Methods and systems for mounting wind turbine blades to hubs

Abstract

The present disclosure relates to methods for mounting wind turbine blades on hubs The method comprises attaching a blade holder to the wind turbine blade, hoisting the blade holder and wind turbine blade with a crane and positioning the wind turbine blade in proximity to the hub and determining oscillations of the hub with one or more sensors. The method further comprises activating one or more fans on the blade holder based on the determined oscillations of the hub to cause the blade to oscillate and synchronize an oscillation of the blade with the oscillations of the hub. The method also comprises moving the blade towards the hub and mounting the blade to the hub.

Description

GENERAL ELECTRIC RE OVABLES ESPANA S.L. DECEMBER 20, 2024 GE 701195-WO-1 P5548PC00METHODS AND SYSTEMS FOR MOUNTING WIND TURBINE BLADES TO HUBSFIELD

[0001] The present disclosure relates to mounting of blades to a wind turbine hub, and more particularly to method for mounting a wind turbine blade to a hub including synchronization of a movement of the blade with a movement of the hub. The present disclosure further relates to blade holders and systems adapted for such methods.BACKGROUND

[0002] Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly ("directly driven" or "gearless") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

[0003] The wind turbine hub may be rotatably coupled to a front of the nacelle. The wind turbine hub may be connected to a rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of a wind turbine tower that contains and protects e.g. the gearbox (if present) and the generator and, depending on the wind turbine, further components such as a power converter, and auxiliary systems.

[0004] Wind turbine blades are generally coupled to the hub by a pitch bearing. A pitch bearing typically comprises an inner ring and an outer ring, and usually a plurality of rolling or roller elements between the inner and outer ring. A wind turbine blade may be attached either to the inner ring or to the outer ring, whereas the hub may be attached to the other of the inner and outer rings. The attachment may for example be performed with nuts and bolts.

[0005] The installation of wind turbine blades has become more and more of a challenging task due to the general tendency to increase the size and weight of modern wind turbine blades. Blades of modern wind turbines may be more than 70 or 80 meters long, or even morethan 100 meters long. During installation, the wind turbine blades may be hoisted towards the rotor hub.

[0006] A known way of mounting a wind turbine includes the steps of transporting the different elements to the site of the wind turbine, assembling the tower sections, lifting the wind turbine nacelle with a large crane and mounting the nacelle on top of the tower. Then the wind turbine rotor hub can be lifted with the crane and mounted to a rotor shaft and / or the nacelle. Alternatively, the hub can be mounted to the nacelle and then the nacelle-hub assembly can be hoisted.

[0007] Afterwards, one or more blades are mounted to the wind turbine rotor hub. The rotor hub generally comprises a plurality of annular mounting flanges. Pitch bearings can be arranged with the mounting flanges. The blade can comprise a plurality of fasteners, such as bolts, or pins or studs at its blade root. During installation, these fasteners are to be fitted into openings in the mounting flange or pitch bearing on the hub.

[0008] It is also known to hoist a complete rotor assembly, i.e. the hub with the plurality of blades, and mount it to e.g. the nacelle. But in order to mount a complete rotor assembly, a large surface area is required, which is typically not available e.g. in the case of offshore wind turbines. Further, the mass of a complete rotor assembly can be significant and may exceed the crane capabilities or the tools for fixing the hub.

[0009] It is further known to mount blades individually. It is known to mount each of the plurality of blades substantially horizontally (e.g. -30° - +30° with respect to a horizontal plane) or substantially vertically.

[0010] Wind is inherently variable and winds from different directions, turbulent winds, and wind gusts can act on the wind turbine blade during hoisting and may provoke sudden movements and possibly oscillations of the blade during the hoisting operation. Fitting the blade to a hub may thus be complicated and time-consuming.

[0011] For offshore installations, the installation procedures can be even more complicated. The vessel carrying a crane may move under wind and wave forces. Also, the wind turbine tower and the nacelle mounted on top of the tower can move under wind and wave forces.

[0012] Wind turbine farms may also be situated in remote sites, e.g. on hill-tops and typically in these places the lifting of the wind turbine blade may be subject to high winds.

[0013] Frequently, difficulties can arise during the lifting operation due to oscillations. In order to perform the installation of the blade, manual aid is often required e.g. the blade is stabilized with ropes. Still, oscillations during hoisting operations can lead to possible damageto the wind turbine blade or to other parts of the wind turbine. If for example a sudden movement occurs when a wind turbine blade is close to the hub, parts or components may be damaged e.g. the blade, a pitch bearing, or blade fasteners.

[0014] The present disclosure provides systems and methods to at least partially overcome some of the aforementioned drawbacks.SUMMARY

[0015] In an aspect of the present disclosure, a method for mounting a wind turbine blade on a hub is provided. The method comprises attaching a blade holder to the wind turbine blade and hoisting the blade holder and wind turbine blade with a crane and positioning the wind turbine blade in proximity to the hub. The method further comprises determining oscillations of the hub with one or more sensors, activating one or more fans on the blade holder based on the determined oscillations of the hub to cause the blade to oscillate and to synchronize an oscillation of the blade with the determined oscillations of the hub. The method further comprises moving the blade towards the hub and mounting the blade on the hub.

[0016] According to this aspect, the installation of a wind turbine blade on a hub may be enhanced, enabling the installation process to be carried out at more demanding wind conditions (e.g. high wind speeds, gusty wind). Installation time per blade may be substantially reduced, as the installation window may be enlarged.

[0017] The activated fans may excite the blade in one or more directions of the blade. The method allows to synchronize the movement of the blade to the movement of the hub using a plurality of fans. Once the relative movement between the blade and the hub is substantially reduced, the blade can be mounted to a mounting area of the hub. Different degrees of freedom of the blade may be independently controlled, allowing an efficient and effective synchronization of the movements of the blade to the movements of the hub.

[0018] The fans may be used such that the pattern of movement of the blade may substantially imitate the pattern of movements of the hub without having to mechanically connect them together, which may be a more burdensome process.

[0019] Throughout the present disclosure, synchronizing an oscillation of the blade with an oscillation of the hub may be understood as substantially reducing the relative movement between the blade and the hub e.g. reducing 40 - 99% of the relative movement between the blade and the hub, preferably reducing the relative movement more than 50%, more preferably more than 80%.

[0020] Throughout the present disclosure, a blade holder may be regarded as a tool configured to connect the blade to a crane. The blade holder may be used to safely grip the wind turbine blade with the crane.

[0021] In a further aspect of the present disclosure, a blade holder configured for holding a blade is provided. The blade holder comprises one or more blade holder sensors for measuring movement or position of the blade holder, one or more fans and a control system. The control system is configured to receive signals from one or more hub sensors on a hub of a wind turbine, determine movement of the hub based on the received signals from the hub sensors, receive signals from the blade holder sensors, determine movements of the blade holder based on the received signals from the blade holder sensors, and to drive the fans to synchronize the movement of the blade holder with the movement of the hub.

[0022] In yet a further aspect of the present disclosure, a system for synchronizing movements of a wind turbine blade with movement of a hub of a wind turbine is provided. The system comprises a blade holder configured for holding a blade and a hub sensor system configured to be mounted on the hub of the wind turbine. The blade holder comprises one or more blade holder sensors for measuring movement position of the blade holder, one or more fans and a control system. The hub sensor system is configured to measure signals indicative of movements of the hub and to transmit the signals to the control system of the blade holder. The control system of the blade holder is configured to receive the signals from the hub sensor system, determine movement of the hub based on the received signals from the hub sensors, receive signals from the blade holder sensors, determine movements of the blade holder based on the received signals from the blade holder sensors, and to drive the fans to synchronize the movement of the blade holder with the movement of the hub.

[0023] Additional objects, advantages and features of embodiments of the present disclosure will become apparent to those skilled in the art upon examination of the description, or may be learned by practice.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 schematically illustrates a perspective view of one example of a wind turbine;

[0025] Figure 2 illustrates an example of a hub and a nacelle of a wind turbine;

[0026] Figure 3 shows a flow chart of an example of a method for mounting a wind turbine blade to a hub;

[0027] Figure 4a schematically shows a wind turbine blade connected to a blade installation tool 130 according to an example of the present disclosure;

[0028] Figure 4b schematically shows a top view of the wind turbine blade shown in figure 4a.DETAILED DESCRIPTION OF EXAMPLES

[0029] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the teaching. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0030] Figure 1 is a perspective view of an example of a wind turbine 10. In the example, the wind turbine 10 is a horizontal-axis wind turbine. Alternatively, the wind turbine 10 may be a vertical-axis wind turbine. In the example, the wind turbine 10 includes a tower 15 that extends from a support system 14 on a ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 that is coupled to nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from the hub 20. In the example, the rotor 18 has three rotor blades 22. In an alternative embodiment, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in figure 1) between a support system 14 and the nacelle 16. In an alternative embodiment, the tower 15 is any suitable type of a tower having any suitable height. According to an alternative, the tower can be a hybrid tower comprising a portion made of concrete and a tubular steel portion. Also, the tower can be a partial or full lattice tower.

[0031] The rotor blades 22 are spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. The rotor blades 22 are mated to the hub 20 by coupling a blade root portion 24 to the hub 20 at a plurality of load transfer regions 26. The load transfer regions 26 may have a hub load transfer region and a blade load transfer region (both not shown in figure 1). Loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0032] In examples, the rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 m or more. Rotor blades 22 may have any suitable length that enables the wind turbine 10 to function as described herein. As wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 is rotated about a rotor axis 30. As the rotor blades 22 are rotated and subjected to centrifugal forces, the rotor blades 22 are also subjected to various forces and moments. As such, the rotor blades 22 may deflect and / or rotate from a neutral, or non-deflected, position to a deflected position.

[0033] Moreover, a pitch angle of the rotor blades 22, i.e., an angle that determines an orientation of the rotor blades 22 with respect to the wind direction, may be changed by a pitch system 32 to control the load and power generated by the wind turbine 10 by adjusting an angular position of at least one rotor blade 22 relative to wind vectors. Pitch axes 34 of rotor blades 22 are shown. During operation of the wind turbine 10, the pitch system 32 may particularly change a pitch angle of the rotor blades 22 such that the angle of attack of (portions of) the rotor blades are reduced, which facilitates reducing a rotational speed and / or facilitates a stall of the rotor 18.

[0034] In the example, a blade pitch of each rotor blade 22 is controlled individually by a wind turbine controller 36 or by a pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by said control systems.

[0035] Further, in the example, as the wind direction 28 changes, a nacelle 16 may be rotated about a yaw axis 38 to position the rotor blades 22 with respect to wind direction 28.

[0036] In the example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed system throughout the wind turbine 10, on the support system 14, within a wind farm, and / or at a remote-control center. The wind turbine controller 36 includes a processor 40 configured to perform the methods and / or steps described herein. Further, many of the other components described herein include a processor.

[0037] As used herein, the term “processor” is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific, integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and / or a control system can also include memory, input channels, and / or output channels.

[0038] Figure 2 is an enlarged sectional view of a portion of the wind turbine 10. In the example, the wind turbine 10 includes the nacelle 16 and the rotor 18 that is rotatably coupled to the nacelle 16. More specifically, the hub 20 of the rotor 18 is rotatably coupled to an electricgenerator 42 positioned within the nacelle 16 by the main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In the example, the main shaft 44 is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle 16. A rotation of the main shaft 44 drives the gearbox 46 that subsequently drives the high-speed shaft 48 by translating the relatively slow rotational movement of the rotor 18 and of the main shaft 44 into a relatively fast rotational movement of the high-speed shaft 48. The latter is connected to the generator 42 for generating electrical energy with the help of a coupling 50. Furthermore, a transformer 90 and / or suitable electronics, switches, and / or inverters may be arranged in the nacelle 16 in order to transform electrical energy generated by the generator 42 having a voltage between 400V to 6k V into electrical energy having medium voltage, e.g. 10 - 66 KV. Said electrical energy is conducted via power cables from the nacelle 16 into the tower 15.

[0039] The gearbox 46, generator 42 and transformer 90 may be supported by a main support structure frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing that is connected to the main frame 52 by one or more torque arms 99. In the example, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Furthermore, the generator 42 can be mounted to the main frame 52 by decoupling support means 54, in particular in order to prevent vibrations of the generator 42 to be introduced into the main frame 52 and thereby causing a noise emission source.

[0040] Optionally, the main frame 52 is configured to carry the entire load caused by the weight of the rotor 18 and components of the nacelle 16 and by the wind and rotational loads, and furthermore, to introduce these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and any associated fastening, support, and / or securing device including, but not limited to, main frame 52, and forward support bearing 60 and aft support bearing 62, are sometimes referred to as a drive train 64.

[0041] In some examples, the wind turbine may be a direct drive wind turbine without a gearbox 46. Generators 42 operate at the same rotational speed as the rotor 18 in direct drive wind turbines. They therefore generally have a much larger diameter than generators used in wind turbines having a gearbox 46 for providing a similar amount of power than a wind turbine with a gearbox.

[0042] The nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 and thereby also the rotor 18 about the yaw axis 38 to control the perspective of the rotor blades 22 with respect to the wind direction 28.

[0043] For positioning the nacelle 16 appropriately with respect to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system 58 which may include a wind vane and anemometer. The meteorological measurement system 58 can provide information to the wind turbine controller 36 that may include wind direction 28 and / or wind speed. In the example, the pitch system 32 is at least partially arranged as a pitch assembly 66 in the hub 20. The pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in figure 1) for modulating the pitch angle of a rotor blade 22 along the pitch axis 34. Only one of three pitch drive systems 68 is shown in figure 2.

[0044] In the example, the pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and to a respective rotor blade 22 (shown in figure 1) for rotating the respective rotor blade 22 about the pitch axis 34. The pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. The pitch drive motor 74 is coupled to the pitch drive gearbox 76 such that the pitch drive motor 74 imparts mechanical force to the pitch drive gearbox 76. The pitch drive gearbox 76 is coupled to the pitch drive pinion 78 such that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. The pitch bearing 72 is coupled to pitch drive pinion 78 such that the rotation of the pitch drive pinion 78 causes a rotation of the pitch bearing 72.

[0045] Pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of a rotor blade 22 upon receipt of one or more signals from the wind turbine controller 36. In the example, the pitch drive motor 74 is any suitable motor driven by electrical power and / or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components such as, but not limited to, hydraulic cylinders, springs, and / or servomechanisms. In certain embodiments, the pitch drive motor 74 is driven by energy extracted from a rotational inertia of hub 20 and / or a stored energy source (not shown) that supplies energy to components of the wind turbine 10.

[0046] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive system 68 according to control signals from the wind turbine controller 36, in case of specific prioritized situations and / or during rotor 18 overspeed. In the example, the pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a respective pitch drive system 68 for controlling pitch drive system 68 independently from the wind turbine controller 36. In the example, the pitch control system 80 is coupled to the pitch drive system 68 and to a sensor 70. During normal operation of the wind turbine 10, the wind turbine controller 36 may control the pitch drive system 68 to adjust a pitch angle of rotor blades 22.

[0047] According to an embodiment, a power generator 84, for example comprising a battery and electric capacitors, is arranged at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and to the pitch drive system 68 to provide a source of power to these components. In the example, the power generator 84 provides a continuing source of power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, power generator 84 provides power to the pitch assembly 66 only during an electrical power loss event of the wind turbine 10. The electrical power loss event may include power grid loss or dip, malfunctioning of an electrical system of the wind turbine 10, and / or failure of the wind turbine controller 36. During the electrical power loss event, the power generator 84 operates to provide electrical power to the pitch assembly 66 such that pitch assembly 66 can operate during the electrical power loss event.

[0048] In the example, the pitch drive system 68, the sensor 70, the pitch control system 80, cables, and the power generator 84 are each positioned in a cavity 86 defined by an inner surface 88 of hub 20. In an alternative embodiment, said components are positioned with respect to an outer roof surface of hub 20 and may be coupled, directly or indirectly, to the outer roof surface.

[0049] Figure 3 shows a flow chart of a method 300 for mounting a wind turbine blade on a hub according to an example of the present disclosure.

[0050] The method 300 comprises, at step 302, attaching a blade holder 130 to the wind turbine blade 22, at step 304, hoisting the blade holder 130 and wind turbine blade 22 with a crane and positioning the wind turbine blade 22 in proximity to the hub 20.

[0051] The blade holder 130 is configured to hold the blade and may be configured to be connected to a hoisting system i.e. a crane may hoist the blade through the blade holder. The blade holder 130 comprises one or more fans 110 mounted to it. In some examples, the one or more fans 110 may be installed to the blade holder 130 before the blade holder 130 is mounted to the blade 22. In other examples, the one or more fans 110 may be installed to the blade holder 130 after the blade holder 130 has been attached to the wind turbine blade 22.

[0052] In some examples, the method may comprise yawing a nacelle to align a flange of the hub with the blade. The method may comprise activating the yaw drive mechanism 56 of the nacelle and rotating the nacelle about a yaw axis, such that the hub 20 may be rotated to a desired mounting position. The nacelle may be actively used to position the hub such that its mounting area may be oriented correctly with the blade, facilitating the step of positioning the blade in proximity to the hub e.g. if the position of the blade has changed due to the wind direction. The nacelle may be yawed before hoisting the blade with the crane or afterwards.

[0053] Figure 4a schematically shows a blade holder 130 holding a wind turbine blade 22. The blade 22 and the blade holder 130 are hoisted with a crane (not shown) and are positioned in proximity to the hub 20.

[0054] The method 300 for mounting a wind turbine blade 22 to a hub may comprise hoisting the blade holder 130 and wind turbine blade 22 with a crane, wherein at least three fans are mounted to the blade holder 130.

[0055] The fans may comprise one or more blades which rotate around an axis. The fans may be mounted to the blade holder 130 in different positions i.e. the rotational axis of the fans may be arranged facing different directions. In the example schematically shown in figure 4a, four fans 111, 112, 113, 114 are mounted to the blade holder 130.

[0056] In some examples, the plurality of fans may comprise one or more fans with a rotational axis substantially parallel to the longitudinal axis of the blade e.g. fan 111 in figure 4a. In some examples, the plurality of fans may comprise one or more fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade e.g. fans 112, 113 and 114 in figure 4a. The one or more fans may be used to drive an oscillation of the blade in different directions.

[0057] The method 300 for mounting a wind turbine blade 22 to a hub 20 further comprises, at step 306, determining oscillations of the hub with one or more sensors 123.

[0058] In some examples, the one or more sensors may be sensors permanently installed on the hub. In other examples, the one or more sensors may be installed on the hub temporarily i.e. the one or more sensors may be removed after the wind turbine blade installation and may be further installed on another wind turbine hub.

[0059] In some examples, the sensors 123 of the hub may include an accelerometer and / or a position sensor. The sensors may be configured to determine oscillations of the hub which may be caused e.g. by the wind and / or sea waves crashing into the wind turbine tower.

[0060] In some examples, the method 300 may further comprise determining movements of the blade 22 using one or more sensors on the blade holder 130. In the example shown in figure 4a, two sensors 121, 122 are mounted to the blade holder 130. The sensors 121, 122 mounted to the blade holder may include an accelerometer or a position sensor.

[0061] In some examples, the method may comprise mounting at least two sensors 121 , 122 in the blade holder 130. The sensors may be configured to measure movement and / or position of the blade holder and therefore, of the blade. The sensors may comprise laser sensors, acceleration sensors and / or global positioning system (GPS) sensors. In someexamples, laser sensors may be used to measure a distance between the blade holder and the hub.

[0062] In some examples, the sensors 123, 121, 122 may be communicatively connected to a control system. The control system may be configured to receive data related to the movement or position of the hub and the blade, obtain the relative movement between the blade and the hub and to activate one or more of the fans in view of the received data.

[0063] In some examples, the control system may be located on the blade holder 130 and may be configured to receive one or more signals from the one or more sensors 123 arranged on the hub 20 and determine movement of the hub 20 based on the received signals from the hub sensors 123. The control system may further receive signals from the blade holder sensors 121, 122 and may be configured to determine movements of the blade holder based on the received signals from the blade holder sensors 123. The control system may obtain relative movements between the blade 22 and the hub 20 which may be later used to synchronize movement of the blade holder 130 with movement of the hub 20.

[0064] The method 300 further comprises, at step 308, activating one or more fans 111, 112, 113, 114 on the blade holder 130 based on the determined oscillations of the hub 20 to cause the blade 22 to oscillate and synchronize an oscillation of the blade 22 with the oscillations of the hub 20.

[0065] When hoisted by a crane, the wind turbine blade 22 may be subjected to winds which may cause it to move or oscillate, making the mounting process more challenging. During the installation of an offshore wind turbine, the crane, and therefore the blade, may also be subjected to oscillations caused by sea waves. Further, the hub may also be subjected to movements caused by the wind and / or sea waves crashing into the wind turbine tower. Although both the blade and the hub may oscillate due to external forces, there is a relative motion between them, as their movements are not the same i.e. they are not synchronized.

[0066] Activating the fans may drive or excite the blade in one or more directions. The fans may be used such that movements of the blade may be synchronized with movements of the hub i.e. such that the relative motion between the blade and the hub is reduced as much as possible, preferably by at least 50% m. The fans may excite the blade such that the movement of the blade substantially imitates the movement of the hub.

[0067] The hub and the blade may oscillate in different directions. In some examples, the method 300 for mounting a wind turbine blade 22 to a hub 20 may comprise synchronizing the oscillation of the blade 22 with the oscillation of the hub 20 in a direction parallel to the longitudinal axis L of the blade 1D, 2D. I.e. the fans may be used to synchronize the oscillationof the blade in a direction parallel to the longitudinal axis L of the blade with the oscillation of the hub.

[0068] Figure 4b schematically shows a simplified top view of the wind turbine blade 22 connected to the blade installation tool 130 of figure 4a. The arrows in the figure show directions 1 D, 2D, 3D and 4D which are directions in which the plurality of fans may drive oscillations i.e. direction in which the fans may excite the blade.

[0069] As schematically shown in figure 4a, the plurality of fans may comprise one or more fans with a rotational axis substantially parallel to the longitudinal axis of the blade e.g. fan 111 in figure 4a.

[0070] In some examples, a first fan of the plurality of fans with a rotational axis substantially parallel to the longitudinal axis L of the blade 111 may drive an oscillation in a first longitudinal direction 1D. In some examples, driving an oscillation in a first longitudinal direction 1D may comprise exciting the blade towards the hub 20.

[0071] In some examples, a second fan of the plurality of fans with a rotational axis substantially parallel to the longitudinal axis of the blade drives an oscillation in a second longitudinal direction 2D, opposite to the first longitudinal direction. In some examples, driving an oscillation in a second longitudinal direction 2D opposite to the first longitudinal direction 1 D may comprise exciting the blade away from the hub 20.

[0072] In some examples, one or more of the fans may be bidirectional fans. A bidirectional fan may be configured to drive an oscillation in two opposing directions. Fan 111 shown in figure 4a may be a bidirectional fan and may be configured to drive an oscillation in the first longitudinal direction 1D parallel to the longitudinal axis of the blade and in the second longitudinal direction 2D, opposite to the first longitudinal direction 1D.

[0073] In some examples, the method 300 may comprise synchronizing the oscillation of the blade 22 with the oscillation of the hub 20 in a substantially horizontal direction perpendicular to the longitudinal axis of the blade 3D, 4D.

[0074] In these examples, the plurality of fans may comprise one or more fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade 112, 113.

[0075] In some examples, a first fan of the plurality of fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade 112 drives the oscillation in a first transverse direction 3D, and a second fan of the plurality of fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade 113 drives the oscillation in a second transverse direction 4D, opposite to the first transverse direction.

[0076] In further examples, the method may comprise synchronizing the oscillation of the blade with the oscillation of the hub in a substantially vertical direction 5D perpendicular to the longitudinal axis of the blade.

[0077] A third fan of the plurality of fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade 114 may drive an oscillation in a first vertical direction 5D (schematically shown with an arrow in figure 4a). In some examples, the blade may be excited upwards. A fourth fan of the plurality of fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade may drive an oscillation in a second vertical direction 6D, opposite to the first vertical direction 5D.

[0078] In some examples, synchronizing a motion between the blade 22 and the hub 20 may comprise adjusting the airflow provided by the fans. In some examples, adjusting the air flow may comprise adjusting the speed of the plurality of fans i.e. adjusting the revolutions per minute of the fans. The speed of the plurality of fans may be adjusted according to the measurements of the plurality of sensors such that the relative motion between the blade and the hub may be substantially brought to zero i.e. such that the movements and oscillations of the longitudinal axis of the blade root and the movements and oscillations of the longitudinal axis of the mounting area of the hub are substantially the same.

[0079] In further examples, one or more fans with a variable pitch to modify their thrust may be used. Fans with adjustable blades may be used, and adjusting the airflow of the fans may comprise adjusting an inclination of the blades of the fans (and optionally maintaining a constant operational speed). The inclination of the blades may determine the flow rate and pressure which are provided by the fan.

[0080] The method 300 may further comprise activating one or more fans 111, 112, 113, 114 and aligning the blade 22 with a mounting area of the hub 20. Throughout the present disclosure, aligning the blade with a mounting area of the hub may be regarded as positioning the blade in a position such that the central axis of the blade root end is substantially collinear with the central axis of the mounting area of the hub. Once both elements are aligned, they may be moved closer to each other and the blade may be mechanically joined to the mounting area e.g. via the pitch bearing.

[0081] In some examples, the method may comprise controlling the crane and aligning the blade 22 with a mounting area of the hub 20. In further examples, both the crane and the fans 111, 112, 113, 114 may be used to align the blade 22 to the mounting area of the hub 20.

[0082] The method 300 may further comprise, at step 310, moving the blade 22 towards the hub 20. Once there is substantially no relative motion between the blade 22 hoisted by thecrane and the hub 20, the blade 22 and the hub 20 may be approached in a controlled and reliable manner. Accordingly, after synchronizing the blade and hub movements, the blade may be brought towards the hub.

[0083] In some examples, the method may comprise using the crane to move the blade 22 towards the hub 20. In other examples, the method may comprise using one or more fans 111, 112, 113, 114 to move the blade towards the hub.

[0084] In some examples, moving the blade towards the hub may comprise activating one or more fans and moving the wind turbine blade 22 in a first longitudinal direction 1D parallel to the longitudinal axis of the blade towards the hub. Accordingly, the one or more fans 111, 112, 113, 114 may be used to bring the blade to the mounting area of the hub.

[0085] In further examples, moving the blade 22 towards the hub 20 may comprise controlling the crane and moving the wind turbine blade in the first longitudinal direction 1D towards the hub.

[0086] The method may further comprise removing the connection between the blade 22 and the blade holder 130. The blade holder 130 may be then used to mount another wind turbine blade 22 to the hub 20, carrying the method 300 explained with respect to figures 3 -4b.

[0087] In another aspect of the present disclosure, a blade holder 130 configured for holding a blade 22 is provided. The blade holder 130 comprises one or more blade holder sensors 123 for measuring movement or position of the blade holder 130, one or more fans 111, 112, 113, 114 and a control system. The control system is configured to receive signals from one or more hub sensors 123 on a hub 20 of a wind turbine, determine movement of the hub 20 based on the received signals from the hub sensors 123, receive signals from the blade holder sensors 121, 122, determine movements of the blade holder 130 based on the received signals from the blade holder sensors 121, 122, and to drive the fans 111 , 112, 113, 114 to synchronize the movement of the blade holder 130 with the movement of the hub 20.

[0088] In some examples, the blade holder sensors 121, 122 may include a position sensor. In other examples, the blade holder sensor 121, 122 may include an accelerometer. In yet further examples, the blade holder sensors 121, 122 may include a laser sensor.

[0089] In some examples, the fans 111, 112, 113, 114 may include one or more fans configured to cause an oscillation of the blade holder 130 substantially parallel to a longitudinal axis of the wind turbine blade 1 D, 2D.

[0090] In some examples, the fans 111, 112, 113, 114 may include one or more fans configured to cause an oscillation of the blade holder 130 substantially horizontally and perpendicular to the longitudinal axis of the wind turbine blade 3D, 4D.

[0091] In some examples, one or more of the fans 111, 112, 113, 114 may be a bidirectional fan. The same fan may be used to cause an oscillation of the blade holder 130 in opposite directions e.g. 1D and 2D, or 3D and 4D.

[0092] In yet a further aspect of the present disclosure, a system for synchronizing movements of a wind turbine blade 22 with movement of a hub 20 of a wind turbine is provided.

[0093] The system comprises a blade holder 130 configured for holding a blade 22 and a hub sensor system configured to be mounted on the hub of the wind turbine. The blade holder 130 comprises one or more blade holder sensors 123 for measuring movement or position of the blade holder 130. The blade holder 130 further comprises one or more fans 111, 112, 113, 114 and a control system.

[0094] In some examples, the blade holder 130 may include at least three fans.

[0095] The hub sensors system is configured to measure signals indicative of movements of the hub and to transmit the signals to the control system of the blade holder. The control system of the blade holder is configured to receive the signals from the hub sensor system, determine movement of the hub based on the received signals from the hub sensors, receive signals from the blade holder sensors, determine movements of the blade holder based on the received signals from the blade holder sensors and drive the fans to synchronize the movement of the blade holder with the movement of the hub.

[0096] In some examples, the system may be configured to send signals indicative of the movements of the blade holder 130 and of the hub 20 to a crane. The crane may be further configured to move the blade based on the signals received from the system.

[0097] This written description uses examples to disclose the teaching, including the preferred embodiments, and also to enable any person skilled in the art to practice the teaching, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance withprinciples of this application. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

CLAIMS1. A method (300) for mounting a wind turbine blade (22) on a hub (20), the method comprising:attaching (302) a blade holder (130) to the wind turbine blade (22);hoisting (304) the blade holder (130) and wind turbine blade (22) with a crane and positioning the wind turbine blade (22) in proximity to the hub (20);determining oscillations (306) of the hub (20) with one or more sensors (123); activating (308) one or more fans (111, 112, 113, 114) on the blade holder (130) based on the determined oscillations of the hub (20) to cause the blade (22) to oscillate and to synchronize an oscillation of the blade (22) with the determined oscillations of the hub (20);moving (310) the blade (22) towards the hub (20); andmounting (312) the blade (22) on the hub (20).

2. The method (300) of claim 1 , comprising synchronizing the oscillation of the blade (22) with the oscillation of the hub (20) in a direction parallel (1D, 2D) to the longitudinal axis (L) of the blade.

3. The method (300) of claim 2, wherein a first fan of the plurality of fans with a rotational axis substantially parallel to the longitudinal axis of the blade (111) drives an oscillation in a first longitudinal direction (1D), and optionally, wherein a second fan of the plurality of fans with a rotational axis substantially parallel to the longitudinal axis of the blade drives an oscillation in a second longitudinal direction (2D), opposite to the first longitudinal direction.

4. The method (300) of any of claims 1 - 3, comprising synchronizing the oscillation of the blade (22) with the oscillation of the hub (20) in a substantially horizontal direction (3D, 4D) perpendicular to the longitudinal axis (L) of the blade.

5. The method (300) of claim 4, wherein a first fan of the plurality of fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade (112) drives the oscillation in a first transverse direction (3D), optionally wherein a second fan of the plurality of fans with a rotational axis substantially perpendicular to the longitudinal axis of the blade (113) drives the oscillation in a second transverse direction (4D), opposite to the first transverse direction (3D).

6. The method (300) of any of claims 1 - 5, comprising using one or more of the fans (111, 112, 113, 114) to move the blade (22) towards the hub (20).

7. The method (300) of any of claims 1 - 6, comprising determining movements of the blade (22) using one or more sensors (121, 122) on the blade holder (130), optionally wherein the sensors (121, 122) on the blade holder include an accelerometer or a position sensor.

8. The method (300) of any of claims 1 - 7, wherein the sensors (123) for determining oscillations of the hub are mounted on the hub and include an accelerometer and / or a position sensor.

9. A blade holder (130) configured for holding a blade (22), comprising:one or more blade holder sensors (121, 122) for measuring movement or position of the blade holder (130);one or more fans (111, 112, 113, 114); anda control system, wherein the control system is configured to:receive signals from one or more hub sensors (123) on a hub (20) of a wind turbine; determine movement of the hub (20) based on the received signals from the hub sensors (123);receive signals from the blade holder sensors (121, 122);determine movements of the blade holder (130) based on the received signals from the blade holder sensors (121, 122); andto drive the fans (111, 112, 113, 114) to synchronize the movement of the blade holder (130) with the movement of the hub (20).

10. The blade holder (130) of claim 9, wherein the blade holder sensors (121, 122) include a position sensor and / or an accelerometer.

11. The blade holder (130) of claim 9 or 10, wherein the fans (111, 112, 113, 114) include one or more fans to cause an oscillation of the blade holder (130) substantially parallel to a longitudinal axis (L) of the wind turbine blade (22).

12. The blade holder (130) of any of claims 9 - 11, wherein the fans (111, 112, 113, 114) include one or more fans to cause an oscillation of the blade holder (130) substantially horizontally and perpendicular to the longitudinal axis (L) of the wind turbine blade.1913. The blade holder (300) of any of claims 9 - 12, wherein one or more of the fans (111, 112, 113, 114) is a bidirectional fan.

14. A system for synchronizing movements of a wind turbine blade (22) with movements of a hub (20) of a wind turbine, the system comprising:a blade holder (130) according to any of claims 9 - 13 and;a hub sensor system (123) configured to be mounted on the hub (20) of the wind turbine and configured to measure signals indicative of movements of the hub and to transmit the signals to the control system of the blade holder (130).

15. The system of claim 14, further configured to send signals indicative of the movements of the blade holder and of the hub to a crane.

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