Individual Pitch Research Articles

Active tip deflection control for wind turbines

This paper studies the use of blade tip sensors for load reductions and blade-tower clearance control. Typically, modern blade tip sensors measure flapwise tip deflection distances at a high sampling rate, and such measurements can be utilised as feedback signals for control operations. Thus, this paper proposes a novel blade pitch control design based on the tip deflection measurements and individual pitch control (IPC). Firstly, an IPC system design is presented, using the tip deflection measurements to alleviate turbine fatigue loads caused by differential loads such as wind shear, yaw misalignment and turbulence. Secondly, a novel implementation of IPC with tip trajectory tracking feature is proposed where the blade tips are guided along a fixed trajectory to maximise blade-tower clearance. The motivation of this implementation is to reduce the chance of blade-tower interactions for large and flexible rotors. The presented controller is implemented in HAWC2, and high fidelity load measurements are produced using the DTU10MW reference wind turbine. The simulation results showed that the fatigue damage reduction on key turbine components and the improved blade-tower clearance can be achieved simultaneously. Lifetime equivalent load reductions were seen in both rotating and fixed frame components under the normal operating conditions.

Effect of load reduction mechanisms on loads and blade bearing movements of wind turbines

AbstractThe power control of wind turbines is usually realized via a change in the pitch angle of the rotor blades. Pitching facilitates the exact control of the turbines and the reliable deceleration of the rotor when required. Pitch movements can moreover be used for load control. One of these methods is called individual pitch control (IPC). IPC controls the blades individually and brings about a significant reduction in the fatigue loads and extreme loads placed on the structural components, while at the same time reducing the yield of the turbine only slightly. The lower loads reduce material costs, and thus, the cost of energy (CoE) is reduced, despite the slight reduction in yield. The method is nevertheless not used everywhere since the additional movement cycles put the rotor blade bearings in particular under stress. Special attention must be paid to small amplitude oscillating movements, which carry a high risk of inducing surface damage in the rolling contacts of the blade bearings. This paper uses a cycle analysis of the IWT7.5‐164 reference turbine to illustrate the differences in the movement patterns of wind turbine blade bearings with and without IPC. Moreover, model calculations with single contacts are used to show which of the movement patterns carries a risk of inducing surface damage. The use of IPC leads to the expected load reduction at the blade root. In current literature, IPC is usually assumed to have a negative influence on the life expectancy of blade bearings, but the findings of this study contradict this. The summed blade bearing movement is increased, although the number of very small pitch angles occurring is reduced. This reduction reduces the risk of wear in the blade bearings.

System-level design studies for large rotors

Abstract. We examine the effect of rotor design choices on the power capture and structural loading of each major wind turbine component. A harmonic model for structural loading is derived from simulations using the National Renewable Energy Laboratory (NREL) aeroelastic code FAST to reduce computational expense while evaluating design trade-offs for rotors with radii greater than 100 m. Design studies are performed, which focus on blade aerodynamic and structural parameters as well as different hub configurations and nacelle placements atop the tower. The effects of tower design and closed-loop control are also analyzed. Design loads are calculated according to the IEC design standards and used to create a mapping from the harmonic model of the loads and quantify the uncertainty of the transformation. Our design studies highlight both industry trends and innovative designs: we progress from a conventional, upwind, three-bladed rotor to a rotor with longer, more slender blades that is downwind and two-bladed. For a 13 MW design, we show that increasing the blade length by 25 m, while decreasing the induction factor of the rotor, increases annual energy capture by 11 % while constraining peak blade loads. A downwind, two-bladed rotor design is analyzed, with a focus on its ability to reduce peak blade loads by 10 % per 5∘ of cone angle and also reduce total blade mass. However, when compared to conventional, three-bladed, upwind designs, the peak main-bearing load of the upscaled, downwind, two-bladed rotor is increased by 280 %. Optimized teeter configurations and individual pitch control can reduce non-rotating damage equivalent loads by 45 % and 22 %, respectively, compared with fixed-hub designs.

Mitigation of Flickering in DFIG Based Wind Turbines using Individual Pitch Control

due to the breeze beat boom, wind shear and tower shadow affects, community related breeze generators are the wellsprings of power modifications which additionally can also supply shimmer over the span of regular development. This paper proposes a model of a MW-set up variable-pace wind turbine with a doubly continued confirmation generator to research the blaze transmission and equalization problems. To facilitate the flashes we were the usage of a man or female make commitments manage contraption the earlier days. on this paper, a moved pitch territory control method relying on the smooth cause is proposed for the variable-rhythm wind turbine systems, in which the generator pace slip-up and exchange speed blunder are utilized as manage enter elements for the cushy cause controller (FLC). The pitch vicinity reference is made through manner of the use of the FLC, that could capture up at the nonlinear regular for the pitch element to the breeze pace. This paper offers head alternate of wind energy, wind turbine linearization and dynamic displaying are settled. The feathery reason controller is carried out for trade draining edge of wind turbine and customary energy might be collect. The square represent of proposed pitch oversee which consolidates pitch controller, actuator version and turbine linearized displayed with the nice valuable asset of the usage of Matlab/Simulink programming.

PDE-Based Modeling and Control for Power Generation Management of Wind Farms

This paper introduces a partial differential equation (PDE) based modeling paradigm for wind farms. The PDE model governs the evolution of a function that represents the distribution of the wind turbines over a range of pitch angles, yaw angles, and wind speeds. The PDE model is embedded into a hierarchical control architecture, in which the central (top) level controller uses the feedback of the individual pitch and yaw angles of the turbines in the farm and synthesizes universal changes in pitch and yaw angles such that the cumulative power generated by the farm tracks a desired power generation trajectory. The controller ensures good tracking performance while satisfying the constraints of the pitch and yaw actuator dynamics. The control design is performed on the PDE model using a framework that includes dynamic inversion, model predictive control and linear matrix inequalities.

Enhanced Yaw Stability of Downwind Turbines

It is shown, in a novel experimental study using a sub-scale model of a 5MW downwind turbine, that individual pitch control based on a sinusoidal pitching scheme that is locked to the phase of the rotor rotation further improves the yaw stability of a downwind turbine. The optimum pitching amplitude is observed to be insensitive to yaw angle. Furthermore, a positive pitching amplitude improves yaw stability at negative yaw angles, while at positive yaw angles, negative pitching amplitude improves yaw stability. Thus, individual pitch control further improves the superior yaw characteristics of downwind turbines compared to upwind configurations.

The relationship between variability in baseball pitching kinematics and consistency in pitch location

ABSTRACT The purpose of this study was to explore the relationship between variability in pitching kinematics and consistency in pitch location. Data were collected for 47 healthy baseball pitchers throwing ten full-effort fastballs to the centre of the strike zone. For each pitch, 20 kinematic parameters were calculated with an automated motion capture system while pitch location was measured with a PITCHf/x system. Variability of each kinematic parameter was defined for each pitcher as the standard deviation among his fastballs thrown. For calculating consistency, each pitcher’s mean pitch location was first calculated. The distances from each individual pitch to the mean pitch location were then found for each pitcher tested. A consistency metric was then calculated for each pitcher by averaging these distances. A multiple linear regression model was developed using stepwise regression with backwards elimination. The resulting model explained 58% of the variance in the consistency metric and included five parameters, three at foot contact (upper trunk tilt, shoulder abduction, and shoulder horizontal abduction) and two at time of maximum shoulder external rotation (shoulder external rotation and shoulder horizontal adduction). Reducing variability at the shoulder during the early portions of the pitching motion may improve consistency of ball location.

Effect of installation errors on beveloid gears’ precision ground by cone-shape worm wheel

Both the mathematical model of a cone-shape worm wheel and the mathematical model of cone-shape worm wheel grinding beveloid gears with installation errors of a gear workpiece and a cone-shape worm wheel are developed. The effect of the installation errors including gears’ incline error, eccentric error, mounting angle error of a cone-shape worm wheel and coupling error of installation errors mentioned on gears’ surface deviation is investigated. The sensitivity of tooth surface deviation to installation errors mentioned is analyzed. The results show that the helix slope deviation, helix total deviation and tooth cumulative pitch deviation are more sensitive to gears’ incline error. The tooth cumulative pitch deviation, profile total deviation, profile slope deviation are more sensitive to gears’ eccentric error. The effect of gears’ incline error and eccentric error on cumulative pitch deviation and individual cumulative pitch deviation is inverse which lead that coupling error including gears’ incline error and eccentric error causes smaller cumulative pitch deviation and individual cumulative pitch deviation compared to gears’ incline error or eccentric error. Moreover Effect of the mounting angle error of cone-shape worm wheel on gears’ surface deviation is very limited.

Individual pitch control strategy for reducing aerodynamic loads and torque ripples

In this article, a new pitch control scheme is proposed for three‐bladed wind turbines to reduce two types of ripples caused by wind shear and tower shadow, including 1P aerodynamic loads and multiples of 3P torque ripples. These ripples are mathematically proven to be associated with wind power by using an equivalent wind speed model. An individual pitch control strategy is then proposed to reduce the impacts of the two types of ripples on wind turbines. In the proposed pitch control strategy, two band‐pass filters are implemented to obtain the ripple components, and a supplementary pitch angle reference signal is generated for each wind blade based on the ripple components and rotor azimuth. By adding the supplementary pitch angle adjustment signal to the existing pitch angle reference, a new pitch angle reference signal is produced to reduce 1P aerodynamic loads and multiples of 3P torque ripples. Several tests show that the proposed pitch control strategy has a good performance to alleviate the 1P aerodynamic load ripples and multiples of 3P torque ripples. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A Comparative Study on Primary Bearing Rating Life of a 5-MW Two-Blade Wind Turbine System Based on Two Different Control Domains

Recently, the importance of individual pitch control (IPC) capability in wind turbine systems has been emphasized to achieve the desired power performance and mitigate the aerodynamic imbalance load for the mechanical integrity. Compared to collective pitch control (CPC), which assigns identical pitch angles for all employed blades, IPC is capable of generating other various sets of pitch angles to manipulate the aerodynamic load. Thus, the mechanical elements of wind turbine systems may take advantages from this variation, which allows wind turbines to have lighter designs and longer lifetimes. One of the essential mechanical components in the wind turbine is a primary bearing supporting the blades–rotor–shaft unit, which has not been fully investigated yet among the structural elements in the wind turbine system. In this regard, this research focuses on predicting the bearing life span of a NACA64-A17 two-blade 5-MW wind turbine system for the domains of allowable individual pitch angles by IPC. In particular, under the effect of various wind speeds, a bearing life span was determined based on the average value of load cases—satisfying both appropriate power level and the allowable domain of pitch control angles, which were possibly conveyed by IPC—and the result was compared with the bearing life predicted based on the domain of pitch angles, as generated by the CPC strategy. Consequently, in the ranges of high wind speeds, it was found that the average applied load to the bearing is reduced under the domain of the IPC-based pitch angle, resulting in possibly increasing the life span of the bearing. With the presented results, it is hoped that this work will provide important insights for those that majorly concern designing the primary bearing of the IPC-based wind turbine system.

Estimation and Control of Wind Turbine Tower Vibrations Based on Individual Blade-Pitch Strategies

In this brief, we present a method to estimate the tower fore-aft velocity based upon measurements from blade load sensors. In addition, a tower dampening control strategy is proposed based upon an individual blade pitch control architecture that employs this estimate. The observer design presented in this brief exploits the Coleman transformations that convert a time-varying turbine model into one that is linear and time-invariant, greatly simplifying the observability analysis and subsequent observer design. The proposed individual pitch-based tower controller is decoupled from the rotor speed regulation loop and hence does not interfere with the nominal turbine power regulation. Closed-loop results, obtained from high fidelity turbine simulations, show close agreement between the tower estimates and the actual tower velocity. Furthermore, the individual-pitch-based tower controller achieves a similar performance compared with the collective-pitch-based approach but with negligible impact upon the nominal turbine power output.

Calculating wind turbine component loads for improved life prediction

Wind turbines life time is commonly predicted based on statistical methods. However, the success of statistics-based maintenance depends on the amount of variation in the system design, usage and load. Life time prediction based on physical models seeks to overcome this drawback by considering the actual design and evaluating the specific usage, load and operating condition of the considered systems. In this paper, a load-based maintenance approach is proposed to predict wind turbines life time. Physical models are used to evaluate load profiles at wind turbine blade root, rotor hub center and tower head. The effects of surface roughness, side winds, yaw misalignment, rotor tilt and blade cone angle, individual blade pitching and wind turbulences are considered and quantified. It is shown that centrifugal, gravity, Euler and Coriolis accelerations dominate the blade root loads. Tilt and cone angle, as well as individual blade pitching, affect the rotor hub and dynamic tower head loads. Further, the actual wind speed distribution is considered which is also proven to be a critical life time prediction parameter. Finally, a set of parameters is proposed that need to be monitored in a specific wind turbine to enable the practical implementation of a predictive maintenance policy.

Multivariable robust blade pitch control design to reject periodic loads on wind turbines

The demand on sustainable operations of large-scale wind turbines necessitates the concurrent advancement of power regulation and load mitigation through blade pitch control. Traditional collective pitch control (CPC) mechanisms can only deal with symmetric disturbances. The advent of individual pitch control (IPC) provides new opportunities to mitigate asymmetric or periodic loads on blades. Nevertheless, difficulties in control synthesis remain. In order for IPC to be truly effective, the complicated dynamic coupling between turbine components has to be accounted for. Moreover, wind turbine dynamics is highly nonlinear, and significant modeling uncertainties exist. In this research, a multivariable robust IPC framework is developed, aiming at rejecting periodic loads. The inter-blade coupling is explicitly modeled to provide response characteristics in the frequency domain. Subsequently, the structured singular values (μ)-synthesis strategy is adopted, as it shows distinct capability of dealing with periodic loads. In particular, weighting functions can be tailored to suppress response peaks at periodic frequencies with guaranteed robustness. Systematic case investigations indicate that, with the proposed IPC strategy, one can achieve significant periodic load mitigation as well as fatigue alleviation in speed-varying wind fields.

Development of Hardware-in-the-Loop-Simulation Testbed for Pitch Control System Performance Test

This paper deals with the development of a wind turbine pitch control system and the construction of a Hardware-in-the-Loop-Simulation (HILS) testbed for the performance test of the pitch control system. When the wind speed exceeds the rated wind speed, the wind turbine pitch controller adjusts the blade pitch angles collectively to ensure that the rotor speed maintains the rated rotor speed. The pitch controller with the individual pitch control function can add individual pitch angles into the collective pitch angles to reduce the mechanical load applied to the blade periodically due to wind shear. Large wind turbines often experience mechanical loads caused by wind shear phenomena. To verify the performance of the pitch control system before applying it to an actual wind turbine, the pitch control system is tested on the HILS testbed, which acts like an actual wind turbine system. The testbed for evaluating the developed pitch control system consists of the pitch control system, a real-time unit for simulating the wind and the operations of the wind turbine, an operational computer with a human–machine interface, a load system for simulating the actual wind load applied to each blade, and a real pitch bearing. Through the several tests based on HILS test bed, how well the pitch controller performed the given roles for each area in the entire wind speed area from cut-in to cut-out wind speed can be shown.

Fatigue load mitigation in wind turbine using a novel anticipatory predictive control strategy

Wind energy has become a recent evolving source of renewable energy which needs an extensive exploration. The increased configuration of wind turbine instantaneously increases the structural loading of wind turbine components. The prolonged loading on structural components imposes a great impact on the lifetime of the wind turbine and reduces the feasibility of thinner rotor blade. These economical detriments due to the structural damage of turbine are dealt effectively by proposing an anticipatory preview-based control strategy for individual pitching of blades. The proposed multiple point model predictive controller with fuzzy logic switching, exploits the preview wind measurement from the light detection and ranging system which predicts the wind speed in advance. The utmost objective of the proposed controller is its optimized individual blade pitching to reduce the fatigue loads on the wind turbine components using the preview wind data. The blade root bending moment of individual blades and the tower fore-aft deflection which are chosen as the parameters of fatigue stress to be analyzed and controlled. The National Renewable Energy Laboratory’s Fatigue, Aerodynamics, Structures and Turbulence 5 MW baseline onshore wind turbine is used for validating the proposed controller in MATLAB simulation. The non-linear wind field is simulated using the TurbSim software, and the short-term and lifetime damage equivalent loads of the wind turbine for the simulated wind field is analyzed using the MLife software of the National Renewable Energy Laboratory. The proposed controller is compared with the typical model predictive controller and linear quadratic-based controller.

Vibration and Performance Analyses Using Individual Blade Pitch Controls for Lift-Offset Rotors

This work attempts to reduce the hub vibratory loads of a lift-offset rotor using IBC (individual blade pitch control) in high-speed forward flight. As a lift-offset rotor for the present study, the rigid coaxial rotor of a XH-59A compound helicopter is considered and CAMRAD II is used to predict the hub vibration and rotor performance. Using the IBC with a single harmonic input at 200 knots, the vibration index of the XH-59A rotor is minimized by about 62% when the 3/rev actuation frequency is applied with the IBC amplitude of 1° and control phase angle of 270° (3P/1°/270°); however, the rotor effective lift-to-drag ratio decreases by 3.43%. When the 2/rev actuation frequency with the amplitude of 2° and control phase angle of 270° (2P/2°/270°) and the 3/rev actuation frequency using the magnitude of 1° and control phase angle of 210° (3P/1°/210°) are used in combination for the IBC with multiple harmonic inputs, the vibration index is reduced by about 62%, while the rotor effective lift-to-drag ratio increases by 0.37% at a flight speed of 200 knots. This study shows that the hub vibration of the lift-offset rotor in high-speed flight can be reduced significantly but the rotor performance increases slightly, using the IBC with multiple harmonic inputs.

Wind tunnel setup for experimental validation of wind turbine control concepts under tailor-made reproducible wind conditions

To speed up validation and prototyping of novel control and design concepts in wind energy, wind tunnel experiments should be used in synergy with numerical simulations and field experiments. The paper presents a wind tunnel setup consisting of a scaled wind turbine model MoWiTO and an active grid for generation of tailor-made and reproducible inflow conditions. To demonstrate that the presented experimental setup is suitable for fast validation of advanced control concepts, several control algorithms have been implemented and validated in various inflow conditions, such as turbulent and sheared inflows, and wind gusts. The tested control algorithms include the baseline collective pitch and torque control, individual pitch control for load reduction, and a control algorithms for compensation of static aerodynamic imbalances. All control algorithms resulted in an expected behaviour of the model wind turbine, thus emphasizing that the presented experimental setup can be used for fast and inexpensive testing of control concepts.

Rejection of varying-frequency periodic load disturbances in wind-turbines through active disturbance rejection-based control

Wind turbines are complex mechatronic systems subject to different kinds of disturbances. Among all disturbance sources, those from periodic nature are the most relevant and important for maintaining the structural health of the entire wind turbine. However, periodic disturbances in wind turbines, mainly given by wind shear, tower shadow and rotational sampling of turbulence, have a variable fundamental frequency that changes as function of the turbine angular speed. In consequence, conventional controllers have issues to mitigate such varying-frequency periodic loads. This paper proposes two individual pitch control schemes to attenuate the main periodic load components of blade flap-wise and hub yaw/tilt-wise bending moments in horizontal-axis wind turbines under varying-frequency conditions. Both proposals are founded on the paradigm of Active Disturbance Rejection Control (ADRC): the former is formulated in the time-domain using a Linear-Time-Invariant (LTI) standard controller, while the latter is designed in the angular position domain using a Linear-Position-Invariant (LPI) approach. Several realistic simulations with different wind turbulence intensities and average wind speeds are performed using a 5 MW three-bladed horizontal-axis wind turbine implemented in the FAST code by NREL. Simulation results of the proposed control schemes show improved load reductions compared with other control techniques.

Effectiveness of individual pitch control on a 5 MW downwind turbine

A novel experimental study of individual pitch control on downwind turbines is conducted. The experiment is accomplished using a sub-scale model of a 5 MW downwind turbine. It is shown that individual pitch control based on sinusoidal/cosinusoidal pitching schemes that are locked to the phase of the rotor rotation further improves the power output, yaw stability and mitigates the unsteady loads of a downwind turbine through the intelligent control system. The optimum pitching amplitude is observed to be insensitive to yaw angle. Furthermore, a negative sinusoidal pitching amplitude improves power and reduces overall unsteadiness at zero yaw angle. In the case of positive yaw; a positive cosinusoidal pitching amplitude improves power, reduces overall unsteadiness and improves yaw stability. In the case of negative yaw; when a positive sinusoidal pitching amplitude alleviates overall unsteadiness, improves yaw stability but reduces power while a positive cosinusoidal pitching amplitude increases power coefficient, alleviates overall unsteadiness but reduces yaw stability. Moreover, positive rotor yaw angle which is more stable than negative can be used to alleviate loads on downwind turbines during operation because overall unsteadiness is observed larger when the nacelle has a negative yaw angle, compared to when nacelle has a positive yaw angle.

A Study on the Capability of Backward Swept Blades to Mitigate Loads of Wind Turbines in Shear Flow

The vertical wind shear is one of the major sources of fatigue loads on the blades of a horizontal axis wind turbine. Traditionally, the active individual pitch control system is used to alleviate the cyclic load fluctuations, which requires sensors and actuators. In this paper, a passive load control technique by using backward swept blades is explored of its potential capability of mitigating load variations in shear wind. An advanced aeroelastic model based on free wake vortex lattice model (FWVLM) and geometrically exact beam theory (GEBT) is developed for the study. Both the aerodynamic and structural solvers are able to account for the three-dimensional (3D) shape effects of the undeformed and deformed swept blades. The NREL 5-MW reference wind turbine is analyzed by adding backward sweep to the baseline blade. Comparisons are made between the baseline and swept blades for the time-varying root moments and rotor moments under sheared inflow. Different amounts of tip sweep are discussed. An effective reduction in the amplitude of the flapwise root moment variations is obtained, while the edgewise root moment is less influenced. Reduced mean values of the rotor yaw and tilt moments are also achieved, at the cost of increased blade root torsion moment.