Patent Description:
A wind turbine converts wind power into electrical energy using the aerodynamic force on its blades to operate a generator via a series of drive train components. As the various components of the wind turbine rotate structural borne noise is generated due to the vibrations of these mechanical parts, for example vibrations can be generated from tooth meshing between gears.

The vibrations are transferred to the wind turbine and emitted as noise by the wind turbine structure, for example by the tower or blades, and at certain frequency bands (tonalities) the noise, if left unchecked, could reach unacceptable levels and also generate undesirable loads.

The effects of these vibrations are particularly evident at resonant frequencies where the vibrations are amplified. Documents <CIT> and <CIT> are prior art examples of detuner systems for wind turbines.

A first aspect of the invention provides a detuner system for a wind turbine, comprising: a drive train component having a natural frequency and configured to rotate about an axis of rotation at a range of different speeds; and a controller for selectively interacting with the drive train component, wherein the controller is configured to cause a step change in the natural frequency of the drive train component at a first threshold of the rotational speed range, and to cause a step change in the natural frequency of the drive train component at a second threshold of the rotational speed range, wherein the rotational speed range at the second threshold is different to the rotational speed at the first threshold.

A further aspect of the invention provides a wind turbine comprising the detuner system according to the first aspect.

A further aspect of the invention provides a method of operating a wind turbine, the wind turbine comprising: a drive train component having a natural frequency and configured to rotate about an axis; and a controller for selectively interacting with the drive train component, the method comprising: rotating the drive train component about the axis at a range of different speeds; causing a step change in the natural frequency of the drive train component at a first threshold of the rotational speed range; and causing a step change in the natural frequency of the drive train component at a second threshold of the rotational speed range different to the first threshold.

The controller is arranged to selectively interact with the drive train component at at least the first and second thresholds of the rotational speed range to cause the step changes in the natural frequency. The controller may include fully active or partially active control elements. In other words, the controller may be configured to regulate or command the step change in the natural frequency of the drive train component. The detuner system allows particular frequencies and frequency bands, such as resonant frequencies, to be avoided, damped or cancelled. This can reduce the noise emitted by the wind turbine. The detuner system may be activated only when it is required and without interrupting the continued operation of the wind turbine.

The controller may be configured to cause a change in the natural frequency by altering one or more of the: mass, mass moment, stiffness, and/or damping of at least a portion of the drive train component. For example, the controller may be coupled to an actuator or effector for moving a mass or changing the stiffness or other property of a component of the system so as to cause the change in the natural frequency.

The natural frequency of the drive train component below the first threshold of the rotational speed range and/or above the second threshold of the rotational speed range may be constant.

The first threshold and/or second threshold of the rotational speed range may be configured to be determined based on the operational power of the wind turbine.

The first threshold and/or second threshold of the rotational speed range may be configured to be determined prior to rotating the drive train component.

The first threshold and/or second threshold of the rotational speed range may be configured to be determined based on a threshold vibrational amplitude of the rotating drive train component.

The detuner system may comprise two or more threshold vibrational amplitudes of the rotating drive train component.

A limited band of the rotational speed may be defined between the first threshold and the second threshold of the rotational speed range. The detuner system may comprise two or more limited bands of the rotational speed range.

The detuner system may comprise a mass for interacting with the drive train component, wherein the controller is configured to enable movement of the mass relative to the drive train component.

The mass may be configured to move radially with respect to the axis of the drive train component.

The mass may be configured to move axially along the axis of the drive train component.

The natural frequency between the first and second thresholds of the rotational speed range may be altered. Alternatively, the natural frequency may be constant between the first and second thresholds of the rotational speed range.

A position of the mass relative to the drive train component at a speed below the first threshold of the rotational speed and at a speed above the second threshold of the rotational speed may be substantially the same.

The natural frequency may be a torsional natural frequency and/or a bending natural frequency.

The detuner system may comprise a high-speed shaft and a low-speed shaft, wherein the controller is configured to interact with the high-speed shaft.

Natural frequency is the frequency that a system tends to oscillate at in the absence of any external forces.

A step change may be a significant change in the natural frequency such that there is a notable, significant change in the natural frequency of the drive train component. The step change may occur over a short time period, e.g. of the order of <NUM> second or less.

<FIG> shows a wind turbine <NUM> including a tower <NUM> mounted on a foundation and a nacelle <NUM> disposed at the apex of the tower <NUM>. The wind turbine <NUM> depicted here is an onshore wind turbine such that the foundation is embedded in the ground, but the wind turbine <NUM> could be an offshore installation in which case the foundation would be provided by a suitable marine platform.

A rotor <NUM> is operatively coupled via a gearbox to a generator housed inside the nacelle <NUM>. The rotor <NUM> includes a central hub <NUM> and a plurality of rotor blades <NUM>, which project outwardly from the central hub <NUM>. It will be noted that the wind turbine <NUM> is the common type of horizontal axis wind turbine (HAWT) such that the rotor <NUM> is mounted at the nacelle <NUM> to rotate about a substantially horizontal axis defined at the centre at the hub <NUM>. While the example shown in <FIG> has three blades, it will be realised by the skilled person that other numbers of blades are possible.

When wind blows against the wind turbine <NUM>, the blades <NUM> generate a lift force which causes the rotor <NUM> to rotate, which in turn causes the rotation of components within the drive train <NUM> in order to allow a generator <NUM> within the nacelle <NUM> to generate electrical energy.

<FIG> shows the drive train <NUM> inside the nacelle <NUM> of a wind turbine <NUM>. The drive train <NUM> includes a series of components connected between the rotor <NUM> and a generator <NUM>. The drive train <NUM> includes an input shaft <NUM> (low speed shaft) attached between the rotor <NUM> and a gearbox <NUM>, an output shaft <NUM> (high speed shaft) downstream of the gearbox <NUM>, a brake <NUM> coupled between the output shaft <NUM> and an auxiliary shaft <NUM>, and a generator <NUM> coupled to the auxiliary shaft <NUM>, such that a mechanical driving force is transferred from the rotor <NUM> to the generator <NUM> to generate electricity.

As a result of the relative mechanical motion between parts, vibrations are generated, for example due to misalignment between the drive train <NUM> components. A significant source of mechanical noise is the gearbox <NUM>, which can cause vibrations due to imperfections in the gear shape and pitch. Vibrations are also an inherent characteristic of any moving system with multiple components that move relative and are in contact with each other. The vibrations can produce audible noises (structural borne noise) at certain frequencies and/or discrete frequency bands (tonalities), particularly at the resonant frequencies of the drive train components.

The amplitude A (or response) of the vibrations generated by the components of the drive train <NUM> are dependent upon the rotational frequency F (or speed) of the drive train component, and may include one or more resonant frequencies, as shown in <FIG> depicting the response at a variety of frequencies/speeds at the source of the vibrations. The resonant frequency can be a torsional resonant frequency or a bending resonant frequency. These vibrational responses are then propagated directly from the component into the air.

The vibrational response may be transmitted to another component of the wind turbine, as shown in <FIG> depicting the response at a variety of frequencies/speeds at the other wind turbine component. In the process the vibrational response may change (as compared with the response at the source), for example the amplitude A of each resonant peak may decrease or increase, and the number of resonant peaks may increase or decrease.

The transmitted vibrational response may then be radiated by a surface of the wind turbine, such as the tower <NUM>, nacelle <NUM>, or blades <NUM> for example - so called 'structure borne noise' or SBN. As shown in <FIG> the radiating surface will have resonant frequencies (broken line and solid line) which may combine with the transmitted vibrational response (solid line in <FIG>), to produce the depicted response of <FIG> at a variety of frequencies/speeds at the radiating surface.

Whilst vibrations of components of the drive train <NUM> are mostly unavoidable, they may not be a problem. For example, if the source vibration level is low there may be no appreciable tonality. Even if the source vibration level is high, it may not be effectively transmitted into the other component(s) of the wind turbine, resulting in no appreciable tonality. Even if the source vibration level is high, and it is effectively transmitted into the other component(s) of the wind turbine, it may not be effectively radiated from a surface of the wind turbine, resulting in no appreciable tonality.

However, at certain rotational speeds of the components of the drive train <NUM> the source vibration level may be high and may be effectively transmitted into another component of the wind turbine and may be effectively radiated from a surface of the wind turbine, resulting in appreciable tonality. As shown in <FIG>, the amplitude A of the resultant noise, or tonal audibility, received at a microphone or receiver (not shown) some distance away from the wind turbine may be greater than an acceptable threshold T, or 'tone line level'. The threshold T may be different at different rotational speeds. There may be more than one threshold T, i.e. multiple tone line levels. Each threshold may be tailored for different scenarios, such as operational importance, wind turbine location and weather conditions.

This invention generally relates to avoiding or cancelling the amplitude peaks above the tone line level or threshold T at the receiver by changing the natural frequency of one or more components of the drive train <NUM> for a limited band of the rotational speed of the component(s). The limited band of the rotational speed is defined between a first threshold of the rotational speed range and a second threshold of the rotational speed range of components of the drive train <NUM>. Tonality is caused by vibration sources which excite system resonances to radiate tones. When an excitation source crosses a resonance frequency of a component the amplitudes are significantly amplified.

The natural frequency is a system characteristic that depends on the mass, mass moment, stiffness, and damping of a component or components. The dependence of the natural frequency on each of these parameters may vary, for example, depending on the structure of the drive train components, the interaction of components of the wind turbine, and the type of natural frequency (e.g. bending or torsional natural frequency).

<FIG> shows a detuner system <NUM> attached to a rotating shaft, e.g. the output shaft <NUM> of the drive train <NUM>. The output shaft <NUM> is rotatable about an axis of rotation <NUM>. The detuner system <NUM> may be a tonality detuner, which is a device which is used to jump or avoid resonances during operation without impacting the operation, e.g. of the drive train <NUM>. The detuner system <NUM> includes a mass <NUM> coupled to an actuator <NUM> by a lever <NUM>, with movement of the mass <NUM> relative to the output shaft <NUM> being controlled by a controller <NUM> connected to the actuator <NUM>. The actuator <NUM> is attached to an outer radial face <NUM> of the drive train component. When the output shaft <NUM> rotates about the axis of rotation <NUM>, the output shaft <NUM> vibrates at a frequency F dependent on the speed of rotation S of the output shaft <NUM>. This F/S excitation relationship is approximately linear, as shown in <FIG>.

At a certain speed of rotation S of the output shaft <NUM>, the vibrational frequency F matches a resonance frequency <NUM> of the output shaft <NUM>. At this resonance frequency <NUM> there is a significant increase in the amplitude of the vibrational excitation of the output shaft <NUM>, which may be transmitted through the wind turbine and result in a significant increase in the tonal noise emitted or radiated by a surface of the wind turbine. The tonal noise observed at a receiver can increase above an acceptable threshold amplitude across a band of frequencies, such that a lower frequency bound <NUM> and an upper frequency bound <NUM> on either side of the resonance frequency <NUM> are defined. A lower rotational speed bound <NUM> and an upper speed rotational bound <NUM> can be defined, within which the vibrations of the output shaft <NUM> lie within the band of frequencies bounded by the lower frequency bound <NUM> and the upper frequency bound <NUM>.

The natural frequency <NUM> of the output shaft <NUM> can be changed, e.g. by altering the mass distribution or inertial properties or stiffness or damping of the output shaft <NUM>, such that the rotational speed of the output shaft at which resonance occurs is shifted to a lower or higher rotational speed. The effect of causing a change in the natural frequency of the output shaft <NUM> is that the natural frequency of adjacent components of the drive train <NUM> and the wind turbine <NUM> as a whole may also be altered. In the example shown in <FIG> the inertia of the output shaft <NUM> is increased or decreased when the rotational speed gets close to exciting the resonance such that the resonance is at a higher or lower frequency. When the speed has passed the resonance frequency, i.e. is outside the speed band bounded by the lower rotational speed bound <NUM> and the upper rotational speed bound <NUM>, the inertia is put back to normal. In the example shown in <FIG>, the mass <NUM> is moved to change the inertia of the output shaft <NUM>. The mass <NUM> in this example is moved radially and axially with respect to the axis of rotation <NUM> of the output shaft <NUM> by the actuator <NUM>. The motion of the mass <NUM> on the lever arm <NUM> about the actuator <NUM> causes the torsional natural frequency and the bending natural frequency to change.

The actuation of the mass <NUM> is controlled by a controller <NUM> connected to the actuator. The natural frequency of the output shaft <NUM> is altered for a limited band of the rotational speed range. In the example shown in <FIG>, the mass <NUM> is moved from a first position (shown in <FIG>) to a second position (shown in <FIG>) at a lower bound (first threshold) <NUM> of the limited band of the rotational speed range, and then the mass <NUM> is moved from the second position (<FIG>) back to the first position (<FIG>) at an upper bound (second threshold) <NUM> of the rotational speed range, such that the vibrational frequency of the output shaft <NUM> is different to the natural frequency of the output shaft <NUM> within the limited band. The output shaft <NUM> has a first natural frequency at the first position (<FIG>) of the mass <NUM>, and a second natural frequency at the second position (<FIG>) of the mass <NUM>.

The detuner system <NUM> is able to selectively alter a natural frequency of the drive train components in order to jump/avoid resonant frequencies, without affecting the operation of the wind turbine <NUM>.

In an alternative example shown in <FIG>, there are two resonant frequencies of the component that is the source of the vibration, e.g. the output shaft <NUM>, within the rotational speed range. In this case, two limited bands of the rotational speed range are defined. The mass <NUM> is moved from a first position to a second position at a lower bound (first threshold) 33a of the first limited band of the rotational speed range. Then the mass <NUM> is moved from the second position back to the first position at an upper bound (second threshold) 34a of the first rotational speed range. The mass <NUM> is then maintained at the first position until the rotational speed is increased up to the lower bound (first threshold) 33b of the second rotational speed range, at which point the process repeats between the lower bound (first threshold) 33b and upper bound (second threshold) 34b of the second rotational speed range. The advantage is that this allows multiple resonant frequencies to be targeted by the detuner system without changing the natural frequency over an extended frequency range between the two resonant frequencies.

In an alternative example shown in <FIG>, the natural frequency below the first threshold of the rotational speed range and the natural frequency above the second threshold of the rotational speed range may be different.

In a further example, the drive train component may have more than one mass <NUM> able to actuate relative to the drive train component. For example, <FIG> shows a detuner system <NUM> including four masses 21a, 21b, 21c, 21d attached to the output shaft <NUM>. The output shaft <NUM> is rotatable about the axis of rotation <NUM>. Each mass 21a, 21b, 21c, 21d of the detuner system <NUM> is coupled to a respective actuator 23a, 23b, 23c, 23d by a lever 22a, 22b, 22c, 22d. As in the previous examples, movement of the mass <NUM> relative to the output shaft <NUM> is controlled by a controller (not shown) connected to the actuator <NUM>.

When the output shaft <NUM> rotates about the axis of rotation <NUM>, the output shaft <NUM> vibrates at a frequency F dependent on the speed of rotation S of the output shaft <NUM>. The vibrations can contribute to the resonance of the output shaft <NUM> and the system as a whole. Movement of the four masses <NUM> provides increased options to change the natural frequency of the output shaft <NUM> and the system as a whole. For example, <FIG> shows a configuration in which all four masses 21a-d are actuated about the axis of the actuator 23a-d through an acute angle, <FIG> shows a configuration in which all four masses 21a-d are actuated about the axis of the actuator 23a-d through an obtuse angle. In the examples shown in <FIG> and <FIG> the masses 21a-d are positioned at the same radial distance from the axis of rotation <NUM> of the output shaft <NUM> but different axial locations along the axis of rotation <NUM>, and therefore would be expected to have a substantially equivalent affect upon the torsional natural frequency but a different affect upon the natural bending frequency.

The masses 21a-d may be actuated towards the axis of rotation <NUM> of the output shaft <NUM>, as shown in <FIG>. This may require cut-outs or fillets (not shown) to be made in the output shaft <NUM> to accommodate the masses 21a-d.

Each of the masses 21a-d may be actuated to different axial positions along the axis of rotation <NUM>. For example, <FIG> shows a configuration in which a first mass 21a and a fourth mass 21d are moved axially further outboard of their respective actuators 23a,d in comparison to a second mass 21b and a third mass 21c. In <FIG>, an example is shown in which a first mass 21a, a second mass 21b, and a third mass 21c are all positioned axially inboard of their respective actuators 23a,b,c, but a fourth mass 21d is positioned axially outboard of its actuator 23d.

The masses 21a-d may also be positioned at different radial positions relative to the axis of rotation <NUM>. For example <FIG> shows an example in which the first mass 21a and fourth mass 21d are positioned at a first radial distance H1 from the axis of rotation <NUM>, and the second mass 21b and third mass 21c are positioned at a second radial distance H2 from the axis of rotation, wherein the second radial distance H2 is smaller than the first radial distance H1. <FIG> shows an example in which the first mass 21a is at a maximum radial extent of the lever 22a, the lever 22b of the second mass 21b is oriented to be parallel to the axis of rotation <NUM> but with the second mass 21b positioned axially outboard of its actuator 23b, the lever 22c of the third mass 21c is oriented to be parallel to the axis of rotation <NUM> but with the third mass 21c positioned axially inboard of its actuator 23c, and the fourth mass 21d is positioned at a radial position between the maximum and minimum extent of the lever 23d.

Each configuration may be arranged to target a specific frequency or be tailored for a specific mode of operation. In both the configurations with one mass <NUM>, or configurations with a plurality of masses <NUM>, the radial and axial position of each mass <NUM> can be tailored to selectively alter the bending and/or torsional natural frequency of the drive train component.

In the previous examples the drive train component is an output shaft <NUM>. The invention is particularly applicable to the output shaft <NUM> due to the relative high speed of rotation of this component (with respect to other drive train components). This means that the mass can be smaller, or the effects of an equivalent mass amplified. However, it will be understood that the invention is also applicable for use on any other rotating part of the drive train <NUM>, for example, the input shaft <NUM>, the gearbox <NUM> (or one or more of its gears), the brake <NUM>, the auxiliary shaft <NUM>, the generator <NUM>, the non-drive end of the generator, or any other suitable component known in the art. In an alternative example, the wind turbine <NUM> may not comprise a gearbox. In this case, the drive train component may be a component of a direct drive turbine system.

In the previous examples, the actuator <NUM> is positioned on an outer radial face <NUM> of the output shaft <NUM> that is parallel to the axis of rotation. In an alternative example, the actuator <NUM> may be positioned on a radial edge <NUM> of the drive train component perpendicular to the axis of rotation <NUM>. This may be particularly suitable for disc-like components of the drive train, such as the brake <NUM>, as shown in <FIG>.

In an alternative example shown in <FIG>, the controller <NUM> may include a latch for selectively releasing a mass <NUM> on a spring <NUM>. The latch <NUM> holds the mass <NUM> in a constant radial position relative to the axis of rotation <NUM> of the output shaft <NUM> until a particular rotational speed and/or vibrational frequency of the output shaft <NUM> is reached. The latch <NUM> may be passively actuated, such that the mass <NUM> is released at a pre-set condition, or the latch <NUM> may be actively actuated by the controller <NUM> by measuring the state of the drive train component and responding at an appropriate rotational speed and/or vibrational frequency value. The controller <NUM> may then move the mass <NUM> back towards the axis of rotation, for example the controller may reset the position of the mass <NUM> back to its original position. The latch <NUM> may be a spring latch, a magnetic latch, or any other suitable latch known in the art. In this way, the controller may be fully active or may be partially active, partially passive.

In an example shown in <FIG>, the spring <NUM> may be a non-linear spring that is able to control the position of the mass <NUM>. For example, the stiffness of the spring can be controlled by a variable electro-magnetic field (not shown), such that for a limited band of the rotational speed of the output shaft <NUM> the stiffness of the spring can be reduced to allow radial movement of the mass <NUM> relative to the axis of rotation <NUM>. The spring may be oriented such that it extends at an angle to the axis of rotation <NUM>. This allows the relative change in the bending natural frequency and torsional natural frequency to be tailored. The controller <NUM> may then control an actuator to move the mass <NUM> back towards the axis of rotation, for example to its original position.

The lever arm <NUM> extending from the output shaft <NUM> to the mass <NUM> may include a piezoelectric element <NUM>, as shown in <FIG>. The piezoelectric element <NUM> allows the stiffness of the lever arm <NUM> to be changed. A controller <NUM> can be used to control the application of electric current to the piezoelectric element <NUM> in order to provide the change in stiffness of the lever arm <NUM>, as shown in <FIG>. The effect of the change in stiffness is to change the inertial properties of the output shaft <NUM> and alter the natural frequency, such that the natural frequency of the drive train component (in this case an output shaft <NUM>) may be changed for a limited band of the operational speed range.

In an alternative example the mass <NUM> may be a liquid, such as oil. The liquid may be pumped relative to one or more drive train components to change the natural frequency of the drive train components. <FIG> show an example in which oil <NUM> is held in an oil reservoir <NUM> until a lower bound <NUM> of the rotational speed range of the output shaft is reached. Oil <NUM> is then pumped along a pipe <NUM> by a pump <NUM> into an oil cavity <NUM> adjacent to the output shaft <NUM>. The effect of displacing the oil relative to the output shaft <NUM> is to cause the natural frequency of the output shaft <NUM> to be altered. At an upper bound <NUM> of the rotational speed range the oil <NUM> may then be pumped back along the pipe <NUM> by the pump <NUM> into the oil reservoir <NUM>, such that the natural frequency of the output shaft <NUM> returns to its starting value. The pump may be an oil lubrication pump. The oil may also be part of an oil lubrication system. A controller (not shown) is used to control a valve that determines the flow of oil that is pumped relative to one or more of the drive train components. The controller may include one or more pressure relief valves that determine the liquid pressure at which the liquid is moved from the reservoir <NUM> to the oil cavity <NUM>.

The controller <NUM> may be linked to the main control system of the wind turbine. The controller <NUM> may communicate with the main control system of the wind turbine. Alternatively the controller <NUM> may be separate and independent of the main control system of the wind turbine.

The detuner system <NUM> may be suitably mounted or integrated into many components of the drive train <NUM>, for example, the input shaft <NUM>, the gearbox <NUM> (or one or more of its gears), the output shaft <NUM>, the brake <NUM>, the auxiliary shaft <NUM>, the generator <NUM>, the non-drive end of the generator, or any other suitable component known in the art.

It may be positioned within one of these components or at the interface between one or more of them. The detuner system <NUM> may be suitably positioned within the drive train <NUM> to cancel vibrational modes by counter phase vibrations. For example, by changing the natural frequency of one drive train component such that the vibrations counter the vibrations of an adjacent drive train component.

It will be clear that there may be one limited band of the rotational speed, or alternatively more than one limited band of the rotational speed. wherein the speed range defined by each respective limited band may be smaller or larger than each other limited band of the rotational speed. For example a second limited band may be larger or smaller than a first limited band. Outside of the limited bands of the rotational speed range the natural frequency of the drive train component is left substantially unchanged.

The position of the mass <NUM> relative to the drive train component and/or the stiffness of the lever arm <NUM> may be the same at rotational speeds above and below the limited band of the rotational speed range. Alternatively, the relative position of the mass <NUM> relative to the drive train component and/or the stiffness of the lever arm <NUM> may be different above the rotational speed range than below the rotational speed range, although in both cases the position of the mass <NUM> and/or stiffness of the lever arm <NUM> will be substantially constant at rotational speeds outside of the limited band.

The detuner system <NUM> may be configured to change the torsional and/or bending natural frequency of the drive train component. The detuner system <NUM> may be configured to control the relative changes of the torsional natural frequency and bending natural frequency, such that in a first configuration the torsional natural frequency is increased by more than the bending natural frequency, and in a second configuration the bending natural frequency is increased more than the torsional natural frequency. The proportional changes of the bending and torsional natural frequencies may be controlled.

The natural frequency of the drive train component may be increased and/or decreased. The natural frequency may be maintained between the first and second thresholds of the rotational speed range. The natural frequency of the drive train component below the first threshold of the rotational speed range and/or above the second threshold of the rotational speed range may be constant.

The limited band of the rotational speed range of the drive train component may be predetermined prior to operation. In this case, the limited band of the rotational speed range, defined between a lower bound <NUM> and an upper bound <NUM> of the rotational speed range of the drive train component, may be equally spaced apart from the expected position of the resonant frequency. Alternatively, the natural frequency may be closer to the upper <NUM> or lower <NUM> bound of the limited band of the rotational speed range.

The limited band of the rotational speed range of the drive train component may be predetermined based on a threshold vibrational amplitude of the rotating drive train component. The vibrational amplitude may be actively measured. The detuner system <NUM> may predict the onset of a resonant frequency based on a measured vibrational response. There may be one or more vibrational frequency amplitudes.

In the examples shown, the actuator <NUM> is a rotary actuator. In alternative examples, the actuator <NUM> may be a linear actuator. In this case the actuator may be oriented such that the mass <NUM> moves only radially from the axis of rotation <NUM>, or the mass <NUM> moves only axially along the axis of rotation <NUM>, or combines both radial and axial movement of the mass <NUM>.

The spring <NUM> may be an axially extending spring or a torsional spring.

Claim 1:
A detuner system (<NUM>) for a wind turbine (<NUM>), comprising:
a drive train component (<NUM>) having a natural frequency and configured to rotate about an axis of rotation at a range of different speeds; the detuner system is characterized in that it further comprises
a controller (<NUM>) for selectively interacting with the drive train component (<NUM>),
wherein the controller (<NUM>) is configured to cause a step change in the natural frequency of the drive train component above a first threshold (<NUM>) of the rotational speed range, and to cause a step change in the natural frequency of the drive train component below a second threshold (<NUM>) of the rotational speed range,
wherein the rotational speed at the second threshold (<NUM>) is different to the rotational speed at the first threshold (<NUM>).