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Showing papers on "Blade pitch published in 2011"


Journal ArticleDOI
TL;DR: In this paper, the wake interference effect on the performance of a downstream wind turbine was investigated experimentally and the effects of these parameters on the total power output from the turbines were also estimated.

311 citations


Proceedings ArticleDOI
04 Jan 2011
TL;DR: In this article, the propeller speed (RPM) was fixed while changing the wind-tunnel speed to sweep over a range of advance ratios until reaching the windmill state (zero thrust).
Abstract: While much research has been carried out on propellers for full-scale aircraft, not much data exists on propellers applicable to the ever growing number of UAVs. Many of these UAVs use propellers that must operate in the low Reynolds number range of 50,000 to 100,000 based on the propeller chord at the 75% propeller-blade station. Tests were performed at the University of Illinois at Urbana-Champaign (UIUC) to quantify the propeller efficiency at these conditions. In total, 79 propellers were tested and the majority fit in the 9- to 11-in diameter range. During the tests, the propeller speed (RPM) was fixed while changing the wind-tunnel speed to sweep over a range of advance ratios until reaching the windmill state (zero thrust). To examine Reynolds number effects, typically four RPM’s were tested in the range 1,500 to 7,500 RPM depending on the propeller diameter. Propeller efficiencies varied greatly from a peak near 0.65 (for an efficient pr opeller) to near 0.28 (for an exceptionally poor propeller). Thus, these results indicate that proper propeller selection for UAVs can have a dramatic effect on aircraft performance.

302 citations


Journal ArticleDOI
TL;DR: In this article, a data-mining-based prediction model is built to monitor the performance of a blade pitch, and five data mining algorithms have been evaluated to evaluate the quality of the models for prediction of blade faults.
Abstract: A data-mining-based prediction model is built to monitor the performance of a blade pitch. Two blade pitch faults, blade angle asymmetry, and blade angle implausibility were analyzed to determine the associations between them and the components/subassemblies of the wind turbine. Five data-mining algorithms have been studied to evaluate the quality of the models for prediction of blade faults. The prediction model derived by the genetic programming algorithm resulted in the best accuracy and was selected to perform prediction at different time stamps.

172 citations


Journal ArticleDOI
T.Y. Chen1, L.R. Liou1
TL;DR: In this paper, the effects of tunnel blockage on the turbine power coefficient in wind tunnel tests of small horizontal-axis wind turbines were quantitatively investigated by measuring the tunnel velocities with and without rotors using a pitot-static tube under various test conditions.

170 citations


Journal ArticleDOI
TL;DR: In this paper, support vector machines (SVM) are used for fault detection and isolation in a variable speed horizontal-axis wind turbine composed of three blades and a full converter.

162 citations


Journal ArticleDOI
TL;DR: In this article, a small Darrieus hydrokinetic turbine with fixed pitch blades typically suffers from poor starting torque, low efficiency and shaking due to large fluctuations in both radial and tangential force with azimuth angle.

116 citations


Journal ArticleDOI
TL;DR: In this paper, individual blade pitch state space (IBP SS) control and disturbance accommodating control (DAC) that reject wind speed perturbations are applied on a 5MW wind turbine mounted on the barge and tension leg floating platforms for performance comparison in above rated wind speed region.

102 citations


Journal ArticleDOI
TL;DR: In this article, combined feedback/feedforward blade pitch control is compared to industry standard feedback control when simulated in realistic turbulent winds, and two feedforward designs are studied: collective-pitch model-inverse feedforward using a non-causal series expansion and individual-Pitch gain-scheduled shaped compensator.

98 citations


Journal ArticleDOI
TL;DR: In this paper, a pitch control system for a large wind turbine driven by a variable-speed pump-controlled hydraulic servo system was developed and verified for the path tracking control and path-positioning control of the pitch controller of the wind turbines by practical experiments in a full-scale test rig under different path profiles, load torques, and random wind speeds.

97 citations


Journal ArticleDOI
TL;DR: In this paper, a light detection and ranging system is used to measure conditions at a distance in front of wind turbines and is therefore suited to providing preview information of wind disturbances before they impact the turbine blades.

91 citations


Journal ArticleDOI
01 Mar 2011-Energy
TL;DR: In this paper, a lifting surface method with time marching free wake model is used to investigate the periodic unsteady nature in the wind shear, and the blade airloads and performance of the turbine are also predicted under IPC control.

Journal ArticleDOI
TL;DR: This paper presents a feedback/feedforward nonlinear controller for variable-speed wind turbines with doubly fed induction generators that simultaneously enables control of the active power in both the maximum power tracking and power regulation modes.
Abstract: This paper presents a feedback/feedforward nonlinear controller for variable-speed wind turbines with doubly fed induction generators. By appropriately adjusting the rotor voltages and the blade pitch angle, the controller simultaneously enables: 1) control of the active power in both the maximum power tracking and power regulation modes; 2) seamless switching between the two modes; and 3) control of the reactive power so that a desirable power factor is maintained. Unlike many existing designs, the controller is developed based on original, nonlinear, electromechanically-coupled models of wind turbines, without attempting approximate linearization. Its development consists of three steps: 1) employ feedback linearization to exactly cancel some of the nonlinearities and perform arbitrary pole placement; 2) design a speed controller that makes the rotor angular velocity track a desired reference whenever possible; and 3) introduce a Lyapunov-like function and present a gradient-based approach for minimizing this function. The effectiveness of the controller is demonstrated through simulation of a wind turbine operating under several scenarios.

Journal ArticleDOI
TL;DR: Investigations regarding the influence of design parameters in low head axial flow turbines like blade profiles, blade height and blade number for micro-hydro application continue to be inadequate, even though there is a need and potential for the application of such turbines.

Journal ArticleDOI
TL;DR: In this paper, the flow field in a cross-sectional plane of a scaled Beaver DHC aircraft propeller has been measured by means of a stereoscopic PIV setup, and phase-locked measurements are obtained in a rotational frequency range from 18,900 to 21,000rpm, at a relative Mach number of 0.6 at ¾ propeller radius.
Abstract: The flow field in a cross-sectional plane of a scaled Beaver DHC aircraft propeller has been measured by means of a stereoscopic PIV setup. Phase-locked measurements are obtained in a rotational frequency range from 18,900 to 21,000 rpm, at a relative Mach number of 0.6 at ¾ propeller radius. The use of an adapted formulation of the momentum equation in differential form for rotating frame of references, integrated with isentropic relations as boundary conditions, allowed to compute the pressure field around the blade and the surface pressure distribution directly from the velocity data in the compressible regime. The procedure, extended to the computation of the aerodynamic lift and drag coefficients by a momentum contour integral approach, proved to be able to couple the aerodynamical loads to the flow field on the moving propeller blade, comparing favorably with a numerical simulation of the entire scaled model. Results are presented for two propeller rotation speeds and three different yawing angles.

Proceedings ArticleDOI
04 Jan 2011
TL;DR: In this paper, combined feedback/feedforward blade pitch control is compared to industry standard feedback control when simulated in realistic turbulent winds, and three feedforward designs are studied: Non-Causal Series Expansion, Preview Control, and Optimized FIR Filter.
Abstract: Combined feedback/feedforward blade pitch control is compared to industry standard feedback control when simulated in realistic turbulent winds. The feedforward controllers are designed to reduce fatigue loads, increasing turbine lifetime and therefore reducing the cost of energy. Three feedforward designs are studied: Non-Causal Series Expansion, Preview Control, and Optimized FIR Filter. The input to the feedforward controller is a measurement of incoming wind speed, which could potentially be provided by lidar. Noncausal series expansion and Preview Control methods reduce blade root loads but increase tower bending in simulation results. The optimized FIR filter reduces loads overall, keeps pitch rates low, and maintains rotor speed regulation and power capture, while using imperfect wind measurements provided by a lidar model.

Patent
Henrik Stiesdal1
07 Nov 2011
TL;DR: In this article, a method for yaw control for a wind turbine comprising a rotor with a rotor blade, the rotor defining a rotor axis and a rotor plane to which the rotor axis is perpendicular to the wind direction, where the turning of the rotor is performed based on the measurement of a wind speed in the rotor plane at the rotor blade is provided.
Abstract: A method for yaw control for a wind turbine comprising a rotor with a rotor blade, the rotor defining a rotor axis and a rotor plane to which the rotor axis is perpendicular, in which the rotor axis is turned to minimise the yaw angle between the ambient wind direction and the rotor axis is provided, wherein the turning of the rotor axis is performed based on the measurement of a wind speed in the rotor plane at the rotor blade Furthermore, a wind turbine which comprises a rotor which includes a rotor axis and a rotor plane perpendicular to the rotor axis and an anemometer for measuring the ambient wind speed is provided The wind turbine further comprises an anemometer which is located such at a rotor blade at a particular distance from the rotor axis as to allow for measuring a wind speed in the rotor plane

Journal ArticleDOI
TL;DR: In this article, the authors applied a numerical model based on the vorticity transport formulation of the Navier-Stokes equations to the prediction of the aerodynamic performance of a vertical-axis wind turbine that consists of three curved rotor blades that are twisted helically around the rotational axis of the rotor.
Abstract: Accurate simulations of the aerodynamic performance of vertical-axis wind turbines pose a significant challenge for computational fluid dynamics methods. The aerodynamic interaction between the blades of the rotor and the wake that is produced by the blades requires a high-fidelity representation of the convection of vorticity within the wake. In addition, the cyclic motion of the blades induces large variations in the angle of attack on the blades that can manifest as dynamic stall. The present paper describes the application of a numerical model that is based on the vorticity transport formulation of the Navier–Stokes equations, to the prediction of the aerodynamics of a verticalaxis wind turbine that consists of three curved rotor blades that are twisted helically around the rotational axis of the rotor. The predicted variation of the power coefficient with tip speed ratio compares very favorably with experimental measurements. It is demonstrated that helical blade twist reduces the oscillation of the power coefficient that is an inherent feature of turbines with non-twisted blade configurations.

Book ChapterDOI
01 Jan 2011
TL;DR: In this article, an experimental modal analysis of the SNL sensored rotor blade (a modified CX-100 rotor blade) with embedded DC accelerometers was performed when hung with free boundary conditions and when mounted to a Micon 65/13 wind turbine.
Abstract: At the end of 2008 the United States became the largest producer of wind energy with 25,369 MW of electricity. This accounts for 1.25% of all U.S. electricity generated and enough to power 7 million homes. As wind energy becomes a key player in power generation and in the economy, so does the performance and reliability of wind turbines. To improve both performance and reliability, smart rotor blades are being developed that collocate reference measurements, aerodynamic actuation, and control on the rotor blade. Towards the development of a smart blade, SNL has fabricated a sensored rotor blade with embedded distributed accelerometer measurements to be used with operational loading methods to estimate the rotor blade deflection and dynamic excitation. These estimates would serve as observers for future smart rotor blade control systems. An accurate model of the rotor blade was needed for the development of the operational monitoring methods. An experimental modal analysis of the SNL sensored rotor blade (a modified CX-100 rotor blade) with embedded DC accelerometers was performed when hung with free boundary conditions and when mounted to a Micon 65/13 wind turbine. The modal analysis results and results from a static pull test were used to update an existing distributed parameter CX-100 rotor analytical blade model. This model was updated using percentage error estimates from cost functions of the weighted residuals. The model distributed stiffness parameters were simultaneously updated using the static and dynamic experimental results. The model updating methods decreased all of the chosen error metrics and will be used in future work to update the edge-wise model of the rotor blade and the full turbine model.

Patent
Jacob Krogh Kristoffersen1
22 Dec 2011
TL;DR: In this article, a light detection and ranging device is used to determine expected properties of wind in each respective section of the rotor plane so that the pitch reference value may be adjusted accordingly.
Abstract: Embodiments of the invention generally relate to controlling a wind turbine comprising blades attached to a rotor hub for rotation in a rotor plane and a control system for individually pitching the blades relative to the hub. The rotor planes divided into a plurality of predefined section, wherein each section has an associated pitch reference value. A light detection and ranging device may be used to determine expected properties of wind in each respective section of the rotor plane so that the pitch reference value may be adjusted accordingly.

Journal ArticleDOI
TL;DR: In this article, the authors used a second-order nonlinear beam finite element method to predict the average thrust of a cycloidal rotor with moderately flexible blades and a multibody-based largedeformation analysis (especially applicable for extremely flexible blades).
Abstract: This paper describes the aeroelastic model to predict the blade loads and the average thrust of amicro-air-vehiclescale cycloidal rotor. The analysis was performed using two approaches: one using a second-order nonlinear beam finite element method analysis for moderately flexible blades and a second using a multibody-based largedeformation analysis (especially applicable for extremely flexible blades) incorporating a geometrically exact beam model. An unsteady aerodynamic model is included in the analysis with two different inflow models: single streamtube and double-multiple streamtube inflowmodels. For the cycloidal rotors usingmoderately flexible blades, the aeroelastic analysis was able to predict the average thrust with sufficient accuracy over awide range of rotational speeds, pitching amplitudes, and number of blades. However, for the extremely flexible blades, the thrust was underpredicted at higher rotational speeds, and thismaybebecause of the overprediction of blade deformations. The analysis clearly showed that the reason for the reduction in the thrust-producing capability of the cycloidal rotorwith blade flexibility may be attributed to the large nosedown elastic twisting of the blades in the upper half cylindrical section, which is not compensated by a noseup pitching in the lower half-section. The inclusion of the actual blade pitch kinematics, unsteady aerodynamics, and flow curvature effects was found crucial in the accurate lateral force prediction.

Journal ArticleDOI
TL;DR: In this paper, the shape of rotor blade plays an important role in determining the overall aerodynamic performance of a 5KW horizontal axis wind turbine and a computer program is developed to automate the complete procedure.
Abstract: The basic principle of wind turbine converting wind energy into electricity comes from the lift produced by the air flowing through the rotor. The shape of rotor blade plays an important role in determining the overall aerodynamic performance of a horizontal axis wind turbine. In this work, blade is designed for a 5KW horizontal axis wind turbine which is already in market. For designing blade, blade element momentum theory (BEMT) is used and a computer program is developed to automate the complete procedure. Two NACA airfoils are taken for the comparative calculation of elemental power coefficient and other parameters such as chord, thickness and twist distribution. The airfoil taken for designing the blade is same from root to tip. Stresses are maximum at the blade root. In this work, the blade root is thickest portion of the blade and twist is maintained such that the angle of attack will be maximum at every station of the blade. In the designed blade, the elemental power coefficient is maximum in transition segment. The present method is useful for predicting the performance of wind turbine blade.

Patent
09 Sep 2011
TL;DR: A rotor blade assembly for a wind turbine and a method for increasing a loading capability of a rotor blade within a maximum load limit for wind turbine are disclosed in this paper, where the rotor blades have surfaces defining a pressure side, a suction side, leading edge, and a trailing edge extending between a tip and a root.
Abstract: A rotor blade assembly for a wind turbine and a method for increasing a loading capability of a rotor blade within a maximum load limit for a wind turbine are disclosed. The rotor blade assembly includes a rotor blade having surfaces defining a pressure side, a suction side, a leading edge, and a trailing edge extending between a tip and a root. The rotor blade assembly further includes an extension connected to a surface of the rotor blade, the extension having at least one design characteristic configured for increasing a loading capability of the rotor blade within a maximum load limit for the wind turbine. The design characteristic is one of extension length, extension width, extension curvature, span-wise extension location, chord-wise extension location, or extension angle with respect to a chord line of the rotor blade.

Journal ArticleDOI
TL;DR: In this article, an H∞ optimization-based approach for the detection and isolation of faults in a horizontal axis wind turbine is presented, where the primary residuals are generated from separate parity equations for each of the blade pitch and drivetrain subsystems.

ReportDOI
01 Oct 2011
TL;DR: In this article, the authors examined the accuracy of different measurement scenarios that rely on coherent continuous-wave or pulsed Doppler LIDAR systems to determine their applicability to wind turbine feed-forward control systems.
Abstract: This report examines the accuracy of measurements that rely on Doppler LIDAR systems to determine their applicability to wind turbine feed-forward control systems and discusses feed-forward control system designs that use preview wind measurements. Light Detection and Ranging (LIDAR) systems are able to measure the speed of incoming wind before it interacts with a wind turbine rotor. These preview wind measurements can be used in feed-forward control systems designed to reduce turbine loads. However, the degree to which such preview-based control techniques can reduce loads by reacting to turbulence depends on how accurately the incoming wind field can be measured. The first half of this report examines the accuracy of different measurement scenarios that rely on coherent continuous-wave or pulsed Doppler LIDAR systems to determine their applicability to feed-forward control. In particular, the impacts of measurement range and angular offset from the wind direction are studied for various wind conditions. A realistic case involving a scanning LIDAR unit mounted in the spinner of a wind turbine is studied in depth with emphasis on choices for scan radius and preview distance. The effects of turbulence parameters on measurement accuracy are studied as well. Continuous-wave and pulsed LIDAR models based on typicalmore » commercially available units were used in the studies present in this report. The second half of this report discusses feed-forward control system designs that use preview wind measurements. Combined feedback/feed-forward blade pitch control is compared to industry standard feedback control when simulated in realistic turbulent above-rated winds. The feed-forward controllers are designed to reduce fatigue loads, increasing turbine lifetime and therefore reducing the cost of energy. Three feed-forward designs are studied: non-causal series expansion, Preview Control, and optimized FIR filter. The input to the feed-forward controller is a measurement of incoming wind speeds that could be provided by LIDAR. Non-causal series expansion and Preview Control methods reduce blade root loads but increase tower bending in simulation results. The optimized FIR filter reduces loads overall, keeps pitch rates low, and maintains rotor speed regulation and power capture, while using imperfect wind measurements provided by the spinning continuous-wave LIDAR model.« less

Proceedings ArticleDOI
01 Jan 2011
TL;DR: In this paper, the authors describe the extension of a well proven state-of-the-art simulation tool for coupled floating structures to accommodate offshore wind turbine applications, both floating and fixed.
Abstract: This paper describes the extension of a well proven state-of-the-art simulation tool for coupled floating structures to accommodate offshore wind turbine applications, both floating and fixed. All structural parts, i.e. rotor blades, hub, nacelle, tower, vessel and mooring system, are included in the finite element model of the complete system. The aerodynamic formulation is based on the blade element momentum theory. A control algorithm is used for regulation of blade pitch angle and electrical torque. The system response is calculated by nonlinear time domain analysis. This approach ensures dynamic equilibrium every time step and gives a proper time domain interaction between the blade dynamics, the mooring dynamics and the tower motions. The developed computer code provides a tool for efficient analysis of motions, support forces and power generation potential, as influenced by waves, wind, and current. Some key results from simulations with wind and wave loading are presented in the paper. The results are compared with results obtained with a rigid blade model and quasi-static model of the anchor lines. The modelled wind turbine is the NREL offshore 5-MW baseline wind turbine, specifications of which are publicly available. In the accompanying paper, Global Analysis of a Floating Wind Turbine Using an Aero-Hydro-Elastic Numerical Model. Part 2: Benchmark Study, results from the new analysis tool are benchmarked against results from other analysis tools.Copyright © 2011 by ASME

Patent
22 Feb 2011
TL;DR: In this paper, a system and method to increase efficiency of turbines in wind farms is presented, where a sensor is configured to generate a wind map of an inflow of wind.
Abstract: A system and method are provided to increase efficiency of turbines in wind farms. A sensor is configured to generate a wind map of an inflow of wind. A controller is configured to generate a control signal based the wind map. A pitch adjustment device configured to adjust pitch of a blade of the turbine based on the control signal.

Journal ArticleDOI
TL;DR: In this paper, an aerodynamic model based on blade element and momentum theory is used to predict the helicopter performance and the propagation of these uncertainties to the performance parameters, such as thrust coefficient and power coefficient, are studied using Monte Carlo Simulations.
Abstract: The effect of structural and aerodynamic uncertainties on the performance predictions of a helicopter is investigated. An aerodynamic model based on blade element and momentum theory is used to predict the helicopter performance. The aeroelastic parameters, such as blade chord, rotor radius, two-dimensional lift-curve slope, blade profile drag coefficient, rotor angular velocity, blade pitch angle, and blade twist rate per radius of the rotor, are considered as random variables. The propagation of these uncertainties to the performance parameters, such as thrust coefficient and power coefficient, are studied using Monte Carlo Simulations. The simulations are performed with 100,000 samples of structural and aerodynamic uncertain variables with a coefficient of variation ranging from 1 to 5%. The scatter in power predictions in hover, axial climb, and forward flight for the untwisted and linearly twisted blades is studied. It is found that about 20-25% excess power can be required by the helicopter relative to the determination predictions due to uncertainties.

Proceedings ArticleDOI
13 Oct 2011
TL;DR: This paper considers a static wind model for a three-bladed, horizontal-axis, pitch-controlled wind turbine and shows that very similar performance can be achieved by using only load measurements, with no knowledge of the wind field or wind turbine model.
Abstract: We consider a static wind model for a three-bladed, horizontal-axis, pitch-controlled wind turbine. When placed in a wind field, the turbine experiences several mechanical loads, which generate power but also create structural fatigue. We address the problem of finding blade pitch profiles for maximizing power production while simultaneously minimizing fatigue loads. In this paper, we show how this problem can be approximately solved using convex optimization. When there is full knowledge of the wind field, numerical simulations show that force and torque RMS variation can be reduced by over 96% compared to any constant pitch profile while sacrificing at most 7% of the maximum attainable output power. Using iterative learning, we show that very similar performance can be achieved by using only load measurements, with no knowledge of the wind field or wind turbine model.

Patent
31 Jan 2011
TL;DR: In this article, a method of in situ calibrating load sensors of a horizontal axis wind turbine is described, where the calibration is based only on measurements carried out, when the generator is cut out.
Abstract: A method of in situ calibrating load sensors of a horizontal axis wind turbine is described. The wind turbine comprises a rotor including a hub and a number of wind turbine blades, which extend radially from the hub, the hub being connected to a drive train including a generator, which converts mechanical rotational motion of the rotor into electrical energy, wherein said number of blades comprises at least a first wind turbine blade provided with a number of first load sensors positioned in a first cross-section of the first wind turbine blade. The method comprises the steps of: a) determining a rotor azimuth angle of the first wind turbine blade, b) determining a pitch angle of the first wind turbine blade, c) measuring loads in the first cross-section of the first wind turbine blade using the first load sensors, d) calculating theoretical loads based on at least the rotor azimuth angle and the pitch angle of the blade determined in steps a) and b), e) comparing the loads measured in step c) with the theoretical loads calculated in step d), and f) calibrating the first load sensors based on the comparison of step e), wherein the calibration are based only on measurements carried out, when the generator is cut out.

Patent
18 Aug 2011
TL;DR: In this article, an open loop control algorithm for incrementally or positively adjusting the pitch angles of individual rotor blades may be used to increase spacing between the base of the turbine tower and an approaching blade tip.
Abstract: In a wind turbine, an open loop control algorithm for incrementally or positively adjusting the pitch angles of individual rotor blades may be used to increase spacing between the base of the turbine tower and an approaching blade tip. As each rotating blade passes in front of the tower base, a minimum clearance distance may be assured to avoid blade tip strikes of the base. In accordance with at least one embodiment of the control algorithm, as each blade approaches the tower base, it may be feathered to reduce its power loading, and to facilitate increased clearance beyond the normal unloading or feathering produced by the so-called tower shadow effect. To offset resultant loss of torque, the remaining blades may be correspondingly pitched toward power, i.e. into the wind, to balance and/or smooth out the overall rotor torque curve, and thus to avoid torque ripples.