Damping device for a wind turbine
By using magnet devices to generate variable magnetic force in a wind turbine to damp vibration, the problems of large and heavy damping devices in the prior art are solved, and effective adaptation to multiple resonant frequencies and noise reduction are achieved.
Patent Information
- Application Number
- CN202380054501.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-07-08
- Filing Date
- 2023-06-21
- Publication Date
- 2025-03-07
AI Technical Summary
Vibration in wind turbines leads to fatigue stress and noise problems, existing damping devices are usually large and heavy, and tuning is difficult to effectively combat multiple resonant frequencies simultaneously.
The magnet device is used to dampen by magnetic force, including a base fixed to the surface of the wind turbine and a magnet device, to damp or cancel vibrations by using the magnetic action between the first magnet and the second magnet, and to adapt vibrations at different frequencies through a variable magnetic field.
It provides a lightweight, space-saving solution that can effectively reduce or prevent tone noise and adapt to vibrations at different frequencies, avoiding dependence on large mechanical damping devices.
Smart Images
Figure CN119585523A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure generally relates to an apparatus and corresponding method for damping vibrations in a wind turbine. Background Art
[0002] Typical wind turbine generator (WTG) components vibrate during operation, the magnitude and frequency of the vibrations depending on wind load, the rotational speed of the rotor and other operating factors. Such vibrations lead to fatigue stresses in the components of the WTG and may therefore shorten component life. In addition, vibrations generated in rotating components of the WTG (e.g., gearboxes or other components of the drive train) may be transmitted through the structure of the WTG and emitted as noise from the tower, nacelle or blades, thus resulting in tonal noise or tones. It is desirable to limit the level of tonal noise generated by the WTG, for example to comply with operating regulations.
[0003] It is known to mount vibration damping devices on and / or in a WTG, for example in a nacelle, to counteract oscillations and prevent resonances. However, these devices typically rely on mechanical or fluid devices for absorbing energy from the resonant system. Such devices are typically large and heavy, which means that installing and maintaining the damping device can be difficult and costly within the limited space available in the nacelle.
[0004] Furthermore, depending on operating conditions (e.g., rotational speed), WTG resonances can be excited at multiple different frequencies, so a damping device tuned to mitigate resonances at a particular frequency will fail to damp other resonances. In the worst case, tuned damping devices may exacerbate resonances at frequencies other than those for which they were tuned.
[0005] It is in this context that the present invention is designed. Summary of the invention
[0006] According to one aspect of the present invention, a damping device for a wind turbine is provided. The damping device includes: a base capable of being fixed to the surface of the wind turbine; and a magnet device. The magnet device includes a first magnet and a second magnet. The first magnet is fixed relative to the base and is arranged to generate a first magnetic field. When the base is fixed to the surface, the second magnet is supported by the base to be spaced apart from the first magnet. The second magnet is arranged to generate a second magnetic field, which interacts with the first magnetic field to generate a magnetic force acting between the first magnet and the second magnet. In this way, the magnetic force is used to damp or offset vibrations in the surface. At least one of the first magnetic field and the second magnetic field is variable, so that vibrations of varying frequencies can be resolved.
[0007] This device for generating a magnetic force for damping or counteracting vibrations in a surface provides a lightweight and space-saving solution for reducing or preventing tonal noise in a wind turbine. Because the first magnetic field and / or the second magnetic field are variable, the magnitude of the magnetic force can be varied and controlled for a given spacing between the first magnet and the second magnet. This in turn allows the magnetic force to be manipulated to act as a damping force that can target vibrations of a range of different frequencies.
[0008] The base may include a first magnet, which may be a permanent magnet. Alternatively, the first magnet may include a solenoid and / or an electromagnet. By integrating the first magnet with the base, the damping device may be magnetically coupled to a surface of the wind turbine, thereby advantageously alleviating the need for additional connection means, which may increase the weight and bulk of the device and may cause stress concentrations in the surface.
[0009] The second magnet may also include a solenoid and / or an electromagnet. In embodiments where the first magnet is a solenoid and / or an electromagnet, the second magnet may be a permanent magnet. The damping means may include a substantially rigid coupling that couples the second magnet to the base. Rigid couplings are particularly advantageous in embodiments where surface vibrations are actively cancelled because the rigid coupling efficiently transfers the forces that cause the anti-phase vibrations to the surface.
[0010] As an alternative to the rigid coupling, the damping device may also include a damping mass and a spring device. In such an embodiment, the damping mass is supported by the base so as to be movable relative to the base while being fixed relative to the second magnet. Accordingly, the spring device is configured to act between the base and the damping mass to bias the damping mass relative to the base. For example, the spring device may be configured to bias the damping mass away from the base or toward the base. The damping mass and the spring device are used together as a tuned mass damper, also referred to as a harmonic absorber or a dynamic absorber. In some embodiments, the second magnet may include a damping mass. In such an embodiment, the second magnet may include a solenoid arranged around the damping mass. The solenoid may be fixed relative to the damping mass to form an electromagnet.
[0011] The spring means may comprise one or more resilient members, such as springs including helical springs or leaf springs, or elastic material elements. The spring means may be made of rubber, coiled metal or any other suitable material.
[0012] The damping device may further comprise a sensor, such as a displacement sensor, configured to generate a signal indicative of the spacing between the base and the damping mass, which sensor may for example be mounted on the base or on a surface next to the base. Additionally or alternatively, the damping device may comprise a sensor configured to generate a signal indicative of vibrations on the surface, such as an accelerometer optionally mounted on the base or on a surface next to the base.
[0013] The damping device may further include a controller configured to control the magnet device to change the magnetic force. In an embodiment comprising a sensor configured to generate a signal indicating a vibration on a surface, the controller may be configured to control the magnet device according to the signal. More preferably, the controller may be configured to control the magnet device to change the magnetic force in antiphase with the indicated vibration. In an embodiment comprising a damping mass and a spring device, the controller may be configured to control the magnet device to change the magnetic force, thereby mimicking the changed spring stiffness of the spring device. In such embodiments that also include a sensor configured to generate a signal indicating the spacing between the base and the damping mass, the controller may be configured to control the magnet device according to the signal. In each case, the controller may be configured to control the magnet device according to a signal indicating an operating parameter of the wind turbine, the operating parameter including any one or more of the following: generator speed or its derivative; rotor speed or its derivative; blade pitch; or power output.
[0014] According to another aspect of the invention, a damping system for a wind turbine is provided. The damping system comprises a base, a damping mass, a spring arrangement, a magnet arrangement and a controller. Similar to the above-described embodiments, the base is capable of being fixed to a surface of the wind turbine, and when the base is fixed to the surface, the base supports the damping mass to be movable relative to the base. The spring arrangement is configured to act between the base and the damping mass to bias the damping mass relative to the base, for example away from the base or towards the base. The magnet arrangement is configured to generate a variable magnetic force acting on the damping mass, and the controller is configured to control the magnet arrangement to generate the variable magnetic force.
[0015] The magnet arrangement may comprise a magnet which is fixed relative to the damping mass.
[0016] The damping system may comprise the damping device of the above aspect such that the base, the damping mass, the spring means and the magnet means of the damping system are defined by corresponding features of the damping device.
[0017] The invention also extends to a wind turbine comprising a damping system or a damping arrangement of the above aspect.
[0018] According to a third aspect of the invention, there is provided a method for damping vibrations in a wind turbine. The method first comprises fixing a first magnet to a surface of the wind turbine, the first magnet being arranged to generate a first magnetic field. The method further comprises supporting a second magnet at a position spaced apart from the first magnet, so that the second magnet is arranged to generate a second magnetic field, the second magnetic field interacting with the first magnetic field to generate a magnetic force acting between the first magnet and the second magnet to damp vibrations in the surface. The method further comprises changing at least one of the first magnetic field and the second magnetic field to change the magnetic force. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order that the present invention may be more fully understood, it will now be described, by way of example only, with reference to the following drawings, in which like features are assigned like reference numerals, and in which:
[0020] Figure 1 is a front view of a wind turbine including a damping device according to an embodiment of the present invention;
[0021] Figure 2 yes Figure 1 a transverse cross-sectional view of a wind turbine showing a damping device; and
[0022] Figure 3 is a schematic diagram of a damping device according to an embodiment of the present invention. DETAILED DESCRIPTION
[0023] In general, embodiments of the present invention provide damping devices that use magnetic interactions to remove energy from an oscillating system. While embodiments of the present invention can in principle be used to damp vibrations in various structures, the described embodiments are particularly suitable for installation or retrofitting in wind turbines to damp vibrations generated by rotating components, thereby reducing tonal noise.
[0024] In an embodiment to be described, the damping device comprises a magnet arrangement configured to generate a variable magnetic force acting on a component of the damping device to damp vibrations in a surface on which the damping device is mounted, the magnetic force thus defining the damping force.
[0025] The magnet arrangement may be used in conjunction with a tuned mass damper, for example, in which case the damping force may act on the damping mass of the tuned mass damper. For example, the damping force may be controlled to produce a variable resistance to movement of the damping mass, thereby increasing the biasing force provided by the spring arrangement supporting the damping mass, and thereby mimicking the effect of changing the stiffness of the spring arrangement. Changing this stiffness in turn changes the frequency at which the mass damper is effectively tuned, and thereby enables targeting of various resonant frequencies.
[0026] Alternatively, the damping force may be controlled in dependence on measurements of vibrations in the mounting surface, e.g. varying the damping force in anti-phase with the measured vibrations and thereby providing active damping that actively counteracts vibrations in the wind turbine surface. The damping force may oscillate, e.g. to act in opposite directions, or may act in only one direction, but with varying magnitude.
[0027] The device may include: a base for attaching the device to the wind turbine; and a magnet device at least partially supported by the base. The magnet device may include a first magnet and a second magnet, wherein the first magnet is fixed relative to the base and the second magnet is supported by the base, for example by a support structure connected to the base, so that the first magnet and the second magnet are spaced apart from each other. In some embodiments, the first magnet defines the base. The first magnet and the second magnet are configured to generate corresponding magnetic fields, which interact to generate a damping force, so that in this case, the damping force acts between the magnets, for example as a repulsive force for pushing the magnets apart. At least one of the magnetic fields is variable, so that the damping force is correspondingly variable. For example, one or both of the magnets may include a solenoid or an electromagnet. Either of the first magnet and the second magnet may include a permanent magnet.
[0028] However, the magnet arrangement may also comprise a single variable magnet which generates the damping force.
[0029] By utilizing magnetic interactions to modify the damping characteristics of the device or to induce anti-phase damped oscillations, embodiments of the present invention provide variable damping that can target resonances at multiple different frequencies and thus account for varying operating conditions in the WTG. The described device may also eliminate the need for mechanical or fluid damping devices that would otherwise be large and heavy. Thus, the described device provides a lighter, more compact damping solution that can be more easily installed within the limited space available in a wind turbine.
[0030] If the base comprises magnets of the magnet arrangement, advantageously the magnetic properties of the base allow the damping device to be magnetically coupled to a ferromagnetic surface of the wind turbine, in particular if the magnets are permanent magnets. This avoids the need for mechanical fasteners, which require holes to be drilled in the surface of the wind turbine and in the base. In turn, stress concentrations and fatigue problems that may arise around the holes and mechanical fasteners are eliminated. Furthermore, vibrations between the surface of the wind turbine and the damping device are reduced, which means that the effectiveness of the damping device is improved. By eliminating the need for mechanical fasteners, the installation and placement of the damping device is simplified, which means that the device is also suitable for retrofitting in existing wind turbines.
[0031] To provide background for the present invention, Figure 1A typical horizontal axis WTG, also referred to hereinafter as a wind turbine 2, is shown comprising a nacelle 4 mounted atop a tower 6 supporting a forward-facing rotor 8 comprising a plurality of co-planar blades 10. Figure 2 As shown, the rotor 8 is connected to a power train or drive train 12 housed within the nacelle 4. The drive train 12 includes the components required to convert the rotation of the rotor 8 into electricity, including a generator 14, a gear system 16, and a controller 18. In use, undesirable vibrations generated by the rotor 8 and the drive train components 12 are transmitted to other components of the wind turbine, such as the nacelle 4 and the blades 10, thereby causing tonal noise.
[0032] like Figure 2 As shown, the vibration damping device 20 is coupled to the inner surface 22 of the nacelle 4. In this embodiment, it is envisaged that the nacelle 4 includes an internal structural frame made of steel. In this way, the damping device 20 is magnetically coupled to the frame, as will be described below with respect to Figure 3 However, it should be understood that Figure 2 The placement of the damping devices 20 in is purely illustrative, and in practice, one or more damping devices 20 may be positioned elsewhere in the nacelle or anywhere in or on the wind turbine 2, such as on a particular drive train component 12, depending on where the damping force may be most effective in reducing vibrations.
[0033] Now go to Figure 3 , an example of a damping device 20 is shown. As shown, the damping device 20 includes a damping mass 22, which is coupled to a base 24 via an elastic device or spring device 26. In this example, the spring device 26 includes a linear spring element 32 in the general form of a coil spring, the spring element 32 having a first end 28 and an opposite second end 30. The first end 28 is coupled to the base 24 and the second end 30 is coupled to the damping mass 22. The first end 28 and the second end 30 of the spring device 26 can be mechanically fastened and / or adhered to and / or integrated with the base 24 and the damping mass 22, respectively.
[0034] The spring arrangement and the damping mass 22 together form a damping assembly 31 which defines a tuned mass damper, also known as a harmonic absorber or a dynamic absorber. However, unlike conventional tuned mass dampers, the effective stiffness of the damping assembly 31 is not determined solely by the characteristics of the spring arrangement 26, but is variable. Since the frequency at which the damping assembly 31 primarily damps vibrations is related to its stiffness, the ability to vary its stiffness means that the frequency at which the damping assembly 31 damps vibrations is correspondingly variable, as will become clear from the following description.
[0035] The base 24 is defined by a rigid block having an upper surface 34 and a lower surface 36. The second end 30 of the spring device 26 is coupled to the upper surface 34 of the base.
[0036] The base 24 comprises a permanent magnet 38 which defines a first magnet of a magnet arrangement of the damping device 20. Thus, the base 24 is configured to magnetically couple the damping device 20 to a ferromagnetic surface 40, such as a steel frame of the nacelle 4. That is, the permanent magnet 38 generates a magnetic field whose size and strength are suitable for inducing sufficient magnetic attraction between the base 24 and the surface 40 to resist the weight of the damping device 20.
[0037] More specifically, permanent magnet 38 generates a first magnetic field and is arranged with base 24 so that its magnetic axis (referred to as the first magnetic axis) 44 is substantially perpendicular to surface 40. In this example, permanent magnet 38 is oriented so that its north pole (N1) engages surface 40 and its south pole ( S1 )exist Figure 3 Faces downward in the orientation shown.
[0038] The damping mass 22 takes the form of a cylindrical solid mass comprising a ferromagnetic material, such as steel. The damping mass 22 is housed within a coil of electrically conductive wire forming a solenoid 48, which forms part of an electrical circuit. The solenoid 48 is configured to generate a second magnetic field around the damping mass 22 when energized. Thus, the solenoid 48 and the damping mass 22 together form an electromagnet 54, which defines a second magnet of the magnet arrangement. The electromagnet 54 has a magnetic axis (referred to as the second magnetic axis) 52, which is aligned with the longitudinal axis of the damping mass 22. As will be appreciated, the characteristics of the second magnetic field can be varied by varying the corresponding characteristics of the current passing through the solenoid 48.
[0039] The damping mass 22 and the base 24 are spaced apart from each other and arranged relative to each other so that the first magnetic axis 44 and the second magnetic axis 52 are aligned and therefore parallel to each other. In addition, the damping mass 22 is configured and oriented so that the south pole (S2) of the electromagnet 54 is closer to the surface 40 than the north pole (N2) thereof. In this manner, the respective south poles (S1, S2) of the base 24 and the damping mass 22 face each other. It should be understood that this arrangement can be reversed so that the respective north poles (N1, N2) face each other without affecting the operating mode described below.
[0040] The spacing of the damping mass 22 and the base 24 and the respective strengths of their magnetic fields are such that the first magnetic field and the second magnetic field overlap and interact when the electromagnet 54 is operated. Due to the relative orientation of the magnetic fields, the base 24 and the damping mass 22 are configured to magnetically repel each other when the electromagnet 54 is operated. In other words, when the electromagnet 54 is activated, a repulsive magnetic force is generated between the base 24 and the damping mass 22, and the magnitude of the magnetic force can vary depending on the current applied to the solenoid 48.
[0041] The magnitude of the magnetic force also depends on the relative positions of the first and second magnetic fields and therefore varies as damping mass 22 moves. Generally speaking, if the strengths of the first and second magnetic fields remain constant, the magnetic force increases as damping mass 22 moves toward base 24.
[0042] The magnetic force supplements the biasing force or "spring force" generated by the spring element 32 acting between the base 24 and the damping mass 22. In this example, the spring element 32 is configured to bias the damping mass 22 away from the base 24, so that the spring force and the magnetic force act in the same direction. Therefore, the effective stiffness of the damping assembly 31 is a function of the combination of the magnetic force and the spring force. Because the magnetic force is variable and controllable, the effective stiffness of the damping assembly 31 is correspondingly variable and controllable. In general, increasing the magnitude of the magnetic force has the effect of increasing the overall stiffness of the damping assembly 31.
[0043] Depending on the stiffness of the spring element 32, the spring force generated by the spring element 32 increases when the spring element 32 is compressed by the movement of the damping mass 22. In the present example, the spring element 32 is linear, so the spring force increases linearly with compression. However, in other examples, the spring element can be replaced with a nonlinear elastic member, such as a rubber element, in which case the spring force varies nonlinearly with the movement of the damping mass 22.
[0044] When the first magnet and the second magnet move together, the magnetic force defined by the magnetic repulsion between the first magnet and the second magnet also increases approximately linearly, which in this example complements the distribution of the spring force. In other examples using elastic members that produce nonlinear spring forces, this can be solved by monitoring the movement of the damping mass 22 and controlling the magnetic force accordingly. This may require changing the magnetic force in a manner corresponding to the spring force when the damping mass 22 moves to match the nonlinear distribution of the spring force, or changing the magnetic force to compensate for the nonlinearity of the spring force so that the overall stiffness of the damping device is linear. In this way, the magnet device can be used to mimic the increase in the stiffness of the spring element 32.
[0045] Conversely, when the base 24 is excited, the damping assembly 31, which is actually stiffer, absorbs the higher frequency resonance. Therefore, the magnet arrangement can be used to increase the effective stiffness of the damping assembly 31 to achieve the target resonance at a higher frequency, and correspondingly, the effective stiffness of the damping assembly 31 can be reduced to achieve the target resonance at a lower frequency.
[0046] The damping device 20 also includes a controller 56 that is configured to operate in a dynamic mode. According to the dynamic mode, the controller is configured to receive signals indicative of the speed of the rotor and / or the generator, and determine the vibration frequency of the surface 40 (and, by extension, the base 24) based on these signals. The controller is also configured to determine a target damping frequency and / or a target effective stiffness of the damping assembly 31 required to reduce the vibration frequency, and to control the current through the solenoid 48 to achieve the target damping frequency and / or the target effective stiffness. That is, the controller 56 is configured to dynamically adjust the strength of the second magnetic field as a way of adjusting the repulsive force between the base 24 and the damping mass 22, thereby adjusting the effective stiffness of the damping assembly 31.
[0047] The controller 56 may be a dedicated controller, or it may be implemented as a control block or module within an existing controller of the wind turbine 2 , such as a turbine controller.
[0048] The damping device 20 also includes a displacement sensor 58 mounted on the base 24 and communicatively coupled to the controller 56, the displacement sensor 58 being configured to generate a signal indicative of the spacing between the base 24 and the damping mass 22. Suitable sensors may include, for example, optical distance sensors, ultrasonic sensors, or linear position sensors. The displacement sensor 58 is configured to repeatedly measure the distance to the damping mass 22 and transmit the measurement data to the controller 56. As will be appreciated, as the damping mass 22 vibrates relative to the base 24, the measurement data over time will include peaks and valleys.
[0049] The controller 56 is configured to monitor the measurement data and compare the measured distance change with the expected distance change. Therefore, the controller 56 is also configured to apply a corrective damping force when a lower than expected distance change is measured. In this way, the displacement sensor 58 and the controller cooperate to diagnose and correct errors in the target effective stiffness.
[0050] The displacement sensor 58 also enables monitoring of the movement of the damping mass 22, which may be necessary if, as described above, a nonlinear elastic member is used to provide a spring force between the base 24 and the damping mass 22. In this case, the controller 56 can synchronize the change in the magnetic force with the change in the spring force so that the magnetic force changes in a curve similar to the spring force.
[0051] In addition, the controller 56 is configured to identify irregularities in the received distance variation data, which indicate erroneous operation of the damping device 20 resulting in unacceptable tonal noise. The controller 56 may also be configured to address such faulty operation, for example by shutting down the wind turbine 2. In this way, the displacement sensor 58 and the controller 56 are used together to prevent the wind turbine from operating under conditions that produce tonal noise that does not comply with current regulations.
[0052] In this example, the controller 56 is additionally configured to operate in an active mode. To this end, in this example, the displacement sensor 58 is accompanied by a vibration sensor 60 , such as an accelerometer, which is mounted on the base 24 beside the displacement sensor 58 .
[0053] The vibration sensor 60 is configured to detect vibrations in the surface 40, such as the amplitude and phase of the vibrations, and transmit corresponding data to the controller 56. When in the active mode, the controller 56 is configured to control the second magnetic field so as to drive the damping mass 22 to vibrate in anti-phase with the surface 40, thereby neutralizing the surface vibrations. For example, by oscillating the current in the solenoid, the strength and / or polarity of the second magnetic field can be oscillated. In turn, the resulting oscillating magnetic force causes the damping mass to oscillate accordingly.
[0054] When operating in active mode, the distance change data received by the controller 56 from the displacement sensor 58 can additionally be used to inform precise control of the anti-phase movement. Thus, the controller 56 can use signals received from both the displacement sensor 58 and the vibration sensor 60 simultaneously.
[0055] In other embodiments, the controller may be configured to operate in only one of the active mode and the dynamic mode, in which case only one of the vibration sensor and the displacement sensor is required.
[0056] The skilled person will appreciate that modifications may be made to the specific embodiments described above without departing from the inventive concept defined by the claims.
[0057] For example, the damping device can be configured with a spring force and a magnetic force that act in different directions than the above examples. For example, the spring force can be used to bias the damping mass away from the base. Similarly, the first magnet and the second magnet can be oriented to generate an attractive magnetic force between them. The spring force and the magnetic force can act in opposite directions.
[0058] For a damping device configured to operate in a dynamic mode and including a damping assembly having a damping mass supported to be movable relative to a base, in some embodiments, a single magnet is used to resist or accelerate the movement of the damping mass, thereby changing the effective stiffness of the device. For example, a solenoid disposed around the damping mass may be configured to generate a magnetic field that is used to directly move the damping mass, such as in the manner of a solenoid actuator.
[0059] As described above, the first magnet and the second magnet can be connected by a rigid connection rather than by a spring. This may be useful for a damping device configured to actively cancel vibrations, because the anti-phase vibrations generated in the damping device can be more effectively transferred to the vibrating surface through the rigid connection.
Claims
1. A damping device for a wind turbine, the damping device comprising: a base capable of being secured to a surface of the wind turbine; as well as A magnet device, the magnet device comprising: a first magnet, the first magnet being fixed relative to the base, the first magnet being arranged to generate a first magnetic field; and a second magnet, when the base is fixed to the surface, the second magnet is supported by the base to be separated from the first magnet, and the second magnet is arranged to generate a second magnetic field, and the second magnetic field interacts with the first magnetic field to generate a magnetic force acting between the first magnet and the second magnet; wherein at least one of the first magnetic field and the second magnetic field is variable.
2. The damping device according to claim 1, wherein: The base includes the first magnet.
3. A damping device according to any one of the preceding claims, wherein: The first magnet includes a permanent magnet.
4. The damping device according to claim 1 or 2, wherein: The first magnet comprises a solenoid and / or an electromagnet.
5. A damping device according to any one of the preceding claims, wherein: The second magnet includes a solenoid and / or an electromagnet.
6. A damping device according to any one of the preceding claims, comprising: a damping mass supported by the base to be movable relative to the base, the damping mass being fixed relative to the second magnet; as well as Spring means act between the base and the damping mass to bias the damping mass relative to the base.
7. The damping device according to claim 6, wherein: The damping mass and the spring arrangement together form a tuned mass damper.
8. The damping device according to claim 6 or 7, wherein: The spring arrangement comprises at least one elastic member.
9. The damping device according to any one of claims 6 to 8, wherein: The second magnet comprises the damping mass.
10. The damping device according to claim 9, wherein: The second magnet includes a solenoid disposed around the damping mass.
11. The damping device according to claim 10, wherein: The solenoid is fixed relative to the damping mass.
12. A damping device according to any one of claims 6 to 11, comprising a sensor configured to generate a signal indicative of the spacing between the base and the damping mass.
13. A damping device according to any one of claims 1 to 5, comprising a rigid coupling coupling the second magnet to the base.
14. A damping device as claimed in any preceding claim, comprising a sensor configured to generate a signal indicative of vibration of the surface.
15. A damping device according to any preceding claim, comprising a controller configured to control the magnet arrangement to vary the magnetic force.
16. A damping device according to claim 15 when dependent on claim 14, wherein: The controller is configured to control the magnet arrangement in dependence on the signal indicative of vibration of the surface.
17. The damping device according to claim 16, wherein: The controller is configured to control the magnet arrangement to vary the magnetic force in anti-phase with the indicated vibration.
18. A damping device according to claim 15 when dependent on any one of claims 6 to 12, wherein: The controller is configured to control the magnet arrangement to vary the magnetic force so as to mimic a varying spring rate of the spring arrangement.
19. A damping device according to claim 18 when dependent on claim 12, wherein: The controller is configured to control the magnet arrangement in dependence on the signal indicative of a separation between the base and the damping mass.
20. A damping system according to any one of claims 15 to 19, wherein: The controller is configured to control the magnet arrangement in accordance with a signal indicative of any one or more of: generator speed; rotor speed; blade pitch; or power output.
21. A damping system for a wind turbine, the damping system comprising: a base capable of being secured to a surface of the wind turbine; a damping mass supported by the base to be movable relative to the base when the base is secured to the surface; a spring arrangement acting between the base and the damping mass to bias the damping mass relative to the base; a magnet arrangement configured to generate a variable magnetic force acting on the damping mass; as well as A controller is configured to control the magnet arrangement to generate the variable magnetic force.
22. The damping system of claim 21, wherein: The magnet arrangement comprises a magnet which is fixed relative to the damping mass.
23. A damping system according to claim 21 or 22, comprising a damping device according to any one of claims 1 to 20.
24. A wind turbine comprising a damping device according to any one of claims 1 to 20 or a damping system according to any one of claims 21 to 23.
25. A method of damping vibrations in a wind turbine, the method comprising: securing a first magnet to a surface of the wind turbine, the first magnet being arranged to generate a first magnetic field; supporting a second magnet spaced apart from the first magnet, the second magnet being arranged to generate a second magnetic field that interacts with the first magnetic field to generate a magnetic force acting between the first magnet and the second magnet to damp vibrations in the surface; as well as At least one of the first magnetic field and the second magnetic field is changed to change the magnetic force.