Pitch assembly and related methods

Abstract

To provide pitch assemblies and methods for determining one or more pitch references for a pitch control system of a wind turbine.SOLUTION: The present disclosure relates to pitch assemblies and methods for determining one or more pitch references for a pitch control system of a wind turbine. The assembly comprises: a wind turbine hub; a pitch bearing including a hub bearing ring configured to be attached to a hub flange and a blade bearing ring configured to be attached to a wind turbine blade; a target configured to be attached to one of the blade bearing ring and the hub; and a sensor configured to be connected to the other of the wind turbine hub and the blade bearing ring, and configured to sense the target such that a position of the target with respect to the sensor can be determined.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to wind turbines, and more particularly to a pitch assembly and method for determining one or more pitch references for a pitch control system of a wind turbine.

Background Art

[0002] Generally, modern wind turbines are used to supply electricity to the power grid. This type of wind turbine generally includes a tower and a rotor disposed on the tower. The rotor, typically including a hub and a plurality of blades, is adapted to rotate under the influence of wind on the blades. The rotation typically generates torque that is transmitted directly through the rotor shaft or through a gearbox to a generator. In this way, the generator generates electricity that can be supplied to the power grid.

[0003] The wind turbine hub may be rotatably coupled to the front of the nacelle. The wind turbine hub can be connected to a rotor shaft, which can then be rotatably mounted within the nacelle using one or more rotor shaft bearings disposed within a frame inside the nacelle. The nacelle is, for example, a housing disposed on top of a wind turbine tower that houses and protects additional components such as a gearbox (if present) and a generator, as well as a power converter and auxiliary systems depending on the wind turbine.

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

[0005] When a pitch bearing ring rotates relative to another bearing ring, for example using an electric or hydraulic pitch actuator, the blades can rotate relative to the hub. For example, a blade mounted on an inner bearing ring can rotate relative to the hub. This rotation of wind turbine blades is sometimes commonly referred to as blade "pitch." In (electric)mechanical pitch systems, a pinion can mesh with an annular gear, usually provided on the bearing ring to which the blades are joined, in order to rotate the wind turbine blades. Pitch can adjust the loads acting on the blades and wind turbine, and is used to adapt the blades to typical wind conditions and optimize or improve the operation of the wind turbine. Blade pitch can also be used when stopping a wind turbine. In such cases, the blades are pitched to a "feather" position.

[0006] To precisely control the pitch angle during operation, an initial reference or homing reference must be known and defined in the control system, for example, by the pitch control system and the wind turbine controller. This initial reference point later serves as the reference for pitching the blades. For example, the wind turbine controller may indicate the pitch system to pitch the blades to 30°, and 30° is applied relative to this initial point or reference point.

[0007] The pitch homing criterion, i.e., the starting point or axis on which the pitch angle is measured, calculated, or indicated, can, in some examples, indicate a pitch position that should be maintained at wind speeds lower than the nominal wind speed. This position may be known as "below rated pitch position" or "default pitch position." In these examples, the rotor blades can be positioned in the feather position by pitching at an angle of approximately 90°.

[0008] Once the wind turbine blades are mounted to the hub at the installation site, it is known to establish a pitch homing criterion. For example, the wind turbine blades may have projections that extend inward into the hub, which can be detected by a device inside the hub. In some of these examples, the hub may include a laser and a sensor. The laser can emit light substantially parallel to the length of the blade, and the sensor can collect one or more reflections of this light. As the wind turbine blades are pitched, the blade flange may block the light emitted by the laser, and the light collected by the sensor may change. Thus, the collision of the emitted light with the blade flange can indicate a pitch homing criterion.

[0009] Since the blade projections are positioned at specific circumferential positions on the inner surface of the blade, and the laser and sensors are positioned at specific circumferential positions inside the hub, a pitch reference can be established. After the blade projections are aligned with the laser and sensors, the pitch reference can become known to the wind turbine control system, such as the pitch control system and / or the main wind turbine controller.

[0010] Such systems and methods for determining pitch homing criteria may require considerable time on-site, whether onshore or offshore, for installation and commissioning. Therefore, workers may need to remain at high altitudes, and potentially for extended periods, under conditions lower than ideal weather conditions. Weather conditions can be particularly harsh in offshore environments. Setting initial pitch homing criteria can pose significant risks to the workers involved. Furthermore, the homing process is time-consuming, which can make the installation process very expensive, especially for offshore wind turbines.

[0011] Establishing the pitch homing reference as accurately as possible is crucial, both at the single-blade and rotor levels. An inaccurate pitch reference can cause one or more wind turbine blades to be in a position that is not their actual position as indicated by the wind turbine controller, potentially leading to reduced energy output and increased stress on the turbine. Furthermore, if the pitch homing reference is not substantially the same for each blade of the rotor, load imbalances can occur. Consequently, this can shorten the lifespan of the wind turbine and increase the need for maintenance and repairs. [Overview of the Initiative]

[0012] In one aspect of the present disclosure, a pitch assembly is provided. The pitch assembly includes a wind turbine hub, a pitch bearing, a sensor, and a target. The pitch bearing includes a hub bearing ring configured to be mounted on a hub flange and a blade bearing ring configured to be mounted on a wind turbine blade. The target is configured to be mounted on either the blade bearing ring or the wind turbine hub. The sensor is configured to be connected to the other of the wind turbine hub and the blade bearing ring and is configured to detect the target so that the position of the target relative to the sensor can be determined.

[0013] According to this embodiment, the sensor can be mounted at a specific position on the hub, and the target can be mounted at a specific position on the bearing ring to which the wind turbine blades can be later joined. Alternatively, the sensor can be mounted at a specific position on the bearing ring to which the wind turbine blades can be later joined, and the target can be mounted on the hub. The target can be detected by the sensor. The position of the target relative to the sensor can be determined. Any sensor that can know the position of the target relative to the sensor can be used. For example, a magnetic sensor, an inductive sensor, a capacitive sensor, or a color sensor can be used.

[0014] By positioning a target or sensor on the blade bearing ring to determine the pitch reference, pitch homing reference, or another pitch reference, the need to mount the wind turbine blades to the hub to determine the pitch reference can be avoided. Thus, the determination can be made even before transporting the hub and blades to the wind turbine installation site, and even before the wind turbine is installed on-site. For example, the alignment may be performed at the hub assembly plant. Because the alignment can be done in advance, the time required for wind turbine installation and commissioning can be reduced. In addition, worker safety may be improved because workers do not need to perform the alignment on-site in hubs or nacelles at heights of, for example, 70 meters, 100 meters or more. Both embodiments may be particularly relevant to offshore wind turbines, where weather and environmental conditions can increase the difficulty and risks of wind turbine installation and commissioning.

[0015] Throughout this disclosure, “Pitch System Reference” or “Pitch Reference” can be understood as at least a reference point or axis of a pitch control system. Such reference may be a “Pitch Homing Reference” or another reference that may be considered relevant or of interest.

[0016] In this specification, “pitch homing reference” can be understood as a reference point or axis where the pitch angle can be determined, calculated, measured, or indicated by, for example, a pitch control system and / or a main wind turbine controller. In particular, this reference point may be “0” or a starting point for pitching the wind turbine blades. In some examples, the pitch homing reference may indicate a pitch position that should be maintained at a wind speed lower than the nominal wind speed. A pitch reference different from the pitch homing reference may indicate, for example, the feather position of the wind turbine blades.

[0017] A further aspect of the present disclosure provides a method for determining a reference point for a pitch control system, which is a reference point for the pitch control system. The method includes the step of mounting a first bearing ring of a pitch bearing to a hub flange of a wind turbine hub. The method further includes the step of determining the pitch reference by a sensor that detects when a target is in a predetermined position relative to the sensor as a second bearing ring of the pitch bearing is rotated.

[0018] A further aspect of the present disclosure provides a method for determining a reference that can be used for or during the pitch of a wind turbine blade. The method includes the steps of: attaching a first ring of a pitch bearing to a hub flange of a wind turbine hub; attaching a light-emitting device (LECD) including a light source and a light sensor to the hub at a first reference position; attaching a target to a second ring of the pitch bearing at a second reference position; emitting light outward from the hub parallel to the pitch axis; rotating the second bearing ring; and determining a pitch reference by detecting a change in light received by the light sensor when the first and second reference positions are aligned substantially parallel to the pitch axis.

[0019] Throughout this disclosure, a light-emitting diode (LECD) can be understood as a set of light-emitting elements and light-receiving elements. These light emitters and light sensors may be arranged together inside a case or device that houses them, such as a laser sensor. Alternatively, they may be separate elements; for example, the light sensor may be a camera, and the light emitter may be a laser or light-emitting diode (LED). If the light emitters and light sensors belong to the same device, they may be controlled dependently, i.e., they may share a control processing unit (CPU) and memory. If the light emitters and light sensors are separate elements, they do not have to share a CPU and memory. In this case, an additional device, such as a controller located in a hub, can collect data from both elements and operate on this data. In some examples, the emitters and sensors may be coupled together and communicate with each other as needed, for example, to control the emission of light at a specific time and / or frequency.

[0020] The “predetermined reflective properties” used throughout this disclosure can be understood as a target having known reflective properties, that is, when the target interferes with the light beam from the LECD, and in that case, how the target interferes with the light beam is known, and therefore can be detected and identified. [Brief explanation of the drawing]

[0021] [Figure 1] This diagram schematically shows a perspective view of an example of a wind turbine. [Figure 2] This figure shows a simplified internal view of an example of a wind turbine nacelle. [Figure 3] This diagram schematically shows an example of a pitch assembly for setting the pitch reference of a pitch control system. [Figure 4] This diagram schematically shows an example of a pitch assembly target. [Figure 5] This diagram schematically shows an example of a light-emitting diode (LECD) mounted on a support. [Figure 6] FIG. is a schematic view showing an example of a LECD attached to another support. [Figure 7A] FIG. is a schematic top view of a pitch bearing attached to a hub flange, showing an exemplary configuration in which a pitch homing reference can be determined indirectly from another detected pitch reference. [Figure 7B] FIG. is a schematic top view of a pitch bearing attached to a hub flange, showing an exemplary configuration in which a pitch homing reference can be determined indirectly from another detected pitch reference. [Figure 8] FIG. is a schematic radial cross-sectional view of an example of a pitch assembly. [Figure 9] FIG. is a schematic view of an example of a method for setting a pitch reference of a pitch control system of a wind turbine using the pitch assembly described herein. [Figure 10] FIG. is a schematic view of an example of a method for determining a reference that can be used for or during pitching of a wind turbine blade using the pitch assembly described herein.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] Here, embodiments of the present invention will be referred to in detail, one or more examples of which are shown in the drawings. Each example is presented as illustrative of the invention and not limiting thereof. Indeed, it will be apparent to those skilled in the art that various modifications and changes can be made to the present invention without departing from the scope or spirit thereof. For example, features illustrated or described as part of one embodiment can be used with another embodiment to obtain yet another embodiment. Accordingly, the present invention is intended to embrace such modifications and changes that fall within the scope of the appended claims and their equivalents.

[0023] Figure 1 shows a perspective view of an example of a wind turbine 160. As shown, the wind turbine 160 includes a tower 170 extending from a support surface 150, a nacelle 161 mounted on the tower 170, and a rotor 115 coupled to the nacelle 161. The rotor 115 includes a rotatable hub 110 and at least one rotor blade 120 coupled to the hub 110 and extending outward from the hub 110. For example, in the illustrated embodiment, the rotor 115 includes three rotor blades 120. However, in alternative embodiments, the rotor 115 may include more or fewer rotor blades 120 than three. Each rotor blade 120 may be spaced around the hub 110 to facilitate the rotation of the rotor 115 and to allow kinetic energy from the wind to be converted into usable mechanical energy, and subsequently electrical energy. For example, the hub 110 may be rotatably coupled to a generator 162 (Figure 2) positioned within the nacelle 161, enabling the generation of electrical energy.

[0024] Figure 2 shows a simplified internal view of an example of the nacelle 161 of the wind turbine 160 of Figure 1. As shown, the generator 162 may be located within the nacelle 161. Generally, the generator 162 may be coupled to the rotor 115 of the wind turbine 160 to generate electricity from the rotational energy generated by the rotor 115. For example, the rotor 115 may include a main rotor shaft 163 coupled to the hub 110 for rotation together with the hub 110. The generator 162 may then be coupled to the rotor shaft 163 so that the rotation of the rotor shaft 163 drives the generator 162. For example, in the illustrated embodiment, the generator 162 includes a generator shaft 166 rotatably coupled to the rotor shaft 163 through a gearbox 164.

[0025] It should be understood that the rotor shaft 163, gearbox 164, and generator 162 can generally be supported within the nacelle 161 by a support frame or bed plate 165 positioned at the top of the wind turbine tower 170.

[0026] The nacelle 161 may be rotatably coupled to the tower 170 via a yaw system 20 so that the nacelle 161 can rotate about the yaw axis YA, or there may be other ways to position the rotor at a desired angle to the wind. If a yaw system 20 is present, such a system typically includes a yaw bearing having two bearing components configured to rotate relative to one another. The tower 170 is coupled to one of the bearing components, and the bed plate or support frame 165 of the nacelle 161 is coupled to the other bearing component. The yaw system 20 includes an annular gear 21, a plurality of yaw drive units 22 having motors 23, a gearbox 24, and a pinion 25 for meshing with the annular gear 21 to rotate one of the bearing components relative to the other.

[0027] As described above, the blade 120 is coupled to the hub 110 by a pitch bearing 100 between the blade 120 and the hub 110. The pitch bearing 100 includes an inner ring 103 and an outer ring 104. The wind turbine blade may be mounted on either the inner ring or the outer ring of the bearing, and the hub is connected to the other. When the pitch system 107 is actuated, the blade 120 can perform rotational motion relative to the hub 110. Thus, the inner bearing ring can perform rotational motion relative to the outer bearing ring in Figure 2. The pitch system 107 in Figure 2 includes a pinion 108 that meshes with an annular gear 109 provided on the inner bearing ring to rotate the wind turbine blade around the pitch axis PA.

[0028] Figure 3 schematically shows an example of a pitch assembly 300. The pitch assembly 300 is suitable for setting the pitch reference of a pitch control system, for example, the pitch homing reference of a wind turbine blade 120.

[0029] The pitch assembly 300 includes a wind turbine hub 110, a pitch bearing 100, a sensor (305), and a target 310.

[0030] The pitch bearing 100 includes a blade bearing ring 101 and a hub bearing ring 102. The hub bearing ring 102 is configured to be mounted on a hub flange 440 (see, for example, Figure 8), and the blade bearing ring 101 is configured to be mounted on a wind turbine blade 120, more specifically on the blade mounting flange.

[0031] The target 310 is configured to be attached to either the blade bearing ring 101 or the wind turbine hub 110. For example, the target 310 may be configured to be attached to the blade bearing ring 101.

[0032] The sensor 305 is configured to be connected to the blade bearing ring 101 and the other to the wind turbine hub 110. For example, the sensor may be configured to be mounted on the wind turbine hub 110. The sensor 305 is configured to detect the target 310 so that the position of the target 310 relative to the sensor 305 can be determined.

[0033] In some examples, detecting target 310 can indicate that target 310 and sensor 305 have been aligned in a direction substantially parallel to, for example, the pitch axis. Alignment can indicate that a pitch homing criterion has been reached, or that an additional or intermediate criterion has been achieved. In the second case, the pitch homing criterion may be determined from an additional or intermediate criterion by knowing the angular distance between the alignment position and the desired pitch homing criterion.

[0034] In some examples, the sensor 305 may be a light-emitting concentrator 305 (LECD, better shown in Figure 5). The LECD 305 includes a light source configured to emit light. The LECD 305 in this example also includes a light sensor configured to receive one or more reflections of the emitted light. The target 310 may have predetermined reflective properties so that the position of the target 310 relative to the LECD 305 can be determined.

[0035] In Figure 3, the hub bearing ring 102 is the outer bearing ring 104, and the blade bearing ring 101 is the inner bearing ring 103. In other examples, the order may be reversed.

[0036] The hub flange to which the bearing ring can be attached, and the attached bearing ring, define the circumferential direction 320 and the radial direction 321. In this case, the pitch axis may be substantially perpendicular to the directions of the circumferential direction 320 and the radial direction 321.

[0037] In some examples, the light source may be configured to emit light outward 111 of the hub 110. In Figure 3, reference numeral 112 denotes the inside of the hub 110. In this example or other examples, the light source may be configured to emit light substantially parallel to the pitch axis PA (see Figure 2).

[0038] When light is radiated outward 111 of the hub 110, it is understood that the target 310 is above the LECD 305. "Above" can generally be understood as being within a plane on a reference (including the radial 321 and circumferential 320 directions). More clearly in Figures 3 and 6, the target 310 is above the LECD 305. However, this does not rule out the possibility that in some other examples, the light may be radiated inward 112 of the hub 110, and the target 310 may be below the LECD 305.

[0039] The light source and light sensor of the LECD305 are considered to be included in element 305 in Figure 3, and generally in the illustrated diagram. However, it should be noted that element 305 may refer only to the light source, and the light sensor may be located elsewhere. For example, the light source and light sensor may be separate elements that are located inside 112 of the hub 110 at a certain distance from each other along the radial direction 321 or the circumferential direction 320.

[0040] As the blade bearing ring 101 rotates using the pitch system, the target 310 can change the light emitted by the light source at several positions. As a result, the light collected by the light sensor can change substantially. For example, the light sensor may detect a substantially constant light input, but if the target interferes with the emitted light, the amount of light received by the sensor may increase or decrease substantially due to the effect of the light emitted by the light source on the target.

[0041] Therefore, the change in light received by the sensor due to the target 310 altering the light emitted by the light source can indicate that a specific position has been achieved. This specific position may be a pitch homing criterion in some examples. In some other examples, this specific position may be used to determine the pitch homing criterion, as will be further described below.

[0042] Modifying the light emitted by the light source using target 310 may include modifying the reflection (e.g., trajectory) of the emitted light. By modifying the light emitted by the light source, the amount of light received by the light sensor can be changed. Target 310 may be specifically configured to modify the light emitted by the light source.

[0043] In some examples, the target 310 can change the light emitted by the light source when the light source and the target 310 are aligned along the pitch axis. In other examples, this particular alignment is not necessary.

[0044] The pitch homing criteria, and optionally additional pitch criteria, can be stored for later reference to the wind turbine controller, e.g., the main wind turbine controller, and the pitch system controller. One or more pitch criteria may also be referenced to the pitch motor.

[0045] The pitch reference can be obtained by attaching the target 310 to the blade bearing ring 101 (or the wind turbine hub 110, and a sensor to the blade bearing ring 101), so it is not necessary to connect the wind turbine blades 120 to the hub 110 by the blade bearing ring 101 in order to determine the pitch reference. Therefore, the pitch reference can be obtained, for example, in an assembly plant, before transporting the wind turbine components to the installation site. This reduces installation and commissioning time, as well as the risks to the workers performing the installation and commissioning.

[0046] This may be particularly important for offshore installations and commissioning, where environmental and atmospheric conditions may make successful and smooth installation and commissioning difficult.

[0047] Careful and precise mounting of the target 310 to the blade bearing ring 101 or hub 110, and careful and precise mounting of the light source and light sensor to the hub 110 or blade bearing ring 101 can help reduce errors when determining the pitch reference. Similarly, careful and precise mounting of the wind turbine blade 120 to the blade bearing ring 101 can reduce errors during pitching.

[0048] In some examples, as shown in Figure 4, for instance, the target 310 may include a target portion 315 having different reflective properties from the other parts of the target 310, for example, all the other parts of the target 310. The target portion 315 may cause variations in the reflection of light emitted by the light source, and therefore the light received by the light sensor. The target portion 315 may alter the trajectory of the incoming light, or it may remain inactive. The target portion 315 may be made of a different material from the other target portions, including all the other target portions, or may include such a material. In some examples, the target portion 315 may be more reflective than the rest of the target portions. For example, the target portion 310 may have a reflective coating. In some other examples, the target portion 315 may be a slit.

[0049] By defining one or more parts of the target 310 that can change the synchrotron radiation, it is possible to detect not only the difference in the light received when the target 310 changes its radiation and when it does not, but also further differences in the light reflected by different parts of the target 310. This then allows for a more accurate determination of the pitch reference.

[0050] The extension of the target portion 315, such as a slit, in the circumferential direction 320 may be less than 1 mm, and optionally less than 0.5 mm. The shorter the target portion 315 in the circumferential direction 320, the higher the accuracy of establishing the pitch reference.

[0051] The target 310 may be attached to the blade bearing ring 101 or the hub 110 in different ways. In the examples in Figures 3 and 4, mechanical fasteners 325 such as bolts, screws, or rivets are used. In some other examples, other fasteners, such as adhesives, may be used alternatively or additionally. In general, any number of fasteners and any type of fasteners can be used. The type of fastener can be selected, for example, depending on whether the target 310 is to remain attached during the operation of the wind turbine 160 or whether the target 310 is to be removed before the wind turbine 160 starts operation.

[0052] The target 310 may be mounted on a side 330 of the blade bearing ring 101 on which the drive unit operates. In some examples, the drive unit may include an electric motor, a reduction gear, and a pinion 108. In other examples, the target 310 may be mounted on a different side of the blade bearing ring 101.

[0053] The pitch assembly 300 may further include a support 335 to which a sensor can be mounted. If the sensor is an LED, a light source, and optionally a light sensor, may be mounted on the support 335. The support 335 can help position the light source at a more suitable location for transmitting light, for example, near the target 310. The support 335 may be positioned on the platform 340 inside the hub 110 when the target 310 is mounted on the bearing inner ring 103.

[0054] When the inner bearing ring 103 is attached to the hub 110 and the target 310 is attached to the outer bearing ring 104, at least the platform 340 for supporting the light source may be located outside 111 of the hub 110. In this case, the platform 340 may be directly attached to the hub 100, or additional connectors may be provided to enable a mechanical connection between the hub 110 and the platform 340. In some of these examples, the outer bearing ring 104 may include an annular gear 109 for rotating the outer bearing ring 104 relative to the inner bearing ring 103 and the hub 110.

[0055] If the target 310 is attached to the hub 110 instead of the sensor 305, the support 335 can also be used to connect the target 310 to the hub 110.

[0056] In some examples, the support 335 may include a reflector 350 and have a height that allows the target 310 to pass between the light source and the reflector. Since the light emitted by the light source may collide with the reflector 350 unless the target 310 changes the path the emitted light follows, the reflections collected by the light sensor can provide a more constant, flatter, and less variable progression of received light over time than in the absence of the reflector 350. Thus, the passage of the target 310 above (or below) the light source can be detected more easily and clearly. Therefore, the use of the reflector 350 can improve the accuracy of determining the pitch reference.

[0057] The distance between the reflector 350 and the support 335 and / or between the reflector 350 and the light source can be adjusted so that the target 310 passes between the light source and the reflector 350 as the blade bearing ring 101 rotates. Additionally or alternatively, the dimensions of the target 310 and the location on which it is mounted on the blade bearing ring 101 may be adapted to satisfy this condition.

[0058] The reflector 350 may be located on the upper part 355 of the support 335. In the example of Figure 5, the LECD 305 and reflector 350 face the side 360 ​​of the support 335, but in other examples, the LECD 305 and reflector 350 may face the other rear surface 365 of the support 335 or be substantially in the center.

[0059] As shown in Figure 5, the light source and reflector 350 may be aligned in a direction parallel to the pitch axis, but it should be noted that this is not necessary.

[0060] In this example, if the target 310 is not positioned between the light emitter and the reflector, substantially all of the emitted light is received by the condenser. When the target 310 is positioned between the light emitter and the reflector, the amount of received light decreases. Therefore, the system can identify that the target 310 is located at a known position or within a small range of a known position. As the bearing ring with the target 310 rotates further, the target portion 315 is positioned between the light emitter and the reflector. If the target portion is formed as a slit, the light is again reflected substantially completely. The precise positions of the target 310 and the target portion 315 relative to the LECD 305 can be identified.

[0061] In some examples, the support 335 may further include a mechanical switch 370. The mechanical switch 370 is configured to contact the target 310 when the blade bearing ring 101 rotates, for example, when the target 310 is aligned with the light source in a direction substantially parallel to the pitch axis. In some of these examples, the mechanical switch 370 may be a limit switch. As the blade bearing ring 101 with the mounted target 310 moves, it can engage the mechanical switch 370. The position in which this occurs can be interpreted as a check, for example, a check that the feather position has been reached.

[0062] The support 335 may include only the reflector 350 as shown in Figure 5, only one or more mechanical switches 370 as shown in Figure 6, or it may include the reflector 350 and one or more mechanical switches 370 (not shown).

[0063] In some examples, an additional pitch criterion may be determined first, and the pitch homing criterion may be obtained later from the additional criterion. For example, the position where target 310, e.g., target portion 315, changes the light emitted by the light source and therefore also received by the light sensor does not have to indicate a position where the initial pitch angle can be changed, e.g., "0" or "less than the default rated pitch position," but can indicate another position, e.g., a position close to the feather position. As long as the position of target portion 315 is known with respect to this desired "zero" position, the information is sufficient for the control system.

[0064] Figures 7A and 7B schematically show top views of a pitch bearing mounted on a hub flange, each illustrating an exemplary configuration in which the pitch homing reference may be indirectly determined from another detected pitch reference. For simplicity, these figures assume that the light source and light sensor are located inside the LECD305 and that the light is emitted substantially parallel to the pitch axis.

[0065] In these figures, the target 310 and sensor 305 can be positioned at precise and known locations. For example, if an LECD is used, the light source and the photosensor can be positioned at precise and known locations relative to the blade bearing ring 101 and the hub 110, respectively, so that when the emitted light reaches the target 310 and the photosensor detects it, an indication of the feather position (labeled as FP in Figures 7A and 7B) of the wind turbine blade 120 attached to the blade bearing ring 101 can be found. If such a position is not the desired pitch reference (labeled as PR in Figures 7A and 7B), this additional reference can be detected by the light striking the target 310, and the pitch homing reference position can be determined later.

[0066] For example, as schematically shown in Figure 7A, if the pitch homing reference PR is considered to indicate a pitch position that should be maintained in a first operating range that is lower than the nominal wind speed, for example, above the cut-in wind speed, then the target 310 may be mounted on this desired portion of the bearing, and the LECD 305 may be mounted at a position between 80 and 90° from this initial pitch reference, for example, at a position 88.5° away from the pitch homing reference. When light emitted by the LECD 305 strikes the target 310, which is detected by the sensor, and the position of 88.5°, and therefore the feather position, the target 310 deflects the light emitted by the light source, and the position below the rated pitch can be determined by subtracting 88.5° from the position found by the light sensor detecting this event 310.

[0067] Here again, it should be noted that the pitch homing criterion may correspond to a position other than the pitch position that should be maintained at a wind speed lower than the nominal wind speed. Such a situation is schematically represented in Figure 7B. In this example, the alignment of target 310 and LECD 305 can substantially again indicate the feather position, but the pitch homing criterion may be about 45° away from the feather position, for example, 45.3°. For example, once the feather position is determined using LECD 305, 45.3° can be subtracted from the feather position to find the pitch homing criterion.

[0068] Similarly, the additional references indicating the feather position in Figures 7A and 7B do not necessarily have to indicate such a feather position; they could be any other position.

[0069] In this way, two different criteria of interest to the pitch control system can be established relatively easily, quickly, and accurately.

[0070] When the wind turbine is operating, if one or more mechanical switches 370 are present, targets 310 entering them may indicate that an additional criterion, such as a feather position, has been achieved. This can serve as confirmation that a desired additional criterion has been achieved.

[0071] In some examples, the blade bearing ring 101 is configured to allow the wind turbine blades 120 to be mounted on the blade bearing ring 101 in a limited number of positions, particularly in a single position.

[0072] To minimize errors when pitching the blade 120, once a pitch homing reference is determined, the blade 120 will be connected to the blade bearing ring 101 at specific positions according to the determined homing pitch reference. The blade 120 and / or blade bearing ring can be configured for this purpose, i.e., they can be configured such that incorrect mounting of the blade is (almost) impossible.

[0073] In some examples, the blade bearing ring 101 may include one or more wind turbine blade mounting indicators 405. These indicators can enable the wind turbine blades 120 to be mounted on the blade bearing ring 101 in specific intended positions. Thus, errors in pitching the blades 120 can be avoided or at least minimized. In some examples, the indicators may be visual.

[0074] In some examples, the wind turbine blade mounting indicator 405 may include complementary recesses and / or protrusions to the projections and / or recesses of the wind turbine blade joining flange 430, which is configured to be mounted to the blade bearing ring 101. These projections and / or recesses may have a specific size and shape to facilitate mounting and improve its precision.

[0075] When a ring extender is used, referring to Figure 8, the assembly 300 may further include a ring extender 410, the ring extender 410 including one or more wind turbine blade mounting indicators 405, for example, recesses 405 complementary to projections or fasteners on the wind turbine blade mounting flange 430 joined to the ring extender 410.

[0076] In some examples, the ring extender 410 may be formed integrally with the blade bearing ring 101. If, instead, the ring extender 410 and the blade bearing ring 101 are separate pieces, the ring extender 410 may include one or more wind turbine blade mounting indicators 405 on the ring extender joint side 435 configured to be attached to the wind turbine blade 120, such as projections and / or recesses with complementary recesses and / or projections, respectively.

[0077] Optionally, the ring extender 410 and the blade bearing ring 101 may also have complementary mounting indicators 405, such as recesses and / or protrusions, on the sides that can be joined to each other.

[0078] In some examples, one of the blade bearing ring 101 and the wind turbine blade 120 includes a fastener, and the other is configured to receive the fastener. In some examples, the fastener may be a projection that is received by a complementary recess, as described above. A ring extender 410 is also intended, and if present, the above description regarding the possible locations of the fastener and corresponding fastener receiving elements also applies.

[0079] In several other examples, paint, for example, paint of a particularly easily distinguishable color, may be useful in indicating the desired orientation of the wind turbine blades 120 relative to the hub 110.

[0080] Although the blade 120 should be mounted in a single intended position, if several mounting indicators 405 or fasteners are provided, it is possible that the blade 120 may be mounted in an undesirable position. In some examples, the mounting indicators 405 may have different shapes, dimensions, and / or colors to avoid or at least reduce the possibility of misplacing the blade 120 on the blade bearing ring 101. In some examples, two or more types of indicators may be used, for example, fasteners and paint may be used together.

[0081] In some examples, the pitch assembly 300 may include a wind turbine blade 120 that includes one or more wind turbine blade mounting indicators 405, such as recesses and / or protrusions complementary to, for example, protrusions and / or recesses of, the blade bearing ring 101 or ring extender 410. The wind turbine blade 120 may also include one or more fasteners, or be configured to receive one or more fasteners. The blade 120 may additionally or alternatively include painted marks.

[0082] In some cases, guide bushings may be used. That is, the bushing of the bearing ring may have a diameter that decreases from a first end to a second end where a stud or other fastener is received. In this way, the precise mounting of the blade to the bearing ring can be further facilitated.

[0083] While the text refers to recesses and / or protrusions, please understand that a single recess and / or single protrusion within a piece (blade joining flange, blade bearing ring, ring extender) is also an option.

[0084] In another aspect of the present invention, a method 500 is provided for determining a reference point for a pitch control system, which is a reference point for the pitch control system. This method uses the pitch assembly 300 described above, for example with reference to any of Figures 3 to 8. The description relating to one or more of these figures may be applied directly to this method.

[0085] The method includes the step of attaching the first bearing ring 102 of the pitch bearing 100 to the hub flange 440 of the wind turbine hub 110 in block 510. The first bearing ring 102 was previously called the hub bearing ring 102. The first bearing ring 102 may be the inner bearing ring 103 or the outer bearing ring 104.

[0086] The first bearing ring 102 may be attached to the hub 110, such as a hub flange 440, by a bolted connection, for example, as shown in Figure 8. Referring to Figure 8, the end of the bolt 415 may be inserted through the opening of the first ring 102, for example, screwed in, or bolted in. The other end of the bolt 415 may be fixed to a nut 420. A washer 425 may be further placed between the first bearing ring 102 and the nut 420.

[0087] The method further includes the step of determining a pitch reference by a sensor 305 that detects when the second bearing ring 101 of the pitch bearing 100 is rotated, thereby determining that the target 310 is in a predetermined position relative to the sensor 305.

[0088] The rotation may be driven, for example, by the pinion 108 engaging with the annular gear 109 on the second bearing ring 101. The second bearing ring 101, unlike the first bearing ring 102, has previously been called the blade bearing ring 101. The second bearing ring 101 may be the inner bearing ring 103 or the outer bearing ring 104.

[0089] As described above, a sensor that detects a target can indicate that a specific criterion has been met. For example, when an LED is used as the sensor, a change in light received by the light sensor, caused by the target 310 blocking the light emitted by the light source, can indicate that a specific criterion has been met. The specific criterion may already be a pitch homing criterion in some examples, or it may be an additional criterion in other examples. That is, the determined criterion can indicate a criterion from which the homing criterion can be determined. In some examples, the method may further include a step of calculating the pitch homing criterion from the determined criterion. For example, the additional criterion may indicate the feather position, and then the pitch homing criterion can be obtained from the feather position criterion. In any case, an accurate pitch criterion can be obtained.

[0090] Since the wind turbine blades 120 do not need to be attached to the pitch bearing 100, especially for determining the pitch reference of the pitch homing criterion, this method can be performed away from the installation site, whether on land or offshore. Therefore, installation and commissioning times can be reduced, and worker safety can be increased as workers do not need to spend so much time at high altitudes, possibly in less-than-ideal weather conditions.

[0091] If the sensor is an LED, the step of detecting that the target is in a predetermined position may include detecting a change in the light received by the light sensor when the target 310 changes the light emitted by the light source.

[0092] The sensor in the illustrated example is generally an LECD, but other sensors may be used. In general, any sensor capable of detecting the position of a target relative to the sensor can be used. For example, inductive, capacitive, or magnetic sensors can be used. Contact sensors or color sensors may also be used. The sensor can be used in combination with a suitable target, i.e., a target that enables detection by such a sensor.

[0093] Before rotating the second bearing ring 101, the sensor 305 can be attached to either the wind turbine hub 110 or the second bearing ring 101. The sensor is configured to detect the target 310 so that its position relative to the sensor 305 can be determined.

[0094] The sensor may be an LECD305 including a light source and a light sensor. The sensor or LECD305 may be mounted on the inner 112 portion or the outer 111 portion of the hub 110. As described above, the light source may, in some examples, be configured to emit light toward the outer 111 portion of the hub 110. The light sensor is configured to receive one or more reflections of the emitted light. In some examples, the light may be emitted substantially parallel to the pitch axis (PA).

[0095] The sensor or LECD305 may be attached to the hub 110, for example, to the platform 340 on the inside 112 or outside 111 of the hub 110, by mechanical and / or adhesive fasteners. The sensor or LECD305 may be attached to the hub 110 directly or indirectly. Indirect attachment may include a support 335. In such an example, the sensor or LECD305 may be attached to the support 335, for example to the upper part 355 of the support 335, and the support 335 may be attached to the hub 110, for example to the platform 340. For example, if the blade bearing ring 101 is the outer bearing ring 104, the sensor or LECD305 may be positioned appropriately and an arm may be used to connect it to the hub 110. The light source and the light sensor may be attached to the hub 110 separately. In some examples, the light source may be attached to the support 335 and the light sensor may be attached to the platform 340.

[0096] In other examples, the sensor may be attached to the second bearing ring 101.

[0097] The target 310 may be attached to the other of the second bearing ring 101 and the wind turbine hub 110. As described with respect to Figures 3 to 5, the target 310 can be configured to modify the light emitted by the light source as the second bearing ring 101 rotates. Properties such as the trajectory and / or reflection of the emitted light can be modified by the target 310.

[0098] When an LEDD is used, light may be emitted by a light source. The rotation of the second bearing ring 101 may begin before or after the emission of light begins. Optionally, the light may be emitted outward from the hub and / or substantially parallel to the pitch axis.

[0099] The target 310 may include a target portion 315 having different reflective properties from other parts of the target 310, for example, all other parts of the target 310. In some examples, the target portion 315 may be a piece of a different material from the other parts of the target 310, or may include such a piece. For example, the target portion 315 may be more reflective than the other parts of the target 310. The target portion 315 may include, for example, reflective paint, or it may be a slit. The accuracy of detecting changes in light received by the light sensor can be improved by adding the target portion 315 as described above.

[0100] If the second bearing ring 101 is an inner bearing ring 103, in some examples the target 310 may be mounted on the inner bearing ring 103 side facing the inner side 112 of the hub 110, for example, the side including the annular gear 109. If the second bearing ring 101 is an outer bearing ring 104, in some examples the target may be mounted on the outer bearing ring 104 side facing the outer side 111 of the hub 110. In other words, the target 310 may generally be mounted on the side 330 of the second bearing ring 101 on which the drive mechanism operates. In some other examples the target 310 may be mounted on any other side of the second bearing ring 101.

[0101] In some other examples, the target 310 may be attached to the wind turbine hub 110.

[0102] The target 310 may be attached to the second bearing ring 101 or the hub 110 by one or more fasteners. The one or more fasteners may include mechanical fasteners 325 and / or adhesive fasteners. The target 310 may be joined to the second bearing ring 101 before or after the pitch bearing 100, in particular the first bearing ring 102, is attached to the hub 110.

[0103] Similarly, the sensor or LECD305 may be mounted on the hub 110 or the second bearing ring 101 before or after the pitch bearing 100 is mounted on the hub 110, and before or after the target 310 is mounted on the second bearing ring 101 or the hub 110.

[0104] In some examples where the support 335 is used, the support 335 may include a reflector 350 as described above. The reflector 350 can help more easily and clearly detect changes in the light received by the light sensor. If a target portion 315 is present, the reflector 350 can be used in any configuration of the target portion 315. The support 335 may optionally or additionally include one or more mechanical switches 370.

[0105] When the pitch homing reference is directly determined, in some examples, the target 310 and the sensor or LECD 305 may be mounted in positions desirable to the pitch reference. For example, the desired positions of the target 310 on the second bearing ring 101 and the sensor or LECD 305 relative to the ring 101 are known in advance. The desired positions may be such that the pitch homing reference is determined when the target 310 and the sensor or light source are aligned by moving the second bearing ring 101. The alignment may be performed along a direction substantially parallel to the pitch axis.

[0106] If the pitch reference is determined indirectly, the target 310 and the sensor may be mounted in any suitable position. For example, the target 310 and the LECD 305 may be mounted in a position where additional reference is found when light emitted by the light source collides with the target 310, for example, the target portion 315, and the light sensor detects this event.

[0107] In some cases, the pitch homing criterion can indicate the pitch position that should be maintained at a wind speed lower than the nominal wind speed.

[0108] In some other examples, the determined criterion may indicate a feather position. In some of these examples, the target 310 and the sensor or LECD305 may be mounted at the same position between approximately 80° and approximately 100° from the desired position on the pitch homing criterion. The pitch homing criterion may be a pitch position below the rated position. "Same position" means that the target 310 and the sensor or LECD305 are positioned at the same angle from the desired pitch homing criterion, for example, approximately 95° away from it.

[0109] The pitch reference can be obtained, for example, by subtracting an angle of approximately 80° to 100° from a position where alignment is performed in a direction substantially parallel to the pitch axis.

[0110] In some examples, the method may further include the step of mounting the wind turbine blades 120 to the second bearing ring 101 or ring extender 410 according to a determined pitch criterion, such as a pitch homing criterion.

[0111] This may include the step of mounting a blade, for example, a wind turbine blade joining flange 430, in a predetermined position. The predetermined position may be indicated by one or more mounting indicators 405 or any indicator in general.

[0112] As described above, the wind turbine blade 120, for example, the wind turbine blade joining flange 430, may include one or more wind turbine blade mounting indicators 405, such as paint, fasteners, fastener receivers, protrusions and / or recesses. If directly joined to the second bearing ring 101, the second bearing ring 101 may include mounting indicators 405 configured to match the indicators 405 of the blade 120.

[0113] In some examples, the step of mounting the wind turbine blade 120 may include the step of inserting fasteners into complementary receptacles.

[0114] In some examples, one or more wind turbine blade mounting indicators 405 may be projections and / or recesses, and the method may include the step of fitting the wind turbine blade joining flange 430, which includes the recesses and / or projections, into complementary projections and / or recesses provided on the second bearing ring 101, respectively. The projections and recesses may have complementary shapes to facilitate insertion of the projections into the recesses, as shown, for example, in Figure 8.

[0115] Multiple types of indicators 405 may be used simultaneously. For example, fasteners and paint may be used together, or projections and / or recesses may be used in combination with paint. Paint marks other than fasteners or projections and / or recesses may help orient the blade 120 relative to the second bearing ring 101 for mounting in a specific intended position.

[0116] Next, the wind turbine blade 120 can be fixed to the blade bearing ring 101 by the bolted connection portion 415.

[0117] If the wind turbine blade 120 is not directly attached to the second bearing ring 101 but is attached to a separate ring extender 410, the method may further include the steps of attaching the ring extender 410 to the second bearing ring 101 and attaching the wind turbine blade 120 to the ring extender, wherein the blade 120 and the ring extender 410 are configured to be attached to a limited number of positions, preferably a single predetermined position. The blade 120 can be attached to the ring extender 410 in the same manner as described above with respect to the connection between the blade 120 and the second bearing ring 101.

[0118] Either the blade 120 or the ring extender 410 may include one or more wind turbine blade mounting indicators 405 on a side configured to make contact, for example, having complementary shapes. For example, the blade 120 may have a certain number of protrusions, and the ring extender 310 may have the same certain number of recesses, and the method may include the step of inserting the blade protrusions into the ring extender recesses.

[0119] If not integrally formed with the second bearing ring 101, the ring extender 401 may further include one or more wind turbine blade mounting indicators 405 configured to bond to one or more wind turbine blade mounting indicators 405 provided on the second bearing ring 101. In some examples, one or more wind turbine blade mounting indicators 405 may be projections and / or recesses. The ring extender 401 may then be attached to the second bearing ring 101.

[0120] In some examples, the sensor or LECD 305 and target 310 can be removed from the hub 110 and second bearing ring 101 before the wind turbine 160 is installed. In some other examples, they may be left installed so that the pitch reference can be re-determined if it is lost during wind turbine operation for any reason, for example, if the pitch control system is modified or after maintenance of the pitch bearings is performed.

[0121] If they are maintained and held in place over their normal operating life, the support 335 may include one or more mechanical switches 370, such as limit switches, to verify that additional criteria have been met. In some examples, even if the location where the collision occurs does not correspond to the pitch angle indicated by the wind turbine controller, one or more mechanical switches 370 on the support 335 can stop the pitch of the blade 120 when it collides with the target 310. The collision can be used as a way to verify that the correct position has been reached by pitching.

[0122] In another embodiment, a method 600 is provided for determining a pitch reference usable for or during the pitch of a wind turbine blade 120. This method uses the pitch assembly 300 described above, for example with reference to any of Figures 3 to 8. The description relating to one or more of these figures may apply directly to this method.

[0123] The method includes the step of attaching the first ring 102 of the pitch bearing 100 to the hub flange 440 of the wind turbine hub 110 in block 610. As previously described, the hub flange 440 and the attached bearing 100 define the circumferential direction 320 and the radial direction 321. The pitch axis is substantially parallel to these directions 320, 321.

[0124] The first bearing ring 102 can be attached to the hub flange 440 by a nut 420 and a bolt 415, for example, as shown in Figure 8.

[0125] The method further includes the step of mounting an LECD, including a light source and a light sensor, to the hub 110 at a first reference setting position 445 in block 620.

[0126] This first position 445 is a predetermined position and represents a reference index, such as a pitch index or an additional reference index. The LECD 305 may be attached to the hub 110, for example, directly to the platform 340 of the hub 110, or indirectly to it, for example, to the support 335.

[0127] The method further includes the step of attaching the target 310 to the second ring 101 of the pitch bearing 100 at a second reference setting position 450 in block 630.

[0128] This second position 450 is also a predetermined position and represents a reference index, such as a pitch reference or an additional reference index. In some examples, the target 310 may be mounted on the side 330 of the second bearing ring 101 on which the drive unit operates.

[0129] The method further includes the step of emitting light parallel to the pitch axis toward the outer 111 of the hub 110 in block 640.

[0130] The method further includes the step of rotating the second bearing ring 101 in block 650. A drive device such as a pinion 108 configured to act on an annular gear 109 can be used. Hydraulic operation is possible instead of mechanical operation.

[0131] Light can begin to be emitted before or after the rotation of the second bearing ring 101.

[0132] The method further includes the step of determining the pitch reference 455 by detecting a change in light received by an optical sensor when the first reference setting position 445 and the second reference setting position 450 are aligned in a direction substantially parallel to the pitch axis in block 660.

[0133] The light source emits light, and the light sensor receives one or more reflections of the emitted light. When the target 310 passes above the light sensor, particularly when the first reference setting position 445 and the second reference setting position 450 are aligned in a direction substantially parallel to the pitch axis, the target 310 can reflect the light emitted by the light source. Thus, the light sensor can detect a change in the light it is receiving, which indicates that the pitch reference has been achieved.

[0134] In some cases, the determined criterion is the pitch homing criterion. Thus, the point or axis from which the pitch angle can be measured, calculated, and / or indicated can be determined directly and accurately without the need to mount the wind turbine blade 120 to the hub flange 440.

[0135] In some other examples, the determined criterion is an intermediate criterion from which the pitch-homing criterion can be calculated from the pitch-homing criterion. This intermediate criterion corresponds to the additional criterion in Method 500. By first calculating the intermediate criterion, two criteria of interest can be obtained using a single LECD 305 and target 310. By knowing that the first criterion setting position 445 and the second criterion setting position 450 are (when aligned) a certain angle away from the desired pitch-homing criterion, the pitch-homing criterion can be quickly found as already described herein.

[0136] In some of these examples, the first reference point 445 and the second reference point 450 are configured to be at the same angle, approximately 80° to 100°, from the pitch homing reference when aligned. In other words, the pitch homing reference and the intermediate reference may be designed to be 80° to 100° apart. In some examples, the pitch homing reference may indicate a pitch position that should be kept at a wind speed lower than the nominal wind speed. The intermediate reference may indicate a feathering position.

[0137] One or more teachings from Method 500 may be applied to Method 600, and vice versa. For example, one or more mechanical switches 370 may be used in Method 600. Ring extenders 410 and / or one or more types of wind turbine blade mounting indicators 405 may also be used in Method 600.

[0138] Although only a few examples are disclosed herein, other substitutions, modifications, uses, and / or equivalents are possible. Furthermore, all possible combinations of the examples described are also covered. Therefore, the scope of this disclosure should not be limited by any particular example, but should be determined solely by a fair reading of the appended claims that follow below. [Explanation of symbols]

[0139] 20 Yaw System 21 Ring gear 22 Yaw drive device 23 Motor 24 Gearbox 25 pinion 100 pitch bearings, bearings, hubs 101 Blade bearing ring, second bearing ring, second ring 102 Hub bearing ring, first bearing ring, first ring 103 Bearing inner ring, inner bearing ring, inner ring 104 Bearing outer ring, outer ring 107 Pitch System 108 pinion 109 Annular gear 110 Wind Turbine Hub 111 Outside 112 Inside 115 Rotor 120 Wind turbine blades, rotor blades 150 Support surface 160 Wind Turbine 161 Nacer 162 Generators 163 Main rotor shaft 164 Gearbox 165 Bed plate, support frame 166 Generator shaft 170 Wind Turbine Towers 300 Pitch Assembly 305 Sensors, Light-Emitting Devices (LECDs), Elements 310 Target, Target portion, Ring extender, Event 315 Target area 320 Circumferential direction 321 Radial 325 Mechanical fasteners 330 Side view 335 Support 340 platforms 350 Reflector 355 Top 360 Side view 365 Rear 370 Mechanical switches 401 Ring Extender 405 Wind turbine blade mounting indicator, recessed 410 Ring Extender 415 Bolts, bolted connection parts 420 nuts 425 Washer 430 Wind turbine blade joining flange 435 Ring extender joint side 440 Hub Flange 445 First reference setting position, first position 450 Second reference setting position, second position 455 pitch standard 500 ways 600 ways

Claims

1. 1. A method (500) for determining a reference for a pitch control system, the pitch reference being a reference point for the pitch control system, the method (500) comprising: Mounting (510) a first bearing ring (102) of the pitch bearing (100) to a hub flange (440) of the wind turbine hub (110); determining (520) a pitch reference by a sensor (305) that detects that a target (310) is in a predetermined position relative to the sensor (305) when rotating a second bearing ring (101) of the pitch bearing (100); Including, the second bearing ring (101) is configured such that wind turbine blades (120) can be attached to the second bearing ring (101) in a limited number of predefined positions; the pitch reference is determined before the wind turbine blade (120) is mounted on the second bearing ring (101). Method (500).

2. 2. The method (500) of claim 1, wherein the blade bearing ring (101) is configured to allow for mounting the wind turbine blades (120) to the blade bearing ring (101) in a single location.

3. The method (500) of claim 1, wherein the target (310) is attached to the blade bearing ring (101) and the sensor (305) is connected to the hub (110).

4. 2. The method of claim 1, wherein the sensor (305) is a light emitting concentrator (LECD) (305) including a light source and a light sensor that emits light by the light source, and detecting that the target (310) is in a predetermined position includes detecting a change in the light received by the light sensor when the target (310) modifies the light emitted by the light source.

5. 5. The method of claim 4, wherein the target includes a target portion having reflectance characteristics different from other portions of the target.

6. 5. The method (500) of claim 4, further comprising a support (335) to which at least the light source is attached, the support (335) including a reflector (350) and having a height such that the target (310) can pass between the light source and the reflector (350).

7. 5. The method (500) of claim 4, further comprising a support (335) to which at least the light source is mounted, the support (335) including a mechanical switch (370) configured to contact the target (310) as the blade bearing ring (101) rotates.

8. The method of claim 4 , wherein the light is emitted substantially parallel to a pitch axis.

9. The method (500) of claim 1, wherein the blade bearing ring (101) includes one or more wind turbine blade attachment indicators (405).

10. The method (500) of claim 1 , wherein the determined criterion is a pitch homing criterion.

11. 11. The method (500) of claim 10, wherein the pitch homing criterion indicates a pitch position to be maintained at wind speeds below a nominal wind speed.

12. The method (500) of claim 10 or 11, wherein the determined criteria indicate a criterion from which a homing criterion can be calculated.

13. The method (500) of claim 12, wherein the determined criterion is indicative of a feather position.

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