Pitch-controlled wind turbine with blade coupling member

Abstract

A pitch-controlled wind turbine 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 of the wind turbine blades (5) extends between a root end (10) coupled to the hub (4) via a pitch mechanism and a tip. The wind turbine (1) further includes at least three blade coupling members (6), each of which extends between a coupling point (7) on one of the wind turbine blades (5) and a coupling point (7) on another of the wind turbine blades (5), the coupling points (7) being located a fixed distance from the root end (10) of the wind turbine blade (5) and a fixed distance from the tip of the wind turbine blade (5). The wind turbine (1) further comprises at least three pretensioning members (8), each of which is coupled to one of the blade coupling members (6) and to the hub portion (4, 9, 26), and the pretensioning members (8) thereby apply pretension to the blade coupling members (6).

Description

Technical Field

[0001] The present invention relates to a pitch-controlled wind turbine comprising a tower, a nacelle attached to the tower, a hub rotatably attached to the nacelle, and at least three wind turbine blades coupled to the hub via a pitch mechanism.

Background Art

[0002] During the operation of a wind turbine, various loads are applied to the components of the wind turbine. For example, the wind turbine blades of a wind turbine are subject to loads due to gravity acting on the wind turbine blades, loads due to wind pressure applied to the wind turbine blades, loads due to changes in wind direction or wind speed, and loads due to turbulence, etc. The gravity acting on the wind turbine blades mainly applies a load in the edge direction to the wind turbine blades, and the wind acting on the wind turbine blades mainly applies a load in the flap direction to the wind turbine blades.

Summary of the Invention

Problems to be Solved by the Invention

[0003] As the size of a wind turbine increases, the loads applied to the wind turbine also increase. To handle such increased loads, the amount of material used in the manufacture of the wind turbine may increase. However, this not only increases the manufacturing cost, but also increases the weight of the wind turbine.

Means for Solving the Problems

[0004] An object of an embodiment of the present invention is to provide a pitch-controlled wind turbine in which the loads in the edge direction and / or flap direction applied to the wind turbine blades are reduced as compared with a conventional wind turbine of the same length.

[0005] The present invention relates to a pitch-controlled wind turbine comprising a tower, a nacelle mounted on the tower, a hub rotatably mounted on the nacelle, and at least three wind turbine blades, each of which extends between a root end and a tip connected to the hub via a pitch mechanism, and the wind turbine further comprises at least three blade coupling members, each of which extends between a coupling point on one wind turbine blade and a coupling point on an adjacent wind turbine blade, and the coupling point (7) of a given wind turbine blade (5) is located at a certain distance from the root end (10) of the wind turbine blade (5) and at a certain distance from the tip of the wind turbine blade (5), and the wind turbine further comprises at least three pre-tension members, each of which is coupled to one of the blade coupling members and to the hub portion, thereby providing a pitch-controlled wind turbine in which each pre-tension member applies pre-tension to the blade coupling member to which the blade coupling member is coupled.

[0006] Accordingly, the present invention provides a pitch-controlled wind turbine, for example, a wind turbine comprising wind turbine blades that can rotate substantially around a longitudinal pitch axis during operation of the wind turbine in order to adjust the angle of attack between the wind turbine blades and the incoming airflow.

[0007] The wind turbine comprises a tower and a nacelle mounted on the tower. The wind turbine further comprises a hub rotatably mounted on the nacelle and at least three wind turbine blades. Each wind turbine blade extends between a root end and a tip, which are coupled to the hub via a pitch mechanism.

[0008] Therefore, the wind turbine blades rotate relative to the nacelle along with the hub, and the tips of the wind turbine blades point away from the hub. Since the wind turbine blades are connected to the hub via a pitch mechanism, each wind turbine blade can rotate relative to the hub, i.e., move in the pitch direction.

[0009] The hub and the wind turbine blades form the rotor of the wind turbine. However, the type of wind turbine is a horizontal-axis wind turbine (HAWT), which typically has a main shaft within 10° of the horizontal. The fact that the blade roots are connected to the hub via a pitch mechanism means that the blades are capable of pitching motion along the longitudinal pitch axis.

[0010] Generally, the nacelle is mounted to the tower via a yaw system so that it can rotate relative to the tower in order to properly orient the rotor according to the wind direction.

[0011] The wind turbine further comprises at least three blade coupling members. Each blade coupling member extends between a coupling point on one wind turbine blade and a coupling point (7) on an adjacent wind turbine blade (5). Thus, each coupling member interconnects two adjacent wind turbine blades. The coupling points on a given wind turbine blade are located at a distance from the root end of the blade, for example, at least 10% of the length from the root end to the tip of the wind turbine blade, and at a distance from the root end to the tip of the wind turbine blade, for example, at least 10% of the length of the wind turbine blade from the root end to the tip. Thus, the coupling points are not located at either the root or the tip, but are located between these two ends, with a distance to each end that is not zero, for example, from the root to the tip, and to both ends, at a position at least 10% of the length of the wind turbine blade.

[0012] The wind turbine further comprises at least three pre-tension members. Each pre-tension member is coupled to one of the blade coupling members and to the hub portion. Thus, the pre-tension members pull the blade coupling members toward the hub, thereby applying tension to the blade coupling members, and the blades coupled by the blade coupling members are subjected to tension toward each other.

[0013] In this application, the term “member” in connection with connecting members and pre-tensioning members should be broadly interpreted to encompass all suitable types of tensioning members, such as ropes made of braided or twisted metal wires (e.g., steel wire), polymer fibers (e.g., polyethylene, polypropylene, nylon, polyester, aramid), inorganic fibers (e.g., carbon fiber), or hybrid ropes of such materials, composite pultruded products, metal rods, etc.

[0014] The blade coupling member may have a different rigidity from that of the pre-tension member, or the rigidity of the blade coupling member and the pre-tension member may be the same. In this application, the term “hub portion” should be interpreted as meaning the hub, or a part or element coupled to the hub in the sense that it rotates with the hub relative to the nacelle. Such a part or element may be coupled to the outer surface of the hub, protrude from the hub, be located inside the hub, or be located in any other appropriate way, as long as it rotates with the hub.

[0015] The pre-tension member may be coupled to the blade coupling member at a position away from each coupling point on the wind turbine blade, or the distance to the coupling point may be substantially equal, i.e., approximately midway between the wind turbine blades along the blade coupling member.

[0016] The pre-tensioned blade coupling member supports the wind turbine blades together such that the loads applied to the wind turbine blades, particularly the loads in the edge direction and the loads in the flap direction, are "shared" between the wind turbine blades via the pre-tensioned blade coupling member. This allows the loads on the wind turbine blades during wind turbine operation to be handled by reducing the thickness of the material. Furthermore, or alternatively, this may be achieved with the same or reduced weight and / or the same or reduced manufacturing cost compared to conventional blades of the same length.

[0017] The pre-tension of the blade coupling member is provided by a pre-tension member that interconnects the blade coupling member and the hub portion. Therefore, the pre-tension of the pre-tension member, as well as the blade coupling member, can be controlled, thereby providing easy access from the hub for servicing and adjustment of the pre-tension. Furthermore, it is possible to adjust how much the average flap direction load is affected by a given pre-tension. For example, a short pre-tension member leads to a larger shift in the average bending moment in the flap direction, while a long pre-tension member leads to a larger reduction in the bending moment amplitude in the edge direction. In short, by using a pre-tension member, the risk of loosening of the blade coupling member is reduced because the pre-tension system is softer than that of the blade coupling member, or because the tension and / or length of the pre-tension member can be actively adjusted.

[0018] A pre-tension member can be positioned to provide an adjustable pre-tension to the blade coupling member. The tension of the blade coupling member can be determined based on the tension of the pre-tension member and the angle between the pre-tension member and the blade coupling member.

[0019] According to this embodiment, the pre-tension of the blade coupling member can be adjusted by appropriately adjusting the pre-tension member, or the adjustment pre-tension mechanism coupled to the pre-tension member. The pre-tension can be adjusted during installation, for example, to obtain a desired pre-tension precisely and / or to appropriately balance the pre-tensions of each blade coupling member.

[0020] Alternatively or additionally, the preload may be adjusted continuously or repeatedly during the operation of the wind turbine. This may be related to ensuring that the preload is appropriate under general operating conditions with respect to ambient conditions such as wind speed, wind shear, turbulence conditions, temperature, humidity, and / or wind turbine conditions such as blade azimuth angle, blade pitch angle, tip velocity / rotational (angular) velocity.

[0021] By designing a pre-tension member to provide an adjustable pre-tension to the blade coupling member, the desired pre-tension can be obtained precisely in a simple manner, and in some cases, that pre-tension can be adapted to general operating conditions.

[0022] Pre-tension adjustment involves, for example, winding or unwinding a pre-tension member around a rotatable member to adjust the length of the pre-tension member, thereby extending or contracting a linear actuator such as a hydraulic actuator, which forms part of or acts on the pre-tension member.

[0023] The connection point may be located on the outer side of the outer surface of the wind turbine blade.

[0024] According to this embodiment, the blade coupling member is coupled to each wind turbine blade at a position located outside the outer surface of the wind turbine blade, such as outside the outer shell of the wind turbine blade. For example, the blade coupling member may be located outside the wind turbine blade, such as outside the shell of the blade, or coupled to a structure that is located outside the wind turbine blade.

[0025] In one aspect of the present invention, the coupling points of a single wind turbine blade are, for example, adjacent to each other or adjacent to each other, or share several structural elements of the coupling point. In a special case, two blade coupling members (coupled to different blades at opposite ends) are coupled to the same coupling point (7) on a single blade. This has the effect that when tension is applied to the blade coupling members, the blade is affected by a single coupled force and is not subjected to tension in two different directions by the blade coupling members. Furthermore, when the coupling points are adjacent, or when the same coupling point is used for both blade coupling members, the coupling points of both blade coupling members can be brought closer to the blade pitch axis or evenly distributed on the blade pitch axis.

[0026] By arranging the connection points on the outer side of the wind turbine blade, the surface of the wind turbine blade can be maintained substantially intact. Further, the wind turbine blade can perform pitch movement without affecting the blade connection member, provided that at least the pitch axis is carefully positioned relative to the connection point. In the structure for connecting the blade connection member to the wind turbine blade, for example, a cover for improving the aerodynamic characteristics of the structure may be provided, for example, in terms of increasing lift and / or reducing drag, so as to minimize the influence on the aerodynamic characteristics of the wind turbine blade.

[0027] The blade connection member can be coupled to each wind turbine blade via a bearing structure attached to the wind turbine blade or forming part of the wind turbine blade. The bearing structure may be, for example, a roller bearing, a sliding bearing, a spherical bearing, or any other suitable type of bearing, or may include them.

[0028] The bearing structure enables the wind turbine blade to rotate relative to the blade connection member via the bearing structure. Thereby, the wind turbine blade can perform pitch movement without affecting the blade connection member, and it is possible to avoid adding undesirable loads, torsions, or tensions to the blade connection member during pitching. When the blade connection member is coupled to the wind turbine blade via the bearing structure, it is preferable that the pitch axis passes through the blade at the position in the blade width direction of the blade connection member. In particular, it has been found advantageous for the pitch axis to pass through the shape formed by the bearing structure at this position in the blade width direction.

[0029] When the bearing structure is a spherical bearing or includes a spherical bearing, the blade connection member can rotate freely relative to the wind turbine blade around the connection point. Thereby, only tension is transmitted between the blade connection member and the wind turbine blade at the connection point.

[0030] If the bearing structure protrudes from the wind turbine blade or is circumferentially positioned relative to the wind turbine blade, a fairing or similar aerodynamic structure may be provided on the bearing structure to improve the aerodynamic characteristics of the wind turbine in the region of the bearing structure.

[0031] The connection point on the wind turbine blade may preferably be located at a distance such as 10% to 60% of the length from the root end to the tip of the wind turbine blade, for example, between 20% and 50% of the length of the wind turbine blade, for example, between 25% and 40% of the length of the wind turbine blade, or for example, about 30% of the length of the wind turbine blade. In other cases, the connection point on the wind turbine blade may preferably be located at a distance from the root end, for example, between 25% to 60% of the length from the root end to the tip of the wind turbine blade, for example, between 35% and 55% of the length of the wind turbine blade, or for example, between 40% and 50% of the length of the wind turbine blade.

[0032] According to this embodiment, the connection point of the wind turbine blade is positioned sufficiently far from both the root end and the tip end of the wind turbine blade.

[0033] The position of the coupling point along the wind turbine blade can be selected in a way that appropriately balances various issues that need to be considered. For example, placing the coupling point near the tip of the wind turbine blade provides very efficient support for the wind turbine blade by the blade coupling member. However, this comes at the cost of high drag generated by the blade coupling member during rotor rotation, thereby reducing energy production. On the other hand, placing the coupling point near the root end of the wind turbine blade reduces the drag generated by the blade coupling member, thereby minimizing the adverse effect on the wind turbine's energy production. However, this also comes at the cost of high drag generated by the blade coupling member during rotor rotation, thereby reducing energy production. On the other hand, placing the coupling point near the root end of the wind turbine blade reduces the drag generated by the blade coupling member, thereby minimizing the adverse effect on the wind turbine's energy production. Furthermore, by placing the coupling point within this region, the blade coupling member can be securely attached to the wind turbine blade at a point where the structural rigidity of the wind turbine blade is sufficiently high. For example, because the structural rigidity of a wind turbine blade decreases towards the tip, connecting the blade coupling member too close to the tip can cause significant pre-deformation in the wind turbine blade, potentially hindering its ability to pitch.

[0034] The joint points on the wind turbine blade can be positioned where the thickness-to-chord ratio of the wind turbine blade is between 20% and 50%, for example, between 25% and 35%, or between 30% and 45%. This is also the region of the wind turbine blade where a balance is maintained between efficient support and introduction drag, and sufficient structural rigidity of the wind turbine blade is obtained, as mentioned above.

[0035] Next, the present invention will be described in more detail with reference to the attached drawings. [Brief explanation of the drawing]

[0036] [Figure 1]This figure shows a wind turbine according to a first embodiment of the present invention. [Figure 2] This figure shows a wind turbine according to a first embodiment of the present invention. [Figure 3] This is a side view of a wind turbine according to a second embodiment of the present invention. [Figure 4] This figure shows a wind turbine blade for a wind turbine according to one embodiment of the present invention. [Figure 5] This figure shows a wind turbine blade for a wind turbine according to one embodiment of the present invention. [Figure 6] This figure shows a wind turbine blade for a wind turbine according to one embodiment of the present invention. [Figure 7] This figure shows a wind turbine blade for a wind turbine according to an alternative embodiment of the present invention. [Figure 8] This figure shows a wind turbine blade for a wind turbine according to an alternative embodiment of the present invention. [Figure 9] This figure shows a wind turbine blade for a wind turbine according to an alternative embodiment of the present invention. [Figure 10] This figure shows a wind turbine blade for a wind turbine according to an alternative embodiment of the present invention. [Figure 11] This figure shows a curved wind turbine blade for a wind turbine according to one embodiment of the present invention. [Figure 12] This figure shows a curved wind turbine blade for a wind turbine according to one embodiment of the present invention. [Figure 13] This diagram shows the pitching of a wind turbine blade with its pitch axis positioned outward relative to the wind turbine blade. [Figure 14] This figure shows the attachment of a blade coupling member to a wind turbine blade according to two embodiments of the present invention. [Figure 15] This figure shows the attachment of a blade coupling member to a wind turbine blade according to two embodiments of the present invention. [Figure 16]This figure shows the attachment of a pre-tension member to a hub according to two embodiments of the present invention. [Figure 17] This figure shows the attachment of a pre-tension member to a hub according to two embodiments of the present invention. [Figure 18] This diagram shows the hub section equipped with individual tension adjustment mechanisms.

[0037] Each wind turbine blade may comprise two separate parts: an inner blade section including the root end and an outer blade section including the tip. The inner and outer blade sections are joined to each other at a dividing point, and the joining point on the wind turbine blade may be located at the dividing point.

[0038] According to this embodiment, each wind turbine blade is formed from two parts, namely an inner blade section and an outer blade section, which can be manufactured separately and then joined together to form a wind turbine blade. This is sometimes called a "split wind turbine blade." This also allows the blade components to be transported individually to the wind turbine installation site, so even large wind turbine blades can be transported without incurring excessive transportation costs.

[0039] When using such segmented wind turbine blades, it has been found to be advantageous to position the connection point, i.e., the point where the blade connecting member is connected to the wind turbine blade, at the segmented position where the inner blade section and the outer blade are connected, so that a suitable member mounting structure can be added to this position on the wind turbine blade without significantly reducing the strength or aerodynamic characteristics of the wind turbine blade. For example, if the blade connecting member is connected to the wind turbine blade via a bearing structure, the bearing structure can advantageously form the interface between the inner blade section and the outer blade section.

[0040] The hub may include a hub portion extending substantially along the direction defined by the hub's axis of rotation, and a pre-tension member may be coupled to the hub portion. The hub portion may extend, for example, forward of the rotor surface defined by the rotor of a wind turbine, i.e., toward the incoming wind if the wind turbine is an upwind wind turbine.

[0041] According to this embodiment, the pre-tension member is not directly coupled to the hub, but rather to a member forming a hub portion that extends from the hub in a direction defined by the hub's axis of rotation. Furthermore, the coupling point between the pre-tension member and the hub portion can be located away from the point where the wind turbine blade is coupled to the hub, in a direction defined by the hub's axis of rotation. As a result, the pre-tension member pulls the blade coupling member not only toward the hub, but also toward the direction of the hub's axis of rotation, and thus away from the tower. This also pulls the wind turbine blade in this direction, producing an effect on the wind turbine blade similar to that of introducing a coning angle. This reduces the load in the edge direction at the blade root, particularly in the flap direction, and also ensures tower clearance.

[0042] The hub portion may be configured to provide adjustable pretension and / or adjustable stiffness to the blade coupling member via a pretension member and / or pretension member. According to this embodiment, as described above, the adjustable pretension is obtained by a mechanism coupled to or forming part of the hub portion. The adjustment mechanism may be, for example, a hydraulic actuator, or another type of (linear) actuator such as an electric, pneumatic, or mechanical (such as a spring-type) actuator. In this case, the hub portion may be provided with a hydraulic piston, for example, a piston that is movable along the direction defined by the rotation axis of the hub. Such a mechanism may be used, for example, to adjust the pretension of the blade coupling member to handle flap-direction loads and / or control tower clearance during high-thrust operation of a wind turbine.

[0043] The ability to individually adjust the tension of each blade pre-tension member proved to be highly advantageous, as it improved the balance of tension in the blade coupling members. Furthermore, individual adjustment improved control and reduced the risk of loosening of the blade coupling members. This is preferably achieved by having an independent adjustment mechanism, such as another type of (linear) actuator, such as hydraulically actuated, electrically actuated, pneumatically actuated, mechanically spring actuated, or a combination thereof, acting individually on each pre-tension member. Surprisingly, by using individually adjusted pre-tension members, it was found that the actuator could also function as a vibration damper for the blade coupling members and pre-tension members by adjusting the effective stiffness of the pre-tension members. Furthermore, the carefully controlled piston movement reduced vibration of the blade coupling members and / or pre-tension members, thereby reducing fatigue wear of the wind turbine components, thus reducing acoustic radiation from the blade coupling members, pre-tension members, and / or wind turbine generators. Thus, the use of individually adjusted pre-tension members proved to be highly advantageous.

[0044] The hub portion may include an adjustment mechanism including a linear actuator positioned in the direction between the rotation axis of the hub and the connection point between the blade coupling member and the pre-tension member. This allows for a simple and efficient method of individually adjusting the distance between the hub and the connection point between the blade coupling member and adjusting the tension of the corresponding pre-tension member. The linear actuator in this embodiment of the present invention is preferably a hydraulic linear actuator (e.g., a hydraulic piston) or a pneumatic actuator, as this has been shown to enable controlled operation under high tension and also to function as a vibration damper. The blade coupling member and / or pre-tension member are adjusted by adjusting the effective stiffness of the pre-tension member and / or by canceling vibrations by the movement of the piston. It has been found to be particularly advantageous that hydraulic and pneumatic actuators can be directly switched from a master mode (controlling the length of the actuator piston) to a first slave mode (maintaining tension in the blade coupling cable or pre-tension cable in accordance with the wind load on the blade) and / or a second slave mode (damping vibrations of the blade coupling cable or pre-tension cable based on sensor inputs related to tension or vibration). Other types of linear actuators are also useful, such as electric actuators, mechanical (spring-type) actuators, or combinations thereof, such as a combination of springs and hydraulic actuators.

[0045] Alternatively, the pre-tension members may be coupled to a common point located inside the hub. This common point within the hub may be "floating" in the sense that it can move slightly to distribute the load among the pre-tension members during the operation of the wind turbine. Furthermore, by coupling the pre-tension members to this common point, tension can be applied to the pre-tension members from this common point. This has the advantage that only one position is needed to apply tension to all the pre-tension members, for example, by moving the common point back and forth along the hub's axis of rotation, or by moving the common point away from the hub's axis of rotation, thereby changing the tension ratio of all the pre-tension members. Such movement can be performed, for example, using one or more hydraulic actuators.

[0046] The setting and / or adjustment of the pre-tension of the pre-tension members, and by extension the blade coupling members, can be done once as part of the installation or commissioning of the wind turbine. However, it is preferable that the pre-tension be adjusted several times periodically, for example, after measuring the pre-tension in at least one of the blade coupling members or at least one of the pre-tension members. This measurement may be part of a program that periodically monitors the blades, blade coupling members, pre-tension members, and / or adjustment mechanisms via at least one sensor located in the blades, blade coupling members, pre-tension members, and / or adjustment mechanisms. In some cases, the pre-tension is adjusted by the orientation of the blades during rotor rotation. In other cases, the pre-tension is adjusted as part of the pitching process, i.e., before, during, and / or after pitching.

[0047] Wind turbine blades can have a defined coning angle in the range of 2° to 20°, such as in the range of 5° to 10°. In this application, the term “corning angle” should be interpreted as the angle between a plane substantially perpendicular to the direction defined by the hub’s axis of rotation and the direction in which one of the wind turbine blades extends along it. Therefore, increasing the coning angle moves the tip of the wind turbine blade further away from the plane passing through the center of the blade root and perpendicular to the hub’s axis of rotation.

[0048] Introducing a coning angle enhances tower clearance and reduces flap-direction loads at the root end of the wind turbine blades. The coupling point on the wind turbine blade may be located on or near the pitch axis of the wind turbine blade. In this context, the term “pitch axis” should be interpreted as meaning the axis on which the wind turbine blade rotates when performing pitch direction movement. In this application, a coupling point located “on or near” the pitch axis means that the distance from the coupling point to the pitch axis is within a) 2% of the rotor diameter and b) the maximum distance of the two blade chord lengths at the coupling point from the pitch axis when the blades are not wind-loaded.

[0049] Therefore, according to this embodiment, when the wind turbine blade rotates during pitching, the coupling point does not move, or moves only within a very limited range. Consequently, the blade coupling member also does not move, or moves only within a very limited range. This minimizes changes in tension in the blade coupling member and minimizes the force acting on the coupling point. Furthermore, this maintains complete freedom during pitching.

[0050] Alternatively, the coupling points on the wind turbine blades may be positioned at an offset location relative to the pitch axis. In this case, the blade coupling members would move during pitching. In this case, the wind turbine blades can be interconnected in a way that allows for collective pitching of the wind turbine blades, but individual pitching is only possible within a limited range.

[0051] The relative position of the pitch axis and the connection point can be advantageously selected in a way that minimizes the pitch load, i.e., the load required to pitch the wind turbine blades at various wind speeds. In particular, it has been found to be very advantageous to position the connection point of the blade coupling member on or near the blade pitch axis as defined above.

[0052] Each wind turbine blade may have at least one groove formed in the outer shell of the wind turbine blade, the at least one groove being positioned to receive a portion of the blade coupling member. It is advantageous for the groove to be formed on the positive pressure side of the wind turbine blade.

[0053] According to this embodiment, the blade coupling members may be housed within each groove at one pitch angle and positioned outside each groove at other pitch angles. This allows the coupling points to be located on or near the pitch axis, even if they extend inside the wind turbine blades, and enables the wind turbine blades to move in the pitch direction without colliding with the blade coupling members.

[0054] Each wind turbine blade may curve in at least one direction between its root end and tip, so that the pitch axis of the wind turbine blade is located outward relative to the wind turbine blade, at least at the joint. The wind turbine blade may be curved in the flapwise direction and / or edgewise direction. For example, the curvature of the wind turbine blade may take the form of a sweep of the wind turbine blade. The curve may extend along the entire length of the wind turbine or along only a portion of the length of the wind turbine blade. For example, if the wind turbine blade is divided into an inner blade section and an outer blade section, only one of the blade sections may be curved, for example, if the blade section is divided into an outer blade section. The outer blade section may be curved. Alternatively or additionally, the curvature may be introduced in the form of an angle between the inner blade section and the outer blade section.

[0055] According to this embodiment, the coupling point can be located on or near the pitch axis, even though it is located on the outside of the wind turbine blade. This allows the wind turbine blade to move in the pitch direction without colliding with the blade coupling member.

[0056] Each wind turbine blade may extend along its longitudinal direction, and this longitudinal direction may form a non-zero angle with respect to the pitch axis of the wind turbine blade's pitch mechanism. The non-zero angle may be in the range of 0.1° to 10.0°, for example, in the range of 0.5° to 3.0°. Because each wind turbine blade extends along a direction that forms a non-zero angle with respect to the pitch axis, the pitch axis and the direction of the wind turbine blade do not coincide. Therefore, the wind turbine blade rotates around an axis that does not coincide with its longitudinal axis during movement in the pitch direction.

[0057] According to this embodiment, as in the situation described above, the axes do not coincide, so the pitch axis may be located outside the wind turbine blade at the position of the coupling point.

[0058] A non-zero angle between the pitch axis and the longitudinal direction of the wind turbine blade can be obtained, for example, by introducing one or more wedges at the root end of the wind turbine blade. In this case, one or more shims may be coupled to the hub and the wind turbine blade, and to adjacent shims if possible, via separate bearings. This allows the shims to rotate independently, thereby changing the angle between the pitch axis and the longitudinal direction of the wind turbine blade. Furthermore, the pitch can be operated separately, for example, by performing collective pitch through one bearing and individual pitch through another bearing. This can potentially reduce the load on the pitch mechanism, particularly the bearings.

[0059] The pre-tensioning member and / or blade coupling member may include a vibration damping mechanism.

[0060] According to this embodiment, vibrations of the pre-tension member and / or blade coupling member are dampened during the operation of the wind turbine, thereby reducing the load on the member and the wind turbine blades. Furthermore, the wire rope may passively provide additional structural damping to the blade movement because the individual fibers within the wire rope interact with each other when stretched.

[0061] The vibration damping mechanism may be a passive vibration damping mechanism such as an oil damper or a flexible member. In this case, vibration damping is provided automatically when the wind turbine is in operation. Alternatively, the vibration damping mechanism may be an active vibration damping mechanism such as a hydraulic cylinder. In this case, vibration damping can be actively controlled.

[0062] Aerodynamic devices may be provided on the pre-tension members and / or blade coupling members. According to this embodiment, the aerodynamic adverse effects caused by the mounting members between wind turbine blades are reduced by providing aerodynamic devices on the members, thereby improving the aerodynamic properties of the members. The aerodynamic devices may be of a type that increases the lift of the members and / or reduces the drag. For example, the aerodynamic devices may be in the form of blades or droplets.

[0063] The wind turbine may also be an upwind wind turbine. In this case, the rotor of the wind turbine faces the incoming wind, and the resulting flap-direction load on the wind turbine blades pushes the wind turbine blades toward the hub. Blade coupling members are very well suited to mitigating such flap-direction loads.

[0064] Alternatively, the wind turbine may be a downwind type. In this case, the rotor of the wind turbine is oriented in the opposite direction to the incoming wind, so that the flap-direction load on the wind turbine blades caused by the wind pushes the wind turbine blades away from the hub. [Modes for carrying out the invention]

[0065] Figures 1 and 2 show a pitch-controlled wind turbine 1 according to a first embodiment of the present invention. Figure 1 is a front view of the wind turbine 1, and Figure 2 is a side view of the wind turbine 1.

[0066] The wind turbine 1 comprises a tower 2 and a nacelle 3 attached to the tower 2. A hub 4 supporting three wind turbine blades 5 is rotatably mounted to the nacelle 3.

[0067] The three blade coupling members 6 interconnect adjacent wind turbine blades 5 between coupling points 7 on the wind turbine blades 5. Furthermore, the wind turbine 1 is equipped with three pre-tension members 8, each of which extends between one of the blade coupling members. In this way, the pre-tension members 8 provide pre-tension to the blade coupling members 6.

[0068] The pre-tensioned blade coupling member 6 causes the wind turbine blades 5 to mutually support each other, in the sense that the loads applied to the wind turbine blades 5, particularly the loads in the edge direction and the loads in the flap direction, are "shared" among the wind turbine blades 5.

[0069] Figure 3 is a side view of a pitch-controlled wind turbine 1 according to a second embodiment of the present invention. The wind turbine 1 in Figure 3 is very similar to the wind turbine 1 in Figures 1 and 2. Therefore, it will not be described in detail here. The blade coupling member is not visible in Figure 3.

[0070] In the embodiment of Figure 3, the pre-tension member 8 is not directly coupled to the hub 4. Instead, the pre-tension member 8 is coupled to the hub portion in the form of a hub portion 9 extending from the hub. The axis of rotation of the hub 4 is indicated along the direction substantially defined by the axis of rotation of the hub 4, as shown in Figure 4. This causes the coupling point of the pre-tension member 8 to be further away from the hub 4 than in the embodiments of Figures 1 and 2, thereby further away from the position where the wind turbine blade 5 is coupled to the hub 4. This, as a result, also pulls the pre-tension member 8 away from the hub 4 and the blade coupling member (not shown) and away from the tower 2. This also pulls the wind turbine blade 5 in this direction, thereby further reducing the edge-direction and flap-direction loads at the root of the wind turbine blade 5, ensuring tower clearance similar to that when a coning angle is introduced. It has been found that the use of coupling members tends to increase the rigidity of the inner portion of the blade.

[0071] Figures 4 to 6 show a wind turbine blade 5 for a wind turbine according to one embodiment of the present invention. Figure 4 is a perspective view of the wind turbine blade 5, Figure 5 is a cross-sectional view of the wind turbine blade 5 along its longitudinal direction, and Figure 6 is a cross-sectional view of the wind turbine blade 5 along its blade chord direction.

[0072] The wind turbine blade 5 comprises a root end 10 configured to be coupled to a hub via a pitch mechanism, and a tip (not shown) located on the opposite side of the root end 10. The wind turbine blade 5 is formed from an inboard blade including an inner blade portion 5a that constitutes the root end 10 and an outer blade portion 5b that constitutes the tip. The inner blade portion 5a and the outer blade portion 5b are coupled to form the wind turbine blade 5.

[0073] A bearing structure 11 is positioned where the inner blade portion 5a and the outer blade portion 5b are joined. The two blade connecting members 6 are connected to the wind turbine blade 5 via a connection point 7 on the bearing structure 11. As a result, the blade connecting members 6 do not rotate with the wind turbine blade 5 when the wind turbine blade 5 moves in the pitch direction. This prevents unnecessary twisting or tension from being applied to the blade connecting members 6 during the pitching of the wind turbine blade 5.

[0074] Figure 5 shows that the bearing structure 11 comprises a portion 11a that is bolted to the blade portions 5a and 5b, and a portion 11b that has a blade connecting member 6 connected thereto. The two portions 11a and 11b of the bearing structure 11 can rotate relative to each other.

[0075] Figure 6 is a cross-sectional view of the bearing structure 11 along the blade chord direction of the wind turbine blade 5 in Figure 4. Thus, Figure 6 is essentially a side view of the bearing structure 11, clearly showing the two parts 11a and 11b of the bearing structure 11.

[0076] Figures 7 to 10 show wind turbine blades 5 for a wind turbine according to an alternative embodiment of the present invention. Figure 7 is a perspective view of the wind turbine blade 5, and Figures 8 to 10 are perspective views of the wind turbine blade 5. Figures 8 to 10 are cross-sectional views of the wind turbine blade 5 along the blade chord direction.

[0077] The wind turbine blades 5 in Figures 7 to 10 are very similar to the wind turbine blades 5 in Figures 4 to 6, and therefore a detailed explanation is omitted here.

[0078] In the wind turbine blades 5 shown in Figures 7 to 10, the bearing structure 11 is located inside the outer shell of the wind turbine blade 5. This can be seen in Figure 7. As a result, the connection point 7 between the bearing structure 11 and the blade coupling member 6 is also located inside the outer shell of the wind turbine blade 5, and is closer to the pitch axis 12 of the wind turbine blade 5 than in the embodiment shown in Figures 4 to 6. This minimizes the load applied to the blade coupling member 6 and minimizes the force applied to the connection point 7.

[0079] To prevent the wind turbine blade 5 from colliding with the blade coupling member 6 during pitching, the wind turbine blade 5 is provided with a groove 13 formed on the positive pressure surface of the wind turbine blade 5. The groove 13 is positioned to receive a portion of the blade coupling member 6. In Figure 7, one of the blade coupling members 6 is received in the groove 13.

[0080] Figure 8 is a cross-sectional view of the wind turbine blade 5 in Figure 7 along the blade chord direction. The wind turbine blade 5 has a pitch angle at which one of the blade coupling members 6 is received in the groove 13. Movement in the pitch direction is indicated by arrow 14.

[0081] In Figure 9, the wind turbine blade 5 is moved to a pitch angle where the blade coupling member 6 can no longer be received within the groove 13.

[0082] Figure 10 shows a similar embodiment in the form of a cross-sectional view of a wind turbine blade 5 along the blade chord direction. The wind turbine blade 5 has a pitch angle at which one of the blade coupling members 6 is received in the groove 13. In the embodiment of Figure 10, two of the blade coupling members 6 are provided with aerodynamic devices in the form of blade-shaped portions 15. This improves the aerodynamic characteristics of the blade coupling members 6, thereby minimizing the adverse effect on the efficiency of the wind turbine caused by providing the blade coupling members 6 to the wind turbine.

[0083] Figures 11 and 12 show a curved wind turbine blade 5 for a wind turbine according to one embodiment of the present invention. Figure 11 is a view of the wind turbine blade 5 along the blade chord direction, and Figure 12 is a view of the wind turbine blade 5 along a direction perpendicular to the blade chord direction.

[0084] In Figures 11 and 12, the dotted lines represent examples of conventional wind turbine blades, and the solid lines represent wind turbine blades 5 used in a wind turbine according to an embodiment of the present invention. The dashed lines indicate the positions where the wind turbine blade 5 is divided into an inner portion and an outer portion.

[0085] Figure 11 shows the leading edge 17 and trailing edge 18 of the illustrated wind turbine blade 5. It can be seen that the wind turbine blade 5 according to the present invention is curved compared to the conventional wind turbine blade 5. The pitch axis 12 of the wind turbine blade 5 according to the present invention is located on the outer leading edge 17 side and at the split position 16.

[0086] Figure 12 shows the positive pressure surface 19 and the suction surface 20 for each of the wind turbine blades 5 shown. Furthermore, the wind turbine blade 5 according to the present invention is curved compared to a conventional wind turbine blade 5 so that the pitch axis of the wind turbine blade 5 according to the present invention is located outside the wind turbine blade 5 at the positive pressure surface 19 and the split position 16 along this direction.

[0087] Thus, the wind turbine blade 5 used in the wind turbine according to the embodiment of the present invention is curved along two directions, and has a shape that causes the pitch axis 12 of the wind turbine blade 5 to be positioned at the split position 16 outside the leading edge 17 and outside the positive pressure surface 19 of the wind turbine blade 5. Therefore, when the blade coupling member is coupled to the wind turbine blade 5 at the split position 16, the coupling point can be located on or near the pitch axis 12, and outside the wind turbine blade 5. This makes it possible to easily couple the blade coupling member to the wind turbine blade 5 while reducing the load on the blade coupling member and coupling point during pitching of the wind turbine blade 5.

[0088] The wind turbine blades 5 in Figures 11 and 12 are not drawn to a constant scale in order to highlight the modified shape of the wind turbine blades 5 according to the present invention.

[0089] Figure 13 shows the pitching of a wind turbine blade 5 having a pitch axis 12 positioned outward relative to the wind turbine blade 5. The dashed line represents a conventional wind turbine blade 5, and the solid line represents a conventional wind turbine blade 5, with two extreme pitch angles.

[0090] In the present invention, the blade coupling member is coupled to the wind turbine blade 5 at a coupling point 7 located outside the wind turbine blade 5 and at or near the position of the pitch axis 12. As can be seen from Figure 13, this allows the wind turbine blade 5 to perform movement in the pitch direction without affecting the blade coupling member.

[0091] Figure 14 shows a wind turbine blade 5 used in a wind turbine according to one embodiment of the present invention. The wind turbine blade 5 comprises an inner blade portion 5a and an outer blade portion 5b connected to each other via a cast structure 21. A blade coupling member 6 is connected to the cast structure 21 via a hinge 22, which forms a connection point 7 between the blade coupling member 6 and the wind turbine blade 5. The wind direction is indicated by an arrow 27.

[0092] Since the blade coupling member 6 is coupled to the wind turbine blade 5 via the hinge 22, the blade coupling member 6 can move relative to the wind turbine blade 5. This may be relevant, for example, during pitching of the wind turbine blade 5.

[0093] Figure 15 shows a wind turbine blade 5 used in a wind turbine according to an alternative embodiment of the present invention. Similar to the embodiment in Figure 14, the wind turbine blade 5 comprises an inner blade portion 5a and an outer blade portion 5b connected via a cast structure 21. In the embodiment of Figure 15, the blade coupling member 6 is connected to the cast structure 21 via a spherical bearing 23 and a flexible cable 24. The spherical bearing 23 allows the blade coupling member 6 to move freely relative to the wind turbine blade 5. The flexible cable 24 provides damping to the blade coupling member 6. The wind direction is indicated by arrow 27.

[0094] Figure 16 is a cross-sectional view of a hub 4 for a wind turbine according to one embodiment of the present invention. Three pre-tension members 8 are coupled to the hub 4. The pre-tension provided by the pre-tension members 8 can be individually adjusted by an adjustment mechanism 25 located inside the hub 4. This allows the pre-tension of all three pre-tension members 8 to be adjusted from within the hub 4. This makes it easy to adjust the individual pre-tension of the pre-tension members 8 and can be performed substantially simultaneously, thus avoiding the following problem: Large differences in the pre-tension of the pre-tension members 8 result in uneven forces acting on the wind turbine blades.

[0095] Figure 17 is a cross-sectional view of a hub 4 for a wind turbine according to an alternative embodiment of the present invention. The hub 4 in Figure 17 also has three pre-tension members 8 connected to it, and the pre-tension provided by each of the pre-tension members 8 can be individually adjusted by an adjustment mechanism 25. However, in the hub 4 of Figure 17, the pre-tension members 8 are connected to a common fixed part 26 located inside the hub 4. The fixed part 26 floats in the sense that it can move inside the hub 4. This allows for a certain degree of load distribution and balance among the pre-tension members 8 during the operation of the wind turbine.

[0096] Figure 18 shows a hub portion 9 with tension adjustment mechanisms 25 that operate individually for each of the pre-tension members 8. The adjustment mechanisms 25 form part of the hub portion 9 and are positioned at the connection point between the blade coupling member (6) and the pre-tension member (7) in the direction of the rotation axis of the hub (28). Typically, the adjustment mechanisms are positioned on a member that extends along the rotation axis of the rotor, such as a tripod or beam, which provides a stable fixing point for the adjustment mechanisms. The adjustment mechanisms preferably comprise a linear actuator such as hydraulic, electric, pneumatic, mechanical, or any of these. The hub portion 9 may extend beyond the nose cone. Preferably, the hub portion 9 extends beyond the nose cone until the direction of the pre-tension members intersects with the rotation axis 28 upwind in the plane defined by the blade coupling point 7, in order to increase the rigidity of the rotor.

Claims

1. A pitch-controlled wind turbine (1) comprising a tower (2), a nacelle (3) attached to the tower (2), a hub (4) rotatably attached to the nacelle (3), and at least three wind turbine blades (5), wherein each of the at least three wind turbine blades (5) extends between a root end (10) and a tip, which are connected to the hub (4) via a pitch mechanism. The pitch-controlled wind turbine (1) further comprises at least three blade coupling members (6), each of which extends between a coupling point (7) on one wind turbine blade (5) and a coupling point (7) on an adjacent wind turbine blade (5), and the coupling points (7) of a given wind turbine blade (5) are positioned at a certain distance from the root end (10) of the at least three wind turbine blades (5) and at a certain distance from the tip of each of the at least three wind turbine blades (5). The pitch-controlled wind turbine (1) further comprises at least three pre-tension members (8), each of which is coupled to each of the at least three blade coupling members (6) such that it extends between each of the at least three blade coupling members (6) and the hub portion (4) between the adjacent wind turbine blades (5).

2. A pitch-controlled wind turbine (1) according to claim 1, wherein the at least three pre-tension members (8) provide an adjustable pre-tension to the blade coupling member (6) through the coupling.

3. A pitch-controlled wind turbine (1) according to claim 1 or 2, wherein the coupling point (7) is located outside the outer surface of the at least three wind turbine blades (5).

4. A pitch-controlled wind turbine (1) according to any one of claims 1 to 3, Each of the at least three blade coupling members (6) is coupled to each of the at least three wind turbine blades (5) via a bearing structure (11) attached to each of the at least three wind turbine blades (5), or to a portion of each of the at least three wind turbine blades (5), in a pitch-controlled wind turbine (1).

5. A pitch-controlled wind turbine (1) according to any one of claims 1 to 4, The pitch-controlled wind turbine (1) is configured such that the coupling points (7) on each of the at least three wind turbine blades (5) are positioned at a distance from the root end (10) that is between 10% and 60% of the length from the root end (10) to the tip of each of the at least three wind turbine blades (5).

6. A pitch-controlled wind turbine (1) according to any one of claims 1 to 5, The coupling point (7) on each of the at least three wind turbine blades (5) is positioned such that the thickness-to-chord ratio of each of the at least three wind turbine blades (5) is between 20% and 50% in a pitch-controlled wind turbine (1).

7. A pitch-controlled wind turbine (1) according to any one of claims 1 to 6, A pitch-controlled wind turbine (1) comprising, in each of the at least three wind turbine blades (5), an inner blade portion (5a) including the root end (10) and an outer blade portion (5b) including the tip, wherein the inner blade portion (5a) and the outer blade portion (5b) are joined to each other at a split position (16), and the joining point (7) on each of the at least three wind turbine blades (5) is located at the split position (16).

8. A pitch-controlled wind turbine (1) according to any one of claims 1 to 7, The hub (4) comprises a hub portion (9) extending from the hub (4) substantially along a direction defined by the axis of rotation of the hub (4), and the pitch-controlled wind turbine (1) is coupled to the hub portion (9).

9. A pitch-controlled wind turbine (1) according to claim 8, The hub portion (9) is positioned to provide adjustable pretension to the at least three pretension members (6) and / or the at least three blade coupling members (6) via the at least three pretension members (8) of the pitch-controlled wind turbine (1).

10. A pitch-controlled wind turbine (1) according to any one of claims 1 to 7, The pre-tension member (8) is connected to a common point (26) located inside the hub (4) of the pitch-controlled wind turbine (1).

11. A pitch-controlled wind turbine (1) according to any one of claims 1 to 10, The pitch-controlled wind turbine (1) comprises at least three wind turbine blades (5) that define a coning angle between 2° and 20°.

12. A pitch-controlled wind turbine (1) according to any one of claims 1 to 11, The coupling point (7) on the at least three wind turbine blades (5) is located on or near the pitch axis (12) of the at least three wind turbine blades (5) in a pitch-controlled wind turbine (1).

13. A pitch-controlled wind turbine (1) according to any one of claims 1 to 12, Each of the at least three wind turbine blades (5) is provided with at least one groove (13) formed in the outer shell of each of the at least three wind turbine blades (5), and the at least one groove (13) is arranged to receive a portion of the at least three blade coupling members (6) in a pitch-controlled wind turbine (1).

14. A pitch-controlled wind turbine (1) according to any one of claims 1 to 13, Each of the at least three wind turbine blades (5) is curved in at least one direction between the root end (10) and the tip, thereby causing the pitch axis (12) of the at least three wind turbine blades (5) to be positioned outward with respect to the at least three wind turbine blades (5) at least at the connection point (7) in a pitch-controlled wind turbine (1).

15. A pitch-controlled wind turbine (1) according to any one of claims 1 to 14, Each of the at least three wind turbine blades (5) extends along its longitudinal direction, and the longitudinal direction forms a non-zero angle with respect to the pitch axis (12) of the pitch mechanism of the at least three wind turbine blades (5) in a pitch-controlled wind turbine (1).

16. A pitch-controlled wind turbine (1) according to any one of claims 1 to 15, The at least three pre-tension members (8) and / or the at least three blade coupling members (6) are a pitch-controlled wind turbine (1) including a vibration damping mechanism.

17. A pitch-controlled wind turbine (1) according to any one of claims 1 to 16, A pitch-controlled wind turbine (1) is provided with aerodynamic devices (15) on at least three pre-tension members (8) and / or at least three blade coupling members (6).

18. A pitch-controlled wind turbine (1) according to any one of claims 1 to 17, The pitch-controlled wind turbine (1) is an upwind-type wind turbine.

19. A pitch-controlled wind turbine (1) according to any one of claims 1 to 18, A pitch-controlled wind turbine (1) wherein, of the at least three wind turbine blades, one of the coupling points (7) is arranged adjacent to one another, and / or two blade coupling members (6) are coupled to the same coupling point (7).

20. A pitch-controlled wind turbine (1) according to any one of claims 1 to 19, The tensions of at least three pre-tension members (8) are individually adjustable in the pitch-controlled wind turbine (1).

21. A pitch-controlled wind turbine (1) according to claim 9, The hub portion (9) is a pitch-controlled wind turbine (1) equipped with an adjustment mechanism (25) having a linear actuator positioned in the direction between the rotation axis of the hub (28) and the connection point between the at least three blade coupling members (6) and the at least three pre-tension members (8).

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