NOISE CONTROL OF WIND TURBINE

Abstract

A method of adapting noise emission configurations of plural wind turbines, the method including: determining total wind turbine related noise levels at plural locations; determining, among the plural locations, a critical location having a most critical, in particular highest, total wind turbine related noise level; if the most critical total wind turbine related noise level is above a noise threshold: reducing the noise emission configuration of a wind turbine having the highest noise to power impact ratio, is provided.

Claims

1. A method of adapting noise emission configuration of a plurality wind turbines, the method comprising: determining total wind turbine related noise levels at a plurality of locations; determining, among the plurality of locations, a critical location having a most critical total wind turbine related noise level; and if the most critical total wind turbine related noise level is above a noise threshold: reducing a noise emission configuration of a wind turbine having a highest noise to power impact ratio.

2. The method according to claim 1, wherein the most critical total wind turbine related noise level is that one of the total wind turbine related noise levels for which a noise difference between the total wind turbine related noise level of a considered location and the noise threshold defined for the considered location is maximal.

3. The method according to claim 1, wherein reducing the noise emission configuration is performed by a predetermined speed decrement.

4. The method according to claim 1, further comprising: if the most critical wind turbine related noise level at the critical location is below the noise threshold: increasing the noise emission configuration of the wind turbine having the lowest noise to power impact ratio, thereby not exceeding a nominal rotational speed.

5. The method according to claim 1, wherein increasing a rotational speed of the wind turbine having the lowest noise to power impact ratio is performed by a predetermined speed increment.

6. The method according to claim 1, wherein determining the total wind turbine related noise levels at the plurality of locations comprises: determining individual wind turbine related noise levels at the plurality of locations for each of the plurality of wind turbines by applying a noise model; and determining the total wind turbine related noise levels at the plurality of locations based on the individual wind turbine related noise levels at the plurality of locations by forming a sum of individual wind turbine related noise levels.

7. The method according to claim 1, further comprising: determining the wind turbine having the highest noise to power impact ratio; and/or determining the wind turbine having the lowest noise to power impact ratio.

8. The method according to claim 1, wherein determining total wind turbine related noise levels and/or determining individual wind turbine related noise levels at the 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 direction angle between a rotation shaft 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.

9. The method according to claim 1, further comprising: setting a yaw offset set point and/or pitch angle set point to at least one wind turbine.

10. The method according to claim 1, wherein method steps are performed regularly with a predetermined time interval between 30 seconds and 5 minutes, and/or wherein the method is performed by a central park controller.

11. The method according to claim 1, wherein the plurality of locations are positions at which noise levels are required to meet certain criteria.

12. The method according to claim 1, wherein location specific noise thresholds are defined or all noise thresholds are the same.

13. A method of controlling rotational speed of a plurality of wind turbines, the method comprising: performing the method according to claim 1; and adjusting the rotational speed of the wind turbines according to the determined noise emission configurations.

14. A wind park controller, adapted to control or carry out a method according claim 1.

15. The wind park comprising a wind park controller according to claim 14.

16. The method according to claim 1, wherein the noise emission configuration of the wind turbine is a rotational speed set point of the wind turbine.

Description

BRIEF DESCRIPTION

[0041] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0042] FIG. 1 schematically illustrates a wind park according to an embodiment of the present invention including a wind park controller according to an embodiment of the present invention which is adapted to carry out a method according to an embodiment of the present invention; and

[0043] FIG. 2 shows graphs illustrating the performance of a method according to an embodiment of the present invention compared to a conventional method.

DETAILED DESCRIPTION

[0044] The illustration in the drawings is in schematic form.

[0045] The wind park 1 according to an embodiment of the present invention comprises plural wind turbines 3a, 3b, 3c, 3d having respective rotors 2 at which rotor blades 4 are mounted and further comprises a wind park controller 5 according to an embodiment of the present invention which is adapted to control or carry out a method of adapting rotational speed set points of plural wind turbines 3a, 3b, 3c, 3d and/or is adapted to carry out a method of controlling the rotational speed of plural wind turbines 3a, 3b, 3c, 3d according to embodiments of the present invention.

[0046] Thereby, during the method, total wind turbine related noise levels are determined at plural locations 7a, 7b, 7c, 7d which may be located at houses for example around the wind park 1. The total wind turbine related noise levels (according to a first scenario) are indicated by respective columns 9a, 9b, 9c, 9d having a height corresponding to the strength of the total wind turbine related noise levels. Columns 11a, . . . , 11d indicate respective noise thresholds also depicted as columns, their height indicating the strength of the noise threshold.

[0047] During the method, in the first scenario location a critical location 7c, is determined which has a most critical, in particular highest, total wind turbine related noise level 9c. In particular, the difference between the total wind turbine related noise level 9c and the respective noise threshold 11c for the location 7c is highest among all locations 7a, 7b, 7c, 7d. Thus, location 7c is determined as the critical location. As can be taken 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, it is identified a wind turbine (in the illustrated example wind turbine 3b) which has the highest noise to power impact ratio. In particular, the wind turbine 3b is closest to the critical location 7c and reducing its rotational speed set point most effectively results in a decrease of the noise level as experienced at the location 7c. Thus, the rotational speed set point of the wind turbine 3b is reduced, for example by a predetermined speed decrement. The method is then continuously and repeatedly performed.

[0048] According to another second scenario supported by the method instead of the total wind turbine related noise levels 9a, 9b, 9c, 9d, the total wind turbine related noise levels 13a, 13b, 13c, 13d are determined. As can be taken from FIG. 1, all these noise levels in the second considered scenario are below the respective noise thresholds 11a, 11b, 11c, 11d. Further, anyway, a critical location (in the illustrated example location 7d) is determined as the one whose total wind turbine related noise level 13d is closest to the respective threshold 11d. Thus, the noise difference between the total wind turbine related noise level 13d and the respective noise threshold 11d is maximal among all locations 7a, 7b, 7c, 7d.

[0049] In a further method step (in the second scenario), the wind turbine (in the considered example wind turbine 3a) is identified which has the lowest noise to power impact ratio for the critical location 7d. In fact, from FIG. 1 it becomes obvious that the wind turbine 3a is farthest away from the critical location 7d. In another method step, the rotational speed set point of the wind turbine 3a is increased, in particular, by a predetermined speed increment.

[0050] It should be understood that the total wind turbine related noise level at each location is calculated as the sum of individual wind turbine related noise level as generated by the individual wind turbines 3a, 3b, 3c, 3d. The individual wind turbine related noise levels are calculated using a noise model. For adjusting the noise emission (in particular adjusting rotational speed set point), the wind park controller 5 supplies control signals 15a, 15b, 15c, 15d to controllers 6 of the respective wind turbines 3a, 3b, 3c, 3d. Furthermore, the central park controller receives operational data 17a, 17b, 17c, 17d from the individual wind turbines based on which, using a noise model, the central controller determines the respective noise levels at the respective locations. The park controller 5 may receive also location information regarding the plural locations 7a, 7b, 7c, 7d, and/or other environmental data relating to wind 14, such as wind speed, wind direction etc.

[0051] An embodiment of the present invention is to utilize that the turbines are not experiencing the same conditions (different noise source level, for example due to wake operation), and the emission of the noise from the turbine is not the same for different angles relative to the turbine rotor (noise source directivity). In addition, the damping of the sound during the propagation to the neighbours, for example the locations 7a, 7b, 7c, 7d (for example due to air absorption) may depend on the atmospheric conditions.

[0052] The FIG. 2 illustrates in a coordinate system having an abscissa 19 indicating the minimum noise budget in decibel and having an ordinate 21 indicating the percentage, a distribution (histogram) of the calculated historical noise budget. Thereby, 0 decibel means that the noise is exactly on the noise limit, 1 decibel means that the noise could be 1 decibel higher and still stay under the threshold. Thereby, the curve 23 shows the distribution of the noise budget with the conventional noise control method. The curve 25 shows an example of a distribution as achieved using embodiments of the present invention with simulated active noise control, wherein the noise is increased to just stay below the limit.

[0053] According to an embodiment of the present invention, a central park controller is provided which is calculating the noise emission configuration for all the wind turbines in the wind farm 1. Thereby, according to an embodiment, the noise emission configuration (in particular rotational speed set point(s)) may be recursively calculated by the following steps: [0054] 1. Calculate the actual noise impact of each of the wind turbines for all relevant neighbour locations, for example locations 7a, 7b, 7c, 7d. [0055] 2. Calculate the actual total noise (for example 9a, 9b, 9c, 9d or 13a, 13b, 13c, 13d) for all relevant neighbour locations (for example location 7a, 7b, 7c, 7d) [0056] 3. Identify the neighbour location with the most critical (highest) noise level [0057] 4. Calculate the turbine with the highest and the lowest noise/power impact ratio (in particular for the critical neighbour location or for an average of all locations) [0058] 5. If the noise level is higher than the threshold level, then reduce noise emission configuration, in particular speed set point of the wind turbine with the highest noise/power impact ratio by a small quantity [0059] 6. If the noise level is lower than the threshold level, then increase noise emission configuration, in particular speed set point, of the wind turbine with the lowest impact which is curtailed by a small quantity.

[0060] The above steps 1 to 6 may for example be repeated for example every 1 min (or a longer/shorter time interval).

[0061] According to an embodiment of the present invention, the noise calculation may be based on data for turbine noise emission as a function of direction, distance, rotor speed, and pitch angle. It could be extended with dependency to air temperature, humidity and pressure or other atmospheric parameters. It could also be extended with dependency on measured sound levels with one or more microphones, anywhere between or beyond the wind turbine and the neighbour locations. In this way, a closed-loop controller may be obtained.

[0062] The noise threshold may depend on local noise regulations and may be a function of the wind speed of the turbine or average of turbines close to a neighbour location and may also be a function of time and day. It could also be extended with a safety margin as a function of turbulence and air density or other factors affecting the noise.

[0063] Besides calculating the optimum speed set point, as described above, the central park controller (for example controller 5) may also introduce intentional yaw offsets or other control changes (such as pitch angle) to the individual turbines. For example, a yaw offset may affect the source noise of down wind turbines by changing the turbulence intensity and mean flow speed. Moreover, an intentional yaw offset may also affect neighbour noise levels due to the directivity of the wind turbine noise. Instead of simply curtailing (speed reduction) the most critical turbine, it could be more efficient (in terms of the annual energy output) to yaw the turbine in order to divert the main noise radiation away from the nearest neighbour.

[0064] Preliminary simulations with data from two existing wind farms indicate that the annual energy production can be increased by up to 4% with this technology, depending on how advanced the noise model is.

[0065] Additionally, a microphone may be installed at each location and then control the noise level according to that measured noise level, thereby achieving a closed-loop feedback. However, it may be difficult to distinguish the noise generated by the wind turbines from other environmental noise, such as traffic noise or a crying baby.

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

[0067] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0068] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.