A Deflection Monitoring System for a Wind Turbine Blade

Abstract

A wind turbine blade comprising a system for monitoring the deflection of a wind turbine blade is described. The system comprises a wireless range-measurement system, having at least one wireless communication device located towards the root end of the blade and at least one wireless communication device located towards the tip end of the blade and internally within the blade body. Radio absorbing material is arranged internally in the blade body in the wireless communication path between the root-and tip devices.

Claims

1. A wind turbine blade (10) comprising an airfoil profile body having a pressure side (52) and a suction side (54), and a leading edge (18) and a trailing edge (20) with a chord length (60) extending there between, the blade having a tip end (14) and a root end (16), the wind turbine blade further comprising: at least one tip communication device (72) located towards said tip end, at least one root communication device (70) located towards said root end, said at least one root communication device being in wireless radio communication with said at least one tip communication device via a wireless communication path, to monitor the distance between said at least one tip communication device and said at least one root communication device to determine a movement of said at least one tip communication device relative to said at least one root communication device indicative of a blade deflection, wherein said at least one tip communication device is provided internally in the airfoil profile body, and wherein at least one radio wave absorbing material (80) is arranged internally in the airfoil profile body and in said wireless communication path.

2. A wind turbine blade according to claim 1, wherein said radio wave absorbing material (80) is arranged between the at least one tip communication device (72) and the at least one root communication device (70) at a distance from the tip communication device of between 0.2-3.0 m, preferably of between 0.5-2 m.

3. A wind turbine blade according to claim 1, wherein said radio wave absorbing material (80) is arranged in one or more cavities in the airfoil profile body at a distance from the tip communication device (72) and between said at least one tip communication device and said at least one root communication device (70) to partly or fully block the communication path in a first cavity defined by the free space between a leading edge shear web (86) and a first interior surface of the airfoil profile body facing the leading edge, to partly or fully block the communication path in a second cavity defined by the free space between said leading edge shear web, a trailing edge shear web and a second interior surface of the airfoil profile body and/or to partly or fully block the communication path in a third cavity defined by the free space between said trailing edge shear web and a third interior surface of the airfoil profile body facing the trailing edge.

4. A wind turbine blade according to claim 1, wherein said radio wave absorbing material (80) has a thickness in the longitudinal direction of the blade of 5-300 mm, preferably of 20-200 mm, such as 50-150 mm.

5. A wind turbine blade according to claim 1, wherein said radio wave absorbing material (80) is arranged as a panel comprising one or more sheets (82) of one or more radio absorbing materials.

6. A wind turbine blade according to claim 5, wherein said one or more sheets (82) comprise polymeric foam.

7. A wind turbine blade according to claim 6, wherein said polymeric foam is selected from the group consisting of PUR, PS, PP, PE, PVC and combinations thereof.

8. A wind turbine blade according to claim 5, wherein said panel comprises an outer material (84), partly or fully encapsulating said sheets (82) of one or more radio absorbing materials, said outer material being selected from the group consisting of PTFE, PP, PE, PC, PS, ABS, PBT, natural rubber, synthetic rubber and combinations thereof.

9. A wind turbine blade according to claim 1, wherein said radio wave absorbing material (80) comprises carbon.

10. A wind turbine blade according to claim 1, wherein said radio wave absorbing material is arranged as a passive device comprising interspaced metal plates (200).

11. A wind turbine blade according to claim 10, wherein said interspaced metal plates are copper plates.

12. A wind turbine blade according to claim 10 wherein the distance between said interspaced metal plates is in the range of 1-10 cm, preferably 2-8 cm, such as 3-5 cm.

13. A wind turbine blade according to claim 10, wherein the number of said interspaced metal plates is between 2 and 20, such as between 5 and 15.

14. A wind turbine blade according to claim 1, wherein said at least one tip communication device (72) comprises an antenna transmitting a narrow time-domain pulse from a pulse generator, and said at least one root communication device (70) comprises an antenna receiving said narrow time-domain pulse.

15. A wind turbine blade (10) according to claim 1, wherein said at least one tip communication device (72) is located between 0.5 and 5 m from the tip end of the airfoil profile body, preferably between 2-4 m form the tip end of the airfoil profile body.

16. A wind turbine blade (10) according to claim 1, wherein said at least one root communication device (70) is arranged externally on the airfoil profile body.

17. A wind turbine (2) having at least one wind turbine blade (10) as claimed in claim 1.

18. A wind turbine (2) as claimed in claim 17, further comprising a pitch control system operable to adjust the pitch of at least one wind turbine blade of said wind turbine, wherein the input to said pitch control system is at least partially based on the determined movement of said at least one tip communication device (72) relative to said at least one root communication device (70) indicative of a blade deflection.

19. A blade deflection monitoring system for installation on a wind turbine blade, the wind turbine blade comprising an airfoil profile body having a pressure side (52) and a suction side (54), and a leading edge (18) and a trailing edge (20) with a chord length (60) extending there between, the blade having a tip end (14) and a root end (16), the monitoring system comprising: at least one tip communication device (72) for installation towards the tip end of a wind turbine blade (10), at least one root communication device (70) for installation towards the root end of a wind turbine blade, and a controller to operate said communication devices in wireless radio communication to monitor the distance between said at least one tip communication device and said at least one root communication device when installed on a wind turbine blade to determine a movement of said at least one tip communication device relative to said at least one root communication device indicative of a blade deflection, wherein said at least one tip communication device is provided internally in the airfoil profile body, and wherein at least one radio wave absorbing material (80) is arranged internally in the airfoil profile body and in said wireless communication path.

Description

Description of the Invention

[0090] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0091] FIG. 1 shows a wind turbine;

[0092] FIG. 2 shows a schematic view of a wind turbine blade;

[0093] FIG. 3 shows a schematic view of an airfoil profile of the blade of FIG. 2;

[0094] FIG. 4 illustrates a wind turbine blade having a blade deflection monitoring system according to an embodiment of the invention;

[0095] FIG. 5 is a cross-sectional view of an embodiment of the blade of FIG. 4 taken at the root end of the blade;

[0096] FIG. 6a shows the interior of the airfoil profile body at the tip end showing a tip communication device and radio wave absorbing material arranged according to an embodiment of the invention;

[0097] FIG. 6b shows radio wave absorbing material arranged as a panel according to an embodiment of the invention.

[0098] FIG. 7 shows a schematic view of radio signal propagation from a tip communication device arranged in the interior of the blade according to the invention.

[0099] FIG. 8 shows a schematic drawing of the radio wave absorbing material in the form of interspaced metal plates arranged at a distance for the tip communication device.

[0100] It will be understood that the attached drawings are illustrative only, and are not provided to scale.

[0101] FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called Danish concept with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The rotor has a radius denoted R.

[0102] FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 which may be used according to an embodiment of the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

[0103] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 is typically constant along the entire root area 30. The transition region 32 has a transitional profile 42 gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile 50 of the airfoil region 34. The chord length of the transition region 32 typically increases substantially linearly with increasing distance r from the hub.

[0104] The airfoil region 34 has an airfoil profile 50 with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

[0105] It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

[0106] FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during usei.e. during rotation of the rotornormally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber and lower camber, which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

[0107] Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position df of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position dt of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c.

[0108] Wind turbine blades are generally formed from fibre-reinforced plastics material, i.e. glass fibres and/or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be in excess of 30-40 metres in length, having blade root diameters of several metres.

[0109] With reference to FIG. 4, a wind turbine blade 10 is shown having a blade deflection monitoring system according to an embodiment of the invention. The deflection monitoring system comprises at least one root end wireless communication device 70 arranged at the exterior side of the hollow blade body in the root region and at least one tip end wireless communication device 72 arranged in the interior side of the blade body. The tip end wireless communication device may for example be mounted on a leading edge web in a typical blade having a box spar design with a leading edgeand trailing edge shear web. The respective wireless devices 70,72 are operable to establish a communication link, and perform a range measurement between the different devices 70,72. In the communication path between the root end wireless communication device 70 and the tip and wireless communication device 72 a radio wave absorbing material 80 is arranged. Typically the radio wave absorbing material 80 may be arranged to effectively absorb the radio waves within the hollow blade body between the leading edge web and the blade shell. This implies that the circumferential shape of the absorber may be adapted to the circumferential contour of the hollow space between the leading edge web and the shell to fully block the communication path by attaching the absorber to the shell and web along its circumference, for example by use of adhesive or mechanical attaching means such as bolts, brackets and the like. The blade 10 may further comprise a controller (not shown) which is operable to receive the range measurement details from the communication devices in order to determine the measured blade deflection.

[0110] In one aspect, the root and tip devices 70,72 are located at the leading edge 18 of the wind turbine blade 10. As a communication device mounted on the leading or trailing edge 18,20 is less susceptible to flapwise bending than a sensor mounted on the pressure or suction sides of the blade 10, and as the magnitude of the edgewise bending of the blade 10 is understood to be significantly less than that of flapwise bending, this provides for improved reliability of the communications link between the root and tip devices 70,72, as the communications path between devices is less likely to be disturbed by bending of the blade 10.

[0111] Additionally or alternatively, the root and tip devices 70,72 may be mounted at the blade trailing edge 20.

[0112] In a preferred embodiment of the invention, preferably first and second root end communication devices are provided 70a, 70b. FIG. 5 illustrates a cross-sectional view of the first and second root end communication devices 70a, 70b located at the substantially circular root end 16 of the blade 10. The root devices 70a, 70b are provided on the distal ends of respective first and second brackets 74a, 74b.

[0113] With reference to FIG. 5, the height of the brackets 74a, 74b is selected such that the root devices 70a, 70b provided on the distal ends of the respective brackets 74a, 74b are located at a height H above the external surface of the wind turbine blade. Furthermore, the brackets 74a, 74b are positioned such that the respective root devices 70a, 70b are separated by a distance D, preferably above the leading edge 18 of the blade 10.

[0114] As the deflection characteristics of the wind turbine blade 10 may be determined from the details of the blade construction, and additionally as each wind turbine blade 10 has a maximum certified deflection level defining an allowable range of blade deflection shapes, it is possible to configure the arrangement of the blade deflection monitoring system of the invention based on the wind turbine blade in question.

[0115] It may be advantageous to suppress signal reflections from the external surface of the blade. In particular when the blade is deflected or in case of a non-deflected pre-bent blade, signals from the tip communication device may be reflected from the blade and obscure the signals received by the root communication device.

[0116] Thus, the external blade surface may be made less reflective at positions close to the line of sight between the root-and tip devices through surface treatment in the form of radio wave absorbing coatings or otherwise providing the surface with a scattering effect, for example by roughening the surface and/or provide small indentions and protrusions on the surface.

[0117] In this context the line of sight is to be understood as the direct line between tip a tip communication device and a root communication device passing through any obstacles located in the way, for example the laminate of the airfoil shell body.

[0118] FIG. 6a illustrates the tip end of the blade having mounted tip communication device 72 and radio wave absorbing material 80. In the shown embodiment, the tip communication device 72 is mounted on a leading edge shear web 86 and facing the leading edge and the absorbing material 80 is arranged as a bulkhead-like panel, substantially sealing off the hollow space between the leading edge shear web and the blade shell at a position in the communication path.

[0119] In other embodiments, the tip communication device may be mounted between the shear webs or on the trailing edge shear web and facing the trailing edge. Also, radio wave absorbing material 80 may be arranged between the shear webs or in the hollow space between the trailing edge shear web and the blade shell,

[0120] FIG. 6b shows the radio wave absorbing material 80 arranged in a panel in more detail. The panel comprises sheets or layers 82 of radio wave absorbing material sandwiched between panels 84 to provide a radio wave absorbing bulkhead-like panel being shaped to fit the hollow space between the shear web and the blade shell at a position in the communication path to seal off/block the hollow space between the shear web and the blade shell at a position in the communication path.

[0121] The layers 82 may, for example, be made of polyurethane foam material comprising carbon, and the panels 84 may, for example, be made of PTFE.

[0122] It should be noted that the radio wave absorbing material can also be a block of material that is not layered but formed from one piece. It should further be noted that the panels 84 may be partly or fully encapsulate the radio wave absorbing material and that the radio wave absorbing material may also be provided without panels 84 in some embodiments.

[0123] FIG. 7 shows a schematic drawing of tip communication device 72 sending radio signals towards one or more root communication devices (not shown). Radio absorbing material 80 is indicated with dashed lines. Diffracted pulse 100 will travel towards the root while guided pulse 101 and multipath component 102 will be at least partly suppressed by absorbing material 80.

[0124] Surface wave 103 will also be less pronounced having absorber material 80 in place. The positioning of radio wave absorbing material 80 relative to tip communication device 72 has to be optimized with respect to suppressing pulse components 101, 102 and 103 while still allowing sufficient energy in the form of component 100 to reach the root to obtain precise measurements.

[0125] FIG. 8 shows a schematic drawing of the radio wave absorbing material 80 in the form of interspaced metal plates 200 arranged at a distance for the tip end wireless communication device 72.

[0126] In a further aspect, preferably the root devices are located within 0-25% of the length of the blade from the root end of the blade. Preferably, the root devices are located within 10 metres along the longitudinal direction of the blade from the root end of the blade.

[0127] It will be understood that said at least one tip communication device and/or said at least one root communication device is selected from one of the following: a receiver, a transmitter, a receiver-transmitter circuit, or a transceiver. It will further be understood that the at least one tip communication device may comprise an antenna provided towards said tip end, the antenna coupled to a receiver, transmitter, receiver-transmitter circuit, or transceiver device provided at a separate location, e.g. towards the blade root end.

[0128] Preferably, the communications link is using Ultra Wide Band (UWB) technology, but it will be understood that any other suitable radio-based communication and ranging technology may be used.

[0129] Further features of the system of the invention may include the use of specialized antenna designs such as directional or circular polarized antennas for the root or tip devices, in order to further improve the communications link between the devices, and/or the implementation of pulse shape detection techniques for received signals.

[0130] It will be understood that the blade deflection monitoring system of the invention may comprise any suitable control system for the efficient and effective operation of the system.

[0131] The invention provides a system to ensure accurate monitoring of blade deflection, having improved signal quality. The tip communication device is provided inside the hollow blade body, thereby protecting the device from harsh outdoor environment and eliminating any noise issues that may arise as a consequence of arranging such communication device on the exterior side of the blade at the tip end of the blade. A radio wave absorbing material is arranged inside the blade in the communication path between the tip communication device and the root communication device at a distance from the tip communication device to improve signal quality and effectively suppress unwanted signal components that may obscure the distance measurement and thereby, the measured deflection of the blade.

[0132] As a result of this configuration, the deflection monitoring system has relatively low power requirements, and provides improved reliability and signal quality compared to prior art wireless deflection monitoring systems.

[0133] The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.