WO2011150927A1 - Improved method and apparatus for measuring wind velocity - Google Patents

Improved method and apparatus for measuring wind velocity Download PDF

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Publication number
WO2011150927A1
WO2011150927A1 PCT/DK2011/050179 DK2011050179W WO2011150927A1 WO 2011150927 A1 WO2011150927 A1 WO 2011150927A1 DK 2011050179 W DK2011050179 W DK 2011050179W WO 2011150927 A1 WO2011150927 A1 WO 2011150927A1
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WO
WIPO (PCT)
Prior art keywords
wind
wind turbine
optical
sensor
broadband
Prior art date
Application number
PCT/DK2011/050179
Other languages
French (fr)
Inventor
Niels Anker Ho-Olesen
Jens Jakob Wedel-Heinen
Carsten Hein Westergaard
Original Assignee
Vestas Wind Systems A/S
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Publication of WO2011150927A1 publication Critical patent/WO2011150927A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D80/00—Details, components or accessories not provided for in groups F03D1/00 - F03D17/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/95—Lidar systems specially adapted for specific applications for meteorological use
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D17/00—Monitoring or testing of wind motors, e.g. diagnostics
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D7/00—Controlling wind motors 
    • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
    • F03D7/022—Adjusting aerodynamic properties of the blades
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P13/00—Indicating or recording presence, absence, or direction, of movement
    • G01P13/0006—Indicating or recording presence, absence, or direction, of movement of fluids or of granulous or powder-like substances
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P13/00—Indicating or recording presence, absence, or direction, of movement
    • G01P13/02—Indicating direction only, e.g. by weather vane
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
    • G01P5/26—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/30—Control parameters, e.g. input parameters
    • F05B2270/32—Wind speeds
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/30—Control parameters, e.g. input parameters
    • F05B2270/321—Wind directions
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2270/00—Control
    • F05B2270/80—Devices generating input signals, e.g. transducers, sensors, cameras or strain gauges
    • F05B2270/804—Optical devices
    • F05B2270/8042—Lidar systems
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction

Definitions

  • the present invention relates to wind turbines and more specifically to a wind turbine wind sensor having a broadband light source.
  • many wind turbines are provided with an anemometer or other type of wind sensor that provides information about the incident wind speed and direction. Such information is useful for monitoring the amount of wind available at the site for energy generation purposes.
  • the yaw of the wind turbine nacelle may be adjusted depending on the measured wind direction, so that the rotor blades face fully into the incident wind during times of energy production.
  • the pitch of the rotor blades may be adjusted depending on the wind speed, so that the amount of energy extracted from the incident wind can be carefully controlled to meet demand and satisfy other operational parameters. It is often necessary, for example, to angle the plane of the wind turbine rotor blades out of the wind, or to adjust the pitch of the rotor blades to spill the wind, to avoid structural problems or electrical overloads associated with wind speeds that are too high.
  • LIDAR Light Detection and Ranging
  • US 6,320,272 of Lading et al teaches the use of a laser wind velocity measurement system such as a LIDAR apparatus mounted on the nacelle of a wind turbine.
  • LIDAR operates by emitting a laser beam in front of the wind turbine to measure the conditions at a distance in front of the wind turbine.
  • the distance is typically arranged to be between 0.5 and 10 rotor diameters away from the turbine, which is therefore in the order of 50 to 300m for a large modern wind turbine.
  • LIDAR operates in a known manner by scattering radiation from natural aerosols (Mie scattering of dust, pollen, water droplets etc.) or off molecules exited by the laser light (Rayleigh scattering) and by measuring the Doppler shift between the outgoing and returning radiation in order to calculate information about the air flow.
  • This information may include wind speed and direction and wind shear in the vertical and horizontal directions, although the parameters that can be calculated will depend on the complexity of the LIDAR used.
  • the operational parameters of the wind turbine can be adjusted based on the future value of the wind, so that the wind turbine can operate more efficiently.
  • Scanning LIDAR systems are often used on wind turbines to measure the wind velocity vector more accurately. Scanning may be achieved, for example, by mounting a single beam Lidar in the hub or spinner of the rotor with the beam angled away from the axis of rotation of the hub. As the rotor rotates, the beam scans an area of the advancing wind front.
  • existing Lidar systems for wind turbines utilise a narrow wavelength laser beam which is focussed at a specific focal point in front of the wind turbine. The volume of the beam, which corresponds to the measurement volume of the Lidar, is therefore relatively small. In order to scan a desired area, it is therefore necessary to sweep the laser beam such that the focal point travels over the entire area to be measured. This process is time consuming and therefore does not allow the adjustment of the wind turbine parameters to be carried out as efficiently as would be desired. We have therefore appreciated the need to provide an improved wind turbine wind sensor which allows more efficient scanning.
  • a wind turbine optical wind sensor apparatus comprising: a broadband optical light source arranged to emit a broadband sensor beam for illuminating particles carried in the wind passing through the sensor beam; an arrangement of optical elements arranged to spread the broadband sensor beam into a sensor beam pattern; a light receiving device for detecting back- scattered light that has been reflected by the particles carried in the wind passing through the sensor beam pattern; and a controller for processing the light detected by the light receiving device to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.
  • a method of operating such a wind turbine optical sensor apparatus comprising: emitting a broadband sensor beam; dispersing the broadband sensor beam to form a dispersed beam pattern; receiving the back-scattered light that has been reflected by particles carried in the wind passing through the sensor beam; and processing the back-scattered light with a controller to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.
  • a method of controlling a wind turbine comprising measuring at least one of the wind speed and direction at a position upwind of the wind turbine using the method according to the first aspect of the invention as described above and based on the measured wind speed and direction, outputting one or more control signals from the controller for adjusting an operational parameter of the wind turbine.
  • narrowband refers to a radiation source emitting a beam of radiation having a relatively large bandwidth, a range of wavelengths, or multiple of discrete wavelengths originating from the same source.
  • the emitted sensor beam therefore contains a mixture of different frequencies or colours of light. Examples of such a source would be a high power super-continuum laser sources or a multi-line laser.
  • the apparatus and methods of the present invention advantageously allow a larger measurement area to be scanned more rapidly than using existing devices.
  • the invention uses a broadband laser source in combination with an arrangement of optical elements to form a dispersed beam in which the sensor beam has been dispersed or spread to form a dispersed beam pattern having a focal area that is greater than the focal point of the original sensor beam.
  • the volume of the sensor beam is increased such that measurements of the wind vector can be taken simultaneously at all of the points in the beam pattern.
  • This allows for a more rapid determination of the wind speed in front of the wind turbine such that the wind turbine can be operated in a more efficient manner in response to changes in the wind speed or direction.
  • the arrangement of optical elements of the present invention may be arranged such that the back-scattered light is compressed back into a single beam as it propagates backwards through the prismatic arrangement.
  • the apparatus further comprises a second arrangement of optical elements for dispersing the received beam in the same way as the original sensor beam so that a dispersed received beam is projected onto the light receiving device.
  • the shape and form of the sensor beam pattern will depend upon the optical elements incorporated into the apparatus and can be readily predicted on the basis of standard physics principles
  • the arrangement of optical elements for dispersing the broadband sensor beam comprises a prismatic arrangement for dispersing the different wavelengths of light in the broadband sensor beam in different directions.
  • the prismatic arrangement preferably comprises one or more two dimensional prisms which disperse the different wavelengths of light to form a two dimensional fan beam having a focal line substantially perpendicular to the axis of the beam. With this arrangement, it is possible to simultaneously measure the velocity distribution of the wind along the entire focal line.
  • Wave length sensitive splits can be made with holographic lens elements or diffraction gratings.
  • At least a part of the arrangement of optical elements for spreading the sensor beam is mounted for rotation or for oscillating back and forth.
  • the rotation or oscillation of the optical elements brings about the sweeping or scanning of the sensor beam pattern such that the air or wind conditions can be measured over a larger area and in different planes, to allow additional components of the three-dimensional wind vector to be measured.
  • the measurement area will be in a plane perpendicular to the direction of the sensor beam and at a substantially constant distance from the wind turbine.
  • the scanning of a sensor beam pattern rather than a sensor beam having a single focal point allows an area of a given size to be scanned far more rapidly.
  • the length of time required to cover an entire measurement area using a fan shaped beam is significantly less than that required to cover the same measurement area using a focussed sensor beam with a single measurement point.
  • the more rapidly the apparatus is able to scan a large measurement area the more effectively the wind turbine is able to adjust to account for future wind turbines and therefore the more efficiently the turbine is able to capture energy from the incident wind.
  • Scanning may also be achieved by mounting the apparatus in the hub or spinner of the rotor with the sensor beam angle away from the axis of rotation of the hub. As the rotor rotates, so the beam scans an area of the advancing wind front.
  • the apparatus according to the present invention is preferably a type of Doppler anemometer device that relies on the Doppler effect to measure wind velocity at a position upwind of the wind turbine.
  • an anemometer device that does not use the Doppler effect may be used.
  • the broadband optical light source is preferably a broadband laser that emits a broad spectrum laser beam. More preferably, the apparatus according to the invention comprises a Laser Doppler anemometer, such as a Lidar, with a broadband pulsed laser source. Suitable types of lasers include but are not limited to an Ar-lon laser and a high power super-continuum laser.
  • the Lidar used in preferred embodiments of the present invention operates in a known manner either by detecting air molecules or by detecting particles in the air stream and calculating information about the air flow from these measurements. This information may include wind speed direction and wind shear in the vertical and horizontal directions. It may also be possible with certain Lidar arrangements to detect air disturbances such as turbulence or gusts.
  • the wavelength of the broadband laser source is between 200 nm and 2000 nm.
  • the bandwidth ( ⁇ ) of the broadband laser source is at least 200 nm.
  • the light receiving device of the apparatus of the present invention will typically be in the form of a photodetector that detects the beam of back-scattered light reflected by particles within the air stream being illuminated by the sensor beam pattern.
  • the apparatus is a form of Doppler anemometer (as described above) the reflected or back-scattered light will be combined with a reference beam and the combined beam will be directed at the light receiving means.
  • the controller analyses the light beam in order to measure the Doppler shift of the back-scattered light relative to the reference beam and thereby determine the component of the air velocity in the direction of the sensor beam.
  • the reference beam typically corresponds to a portion of the sensor beam from the optical light source which has been separated from the main sensor beam using suitable optical means, such as a beam splitter.
  • the received light is preferably spread or dispersed before being projected onto the light receiving means.
  • the light receiving means must therefore be suitably adapted to receive the shape of the spread or dispersed beam.
  • the light receiving means is preferably a linear receiver.
  • the controller outputs one or more control signals for varying an operational parameter of the wind turbine.
  • the controller may be adapted to output a control signal to control a pitch actuation system for adjusting the pitch angle of one or more of the blades of the wind turbine based on the future expected wind speed and direction.
  • the pitch of the blades may be adjusted in order to maximise the energy extracted from the incident wind.
  • the blades can be angled out of the wind in order to avoid structural damage or electrical overloads.
  • the controller may be adapted to output a control signal in response to the detection of an extreme event, such as turbulence or a gust.
  • the control signal may comprise, for example, a yaw signal and/or a power signal.
  • the power signal may comprise a generator shutdown command, a rotor speed command, a generator power output command and/or a torque command.
  • the invention also provides a wind turbine with a wind sensor apparatus as described above installed on it.
  • the wind sensor apparatus may be mounted in any suitable position on the wind turbine but is preferably arranged to measure the wind velocity in front of the wind turbine.
  • a wind sensor apparatus according to the invention may be mounted, for example, on the wind turbine nacelle, the wind turbine tower or on one or more of the blades of the wind turbine rotor.
  • Figure 1 is a front view of a horizontal axis wind turbine
  • Figure 2 is a side view of the wind turbine of Figure 1 with the blades only partially shown;
  • FIG 3 is a schematic representation of the wind sensor apparatus mounted on the wind turbine of Figures 1 and 2.
  • Figure 1 illustrates a wind turbine 1 , comprising a wind turbine tower 2 on which a wind turbine nacelle 3 is mounted.
  • a wind turbine rotor 4 comprising at least one wind turbine blade 5 is mounted on the turbine.
  • a cup anemometer 6 and an ultrasonic wind sensor 7 are arranged on the upper surface of the nacelle 3.
  • the wind turbine illustrated in Figure 1 may be a small model intended for domestic or light utility usage, or for example may be a large model, such as those that are suitable for use in large scale electricity generation on a wind farm. In the latter case, the diameter of the rotor may be as large as 100 metres or more.
  • the invention is not limited to three bladed turbines although most commercial wind turbines use a three bladed rotor.
  • Wind sensor apparatus 10 is mounted on the upper surface of the nacelle 3 in order to measure the wind velocity at a position upwind of the wind turbine.
  • the wind sensor apparatus 10 includes a Lidar arrangement comprising an Ar-ion broadband laser source 12. As illustrated in Figure 3, the sensor beam 14 emitted by the laser source 12 passes through a beam splitter 16 which bends a small fraction of the sensor beam at approximately 90 degrees to form a reference beam 16. The remaining fraction of the sensor beam 14 continues forward to pass through a prismatic arrangement 18 which disperses the sensor beam 14 to form a fan shaped sensor beam 20 focused along a focal line, which lies substantially perpendicular to the sensor beam 14 from the wind turbine. The apparatus 10 senses the wind conditions along the focal line.
  • the prismatic arrangement 18 comprises a prism 22 which is mounted for rotation and through which the sensor beam 14 passes.
  • the rotation of the prism 22 during operation of the apparatus causes the fan shaped sensor beam 20 to scan so that the focal line sweeps over an area of the advancing wind front.
  • the sensor beam 20 As described above, particles in the air stream at the position of the focal line cause the sensor beam 20 to be reflected back towards the laser source 12.
  • the reflected beam 24 passes back through the prismatic arrangement 18 which compresses the dispersed reflected beam 24 into a single, narrow beam.
  • the beam splitter 16 bends a large fraction of the reflected beam at approximately 90 degrees towards a linear receiver 26.
  • the reflected beam Before reaching the linear receiver 26 the reflected beam passes through a second prismatic arrangement 28 which disperses the beam again so that the different wavelengths of the beam are projected at different points along the linear receiver 26.
  • the arrangement of the components described above is such that the reflected beam 24 mixes with the reference beam 14 before being projected onto the linear receiver 26.
  • the light signals received at the linear receiver 26 are processed by a controller (not shown) which determines wind velocity in a known manner from the measured Doppler shift of the reflected beam relative to the reference beam. Based on the determined wind velocity, the controller generates an output signal which is transmitted to the pitch actuator apparatus such that the pitch of the blades can be adjusted to suit the future wind conditions.

Abstract

A wind turbine optical wind sensor apparatus (10) comprises: a broadband optical light source (12) arranged to emit a broadband sensor beam (14) for illuminating particles carried in the wind passing through the sensor beam; an arrangement of optical elements(18) arranged to spread the broadband sensor beam (14) into a beam pattern (20); a light receiving device (26) for detecting back-scattered light that has been reflected by the particles carried in the wind passing through the sensor beam pattern; and a controller for processing the light detected by the light receiving device to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.

Description

IMPROVED METHOD AND APPARATUS FOR MEASURING WIND VELOCITY
The present invention relates to wind turbines and more specifically to a wind turbine wind sensor having a broadband light source.
In order to safely and efficiently extract energy from the wind, many wind turbines are provided with an anemometer or other type of wind sensor that provides information about the incident wind speed and direction. Such information is useful for monitoring the amount of wind available at the site for energy generation purposes. For example, the yaw of the wind turbine nacelle may be adjusted depending on the measured wind direction, so that the rotor blades face fully into the incident wind during times of energy production. Furthermore, the pitch of the rotor blades may be adjusted depending on the wind speed, so that the amount of energy extracted from the incident wind can be carefully controlled to meet demand and satisfy other operational parameters. It is often necessary, for example, to angle the plane of the wind turbine rotor blades out of the wind, or to adjust the pitch of the rotor blades to spill the wind, to avoid structural problems or electrical overloads associated with wind speeds that are too high.
Accurate information regarding wind speed and direction is therefore a crucial input in wind turbine control and monitoring systems.
It is known to employ mechanical anemometers, such as cup anemometers for the measurement of wind speed at a wind turbine. However, such mechanical anemometers are liable to fail through the accumulation of dirt and ice on their moving parts. Furthermore, mechanical anemometers are typically only capable of measuring the wind speed at the turbine. There is therefore an inevitable delay between the measurement of the wind speed by the anemometer and the adjustment of the nacelle or blades to compensate for the wind conditions. It is therefore preferable to measure the wind speed and direction a short distance ahead of the wind turbine so that the wind turbine can be adjusted in advance of any changes in wind condition.
The use of laser based wind sensors, such as those based on LIDAR (Light Detection and Ranging) is known. For example. US 6,320,272 of Lading et al teaches the use of a laser wind velocity measurement system such as a LIDAR apparatus mounted on the nacelle of a wind turbine. LIDAR operates by emitting a laser beam in front of the wind turbine to measure the conditions at a distance in front of the wind turbine. The distance is typically arranged to be between 0.5 and 10 rotor diameters away from the turbine, which is therefore in the order of 50 to 300m for a large modern wind turbine. LIDAR operates in a known manner by scattering radiation from natural aerosols (Mie scattering of dust, pollen, water droplets etc.) or off molecules exited by the laser light (Rayleigh scattering) and by measuring the Doppler shift between the outgoing and returning radiation in order to calculate information about the air flow. This information may include wind speed and direction and wind shear in the vertical and horizontal directions, although the parameters that can be calculated will depend on the complexity of the LIDAR used. The operational parameters of the wind turbine can be adjusted based on the future value of the wind, so that the wind turbine can operate more efficiently.
Scanning LIDAR systems are often used on wind turbines to measure the wind velocity vector more accurately. Scanning may be achieved, for example, by mounting a single beam Lidar in the hub or spinner of the rotor with the beam angled away from the axis of rotation of the hub. As the rotor rotates, the beam scans an area of the advancing wind front. However, existing Lidar systems for wind turbines utilise a narrow wavelength laser beam which is focussed at a specific focal point in front of the wind turbine. The volume of the beam, which corresponds to the measurement volume of the Lidar, is therefore relatively small. In order to scan a desired area, it is therefore necessary to sweep the laser beam such that the focal point travels over the entire area to be measured. This process is time consuming and therefore does not allow the adjustment of the wind turbine parameters to be carried out as efficiently as would be desired. We have therefore appreciated the need to provide an improved wind turbine wind sensor which allows more efficient scanning.
According to a first aspect of the invention there is provided a wind turbine optical wind sensor apparatus comprising: a broadband optical light source arranged to emit a broadband sensor beam for illuminating particles carried in the wind passing through the sensor beam; an arrangement of optical elements arranged to spread the broadband sensor beam into a sensor beam pattern; a light receiving device for detecting back- scattered light that has been reflected by the particles carried in the wind passing through the sensor beam pattern; and a controller for processing the light detected by the light receiving device to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.
According to a second aspect of the present invention there is provided a method of operating such a wind turbine optical sensor apparatus comprising: emitting a broadband sensor beam; dispersing the broadband sensor beam to form a dispersed beam pattern; receiving the back-scattered light that has been reflected by particles carried in the wind passing through the sensor beam; and processing the back-scattered light with a controller to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.
According to a third aspect of the present invention there is provided a method of controlling a wind turbine comprising measuring at least one of the wind speed and direction at a position upwind of the wind turbine using the method according to the first aspect of the invention as described above and based on the measured wind speed and direction, outputting one or more control signals from the controller for adjusting an operational parameter of the wind turbine.
The term "broadband" refers to a radiation source emitting a beam of radiation having a relatively large bandwidth, a range of wavelengths, or multiple of discrete wavelengths originating from the same source. The emitted sensor beam therefore contains a mixture of different frequencies or colours of light. Examples of such a source would be a high power super-continuum laser sources or a multi-line laser.
The apparatus and methods of the present invention advantageously allow a larger measurement area to be scanned more rapidly than using existing devices. The invention uses a broadband laser source in combination with an arrangement of optical elements to form a dispersed beam in which the sensor beam has been dispersed or spread to form a dispersed beam pattern having a focal area that is greater than the focal point of the original sensor beam. In this way, the volume of the sensor beam is increased such that measurements of the wind vector can be taken simultaneously at all of the points in the beam pattern. This in turn allows for a more rapid determination of the wind speed in front of the wind turbine such that the wind turbine can be operated in a more efficient manner in response to changes in the wind speed or direction.
The arrangement of optical elements of the present invention may be arranged such that the back-scattered light is compressed back into a single beam as it propagates backwards through the prismatic arrangement. In this case, preferably the apparatus further comprises a second arrangement of optical elements for dispersing the received beam in the same way as the original sensor beam so that a dispersed received beam is projected onto the light receiving device.
The shape and form of the sensor beam pattern will depend upon the optical elements incorporated into the apparatus and can be readily predicted on the basis of standard physics principles
Preferably, the arrangement of optical elements for dispersing the broadband sensor beam comprises a prismatic arrangement for dispersing the different wavelengths of light in the broadband sensor beam in different directions. This forms a fan or cone shaped beam in which each wavelength of light is refracted at a different angle. The prismatic arrangement preferably comprises one or more two dimensional prisms which disperse the different wavelengths of light to form a two dimensional fan beam having a focal line substantially perpendicular to the axis of the beam. With this arrangement, it is possible to simultaneously measure the velocity distribution of the wind along the entire focal line. There are several other ways that a split can be made. Wave length sensitive splits can be made with holographic lens elements or diffraction gratings.
In particularly preferred embodiments of the present invention, at least a part of the arrangement of optical elements for spreading the sensor beam is mounted for rotation or for oscillating back and forth. The rotation or oscillation of the optical elements brings about the sweeping or scanning of the sensor beam pattern such that the air or wind conditions can be measured over a larger area and in different planes, to allow additional components of the three-dimensional wind vector to be measured. Typically, the measurement area will be in a plane perpendicular to the direction of the sensor beam and at a substantially constant distance from the wind turbine.
The scanning of a sensor beam pattern rather than a sensor beam having a single focal point allows an area of a given size to be scanned far more rapidly. For example, in the case of a prismatic arrangement, the length of time required to cover an entire measurement area using a fan shaped beam is significantly less than that required to cover the same measurement area using a focussed sensor beam with a single measurement point. The more rapidly the apparatus is able to scan a large measurement area, the more effectively the wind turbine is able to adjust to account for future wind turbines and therefore the more efficiently the turbine is able to capture energy from the incident wind.
Scanning may also be achieved by mounting the apparatus in the hub or spinner of the rotor with the sensor beam angle away from the axis of rotation of the hub. As the rotor rotates, so the beam scans an area of the advancing wind front.
The apparatus according to the present invention is preferably a type of Doppler anemometer device that relies on the Doppler effect to measure wind velocity at a position upwind of the wind turbine. However, it could be envisaged that an anemometer device that does not use the Doppler effect may be used.
The broadband optical light source is preferably a broadband laser that emits a broad spectrum laser beam. More preferably, the apparatus according to the invention comprises a Laser Doppler anemometer, such as a Lidar, with a broadband pulsed laser source. Suitable types of lasers include but are not limited to an Ar-lon laser and a high power super-continuum laser.
The Lidar used in preferred embodiments of the present invention operates in a known manner either by detecting air molecules or by detecting particles in the air stream and calculating information about the air flow from these measurements. This information may include wind speed direction and wind shear in the vertical and horizontal directions. It may also be possible with certain Lidar arrangements to detect air disturbances such as turbulence or gusts. Preferably, the wavelength of the broadband laser source is between 200 nm and 2000 nm.
Preferably, the bandwidth (□□) of the broadband laser source is at least 200 nm. The light receiving device of the apparatus of the present invention will typically be in the form of a photodetector that detects the beam of back-scattered light reflected by particles within the air stream being illuminated by the sensor beam pattern. Typically, where the apparatus is a form of Doppler anemometer (as described above) the reflected or back-scattered light will be combined with a reference beam and the combined beam will be directed at the light receiving means. The controller analyses the light beam in order to measure the Doppler shift of the back-scattered light relative to the reference beam and thereby determine the component of the air velocity in the direction of the sensor beam.
The reference beam typically corresponds to a portion of the sensor beam from the optical light source which has been separated from the main sensor beam using suitable optical means, such as a beam splitter. As described above, the received light is preferably spread or dispersed before being projected onto the light receiving means. The light receiving means must therefore be suitably adapted to receive the shape of the spread or dispersed beam. For example, where a prism is used to disperse the light into a fan shaped beam, the light receiving means is preferably a linear receiver.
Preferably, the controller outputs one or more control signals for varying an operational parameter of the wind turbine. For example, the controller may be adapted to output a control signal to control a pitch actuation system for adjusting the pitch angle of one or more of the blades of the wind turbine based on the future expected wind speed and direction. Under normal wind conditions, the pitch of the blades may be adjusted in order to maximise the energy extracted from the incident wind. Alternatively, if the detected wind speed is too high, the blades can be angled out of the wind in order to avoid structural damage or electrical overloads.
Alternatively or in addition, the controller may be adapted to output a control signal in response to the detection of an extreme event, such as turbulence or a gust. The control signal may comprise, for example, a yaw signal and/or a power signal. The power signal may comprise a generator shutdown command, a rotor speed command, a generator power output command and/or a torque command.
The invention also provides a wind turbine with a wind sensor apparatus as described above installed on it. The wind sensor apparatus may be mounted in any suitable position on the wind turbine but is preferably arranged to measure the wind velocity in front of the wind turbine. A wind sensor apparatus according to the invention may be mounted, for example, on the wind turbine nacelle, the wind turbine tower or on one or more of the blades of the wind turbine rotor. Embodiments of the invention will now be further described, by way of example only, and with reference to the accompanying figures in which:
Figure 1 is a front view of a horizontal axis wind turbine;
Figure 2 is a side view of the wind turbine of Figure 1 with the blades only partially shown; and
Figure 3 is a schematic representation of the wind sensor apparatus mounted on the wind turbine of Figures 1 and 2.
Figure 1 illustrates a wind turbine 1 , comprising a wind turbine tower 2 on which a wind turbine nacelle 3 is mounted. A wind turbine rotor 4 comprising at least one wind turbine blade 5 is mounted on the turbine. A cup anemometer 6 and an ultrasonic wind sensor 7 are arranged on the upper surface of the nacelle 3. The wind turbine illustrated in Figure 1 may be a small model intended for domestic or light utility usage, or for example may be a large model, such as those that are suitable for use in large scale electricity generation on a wind farm. In the latter case, the diameter of the rotor may be as large as 100 metres or more. The invention is not limited to three bladed turbines although most commercial wind turbines use a three bladed rotor.
Wind sensor apparatus 10 is mounted on the upper surface of the nacelle 3 in order to measure the wind velocity at a position upwind of the wind turbine. The wind sensor apparatus 10 includes a Lidar arrangement comprising an Ar-ion broadband laser source 12. As illustrated in Figure 3, the sensor beam 14 emitted by the laser source 12 passes through a beam splitter 16 which bends a small fraction of the sensor beam at approximately 90 degrees to form a reference beam 16. The remaining fraction of the sensor beam 14 continues forward to pass through a prismatic arrangement 18 which disperses the sensor beam 14 to form a fan shaped sensor beam 20 focused along a focal line, which lies substantially perpendicular to the sensor beam 14 from the wind turbine. The apparatus 10 senses the wind conditions along the focal line.
The prismatic arrangement 18 comprises a prism 22 which is mounted for rotation and through which the sensor beam 14 passes. The rotation of the prism 22 during operation of the apparatus causes the fan shaped sensor beam 20 to scan so that the focal line sweeps over an area of the advancing wind front.
As described above, particles in the air stream at the position of the focal line cause the sensor beam 20 to be reflected back towards the laser source 12. The reflected beam 24 passes back through the prismatic arrangement 18 which compresses the dispersed reflected beam 24 into a single, narrow beam. The beam splitter 16 bends a large fraction of the reflected beam at approximately 90 degrees towards a linear receiver 26. Before reaching the linear receiver 26 the reflected beam passes through a second prismatic arrangement 28 which disperses the beam again so that the different wavelengths of the beam are projected at different points along the linear receiver 26.
The arrangement of the components described above is such that the reflected beam 24 mixes with the reference beam 14 before being projected onto the linear receiver 26. The light signals received at the linear receiver 26 are processed by a controller (not shown) which determines wind velocity in a known manner from the measured Doppler shift of the reflected beam relative to the reference beam. Based on the determined wind velocity, the controller generates an output signal which is transmitted to the pitch actuator apparatus such that the pitch of the blades can be adjusted to suit the future wind conditions.

Claims

CLAIMS:
1. A wind turbine optical wind sensor apparatus comprising:
a broadband optical light source arranged to emit a broadband sensor beam for illuminating particles carried in the wind passing through the sensor beam;
an arrangement of optical elements arranged to spread the broadband sensor beam into a beam pattern;
a light receiving device for detecting back-scattered light that has been reflected by the particles carried in the wind passing through the sensor beam pattern; and
a controller for processing the light detected by the light receiving device to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.
2. The wind turbine optical wind sensor apparatus according to claim 1 wherein the arrangement of optical elements comprises a prismatic arrangement for dispersing the different wavelengths of light in the sensor beam in different directions to form a dispersed sensor beam.
3. The wind turbine optical wind sensor apparatus according to claim 2 further comprising a second prism for dispersing the different wavelengths of the back-scattered light to form a dispersed received beam to be projected onto the light receiving device.
4. The wind turbine optical wind sensor apparatus according to claim 1 wherein the arrangement of optical elements comprises a polarisation filter or a holographic lens.
5. The wind turbine optical wind sensor apparatus according to any preceding claim wherein the arrangement of optical elements for spreading the broadband sensor beam is mounted for rotation.
6. The wind turbine optical wind sensor apparatus according to any of claims 1 to 4 wherein the arrangement of optical elements for spreading the broadband sensor beam is mounted for oscillating back and forth.
7. The wind turbine optical wind sensor apparatus according to any preceding claim wherein the broadband optical light source is a broadband laser source, preferably a pulsed broadband laser source.
8. The wind turbine optical wind sensor apparatus according to claim 7 wherein the wavelength of broadband laser source is preferably between 700 nm and 1000 nm.
9. The wind turbine optical wind sensor apparatus according to claim 7 or 8 wherein the bandwidth of the broadband laser source is greater than 200 nm.
10. The wind turbine optical wind sensor apparatus according to any preceding claim wherein the controller detects wind turbulence or a gust from the light detected by the light receiving device.
1 1. The wind turbine optical wind sensor apparatus according to any preceding claim wherein the controller outputs one or more control signals for varying an operational parameter of the wind turbine.
12. A wind turbine comprising the wind sensor apparatus according to any preceding claim.
13. The wind turbine according to claim 12 wherein the wind sensor apparatus is mounted on the wind turbine nacelle, the wind turbine tower or a blade of the wind turbine rotor.
14. A method of operating a wind turbine wind sensor apparatus comprising:
emitting a broadband sensor beam;
spreading the broadband sensor beam to form a sensor beam pattern;
receiving the back-scattered light that has been reflected by particles carried in the wind passing through the sensor beam pattern; and
processing the back-scattered light with a controller to determine at least one of the speed and direction of the particles reflecting the light and the wind in which the particles are carried.
15. A method of controlling a wind turbine comprising sensing at least one of the wind speed and direction at a position upwind of the wind turbine using the method of claim 14 and based on the measured wind speed and direction, outputting one or more control signals from the controller for adjusting an operational parameter of the wind turbine.
16. A method of controlling a wind turbine according to claim 15 comprising outputting a control signal to control a pitch actuation system for adjusting the pitch angle of one or more of the blades of the wind turbine.
17. An apparatus substantially as described herein and with reference to the drawings.
18. A method substantially as described herein and with reference to the drawings.
PCT/DK2011/050179 2010-05-29 2011-05-27 Improved method and apparatus for measuring wind velocity WO2011150927A1 (en)

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GB1009679A GB2480701A (en) 2010-05-29 2010-06-09 Method and apparatus for optically measuring wind velocity

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