Patent Description:
Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modem wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.

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

Such pitch adjustment requires information about the wind loads acting on the rotor blades. This information is difficult to obtain, e.g. due to the stochastic distribution of the wind, the dynamic nature of the system itself and the transfer of loads between different components of the system. Dynamic simulations can provide estimated values but it would be advantageous to monitor actual parameters that allow a reliable estimation of wind loads. <CIT> Al relates to individual pitch control with hub sensor. <CIT> Al relates to systems and methods for reducing loads acting on a wind turbine in response to transient wind conditions <CIT> relates to wind turbine monitoring.

Accordingly, the present disclosure is directed to systems and methods that allow monitoring of wind loads acting on rotor blades.

In one aspect, the present disclosure is directed to a system for measuring displacements 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 a displacement of the reference plane without physical contact.

In one embodiment, 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. 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 may be configured to detect a radial, axial and/or tilting displacement of the reference plane relative to the hub.

In another embodiment, the reference plane has a fixed position with respect 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 as 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, to the blade root of the rotor blade. Especially, the displacement sensor may be configured to detect a radial, axial and/or tilting displacement of the reference plane relative to the blade root.

In one embodiment, the system may further include a controller that is communicatively coupled to the displacement sensor. The controller may be configured to determine a bending moment exerted on a part of the rotor blade, e.g. the blade root of the rotor blade, based on signals received from the displacement sensor.

In further embodiments, the system may comprise a pitch adjustment mechanism which is communicatively coupled with the controller. The pitch adjustment mechanism may be configured to adjust a pitch angle of the rotor blade by rotating the rotor blade around a longitudinal axis (pitch axis) of the rotor blade. The pitch adjustment mechanism may allow the controller to adjust the pitch angle of the rotor blade in dependence of the (processed) data received from the displacement sensor, for example the determined bending moments exerted on a the blade root of the rotor blade. This allows the controller to control loads and/or forces from wind acting on the rotor blade.

In additional embodiments, the system may further comprise a communication path which is configured to transfer the signals received from the displacement sensor to the controller. Specifically for embodiments where the displacement sensor is fixed to the hub, the communication path may 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 the other way around. According to one aspect, the rotor blade includes the reference plane.

According to one aspect, the displacement sensor is mounted in the interior of the hub. For example, the reference plane may be a surface facing the center of the hub.

According to another aspect, the displacement sensor is mounted on the exterior of the hub. Then, the reference plane may be on the exterior of the hub as well. For example, the reference plane may be a surface facing the center of the hub.

In some embodiments, the system comprises a plurality of displacement sensors. In particular, the system may 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 may comprise exactly four displacement sensors.

According to one aspect, the system comprises a plurality of displacement sensors which are mounted around a longitudinal axis (pitch axis) of the rotor blade. For example, the displacement sensors may be mounted around the longitudinal axis of the rotor blade at a uniform distance from each other, e.g. two sensors at <NUM> and <NUM> o'clock; three sensors at <NUM>, <NUM> and <NUM> o'clock; four sensors at <NUM>, <NUM>, <NUM> and <NUM> o'clock. Alternatively, the displacement sensors may be mounted around the longitudinal axis of the rotor blade at a <NUM> degree angle to each other.

In another aspect, the present disclosure is directed to a method for measuring displacements of a blade root of a rotor blade of a wind turbine. The method comprises contactless measuring of a displacement of a reference plane relative to a displacement sensor. The contactless measuring of the displacement of the reference plane may be relative to the hub. Such contactless measuring may be performed with at least one displacement sensor fixed to a hub. In this case, the reference plane may be configured to move with a rotor blade which is coupled to the hub as the rotor blade moves relative to the hub. Alternatively, the contactless measuring of the displacement of the reference plane may be relative to the rotor blade. Then, the contactless measuring may be performed with the reverse arrangement, i.e. with at least one displacement sensor fixed to a rotor blade while the reference plane has a fixed position with respect to the hub.

In some embodiments, the method may further comprise transferring a signal from the displacement sensor to a controller. Such transfer may be realized with a communication path.

In some embodiments, the method may further comprise receiving the signal from the displacement sensor with the controller.

In some embodiments, the method may further comprise determining, with the controller, a bending moment exerted on a blade root of the rotor blade based on signals received from the displacement sensor.

In some embodiments, the method may further comprise adjusting a pitch angle of the rotor blade by rotating the rotor blade around a longitudinal axis of the rotor blade. Such adjustment may be realized with a pitch adjustment mechanism. The pitch adjustment mechanism may be controlled by the controller.

It should be understood that the method may further include any of the additional steps and/or features as described herein.

These and other features, aspects and advantages of the present invention will be further supported and described with reference to the following description and appended claims.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of an exemplary wind turbine <NUM> according to the present disclosure. As shown, the wind turbine <NUM> generally includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM> mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. The rotor blades <NUM> may be mated to hub <NUM> by coupling a blade root <NUM> (cf. <FIG>) of the respective rotor blade to hub <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. As illustrated in <FIG>, an electric generator <NUM> positioned within the nacelle <NUM> and rotatably coupled to the hub <NUM> may generate electrical energy from the rotational energy of the rotor <NUM>.

The wind turbine <NUM> may also include a wind turbine controller <NUM> centralized within the nacelle <NUM>. However, in other embodiments, the controller <NUM> may be located within any other component of the wind turbine <NUM> or at a location outside the wind turbine <NUM>. Further, the controller <NUM> may be communicatively coupled to any number of the components of the wind turbine <NUM> in order to control the components. As such, the controller <NUM> may include a computer or other suitable processing unit. Thus, in several embodiments, the controller <NUM> may include suitable computer-readable instructions that, when implemented, configure the controller <NUM> to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals.

Referring now to <FIG>, a simplified, internal view of one embodiment of the nacelle <NUM> of the wind turbine <NUM> shown in <FIG> is illustrated, particularly illustrating the drivetrain components thereof. The generator <NUM> may be coupled to the rotor <NUM> for producing electrical power from the rotational energy generated by the rotor <NUM>. The rotor <NUM> may be coupled to the main shaft <NUM>, which is rotatable via a main bearing (not shown). The main shaft <NUM> may, in turn, be rotatably coupled to a gearbox output shaft <NUM> of the generator <NUM> through a gearbox <NUM>. The gearbox <NUM> may include a gearbox housing <NUM> that is connected to a bedplate <NUM> by one or more torque arms <NUM>. More specifically, in certain embodiments, the bedplate <NUM> may be a forged component in which the main bearing (not shown) is seated and through which the main shaft <NUM> extends. As is generally understood, the main shaft <NUM> provides a low speed, high torque input to the gearbox <NUM> in response to rotation of the rotor blades <NUM> and the hub <NUM>. Thus, the gearbox <NUM> thus converts the low speed, high torque input to a high speed, low torque output to drive the gearbox output shaft <NUM> and, thus, the generator <NUM>.

The wind turbine <NUM> may include one or more yaw drive mechanisms <NUM> communicatively coupled to the controller <NUM>. The yaw drive mechanism(s) <NUM> may be configured to change the angle of the nacelle <NUM> relative to the wind direction, e.g. by engaging a yaw bearing <NUM> of the wind turbine <NUM>.

Furthermore, controller <NUM> may be communicatively coupled to one or more pitch adjustment mechanisms <NUM>. Specifically, each rotor blade <NUM> may include a pitch adjustment mechanism <NUM> configured to rotate each rotor blade <NUM> about its longitudinal axis (pitch axis) <NUM> via a pitch bearing <NUM>. The longitudinal axis passes through the rotor blade from the tip of the rotor blade to the blade root <NUM>. In particular, the longitudinal axis may be a straight line, infinitely long, infinitely thin and unlimited in both directions. The pitch angle of rotor blades <NUM> describes an angle that determines a perspective of rotor blades <NUM> with respect to the direction of the wind. The pitch angle may be changed by pitch adjustment system <NUM> to control the load and power generated by wind turbine <NUM> by adjusting an angular position of at least one rotor blade <NUM> relative to wind vectors. During operation of wind turbine <NUM>, pitch system <NUM> may change a pitch of rotor blades <NUM> such that rotor blades <NUM> are moved to a feathered position, such that the perspective of at least one rotor blade <NUM> relative to wind vectors provides a minimal surface area of rotor blade <NUM> to be oriented towards the wind vectors, which facilitates reducing a rotational speed of rotor <NUM> and/or facilitates a stall of rotor <NUM>. In one exemplary embodiment, a pitch angle of each rotor blade <NUM> is controlled individually by a controller <NUM>. Alternatively, the pitch angle for all rotor blades <NUM> may be controlled simultaneously by controller <NUM>.

Wind turbines may be exposed to stochastic wind loads acting especially on the rotor blades of the wind turbines. The alternating wind loads acting on the rotor blades <NUM> are transferred also to other components of the wind turbine. Particularly, the loads may be transferred from the blade root <NUM> of rotor blade <NUM> to the pitch bearing <NUM> causing for example axial and radial forces and tilting moments acting on the pitch bearing <NUM>.

Rotor blade <NUM> may comprise a rotating component 40a of the pitch bearing <NUM> or more specifically, the blade root <NUM> may comprise the rotating component 40a of the pitch bearing <NUM>. The hub may comprise a corresponding non-rotating component 40b of the pitch bearing <NUM>. The rotating component 40a as well as the non-rotating component 40b may be a ring, respectively. For example, the rotating component 40a may be an inner ring which is surrounded by an outer ring being part of the non-rotating component 40b. The rotating component 40a may also be an outer ring surrounding an inner ring being part of the non-rotating component 40b.

<FIG> illustrates a displacement of the rotating component 40a due to forces and moments acting on the blade root <NUM> of a rotor blade <NUM> attached to the rotating component 40a. In <FIG> the rotating component 40a is provided as an inner ring whereas the non-rotating component 40b is provided as an outer ring. The non-rotating component 40b is assumed to be fixed while the rotating component 40a gets displaced due to external loads. Such displacement may be accompanied with the deformation of rolling elements (e.g. balls, rollers) of the pitch bearing <NUM>. The displacements of a blade root <NUM> may be reflected by a displacement <NUM> of a reference plane <NUM>. In <FIG>, the reference plane <NUM> is configured to move with the blade root <NUM> of a rotor blade <NUM> as the blade root <NUM> of a rotor blade <NUM> moves relative to the hub.

<FIG> illustrate a system <NUM> for measuring displacements of a blade root <NUM> of a rotor blade <NUM> of a wind turbine according to the present disclosure. The displacements of the blade root <NUM> (including the rotating component 40a) may reflect moments acting on the blade root <NUM> and, thus, loads acting on the rotor blade <NUM>. Hence, measurement of displacements of the blade root <NUM> of rotor blade <NUM> may be used to determine or at least estimate wind loads acting on the rotor blade <NUM>. As shown, the system <NUM> comprises a hub <NUM> and a rotor blade <NUM>, wherein the rotor blade <NUM> is coupled to the hub <NUM> by a pitch bearing <NUM> as described above. In the following, it is understood that the rotor blade <NUM> includes the blade root <NUM>, the rotating component 40a and any other component attached to the rotor blade <NUM> in such a way that the component rotates with the rotor blade <NUM> as the rotor blade <NUM> rotates relative to the hub <NUM>.

The system <NUM> further comprises a reference plane <NUM>. In <FIG> the reference plane <NUM> is configured to move with the rotor blade <NUM> as the rotor blade moves relative to the hub <NUM>. According to one aspect, the rotor blade comprises the reference plane <NUM>. For example, the reference plane <NUM> may be a surface of blade root <NUM>, as for instance illustrated in <FIG>. In another embodiment, the reference plane <NUM> may be a surface of a flange or bracket attached to the rotor blade <NUM>, as for instance illustrated in <FIG>.

In several embodiments, the pitch bearing <NUM> comprises a rotating component 40a and a non-rotating component 40b as for example described with reference to <FIG>. The non-rotating component 40b may be attached to the hub <NUM> whereas the rotating component 40a may be attached to the rotor blade <NUM>. The non-rotating component 40b as well as the rotating component 40a may comprise bolts 170a providing, for instance, the attachment to the hub <NUM> and the rotor blade <NUM>, respectively. According to one aspect, the reference plane <NUM> may be attached to the rotating component 40a of the pitch bearing or may be a part of the rotating component 40a of the pitch bearing. In one embodiment, the reference plane <NUM> may be a surface of the pitch bearing <NUM>, in particular, of the rotating component 40a of the pitch bearing <NUM>, as for instance illustrated in <FIG>. For example, the reference plane <NUM> may be a part of a bottom surface of the rotating component 40a, wherein the bottom surface may be a surface pointing to the interior or the center of the hub. Also the bolts 170a may provide the reference plane <NUM>, as for instance illustrated in <FIG>.

<FIG> illustrate the reference plane <NUM> as a bottom surface. A bottom surface essentially faces the center of the hub. A bottom surface may be essentially perpendicular to the pitch axis <NUM>. However, the reference plane <NUM> may also be a surface that does not face the center of the hub. For example, the reference plane <NUM> may face a side wall of the hub as for instance illustrated in <FIG>.

In <FIG> the reference plane <NUM> is located in the interior of the hub <NUM>. However, the reference plane <NUM> may also be located at the exterior of the hub. The latter, for instance, may be advantageous for an arrangement where the rotor blade <NUM> is attached to the outer component of the pitch bearing <NUM>, for example, where the rotating component 40a of the pitch bearing <NUM> is an outer ring as illustrated in <FIG>. In analogy to <FIG> and the description above, the reference plane <NUM> may be a surface of any component of the rotor blade <NUM>, e.g. blade root <NUM>, rotating component 40a or any other component rotating as the rotor blade <NUM> rotates relative to the hub <NUM>. The reference plane <NUM> may be a bottom surface, as illustrated in <FIG>, or may be another surface, e.g. a surface facing the hub.

The material of the reference plane <NUM> may be chosen such that a displacement sensor, as discussed below, can detect a displacement of the reference surface relative to the hub. Suitable materials of the reference plane <NUM> may be metals such as steel, copper, aluminum.

Further, the system <NUM> includes at least one displacement sensor <NUM>. In <FIG>, the displacement sensor <NUM> is fixed to the hub <NUM>. The displacement sensor <NUM> in those embodiments is configured to detect a displacement <NUM> of the reference plane <NUM> relative to the hub <NUM> without physical contact. For example, the displacement sensor <NUM> may be mounted such that the displacement sensor <NUM> faces the rotor blade <NUM>. For example, the displacement sensor <NUM> may be mounted opposite the reference plane <NUM> such that the displacement sensor <NUM> faces the reference plane <NUM>. According to one aspect, the displacement sensor <NUM> is configured to detect a radial, axial and/or tilting displacement of the reference plane <NUM> relative to the hub.

The displacement sensor <NUM> may be fixed to the hub <NUM> directly, as for instance shown in <FIG>, or indirectly, e.g. using a flange or brackets <NUM> mounted on the hub <NUM>, as for instance shown in <FIG>, <FIG>, <FIG> and <FIG>. The displacement sensor <NUM> may also be mounted on the non-rotating component 40b of the pitch bearing <NUM>. The displacement sensor <NUM> may be mounted in the interior of the hub, as for instance shown in <FIG>. Such an installation of the displacement sensor <NUM> in the interior of the hub <NUM> offers the advantage that the displacement sensor <NUM> is less exposed to environmental influences. Especially offshore wind turbines can be subject to extreme environmental influences which can cause damage especially to those components attached to the outside of the wind turbine <NUM>. However, the displacement sensor <NUM> may also be mounted externally to the hub, as for instance shown in <FIG>. In particular, such installation may be advantageous for an arrangement where the rotor blade <NUM> is attached to the outer component of the pitch bearing <NUM>.

As an alternative to the arrangements in <FIG>, the reverse arrangement is possible. In a reverse arrangement the displacement sensor <NUM> is fixed to the rotor blade <NUM> while the reference plane <NUM> has a fixed position with respect to the hub <NUM>. According to one aspect, the hub comprises the reference plane <NUM>. For example, the reference plane <NUM> may be part of the hub <NUM> or may be a part of a component that is firmly fixed to the hub. The displacement sensor <NUM> may be fixed to the rotor blade <NUM>, in particular to the blade root <NUM>, or to a surface of a flange or bracket attached to the rotor blade <NUM>. The displacement sensor <NUM> may also be fixed to the pitch bearing <NUM>, in particular, to the rotating component 40a of the pitch bearing <NUM>, or to bolts 170a. One exemplary reverse arrangement is shown in <FIG> showing the displacement sensor <NUM> fixed to the bottom surface of the blade root <NUM> while a flange <NUM> mounted on the hub <NUM> comprising the reference plane <NUM>.

The displacement sensor <NUM> may be a sensor emitting field such as an electromagnetic field and detecting changes in the field. According to one aspect, the displacement sensor <NUM> is a proximity sensor. A proximity sensor is a sensor being able to detect the presence of a nearby object without physical contact. For example, the proximity sensor may be a capacitive, inductive, magnetic or optical sensor. An inductive sensor may be advantageous in case the reference plane is made from metal.

In some embodiments, the system <NUM> comprises only one displacement sensor <NUM>. Already one displacement sensor <NUM> may provide a wide range of useful information allowing a meaningful estimation of wind loads and moments acting on the rotor blade <NUM>. The omission of multiple sensors further contributes to cost savings for material as well as in construction and maintenance. For example, the displacement sensor <NUM> is mounted in such a way that the displacement sensor <NUM> detects the displacement of such a reference plane <NUM> which is exposed to relatively large displacements. Such position may be derived from those skilled in the art based on the main wind load direction. For example, the displacement sensor <NUM> may be mounted around the longitudinal axis of the rotor blade, similar to a number on a dial. If a virtual vector between <NUM> o'clock and <NUM> o'clock of such dial would reflect the main wind load direction (dominant direction), the displacement sensor <NUM> may be mounted either at <NUM> or at <NUM> o'clock.

In some embodiments, the system <NUM> comprises a plurality of displacement sensors <NUM>. In this case, each displacement sensor <NUM> may have its own reference plane <NUM>, such that the system also comprises a plurality of reference planes <NUM>. For example, the reference planes <NUM> may be a surface of different bolts 170a, respectively. Alternatively, the plurality of displacement sensor <NUM> may use the same continuous surface as reference planes <NUM>, e.g. the bottom surface of the rotating component 40a of the pitch bearing <NUM>. Such surface may be considered as a plurality of reference planes <NUM> into which the continuous surface is virtually divided.

The plurality of displacement sensors increases the number of measurement data. In particular, this enables a more accurate estimation of wind loads acting on the rotor blade <NUM>. More than one displacement sensors <NUM> may also provide a self-verifying system as described below. According to one aspect, the plurality of displacement sensors <NUM> is mounted around the longitudinal axis of the rotor blade, similar to the numbers on a dial.

For example, the system <NUM> may comprise two displacement sensors <NUM>. In some embodiments, the two displacement sensors <NUM> may be mounted around the longitudinal axis of the rotor blade at a uniform distance from each other, i.e. at <NUM> and at <NUM> o'clock. The two displacement sensors <NUM> may be mounted such that a vector between them reflects the main wind load direction (dominant direction). Two opposing displacement sensors <NUM>, such as those at <NUM> and <NUM> o'clock, may detect essentially the same displacement of the corresponding reference planes <NUM> (with reversed sign/direction). However, such arrangement allows the measured values to be mutually validated, so that the system checks itself and the data becomes more accurate.

The two displacement sensors <NUM> may also be mounted such that they monitor particularly the flapwise or the edgewise movement of the rotor blade <NUM> by detecting the displacement of a corresponding reference plane <NUM>. In some embodiments, the two displacement sensors <NUM> may be mounted around the longitudinal axis of the rotor blade at an angle of <NUM> degree to each other, i.e. at <NUM> and at <NUM> o'clock. This way, the two displacement sensors <NUM> may simultaneously monitor the flapwise and the edgewise movement of the rotor blade. For example, one displacement sensor <NUM> may particularly monitor an edgewise movement of the rotor blade whereas the other one particularly monitors a flapwise movement of the rotor blade. In case the displacement sensors <NUM> are fixed to the hub, the displacement sensors may be arranged such that they monitor the flapwise or the edgewise movement of the rotor blade <NUM> when the rotor blade <NUM> is in its full power position. For example, one displacement sensor <NUM> may be mounted along a virtual vector reflecting the dominant direction and the other displacement sensor <NUM> may be mounted along a virtual vector reflecting the corresponding perpendicular direction. In case the displacement sensors <NUM> are mounted on the rotor blade <NUM>, the displacement sensors rotate together with the rotor blade <NUM> and, thus, they can be easily arranged in a way that they always measure the flapwise and the edgewise moments. For the latter, a determination of edgewise and the flapwise loads may dispense with a coordinate transformation from a fixed into a rotating frame.

In some embodiments, the system <NUM> may comprise three displacement sensors <NUM>. The three displacement sensors <NUM> may be mounted around the longitudinal axis of the rotor blade at a uniform distance from each other, i.e. at <NUM>, <NUM> and at <NUM> o'clock. Alternatively, the three displacement sensors <NUM> may be mounted around the longitudinal axis of the rotor blade at an angle of <NUM> degree to each other, i.e. at <NUM>, <NUM> and at <NUM> o'clock. For example, the displacement sensors <NUM> mounted at <NUM> and <NUM> o'clock are mounted in such a way that a vector between them reflects the dominant direction (direction of main wind load). The displacement sensor <NUM> mounted at <NUM> o'clock may be mounted on a virtual line reflecting a non-dominant direction. The displacement sensors <NUM> mounted at <NUM> and <NUM> o'clock may detect the displacement of such reference planes <NUM> which are exposed to relatively large displacements compared to the displacement of the reference plane <NUM> of the displacement sensor <NUM> mounted at <NUM> o'clock.

In other embodiments, the system <NUM> may comprise four displacement sensors <NUM>. For example, the four displacement sensors <NUM> may be mounted around the longitudinal axis of the rotor blade at <NUM>, <NUM>, <NUM> and <NUM> o'clock, as for instance illustrated in <FIG>. Two of the four displacement sensors <NUM>, e.g. those at <NUM> and <NUM> o'clock, may be configured to monitor particularly the flapwise movement of the rotor blade by detecting the displacement of corresponding reference planes <NUM>. The other two displacement sensors <NUM>, e.g. those at <NUM> and <NUM> o'clock may be configured to monitor particularly the edgewise movement of the rotor blade by detecting the displacement of a corresponding reference planes <NUM>. With such configuration the measured data of each displacement sensor <NUM> is validated by one of the other displacement sensors <NUM>, such that the accuracy of the data can be evaluated and the data can be interpreted and processed, accordingly.

In other embodiments, the system <NUM> may comprise more than four displacement sensors <NUM>.

The displacement sensor(s) <NUM> may be communicatively coupled to the controller <NUM>. Thus, the controller <NUM> may be provided with actual measured data that allow a determination or meaningful estimation of moments acting on the rotor blade <NUM>. The controller <NUM> may process the data received from the displacement sensor(s) <NUM>. For example, controller <NUM> may be configured to determine a bending moment exerted on a part of the rotor blade <NUM>. In particular, the controller <NUM> may be configured to determine a bending moment exerted on the blade root <NUM> of the rotor blade <NUM> based on signals received from the displacement sensor(s) <NUM>. Rotor blade bending moments allow an estimation of wind loads acting on rotor blades. The controller <NUM> provided with actual measured data may determine a bending moment instead of using estimated values provided by an algorithm. Hence, according to one aspect of the invention system <NUM> is a system for determining a bending moment of the blade root <NUM> of the rotor blade <NUM>.

With the data measured by the displacement sensor(s) <NUM> controller <NUM> may also determine or estimate other influences and/or changes regarding the rotor blades <NUM>. For example, ice accretion or fouling can influence the weight of the rotor blade <NUM> and, thus, may influence the displacement of the reference plane <NUM>. Hence, controller <NUM> may be configured to determine ice accretion or fouling of the rotor blades based on signals received from the displacement sensor(s) <NUM>.

In additional embodiments, the system <NUM> may further comprise a communication path <NUM>. The communication path <NUM> may be configured to transfer the data received from the displacement sensor(s) <NUM> to the controller <NUM>. The communication path <NUM> may comprise a cable. The communication path <NUM> may be configured to transfer the signals from the displacement sensor <NUM> to the controller <NUM> without transferring the signals from the rotor blade <NUM> to the hub <NUM>. The latter is particularly relevant for the arrangement in which the displacement sensor <NUM> is fixed to the hub. The controller <NUM> is not located in rotor blade <NUM>. Moreover, if each displacement sensor <NUM> is fixed to the hub <NUM>, the displacement sensors <NUM> are also not located in rotor blade <NUM>. Consequently, there is no need to transfer the data received from the displacement sensor(s) <NUM> from or to the rotor blade <NUM>. This avoids the need for complicated and potentially vulnerable installations that allow data to be transferred between two components, wherein one is rotating relative to the other. For example, with such communication path <NUM> there is no need to pass cables from the hub <NUM> to the rotor blade <NUM> rotating relative to the hub <NUM>. The latter is necessary, for example, when measuring the bending moment of the blade root with strain gauges or fiber Bragg gauges.

Strain gauges or fiber Bragg gauges measurement devices are very sensitive equipment, whereas system <NUM> using displacement sensor(s) <NUM> is a very stable and reliable system. In particular, system <NUM> with displacement sensor <NUM> fixed to the hub is not dependent on an additional connection between rotor blade and hub (next to the one via the bearing), which is favored for example by the non-contact measurement of the displacement sensor(s) <NUM> and by the communication path <NUM> as described above.

In further embodiments, the system <NUM> may comprise a pitch adjustment mechanism <NUM> as described above. With the pitch adjustment mechanism <NUM> the controller <NUM> may adjust the pitch angle of the rotor blade <NUM> in dependence of the determined bending moments exerted on a the blade root <NUM> of the rotor blade <NUM>. The adjustment of the pitch angle allows system <NUM> to control loads and/or forces from wind acting on the rotor blade <NUM>.

In another aspect, the present disclosure is directed to a nacelle assembly of a wind turbine <NUM> mounted atop a tower <NUM>. The nacelle assembly comprises a nacelle <NUM>, a hub <NUM> and a plurality of rotor blades <NUM>. According to one aspect, the number of rotor blades is three. The rotor blades <NUM> may be coupled to the hub <NUM> with a plurality of pitch bearings <NUM>. Further, the nacelle assembly comprises a plurality of reference planes <NUM> as those described with reference to system <NUM>. Each reference plane <NUM> may be configured to move with one rotor blade <NUM> of the plurality of rotor blades as the rotor blade <NUM> moves relative to the hub <NUM>. In particular, the rotor blade <NUM> may comprise the reference plane <NUM>. The nacelle assembly may further comprise a plurality of displacement sensors <NUM> which are fixed to the hub <NUM>. Each of the displacement sensors <NUM> may be configured to detect a displacement of one reference plane <NUM> of the plurality of reference planes relative to the hub <NUM> without physical contact. Alternatively, each reference plane <NUM> of the plurality of reference planes may have a fixed position with respect to the hub <NUM> while each displacement sensor <NUM> of the plurality of displacement sensors is fixed to a rotor blade <NUM> of the plurality of rotor blades. In this case, each of the displacement sensors <NUM> may be configured to detect without physical contact a displacement of one reference plane <NUM> of the plurality of reference planes relative to a blade root <NUM> of the respective rotor blade <NUM> to which the displacement sensor <NUM> is fixed. The plurality of displacement sensors <NUM> and reference planes <NUM> may form a plurality of sensor-plane pairs, wherein each pair sensor-plane pair is assigned to one rotor blade <NUM>, respectively. In particular, each rotor blade <NUM> may be attributed to the same number of sensor-plane pairs. For example, each rotor blade <NUM> may be attributed with four sensor-plane pairs. The plurality of displacement sensors <NUM> may be communicatively coupled to a controller <NUM> as described with reference to system <NUM>. Controller <NUM> may be configured to determine a bending moment exerted on a blade root <NUM> of the rotor blade <NUM> based on signals received from the displacement sensors <NUM>.

Referring now to <FIG>, a flow diagram of one embodiment of a method <NUM> for measuring displacements of a blade root of a rotor blade of a wind turbine, such as the wind turbine <NUM> of <FIG>, is illustrated. Method <NUM> may be performed with system <NUM>. As shown at <NUM>, method <NUM> comprises contactless measuring performed with at least one displacement sensor <NUM>. The contactless measuring comprises measurement of a displacement <NUM> of a reference plane <NUM>. The reference plane <NUM> may configured to move with the rotor blade <NUM> which is coupled to the hub <NUM> as the rotor blade <NUM> moves relative to the hub <NUM> while the displacement sensor <NUM> fixed to the hub <NUM>. For example, the rotor blade <NUM> may comprise the reference plane <NUM>. Alternatively, the reference plane <NUM> may have a fixed position with respect to the hub <NUM> while the displacement sensor <NUM> is fixed to the rotor blade <NUM>.

The method may further comprise transfer of a signal from the displacement sensor(s) <NUM> to a controller <NUM> as illustrated at <NUM>. Such transfer may be realized with a communication path <NUM> as described above. As shown at <NUM>, the method may further comprise receiving the signal from the displacement sensor <NUM> with the controller <NUM>.

In some embodiments, the method may further comprise a determination step <NUM> being determining a bending moment exerted on a blade root <NUM> of the rotor blade <NUM>. This determination may be based on signals received from the displacement sensor(s) <NUM>. Step <NUM> may be performed with controller <NUM>. Controller <NUM> may further communicate with the pitch adjustment mechanism in order to adjust a pitch angle of the rotor blade (step <NUM>) by rotating the rotor blade around a longitudinal axis <NUM> of the rotor blade <NUM>. The adjustment of the pitch angle controls the wind load and power generated by wind turbine <NUM>. According to one aspect, determination step <NUM> comprises determining a flapwise and an edgewise bending moment.

In some embodiments, the method may further comprise a calibration step <NUM>. Calibration step <NUM> is further illustrated in <FIG>. Calibration of method <NUM> may take place after installation of system <NUM>. For calibration of method <NUM> one may perform several pitch rolls, i.e. changing the pitch angle of the rotor blade <NUM> by rotating the rotor blade <NUM> around a longitudinal axis by at least <NUM> degree, with hub <NUM> in several positions. The orientation of the rotor blade <NUM> may be different for each static position of the hub <NUM>. According to one aspect, the static positions of hub <NUM> are chosen such that the rotor blade <NUM> experiences a different influence of gravity in each position. An unloaded displacement of the reference plane <NUM> is measured while the pitch rolls take place, wherein the unloaded displacement describes a displacement <NUM> without wind loads acting on rotor blade <NUM>. Using the measured unloaded displacement as well as considering the static moment of rotor blade <NUM> may allow to determine an unloaded state as function of the pitch angle and the orientation of the rotor blade <NUM> (step <NUM>). As shown at <NUM>, a static position of hub <NUM> may be adjusted. The pitch rolls at this position of hub <NUM> may be performed in a first direction (step <NUM>). Optionally, another pitch roll at the same position of hub <NUM> is performed in a second direction, wherein the second direction is opposite to the first direction (step <NUM>). Steps <NUM>, <NUM> and optionally step <NUM> may be repeated at least three times (step <NUM>). In dependence of the orientation of rotor blade <NUM>, the different positions of hub <NUM> may lead to different forces and moments acting on the rotor blade <NUM>. According to one aspect, the calibration step comprises four static positions of hub <NUM> wherein rotor blade <NUM> points once upwards, once to the right, once downwards and once to the left. For example, at a first static position rotor blade <NUM> may point downwards, i.e. rotor blade <NUM> is particularly perpendicular to the ground. In this position, no bending moment is exerted on the blade root <NUM> and only the blade mass determines the unloaded displacement. At a second static position rotor blade <NUM> may point upwards, wherein also no bending moment is exerted on the blade root <NUM> and only blade mass determines the unloaded displacement. In the first and second static position, the weight force of the blade mass acts in opposite directions relative to the displacement sensor(s) <NUM> in the hub. Measurements at the first and second static position allow determination of an unloaded "zero point". In a third and fourth static position blade root <NUM> may point to the left and to the right, respectively, i.e. rotor blade is particularly parallel to the ground. In the third and fourth position bending moment is exerted on the blade root <NUM> due to the blade mass. Measurements at the third and fourth static position act as calibration load. It is to be understood that the terms first, second, etc. do not reflect the sequence of the steps. For example, the measurement at the third position may take place previous to the measurement at the first position.

There is also the possibility to do the "zero point"-mapping before the rotor blades are mounted to the hub. As part of the end-of-production-line-functionality-test the rotating component 40a of each pitch bearing <NUM> may be rotated by at least <NUM> degree while the unloaded displacement of rotating component 40a is measured. With this calibration step eliminate <NUM> of the <NUM> described calibration positions above may be eliminated as one would only need one calibration load, i.e. one static position with rotor blade <NUM> pointing to the left or right.

Claim 1:
A system (<NUM>) of a wind turbine (<NUM>), the system comprising:
a hub (<NUM>) comprising a non-rotating component (40b) of a pitch bearing (<NUM>),
a rotor blade (<NUM>) comprising a blade root attached to a rotating component (40a) of the pitch bearing (<NUM>),
a plurality of non-contact displacement sensors (<NUM>) operably facing the rotor blade and fixed directly or indirectly to the hub (<NUM>), and
a respective reference plane (<NUM>) associated with each of the plurality of non-contact displacement sensors (<NUM>), the respective reference planes defined by a component (40a, 170a) that moves with the rotor blade (<NUM>) as the rotor blade moves relative to the hub (<NUM>),
wherein each of the plurality of displacement sensors (<NUM>) is configured to detect a relative movement between the respective reference plane (<NUM>) and the hub (<NUM>) without being physically connected to the component defining the respective reference plane (<NUM>), and
wherein the plurality of displacement sensors (<NUM>) are mounted opposite to and facing their respective reference plane (<NUM>).