Reducing Seismic Loads on Wind Turbines

Abstract

The present invention describes a wind turbine (100) comprising: i) a tower (120); ii) a wind rotor (110) disposed at a top portion of the tower (120), the wind rotor (110) having at least one blade (114), the at least one blade (114) being disposed at a first blade pitch position; and iii) a seismic event control device (153) configured to actuate the at least one blade (114) from the first blade pitch position to a second blade pitch position different from the first blade pitch position, thereby reducing seismic loads acting on the wind turbine (100).

Description

[Technical field]

[0001] FIELD OF THEINVENTION The present invention relates to the technical field of wind turbines. The present invention particularly relates to wind turbines with seismic event control devices. The present invention further relates to a method for reducing seismic loads acting on a wind turbine. Furthermore, the present invention relates to the particular use of blade pitch actuation.

[0002] Technology background It may be considered common to install wind turbines in particularly windy environments, for example offshore, to generate efficient electricity. However, some of these environments are seismically active regions, for example in the Asia-Pacific region. Therefore, the response of the wind turbine and its supporting structure to seismic events may need to be evaluated so that future seismic loads can be determined when the seismic events have a certain probability of occurring.

[0003] Depending on local regulations, wind turbine structures must meet the following standards: i) No Damage Criterion: This condition requires that the seismic loads do not exceed the material yield strength of any load-bearing components. In countries like Japan, wind turbines are expected to maintain their structural integrity for low severity seismic events; ii) No-collapse criteria: This condition allows for local exceedance of the material yield strength of load-bearing components. However, this condition requires that the ultimate strength of the materials is not exceeded and there is no spalling or catastrophic failure of any load-bearing components. In countries like Japan, wind turbines are expected to meet the no-collapse criteria for extremely rare earthquake events of medium to high severity (return period 475 years): It may even have to be proven that the above condition can be satisfied.

[0004] For typical offshore wind turbines located in the Asia-Pacific region, including Japan, Korea, and Taiwan, the risk of seismic loading may often drive wind turbine design because seismic loads on the wind turbine tower and support structure may be significantly higher than non-seismic loads. Thus, meeting seismic requirements may require increased tower and support structure costs, which may make the wind turbine project economically unfeasible. Additionally, high seismic loads on the blades or other nacelle (RNA) components may make future sites or turbine types technically impractical for offshore sites in these regions.

[0005] During an earthquake, the support structure of a wind turbine is subjected to seismic accelerations that are transmitted through rock and soil layers to the support structure. One of the most difficult challenges with high seismic loads can occur when the frequency components of these seismic accelerations match one of the structural frequencies of the wind turbine and the support structure. This "resonance" can cause significant vibrations and therefore critical loads in one or more of the turbine structural components (e.g., blades can break).

[0006] To reduce seismic loads on wind turbines, a conventional approach is to modify the design of the wind turbine's support structure to avoid seismic frequencies that can excite the turbine's structural modes.

[0007] However, this approach can have many drawbacks, since it incurs significant additional costs. Moreover, this approach cannot be used when seismic frequencies excite structural modes of the RNA, since redesign of the RNA is generally not possible for site-specific load calculations. US Patent Application Publication No. 2011 / 0293418 describes an apparatus and method for controlling a wind turbine, in particular a shutdown sequence. DE 10 2018 132 413 A1 describes a method for determining different vibrations of a wind energy plant. WO 2010 / 083835 describes a wind turbine equipped with an alarm system. EP 2 589 800 A1 describes a pitch control device for a wind turbine.

[0008] It may be necessary to provide a wind turbine that can be operated robustly and steadily even during a seismic event.

[0009] Summary of the Invention This need can be met by the subject matter of the independent claims. Advantageous embodiments of the invention are set forth in the dependent claims.

[0010] According to a first aspect of the present invention there is provided a wind turbine comprising: i) a tower; ii) a wind rotor arranged at the top part of the tower and having at least one blade, in particular three blades, the at least one blade being arranged at a first blade pitch position (normal blade position), in particular at a first blade pitch angle; iii) a seismic event control device configured to actuate (as a response to a seismic event) at least one blade from a first blade pitch position to a second blade pitch position (seismic load reducing blade position), in particular a second blade pitch angle, different from the first blade pitch position, thereby reducing seismic loads acting on the wind turbine; A wind turbine is provided comprising: This results in: a) the first blade edge resonant frequency of the first blade pitch position being closer to the seismic event dominant resonant frequency than the second blade edge resonant frequency of the second blade pitch position; and / or b) the first blade pitch position is a non-energy producing position and the second blade pitch position is an energy producing position.

[0011] According to a second aspect of the invention there is provided a method for reducing seismic loads acting on a wind turbine during a seismic load causing event, in particular during an earthquake, the wind turbine comprising a tower and a wind rotor arranged at a top portion of the tower and comprising at least one blade, the at least one blade being arranged in a first blade pitch position. The method comprises: i) obtaining information indicative of events causing seismic loads, e.g. earthquake warnings, and in particular thereafter; ii) actuating at least one blade from a first blade pitch position to a second blade pitch position different from the first blade pitch position; Includes. This results in: a) the first blade edge resonant frequency of the first blade pitch position being closer to the seismic event dominant resonant frequency than the second blade edge resonant frequency of the second blade pitch position; and / or b) the first blade pitch position is a non-energy producing position and the second blade pitch position is an energy producing position.

[0012] The present invention An example to make it easier to understand describes the use of wind turbine blade pitch actuation to reduce seismic loads acting on a wind turbine, in particular by avoiding resonance (coincidence, amplification) of seismic event dominant resonant frequencies with blade edge resonant frequencies.

[0013] The present invention An example to make it easier to understand According to the present invention, a wind turbine is i) a tower; ii) a wind rotor arranged at the top of the tower and having at least one blade, in particular three blades; iii) a controller configured to maintain at least one blade in an energy producing blade pitch position during a seismic event, thereby reducing seismic loads acting on the wind turbine; and A wind turbine is provided comprising:

[0014] In the context of this specification, the term "blade pitch position" may refer in particular to the "blade pitch angle". The definition of the blade pitch angle is known in the field of wind turbines as the angle between the chord line of the blade and the plane of rotation of the blade (a reference line on the rotor hub). In other words, the blade pitch angle is the angle at which the turbine blade is placed relative to the plane of rotation, i.e. the angle measured between the plane of rotation and a straight line (chord line) from one edge of the blade to the other edge of the blade. This chord line is an imaginary straight line connecting the leading and trailing edges of the blade (see also Figures 3 and 4 for illustration). The pitch actuation may be, for example, a hydraulic or electric pitch actuation.

[0015] In the context of this specification, the term "seismic event" may refer in particular to events related to ground movement, such as earthquakes, which, if of a certain intensity, may cause wind turbines to shake and generate seismic loads that may lead to damage and failure of the wind turbines.

[0016] In the context of this specification, the term "seismic event control device" may refer to any device configured to take into account seismic event related / indicative information, in particular when performing control and / or adjustment actions. The seismic event control device may be one processor or multiple processors. Furthermore, the seismic event control device may be a control system of the wind turbine or may be software implemented on the wind turbine control system. In a particular example, no hardware is added to an existing wind turbine, but the seismic event control software is implemented in the wind turbine control device (controller), which then becomes (at least in part) the seismic event control device. The seismic event control device may include a blade pitch adjustment device or may be coupled to the blade pitch adjustment device. In the latter case, the blade pitch adjustment device may control and / or adjust the blade pitch adjustment device, in particular to reduce seismic loads acting on the wind turbine. The seismic event control device may detect the seismic event indicative information itself (e.g., using a detector) or may receive the seismic event indicative information from another (external) device.

[0017] The seismic event controller may directly actuate the blades (e.g., if the blade pitch position adjustment device is part of the seismic event controller) or the actuation may be triggered by the blade pitch position adjustment device. Both options are covered in the term "actuation" herein. Additionally, the seismic controller may pre-adjust the blade pitch position.

[0018] In the context of this specification, the terms "information indicative of a seismic event" or "information indicative of loads causing a seismic event" may include any information related to a current or potential seismic event. In a basic example, the indicative information may be that the wind turbine is located in an area with a high risk of a seismic event. In another example, the information may be an earthquake warning, for example, that the ground has started to move. In a more advanced example, the information may include specific information regarding the characteristics of the ground and how to actuate the blade pitch angle accordingly.

[0019] According to an exemplary embodiment, the invention may be based on the idea that the blade pitch angles can be actuated in a specific manner to reduce seismic loads, allowing the wind turbine to operate robustly and stably even during a seismic (load-inducing) event.

[0020] Conventional approaches to reduce seismic loads on wind turbines are primarily limited to structural design (e.g., more robust support structures), which are however costly and in some respects suboptimal (e.g., seismic redesigns typically require heavier structures).

[0021] The inventors have now observed that the greatest seismic loads may occur within a wind turbine structure when the blade pitch positions are in a non-energy producing regime, e.g., when left in the feathered position, such as occurs at the end of a turbine shutdown (and / or during extreme wind speeds). Based on this observation, the inventors have further discovered that a surprisingly efficient and reliable reduction in seismic loads on a wind turbine may be achieved when the blade pitch positions are optimized such that critical seismic loads are reduced as much as possible (e.g., by adjusting the blade pitch positions to an energy producing regime).

[0022] A direct consequence of the optimized blade pitch position is reduced seismic loads acting on the wind turbine and the wind turbine's supporting structure. In this manner, the blade pitch positions can be adjusted (collectively or individually) to change the structural frequency and / or another aeroelastic characteristic of the wind turbine to reduce seismic loads. Furthermore, the change in blade pitch position can also change the aerodynamic and / or rotational forces on the wind turbine, which can further reduce the loads experienced by the wind turbine during a seismic event. In an example, resonance between (seismic) ground frequencies (one or more dominant resonant frequencies of the seismic event and / or one or more amplified frequencies of the soil / subsurface layer) and blade frequencies (one or more resonant frequencies of the blade edge) is avoided by pitching the blades.

[0023] Exemplary embodiments According to the embodiment, the blade frequency is closer to the ground frequency of the seismic event at the first blade pitch position than at the second blade pitch position. In other words, the first blade edge resonant frequency at the first blade pitch position is closer to the dominant seismic event resonant frequency than the second blade edge resonant frequency at the second blade pitch position. Thus, the blade edge resonant frequency is closer (more similar) to the dominant seismic event resonant frequency (in other words, the amplification frequency of the soil layer / ground layer) at the first blade pitch position than at the second blade pitch position. Therefore, the first blade edge resonant frequency occurring at the first blade pitch position can be closer to said dominant seismic event resonant frequency (the amplification frequency of the soil layer) than the second blade edge resonant frequency occurring at the second blade pitch position. In this way, the inventors have found that the resonance (coincidence, amplification) between the blade (resonant) frequency and the (seismic) ground amplification frequency can be efficiently reduced.

[0024] According to a further embodiment, the first blade pitch position is a non-energy producing position, particularly one of the group consisting of a feathered position, an idle position, a turbine stopped position, and an extreme wind position. The inventors have discovered that seismic loads acting on the wind turbine can be significantly reduced if the blade pitch angle is not in a non-energy producing regime during a seismic event.

[0025] The term "non-energy producing" can refer to a wind turbine operating state where (essentially) no electrical energy is produced. In this state, the blade pitch angle is typically greater than 50°, especially around 90°. The non-energy producing regime is typically entered when the wind turbine is in the off or feathered position, or during extreme wind conditions where the wind turbine load is too strong for energy production.

[0026] According to a further embodiment, the second blade pitch position is an energy producing position. Similarly, the inventors have discovered that seismic loads acting on the wind turbine can be significantly reduced if the blade pitch angle is in an energy producing position during a seismic event.

[0027] The term "energy production" can refer to the operating condition of a wind turbine in which electrical energy is produced. It can be performed at light and high wind speeds, but not at extreme wind speeds. In order to collect as much wind power as possible, the blade pitch angle is in this regime generally below 50°, especially below 30°.

[0028] As a result of the above-mentioned subject matter, the blade pitch position of a wind turbine in a seismically active region may (essentially) always be in an energy producing position to prepare for a potential seismic event.

[0029] According to a further particular embodiment, the first blade position may be an energy producing position. According to a further particular embodiment, the second blade position may be a non-energy producing position.

[0030] According to a further embodiment, the first blade pitch position is defined by a first blade pitch angle and the second blade pitch position is defined by a second blade pitch angle, and actuating the blade pitch angle of the at least one blade comprises rotating the at least one blade about an axis aligned substantially parallel to a longitudinal extension of the at least one blade. By using the blade pitch angle, the blade pitch position can be adjusted very precisely.

[0031] According to a further embodiment, the first blade pitch angle is greater than 50°. According to a further embodiment, the second blade pitch angle is less than 50°. According to a further embodiment, the second blade pitch angle is less than 30°, in particular less than 20°.

[0032] As mentioned above, regimes above 50° can be considered as non-energy producing regimes that may be unsuitable for seismic events, whereas regimes below 50°, particularly below 30° or below 20°, can be considered as energy producing regimes that may be suitable for entering during a seismic event.

[0033] In one example, when the blade pitch angle is close to the traditional passive idling pitch angle, i.e., in the range of 60°-89°, the tower top seismic loads can be extremely large and could traditionally only be reduced by expensive tower and support structure designs and impractical nacelle constructions. However, by lowering the blade pitch angle towards near 20°, a load reduction of over 50% can be achieved (see also Figure 2). This load reduction can result in significant cost savings when designing wind turbines and / or support structures. Furthermore, the effective reduction of seismic loads can make previously impractical projects feasible in seismically active regions.

[0034] According to a further embodiment, the second blade position is pre-specified (pre-specified set point). According to a further embodiment, the second blade position is dynamically set (dynamically calculated set point). Thus, depending on the current situation, an advantageous approach can be selected.

[0035] According to a further embodiment, the wind turbine comprises two or more, in particular exactly three, blades, and the seismic event control device is configured to actuate (trigger actuation) the blade pitch angle of each of the two or more blades collectively or individually. Depending on the respective situation, it may be advantageous to control / adjust all blades collectively or to control / adjust each blade individually.

[0036] According to a further embodiment, the seismic event control device is configured to obtain information indicative of a seismic event, particularly prior to actuating the at least one blade, such that the seismic event control device can efficiently react to a potential seismic event.

[0037] According to a further embodiment, the wind turbine further comprises a seismic event detector for detecting information indicative of a seismic event.

[0038] According to a further embodiment, the wind turbine is configured to obtain information indicative of a seismic event from an external seismic event detector.

[0039] According to a further embodiment, the wind turbine further comprises a back-up power supply, which may provide the advantage that the wind turbine can be operated particularly safely and robustly.

[0040] If a wind turbine loses access to the power grid during a seismic event, the wind turbine may be unable to actuate the blade pitch position. In such cases, it may be extremely beneficial to apply auxiliary or back-up power to allow the blade pitch angle actuation to function properly.

[0041] According to further embodiments, the actuation (seismic load response) comprises an actuation of a dynamically calculated blade pitch position or an actuation of a predetermined blade pitch position. Thus, depending on the current situation, an advantageous approach can be selected.

[0042] In the exemplary embodiment, a proper knowledge of the expected spectral energy of seismic events at the rock and mud line (ground) is assumed. Furthermore, a good knowledge of the turbine's structural frequency and the change of the turbine's structural frequency over the blade pitch angle is also assumed. Based on the available information, the blade pitch positions can be determined (e.g., using aeroelastic turbine simulations) that minimize the turbine's structural loads when the turbine is exposed to a seismic event. This can be performed at a specific location, or at a general level. These blade pitch positions can be used as default pitch positions. If an earthquake detection system is used, based on external communication, dedicated earthquake sensors on the turbine structure or turbine site, or where a turbine standard signal is used, such detection system may directly trigger the turbine to enter the blade pitch positions defined above. These blade pitch positions can also be used as safe pitch positions for the turbine to enter when a critical or critical event occurs (determined by the turbine controller (seismic event control device)), ensuring that the wind turbine enters a state that is least susceptible to earthquake-induced loads. The blade pitch position may be the same for all three blades, or the blade pitch position may vary for each individual blade, for example to spread out the in-plane and out-of-plane resonant frequencies, thereby reducing resonant effects.

[0043] According to a further embodiment, the seismic event control device is further configured to: i) obtain information indicative of ground properties; ii) associate the information indicative of ground properties with a respective blade pitch position, in particular based on the operational data; and iii) apply the associated information (to provide for) actuation. This may provide the advantage that seismic event indicative information is actively determined and associated with advantageous blade pitch positions, such that favorable blade pitch positions at seismic events may be directly utilized.

[0044] In an exemplary embodiment, complete knowledge of the ground (soil and rock) characteristics, which is generally difficult to obtain in advance, may not be necessary in this example. However, adequate knowledge of the expected spectral energy of a seismic event may be required. Furthermore, knowledge of the turbine structural frequency and the change in the turbine structural frequency over the blade pitch angle is presumed. After installation, the wind turbine controller (including the seismic event control device) can collect further information about the ground characteristics based on the operational data (such as the frequency of the first support structure). The turbine controller can perform dedicated experiments to determine further ground characteristics. Based on the ground characteristics determined in the field, the blade pitch position can be defined as a default pitch position in case of light wind speeds, or as a safe blade pitch position in case of a fault condition or an earthquake detection system (as described in the example above). Ground characteristics may change over time, in which case the turbine controller continuously tracks such characteristics and updates the blade pitch position accordingly. Look-up tables may be pre-generated (e.g., using an aeroelastic turbine simulation) for use by the turbine controller to relate measured ground properties to optimal blade pitch positions that minimize turbine seismic loads. An example of such a look-up table may include a particular turbine natural frequency [Hz] and the corresponding blade pitch position for each blade.

[0045] According to a further embodiment, the seismic event control device is further configured to: i) obtain feedback information of the turbine load, in particular a proxy signal, and ii) apply the feedback information for (providing / triggering) actuation, which may provide the advantage of allowing efficient actuation taking into account the current turbine load even when there is not much seismic event indicative information available.

[0046] In the exemplary embodiment, it is assumed that there is essentially no knowledge of the ground (soil and rock) properties, seismic spectral energy, or structural properties of the turbine. External communication, dedicated seismic sensors, or earthquake detection systems based on standard turbine signals may be required. Furthermore, signals that serve as (preferably linear) proxies for the critical turbine loads can be used. This particular example may be based on an active pitch control of the seismic event controller that is enabled upon receiving a trigger signal from the seismic detection system. Once enabled, the active controller may use feedback from the (proxies for) turbine load signals to command the blade pitch positions to minimize the seismic loads. The control action may be based on a static or dynamic, linear or non-linear transfer function between the (multivariable) feedback load signal and the pitch position actuator. The active controller may actively command the same position for all three blades or perform individual pitch control to reduce the seismic loads.

[0047] According to a further embodiment, the method further comprises maintaining at least one blade in the second blade position, particularly for extended periods, and more particularly during periods of non-energy production, to anticipate a future, particularly sudden / unforeseen / undetectable, seismic event, which may have the advantage that seismic loads acting on the wind turbine are reduced even if the earthquake occurs suddenly and there is no time to further adapt the blade pitch position.

[0048] Typically, the blade pitch position is actuated to the first blade pitch position as a "safe" position in case of non-energy production, grid failure, internal failure, maintenance, or light wind conditions (in other words, when the wind turbine is shut down). However, the blade pitch position is maintained in the second blade pitch position (specifically most of the time, or (essentially) all the time) to efficiently reduce seismic loads in case of a sudden seismic event.

[0049] According to a further embodiment, there is provided a method for reducing seismic loads acting on a wind turbine during a seismic load causing event, in particular an earthquake, the wind turbine comprising a tower and a wind rotor arranged at a top portion of the tower and comprising at least one blade, the method comprising: maintaining the at least one blade in a second blade position in anticipation of an upcoming seismic event, the blade frequency being closer (more similar) to the ground frequency of the seismic event at a first blade pitch position different from the second blade position than at the second blade pitch position.

[0050] The above and further aspects of the present invention will be apparent from and explained with reference to the following examples of embodiments. The present invention will be explained in more detail below with reference to the following examples, but the present invention is not limited thereto. [Brief description of the drawings]

[0051] [Figure 1] 1 illustrates a wind turbine in accordance with an exemplary embodiment of the present invention; [Diagram 2] FIG. 1 illustrates a method for reducing seismic loads on a wind turbine according to an exemplary embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing a general definition of a blade pitch angle. [Figure 4] FIG. 2 is a diagram showing a general definition of a blade pitch angle.

[0052] Detailed Description The description in the figures is schematic. It should be noted that similar or identical elements or features in different drawings are given the same reference numbers or are given reference numbers that differ from the corresponding reference numbers only in the first digit. To avoid unnecessary repetition, elements or features already described with respect to the previous embodiments will not be described again in the remainder of the description.

[0053] Additionally, as shown in the figures, spatially relative terms such as "front" and "back", "top" and "bottom", "left" and "right" are used to describe the relationship of an element to another element. Thus, the spatially relative terms may be applied in an orientation different from that shown in the figures when used. Clearly, all such spatially relative terms refer only to the orientation shown in the figures for ease of description and are not necessarily limiting, as a device according to an embodiment of the invention may be in an orientation different from that shown in the figures when used.

[0054] According to an exemplary embodiment, it can be considered that when a wind turbine is subjected to a seismic event, the wind turbine may face maximum turbine loads when the acceleration spectrum of the earthquake excites the natural frequencies of the turbine structure. The natural frequencies of some wind turbine structural modes, including the first blade mode, are directly dependent on the blade pitch position. However, the blade pitch positions below the cut-in wind speed, above the cut-out wind speed and in the operating regime are traditionally designed only with the optimal turbine loads for maximum power generation and not seismic loads. When the turbine is subjected to seismic loads, this blade pitch position may not be optimal. As a specific example, maximum seismic loads may be experienced when the blades are in the feather position and unacceptably high seismic loads occur when the wind speed is low.

[0055] 1 shows a wind turbine 100 according to one embodiment of the present invention. The wind turbine 100 comprises a tower 120 (with supporting structural objects not shown) attached to the ground in an area where seismic events such as earthquakes may occur. The wind turbine 100 may be located onshore or offshore.

[0056] A nacelle 122 is arranged on top of the tower 120. Between the tower 120 and the nacelle 122 there is provided a yaw adjustment section 121 which allows the nacelle 122 to rotate about a vertical axis (not shown) aligned on the longitudinal extension of the tower 120. By appropriately controlling the yaw adjustment section 121 it is possible to ensure that the nacelle 122 is always properly aligned with the current wind direction during normal operation of the wind turbine 100.

[0057] The wind turbine 100 further comprises a wind rotor 110 having three blades 114. In the perspective view of Fig. 1, only two blades 114 are visible. The rotor 110 is rotatable about a rotation axis 110a. The blades 114 are attached to a hub 112, extend radially relative to the rotation axis 110a and rotate in a plane of rotation RP.

[0058] Between the hub 112 and the blades 114, a blade pitch angle adjustment device 116 is provided, and the blade pitch angle of each blade 114 is adjusted by rotating each blade 114 about an axis aligned substantially parallel to the longitudinal extension of each blade 114. By controlling the blade pitch angle adjustment device 116, the blade pitch angle of each blade 114 can be adjusted so as to extract maximum wind power from the available wind mechanical power driving the wind rotor 110, at least when the wind is not too strong.

[0059] As can be seen in Fig. 1, a gearbox 124 is provided in the nacelle 122. Using the gearbox 124, the rotational speed of the rotor 110 is converted to a higher rotational speed on a shaft 125, which is coupled in a known manner to an electromechanical converter 140. The electromechanical converter is a generator 140. It is pointed out in this respect that the gearbox 124 is optional and that the generator 140 may be directly coupled to the rotor 110 by the shaft 125 without changing the rotational speed. In this case, the wind turbine is a so-called direct drive (DD) wind turbine.

[0060] Additionally, a brake 126 is provided to safely stop operation of the wind turbine 100 or rotor 110 in the event of an emergency.

[0061] The wind turbine 100 further comprises a control system for operating the wind turbine 100 with high efficiency. For example, apart from controlling the yaw adjustment device 121, the illustrated control system also adjusts the blade pitch angle of the rotor blades 114 using the actuators 116 in an optimized manner.

[0062] The control system includes an earthquake event controller 153 configured to actuate the blades 114 from a first blade pitch position to a second blade pitch position different from the first blade pitch position, respectively, to reduce earthquake loads acting on the wind turbine 100. In the illustrated example, the earthquake event controller 153 controls / adjusts the blade pitch angle adjuster 116.

[0063] The earthquake event controller 153 further obtains information indicative of an earthquake event, which may be determined by the earthquake event controller 153 itself or may be obtained from an external earthquake event detection device 160, as shown in FIG.

[0064] FIG. 2 shows a diagram to explain how the actuation of the blade pitch angle can be used to reduce seismic loads acting on a wind turbine. The diagram shows the change in the bending moment at the top of the tower as a function of the (collective) blade pitch position. In particular, a simulation of an offshore wind turbine was performed. FIG. 2 shows along the x-axis the blade pitch angle [°] and along the y-axis the seismic load at the top of the tower [arbitrary units]. It can be seen that as a result of the implementation of the actuation of the blade pitch angle, the seismic load (bending moment) at the top of the tower is reduced. In particular, it can be seen that the seismic load is extremely large in the non-energy production regime and in the feather position (around 90°). Also, the seismic load is relatively large even at the idle pitch angle (in the range of 60°-86°). In contrast to this, at blade pitch angles in the energy production regime, for example below 30°, in particular below 20°, the seismic load on the tower is relatively small.

[0065] 3 and 4 show a common definition of blade pitch angle, which is the angle between the chord line CL of the blade 114 relative to the plane of rotation RP of the blade 114. The chord line CL is herein an imaginary line from the leading edge to the trailing edge of the blade 114.

[0066] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the articles "a" or "an" does not exclude a plurality. Also, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A wind turbine (100), comprising: Tower (120), a wind rotor (110) disposed at a top portion of the tower (120) and comprising at least one blade (114), the at least one blade (114) being disposed at a first blade pitch position; an earthquake event control device (153) configured to actuate the at least one blade (114) from the first blade pitch position to a second blade pitch position different from the first blade pitch position to reduce earthquake loads acting on the wind turbine (100); Equipped with a first blade edge resonant frequency at the first blade pitch position is closer to a seismic event dominant resonant frequency than a second blade edge resonant frequency at the second blade pitch position; and / or the first blade pitch position is a non-energy producing position and the second blade pitch position is an energy producing position; the seismic event controller (153) is further configured to obtain information indicative of ground characteristics, associate the information indicative of ground characteristics with each blade pitch position based on the operational data, and apply the associated information to the operation. A wind turbine (100).

2. The wind turbine (100) of claim 1 , wherein the first blade pitch position is a feathered position or an idle position.

3. the first blade pitch position is defined by a first blade pitch angle; the second blade pitch position is defined by a second blade pitch angle; Actuating the blade pitch angle of the at least one blade (114) includes rotating the at least one blade (114) about an axis aligned substantially parallel to a longitudinal extension of the at least one blade (114). The wind turbine (100) of claim 1 or 2.

4. The wind turbine (100) of claim 1 or 2, wherein the second blade pitch position is pre-specified.

5. The wind turbine (100) of claim 1 or 2, wherein the second blade pitch position is dynamically set.

6. The wind turbine (100) comprises two or more blades (114); the seismic event control device (153) is configured to collectively or individually actuate a blade pitch angle of each of the two or more blades (114). The wind turbine (100) of claim 1 or 2.

7. The wind turbine (100) of claim 1 or 2, wherein the seismic event controller (153) is configured to obtain information indicative of a seismic event prior to actuating the at least one blade (114).

8. the wind turbine (100) further comprising a seismic event detector for detecting information indicative of a seismic event; and / or The wind turbine (100) is configured to obtain information indicative of a seismic event from an external seismic event detector. The wind turbine (100) of claim 1 or 2.

9. The wind turbine (100) of claim 1 or 2, further comprising a back-up power source.

10. The earthquake event control device (153) further comprises: Obtain feedback information on turbine load; Applying the feedback information to act The wind turbine (100) of claim 1 or 2, configured as follows:

11. 1. A method of reducing seismic loads acting on a wind turbine (100) during a seismic load causing event, the wind turbine (100) comprising: a tower (120); and a wind rotor (110) disposed at a top portion of the tower (120), the wind rotor (110) comprising at least one blade (114), the at least one blade (114) being disposed in a first blade pitch position, the method comprising: obtaining information indicative of an event causing a seismic load; actuating the at least one blade (114) from the first blade pitch position to a second blade pitch position different from the first blade pitch position, thereby reducing seismic loads acting on the wind turbine (100); Including, a first blade edge resonant frequency at the first blade pitch position is closer to a seismic event dominant resonant frequency than a second blade edge resonant frequency at the second blade pitch position; and / or the first blade pitch position is a non-energy producing position and the second blade pitch position is an energy producing position; and reducing seismic loads on the wind turbine (100) further comprises obtaining information indicative of ground properties, associating the information indicative of ground properties with each blade pitch position based on the operational data, and applying the associated information to the operation. method.

12. The method of claim 11 , further comprising maintaining the at least one blade (114) in the second blade pitch position to prepare for a future seismic event.

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