阅读说明：本技术 控制风力涡轮机噪声 (Controlling wind turbine noise ) 是由 M·古普塔 K·D·马德森 E·斯洛斯 于 2018-12-14 设计创作，主要内容包括：提供了一种用于控制由包括多个风力涡轮机10a-c的风力发电厂1产生的音调噪声的可听水平的方法400。方法400包括：将风力涡轮机识别401为对在噪声接收点3处可听见的音调噪声的水平做出贡献；并调节除了识别出的风力涡轮机之外的风力涡轮机的一个或多个操作参数,以便降低在噪声接收点3处可听见的由识别出的风力涡轮机产生的音调噪声的水平,由此降低在噪声接收点3处可听见的音调噪声的水平。还提供了配置为执行方法400的控制器,包括控制器的风力涡轮机10和风力发电厂1,以及计算机程序,该计算机程序在由计算装置执行时使计算装置执行方法400。(A method 400 for controlling an audible level of tonal noise generated by a wind power plant 1 comprising a plurality of wind turbines 10a-c is provided. The method 400 includes: identifying 401 the wind turbine as contributing to the level of tonal noise audible at noise reception point 3; and adjusting one or more operating parameters of the wind turbines other than the identified wind turbine so as to reduce the level of tonal noise audible at the noise reception point 3 produced by the identified wind turbine, thereby reducing the level of tonal noise audible at the noise reception point 3. There is also provided a controller configured to perform the method 400, a wind turbine 10 and a wind power plant 1 comprising the controller, and a computer program which, when executed by a computing device, causes the computing device to perform the method 400.)

1. A method of controlling the audible level of tonal noise produced by a wind power plant comprising a plurality of wind turbines, the method comprising:

-identifying the wind turbine as contributing to the level of tonal noise audible at the noise reception point; and

-adjusting one or more operating parameters of the wind turbines other than the identified wind turbine so as to reduce the level of tonal noise audible at the noise reception point produced by the identified wind turbine, thereby reducing the level of tonal noise audible at the noise reception point.

2. The method of claim 1, wherein one or more operating parameters of the wind turbines other than the identified wind turbine are adjusted to change the wind profile at the identified wind turbine.

3. The method of claim 2, wherein one or more operating parameters of the wind turbines other than the identified wind turbine are adjusted in order to change the wind speed at the identified wind turbine.

4. A method according to any of the preceding claims, wherein the wind turbine other than the identified wind turbine is a wind turbine upwind of the identified wind turbine and/or a neighbouring wind turbine of the identified wind turbine.

5. A method according to any of the preceding claims, wherein adjusting the one or more operating parameters of the wind turbines other than the identified wind turbine comprises changing the RPM, power output and/or blade pitch of the wind turbine upwind of the identified wind turbine in order to increase the wind speed at the identified wind turbine.

6. A method according to any of the preceding claims, wherein one or more operating parameters of the wind turbines other than the identified wind turbine are adjusted in order to mask tonal noise generated by the identified wind turbine.

7. The method of claim 6, wherein the RPM, blade pitch, and/or power output of the wind turbines other than the identified wind turbine are varied to mask tonal noise generated by the identified wind turbine.

8. A method according to claim 6 or claim 7, wherein the wind turbines other than the identified wind turbine are wind turbines downwind of the identified wind turbine and/or neighbouring wind turbines of the identified wind turbine.

9. A method according to any of the preceding claims, wherein adjusting one or more operating parameters of the wind turbines other than the identified wind turbine comprises changing the RPM, power output and/or blade pitch of the wind turbines other than the identified wind turbine in order to mask tonal noise produced by the identified wind turbine.

10. The method of any preceding claim, further comprising adjusting one or more operating parameters of the identified wind turbine so as to reduce the level of tonal noise produced by the identified wind turbine, thereby reducing the level of tonal noise audible at the noise reception point.

11. The method of any preceding claim, further comprising adjusting operation of one or more auxiliary devices of a wind turbine of the wind power plant.

12. A method according to any of the preceding claims, wherein the adjustment of the operating parameter of the wind turbine is constrained by the power output of the wind power plant in order to limit the reduction of the power output associated with the adjustment of the operating parameter of the wind turbine.

13. A method according to any of the preceding claims, wherein adjusting one or more operating parameters of the wind turbines other than the identified wind turbine comprises:

-determining a control strategy for reducing the level of audible tonal noise produced by the identified wind turbine at the noise reception point, the determination of the control strategy being constrained by the power output of the wind power plant in order to limit the reduction of the power output associated with the control strategy; and

-adjusting one or more operating parameters of the wind turbine other than the identified wind turbine according to the determined control strategy.

14. A method according to any of the preceding claims, wherein the one or more operating parameters are adjusted in order to move the identified wind turbine out of an operating region known to produce tonal noise.

15. The method of any of the preceding claims, wherein the operating parameter is adjusted in response to determining that the level of audible tonal noise at the noise reception point does not comply with a predefined tonal noise requirement of the wind power plant for longer than a predefined length of time.

16. A method according to any of the preceding claims, wherein the operating parameter is adjusted in response to determining that the identified wind turbine has been operating in an operating region known to produce tonal noise for longer than a predefined length of time.

17. A controller for controlling a wind turbine or a wind power plant, the controller being configured to perform the method according to any of claims 1 to 16.

18. A wind turbine comprising a controller according to claim 17.

19. A wind power plant comprising a controller according to claim 17.

20. A computer program which, when executed by a computing device, causes the computing device to perform the method of any of claims 1 to 16.

Technical Field

The invention relates to a system and a method for controlling the audible level of tonal noise generated by wind turbines in a wind power plant.

Background

Noise emissions from wind turbines are a well known problem and have been the subject of widespread work. The procedure for measuring the noise of a wind turbine is described in the third edition of the international standard IEC 61400-11.

Noise emissions from wind turbines include mechanical noise and aerodynamic noise. Mechanical noise includes noise driven by components within the nacelle, such as the wind turbine drive train. Such noise may radiate directly from the surface of the vibrating component to the surroundings (so-called airborne noise) or through the wind turbine tower or blades as the vibrations of the components are conducted through the structure of the wind turbine (so-called structural noise SBN). Aerodynamic noise comes from the wind turbine blades and includes noise, for example, due to vortex shedding.

The frequency spectrum of the noise generated by the wind turbine includes broadband noise and noise of different frequencies. Noise at different frequencies (known as tonal noise) is generally considered to be more objectionable to wind turbine neighbors and more likely to be the subject of noise complaints.

While it is desirable to keep the level of audible tonal noise acceptably low, it is also desirable to keep the power output of the wind power plant high. Typically, wind turbines of a wind power plant will operate according to operating parameters that provide high power output while meeting noise and safety requirements.

European patent No. 2337952 describes a system and method for controlling noise emissions of wind turbines in a wind farm. These methods include measuring wind speed and wind direction and using them to generate a wind turbine noise emission model to predict noise based on the geographic location of the turbine, the geographic location of the noise emission point, and the operating parameters of the wind turbine. Operation of wind turbines in the wind farm is controlled to prevent the predicted noise from exceeding a predetermined threshold.

The method described in european patent No. 2337952 may be well suited to control the general noise level emitted by a wind turbine, but may be less well suited to control tonal noise levels. This is because it is often difficult to predict when a wind turbine will produce tonal noise, as the tonal noise may come from the resonance of one or more components. Furthermore, the application of the emission model may reduce the power output of the wind power plant more than desired.

International patent application publication No. WO 2017/198271 a1 describes techniques for using vibration data to identify operating parameters for which a turbine may produce tonal noise. Such an operating area can then be avoided. While these techniques are suitable for controlling tonal noise levels produced by wind turbines, they may still reduce the power output of the wind power plant more than desired.

Disclosure of Invention

The embodiments described herein allow for reducing the audible level of tonal noise produced by a wind power plant while limiting the associated reduction in power output.

The invention is defined in the independent claims, to which reference should now be made. Preferred features are detailed in the dependent claims.

According to an aspect of the invention, a method of controlling the audible level of tonal noise generated by a wind power plant comprising a plurality of wind turbines is provided. The method comprises the following steps: identifying the wind turbine as contributing to the level of audible tonal noise at the noise reception point; and adjusting one or more operating parameters of the wind turbines other than the identified wind turbine so as to reduce the level of tonal noise audible at the noise reception point produced by the identified wind turbine, thereby reducing the level of tonal noise audible at the noise reception point.

Methods focused on tonal noise control of the operation of wind turbines identified as contributing to tonal noise levels are typically limited to derating (de-rating) individual wind turbines. This may result in a relatively large drop in the power output of the wind power plant. However, by taking into account the effect that one turbine may have on tonal noise produced by another turbine, or at least the level of that tonal noise that is audible at the point of noise reception (such as personnel near the power plant), additional flexibility in tonal noise control is provided, and it is possible to reduce the audible tonal noise level while avoiding substantial reductions in power output.

One or more operating parameters of the wind turbines other than the identified wind turbine may be adjusted to change a wind profile at the identified wind turbine, such as a wind speed and/or direction at the identified wind turbine. For a given wind profile, a wind turbine may have a relatively large operating region in which tonal noise is produced, meaning that significant changes to its operating parameters may be required to move it out of the "critical" operating region. This is likely to be associated with a significant drop in power output. However, with respect to wind profiles, the critical areas may be very narrow, and thus altering the wind profile experienced by a wind turbine may provide a way to reduce the level of tonal noise generated by the wind turbine while not significantly reducing its power output. Since the wind profile experienced by a wind turbine may be affected by surrounding wind turbines (particularly adjacent turbines and/or upstream wind turbines) due to effects such as wind shielding, the change to the operating parameters of one or more surrounding wind turbines may reduce tonal noise while not significantly reducing the power output of the wind power plant.

Adjusting the one or more operating parameters of the wind turbine other than the identified wind turbine may include changing an RPM, a power output, and/or a blade pitch of the wind turbine upwind of the identified wind turbine in order to increase a wind speed at the identified wind turbine. Wind turbines may be prone to tonal noise when they experience relatively low wind speeds, which may be caused by the turbine's wind being kept out of the wind upwind. Adjusting one or more operating parameters of the turbine upwind such that the identified wind turbine sees a "clear" wind may reduce tonal noise levels produced by the identified wind turbine without significantly reducing the power output of the wind power plant.

The one or more operating parameters of the wind turbines other than the identified wind turbine may be adjusted to mask tonal noise produced by the identified wind turbine. Tonal noise is characterized by different frequencies in the distribution of otherwise wideband noise levels. Thus, the level of tonal noise audible at the noise reception point may be reduced by providing additional noise to mask the different frequencies. While this may increase the overall noise level at the noise reception point, it may be acceptable if the generated noise profile masks noise at different frequencies that are more objectionable to personnel near the power plant. In some embodiments, the operating parameters may be varied to mask specific tones identified as being produced by the identified wind turbine.

The RPM, blade pitch, and/or power output of the wind turbines other than the identified wind turbine may be varied to mask tonal noise generated by the identified wind turbine. Wind turbines that rotate faster and/or output more power are generally louder and therefore may be better at shielding noise.

The wind turbines other than the identified wind turbine may be wind turbines downwind of the identified wind turbine and/or adjacent wind turbines of the identified wind turbine. In some cases, it may not be possible to alter the wind profile experienced by a wind turbine that has been identified as contributing to tonal noise levels. For example, for a given wind direction, there may be no or only a very small number of wind turbines upstream of the identified wind turbine. In this case, masking of the tones may be particularly useful, and turbines in the downwind direction (especially adjacent wind turbines in the downwind direction) may provide optimal masking.

The method may further include adjusting one or more operating parameters of the identified wind turbine to reduce the level of tonal noise produced by the identified wind turbine, thereby reducing the level of audible tonal noise at the noise reception point. Adjusting one or more operating parameters of the identified wind turbine may include changing an RPM, a blade pitch, and/or a power output of the identified wind turbine. While embodiments contemplate the effect of other wind turbines on the level of tonal noise produced by an identified wind turbine that is audible at the noise reception point, it may still be beneficial to adjust the operation of an identified turbine. For example, relatively small adjustments of both the identified wind turbine and the upstream wind turbine may be used to move the turbine out of the critical operating area. On the other hand, moving an identified wind turbine out of a critical operating region based on changes to the operating parameters of the identified wind turbine alone or changes to an upstream turbine alone may require more significant changes.

A method according to any preceding claim, further comprising adjusting operation of one or more auxiliary devices (such as cooling fans) of the wind turbine of the wind power plant. In some cases, the auxiliary equipment may also generate noise that is objectionable to personnel in the vicinity of the power plant, and its adjustment may reduce the level of noise that is audible at the noise receiving point. Furthermore, the noise generated by the auxiliary equipment may be used to mask tonal noise generated by one or more wind turbines of the wind power plant.

The adjustment of the operating parameter of the wind turbine may be constrained so as to limit the reduction of power output associated with the adjustment of the operating parameter of the wind turbine. Constraining regulation in this manner may ensure that changes to operating conditions do not come at the expense of power output. This is particularly important in case the wind power plant currently complies with the tonal requirements of the plant, since in this case it may not be necessary to make any changes to the operation of the wind power plant.

Adjusting one or more operating parameters of the wind turbine other than the identified wind turbine may include: a control strategy for reducing the level of audible tonal noise produced by the identified wind turbine at the noise reception point is determined, the determination of the control strategy being constrained by the power output of the wind power plant so as to limit the reduction of the power output associated with the control strategy. One or more operating parameters of the wind turbines other than the identified wind turbine may then be adjusted according to the determined control strategy. The control strategy may be a control strategy for moving the operation of the wind turbine out of an operating region known to emit tonal noise.

One or more operating parameters may be adjusted to move the identified wind turbine out of an operating region known to produce tonal noise. Such an operating region may be known based on previous use or testing of the wind turbine or a component thereof, such as a gearbox.

The operating parameter may be adjusted in response to determining that the level of audible tonal noise at the noise reception point has not met the predefined tonal noise requirement of the wind power plant for longer than a predefined length of time. Additionally or alternatively, the operational parameters may be adjusted in response to determining that the identified wind turbine has been operating in an operating region known to produce tonal noise for longer than a predefined length of time. This avoids unnecessary changes to the operation of the wind power plant, which may be associated with a drop in power output. For example, an increase in the audible tonal noise level at the noise reception point may be due to a brief change in the incident wind speed or direction.

A controller for controlling a wind turbine or a wind power plant is also provided. The controller is configured to perform a method of controlling an audible level of tonal noise produced by a wind power plant comprising a plurality of wind turbines.

A wind turbine and a wind power plant comprising the controller are also provided.

A computer program is also provided which, when executed by a computing device, causes the computing device to perform a method of controlling the audible level of tonal noise generated by a wind power plant comprising a plurality of wind turbines.

Drawings

Embodiments will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 shows a large modern wind turbine.

FIG. 2 shows a simplified cross-sectional view of the nacelle from the side;

FIG. 3 is a perspective view of a landscape with a wind power plant;

FIG. 4 is a flow chart showing a method of controlling the audible level of tonal noise produced by a wind power plant comprising a plurality of wind turbines; and

fig. 5 illustrates exemplary noise data showing audible noise at a noise reception point.

Like reference numerals are used for like elements throughout the specification and drawings.

Detailed Description

Fig. 1 shows a large modern wind turbine 10 known in the art, comprising a tower 11 and a wind turbine nacelle 13 positioned on top of the tower. The wind turbine blades 15 of the turbine rotor 12 are mounted on a common hub 14 which is connected to the nacelle 13 by a low speed shaft extending from the front of the nacelle. The wind turbine blades 15 of the turbine rotor 12 are connected to the hub 14 by pitch bearings 16, enabling each blade to rotate about its longitudinal axis. The pitch angle of blades 15 may then be controlled by linear actuators, stepper motors, or other means for rotating the blades. The wind turbine 10 is shown with three turbine blades 15, but it should be understood that the wind turbine may have another number of blades, for example one, two, four, five or more.

Fig. 2 shows a simplified cross-sectional view of the nacelle 13 of the wind turbine 10 from the side. The nacelle 13 exists in a number of variations and configurations, but in most cases includes one or more of the following components: a gearbox 131, a coupling (not shown), some kind of braking system 132 and a generator 133. The nacelle may also include transducers 134 (also referred to as inverters) and other peripheral devices, such as other power processing equipment, control cabinets, hydraulic systems, cooling systems, and the like.

A wind turbine, such as wind turbine 10, operates according to a set of operating parameters. Some operating parameters (such as wind speed and wind direction) are independent of wind turbine 10. Other operating parameters (such as RPM, torque, blade pitch angle, and power output) may be set by the controller, as explained in more detail below. By testing and using wind turbine 10 (or similar models), the relationship between the various operating parameters is generally known to some extent. For example, for a given wind speed and direction, the power output may be referred to as a function of blade pitch, RPM, and torque. This allows a wind turbine 10 that is experiencing a given set of fixed operating parameters, such as wind speed and wind direction, to operate using a variable set of operating parameters that provide high power output, such as blade pitch, RPM, and torque.

Fig. 3 shows a wind power plant 1 comprising a plurality of wind turbines 10a, 10b, 10c according to an embodiment of the present invention. The wind power plant 1 is located relatively close to the personnel 2 in the vicinity of the plant that may be affected by the noise (including tonal noise) generated by the wind power plant.

As mentioned above, the wind turbines 10a, 10b, 10c of the wind power plant 1 are operated according to various operating parameters. These operating parameters are typically set by one or more controllers (not shown in fig. 3). For example, each wind turbine 10a-c may have its own turbine controller in communication with a central plant controller. Each turbine controller may then be responsible for setting the operating parameters of the associated turbine 10a-c based on the parameters received from the power plant controller.

The turbine controller may also be responsible for communicating data to the power plant controller so that the power plant controller can determine the appropriate parameters of the turbines 10 a-c. For example, each turbine controller may transmit the current operating parameters of its associated turbine to the power plant controller along with various other data (such as data from sensors associated with the turbine). Exemplary sensors include wind speed and direction sensors, vibration sensors, sensors associated with the Condition Monitoring System (CMS) of the wind turbine, and microphones 4a, 4b, 4c, although some or all of these sensors may be independent of the turbine and may be coupled directly to the power plant controller. Based on this data and the known relationships between the various operating parameters, the plant controller determines and communicates the operating parameters for the turbines 10a-c to the various turbine controllers.

In general, it is desirable to operate the wind turbines 10a-c of the wind power plant 1 using operating parameters that provide a maximum power output that meets other operating requirements of the wind power plant. These other operational requirements will typically include, for example, safety requirements that will vary depending on the wind conditions, noise requirements that will vary depending on the country in which the power plant 1 is located (different countries allow for different noise levels), the location of the wind power plant (e.g. taking into account the distance to the nearest nearby person 2) and the time of day (e.g. the noise requirements at night may be more stringent so as not to affect the sleep of nearby persons).

It is sometimes necessary to adjust operating parameters of one or more wind turbines 10a-c of the wind power plant 1 in order to comply with noise requirements of the plant. For example, if a microphone located at a noise receiving point 3 at or near a person 2 near the power plant measures a noise level that does not meet the noise requirements of the power plant, the power plant controller may take action by adjusting operating parameters of one or more turbines 10 a-c. As another example, a noise level measured by the microphones 4a, 4b, 4c positioned at or near the turbines 10a, 10b, 10c may indicate that the turbines are emitting a lot of noise, in which case the power plant controller may take action.

Attempts to reduce the noise level generally involve reducing the power output of the wind power plant 1. This is because, in general, there is a positive correlation between the power output of a wind turbine 10a-c and the overall noise level it emits.

However, such a correlation between power output and noise level is not necessarily applicable to tonal noise that may be due to resonances in one or more components of wind turbines 10a-c, which may typically occur within a relatively narrow set of operating conditions ("critical" operating region). In view of this, by modifying the operating parameters of the turbine such that it moves outside the critical operating region, tonal noise produced by the wind turbine can be reduced, thereby reducing the level of tonal noise audible at the noise reception point 3 without substantially reducing the power output of the turbine and the wind power plant. For example, international patent application publication number WO 2017/198271 a1 describes the use of vibration data in determining critical operating regions of a wind turbine such that critical operating regions may be avoided. Knowledge of these critical operating regions may be used to reduce the level of tonal noise emitted by the wind turbine without significantly affecting its power output.

While this represents an improvement over techniques that simply reduce the power output of one or more turbines 10a, 10b, 10c to reduce the noise level, the embodiments described herein provide further improvements. In particular, the embodiments described herein not only adjust the operating parameters of wind turbines identified as emitting tonal noise, but also take plant-level approaches that focus on reducing the overall level of tonal noise audible at the noise reception point 3. In doing so, embodiments account for the wind turbine's possible effect on the level of tonal noise emitted by another wind turbine and/or on the level of tonal noise emitted by another wind turbine that is audible at the noise reception point.

To this end, FIG. 4 is a flow chart illustrating a method 400 of controlling the audible level of tonal noise generated by a wind power plant 1 comprising a plurality of wind turbines 10 a-c.

According to the method 400, the wind turbine is identified 401 as contributing to the level of tonal noise audible at the noise reception point 3. The identifying 401 may be performed by a turbine controller, a power plant controller, or another computer.

The noise receiving point 3 will typically be at or near the person 2 near the wind turbine. This is because the invention is generally directed to ensuring that the wind power plant 1 complies with the noise requirements of the wind power plant, and that the noise requirements of the wind power plant are generally based on the level of noise audible to persons in the vicinity of the wind power plant. In principle, however, the noise receiving point 3 may be any point where wind turbine noise is audible.

The wind turbine may be identified as contributing to the audible level of tonal noise at the noise reception point in any of a number of different ways. One embodiment is shown in fig. 5. Fig. 5 is a graph 500 of sound pressure as a function of frequency. Line 501 represents the total sound pressure audible at the noise receiving point 3 and is visible from the different peaks in the otherwise broad-band spectrum, including tonal noise. The other lines 502a-c represent the individual contributions of the three wind turbines 10a-c to the total sound pressure 501. Because there are different peaks in the line 502b that generally correspond to different peaks in the total sound pressure 501, one of the wind turbines 10b may be identified as contributing to the level of audible tonal noise at the noise reception point. It should be appreciated that wind turbine 10b could have been identified based solely on line 502b as contributing to the audible tonal noise level at noise receiving point 3 without comparing it to overall noise level 501. It will also be appreciated that there are various other criteria that identify the turbine as contributing to the level of tonal noise that is audible at the noise reception point 3. For example, a sound pressure threshold or a threshold deviation in sound pressure may be used to identify the turbine as contributing to the level of tonal noise at the noise receiving point 3.

In other embodiments, instead of or in addition to using noise measurements/models, turbines may be identified based on determining that the turbine is operating or predicted to operate within a critical operating region where the turbine is known to emit tonal noise. In some embodiments, the turbine may be identified based on predicted wind conditions at the turbine. For example, the wind conditions at the turbine in the downwind direction may be estimated based on wind conditions measured at the leading turbine or meteorological mast of the power plant 1 and based on previous experience and/or simulations (e.g. CFD-computational fluid dynamics). Based on the estimated wind conditions at the turbine in the downwind direction, the turbine may then be identified as a candidate for producing tonal noise. For example, it may be determined that if a downwind wind turbine is operating at its current operating conditions (such as RPM, blade pitch, torque and power output) and experiences estimated wind conditions, it will be operating within a critical operating region and therefore will likely produce tonal noise.

It should also be understood that although FIG. 5 shows only three wind turbines 10a-c contributing 502a-c to the overall noise level 501 audible at noise sink 3, and only one turbine 10b contributing to the level of tonal noise audible at noise sink 3, this is for ease of illustration. There may be more or fewer wind turbines contributing to the overall noise level 501 and more than one wind turbine may be identified as contributing to the level of audible tonal noise at noise reception point 3.

The individual contributions 502a-c to the overall noise level 501 from each wind turbine 10a-c may be determined in a number of ways. For example, the microphones 4a-c may be positioned in the vicinity of the wind turbines 10a-c and measure the sound pressure in the vicinity of the wind turbines 10 a-c. Starting from the sound pressures measured by the microphones 4a-c, the corresponding audible noise levels 501a-c may be approximated using a noise propagation model, such as the Nord 2000 noise propagation model. In other cases, as described in International patent application publication No. WO 2017/198271A 1, instead of using microphones 4a-c to measure the noise emitted by wind turbines 10a-c, vibration sensors may be used to measure vibration levels of components of wind turbines 10a-c, and corresponding noise levels may be estimated. These estimated noise levels may be converted to corresponding audible noise levels 501a-c using a noise propagation model, such as the Nord 2000 model.

The overall sound pressure 501 audible at the noise reception point 3 can also be determined in various ways. In one embodiment, a microphone positioned at or near the noise reception point 3 measures the level of noise audible at the noise reception point. In another embodiment, microphones 4a-c measure the noise emitted by wind turbines 10a-c, and propagate these measurements to noise receiving point 3 using a noise propagation model (such as the Nord 2000 mode). The propagated noise levels may then be combined to give an overall noise level. In another embodiment, as described in International patent application publication No. WO 2017/198271A 1, vibration sensors may be used to measure vibration levels of components of wind turbines 10a-c, and corresponding noise levels may be estimated. These estimated noise levels may be converted to corresponding audible noise levels 501a-c using a noise propagation model, such as the Nord 2000 model. The propagated noise levels may then be combined to give an overall noise level.

Returning to FIG. 4, after wind turbine 10b has been determined to contribute to the level of audible tonal noise at noise reception point 3, one or more operating parameters of one or more wind turbines different from the identified wind turbine are adjusted 402. This adjustment is to reduce the level of tonal noise produced by the identified wind turbine 10b that is audible at the noise receiving point 3. The one or more wind turbine operating parameters adjusted 402 may include RPM, torque, power output, and blade pitch, or any combination thereof.

In some cases, wind turbine operating parameters of different wind turbines are adjusted in order to change the wind profile experienced by the identified wind turbine 10 b. For example, the operating parameters of other wind turbines (such as turbine 10a) are adjusted in order to change the wind characteristics (such as wind speed and wind direction) that arrive at the identified wind turbine 10 b. This may have the effect of reducing the level of tonal noise emitted by the identified wind turbine 10b, and thus also the level of tonal noise audible at the noise reception point 3. Furthermore, this may enable a reduction in the level of tonal noise emitted by the identified wind turbine 10b with a smaller reduction in the power output of the power plant 1 than could be achieved by merely changing the operating parameters of the identified wind turbine 10 b.

In particular, as described above, wind turbine 10b may emit tonal noise when it is operating within a key set of operating parameters. This critical set of operating parameters will typically be narrower for some operating parameters than for others. For example, a critical set of operating parameters may cover a relatively large range of RPM values, but only a relatively small range of torque values. In some cases, the critical set of operating parameters may be relatively narrow in terms of the wind profile experienced by the turbine. That is, if the wind speed experienced by the identified turbine 10b may only increase by a small amount, it is possible to achieve a significant reduction in the level of tonal noise emitted by the identified turbine 10 b.

The wind profile experienced by the identified wind turbine is independent of the identified wind turbine and therefore cannot be adjusted by adjusting the operating parameters of the identified wind turbine 10 b. However, the wind profile may not be independent of the operating parameters of the other wind turbines in the wind power plant 1. For example, if the wind direction is in the direction indicated by arrow 5 in fig. 3, the identified turbine 10b will be shielded from the wind to some extent by the turbine 10a in the upwind direction. The wind characteristics experienced by the identified turbine 10b may then depend on the operating parameters of the turbine 10a in the upwind direction. Thus, changing operating parameters (such as the torque, RPM, and/or blade pitch of turbine 10a upwind direction) may result in a change in the wind profile (such as increased wind speed) at the identified turbine, which moves the identified wind turbine 10b away from the critical operating area so that it emits less tonal noise. In some cases, the drop in power output of other wind turbines (such as turbine 10a), if any, may be less than the drop in power output of identified wind turbine 10b due to changing only the operating parameters of the identified wind turbine.

Alternatively or additionally, in addition to adjusting operating parameters of other wind turbines to change the wind profile at the identified wind turbine 10b, one or more operating parameters of one or more wind turbines different from the identified wind turbine 10b may be adjusted to mask tonal noise emitted by the identified wind turbine 10 b. That is, not only is there a focus on reducing the level of tonal noise emitted by the identified turbine 10b, other turbines (such as turbine 10a) may also be used to mask the tonal noise emitted by the identified turbine 10b, thereby reducing the level of tonal noise audible at the noise sink 3.

It will be appreciated that providing masking noise or energy may result in an increase in the overall noise level (sound pressure) audible at the noise receiving point 3. However, this may still result in a reduction of the level of audible tonal noise at the noise reception point 3, and in many cases the level of audible tonal noise is important, as people 2 in the vicinity of the wind power plant often find tonal noise more objectionable. For example, referring to FIG. 5, if masking noise can be provided to hide different peaks of line 501 within a higher level of broadband noise, then the nearby power plant personnel 2 may find the noise they can hear less objectionable.

The one or more wind turbine operating parameters adjusted 402 may include RPM, torque, power output, and blade pitch, or any combination thereof. In some cases, the operating parameters may be adjusted to mask one or more particular tones that have been identified in tonal noise emitted by the identified turbine 10 b. For example, the operating parameters of one or more adjacent turbines may be adjusted such that they emit a higher level of noise (e.g., broadband noise) in frequencies around the identified tone in order to mask the tone. As another example, an operating parameter (of an identified turbine or other turbine) may be adjusted such that noise originating from one or more particular components of the turbine (such as a hydraulic power unit, a gear, or a generator) masks a particular identified tone.

The most effective masking of tonal noise emitted by the identified turbine 10b may be provided by the identified turbine 10b downwind and/or adjacent turbines.

Although the embodiments described herein relate to modifying operating parameters of wind turbines other than the identified wind turbine in order to reduce the level of tonal noise emitted by the identified turbine that is audible at the noise receiving point 3, embodiments may also relate to modifying operating parameters of the identified wind turbine. In some cases, the best results in terms of reducing the audible level of tonal noise while limiting the power output of the wind power plant 1 will be achieved by adjusting the operating parameters of the identified wind turbine and other wind turbines. For example, if a wind turbine is identified as contributing tonal noise at the noise reception point, the operating parameters of the identified wind turbine may be adjusted to move its operation away from the critical zone, while the operating parameters of the turbine in the upwind direction may be adjusted to change the wind profile at the identified turbine to move the operation of the identified wind further away from the critical zone. At the same time, the operating parameters of the turbine in the downwind direction may be modified in order to generate masking energy to mask tonal noise emitted by the identified turbine. In general, the reduction in power output may be less than what can be achieved by merely adjusting the identified operating parameters of the wind turbine.

Other plant-level measures may be taken to mask tonal noise emitted by the identified wind turbines 10b in order to reduce the level of tonal noise emitted by the turbines and to reduce the overall level of noise emitted by the wind plant. For example, gurney flaps or speakers of the identified turbine 10b or other turbines may be used to provide masking noise. The operation of the turbine auxiliary equipment, such as cooling fans, lubrication pumps and hydraulic units, may also be varied to provide masking noise or if they themselves cause objectionable noise.

Changes to the operating parameters of the turbines (both the identified turbines and turbines other than the identified turbines) may be constrained by the power output of the wind power plant 1. For example, the power plant controller may consider a number of different possible adjustments to the operating parameters and select the adjustment that provides the best power output at the plant level while reducing audible tonal noise at the noise reception point. As mentioned above, through testing and prior use, the power output of the wind turbine (and hence the power plant) as a function of various operating parameters is typically known to some extent, and thus the controller may use the power plant power output to constrain changes.

In some embodiments, the controller may determine a control strategy for adjusting the operating parameter. For example, the power plant controller may determine that the identified wind turbine is operating within a critical operating region known to emit tonal noise and then determine a control strategy for moving the identified turbine outside of the critical operating region. In doing so, the controller may constrain changes to the operating parameters (of both the identified turbine and other turbines in addition to the identified turbine) based on the power output of the wind power plant.

In response to determining that the wind power plant 1 does not comply with the noise requirements of the wind power plant 3, the wind turbine may be identified 401 as contributing to the level of audible tonal noise at the noise reception point 3, or the operational parameters may be adjusted 402. Preferably, the plant controller will not adjust the operating parameters of the turbines unless the wind power plant 1 does not meet the noise requirements for at least a predetermined amount of time. In this way, the operating parameters of the turbine are not unnecessarily changed, for example due to a brief change in wind conditions which may subside relatively quickly. The appropriate amount of time may be selected by the plant operator, but may be, for example, greater than about 30 seconds or one minute.

Although the embodiment has been described for a single noise receiving point 3, it should be understood that the embodiment may also be performed for a plurality of receiving points, such as for a plurality of nearby persons of a wind power plant.

Various embodiments having various optional features are described above. It will be understood that any combination of one or more optional features is possible, in addition to any mutually exclusive feature.