Wind turbine generator with at least one vibration damping device, power plant with said wind turbine generator, vibration damping device, blade with said vibration damping device, method for damping at least one coupled mode vibration of a wind turbine generator, and method for assembling a wind turbine generator

Abstract

The wind turbine generator comprises a support structure including a tower, a nacelle connected to the tower, two or more blades attached to a hub connected to the nacelle, and at least one vibration damping device disposed inside at least one of the two or more blades, the at least one vibration damping device being tuned to one or more common frequencies of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration damping device, wherein the at least one coupled mode vibration at the one or more common frequencies is a combination of vibration of the support structure and vibration of at least one of the two or more blades, and the vibration of the support structure and vibration of at least one of the two or more blades is caused by forces transmitted through the support structure during seismic activity of the ground on which the support structure is located.

Description

[Technical Field]

[0001] Aspects of the invention relate to a wind turbine generator with at least one vibration damping device inside at least one blade, a power plant comprising the wind turbine generator, a vibration damping device, a blade comprising at least one vibration damping device, a method for mitigating at least one coupled mode vibration of a wind turbine generator, and a method for assembling a wind turbine generator. [Background technology]

[0002] For example, wind turbine generators deployed to generate electricity may experience undesirable oscillations / vibrations due to their design, current weather conditions, and / or sudden seismic activity. Such vibrations may affect a single component of the wind turbine generator or may affect the entire wind turbine generator.

[0003] Vibrations can cause dangerously high loads on wind turbine generator components, which can lead to sudden collapse, or at least fatigue damage and possibly shortened life of the wind turbine generator and its components.

[0004] For example, a crack in a component of a wind turbine generator may grow more or less slowly due to such vibrations until it eventually leads to failure of the component. Vibrations therefore add an uncertainty factor to estimates of the loads and wear on various components of the wind turbine generator. Vibrations also cause uncertainty regarding the expected lifespan of the components and / or the wind turbine generator, potentially requiring the design to be stronger, heavier, and therefore more expensive, than would otherwise be the case.

[0005] Also, in extreme cases, severe vibrations can pose an imminent risk of damaging components and thus rendering the wind turbine generator inoperable.

[0006] Power plants containing one or more wind turbine generators can be located in essentially any part of the world, both on land and offshore. Some geographic regions have a higher risk of seismic activity than others. Power plants located in areas with a higher risk of seismic activity naturally have an increased risk of wind turbine generator vibrations caused by seismic activity.

[0007] Seismic activity, for example during an earthquake, can induce forces around the base / foundation of the wind turbine generator tower. These forces can be transmitted through the support structure, including the tower, towards the nacelle and further onto the blades, causing harmful vibrations in both the support structure and the blades.

[0008] The vibrations caused by seismic activity are very difficult to predict due to the sporadic nature of seismic activity. The magnitude of the seismic activity, and the amount of force it generates, is also very difficult to predict and can range from mild seismic activity causing moderate forces and vibrations to very severe seismic activity causing component-destroying forces and vibrations.

[0009] Thus, random, isolated seismic activity, for example associated with an earthquake, can cause alarming and severe vibrations in the wind turbine generator, which can create severe and damaging loads, particularly around the connection between the tower and the nacelle, which can cause damage to the wind turbine generator and its components, particularly around the tower top and nacelle. Summary of the Invention [Problem to be solved by the invention]

[0010] SUMMARY OF THE INVENTION It is an object of the present invention to provide a solution that reduces or overcomes the above-mentioned problems related to vibrations in wind turbine generators caused by seismic activity.

[0011] The above and further objects are solved by the subject matter of the aspects of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims. [Means for solving the problem]

[0012] According to a first aspect of the present invention, there is provided a wind turbine generator comprising: a support structure including a tower; A nacelle connected to the tower; two or more blades attached to a hub connected to a nacelle; at least one vibration damping device disposed within at least one of the two or more blades, the at least one vibration damping device being tuned to one or more common frequencies of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration damping device; the at least one coupled mode vibration at the one or more common frequencies is a combination of vibration of the support structure and vibration of at least one of the two or more blades; The vibration of the support structure and at least one of the two or more blades is caused by forces transmitted through the support structure during seismic activity of the ground in which the support structure is located.

[0013] Thus, according to the present invention, at least one vibration damping device is disposed within at least one of the two or more blades and tuned to one or more common frequencies of at least one coupled mode vibration. The placement of at least one vibration damping device within at least one blade provides an efficient reduction of the experienced coupled mode vibration. This is due to the fact that the targeted coupled mode vibration is significantly affected by the movement of the blades, particularly large, heavy blades. Furthermore, the combination of placing at least one vibration damping device within at least one blade and tuning it to one or more common frequencies of the coupled mode vibration provides the targeted damping effect precisely at the frequencies where it is most affected, i.e., where the coupled mode vibration due to seismic activity has the highest amplitude.

[0014]

[0009] Thereby, coupled mode vibrations caused by seismic activity are efficiently reduced by the at least one vibration damping device, which is particularly adapted to mitigate coupled mode vibrations at the one or more common frequencies thereof. Thus, sometimes surprisingly severe coupled mode vibrations in wind turbine generators, particularly around the connection between the tower and the nacelle, can be significantly reduced by the present invention. Thus, loads at the tower top, for example due to coupled mode vibrations, are efficiently addressed, thereby reducing the risk of damage and fatigue / wear of wind turbine generator components.

[0015] This protection against severe coupled mode vibrations significantly reduces the loads on the rotor, nacelle, and assembly (RNA) components, thereby reducing the risk of violating RNA type certification and avoiding complex design changes in the RNA structure by utilizing at least one vibration damping device according to the present invention.

[0016] Generally, reducing RNA component loadings would otherwise be very difficult to achieve at a particular power plant site, and modifying / reissuing an RNA type certificate for a power plant due to site-specific conditions is a costly and time-consuming process that can be avoided when aspects and embodiments of the present invention are utilized.

[0017] Due to the efficient protection against coupled mode vibrations provided by the at least one vibration damping device, the wind turbine generator does not need to be designed differently to cope with extreme vibrations caused by seismic activity, which may reduce the overall weight and cost of the tower and wind turbine generator.

[0018] According to one embodiment of the present invention, the one or more common frequencies of the at least one coupled mode vibration include frequencies in a range between a first natural frequency and a second natural frequency of the support structure.

[0019] Due to knowledge of the location / frequency of the at least one coupled mode vibration, the at least one vibration damping device can be precisely tuned to that frequency to provide an optimal impact / reduction on the coupled mode vibration. Thus, the at least one vibration damping device may be controlled to protect the wind turbine generator precisely against vibrations with the largest amplitudes, thereby efficiently reducing the most damaging vibrations.

[0020] According to one embodiment of the present invention, the at least one vibration damping device comprises a liquid damper including at least one liquid reservoir.

[0021] Liquid dampers are low-complexity, low-cost dampers that, when placed within a blade in accordance with various embodiments described herein and tuned to a common frequency, provide efficient reduction of coupled-mode vibrations caused by seismic activity.

[0022] According to one embodiment of the present invention, the liquid damper is tuned to one or more common frequencies of at least one coupled mode vibration by controlling the level of liquid in the container.

[0023] This allows the liquid damper to be precisely tailored to efficiently damp coupled mode vibrations at these frequencies.

[0024] According to one embodiment of the present invention, the at least one vibration damping device comprises at least one mass element, at least one spring element and at least one damping element.

[0025] Such damping devices can be adapted to damp vibrations at specific frequencies, i.e., are useful for efficiently reducing coupled mode vibrations in wind turbine generators. Also, many such damping devices, i.e., damping devices comprising a mass, a spring, and a damping element, are available on the market. Therefore, off-the-shelf damping devices can be used at low cost, which reduces manufacturing costs.

[0026] According to one embodiment of the present invention, the at least one vibration damping device comprises a friction spring damper.

[0027] Friction spring dampers are robust and efficient dampers that can be easily tuned to reduce vibration at target frequencies and can be deployed with the blades of wind turbine generators.

[0028] According to one embodiment of the present invention, the friction spring damper is tuned to one or more common frequencies of at least one coupled mode vibration by adjusting one or more of the following: a weight of the at least one mass element; a spring constant of the at least one spring element; The damping effect of said at least one damping element.

[0029] This allows one or more parameters of the friction spring damper to be adjusted to maximize vibration reduction at a precisely selected frequency.

[0030] According to one embodiment of the present invention, at least one vibration damping device includes one or more of the following items: at least one pendulum damper; at least one eddy current damper; At least one hydraulic damper.

[0031] Thus, several different dampers may be utilized for mitigation of coupled mode vibrations, which provides increased implementation flexibility: different dampers are better in different implementations, and the possibility to select a damper from a set of dampers essentially allows the optimum damper for each implementation to be found.

[0032] According to one embodiment of the present invention, the at least one vibration damping device is positioned closer to the tip of the blade than to the root of the blade.

[0033] Locating at least one vibration damping device on the outer half of the blade, towards the tip of the blade, provides a more efficient reduction in vibrations, ie a more efficient damping capacity.

[0034] According to one embodiment of the present invention, at least one vibration damping device is arranged in a direction within the blade so that vibrations in the direction of the blade edge are reduced.

[0035] This provides improved damping capacity for the at least one damping device.

[0036] According to one embodiment of the present invention, the support structure comprises a monopile foundation.

[0037] Wind turbine generators with monopile foundations have been found to be particularly sensitive to seismic activity, and therefore, locating at least one vibration damping device within at least one of the two or more blades of such wind turbine generators significantly reduces the risk of component damage and / or fatigue / wear in the wind turbine generator.

[0038] According to one embodiment of the invention, the two or more blades have a length that results in a rotor radius of at least 150 m for the wind turbine generator.

[0039] Large wind turbine generators tend to be subject to higher seismic loads, and disposing at least one vibration damping device herein within at least one of two or more blades of such large wind turbine generators reduces the risk of component damage and / or fatigue / wear, and also increases the expected component lifespan and reduces the overall cost of the wind turbine generator.

[0040] According to one embodiment of the present invention, the wind turbine generator is an offshore wind turbine generator.

[0041] Many power plants that experience seismic activity are located at sea. Due to constraints on the construction and transportation of offshore wind turbine generators, offshore wind turbine generators tend to be larger than onshore wind turbine generators. Larger wind turbine generators are generally more susceptible to seismic loads. Therefore, offshore wind turbine generators, which often have submerged monopile foundations, are more exposed to seismic loads, for example, during earthquakes. By disposing at least one vibration damping device described herein inside at least one of two or more blades, vibration problems caused by seismic activity in such offshore wind turbine generators are significantly reduced.

[0042] According to a second aspect of the present invention, there is provided a power plant configured to supply power to a power grid, the power plant comprising one or more of the wind turbine generators disclosed herein.

[0043] This provides the above-mentioned efficient damping of coupled mode vibrations caused by seismic activity to one or more wind turbine generators within the power plant, resulting in an overall reduced risk of damage and / or fatigue / wear of components within the power plant.

[0044] According to a third aspect of the present invention, there is provided a vibration damping device arranged within a blade of a wind turbine generator, the wind turbine generator comprising: a support structure including a tower; A nacelle connected to the tower; two or more blades attached to a hub connected to the nacelle; the at least one vibration-damping device is tuned to one or more common frequencies of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration-damping device; the at least one coupled mode vibration at the one or more common frequencies is a combination of vibration of the support structure and vibration of at least one of the two or more blades; The vibration of the support structure and at least one of the two or more blades is caused by forces transmitted through the support structure during seismic activity of the ground in which the support structure is located.

[0045] The positioned vibration damping device provides efficient damping of coupled mode vibrations. By being positioned within the blade and tuned to one or more common frequencies of at least one coupled mode vibration, the coupled mode vibrations are specifically targeted and reduced by the vibration damping device, as described above.

[0046] According to a fourth aspect of the present invention, there is provided a blade for a wind turbine generator, the wind turbine generator comprising: a support structure including a tower; A nacelle connected to the tower; two or more blades attached to a hub connected to the nacelle, the blades comprising: the at least one vibration-damping device is tuned to one or more common frequencies of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration-damping device; the at least one coupled mode vibration at the one or more common frequencies is a combination of vibration of the support structure and vibration of at least one of the two or more blades; Vibration of the support structure and at least one of the two or more blades is caused by forces transmitted through the support structure during seismic activity of the ground in which the support structure is located.

[0047] Utilizing such blades in wind turbine generators, i.e., blades including at least one vibration damping device tuned to one or more common frequencies of at least one coupled mode vibration, provides efficient protection against harmful coupled mode vibrations, as described above. Due to the large size and high weight of today's wind turbine generator blades, the targeted coupled mode vibrations are significantly affected by blade motion. Therefore, the experienced coupled mode vibrations can be effectively reduced by locating at least one damping device within one or more blades.

[0048] According to a fifth aspect of the present invention, there is provided a method of mitigating at least one coupled mode vibration of a wind turbine generator, the wind turbine generator comprising: a support structure including a tower; A nacelle connected to the tower; two or more blades attached to a hub connected to a nacelle; at least one vibration damping device disposed within at least one of the two or more blades, the method comprising: determining one or more common frequencies of at least one coupled mode vibration that is a combination of vibration of the support structure and vibration of at least one of the two or more blades, the vibration caused by forces transmitted through the support structure during seismic activity of a ground on which the support structure is located; and tuning at least one vibration damping device to the determined one or more common frequencies.

[0049] The presented method may be utilized to provide efficient protection against harmful coupled mode vibrations during seismic activity, as described above.

[0050] According to a sixth aspect of the present invention, there is provided a method of assembling a wind turbine generator, the method comprising the steps of: assembling a support structure including a tower; connecting the nacelle to the tower; attaching two or more blades to a hub connected to a nacelle; determining one or more common frequencies of at least one coupled mode vibration that is a combination of vibration of the support structure and vibration of at least one of the two or more blades, the vibration caused by forces transmitted through the support structure during seismic activity of a ground on which the support structure is located; disposing at least one vibration damping device within at least one of the two or more blades; and tuning at least one vibration damping device to the determined one or more common frequencies.

[0051] The presented method can be utilized to assemble wind turbine generators, as described above, with efficient protection against coupled mode vibrations during seismic activity.

[0052] The vibration damping device of the third aspect, the blade of the fourth aspect, and the methods of the second to sixth aspects each have advantages corresponding to those described above for the wind turbine generator according to the first aspect of the invention and its embodiments, in addition to those described above. Further advantageous embodiments of the wind turbine generator, the power plant, the vibration damping device, the blade, the method for damping at least one coupled mode vibration, and the method for assembling a wind turbine generator according to the invention, as well as further advantages of the embodiments of the invention, will become apparent from the detailed description of the embodiments.

[0053] Aspects and embodiments of the present invention will now be described in more detail, by way of example only, by way of embodiments and with reference to the enclosed drawings, in which like references are used for like parts and in which: [Brief explanation of the drawings]

[0054] [Figure 1] 1 is a schematic diagram illustrating an example of a power plant in which aspects and embodiments of the present invention may be implemented. [Figure 2] 1 is a schematic diagram illustrating a wind turbine generator in which aspects and embodiments of the present invention may be implemented; [Figure 3] 1 shows an exemplary frequency spectrum momentum chart that schematically illustrates coupled mode oscillations. [Figure 4a] 1 is a schematic diagram illustrating an example of a vibration damping device in a blade according to various embodiments of the present invention. [Figure 4b] 1 is a schematic diagram illustrating an example of a vibration damping device in a blade according to various embodiments of the present invention. [Figure 5] FIG. 1 is a flow chart diagram of a method according to an aspect of the present invention. [Figure 6] FIG. 1 is a flow chart diagram of a method according to an aspect of the present invention. [Figure 7] 1 is a frequency spectrum illustrating the effect of the present invention on tower loading. DETAILED DESCRIPTION OF THE INVENTION

[0055] 1 illustrates, in a schematic manner, a non-limiting example of a power plant 200 in which aspects and embodiments of the present invention may be implemented. Aspects and embodiments of the present invention may, of course, be implemented in any essentially solution in which one or more wind turbine generators 100 are used, and are not limited to the example power plant of FIG. 1 or to implementation in such a power plant.

[0056] The power plant 200 is configured to supply power or electrical energy to a power grid 202. The power plant 200 includes one or more power generation units, such as wind turbine generators 100. According to some embodiments, the power plant 200 may also include one or more other power generation units 203, such as, for example, solar photovoltaic panels and fuel cells. The wind turbine generators, solar photovoltaic panels, and fuel cells may also generally be described as power sources for the power plant 200 or as generators for the power plant 200. The power plant 200 may also include an energy storage system 205.

[0057] The power plant 200 may be connected or connectable to an electric power grid 202 via a point of common coupling (PCC) 204. In some embodiments, the electric power grid 202 may be referred to as a utility grid, a distribution grid, or a power network. For example, the power plant 200 may be located offshore or onshore.

[0058] The power plant 200 may include a controller 210 configured to control the power plant 200. According to some embodiments, the controller 210 may comprise or be referred to as a power plant controller (PPC). As shown schematically in FIG. 1, the power plant controller (PPC) controls the wind turbine generator 100, the power generating units 203, and the energy storage system 205.

[0059] 2 schematically illustrates an example of the wind turbine generator 100 of the power plant 200 of FIG. 1 in which aspects and embodiments presented herein may be implemented. The wind turbine generator 100 may include two or more blades 130 attached to a rotor 131, e.g., a rotor 131 including three or more blades. The wind turbine generator 100 includes a support structure 120 including a tower 121 and a foundation 123. The wind turbine generator 100 also includes a nacelle 110 attached / connected to a tower top 122. The rotor 131 may be connected, such as rotatably connected or mounted, to the nacelle 110. The wind turbine generator 100 may include a generator 111 to which the rotor 131 is connected. The rotor 131 is configured to drive the generator 111. The nacelle may house the generator 111.

[0060] The rotor 131 is rotatable by the action of the wind. Rotational energy of the two or more blades 130 and rotor 131 due to the wind may be transmitted to the generator 111 via a coupling 112 including, for example, one or more shafts. Thus, the wind turbine generator 100 may be described as configured to convert kinetic energy of the wind into mechanical or rotational energy by the two or more blades 130, which is then converted into electrical power by the generator 111. The wind turbine generator 100 may include one or more power converters 113 connected to the generator 111. The wind turbine generator 100 and / or the generator 111 may be connected to the electrical power grid 102 via the one or more power converters 113. The one or more power converters 113 may include a first power converter for converting AC power from the generator 111 to DC power. The one or more power converters 113 may include a second power converter for converting DC power from the first power converter to AC power supplied to the electrical power grid 102. The nacelle 110 may house one or more power converters 113, or the one or more power converters 113 may be located elsewhere.

[0061] 2 , the wind turbine generator 100 may include a controller 140 for controlling the wind turbine generator 100. The controller 140 of the wind turbine generator 100 may be configured to communicate with and / or be connected to or be part of a controller 210 of the power plant 200.

[0062] As shown schematically in FIG. 2 , the wind turbine generator 100 may be, for example, an offshore wind turbine generator with a tower 121 disposed underwater 150 in the ocean. The wind turbine generator 100 may be disposed such that its tower 121 is attached to a base / foundation 123 or in the ground 160. In some parts of the world, seismic activity 161 in the ground 160 occurs from time to time. The seismic activity 161 then induces forces 162 around the base / foundation 123 of the tower 121. These forces 162 due to the ground seismic activity 161 also generate forces 163 that are transmitted through the tower toward the nacelle 110. Thus, forces resulting from the seismic activity 161 in the ground on which the wind turbine generator 100 is located may be transmitted to the support structure 120. These forces then travel through the support structure 120 toward the nacelle 110, the rotor 131, and ultimately toward the two or more blades 130.

[0063] These forces 163, which transmit through the support structure 120 towards the tower top 122 and the two or more blades 130, can cause vibrations in both the support structure 120 and the two or more blades 130. These vibrations can cause significant loads on the wind turbine generator 100, as shown schematically in Figure 2, and can, for example, cause serious damage to the tower top 122. Of course, although Figure 2 shows a schematic representation of an offshore wind turbine generator, corresponding forces due to seismic activity 161 can also occur in onshore wind turbine generators, i.e., wind turbine generators located on land where seismic activity occurs.

[0064] According to one aspect of the present invention, there is provided a wind turbine generator 100. The wind turbine generator 100 comprises a support structure 120 including a tower 121, as described above, and a nacelle 110 connected to the tower 121. The wind turbine generator 100 further comprises two or more blades 130 attached to a hub 131 connected to the nacelle 110.

[0065] The wind turbine generator 100 includes at least one vibration damping device 400, shown schematically in Figure 2 and described in more detail below in relation to Figures 4a-4b, disposed within at least one of the two or more blades 130. The at least one vibration damping device 400 is configured, in particular, to damp coupled mode vibrations of the wind turbine generator 100 caused by seismic activity.

[0066] As described above, seismic activity 161 in the ground 160 on which the support structure 120 is located generates forces 163 that transmit through the support structure 120. These forces can cause vibration of the support structure 120, which can cause vibration of at least one of the two or more blades 130. The combined vibration of the support structure 120 and at least one of the two or more blades 130 has been found by the inventors to cause at least one coupled mode vibration at one or more common frequencies fcommon, as described in more detail below.

[0067] According to an embodiment of the present invention, at least one vibration damping device 400 disposed within at least one of the blades 130 is tuned to one or more common frequencies fcommon of at least one coupled mode vibration, such that the at least one coupled mode vibration is efficiently mitigated / reduced by the at least one vibration damping device 400 mounted within the at least one blade 130, as shown schematically in FIG.

[0068] Generally, the support structure 120 has its own oscillation / vibration mode at the support structure's 120 natural frequency, fstructure. Correspondingly, the two or more blades 130 have their own oscillation / vibration modes at the blade's other natural frequency, fblade. As is well known to those skilled in the art, natural / natural frequencies are specific discrete frequencies at which each particular component / device / system is more prone to oscillate / vibrate compared to other frequencies. The natural / natural frequencies of a component / apparatus / system are, in other words, the frequencies at which the component / apparatus / system tends to vibrate in the absence of a driving force. Thus, the support structure 120 has one set of natural / natural frequencies, fstructure, and the blades 130 have another set of natural / natural frequencies, fblade, where these sets of natural / natural frequencies are different, and fstructure≠fblade.

[0069] The inventors of the wind turbine generator 100 and at least one vibration damping device 400 presented herein have found that when forces caused by seismic activity are transmitted through the support structure 120 towards the nacelle 110 during seismic activity, the vibration modes of the support structure 120 and the vibration modes of the two or more blades 130 are coupled / combined such that new vibrations / vibration modes appear. Thus, the vibration modes of the support structure 120 and the vibration modes of the two or more blades 130 interact with each other such that new coupled vibrations / vibration modes are generated. The present invention makes use of the fact that these new coupled vibration modes occur at new natural frequencies fcommon that are different from the natural frequencies of the support structure and the blades, where fcommon≠fstructure and fcommon≠fblade. These new natural frequencies fcommon of the coupled vibration modes are referred to herein as one or more common frequencies fcommon, to indicate that these frequencies are coupled / resulting / combined frequencies caused during seismic activity as a result of the combination / interaction of vibration of the support structure 120 at its one or more support natural frequencies fstructure and vibration of at least one blade 130 at its one or more blade natural frequencies fblade.

[0070] 3 shows a schematic, non-limiting example of a frequency spectrum chart of moment amplitudes, showing the natural frequencies of the support structure fstructure and blade fblade, and the natural frequency of the coupled mode vibration fcommon. The exemplary frequency spectrum chart of FIG. 3 is shown to illustrate the principles of the solutions presented herein, but is not intended to limit the solutions described herein.

[0071] In the illustrated example of Figure 3, the momentum of a first mode at a first natural / natural frequency of the support structure (support structure first mode; fstructure_1st) and a second mode at a second natural / natural frequency of the support structure (support structure second mode; fstructure_2nd) are shown. Also shown are the momentum of a first mode at a first natural / natural frequency of the blade (blade edge first mode; fblade_1st) and the momentum of a second mode at a second natural / natural frequency of the blade (blade edge second mode; fblade_2nd).

[0072] Furthermore, the momentum of coupled mode oscillations / vibrations (coupled modes at a common frequency; fcommon) is also shown in the exemplary frequency spectrum chart of Figure 3. As shown in the figure, the momentum of coupled mode oscillations is much larger, i.e., has higher amplitude, than the momentum at the respective natural frequencies of the support structure fstructure and the blade fblade. The coupled mode oscillations / vibrations occur at one or more common / coupled frequencies fcmmon that are different from the natural frequencies of the support structure and the blade, and as noted above, fcommon≠fstructure and fcommon≠fblade.

[0073] Thus, during earthquakes and other seismic activity, severe loads may be applied to a tower top, for example, a nacelle, due to coupled mode vibrations at one or more of these common frequencies fcommon that are different / distinct from the natural / lateral frequencies of both the support structure and the blades, where fcommon ≠ fstructure and fcommon ≠ fblade.

[0074] Thus, in the non-limiting example shown in FIG. 3, at least one vibration damping device 400 according to various embodiments of the present invention should be placed inside at least one of the blades 130 of the wind turbine generator 100 and tuned to high amplitude vibrations at the common frequency fcommon.

[0075] According to various embodiments of the present invention, the at least one vibration damping device is tuned to the common frequency fcommon of the at least one coupled mode vibration, so that the damping effect of the at least one vibration damping device 400 can be targeted at the frequencies it affects most, i.e. the frequencies at which the vibrations have their greatest magnitude, such that the at least one vibration damping device is specifically adapted to efficiently damp the at least one coupled mode vibration, thereby reducing the risk of damage and fatigue / wear of the wind turbine generator components.

[0076] The inventors of the vibration damping device and wind turbine generator described herein have discovered that at least one vibration damping device disposed within at least one of the two or more blades 130, appropriately tuned to one or more common frequencies fcommon of at least one coupled mode vibration, effectively damps the momentum of the coupled mode vibration, thereby effectively reducing the loads at, for example, the tower top 122 due to the coupled mode vibration.

[0077] According to one embodiment, as shown schematically in FIG. 2, at least one vibration damping device 400 disposed within at least one of the two or more blades 130 is tuned to at least one coupled mode vibration having a frequency within a range between the first natural frequency fstructure_1st and the second natural frequency fstructure_2nd of the support structure 120.

[0078] The inventors have found that one of the common frequencies fcommon is located in a frequency range between the first natural frequency fstructure_1st and the second natural frequency fstructure_2nd of the support structure, and therefore, by tuning / calibrating at least one vibration damping device 400 to a value within this frequency range, coupled mode vibrations are effectively reduced.

[0079] Thus, the one or more common frequencies fcommon may be determined based on the first and second natural frequencies fstructure_1st and fstructure_2nd of the support structure 120. According to various embodiments, the first and second natural frequencies fstructure_1st and fstructure_2nd of the support structure 120 may be derived by numerical analysis, for example, eigenvalue analysis, during the design process of the support structure.

[0080] Generally, it may not be feasible to perform frequency measurements related to the frequencies of coupled mode vibrations in the field. Therefore, the eigenfrequencies of the support structure fstructure and / or the blades fblade may be determined by numerical eigenvalue analysis, which may include, for example, frequency analysis using time-domain methods, when the support structure 120 and / or the blades 130, respectively, are designed. The results of this eigenvalue analysis may be verified during commissioning of the wind turbine generator 100.

[0081] Based on the first natural frequency fstructure_1st and the second natural frequency fstructure_2nd of the support structure thus determined, a common frequency fcommon of at least one coupled mode vibration is determined as described above, and at least one vibration damping device 400 is adjusted / calibrated to the common frequency fcommon thus determined.

[0082] For example, as shown schematically in the non-limiting example of Figure 3, coupled mode oscillations / vibrations may occur at a common frequency fcommon essentially midway between the first natural / natural frequency_1st and the second natural / natural frequency_2nd of the support structure, i.e., in a frequency range essentially midway between the first natural / natural frequency_1st and the second natural / natural frequency_2nd of the support structure. The at least one vibration damping device 400 should then be tuned to this particular frequency in order to efficiently reduce these coupled mode vibrations.

[0083] Vibration damping device 400 tuned or calibrated to a particular frequency means herein that the damping effect of vibration damping device 400 is highest for that particular frequency. Thus, when vibration damping device 400 is tuned to a common frequency fcommon, vibration damping device 400 is set / arranged to significantly damp / mitigate coupled-mode vibrations at this common frequency fcommon. Vibrations at frequencies other than the common frequency fcommon are damped / mitigated less than coupled-mode vibrations at this common frequency fcommon are damped. In other words, when vibration damping device 400 is tuned to a common frequency fcommon, it is adapted to achieve a targeted significant reduction of coupled-mode vibrations at that common frequency fcommon.

[0084] The wind turbine generator 100 and / or at least one vibration damping device 400 presented herein may be particularly useful in geographic locations and / or implementations where vibrations / swaying due to seismic activity are likely to affect the wind turbine generator 100. For example, due to their structural nature, support structures 120 including monopile foundations have generally been found to be more likely to suffer from severe tower-top problems caused by seismic activity than support structures including jacket foundations. This is due to the characteristics of the monopile structure, where momentum loads from seismic activity can be transferred to the tower top via the directly connected piles. Additionally, monopile foundations are often used for offshore implementation / location of wind turbine generators. Furthermore, many power plants that experience and are affected by seismic activity are located offshore, i.e., at sea, and typically have submerged monopile foundations.

[0085] Therefore, the solutions presented herein for mitigating coupled mode vibrations can be utilized, according to various embodiments, to efficiently reduce coupled vibrations in wind turbine generators 100 that are equipped with monopile foundations and / or are located offshore.

[0086] Furthermore, the solutions presented herein may, according to some embodiments, be utilized in wind turbine generators having long / large blades, for example blades 130 having a length Lb, such that the rotor radius Drotor of the wind turbine generator 100 is at least 150 m, Drotor≧150 m. The inventors have found that wind turbine generators having such large rotor radii Drotor are sensitive to seismic activity and are particularly important to protect as described herein.

[0087] According to one embodiment, shown schematically in Figure 4a, the at least one vibration damping device 400 comprises a liquid damper 410 including at least one reservoir 411 for containing a liquid. The liquid damper is a passive damper that uses the inertia of the liquid suspended in the reservoir 411 to reduce coupled mode vibrations.

[0088] The liquid damper's container 411 can have a variety of shapes / forms / configurations / designs, according to various embodiments. For example, the container 411 can be box-shaped, i.e., have an essentially rectangular cross-section with at least partially straight walls. The container 411 can also have curved walls, e.g., to have a U-shaped or O-shaped cross-section.

[0089] According to one embodiment, a liquid damper 410 having a box-shaped container 411 may be tuned to one or more common frequencies fcommon of at least one coupled mode vibration by controlling the liquid level Hl 412 in the container 411.

[0090] The container 411 may have, for example, a width, height, and length L that meet certain criteria relative to each other and / or relative to the liquid level Hl such that the damping characteristics of the liquid damper 410 are optimized.

[0091] More specifically, the liquid damper 410 may be tuned to a damping frequency fd by adjusting the liquid level Hl according to the following equation: JPEG2025538767000002.jpg2385where, -fd is the damping frequency. -g is the acceleration due to gravity. -L is the length of the container. -Hl is the liquid level.

[0092] Therefore, when the liquid damper 410 is tuned by adjusting the liquid level Hl so that its damper frequency corresponds to one or more common frequencies fcommon, the coupled mode vibrations occurring at these one or more common frequencies fcommon are efficiently attenuated by the liquid damper.

[0093] According to one embodiment, the liquid damper 410 is positioned closer to the blade tip 132 than to the blade root 133. Thus, the liquid damper 410 is mounted on the outer half of the blade 130 towards the tip 132, i.e., at a spanwise position of 50-100%, and according to one embodiment, preferably as far as possible on the blade 130, which improves its vibration damping properties. Also, according to one embodiment, the liquid damper can be positioned inward of the blade 130 so that edgewise vibrations of the blade 130 are reduced.

[0094] According to one embodiment, the at least one vibration damping device 400 comprises at least one mass element 423 , at least one spring element 422 and at least one damping element 421 .

[0095] One such vibration damping device, shown schematically in Figure 4b, is a friction spring damper 420 including a mass element 423 attached to at least one fixed component 424 of the blade via at least one spring element 422, and at least one damping element 421. For example, the at least one spring element 422 and the at least one damping element 421 may be arranged in parallel between the fixed component 424 and the mass element 423. The at least one fixed component 424 may essentially be any fastened internal part of the blade, such as the inner casing / housing of the blade 130 or any other part of the internal structure of the blade 130.

[0096] To efficiently reduce the coupled mode vibrations, the friction spring damper 420 is tuned to one or more common frequencies fcommon of the at least one coupled mode vibration by adjusting the mass of the mass element 423, by adjusting the spring constant of the at least one spring element 422, and / or by adjusting the damping action of the at least one damping element 421, so that the damping frequency fd of the friction spring damper corresponds to the common frequency fcommon.

[0097] According to one embodiment, the at least one vibration damping device 400 is positioned within the blade 130 closer to the blade tip 132 than to the blade root 133, for example as far as possible on the blade 130, thereby improving its vibration damping properties. The at least one vibration damping device 400 may also be positioned, according to one embodiment, in a direction that reduces vibrations along the edge of the blade 130.

[0098] According to various embodiments, the at least one vibration damping device 400 may comprise at least one pendulum damper, at least one eddy current damper, and / or at least one hydraulic damper.

[0099] In general, essentially any suitable vibration damping device 400 that is suitable for placement within the blade 130 of the wind turbine generator 100 and that is capable of being tuned to the common frequency fcommon of coupled mode vibrations can be utilized as a damper in accordance with various embodiments of the present invention. For most of these vibration damping devices 400, their damping properties against coupled mode vibrations are improved when they are placed along the outer half of the length Lb of the blade 130 and / or when they are oriented relative to the blade edge to reduce edgewise vibrations of the blade 130.

[0100] According to one aspect of the present invention, a method 500 for mitigating at least one coupled mode vibration of a wind turbine generator 100 is presented.

[0101] FIG. 5 shows a flow chart diagram of a method 500 .

[0102] The method is applicable to the wind turbine generator 100 described above, which comprises a support structure 120 including a tower 121, a nacelle 110 connected to the tower 121, and two or more blades 130 attached to a hub 131 connected to the nacelle 110. The wind turbine generator 100 further comprises at least one vibration damping device 400 as described herein disposed within at least one blade of the two or more blades 130.

[0103] In a first step 510 of the method, one or more common frequencies fcommon of at least one coupled mode vibration, which is a combination of vibration of the support structure 120 and vibration of at least one of the two or more blades 130, are determined. As described above, these vibrations are caused by forces transmitted through the support structure 120 during seismic activity 161 in the ground 160 in which the support structure 120 is located. As described above, the common frequency fcommon of the at least one coupled mode vibration can be determined based on the first and second natural frequencies fstructure_1st and fstructure_2nd of the support structure. The first and second natural frequencies fstructure_1st and fstructure_2nd of the support structure can be determined by numerical analysis, for example, a specific eigenvalue analysis, during the design process of the support structure.

[0104] In a second step 520 of the method, the at least one vibration damping device 400 is tuned to the one or more common frequencies fcommon determined in the first step 510. This causes the at least one vibration damping device 400 to be specifically tuned to target coupled mode vibrations caused by seismic activity, such that these vibrations are effectively reduced in amplitude / power.

[0105] According to one aspect of the present invention, a method 600 for assembling a wind turbine generator 100 is provided.

[0106] 6 shows a flowchart diagram of a method 600 that is applicable to the wind turbine generator 100 described above that, when assembled, comprises a support structure 120 that includes a tower 121, a nacelle 110 connected to the tower 121, and two or more blades 130 attached to a hub 131 connected to the nacelle 110. The assembled wind turbine generator 100 further comprises at least one vibration damping device 400 as described herein disposed within at least one of the two or more blades 130.

[0107] In the first step 610 of the method, a support structure 120 including a tower 121 is erected.

[0108] In a second step 620 of the method, the nacelle 110 is connected to the tower 121 .

[0109] In a third step 630 of the method, two or more blades 130 are attached to a hub 131 connected to the nacelle 110. In a fourth step 640 of the method, one or more common frequencies fcommon of the at least one coupled mode vibration are determined. As described above, the at least one coupled mode vibration is a combination of vibration of the support structure 120 and vibration of at least one of the two or more blades 130, caused by forces transmitted through the support structure 120 during seismic activity 161 in the ground 160 in which the support structure 120 is located.

[0110] In a fifth step 650 of the method, at least one vibration damping device 400 is disposed within at least one of the two or more blades 130 .

[0111] In a sixth step 660 of the method, at least one vibration damping device 400 is tuned to the determined one or more common frequencies fcommon, so that vibrations at these frequencies are effectively reduced in amplitude / power.

[0112] It should be noted that the method steps shown in Figures 5-6 and described herein do not necessarily have to be performed in the order shown in these figures: the steps may be performed in essentially any suitable order, so long as the physical requirements and information needed to perform each step are available at the time the step is performed.

[0113] Figure 7 shows the effect of the present invention on tower load / moment. This figure shows the tower load / moment as a function of frequency. The load / moment amplitude is highest at the frequency of the coupled mode vibration fcommon, which, as mentioned above, is located between the first natural frequency of the support structure (support structure first mode; fstructure_1st) and the second natural frequency of the support structure (support structure second mode; fstructure_2nd).

[0114] The tower load / moment amplitude of an undamped wind turbine generator turbine, i.e. a wind turbine generator turbine that does not implement any of the aspects or embodiments of the present invention, is shown as dashed curve 701. Also shown in the figure as solid curve 702 is the tower load / moment amplitude of a wind turbine power plant equipped with a liquid damper according to one of the embodiments described herein tuned to the frequency of the coupled mode vibration fcommon.

[0115] As can be seen in Figure 7, the amplitude of the tower load / moment is significantly reduced at the critical coupled mode vibration frequency fcommon, which reduces the risk of damage and / or fatigue / wear to the wind turbine generator, as discussed above.

[0116] The invention is not limited to the embodiments described above, but rather relates to and encompasses all different embodiments that fall within the scope of the independent claims.

Claims

1. The wind turbine generator (100) comprises: a support structure (120) including a tower (121); a nacelle (110) connected to the tower (121); two or more blades (130) attached to a hub (131) connected to the nacelle (110); at least one vibration damping device (400) disposed within at least one of the two or more blades (130), the at least one vibration damping device (400) being tuned to one or more common frequencies (fcommon) of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration damping device (400); the at least one coupled mode vibration at the one or more common frequencies (fcommon) is a combination of vibration of the support structure (120) and vibration of at least one of the two or more blades (130); 1. A wind turbine generator (100) according to claim 1, wherein the vibration of the support structure (120) and the vibration of the at least one of the two or more blades (130) are caused by forces transmitted through the support structure (120) during seismic activity (161) of a ground (160) on which the support structure (120) is located.

2. 2. The wind turbine generator (100) of claim 1, wherein the one or more common frequencies (fcommon) of the at least one coupled mode vibration include frequencies in a range between a first natural frequency (fstructure_1st) and a second natural frequency (fstructure_2nd) of the support structure (120).

3. The wind turbine generator (100) of claim 1 or 2, wherein the at least one vibration damping device (400) comprises a liquid damper (410) including at least one liquid reservoir (411).

4. 4. The wind turbine generator (100) of claim 3, wherein the liquid damper (410) is tuned to the one or more common frequencies (fcommon) of the at least one coupled mode vibration by controlling a level of liquid (412) in the container (411).

5. 3. The wind turbine generator (100) of claim 1 or 2, wherein the at least one vibration damping device (400) comprises at least one mass element (423), at least one spring element (422), and at least one damping element (421).

6. The wind turbine generator (100) of claim 5, wherein the at least one vibration damping device (400) comprises a friction spring damper (420).

7. The friction spring damper (420) is tuned to the one or more common frequencies (fcommon) of the at least one coupled mode vibration by adjusting one or more of the following: the weight of said at least one mass element (423); a spring constant of said at least one spring element (422); the damping effect of said at least one damping element (421); The wind turbine generator (100) of claim 6.

8. 3. The wind turbine generator (100) of claim 1 or 2, wherein the at least one vibration damping device (400) comprises one or more of: at least one pendulum damper; at least one eddy current damper; and at least one hydraulic damper.

9. 9. The wind turbine generator (100) of claim 1, wherein the at least one vibration damping device (400) is positioned closer to the blade tip (132) than to the blade root (133).

10. 10. The wind turbine generator (100) of claim 1, wherein the at least one vibration damping device (400) is arranged in a direction within the blade (130) such that edgewise vibrations of the blade (130) are reduced.

11. The wind turbine generator (100) of any one of claims 1 to 10, wherein the support structure (120) comprises a monopile foundation.

12. 12. The wind turbine generator (100) of claim 1, wherein the two or more blades (130) have a length (L) that results in a rotor radius (Drotor) of at least 150 m for the wind turbine generator (100).

13. 13. A wind turbine generator according to any one of claims 1 to 12, wherein the wind turbine generator is an offshore wind turbine generator.

14. A power plant (200) configured to supply power to a power grid (202), the power plant (200) comprising one or more wind turbine generators (100) according to any one of claims 1 to 13.

15. A vibration damping device (400) disposed within a blade (130) of a wind turbine generator (100), the wind turbine generator (100) comprising: a support structure (120) including a tower (121); a nacelle (110) connected to the tower (121); two or more blades (130) attached to a hub (131) connected to the nacelle (110); the at least one vibration damping device (400) is tuned to one or more common frequencies (fcommon) of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration damping device (400); the at least one coupled mode vibration at the one or more common frequencies is a combination of vibration of the support structure (120) and vibration of at least one of the two or more blades (130); A vibration damping device (400) in which the vibration of the support structure (120) and the vibration of at least one of the two or more blades (130) are caused by forces transmitted through the support structure (120) during seismic activity (161) of the ground (160) on which the support structure (120) is located.

16. A blade (130) for a wind turbine generator (100), the wind turbine generator (100) comprising: a support structure (120) including a tower (121); a nacelle (110) connected to the tower (121); two or more blades (130) attached to a hub (131) connected to the nacelle (110), the blades (130) comprising: the at least one vibration damping device (400) is tuned to one or more common frequencies (fcommon) of the at least one coupled mode vibration such that the at least one coupled mode vibration is attenuated by the at least one vibration damping device (400); the at least one coupled mode vibration at the one or more common frequencies is a combination of vibration of the support structure (120) and vibration of at least one of the two or more blades (130); The vibration of the support structure (120) and at least one of the two or more blades (130) is caused by forces transmitted through the support structure (120) during seismic activity (161) of the ground (160) on which the support structure (120) is located.

17. 1. A method (500) for mitigating at least one coupled mode vibration of a wind turbine generator (100), the wind turbine generator (100) comprising: a support structure (120) including a tower (121); a nacelle (110) connected to the tower (121); two or more blades (130) attached to a hub (131) connected to the nacelle (110); at least one vibration damping device (400) disposed within at least one of the two or more blades (130), the method comprising: determining (510) one or more common frequencies (fcommon) of at least one coupled mode vibration that is a combination of vibration of the support structure (120) and vibration of at least one of the two or more blades (130), the vibration being caused by forces transmitted through the support structure (120) during seismic activity (161) of the ground (160) on which the support structure (120) is located; and tuning (520) said at least one vibration damping device (400) to said determined one or more common frequencies (fcommon).

18. A method (600) of assembling a wind turbine generator (100), the method comprising: Assembling (610) a support structure (120) including a tower (121); connecting (620) a nacelle (110) to said tower (121); Attaching (630) two or more blades (130) to a hub (131) connected to the nacelle (110); determining (640) one or more common frequencies (fcommon) of at least one coupled mode vibration that is a combination of vibration of the support structure (120) and vibration of at least one of the two or more blades (130), the vibration caused by forces transmitted through the support structure (120) during seismic activity (161) of the ground (160) on which the support structure (120) is located; disposing (650) at least one vibration damping device (400) within at least one of the two or more blades (130); and tuning (660) the at least one vibration damping device (400) to the determined one or more common frequencies (fcommon).

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