Cut-out Wind Speed Research Articles

A Reliability Evaluation Model for the Power Devices Used in Power Converter Systems Considering the Effect of the Different Time Scales of the Wind Speed Profile

This paper presents a reliability assessment model for the power semiconductors used in wind turbine power converters. In this study, the thermal loadings at different timescales of wind speed are considered. First, in order to address the influence of long-term thermal cycling caused by variations in wind speed, the power converter operation state is partitioned into different phases in terms of average wind speed and wind turbulence. Therefore, the contributions can be considered separately. Then, in regards to the reliability assessment caused by short-term thermal cycling, the wind profile is converted to a wind speed distribution, and the contribution of different wind speeds to the final failure rate is accumulated. Finally, the reliability of an actual power converter semiconductor for a 2.5 MW wind turbine is assessed, and the failure rates induced by different timescale thermal behavior patterns are compared. The effects of various parameters such as cut-in, rated, cut-out wind speed on the failure rate of power devices are also analyzed based on the proposed model.

Stochastic dynamic load effect and fatigue damage analysis of drivetrains in land-based and TLP, spar and semi-submersible floating wind turbines

This paper deals with the feasibility of using a 5 MW drivetrain which is designed for a land-based turbine, on floating wind turbines. Four types of floating support structures are investigated: spar, TLP and two semi-submersibles. The fatigue damage of mechanical components inside the gearbox and main bearings is compared for different environmental conditions, ranging from cut-in to cut-out wind speeds. For floating wind turbines, representative wave conditions are also considered. All wind turbines are ensured to follow similar power curves, but differences in the control system (integral to different concepts) are allowed. A de-coupled analysis approach is employed for the drivetrain response analysis. First, an aero-hydro-servo-elastic code is employed for the global analysis. Next, motions, moments and forces from the global analysis are applied on the gearbox multi body model and the loads on gears and bearings are obtained. The results suggest that the main bearings sustain more damage in floating wind turbines than on land-based. The highest main bearing damage is observed for the spar floating wind turbine. The large wave induced axial load on the main shaft is found to be the primary reason of this high damage in the spar wind turbine. Apart from the main bearings - which are located on the main shaft outside the gearbox - other bearings and gears inside the gearbox hold damages in floating wind turbines equal or even less than in the land-based turbine. It is emphasized that the results presented in this study are based on a drivetrain with two main bearings, which considerably reduces the non-torque loads on the gearbox.

A Simulation Approach to Evaluate Operational Economics of Wind Power Investments in Turkey

 Abstract—It is crucial to analyze the wind distribution throughout the year and the expected annual power generation (Mwh) to evaluate a wind power investment. The cut-in and cut-out wind speeds along with the size of the wind turbine should carefully be included to the analysis as they will affect the amount of power generation. On the other hand, the capital cost and cost of power generation each year should be allocated to the economic life of the project using an appropriated discount rate. In this paper, an economic analysis method and a wind simulation approach is developed to evaluate the expected annual power generation of a wind project. The revenue is calculated using expected power amount and the power price ($/Mwh) and the net return is found by subtracting the cost. The necessary economic analysis is then performed using net present value and payback method. The weibull distribution is assumed for the wind and operational characteristics of the turbine are included.

Operating wind turbines in strong wind conditions by using feedforward-feedback control

Due to the increasing penetration of wind energy into power systems, it becomes critical to reduce the impact of wind energy on the stability and reliability of the overall power system. In precedent works, Shen and his co-workers developed a re-designed operation schema to run wind turbines in strong wind conditions based on optimization method and standard PI feedback control, which can prevent the typical shutdowns of wind turbines when reaching the cut-out wind speed. In this paper, a new control strategy combing the standard PI feedback control with feedforward controls using the optimization results is investigated for the operation of variable-speed pitch-regulated wind turbines in strong wind conditions. It is shown that the developed control strategy is capable of smoothening the power output of wind turbine and avoiding its sudden showdown at high wind speeds without worsening the loads on rotor and blades.

Wind Resource Assessment in Europe Using Emergy

In context of increasing use of renewable sources, it is of importance to correctly evaluate the actual sustainability of their implementation. Emergy analysis is one of the possible methods useful for such an assessment. This work aims to demonstrate how the emergy approach can be used to assess the sustainability of wind energy resource in Europe. The Emergy Index of Sustainability (EIS) and the Emergy Yield Ratio (EYR) are used to analyze 90 stations of European regions for three types of wind turbines. To do so, the simplified Chou wind turbine model is used for different set of parameters as: nominal power and size of the wind turbines, and cut-in and cut-out wind speeds. Based on the calculation of the emergy indices, a mapping is proposed to identify the most appropriate locations for an implementation of wind turbines in European regions. The influence of the wind turbine type on the sustainability is also analyzed, in link with the local wind resource. Thus, it is concluded that the emergy sustainability indices are sensitive to the wind turbine design parameters (size, cut-in and cut-out wind speed).

Finite Element Analysis of Concrete Filled Double Skin Steel Tubes for Wind Turbine Tower

In order to save the steel consumption,ensure the better economy of wind turbine tower,this paper designeda new concrete filled double skin steel tube for wind turbine tower,based on the parameters of 1. 5 MW wind turbine tower.A three-dimensional finite element model of wind turbine tower was built by using the finite element software ANSYS,then the static strength analysis and modal analysis were carried out,in which the stress and displacement at the top of the tower were calculated under three kinds of working conditions: normal operation with rated wind speed,normal operation with cutout wind speed and shutdown under extreme wind conditions,the natural frequency and mode shapes of the tower were obtained as well. The results show that the tower does not resonate with blades,and its structure can meet the strength and stiffness requirements of engineering.

Wind turbine optimal control during storms

This paper proposes a control algorithm that enables wind turbine operation in high winds. With this objective, an online optimization procedure is formulated that, based on the wind turbine state, estimates those extremal wind speed variations that would produce maximal allowable wind turbine loads. Optimization results are compared to the actual wind speed and, if there is a danger of excessive loading, the wind turbine power reference is adjusted to ensure that loads stay within allowed limits. This way, the machine can operate safely even above the cut-out wind speed, thereby realizing a soft envelope-protecting cut-out. The proposed control strategy is tested and verified using a high-fidelity aeroservoelastic simulation model.

Fatigue loading on a 5MW offshore wind turbine due to the combined action of waves and current

In the design of an offshore wind turbine the natural frequencies of the structure are of importance. In the design of fixed offshore wind turbine support structures it cannot be avoided that the first eigenmode of the structure lies in the frequency band of wave excitation. This study indicates that wave-current interaction should be taken into account for support structure design load calculations.Wave-current interaction changes the shape of the wave spectrum and the energy content in the wave frequency range of 0.2 – 0.35Hz. This is in the range of natural frequencies fixed offshore wind turbine structures are designed for. The waves are affected by the current in two ways. First there is a frequency shift, Doppler effect, for the fixed observer when the wave travels on a current. Second the shape of the wave is modified in case the wave travels from an area without current into an area with current. Due to wave-current interaction the wave height and wave length change. For waves on an opposing current the wave energy content increases, while for wave on a following current the wave energy content slightly reduces.Simulations of normal production cases between cut-in and cut-out wind speed are performed for a 5MW wind turbine in 20m water depth including waves with 1) a following current, 2) an opposing current and 3) no current present. In case of waves having an opposing current, the 1Hz equivalent fore-aft tower bending moment at the seabed is about 10% higher compared to load cases with waves only.

Offset-Free Model Predictive Control for Wind Power Generation Systems

Due to wind power generation system (WGS) is strongly nonlinear, multi-input multi-output and with high turbulent disturbance, we build a offset-free model considering system noise and measurement noise and its predictive controller for all operating area from cut-in speed to the cut-out wind speed. Finally we predict the optimum generator torque and pitch control signal. By add damping mode in drive train using torque control, the purpose of smoother power and less torsional torque pulsation on drive train are achieved. Simulation results shows that this predictive controller is able to reduce the impact of noise and interference on the system, ensuring constant power output and reducing the torque pulsation.

A Reliability Based Model for Wind Turbine Selection

A wind turbine generator output at a specific site depends on many factors, particularly cut- in, rated and cut-out wind speed parameters. Hence power output varies from turbine to turbine. The objective of this paper is to develop a mathematical relationship between reliability and wind power generation. The analytical computation of monthly wind power is obtained from weibull statistical model using cubic mean cube root of wind speed. Reliability calculation is based on failure probability analysis. There are many different types of wind turbines commercially available in the market. From reliability point of view, to get optimum reliability in power generation, it is desirable to select a wind turbine generator which is best suited for a site. The mathematical relationship developed in this paper can be used for site-matching turbine selection in reliability point of view.

Viability and economic analysis of wind energy resource for power generation in Johannesburg, South Africa

In this study, wind characteristics and wind power potential of Johannesburg are investigated using 5-min average time series wind speed collected between 2005 and 2009 at anemometer height of 10 m. The statistical distribution that best fits the empirical wind speed data at the site of study is first determined based on the coefficient of determination and root mean square error criteria. The statistical parameters and wind power density based on this model are estimated for different months of the year using standard deviation method. Economic analyses of some wind turbines are also carried out. Some of the key results show that the site is only suitable for small wind turbines in a standalone application. A 10 kW wind turbine with cut-in wind speed of 3.5 m/s, rated wind speed of 9 m/s, and cut-out wind speed of 25 m/s seems most appropriate in Johannesburg with the lowest cost that varies from 0.25 to 0.33 $/kWh.

Validation of historical and future statistically downscaled pseudo-observed surface wind speeds in terms of annual climate indices and daily variability

Surface wind speed variability cannot be resolved by the current generation of Global Climate Models (GCMs) due to their relatively coarse spatial discretization. Downscaling techniques are thus needed to generate finer scale projections of variables like near surface wind speeds. However, classical statistical downscaling experiments are unable to infer which model performs better in a future climate change scenario, as one cannot know the true change in the variable of interest. Additionally, the ability of models to reproduce historical climatologies does not necessarily imply that they will be able to accurately simulate future climate conditions. Moreover, conventional comparisons between downscaling methods have been carried out in terms of standard model performance measures, e.g., correlations and mean squared errors, with infrequent treatment of characteristics such as the ability to reproduce extreme value statistics. To address these limitations, we employ a pseudo-observation downscaling verification approach, which allows one to estimate model performance in the context of future climate projections by replacing historical and future observations with model simulations from a Regional Climate Model (RCM) nested within the domain of the GCM. The new validation methodology compares historical and future RCM pseudo-observations in terms of both downscaled daily variability and annual climate indices characterized by the proposed Wind INDices for the validation of EXtremes (WINDEX).Specifically, present and future downscaled daily maximum wind speed series at a hypothetical offshore wind energy plant northwest of Haida Guaii, Canada were generated using a variety of linear and nonlinear methods. The models used outputs from the coarse resolution Canadian Global Climate Model (CGCM) 3.1 T47 20th century and SRES A2 transient simulations as predictors and outputs from the Canadian Regional Climate Model (CRCM) 4.2 forced with CGCM 3.1 boundary conditions as pseudo-observations. Downscaled series were obtained for the 1970–1999 and 2040–2069 simulated periods. In general, an artificial neural network model using predictors from the nearest 9 CGCM grid cells performed best in terms of daily variability, as indicated by mean absolute errors, for the historical and future periods, whereas the best performance in terms of annual extremes, as indicated by indices of agreement for WINDEX, was obtained by a variant of the probabilistic quantile-matching method. This suggests that the best models for representing day-by-day wind variability need not necessarily be the best at simulating specific indices of wind extremes like number of days below the cut-in wind speed or number of days above the cut-out wind speed.

공력해석 및 구조시험을 통한 소형 복합재 블레이드의 구조 안전성 평가

This paper deals with the aerodynamic analysis and structural test under estimated loading condition for small composite blade, which is utilized in dual rotor wind turbine system. Firstly, the front and rear blades of dual rotor wind turbine system were modeled using reverse engineering method. And using finite volume method, the aerodynamic forces were analyzed at the rated and cutout wind speed to identify the pressure distribution on blades. And then, the full scale structural tests were conducted according to load and strength based methodology in IEC 61400-2 to identify the structural integrity of composite blade.

Wind Turbine Control Using PI Pitch Angle Controller

This paper suggests two methods to calculate the gains of a proportional-Integral pitch angle controller for a 5 MW wind turbine. The first method is analytical and the second one is based on simulation. Firstly, the power coefficient characteristics for different pitch angles are calculated. Secondly, the output powers vs. rotor speed curves from cut-in to cut-out wind speeds are simulated. The results from first and second analyses used to find the control gains at different wind speeds. Finally, the results are compared using a wind turbine model to determinate turbine's tracking characteristic.

Durations distribution of Rayleigh process with application to wind turbines

In the present paper, approximations to certain functions of the Rayleigh process distribution, beyond extreme thresholds, is derived. A close agreement between the results obtained and the corresponding results of the exact distributions confirms the validity of the present work. The derived approximations are implemented to analyze a real wind speed data and the results obtained are provided in this article. The behavior of a wind turbine (WT) is characterized by its power curve, which includes two extreme points: cut-in wind speed and cut-out wind speed. Therefore, accurate prediction of wind speed durations beyond these two thresholds will enable engineers to acquire several probabilistic statements such as the availability of electric power generation. These findings will be beneficial to design an efficient and reliable wind energy conversion system.

Energy and reliability benefits of wind energy conversion systems

The electrical energy production and reliability benefits of a wind energy conversion system (WECS) at a specific site depend on many factors, including the statistical characteristics of the site wind speed and the design characteristics of the wind turbine generator (WTG) itself, particularly the cut-in, rated and cut-out wind speed parameters. In general, the higher the degree of the wind site matching with a WECS is, the more are the energy and reliability benefits. An electrical energy production and reliability benefit index designated as the Equivalent Capacity Ratio (ECR) is introduced in this paper. This index can be used to indicate the electrical energy production, the annual equivalent utilization time and the credit of a WECS, and quantify the degree of wind site matching with a WECS. The equivalent capacity of a WECS is modeled as the expected value of the power output random variable with the probability density function of the site wind speed. The analytical formulation of the ECR is based on a mathematical derivation with high accuracy. Twelve WTG types and two test systems are used to demonstrate the effectiveness of the proposed model. The results show that the ECR provides a useful index for a WTG to evaluate the energy production and the relative reliability performance in a power system, and can be used to assist in the determination of the optimal WTG type for a specific wind site.

Database for validation of design load extrapolation techniques

AbstractExtrapolation techniques used for predicting long‐term wind turbine loads have produced highly variable loading estimates dependent on the individual designer implementation. To reduce such variability, more precise definition and validation of these techniques are necessary. As part of a wider effort to test loads extrapolation techniques used in wind turbine design, two data sets were created. The first data set was created as an example typical of what designers use to extrapolate loads according to wind turbine design standards. The second data set was a series of year‐long simulations that could be used to quantify the accuracy of extrapolation methods. Due to the large number of simulations, care was taken not to reproduce random samplings in individual time series. Additionally, a grid computing architecture was used to run the simulations in a reasonable time frame. The wind speeds where loads were highest were identified, which varied with loading type. The identification of dominant wind speeds is important to ensure an adequate number of simulations at such speeds, which often influence extrapolated loads. In‐plane loads and deflections tended to be dominated by high wind speeds near cut‐out wind speed. Out‐of‐plane loads and deflections were most influenced by winds that were near the rated wind speed. Some loads were influenced by a range of wind speeds. The loads dominated by high wind speeds had greater variability in the extreme values, which could be a reflection of the greatly varying wind and also greater sensitivity to higher energy content of the wind at such speeds. Copyright © 2008 John Wiley & Sons, Ltd.

Power loss in the upper cut‐out wind speed interval

AbstractTime series of mean wind speeds at several sites in Denmark have been used to estimate the power loss for wind turbines in the wind speed interval from where the operation has to stop at high winds to where a lower wind speed allows the operation to resume. For inland wind turbines the fractional loss is less than 0·25%. For offshore wind turbines it may be as high as about 1·5%. To facilitate the estimation of ‘dead zone’ power loss for offshore wind turbines, an engineering model for the sea surface state has been developed on the basis of a generalization of Charnock's roughness model and the geostrophic drag law. This model predicts the surface friction velocity and the surface roughness as functions of the geostrophic wind speed and the length of the water fetch. Copyright © 2004 John Wiley & Sons, Ltd.

Assessment of wind characteristics and wind turbine characteristics in Taiwan

Wind characteristics and wind turbine characteristics in Taiwan have been thoughtfully analyzed based on a long-term measured data source (1961–1999) of hourly mean wind speed at 25 meteorological stations across Taiwan. A two-stage procedure for estimating wind resource is proposed. The yearly wind speed distribution and wind power density for the entire Taiwan is firstly evaluated to provide annually spatial mean information of wind energy potential. A mathematical formulation using a two-parameter Weibull wind speed distribution is further established to estimate the wind energy generated by an ideal turbine and the monthly actual wind energy generated by a wind turbine operated at cubic relation of power between cut-in and rated wind speed and constant power between rated and cut-out wind speed. Three types of wind turbine characteristics (the availability factor, the capacity factor and the wind turbine efficiency) are emphasized. The monthly wind characteristics and monthly wind turbine characteristics for four meteorological stations with high winds are investigated and compared with each other as well. The results show the general availability of wind energy potential across Taiwan.

A nomogram method for estimating the energy produced by wind turbine generators

A simple nomogram is constructed to estimate the power generated by a wind turbine generator (WTG) operated at near maximum efficiency using optimum tip-speed ratio between cut-in and rated wind speed, and at constant power using optimum pitch control between rated and cut-out wind speed. The nomogram is based on information that is readily available for commercial WTGs as well as some simple statistical quantities for the wind at the site. When the wind speed is described by a Weibull distribution, the power of a WTG is estimated in terms of three generalized non-dimensional parameters. When a Rayleigh distribution is employed only two parameters are necessary. A second nomogram is also developed for those less common cases where a small correction of the results of the first nomogram is needed. A mathematical analysis is presented which allows for the construction of single chart nomograms without sacrificing the necessary accuracy. Two application examples demonstrate the degree of accuracy achieved by the nomograms and the advantages they offer for parametric analyses as regards convenience and labor.