Showing papers on "Blade pitch published in 2009"

A tutorial on the dynamics and control of wind turbines and wind farms

Abstract: Wind energy is currently the fastest-growing energy source in the world, with a concurrent growth in demand for the expertise of engineers and researchers in the wind energy field. There are still many unsolved challenges in expanding wind power, and there are numerous problems of interest to systems and control researchers. In this paper, we first review the basic structure of wind turbines and then describe wind turbine control systems and control loops. Of great interest are the generator torque and blade pitch control systems, where significant performance improvements are achievable with more advanced systems and control research. We describe recent developments in advanced controllers for wind turbines and wind farms, and we also outline many open problems in the areas of modeling and control of wind turbines.

Reduction of Wind Turbine Noise using Optimized Airfoils and Trailing-Edge Serrations

Abstract: Acoustic field measurements were carried out on a 94-m-diam three-bladed wind turbine with one standard blade, one blade with trailing-edge serrations, and one blade with an optimized airfoil shape. A large horizontal microphone array, positioned at a distance of about one rotor diameter from the turbine, was used to locate and quantify the noise sources in the rotor plane and on the individual blades. The acoustic source maps show that for an observer at the array position, the dominant source for the baseline blade is trailing-edge noise from the blade outboard region. Because of convective amplification and directivity, practically all of this noise is produced during the downward movement of the blade, which causes the typical swishing noise during the passage of the blades. Both modified blades show a significant trailing-edge noise reduction at low frequencies, which is more prominent for the serrated blade. However, the modified blades also show tip noise at high frequencies, which is mainly radiated during the upward part of the revolution and is most important at low wind speeds due to high tip loading. Nevertheless, average overall noise reductions of 0.5 and 3.2 dB are obtained for the optimized blade and the serrated blade, respectively.

A comparison of smart rotor control approaches using trailing edge flaps and individual pitch control

Abstract: Modern wind turbines have been steadily increasing in size, and have now become very large, with recent models boasting rotor diameters greater than 120 m. Reducing the loads experienced by the wind turbine rotor blades is one means of lowering the cost of energy of wind turbines. Wind turbines are subjected to signiflcant and rapid ∞uctuating loads, which arise from a variety of sources including: turbulence in the wind, tower shadow, wind shear, and yawed ∞ow conditions. \Smart rotor control" concepts have emerged as a major topic of research in the attempt to reduce fatigue loads on wind turbines. In this approach, aerodynamic load control devices are distributed along the span of the wind turbine blade, and through a combination of sensing, control, and actuation, these devices dynamically control the loads on the blades. This research investigates the load reduction potential of smart rotor control devices, namely trailing edge ∞aps (TEFs), in the operation of a 5 MW wind turbine in the aeroelastic design code \GH Bladed." Speciflcally in this paper, the fatigue load reductions achieved using trailing edge ∞aps are evaluated, and the performance is compared to another promising load reduction technique, individual pitch control. A feedback control approach is implemented for load reduction, which utilizes a multiblade coordinate transformation, so that variables in the rotating frame of reference can be mapped into a flxed frame of reference. Single input single output (SISO) control techniques for linear time invariant (LTI) systems are then employed to determine the appropriate response of the TEFs based on the loads on the blades. The use of TEFs and this control approach is shown to efiectively reduce the fatigue loads on the blades, relative to a baseline controller. The load reduction potential is also compared to an alternative individual pitch control approach, in the time and frequency domain. The efiects on the pitch and power systems are brie∞y evaluated, and the limitations of the analysis are assessed.

H-Darrieus Wind Turbine with Blade Pitch Control

Abstract: A procedure for computing the optimal variation of the blades' pitch angle of an H-Darrieus wind turbine that maximizes its torque at given operational conditions is proposed and presented along with the results obtained on a 7 kW prototype. The CARDAAV code, based on the “Double-Multiple Streamtube” model developed by the first author, is used to determine the performances of the straight-bladed vertical axis wind turbine. This was coupled with a genetic algorithm optimizer. The azimuthal variation of the blades' pitch angle is modeled with an analytical function whose coefficients are used as variables in the optimization process. Two types of variations were considered for the pitch angle: a simple sinusoidal one and one which is more general, relating closely the blades' pitch to the local flow conditions along their circular path. A gain of almost 30% in the annual energy production was obtained with the polynomial optimal pitch control.

Discrete element simulation of free flowing grains in a four‐bladed mixer

Abstract: Numerical simulations of granular flow in a cylindrical vessel agitated by a four-blade impeller were performed using the discrete element method. Velocity, density, and stress profiles within the mixer displayed a periodic behavior with a fluctuation frequency equal to that of the blade rotation. Blade orientation was found to affect flow patterns and mixing kinetics. For an obtuse blade pitch orientation, a three-dimensional recirculation zone develops in-front of the blade due to formation of heaps where the blades are present. This flow pattern promotes vertical and radial mixing. No recirculation zone was observed when the blade orientation was changed to an acute blade pitch. The system's frictional characteristics are shown to strongly influence the granular behavior within the mixer. At low friction coefficients, the 3-D recirculation in front of the obtuse blade is not present reducing convective mixing. Higher friction coefficients lead to an increase in granular temperature which is associated with an increase in diffusive mixing. Normal and shear stresses were found to vary with mixer height with maximum values near the bottom plate. Additionally, a strong dependence between the magnitude of the shear stresses and the friction coefficient of the particles was found. The stress tensor characteristics indicate that the granular flow in our simulations occurs in the quasi-static regime. At the same time, the averaged pressure was found to vary linearly with bed height and could be predicted by a simple hydrostatic approximation. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Blade Offset and Pitch Effects on a High Solidity Vertical Axis Wind Turbine

Abstract: A high solidity, small scale, 2.5m diameter by 3m high Vertical Axis Wind Turbine (VAWT) consisting of three NACA 0015 profile blades, each with a span of 3m and a chord length of 0.4m, was tested in an open-air wind tunnel facility to investigate the effects of preset toe-in and toe-out turbine blade pitch. The effect of blade mount-point offset was also investigated. The results from these tests are presented for a range of tip speed ratios, and compared with an extensive base data set obtained for a nominal wind speed of 10m/s. Results show measured performance decreases of up to 47% for toe-in, and increases of up to 29% for toe-out blade pitch angles, relative to the zero preset pitch case. Also, blade mount-point offset tests indicate decreases in performance as the mount location is moved from mid-chord towards the leading edge, as a result of an inherent toe-in condition. Observations indicate that these performance decreases may be minimized by compensating for the blade mount offset with a toe-o...

Controlling Platform Motions and Reducing Blade Loads for Floating Wind Turbines

Abstract: Offshore sites hold great promise for the growth of wind energy. To tap the vast resource in deep water sites, new support structures, such as those that float, are needed. For floating structures to succeed, they must withstand the offshore wind and wave environment. Two new methods for controlling a floating turbine and reducing the platform and blade loads are presented. The first is a method for controlling collective blade pitch and reducing platform pitch motion, a significant problem for floating structures. The rated generator speed is made a function of the platform pitch velocity. When the platform is pitching upwind, the set point generator speed is set to a larger value, and vice versa. For constant generator torque, this approach essentially makes the rated power a variable that depends on the platform pitch velocity. Fundamentally, this control approach trades power variability for platform pitch variability. The results will show substantial reductions in platform pitch motion but minor inc...

LQG Design for Megawatt-Class WECS With DFIG Based on Functional Models' Fidelity Prerequisites

Abstract: With the increasing trend of connecting high penetrations of wind energy conversion systems (WECSs) to the transmission networks comes the challenge of updating the grid code for the connection of megawatt-class wind turbines. Starting with each WECS entity in the wind farm, the specifications would require the ability to complement some of the power system control services-voltage and frequency control-currently carried out by conventional synchronous generation. This paper investigates output power stability of a WECS in a highly fluctuating wind environment. Based on a performability model, a control strategy is devised for maximizing energy conversion in low to medium winds, and maintaining rated output in above rated winds while keeping torsional torque fluctuations to a minimum. Control is exercised via collective blade pitch control as well as generator torque control. The fundamental philosophy behind the proposed control strategy for the wind turbine coupled to an asynchronous doubly fed induction generator is general and can be easily extended to other WECS configurations.

A Comparison of Multi-Blade Coordinate Transformation and Direct Periodic Techniques for Wind Turbine Control Design

Abstract: The inherent periodic behavior of an operating wind turbine is not well accommodated by common time-invariant analysis and control techniques. A multi-blade coordinate transformation (MBC) helps to overcome this issue for rotors with three or more blades by mapping the dynamic state variables into a non-rotating reference frame. A number of researchers have applied MBC for modal analyses and individual blade pitch controller designs. They do so by assuming the transformed system model from MBC is time-invariant, which is not often the case. The paper explores the validity of the time-invariant assumption by comparison to direct periodic techniques, which retain all periodic system information. In a modal analysis study, eigenvalues of a system after MBC are compared to direct Floquet modes. In an individual blade pitch control design study, a linear quadratic regulation (LQR) design after MBC is compared to direct periodic LQR. A 5-MW three-bladed wind turbine model is used to quantify performance differences. Normal operating conditions are considered as well as conditions selected to increase the harmonics that are unfiltered by MBC. It is found that the direct periodic methods produce almost identical results to timeinvariant methods after MBC under all conditions studied. MBC is recommended for threebladed turbines, which can be followed by Floquet analysis or periodic control design methods if necessary.

Active aerodynamic blade control design for load reduction on large wind turbines

Abstract: Through numerical simulations that use trailing edge flaps as active aerodynamic load control devices on wind turbines that range from 0.6MW-5MW rated power, a 20-32% reduction in blade root flap bending moments was achieved. This allows the turbine blade lengths to be increased, without exceeding original fatigue damage on the system, resulting in larger swept rotor area. This study developed and simulated several independent flap control designs (including tip deflection and tip rate deflection feedback) that seamlessly integrated with existing pitch control strategies to reduce loads sufficiently to allow 10% rotor extension and increased energy capture (see reference [1] for methodology).

Lowering and raising a single wind turbine rotor blade from six-o'clock position

Abstract: A method and lifting arrangement for lowering and raising a single rotor blade of a wind turbine from a six-o'clock position is provided. Lifting fixtures are symmetrically installed on a hub surface about the rotor blade being replaced. Lifting lines from coordinated ground winches pass over the lifting fixtures to support the blade and attach to a blade harness. The blade harness attaches over a substantial length of the rotor blade, distributing the blade weight broadly. A tail pick crane facilitates transfer of the rotor blade between a vertical and a horizontal position stored position.

A Four-Quadrant Thrust Estimation Scheme for Marine Propellers: Theory and Experiments

Abstract: A thrust estimation scheme for marine propellers that can operate in the full four-quadrant range of the propeller shaft speed and the vessel speed has been developed. The scheme is formed by a nonlinear observer to estimate the propeller torque and the propeller shaft speed and by a mapping to compute the thrust from the observer estimates. The mapping includes the estimation of the propeller advance ratio. The advance speed is assumed to be unknown, and only measurements of shaft speed and motor torque have been used. The robustness of the scheme is demonstrated by Lyapunov theory. The proposed method is experimentally tested on an electrically driven fixed pitch propeller in open-water conditions, in waves and with a wake screen that scales the local flow down in order to simulate one of the effects of the interaction between the propeller and the vessel hull.

Exploring the Limits in Individual Pitch Control

Abstract: Individual pitch control (IPC) is an advanced wind turbine control method for fatigue load reduction. The conventional IPC algorithm (cyclic pitch control) aims at achieving 1p blade load reduction by mitigating the static rotor tilt and yaw moments. Besides these existing IPC methods, this paper presents a novel application of IPC: rotor balancing. Imperfections in the blades lead to aerodynamic and/or mass unbalance that result in variations at the rotational frequency 1p in the rotor tilt and yaw moments. The new IPC algorithm compensates for such rotor unbalance by adding quasi-steady offsets to the blade pitch angles. As a second contribution, an anti-windup߿ݠIPC implementation is proposed for dealing with blade actuator limitations. Detailed nonlinear simulations are used to validate the proposed IPC algorithms.

System and method for reducing rotor loads in a wind turbine upon detection of blade-pitch failure and loss of counter-torque

Abstract: A system and method for reducing rotor loads in a wind turbine that includes a brake and one or more rotor blades coupled to a rotor. Upon detection of a loss of counter torque and a blade-pitch failure in at least one rotor blade, a processor reduces a generator overspeed threshold value by a predetermined amount and determines a brake-release threshold value. The brake is applied to slow the rotor if the generator/rotor speed exceeds the reduced generator/rotor overspeed threshold value. In addition, the brake is applied to slow the rotor until the generator/rotor speed is below the brake-release threshold value. The rate of change of the pitch angle of the rotor blade may be varied as the blade moves toward feather in response to the detected blade-pitch failure.

Combined Feed-forward/Feedback Control of Wind Turbines to Reduce Blade Flap Bending Moments y

Abstract: In above rated conditions, wind turbines are often subjected to undesirable high structural loading. We investigate two feedback control techniques in combination with a feedforward control method for reducing blade ap bending loads in above rated wind conditions. The feedback controls studied include both disturbance accommodating/tracking and integral augmented/repetitive types that incorporate models of persistent disturbances at DC (step changes in wind) and at the once per revolution frequency. Each method is combined with a feed-forward method utilizing the wind speed as measured at the blade tips and also based on the blade tip average wind speed. Performance is assessed by simulating the combined feed-forward/feedback systems on a three bladed turbine model with the National Renewable Energy Lab’s FAST wind turbine code. It is found that feedforward of blade tip average wind speed measurements can provide signicant reduction of blade root loads and improved speed regulation in time varying wind that is uniform across the rotor plane. However, the improvements are not as great in non-uniform and turbulent conditions in which case the blade tip average wind speed measurements provide incomplete information for conditions that can be unique at each blade. We use an extension of the linearized turbine model to design feed-forward compensation that uses individual measurements of the wind at each blade tip. Results suggest that using blade local measurements provides substantially greater reduction in blade loads, but assessing the full potential of using this more detailed information requires more accurate modeling of the way perturbations local to each blade couple into the turbine.

Tilt Actuation for a Rotorcraft

Abstract: An aircraft is equipped with hingeless rotors on tilting nacelles, and the tilt angles of the nacelles are controlled using either or both of an actuator and a mast moment generated by a hingeless rotor. An aircraft with two or more rotors on tilting nacelles can achieve control of yaw orientation by differential tilt of its nacelles or masts. Hingeless rotors can be manipulated to control a tilt angle of a mast by changing the rotor blade pitch to produce a mast moment. The rotor and nacelle tilt of a tiltrotor rotorcraft can be controlled and effected in order to manipulate the yaw orientation and flight mode of a rotorcraft such as a tiltrotor. The use of mast moment to control nacelle tilt angle can reduce tilt actuator loads and allows for the control of nacelle tilt even in the event of an actuator failure.

System and method for controlling wind turbine actuation

Abstract: A wind turbine includes a plurality of wind turbine blades attached to a rotor positioned atop a tower affixed to a tower foundation. At least one blade pitch sensor is configured to measure blade pitch angles for one or more of the wind turbine blades. A rotor/generator speed sensor is configured to measure the rotational speed of the wind turbine rotor, a corresponding wind turbine generator, or both. A wind turbine nacelle yaw sensor is configured to measure the nacelle yaw, while at least two tower-base bending sensors are configured without use of adhesives, cements or bonding agents to provide large-area measurement of tower deflection. A controller is configured to adjust the pitch angle of one or more of the wind turbine blades in response to the measured one or more blade pitch angles, the measured rotational speed, the measured nacelle yaw and measured tower longitudinal deflection.

Pitch control for improving the low-voltage ride-through of wind farm

Abstract: One of the major concerns for the stability of power systems including large amount of wind turbine generators is how to improve the Low-Voltage Ride-Through (LVRT) capability of wind turbine generators during voltage dip occurring in power networks. In order to achieve LVRT improvement, this paper proposes a new method of pitch angle control for induction-generator-type of wind turbine. If the turbine rotor speed can be reduced quickly during voltage dip so as not to rise over the maximum speed, then the sudden disconnection of wind turbine generator can be avoided. The proposed pitch control system can modify the pitch angle in the short response time by the coordination of protective relay for wind turbine. The simulation study shows that the proposed pitch control system is effective to enhance LVRT capability of induction-generator type of wind turbine.

Condition monitoring system for wind turbine generator and method for operating wind turbine generator

Abstract: A wind turbine generator condition monitoring system (200) includes a plurality of rotor shaft angular velocity sensors (206/208) The system also includes at least one processor (216) coupled to the plurality of rotor shaft velocity sensors The at least one processor is programmed to determine a difference between each of the plurality of rotor shaft angular velocity sensors of at least one of an angular displacement, an angular velocity, and an angular acceleration of the rotor shaft An output of the at least one processor including at least one of a wind turbine generator yaw orientation signal (336) and a wind turbine generator blade pitch orientation signal (336)

Alleviation of unbalanced rotor loads by single blade controllers

Abstract: A novel approach to reducing the unbalance rotor loads by pitch control is presented in this paper. Each blade has its own actuator, sensors and controller. These localised blade control systems operate in isolation without need of communication with each other. This single blade control approach to regulation of unbalanced rotor loads has several advantages including being straightforward to design and easy to tune. Furthermore, it does not affect the operation of the central controller and the latter need not be re-designed when used in conjunction with the single blade controllers. Their performance is assessed using BLADED simulations.

Hydro turbine generator

Abstract: A hydroelectric turbine generator and control system is provided that optimizes the maximum possible power output at all times by strictly monitoring power output from the generator unit and modulating the wicket gate angle and the runner blade pitch independently of one another. The hydroelectric turbine generator includes a means for separately controlling wicket gate angle and runner blade pitch. The wicket gate angle control mechanism controls the flow into the system, pre conditions flow for maximum power and maintains reservoir level. The runner blade pitch control mechanism continuously monitors the system power output based on actual power produced, and adjusts system parameters in order to achieve maximum power output.

Combined Individual Pitch Control and Active Aerodynamic Load Controller Investigation for the 5MW UPWIND Turbine.

Abstract: This paper investigates the combined performance of Individual Blade Pitch (IPC) and Active Aerodynamic Load Control (AALC) applied to the 5MW UpWind reference turbine. IPC is an advanced wind turbine control method for fatigue load reduction. IPC is realized by reducing the 1p blade load through mitigation of the static rotor tilt and yaw moments. AALC uses trailing edge flap devices to reduce fatigue loads or bending moments. This work is motivated by assessing the benefit for the combination of using both approaches one which addresses low frequency (such as the 1p loading) and the other addresses, in addition, higher frequency loading on the blades. This study developed and simulated several IPC and AALC designs to reduce blade loads and potentially pitch duty cycles. The numerical simulations were performed on the NREL 5MW UpWind reference wind turbine model. Two IEC turbulent wind conditions (16 mps and 20 mps) were explored. Results are shown for pitch angles and rates, flap angles and rates, blade flapwise root moments, blade flapwise tip deflections, and flap bending moment power spectral density plots. Other relevant wind turbine components, such as tower moments were also monitored. This study shows that the combined controller designs, when compared with a baseline conventional collective pitch control strategy, demonstrate the trade-os, load reductions, and potential performance benefits for future large wind turbine control design.

Monitoring of wind turbines

Abstract: Method and apparatus for determining the deflection or curvature of a rotating blade, such as a wind turbine blade or a helicopter blade. Also, methods and apparatus for establishing an inertial reference system on a rotating blade.

Blade Pitch Angle Control and its Capacity Reduction Effect on Battery for Load Frequency Control in Power System with a Large Capacity of Wind Power Generation

Abstract: Considering interconnection of a large-capacity of wind power generation to the utility grid, it is of great concern that its output power fluctuation has adverse influences, e.g. frequency fluctuation. There have so far been some research works on installation of battery energy storage systems (BESS), as a solution of these problems. However, owing to very high cost of the BESS, its capacity should be as small as possible. In this paper, not only the installation of the BESS as one of measures of suppressing the frequency fluctuation caused by wind power generation, but also blade pitch angle control for blunting the output power of wind turbine generators (WTGs) is also considered. This paper proposes a coordinated control method of the BESS and the blade pitch angle, and evaluates reduction of the capacity of the BESS and the power generation loss caused by blunting the output power which should be originally generated by WTGs.

Method and system for controlling a wind turbine

Abstract: A control system for a wind turbine having a tower, a generator, and at least one rotor blade. The control system includes a sensor configured to measure an angle of inclination of the tower with respect to a surface, at least one pitch assembly configured to adjust a pitch angle of the rotor blade, and a controller configured to control at least one of the pitch assembly and the generator based on the measured angle of inclination.