A METHOD AND A SYSTEM FOR TRACKING MOTION OF A BLADE

Abstract

The present invention relates to a method and a system for tracking the motion of a blade of a wind turbine. One embodiment relates to a blade motion tracking system for installation on a wind turbine blade, where the wind turbine blade comprises a blade root and a blade tip. The system comprises at least one light module comprising at least a first light source, preferably adapted to emit light in the direction of the blade root. An optical measuring device is provided, preferably located at the blade root, adapted to receive light emitted from the first light source(s). The optical measuring device is preferably a position sensitive detector identifying the position of the first light source relative to the position sensitive detector. A single light source located at the tip of the blade, close to the tip of the or towards the tip of the blade, is sufficient to measure deflection of the blade. Advantageously the first light source is modulated with a predefined modulation frequency such that light from the first light source can be distinguished from ambient light and thereby minimize the influence of the ambient light conditions during detection.

Claims

1. A blade motion tracking system for installation on a wind turbine blade, where the wind turbine blade comprises a blade root and a blade tip, and a leading edge and a trailing edge with a chord length extending therebetween of each blade section; said system comprising at least one light module comprising a first light source in a blade section at a predetermined distance from the blade root, said first light source configured for having a predefined modulation frequency, and an optical measuring device adapted to receive light emitted from the first light source, and wherein the optical measuring device comprises at least one position sensitive detector (PSD) for identifying the position of the first light source relative to the position sensitive detector, and wherein the optical measuring device is configured for distinguishing the first light source from ambient light conditions based on the predefined modulation frequency.

2. The system according to claim 1, wherein the light module is provided near the tip of the blade.

3. The system according to claim 1, wherein the optical measuring device, or at least a PSD thereof, is provided at the blade root.

4. The system according to claim 1, wherein the PSD is a one-dimensional PSD.

5. The system according to claim 1, wherein the PSD is at least a two-dimensional PSD.

6. The system according to claim 1, wherein the PSD is a non-discrete PSD.

7. The system according to claim 1, wherein the light module comprises at least a second light source, adapted to emit light in the direction of the blade root, the first and second light sources provided on or near the leading edge and the trailing edge respectively in a blade section at a predetermined distance from the blade root, and wherein the optical measuring device is configured for receiving light emitted from the light sources, and wherein the PSD is at least a two-dimensional PSD configured for identifying the position of each of the first and second light sources relative to the PSD.

8. The system according to claim 7, wherein the second light source is modulated with a predefined modulation frequency, which is different from the modulation frequency of the first light source, and wherein the optical measuring device is configured for distinguishing the first light and second light sources 1) from each other based on the different modulation frequencies, and 2) from ambient light conditions based on the predefined modulation frequencies.

9. The system according to claim 1, wherein the position sensitive detector is provided with a lens and an optical filter adapted to receive the light from the light source(s)s through said lens and said filter.

10. The system according to claim 1, wherein the position sensitive detector further comprises a signal processing system for demodulating an output signal from the PSD to identify the relative position of the first light source and optionally the second light source.

11. The system according to claim 1, wherein one or more further light modules are provided in one or more blade sections between the root and the tip region, and wherein the optical measuring device is capable of identifying each of the light sources in the multiple light modules.

12. The system according to claim 7, wherein a multiple of modulation frequencies are used for the light sources.

13. The system according to claim 1, wherein the light source(s) is an LED.

14. The system according to claim 1, wherein the light source(s) is a laser.

15. (canceled)

16. A method for tracking the motion of a blade of a wind turbine, where the wind turbine blade comprises a blade root and a blade tip, and a leading edge and a trailing edge with a blade section extending therebetween of each blade section; the method comprising the steps of: providing at least a first light module comprising at least a first light source modulated with a predefined modulation frequency; providing a position sensitive detector (PSD), preferably at the blade root, adapted to receive light emitted from the first light source of said first light module, and distinguishing the first light source from ambient light by means of the predefined modulation frequency, and identifying the relative position of first light source, by means of the position sensitive detector.

17. The method according to claim 16 wherein the at least first light module further comprises at least a second light source, and wherein the first and second light sources are provided on the leading edge and the trailing edge, respectively, in a predetermined blade section, preferably near the blade tip, said first and second light sources being frequency modulated with different predefined modulation frequencies, providing an optical measuring device, preferably at the blade root, adapted to receive the light emitted from the light sources of said first light module, and distinguishing each light source based on the different modulation frequencies and identifying the relative position of each of the light sources in the position sensitive detector.

18. The method according to claim 16, wherein the light module is provided near or on the tip of the blade.

19. The method according to claim 16, wherein the optical measuring device, or at least a PSD thereof, is provided at the blade root.

20. The method according to claim 16, wherein the PSD is a one-dimensional PSD.

21. The method according to claim 16, wherein the PSD is a non-discrete PSD.

22. The method according to claim 16, whereby the method is performed with a data rate allowing for real-time tracking of the blade motion.

23. The method according to claim 16, whereby the tracking of the blade motion includes a plurality of light modules with light sources on the leading edge and trailing edge of a multiple of blade sections.

24. The method according to claim 16, whereby the light sources are synchronised.

25. (canceled)

26. The method according to claim 16, whereby the light source(s) is/are provided on a rear side of the wind turbine blades.

27. A method of controlling a wind turbine having a rotor with a plurality of wind turbine blades, the wind turbine having a blade motion tracking system comprising: at least one light module comprising a first light source in a blade section at a predetermined distance from a blade root, said first light source configured for having a predefined modulation frequency, and an optical measuring device adapted to receive light emitted from the first light source, and wherein the optical measuring device comprises at least one position sensitive detector (PSD) for identifying the position of the first light source relative to the position sensitive detector, and wherein the optical measuring device is configured for distinguishing the first light source from ambient light conditions based on the predefined modulation frequency; wherein at least a wind turbine blade pitch and a yaw of the rotor are controlled using measurements of blade tracking by performing a method according to claim 16.

Description

DESCRIPTION OF DRAWINGS

[0035] In the following the invention is described with reference to the accompanying drawings, in which:

[0036] FIG. 1 is a schematic perspective view of a wind turbine to which the invention pertains;

[0037] FIG. 2 is a perspective schematic view of an embodiment of the invention;

[0038] FIG. 3 is a schematic illustration of a position sensitive detector according to an embodiment of the invention;

[0039] FIG. 4 is a schematic illustration of the image of two light spots on a position sensor detector;

[0040] FIG. 5 is a block diagram for non-synchronized blade bending detection according to one embodiment of the invention.

[0041] FIG. 6 is a block diagram for non-synchronized blade bending and blade torsion detection according to one embodiment of the invention.

[0042] FIG. 7 is a block diagram for synchronized blade bending detection according to another embodiment of the invention.

[0043] FIG. 8 is a block diagram for synchronized blade bending and blade torsion detection according to another embodiment of the invention.

[0044] FIG. 9 shows experimental results demonstrating measurement of bending with two light sources and a non-discrete PSD.

[0045] FIG. 10 shows experimental results demonstrating measurement of torsion with two light sources and a non-discrete PSD.

DETAILED DESCRIPTION

[0046] FIG. 1 shows a wind turbine of the kind to which the invention pertains. The wind turbine comprises a substantially vertical tower 2, a nacelle 4 and a rotor with a substantially horizontal rotor shaft. The rotor includes three blades 6 mounted in a hub 8. The blades 6 extend radially from the hub 8, and comprise a blade root 10 where the blades 6 are mounted to the hub 8 and a blade tip 12 furthest from the hub 8. The blades 6 have a leading edge 18 and a trailing edge 20.

[0047] In the blade tip 12, a light module 14 is provided. The light module 14 comprises a first light source 14′ on the leading edge 18 of the blade 6 and a second light source 14″ on the trailing edge 20 of the blade 6. The light sources 14′, 14″ are directed along the blade 6 on which they are mounted toward the hub 8. On the hub 8 at the foot of each blade 6 or at the blade root 10, an optical measurement device 16 is provided.

[0048] With reference also to FIGS. 2 and 3, the optical measuring device 16 and two light sources 14′, 14″ are mounted on a particular blade cross-section of the blade 6. The optical measuring device 16 is mounted on the blade root 10 and pointed towards the light sources 14′, 14″. The blades of the rotor will bend during operation. The light sources 14′, 14″ and the optical measuring device 16 are provided on the rear side of the blades 6, i.e. the suction side of the blade at the leeward (or downwind) side during operation in order to ensure an uninterrupted visible connected between the components when the blade 6 bends during operation due to the wind loading. The area of vision of the optical measuring device 16 is aligned with the blade coordinate system and its size at the light sources 14′, 14″ is large (as indicated by the x-y coordinate system 22 at the position of the light sources 14′, 14″) and designed to fit the possible motion of the blade section of the light sources 14′, 14″. As an example, the light sources 14′, 14″ can be produced by optical fibers connected to a source at the blade root 10, or by self-sustained LEDs with a gravity-based power generator. Inside the optical measuring device 16, the light sources are projected onto a position sensitive detector (PSD) 24, where a lens 28 and an optical filter 30 has collected and focused the light into the dots 26′ and 26″ corresponding to the leading edge 18 and trailing edge 20, respectively.

[0049] FIG. 4 illustrates ideally how the image of two light spots from two light sources 14′, 14″ is located on the front surface of the PSD module 24 under three different blade bending conditions, neutral position, only blade bending and with both blade bending and blade torsion present.

[0050] By using the PSD 24 according to the invention, it is possible to achieve on-line tracking of the blade motion with a sufficiently high data rate that can monitor the oscillations and vibrations in the blade in real-time. With reference to FIGS. 5 and 6, examples are described of how the signal processing may be carried out.

[0051] FIG. 5 shows an example in the form of a block diagram for non-synchronized blade bending detection according to one embodiment of the invention.

[0052] In this non-synchronized detection scheme, the light source 14 frequency modulated with frequency f matched to the center frequency fc of a bandpass filter 27, to minimize background light influence. As an example, the frequency f could be 1000 Hz. In front of the optical based PSD 24 both a focusing lens 28 and an optical bandpass filter 30 with a center wavelength matched to the emission wavelength of the light source 14 are mounted. The optical filter 30 reduces significantly the influence of ambient light distortion on the optical detector 24. However, also a predefined frequency modulation of the light source 14 help to distinguish the light source 14 from the ambient light. In the signal conditioning device 32, the output current from the PSD 24 is converted to voltage, amplified, noise filtered and conditioned according to the specific PSD 24 used. A typical PSD module 24 has four output signals, from which the X and Y components can be calculated. After the signals have passed through bandpass filter 27 the x- and y-positions for light source 14 are available. In order to determine the actual blade bending θ, an arithmetic calculation can to be carried out in the angle computation device 34.

[0053] FIG. 6 shows an example block diagram for non-synchronized blade bending and blade torsion detection according to one embodiment of the invention.

[0054] In this non-synchronized detection scheme, each of the two light sources 14′, 14″ are frequency modulated with frequencies f.sub.1 and f.sub.2 matched to the center frequencies f.sub.c1 and f.sub.c2 of a first bandpass filter 27′ and a second bandpass filter 27″, respectively, to minimize background light influence. As an example, the frequencies could be 1000 Hz and 3000 Hz, respectively. In front of the optical based PSD 24 both a focusing lens 28 and an optical bandpass filter 30 with a center wavelength matched to the emission wavelength of the light sources 14′, 14″ are mounted. The optical filter 30 reduces significantly the influence of ambient light distortion on the optical detector 24. However, also a predefined frequency modulation of the light sources help to distinguish the light sources from the ambient light. In the signal conditioning device 32, the output currents from the PSD 24 is converted to voltages, amplified, noise filtered and conditioned according to the specific PSD 24 used. A typical PSD module 24 has four output signals, from which the X and Y components can be calculated. After the signals have passed through bandpass filters 27′ and 27″, respectively the x- and y-positions for light sources 14′ and 14″ are available. In order to determine the actual blade bending θ and blade torsion φ, arithmetic calculations can to be carried out in the angle computation device 34.

[0055] FIG. 7 shows an example block diagram for synchronized blade bending detection according to another embodiment of the invention. The synchronized detection is found advantageous as the signal-to-noise ratio can be improved and that the light intensity and thereby the power consumption of the light sources thereby can be reduced.

[0056] In this synchronized detection scheme, the light source is frequency modulated with frequency f determined by the modulator 36. As an example, the frequency could be 1000 Hz. In front of the optical based PSD 24 both a focusing lens 28 and an optical bandpass filter 30 with a center wavelength matched to the emission wavelength of the light source 14 is mounted. The optical filter 30 reduces significantly the influence of ambient light distortion on the optical detector 24. In the signal conditioning device 32, the output current from the PSD 24 is converted to voltage, amplified, noise filtered and conditioned according to the specific PSD 24 used. A typical PSD module 24 has four output signals, from which the X and Y components can be calculated. In the Demodulators 38 the modulator signal is mixed with the conditioned signals from the PSD module 24. The output from the demodulators 38 is lowpass filtered with a frequency corresponding to the required time constant of the overall system. After proper signal filtering the x and y-positions for light source 14 are available. In order to determine the actual blade bending θ, an arithmetic calculation can to be carried out in the angle computation device 34.

[0057] FIG. 8 shows an example block diagram for synchronized blade bending and blade torsion detection according to another embodiment of the invention. The synchronized detection is found advantageous as the signal-to-noise ratio can be improved and that the light intensity and thereby the power consumption of the light sources thereby can be reduced.

[0058] In this synchronized detection scheme, each of the two light sources are frequency modulated with two different frequencies f.sub.1 and f.sub.2 determined by the modulators 36′ and 36″. As an example, the frequencies could be 1000 Hz and 3000 Hz respectively. In front of the optical based PSD 24 both a focusing lens 28 and an optical bandpass filter 30 with a center wavelength matched to the emission wavelength of the light sources 14′, 14″ are mounted. The optical filter 30 reduces significantly the influence of ambient light distortion on the optical detector 24. In the signal conditioning device 32, the output currents from the PSD 24 are converted to voltages, amplified, noise filtered and conditioned according to the specific PSD 24 used. A typical PSD module 24 has four output signals, from which the X and Y components can be calculated. In the Demodulators 38′ and 38″ the modulator signals are mixed with the conditioned signals from the PSD module 24. The output from the demodulators 38′, 38″ are lowpass filtered with a frequency corresponding to the required time constant of the overall system. After proper signal filtering the x and y-positions for light source 14′ and 14″ are available. In order to determine the actual blade bending θ and blade torsion φ, arithmetic calculations can to be carried out in the angle computation device 34. Thus, the determination of the blade motion by edgewise and flapwise translations and torsional rotation can be detected in real time and can be used for controlling the wind turbine during its operation. By the present disclosure it is further realized that more blade sections can be tracked by using more light modules 14 with light sources 14′, 14″ having different modulation frequencies.

[0059] FIG. 9 shows experimental results demonstrating measurement of bending with two light sources and a non-discrete PSD (S 1880 Hamamatsu) and a 50 mm focusing lens, 5 m from two LED light sources having 11 cm center distance. The total 50 cm light source bending was in the x-direction of the set-up. The radiant power of each lamp is 2.6 Wand the NIR wavelength is 850 nm. The modulation frequencies are 2.5 and 5 kHz respectively. Data are digitized using a DAQ card from National Instruments with a sampling rate of 50 kHz. The signal processing is carried out using Matlab software. As seen from this experiment bending can be measured by means of a single light source and/or a one-dimensional PSD because the X-position does not change.

[0060] FIG. 10 shows experimental results demonstrating measurement of torsion with two light sources and a non-discrete PSD. FIG. 8 shows experimental results using a PSD (S1880 Hamamatsu) and a 50 mm focusing lens, 5 m from two LED light sources having 11 cm center distance. The light sources demonstrated a maximum 16-degree torsion. The radiant power of each lamp is 2.6 Wand the NIR wavelength is 850 nm. The modulation frequencies are 2.5 and 5 kHz respectively. Data are digitized using a DAQ card from National Instruments with a sampling rate of 50 kHz. The signal processing is carried out using Matlab software.

[0061] The invention is described above with reference to some currently preferred embodiments. It is however realized that other variants and embodiments can be carried out without departing from the accompanying claims.

Further Details of the Present Disclosure

[0062] 1. A blade motion tracking system for installation on a wind turbine blade, where the wind turbine blade comprises a blade root and a blade tip, and a leading edge and a trailing edge with a chord length extending therebetween of each blade section; said system comprising [0063] at least one light module comprising a first light source and a second light source provided on or close to the leading edge and the trailing edge respectively in a blade section at a predetermined distance from the blade root, said first and second light sources being adapted to emit light in the direction of the blade root; [0064] an optical measuring device is provided at the blade root adapted to receive the light emitted from the light sources, and wherein the optical measuring device is a position sensitive detector identifying the position of each of the first and second light sources relative to the position sensitive detector. [0065] 2. A system according to item 1, wherein the light module is provided near the tip of the blade. [0066] 3. A system according to item 1 or 2, wherein the position sensitive detector is provided with a lens and an optical filter adapted to receive the light from the first and second light sources through said lens and said filter. [0067] 4. A system according to any one of the preceding items, wherein the first and second light sources are frequency modulated. [0068] 5. A system according to any one of the preceding items, wherein the position sensitive detector further comprises a signal processing system for demodulating the output signal to identify the relative position each of the first and second light sources. [0069] 6. A system according to any one of the preceding items, wherein one or more further light modules provided in one or more blade sections between the root and the tip region, and wherein the optical measuring device is capable of identifying each of the light source in the multiple light modules. [0070] 7. A system according to any one of the preceding items, wherein a multiple of modulation frequencies are used for each of the light sources. [0071] 8. A system according to any one of the preceding items, wherein the light source is an LED. [0072] 9. A system according to any one of items 1 to 7, wherein the light source is a laser. [0073] 10. A method of tracking the motion of a blade of a wind turbine, where the wind turbine blade comprises a blade root and a blade tip, and a leading edge and a trailing edge with a blade section extending therebetween of each blade section; the method comprising the steps of: [0074] providing at least a first light module comprising a first light source and a second light source provided on or close to the leading edge and the trailing edge, respectively, in a predetermined blade section, preferably near the blade tip, said first and second light sources being adapted to 1) being frequency modulated with different modulation frequencies, and 2) emitting light in the direction of the blade root; and [0075] providing an optical measuring device at the blade root adapted to receive the light emitted from the light sources of said first light module, and [0076] distinguishing each light source based on the modulation frequency and identifying the relative position of each of the light sources in the optical measuring device, which is a position sensitive detector. [0077] 11. A method according to item 10, whereby the method is performed with a data rate allowing for real-time tracking of the blade motion. [0078] 12. A method according to item 10 or 11, whereby the tracking of the blade motion includes a plurality of light modules with light sources on or close the leading edge and trailing edge of a multiple of blade sections. [0079] 13. A method according to any one of items 10 to 12, whereby the light sources are synchronised. [0080] 14. A method according to any one of items 10 to 13, whereby the position sensitive detector further comprises a signal processing system, which demodulates the output signal to identify the relative position each of the light sources. [0081] 15. A method according to any one of items 10 to 14, whereby the light sources are provided on the rear side of the wind turbine blades. [0082] 16. A method of controlling a wind turbine having a rotor with a plurality of wind turbine blades having a system according to any of one items 1 to 9, where at least the wind turbine blade pitch and the yaw of the rotor are controlled using measurements of blade tracking by performing a method according to any one of items 10 to 15.