WO2024193781A1

WO2024193781A1 - Pitch-controlled wind turbine

Info

Publication number: WO2024193781A1
Application number: PCT/DK2024/050051
Authority: WO
Inventors: Thomas S. Bjertrup Nielsen; Kim Hylling SØRENSEN; Torben Juul Larsen; Robert Thomas RUDOLF; Mikkel Kiilerich ØSTERLUND
Original assignee: Vestas Wind Systems A/S
Priority date: 2023-03-21
Filing date: 2024-03-18
Publication date: 2024-09-26

Abstract

According to the present invention there is provided a pitch-controlled wind turbine comprising a tower, a nacelle mounted on the tower, and a rotor rotatably mounted to the nacelle. The rotor defines a rotor axis and a rotor plane perpendicular to the rotor axis. The rotor comprises a hub and a plurality of wind turbine blades, each blade extending in a spanwise direction between a blade root defined by an inboard portion of the blade and a blade tip defined by an outboard portion of the blade. Each blade is rotatably connected to the hub via a respective pitch mechanism such that each blade is rotatable about a pitch axis. Further, each blade comprises a windward side and a leeward side which meet at a leading edge and a trailing edge to define an airfoil profile. The airfoil profile has a chord and a flapwise thickness, the chord being the distance between the leading and trailing edges and the flapwise thickness being the distance between the windward and leeward sides in a flapwise direction orthogonal to the chord. The pitch-controlled wind turbine is configured to reduce loading of the inboard portion of each wind turbine blade in use. Accordingly, each blade further comprises a connection location located between the blade root and the blade tip at a radial distance r from the rotor axis. The connection location defines an inboard end of the outboard portion and an outboard end of the inboard portion. The turbine further comprises a plurality of blade connecting members, and each blade connecting member is connected between corresponding connection locations of a pair of wind turbine blades.

Description

Pitch-controlled wind turbine

Technical field

The present invention relates to a pitch-controlled wind turbine comprising a tower, a nacelle mounted on the tower, and a rotor rotatably mounted to the nacelle, where the rotor comprises a hub and a plurality of wind turbine blades.

Background

There is a continuing desire to generate increased levels of power from onshore and offshore wind farms. One way to achieve this is to provide modern wind turbines with larger wind turbine blades. The provision of larger blades increases the swept area of the rotor, allowing the wind turbine to capture more energy from the wind. However, wind turbine blades experience various loads and stresses in use, and increasing the length of a wind turbine blade increases the magnitude of loads that the blade must withstand. For example, flapwise loads resulting from wind pressure on the blade, and edgewise loads resulting from the weight of the blade, are both greater for larger blades.

To withstand the increased loading in use, large blades are typically manufactured using more material near an inboard end comprising a blade root at which the blade is attached to a rotor hub. For example, more material may be used by increasing the diameter of the blade root, and/or by increasing the thickness of the blade near the inboard end. Each of these solutions increases the rigidity and strength of the inboard end of the blade such that it can support increased loading. However, in practice, each of these solutions also has drawbacks and limitations. For example, increasing the root diameter can make it more difficult to manufacture and transport the blade, using more material near the inboard end increases the weight and cost of the blade.

Further, blades may be connected to the hub via a pitch mechanism for rotating the blades relative to the hub. Larger blades typically impart higher loading on the pitch mechanism and require a greater force to rotate.

It is against this background that the present invention has been devised. Summary

It will be appreciated that as used herein, references to the rotor plane refer to a plane perpendicular to the rotor axis and located at the intersection point p along the rotor axis where the pitch axis of each blade intersects or is closest to the rotor axis. Further, it should be understood that references to each “connection location” refer to a location along the spanwise length of the blade. In some examples a plurality of blade connecting members may be connected to a blade at the same connection location, but at different points around the airfoil profile of the blade at the connection location.

The blade connecting members connected between corresponding connection locations of a pair of wind turbine blades advantageously reduce loading of the inboard portion of the blades in use because some of the blade loads are diverted to the blade connecting members instead of progressing to the hub via the inboard portion of the respective loaded blade. In particular, loads may be transferred from a higher loaded blade to a lesser loaded blade via a blade connecting member in use. The blade connecting members may reduce edgewise loads, flapwise loads or both edgewise loads and flapwise loads in the inboard portion of a higher loaded blade. The arrangement of blade connecting members is particularly advantageous for reducing edgewise fatigue loads, i.e. gravity driven loads. Accordingly, the blade connecting members facilitate the use of larger blades without necessitating an increase in blade root diameter to support the increased loads of such larger blades, because some of the blade loads are transferred to the blade connecting members, bypassing the inboard portion and blade root of the respective blade.

Each pitch mechanism preferably comprises a pitch bearing via which each respective blade is connected to the hub. Additionally, in some preferred examples each pitch mechanism may include a pitch drive, such as a geared drive or an actuator, for applying a force to each blade to rotate the blade about its respective pitch axis.

In some examples, each blade may be inclined such that, in a plane perpendicular to the rotor plane, an inboard centreline of the blade is inclined at a coning angle of between 3 degrees and 12 degrees relative to the rotor plane to reduce loading of the inboard portion of each wind turbine blade in use.

As used herein, the inboard centreline of the blade connects a centre point of the blade root and a blade centre at the connection location. The blade centre is defined as the intersection of the chord defined between the leading and trailing edges and the flapwise thickness orthogonal to the chord at the maximum flapwise thickness, at the connection location. It will be appreciated that the coning angle may be measured between the inboard centreline of the blade and the rotor plane at 0 degrees pitch, i.e. when the blades are not pitched relative to the hub.

Further, for additional context it should be understood that the coning angle is determined by the configuration of components on a hub side of the pitch bearing. Accordingly, pitching the blades, i.e. rotating about the pitch axis, may vary the inclination of the inboard centreline, and a position of 0 degrees pitch is therefore used as the reference configuration. In some examples the coning angle may therefore be defined with reference to the pitch axis of the blade. For example, each blade may be inclined such that, in a plane perpendicular to the rotor plane, the pitch axis of the blade is inclined at a coning angle of between 3 degrees and 12 degrees relative to the rotor plane.

In some preferred examples, each blade may be inclined with a coning angle of between 5 degrees and 10 degrees between the inboard centreline and the rotor plane. Increasing the coning angle reduces the flapwise loading of each blade and may help to reduce the risk of the blades striking the tower in use. However, increasing the coning angle also reduces the effective swept area of the rotor, thereby reducing the maximum potential annual energy production (AEP) of the wind turbine. Further, the rotor may be rotatably mounted to the nacelle via a main bearing in some examples. An increase in coning angle may result in increasing loading of the main bearing, thereby requiring additional strengthening of the main bearing at increased cost. The above stated ranges provide an advantageous compromise between reduced flapwise loading, increased main bearing loading, and annual energy production.

In some examples, each blade may be inclined such that, in a plane perpendicular to the rotor plane, an inboard centreline of the blade is inclined at an out-of-plane shim angle of between -2 degrees and -0.5 degrees or between 0.5 degrees and 2 degrees relative to the pitch axis to reduce loading such as pitch loadings of the inboard portion of the blade in use. In preferred examples, the inboard centreline of the blade is inclined at an out-of- plane shim angle of between -2 degrees and -1 degree or between 1 degree and 2 degrees relative to the pitch axis to reduce loading of the inboard portion of the blade in use.

Again it will be appreciated that for reference, in preferred examples the out-of-plane shim angle may be measured between the inboard centreline and the pitch axis at 0 degrees pitch, i.e. when the blades are not pitched relative to the hub. It will be appreciated that the measurement of the out-of-plane shim angle is between the inboard centreline and a transposition of the pitch axis into the plane perpendicular to the rotor plane.

In preferred examples, each blade may be inclined at an out-of-plane shim angle of between -1 degree and -0.5 degrees or between 0.5 degrees and 1 degree. Inclining each blade at an out-of-plane shim angle may help to reduce flapwise and edgewise loading, as well as reducing the risk of the blades striking the tower in use. Further, such out-of- plane inclination is particularly advantageous for reducing pitch loads, i.e. loading of the pitch mechanism of a respective blade, in use.

In some examples, each blade may be inclined such that, in a plane parallel to the rotor plane, an inboard centreline of the blade is inclined at an in-plane shim angle of between -1 degree and -0.5 degrees or between 0.5 degrees and 3 degrees relative to the pitch axis to reduce loading such as pitch loadings of the inboard portion of the blade in use.

Again it will be appreciated that for reference, in preferred examples the out-of-plane shim angle may be measured between the inboard centreline and the pitch axis at 0 degrees pitch, i.e. when the blades are not pitched relative to the hub. It will be appreciated that the measurement of the in-plane shim angle is between the inboard centreline and a transposition of the pitch axis into the plane parallel to the rotor plane.

In preferred examples, each blade may be inclined at an in-plane shim angle of between 1 degree and 3 degrees in use. Inclining each blade at an in-plane shim angle may help to reduce flapwise and edgewise loading. Further, such in-plane inclination is particularly advantageous for reducing pitch moment loads. For example, a negative in-plane shim angle inclination may be advantageous for when the turbine is configured for a service operation. Further, these in-plane shim angles, in particular positive in-plane shim angle inclination, help to reduce moment loads about the pitch axis of each blade, thereby reducing the mechanical effort required of each pitch mechanism to vary the pitch of the respective blade in use.

In some examples, the pitch-controlled wind turbine may further comprise one or more shim angle adjustment members between the hub and each blade root to set the shim angle of each blade. Accordingly, in some examples the blades may be connected to the hub via a respective shim angle adjustment member.

In some examples, at least the inboard portion of each blade may comprise a pre-bend such that, in a plane perpendicular to the rotor plane, an inboard centreline of the blade is inclined at an out-of-plane shim angle of between -2 degrees and -0.5 degrees or between 0.5 degrees and 2 degrees relative to the pitch axis. In a preferred example, the inboard centreline of the blade is inclined at an out-of-plane shim angle of between -2 degrees and -1 degree or between 1 degree and 2 degrees relative to the pitch axis. Additionally or alternatively, in some examples, at least the inboard portion of each blade may comprise a pre-bend such that, in a plane parallel to the rotor plane, an inboard centreline of the blade is inclined at an in-plane shim angle of between -1 degree and -0.5 degrees or between 0.5 degrees and 3 degrees relative to the pitch axis. In a preferred example, the inboard centreline of the blade is inclined at an in-plane shim angle of between 1 degree and 3 degrees relative to the pitch axis. The above-described advantages of in-plane and out-of-plane shim angle inclination apply equally to examples where the inclination is provided by the pre-bent inboard portion of the blades.

In some examples, the rotor may be mounted to the nacelle such that the rotor axis is inclined at a tilt angle of between 0 degrees and 8 degrees relative to horizontal. In some preferred examples, the rotor may be mounted to the nacelle such that the rotor axis is inclined at a tilt angle of between 2 degrees and 6 degrees, relative to horizontal. Increasing the tilt angle advantageously reduces the risk of the blades striking the tower in use.

As described previously, in some examples a sufficient blade-to-tower clearance to reduce the risk of blades striking the tower may be achieved by increasing the cone angle, and/or increasing the out-of-plane shim angle, and/or increasing the prebend i.e. sweep of the blades of the turbine. Accordingly, it should be noted that in some advantageous examples, for example, where at least one of cone angle, out-of-plane shim angle, or prebend, is increased, the turbine may not require a high tilt angle, i.e. the tilt angle may be reduced, whilst still achieving the required blade-to-tower clearance to ensure safe operation.

Further still, it will be appreciated that the blade connecting members connected between corresponding connection locations of a pair of wind turbine blades provide an additional factor of safety for reducing the risk of tower strikes. As such, the tilt angle may be reduced compared to a typical wind turbine (not comprising blade connecting members) because the arrangement of the blade connecting members provides additional safety for the blade- to-tower clearance. Alternatively, or additionally, the prebend of the blades away from the tower may be reduced, which may increase the swept area at low wind speeds and hence increase energy production at low wind. This is particularly advantageous for low wind sites where blades may still need to be designed with prebend based on rare extreme wind situations.

As previously described, an increased coning angle may result in a reduction in the swept area of the rotor and therefore lower AEP. Accordingly, it should be understood that in some examples, the disadvantages of increasing the coning angle may be compensated by reducing the tilt angle.

According to some preferred examples the connection location of each blade may comprise split connection points with a first connection point and a second connection point. The blade connecting member hence being connected from the first connection point to the blade following during rotation of the rotor, and the blade connecting member being connected from the second connection point to the blade leading during rotation of the rotor. The first connection point and the second connection point may be separated by 0.3 m to 2 m and preferably by 0.4 m to 1.5 m. In other examples, the first connection point and the second connection point are located to the windward side of the airfoil profile.

According to some preferred examples, the connection location of each blade may comprise split connection points with a first connection point and a second connection point. The blade connecting member hence being connected from the first connection point to the blade following during rotation of the rotor, and the blade connecting member being connected from the second connection point to the blade leading during rotation of the rotor. The first connection point may be arranged to the windward side 38 of the airfoil profile and the second connection point may be arranged to the leeward side 40 of the airfoil profile. The first connection point and the second connection point are separated by 1.0 m to 3.5 m, preferably by 1.2 m to 3.0 m.

In some examples, the first connection point and the second connection point are located from a maximum flapwise thickness towards the leading edge. Furthermore, the first connection point and the second connection point are located in a leading-edge region of the airfoil profile.

Advantageously, the first connection point and the second connection point may be separated in the spanwise direction S by 0.3 m to 2 m, and preferably by 0.5 m to 1 .5 m.

Alternatively or additionally, the first connection point and the second connection point may be separated in the spanwise direction S and the second connection point may be arranged closer to the blade root than the first connection point.

Alternatively or additionally, the first connection point and the second connection point may be separated by a distance in a plane parallel to the chord and orthogonal to the spanwise direction S of 0.3 m to 2 m, and preferably by 0.5 m to 1 .5 m.

In some examples, each blade connecting member may extend directly between corresponding connection locations of a pair of wind turbine blades. The blade connecting members transfer blade loads between the connected blades, in particular between a higher loaded blade and a lower loaded blade, in use. In high wind conditions, for example near the rated wind speed, the aerodynamic loading of the blades may be increased, causing the blades to bend or flex downwind under the force of the incident wind, thereby increasing the tension in the blade connecting members. The increased tension may mean that a greater proportion of blade loads are transferred to the blade connecting members in use.

Attaching the blade connecting members directly between corresponding connection locations of a pair of wind turbine blades orientates the blade connecting members in an advantageous configuration for reducing edgewise loading and fatigue, e.g. loads directed along the chord between the leading and trailing edges.

Alternatively, in other examples, the pitch-controlled wind turbine may further comprise a support structure and one or more tension members. The support structure may extend from the hub to define a support point, and the or each tension member may be connected between the support point and an attachment point of a blade connecting member. In preferred examples, the support point may be located upwind relative to each connection location.

Accordingly, in some preferred examples, each connection location may be located upwind of the rotor plane, and the support point may be located upwind of each connection location. It follows that in some preferred examples, the support structure may extend from the hub in an upwind direction. Further, in some preferred examples the support point may be located substantially on the rotor axis. It will be appreciated that “support point” should be understood to refer to a location at which each respective tension member is connected to the support structure.

Advantageously, this configuration provides a tension force pulling the blade connecting member(s) and wind turbine blades in an upwind direction, thereby reducing flapwise loading of the inboard portion of each blade. Additionally, the support structure and the or each tension member provide an additional load path for transferring loads, including flapwise loads, from the blades to the hub.

In some examples, each tension member may be connected to the support point via a respective linear actuator configured to adjust the tension in the tension member and the associated blade connecting member.

Advantageously, this configuration facilitates control of the tension of the tension member and blade connecting member to control how much load is transferred from the blade to the connecting member and subsequently to the hub. This configuration also facilitates control of the length and tension of the respective blade connecting member, which may relate to a reduction in flapwise and/or edgewise loading. This also facilitates control of the stiffness response of the tension member and blade connecting member to vary the stiffness response thereof relative to the inboard portion of the blade and thereby control the distribution of loading between the blade connecting member and the inboard portion of the blade. Changing the overall stiffness characteristics using the above-described system may be simpler and more cost effective than reengineering and changing the design and materials of the blades and blade connecting members.

As described previously, the rotor plane P is located at the intersection point p. In some preferred examples, the support point may be located at an axial distance D of between 0.02R and 0.16R from the intersection point in the upwind direction, where R is the radius of the rotor. Accordingly, it may also be said that the support point may be located at an axial distance D of between 0.02R and 0.16R from the rotor plane in the upwind direction.

In some preferred examples, the support point may be located at an axial distance D of between 0.04R and 0.14R from the intersection point in the upwind direction. In some examples, increasing the axial distance D between the intersection point and the support point may increase the amount of flapwise loading transferred from the blade to the blade connecting members and tension members. In particular, increasing the axial distance D changes the orientation of the resultant force vector of the blade connecting member(s) connected to the blade such that a component of the resultant vector directed in the flapwise direction is increased.

Advantageously, increasing the axial distance D reduces flapwise loading of the inboard portion of the blade without appreciably altering the centre of mass of the rotor, i.e. the centre of mass is not moved particularly further away from the nacelle. As such, increasing the axial distance D does not appreciably increase the loads and wear on a main bearing via which the rotor is coupled to the nacelle.

In some examples, each blade connecting member may comprise a first portion extending between the attachment point and a connection location of a blade, and a second portion extending between the attachment point and a connection location of a different blade, where the first portion is the leading portion during rotation of the rotor. It is preferred that the first portion is equal to or longer than the second portion. The first portion may have a length of at most 0.65L, preferably at most 0.55L, more preferably 0.5L, where L is the combined length of the first and second portions of the blade connecting member. As such, in some preferred examples, the first and second portions of the blade connecting member may each have a length of 0.5L, i.e. the first and second portions may be the same length. In some examples such a configuration may be advantageous for balancing loads in the first and second portions of the connecting member.

Alternatively, in some other examples, the first portion of the connecting member may have a length of between 0.65L and 0.45L, preferably between 0.60L and 0.48L, more preferably between 0.55L and 0.5L. In such examples the blade connecting member and tension member may therefore have an asymmetrical configuration, and preferably the first portion of the connecting member is longer than the second portion.

With reference to the direction of rotation of the rotor, each pair of connected wind turbine blades comprises a leading blade and a following blade, where the leading blade leads the following blade through the rotation cycle. In some examples, the first portion of the connecting member may extend between the attachment point and the leading blade, and the second portion of the connecting member may extend between the attachment point and the following blade. Accordingly the first portion of the connecting member may be referred to as a leading portion, and the second portion of the connecting member may be referred to as a following portion in relation to the rotation of the rotor.

Accordingly, in any of the examples described above where the first portion of the connecting member has a length that is longer than 0.5L, i.e. an asymmetrical configuration, the first portion connected to the leading blade may be longer in length than the second portion of the connecting member connected to the following blade.

In some examples, each blade connecting member may comprise a first portion extending between the attachment point and a connection location of a blade, and a second portion extending between the attachment point and a connection location of a different blade. When projected to the rotor plane, an angle J defined between the tension member and the first portion of the blade connecting member may be between 92 degrees and 110 degrees and preferably J may be between 94 degrees and 105 degrees. In some preferred examples where - and particularly advantageously where the length of the first portion of the blade connecting member may be the same as the second portion - the angle J may be between 95 degrees and 105 degrees.

In some examples, an angle K between the projection to a vertical plane parallel to the rotor axis of the second portion of the blade connecting member connected to a blade oriented in 12 o’clock position and the tension member connected to the attachment point of the same blade connecting member may be between 180 degrees and 160 degrees and preferably K is between 179 degrees and 170 degrees. In some examples, the connection location may be located at a radial distance rof between 0.25R and 0.6R from the rotor axis, where R is the radius of the rotor. In some preferred examples, the connection location may be located at a radial distance rof between 0.30R and 0.55R, and more preferably between 0.4R and 0.5R, from the rotor axis. Spacing the connection location away from the blade root ensures that a substantial proportion of the blade loads may be transferred to the blade connecting member at the connection location, bypassing the blade root. Further, spacing the connection location away from the blade tip reduces the effect of increased drag caused by the connection location, and also reduces the noise resulting from the connection location and associated blade connecting member(s) in use. It was found to be particularly advantageous when the connection location is located at a radial distance r of between 0.30R and 0.55R, and the support point is located at an axial distance D of between 0.02R and 0.16R from the intersection point in the upwind direction as this was found to provide a strong protection against tower hit of the blades and reduce the requirement of pre-bending of blades so a larger efficient rotor diameter is realized for lower wind speeds.

In some preferred examples, the rotor may comprise three wind turbine blades. Each blade may be connected to two other blades via a respective blade connecting member such that the loads experienced by each blade are shared with each other blade in use. As described previously, the connection of blade connecting members between each pair of blades facilitates distribution of loading, such as flapwise loading and in particular edgewise loading, between the blades and blade connecting members.

It follows that in some examples, each blade may comprise two connection points located at the connection location. Each blade connecting member may be connected to a separate connection point. Such a configuration may facilitate a simpler assembly process for attaching a blade connecting member to a respective connection point. Attaching the blade connecting members to separate connection points may be additionally advantageous for pitching the wind turbine blades, where it may be preferably to allow the blade connecting members to move substantially independently. As such, this configuration may help to reduce moment loads about the pitch axis of each blade, thereby reducing the mechanical effort required of each pitch mechanism to vary the pitch of the respective blade in use.

Further, in some examples, at the respective connection location, each blade may comprise one or more connection points for connecting one or more blade connecting members, and at least one connection point may be located on the windward side of the respective blade in a leading-edge region of the airfoil profile. It will be appreciated that the leading-edge region may be defined relative to the leading edge of the blade at the connection location. For example, in some examples, the leading-edge region may be defined as a region spanning up to 0.5C away from the leading edge (i.e. in front of or behind the leading edge), where C is the total chord distance between the leading edge and the trailing edge at the connection location. In preferred examples, the leading-edge region may extend up to 0.25C from the leading edge at the connection location.

Connecting a blade connecting member to a connection point located in a leading-edge region of the airfoil profile may advantageously reduce the pitch loads in some examples. For example, aerodynamic forces may provide a positive pitch moment on the blade, and the tension in the blade connecting members connected in the leading-edge region may provide a negative pitch moment on the blade, thereby counteracting and/or alleviating at least some of the pitch moments. Further, providing one or more connection points in the above-stated region of the blade may also reduce the risk of interference or contact between the blade connecting member and the blade to which it is connected during pitching of the wind turbine blade.

In some examples, the connection points may be located relatively close together at the connection location. For example, the connection points at a given connection location may be separated by up to 0.2C, preferably up to 0.15C, more preferably up to 0.1 C, where C is the total chord distance between the leading edge and the trailing edge at the connection location.

In some other examples, the connection points may be located further apart at the connection location. For example a blade may comprise a connection point located near to the leading edge, i.e. in the leading-edge region, and a second connection point for another blade connecting member located on the windward side outside of the leadingedge region.

Brief description of the drawings

Examples of the present invention will now be described by way of non-limiting example only, with reference to the accompanying figures, in which:

Figure 1 is a schematic perspective view of a pitch-controlled wind turbine comprising blade connecting members connected between blades of the turbine;

Figure 2a is a schematic plan view of a blade of the turbine; Figure 2b is a schematic cross-sectional view of the blade at a connection location for connecting a blade connecting member to the blade;

Figure 2c is a schematic plan view of a blade of the turbine with split connection points;

Figure 2d is a schematic cross-sectional view of the blade at a connection location with split connection points for connecting a blade connecting member to the blade;

Figure 2e is a schematic plan view of a blade of the turbine with split connection points;

Figure 2f is a schematic plan view of a blade of the turbine with split connection points;

Figure 3 is an enlarged schematic perspective view of a rotor of the pitch-controlled wind turbine;

Figure 4 is a schematic side view of an example of a rotor rotatably mounted to a nacelle of the turbine;

Figure 5 is another schematic side view of an example of a rotor rotatably mounted to a nacelle of the turbine;

Figure 6 is a schematic front view of a rotor of the pitch-controlled wind turbine in a plane parallel to a rotor plane of the turbine;

Figure 7 is a schematic perspective view of a rotor comprising a support structure and a plurality of tension members connected between the support structure and a respective blade connecting member;

Figure 8 is a schematic side view of an upper part of the wind turbine shown in Figure 7 with one blade in the 12 o’clock position;

Figure 9 is a schematic front view of the rotor comprising tension members in a plane parallel to the rotor plane; and

Figure 10 is a schematic front view of another example of a rotor comprising tension members in a plane parallel to the rotor plane.

Detailed description

Figure 1 is a schematic perspective view of a pitch-controlled wind turbine 10. The turbine 10 comprises a tower 12 and a nacelle 14 mounted on the tower 12. A rotor 16 is rotatably mounted to the nacelle 14. Accordingly, the rotor 16 defines a rotor axis A. Typically the nacelle 14 houses powertrain components of the turbine 10, such as a gearbox and generator, for converting kinetic energy from the rotor 16 into electrical power.

The rotor 16 comprises a hub 18 and a plurality of wind turbine blades 20. The hub 18 may be rotatably mounted to the nacelle 14 via a main bearing (not shown). Each blade 20 extends in a spanwise direction (S) between a blade root 22 and a blade tip 24. The blade root 22 is defined by an inboard portion 26 of the blade 10 and the blade tip 24 is defined by an outboard portion 28 of the blade 20. Each blade 10 is rotatably connected to the hub 18 via a respective pitch mechanism (not shown) such that each blade 20 is rotatable about a pitch axis B relative to the hub 18 (shown in Figures 3 and 5 for example). Whilst not shown, it will be appreciated that each pitch mechanism preferably includes a pitch bearing via which the respective blade 20 is connected to the hub 18, and a pitch drive to rotate the blade 20 about its pitch axis B.

The pitch-controlled wind turbine 10 is configured to reduce loading of the inboard portion 26 of each wind turbine blade 20 in use. As such, each blade 20 comprises a connection location 30 located between the blade root 22 and the blade tip 24, and the turbine 10 comprises a plurality of blade connecting members 32. Each connecting member 32 is connected between corresponding connection locations 30 of a pair of wind turbine blades 10. In use, a portion of the loads experienced by each blade 10 are transferred to the blade connecting member 32 instead of progressing to the hub 18 via the inboard portion 26 of the respective loaded blade 20. The blade connecting members 32 therefore advantageously reduce loading of the inboard portion 26 of the blades 20 in use. In some examples, as shown in Figure 1 , the rotor 16 comprises three wind turbine blades 20 and each blade 20 may therefore be connected to two other blades 20 via a respective blade connecting member 32. Accordingly, loads experienced by each blade 20 are shared with each other blade 20 in use.

Examples of the rotor 16 and blades 20 of the pitch-controlled wind turbine 10 will now be described with reference to the remaining figures.

Figure 2a shows a plan view of a blade 20 of the pitch-controlled wind turbine 10 and Figure 2b shows a schematic cross-sectional view of the blade 20 at the connection location 30. Referring initially to Figure 2a and with reference also to Figure 1 , the connection location 30 is located at a radial distance r from the rotor axis A. In some examples, the radial distance r may be between 0.25R and 0.6R from the rotor axis, where R is the radius of the rotor 16. The connection location 30 defines an inboard end 34 of the outboard portion 28 and an outboard end 36 of the inboard portion 26. Accordingly, as previously described, loads experienced by each blade 20 in use are transferred to the blade connecting members 32 at the respective connection location 30 such that the loads experienced by the inboard portion 26 of each blade 20 are reduced.

With reference now to Figure 2b, each blade 20 comprises a windward side 38 and a leeward side 40 which meet at a leading edge 42 and a trailing edge 44. The blade 20 defines an airfoil profile configured for extracting energy from wind incident on the blade 20 in use. The airfoil profile has a chord between the leading and trailing edges 42, 44. The chord length at the connection location 30 is referred to herein as chord length C. The airfoil profile also has a flapwise thickness t which is the distance between the windward and leeward sides 38, 40 in a flapwise direction orthogonal to the chord. A leading-edge region 48 may be defined within 0.5C of the leading edge, i.e. within a radius of 0.5C, where C is the chord length at the connection location.

As described previously with reference to Figure 1 , in some examples each blade 20 may be connected to a plurality of other wind turbine blades 20. Accordingly, a plurality of blade connecting members 32 may be connected to a blade 20 at the connection location 30. As shown in Figure 2b, in some examples, each blade 20 may have one connection point 46 located at the connection location 30 for connecting blade connecting members 32 to the blade 20. Accordingly, in some examples each blade connecting member 32 may be connected to the same connection point 46 on the blade 20. Still with reference to Figure 2b, in some examples each blade 20 may comprise a connection point 46 located on the windward side 38 in the leading-edge region 48 of the airfoil profile. This location of the connection point 46 was found to be particularly advantageous when combined with the coning angle of between 3 degrees and 12 degrees.

As shown in Figure 2c, 2d, 2e and 2f in some examples, each blade 20 may comprise split connection points 46a, 46b with the first connection point 46a and the second connection point 46b located at the connection location 30 for connecting blade connecting members 32 to the blade 20, where the first connection point 46a and the second connection point 46b are separated by a distance. Accordingly, in some examples each blade connecting member 32 may be connected to a separate connection point 46a, 46b on the blade 20. It is preferred that the blade connecting member being connected from the first connection point 46a to the blade following during rotation of the rotor, and the blade connecting member being connected from the second connection point 46b to the blade leading during rotation of the rotor.

In some examples, it was found to be highly advantageous that the first connection point 46a and the second connection point 46b are separated by 0.3 m to 2 m, preferably by 0.4 m to 1.5 m. It was found to be particularly advantageous when the connection points are fixed relative to the blade surfaces, so when the blade is pitched, then the connection points are rotated around the pitch axis of the blade together with the blade surface. This allows for smart adjustment of the tension in the blade connecting members through pitching of the blades. Examples of blades with the connection points being fixed relative to the blade surfaces are shown in the various designs of Fig. 2a to Fig. 2f. In some cases, for example for pitch-controlled wind turbines having a spanwise length of the blades of at least 100 m, it may be useful to express the separation in terms of C, where C is the total chord distance between the leading edge and the trailing edge length at the connection location 46. In some examples, the first connection point 46a and the second connection point 46b are separated 0.07C to 0.6C, and preferably 0.09 to 0.4C.

In Figure 2c, 2d and 2e, both the first connection point 46a and the second connection point 46b are to the leeward side 38 of the airfoil profile, which may be an advantage for example in designing of aerodynamic fairing at the connection points.

In Figure 2f, the first connection point is arranged to the windward side 38 of the airfoil profile and the second connection point is arranged to the leeward side 40 of the airfoil profile. This may in some cases for example allow for further separation of the connection points or reduced risk of connecting members touching each other during pitching. In some examples it may be advantageous that the first connection point 46a and the second connection point 46b are separated by 1.0 m to 3.5 m, and preferably by 1.2 m to 3.0 m. In some cases, for example for pitch-controlled wind turbines having a spanwise length of the blades of at least 100 m, it may be useful to express the separation in terms of C. In some examples, with the first connection point arranged to the windward side 38 of the airfoil profile and the second connection point arranged to the leeward side 40, the first connection point 46a and the second connection point 46b may be by 0.20C to 0.8C, and preferably 0.3 to 0.6C.

With reference to Figure 2c and 2e, in some examples each blade 20 may comprise the connection points 46a and 46b located on the windward side 38 in the leading-edge region 48 of the airfoil profile. This location of the connection points 46a, 46b was found to be particularly advantageous when combined with the coning angle of between 3 degrees and 12 degrees. The use of split connection points was found to be highly advantageous as it allows for separate structures for transfer of the load from the connection point to the main load carrying structure of the blade, such as a spar or a spar cap. Further, it was found that for pitch regulated turbines it may allow for more optimum variation of tension in connecting members during pitching. It was found to allow for smarter arrangement of connecting members where full pitch (for example from -10 to +90 degrees) without the connecting members being in colliding with the blade or with each other.

As shown in Figure 2c and 2d, in some examples, the first connection point 46a and the second connection point 46b may be located at the same radial distance r from the rotor axis as the connection location 30 and hence be in the blade cross-section at the connection location 30. This was found to be particularly advantageous when the blade is a split blade ant the connection location 30 being located at the blade split as the blade slit typically would be reinforced due to the blade split, so the need for further reinforcement to transfer loads from the connection points to the load carrying structure of the blade may be limited. It was found to be advantageous that the first connection point 46a and the second connection point 46b are separated by a distance 49 in a plane parallel to the chord and orthogonal to the spanwise direction S of 0.3 m to 2 m, preferably by 0.5 m to 1.5 m. In some cases, for example for pitch-controlled wind turbines having a spanwise length of the blades of at least 100 m, it may be useful to express the separation in terms of C. In some examples, the first connection point 46a and the second connection point 46b are separated in a plane parallel to the chord and orthogonal to the spanwise direction S by 0.05C to 0.6C, and preferably 0.1 to 0.4C.

In some examples, at the connection location 30, the first connection point 46a and the second connection point 46b may be separated in the spanwise direction S. Preferably, the second connection point 46b being closer to the blade root and the first connection point 46a being further away from the blade root. Preferably the average spanwise position of the first connection point 46a and the second connection point 46b is the connection location 30. It was found to be advantageous that the first connection point 46a and the second connection point 46b are separated by a distance 51 in the spanwise direction S of 0.3 m to 2 m, preferably by 0.5 m to 1.5 m. In some cases, for example for pitch- controlled wind turbines having a spanwise length of the blades of at least 100 m, it may be useful to express the separation in terms of C. In some examples, the first connection point 46a and the second connection point 46b are separated in the spanwise direction S by 0.05C to 0.6C, and preferably 0.1 to 0.4C. As shown in Figure 2e, in some examples, the first connection point 46a and the second connection point 46b may be separated in the spanwise direction S and in the chordwise direction with the connection location 30 being the position between the first connection point 46a and the second connection point 46b. This arrangement allows for better separation of the connection members 32 during operation of the wind turbine including pitching of the blades. Further, it may allow for easier installation and/or servicing of the connection members 32. It was found to be advantageous that the first connection point 46a and the second connection point 46b are separated by a distance 51 in the spanwise direction S and in the chordwise direction of 0.3 m to 2 m, preferably by 0.5 m to 1 .5 m. In some cases, for example for pitch-controlled wind turbines having a spanwise length of the blades of at least 100 m, it may be useful to express the separation in terms of C. In some examples, the first connection point 46a and the second connection point 46b separated by a distance 51 in the spanwise direction S and in the chordwise direction by 0.05C to 0.6C, and preferably 0.1 to 0.4C. Reference is now made to Figure 3, which shows an enlarged schematic perspective view of the rotor 16. In particular, Figure 3 shows the pitch axes B of the blades 20, i.e. the respective axis B about which each blade 20 rotates relative to the hub 18. The pitch axes B intersect the rotor axis A at an intersection point p. Notably, the intersection point p also defines a rotor plane P which is perpendicular to the rotor axis A and located at the intersection point p of the rotor axis A and the pitch axes B.

Figure 3 also indicates a respective inboard centreline 50 of each blade 20. As used herein, the inboard centreline 50 of each blade 20 connects a centre point of the blade root 22 and a blade centre 52 of the respective blade 20 at its connection location 30. With brief reference again to Figure 2b, the blade centre 52 at the connection location 30 may be defined as the intersection of the chord C and the flapwise thickness tat the connection location 30.

Figure 4 shows a schematic side view of an example of the rotor 16 connected to the nacelle 14. Typically, the hub 18 and any components connected between the hub 18 and the pitch bearing contribute to the inclination of each blade 20 relative to the rotor plane P. To clearly show the inclination relative to the rotor plane P, the side view in Figure 4 is in a plane Q perpendicular to the rotor plane P. Further, only two blades 20 are shown in Figure 4 for clarity, but it will be appreciated that the same description applies equally to each blade 20 of the rotor 16. As shown in Figure 4, in some examples, each blade 20 may be inclined relative to the rotor plane P at a coning angle W. The coning angle W/may be measured between the rotor plane P and the inboard centreline 50 of the blade 20. To reduce loading of the inboard portion 26 in use, in some advantageous examples the coning angle W/may be between 3 degrees and 12 degrees.

In some examples, the inclination of the blade 20 relative to the rotor plane P may be determined by components on the blade side of the pitch bearing. For example, as shown in Figure 5, which also shows a schematic side view of an example of the rotor 16 connected to the nacelle 14, the turbine 10 may comprise a shim angle adjustment member 54 between the hub 18 and each blade root 22 to set a shim angle of each blade 20. Accordingly, in some examples each blade 20 may be inclined at an out-of-plane shim angle X relative to the respective pitch axis B. For example, the out-of-plane shim angle X between the inboard centreline 50 and the pitch axis B may be between -2 degrees and 2 degrees to reduce loading of the inboard portion 26 of the blade 20 in use.

Figure 5 also indicates a tilt angle /of the rotor 16 mounted to the nacelle 14. The tilt angle Y may be measured between the rotor axis A and a horizontal reference line H. For example, the rotor 16 may be mounted to the nacelle 14 such that the rotor axis A is inclined at a tilt angle Y of between 0 degrees and 8 degrees relative to the horizontal H. The tilt angle Y may help to reduce the risk of the blades 20 striking the tower 12 in high wind conditions in use.

Reference is now made to Figure 6 which shows a plane parallel to the rotor plane P. As shown, in some examples each blade 20 may be additionally or alternatively inclined at an in-plane shim angle Z relative to the pitch axis B. It will be appreciated that the pitch axis B is transposed into the plane parallel to the rotor plane P for the purpose of measuring the in-plane shim angle Z. In some examples, the in-plane shim angle Z between the inboard centreline 50 and the pitch axis B may be between -1 degree and 3 degrees to reduce loading of the inboard portion 26 of the blade 20 in use. Again, as shown in Figure 6, the in-plane shim angle Z may be determined, at least in part, by a shim angle adjustment member 54 arranged between the hub 18 and each blade root 22, such as between the blade bearing and the blade.

Whilst Figures 5 and 6 show examples wherein the in-plane and out-of-plane inclination of the blade 20 is influenced by adjustment members 54 arranged between the hub 18 and the respective blade root 22, in some examples (not shown) each blade 20 may be prebent, i.e. may have an amount of sweep, which contributes to the in-plane and/or out-of- plane inclination. For example, an inboard portion 26 of each blade 20 may be pre-bent such that, in a plane Q perpendicular to the rotor plane P, the inboard centreline 50 of the blade 20 is inclined at an out-of-plane shim angle X of between -2 degrees and 2 degrees relative to the pitch axis B. Further, the inboard portion 26 may be pre-bent such that the inboard centreline 50 of the blade 20 is inclined at an in-plane shim angle Z of between -1 degree and 3 degrees relative to the pitch axis B, in a plane parallel to the rotor plane P.

Referring now to Figures 7 and 8, these figures show examples of a turbine 10 comprising a rotor 16 comprising blade connecting members 32 connected between corresponding connection locations 30 of different blades 20 to share blade loads between the blades 20. Figure 7 shows a schematic perspective view and Figure 8 shows a schematic side view of a part of the wind turbine.

As shown in Figure 7 and 8, in some examples the wind turbine 10 may also include a support structure 56 that extends from the hub 18 of the rotor 16. In such an example, the support structure 56 may define a support point 58 located upwind relative to the connection location 30 of each blade 20. For example, the support point 58 may be located at an axial distance D of between 0.02R and 0.16R from the intersection point p in the upwind direction, where R is the radius of the rotor 16.

Further, the turbine 10 may include a tension member 60 connected between the support point 58 and an attachment point 62 of each respective blade connecting member 32. Each tension member 60 advantageously provides an additional load path for transferring blade loads to the hub 18 which bypasses the inboard portion 26 of each blade 20, thereby reducing loading of the inboard portion 26. The tension members 60 and support structure 56 may provide a tension force pulling the blades 20 in an upwind direction, thereby reducing flapwise loading of the inboard portion 26, in particular.

As shown in Figures 7 and 8, in some examples, each tension member 60 may be connected to the support point 58 via a respective linear actuator 64. Such an actuator 64 preferably has an adjustable length and may therefore be configured to adjust the tension in the tension member 60 and the associated blade connecting member 32.

Referring now additionally to Figure 9, which shows a plane parallel to the rotor plane P, in examples comprising a tension member 60, each blade connecting member 32 may comprise a first portion 32a and a second portion 32b defined by the attachment point 62. For example, the first portion 32a of a respective blade connecting member 32 may extend between the attachment point 62 and a connection location 30 of a given blade 20, and the second portion 32b may extend between the attachment point 62 and a connection location 30 of a different blade 20. As shown in Figure 9, in some examples the first and second portions 32a, 32b of a respective connection member 32 may be the same length. Accordingly, it can be said that in some examples the first and second portions 32a, 32b may each have a length of 0.5L, where L is the combined length of the first and second portions 32a, 32b of the blade connecting member 32.

With reference still to Figure 9 it will be appreciated that varying the length of the tension member 60 connected between the support structure 56 and the blade connecting member 32 varies an angle J defined between the tension member 60 and the first portion 32a of the blade connecting member 32 when projected to the rotor plane P. For example, as shown in Figure 9, in some examples the angle J between the tension member 60 and the first portion 32a of the blade connecting member 32 when projected to the rotor plane P may be between 92 degrees and 110 degrees and preferably between 94 degrees and 105 degrees. In preferred embodiments - and particularly advantageously where the length of the first portion 32a of the blade connecting member 32 is the same as the second portion 32b - the angle J is between 95 degrees and 105 degrees.

With brief reference again to Figure 8, an angle K is defined as the angle between the projection to a vertical plane parallel to the rotor axis of the second portion 32b of the blade connecting member 32 connected to a blade oriented in 12 o’clock position and the tension member 60 connected to the attachment point 62 of the same blade connecting member 32. It will be appreciated that the angle K may be changed by the design of the wind turbine by varying the length of the tension member 60, the position of the connection points 46, the axial distance D, the out of plane shim angle X, coning angle W and the position of the support point 58. In preferred embodiments, K may be between 180 degrees and 160 degrees, and advantageously K may be between 179 degrees and 170 degrees.

Finally, with reference to Figure 10, in some examples the first and second portions 32a, 32b of a blade connecting member 32 may not be of equivalent length, i.e. may not each be 0.5L in length. In some examples, an asymmetrical configuration of the portions 32a, 32b of the blade connecting members 32 may be advantageous. For example, as shown in Figure 10, the first portion 32a may have a length between 0.65L and 0.45L and correspondingly the second portion 32b may have a length that is the remainder of the length of the blade connecting member 32, i.e. between 0.35L and 0.55L dependent on the length of the first portion 32a. With reference to the direction of rotation of the rotor 16 indicated by the arrows in Figure 10, the first portion 32a leads the second portion 32b through the rotation cycle. Providing a longer first portion 32a than second portion 32b may lead to more favourable combination of contact angles at the connection location 30. Furthermore, providing a first portion 32a with a different length than the second portion may lead to may overall lead to a reducing drag and/or a reducing noise and/or reducing wear of the connecting member 32 as compared to embodiments with same length of first portion 32a and second portion 32b.

It will be appreciated that the description provided above serves to demonstrate a plurality of possible examples of the present invention. Features described in relation to any of the examples above may be readily combined with any other features described with reference to different examples without departing from the scope of the invention as defined in the appended claims.

Claims

1. A pitch-controlled wind turbine (10) comprising a tower (12), a nacelle (14) mounted on the tower (12), and a rotor (16) rotatably mounted to the nacelle (14), the rotor (16) defining a rotor axis (A) and a rotor plane (P) perpendicular to the rotor axis (A), the rotor (16) comprising a hub (18) and a plurality of wind turbine blades (20), each blade (20) extending in a spanwise direction (S) between a blade root (22) defined by an inboard portion (26) of the blade (20) and a blade tip (24) defined by an outboard portion (28) of the blade (20), and each blade (20) being rotatably connected to the hub (18) via a respective pitch mechanism such that each blade (20) is rotatable about a pitch axis (B); each blade (20) comprising a windward side (38) and a leeward side (40) which meet at a leading edge (42) and a trailing edge (44) to define an airfoil profile, the airfoil profile having a chord and a flapwise thickness, the chord being the distance (C) between the leading (42) and trailing edges (44) and the flapwise thickness (t) being the distance between the windward (38) and leeward sides (40) in a flapwise direction orthogonal to the chord; wherein the pitch-controlled wind turbine (10) is configured to reduce loading of the inboard portion (26) of each wind turbine blade (20) in use; wherein each blade (20) further comprises a connection location (30) located between the blade root (22) and the blade tip (24) at a radial distance (r) from the rotor axis (A), the connection location (30) defining an inboard end (34) of the outboard portion (28) and an outboard end (36) of the inboard portion (26); and wherein the pitch-controlled wind turbine (10) further comprises a plurality of blade connecting members (32), each blade connecting member (32) being connected between corresponding connection locations (30) of a pair of wind turbine blades (20).

2. The pitch-controlled wind turbine (10) of Claim 1 , wherein each blade (20) is inclined such that, in a plane perpendicular to the rotor plane (P), an inboard centreline (50) of the blade (20) is inclined at an out-of-plane shim angle (X) of between -2 degrees and -0.5 degrees or between 0.5 degrees and 2 degrees relative to the pitch axis (B) to reduce loading of the inboard portion (26) of the blade (20) in use, preferably the inboard centreline (50) of the blade (20) is inclined at an out-of-plane shim angle (X) of between -2 degrees and -1 degree or between 1 degree and 2 degrees relative to the pitch axis (B) to reduce loading of the inboard portion (26) of the blade (20) in use.

3. The pitch-controlled wind turbine (10) of Claim 1 or Claim 2, wherein each blade (20) is inclined such that, in a plane parallel to the rotor plane (P), an inboard centreline (50) of the blade (20) is inclined at an in-plane shim angle (Z) of between -1 degree and - 0.5 degrees or between 0.5 degrees and 3 degrees relative to the pitch axis (B) to reduce loading of the inboard portion (26) of the blade (20) in use, preferably the inboard centreline (50) of the blade (20) is inclined at an in-plane shim angle (Z) of between 1 degree and 3 degrees relative to the pitch axis (B) to reduce loading of the inboard portion (26) of the blade (20) in use.

4. The pitch-controlled wind turbine (10) of Claim 2 or Claim 3, further comprising one or more shim angle adjustment members (54) between the hub (18) and each blade root (22) to set the shim angle of each blade (20).

5. The pitch-controlled wind turbine (10) of any preceding claim, wherein at least the inboard portion (26) of each blade (20) comprises a pre-bend such that, in a plane perpendicular to the rotor plane (P), an inboard centreline (50) of the blade (20) is inclined at an out-of-plane shim angle (X) of between -2 degrees and -0.5 degrees or between 0.5 degrees and 2 degrees relative to the pitch axis (B), preferably the inboard centreline (50) of the blade (20) is inclined at an out-of-plane shim angle (X) of between -2 degrees and -1 degree or between 1 degree and 2 degrees relative to the pitch axis (B).

6. The pitch-controlled wind turbine (10) of any preceding claim, wherein at least the inboard portion (26) of each blade (20) comprises a pre-bend such that, in a plane parallel to the rotor plane (P), an inboard centreline (50) of the blade (20) is inclined at an in-plane shim angle (Z) of between -1 degree and -0.5 degrees or between 0.5 degrees and 3 degrees relative to the pitch axis (B), preferably the inboard centreline (50) of the blade (20) is inclined at an in-plane shim angle (Z) of between 1 degree and 3 degrees relative to the pitch axis (B).

7. The pitch-controlled wind turbine (10) of any preceding claim, wherein the connection location (30) of each blade (20) comprise split connection points (46) with a first connection point (46a) and a second connection point(46b), the blade connecting member (32) being connected from the first connection point (46a) to the blade (20) following during rotation of the rotor (16), and the blade connecting member (32) being connected from the second connection point (16b) to the blade (20) leading during rotation of the rotor (16), and wherein the first connection point (46a) and the second connection point (46b) are separated by 0.3 m to 2 m, preferably by 0.4 m to 1 .5 m.

8. The pitch-controlled wind turbine (10) of claim 7, wherein the first connection point (46a) and the second connection point (46b) are located to the windward side (38) of the airfoil profile.

9. The pitch-controlled wind turbine (10) of any preceding claim, wherein the connection location (30) of each blade (20) comprise split connection points (46a, 46b) with a first connection point (46a) and a second connection point (46b), the blade connecting member (32) being connected from the first connection point (46a) to the blade (20) following during rotation of the rotor (16), and the blade connecting member (32) being connected from the second connection point (46b) to the blade (20) leading during rotation of the rotor, wherein the first connection point (46a) is to the windward side (38) of the airfoil profile and the second connection point (46b) is to the leeward side (40) of the airfoil profile and wherein the first connection point (46a) and the second connection point (46b) are separated by 1 .0 m to 3.5 m, preferably by 1 .2 m to 3.0 m.

10. The pitch-controlled wind turbine (10) of any of claim 7 to 9, wherein the first connection point (46a) and the second connection point (46b) are located from a maximum flapwise thickness towards the leading edge (42), and preferably the first connection point (46a) and the second connection point (46b) are located in a leading-edge region (48) of the airfoil profile.

11. The pitch-controlled wind turbine (10) of any of claim 7 to 10, wherein the first connection point (46a) and the second connection point (46b) are separated in the spanwise direction (S) by 0.3 m to 2 m, preferably by 0.5 m to 1 .5 m.

12. The pitch-controlled wind turbine (10) of any of claim 7 to 11 , wherein the first connection point (46a) and the second connection point (46b) are separated in the spanwise direction (S) and the second connection point (46b) is arranged closer to the blade root (22) than the first connection point (46a).

13. The pitch-controlled wind turbine (10) of any of claim 7 to 12, wherein the first connection point (46a) and the second connection point (46b) are separated by a distance in a plane parallel to the chord and orthogonal to the spanwise direction (S) of 0.3 m to 2 m, preferably by 0.5 m to 1.5 m.

14. The pitch-controlled wind turbine (10) of any preceding claim, further comprising a support structure (56) and one or more tension members (60), wherein the support structure (56) extends from the hub (18) to define a support point (58), wherein the or each tension member (60) is connected between the support point (58) and an attachment point (62) of a blade connecting member (32), and wherein the support point (58) is located upwind relative to each connection location (30).

15. The pitch-controlled wind turbine (10) of Claim 14, wherein each pitch axis (B) intersects the rotor axis at an intersection point, and wherein the support point is located at an axial distance D of between 0.02R and 0.16R from the intersection point in the upwind direction, where R is the radius of the rotor.

16. The pitch-controlled wind turbine (10) of any of Claims 14 or Claim 15, wherein each blade connecting member (32) comprises a first portion (32a) extending between the attachment point (62) and a connection location (30) of a blade (20), and a second portion (32b) extending between the attachment point (62) and a connection location (30) of a different blade (20),

And wherein the first portion (32a) has a length of at most 0.65L, preferably at most 0.55L, more preferably 0.5L, where L is the combined length of the first (32a) and second (32b) portions of the blade connecting member (32).

17. The pitch-controlled wind turbine (10) of any of Claims 14 to 16, wherein each blade connecting member (32) comprises a first portion (32a) extending between the attachment point (62) and a connection location (30) of a blade (20), and a second portion (32b) extending between the attachment point (62) and a connection location (30) of a different blade (20), wherein when projected to the rotor plane (P), an angle defined between the tension member (60) and the first portion (32a) of the blade connecting member (32) is between 92 degrees and 110 degrees, preferably J is between 94 degrees and 105 degrees, and more preferably the length of the first portion (32a) is the same as the second portion (32b) and the angle J is between 95 degrees and 105 degrees.

18. The pitch-controlled wind turbine (10) of any of Claims 14 to 17, wherein an angle K between the projection to a vertical plane parallel to the rotor axis (A) of the second portion (32b) of the blade connecting member (32) connected to a blade (20) oriented in 12 o’clock position and the tension member (60) connected to the attachment point (62) of the same blade connecting member (32) is between 180 degrees and 160 degrees, preferably is between 179 degrees and 170 degrees.

19. The pitch-controlled wind turbine (10) of any preceding claim, wherein the connection location (30) is located at a radial distance (r) of between 0.25R and 0.6R from the rotor axis (A), where R is the radius of the rotor (16).