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Special Issue "Wind Turbines"

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A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 March 2012)

Special Issue Editors

Guest Editor
Prof. Dr. Frede Blaabjerg (Website)

Department of Energy Technology, Aalborg University, DK-9220 Aalborg East, Denmark
Fax: +45 9815 1411
Interests: wind power research; power electronics; control of wind turbines and wind farms; interconnection to grid; generators; power converters; ride-through operation
Guest Editor
Prof. Dr. Lance Manuel (Website)

Mechanics, Uncertainty, and Simulation in Engineering (MUSE), Dept. of Civil, Architectural, and Environmental Engineering, The University of Texas At Austin (UT-Austin), TX, USA.
Fax: +1 512 471 7259
Interests: probabilistic methods; structural dynamics; wind turbine inflow characterization and loads
Guest Editor
Prof. Dr. Mark J. Balas (Website)

Department of Electrical & Computer Engineering, College of Engineering and Applied Science, Laramie, WY 82071, USA
Phone: +1 307 766 5599
Fax: +1 307 766 2248
Interests: aerodynamics including design and optimization; aircraft design; experimental and computational fluid dynamics; biofluiddynamics; wind energy; aero-hydrodynamics of sailing

Special Issue Information

Dear Colleagues,

This issue 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 incl 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
Prof. Dr. Lance Manuel
Prof. Dr. Mark J. Balas
Guest Editors

Related Special Issues

Published Papers (27 papers)

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Open AccessArticle Real-Time Control of Active and Reactive Power for Doubly Fed Induction Generator (DFIG)-Based Wind Energy Conversion System
Energies 2015, 8(9), 10389-10408; doi:10.3390/en80910389
Received: 13 July 2015 / Revised: 6 August 2015 / Accepted: 15 September 2015 / Published: 21 September 2015
PDF Full-text (557 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the modeling, rapid control prototyping, and hardware-in-the-loop testing for real-time simulation and control of a grid-connected doubly fed induction generator (DFIG) in a laboratory-size wind turbine emulator for wind energy conversation systems. The generator is modeled using the direct-quadrature [...] Read more.
This paper presents the modeling, rapid control prototyping, and hardware-in-the-loop testing for real-time simulation and control of a grid-connected doubly fed induction generator (DFIG) in a laboratory-size wind turbine emulator for wind energy conversation systems. The generator is modeled using the direct-quadrature rotating reference frame circuit along with the aligned stator flux, and the field-oriented control approach is applied for independent control of the active and reactive power and the DC-link voltage at the grid side. The control of the active, reactive power and the DC-link voltage are performed using a back-to-back converter at sub- and super-synchronous as well as at variable speeds. The control strategy is experimentally validated on an emulated wind turbine driven by the Opal-RT real-time simulator (OP5600) for simultaneous control of the DC-link voltage, active and reactive power. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Fault Diagnosis and Fault-Tolerant Control of Wind Turbines via a Discrete Time Controller with a Disturbance Compensator
Energies 2015, 8(5), 4300-4316; doi:10.3390/en8054300
Received: 13 March 2015 / Revised: 13 April 2015 / Accepted: 4 May 2015 / Published: 12 May 2015
Cited by 2 | PDF Full-text (1660 KB) | HTML Full-text | XML Full-text
Abstract
This paper develops a fault diagnosis (FD) and fault-tolerant control (FTC) of pitch actuators in wind turbines. This is accomplished by combining a disturbance compensator with a controller, both of which are formulated in the discrete time domain. The disturbance compensator has [...] Read more.
This paper develops a fault diagnosis (FD) and fault-tolerant control (FTC) of pitch actuators in wind turbines. This is accomplished by combining a disturbance compensator with a controller, both of which are formulated in the discrete time domain. The disturbance compensator has a dual purpose: to estimate the actuator fault (which is used by the FD algorithm) and to design the discrete time controller to obtain an FTC. That is, the pitch actuator faults are estimated, and then, the pitch control laws are appropriately modified to achieve an FTC with a comparable behavior to the fault-free case. The performance of the FD and FTC schemes is tested in simulations with the aero-elastic code FAST. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Turbulent Flow Characteristics and Dynamics Response of a Vertical-Axis Spiral Rotor
Energies 2013, 6(6), 2741-2758; doi:10.3390/en6062741
Received: 28 March 2013 / Revised: 15 May 2013 / Accepted: 17 May 2013 / Published: 29 May 2013
Cited by 2 | PDF Full-text (1148 KB) | HTML Full-text | XML Full-text
Abstract
The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. [...] Read more.
The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent flow features near the rotor blades are simulated with Spalart-Allmaras turbulence model. The torque coefficient of the proposed rotor is satisfactory in terms of its magnitude and variation through the rotational cycle. Along the height of the rotor, distinct spatial turbulent flow patterns vary with the upstream air velocity. Subsequent experiments involving a disk generator gives an in-depth understanding of the dynamic response of the proposed rotor under different operation conditions. The optimal tip-speed ratio of the spiral rotor is 0.4–0.5, as is shown in both simulation and experiment. Under normal and relative-motion flow conditions, and within the range of upstream air velocity from 1 to 12 m/s, the output voltage of the generator was monitored and statistically analyzed. It was found that normal air velocity fluctuations lead to a non-synchronous correspondence between upstream air velocity and output voltage. In contrast, the spiral rotor’s performance when operating from the back of a moving truck was significantly different to its performance under the natural conditions. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Time Domain Modeling and Analysis of Dynamic Gear Contact Force in a Wind Turbine Gearbox with Respect to Fatigue Assessment
Energies 2012, 5(11), 4350-4371; doi:10.3390/en5114350
Received: 26 August 2012 / Revised: 23 October 2012 / Accepted: 23 October 2012 / Published: 1 November 2012
Cited by 7 | PDF Full-text (4986 KB) | HTML Full-text | XML Full-text
Abstract
The gearbox is one of the most expensive components of the wind turbine system. In order to refine the design and hence increase the long-term reliability, there has been increasing interest in utilizing time domain simulations in the prediction of gearbox design [...] Read more.
The gearbox is one of the most expensive components of the wind turbine system. In order to refine the design and hence increase the long-term reliability, there has been increasing interest in utilizing time domain simulations in the prediction of gearbox design loads. In this study, three problems in time domain based gear contact fatigue analysis under dynamic conditions are discussed: (1) the torque reversal problem under low wind speed conditions, (2) statistical uncertainty effects due to time domain simulations and (3) simplified long term contact fatigue analysis of the gear tooth under dynamic conditions. Several recommendations to deal with these issues are proposed based on analyses of the National Renewable Energy Laboratory’s 750 kW land-based Gearbox Reliability Collaborative wind turbine. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle A Comparison of Wind Flow Models for Wind Resource Assessment in Wind Energy Applications
Energies 2012, 5(11), 4288-4322; doi:10.3390/en5114288
Received: 10 August 2012 / Revised: 22 October 2012 / Accepted: 23 October 2012 / Published: 29 October 2012
Cited by 10 | PDF Full-text (4555 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this work was to assess the accuracy of various coupled mesoscale-microscale wind flow modeling methodologies for wind energy applications. This is achieved by examining and comparing mean wind speeds from several wind flow modeling methodologies with observational measurements from [...] Read more.
The objective of this work was to assess the accuracy of various coupled mesoscale-microscale wind flow modeling methodologies for wind energy applications. This is achieved by examining and comparing mean wind speeds from several wind flow modeling methodologies with observational measurements from several 50 m met towers distributed across the study area. At the mesoscale level, with a 5 km resolution, two scenarios are examined based on the Mesoscale Compressible Community Model (MC2) model: the Canadian Wind Energy Atlas (CWEA) scenario, which is based on standard input data, and the CWEA High Definition (CWEAHD) scenario where high resolution land cover input data is used. A downscaling of the obtained mesoscale wind climate to the microscale level is then performed, where two linear microscale models, i.e., MsMicro and the Wind Atlas Analysis and Application Program (WAsP), are evaluated following three downscaling scenarios: CWEA-WAsP, CWEA-MsMicro and CWEAHD-MsMicro. Results show that, for the territory studied, with a modeling approach based on the MC2 and MsMicro models, also known as Wind Energy Simulation Toolkit (WEST), the use of high resolution land cover and topography data at the mesoscale level helps reduce modeling errors for both the mesoscale and microscale models, albeit only marginally. At the microscale level, results show that the MC2-WAsP modeling approach gave substantially better results than both MC2 and MsMicro modeling approaches due to tweaked meso-micro coupling. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Investigation of Site-Specific Wind Field Parameters and Their Effect on Loads of Offshore Wind Turbines
Energies 2012, 5(10), 3835-3855; doi:10.3390/en5103835
Received: 27 July 2012 / Revised: 3 September 2012 / Accepted: 24 September 2012 / Published: 8 October 2012
Cited by 6 | PDF Full-text (4298 KB) | HTML Full-text | XML Full-text
Abstract
The main contributing factors to unsteady loading of Offshore Wind Turbines (OWT) are wind shear, turbulence, and waves. In the present paper, the turbulence intensity and the wind shear exponent are investigated. Using data from the FINO 1 research platform, these parameters [...] Read more.
The main contributing factors to unsteady loading of Offshore Wind Turbines (OWT) are wind shear, turbulence, and waves. In the present paper, the turbulence intensity and the wind shear exponent are investigated. Using data from the FINO 1 research platform, these parameters are analyzed and compared with the proposed wind field parameters in the IEC standard 61400-3. Based on this analysis, aeroelastic simulations are performed to determine the effect of wind field parameters on the fatigue and the extreme loads on the rotor blades. For the investigations, the aeroelastic model of a 5 MW OWT is used with a focus on design load cases in an operating state (power production). The fatigue loads are examined by means of the damage-equivalent load-range approach. In order to determine the extreme loads with a recurrence period of 50 years, a peak over threshold extrapolation method and a novel method based on average conditional exceedance rates are used. The results show that the requirements of the IEC standard are very conservative for the design of the rotor blades. Therefore, there could be a large optimization potential for the reduction of weight and cost of the rotor blades. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Feasibility Study of Micro-Wind Turbines for Powering Wireless Sensors on a Cable-Stayed Bridge
Energies 2012, 5(9), 3450-3464; doi:10.3390/en5093450
Received: 15 June 2012 / Revised: 3 August 2012 / Accepted: 27 August 2012 / Published: 6 September 2012
Cited by 13 | PDF Full-text (1531 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the feasibility of using micro-wind turbines to power wireless sensors on a cable-stayed bridge is comprehensively investigated. To this end, the wind environment around a bridge onto which a turbine is installed is examined, as is the power consumption [...] Read more.
In this study, the feasibility of using micro-wind turbines to power wireless sensors on a cable-stayed bridge is comprehensively investigated. To this end, the wind environment around a bridge onto which a turbine is installed is examined, as is the power consumption of a wireless sensor. Feasible alternators and rotors are then carefully selected to make an effective small wind generator (known as a micro-wind turbine). Using the three specially selected micro-wind turbines, a series of experiments was conducted to find the turbine best able to generate the largest amount of power. Finally, a horizontal-axis micro-wind turbine with a six-blade rotor was combined with a wireless sensor to validate experimentally its actual power-charging capability. It is demonstrated that the micro-wind turbine can generate sufficient electricity to power a wireless sensor under moderate wind conditions. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle More Wind Power Integration with Adjusted Energy Carriers for Space Heating in Northern China
Energies 2012, 5(9), 3279-3294; doi:10.3390/en5093279
Received: 13 April 2012 / Revised: 10 August 2012 / Accepted: 20 August 2012 / Published: 31 August 2012
Cited by 3 | PDF Full-text (748 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
In Northern China, due to the high penetration of coal-fired cogeneration facilities, which are generally equipped with extraction-condensing steam turbines, lots of wind power resources may be wasted during the heating season. In contrast, considerable coal is consumed in the power generation [...] Read more.
In Northern China, due to the high penetration of coal-fired cogeneration facilities, which are generally equipped with extraction-condensing steam turbines, lots of wind power resources may be wasted during the heating season. In contrast, considerable coal is consumed in the power generation sector. In this article, firstly it is revealed that there exists a serious divergence in the ratio of electrical to thermal energy between end users’ demand and the cogenerations’ production during off-peak load at night, which may negate active power-balancing of the electric power grid. Secondly, with respect to this divergence only occurring during off-peak load at night, a temporary proposal is given so as to enable the integration of more wind power. The authors suggest that if the energy carrier for part of the end users’ space heating is switched from heating water to electricity (e.g., electric heat pumps (EHPs) can provide space heating in the domestic sector), the ratio of electricity to heating water load should be adjusted to optimize the power dispatch between cogeneration units and wind turbines, resulting in fuel conservation. With this proposal, existing infrastructures are made full use of, and no additional ones are required. Finally a numerical simulation is performed in order to illustrate both the technical and economic feasibility of the aforementioned proposal, under ongoing infrastructures as well as electricity and space heating tariff conditions without changing participants’ benefits. The authors aim to persuade Chinese policy makers to enable EHPs to provide space heating to enable the integration of more wind power. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Power Control Design for Variable-Speed Wind Turbines
Energies 2012, 5(8), 3033-3050; doi:10.3390/en5083033
Received: 25 June 2012 / Revised: 3 August 2012 / Accepted: 3 August 2012 / Published: 13 August 2012
Cited by 11 | PDF Full-text (1935 KB) | HTML Full-text | XML Full-text
Abstract
This paper considers power generation control in variable-speed variable-pitch horizontal-axis wind turbines operating at high wind speeds. A dynamic chattering torque control and a proportional integral (PI) pitch control strategy are proposed and validated using the National Renewable Energy Laboratory wind turbine [...] Read more.
This paper considers power generation control in variable-speed variable-pitch horizontal-axis wind turbines operating at high wind speeds. A dynamic chattering torque control and a proportional integral (PI) pitch control strategy are proposed and validated using the National Renewable Energy Laboratory wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. Validation results show that the proposed controllers are effective for power regulation and demonstrate high-performances for all other state variables (turbine and generator rotational speeds; and smooth and adequate evolution of the control variables) for turbulent wind conditions. To highlight the improvements of the provided method, the proposed controllers are compared to relevant previously published studies. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Fault Detection of Wind Turbines with Uncertain Parameters: A Set-Membership Approach
Energies 2012, 5(7), 2424-2448; doi:10.3390/en5072424
Received: 27 April 2012 / Revised: 11 June 2012 / Accepted: 6 July 2012 / Published: 13 July 2012
Cited by 16 | PDF Full-text (573 KB) | HTML Full-text | XML Full-text
Abstract
In this paper a set-membership approach for fault detection of a benchmark wind turbine is proposed. The benchmark represents relevant fault scenarios in the control system, including sensor, actuator and system faults. In addition we also consider parameter uncertainties and uncertainties on [...] Read more.
In this paper a set-membership approach for fault detection of a benchmark wind turbine is proposed. The benchmark represents relevant fault scenarios in the control system, including sensor, actuator and system faults. In addition we also consider parameter uncertainties and uncertainties on the torque coefficient. High noise on the wind speed measurement, nonlinearities in the aerodynamic torque and uncertainties on the parameters make fault detection a challenging problem. We use an effective wind speed estimator to reduce the noise on the wind speed measurements. A set-membership approach is used generate a set that contains all states consistent with the past measurements and the given model of the wind turbine including uncertainties and noise. This set represents all possible states the system can be in if not faulty. If the current measurement is not consistent with this set, a fault is detected. For representation of these sets we use zonotopes and for modeling of uncertainties we use matrix zonotopes, which yields a computationally efficient algorithm. The method is applied to the wind turbine benchmark problem without and with uncertainties. The result demonstrates the effectiveness of the proposed method compared to other proposed methods applied to the same problem. An advantage of the proposed method is that there is no need for threshold design, and it does not produce positive false alarms. In the case where uncertainty on the torque lookup table is introduced, some faults are not detectable. Previous research has not addressed this uncertainty. The method proposed here requires equal or less detection time than previous results. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Sliding Mode Control Strategy for Wind Turbine Power Maximization
Energies 2012, 5(7), 2310-2330; doi:10.3390/en5072310
Received: 15 March 2012 / Revised: 25 June 2012 / Accepted: 3 July 2012 / Published: 9 July 2012
Cited by 15 | PDF Full-text (399 KB) | HTML Full-text | XML Full-text
Abstract
The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, a sliding mode control for variable speed wind turbine that incorporates a doubly fed induction generator is described. The electrical system incorporates [...] Read more.
The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, a sliding mode control for variable speed wind turbine that incorporates a doubly fed induction generator is described. The electrical system incorporates a wound rotor induction machine with back-to-back three phase power converter bridges between its rotor and the grid. In the presented design the so-called vector control theory is applied, in order to simplify the electrical equations. The proposed control scheme uses stator flux-oriented vector control for the rotor side converter bridge control and grid voltage vector control for the grid side converter bridge control. The stability analysis of the proposed sliding mode controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally simulated results show, on the one hand, that the proposed controller provides high-performance dynamic characteristics, and on the other hand, that this scheme is robust with respect to the uncertainties that usually appear in the real systems. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Energy Storage System with Voltage Equalization Strategy for Wind Energy Conversion
Energies 2012, 5(7), 2331-2350; doi:10.3390/en5072331
Received: 21 March 2012 / Revised: 29 May 2012 / Accepted: 26 June 2012 / Published: 9 July 2012
Cited by 8 | PDF Full-text (1202 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, an energy storage system with voltage equalization strategy for wind energy conversion is presented. The proposed energy storage system provides a voltage equalization strategy for series-connected lead-acid batteries to increase their total storage capacity and lifecycle. In order to [...] Read more.
In this paper, an energy storage system with voltage equalization strategy for wind energy conversion is presented. The proposed energy storage system provides a voltage equalization strategy for series-connected lead-acid batteries to increase their total storage capacity and lifecycle. In order to draw the maximum power from the wind energy, a perturbation-and-observation method and digital signal processor (DSP) are incorporated to implement maximum power point tracking (MPPT) algorithm and power regulating scheme. In the proposed energy storage system, all power switches have zero-voltage-switching (ZVS) feature at turn-on transition. Therefore, the conversion efficiency can be increased. Finally, a prototype energy storage system for wind energy conversion is built and implemented. Experimental results have verified the performance and feasibility of the proposed energy storage system for wind energy conversion. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Power System Stability of a Small Sized Isolated Network Supplied by a Combined Wind-Pumped Storage Generation System: A Case Study in the Canary Islands
Energies 2012, 5(7), 2351-2369; doi:10.3390/en5072351
Received: 17 April 2012 / Revised: 1 June 2012 / Accepted: 26 June 2012 / Published: 9 July 2012
Cited by 7 | PDF Full-text (1447 KB) | HTML Full-text | XML Full-text
Abstract
Massive integration of renewable energy sources in electrical power systems of remote islands is a subject of current interest. The increasing cost of fossil fuels, transport costs to isolated sites and environmental concerns constitute a serious drawback to the use of conventional [...] Read more.
Massive integration of renewable energy sources in electrical power systems of remote islands is a subject of current interest. The increasing cost of fossil fuels, transport costs to isolated sites and environmental concerns constitute a serious drawback to the use of conventional fossil fuel plants. In a weak electrical grid, as it is typical on an island, if a large amount of conventional generation is substituted by renewable energy sources, power system safety and stability can be compromised, in the case of large grid disturbances. In this work, a model for transient stability analysis of an isolated electrical grid exclusively fed from a combination of renewable energy sources has been studied. This new generation model will be installed in El Hierro Island, in Spain. Additionally, an operation strategy to coordinate the generation units (wind, hydro) is also established. Attention is given to the assessment of inertial energy and reactive current to guarantee power system stability against large disturbances. The effectiveness of the proposed strategy is shown by means of simulation results. Full article
(This article belongs to the Special Issue Wind Turbines)
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Open AccessArticle On Space-Time Resolution of Inflow Representations for Wind Turbine Loads Analysis
Energies 2012, 5(7), 2071-2092; doi:10.3390/en5072071
Received: 13 April 2012 / Revised: 30 May 2012 / Accepted: 15 June 2012 / Published: 25 June 2012
Cited by 6 | PDF Full-text (3323 KB) | HTML Full-text | XML Full-text
Abstract
Efficient spatial and temporal resolution of simulated inflow wind fields is important in order to represent wind turbine dynamics and derive load statistics for design. Using Fourier-based stochastic simulation of inflow turbulence, we first investigate loads for a utility-scale turbine in the [...] Read more.
Efficient spatial and temporal resolution of simulated inflow wind fields is important in order to represent wind turbine dynamics and derive load statistics for design. Using Fourier-based stochastic simulation of inflow turbulence, we first investigate loads for a utility-scale turbine in the neutral atmospheric boundary layer. Load statistics, spectra, and wavelet analysis representations for different space and time resolutions are compared. Next, large-eddy simulation (LES) is employed with space-time resolutions, justified on the basis of the earlier stochastic simulations, to again derive turbine loads. Extreme and fatigue loads from the two approaches used in inflow field generation are compared. On the basis of simulation studies carried out for three different wind speeds in the turbine’s operating range, it is shown that inflow turbulence described using 10-meter spatial resolution and 1 Hz temporal resolution is adequate for assessing turbine loads. Such studies on the investigation of adequate filtering or resolution of inflow wind fields help to establish efficient strategies for LES and other physical or stochastic simulation needed in turbine loads studies. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Two LQRI based Blade Pitch Controls for Wind Turbines
Energies 2012, 5(6), 1998-2016; doi:10.3390/en5061998
Received: 15 February 2012 / Revised: 16 April 2012 / Accepted: 15 June 2012 / Published: 20 June 2012
Cited by 4 | PDF Full-text (372 KB) | HTML Full-text | XML Full-text
Abstract
As the wind turbine size has been increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control in addition to maximum wind power capture. In this paper, we present [...] Read more.
As the wind turbine size has been increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control in addition to maximum wind power capture. In this paper, we present a separate set of collective and individual pitch control algorithms. Both pitch control algorithms use the LQR control technique with integral action (LQRI), and utilize Kalman filters to estimate system states and wind speed. Compared to previous works in this area, our pitch control algorithms can control rotor speed and blade bending moments at the same time to improve the trade-off between rotor speed regulation and load reduction, while both collective and individual pitch controls can be designed separately. Simulation results show that the proposed collective and individual pitch controllers achieve very good rotor speed regulation and significant reduction of blade bending moments. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines
Energies 2012, 5(6), 1816-1834; doi:10.3390/en5061816
Received: 31 March 2012 / Revised: 8 June 2012 / Accepted: 8 June 2012 / Published: 15 June 2012
Cited by 9 | PDF Full-text (392 KB) | HTML Full-text | XML Full-text | Correction
Abstract
Consequences of failure of offshore wind turbines (OWTs) is in general lower than consequences of failure of, e.g., oil & gas platforms. It is reasonable that lower fatigue design factors can be applied for fatigue design of OWTs when compared to other fixed offshore structures. Calibration of appropriate partial safety factors/Fatigue Design Factors (FDF) for steel substructures for OWTs is the scope of this paper. A reliability-based approach is used and a probabilistic model has been developed, where design and limit state equations are established for fatigue failure. The strength and load uncertainties are described by stochastic variables. SN and fracture mechanics approaches are considered for to model the fatigue life. Further, both linear and bi-linear SN-curves are formulated and various approximations are investigated. The acceptable reliability level for fatigue failure of OWTs is discussed and results are presented for calibrated optimal fatigue design factors. Further, the influence of inspections is considered in order to extend and maintain a given target safety level. Full article
(This article belongs to the Special Issue Wind Turbines)
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Open AccessArticle A Closed-Form Technique for the Reliability and Risk Assessment of Wind Turbine Systems
Energies 2012, 5(6), 1734-1750; doi:10.3390/en5061734
Received: 5 April 2012 / Revised: 25 May 2012 / Accepted: 29 May 2012 / Published: 4 June 2012
Cited by 3 | PDF Full-text (238 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a closed-form method to evaluate wind turbine system reliability and associated failure consequences. Monte Carlo simulation, a widely used approach for system reliability assessment, usually requires large numbers of computational experiments, while existing analytical methods are limited to simple [...] Read more.
This paper proposes a closed-form method to evaluate wind turbine system reliability and associated failure consequences. Monte Carlo simulation, a widely used approach for system reliability assessment, usually requires large numbers of computational experiments, while existing analytical methods are limited to simple system event configurations with a focus on average values of reliability metrics. By analyzing a wind turbine system and its components in a combinatorial yet computationally efficient form, the proposed approach provides an entire probability distribution of system failure that contains all possible configurations of component failure and survival events. The approach is also capable of handling unique component attributes such as downtime and repair cost needed for risk estimations, and enables sensitivity analysis for quantifying the criticality of individual components to wind turbine system reliability. Applications of the technique are illustrated by assessing the reliability of a 12-subassembly turbine system. In addition, component downtimes and repair costs of components are embedded in the formulation to compute expected annual wind turbine unavailability and repair cost probabilities, and component importance metrics useful for maintenance planning and research prioritization. Furthermore, this paper introduces a recursive solution to closed-form method and applies this to a 45-component turbine system. The proposed approach proves to be computationally efficient and yields vital reliability information that could be readily used by wind farm stakeholders for decision making and risk management. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle A Power Smoothing Control Strategy and Optimized Allocation of Battery Capacity Based on Hybrid Storage Energy Technology
Energies 2012, 5(5), 1593-1612; doi:10.3390/en5051593
Received: 19 November 2011 / Revised: 12 April 2012 / Accepted: 3 May 2012 / Published: 21 May 2012
Cited by 12 | PDF Full-text (562 KB) | HTML Full-text | XML Full-text
Abstract
Wind power parallel operation is an effective way to realize the large scale use of wind power, but the fluctuations of power output from wind power units may have great influence on power quality, hence a new method of power smoothing and [...] Read more.
Wind power parallel operation is an effective way to realize the large scale use of wind power, but the fluctuations of power output from wind power units may have great influence on power quality, hence a new method of power smoothing and capacity optimized allocation based on hybrid energy storage technology is proposed in terms of the uncontrollable and unexpected characteristics of wind speed in wind farms. First, power smoothing based on a traditional Inertial Filter is introduced and the relationship between the time constant, its smoothing effect and capacity allocation are analyzed and combined with Proportional Integral Differential (PID) control to realize power smoothing control of wind power. Then wavelet theory is adopted to realize a multi-layer decomposition of power output in some wind farms, a power smoothing model based on hybrid energy storage technology is constructed combining the characteristics of the Super Capacitor (SC) and Battery Energy Storage System (BESS) technologies. The hybrid energy storage system is available for power fluctuations with high frequency-low energy and low frequency-high energy to achieve good smoothing effects compared with a single energy storage system. The power fluctuations filtered by the Wavelet Transform is regarded as the target value of BESS, the charging and discharging control for battery is completed quickly by Model Algorithm Control (MAC). Because of the influence of the inertia and the response speed of the battery, its actual output is not completely equal to the target value which mainly reflects in high-frequency part, the difference part uses SC to compensate and makes the output of battery and SC closer to the target value on the whole. Compared with the traditional Inertial Filter and PID control method, the validity of the model was verified by simulation results. Finally under the premise of power grid standards, the corresponding capacity design had been given to reduce the size of the energy storage devices as far as possible, which has a certain practical engineering value. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle A Novel Maximum Power Point Tracking Control for Permanent Magnet Direct Drive Wind Energy Conversion Systems
Energies 2012, 5(5), 1398-1412; doi:10.3390/en5051398
Received: 20 March 2012 / Revised: 9 May 2012 / Accepted: 11 May 2012 / Published: 15 May 2012
Cited by 15 | PDF Full-text (1150 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a novel optimal current given (OCG) maximum power point tracking (MPPT) control strategy based on the theory of power feedback and hill climb searching (HCS) for a permanent magnet direct drive wind energy conversion system (WECS). The presented strategy [...] Read more.
This paper proposes a novel optimal current given (OCG) maximum power point tracking (MPPT) control strategy based on the theory of power feedback and hill climb searching (HCS) for a permanent magnet direct drive wind energy conversion system (WECS). The presented strategy not only has the advantages of not needing the wind speed and wind turbine characteristics of the traditional HCS method, but it also improves the stability and accuracy of MPPT by estimating the exact loss torque. The OCG MPPT control strategy is first carried out by simulation, then an experimental platform based on the dSPACE1103 controller is built and a 5.5 kW permanent magnet synchronous generator (PMSG) is tested. Furthermore, the proposed method is compared experimentally with the traditional optimum tip speed ratio (TSR) MPPT control. The experiments verify the effectiveness of the proposed OCG MPPT strategy and demonstrate its better performance than the traditional TSR MPPT control. Full article
(This article belongs to the Special Issue Wind Turbines)
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Open AccessArticle An Improved Maximum Power Point Tracking Method for Wind Power Systems
Energies 2012, 5(5), 1339-1354; doi:10.3390/en5051339
Received: 6 April 2012 / Revised: 1 May 2012 / Accepted: 2 May 2012 / Published: 7 May 2012
Cited by 23 | PDF Full-text (2131 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes an improved maximum power point tracking (MPPT) method for wind power systems. The proposed method combines hysteresis control with tip speed ratio (TSR) control using a power coefficient curve. It has fast dynamic characteristics with the TSR control using [...] Read more.
This paper proposes an improved maximum power point tracking (MPPT) method for wind power systems. The proposed method combines hysteresis control with tip speed ratio (TSR) control using a power coefficient curve. It has fast dynamic characteristics with the TSR control using data obtained from an anemometer. Moreover it can track the maximum power point (MPP) with hysteresis control even when there is incomplete data. Since the proposed method selects the operating mode according to the operation state of the generator of three control modes, the controllers do not interfere with each other and they provide excellent performance. The effectiveness of the proposed algorithm is verified by simulation and experiments based on a 3 kW wind turbine system. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle The Effect of Additional Mooring Chains on the Motion Performance of a Floating Wind Turbine with a Tension Leg Platform
Energies 2012, 5(4), 1135-1149; doi:10.3390/en5041135
Received: 22 February 2012 / Revised: 5 April 2012 / Accepted: 6 April 2012 / Published: 20 April 2012
Cited by 9 | PDF Full-text (1048 KB) | HTML Full-text | XML Full-text
Abstract
In this study, two types of floating offshore wind turbine (FOWT) systems were proposed: a traditional tension leg platform (TLP) type and a new TLP type with additional mooring chains. They were both based on the National Renewable Energy Laboratory 5 MW [...] Read more.
In this study, two types of floating offshore wind turbine (FOWT) systems were proposed: a traditional tension leg platform (TLP) type and a new TLP type with additional mooring chains. They were both based on the National Renewable Energy Laboratory 5 MW offshore wind turbine model. Taking the coupled effect of dynamic response of the top wind turbine, tower support structure and lower mooring system into consideration, not only were the 1/60 scale model tests for the two floating wind turbine systems done in HIT’s wind-wave tunnel according to the typical design conditions in IEC61400-3 code, but also the numerical simulations corresponding to the scaled model tests were performed by advanced numerical tools. As a result, the numerical results displayed good agreement with the test data. Moreover, the additional mooring chains could play an active role in reducing the surge displacement, surge acceleration and typical tension leg force responses of the FOWT system, which is very beneficial for ensuring the good operational performance and the safety of the FOWT system. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle H Based Control for Load Mitigation in Wind Turbines
Energies 2012, 5(4), 938-967; doi:10.3390/en5040938
Received: 25 January 2012 / Revised: 20 March 2012 / Accepted: 31 March 2012 / Published: 17 April 2012
Cited by 20 | PDF Full-text (1023 KB) | HTML Full-text | XML Full-text
Abstract
This article demonstrates a strategy to design multivariable and multi-objective controllers based on the H norm reduction applied to a wind turbine. The wind turbine model has been developed in the GH Bladed software and it is based on a 5 [...] Read more.
This article demonstrates a strategy to design multivariable and multi-objective controllers based on the H norm reduction applied to a wind turbine. The wind turbine model has been developed in the GH Bladed software and it is based on a 5 MW wind turbine defined in the Upwind European project. The designed control strategy works in the above rated power production zone and performs generator speed control and load reduction on the drive train and tower. In order to do this, two robust H MISO (Multi-Input Single-Output) controllers have been developed. These controllers generate collective pitch angle and generator torque set-point values to achieve the imposed control objectives. Linear models obtained in GH Bladed 4.0 are used, but the control design methodology can be used with linear models obtained from any other modelling package. Controllers are designed by setting out a mixed sensitivity problem, where some notch filters are also included in the controller dynamics. The obtained H controllers have been validated in GH Bladed and an exhaustive analysis has been carried out to calculate fatigue load reduction on wind turbine components, as well as to analyze load mitigation in some extreme cases. The analysis compares the proposed control strategy based on H controllers to a baseline control strategy designed using the classical control methods implemented on the present wind turbines. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Analysis of the Induction and Wake Evolution of an Offshore Floating Wind Turbine
Energies 2012, 5(4), 968-1000; doi:10.3390/en5040968
Received: 3 February 2012 / Revised: 29 March 2012 / Accepted: 9 April 2012 / Published: 17 April 2012
Cited by 15 | PDF Full-text (14236 KB) | HTML Full-text | XML Full-text
Abstract
The degrees-of-freedom associated with offshore floating wind turbines (OFWTs) result in a more dynamic flow field. The resulting aerodynamic loads may be significantly influenced by these motions via perturbations in the evolving wake. This is of great interest in terms of OFWT [...] Read more.
The degrees-of-freedom associated with offshore floating wind turbines (OFWTs) result in a more dynamic flow field. The resulting aerodynamic loads may be significantly influenced by these motions via perturbations in the evolving wake. This is of great interest in terms of OFWT design, placement and simulation. This study presents free vortex wake method (FVM) simulations of the NREL 5-MW wind turbine of a variety of platforms, operating in a range of wind speeds synthesized platform motion time series. Motion-induced wake perturbations are observed to affect induction. Transitions between windmill and propeller states are also observed. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Deviation of Cup and Propeller Anemometer Calibration Results with Air Density
Energies 2012, 5(3), 683-701; doi:10.3390/en5030683
Received: 15 February 2012 / Revised: 27 February 2012 / Accepted: 6 March 2012 / Published: 9 March 2012
Cited by 9 | PDF Full-text (1636 KB) | HTML Full-text | XML Full-text
Abstract
The effect of air density variations on the calibration constants of several models of anemometers has been analyzed. The analysis was based on a series of calibrations between March 2003 and February 2011. Results indicate a linear behavior of both calibration constants [...] Read more.
The effect of air density variations on the calibration constants of several models of anemometers has been analyzed. The analysis was based on a series of calibrations between March 2003 and February 2011. Results indicate a linear behavior of both calibration constants with the air density. The effect of changes in air density on the measured wind speed by an anemometer was also studied. The results suggest that there can be an important deviation of the measured wind speed with changes in air density from the one at which the anemometer was calibrated, and therefore the need to take this effect into account when calculating wind power estimations. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle A Novel Cogging Torque Simulation Method for Permanent-Magnet Synchronous Machines
Energies 2011, 4(12), 2166-2179; doi:10.3390/en4122166
Received: 16 September 2011 / Revised: 22 November 2011 / Accepted: 30 November 2011 / Published: 6 December 2011
Cited by 7 | PDF Full-text (864 KB) | HTML Full-text | XML Full-text
Abstract
Cogging torque exists between rotor mounted permanent magnets and stator teeth due to magnetic attraction and this is an undesired phenomenon which produces output ripple, vibration and noise in machines. The purpose of this paper is to study the existence and effects [...] Read more.
Cogging torque exists between rotor mounted permanent magnets and stator teeth due to magnetic attraction and this is an undesired phenomenon which produces output ripple, vibration and noise in machines. The purpose of this paper is to study the existence and effects of cogging torque, and to present a novel, rapid, half magnet pole pair technique for forecasting and evaluating cogging torque. The technique uses the finite element method as well as Matlab research and development oriented software tools to reduce numerous computing jobs and simulation time. An example of a rotor-skewed structure used to reduce cogging torque of permanent magnet synchronous machines is evaluated and compared with a conventional analysis method for the same motor to verify the effectiveness of the proposed approach. The novel method is proved valuable and suitable for large-capacity machine design. Full article
(This article belongs to the Special Issue Wind Turbines)
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Review

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Open AccessReview Wind Turbine Blade Design
Energies 2012, 5(9), 3425-3449; doi:10.3390/en5093425
Received: 23 April 2012 / Revised: 21 June 2012 / Accepted: 30 August 2012 / Published: 6 September 2012
Cited by 29 | PDF Full-text (1359 KB) | HTML Full-text | XML Full-text
Abstract
A detailed review of the current state-of-art for wind turbine blade design is presented, including theoretical maximum efficiency, propulsion, practical efficiency, HAWT blade design, and blade loads. The review provides a complete picture of wind turbine blade design and shows the dominance [...] Read more.
A detailed review of the current state-of-art for wind turbine blade design is presented, including theoretical maximum efficiency, propulsion, practical efficiency, HAWT blade design, and blade loads. The review provides a complete picture of wind turbine blade design and shows the dominance of modern turbines almost exclusive use of horizontal axis rotors. The aerodynamic design principles for a modern wind turbine blade are detailed, including blade plan shape/quantity, aerofoil selection and optimal attack angles. A detailed review of design loads on wind turbine blades is offered, describing aerodynamic, gravitational, centrifugal, gyroscopic and operational conditions. Full article
(This article belongs to the Special Issue Wind Turbines)

Other

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Open AccessCorrection Correction: Márquez-Domínguez, S.; Sørensen, J.D. Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines. Energies 2012, 5, 1816–1834
Energies 2014, 7(4), 2146-2147; doi:10.3390/en7042146
Received: 29 January 2014 / Accepted: 26 February 2014 / Published: 1 April 2014
PDF Full-text (131 KB) | HTML Full-text | XML Full-text
Abstract The authors wish to make the following correction to this paper [1]. [...] Full article
(This article belongs to the Special Issue Wind Turbines)

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