Reduce noise emissions from wind turbines

Abstract

This invention provides a method for reducing noise emissions from a wind turbine. The method includes receiving data indicating wind conditions near the wind turbine and determining an operating setpoint signal based on the received data, according to the desired operation of the wind turbine. The method includes applying a perturbation signal to the operating setpoint signal to obtain a corrected operating setpoint signal, and using the corrected operating setpoint signal to control the operation of the wind turbine to reduce noise emissions. The perturbation signal is applied such that the corrected operating setpoint signal has a greater time variation than the original operating setpoint signal.

Description

Technical Field

[0001] This invention relates to controlling the operation of wind turbines, and more particularly to reducing the noise emissions of wind turbines by applying a perturbation signal to the desired or optimal operating setpoint signal of the wind turbine. Background Technology

[0002] Wind turbine control technology is used to optimize power and minimize load. Many different loads, such as aerodynamic, gravitational, centrifugal, and inertial loads, act on wind turbines. The load variations experienced by a wind turbine may be caused by wind conditions near the turbine (such as wind shear or turbulence) or by changes in the turbine's operation (such as grid losses).

[0003] As is well known, wind turbines generate sound or noise from various sources, such as mechanical sources like the pitch of the drivetrain and aerodynamic sources from the airflow around the rotor blades. The ever-increasing size of wind turbines has led to growing concerns about noise levels.

[0004] Pitch noise (or pitch audibility) refers to noise at a specific frequency. In wind turbines, this may be related to the generator or rotor speed and may be related to the resonance of the wind turbine's drivetrain. That is, noise may be emitted when a wind turbine operates at a specific generator or rotor speed that corresponds to the resonant frequency of one or more structural components of the wind turbine.

[0005] One known method to reduce this tone noise is to introduce a so-called "avoidance zone" for wind turbine operation, which controls the wind turbine to operate outside a specific range of rotor speeds corresponding to high levels of tone noise. However, a drawback of this method is a loss of wind turbine operating efficiency; for example, power production is reduced when the turbine's optimal operation involves rotor speeds within the avoidance zone.

[0006] Other known methods for addressing tone noise problems include installing tuned mass dampers or replacing the gearbox with a low-vibration unit. However, these methods are disadvantageous because providing the relevant equipment incurs associated costs, as does shutting down the wind turbine to install / replace these components.

[0007] It is against this backdrop that the present invention was proposed. Summary of the Invention

[0008] The inventors of this invention have realized that noise emissions from wind turbines—particularly tonal noise emissions—are related not only to the speed of the wind turbine rotor / generator but also to the variation of the wind turbine rotor / generator speed over time. In particular, the inventors have realized that modifying or perturbing the rotor / generator speed to increase its variation over time can lead to a reduction in noise emissions associated with the wind turbine.

[0009] According to one aspect of the invention, a method for reducing noise emissions from a wind turbine is provided. The method includes receiving data indicating wind conditions near the wind turbine. The method includes determining an operating setpoint signal based on the desired operation of the wind turbine, the operating setpoint signal being determined according to the received data. The method includes applying a disturbance signal to the operating setpoint signal to obtain a corrected operating setpoint signal. The method includes controlling the operation of the wind turbine using the corrected operating setpoint signal to reduce noise emissions from the wind turbine. The disturbance signal is applied such that the corrected operating setpoint signal has a greater time variation than the original operating setpoint signal.

[0010] This method is specifically designed to reduce the audibility of wind turbine emissions. The audibility of a wind turbine can be viewed as the difference between pitch and an audibility standard within each wind speed bin, where pitch is the difference between the pitch level and the masking noise level in the critical band surrounding the pitch within each wind speed bin, and the audibility standard is determined by auditory testing and reflects a frequency-dependent standard curve that reflects the subjective response of a “typical” listener to pitch at different frequencies. The concepts of pitch and audibility are addressed in the IEC 61400-11Ed.3 standard.

[0011] The method may include determining whether a disturbance signal needs to be applied based on data indicating noise emissions from a wind turbine. The method may include activating the application of the disturbance signal only when it is determined that an application of the disturbance signal is necessary. Optionally, the data indicating noise emissions may include received data indicating wind conditions.

[0012] In some embodiments, determining whether a disturbance signal needs to be applied may include determining whether the operating parameters of the wind turbine are within a predefined critical range. In such embodiments, the application of the disturbance signal can only be activated if the operating parameters are determined to be within the specified critical range.

[0013] In some embodiments, determining whether a disturbance signal needs to be applied may include determining whether the time variation of the wind turbine's operating parameters is below a predetermined threshold variation. In such embodiments, the application of the disturbance signal may only be activated if the time variation is below the predetermined threshold variation.

[0014] Determining time variations can include determining the standard deviation of operating parameters. A specified threshold variation can be a specified threshold standard deviation.

[0015] Operating parameters may include the operating setpoint signal.

[0016] Operating parameters may include at least one of the following: wind turbine generator speed; wind turbine power; wind turbine torque; wind turbine audibility; wind speed near the wind turbine; and wind direction near the wind turbine.

[0017] In some embodiments, if it is determined that no disturbance signal needs to be applied, the method may include controlling the operation of the wind turbine using a determined operating setpoint signal.

[0018] In some embodiments, if it is determined that the perturbation signal is not needed when an application with the perturbation signal activated is enabled, the method may include continuing to apply the perturbation signal until a deactivation condition is met. Alternatively or additionally, if it is determined that the perturbation signal is needed when an application with the perturbation signal disabled is enabled is enabled, the method may include applying the perturbation signal only when an activation condition is met.

[0019] A disturbance signal can be applied so that the time average of the corrected operating setpoint signal is approximately equal to the average value of the operating setpoint signal.

[0020] The disturbance signal can be deterministic. Optionally, the disturbance signal can include one or a combination of sine wave, cosine wave, triangular wave, and square wave signals. Optionally, the disturbance signal can be determined based on received data indicating wind conditions. Alternatively, the disturbance signal can be a nondeterministic random signal (optionally with specific time variations).

[0021] The operating setpoint signal can be at least one of the following: a wind turbine generator speed setpoint signal; and a wind turbine power setpoint signal.

[0022] In some embodiments, controlling the operation of a wind turbine may include determining a control output based on a modified operating setpoint signal. In these embodiments, controlling the operation of a wind turbine may include using the determined control output to control the operation of the wind turbine. Optionally, the control output may include a pitch reference value for controlling the pitch of one or more blades of the wind turbine. Optionally, the control output may include a power reference value for controlling the power generation of the wind turbine.

[0023] According to another aspect of the invention, a non-transitory, computer-readable storage medium is provided, having instructions stored thereon that, when executed by a processor, cause the processor to perform the methods described above.

[0024] According to another aspect of the invention, a controller for reducing noise emissions from a wind turbine is provided. The controller is configured to receive data indicating wind conditions near the wind turbine. The controller is configured to determine an operating setpoint signal based on the desired operation of the wind turbine, the operating setpoint signal being determined according to the received data. The controller is configured to apply a disturbance signal to the operating setpoint signal to obtain a corrected operating setpoint signal, and to control the operation of the wind turbine using the corrected operating setpoint signal to reduce noise emissions from the wind turbine. The disturbance signal is applied such that the corrected operating setpoint signal has a greater time variation than the original operating setpoint signal.

[0025] According to another aspect of the invention, a wind turbine is provided, the wind turbine including the controller as described above. Attached Figure Description

[0026] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0027] Figure 1 This is a schematic diagram of a wind turbine according to an example of the present invention;

[0028] Figure 2 Showing Figure 1 The controller of the wind turbine, and the actuator system of the wind turbine controlled by the controller;

[0029] Figure 3 Showing Figure 2 The components or modules of the controller, as well as the controller's inputs and outputs;

[0030] Figure 4 An example of the invention is illustrated schematically. Figure 2 How does the controller disturb the optimal operating setpoint signal of the wind turbine; and

[0031] Figure 5 An example of the invention is shown. Figure 2 The steps of the method executed by the controller. Detailed Implementation

[0032] Figure 1 A wind turbine 10 is shown, and examples of the present invention can be incorporated therein. The wind turbine 10 includes a tower 12 supporting a nacelle 14, on which a rotor 16 is mounted. The rotor 16 includes a plurality of wind turbine blades 18 extending radially from a hub 20. In this example, the rotor 16 includes three blades 18 and a single rotor 16, although other configurations including any suitable number of blades and rotors are possible.

[0033] The wind turbine 10 may include one or more different sensors for measuring various characteristics of the turbine 10's operation, as well as various characteristics of conditions near the turbine 10, such as wind conditions. An optional blade load sensor 181 is shown within each blade 18 (in other examples, there may be multiple blade load sensors, allowing the blade load to be represented by more than a single variable). This sensing element may be a fiber optic strain gauge, a resistance strain gauge, or any other suitable detector. An optional rotor wind speed and / or wind direction detector 182 is also shown—again, this measurement can be performed in several ways, as understood by those skilled in the art, one being via a wind vane and anemometer, and another via lidar, as understood by those skilled in the art from the literature on wind turbine design and control. An optional speed sensor 183 is also shown—for example, it may be in the form of a rotary encoder on the generator shaft of the turbine 10; however, the rotor speed or generator speed can be determined in any suitable manner. Other sensors may be included additionally or alternatively. For example, an accelerometer may be included in a suitable location for measuring lateral or sideways oscillations or vibrations of the tower 12, or a sensor may be included for measuring acceleration values ​​of the wind turbine generator or gearbox. A microphone or other acoustic sensor may be included in or near the turbine 10 for detecting the noise emission level generated by the wind turbine 10.

[0034] Figure 2 An example of a wind turbine control system 22 according to the present invention is shown, which can be used in... Figure 1 This is implemented in a wind turbine 10. Here, the control system 22 includes an actuator system 24 controlled by a control unit or (overall) controller 26. In this particular example, the actuator system 24 may be or may include a pitch system for controlling the pitch of one or more of the wind turbine blades 18, which may include hydraulic actuators 28 arranged to adjust the blade pitch in a known manner. The actual position of the actuators 28 may be controlled by an actuator position control unit 30, which provides positioning command signals to the hydraulic actuators 28. The controller 26 and the actuator system 24 may be replicated for each of the blades 18 of the wind turbine 10 so that the position of each blade 18 can be controlled independently.

[0035] The pitch system of wind turbine 10 is just one example of a controllable wind turbine system. Controller 26 can also be used to control other wind turbine systems and / or components. For example, actuator system 24 can be a converter control system, wherein actuator system 24 can be a power converter of the power generation system of wind turbine 10, which, in a process known as "full power conversion," converts the AC power delivered by the generator via a DC link into a variable frequency AC output, i.e., the generator's synchronous speed is changed independently of the grid voltage and frequency variations.

[0036] In one example method of the invention, the blade pitch of the wind turbine 10 blades 18 can be controlled (individually and / or collectively) according to a control strategy to not only maximize energy production and minimize load, but also reduce noise emissions based on monitored operation of the wind turbine 10. Specifically, the blade pitch can be controlled to reduce tonal noise or tonal audibility caused by the accumulation of resonances in one or more structural components of the wind turbine 10—e.g., the main shaft, tower, etc.—at a specific, critical rotor or generator speed of the wind turbine 10. That is, the pitch is controlled to ensure that prolonged operation of the wind turbine 10 at such critical speeds is avoided. However, unlike conventional methods for preventing wind turbine operation at such critical rotor speeds, in the method of the invention, the operation of the wind turbine 10 is controlled to perturb the rotor speed away from or around a certain value (e.g., the critical rotor speed). Expressed differently, this provides a temporal variation in the rotor speed to ensure that prolonged or long-term operation at a certain rotor speed (e.g., the critical rotor speed) is avoided. Therefore, generally speaking, examples of the present invention lie in methods for preventing resonance from accumulating over time, such as by perturbing the system to break the resonance, or by disrupting the stability of the system in some way.

[0037] Specific examples of implementing this method in controller or control system 26 are as follows Figure 3 The diagram is shown schematically. Controller 26 is configured, for example, from... Figure 3 The wind measurement module or unit 31 shown receives data indicating wind conditions near the wind turbine 10. This data can be obtained from any suitable source. For example, the data could indicate, for instance, wind conditions from... Figure 1 The direct measurement results of wind conditions (such as wind speed and / or wind direction) from the rotor wind speed and / or wind direction detector 182 shown.

[0038] Several functional elements or modules of the controller 26 are shown. The generator (or rotor) speed optimal setpoint unit 32 receives wind measurement data from the wind measurement unit 31. Based on the current wind conditions, the optimal setpoint unit 32 determines the optimal or desired operating setpoint signal for the generator speed in order to optimize the performance of the wind turbine 10 according to a specific control strategy, such as maximizing energy production and / or minimizing load. The optimal setpoint unit 32 then determines the optimal operating setpoint 34 for the generator speed output.

[0039] The tone control unit 36 ​​determines a disturbance signal that will be applied to or superimposed on a determined optimal setpoint signal 34 to reduce tone noise associated with the wind turbine 10, as will be described in more detail below. The tone control unit 36 ​​outputs a determined disturbance signal 38, which is applied to or combined with the determined optimal setpoint signal 34 at element 40. During the operation of the wind turbine 10, these signals are combined to obtain a so-called "corrected setpoint signal" for the generator speed.

[0040] Figure 3 The main controller 44, displaying the determined corrected setpoint signal 42 received by the main controller or control unit 26, determines the output to be sent to instruct one or more actuation systems of the wind turbine 10 to operate the wind turbine 10 in a desired manner. The pitch reference unit 24 and / or the power reference unit 25 receive instructions from the main controller 44 for controlling the pitch of the blades 18 and / or the power generation of the wind turbine 10, respectively. The output determined by the main controller 44 depends in particular on the corrected operating (generator speed) setpoint signal 42.

[0041] Figure 4 The diagram shows in more detail how the disturbance signal 38 is applied to the optimal generator speed setpoint signal 34 to obtain a corrected or generated generator speed setpoint signal. Specifically, Figure 4 An example of the optimal setpoint signal 34 is illustrated. Specifically, the optimal setpoint signal 34 is illustrated as a signal that changes relatively slowly over time. Since the optimal setpoint signal 34 is determined based on wind conditions near the wind turbine 10, the slowly changing optimal setpoint signal 34 indicates slowly changing wind conditions. For example, in this case, wind speed and / or wind direction may be substantially constant, or may vary over a relatively long period of time. Such wind conditions may include relatively benign wind conditions, but not turbulent wind conditions. Specifically, the time variation of the optimal wind speed signal may be on the same or similar time scale as the time variation of wind conditions (such as speed, direction, etc.).

[0042] Figure 4An example of the perturbation signal 38 is also illustrated. Specifically, the perturbation signal 38 is illustrated as having a time variation greater than that of the optimal setpoint signal 34. That is, the change in the perturbation signal 38 occurs on a faster time scale than the change in the optimal setpoint signal 34. This means that when the perturbation signal 38 is applied to the optimal setpoint signal 34 at element 40, the resulting setpoint signal 42 is a signal with a larger time variation than the optimal setpoint signal 34.

[0043] The disturbance signal 38 can be any suitable signal that disturbs the optimal setpoint, either around or away from a certain (optimal) generator speed setpoint value or range of values. The disturbance signal 38 can be symmetrical about a certain generator speed value (e.g., zero generator speed) so that the average value of the corrected signal 42 is substantially equal to the average value of the optimal signal 34. The specific form of the disturbance signal can be random or deterministic. Figure 4 In the example shown, the disturbance signal is in the form of a sine wave; however, the signal can take any suitable form, such as a cosine wave, a triangle wave, and a square wave (which can be used alternately or in any suitable combination). The amplitude, period, and / or specific form of the disturbance signal 38 can be determined based on the detected wind conditions or the determined optimal setpoint 34. For example, there may be certain wind speeds or certain optimal generator speed setpoints—for example, those corresponding to increased wind turbine tone noise levels—where a disturbance signal with a larger amplitude or greater time variation may be desired. Generally speaking, it may be desirable to disturb the optimal setpoint by the smallest possible amount that still achieves the desired effect of reducing tone noise, thereby minimizing interference with the overall operation of the wind turbine.

[0044] exist Figure 4 In the example shown, the corrected setpoint signal 42 has a larger time variation and a larger amplitude than the optimal setpoint signal (shown as a dashed line), but the average value (varying over time) of the corrected setpoint signal 42 is essentially equal to the average value of the optimal setpoint signal 34. One way to increase the time variation of the optimal setpoint signal 34 is to increase its standard deviation: in the example described, the standard deviation of the corrected setpoint signal 42 is larger than that of the optimal setpoint signal 34.

[0045] Disturbance signal 38 can be determined and applied to optimal setpoint signal 34 under all wind conditions and for all optimal generator speed setpoint values. However, the application of disturbance signal 38 may be particularly beneficial under certain wind conditions and / or for certain values ​​of optimal generator speed setpoint 34. Specifically, the application of the setpoint signal may be particularly useful when wind conditions mean that the determined optimal generator speed setpoint corresponds to a generator speed value or range of values ​​that cause an increase in the pitch noise level of the wind turbine 10. As mentioned above, the pitch noise of the wind turbine may be due to prolonged or long-term operation of the wind turbine 10 at a critical generator speed (which corresponds to the resonant frequency of one or more structural components of the wind turbine 10), allowing the excitation level at the resonant frequency to build up. In this respect, relatively stable wind conditions—corresponding to relatively stable or slowly changing optimal setpoints—may be conditions where the application of disturbance signal 38 is necessary or desirable.

[0046] Therefore, controller 26 can be selectively configured to determine whether a disturbance to the optimal setpoint 34 is necessary before determining or applying disturbance signal 38. Specifically, controller 26 can determine that disturbance signal 38 is only needed if optimal operation of wind turbine 10 would result in an increase in tonal noise levels. Thus, the determination of whether a disturbance signal is needed can be based on data indicating the noise emissions of wind turbine 10. This data can be obtained from one or more different suitable sources. For example, data indicating wind conditions from wind measurement unit 31 can be used as noise emission data. In particular, it can be known that certain wind speeds correspond to (optimal) operation of wind turbine 10 that results in an increase in the tonal audibility of wind turbine 10, and therefore it can be determined that a disturbance signal needs to be applied for such wind speeds. As previously mentioned, tonal noise may build up when wind turbine 10 operates for extended periods at certain critical generator speeds, therefore variations in wind speed—and their absolute values—can be used to determine whether a disturbance signal needs to be applied; for example, a stable or slowly changing wind speed may mean that a disturbance needs to be applied to prevent the accumulation of resonant frequency excitations of structural components over time. In this way, controller 26 can activate the determination and / or application of disturbance signal 38 only when it is determined that disturbance signal 38 needs to be applied.

[0047] Data indicating the noise emissions of wind turbine 10—based on which the activation of a disturbance signal is determined—may include direct measurements of the noise emitted by wind turbine 10. For example, such direct measurements may be received from a microphone or other acoustic sensor in or near turbine 10. Controller 26 may then determine that disturbance signal 38 needs to be activated when the detected emission noise from wind turbine 10 exceeds a threshold noise level. Data indicating the noise emissions of wind turbine 10 may also be based on measurements associated with wind turbine operation (such as generator / rotor speed, power generation level, or torque). It may be known that certain levels or values ​​of these parameters are associated with, or result in, high levels of tonal noise; therefore, activation of disturbance signal 38 may be based on the possibility that one or more of these parameters have reached certain levels for a certain period of time.

[0048] Therefore, more broadly speaking, determining whether the disturbance signal 38 needs to be applied may include determining whether the operating parameters of the wind turbine 10 are within a predefined critical range that could lead to high levels of tonal noise. Additionally, or alternatively, this determination may include determining whether the time variation (e.g., standard deviation) of the operating parameter is less than a threshold variation level. The disturbance signal 38 may then be activated only if the operating parameter is determined to be within the specified critical range and / or below the threshold variation level. The operating parameters may be one or more of generator speed, wind turbine power, wind turbine torque, wind turbine tonal noise or audibility, wind speed, and wind direction. The application of the disturbance signal 38 may then be activated only if the operating parameter is determined to be within the specified critical range. Alternatively, or additionally, determining whether the disturbance signal 38 needs to be applied may include determining whether the time variation of one of the wind turbine operating parameters is less than a specified threshold variation, wherein the application of the disturbance signal 38 may be activated only if the time variation is less than the specified threshold variation. When the disturbance signal 38 is deactivated or determined to be unnecessary, the operation of the wind turbine 10 can be controlled using the optimal setpoint signal 34, i.e., the main controller 44 receives the optimal setpoint signal 34 to determine the control output for controlling the blade pitch.

[0049] In one example, the standard deviation of the generator speed reference is measured and tracked as a moving average, i.e., the average standard deviation is monitored over a certain time period (e.g., an average of 10 seconds). In this way, the moving average is maintained to track the evolution of the generator speed. Alternatively, if the (average) standard deviation is below a set threshold and the average generator speed reference is within a specified threshold speed range, then control to reduce tone noise emissions is activated, for example, disturbance signal 38 is activated.

[0050] In examples of applications that activate or deactivate disturbance signals based on whether predetermined conditions (e.g., whether the tone noise level is above a certain level) are met, further consideration can be given to preventing frequent activation or deactivation of such tone control measures. For example, a hysteresis loop could be used, setting different conditions for activation and deactivation to avoid frequent switching between the two when the operation of the wind turbine 10 is near a threshold defining operation with and without disturbance signals. Another option is to maintain the application of disturbance signal 38 for at least a predetermined amount of time after activation, even if it is determined within the predetermined amount of time that disturbance signal 38 is no longer needed. Disturbance signal 38 can also continue to be applied for a predetermined amount of time after it is determined that it is no longer needed. A similar approach can also be applied additionally or alternatively after disturbance signal 38 is deactivated. More generally, disturbance signal 38 can continue to be applied until a deactivation condition is met, where such a condition can be based not only on the noise level being generated but also on factors that ensure repeated switching between activation and deactivation is avoided. A similar activation condition can be used when disturbance signal 38 is deactivated.

[0051] Figure 5 The steps of method 50 according to an embodiment of the present invention are summarized. In step 52, data indicating wind conditions near the wind turbine 10 is received. This can be data received via direct wind measurements or data determined based on some other measurements. For example, blade load measurements using the blade load sensor 181 can be used for this purpose.

[0052] In step 54, an operating setpoint signal 34 is determined based on the desired or optimal operation of the wind turbine 10, such as a desired control strategy for maximizing efficiency and / or minimizing component load. The operating setpoint signal 34—for example, could be a generator speed setpoint—is determined based on received wind condition data.

[0053] In step 56, a disturbance signal 38 is applied to the operating setpoint signal 34 to obtain a corrected operating setpoint signal 42. The disturbance signal 38 is applied such that the corrected operating setpoint signal 42 has a greater time variation than the operating setpoint signal 34—for example, a larger standard deviation over a certain time period. Optionally, before applying the disturbance, a determination of whether the disturbance is necessary is performed. Such a determination may be based on the actual or expected tone noise level from the wind turbine, and the application of the disturbance signal 38 may only be activated if the tone noise level of the wind turbine is above a certain level.

[0054] In step 58, the operation of the wind turbine 10 can be controlled using the modified operating setpoint signal 42 to reduce noise emissions from the wind turbine 10. If the disturbance signal is activated only under certain conditions, then when the disturbance signal is deactivated, i.e., when the disturbance signal 38 is determined to be unnecessary, the operation of the wind turbine 10 can be controlled using the optimal operating setpoint signal 34.

[0055] Many modifications may be made to the described examples without departing from the scope of the appended claims.

[0056] In the example described above, optimal and modified operating setpoint signals were determined for the generator or rotor speed of the wind turbine. However, in different examples, operating setpoint signals for different wind turbine operating parameters may be determined or additionally used to control the operation of the wind turbine. For example, optimal and modified wind turbine power setpoint signals may be determined and used.

[0057] In the example described above, the optimal operating setpoint signal is determined (based on detected wind conditions), and then a disturbance signal is applied to obtain a corrected operating setpoint signal. However, in different examples, instead of performing separate determinations of the optimal setpoint signal and the disturbance signal, the corrected setpoint signal can be determined directly (taking into account contributions from both the optimal and disturbance signals).

[0058] Examples of the invention may include perturbing the generator speed reference to prevent it from operating above resonance, while also utilizing a lookup table (with speed and power constraints) to avoid high levels of excitation driven by torque loads caused by power system excitation.

[0059] Examples of the present invention can be used as part of a model predictive control routine for controlling the operation of a wind turbine. In particular, a cost function can be used to perturb the operation of the wind turbine to avoid operating regions with resonance accumulation. Specifically, the cost function can maintain the time variation (e.g., standard deviation) of the generator speed reference above a threshold level, at least under certain operating conditions. Essentially, the model predictive controller can be configured such that if wind conditions are stable, the controller will take action to increase the time variation of the wind turbine's operation.

[0060] The advantage of examples of this invention is that noise emissions from wind turbines—particularly tonal noise levels—can be reduced without significantly negatively impacting the performance of the wind turbines (i.e., power production levels). This is because the wind turbine can still operate optimally (or near optimally) relative to control strategies (e.g., maximizing energy production) while tonal noise is reduced. In particular, instead of avoiding optimal operating areas to reduce tonal noise emissions, the operation of the wind turbine can be perturbed around the optimal operating area (e.g., a generator speed reference) to prevent the accumulation of resonances caused by slowly varying (stable) operation in certain operating areas, while still maintaining optimal wind turbine operation (at least an average). Embodiments of the invention advantageously simulate wind turbine operation under unstable wind conditions (i.e., when the generator speed reference has a greater degree of time variation to account for changing conditions) and can be applied at any time as an online update.

Claims

1. A method (50) of reducing noise emissions from a wind turbine (10), the method (50) comprising: receiving (52) data indicative of wind conditions in the vicinity of the wind turbine (10); determining (54) an operational set point signal (34) in dependence on a desired operation of the wind turbine (10), the operational set point signal (34) being determined in dependence on the received data; applying (56) a perturbation signal (38) to the operational set point signal (34) to obtain a modified operational set point signal (42); and controlling (58) operation of the wind turbine (10) using the modified operational set point signal (42) to reduce noise emissions from the wind turbine (10), wherein the perturbation signal (38) is applied such that the modified operational set point signal (42) has a greater temporal variation than the operational set point signal (34).

2. The method (50) of claim 1, comprising determining whether the perturbation signal (38) needs to be applied in dependence on data indicative of noise emissions from the wind turbine (10), and activating application of the perturbation signal (38) only when it is determined that the perturbation signal (38) needs to be applied, wherein the data indicative of noise emissions comprises the received data indicative of wind conditions.

3. The method (50) of claim 2, wherein, Determining whether the perturbation signal (38) needs to be applied comprises determining whether an operational parameter of the wind turbine (10) is within a predefined critical range, and wherein application of the perturbation signal (38) is activated only when it is determined that the operational parameter is within the prescribed critical range.

4. The method (50) of claim 2 or claim 3, wherein, Determining whether the perturbation signal (38) needs to be applied comprises determining whether a temporal variation of an operational parameter of the wind turbine (10) is below a prescribed threshold variation, and wherein application of the perturbation signal (38) is activated only when the temporal variation is below the prescribed threshold variation.

5. The method (50) of claim 4, wherein Determining the temporal variation comprises determining a standard deviation of the operational parameter, and wherein the prescribed threshold variation is a prescribed threshold standard deviation.

6. The method (50) of claim 3, wherein The operational parameter comprises the operational set point signal (34).

7. The method (50) of claim 3, wherein The operational parameter comprises at least one of: a wind turbine generator speed; a wind turbine power; a wind turbine torque; a wind turbine tonal audibility; a wind speed in the vicinity of the wind turbine (10); and a wind direction in the vicinity of the wind turbine (10).

8. The method (50) of claim 2 or 3, wherein, If it is determined that the perturbation signal (38) does not need to be applied, the method (50) comprises controlling operation of the wind turbine (10) using the determined operational set point signal (34).

9. The method (50) of claim 2 or 3, wherein, If it is determined that the perturbation signal (38) does not need to be applied while application of the perturbation signal (38) is activated, the method (50) comprises continuing to apply the perturbation signal (38) until a deactivation condition is met; or, if it is determined that the perturbation signal (38) needs to be applied while application of the perturbation signal (38) is deactivated, the method (50) comprises applying the perturbation signal (38) only when an activation condition is met.

10. The method (50) according to any one of claims 1-3, wherein, The disturbance signal (38) is applied such that the time average of the modified operational set point signal (42) is equal to the average of the operational set point signal (34).

11. The method (50) according to any one of claims 1-3, wherein, The disturbance signal (38) is deterministic, wherein the disturbance signal (38) comprises one or a combination of a sine wave signal, a cosine wave signal, a triangular wave signal and a square wave signal, wherein the disturbance signal (38) is determined based on the received data indicative of wind conditions.

12. The method (50) according to any one of claims 1-3, wherein, The operational set point signal (34) is at least one of: a wind turbine generator speed set point signal; and a wind turbine power set point signal.

13. The method (50) according to any one of claims 1-3, wherein, Controlling the operation of the wind turbine (10) comprises determining a control output in dependence on the modified operational set point signal (42), and using the determined control output to control the operation of the wind turbine (10), wherein the control output is a pitch reference value for controlling the pitch of one or more blades (18) of the wind turbine (10).

14. A controller (26) for reducing noise emissions of a wind turbine (10), the controller (26) being configured to: receive data indicative of wind conditions in the vicinity of the wind turbine (10); determine an operational set point signal (34) in dependence on the received data, the operational set point signal (34) being determined in dependence on a desired operation of the wind turbine (10); apply a disturbance signal (38) to the operational set point signal (34) to obtain a modified operational set point signal (42); and control the operation of the wind turbine (10) using the modified operational set point signal (42) to reduce noise emissions of the wind turbine (10), wherein, the disturbance signal (38) is applied such that the modified operational set point signal (42) has a greater temporal variation than the operational set point signal (34).

15. A wind turbine (10) comprising a controller (26) according to claim 14.

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