System for non-contact displacement measurement of blade roots for wind turbines

Abstract

A system for measuring displacement of a blade root of a rotor blade of a wind turbine is disclosed. The system comprises a hub, a rotor blade coupled to the hub by a pitch bearing. The system further comprises a reference plane and at least one displacement sensor. The reference plane is configured to move with the rotor blade as the rotor blade moves relative to the hub, while the displacement sensor is fixed to the hub, and the displacement sensor is configured to detect displacement of the reference plane relative to the hub without physical contact. Alternatively, the reference plane has a fixed position relative to the hub, while the displacement sensor is fixed to the rotor blade, and the displacement sensor is configured to detect displacement of the reference plane relative to the rotor blade without physical contact.

Description

TECHNICAL FIELD

[0001] The present subject matter relates generally to wind turbines, and more particularly, to a system and method for measuring displacement of a blade root of a rotor blade of a wind turbine. BACKGROUND

[0002] Wind is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have gained increasing attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind using known airfoil principles and transfer the kinetic energy through rotational energy to turn a shaft that is coupled to the gearbox, or directly to the generator if no gearbox is used. The generator then converts the mechanical energy to electrical energy that can be deployed to a utility grid.

[0003] Wind turbines are exposed to various fluctuating wind loads acting on different components of the wind turbine. In order to control or limit the energy generated by the wind, modern wind turbines typically include rotor blades that are rotatable about their longitudinal axis (pitch axis). By adjusting the pitch angle of the rotor blades, the inflow conditions and thus the wind loads acting on the rotor blades can be influenced in order to improve the efficiency of the wind turbine or to slow down the wind turbine in strong gusts.

[0004] This pitch adjustment requires information about the wind loads acting on the rotor blades. This information is difficult to obtain due to the stochastic distribution of the wind, the dynamic behavior of the system itself, and the load transfer between different components of the system, for example. Dynamic simulations can provide estimates, but it would be advantageous to monitor actual parameters that allow a reliable estimation of the wind loads.

[0005] The present disclosure therefore relates to a system and method that allows monitoring of the wind loads acting on the rotor blades. SUMMARY

[0006] Aspects and advantages of the application will be set forth in part in the following description, or can be obvious from the description, or can be learned through practice of the application.

[0007] In one aspect, the present disclosure relates to a system for measuring displacement of a blade root of a rotor blade of a wind turbine. The system comprises a hub, a rotor blade coupled to the hub by a pitch bearing, a reference plane, and at least one displacement sensor configured to detect displacement of the reference plane without physical contact.

[0008] In one embodiment, the reference plane is configured to move with the rotor blade when the rotor blade moves relative to the hub while the displacement sensor is fixed to the hub. According to one aspect, the displacement sensor is configured to detect a displacement of the reference plane relative to the hub without physical contact. In particular, the displacement sensor can be configured to detect a radial, axial and / or a tilt displacement of the reference plane relative to the hub.

[0009] In another embodiment, the reference plane has a fixed position relative to the hub while the displacement sensor is fixed to the rotor blade. According to one aspect, the displacement sensor is configured to move with the rotor blade when the rotor blade moves relative to the hub while the hub comprises the reference plane. According to one aspect, the displacement sensor is configured to detect a displacement of the reference plane relative to the rotor blade, in particular relative to a blade root of the rotor blade. In particular, the displacement sensor can be configured to detect a radial, axial and / or a tilt displacement of the reference plane relative to the blade root.

[0010] In one embodiment, the system can further comprise a controller communicatively coupled to the displacement sensor. The controller can be configured to determine a bending moment exerted on a portion of the rotor blade, e.g. a blade root of the rotor blade, based on the signals received from the displacement sensor.

[0011] In a further embodiment, the system can comprise a pitch adjustment mechanism communicatively coupled to the controller. The pitch adjustment mechanism can be configured to adjust a pitch angle of the rotor blade by rotating the rotor blade about a longitudinal axis of the rotor blade (pitch axis). The pitch adjustment mechanism can allow the controller to adjust the pitch angle of the rotor blade depending on the (processed) data received from the displacement sensor, e.g. the determined bending moment exerted on the blade root of the rotor blade. This allows the controller to control the load and / or forces from the wind acting on the rotor blade.

[0012] In a further embodiment, the system can further comprise a communication path configured to transfer the signals received from the displacement sensor to the controller. In particular, for embodiments in which the displacement sensor is fixed to the hub, the communication path can be configured to transfer the signals from the displacement sensor to the controller without transferring the signals from the rotor blade to the hub or vice versa. According to one aspect, the rotor blade comprises the reference plane.

[0013] According to one aspect, the displacement sensor is mounted inside the hub. For example, the reference plane can be a surface facing towards the center of the hub.

[0014] According to another aspect, the displacement sensor is mounted on the outside of the hub. Then, the reference plane can also be on the outside of the hub. For example, the reference plane can be a surface facing towards the center of the hub.

[0015] In some embodiments, the system comprises a plurality of displacement sensors. In particular, the system can comprise at least two displacement sensors. In some embodiments, the system comprises at least three displacement sensors. In further embodiments, the system comprises at least four displacement sensors. For example, the system can comprise exactly four displacement sensors.

[0016] According to one aspect, the system comprises a plurality of displacement sensors mounted around the longitudinal axis (pitch axis) of the rotor blade. For example, the displacement sensors can be mounted around the longitudinal axis of the rotor blade at a uniform distance from each other, e.g. two sensors at 6 o'clock and 12 o'clock; three sensors at 2, 6 and 10 o'clock; four sensors at 3, 6, 9 and 12 o'clock. Alternatively, the displacement sensors can be mounted around the longitudinal axis of the rotor blade at an angle of 90 degrees from each other.

[0017] In another aspect, the present disclosure relates to a method for measuring a displacement of a blade root of a rotor blade of a wind turbine. The method comprises a non-contact measurement of a displacement of a reference plane relative to a displacement sensor. The non-contact measurement of the displacement of the reference plane can be relative to the hub. Such a non-contact measurement can be performed with at least one displacement sensor fixed to the hub. In this case, the reference plane can be configured to move with the rotor blade coupled to the hub as the rotor blade moves relative to the hub. Alternatively, the non-contact measurement of the displacement of the reference plane can be relative to the rotor blade. Then, the non-contact measurement can be performed with the opposite arrangement, i.e. with at least one displacement sensor fixed to the rotor blade, while the reference plane has a fixed position relative to the hub.

[0018] In some embodiments, the method can further comprise transmitting a signal from the displacement sensor to a controller. Such a transmission can be achieved with a communication path.

[0019] In some embodiments, the method can further comprise receiving a signal from the displacement sensor with the controller.

[0020] In some embodiments, the method can further comprise determining a bending moment exerted on the blade root of the rotor blade with the controller based on the signal received from the displacement sensor.

[0021] In some embodiments, the method can further comprise adjusting a pitch angle of the rotor blade by rotating the rotor blade around a longitudinal axis of the rotor blade. Such an adjustment can be achieved with a pitch adjustment mechanism. The pitch adjustment mechanism can be controlled by the controller.

[0022] The present invention also comprises the following technical solutions:

[0023] Technical Solution 1. A system (100) for measuring displacement of a blade root (24) of a rotor blade (22) of a wind turbine, the system comprising:

[0024] a hub (20),

[0025] a rotor blade (22) coupled to the hub by a pitch bearing (40),

[0026] a reference plane (110), and

[0027] at least one displacement sensor (120),

[0028] wherein the displacement sensor is configured to detect displacement (122) of the reference plane relative to the hub without physical contact,

[0029] wherein the reference plane is configured to move with the rotor blade when the rotor blade moves relative to the hub and the displacement sensor is fixed to the hub.

[0030] Technical Solution 2. A system (100) for measuring displacement of a blade root (24) of a rotor blade (22) of a wind turbine, the system comprising:

[0031] a hub (20),

[0032] a rotor blade (22) coupled to the hub by a pitch bearing (40),

[0033] a reference plane (110), and

[0034] at least one displacement sensor (120),

[0035] wherein the displacement sensor is configured to detect displacement (122) of the reference plane relative to the rotor blade without physical contact,

[0036] wherein the reference plane has a fixed position relative to the hub and the displacement sensor is fixed to the rotor blade.

[0037] Technical Solution 3. The system of Technical Solution 1 or 2, further comprising:

[0038] a controller (26) communicatively coupled to the displacement sensor, wherein the controller is configured to determine a bending moment exerted on the blade root (24) of the rotor blade based on signals received from the displacement sensor.

[0039] Technical Solution 4. The system of Technical Solution 3, further comprising:

[0040] a pitch adjustment mechanism (32) communicatively coupled with the controller and configured to adjust a pitch angle of the rotor blade by rotating the rotor blade about a longitudinal axis (28) of the rotor blade,

[0041] wherein the controller is configured to adjust the pitch angle of the rotor blade according to the determined bending moment with the pitch adjustment mechanism to control a load and / or force from wind acting on the rotor blade.

[0042] Technical solution 5. The system according to any of the preceding technical solutions, further comprising:

[0043] a communication path (130) configured to transfer the signal received from the displacement sensor to the controller without transferring the signal from the rotor blade to the hub or vice versa.

[0044] Technical solution 6. The system according to any of the preceding technical solutions, wherein the displacement sensor is configured to detect radial, axial and / or tilt displacement of the reference plane.

[0045] Technical solution 7. The system according to any of the preceding technical solutions, wherein the system comprises at least two displacement sensors, preferably at least three displacement sensors, more preferably four displacement sensors.

[0046] Technical solution 8. The system according to any of the preceding technical solutions, wherein the system comprises a plurality of displacement sensors mounted around a longitudinal axis (28) of the rotor blade, in particular mounted at a uniform distance from each other around the longitudinal axis of the rotor blade, or mounted at an angle of 90 degrees from each other.

[0047] Technical solution 9. The system according to any of the preceding technical solutions, wherein the displacement sensor is mounted inside the hub, and wherein the reference plane is a surface facing the interior of the hub, in particular wherein the reference plane is a surface facing the center of the hub.

[0048] Technical solution 10. A method for measuring displacement of a blade root (24) of a rotor blade (22) of a wind turbine (10), the method comprising:

[0049] - non-contact measurement of displacement of a reference plane relative to a hub with at least one displacement sensor fixed to the hub, wherein the reference plane is configured to move with a rotor blade coupled to the hub when the rotor blade moves relative to the hub.

[0050] Technical solution 11. A method for measuring displacement of a blade root (24) of a rotor blade (22) of a wind turbine (10), the method comprising:

[0051] contactless measuring displacement of a reference plane relative to the rotor blade with at least one displacement sensor fixed to the rotor blade, wherein the reference plane has a fixed position relative to the hub.

[0052] Technical solution 12. The method according to technical solution 10 or 11, further comprising:

[0053] - transmitting a signal from the displacement sensor to a controller with a communication path,

[0054] - receiving the signal from the displacement sensor with the controller, and

[0055] determining a bending moment exerted on the blade root of the rotor blade based on the signal received from the displacement sensor with the controller.

[0056] Technical solution 13. The method according to technical solution 10 or 12, wherein the signal received from the displacement sensor is transmitted to the controller without transmitting the signal from the rotor blade to the hub or vice versa.

[0057] Technical solution 14. The method according to any of the technical solutions 10 to 13, further comprising:

[0058] - adjusting a pitch angle of the rotor blade with a pitch adjustment mechanism by rotating the rotor blade around a longitudinal axis of the rotor blade.

[0059] Technical solution 15. The method according to any of the technical solutions 10 to 14, further comprising a calibration step, wherein the calibration step comprises the following steps, which are interchangeable:

[0060] a) adjusting a static position of the hub such that the rotor blade has a certain orientation,

[0061] b) changing a pitch angle of the rotor blade at the static position by rotating the rotor blade at least 360 degrees in a first direction around a longitudinal axis while measuring an unloaded displacement of the reference plane,

[0062] c) optionally, changing the pitch angle of the rotor blade at the static position by rotating the rotor blade at least 360 degrees in a second direction around the longitudinal axis while measuring the unloaded displacement of the reference plane, wherein the second direction is opposite to the first direction,

[0063] d) repeating steps a) to c) at least three times such that the orientation of the rotor blade is different for each static position of the hub,

[0064] e) determining the unloaded state of the reference plane from the unloaded displacements as a function of the pitch angle and rotor blade orientation.

[0065] It will be appreciated that the method can also comprise any additional steps and / or features as described herein.

[0066] These and other features, aspects, and advantages of the present application will be further supported and described, with reference to the following description and appended claims. The accompanying drawings illustrate embodiments of the present application and, together with the description, serve the explanation of the principles of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0067] In the description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration embodiments of the application for which the principles of the application are applicable, and in which:

[0068] Figure 1 a perspective view of one embodiment of a wind turbine according to the present disclosure is shown;

[0069] Figure 2 a simplified internal view of one embodiment of a nacelle of a wind turbine according to the present disclosure is shown, in particular the nacelle during normal operation;

[0070] Figure 3 a displacement of a bearing component due to forces and moments acting on a rotor blade attached to the bearing component is shown;

[0071] Figures 4 to 9 an exemplary embodiment of a system for measuring the displacement of a blade root according to the present disclosure is shown;

[0072] Figure 10 an exemplary arrangement of four displacement sensors fixed to a hub according to the present disclosure is shown;

[0073] Figure 11 a flow chart of one embodiment of a method for measuring the displacement of a blade root according to the present disclosure is shown

[0074] Figure 12 a flow chart of one embodiment of a calibration step of a method for measuring the displacement of a blade root according to the present disclosure is shown. DETAILED DESCRIPTION

[0075] Reference will now be made in detail to embodiments of the application, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the application and is not meant as a limitation of the application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the scope of the application. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield still a further embodiment. Thus, it is intended that the present application covers modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

[0076] Reference will now be made to the drawings, in which Figure 1 A perspective view of one embodiment of an exemplary wind turbine 10 in accordance with the present disclosure is shown. As shown, the wind turbine 10 generally includes a tower 12 extending from a support surface 14, a nacelle 16 mounted on the tower 12, and a rotor 18 coupled to the 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. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in alternative embodiments, the rotor 18 can include more or less than three rotor blades 22. The rotor blades 22 can cooperate with the hub 20 by coupling blade roots 24 (see Figure 4 ) of the respective rotor blades to the hub 20. Each rotor blade 22 can be spaced about the hub 20 to facilitate rotation of the rotor 18, such that kinetic energy can be converted from the wind into usable mechanical energy, and subsequently electrical energy. As shown in Figure 2 , a generator 24 positioned within the nacelle 16 and rotatably coupled to the hub 20 can generate electrical energy from the rotational energy of the rotor 18.

[0077] The wind turbine 10 can also include a wind turbine controller 26 centralized within the nacelle 16. However, in other embodiments, the controller 26 can be located within any other component of the wind turbine 10 or at a location external to the wind turbine 10. Further, the controller 26 can be communicatively coupled to any number of components of the wind turbine 10 in order to control the components. As such, the controller 26 can include a computer or other suitable processing unit. Thus, in several embodiments, the controller 26 can include suitable computer readable instructions that, when implemented, configure the controller 26 to perform various different functions, such as receiving, communicating, and / or executing wind turbine control signals.

[0078] Reference will now be made to Figure 2 , which shows Figure 1A simplified internal view of one embodiment of the nacelle 16 of the wind turbine 10 shown in FIG. 1 is shown in FIG. 2, particularly showing its drive train components. A generator 24 can be coupled to the rotor 18 to generate electrical energy from rotational energy generated by the rotor 18. The rotor 18 can be coupled to a main shaft 34, which is rotatable via a main bearing (not shown). The main shaft 34, in turn, can be rotatably coupled to a gearbox output shaft 36 of the generator 24 by way of a gearbox 30. The gearbox 30 can include a gearbox housing 38, which is connected to a bedplate 46 by one or more torque arms 48. More particularly, in certain embodiments, the bedplate 46 can be a forged component in which the main bearing (not shown) is seated and through which the main shaft 34 extends. As generally understood, the main shaft 34 provides a low speed, high torque input to the gearbox 30 in response to rotation of the rotor blades 22 and hub 20. The gearbox 30 thus converts the low speed, high torque input to a high speed, low torque output to drive the gearbox output shaft 36, and thus the generator 24.

[0079] The wind turbine 10 can include one or more yaw drive mechanisms 42 communicatively coupled to the controller 26. The yaw drive mechanisms 42 can be configured to change the angle of the nacelle 16 relative to the wind direction, for example, by engaging a yaw bearing 44 of the wind turbine 10.

[0080] Further, the controller 26 can be communicatively coupled to one or more pitch adjustment mechanisms 32. In particular, each rotor blade 22 can include a pitch adjustment mechanism 32 configured to rotate each rotor blade 22 about its longitudinal axis (pitch axis) 28 via a pitch bearing 40. The longitudinal axis passes through the rotor blade from its tip to its root 24. In particular, the longitudinal axis can be a straight line, infinite in length, infinitely thin, and unrestricted in both directions. The pitch angle of a rotor blade 22 describes the perspective of the rotor blade 22 relative to the wind direction. The pitch angle can be changed by the pitch adjustment system 32 to control the load and power generated by the wind turbine 10 by adjusting the angular position of at least one rotor blade 22 relative to the wind vector. During operation of the wind turbine 10, the pitch system 32 can change the pitch of the rotor blades 22 such that the rotor blades 22 move to a feathered position such that the perspective of the at least one rotor blade 22 relative to the wind vector provides a minimum surface area of the rotor blade 22 oriented toward the wind vector, which helps to reduce the rotational speed of the rotor 18 and / or to stall the rotor 18. In one example embodiment, the pitch angle of each rotor blade 22 is individually controlled by the controller 26. Alternatively, the pitch angle of all rotor blades 22 can be simultaneously controlled by the controller 26.

[0081] Wind turbines can be exposed to random wind loads, in particular acting on the rotor blades of the wind turbine. Alternating wind loads acting on the rotor blades 22 are also transferred to other components of the wind turbine. In particular, loads can be transferred from the blade root 24 of the rotor blade 22 to the pitch bearing 40, resulting in axial and radial forces and tilting moments acting on the pitch bearing 40, for example.

[0082] The rotor blade 22 can comprise a rotating part 40a of the pitch bearing 40, or more specifically, the blade root 24 can comprise the rotating part 40a of the pitch bearing 40. The hub can comprise a corresponding non-rotating part 40b of the pitch bearing 40. The rotating part 40a as well as the non-rotating part 40b can be rings, respectively. For example, the rotating part 40a can be an inner ring surrounded by an outer ring being part of the non-rotating part 40b. The rotating part 40a can also be an outer ring surrounding an inner ring being part of the non-rotating part 40b.

[0083] Figure 3 A displacement of the rotating part 40a due to forces and moments acting on the blade root 24 of the rotor blade 22 attached to the rotating part 40a is shown. In Figure 3 In the case where the rotating part 40a is provided as an inner ring and the non-rotating part 40b is provided as an outer ring, it is assumed that the non-rotating part 40b is fixed, while the rotating part 40a is displaced due to external loads. This displacement can be accompanied by a deformation of the rolling elements (e.g. balls, rollers) of the pitch bearing 40. The displacement of the blade root 24 can be reflected by a displacement 122 of the reference plane 110. In Figure 3 In the case where the reference plane 110 is configured to move with the blade root 24 of the rotor blade 22 when the blade root 24 of the rotor blade 22 moves relative to the hub, the reference plane 110 can be configured to move with the rotating part 40a of the pitch bearing 40 when the rotating part 40a moves relative to the non-rotating part 40b of the pitch bearing 40.

[0084] Figures 4 to 9 A system 100 for measuring a displacement of a blade root 24 of a rotor blade 22 of a wind turbine according to the present disclosure is shown. The displacement of the blade root 24 (including the rotating part 40a) can reflect a moment acting on the blade root 24, and thus a load acting on the rotor blade 22. Thus, a measurement of the displacement of the blade root 24 of the rotor blade 22 can be used to determine or at least estimate the wind load acting on the rotor blade 22. As shown, the system 100 comprises a hub 20 and a rotor blade 22, wherein the rotor blade 22 is coupled to the hub 20 by a pitch bearing 40 as described above. In the following, it is to be understood that the rotor blade 22 comprises the blade root 24, the rotating part 40a, and any other component attached to the rotor blade 22 such that the component rotates with the rotor blade 22 when the rotor blade 22 rotates relative to the hub 20.

[0085] The system 100 further comprises a reference plane 110. In Figures 4 to 8 , the reference plane 110 is configured to move with the rotor blade 22 when the rotor blade moves relative to the hub 20. According to one aspect, the rotor blade comprises the reference plane 110. For example, the reference plane 110 can be a surface of the blade root 24, as for example shown in Figure 4 . In another embodiment, the reference plane 110 can be a surface of a flange or bracket attached to the rotor blade 22, as for example shown in Figure 7 .

[0086] In several embodiments, the pitch bearing 40 comprises a rotating part 40a and a non-rotating part 40b, as for example described with reference to Figure 3 . The non-rotating part 40b can be attached to the hub 20, while the rotating part 40a can be attached to the rotor blade 22. The non-rotating part 40b as well as the rotating part 40a can comprise bolts 170a, which for example provide the attachment to the hub 20 and the rotor blade 22, respectively. According to one aspect, the reference plane 110 can be attached to the rotating part 40a of the pitch bearing or can be part of the rotating part 40a of the pitch bearing. In one embodiment, the reference plane 110 can be a surface of the pitch bearing 40, in particular of the rotating part 40a of the pitch bearing 40, as for example shown in Figure 5 . For example, the reference plane 110 can be part of a bottom surface of the rotating part 40a, wherein the bottom surface can be a surface pointing towards the interior or center of the hub. The bolts 170a can also provide the reference plane 110, as for example shown in Figure 6 .

[0087] Figures 4 to 6 The reference plane 110 is shown as a bottom surface. The bottom surface is essentially facing towards the center of the hub. The bottom surface can be essentially perpendicular to the pitch axis 28. However, the reference plane 110 can also be a surface not facing towards the center of the hub. For example, the reference plane 110 can face towards a sidewall of the hub, as for example shown in Figure 7 .

[0088] In Figures 4 to 7 , the reference plane 110 is located inside the hub 20. However, the reference plane 110 can also be located outside the hub. For example, the latter can be advantageous for an arrangement in which the rotor blade 22 is attached to an outer part of the pitch bearing 40, for example, wherein the rotating part 40a of the pitch bearing 40 is an outer ring as for example shown in Figure 8 . Similar to Figures 4 to 7 and the above description, the reference plane 110 can be a surface of any part of the rotor blade 22, for example the blade root 24, the rotating part 40a or any other part that rotates with the rotor blade 22 relative to the hub 20. The reference plane 110 can be a bottom surface, as for example shown in Figure 8The reference surface can be the surface 110 shown in Fig. 1, or it can be another surface, e.g. a surface facing the hub.

[0089] The material of the reference surface 110 can be chosen such that the displacement sensor can detect a displacement of the reference surface relative to the hub as described below. A suitable material of the reference surface 110 can be a metal, such as steel, copper, aluminium.

[0090] Furthermore, the system 100 comprises at least one displacement sensor 120. In Figures 4 to 8 In embodiments, the displacement sensor 120 is fixed to the hub 20. In these embodiments, the displacement sensor 120 is configured to detect a displacement 122 of the reference surface 110 relative to the hub 20 without physical contact. For example, the displacement sensor 120 can be mounted such that the displacement sensor 120 faces the rotor blade 22. For example, the displacement sensor 120 can be mounted opposite the reference surface 110 such that the displacement sensor 120 faces the reference surface 110. According to an aspect, the displacement sensor 120 is configured to detect a radial, axial and / or tilt displacement of the reference surface 110 relative to the hub.

[0091] The displacement sensor 120 can be fixed directly to the hub 20, as for example shown in Figure 7 or indirectly to the hub 20, e.g. using a flange or bracket 160 mounted on the hub 20, as for example shown in Figure 4 , Figure 5 , Figure 6 and Figure 8 . The displacement sensor 120 can also be mounted on a non-rotating part 40b of the pitch bearing 40. The displacement sensor 120 can be mounted in an interior of the hub, as for example shown in Figures 4 to 7 . Such a mounting of the displacement sensor 120 in the interior of the hub 20 provides the advantage that the displacement sensor 120 is less exposed to environmental influences. Especially offshore wind turbines can be subject to extreme environmental influences which can lead to damages, especially to components attached to the exterior of the wind turbine 10. However, the displacement sensor 120 can also be mounted outside the hub, as for example shown in Figure 8 . In particular, such a mounting can be advantageous for arrangements in which the rotor blade 22 is attached to an outer part of the pitch bearing 40.

[0092] As Figures 4 to 8Alternatively arrangements are possible in which the arrangement in FIG. 1 is reversed. In the reversed arrangement, the displacement sensor 120 is fixed to the rotor blade 22, while the reference plane 110 has a fixed position relative to the hub 20. According to one aspect, the hub comprises the reference plane 110. For example, the reference plane 110 can be a part of the hub 20, or can be a part of a component fixedly secured to the hub. The displacement sensor 120 can be fixed to the rotor blade 22, in particular to the blade root 24, or to a surface of a flange or bracket attached to the rotor blade 22. The displacement sensor 120 can also be fixed to the pitch bearing 40, in particular to the rotating component 40a of the pitch bearing 40, or to the bolt 170a. Figure 9 One exemplary reversed arrangement is shown in FIG. 2, which shows a displacement sensor 120 fixed to the bottom surface of the blade root 24, while a flange 160 mounted on the hub 20 comprises the reference plane 110.

[0093] The displacement sensor 120 can be a sensor that emits a field, such as an electromagnetic field, and detects changes in the field. According to one aspect, the displacement sensor 120 is a proximity sensor. A proximity sensor is a sensor that is able to detect the presence of a nearby object without physical contact. For example, the proximity sensor can be a capacitive, inductive, magnetic, or optical sensor. In case the reference plane is made of metal, an inductive sensor can be advantageous.

[0094] In some embodiments, the system 100 comprises only one displacement sensor 120. One displacement sensor 120 can already provide a wide range of useful information, allowing for meaningful estimates of wind loads and moments acting on the rotor blade 22. Omitting multiple sensors further contributes to saving material and costs for construction and maintenance. For example, the displacement sensor 120 can be mounted such that it detects displacements of such a reference plane 110 that is exposed to relatively large displacements. Such a position can be derived by a person skilled in the art based on the main wind load direction. For example, the displacement sensor 120 can be mounted around the longitudinal axis of the rotor blade, similar to a number on a clock face. If a virtual vector between 12 o'clock and 6 o'clock on such a clock face would reflect the main wind load direction (prevailing direction), the displacement sensor 120 can be mounted at 6 o'clock or 12 o'clock.

[0095] In some embodiments, the system 100 comprises multiple displacement sensors 120. In this case, each displacement sensor 120 can have its own reference plane 110, such that the system also comprises multiple reference planes 110. For example, the reference planes 110 can be the surfaces of different bolts 170a, respectively. Alternatively, the multiple displacement sensors 120 can use the same continuous surface as the reference plane 110, for example the bottom surface of the rotating part 40a of the pitch bearing 40. This surface can be considered as multiple reference planes 110 that the continuous surface is actually divided into.

[0096] The multiple displacement sensors increase the amount of measurement data. In particular, this enables a more accurate estimation of the wind load acting on the rotor blade 22. More than one displacement sensor 120 can also provide a self-verification system as described below. According to one aspect, the multiple displacement sensors 120 are mounted around the longitudinal axis of the rotor blade, similar to the numbers on a dial.

[0097] For example, the system 100 can comprise two displacement sensors 120. In some embodiments, the two displacement sensors 120 can be mounted at a consistent distance from each other around the longitudinal axis of the rotor blade, i.e. at 6 o’clock and 12 o’clock. The two displacement sensors 120 can be mounted such that the vector between them reflects the main wind load direction (prevailing direction). Two opposing displacement sensors 120, such as at 6 o’clock and 12 o’clock, can detect substantially the same displacement of the corresponding reference plane 110 (with opposite signs / directions). However, this arrangement allows the measurement values to verify each other, such that the system checks itself and the data becomes more accurate.

[0098] The two displacement sensors 120 can also be mounted such that they monitor the flapwise or edgewise movement of the rotor blade 22 in particular by detecting the displacement of a corresponding reference plane 110. In some embodiments, the two displacement sensors 120 can be mounted at an angle of 90 degrees to each other around the longitudinal axis of the rotor blade, i.e. at 9 o'clock and 12 o'clock. In this way, the two displacement sensors 120 can monitor the flapwise and edgewise movement of the rotor blade simultaneously. For example, one displacement sensor 120 can monitor the edgewise movement of the rotor blade in particular, while the other displacement sensor monitors the flapwise movement of the rotor blade in particular. In case the displacement sensors 120 are fixed to the hub, the displacement sensors can be arranged such that they monitor the flapwise or edgewise movement of the rotor blade 22 when the rotor blade 22 is in its full power position. For example, one displacement sensor 120 can be mounted along a virtual vector reflecting the prevailing direction, while the other displacement sensor 120 can be mounted along a virtual vector reflecting the corresponding perpendicular direction. In case the displacement sensors 120 are mounted on the rotor blade 22, the displacement sensors rotate with the rotor blade 22 and, thus, they can easily be arranged such that they always measure the flapwise and edgewise moments. For the latter, the determination of the edgewise and flapwise loads can save the coordinate transformation from the fixed reference frame to the rotating reference frame.

[0099] In some embodiments, the system 100 can comprise three displacement sensors 120. The three displacement sensors 120 can be mounted at a uniform distance from each other around the longitudinal axis of the rotor blade, i.e. at 2 o'clock, 6 o'clock and 10 o'clock. Alternatively, the three displacement sensors 120 can be mounted at an angle of 90 degrees to each other around the longitudinal axis of the rotor blade, i.e. at 6 o'clock, 9 o'clock and 12 o'clock. For example, the displacement sensors 120 mounted at 6 o'clock and 12 o'clock can be mounted such that the vector between them reflects the prevailing direction (direction of the prevailing wind load). The displacement sensor 120 mounted at 9 o'clock can be mounted on a virtual line reflecting the non-prevailing direction. The displacement sensors 120 mounted at 6 o'clock and 12 o'clock can detect the displacement of such reference planes 110 that are subjected to a relatively large displacement compared to the displacement of the reference plane 110 of the displacement sensor 120 mounted at 9 o'clock.

[0100] In other embodiments, the system 100 can comprise four displacement sensors 120. For example, the four displacement sensors 120 can be mounted at 3 o'clock, 6 o'clock, 9 o'clock and 12 o'clock around the longitudinal axis of the rotor blade, as for example Figure 10Two of the four displacement sensors 120, for example the displacement sensors at 3 and 9 o'clock, can be configured to monitor, in particular, the flapping directional movement of the rotor blade by detecting the displacement of the corresponding reference plane 110. The other two displacement sensors 120, for example the displacement sensors at 6 o'clock and 12 o'clock, can be configured to monitor, in particular, the edgewise movement of the rotor blade by detecting the displacement of the corresponding reference plane 110. With this configuration, the measurement data of each displacement sensor 120 is verified by one of the other displacement sensors 120, so that the accuracy of the data can be assessed and the data can be interpreted and processed accordingly.

[0101] In other embodiments, the system 100 can comprise more than four displacement sensors 120.

[0102] The displacement sensor(s) 120 can be communicatively coupled to the controller 26. Thus, the controller 26 can be provided with actual measured data, which allows to determine or meaningfully estimate the moment acting on the rotor blade 22. The controller 26 can process the data received from the displacement sensor(s) 120. For example, the controller 26 can be configured to determine a bending moment exerted on a portion of the rotor blade 22. In particular, the controller 26 can be configured to determine a bending moment exerted on the blade root 24 of the rotor blade 22 based on the signals received from the displacement sensors 120. The rotor blade bending moment allows to estimate the wind load acting on the rotor blade. Instead of using an estimated value provided by an algorithm, the controller 26, which is provided with actual measured data, can determine the bending moment. Thus, according to one aspect of the present invention, the system 100 is a system for determining a bending moment of the blade root 24 of the rotor blade 22.

[0103] With the data measured by the displacement sensor(s) 120, the controller 26 can also determine or estimate other influences and / or changes with respect to the rotor blade 22. For example, ice accretion or fouling can influence the weight of the rotor blade 22 and, thus, the displacement of the reference plane 110. Thus, the controller 26 can be configured to determine an ice accretion or fouling of the rotor blade based on the signals received from the displacement sensor(s) 120.

[0104] In a further embodiment, the system 100 can also comprise a communication path 130. The communication path 130 can be configured to transfer data received from the displacement sensor(s) 120 to the controller 26. The communication path 130 can comprise a cable. The communication path 130 can be configured to transfer signals from the displacement sensor 120 to the controller 26 without transferring signals from the rotor blade 22 to the hub 20. The latter is particularly relevant for an arrangement in which the displacement sensor 120 is fixed to the hub. The controller 26 is not located in the rotor blade 22. Furthermore, if each displacement sensor 120 is fixed to the hub 20, the displacement sensor 120 is also not located in the rotor blade 22. Therefore, there is no need to transfer data received from the displacement sensor(s) 120 from or to the rotor blade 22, which avoids the need for complex and potentially fragile means allowing the transfer of data between two components, one of which rotates relative to the other. For example, with such a communication path 130, there is no need to transfer a cable from the hub 20 to the rotor blade 22, which rotates relative to the hub 20. Such a communication path is necessary, for example, when measuring the bending moment of the blade root with strain gauges or fiber Bragg gauges.

[0105] Strain gauge or fiber Bragg gauge measuring devices are very sensitive equipment, whereas the system 100 using the displacement sensor(s) 120 is a very stable and reliable system. In particular, the system 100 with displacement sensors 120 fixed to the hub does not rely on additional connections between the rotor blade and the hub (in addition to the connection via the bearing), which is advantageous, for example, by the non-contact measurement of the displacement sensor 120 and by the communication path 130 as described above.

[0106] In a further embodiment, the system 100 can comprise a pitch adjustment mechanism 32 as described above. With the pitch adjustment mechanism 32, the controller 26 can adjust the pitch angle of the rotor blade 22 depending on the determined bending moment exerted on the blade root 24 of the rotor blade 22. The adjustment of the pitch angle allows the system 100 to control the load and / or force from the wind acting on the rotor blade 22.

[0107] In another aspect, this disclosure relates to a nacelle assembly of a wind turbine 10 mounted on top of a tower 12. The nacelle assembly includes a nacelle 16, a hub 20, and a plurality of rotor blades 22. According to one aspect, the number of rotor blades is three. The rotor blades 22 can be coupled to the hub 20 via a plurality of pitch bearings 40. Additionally, the nacelle assembly includes a plurality of reference planes 110, as described in reference system 100. Each reference plane 110 can be configured to move together with one of the rotor blades 22 as the rotor blades 22 move relative to the hub 20. In particular, the rotor blades 22 may include reference planes 110. The nacelle assembly may also include a plurality of displacement sensors 120 fixed to the hub 20. Each displacement sensor 120 can be configured to detect the displacement of one of the reference planes 110 relative to the hub 20 without physical contact. Alternatively, each of the plurality of reference planes 110 may have a fixed position relative to the hub 20, while each of the plurality of displacement sensors 120 is fixed to one of the rotor blades 22. In this configuration, each displacement sensor 120 can be configured to detect the displacement of one of a plurality of reference planes 110 relative to the blade root 24 of a corresponding rotor blade 22 without physical contact, the displacement sensor 120 being fixed to the rotor blade. The plurality of displacement sensors 120 and reference planes 110 can form a plurality of sensor plane pairs, wherein each sensor plane pair is assigned to one rotor blade 22. Specifically, each rotor blade 22 can belong to the same number of sensor plane pairs. For example, each rotor blade 22 can belong to four sensor plane pairs. The plurality of displacement sensors 120 can be communicatively coupled to a controller 26, as described in reference system 100. The controller 26 can be configured to determine the bending moment applied to the blade root 24 of the rotor blade 22 based on signals received from the displacement sensors 120.

[0108] For reference now Figure 11 The flowchart illustrates an embodiment of a method 200 for measuring the displacement at the blade root of a rotor blade of a wind turbine, such as a... Figure 1 The wind turbine 10. Method 200 can be performed using system 100. As shown at 204, method 200 includes a non-contact measurement performed using at least one displacement sensor 120. The non-contact measurement includes measuring the displacement 122 of a reference plane 110. The reference plane 110 can be configured to move together with the rotor blade 22 coupled to the hub 20 as the rotor blade 22 moves relative to the hub 20 and the displacement sensor 120 is fixed to the hub 20. For example, the rotor blade 22 may include the reference plane 110. Alternatively, the reference plane 110 may have a fixed position relative to the hub 20 while the displacement sensor 120 is fixed to the rotor blade 22.

[0109] The method can also include communicating signals from the displacement sensor(s) 120 to the controller 26, as indicated at 206. Such communication can be accomplished using the communication path 130 as described above. The method can also include receiving signals from the displacement sensor 120 with the controller 26, as indicated at 208.

[0110] In some embodiments, the method can also include a determining step 210 that determines a bending moment exerted on the blade root 24 of the rotor blade 22. The determination can be based on the signals received from the displacement sensor(s) 120. Step 210 can be performed with the controller 26. The controller 26 can also communicate with a pitch adjustment mechanism to adjust the pitch angle of the rotor blade by rotating the rotor blade about the longitudinal axis 28 of the rotor blade 22 (step 212). Adjustment of the pitch angle controls the wind load and power generated by the wind turbine 10. According to one aspect, the determining step 210 includes determining a flapwise bending moment and an edgewise bending moment.

[0111] In some embodiments, the method can also include a calibration step 202. The calibration step 202 can be performed prior to the determining step 210. The calibration step 202 can include rotating the rotor blade 22 about the longitudinal axis 28 to a plurality of predetermined positions. The calibration step 202 can also include determining a displacement of the rotor blade 22 at each of the predetermined positions. The calibration step 202 can also include determining a calibration curve that relates the displacement of the rotor blade 22 to the bending moment exerted on the blade root 24 of the rotor blade 22. The calibration curve can be determined by fitting a curve to the displacements determined at the predetermined positions. The calibration curve can be stored in the controller 26. Figure 11The method 200 is further illustrated in Fig. 2. The calibration of the method 200 can be performed after installation of the system 100. For calibrating the method 200, several pitch rolls can be performed, i.e. the pitch angle of the rotor blade 22 is changed by rotating the rotor blade 22 around the longitudinal axis with the hub 20 in several positions. The orientation of the rotor blade 22 can be different for each static position of the hub 20. According to one aspect, the static positions of the hub 20 are chosen such that the rotor blade 22 experiences different gravitational influences in each position. The load-free displacement of the reference plane 110 is measured while the pitch roll occurs, wherein the load-free displacement describes the displacement 122 without wind load acting on the rotor blade 22. Using the measured load-free displacement and taking into account the static moment of the rotor blade 22 can allow to determine the load-free state depending on the pitch angle and the orientation of the rotor blade 22 (step 222). The static position of the hub 20 can be adjusted as indicated at 214. The pitch roll at this position of the hub 20 can be performed in a first direction (step 216). Optionally, another pitch roll at the same position of the hub 20 is performed in a second direction, wherein the second direction is opposite to the first direction (step 218). Steps 214, 216 and optionally 218 can be repeated at least three times (step 220). Depending on the orientation of the rotor blade 22, different forces and moments can act on the rotor blade 22 for different positions of the hub 20. According to one aspect, the calibration steps comprise four static positions of the hub 20, wherein the rotor blade 22 is once pointing upwards, once pointing to the right, once pointing downwards and once pointing to the left. For example, at a first static position, the rotor blade 22 can point downwards, i.e. the rotor blade 22 is particularly perpendicular to the ground. In this position, no bending moment is applied on the blade root 24 and only the blade mass determines the load-free displacement. In a second static position, the rotor blade 22 can point upwards, wherein also no bending moment is applied on the blade root 24 and only the blade mass determines the load-free displacement. In the first and second static position, the gravitational force of the blade mass acts in opposite directions with respect to the displacement sensor(s) 120 in the hub. The measurements at the first and second static position allow to determine the “zero point” of the load-free. In a third and fourth static position, the blade root 22 can point to the left and right, respectively, i.e. the rotor blade is particularly parallel to the ground. In the third and fourth position, a bending moment is applied on the blade root 24 due to the blade mass. The measurements at the third and fourth static position serve as calibration load. It should be understood that the terms first, second, etc. do not reflect the order of the steps. For example, the measurement at the third position can occur before the measurement at the first position.

[0112] It is also possible to perform a "zero-point" mapping before the rotor blade is mounted to the hub. As part of the end-of-line functional test, the rotating part 40a of each pitch bearing 40 can be rotated at least 360 degrees while measuring the unloaded displacement of the rotating part 40a. By this calibration step, 3 of the 4 calibration positions described above can be eliminated, as only one calibration load will be required, i.e. the rotor blade 22 pointing in one static position to the left or to the right.

[0113] This written description uses examples to disclose the application, including the best mode, and also to enable any person skilled in the art to practice the application, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the application is defined by the claims, and can 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 include structural elements that do not differ from the literal language of the claims, or if they include other equivalents to the literal languages of the claims.

Claims

1. A system (100) of a wind turbine, the system comprising: a hub (20) comprising a non-rotating part (40b) of a pitch bearing (40), a rotor blade (22) comprising a blade root attached to a rotating part (40a) of the pitch bearing (40), a plurality of non-contact displacement sensors (120) operable to face the rotor blade and to be fixed directly or indirectly to the hub (20), and a respective reference plane (110) associated with each of the plurality of non-contact displacement sensors (120), the respective reference plane being defined by a part that moves together with the rotor blade when the rotor blade moves relative to the hub, wherein the system is configured for measuring a displacement of the blade root, wherein each of the plurality of displacement sensors (120) is configured to detect a relative movement between the respective reference plane (110) and the hub (20) without being physically connected to the part defining the respective reference plane (110), and wherein the plurality of displacement sensors (120) is mounted opposite and facing the respective reference plane (110).

2. The system according to claim 1, further comprising: a controller (26) communicatively coupled to the plurality of displacement sensors, wherein the controller is configured to determine a bending moment exerted on a blade root (24) of the rotor blade based on signals received from the plurality of displacement sensors.

3. The system according to claim 2, further comprising: a pitch adjustment mechanism (32) communicatively coupled to the controller and configured to adjust a pitch angle of the rotor blade by rotating the rotor blade around a longitudinal axis (28) of the rotor blade, wherein the controller is configured to adjust the pitch angle of the rotor blade according to the determined bending moment using the pitch adjustment mechanism to control a load and / or force from wind acting on the rotor blade.

4. The system according to claim 2 or 3, further comprising: a communication path (130) configured to transfer the signals received from the plurality of displacement sensors to the controller without transferring the signals from the rotor blade to the hub or vice versa.

5. The system of any one of claims 1 to 3, wherein, The plurality of displacement sensors is configured to detect radial, axial and / or tilt displacements of the respective reference plane.

6. The system of any one of claims 1 to 3, wherein, The system comprises two displacement sensors.

7. The system of any one of claims 1 to 3, wherein, The system comprises at least three displacement sensors.

8. The system of any one of claims 1 to 3, wherein, The system comprises four displacement sensors.

9. The system of any one of claims 1 to 3, wherein, The plurality of displacement sensors is mounted around a longitudinal axis (28) of the rotor blade.

10. The system of claim 9, wherein, The plurality of displacement sensors is mounted at a uniform distance from each other around a longitudinal axis of the rotor blade.

11. The system of claim 9, wherein, The plurality of displacement sensors is mounted at a 90-degree angle to each other.

12. The system of any one of claims 1 to 3, wherein, The plurality of displacement sensors is mounted inside the hub, and wherein the respective reference plane is a surface facing the interior of the hub.

13. The system of claim 12, wherein, The respective reference plane is a surface facing the center of the hub.

14. A method for measuring displacement of a blade root (24) of a rotor blade (22) of a wind turbine (10), the method comprising: non-contact measurement of relative movement of the respective reference plane with respect to the hub with a plurality of displacement sensors of a system according to any one of claims 1 to 13.

15. The method according to claim 14, further comprising: communicating signals from the plurality of displacement sensors to a controller of the system with a communication path of the system, receiving the signals from the plurality of displacement sensors with the controller, and determining a bending moment exerted on the blade root of the rotor blade based on the signals received from the plurality of displacement sensors with the controller.

16. The method of claim 15, wherein, The signals received from the plurality of displacement sensors are communicated to the controller without communicating the signals from the rotor blade to the hub or vice versa.

17. The method according to any one of claims 14 to 16, further comprising: adjusting a pitch angle of the rotor blade with a pitch adjustment mechanism of the system by rotating the rotor blade about a longitudinal axis of the rotor blade.

18. The method of any one of claims 14 to 16, further comprising a calibration step, wherein, The calibration step comprises the following steps, which are interchangeable: a) adjusting a static position of the hub such that the rotor blade has a certain orientation, b) changing a pitch angle of the rotor blade at the static position by rotating the rotor blade at least 360 degrees in a first direction about a longitudinal axis while measuring an unloaded displacement of the reference plane, c) changing the pitch angle of the rotor blade at the static position by rotating the rotor blade at least 360 degrees in a second direction about the longitudinal axis while measuring an unloaded displacement of the reference plane, wherein the second direction is opposite to the first direction, d) repeating steps a) to c) at least three times such that the orientation of the rotor blade is different for each static position of the hub, e) determining an unloaded state of the reference plane from the unloaded displacements as a function of the pitch angle and rotor blade orientation.

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