Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower, a nacelle and a rotor. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. This rotation is normally transmitted to a generator, either directly ("directly driven") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

In order to extract more energy from the wind, the size of the rotor diameter has increased significantly over the last years by increasing the dimensions of the wind turbine blades. The larger size of the blades implies higher aerodynamic loads that are transferred through the blades into the rotor, nacelle and tower. For example, larger rotor blades may experience increased stresses, deformations and vibrations due to higher aerodynamical moments and others, and these are transmitted to the rotor hub and to the nacelle. The transmitted stresses, deformations and vibrations may lead to challenging design constraints, both in terms of extreme events and fatigue life requirements.

The likelihood of structural failure in wind turbine components, such as a frames of the wind turbine nacelle, is generally compensated by the manufacture of bigger, heavier and more resistant components. In the case of the nacelle frames, this approach leads to an increase in material costs, and a considerable increase in the overall weight of the nacelle. Further, the installation of bigger frames may require providing more robust tower structures so that the tower can safely withstand the nacelle and the loads acting on it. Even if bigger and heavier frames are used, they can still suffer and ultimately fail due to dynamic loads.

The present disclosure provides examples of systems and methods that avoid or reduce premature failure of frames of the wind turbine nacelle and that overcome some of the drawbacks of existing approaches.

In a first aspect, a wind turbine is provided. The wind turbine comprises a wind turbine tower, and a nacelle including a primary frame, wherein the primary frame is connected to the tower. The wind turbine further comprises a secondary structure that is connected to the primary frame and one or more flexible couplings between the primary frame and the secondary structure configured to reduce transmission of deformations from the primary frame to the secondary structure.

According to this first aspect, the one or more flexible couplings installed between the primary frame and the secondary structure of the wind turbine reduce the magnitude of the deformations transferred from the primary frame to the secondary structure, thus reducing the level of stress induced into the secondary structure. The primary frame may suffer asymmetric deformations due to asymmetric loads on the wind turbine rotor. These asymmetric deformations of the primary frame, if transferred to the secondary structure, could lead to significant stresses and strains in the secondary structure. The flexible couplings can avoid or significantly reduce those stresses. Thus, the secondary structure may be manufactured taking into account a narrower load envelope compared with a scenario where the flexible coupling is not provided. As a result, the secondary structure may be manufactured as a lighter frame and may have a simpler structure.

In another aspect, a method of refurbishing a secondary structure of a wind turbine, that is connected to a primary frame is provided. The method comprises cutting a piece of a structural element of the secondary structure that is connected to the primary frame and providing a flexible coupling in a portion of the structural element in replacement of the cut piece. The method then further comprises coupling the secondary structure to the primary frame through the flexible coupling, wherein the flexible coupling is configured to reduce transmission of deformations of the primary frame to the secondary structure.

The method according to this aspect allows refurbishing a secondary structure of a wind turbine in wind turbines that are already in operation. Particularly, the method allows considerably increasing the service life of nacelle frame assemblies.

In yet a further aspect, a secondary structure of a wind turbine is provided. The secondary structure comprises a plurality of structural elements configured to be connected to a primary frame of the wind turbine. At least one of the structural elements comprises a flexible coupling configured to reduce the transmission of horizontal deformations of the primary frame to the secondary frame. And at least another one of the structural elements comprises a flexible coupling configured to reduce the transmission of both horizontal and vertical deformations of the primary frame to the secondary structure.

And in yet a further aspect, a method for reducing oscillations in a secondary structure is provided. The secondary structure is connected to a primary frame of a wind turbine. The method comprises providing one or more flexible couplings between the primary frame and the secondary structure, such that deformations of the primary frame are partially absorbed by the flexible couplings, and at least some of the oscillations of the primary frame are not transmitted to the secondary structure.

Throughout the present disclosure, a primary frame is to be regarded as a load carrying structure arranged in the main load path between the wind turbine rotor and wind turbine tower. the primary frame is the load carrying structure that transmits the loads to the tower, generally through a yaw bearing. A primary frame may also be called a central frame or a main frame.

A secondary structure as used throughout the present disclosure may be regarded as a (load-carrying) structure that is not arranged in the main load path. The secondary structure may be used for accommodating or housing auxiliary systems such as auxiliary mechanical or electrical systems, and in particular the power conversion assembly or components thereof.

Throughout the present disclosure, a vertical direction should be understood as a direction substantially parallel to the direction of gravity, and a horizontal direction should be understood as a direction substantially parallel to ground and perpendicular to the vertical direction.

Reference now will be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the drawings.

As wind strikes the rotor blades <NUM> from a wind direction <NUM>, the rotor <NUM> is rotated about a rotor axis <NUM>. As the rotor blades <NUM> are rotated and subjected to centrifugal forces, the rotor blades <NUM> are also subjected to various forces and moments. As such, the rotor blades <NUM> may deflect and/or rotate from a neutral, or non-deflected, position to a deflected position.

In the example, the wind turbine controller <NUM> is shown as being centralized within the nacelle <NUM>, however, the wind turbine controller <NUM> may be a distributed system throughout the wind turbine <NUM>, on the support system <NUM>, within a wind farm, and/or at a remote-control center. The wind turbine controller <NUM> includes a processor <NUM> configured to perform the methods and/or steps described herein. Further, many of the other components described herein include a processor.

<FIG> is an enlarged sectional view of a portion of the wind turbine <NUM>. In the example, the wind turbine <NUM> includes the nacelle <NUM> and the rotor <NUM> that is rotatably coupled to the nacelle <NUM>. More specifically, the hub <NUM> of the rotor <NUM> is rotatably coupled to an electric generator <NUM> positioned within the nacelle <NUM> by the main shaft <NUM>, a gearbox <NUM>, a high-speed shaft <NUM>, and a coupling <NUM>. In the example, the main shaft <NUM> is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle <NUM>. A rotation of the main shaft <NUM> drives the gearbox <NUM> that subsequently drives the high-speed shaft <NUM> by translating the relatively slow rotational movement of the rotor <NUM> and of the main shaft <NUM> into a relatively fast rotational movement of the high-speed shaft <NUM>. The latter is connected to the generator <NUM> for generating electrical energy with the help of a coupling <NUM>. Furthermore, a transformer <NUM> and/or suitable electronics, switches, and/or inverters may be arranged in the nacelle <NUM> in order to transform electrical energy generated by the generator <NUM> having a voltage between 400V to <NUM> V into electrical energy having medium voltage (<NUM> - <NUM> KV). Said electrical energy is conducted via power cables from the nacelle <NUM> into the tower <NUM>.

The gearbox <NUM>, generator <NUM> and transformer <NUM> may be supported by a main support structure frame of the nacelle <NUM>, optionally embodied as a main frame <NUM>. The gearbox <NUM> may include a gearbox housing that is connected to the main frame <NUM> by one or more torque arms <NUM>. In the example, the nacelle <NUM> also includes a main forward support bearing <NUM> and a main aft support bearing <NUM>. Furthermore, the generator <NUM> can be mounted to the main frame <NUM> by decoupling support means <NUM>, in particular in order to prevent vibrations of the generator <NUM> to be introduced into the main frame <NUM> and thereby causing a noise emission source.

In some examples, the wind turbine may be a direct drive wind turbine without gearbox <NUM>. Generator <NUM> operate at the same rotational speed as the rotor <NUM> in direct drive wind turbines. They therefore generally have a much larger diameter than generators used in wind turbines having a gearbox <NUM> for providing a similar amount of power than a wind turbine with a gearbox.

For positioning the nacelle <NUM> appropriately with respect to the wind direction <NUM>, the nacelle <NUM> may also include at least one meteorological measurement system <NUM> which may include a wind vane and anemometer. The meteorological measurement system <NUM> can provide information to the wind turbine controller <NUM> that may include wind direction <NUM> and/or wind speed. In the example, the pitch system <NUM> is at least partially arranged as a pitch assembly <NUM> in the hub <NUM>. The pitch assembly <NUM> includes one or more pitch drive systems <NUM> and at least one sensor <NUM>. Each pitch drive system <NUM> is coupled to a respective rotor blade <NUM> (shown in <FIG>) for modulating the pitch angle of a rotor blade <NUM> along the pitch axis <NUM>. Only one of three pitch drive systems <NUM> is shown in <FIG>.

In the example, the pitch assembly <NUM> includes at least one pitch bearing <NUM> coupled to hub <NUM> and to a respective rotor blade <NUM> (shown in <FIG>) for rotating the respective rotor blade <NUM> about the pitch axis <NUM>.

Pitch drive system <NUM> is coupled to the wind turbine controller <NUM> for adjusting the pitch angle of a rotor blade <NUM> upon receipt of one or more signals from the wind turbine controller <NUM>. The pitch assembly <NUM> may also include one or more pitch control systems <NUM> for controlling the pitch drive system <NUM> according to control signals from the wind turbine controller <NUM>, in case of specific prioritized situations and/or during rotor <NUM> overspeed.

<FIG> schematically illustrates an exploded view of a primary frame and a secondary structure of a wind turbine provided. The wind turbine comprises a wind turbine tower (not shown) and a primary frame <NUM> connected to the tower. The wind turbine further comprises a secondary structure <NUM> that is connected to the primary frame <NUM> and one or more flexible couplings <NUM> between the primary frame <NUM> and the secondary structure <NUM> configured to reduce transmission of deformations from the primary frame to the secondary structure.

The wind turbine comprises a rotor including a plurality of blades (not shown). In this example, the rotor is located at a first side of the primary frame <NUM>. The secondary structure <NUM> is connected to the primary frame <NUM> at a second side of the primary frame <NUM>. The first side is opposite to the second side.

The first side of the primary frame <NUM> at which the rotor is arranged may typically be an upwind side of the primary frame <NUM>. The second side of the primary frame <NUM> may thus be the downwind side. In other examples, the first side of the primary frame <NUM> may be the downwind side, and the second side of the primary frame <NUM> may be the upwind side.

The wind turbine comprises one or more flexible couplings <NUM> between the primary frame <NUM> and the secondary structure <NUM>. The flexible couplings <NUM> are configured to reduce transmission of deformations from the primary frame <NUM> to the secondary structure <NUM>. Note that the flexible couplings <NUM> in <FIG> have been schematically illustrated as a rectangular box of broken lines for simplicity. <FIG> and the discussion below will provide more details regarding examples of the flexible couplings <NUM> that may be used.

The flexible couplings <NUM> may be or comprise any element that reduces the level of loads and stresses induced from the primary frame <NUM> to the secondary structure <NUM> while it withstands the loads acting on the secondary structure <NUM>. Thus, the flexible couplings may provide a secure connection between secondary structure <NUM> and primary frame <NUM>.

In examples, the flexible couplings <NUM> may comprise an elastomeric material or a material substantially more flexible than the material from which the secondary structure <NUM> is manufactured. Additionally, the flexible couplings <NUM> may comprise a metal spring or a grower washer to allow certain degree of motion between the secondary structure <NUM> and the central frame <NUM>. According to the invention, the flexible couplings <NUM> comprise a sliding mechanism that allows relative displacement between the central frame <NUM> and the secondary structure <NUM>.

In some examples, such as in <FIG>, the primary frame <NUM> may comprise a base structure <NUM> including a substantially horizontal plane configured for connecting to a yaw bearing of the tower. Further, the primary frame may also comprise a front structure <NUM> including a substantially vertical plane configured for connecting to a rotor support structure. Additionally, the secondary structure <NUM> may be connected to the primary frame <NUM> at, or near, the base structure <NUM> and at, or near, the front structure <NUM>.

In further examples, the rotor support structure connected to the vertical plane of the primary frame may be a front frame or an intermediate frame. Depending on the arrangement of the wind turbine components, the rotor support structure may also be a stator structure of a generator stator.

In some examples, the wind turbine may be a direct drive wind turbine. In other examples, the wind turbine according to this example may be a wind turbine with a gearbox.

As can be seen in <FIG>, the secondary structure <NUM> may comprise a helipad region <NUM> configured to support all necessary parts and components to form a helipad. A helipad region <NUM> of a nacelle of a wind turbine is generally a platform on top the nacelle that may be used for supplying and removing parts of components of the wind turbine, and also an area from which personnel may be evacuated. It will be clear that a nacelle housing can encompass the frames <NUM>, <NUM> or part of the frames. The secondary structure <NUM> may additionally comprise other structural components intended to receive other nacelle components.

<FIG> schematically illustrates a secondary structure <NUM> of a wind turbine according to one example. The secondary structure <NUM> comprises a plurality of structural elements <NUM>, <NUM> configured to be connected to the primary frame of the wind turbine (not shown in this figure).

At least one of the structural elements <NUM>, e.g. substantially horizontal beams comprises a flexible coupling <NUM> specifically configured to reduce the transmission of horizontal deformations induced on the primary frame. The flexible coupling <NUM> may have specific flexibility in the horizontal direction to achieve such an effect, i.e. the flexible coupling between primary frame <NUM> and horizontal beams <NUM> may have more flexibility in the horizontal direction than in the vertical direction.

Further, at least another one of the structural elements <NUM>, e.g. vertical struts comprises a flexible coupling <NUM> specifically configured to reduce the transmission of both horizontal and vertical deformations of the central frame <NUM> to the secondary structure <NUM>.

Also illustrated in <FIG>, the secondary structure <NUM> may include a trusswork structure <NUM>. The trusswork structure <NUM> may be designed and manufactured in a variety of ways. In some examples, the trusswork structure <NUM> may comprise trusses between external beams arranged equidistantly from adjacent trusses. The trusses may be metal profiles or metal beams. In other examples, the trusses may be composite or hybrid profiles or beams. The trusses may be connected to beams (both external and internal beams) and/or to each other by any fastening element known in the art, i.e. rivets, spot welding, line welding, and others.

In the example illustrated in <FIG>, at least one of the flexible couplings <NUM> may comprise a silentblock. Examples of silentblocks will be discussed in more detail in relation with <FIG>.

In some examples, at least one of the flexible couplings <NUM> is configured to reduce the transmission of deformations and vibrations specifically in a single direction. In some further examples, at least one of the flexible couplings <NUM> is configured to reduce the transmission of deformations and vibrations in at least two directions.

Additionally, the flexible couplings <NUM> substantially reduce the vibrations transmitted from the central frame <NUM> to the secondary structure <NUM> in a frequency range that has a significant influence in the level of stress/damage induced into the secondary frame. Specifically, the frequency range may be between <NUM> and <NUM>.

<FIG> illustrates a detailed view of a flexible coupling <NUM> between a central frame <NUM> and a secondary structure <NUM>. In the above case, the flexible coupling <NUM> comprises a first end coupled to a central frame <NUM>, an intermediate portion including an elastomer material <NUM> and a second end coupled to a secondary structure <NUM>. Thus, deformations in the central frame <NUM> may be at least partially absorbed by the elastomer material <NUM> and the stresses transmitted to the secondary structure <NUM> may be substantially reduced. As previously discussed, other type of flexible couplings <NUM> may be employed for the same purpose, i.e. silentblocks, springs, grower washers, sliding connections and others.

Silentblocks may be formed by an annular cylinder of flexible material inside a considerably rigid casing, i.e. a metallic casing. The flexible material may be connected between two ends of the casing, providing a flexible coupling between the respective ends. In some examples, the silentblocks may comprise an internal crush tube configured to protect the silentblocks from being crushed by the fastener connections that hold it in place. According to the invention, the silentblocks allow sliding at the interface between one fastener connectior and the flexible material.

The flexible coupling <NUM> illustrated in <FIG> is coupled to a horizontal structural element (with reference numeral <NUM> in <FIG>) and has an increased flexibility in a horizontal plane (as compared to e.g. the vertical direction). More relative displacement is allowed in the horizontal plane. Thus, lower stresses are induced into the secondary structure, specifically along the horizontal plane.

<FIG> illustrates a perspective view of a flexible coupling <NUM> standing alone. More precisely, the flexible coupling <NUM> in <FIG> corresponds to the example of the flexible component coupled to the vertical strut <NUM> in <FIG>. The flexible coupling <NUM> in <FIG> comprises a first end <NUM> configured to be connected to a structural element of the secondary structure <NUM> and a second end <NUM> configured to be connected to a structural element of the central frame <NUM>. More precisely, the first end <NUM> may be connected to a substantially vertical structural element <NUM> of the secondary structure <NUM>, whereas the second end <NUM> may be connected at, or near, the base structure <NUM> of the central frame <NUM> (see <FIG>).

<FIG> also shows that the flexible coupling <NUM> may comprise more than one device configured for damping vibrations and mitigate the transmission of associated stresses. More specifically, the flexible coupling <NUM> may comprise two damping devices <NUM>, <NUM>, i.e. two silentblocks. The devices <NUM>, <NUM> may be connected in parallel wherein e.g. a first device <NUM> allows the relative displacement in two directions, i.e. horizontally and vertically, and a second device <NUM> supports the weight of the secondary structure and allows the displacement in a second direction, i.e. vertical direction. The damping characteristics of each of the devices <NUM>, <NUM> may be chosen such as to damp deformation or vibrations of different amplitudes and frequencies. Further, the devices <NUM>, <NUM> may be also configured to withstand different maximum loads acting on them. For example, the second device <NUM> may be configured to withstand higher loads than the first device <NUM>, and vice versa. Other arrangement of devices may be chosen to mitigate stresses and vibrations of certain amplitudes, frequencies and direction of propagation.

In further examples, two or more of such damping devices may be arranged in series, i.e. a load path inevitable passes through both of the damping devices. In a parallel arrangement, parallel load paths between the primary frame and secondary structure may be provided.

In some additional examples, the secondary structure <NUM> may comprise flexible couplings <NUM> in all structural elements that are coupled to the central frame <NUM>. Alternatively, the secondary structure <NUM> may comprise flexible couplings <NUM> in some of the structural elements that are coupled to the central frame <NUM>. In this case, other types of connections between the central frame <NUM> and the secondary structure <NUM> may be employed, i.e. partially rotatable connections.

<FIG> is a flow diagram of an example of a method <NUM> for refurbishing a secondary structure <NUM> of a wind turbine <NUM> according to the present disclosure. The method <NUM> comprises, at block <NUM>, cutting a piece of a structural element <NUM>, <NUM> of the secondary structure <NUM> that is be connected to a primary frame <NUM>. Further, the method <NUM> also comprises, at block <NUM>, providing a flexible coupling <NUM> in a portion of the structural element <NUM>, <NUM> in replacement of the cut piece.

The method <NUM> may further comprise coupling the secondary structure <NUM> to the primary frame <NUM> through the flexible coupling <NUM>. The flexible coupling, as in other examples of the present disclosure is, according to the invention, specifically configured to limit the transmission of deformations from the primary frame <NUM> to the secondary structure.

Further, the method <NUM> may also comprise supporting the structural element <NUM>, <NUM> since before the cutting <NUM> until the moment of coupling to the primary frame, or even until after.

In some examples, supporting the structural element <NUM>, <NUM> may be performed using one or more jacks, e.g. hydraulic jacks or any other suitable system. Additionally, the steps of cutting <NUM> a piece of a structural element <NUM>, <NUM> and providing <NUM> a flexible coupling <NUM> may be performed in all structural elements configured to be connected to the central frame <NUM>. In such a case, a flexible coupling is provided at each of connection of the primary frame to the secondary structure.

Note that some of the technical features described in relation with the wind turbine, the secondary structure and the flexible couplings of the examples of <FIG> may be included in the method <NUM> for refurbishing a wind turbine, and vice versa.

With the method of refurbishing, at the same time, a method for reducing oscillations in the secondary structure is provided. The secondary structure is connected to a primary frame of a wind turbine. By providing one or more flexible couplings between the primary frame and the secondary structure, deformations of the primary frame are partially absorbed by the flexible couplings, and at least some of the oscillations of the primary frame are not transmitted to the secondary structure.

Claim 1:
A wind turbine (<NUM>) comprising:
a wind turbine tower (<NUM>);
a nacelle including a primary frame (<NUM>), the primary frame being connected to the tower (<NUM>);
a secondary structure (<NUM>) connected to the primary frame (<NUM>); and
one or more flexible couplings (<NUM>) between the primary frame (<NUM>) and the secondary structure (<NUM>) configured to reduce transmission of deformations from the primary frame (<NUM>) to the secondary structure (<NUM>), characterized in that
at least one of the flexible couplings (<NUM>) comprises a sliding mechanism that allows relative displacement between the primary frame (<NUM>) and the secondary structure (<NUM>).