Wind turbine

Abstract

In a first aspect of the present invention there is provided a wind turbine comprising a nacelle and a rotor mounted to the nacelle The rotor comprises a hub and a plurality of wind turbine blades attached to the hub. Each blade extends between a blade root and a blade tip, and each blade further comprises a connection point located between the blade root and the blade tip. The wind turbine further comprises a blade connecting member connected between corresponding connection points of a pair of wind turbine blades. The wind turbine further comprises a tension adjustment system attached to the hub and configured to adjust the tension in the blade connecting member. The tension adjustment system comprises an electric motor and a winch, and the winch comprises a winch reel and a winch line. The winch line is attached to the winch reel and to the blade connecting member. The electric motor is coupled to the winch reel to rotate the winch reel and thereby spool the winch line off and onto the winch reel and to thereby adjust the tension in the blade connecting member.

Description

[0001] WIND TURBINE

[0002] Technical field

[0003] The present invention relates generally to wind turbines and more particularly to a wind turbine comprising a blade connecting member connected between a pair of wind turbine blades.

[0004] Background

[0005] Utility-scale wind turbines include a rotor coupled to a generator and configured to rotate about an axis to generate electrical power. The rotor of a horizontal axis wind turbine typically has multiple rotor blades attached to a central hub. One method for increasing the power generated by a wind turbine includes increasing the length of the wind turbine blades to increase the swept area of the rotor. However, increasing the length of a wind turbine blade increases the magnitude of loads, such as wind loads and weight loads, experienced by the blade and transferred to the hub, in use.

[0006] It follows that increasing blade length typically requires an increase in blade root diameter to safely transfer the increased blade loads. However, increasing the blade root diameter introduces further challenges for manufacturing and transporting the blade. Cable-stayed rotors have been developed to address some of these challenges. A cable-stayed rotor may include support cables extending between the blades and / or hub of a rotor to share and transfer blade loads, such that the structural requirements for the blade root may be reduced. Reducing the structural requirements of the blade root mean that the length of a blade can be increased without increasing the root diameter of the blade.

[0007] However, the loads experienced by a wind turbine blade vary during operation of the wind turbine. For example, loads may vary due to variable wind conditions such as wind speed and / or direction, due to different seasonal conditions, or due to different production modes of operating the wind turbine, for example. Different blade loads may require different levels of tension in structural components such as support cables of a cable-stayed rotor. Accordingly, it would be advantageous to configure a wind turbine to facilitate adjustment of the tension in such structural components.

[0008] It is against this background that the present invention has been developed. Summary

[0009] In a first aspect of the present invention there is provided a wind turbine comprising a nacelle and a rotor mounted to the nacelle. The rotor comprises a hub and a plurality of wind turbine blades attached to the hub. Each blade extends between a blade root and a blade tip, and each blade further comprises a connection point located between the blade root and the blade tip. The wind turbine further comprises a blade connecting member connected between corresponding connection points of a pair of wind turbine blades. The wind turbine further comprises a tension adjustment system attached to the hub and configured to adjust the tension in the blade connecting member. The tension adjustment system comprises an electric motor and a winch, and the winch comprises a winch reel and a winch line. The winch line is attached to the winch reel and to the blade connecting member. The electric motor is coupled to the winch reel to rotate the winch reel and thereby spool the winch line off and onto the winch reel and to thereby adjust the tension in the blade connecting member.

[0010] For example, the winch line may be wound, i.e. spooled, at least partially around the winch reel such that the winch line comprises a wound portion on or around the winch reel and a free portion extending away from the winch reel. The free portion of the winch line may be connected to the blade connecting member and may define a free length. Accordingly, the electric motor may be coupled to the winch reel to rotate the winch reel and thereby spool the winch line off and onto the winch reel to vary the free length of the free portion and thereby adjust the tension in the blade connecting member.

[0011] As described previously, the tension adjustment system is attached to the hub, and the winch line of the tension adjustment system is attached to the blade connecting member. As such the tension adjustment system provides the interface between the blade connecting member and the hub. Loading, such as tensile loads, experienced by the blade connecting member may therefore be transferred between the blade connecting member and the hub of the wind turbine via the tension adjustment system. Operation of the tension adjustment system to adjust the tension on the blade connecting member therefore facilitates control of the proportion of blade loads taken up by the blade connecting member and diverted to the hub via the tension adjustment system.

[0012] The tension adjustment system of the wind turbine described herein advantageously provides significant flexibility for assembly and maintenance of the wind turbine, and in particular the rotor including the blade connecting member and tension adjustment system. For example, the tension adjustment system is configured such that the winch line can be spooled off the winch reel, thereby increasing the free length, to slacken the winch line and thereby aid simple connection of the winch line to the blade connecting member. In addition, the tension adjustment system facilitates simple connection of the blade connecting member between the connection points of the pair of wind turbine blades. For example, the blade connecting member can be connected between the connection points in a substantially loose, or slack, state, with the desired operational tension being subsequently applied to the blade connecting member by spooling the winch line further onto the winch reel, i.e. reducing the free length. Following operation of the turbine, the tension adjustment system facilitates slackening the winch line and associated blade connecting member for maintenance and / or replacement of the blade connecting member and associated components of the tension adjustment system. In some examples, the facility to spool the winch line off the winch reel and thereby extend the free length of the winch line and slacken the blade connecting member may mean that maintenance operations can be performed on the blade without disconnecting the blade connecting member from the blades.

[0013] In addition, the tension adjustment system of the wind turbine described herein advantageously facilitates control and / or adjustment of the tension in the blade connecting member during operation of the wind turbine. For example the tension adjustment system is configured such that selective rotation of the winch reel, for example by driving the electric motor in a desired direction, spools the winch line off or onto the winch reel. Accordingly, the tension in the blade connecting member can be varied to facilitate best structural utilisation of the wind turbine blades and blade connecting member for different production modes of the wind turbine. Best structural utilisation may be achieved by actively varying the tension of the blade connecting member based on wind conditions such as wind speed and direction. In some examples, the tension of the blade connecting member may be varied based on factors such as any of temperature, humidity, atmospheric pressure or level of turbulence in the incident wind. Such factors may influence short term adjustment of the tension of the blade connecting member, for example for active control of the tension during operation of the turbine. In some examples, the tension of the blade connecting member may be varied based on factors such as identification of the current season. Such factors may influence long term adjustment of the tension of the blade connecting member.

[0014] The tension adjustment system may also aid turbine optimisation by facilitating compensation for loss of pretension in the blade connecting member over time. For example, as a result of prolonged tensile loading conditions, the blade connecting member may elongate, or creep, over time, resulting in a reduction in the tension of the blade connecting member. Advantageously, the tension adjustment system may be configured to compensate for such elongation or creep, because the winch reel can be rotated to spool the winch line onto the reel and thereby reduce the free length to increase or maintain the desired tension.

[0015] In some examples, the tension adjustment system may also mitigate production tolerances related to the blade connecting member and / or winch line. For example, the blade connecting member may be manufactured with a length accurate to + / - 0.1 m, in some examples. Whilst such a tolerance could result in significant differences in the tension achieved in non-adjustable, i.e. static, systems, the tension adjustment system described herein advantageously ensures that the correct tension can be achieved as desired. For example, irrespective of the manufactured length of the blade connecting member, or the winch line, the correct tension can be achieved and maintained by spooling the winch line off and onto the winch reel to vary the free length of the free portion and thereby adjust the tension in the blade connecting member.

[0016] It follows that the electric motor is coupled to the winch reel such that the electric motor can rotate the winch reel and thereby selectively spool the winch line off and onto the winch reel in accordance with a desired tension for the blade connecting member. Further, it should be appreciated that the terms “attached”, “coupled”, and “connected” may each respectively include direct attachment, coupling, or connection, as well as indirect attachment, coupling, or connection, for example via one or more other components unless explicitly stated otherwise.

[0017] The winch line may be attached directly to blade connecting member. Alternatively, in some other examples the winch line may be connected to the blade connecting member indirectly, via a tension member for example. Accordingly, the winch line may be connected to the tension member and the tension member may be connected to the blade connecting member. In some preferred examples, the tension member may be connected to the blade connecting member at a midpoint, i.e. centre, of the blade connecting member. Accordingly, in some examples the tension member may be referred to as a centre member, or in examples where the tension member comprises a cable, the tension member may therefore be referred to as a centre cable. Including a tension member to connect the winch cable to the blade connecting member may be advantageous for servicing and maintenance. The winch cable may be expected to experience higher wear resulting from spooling the winch line off and onto the winch reel. Accordingly, in the event that repair or replacement is required as a result of such wear, in some advantageous examples only the winch line may need to be repaired or replaced, thereby saving cost and materials.

[0018] It will be appreciated that the term “tension member” should be interpreted broadly to include examples such as flexible tension members and rigid tension members. As such, in some examples, the tension member may comprise a composite member such as a pultrusion, or may alternatively comprise a metal rod, to name a few possible examples. However, in preferred examples, the tension member may comprise a cable. For example, in the present context, a ‘cable’ may be a braided or laid rope of metal wires (such as steel wires, for example), polymer fibres (such as polyethylene, polypropylene, nylon, polyester, aramid fibres, for example), inorganic fibres (such as carbon fibres, for example) or hybrid ropes of such materials. Most preferably the tension member may comprise a polymer rope, such as a braided polymer rope. For example, a tension member may comprise ultrahigh molecular weight polyethylene fibres, such as Dyneema® DM20 based polymer rope.

[0019] In some examples the winch line may be permanently attached to the winch reel. In some other examples, the winch line may be removably attached to the winch reel. A winch line removably attached to the winch reel may be advantageous to facilitate maintenance and / or replacement of the winch line without necessitating disassembly of the winch reel from the rest of the tension adjustment system.

[0020] As previously described, the term attached may include direct attachment and indirect attachment. As such, the wind turbine blades attached to the hub may be attached directly to the hub in some examples. Alternatively, in some other examples, the wind turbine blades may be indirectly attached to the hub via one or more other wind turbine components, such as a pitch bearing, a hub extender, or a blade root extender, for example. Advantageously, a wind turbine blade attached to the hub via a pitch bearing may be rotatable relative to the hub. This facilitates control and adjustment of the angle of attack of the wind turbine blade to optimise energy capture from wind incident on the blade in use. Accordingly, in some examples the rotor may be referred to as a cable-stayed pitchable rotor, wherein the wind turbine blades are supported by the blade connecting members and associated tension adjustment systems, and wherein the blades are rotatable, i.e. pitchable, relative to the hub. Whilst the term winch reel is used herein to describe the component of the winch around which and onto which the winch line may be wound, it should be appreciated that the winch reel may also be referred to as a drum, or spool, in some other examples. Similarly, whilst the term winch line is used herein to describe the component of the winch configured for winding off and onto the winch reel to thereby adjust the tension in the blade connecting member, it should be appreciated that the winch line may also be referred to as a cable, rope belt or strap, in some other examples.

[0021] In some preferred examples, the winch line may have the form of a belt or strap which may be substantially flat, i.e. may have an elongate cross-sectional profile. A winch line configured in this way may be advantageous for maintaining alignment of the winch line with the winch reel during spooling on and off. Further, a belt or strap winch line may also be more resistant to twisting in use. Accordingly, a belt or strap winch line may be advantageous for reducing the risk of tangles or knots in the winch line, and reducing wear on the winch line, during use.

[0022] In the present context, ‘blade connecting member’ should be interpreted broadly to include examples such as flexible connecting members and rigid connecting members. As such, in some examples the blade connecting member may comprise a cable. Preferably the blade connecting member may therefore be a blade connecting cable, and the rotor may be a cable-stayed rotor. For example, in the present context, a ‘cable’ may be a braided or laid rope of metal wires (such as steel wires, for example), polymer fibres (such as polyethylene, polypropylene, nylon, polyester, aramid fibres, for example), inorganic fibres (such as carbon fibres, for example) or hybrid ropes of such materials. Most preferably the tension member may comprise a polymer rope, such as a braided polymer rope. For example, a tension member may comprise ultrahigh molecular weight polyethylene fibres, such as Dyneema® DM20 based polymer rope. In some other examples, a blade connecting member may comprise a composite member such as a pultrusion, or alternatively a blade connecting member may comprise a metal rod, to name a few possible examples.

[0023] Further, in some examples the blade connecting member connected between the connecting points of the pair of wind turbine blades may be formed of a plurality of components. For example, the blade connecting member may comprise a first connecting component connected to a first blade, and a second connecting component connected to a second blade. The first and second connecting components may be connected together, directly or indirectly, to form the blade connecting member. For example, the first and second connecting components may be connected together via a coupling component. In such an example, the winch line, or a tension member, may be connected to the coupling component of the blade connecting member. Such modularization of the blade connecting member and tension adjustment system may be advantageous for assembly and for maintenance of the wind turbine.

[0024] In some examples, the tension adjustment system may further comprise a gear drive. The electric motor may be coupled to the winch reel via the gear drive. For example, the gear drive may comprise a gearing ratio of at least 1 :500, preferably at least 1 :1000, or more preferably at least 1 :1500 between an input shaft coupled to the electric motor and an output shaft coupled to the winch reel. Accordingly, the gear drive may be configured to increase the torque produced by the motor to drive the winch reel. In some examples this may mean that the motor size can be reduced, which may be advantageous for packaging the components on the turbine. Further, the winch reel may experience variable torque because the wind turbine blades experience varying loads, such as wind and weight loads, resulting in variable tension in the blade connecting member and connected winch line. In some examples, the gear drive may provide a degree of damping and / or steady state dynamic behaviour during operation of the wind turbine to counteract the variable torque experienced by the winch reel.

[0025] In some examples, the gear drive of a tension adjustment system configured to provide passive damping and / or steady state dynamic behaviour may comprise a gearing ratio between 1 :1250 and 1 :2000 for cost-efficient design. Conversely in examples where the tension adjustment system is configured to actively vary the tension of the blade connecting member during operation of the wind turbine, the gear drive may comprise a gearing ratio of between 1 :500 and 1 :1250. Such a configuration may reduce the rotational speed required of the electric motor and / or may reduce the time taken to drive the winch reel to spool the winch line off and onto the winch reel and thereby adjust the tension in the blade connecting member.

[0026] In some examples, the tension adjustment system may further comprise a variable frequency drive (VFD) unit. The electric motor may be driven by the variable frequency drive unit. A variable frequency drive advantageously facilitates accurate control of the electric motor resulting in accurate control of the rotation of the winch reel, thereby ultimately facilitating accurate control of the tension in the blade connecting member. In particular, a variable frequency drive may facilitate varied speed control and smooth operation of the electric motor. This is advantageous for adjusting the tension in the blade connecting member smoothly, without jolting the winch reel and winch line which could cause unnecessary localized peak loads during the adjustment.

[0027] In some examples, the wind turbine may comprise a turbine controller. The turbine controller may receive input signals from various sensors, and may control operation of the wind turbine based on the input signals received from the sensors. For example, the turbine controller may be configured to receive input signals from sensors including any of a wind speed sensor, a wind direction sensor, an ambient temperature sensor, a winch reel spooling sensor measuring a rotary position of the winch reel, and a load cell arranged to measure torque and / or strain representative of the tension in the blade connecting member. The turbine controller may be connected to the electric motor of the tension adjustment system to facilitate control of the tension in the blade connecting member, based on input signals received from the sensor(s), by driving the motor to rotate the winch reel and thereby spool the winch line off and onto the winch reel. In some preferred examples, where the tension adjustment system includes a variable frequency drive unit, the turbine controller may be connected to the electric motor via the variable frequency drive unit. In other words, the turbine controller may control the variable frequency drive unit and thereby control the electric motor of the tension adjustment system.

[0028] In some examples, the wind turbine may further comprise at least one rotation lock coupled to the winch reel. The at least one rotation lock is arranged to restrict rotation of the winch reel when the at least one rotation lock is engaged. As described later in more detail, configurations of the tension adjustment system including a rotation lock may provide various different advantages. In general, inclusion of a rotation lock means that a desired blade connecting member tension can be maintained without requiring active, continuous, operation of the electric motor or other components to restrict rotation of the winch reel. Accordingly, in use, after operating the tension adjustment system to set the tension in the blade connecting member, the rotation lock may be engaged such that the tension adjustment system then essentially operates as a passive system, with the tension in the blade connecting member being maintained by the rotation lock inhibiting rotation of the winch reel. Such a configuration may simplify operation of the wind turbine and tension adjustment system, and in some examples may also reduce wear on components such as the gear drive and electric motor.

[0029] As previously described, the term “coupled” used herein may refer to direct attachment of two components, or indirect attachment of two components, for example via one or more other components, unless explicitly stated otherwise. Accordingly, the rotation lock may be directly coupled to the winch reel in some examples. Alternatively, in some other examples, the rotation lock may be coupled to the winch reel via one or more other components, such as a shaft for example. In either example it should be understood that the function of each rotation lock described herein is to restrict rotation of the winch reel when engaged.

[0030] In some examples the electric motor may be coupled to the winch reel via a rotation lock. In other words, a rotation lock may be coupled to the winch reel between the winch reel and the electric motor. Accordingly, the tension adjustment system may be configured such that, in use, engagement of the rotation lock may facilitate isolation of the electric motor from the loaded components such as the winch reel and the winch line. Engagement of a rotation lock located in this position may therefore enable servicing and / or replacement of the electric motor whilst the blade connecting member tension is maintained via the rotation lock, winch reel and winch line.

[0031] As previously described, in some examples the electric motor may be coupled to the winch reel via a gear drive. In such examples, the tension adjustment system may comprise a rotation lock coupled between the gear drive and the winch reel. Accordingly, such a rotation lock may be engaged, in use, to isolate the gear drive from the winch reel, during operation of the wind turbine. As previously described, during operation the blade connecting member may experience variable tension resulting from variable loads, such as wind loads and weight loads, experienced by the blades. The variable tension may cause some, small, rotational movement of the winch reel. An engaged rotation lock coupled between the gear drive and the winch reel may isolate the gear drive from the winch reel such that the gear drive is not exposed to excessive wear resulting from the variable tension rotating the winch reel during turbine operation.

[0032] Alternatively, in some examples in which the tension adjustment system comprises a gear drive, the tension adjustment system may comprise a rotation lock coupled to the winch reel between the gear drive and the electric motor. For example, the gear drive may be coupled to the winch reel, and the electric motor may be coupled to the gear drive via a rotation lock. Accordingly, in some examples the tension adjustment system may be configured such that, in use, the rotation lock can be engaged to thereby isolate the electric motor from the gear drive and the winch reel. In such examples, if no further rotation lock is applied between the gear drive and the winch reel, the gear drive may provide a degree of damping and / or spring force when tensile loads are applied to the winch line from the blade connecting member during operation of the turbine. In some examples, the electric motor may be coupled to a first side of the winch reel, and the tension adjustment system may comprise a rotation lock coupled to an opposing second side of the winch reel. Accordingly, the tension adjustment system in such an example may be considered to include a rotation lock “after” the winch, in particular after the winch reel, going in a direction from the electric motor to the winch. In some preferred examples, the rotation lock coupled to the second side of the winch reel may be coupled directly to the winch reel. A rotation lock positioned in such a way may advantageously be located as close to the winch reel as possible, with no intermediate components between the rotation lock and the winch reel. Such a rotation lock may provide a particularly secure and rigid restraint of the winch reel for maintaining the tension of the blade connecting member.

[0033] Additionally a rotor lock arranged on the second side of the winch reel may facilitate maintenance and / or replacement of all components coupled to the winch reel on the first side of the winch reel. For example, the tension in the blade connecting member may be maintained by engaging the rotation lock on the second side of the winch reel, thereby facilitating maintenance and / or replacement of components such as the electric motor or gear drive, whilst the tension is maintained.

[0034] It should be appreciated that in some examples the electric motor may be coupled to the first side of the winch reel via a rotation lock, as described previously, and an additional rotation lock may be coupled to the opposing second side of the winch reel, as described previously. Accordingly, in some examples the tension adjustment system may comprise a plurality of rotation locks.

[0035] In some examples, the tension adjustment system may further comprise a spring coupling. The electric motor may be coupled to the winch reel via the spring coupling. Coupling the electric motor to the winch reel via a spring coupling may be advantageous for facilitating smooth operation of the winch reel. For example, when driven by the electric motor, the spring coupling may dampen any jolts in the rotational movement provided by the electric motor, to smoothen the supply of torsional power to the winch reel. Accordingly, the spring coupling may help to minimise unnecessary localized peak loads in the winch line and blade connecting member during adjustment of the tension by operating the electric motor. Further, the spring coupling may also serve to protect the electric motor from variations in torque resulting from variable tension in the blade connecting member and winch line in use (e.g. due to blade movement caused by wind gusts or sudden changes in wind direction), thereby improving longevity of the electric motor and associated components. In some examples, the spring coupling may advantageously allow for a greater tolerance in the position of the winch reel relative to components such as the electric motor and / or gear drive. For example, the spring coupling may alleviate minor misalignments between such components whilst still transferring torsional power effectively.

[0036] In some examples, where the blade connecting members and / or the tension member or the winch line is a component with a very high stiffness, the introduction of a spring element may advantageously increase the passive elasticity of the system and hence effectively reduce the stiffness of the blade connecting members and / or the tension member or the winch line.

[0037] In some examples, the tension adjustment system may comprise a rotation lock and the electric motor may be coupled to the spring coupling via the rotation lock. In other words, the tension adjustment system may comprise a rotation lock coupled between the spring coupling and the electric motor. It follows that in some examples the electric motor may therefore be coupled to the winch reel via a rotation lock and the spring coupling.

[0038] Such a configuration may facilitate a degree of passive stiffness adjustment, steady state dynamic behaviour or dampening, via the spring coupling. For example, the spring coupling may comprise an output side coupled to the winch reel and an input side coupled to the electric motor, via the rotation lock. The rotation lock may be engaged to isolate the electric motor and any other components between the electric motor and rotation lock, such as the gear drive in some examples, from the spring coupling and any components coupled to the output side of the spring coupling, such as the winch reel for example. The rotation lock may also substantially restrict but not entirely prohibit rotation of the winch reel. As such, with the rotation lock engaged, rotation of the winch reel may be limited by the biasing force of the spring coupling, but not be entirely prohibited, in some examples. Therefore, the winch line may be incrementally wound off and onto the winch real in dependence on the balance between tension in the blade connecting member and the biasing force of the spring coupling. Accordingly, this configuration may provide some damping and flexibility in the tension maintained in the blade connecting member in a substantially passive manner, without actively controlling the electric motor to rotate the winch reel.

[0039] In some examples, the tension adjustment system may not comprise a separate spring coupling component. For example, the electric motor may be coupled to the winch reel via a shaft, and the shaft may be designed or configured with a specific torsional stiffness such that the shaft itself may be considered to provide a spring coupling and the associated advantages thereof described previously. Accordingly, it should be appreciated that references herein to a spring coupling may also include a shaft having a torsional stiffness comparable to a spring coupling. However, a separate spring coupling component may facilitate simplified maintenance of the tension adjustment system, because a separate spring coupling can be isolated using one or more rotation locks as previously described, and can be repaired or replaced in a simple manner without requiring disassembly of a plurality of components from a common shaft.

[0040] In some examples, the tension adjustment system may further comprise an emergency brake line. The winch line may be spooled onto the winch reel in a first spool direction, and the emergency brake line may be spooled onto a portion of the winch reel in a second spool direction substantially opposite to the first spool direction. Accordingly, the tension adjustment system may be configured such that the emergency brake line may be simultaneously spooled onto the portion of the winch reel when the winch line is spooled off the winch reel.

[0041] The emergency brake line provides a failsafe to limit rotation of the winch reel in the unlikely event that the winch reel is unrestricted and therefore at risk of completely unspooling and causing complete loss of tension in the blade connecting member. Accordingly, the tension adjustment system may be configured to prevent complete loss of tension in the blade connecting member in the event that the winch reel becomes unrestricted. Reasons for an unrestricted reel could include failure of the electric motor, gear drive, one or more rotation locks, or failure of a shaft coupling such components to the winch reel. Preventing complete loss of tension in the blade connecting member is preferable because a completely loose, or slack, blade connecting member could damage a wind turbine blade or other component of the wind turbine.

[0042] In some examples, the emergency brake line may be attached to another component of the tension adjustment system. However, alternatively, in some preferred examples the emergency brake line may be attached to the hub, or another wind turbine component that is fixed and stationary relative to the winch. Accordingly, the emergency brake line may be described as being anchored to the hub, in some examples. In some preferred examples, the emergency brake line may be removably attached to the winch reel and / or to the hub or other wind turbine component. Removably attaching the emergency brake line means that the brake line can be detached during assembly and service operations where the winch line is deliberately spooled off the winch reel further than in normal operation of the tension adjustment system when simply adjusting the tension.

[0043] In some examples, the winch line spooled onto the winch reel may define a first spooled length. The first spooled length may be variable within a first spooled length range when spooling the winch line off and onto the winch reel to adjust the tension in the blade connecting member. Further, the emergency brake line may be attached to the hub, and the emergency brake line spooled onto the portion of the winch reel may define a second spooled length. The second spooled length may be variable within an operational range which is greater than the first spooled length range. As such, the emergency brake line is preferably configured such that the tension adjustment system can vary the tension in the blade connection member by varying the first spooled length within the first spooled length range, throughout operation of the turbine, without exceeding the operational range of the emergency brake line. Accordingly, the tension adjustment system can be operated during normal operation without interference from the emergency brake line.

[0044] In some examples, the winch line may define a maximum first spooled length which is the maximum length of the winch line that can be spooled off and onto the winch reel. Further, the operational range of the emergency brake line may be defined, at least in part, by a maximum second spooled length which is the maximum length of the emergency brake line that can be spooled onto the portion of the winch reel. In some preferred examples, the maximum second spooled length may be shorter than the maximum first spooled length. Such a configuration helps to ensure that, in the event of an unrestricted winch, the amount, i.e. length, of the winch line that is unspooled from the winch reel is less than the maximum first spooled length, because the unspooling of the winch line is limited by the maximum spooled length of the emergency brake line. This ensures that at least some tension is maintained, such that the winch line and blade connecting member are not completely loose. For example, the tension adjustment system may be configured to achieve and maintain an operating tension in the blade connecting member. The emergency brake line may be configured with a maximum second spooled length that ensures that, even with an unrestricted winch, the winch line may only be unspooled to release a maximum of 50% to 90% of the operating tension in the blade connecting member, such that at least 10% to 50% of the operating tension is maintained.

[0045] In some examples, the emergency brake line may be releasably attached to the hub. Accordingly, in some examples the tension adjustment system may be configured such that the emergency brake line can be detached from the hub, for example during an assembly or maintenance operation, to thereby allow the winch line to be unspooled from the winch reel beyond the first spooled length range.

[0046] In some examples, the wind turbine may further comprise a speed activated brake arranged to halt the spooling of the emergency brake line onto the portion of the winch reel when spooling of the emergency brake line reaches a predetermined threshold speed. The predetermined threshold speed may be indicative of an unrestricted winch reel, which may occur for example in the event of a rotation lock failure. Accordingly, the tension adjustment arrangement may be configured to prevent undue unspooling of the winch line in the event that the winch reel becomes unrestricted. Whilst a speed activated brake may introduce slightly more complexity, such a brake may advantageously provide faster reaction times for stopping the winch reel rotating, thereby stopping the winch line from unspooling further off the winch reel. As such, inclusion of a speed activated brake may provide the advantage that less tension is released from the blade connecting member, and more tension can be maintained in the blade connecting member, in the event of an unrestricted winch reel.

[0047] For example, the emergency brake line may be spooled off an emergency brake line reel and onto the portion of the winch reel during normal operation of the tension adjustment system, when the winch line is spooled off the winch reel. The speed activated brake may be configured to activate, and thereby stop rotation of the emergency brake line reel, when the rotational speed of the emergency brake line reel exceeds the threshold. Additionally or alternatively, in some examples, the speed activated brake be a linear brake, and may be configured to activate, for example by clamping the emergency brake line, when a linear speed of the emergency brake line exceeds the threshold.

[0048] The emergency brake line reel may be comprised in an emergency brake line retractor assembly. The emergency brake line retractor assembly may be configured to retract the emergency brake line. For example, the emergency brake line reel may be rotationally biased to thereby motivate the reel to spool the emergency brake line onto the emergency brake line reel. Accordingly, the biased emergency brake line reel may help to maintain some tension in the emergency brake line during operation, i.e. during spooling the emergency brake line off and onto the emergency brake line reel. This may be advantageous to ensure that the emergency brake line does not get tangled or trapped in use.

[0049] The wind turbine may further comprise an auxiliary power supply electrically connected to the electric motor. Inclusion of an auxiliary power supply may facilitate use of the tension adjustment system in situations where power from the wind turbine or grid is not available. As such, the auxiliary power supply may be a back-up power supply. For example, the tension adjustment system may be operated using power from the auxiliary power supply during installation of the wind turbine, during a service operation, or in the event of a maintenance issue or grid failure, to name some non-limiting examples. Accordingly, inclusion of an auxiliary power supply may provide additional flexibility for using the tension adjustment system and may improve reliability.

[0050] In some preferred examples, the auxiliary power supply may be electrically connected to the electric motor via a controller. In some examples, the auxiliary power supply may comprise a battery. Alternatively, in some examples the auxiliary power supply may comprise a capacitor, such as an ultracapacitor.

[0051] In some examples, the tension adjustment system may be configured to electrically charge or recharge the auxiliary power supply during operation of the adjustment system. For example, when the tension adjustment system is operated to reduce tension in the blade connecting member by spooling the winch line off the winch reel, rotation of the winch reel may be driven primarily by the tension in the blade connecting member pulling the connected winch line off the winch reel. Such rotation of the winch reel may drive a shaft coupled to the electric motor. The electric motor may be operable as an electric generator, in some examples. Accordingly, the electric motor, i.e. generator, may be configured to produce power from the shaft driven by rotation of the winch reel during operation of the tension adjustment system, and such generated power may be stored in the auxiliary power supply for subsequent use, when required.

[0052] In some examples, the wind turbine may further comprise a load cell positioned to measure torque experienced by the winch reel. For example, the load cell may be positioned between a rotation lock and the winch reel such that the load cell can measure the torque experienced by the winch reel irrespective of whether the rotor lock is engaged or disengaged. For example the load cell may be positioned on a shaft coupling the winch reel to a rotation lock and other components of the tension adjustment system. A load cell configured to measure the torque experienced by the winch reel may facilitate measurement of the tension in the winch line and thereby also the tension in the blade connecting member. The load cell may be coupled to a controller operably coupled to the electric motor such that the electric motor may be configured to rotate the winch reel and thereby spool the winch line off and onto the winch reel based, at least in part, on the torque measured by the load cell. In some preferred examples, the load cell may be located in the hub. Accordingly, the tension adjustment system, and in particular the load cell, may facilitate indirect measurement of the tension in the blade connecting member whilst the measuring apparatus, i.e. the load cell and associated wiring, remain substantially protected from the external environment.

[0053] In some examples, the wind turbine may comprise a load cell arranged between the tension adjustment system and the hub. Accordingly, the load cell may be arranged to measure a force applied to the tension adjustment system, to pull the tension adjustment system from the hub. The force applied to the tension adjustment system may be resultant of the tension in the blade connecting member. Accordingly, measuring the force applied to the tension adjustment system to pull the system from the hub may facilitate indirect measurement of the tension in the blade connection member.

[0054] In some examples, the tension adjustment system may further comprise a winch reel spooling sensor positioned to measure a rotary position of the winch reel. In some examples, the winch reel spooling sensor may be an angular or rotary position sensor. For example, the winch reel spooling sensor may comprise a rotary encoder. The winch reel spooling sensor may be integrated with the winch, in some examples. As such, the winch reel spooling sensor may be arranged to measure the rotary position of the winch reel directly. Additionally or alternatively, the winch reel spooling sensor may comprise a sensor, such as a rotary encoder, configured to measure rotational movement of a shaft associated with the winch reel. As such, in some examples the winch reel spooling sensor may be configured to measure the rotary position of the winch reel indirectly, i.e. via another associated component.

[0055] A winch reel spooling sensor may preferably be configured to measure the rotary position of the winch reel during rotation of the winch reel when the winch line is spooled off and onto the winch reel to adjust the tension in the blade connecting member. Accordingly, the winch reel spooling sensor may be calibrated such that the free length of the winch line can be determined based on the rotary position of the winch reel measured by the spooling sensor.

[0056] In some examples, inclusion of both a winch reel spooling sensor and a load cell may facilitate simultaneous measurement of both rotary position of the winch reel (and thereby the free length of the winch line), and the torque experienced by the winch reel (representing the tension in the blade connecting member). Such a configuration may therefore facilitate calibrated measurement of the torque experienced by the winch reel at various different rotational positions (i.e. various different free lengths). Such calibrated measurement may be helpful for evaluating performance and / or degradation of the blade connecting member and / or winch line. For example, such a configuration may facilitate condition monitoring, such as monitoring of the elongation of the blade connecting member and / or winch line, over time. Advantageously, the winch reel spooling sensor and the or each load cell may be operable to measure the respective angular position and / or torque without dependence on the active state of the tension adjustment system. Accordingly, even if the electric motor and / or variable frequency drive of the tension adjustment system are not active or engaged, i.e. when the tension adjustment system is in a passive state, the winch reel spooling sensor and the or each the load cell may still be operable to measure the respective position and / or torque.

[0057] In some examples, the rotor may comprise three wind turbine blades attached to the hub and three blade connecting members. Each blade connecting member may be connected between corresponding connection points of a pair of wind turbine blades. The wind turbine may further comprise three tension adjustment systems. Each respective tension adjustment system may be attached to the hub and configured to adjust the tension in a respective blade connecting member independent of the other tension adjustment systems.

[0058] It will be appreciated that all of the features and advantages described previously in relation to examples of the tension adjustment system are equally applicable to each of the three tension adjustment systems in this example. As such, each tension adjustment system in this example comprises at least an electric motor and a winch, wherein the winch comprises a winch reel and a winch line, wherein the winch line is attached to the winch reel and to a respective blade connecting member, and wherein the respective electric motor is coupled to a respective winch reel to rotate the winch reel and thereby spool the respective winch line off and onto the winch reel and to thereby adjust the tension in the respective blade connecting member.

[0059] The tension adjustment system described herein is advantageously compact, meaning that the three separate tension adjustment systems in this example can fit in or on the hub for controlling the tension in each of the three respective blade connecting members.

[0060] In some examples, each of the tension adjustment systems may be communicably coupled to a controller, such as the turbine controller. Each tension adjustment system may be independently controlled and operated by the controller, i.e. independent of the other tension adjustment systems. The tension in each blade connecting member may therefore be independently adjusted by a respective tension adjustment system, for example in dependence on the specific loading conditions of the respective blade connecting member.

[0061] For example, as previously described, the turbine controller may control the tension in a respective blade connecting member based on input signals received from sensors such as wind speed sensor, a wind direction sensor, an ambient temperature sensor, winch reel spooling sensors, and load cells. In some examples, each tension adjustment system may comprise a load cell and / or a winch reel spooling sensor. The or each sensor of each tension adjustment system may be communicably coupled to the controller. Accordingly the controller may be configured to receive input data indicative of the tension in each of the blade connecting members. Accordingly the controller may be configured to vary the tension in a blade connecting member by controlling a respective tension adjustment system based on sensor data received from the respective tension adjustment system.

[0062] In some examples, the controller may be configured to vary the tension in each of the blade connecting members by controlling a respective tension adjustment system based on sensor data received from all of the tension adjustment systems and optionally other wind turbine sensors. Accordingly, the controller may be configured to control the tension in the blade connecting members based on a complete load picture representing the respective tensions in all of the blade connecting members.

[0063] Whilst each tension adjustment system may be configured to independently adjust the tension in a respective blade connecting member, in some examples, the wind turbine may optionally be configured such that all of the tension adjustment systems can be operated in unison, i.e. simultaneously. This may help to ensure even application of tension to each of the blade connecting members, thereby ensuring even loading of the wind turbine blades.

[0064] In some preferred examples, the or each tension adjustment system may be attached to the hub in a position upwind of each connecting point of the respective blades. Advantageously, such a configuration may cause the tension in the blade connecting members to pull the wind turbine blades upwind, thereby reducing the risk of the blade striking a tower of the wind turbine in a high wind situation. In some examples, the wind turbine may comprise an upwind hub extension. In other words, the wind turbine may comprise an extension component or arrangement that extends from the hub in an upwind direction. The tension adjustment system may be coupled to the hub via the upwind extension arrangement. Advantageously, such a configuration may cause the tension in the blade connecting members to pull the wind turbine blades further upwind, thereby further reducing the risk of the blade striking a tower of the wind turbine in a high wind situation. Additionally, such a configuration may effectively increase the stiffness of the wind turbine blade in a spanwise, i.e. longitudinal, direction of the blade. In particular, connecting the blade connecting member to the hub via a tension adjustment system attached to an upwind hub extension may increase the stiffness of an inboard portion of the blade, between the connection point and the blade root.

[0065] As previously described, in some examples, each wind turbine blade may be rotatable, i.e. pitchable, relative to the hub. Accordingly, the wind turbine may comprise a pitch mechanism for rotating each respective blade relative to the hub. In some preferred examples, the pitch mechanisms may be electrical pitch mechanisms. Advantageously, in such examples the existing electrical infrastructure in the wind turbine, included for the pitch mechanisms, can be reused for the electrical motor of the tension adjustment system, thereby minimising the engineering effort required to include the tension adjustment system in the turbine.

[0066] Brief description of the drawings

[0067] Examples of the present invention will now be described by way of non-limiting example only, with reference to the accompanying figures, in which:

[0068] Figure 1 is a schematic perspective view of a wind turbine comprising blade connecting members connected between pairs of wind turbine blades and tension adjustment systems arranged to adjust the tension in the blade connecting members;

[0069] Figure 2 is a schematic diagram of an example of a tension adjustment system;

[0070] Figure 3 is a schematic diagram of another example of a tension adjustment system;

[0071] Figure 4 is a schematic diagram of an example of a tension adjustment system including an emergency brake line.

[0072] Detailed description

[0073] Figure 1 shows a schematic perspective view of a wind turbine 10. The wind turbine 10 features a nacelle 12 and a rotor 14 which is mounted to the nacelle 12. The rotor 14 includes a plurality of wind turbine blades 16 attached to a hub 18. Each blade 16 extends between a blade root 20 and a blade tip 22. The blade root 20 may be attached to the hub 18, for example via a pitch bearing or pitch mechanism in some examples (not shown). Each blade 16 also includes a connection point 24 which is located between the root 20 and tip 22 of the respective blade 16.

[0074] The wind turbine 10 additionally includes a blade connecting member 26 connected between corresponding connection points 24 of a pair of wind turbine blades 16. In some examples, as shown in Figure 1 , the rotor 14 may comprise three wind turbine blades 16. Accordingly the rotor 14 may include three blade connecting members 26, and each connecting member 26 may be connected between corresponding connection points 24 of a pair of wind turbine blades 16. A blade connecting member 26 may be a blade connecting cable. As such, the rotor 14 mounted to the nacelle 12 may therefore be referred to as a cable stayed rotor 14, in some examples.

[0075] Each blade connecting member 26 takes up a proportion of the load experienced by the connected blades 16 in use, and provides a load path via which to transfer loads between the blades 16. In other words, connecting the blade connecting members 26 between neighbouring blades 16 means that some of the load experienced by each blade 16 may be transferred between the blades 16 such that some of the blade loads may be shared. A blade connecting member 26 connected to the hub 18, for example via a tension adjustment system 28 described below, advantageously provides an additional load path to the hub 18 which bypasses the blade root 20 and a portion of the blade 16 between the blade root 20 and the connection point 24. As such, the blade connecting member 26 and associated tension adjustment system 28 facilitates a transfer, or unloading, of some of the blade loads to the hub 18.

[0076] For example, each blade connecting member 26 may be connected to the hub 18 via a respective tension adjustment system 28. Accordingly, a portion of the blade loads taken up by a respective blade connecting member 26 may be transferred to the hub 18 via the respective tension adjustment system 28, thereby bypassing the blade root 20. With reference to the example of Figure 1 , the wind turbine 10 may include three separate tension adjustment systems 28 in some examples. Each tension adjustment system 28 is attached to the hub 18 and configured to adjust the tension in a respective blade connecting member 26, as will now be described.

[0077] With additional reference to the schematic diagram in Figure 2, each tension adjustment system 28 includes an electric motor 30 and a winch 32. The winch 32 includes a winch reel 34 and a winch line 36. The winch line 36 is attached to both the winch reel 34 and a respective blade connecting member 26. The electric motor 30 is coupled to the winch reel 34 and is thereby operable to drive, i.e. rotate, the winch reel 34. It follows that the electric motor 30 and winch reel 34 are configured to spool the winch line 36 off and onto the winch reel 34. Such operation of the tension adjustment system 28 varies a free length L of a free portion 38 of the winch line 36 to thereby facilitate adjustment of the tension in the respective blade connecting member 26. Notably, in examples comprising a plurality of tension adjustment systems 28, as shown in the example of Figure 1 , each tension adjustment system 28 may be configured to adjust the tension in a respective blade connecting member 26 independent of the other tension adjustment systems 28.

[0078] As shown most clearly in Figure 2, in some examples the electric motor 30 of the tension adjustment system 28 may be coupled to the winch reel 34 via a gear drive 40. For example, an input component of the gear drive 40, such as an input shaft, may be coupled to the electric motor 30, and an output component of the gear drive 40, such as an output shaft, may be coupled to the winch reel 34. It should be appreciated that the term coupled may include either direct coupling or indirect coupling. For example, the output shaft of the gear drive 40 may be coupled to the winch reel 34 via one or more other components, including a drive shaft 42 for example. The gear drive 40 may increase the torque applied to the winch reel 34 when rotating the winch reel 34 to spool the winch line 36 off and onto the winch reel 34 to adjust the tension in the blade connecting member 26. Further, operation of the electric motor 30 may be improved by the inclusion of a variable frequency drive (VFD) unit 44 for driving, i.e. controlling, the electric motor 30. Such a VFD unit 44 may provide smooth and varied speed control of the electric motor 30.

[0079] With reference still to Figure 2, in some examples the tension adjustment system 28 may include a load cell 46 configured to measure torque and / or strain which is representative of the tension in the blade connecting member 26. For example, as shown in Figure 2, the load cell 46 may be positioned to measure torque experienced by the winch reel 34. Accordingly, the load cell 46 may be positioned on or in the winch reel 34, or on an associated shaft such as drive shaft 42, for example. In some other examples (not shown), a load cell 46 may be attached between the tension adjustment system 28 and the hub 18 to measure the load applied to the tension adjustment system 28 by the associated blade connecting member 26. Such an arrangement may also facilitate measurement of the tension in the blade connecting member 26. Inclusion of a load cell 46 with the tension adjustment system 28 advantageously facilitates measurement of the tension in the respective blade connecting member 26 without requiring sensors and associated electronic components at the blade connecting member 26, i.e. outboard of the hub 18.

[0080] In some examples the tension adjustment system 28 may include a winch reel spooling sensor 48 positioned to measure a rotary position of the winch reel 34. For example, the winch reel spooling sensor 48 may include a rotary encoder integrated with the winch reel 34 and / or a shaft 42 associated with the winch reel 34. The winch reel spooling sensor 48 may provide data from which the free length L of the free portion 38 of the winch line 36 can be calculated, in use. This may be helpful for condition monitoring and for estimating the tension of blade connecting member 26 following operation of the tension adjustment system 28.

[0081] As previously described, components of the tension adjustment system 28 described as “coupled” together may be directly or indirectly coupled to one another. In some examples, components of the tension adjustment system 28 may be coupled to one another via one or more shafts, such as a drive shaft 42. As will now be described in more detail with reference to Figure 3, in some examples one or more other components, such as rotation locks 50 and / or spring couplings 52, may be coupled between components of the tension adjustment system 28, for example to a shaft such as drive shaft 42.

[0082] With reference now to Figure 3, in some examples the tension adjustment system 28 may include one or more rotation locks 50 coupled to the winch reel 34. Advantageously, a rotation lock 50 may be arranged such that rotation of the winch reel 34 is restricted when the rotation lock 50 is engaged. This means that in some examples, tension in the blade connecting member 26 can be maintained without active control and operation of the electric motor 30. For example, as shown in Figure 3, the electric motor 30 may be coupled to the winch reel 34 via a first rotation lock 50a. When the first rotation lock 50a is engaged the electric motor 30 may therefore be isolated from the winch reel 34.

[0083] Further, in some examples the tension adjustment system 28 may additionally or alternatively include a second rotation lock 50b. For example, the electric motor 30 may be coupled to a first side 54a of the winch reel 34, and the second rotation lock 50b may be coupled to an opposing second side 54b of the winch reel 34. A rotation lock 50b positioned in this way may provide a particularly rigid restraint restricting rotation of the winch reel 34.

[0084] Referring still to Figure 3, the electric motor 30 may be coupled to the winch reel 34 via a spring coupling 52. The spring coupling 52 may smoothen operation of the tension adjustment system 28 by damping fluctuations in torque between the electric motor 30 and winch reel 34. Further, in some examples the electric motor 30 may be coupled to the spring coupling 52 via a rotation lock 50, such as the first rotation lock 50a described previously. Such an arrangement may facilitate some small rotation of the winch reel 34 when the first rotation lock 50a is engaged (if rotation lock 50b is not engaged and / or present), and rotation of the winch reel 34 may be restricted by the biasing force of the spring coupling 52. As such, a spring coupling 52 may also facilitate some damping on the tension in the blade connecting member 26 by damping rotation of the winch reel 34.

[0085] With reference to Figure 4, the tension adjustment system 28 may be configured such that the winch line 36 is wound, i.e. spooled, onto the winch reel 34 in a first spool direction 56a. As such, spooling the winch line 36 onto the winch reel 34 in the first direction 56a may increase the tension in the associated blade connecting member 26. It follows that rotation of the winch reel 34 in an opposing direction may unspool the winch line 36, and thereby reduce the tension in the associated blade connecting member 26.

[0086] In some examples, the tension adjustment system 28 may additionally include back-up means for restricting unintended rotation of the winch reel 34 and unspooling of the winch line 36. For example, the winch reel 34 may be configured such that an emergency brake line 58 is spooled onto a portion 60 of the winch reel 34 in a second spool direction 56b substantially opposite to the first spool direction 56a. As such, the emergency brake line 58 may be simultaneously spooled onto the portion 60 of the winch reel 34 when the winch line 36 is spooled off the winch reel 34. The emergency brake line 58 may be attached to the hub 18 (not shown) to limit spooling of the emergency brake line 58 and thereby limit unspooling of the winch line 36.

[0087] The winch line 36 spooled onto the winch reel 34, i.e. a wound portion of the winch line 36, may define a first spooled length. The first spooled length may be variable within a first spooled length range when the winch line 36 is spooled off and onto the winch reel 34 in use to adjust the tension in the blade connecting member 26. Further, the emergency brake line 58 spooled onto the portion 60 of the winch reel 34 may define a second spooled length. To ensure the tension adjustment system 28 is operable to adjust the tension in the blade connecting member 26 throughout a desired range without limitation by the emergency brake line 58, the tension adjustment system 28 may be configured such that the second spooled length is variable within an operational range which is greater than the first spooled length range. In some examples, the tension adjustment system 28 may include a speed activated brake 62 associated with the emergency brake line 58. For example, the speed activated brake 62 may be arranged to halt the spooling of the emergency brake line 58 onto the portion 60 of the winch reel 34 when spooling of the emergency brake line 58 reaches a predetermined threshold speed. In other words, if the winch line 36 is spooled off the winch reel 34 at a speed beyond a predetermined threshold, such that the emergency brake line 58 is spooled onto the portion 60 of the winch reel 34 at a speed at or beyond a predetermined threshold speed, the speed activated brake 62 may engage and thereby halt the spooling of the emergency brake line 58, thereby also halting unspooling of the winch line 36. Such a configuration may advantageously minimise the amount, i.e. length, of the winch line 36 unintentionally unspooled from the winch reel 34, thereby minimising unintentional loss of tension in the blade connecting member 26.

[0088] In some examples the speed activated brake 62 may be incorporated in an emergency brake line reel 64 which the emergency brake line 58 may be spooled off and onto, as shown in Figure 4. The speed activated brake 62 may be configured to engage and stop rotation of the emergency brake line reel 64 when a rotational speed of the emergency brake line reel 64 exceeds the predetermined threshold. In some other examples (not shown), the speed activated brake 62 may be arranged in line with the emergency brake line 58 such that the emergency brake line 58 passes through the speed activated brake 62. In such an example the brake 62 may be configured to engage when a linear speed of the emergency brake line 58 exceeds the predetermined threshold.

[0089] Finally, with reference again to Figures 2 and 3, in some examples the tension adjustment system 28 may include an auxiliary power supply 66. For example, the auxiliary power supply 66 may include a battery or a capacitor. The auxiliary power supply 66 may be electrically connected to the electric motor 30 to supply power to the motor 30. As such, the wind turbine 10 may be configured such that the tension adjustment system 28 is operable when grid power is not available. Additionally, in some examples the electric motor 30 may be operable as a generator. Accordingly, rotation of the winch reel 34, for example when unspooling the winch line 36 from the winch reel 34 under tension of the attached blade connection member 26, may drive the generator, i.e. electric motor 30, which may charge or recharge the auxiliary power supply 66.

[0090] The description provided herein serves to demonstrate a plurality of possible examples of the present invention. Features described in relation to any of the examples above may be readily combined with any other features described with reference to different examples without departing from the scope of the invention as defined in the appended claims.

Claims

Claims1. A wind turbine (10) comprising a nacelle (12) and a rotor (14) mounted to the nacelle, the rotor comprising a hub (18) and a plurality of wind turbine blades (16) attached to the hub, each blade extending between a blade root (20) and a blade tip (22), and each blade further comprising a connection point (24) located between the blade root and the blade tip; the wind turbine further comprising a blade connecting member (26) connected between corresponding connection points of a pair of wind turbine blades, and a tension adjustment system (28) attached to the hub and configured to adjust the tension in the blade connecting member; wherein the tension adjustment system comprises an electric motor (30) and a winch (32), the winch comprising a winch reel (34) and a winch line (36); wherein the winch line is attached to the winch reel and to the blade connecting member; and wherein the electric motor is coupled to the winch reel to rotate the winch reel and thereby spool the winch line off and onto the winch reel and to thereby adjust the tension in the blade connecting member.

2. The wind turbine (10) of claim 1 , wherein the tension adjustment system (28) further comprises a gear drive (40) , and wherein the electric motor is coupled to the winch reel (34) via the gear drive.

3. The wind turbine (10) of claim 1 or claim 2, wherein the tension adjustment system (28) further comprises a variable frequency drive (VFD) unit (44), and wherein the electric motor (30) is driven by the variable frequency drive unit.

4. The wind turbine (10) of any preceding claim, further comprising at least one rotation lock (50) coupled to the winch reel (34), wherein the at least one rotation lock is arranged to restrict rotation of the winch reel when the at least one rotation lock is engaged.

5. The wind turbine (10) of claim 4, wherein the electric motor (30) is coupled to the winch reel (34) via a rotation lock (50).

6. The wind turbine (10) of claim 4 or claim 5, wherein the electric motor (30) is coupled to a first side (54a) of the winch reel (34), and wherein the tension adjustmentsystem (28) comprises a rotation lock (50) coupled to an opposing second side (54b) of the winch reel.

7. The wind turbine (10) of any preceding claim, wherein the tension adjustment system (28) further comprises a spring coupling (52), and wherein the electric motor (30) is coupled to the winch reel (34) via the spring coupling.

8. The wind turbine (10) of claim 7, wherein the tension adjustment system (28) comprises a rotation lock (50) and wherein the electric motor (30) is coupled to the spring coupling (52) via the rotation lock.

9. The wind turbine (10) of any preceding claim, wherein the winch line (36) is spooled onto the winch reel (34) in a first spool direction (56a), wherein the tension adjustment system (28) further comprises an emergency brake line (58), and wherein the emergency brake line is spooled onto a portion (60) of the winch reel in a second spool direction (56b) substantially opposite to the first spool direction such that the emergency brake line is simultaneously spooled onto the portion of the winch reel when the winch line is spooled off the winch reel.

10. The wind turbine (10) of claim 9, wherein the winch line (36) spooled onto the winch reel (34) defines a first spooled length; wherein the first spooled length is variable within a first spooled length range when spooling the winch line off and onto the winch reel to adjust the tension in the blade connecting member (26); wherein the emergency brake line (58) is attached to the hub (18); wherein the emergency brake line spooled onto the portion (60) of the winch reel defines a second spooled length; and wherein the second spooled length is variable within an operational range which is greater than the first spooled length range.

11. The wind turbine (10) of claim 9 or claim 10, further comprising a speed activated brake (62) arranged to halt the spooling of the emergency brake line (58) onto the portion (60) of the winch reel (34) when spooling of the emergency brake line reaches a predetermined threshold speed.

12. The wind turbine (10) of any preceding claim, further comprising an auxiliary power supply (66) electrically connected to the electric motor (30).

13. The wind turbine (10) of any preceding claim further comprising a load cell (46) positioned to measure torque experienced by the winch reel (34).

14. The wind turbine (10) of any preceding claim, wherein the tension adjustment system (28) further comprises a winch reel spooling sensor (48) positioned to measure a rotary position of the winch reel (34).

15. The wind turbine (10) of any preceding claim, wherein the rotor (14) comprises three wind turbine blades (16) attached to the hub (18) and three blade connecting members (26); wherein each blade connecting member is connected between corresponding connection points (24) of a pair of wind turbine blades; and wherein the wind turbine further comprises three tension adjustment systems (28), each respective tension adjustment system being attached to the hub and configured to adjust the tension in a respective blade connecting member independent of the other tension adjustment systems.

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