Pitch-controlled wind turbine with blade connecting member and segmented blades

Abstract

A pitch controlled wind turbine (1) is disclosed that includes a tower (2), a nacelle (3) mounted to the tower (2), a hub (4) rotatably mounted to the nacelle (3), and at least three wind turbine blades (5). Each wind turbine blade (5) extends between a root end (6) connected to the hub (4) and a tip end (7). The wind turbine (1) further includes at least three blade connection members (8), each blade connection member (8) extending between a connection point (9) on one wind turbine blade (5) and a connection point (9) on an adjacent wind turbine blade (5). The wind turbine blades (5) include an inner blade portion (5a) including a root end (6) and an outer blade portion (5b) including a tip end (7), the inner blade portion (5a) and the outer blade portion (5b) being connected to each other at a split location (10). The division location (10) is located between the root end (6) and the connection point (9).

Description

[Technical Field]

[0001] The present invention relates to a pitch-controlled wind turbine comprising a tower, a nacelle mounted to the tower, a hub rotatably mounted to the nacelle, and at least three wind turbine blades connected to the hub via a pitch mechanism that allows full pitch and / or partial pitch of the wind turbine blades. [Background technology]

[0002] During operation of a wind turbine, components of the wind turbine are subjected to various loads. For example, a wind turbine blade of a wind turbine is subjected to loads due to gravity acting on the wind turbine blade, loads due to wind pressure acting on the wind turbine blade, loads due to changes in wind direction and wind speed, turbulence, etc. Gravity acting on the wind turbine blade mainly generates edgewise loads on the wind turbine blade, and wind acting on the wind turbine blade mainly generates flapwise loads on the wind turbine blade.

[0003] As wind turbines increase in size, the loads placed on them also increase. To accommodate these increased loads, the amount of material used to manufacture the wind turbine increases. However, this increases the weight of the wind turbine as well as the cost of manufacturing it.

[0004] Furthermore, as wind turbine blades increase in size, it becomes increasingly difficult to transport them. One solution to this is to manufacture the wind turbine blade in at least three parts, which are transported separately and then joined together at the site where the wind turbine is to be deployed to form the complete wind turbine blade. This is sometimes referred to as a "split wind turbine blade." However, splitting the wind turbine blade in this manner can weaken the wind turbine blade, in the sense that it has a negative impact on the strength of the wind turbine blade.

[0005] In prior art split wind turbine blades, the splitting location is typically located much closer to the tip end of the wind turbine blade than the root end of the wind turbine blade to achieve splitting at a location where expected loads are low, i.e., to minimize any detriment to the wind turbine blade's ability to handle loads. For example, the splitting location may be located at a distance from the root end that is 70% to 75% of the wind turbine blade's length. However, locating the splitting location this far from the root end requires adding additional mass to the inner portion of the wind turbine blade to carry the additional mass required at the splitting location to provide the wind turbine blade with the necessary strength. Furthermore, accessing the splitting location, for example to provide service or maintenance to the connections between the blade sections, is difficult and typically requires the use of a large crane. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of embodiments of the present invention to provide a pitch-controlled wind turbine that allows for the transportation of large wind turbine blades without reducing the wind turbine's ability to handle loads and without increasing manufacturing costs.

[0007] It is a further object of an embodiment of the present invention to provide a pitch controlled wind turbine with segmented wind turbine blades, which allows for easy service and maintenance of the connections between the blade sections. [Means for solving the problem]

[0008] The present invention provides a pitch-controlled wind turbine comprising a tower, a nacelle mounted to the tower, a hub rotatably mounted to the nacelle, and at least three wind turbine blades, each wind turbine blade extending between a root end connected to the hub and a tip end, the wind turbine further comprising at least three blade connection members, each blade connection member extending between a connection point on one wind turbine blade and a connection point on an adjacent wind turbine blade, the connection point on a given wind turbine blade being located a distance from the root end and a distance from the tip end of the wind turbine blade.

[0009] The wind turbine blade comprises an inner blade portion including a root end and an outer blade portion including a tip end, the inner blade portion and the outer blade portion being connected to each other at a split location located between the root end and a connection point.

[0010] The present invention therefore provides a pitch-controlled wind turbine, i.e., a wind turbine comprising a wind turbine blade that can rotate about a substantially longitudinal pitch axis during operation of the wind turbine to adjust the angle of attack between the wind turbine blade and the oncoming wind. The entire wind turbine blade may be rotatable, in which case the wind turbine blade is typically connected to the hub of the wind turbine via a pitch bearing located at the root end of the wind turbine blade. This is sometimes referred to as "full pitch." In the case of full pitch, it is preferable to bring the full blade pitch together so that the blade section on one side of the split position cannot pitch relative to the blade section on the other side of the split position at the split position. This allows for a relatively simple connection between the blade parts at the split position. Alternatively, only a portion of the wind turbine blade may be rotatable, in which case a pitch bearing is typically provided between the portion of the wind turbine blade that is rotatable and the portion of the wind turbine blade that is fixedly connected to the hub of the wind turbine. This is sometimes referred to as "partial pitch." This is described in more detail below.

[0011] Preferably the wind turbine is a horizontal axis wind turbine.

[0012] The wind turbine comprises a tower and a nacelle mounted to the tower. The wind turbine further comprises a hub rotatably mounted to the nacelle and at least three wind turbine blades. Each wind turbine blade extends between a root end connected to the hub and a tip end. Thus, the wind turbine blade rotates with the hub relative to the nacelle, with the tip of the wind turbine blade pointing away from the hub. As described above, at least a portion of each wind turbine blade can rotate relative to the hub, i.e., can pitch. The hub and the wind turbine blades form the rotor of the wind turbine.

[0013] The nacelle is typically mounted to the tower via a yaw system that allows the nacelle to rotate relative to the tower in order to properly orient the rotor according to the wind direction.

[0014] The wind turbine further comprises at least three blade connection members. Each blade connection member extends between a connection point on one wind turbine blade and a connection point on an adjacent wind turbine blade. Thus, each connection member interconnects two adjacent wind turbine blades. The connection point on a given wind turbine blade is located a distance from the root end and a distance from the tip end of the wind turbine blade. Thus, the connection point is not located at either the root end or the tip end, but rather at a location between these two extremes, at a non-zero distance from each end.

[0015] In the present context, the term "member" in connection members and pretensioning members should be interpreted broadly to encompass any suitable type of tension member, such as braided or twisted ropes of metal wire (such as steel wire), polymer fibers (e.g., polyethylene, polypropylene, nylon, polyester, aramid, etc.), inorganic fibers (e.g., carbon fiber, etc.), or hybrid ropes of such materials, composite pultrusions, metal rods, etc.

[0016] The blade connecting members mutually support the wind turbine blades in the sense that loads on the wind turbine blades, in particular edgewise and flapwise loads, are "shared" between the wind turbine blades via the blade connecting members, so that the loads imposed on the wind turbine blades during operation of the wind turbine can be handled without requiring a higher material thickness and thereby increased weight and higher manufacturing costs.

[0017] Each wind turbine blade includes an inner blade portion including a root end and an outer blade portion including a tip end. The inner blade portion and the outer blade portion are connected to each other at a split location. Thus, the wind turbine blade is a split wind turbine blade as described above, and the inner blade portion and the outer blade portion of the wind turbine blade can be transported separately to the wind turbine site. This enables wind turbine designs where the length of the wind turbine blade exceeds the maximum allowable length for transportation purposes.

[0018] The split location is located between the root end and the connection point. Thus, the blade connection member is connected to the outer blade section or to the split location connecting the outer blade sections, and the split location is located along the wind turbine blade inward from or including the connection point.

[0019] The split location is therefore located at a position where the load sharing provided by the blade connection element is important. The loads occurring in this portion of the wind turbine blade are therefore significantly lower than in a similar wind turbine blade without the blade connection element. Therefore, the strength reduction of the wind turbine blade caused by the splitting of the wind turbine blade can be introduced into this portion of the wind turbine blade without impairing the wind turbine blade's ability to cope with the expected loads. In other words, the blade connection element compensates for the strength reduction introduced by the blade split.

[0020] Therefore, due to the blade connection members and the relative positions of the split locations and connection points, it is possible to design wind turbines with wind turbine blades having lengths that exceed normal transportation requirements without significantly increasing the manufacturing costs of the wind turbine blades and without compromising the ability of the wind turbine blades to handle loads.

[0021] The inner and outer wings may be connected to one another by a bolted connection. Alternatively, the inner and outer wings may be connected to one another by a suitable joining technique, for example, the wings may be glued together. The inner and outer wings may also be coupled to one another via bearings, as will be described in more detail below.

[0022] The split location of the wind turbine blade may be located at a distance from the root end between 15% and 60%, such as between 20% and 50%, such as between 25% and 40% of the length of the wind turbine blade from the root end to the tip end.

[0023] According to this embodiment, the split location is located far enough from the root end and far enough from the tip end. Furthermore, while the inner and outer wings have significant lengths, it is ensured that neither wing exceeds shipping specifications. Furthermore, the split location is close enough to the root end to be easily accessible from the hub for maintenance or service purposes.

[0024] The split locations of the wind turbine blade may be located at locations where the thickness to chord ratio of the wind turbine blade is between 24% and 70%, such as between 24.5% and 55.0%, such as between 26% and 50%.

[0025] According to this embodiment, the splitting position is located far enough away from the root end and far enough away from the tip end, i.e. the above observations are equally applicable here.

[0026] The split locations of the wind turbine blade may be located at locations that define a maximum blade chord.

[0027] According to this embodiment, an intermediate blade section can be inserted between the inner and outer blade sections, with the intermediate blade defining the maximum chord along its entire length. This allows wind turbine blades of various lengths to be manufactured using the same mold for each of the inner and outer blade sections. The application of intermediate blade sections of various lengths allows a series of modularly designed wind turbines with various rotor diameters to be manufactured at minimal manufacturing costs, as will be described in more detail below. Similarly, wind turbine blades with various root diameters can be manufactured by applying different inner blade sections to the same outer blade section.

[0028] The split location of the wind turbine blade may be located at or near the center of gravity of the wind turbine blade, for example, the split location may be located no more than 5% of the length of the wind turbine blade from the center of gravity of the wind turbine blade.

[0029] When attaching a wind turbine blade to a wind turbine, it is advantageous to attach a lifting device to the wind turbine blade at or near the center of gravity of the wind turbine blade in order to balance the wind turbine blade during lifting. By locating the split location at or near the center of gravity of the wind turbine blade, reinforcement of the wind turbine blade at this location is already provided, i.e., no additional reinforcement is required to attach the lifting device.

[0030] The splitting position of the wind turbine blade may be located at a distance of 50 m to 100 m, for example 60 m to 80 m, for example 65 m to 75 m from the tip end, which results in an outer portion of the wind turbine blade that can be handled by conventional means, and particularly if the splitting position of the wind turbine blade is 60 m to 80 m, for example 65 m to 75 m, the outer portion can be transported by road.

[0031] Transporting items longer than 100 meters by land transport is often difficult, expensive, or even impossible. Providing the longest possible outer wing without exceeding transport limitations is advantageous because it allows the inner wing to be as short as possible, thereby locating the split location as close to the root end as possible. This allows for easier access to the connection between the inner and outer wing sections from the hub for service or maintenance.

[0032] Alternatively or additionally, the split point of the wind turbine blade may be located at a position where the weight of the outer blade section is approximately equal to the weight of the inner blade section, so that weight requirements during transportation, handling and lifting of the blade parts can be more easily met.

[0033] The connection point of the wind turbine blade may be located at a distance from the root end that is between 20% and 70%, such as between 25% and 60%, for example between 30% and 55% of the length of the wind turbine blade from the root end to the tip end. The connection point may be a blade portion or a split location of the wind turbine blade.

[0034] According to this embodiment, the blade connecting member connects to the wind turbine blade at a location sufficiently far from the root end of the wind turbine blade and sufficiently far from the tip of the wind turbine blade.

[0035] The location of the connection point along the wind turbine blade can be selected to appropriately balance various issues that need to be taken into account. For example, locating the connection point near the tip end of the wind turbine blade results in very efficient support of the wind turbine blade by the blade connection member. However, this comes at the expense of high drag caused by the blade connection member during rotor rotation, thereby reducing energy production. On the other hand, positioning the connection point near the root end of the wind turbine blade results in low drag caused by the blade connection member, thereby minimizing the negative impact on the wind turbine's energy production. However, support of the wind turbine blade by the blade connection member is less efficient. By locating the connection point at a distance from the root end that is 20% to 70% of the wind turbine blade's length, these considerations are balanced to provide efficient support without introducing unacceptable drag. Furthermore, locating the connection point in this region ensures that the blade connection member can be attached to the wind turbine blade when the wind turbine blade's structural rigidity is sufficiently high. For example, the structural stiffness of a wind turbine blade decreases towards the tip end, i.e., connecting a blade connection member too close to the tip end may result in significant pre-deformation of the wind turbine blade, which may hinder the blade's ability to pitch. The connection points located on a particular blade section also encompass the split locations where this blade section is connected to another blade section.

[0036] Each wind turbine blade further comprises at least one intermediate blade section, wherein the inner blade section and the intermediate blade section are connected to each other at a first dividing point, and the intermediate blade section and the outer blade section are connected to each other at a second dividing point, and the at least first dividing point can be located between the root end and the connecting point.

[0037] According to this embodiment, the wind turbine blade is manufactured from at least three parts: an inner blade section, an outer blade section, and a middle blade section. The middle blade section is arranged between the inner and outer blade sections. In the following, for clarity, only one middle blade section will be described, although it is not excluded that two or more middle blade sections are connected end to end between the inner and outer blade sections.

[0038] According to this embodiment, the wind turbine blade comprises three blade sections, and therefore also defines two division positions where adjacent blade sections are connected to each other. More specifically, the inner blade section and the middle blade section are connected to each other at a first division position, and the middle blade section and the outer blade section are connected to each other at a second division position. Thus, the first division position is closer to the root end than the second division position, and the second division position is closer to the tip end than the first division position.

[0039] At least the first division location is located between the root end and the connection point, ie, as described above.

[0040] The second dividing point may be located between the connection point and the tip end. According to this embodiment, the connection point is formed on the mid-wing portion.

[0041] Although the support provided by the blade connection element is more pronounced in the portion of the wind turbine blade that is located between the root end and the connection point than in the portion of the wind turbine blade that is located between the connection point and the tip end, the load on the wind turbine blade in the latter portion is still reduced by the blade connection element. Thus, if the first dividing position is located between the root end and the connection point, it is also possible to locate the second dividing position in this portion of the wind turbine blade.

[0042] Alternatively, the first and second division locations can be located between the root end of the wind turbine blade and the connection point, i.e. in the part of the wind turbine blade where the support provided by the blade connection member has the highest impact.

[0043] By allowing at least one intermediate blade section to be inserted between the inner and outer blade sections, a modular blade design can be provided, allowing wind turbine blades of various lengths to be manufactured using identical inner and outer blade sections and various lengths and / or numbers of intermediate blade sections disposed between the inner and outer blade sections. This allows only one mold design to be required to manufacture inner blade sections for many different blade sizes, and only one mold design for the outer blade sections. This significantly reduces manufacturing costs and enables wind turbines with multiple different rotor diameters on a production line.

[0044] As mentioned above, the intermediate wing section may have a constant chord along its entire length, and the split location may be located at a location that defines the maximum chord.

[0045] Each wind turbine blade may be provided with at least two connection points, the split location being located between the root end and the first connection point, and the second connection point being located between the first connection point and the tip end.

[0046] According to this embodiment, the wind turbine blades are supported by at least two sets of blade connection members connected to the wind turbine blades at two different positions along the length of the wind turbine blades, i.e., at two different rotor radius positions. This increases the support provided to the wind turbine blades by the blade connection members compared to an embodiment in which two adjacent wind turbine blades are connected via only one blade connection member. Furthermore, the split location is located inward relative to both connection points. Therefore, the split location is located in a part of the wind turbine blade that fully benefits from the support provided by the two sets of blade connection members.

[0047] The pitch controlled wind turbine may further comprise at least three pretensioning members, each pretensioning member connected to one of the blade connection members and to the hub portion, whereby each pretensioning member provides pretension to the blade connection member to which it is connected, preferably by biasing a portion of the blade connection member (such as a point of the blade connection member midway between the blade connection points) towards the hub.

[0048] According to this embodiment, the pretensioning member pulls the wing connecting member towards the hub, whereby the pretensioning member provides pretension to the wing connecting member.

[0049] The wing connecting member may have a stiffness different from that of the pretensioning member, or the stiffness of the wing connecting member and the pretensioning member may be the same.

[0050] In the present context, the term "hub portion" should be taken to mean the hub, or a part or element connected to the hub in the sense that it rotates with the hub relative to the nacelle. Such part or element may be connected to the outer surface of the hub, may protrude from the hub, may be located inside the hub, or may be located in any other suitable way, so long as it rotates with the hub.

[0051] The pretensioning members may, for example, be connected to the blade connection members at positions spaced from each of the connection points on the wind turbine blades, for example at substantially equal distances to the connection points, i.e. approximately midway between the wind turbine blades along the blade connection member.

[0052] According to this embodiment, since the pretensioning in the wing connection member is provided by a pretensioning member interconnecting the wing connection member and the hub section, it is possible to control the pretensioning in the pretensioning member as well as in the wing connection member from the hub, thereby providing easy access for servicing or pretensioning adjustment. Furthermore, it is possible to adjust how much the average flapwise load is affected for a given pretensioning. For example, a short pretensioning member has less effect on the average flapwise bending moment than a long pretensioning member. Finally, the pretensioning system can be softer than the wing connection member, reducing the risk of the member coming loose.

[0053] The pretensioning member may be arranged to provide an adjustable pretension to the wing connecting member, or the pretension provided may be constant.

[0054] The pitch-controlled wind turbine may further comprise a hub extension interconnecting the wind turbine blade and the hub.

[0055] In this context, the term "hub extension" should be taken to mean a component that is connected at one end to the hub and at the opposite end to the root end of the wind turbine blade, thereby introducing a distance between the hub and the wind turbine blade. The wind turbine blade may be connected to the hub extension, for example, via a pitch bearing, thereby allowing the wind turbine blade to perform a pitching movement relative to the hub extension and thereby relative to the hub. The hub extension may have an aerodynamic shape or may comprise aerodynamic enhancing elements such as vanes, vortex generators, Gurney flaps, stall barriers, etc. Alternatively, the hub extension may have any other suitable shape, for example a cylindrical shape.

[0056] The hub extension allows for an increase in rotor diameter without changing the design of the wind turbine blade, which increases the power generation capacity, thereby allowing for an increase in the nominal power of a given wind turbine model without changing the molds used to manufacture the wind turbine blades.

[0057] The blade connecting member may be connected to the respective wind turbine blade via a bearing structure attached to or forming part of the wind turbine blade, which may be or include, for example, a roller bearing, a plain bearing, a spherical bearing, or any other suitable type of bearing.

[0058] The bearing structure allows the wind turbine blade to rotate relative to the blade connection member via the bearing structure, thereby allowing the wind turbine blade to perform a pitching movement without affecting the blade connection member, thereby avoiding undesirable loads, twisting or tension on the blade connection member during pitching.

[0059] If the bearing structure is or comprises a spherical bearing, the blade connecting member can rotate freely relative to the wind turbine blade about the connection point, so that only tension forces are transmitted between the blade connecting member and the wind turbine blade at the connection point.

[0060] If the bearing structure protrudes from or is arranged circumferentially relative to the wind turbine blade, the bearing structure may be provided with a fairing or similar aerodynamic structure in order to improve the aerodynamic properties of the wind turbine blade in the region of the bearing structure.

[0061] The root end of each wind turbine blade may be connected to a hub via a pitch bearing.

[0062] According to this embodiment, the entire wind turbine blade rotates when performing a pitching motion, which is sometimes referred to as "full pitch."

[0063] Alternatively or additionally, each wind turbine blade may include a pitch bearing located at the split location, thereby allowing the outer blade section to pitch relative to the inner blade section, which may be referred to as "partial pitch."

[0064] A wind turbine blade capable of performing partial pitch needs to be divided into an inner blade section and an outer blade section in order to allow one part of the wind turbine blade to perform a pitch movement relative to another part of the wind turbine blade, and therefore a division position for this purpose is advantageously located along the wind turbine blade according to the invention.

[0065] Alternatively, each wind turbine blade may include a pitch bearing located at the connection point, thereby enabling the portion of the wind turbine blade extending from the connection point to the tip end to undergo pitching motion relative to the portion of the wind turbine blade extending from the root end to the connection point.

[0066] According to this embodiment, the wind turbine blade is divided at least in two locations: at the dividing location located at the root end of the wind turbine blade as described above, and at the location where the blade connecting member is connected to the wind turbine blade.

[0067] The inner wing portion of each wind turbine blade may include a first inner wing portion and a second inner wing portion, the first inner wing portion including a leading edge of the inner wing portion and the second inner wing portion including a trailing edge of the inner wing portion, and the first inner wing portion and the second inner wing portion may be connected to each other along a dividing interface extending along a direction defined by the length of the wind turbine blade.

[0068] According to this embodiment, apart from being divided transversely to the longitudinal direction of the wind turbine blade, the wind turbine blade is also divided along this longitudinal direction. However, this additional division is only present in the inner blade portion. It is expected that the chord of the wind turbine blade will be larger at the root end than at the tip end. For large wind turbine blades, the maximum chord length may exceed the maximum transport dimension. Therefore, to enable the wind turbine blade to be transported, it is appropriate to divide the wind turbine blade transversely to the chord direction. Such a division may be referred to as a "chord extension."

[0069] The pitch-controlled wind turbine may be an upwind wind turbine, i.e., a wind turbine with a rotor pointed into the oncoming wind. Alternatively, the wind turbine may be a downwind wind turbine, i.e., a wind turbine with a rotor pointed away from the oncoming wind.

[0070] The invention will now be explained in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0071] [Figure 1] 1 shows a pitch-controlled wind turbine according to a first embodiment of the present invention; [Figure 2] 1 shows a pitch-controlled wind turbine according to a first embodiment of the present invention; [Figure 3] 1 shows a pitch-controlled wind turbine according to a first embodiment of the present invention; [Figure 4] 2 shows a pitch-controlled wind turbine according to a second embodiment of the present invention; [Figure 5] 2 shows a pitch-controlled wind turbine according to a second embodiment of the present invention; [Figure 6] 10 shows a pitch-controlled wind turbine according to a third embodiment of the present invention. [Figure 7] 10 shows a pitch-controlled wind turbine according to a third embodiment of the present invention. [Figure 8]1 is a perspective view of a wind turbine blade for a wind turbine according to an embodiment of the present invention; FIG. [Figure 9] 1 is a side view of a wind turbine blade for a wind turbine according to an alternative embodiment of the present invention; [Figure 10] 1 illustrates the connection of a blade connecting member to a wind turbine blade for a wind turbine according to an embodiment of the present invention; [Figure 11] 1 shows a bearing structure for connecting a blade connecting member to a wind turbine blade for a wind turbine according to an embodiment of the present invention; [Figure 12] 1 shows a bearing structure for connecting a blade connecting member to a wind turbine blade for a wind turbine according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0072] 1 to 3 show a pitch-controlled wind turbine 1 according to a first embodiment of the present invention. Fig. 1 is a front view of the wind turbine 1, Fig. 2 is a side view of the wind turbine 1, and Fig. 3 shows the wind turbine 1 in detail.

[0073] The wind turbine 1 includes a tower 2, a nacelle 3 attached to the tower 2, and a hub 4 attached to the nacelle. Three wind turbine blades 5 are connected to the hub 4. Each wind turbine blade 5 extends between a root end 6 connected to the hub 4 and an oppositely disposed tip end 7.

[0074] The wind turbine 1 further comprises three blade connecting members 8. Each blade connecting member 8 interconnects two adjacent wind turbine blades 5 by being coupled to a connection point 9 on the respective wind turbine blade 5. The wind turbine blades 5 can mutually support each other via the blade connecting members 8 in the sense that loads on the wind turbine blades 5, in particular edgewise loads and flapwise loads, are shared between the wind turbine blades 5 via the blade connecting members 8. In particular, loads on the portion of the wind turbine blade 5 arranged between the root end 6 and the connection point 9 are reduced due to the presence of the blade connecting members 8.

[0075] Each wind turbine blade 5 includes an inner blade portion 5a including a root end 6 and an outer blade portion 5b including a tip end 7. The inner blade portion 5a and the outer blade portion 5b are connected to each other at a split position 10. That is, the wind turbine blade 5 is a so-called "split blade." This allows the inner blade portion 5a and the outer blade portion 5b to be manufactured separately and transported separately to the wind turbine 1 site, where they can be assembled to form the wind turbine blade 5. Therefore, the length of the wind turbine blade 5 is allowed to exceed a maximum length determined by transportation requirements.

[0076] The splitting location 10 is located between the root end 6 and the connection point 9, i.e. the point where the blade connecting member 8 is connected to the wind turbine blade 5. In this way, the splitting location 10 is located in a part of the wind turbine blade 5 where a significant load reduction by the blade connecting member 8 is expected. It can therefore be expected that the wind turbine blade 5 will be able to cope with the loads that occur during operation of the wind turbine 1, despite the weakness of the wind turbine blade 5 introduced by splitting the wind turbine blade 5.

[0077] Furthermore, by locating the dividing position 10 in this portion, the dividing position 10 can be easily accessed from the hub 4.

[0078] Figures 4 and 5 show a pitch-controlled wind turbine 1 according to a second embodiment of the invention. Figure 4 shows a front view of the wind turbine 1 and Figure 5 shows details of the wind turbine 1.

[0079] The wind turbine 1 of Figures 4 and 5 is very similar to the wind turbine 1 of Figures 1 to 3 and will not be described in detail here.

[0080] The wind turbine 1 of Figures 4 and 5 further comprises three pretensioning members 11. Each pretensioning member 11 is connected to one of the blade connection members 8 approximately midway between the connection points 9 on the wind turbine blades 5 and connected to the hub 4. The pretensioning members 11 therefore pull the blade connection members 8 towards the hub 4, thereby providing pretension to the blade connection members 8.

[0081] Thereby, the pretension in the blade connecting member 8 can be adjusted by the pretensioning member 11 and thereby the extension of the wind turbine blades 5 which support each other via the blade connecting member 8 can be controlled.

[0082] The blade connecting member 8 can comprise one or more sub-parts, for example two sub-parts or sections. This is particularly advantageous if the wind turbine is equipped with a pretensioning member. Here, the connecting member 8 can, for example, preferably comprise two sub-sections, each section connecting a blade connection point to a connector element (not shown), to which a pretensioning member is also connected. This allows for a secure and centered connection between the connecting member and the pretensioning member.

[0083] Figures 6 and 7 show a pitch-controlled wind turbine 1 according to a third embodiment of the invention. Figure 6 is a front view of the wind turbine 1 and Figure 7 shows the wind turbine 1 in detail.

[0084] The wind turbine 1 of Figures 6 and 7 is very similar to the wind turbine 1 of Figures 1 to 3 and will not be described in detail here.

[0085] In the wind turbine 1 of Figures 6 and 7, each wind turbine blade 5 further includes a middle blade section 5c disposed between the inner blade section 5a and the outer blade section 5b. The inner blade section 5a and the middle blade section 5c are connected at a first dividing point 10a, and the middle blade section 5c and the outer blade section 5b are connected at a second dividing point 10b. Thus, each wind turbine blade 5 is divided into three blade sections 5a, 5b, and 5c, defining two dividing points 10a and 10b. Both dividing points 10a and 10b are located between the root end 6 and the connection point 9, i.e., in the portion of the wind turbine blade 5 where the load reduction resulting from the support provided by the blade connection member 8 is expected to be most significant. In another example (not shown), the blade connection point is located on the middle blade section 5c. The blade connection point could also be located on the inner blade section 5a, but this is not preferred because the load carried by the connection member would be relatively low.

[0086] Splitting the wind turbine blade 5 into three sections allows for longer wind turbine blades 5 without conflicting with transportation constraints. Furthermore, this allows for a modular design of the wind turbine 1 in the sense that the rotor diameter of the wind turbine 1 can be changed by appropriately selecting the length of the middle blade section 5c without changing the design of the inner and outer blade sections 5a, 5b.

[0087] Figure 8 is a perspective view of a wind turbine blade 5 for a wind turbine according to one embodiment of the present invention. As described above with reference to Figures 1 to 3, the wind turbine blade 5 comprises an inner blade portion 5a and an outer blade portion 5b connected to each other at a dividing position 10.

[0088] The inner wing 5a and the outer wing 5b are connected via pitch bearings 12, which allow the outer wing 5b to perform a pitching movement, i.e., a partial pitch, relative to the inner wing 5a.

[0089] 9 is a side view of a wind turbine blade 5 for a wind turbine according to another embodiment of the present invention. The wind turbine blade 5 is configured by an inner blade portion 5a and an outer blade portion 5b connected at a dividing position 10.

[0090] The inner wing 5a comprises a first inner wing 5a' and a second inner wing 5a''. The first inner wing 5a' comprises a leading edge 13 of the inner wing 5a, and the second inner wing 5a'' comprises a trailing edge 14 of the inner wing 5a.

[0091] The first inner wing portion 5a' and the second inner wing portion 5a'' are connected to each other along a dividing boundary surface 15 that extends substantially along a direction defined by the length of the wind turbine blade 5 and substantially perpendicular to the lateral dividing boundary surface between the inner wing portion 5a and the outer wing portion 5b at the dividing position 10. Thus, the wind turbine blade 5 shown in Figure 9 is divided into three parts: the first inner wing portion 5a', the second inner wing portion 5a'' and the outer wing portion 5b. Here, the blade connection point is preferably on the first inner wing portion 5a' or the outer portion 5b, including the dividing position.

[0092] The chord of the wind turbine blade 5 is larger for the inner blade section 5a than for the outer blade section 5b. By dividing the inner blade section 5a into a first inner blade section 5a' and a second inner blade section 5a'', none of the blade sections 5a', 5a'', 5b has a width that exceeds maximum shipping constraints.

[0093] Figure 10 is a perspective view of a portion of a wind turbine blade 5 for a wind turbine according to an embodiment of the present invention. More specifically, Figure 10 shows a portion of the wind turbine blade 5 including connection points 9, i.e., locations where blade connecting members 8 are connected to the wind turbine blade 5.

[0094] The blade connecting member 8 is connected to the wind turbine blade 5 via a bearing structure 16. This allows the pitching movement of the wind turbine blade 5 without affecting the blade connecting member 8. This avoids undesired loads, twisting or tension on the blade connecting member 8 during pitching of the wind turbine blade 5.

[0095] Figures 11 and 12 show two different bearing structures 16 for connecting a blade connecting member to a wind turbine blade for a wind turbine, according to an embodiment of the present invention. For example, the bearing structures 16 in Figures 11 and 12 may be applied to the wind turbine blade shown in Figure 10.

[0096] The plate-like structure 17 is attached to the wind turbine blade. Figures 11 and 12 show two different configurations for providing this attachment.

[0097] The blade connection member is attached to an eyelet 18 which is rotatably mounted on the plate-like structure 17, so that the wind turbine blade to which the plate-like structure 17 is attached can perform a pitching movement relative to the eyelet 18 and thus relative to the blade connection member connected to the eyelet 18.

Claims

1. 1. A pitch-controlled wind turbine (1) comprising a tower (2), a nacelle (3) mounted on the tower (2), a hub (4) rotatably mounted on the nacelle (3), and at least three wind turbine blades (5), Each wind turbine blade (5) extends between a root end (6) connected to the hub (4) and a tip end (7), and the wind turbine (1) further comprises at least three blade connecting members (8); Each blade connection member (8) extends between a connection point (9) on one wind turbine blade (5) and a connection point (9) on an adjacent wind turbine blade (5); said connection point (9) on a given wind turbine blade (5) is located at a distance from said root end (6) and at a distance from said tip end (7) of said wind turbine blade (5); The wind turbine blade (5) comprises an inner blade portion (5a) including the root end (6) and an outer blade portion (5b) including the tip end (7), the inner blade portion (5a) and the outer blade portion (5b) being connected to each other at a dividing location (10) located between the root end (6) and the connection point (9); the connection point (9) of the wind turbine blade (5) is located at a distance from the root end (6) that is between 20% and 70% of the length of the wind turbine blade (5) from the root end (6) to the tip end (7); 1. A pitch-controlled wind turbine (1), characterized in that the split positions (10) of the wind turbine blade are arranged at positions where the thickness-to-chord ratio of the wind turbine blade is between 24% and 70%.

2. 2. The pitch-controlled wind turbine (1) according to claim 1, wherein the split position (10) of the wind turbine blade (5) is located at a distance from the root end (6) that is between 15% and 60% of the length of the wind turbine blade (5) from the root end (6) to the tip end (7).

3. 3. The pitch-controlled wind turbine (1) according to claim 1 or 2, wherein the splitting position (10) of the wind turbine blade (5) is located at a position that defines a maximum blade chord.

4. 4. The pitch-controlled wind turbine (1) according to any one of claims 1 to 3, wherein the dividing position (10) of the wind turbine blade (5) is located at or near the center of gravity of the wind turbine blade (5).

5. 5. The pitch-controlled wind turbine (1) according to claim 1, wherein the split position (10) of the wind turbine blade (5) is located at a distance of 50 m to 100 m from the tip end (7).

6. 6. The pitch-controlled wind turbine (1) according to any one of claims 1 to 5, wherein the connection point (9) of the wind turbine blade (5) is located at a distance from the root end (6) that is between 25% and 60% of the length of the wind turbine blade (5) from the root end (6) to the tip end (7).

7. 7. The pitch-controlled wind turbine (1) according to any one of claims 1 to 6, wherein each wind turbine blade (5) further comprises at least one intermediate blade section (5c), the inner blade section (5a) and the intermediate blade section (5c) being connected to each other at a first dividing position (10a), and the intermediate blade section (5c) and the outer blade section (5b) being connected to each other at a second dividing position (10b), and at least the first dividing position (10a) being located between the root end (6) and the connection point (9).

8. 8. The pitch-controlled wind turbine (1) according to claim 7, wherein the second dividing position (10b) is located between the connection point (9) and the tip end (7).

9. 9. The pitch-controlled wind turbine (1) according to any one of claims 1 to 8, wherein each wind turbine blade (5) is provided with at least two connection points (9), the split location (10) being located between the root end (6) and a first connection point (9), and the second connection point (9) being located between the first connection point (9) and the tip end (7).

10. 10. The pitch-controlled wind turbine (1) according to any one of claims 1 to 9, further comprising at least three pretensioning members (11), each pretensioning member (11) connected to one of the blade connection members (8) and to the hub portion (4), and each pretensioning member (11) providing pretension to the blade connection member (8) to which it is connected.

11. The pitch-controlled wind turbine (1) according to any one of the preceding claims, further comprising a hub extension interconnecting the wind turbine blades (5) and the hub (4).

12. 12. The pitch-controlled wind turbine (1) according to any one of claims 1 to 11, wherein the blade connecting member (8) is connected to the respective wind turbine blade (5) via a bearing structure (16) attached to or forming part of the wind turbine blade (5).

13. 13. The pitch-controlled wind turbine (1) according to any one of the preceding claims, wherein the root end (6) of each wind turbine blade is connected to the hub (4) via a pitch bearing.

14. 14. The pitch-controlled wind turbine (1) according to any one of claims 1 to 13, wherein each wind turbine blade (5) comprises a pitch bearing (12) arranged at the split location (10) to enable the outer blade portion (5b) to perform a pitching movement relative to the inner blade portion (5a).

15. 14. The pitch-controlled wind turbine (1) according to any one of claims 1 to 13, wherein each wind turbine blade (5) comprises a pitch bearing arranged at the connection point (9) to enable a portion of the wind turbine blade (5) extending from the connection point (9) to the tip end (7) to perform a pitching movement relative to a portion of the wind turbine blade (5) extending from the root end (6) to the connection point (9).

16. 16. The pitch-controlled wind turbine (1) according to any one of claims 1 to 15, wherein the inner wing portion (5a) of each wind turbine blade (5) comprises a first inner wing portion (5a') and a second inner wing portion (5a''), the first inner wing portion (5a') comprising a leading edge (13) of the inner wing portion (5a) and the second inner wing portion (5a'') comprising a trailing edge (14) of the inner wing portion (5a), the first inner wing portion (5a') and the second inner wing portion (5a'') being connected to each other along a dividing interface (15) extending along a direction defined by a length of the wind turbine blade (5).

17. 17. The pitch-controlled wind turbine (1) according to any one of the preceding claims, wherein the wind turbine (1) is an upwind wind turbine.

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