Controlling a wind turbine with modified control parameter in relation to a special grid operation

Abstract

The present invention relates to a control of a wind turbine during special grid operation. The wind turbine comprises a damping system that can reduce vibrational movement of a component of the wind turbine. The damping system is dependent on at least one preset damping control parameter. Upon obtaining a requirement for special grid operation the preset damping control parameter is modified and vibrational movement of the component is monitored. Upon determining a requirement to damp the vibrational movement of the component, the damping system is actuated using the modified control parameter.

Description

[0001] Controlling a wind turbine with modified control parameter in relation to a special grid operation

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to control of a wind turbine, and in particular it relates to control of a wind turbine to dampen component vibrations during special grid operation.

[0004] BACKGROUND OF THE INVENTION

[0005] Modern wind turbines are controlled and regulated continuously with the purpose of ensuring optimal power extraction from the wind under the current wind, and weather, while at the same time ensuring that the loads on the different components of the wind turbine are at any time kept within acceptable limits, and while respecting externally set operational constraints.

[0006] Wind turbines as known in the art comprises a wind turbine tower supporting a nacelle and a rotor with a number of pitch-adjustable rotor blades. An exemplary wind turbine is a horizontal axis wind turbine with a nacelle positioned at the tower top, but also multi-rotor structures are known, such as a multi-rotor turbine with nacelles positioned at a tower structure in the form of one or more support arms extending from a central tower structure.

[0007] A wind turbine is prone vibrations since it comprises a large mass placed at the end of a slender tower or tower structure. These vibrations include nacelle movement in the side-side direction as well as in the fore-aft direction, i.e. tower vibrations. Moreover, the vibrations include blade vibrations, drive train vibration, etc. It is known in the art that the vibrations can be damped by actively pitching of the blades to generate counter forces to reduce the component movement, as well as to actively modify a power setpoint to generate a counter moment to reduce tower vibrations or drive train vibrations.

[0008] It is against this background that the invention has been devised.

[0009] SUMMARY OF THE INVENTION

[0010] The inventors of the present invention have realized that a damping system implemented in a controller of the wind turbine may beneficially be modified when a wind turbine is operated in a special grid operation mode. Accordingly, in a first aspect, there is provided a method of controlling a wind turbine, the wind turbine comprising a number of components, including a tower supporting a nacelle and a rotor with a number of pitch-adjustable rotor blades, an electrical power system connected to an electrical grid, and a drivetrain coupling the rotor with the electrical power system, the wind turbine comprises a damping system actuable to reduce vibrational movement of a component of the wind turbine, an actuation of the damping system being dependent on at least one preset damping control parameter, the method comprises: obtain a requirement for special grid operation; modify the preset damping control parameter; detecting vibrational movement of the component; upon determining a requirement to damp the vibrational movement of the component, actuate the damping system using the modified control parameter.

[0011] A damping system which is tuned to reduce component vibration during normal grid operational may risk having a reduced effectiveness when special grid operation is required or requested or may even risk work against the control of the wind turbine when the special grid operation is required or requested. A damping system is normally meticulous tuned to ensure that on one hand, the damping system effectively damp excessive vibrational movement of a component thereby avoiding shutdown of the wind turbine due to an unallowable high vibrational level of the component, but on the other hand the damping system is also tuned to allow vibrations below a certain low vibrational level to avoid wearing down the actuating system due to increased fatigue exposure from too frequent actuation.

[0012] In one embodiment, the requirement for special grid operation is obtained by detecting an occurrence of an abnormal grid event. An abnormal grid event may involve a low voltage event (LVE). A wind turbine may stay connected during an LVE or may disconnect from the grid during an LVE, depending on the nature of the LVE. As the generator is connected to the electrical grid when the LVE occurs, and possible throughout the event, the electrical system of the wind turbines sees the significant voltage transient or pulse and the rapid change of the grid. This grid change risks to couple to the mechanical components of the wind turbine and if so results in vibrational movement of one or more wind turbine components. The grid change may result in an active power change which either by itself or from a resulting thrust force change on the turbine leads to excitations of the mechanical structure.

[0013] Other types of abnormal grid events, such as a spike event, may likewise result in component vibrations. To prepare the damping system for possible resulting vibrational movement upon occurrence of an abnormal grid event, the preset damping control parameters are modified. The preset damping control parameters is beneficially modified to obtain a faster reaction of the damping system and thereby ensuring early detection of, and early reaction to, component vibrations resulting from the occurrence of the abnormal grid event. If the detected abnormal grid event does not result in excessive component vibrations, the damping system is merely more reactive until the damping control parameter are set back to the preset values. The consequences of a load impact from excessive component vibrations are more severe than the added fatigue impact on the actuating system for the limited period of time where the damping parameters are modified to obtain the faster reaction.

[0014] In one embodiment, the requirement for special grid operation is a request for the wind turbine to form part of the grid forming generators for the electrical grid.

[0015] In an electrical grid certain electrical generators need to be responsible for creating and maintaining the voltage and frequency of the electrical grid, these are so-called grid-forming electrical generators, and certain electrical generators synchronize their output with the voltage and frequency of the grid they are connected to, these are so-called grid-following electrical generators. In a normal grid operation, most wind turbines, if not all wind turbines, connected to an electrical grid is operated in grid -following mode. In many electrical grids grid-forming operation is done by synchronous generators, such as fuel powered turbines. However, as the presence of wind turbines in large electrical grids increases, or if the synchronous generator fails, there may be a requirement for a wind turbine to form part of the grid-forming generators.

[0016] For a grid-forming generator the grid operation is to create and control the voltage and frequency of the electrical grid, this is special grid operation, whereas for a grid-following generator the grid operation is to support the stability of the electrical grid by ensuring that the generated power is in synchronization with the electrical grid voltage and frequency, this is normal grid operation. In grid-following operation, the damping of structural vibrations has a high priority thereby prioritizing keeping fatigue exposure down over control of the electrical power output, whereas in a grid-forming operation, the priority is on voltage and frequency control at the expense on structural fatigue exposure. In grid-forming control the influence of a damping controller is beneficially reduced in order for the damping controller not to jeopardize the grid-forming operation by modifying the present damping parameters to obtain a slower reaction of the damping system. In this regard it is noted that in a grid-forming situation operating with modified damping parameters to obtain a slower reaction of the damping system and a further requirement for special grid operation is obtained by detecting an occurrence of an abnormal grid event, the damping parameters may beneficially be modified to obtain a faster reaction of the damping system and thereby ensuring early detection of, and early reaction to, component vibrations resulting from the occurrence of the abnormal grid event.

[0017] According to a further aspect of the invention there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the first aspect.

[0018] The computer program may be provided on a computer readable storage medium or being downloadable from a communication network. The computer program comprises instructions to cause a data processing system, e.g. in the form of a controller, to carry out the instruction when loaded onto the data processing system.

[0019] In accordance with another aspect of the invention there is provided a control system for a wind turbine, the control system comprising one or more controllers configured to implement the method of the first aspect.

[0020] In general, a controller may be a unit or collection of functional units which comprises one or more processors, input / output interface(s) and a memory capable of storing instructions can be executed by a processor.

[0021] In a further aspect of the invention there is provided wind turbine comprising a number of components, including a tower supporting a nacelle and a rotor with a number of pitch- adjustable rotor blades, an electrical power system connected to an electrical grid, and a drivetrain coupling the rotor with the electrical power system, the wind turbine comprises a damping system actuable to reduce vibrational movement of a component of the wind turbine, an actuation of the damping system being dependent on at least one preset damping control parameter, the wind turbine further comprises a control system comprising one or more controllers configured to implement the method of the first aspect.

[0022] In general the various aspects of the invention may be combined and coupled in any way possible within the scope of the invention. These and other aspects, features and / or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

[0025] Fig. 1 illustrates, in a schematic view, a wind turbine;

[0026] Fig. 2 illustrates, in a schematic view, a wind park;

[0027] Fig. 3 schematically illustrates examples of damping systems;

[0028] Fig. 4 illustrates a schematic figure of two control parameters;

[0029] Fig. 5 schematically illustrates operational steps implemented by a controller of the wind turbine; and

[0030] Fig. 6 illustrates elements of an embodiment where the grid state is an occurrence of an abnormal grid event resulting in vibrations of a component.

[0031] DESCRIPTION OF EMBODIMENTS

[0032] Figure 1 illustrates, in a schematic view, an example of a wind turbine 1. The wind turbine 1 includes a tower 2, a nacelle 3 disposed at the apex of the tower, and a rotor 4 operatively coupled to a generator housed inside the nacelle 3. In addition to the generator, the nacelle houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine 1. The rotor 4 of wind turbine includes a central hub 5 and a plurality of blades 6 that project outwardly from the central hub 5. In the illustrated embodiment, the rotor 4 includes three blades 6, but the number may vary. Moreover, the wind turbine comprises a control system. The control system may be placed inside the nacelle or distributed at a number of locations inside (or externally to) the turbine and communicatively connected. The rotor blades are pitch-adjustable. The rotor blades can be adjusted in accordance with a collective pitch setting, where each of the blades are set to the same pitch value. In addition to that, the rotor blades are adjustable in accordance with individual pitch settings, where each blade may be provided with an individual pitch setting.

[0033] The rotor blades 6 are mechanically connected to an electrical generator via a gearbox. In direct drive systems, and other systems, the gear box may not be present. The mechanical connection coupling the rotor and the electrical generator is typically referred to as the drivetrain. The electrical power generated by the generator is injected into an electrical grid 21 via an electrical converter. The electrical generator and the converter may be based on a full-scale converter (FSC) architecture or a doubly fed induction generator (DFIG) architecture, but other types may be used. The electrical components of the generator and the converter, possibly including further electrical components is typically referred to as he electrical power system.

[0034] Figure 2 illustrates, in a schematic view, an example of a group 20 of wind turbines of a wind park commonly supplying electric energy to an electrical grid 21.

[0035] The wind turbines are connected together in a wind park internal grid, which at a point 22 (typically a point of common coupling PCC, 22) is connected to a utility grid, such as a large- scale electrical grid 21.

[0036] Figure 2 further illustrates a communication network 23 which is connected to the control system of each wind turbine and to a power plant controller PPC 24, also sometimes referred to as a wind park controller or a wind farm controller. The PPC may via network connection 26 to a broader network, e.g. the internet, receive instructions and / or information from the system operator of the electrical grid 21.

[0037] Each wind turbine 1 comprises one or more damping systems actuable to reduce vibrational movement of a component of the wind turbine. Figure 3 A schematically illustrates a general damping system, and figures 3B-3D illustrate embodiments of damping systems in the form of tower vibration damping system, a blade vibration damping system and a drivetrain vibration damping system.

[0038] In embodiments, the damping system is a combination of a control element 30 typically implemented in the wind turbine control system and an actuator 31. The control element receives as input a sensor signal 32 representing the vibration of the component and calculates one or more output signals 33 for the damping actuator 31. Depending on the specific component and type of vibration, the damping system is actuable to adjust a pitch angle setpoint of a rotor blade and / or to adjust a power or torque setpoint of the electrical power system.

[0039] Figure 3B illustrates a damping system to reduce fore-aft tower vibrations as illustrated on Fig. 1 by the arrow 7. In a fore-aft damping system, the sensor input may be an acceleration signal, aFA, where the damping controller 3 OB is implemented to output a collective pitch offset, 0coi, in anti-phase with tower top fore-aft velocity. The collective pitch offset being sent to the pitch actuators 32 ABC of the pitch system.

[0040] Figure 3C illustrates a damping system to reduce side-side tower vibrations as illustrated on Fig. 1 by the arrow 8 or alternative a damping system to reduce edgewise blade vibrations as illustrated on Fig. 1 by the arrow 9. In a side-side tower damping controller 30C, the sensor input may be a sidewards acceleration signal, ass, and in a damping controller 30D to reduce edgewise blade vibrations, the sensor input may be blade load signal, Mei23, in an edgewise direction, one load signal for each blade. In such damping systems the damping controller is implemented to output individual pitch offsets, 0abc, to be send to the respective pitch actuators 32 ABC.

[0041] Figure 3D illustrates a damping system to reduce side-side tower vibrations as illustrated on Fig. 1 by the arrow 8 or alternative a damping system to reduce drivetrain vibrations (not illustrated on Fig. 1). In a side-side tower damping controller 30E, the sensor input may be a sidewards acceleration signal, ass, and in a damping controller 3 OF to reduce drivetrain vibrations, the sensor input may be a drivetrain rotational speed signal, o . In such damping systems the damping controller is implemented to output a power offset signal AP to be added to the power reference sent to the power controller 33 A or a torque offset signal AT to be added to a torque reference sent to the torque controller 33B.

[0042] Figure 3 provides schematic illustrations of a number of damping systems for reducing vibrational movement of certain wind turbine components. Other and different damping systems may be present in a wind turbine as is known to the skilled person.

[0043] The damping control systems comprise a number of preset damping control parameters, typically to control activation level and magnitude of response, but other control parameters are also possible.

[0044] Figure 4 illustrates a schematic figure of two control parameters, an actuation threshold 40 and a response gain 41. In the illustrated implementation, the actuation threshold is implemented as an input signal value below which the response gain is set to zero. The response gain is illustrated as a piecewise linear curve where above the actuation threshold 40 the response gain is linearly increased with the input signal value until a max value 42 above which the response gain saturates to a maximum value 43.

[0045] Figure 4 is typically applicable to a situation where a faster reaction of the damping system is desired, whereas for a situation where a slower reaction of the damping system is desired, the gain would start at a high value and be reduced to a low value, e.g. a zero gain.

[0046] The skilled person would understand that different and more elaborate actuation strategies can be implemented and that Fig. 4 is merely an illustrative example.

[0047] Damping control parameters to control activation level and magnitude of response are preset in a design or tuning phase. The actuation level is typically preset to a level where minor vibrations are not reacted upon in order not to wear out the actuation system too fast, and the response gain is adjusted to ensure sufficiently fast reaction but without risking overshoot effects. The preset values may be dependent on the operational point of the wind turbine. The damping control parameters may be implemented into the control element 30, e.g. as a gain multiplied to the output of the control element. Figure 5 schematically illustrates operational steps of embodiments of the invention, as implemented by a controller of the wind turbine.

[0048] In a first step, a requirement for special grid operation is obtained 50. Following such a determination that the requirement for special grid operation is obtained, the preset damping control parameters are modified 51. The vibrational movement of a component of the wind turbine is detected and upon determining a requirement to damp the vibrational movement of the component, the damping system is actuated 53 using the modified control parameter. The requirement to damp may be set as a given time the input signal needs to be above a certain threshold and may in an embodiment be defined by the activation threshold.

[0049] Figure 6 illustrates elements of an embodiment where the requirement for special grid operation is an occurrence of an abnormal grid event resulting in increased vibrations of a component. The figure illustrates two grid events GE1 and GE2 together with an example vibration curve 60 for a component. An abnormal grid event may involve a low voltage event (LVE) where the grid voltage suddenly drops either to a lower level or to zero voltage. Different types of grid events exist, and abnormal grid event generally relates to a pronounced change in the state of the grid. Such a low voltage event may relate to short- circuits in the grid, connection faults of prominent generators, etc. Examples of other types of abnormal grid events include phase jumps of either of the voltage or current in the electrical grid, and frequency gradients of the electrical voltage or current.

[0050] In figure 6 two low voltage grid events are schematically shown, a short event GE1 and a longer event GE2. Both events occur at time tl and ends a time t2 and t4, respectively. Due to the grid event a voltage pulse is injected into the grid resulting e.g. in an active power or thrust force changes and thereby vibrations of a component. For example a steep rise and fall of a voltage pulse may result in a transient generator torque pulse that via the electromagnetic coupling to the drivetrain may excite vibrations of various components.

[0051] As a vibration is building up, the damping system will at some point register the vibration and start to counter it. However, by modifying the preset damping control parameter upon detecting the abnormal grid event, the damping system can be set to react much faster to vibrational movement and thereby avoid too high vibrational levels and keeping the load exposure level down. This is illustrated in Fig. 6 by that the vibration level is not building up but kept constant already from the beginning, followed by a fast reduction of the vibrational amplitude.

[0052] In an embodiment, the damping control parameter is an actuation threshold 40 and the modification of the damping control parameter is a reduction of the actuation threshold. The damping control parameter may either as an alternative or in addition be a response gain 41 and the modification of the damping control parameter is an increase of the response gain 41, i.e. by setting a steeper slope, increasing the maximum gain 43 or a setting of the response gain to the maximum gain at a lower vibrational level 42.

[0053] In an embodiment, the damping control parameter may be a vibrational level, such as a preset vibrational threshold level. Figure 6 further schematically illustrates a preset vibrational threshold level 61, here illustrated as a root mean square (RMS) vibrational threshold level below which the vibrational level of the component is not considered to be problematic, this may be referred to as a monitor threshold. Moreover, the RMS level 62 of the vibrational signal is also shown, e.g. a RMS signal based on an acceleration signal of the component. Additionally, a preset vibrational threshold level 64 in the form of an alarm level is also shown.

[0054] In an embodiment a delay time is defined during which the modified damping control parameter is maintained. After expiry of the delay time and in the event a vibrational level of the vibrational movement of the component is below the preset vibrational level 61 of the component, the damping control parameter is changed back to the preset value. The vibrational level of the movement may be evaluated based on an RMS value as schematically illustrated in Fig. 6, but other ways of comparing a vibrational level to a threshold exists, including low-pass filtering the vibrational signal. In Fig. 6, the RMS vibrational level is seen to rapidly increase upon the occurrence of the abnormal event at tl, stabilize and slowly decrease until it falls below the threshold 61 at t3. In Fig. 6, for a delay time less than t3, the modified damping control parameters would be used until the time t3, at which time the RMS value the vibration signal 62 drops below the preset vibrational level 61, whereas for a delay time larger than t3, the modified damping control parameters would be used until the expiry of the delay time. In another embodiment, a detection that the abnormal grid event has ended is made and in the event a vibrational level of the vibrational movement of the component is below the preset vibrational level 61 of the component, the damping control parameter is changed back to the preset value. In this embodiment, in Fig. 6, for the grid event GE1, the modified damping control parameters would be used until the time t3 since the event ends at t2 where the vibrational level 62 is above the vibrational level 61. Whereas for the longer grid event GE2, the modified damping control parameters would be used until the expiry of the event at t4.

[0055] In an example where a wind turbine comprises a number of damping systems, exemplified by a fore-aft tower damping system and a side-side tower damping system. Each damping system comprising specific damping control parameters and for each damping system a preset damping control parameter may be modified.

[0056] As an example, the vibrational input signals can be the tower top acceleration in the fore-aft direction and the tower top acceleration in the side-side direction. The damping controller may determine a root mean square value of a moving window for each signal and the preset damping control parameters may be a preset root mean square value threshold defining an activation threshold. A tower may be better damped by the structure itself in the fore-aft direction than in the side-side direction, and consequently a higher preset activation threshold may be set for the fore-aft control parameter than for the side-side control parameter. The fore-aft vibration may be damped by modifying the collective pitch, whereas the side-side vibration may be damped by modifying the individual pitch and / or active power. These are two distinct damping mechanisms and consequently the response gains are tuned differently for the two damping systems. The damping system may comprise two or more damping control parameters and at least one of the preset damping control parameters is modified. In the above example, a fore-aft tower damping system and a side-side tower damping system are used as the exampled, however the principle applies to further damping systems, such as a drivetrain damping system (DTD) and blade damping systems.

[0057] In a concrete example, each damping system comprises three damping control parameters: activation threshold, response gain slope and max response gain.

[0058] Thus the side-side tower damping controller is more responsive than the fore-aft damping controller, both in relation to the preset values and in relation to the modified values. By setting the modified response gain slope to a very high value amounts to set the response gain to max directly.

[0059] In an embodiment, each of the damping systems comprises a damping system specific delay time. For example, for an edgewise blade vibration a relatively short delay time may be needed, at least for some blade types, since as soon as the excitation has stopped the vibration level may decay fast, whereas for side-side tower damping, due to the low structural damping in the side-side direction, a long delay time may be beneficial. In an embodiment, the delay time is set based on the vibrational time constant of the component so that the delay time for a component with a shorter time constant is shorter than the delay time for a component with a longer time constant.

[0060] The detection of the occurrence of the abnormal grid event may be done by the electrical power system by monitoring the electrical grid 21 e.g. by monitoring grid voltage and current and their phases as well as grid frequency.

[0061] The detection of the occurrence of the abnormal grid event may also be done by the electrical power system by monitoring a drivetrain torque, such as monitoring the maximum drive train torque and / or torque slope with time.

[0062] In the examples above, the damping control parameter is one of an actuation threshold and a response gain, and where the modification of the damping control parameter is a modification of at least one them. In an embodiment, the damping control parameter may alternatively or additionally be a vibrational level, so that the modification of the damping control parameter may alternatively or additionally be a modification of a vibrational level. Further damping control parameters may also be included. The vibrational level may be an alarm level above which the wind turbine operational mode is changed to a safe-mode, such as a safety shutdown. It may be beneficial to increase a vibrational alarm level, at least temporally, e.g. as large component vibrations may result from an abnormal grid event and due to the modified damping control, an increased alarm level can be tolerated.

[0063] In an embodiment the vibrational movement of the component is compared to a vibrational threshold level of the component to determine a comparison value, and maintaining the modified damping control parameter as long as the comparison value fulfils a preset comparison criterion. For example, the comparison criterion may be that the difference 63 between the RMS vibration level 62 and an alarm level in the form of an RMS vibrational threshold level 64 is below a specified value. For example, for a long time period where special grid operation is required, it may be beneficial to apply the modified damping control settings as long the monitored vibrational movement is at a given distance from the shutdown threshold defined by the alarm level 64. In particular, for operation with modified damping parameters to obtain a slower reaction of the damping system, such slow reaction can be allowed as long as the turbine is not close to a given alarm level.

[0064] Figure 6 is illustrated for the embodiment where the requirement for special grid operation is obtained by detecting an occurrence of an abnormal grid event. In a further embodiment, the requirement for special grid operation is defined as a request for the wind turbine to form part of the grid forming generators for the electrical grid. This request may in embodiment be provided by a grid operator via the power plant controller 24 to the wind turbines 20, but can also be from the converter of the wind turbine itself.

[0065] In embodiments, the damping control parameter is an actuation threshold and the modification of the damping control parameter is an increase of the actuation threshold allowing the wind turbine to vibrate at a higher level. In an embodiment where the damping control parameter is a response gain the modification of the damping control parameter is a decrease of the response gain or a setting of the response gain to a minimum gain thereby reducing the responsiveness of the damping controller.

Claims

CLAIMS1. A method of controlling a wind turbine, the wind turbine comprising a number of components, including a tower supporting a nacelle and a rotor with a number of pitch- adjustable rotor blades, an electrical power system connected to an electrical grid, and a drivetrain coupling the rotor with the electrical power system, the wind turbine comprises a damping system actuable to reduce vibrational movement of a component of the wind turbine, an actuation of the damping system being dependent on at least one preset damping control parameter, the method comprises: obtain a requirement for special grid operation; modify the preset damping control parameter; detecting vibrational movement of the component; upon determining a requirement to damp the vibrational movement of the component, actuate the damping system using the modified control parameter.

2. The method according to claim 1, wherein the requirement for special grid operation is obtained by detecting an occurrence of an abnormal grid event.

3. The method according to any preceding claims, wherein the damping control parameter is an actuation threshold and wherein the modification of the damping control parameter is a reduction of the actuation threshold.

4. The method according to any preceding claims, wherein the damping control parameter is a response gain and wherein the modification of the damping control parameter is an increase of the response gain or a setting of the response gain to a maximum gain.

5. The method according to any preceding claims, wherein the vibrational movement of the component is compared to a vibrational threshold level of the component to determine a comparison value, and wherein the modified damping control parameter is maintained as long as the comparison value fulfils a preset comparison criterion.

6. The method according to any preceding claims, further comprising a delay time during which the modified damping control parameter is maintained and after expiry of the delay time and in the event a vibrational level of the vibrational movement of thecomponent is below a preset vibrational level of the component, the damping control parameter is changed back to the preset value.

7. The method according to any preceding claims, further comprising detecting that the abnormal grid event has ended and in the event a vibrational level of the vibrational movement of the component is below a preset vibrational level of the component, change the damping control parameter back to the preset value.

8. The method according to any preceding claims, wherein the wind turbine comprises a number of damping systems each comprising specific damping control parameters and wherein for at least one of the damping systems the preset damping control parameter is modified.

9. The method according to any preceding claims, wherein the damping system comprises two or more damping control parameters and wherein at least one of the preset damping control parameters is modified.

10. The method according to claim 6, wherein the delay time of a component is set based on a vibrational time constant of the component so that the delay time for a component with a shorter time constant is shorter than the delay time for a component with a longer time constant.

11. The method according to any preceding claims, wherein the detection of the occurrence of the abnormal grid event is detected by the electrical power system by monitoring the electrical grid or by monitoring a drivetrain torque.

12. The method according to any of the claims 3-11, wherein the requirement for special grid operation is a request for the wind turbine to form part of the grid forming generators for the electrical grid.

13. The method according to claim 12, wherein the damping control parameter is an actuation threshold and wherein the modification of the damping control parameter is an increase of the actuation threshold.

14. The method according to any preceding claims, wherein the damping control parameter is a response gain and wherein the modification of the damping control parameter is a decrease of the response gain or a setting of the response gain to a minimum gain.

15. The method according to any preceding claims, wherein the damping control parameter is a vibrational level.

16. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claims 1 to 15.

17. A control system for a wind turbine, the wind turbine comprising a number of components, including a tower supporting a nacelle and a rotor with a number of pitch- adjustable rotor blades, an electrical power system connected to an electrical grid, and a drivetrain coupling the rotor with the electrical power system, the wind turbine comprises a damping system actuable to reduce vibrational movement of a component of the wind turbine, an actuation of the damping system being dependent on at least one preset damping control parameter, the control system comprising one or more controllers configured to: obtain a requirement for special grid operation; modify the preset damping control parameter; detecting vibrational movement of the component; upon determining a requirement to damp the vibrational movement of the component, actuate the damping system using the modified control parameter.

18. A wind turbine comprising a number of components, including a tower supporting a nacelle and a rotor with a number of pitch-adjustable rotor blades, an electrical power system connected to an electrical grid, and a drivetrain coupling the rotor with the electrical power system, the wind turbine comprises a damping system actuable to reduce vibrational movement of a component of the wind turbine, an actuation of the damping system being dependent on at least one preset damping control parameter, the wind turbine further comprises a control system comprising one or more controllers configured to: obtain a requirement for special grid operation; modify the preset damping control parameter; detecting vibrational movement of the component;upon determining a requirement to damp the vibrational movement of the component, actuate the damping system using the modified control parameter.

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