Noise Control for Wind Turbines

Abstract

A method for adjusting the noise emission configuration (15) of a plurality of wind turbines (3) is described, the method comprising: determining a total wind turbine related noise level (9, 13) at a plurality of locations (7); determining a critical location (7c) having a most critical, in particular a highest total wind turbine related noise level (9c) among the plurality of locations; if the most critical total wind turbine related noise level (9c) is above a noise threshold value (11c): reducing the noise emission configuration of the wind turbine (3b) having the highest noise power impact ratio.

Description

Technical Field

[0001] The invention relates to a method of adjusting the noise emission configuration of a plurality of wind turbines, to a wind park controller, to a wind park and to a method of controlling the noise emission of a single or a plurality of wind turbines. Background Art

[0002] Wind turbines generate noise during operation, i.e. when they rotate and generate electrical energy. Therefore, wind turbines emitting noise disturb the environment. Where wind turbines are installed near buildings, such as private buildings, it may be required that the noise emission remains below a legal maximum sound pressure level. In particular, the total sound pressure at adjacent locations may need to not exceed a given threshold level.

[0003] To conventionally reduce noise emissions from wind turbines, the rotational speed (of the rotor in which the plurality of rotor blades are mounted) has been reduced. A reduction in the rotational speed results in a reduction in emitted noise. Since torque is generally limited, when the rotational speed is reduced, the maximum power will also be reduced. Thus, conventional methods for reducing noise will typically result in a significant reduction in annual electrical energy production, typically 2-4% per year per decibel noise reduction.

[0004] Furthermore, the blade pitch angle has an impact on noise emission and can be configured in conjunction with the speed set point.

[0005] Conventionally, a maximum noise level for each wind speed may be calculated and a fixed noise reduction as a function of wind speed may be defined for the turbines in the wind park. Thus, the noise at a number of adjacent locations may be kept below the noise limit. Therefore, conventionally, it is assumed that the wind speed is the same for all wind turbines in the wind park and that all wind turbines are operating.

[0006] Conventionally known noise control methods may have the disadvantage, inter alia, of significantly reducing the electrical energy or power output.

[0007] Hence, a method of adjusting a rotational speed set point may be needed, a method of controlling the rotational speed of a plurality of wind turbines may be needed, and a wind farm controller and a wind farm may be needed, wherein noise emission regulations are met and the power output of the wind farm is improved. Summary of the invention

[0008] This need may be met by a method of adjusting the noise emission configuration of a plurality of wind turbines, a method of controlling the rotational speed of a plurality of wind turbines, a wind farm controller and a wind farm according to the invention. Advantageous embodiments of the invention are described by preferred embodiments.

[0009] According to an embodiment of the present invention, a method for adjusting the noise emission of multiple wind turbines (in particular, adjusting the rotation speed set point) is provided, the method comprising: determining a total wind turbine related noise level at a single or multiple locations; determining a critical location among the multiple locations having the most critical, in particular, the highest total wind turbine related noise level; if the most critical total wind turbine related noise level is above a noise threshold (for example, defined for the critical location): reducing the noise emission (in particular, reducing the rotation speed set point) of the wind turbine having the highest noise power impact ratio (for example, to the critical location or averaged over all locations).

[0010] As used in the present application, adjusting noise emissions of a plurality of wind turbines may include (eg, in combination) adjusting a set of noise-related operating parameters including pitch angle offset and / or rotational speed, in particular maximum speed and / or yaw angle misalignment offset.

[0011] Additionally, reducing noise emissions may include adjusting a set point of an operating parameter related to noise in order to reduce the noise.

[0012] In particular, adjusting the noise emission of the plurality of wind turbines may comprise adjusting a rotation speed set point of the wind turbines. Furthermore, reducing the noise emission may comprise reducing the rotation speed set point. Further measures may be applied to adjust, in particular reduce, the noise emission, such as changing the blade pitch angle, the yaw angle, defining other electrical reference values, etc.

[0013] The noise level may generally refer to sound pressure or sound power or their dB values. The total wind turbine-related noise level at a particular one of the plurality of locations may not include noise that is not related to any wind turbine of the wind farm, but may be related to other environmental noise, such as from traffic, construction work, industry, etc. Each noise level in the total wind turbine-related noise level for each of the plurality of locations may be determined from the individual wind turbine-related noise levels, such as by adding these noise levels. For example, the total wind turbine-related noise level may be determined using a noise model that models the noise emission of each wind turbine according to operating conditions and / or environmental conditions and / or a distance and / or direction to a respective one of the plurality of locations. As known to the skilled person, conventionally known noise models may be used for this purpose. Thus, for example, any propagation model (e.g., Nord2000 or ISO model, etc.) may be utilized.

[0014] One or more of the plurality of locations may experience a total wind turbine-related noise level that is below a corresponding noise threshold. Other locations of the plurality of locations may experience a noise level that is above a corresponding noise level. A critical location is a location of the plurality of locations that has the most critical total wind turbine-related noise level. For example, the critical location may have the highest total wind turbine-related noise level among all other locations. For the critical location, noise reduction may be required. Therefore, if the most critical total wind turbine-related noise level is above the noise threshold, the rotational speed set point of at least one wind turbine may be reduced. The wind turbine having the highest noise-to-power impact ratio for the critical location may have the best prospects for reducing noise while only slightly reducing power output. Therefore, the particular wind turbine having the highest noise-to-power impact ratio for the critical location is selected, and its rotational speed set point is reduced.

[0015] The method may then be repeated cyclically. For example, in the next cycle or next round, another location may be determined as a critical location and another wind turbine may be adjusted with respect to its rotational speed set point so as to also reduce the noise at the newly determined critical location. The method may be cyclic during the entire operating time of the wind farm or wind turbine. Thereby, it may be ensured that the noise emission requirements are met while the power output is not excessively reduced.

[0016] The noise power impact ratio can be considered as the ratio between the noise level and the power output of the corresponding wind turbine. If the noise power impact ratio is large, the noise emission is greatly reduced when the power output is reduced (including reducing the rotation speed). If the noise power impact ratio is low, the noise emission of the corresponding wind turbine is only slightly reduced when the power output is reduced (including reducing the rotation speed). Therefore, selecting the wind turbine with the highest noise power impact ratio to reduce its rotation speed set point may be most effective for reducing the noise level at the critical location. The corresponding noise power impact ratio can be stored in, for example, a lookup table for all individual wind turbines, and can include, for example, columns for noise, power, and noise power impact ratio. In a particular embodiment, the power impact ratio for a considered wind turbine can be constant, independent of the power output.

[0017] According to an embodiment of the invention, the most critical total wind turbine related noise level is that of the total wind turbine related noise levels for which the noise difference between the total wind turbine related noise level at the considered location and a noise threshold defined for the considered location is the largest.

[0018] For example, if all total wind turbine related noise levels for all locations are above a respective noise threshold, the most critical total wind turbine related noise level may be the highest total wind turbine related noise level above the respective threshold. For example, if according to another example, all total wind turbine related noise levels are below the respective threshold, the most critical total wind turbine related noise level may be the total wind turbine related noise level that is closest to being below the respective threshold. The noise differences between the total wind turbine related noise levels for the considered locations and the noise threshold defined for the considered locations may be calculated in a simple manner, and the maximum of these noise differences may also be determined, from which the most critical total wind turbine related noise level may be derived, and thus also the critical locations in a simple manner. Thus, the method may be simplified and accelerated.

[0019] According to an embodiment of the invention, lowering the rotation speed set point of the wind turbine having the highest noise power impact ratio is performed by a predetermined speed reduction and / or variation of the blade pitch angle.

[0020] When the rotation speed is reduced by a predetermined speed reduction amount, the method may be simplified. In other embodiments, the rotation speed set point may be reduced by a reduction amount which may depend, for example, on the noise difference between the noise level generated by the considered wind turbine at a critical location and a corresponding threshold value. Thereby, a more effective noise reduction may be achieved.

[0021] According to an embodiment of the invention, the method further comprises if the most critical wind turbine associated noise level at the critical location is below a noise threshold (e.g. defined at the critical location): increasing the rotation speed set point of the wind turbine having the lowest noise to power impact ratio (e.g. to the critical location) such that the nominal rotation speed is not exceeded.

[0022] If the most critical wind turbine-related noise level is below the noise threshold, the noise level associated with all wind turbines at all locations will be below the noise threshold. Thus, if any wind turbine is operating below the nominal speed, one or more of these (reduced) wind turbines may be operated at a slightly higher rotational speed. In this case, the wind turbines having the smallest impact on the noise level at the critical locations are determined, and their corresponding rotational speeds are increased. Thereby, the risk of exceeding one or more of the noise thresholds is reduced, while energy output may be increased.

[0023] According to an embodiment of the invention, increasing the rotational speed of the wind turbine with the lowest noise-to-power impact ratio is performed in a predetermined speed increment. When the rotational speed of the wind turbine with the lowest noise-to-power impact ratio is increased by a predetermined speed increment, the method can be improved and accelerated as well as simplified. In other embodiments, the increment by which the rotational speed is increased may depend on the corresponding most critical total wind turbine-related noise level or the difference between the most critical total wind turbine-related noise level and the corresponding noise threshold. For example, if the difference is (negative and) relatively large (as an absolute value), the rotational speed of the wind turbine under consideration may be increased by a larger amount than in the case where the difference is (negative and) relatively small (in an absolute value). Thereby, energy production or power production may be increased without violating noise level requirements.

[0024] According to an embodiment of the invention, determining the total wind turbine related noise level at the plurality of locations comprises: determining an individual wind turbine related noise level for each of the plurality of wind turbines at the plurality of locations, in particular applying a noise model; and determining the total wind turbine related noise level at the plurality of locations based on the individual wind turbine related noise levels at the plurality of locations, in particular by forming a sum of the individual wind turbine related noise levels.

[0025] All wind turbine position pairs of wind turbines and positions may be considered and the respective noise contribution of each wind turbine to each of the plurality of positions may be determined, in particular using a noise model. The individual wind turbine related noise levels of the considered positions may then be summed to determine the total wind turbine related noise level for the considered positions. Thereby, the method may be simplified.

[0026] According to an embodiment of the invention, the method further comprises determining the wind turbine with the highest noise power impact ratio (e.g. to the most critical location); and / or determining the wind turbine with the lowest noise power impact ratio (e.g. to the most critical location).

[0027] The determination of the highest and / or lowest noise power impact ratio may also involve applying a model that models not only the noise emission of the wind turbine but also the power output of the wind turbine. The noise power impact ratio (usually or in this embodiment) may also be calculated as the derivative of the noise as a function of the power output.

[0028] According to an embodiment of the invention, determining the total wind turbine associated noise level and / or determining the individual wind turbine associated noise levels at a plurality of locations is based on: an actual rotational speed of the respective wind turbine and / or a pitch angle of the respective wind turbine and / or a yaw angle of the respective wind turbine and / or a distance between the respective wind turbine and the respective location and / or an orientation angle between a rotation axis of the respective wind turbine and the respective location and / or at least one air parameter, in particular air temperature and / or air humidity and / or air pressure, and / or a nacelle direction and / or at least one measured noise level.

[0029] To determine the noise level, wind speed and / or wind direction may not need to be measured directly or may not be needed at all. Instead, wind speed may be estimated based on the pitch angle and / or rotor speed and / or power output.

[0030] Instead of wind direction, the nacelle position may be used to determine the noise level. If the turbine is configured with a yaw misalignment offset, the position of the nacelle is important for the noise emission pattern rather than the wind direction.

[0031] Hence, all relevant parameters for appropriately and accurately modeling the noise emission and / or power output and / or rotational speed of the wind turbine are available to the method.Different noise models may require one or more of the above mentioned parameters as input.

[0032] According to an embodiment of the invention, the method further comprises setting a yaw offset set point and / or a pitch angle set point for at least one wind turbine, in particular a wind turbine with the highest noise to power impact ratio (e.g. to a critical location). Pitching the blade angle in a positive direction will reduce noise. Pitching the blade angle may generally have a lower noise / power ratio than changing the speed setting.

[0033] Thus, for example, the noise emission direction generated by a specific wind turbine may be changed in order not to (or only slightly to) influence the noise level determined at specific locations, in particular the most critical locations.

[0034] According to an embodiment of the invention, the method steps are performed repeatedly, in particular regularly at predetermined time intervals, in particular between 30 seconds and 5 minutes, and / or wherein the method is performed by a central park controller.The method may be performed during normal operation of the wind park.

[0035] According to an embodiment of the present invention, the location is a location where the noise level is required to meet a certain standard, in particular a location below a noise threshold. Therefore, when the method is performed, local regulations on noise levels can be met.

[0036] According to an embodiment of the present invention, a plurality of location specific noise thresholds are defined or all noise thresholds are the same.For example, a noise threshold may be defined at houses surrounding a wind farm.

[0037] According to an embodiment of the invention, a method of controlling a rotation speed of a plurality of wind turbines is provided, the method comprising: performing a method according to one of the preceding embodiments; and adjusting the rotation speed of the wind turbines according to the determined rotation speed set point.

[0038] Furthermore, a wind farm controller is provided which is adapted to control or perform the method of adjusting a rotational speed set point of a plurality of wind turbines and / or to perform the method of controlling a rotational speed of a plurality of wind turbines as described in one or more of the above mentioned embodiments.

[0039] Furthermore, according to an embodiment of the present invention, a wind farm including a wind farm controller is provided.

[0040] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment.The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A wind farm according to an embodiment of the present invention is schematically illustrated, comprising a wind farm controller according to an embodiment of the present invention, the wind farm controller being adapted to perform a method according to an embodiment of the present invention; and

[0042] Figure 2 A graph illustrating the performance of a method according to an embodiment of the present invention compared to a conventional method is shown. DETAILED DESCRIPTION

[0043] The illustrations in the drawings are in schematic form.

[0044] The wind farm 1 according to an embodiment of the present invention comprises a plurality of wind turbines 3a, 3b, 3c, 3d having respective rotors 2, at which rotor blades 4 are mounted, and the wind farm further comprises a wind farm controller 5 according to an embodiment of the present invention, which is suitable for controlling or executing a method for adjusting a rotation speed set point of the plurality of wind turbines 3a, 3b, 3c, 3d and / or for executing a method for controlling a rotation speed of the plurality of wind turbines 3a, 3b, 3c, 3d according to an embodiment of the present invention.

[0045] Thus, during the method, the total wind turbine related noise level is determined at a plurality of locations 7a, 7b, 7c, 7d which may be located, for example, at premises surrounding the wind farm 1. The total wind turbine related noise level (according to the first scenario) is represented by respective bars 9a, 9b, 9c, 9d having a height corresponding to the intensity of the total wind turbine related noise level. The bars 11a, ..., 11d represent respective noise thresholds, also described as bars, whose heights represent the intensity of the noise thresholds.

[0046] During the method, in a first scenario position, a critical position 7c is determined with the most critical, in particular the highest, total wind turbine related noise level 9c. In particular, the difference between the total wind turbine related noise level 9c and the corresponding noise threshold 11c of the position 7c is the highest among all positions 7a, 7b, 7c, 7d. Therefore, the position 7c is determined as a critical position. As can be derived from the columns 9c, 11c, the most critical total wind turbine related noise level 9c is above the noise threshold 11c. In this first scenario, the wind turbine with the highest noise power impact ratio is identified (in the illustrated example, the wind turbine 3b). In particular, the wind turbine 3b is closest to the critical position 7c, and reducing its rotation speed set point most effectively leads to a reduction in the noise level experienced at the position 7c. Therefore, the rotation speed set point of the wind turbine 3b is reduced, for example, by a predetermined speed reduction amount. The method is then performed continuously and repeatedly.

[0047] According to another second scenario supported by the method instead of the total wind turbine related noise level 9a, 9b, 9c, 9d, the total wind turbine related noise level 13a, 13b, 13c, 13d is determined. Figure 1 As can be seen, all these noise levels in the second considered scenario are below the respective noise thresholds 11a, 11b, 11c, 11d. Moreover, in any case, the critical position (position 7d in the illustrated example) is determined as the position whose total wind turbine related noise level 13d is closest to the respective threshold 11d. Therefore, in all positions 7a, 7b, 7c, 7d, the noise difference between the total wind turbine related noise level 13d and the respective noise threshold 9d is the largest.

[0048] In another method step (in the second scenario), the wind turbine (in the considered example, the wind turbine 3a) having the lowest noise power impact ratio for the critical location 7d is identified. Figure 1 In FIG. 7 , it becomes apparent that wind turbine 3a is furthest from critical position 7d. In a further method step, the rotational speed set point of wind turbine 3a is increased in particular by a predetermined speed increment.

[0049] It will be appreciated that the total wind turbine associated noise level at each location is calculated as the sum of the individual wind turbine associated noise levels generated by the individual wind turbines 3a, 3b, 3c, 3d. The noise model is used to calculate the individual wind turbine associated noise levels. In order to adjust the noise emission (in particular to adjust the rotation speed set point), the wind farm controller 5 supplies control signals 15a, 15b, 15c, 15d to the controllers 6 of the respective wind turbines 3a, 3b, 3c, 3d. In addition, the central farm controller receives operating data 17a, 17b, 17c, 17d from the individual wind turbines, based on which the central controller uses the noise model to determine the respective noise level at the respective location. The farm controller 5 may also receive location information about a plurality of locations 7a, 7b, 7c, 7d and / or other environmental data related to the wind 14, such as wind speed, wind direction, etc.

[0050] Embodiments of the invention take advantage of the fact that turbines do not experience the same conditions (e.g. different noise source levels due to wake operation) and that the emission of noise from a turbine is different for different angles relative to the turbine rotor (noise source directivity). Furthermore, the attenuation of sound during propagation to adjacent locations, e.g. locations 7a, 7b, 7c, 7d (e.g. due to air absorption) may depend on atmospheric conditions.

[0051] Figure 2 The distribution of the calculated historical noise budget is illustrated in a coordinate system with an abscissa 19 representing the minimum noise budget in decibels and an ordinate 21 representing a percentage (histogram). Thus, 0 dB means that the noise is just at the noise limit and 1 dB means that the noise can be 1 dB higher and still remain below the threshold. Thus, curve 23 shows the distribution of the noise budget using a conventional noise control method. Curve 25 shows an example of the distribution achieved using an embodiment of the present invention with simulated active noise control, where the noise is increased to remain just below the limit.

[0052] According to an embodiment of the invention, a central park controller is provided which calculates the noise emission configuration of all wind turbines in the wind park 1. Thus, according to an embodiment, the noise emission configuration (in particular the rotation speed set point(s)) may be calculated recursively by the following steps:

[0053] 1. Calculate the actual noise impact of each wind turbine for all relevant neighbouring locations (eg locations 7a, 7b, 7c, 7d).

[0054] 2. Calculate the actual total noise (e.g. 9a, 9b, 9c, 9d or 13a, 13b, 13c, 13d) of all relevant adjacent positions (e.g. positions 7a, 7b, 7c, 7d),

[0055] 3. Identify the adjacent locations with the most critical (highest) noise levels

[0056] 4. Calculate the turbines with the highest and lowest noise / power impact ratios (particularly for critical adjacent locations or for an average across all locations)

[0057] 5. If the noise level is above a threshold level, the speed set point of the noise emitting configuration, in particular the wind turbine with the highest noise / power impact ratio, is reduced by a small amount.

[0058] 6. If the noise level is below a threshold level, increase the noise emission configuration of the wind turbine, in particular the speed set point, which has the lowest impact being curtailed by a small amount.

[0059] For example, the above steps 1 to 6 may be repeated every 1 minute (or longer / shorter time intervals).

[0060] According to an embodiment of the invention, the noise calculation may be based on data of turbine noise emissions as a function of direction, distance, rotor speed and pitch angle. It may be extended based on air temperature, humidity and pressure or other atmospheric parameters. It may also be extended based on sound levels measured with one or more microphones anywhere between or outside the wind turbine and adjacent locations. In this way, a closed loop controller may be obtained.

[0061] The noise threshold may depend on local noise regulations and may be a function of the wind speed of the turbine or an average of turbines in close proximity and may also be a function of time and date. It may also be extended with a safety margin based on turbulence and air density or other factors affecting noise.

[0062] In addition to calculating the optimal speed set point, as described above, the central field controller (e.g., controller 5) can also introduce intentional yaw offsets or other control changes (such as pitch angle) to individual turbines. For example, yaw offsets can affect the source noise of the downward wind turbine by changing the turbulence intensity and average flow speed. In addition, due to the directionality of wind turbine noise, intentional yaw offsets can also affect neighboring noise levels. Instead of simply scaling back (slowing down) the most critical turbines, it may be more efficient (in terms of annual energy output) to yaw the turbines so as to shift the main noise radiation away from the nearest neighboring areas.

[0063] Initial simulations using data from two existing wind farms suggest that annual power generation could be increased by up to 4% using the technology, depending on how advanced the noise modelling is.

[0064] Additionally, microphones may be installed at each location and the noise level is then controlled based on this measured noise level, thereby achieving a closed loop feedback.However, it may be difficult to distinguish the noise generated by a wind turbine from other ambient noises such as traffic noise or a crying baby.

[0065] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, elements described in association with different embodiments may be combined. It should also be noted that the reference numerals in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A method of adjusting a noise emission configuration (15) of a plurality of wind turbines (3), the method comprising: determining total wind turbine-related noise levels (9, 13) at a plurality of locations (7); determining a critical location having a most critical total wind turbine-related noise level among the plurality of locations; In case all total wind turbine related noise levels at all locations are above the respective noise thresholds, the most critical total wind turbine related noise level is that one of the total wind turbine related noise levels for which the noise difference between the total wind turbine related noise level at the considered location and the noise threshold defined for the considered location is the largest: selecting a wind turbine (3b) having a highest noise power impact ratio for the critical location, wherein the noise power impact ratio is the ratio between the noise level and the power output of the corresponding wind turbine; reducing the noise emission configuration of the wind turbine (3b) having the highest noise power impact ratio, and In case all total wind turbine related noise levels at all locations are below the respective noise threshold, the most critical total wind turbine related noise level is that one of the total wind turbine related noise levels for which the total wind turbine related noise level at the considered location is closest to the noise threshold defined for the considered location: selecting a wind turbine (3a) having a lowest noise-to-power impact ratio for the critical location; The noise emission configuration of a wind turbine (3a) having a lowest noise to power impact ratio is increased so that the nominal rotational speed is not exceeded.

2. The method according to claim 1, wherein: Reducing the noise emission configuration of the wind turbine (3b) having the highest noise power impact ratio comprises reducing the rotation speed set point of the wind turbine (3b) having the highest noise power impact ratio.

3. The method according to claim 2, wherein: Reducing the rotational speed set point of the wind turbine (3b) having the highest noise power impact ratio is performed by a predetermined speed reduction.

4. The method according to claim 1, wherein: Increasing the noise emission profile of the wind turbine (3a) having the lowest noise power impact ratio comprises increasing the rotation speed set point of the wind turbine (3a) having the lowest noise power impact ratio.

5. The method according to claim 4, wherein: Increasing the rotational speed set point of the wind turbine (3a) having the lowest noise power impact ratio is performed by a predetermined speed increment.

6. The method according to any one of claims 1 to 5, wherein: Determining the total wind turbine associated noise level (9, 13) at the plurality of locations comprises: determining an individual wind turbine associated noise level for each of the plurality of wind turbines at the plurality of locations; and An aggregate wind turbine related noise level at the plurality of locations is determined based on the individual wind turbine related noise levels at the plurality of locations.

7. The method according to claim 6, wherein: The individual wind turbine associated noise levels are determined by applying a noise model.

8. The method according to claim 6, wherein: The total wind turbine related noise level is determined by forming a sum of the individual wind turbine related noise levels.

9. The method according to claim 6, wherein: Determining the total wind turbine associated noise level (9, 13) at the plurality of locations and / or determining the individual wind turbine associated noise levels at the plurality of locations is based on: the actual rotational speed of the respective wind turbine, and / or the pitch angle of the respective wind turbine, and / or the yaw angle of the respective wind turbine, and / or the distance between the respective wind turbine and the respective location, and / or the direction angle between the rotation axis of the respective wind turbine and the respective position, and / or at least one air parameter, and / or Cabin orientation, and / or The noise level of at least one measurement.

10. The method according to claim 9, wherein: The at least one air parameter is the air temperature and / or the air humidity and / or the air pressure.

11. The method according to any one of claims 1 to 5, further comprising: A yaw offset setpoint and / or a pitch angle setpoint is set for at least one wind turbine.

12. The method according to claim 11, wherein: The at least one wind turbine is the wind turbine having the highest noise to power impact ratio.

13. The method according to any one of claims 1 to 5, wherein: The method steps are performed repeatedly and / or wherein the method is performed by a central field controller.

14. The method according to claim 13, wherein: The method steps are performed periodically at predetermined time intervals.

15. The method according to claim 14, wherein: The predetermined time interval is between 30 seconds and 5 minutes.

16. The method according to any one of claims 1 to 5, wherein: The position (7) is a position where the noise level is required to be lower than the noise threshold.

17. The method according to any one of claims 1 to 5, wherein: Multiple location specific noise thresholds (11) are defined or all noise thresholds are the same.

18. A method of controlling the rotational speed of a plurality of wind turbines, the method comprising: Execute the method according to any one of claims 1 to 17; as well as The rotational speed of the wind turbine is adjusted according to the determined noise emission profile.

19. A wind farm controller (5) adapted to control or execute the method according to any one of claims 1 to 18.

20. A wind farm (1) comprising a wind farm controller (5) according to claim 19.

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