Existing Wind Turbines Research Articles

2. Blown Away: the Impact of the Wolfe Island Wind Turbines on Local Bat Populations

This study was undertaken in order to explore the extent of migratory bat fatalities and assess the ecological impact stemming from the Wolfe Island wind facility near Kingston, Ontario. As the Wolfe Island wind project is the second largest wind farm in Canada, our research and proposed solutions may bridge the gap between local interests in reducing bat mortality and maximizing energy production. Additionally, bat populations are critical to local agriculture; increased mortality could lead to significant agricultural losses as well as potential impacts on components of the bats’ food web. First, information will be gathered, through the use of peer-reviewed journal articles and news items to support our project focus, to assess the magnitude of local bat population change following the construction of wind turbines on Wolfe Island. Further, we will explore the consequences of bat population decline on the local Kingston area ecosystem. Lastly, possible realistic solutions will be investigated in order to lessen the environmental impact of the existing wind turbines, and possibly to alter future policy regarding turbine construction and location. Preliminary results will be presented and discussed with the appropriate representatives from local and provincial bodies relevant to wind energy, environmental policy and conservation efforts.

Landscape disruption or just a lack of economic benefits? Exploring factors behind the negative perceptions of wind turbines

This paper provides new empirical evidence on the hypothesis that the perception of landscape disruption by wind turbines is a substantially subjective and relative matter. It is based on a survey involving nearly five hundred residents living in six different locations with operational wind turbines in the Czech Republic. Geographical and socioeconomic factors and sociodemographic characteristics that affect local community perceptions of landscape disruption are explored using correlations and a regression analysis model. The results suggest that the expressed perception of landscape disruption is not determined by the number of existing wind turbines, the proximity of residences to them and their visibility from the home but is significantly affected by the perception of the economic favourability of projects (benefits to local communities), perception of other negative impacts of wind turbines (particularly the noise annoyance) and the socio-cultural background of people (particularly the level of education).

Some data on the behaviour of kites (Milvus milvus, Milvus migrans) nesting close to two active wind farms in Saxony, Germany

Abstract The main aim of this study was to evaluate how local pairs of kites behave in the vicinity of two wind farms located in the same region (Saxony, Germany) and at farms which are to be re-powered. We observed three pairs that had located their nests close to active wind farms (a few hundred to 1500 m from the wind farm). Special attention was focused on variation in the intensity of flights and its dependence on the local landscape and to active avoidance of existing wind turbines. Observations were made at the end of the breeding time, when the young were still in the nest and shortly after fledging. Despite the short observation periods, the results seem to show clearly how differentiated the flight patterns of these birds are in relation to the landscape features around the farm. The distance from the nest to the wind farm cannot be the only measure of the level of potential wind-farm-related danger to the birds nesting close to the farm site. Distribution of flights is not random, but clearly concentrated on defined target hunting areas, while other directions are visited infrequently. In the case of both farms, the farm was rarely crossed by the Black Kites (9.9% of all flights) and very rarely (2.8%) by the Red Kites, and such crossing was observed only while the turbine rotors were not in motion or when the rotors were turning slowly (below 5 turns/min.). It may be advisable to conduct special monitoring of movement patterns at breeding time if kite nests are found close to the planned location of the wind farm.

Fault diagnosis and condition monitoring of wind turbines

SummaryThis paper describes a model‐free method for the fault diagnosis and condition monitoring of rotor systems in wind turbines. Both fault diagnosis and monitoring can be achieved without using a model for the wind turbine, applied controller, or wind profiles. The method is based on measurements from standard sensors on modern wind turbines, including moment sensors and rotor angle sensors. This approach will allow the method to be applied to existing wind turbines without any modifications.The method is based on the detection of asymmetries in the rotor system caused by changes or faults in the rotor system. A multiblade coordinate transformation is used directly on the measured flap‐wise and edge‐wise moments followed by signal modulation. Changes or faults in the rotor system will result in unique signatures in the set of modulation signals. These signatures are described through the amplitudes and phase information of the modulation signals. It is possible to detect and isolate which blade is faulty or has been changed based on these signatures. Furthermore, the faulty component can be isolated, ie, the actuator, sensor or blade, and the type of fault can be determined. The method can be used both on‐ and off‐line.

A Vibration Estimation Method for Wind Turbine Blades

This paper reports the development of a vibration monitoring system for wind turbine blades. This system is used to estimate the deflection at the tip blade on a wind turbine tower. Technical accidents of wind turbine blades have become increasingly common. Thus, regular monitoring of the blades is very important to prevent breakdowns, especially in cases when the blades begin to vibrate excessively. The monitoring system developed in this study satisfies two main objectives for practicality. First, our system is easy to install on existing wind turbines. Second, blade deflection is measured in real time. Our system can be operated using a few strain gages attached at the blade root, and the deflection is calculated based on the monitored stress. Thus, direct measurement of deflection at the blade tip is unnecessary. An estimation algorithm for this purpose is adopted based on the experimental modal analysis. This paper focuses on the evaluation of the estimation algorithm to investigate the feasibility of our system. Basic experiments were conducted using a simple blade model of a 300 W scaled wind turbine under rotation. Signals from the strain gages were acquired by a sensor network and sent to a computer through a wireless connection. The results show that the estimation accuracy is acceptably high. Therefore, we conclude that our proposed system is practical.

Disturbance Observer-Based Pitch Control of Wind Turbines for Enhanced Speed Regulation

Time-varying unknown wind disturbances influence significantly the dynamics of wind turbines. In this research, we formulate a disturbance observer (DOB) structure that is added to a proportional-integral-derivative (PID) feedback controller, aiming at asymptotically rejecting disturbances to wind turbines at above-rated wind speeds. Specifically, our objective is to maintain a constant output power and achieve better generator speed regulation when a wind turbine is operated under time-varying and turbulent wind conditions. The fundamental idea of DOB control is to conduct internal model-based observation and cancelation of disturbances directly using an inner feedback control loop. While the outer-loop PID controller provides the basic capability of suppressing disturbance effects with guaranteed stability, the inner-loop disturbance observer is designed to yield further disturbance rejection in the low frequency region. The DOB controller can be built as an on–off loop, that is, independent of the original control loop, which makes it easy to be implemented and validated in existing wind turbines. The proposed algorithm is applied to both linearized and nonlinear National Renewable Energy Laboratory (NREL) offshore 5-MW baseline wind turbine models. In order to deal with the mismatch between the linearized model and the nonlinear turbine, an extra compensator is proposed to enhance the robustness of augmented controller. The application of the augmented DOB pitch controller demonstrates enhanced power and speed regulations in the above-rated region for both linearized and nonlinear plant models.

Fatigue assessment of offshore wind turbines on monopile foundations using multi‐band modal expansion

AbstractOffshore wind turbines (OWTs) are subjected to both quasi‐static loads originating from variations in the thrust force and dynamic loads linked to turbulence, waves and turbine dynamics. Both types of loads contribute to fatigue life progression and thus define the turbine's age. As a structural health monitoring solution, one could thus directly measure the stress history at fatigue critical locations. However, for OWTs on monopile foundations some fatigue critical locations are located below the seabed. Installing strain sensors at these hotspots is therefore impossible for existing wind turbines. This measurement restriction is overcome by reconstructing the full‐field response of the structure based on the limited number of accelerometers and strain sensors (installed at a few easily accessible locations) and a calibrated finite element model of the system. The system model uses a multi‐band modal expansion approach constituted of the quasi‐static and dynamic contributions. These contributions are superimposed to reconstruct the stress history at all degrees of freedom of the finite element model, and the subsequent assess fatigue life consumption at all fatigue hot spots of the OWT. In this paper, the proposed virtual sensing technique is validated by predicting the stresses in the transition piece with 12 days of consecutive measurements from an operational OWT. The data set contains both variations in environmental and operating conditions as well as extreme events. Finally, a full‐field strain assessment in the tower and foundation system of the OWT is demonstrated. Copyright © 2017 John Wiley & Sons, Ltd.

SIMULATION BY MEANS FINITE ELEMENTS OF A PREVENTIVE ANTI-ICING SYSTEM FOR WIND TURBINE BLADES

This paper describes the results of a research project undertaken under a research contract with the company DERSA, entitled “Development of a blade anti-icing system for conventional wind turbine models applicable to operational installations”. The goal of the project was developing and analyzing a system which must prevent the build-up of ice on the outer surface of buildings and must be able to melt it under extreme conditions. The idea is to apply the system to existing wind turbines, so the project starts with numerous conditioning factors and limitations. The chosen system operation has been analyzed using the ANSYS computer application.

The use of long term monitoring data for the extension of the service duration of existing wind turbine support structures

Actual wind energy converter (WEC) are designed for a relatively short service life of 20 years and the limiting criterion is the fatigue safety. However, effective fatigue loading endured by the structural components of the wind turbines (WT) is likely to be much below design assumptions provided by current codes. This paper describes a simple but efficient long term monitoring system that allows owners to verify the fatigue safety of their existing WTs. The monitored data will also help to drastically extend the service life of existing wind turbine support structure and will thus reduce the global environmental footprint of WTs.

Analysis of the performance of a H-Darrieus rotor under uncertainty using Polynomial Chaos Expansion

Due to the growing importance of wind energy, improving the efficiency of energy conversion is essential. Horizontal Axis Wind Turbines are the most well-spread, but H-Darrieus turbines are becoming popular as well due to their simple design and easier integration. Due to the high efficiency of existing wind turbines, further improvements require numerical optimization. One important aspect is to find a better configuration that is also robust, i.e., a configuration that retains its performance under uncertainties. For this purpose, forward uncertainty propagation has to be applied. In the present work, an Uncertainty Quantification (UQ) method, Polynomial Chaos Expansion, is applied to transient, turbulent flow simulations of a variable-speed H-Darrieus turbine, taking into account uncertainty in the preset pitch angle and in the angular velocity. The resulting uncertainty of the performance coefficient and of the quasi-periodic torque curve are quantified. In the presence of stall the instantaneous torque coefficients tend to show asymmetric distributions, meaning that error bars cannot be correctly reconstructed using only mean value and standard deviation. The expected performance was always found to be smaller than in computations without UQ techniques, corresponding to up to 10% of relative losses for λ = 2.5.

Multidisciplinary design optimization of large wind turbines—Technical, economic, and design challenges

Wind energy has experienced a continuous cost reduction in the last decades. A popular cost reduction technique is to increase the rated power of the wind turbine by making it larger. However, it is not clear whether further upscaling of the existing wind turbines beyond the 5–7MW range is technically feasible and economically attractive. To address this question, this study uses 5, 10, and 20MW wind turbines that are developed using multidisciplinary design optimization as upscaling data points. These wind turbines are upwind, 3-bladed, pitch-regulated, variable-speed machines with a tubular tower. Based on the design data and properties of these wind turbines, scaling trends such as loading, mass, and cost are developed. These trends are used to study the technical and economical aspects of upscaling and its impact on the design and cost. The results of this research show the technical feasibility of the existing wind turbines up to 20MW, but the design of such an upscaled machine is cost prohibitive. Mass increase of the rotor is identified as a main design challenge to overcome. The results of this research support the development of alternative lightweight materials and design concepts such as a two-bladed downwind design for upscaling to remain a cost effective solution for future wind turbines.

ГНЕЗДОВАЯ БИОЛОГИЯ ГРАЧА (CORVUS FRUGILEGUS) В АНТРОПОГЕННО ИЗМЕНЕННЫХ СТЕПНЫХ ЭКОСИСТЕМАХ (НА ПРИМЕРЕ БОТИЕВСКОЙ ВЭС)

<p>The article gives a space-structural characteristic of rook (Corvus frugilegus) nesting places in the territory of Botievo wind farm (Zaporizhzhia region). The distribution of the rook colonies around the territory, the structure of the colonies, the dependence of the location of the nests on the height, diameter, condition and species composition of tree and shrub plantings are analyzed and studied. The types and methods of the localization of nests in the trees and their quantitative characteristics are highlighted. The consortium relations of the rook and the risks associated with living near existing wind turbines are described.</p><p>In 2015 some six colonies were found: 2 medium (51-100 nests) and 4 large (101-500 nests) ones. All the colonies were located in the forest belts, mainly represented by locust trees <em>Gleditsia triacanthos</em> (5 colonies) and in the mixed forest consisting of the mulberry <em>Morus sp.</em>, maple <em>Acer</em>, black locust <em>Robinia pseudoacacia,</em> and locust trees (1 colony). The area occupied by colonies had a four-fold difference between 977-3994 m<sup>2</sup>, while the number of the rook nests fluctuated in a seven-fold range - 52-343 nests.</p><p>Analysis of different indicators describing the structure of the rook colonies revealed certain dependence between the breeding area and the number of the occupied trees (r = 0.98); the breeding area and the number of nests (r = 0.71); the number of nests in the colony and the closeness of the trees in the forest belts (r = 0.96); the number of nests and the number of the occupied trees (r = 0.81), the height of the tree and the nest on it (r = 0.64). The characteristic of the location of nests in different rows of the forest belt revealed the shift of the density of the occupation of trees in large colonies to one of the outer rows, where there were 34.8-50.7 percent of all the nests.</p><p>Typology and localization of rook nests in the trees has 11 options of the location. The type of the location of nests near the trunk of the tree dominated (59.74 percent of trees and 67.02 percent of all nests). It is shown that rooks demonstrate the plasticity of the nesting behaviour to the changing environmental conditions.</p><p><em>Keywords: Rook (Corvus frugilegus), Zaporizhia region, wind farm, nesting area, colony structure, spatial distribution, colony.</em></p>

Dynamic Reactive Power Compensation of Large-Scale Wind Integrated Power System

Due to progressive displacement of conventional power plants by wind turbines, dynamic security of large-scale wind integrated power systems is significantly compromised. In this paper we first highlight the importance of dynamic reactive power support/voltage security in large-scale wind integrated power systems with least presence of conventional power plants. Then we propose a mixed integer dynamic optimization based method for optimal dynamic reactive power allocation in large-scale wind integrated power systems. One of the important aspect of the proposed methodology is that unlike static optimal power flow based approaches, the proposed method considers detailed system dynamics and wind turbine grid code compliance while optimizing the allocation of dynamic reactive power sources. We also advocate that in large-scale wind integrated power systems, 1) better utilization of existing wind turbines especially wind farms with additional grid support functionalities like dynamic support (e.g., dynamic reactive power support, etc.) and 2) refurbishment of existing conventional central power plants to synchronous condensers could be one of the efficient, reliable and cost-effective option to address not only the issue of dynamic voltage security but also to strengthen other dynamic capabilities of the system including system inertia, etc. that are also significant challenges in large-scale wind penetrated power system. The proposed methodology is applied to the detailed model of the western Danish power system which is characterized by large-scale wind integration and least presence of central power plants.

Wind Resource Assessment in Complex Urban Environment

A wind energy assessment methodology is proposed for urban environments and applied for a specific urban development. Micro-scale wind energy maps are created using computational fluid dynamics simulations. The wind maps are used to calculate the available wind energy for the 2015 Pan American Games Athletes' Village, in Toronto, Canada. The structure of the urban boundary layer has also been analyzed. It is shown that the maximum available energy can cover an important ratio of typical power requirements for the buildings. However, it is found that existing wind turbines have power curves that are de-coupled from the probability density functions of the wind availability. Therefore, the need for designing new urban wind turbines is discussed and required specifications are highlighted.

Numerical investigation of optimal yaw misalignment and collective pitch angle for load imbalance reduction of rigid and flexible HAWT blades under sheared inflow

Wind shear can strongly influence the cyclic loading on horizontal axis wind turbine blades. These load fluctuation causes a variation of power output and introduces fatigue load. Thus, individual pitch controllers have been developed that are focused on the load alleviations, however, comes at a price of actuator requirements for control. Moreover, these controllers are unable to apply to already existing wind turbines with active yaw and collective pitch control system. Therefore, the investigations for minimizing load imbalance through the adjustments of yaw misalignment and collective pitch angle are implemented for the rigid and flexible blades under the sheared inflow. By applying the optimization process based on a sequential quadratic programming approach, the optimal yaw and pitch angle can be estimated. Then, the numerical simulations for predicting the performance are performed. The results showed that the fluctuation range of the root flapwise bending moment for the rigid blades can be reduced by 84.5%, whereas the vibratory bending moment for the flexible blades can be reduced by up to approximately 82.4% in the best case. Therefore, the magnitudes of load imbalance can be minimized by the adjustment of the optimal yaw misalignment and collective pitch angle without any power loss.

Have Local Government and Public Expectations of Wind Energy Project Benefits Been Met? Implications for Repowering Schemes

Replacing existing wind turbines with new and higher capacity turbines (‘repowering’) is to become a major challenge for planners within the next decade. While the benefits of repowering are evident, it cannot be assumed that the process will proceed automatically and without problems. The acceptance of future developments will be significantly affected by whether expectations of benefits from previous projects have been met, and whether perceived advantages of existing wind farms have outweighed their disadvantages. Therefore, it is important to explore how existing wind farms and their impacts on local development and well-being are assessed. This paper presents the results of a survey with local governments and inhabitants of municipalities in the Czech Republic where wind turbines have been implemented and are in operation. The findings prove that perceived positive effects dominate over negative impacts and that a majority of local authorities and inhabitants are willing to support further development in their backyards. A disruption to local landscape was detected as the main factor behind opposition. However, the significance of visual impact proved to be outweighed by subjective appraisal of economic benefits which is spatially and socially structured. The conclusion presents some implications for designing repowering schemes based on the research.

Comparison and Optimization of Neural Networks and Network Ensembles for Gap Filling of Wind Energy Data

Wind turbines play an important role in providing electrical energy for an ever-growing demand. Due to climate change driven by anthropogenic emissions of greenhouse gases, the exploration and use of sustainable energy sources is essential with wind energy covering a significant portion. Data of existing wind turbines is needed to reduce the uncertainty of model predictions of future energy yields for planned wind farms. Due to maintenance routines and technical issues, data gaps of reference wind parks are unavoidable. Here, we present real-world case studies using multilayer perceptron networks and radial basis function networks to reproduce electrical energy outputs of wind turbines at 3 different locations in Germany covering a range of landscapes with varying topographic complexity. The results show that the energy output values of the turbines could be modeled with high correlations ranging from 0.90 to 0.99. In complex terrain, the RBF networks outperformed the MLP networks. In addition, rare extreme values were better captured by the RBF networks in most cases. By using wind meteorological variables and operating data recorded by the wind turbines in addition to the daily energy output values, the error could be further reduced to more than 20%.

Analysis of grouted connections for offshore wind turbines

In offshore wind turbines grouted connections are generally used to install a transition piece between the steel tower and the monopile foundation. The transition piece is plugged on to the monopile, aligned vertically and the annulus in between is filled with high-strength grout. During service operations unexpected settlement of the transition piece has been observed at several wind turbines. The serious findings have called for additional, extensive numerical analyses for the detailed design of the London Array offshore wind farm. The advanced non-linear finite-element analyses provide a more detailed insight into the structural behaviour of grouted connections. Important effects and a possible mechanism for the settlement at existing wind turbines are detected. The previous practice of designing separately for bending moment and transverse force on the one hand and axial force and torsion on the other hand leads, among other things, to the overestimation of capacity. The interaction has to be taken into account.

Fault-tolerant Control of a Wind Turbine with a Squirrel-cage Induction Generator and Rotor Bar Defects

Wind turbines are usually installed on remote locations and in order to increase their economic competence malfunctions should be reduced and prevented. Faults of wind turbine generator electromechanical parts are common and very expensive. This paper proposes a fault-tolerant control strategy for variable-speed variable-pitch wind turbines in case of identified and characterised squirrel-cage generator rotor bar defect. An upgrade of the torque control loop with flux-angle-based torque modulation is proposed. In order to avoid or to postpone generator cage defects, usage of pitch controller in the low wind speed region is introduced. Presented fault-tolerant control strategy is developed taking into account its modular implementation and installation in available control systems of existing wind turbines to extend their life cycle and energy production. Practical implementation aspects such as estimation of variables used in control and estimate errors are considered and respected in operation, as well as fault-induced asymmetries. Simulation results for the case of a megawatt class wind turbine and the identified rotor bar fault are presented.

Fault-tolerant Control of a Wind Turbine with Generator Stator Inter-turn Faults

Faults of wind turbine generator electromechanical parts are common and very expensive. This paper introduces a generator fault-tolerant control scheme for variable-speed variable-pitch wind turbines that can be applied regardless to the AC generator used. The focus is on generator stator isolation inter-turn fault that can be diagnosed and characterised before triggering the safety device. An extension of the conventional wind turbine control structure is proposed that prevents the fault propagation while power delivery under fault is deteriorated as less as possible compared to healthy machine conditions. Fault-induced and inherent asymmetries of the generator are estimated and respected by the field-oriented control of the generator to eliminate torque oscillations. An approach for asymmetry detection based on an unscented Kalman filter is proposed. Presented fault-tolerant control strategy is developed taking into account its modular implementation and installation in available control systems of existing wind turbines to extend their exploitable life span and increase energy production. Simulation results for the case of a megawatt class wind turbine are presented.