 June 2016
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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
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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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Open AccessArticle Application of a Heat Flux Sensor in Wind Power Electronics
Energies 2016, 9(6), 456; https://doi.org/10.3390/en9060456
Received: 1 February 2016 / Revised: 23 May 2016 / Accepted: 6 June 2016 / Published: 14 June 2016
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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
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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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Open AccessArticle Wind Turbine Driving a PM Synchronous Generator Using Novel Recurrent Chebyshev Neural Network Control with the Ideal Learning Rate
Energies 2016, 9(6), 441; https://doi.org/10.3390/en9060441
Received: 4 March 2016 / Revised: 24 May 2016 / Accepted: 3 June 2016 / Published: 9 June 2016
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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
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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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