METHOD FOR CHANGING THE NOISE EMISSION OF A WIND ENERGY PLANT

Description

[0001] The present invention relates to a method for modifying the sound emission of a wind turbine. The present invention also relates to a wind turbine in which such a method is implemented.

[0002] Wind turbines are well-known and typically feature a generator to produce electrical energy from the rotation of a wind-driven rotor. However, the generator also generates noise. This noise propagates and can be perceived as disturbing noise at a given location. In addition to the generator, other noise sources may also be present in typical wind turbines.

[0003] To protect people at the point of impact, regulations regarding noise emissions must be observed. One of these regulations is determined by a noise measurement according to DIN 61400-11.

[0004] In addition to loudness, i.e., the amplitude of the sound, psychoacoustic effects are also taken into account. It is perceived as particularly disturbing when a sound stands out significantly from the background noise, especially broadband noise generated by the rotor blades. In a sound analysis, this can be recognized, among other things, by the fact that at a specific frequency, the amplitude is locally significantly above a fundamental frequency. This effect is also referred to as tonality.

[0005] Tonality occurs when individual tones stand out clearly or are audible within a sound spectrum. This effect can occur, for example, when a frequency is equal to or nearly equal to a natural frequency, leading to resonance. It can also occur when a sound-generating component itself has a dominant frequency that is radiated as sound and stands out compared to other sound sources.

[0006] Specifications for wind turbines take tonal characteristics into account. The stronger the effect, i.e., the greater the tonal content, the quieter the overall sound generated by the wind turbine must be. The sound amplitude must then be reduced.

[0007] To comply with the regulations, it may be necessary to reduce the rotor speed, thereby reducing the amount of electrical power fed into the grid. It may also be the case that the wind turbine cannot be operated in the affected operating mode and, in the worst case, must be shut down. Examples from the prior art are known from WO2018086671A1 and WO2018046068A1.

[0008] The object of the present invention is therefore to solve one of the aforementioned problems or at least to propose an alternative. In particular, it aims to reduce tonal noise from wind turbines and / or its perception.

[0009] According to the invention, a method according to claim 1 is proposed. The method thus relates to modifying the sound emission of a wind turbine. The underlying wind turbine comprises a nacelle and a generator with a rotor whose rotational speed is adjustable. The rotor has at least one rotor blade. The generator produces sound with at least one characteristic generator sound frequency that depends on the rotor speed. The wind turbine has at least one fan for cooling the nacelle and / or the generator, and the speed of the at least one fan is adjustable. The at least one fan produces sound with a characteristic fan sound frequency that depends on the fan speed. The fan speed of the at least one fan is adjusted as a function of the rotor speed such that the fan sound frequency differs from the at least one generator sound frequency.

[0010] The characteristic generator sound frequency is the frequency that corresponds to a dominant tone of the generator sound. This characteristic generator sound frequency, or dominant tone, is determined by the generator's design.

[0011] Generator noise with a characteristic generator frequency is generally significantly higher in amplitude than other sound with a spectrum around that characteristic generator frequency. Figuratively speaking, the generator noise with the characteristic generator frequency stands out from the sound with the rest of the adjacent spectrum. The greater the difference between the amplitude of the generator noise with the characteristic generator frequency and the amplitude of the sound of the surrounding fundamental spectrum, the more likely the generator noise with the characteristic generator frequency is to be perceived as an unpleasant, distinct tone.

[0012] It has now been recognized that the fan noise of at least one fan can interfere with the generator noise in an unfavorable way, causing the amplitude at the characteristic generator noise frequency to stand out even more from the surrounding background spectrum. Unfavorable interference is understood to mean that the resulting sound from the superposition of generator noise and fan noise has a higher amplitude than the individual noises and / or that at least the peak of the combined sound at the generator noise frequency stands out more from the background spectrum than the peak of the generator noise alone.

[0013] It was discovered that fan noise also exhibits a characteristic fan noise frequency, which can be assigned to a dominant tone. This characteristic fan noise frequency depends on the fan speed and the number of fan rotor blades.

[0014] The fan speed is thus set so that the resulting characteristic fan sound frequency differs from the generator sound frequency, so that fan sound and generator sound do not overlap unfavorably.

[0015] Additionally, it was found that the perceived noise level can be improved by adjusting the fan speed so that the fan noise frequency is close to the generator noise frequency, thus masking the generator noise. It is therefore proposed to adjust the fan speed so that the characteristic fan noise frequency lies in the range of the generator noise frequency, i.e., very close to it.

[0016] On the one hand, this avoids the generator's noise frequency, thus preventing undesirable interference. On the other hand, by approximating the fan's noise frequency to the generator's noise frequency, the generator noise is masked. In other words, the generator noise is broadened in its frequency so that it is no longer perceived as a single tone. The advantage is that this avoids any tonal character.

[0017] How far the fan sound frequency must deviate from the generator sound frequency to achieve an optimum between unfavorable superposition and desired masking can be determined experimentally and / or by simulations.

[0018] It was also recognized that the generator can produce generator noise with several dominant tones, i.e., frequencies. The generator noise then exhibits a peak at several characteristic generator noise frequencies. It is proposed to adjust the fan speed of at least one fan so that the resulting fan noise frequency differs from all generator noise frequencies.

[0019] Furthermore, it was recognized that the fan noise frequencies of multiple fans can also overlap unfavorably, especially when identical fans are operated at the same speed. Therefore, it is further proposed to adjust the fan speeds of the individual fans so that the resulting fan noise frequencies differ from one another. This also avoids unfavorable overlapping noise. Again, it should be taken into account that the fan speeds, and thus the fan noise frequencies, should be set in such a way as to mask the generator noise and / or the noise of the other fans.

[0020] According to the invention, at least one critical fan speed is determined as a function of the rotor speed, and this speed is to be avoided by the respective fan. The fan speed of each fan is set such that the at least one critical fan speed is avoided. The at least one critical fan speed is the same for identical fans. Alternatively or additionally, the at least one critical fan speed corresponds to a fan speed at which the associated fan sound frequency corresponds to the generator sound frequency.

[0021] Determining at least one critical fan speed allows for a simple implementation of the procedure. This can be achieved, for example, by using a function or a table that determines the critical fan speed based on the rotor speed. Alternatively, a calculation equation can be used to calculate the at least one critical fan speed as a function of the rotor speed. Given a specific rotor speed, the at least one critical fan speed can then be determined, and the speed of the respective fan can be adjusted to avoid exceeding this critical speed.

[0022] The characteristic fan noise frequency at a given fan speed is known or can be calculated. Similarly, the characteristic generator noise frequency at a given rotor speed is known or calculable. Therefore, it is also possible to determine which fan speed should be avoided—namely, the speed that results in a characteristic fan noise frequency corresponding to the generator noise frequency.

[0023] It was also particularly noted that the characteristic fan noise frequency is determined by the fan's design. Therefore, at least one critical fan speed is the same for identical fans. This has shown that the calculation or determination of at least one critical fan speed only needs to be performed once for identical fans.

[0024] According to another perspective, the generator sound frequency is a harmonic of a frequency variable of the generator on which the sound depends. Specifically, a harmonic of a pole passing frequency is used. The pole passing frequency indicates how often a rotor pole passes a reference position. The 12th harmonic of this frequency variable is particularly relevant.

[0025] The fan sound frequency is a fundamental frequency or harmonic of the sound generated by the fan. Specifically, the fan sound frequency is... in L A leaf passing frequency. The fan sound frequency. in L particularly dependent on the fan speed nL and a number of fan rotor blades AL determined. In particular, the fan noise frequency is determined according to the formula f L Hz = n L rpm 60 ⋅ A L certainly.

[0026] The frequency of the generator is therefore a physically occurring frequency at the generator that influences the sound. The frequency at which the generator mechanically rotates can, for example, be such a frequency. Preferably, the frequency is the pole passing frequency.

[0027] The pole passing frequency is the frequency at which a rotor pole passes a freely selectable reference point. Depending on the number of rotor poles, it corresponds to a multiple of the rotor's current rotational frequency.

[0028] By repeatedly passing the reference point or another point, sound is generated at the generator's sound frequency.

[0029] It was also recognized that half the pole passing frequency can be a frequency parameter that influences the sound. Here, it was understood that the sound depends on an interaction between the rotor and stator, and thus can depend on the magnetization of each rotor pole. It is therefore specifically proposed to use a harmonic of half the pole passing frequency as the generator sound frequency. Relevant to half the pole passing frequency is how often a reference point is passed by every second pole. This is based on the fact that two adjacent poles are magnetized differently. The magnetization leads to a strong interaction between the rotor and stator, which is essential for the operating principle of the generator and thus for power generation, but which can also influence noise development or sound generation. Because of this changing magnetization, or rather...The direction of magnetization from one pole to the next means that half the pole passing frequency may be relevant instead of the pole passing frequency. For simplification, the number of pole pairs can also be used for the calculation instead of the number of poles.

[0030] The frequency magnitude, and therefore also the generator sound frequency, is thus determined by the generator's design. Furthermore, the frequency magnitude and generator sound frequency depend on the rotor speed.

[0031] Due to its design, a generator has several slots in the stator, i.e., stator slots, with corresponding stator windings. For simplicity, the stator slots can also be referred to simply as slots. In a 6-phase generator, for example, there are six stator slots per rotor pole. Each pole pair, consisting of two rotor poles, therefore has 12 stator slots. One order k of the harmonics corresponds to the number of stator slots per pole pair. In this example, the order is therefore k = 12. The characteristic generator sound frequency is then the 12th harmonic at half the pole passing frequency. The number of slots in the generator is therefore crucial for the characteristic generator sound frequency. Other important harmonics include the 6th and 18th harmonics, especially with respect to half the pole passing frequency.

[0032] With the number of polar pairs PGThe characteristic generator sound frequency is thus determined by the generator and the rotor speed n R. f G Hz = n R rpm 60 ⋅ P G ⋅ k .

[0033] The fan itself also generates sound due to its design, so the fan's sound frequency depends on the fan's construction. Preferably, the fan's sound frequency is the blade pass frequency, which indicates how often a fan rotor blade passes a chosen reference point per second. The passing of the fan rotor blades produces a vibrating noise at the blade pass frequency. However, it is also possible that harmonics, i.e., integer multiples of the blade pass frequency, dominate the spectrum and are considered the fan's sound frequency.

[0034] According to another aspect, the fan speed of at least one fan is specified in such a way that the associated fan sound frequency deviates from the generator sound frequency by a maximum of a predefinable masking deviation in order to mask the generator sound frequency.

[0035] The resulting fan noise frequency is therefore different from the generator noise frequency, but still within the range of the generator noise frequency. The masking deviation is set so that the generator noise and fan noise cannot be perceived as distinct tones. This achieves a broadening of the generator noise frequency at its characteristic frequency. The resulting noise then no longer exhibits a sharp peak at the generator noise frequency and is perceived as less unpleasant.

[0036] The masking of the generator's noise frequency depends on the absolute noise level of the resulting overall noise. For example, masking may be disadvantageous in the lower rotational speed range of the rotor. Masking of the generator's noise frequency is generally not performed when cooling is the primary concern.

[0037] According to another aspect, the critical fan speed n L,i for every fan i determined depending on the rotor speed n R , a number of pole pairs PG of the generator, one or the number of fan rotor blades AL,i the fan i and an order kof the sound produced by the generator. The order k is a characteristic order of the generator and / or can be considered the order of harmonics used as the generator's sound frequency. In particular, or alternatively, it can have the value 6, 12, or 18. Thus, the 6th, 12th, or 18th harmonic can be the generator's sound frequency, respectively. Preferably, the order k characterizes a number of slots, i.e., stator slots, per pole pair. The order k can then correspond to twice the number of phases of the generator, i.e., exactly one number of slots per pole pair. In the case of a 6-phase generator, the order is then 12 (k=12).

[0038] It was specifically observed that the number of pole pairs (i.e., of the rotor), together with the number of phases (i.e., the stator), and the rotor speed determine the generator's sound frequency. Depending on the rotor speed, a critical fan speed, i.e., one that should be avoided, can thus be easily determined. A correspondingly adjusted fan speed can therefore be easily determined and set.

[0039] The critical fan speed is then determined as n L , i = n R ⋅ k ⋅ P G A L , i

[0040] The critical fan speed can therefore be determined by equating the fan sound frequency. in L and generator sound frequency in G and switching according to fan speed.

[0041] The adjustable fan speed of each fan should therefore deviate from this critical fan speed, in particular lie outside a predefined range around the critical fan speed. This ensures that the resulting characteristic fan sound frequency differs from the characteristic generator sound frequency.

[0042] According to another aspect, the wind turbine has several fans for cooling the nacelle and / or the generator. The fan speeds of the fans are adjustable, and each fan generates a sound with a characteristic frequency that depends on its speed. Each fan speed is adjusted, in relation to the rotor speed, so that its sound frequency differs from the generator's sound frequency. Preferably, the fan speeds are set so that their sound frequencies also differ from each other.

[0043] It was discovered that fans can also generate sound with a characteristic fan frequency, which can interfere with each other in an unfavorable way. This would be the case, for example, if every fan, especially identical ones, were set to the same fan speed, resulting in all fans exhibiting a peak in the sound spectrum at the same fan frequency. Due to this interference, the amplitude of the resulting sound at the fan frequency would protrude further from the fundamental spectrum than it would for each fan individually. This is precisely what needs to be avoided, as a pronounced peak in the fundamental spectrum is perceived as unpleasant. Therefore, identical fans are set to different fan speeds.

[0044] This also depends on the rotor speed, as the generator noise frequency must also be avoided by the fans.

[0045] Furthermore, it was discovered that by setting different fan speeds, and thus in particular the resulting different fan noise frequencies, the effect of masking the generator noise can be enhanced, and the fans can also mask each other. Therefore, all fans are used to mask the generator noise frequency.

[0046] Each fan and generator sound exhibits a peak with a certain frequency range at its respective frequency. Adjusting the fan speed aims to slightly overlap these resulting peaks at the edge of the frequency range. By appropriately selecting the fan frequencies, a plateau in the sound amplitude is achieved, extending over a wider frequency range than the individual peaks of the generator or fan sound. This effectively broadens the frequency of the generator sound.

[0047] Because all fan sound frequencies and generator sound frequencies are different from each other, the amplitude of the plateau can be kept low at the same time.

[0048] According to another aspect, at least one frequency difference is specified as the frequency difference between any two fan sound frequencies of any two fans. The fan speeds are adjusted depending on the frequency difference so that the fan sound frequencies of at least two fans have this frequency difference from each other.

[0049] The frequency difference is therefore predetermined to avoid undesirable interference of the sound from two fans. The respective fan speeds are set so that each fan produces a sound with a different fan frequency.

[0050] The sound spectrum of each fan thus exhibits a peak with a certain frequency range at the respective fan's sound frequency. At least one frequency difference is chosen to be small enough to allow for an overlap between the frequency ranges of one fan and the other. However, the frequency difference is simultaneously chosen to be large enough to keep the resulting sound amplitude low. This prevents undesirable superposition with excessively high sound levels and also achieves masking, so that the sound signals from the fans are not perceived as distinct tones.

[0051] According to another aspect, the frequency spacing, defined as the frequency difference between any two fan sound frequencies of two fans, is variably adjustable. Alternatively or additionally, the frequency spacing between the fans themselves is different. Preferably, the frequency spacing is selected based on at least one weather parameter from the list including outside temperature, humidity, atmospheric pressure, precipitation rate, droplet size, snowfall rate, and wind speed.

[0052] It was found that generator noise can be masked particularly effectively if the fan noise frequencies are not all equally spaced. For example, the frequency difference between the first and second fans might be one hertz, while between the second and third fans it might be two hertz, and so on.

[0053] Due to the unequal spacing of the fan sound frequencies, the resulting frequency spectrum can exhibit a plateau. This avoids local frequency peaks that can occur when the spacing between two fan sound frequencies remains constant. Otherwise, multiple peaks can appear in the spectrum, which are perceptible as individual tones and can be perceived as disturbing.

[0054] This is avoided by using unequal intervals between the fan sound frequencies. These unequal intervals allow some of them to be smaller, resulting in a narrower overall spectrum, or plateau. This prevents excessively low fan speeds and consequently poor cooling performance. The variable frequency spacing thus allows for high average cooling performance while maintaining a low amplitude of the resulting sound. With a fixed frequency spacing between all fans, this flexibility in optimization through variation of individual frequency intervals is not possible.

[0055] Through simulations and / or experiments, suitable fan speeds can be found that result in fan sound frequencies with a wide frequency range and a plateau of low sound amplitude in the resulting sound.

[0056] In particular, it was also recognized that weather parameters can influence the sound frequency of the fans, their perception and / or their propagation.

[0057] Weather parameters, in particular, also influence the frequency spacing to be selected between two fans and, especially, the fan speed to be set for each fan. Crucially, this depends on the sound spectrum at the point of impact, i.e., how the sound is perceived there. Therefore, the fan sound frequencies must be set in such a way as to achieve a broadening of the fan sound at the point of impact.

[0058] It was observed that the propagation of the resulting sound is more strongly attenuated as the ambient temperature decreases. At lower temperatures, the amplitude of the sound at the point of immission is therefore lower, thus allowing for sound generation with a higher amplitude. The fan speeds can then be adjusted for improved cooling.

[0059] Humidity also affects sound propagation. The more humid the air, the better the sound can travel. Therefore, the more humid the air, the greater the frequency difference between the fans is chosen to achieve the lowest possible sound plateau. The drier the air, the less critical a high noise level is, and the fans can be adjusted for optimal cooling.

[0060] Similarly, higher atmospheric pressure is associated with increased sound perception. The higher the air pressure, the more important it is to optimize the frequency spacing for acoustics.

[0061] During periods of high precipitation, noise levels at the point of impact are already elevated. Therefore, high noise levels from the wind turbine are less critical. In this case, the frequency spacing can be reduced, and the fans can be used for optimal cooling.

[0062] The size of the droplets, as in rain, also affects the sound emission. The larger the droplets, the louder the ambient noise from the precipitation. In this case, too, the frequency spacing can therefore be chosen more freely.

[0063] During snowfall, the snow masses also dampen the sound. Therefore, as the snowfall increases, the frequency spacing can be smaller.

[0064] Wind speed and / or wind direction also affect sound propagation. Depending on the wind direction, the sound is either driven towards or carried away from the point of origin. Furthermore, at higher wind speeds, the sound is perceived at greater distances. Therefore, a sound-optimized frequency spacing setting should be selected when the wind is blowing towards the point of origin and / or the wind speed is high.

[0065] According to another aspect, the frequency spacing, defined as the frequency difference between the sound frequencies of two fans, is variably adjustable. The frequency spacing between the fans decreases with increasing distance from the generator's sound frequency.

[0066] This has the advantage that a plateau in the volume of the resulting sound is achieved particularly effectively, without a peak forming due to the fan with the greatest frequency difference to the generator sound frequency.

[0067] According to another aspect, the frequency spacing is defined as the frequency difference between any two fan sound frequencies of two fans, depending on the rotor speed. The lower the rotor speed, the smaller the frequency spacing is defined.

[0068] It was discovered that lower rotor speeds also reduce the amplitude of the generator noise. This results in a quieter overall noise level. Consequently, the noise is perceived as less disturbing. It is then also possible to use smaller frequency intervals, allowing the fans to achieve better cooling performance.

[0069] It was also recognized that at lower rotor speeds, the lower sound level often results in a narrower frequency range for the fan noise, especially when the frequency boundary is defined by a sound level. For this reason as well, the frequency spacing can be smaller at lower rotor speeds.

[0070] According to another aspect, the generator sound frequency has a pitch width, in particular an ERB width. The pitch width defines a characteristic frequency range around the generator sound frequency.

[0071] Depending on the tone width, a frequency range to be avoided is determined, defined by an avoidance width. The avoidance width defines the frequency range to be avoided as a range around the generator's sound frequency. The avoidance width is smaller than the tone width, ensuring that the frequency range to be avoided lies within the characteristic frequency range. The fan speed of each fan is adjusted so that the fan's sound frequency lies outside the frequency range to be avoided and / or within the characteristic frequency range.

[0072] This takes into account that, depending on the sound frequency, a region on the basilar membrane in the human ear is stimulated, which can be interpreted as a bandpass filter. The width of the bandpass varies with the frequency. The masking sound should lie within the bandpass to achieve effective masking.

[0073] The pitch width is now understood as the bandwidth exhibited by such a theoretical bandpass filter of the basilar membrane in the ear at the generator's sound frequency. The pitch width is therefore dependent on the generator's sound frequency.

[0074] In particular, the ERB width is used as the pitch width, where ERB is an abbreviation for Equivalent Rectangular Bandwidth. In psychoacoustics, the ERB width describes an approximation of the bandwidth of the filters of the human ear. For simplicity, these filters are assumed to be rectangular.

[0075] It has now been recognized that, in order to mask the generator noise, a background noise must lie within the characteristic frequency range defined by the pitch width.

[0076] For this reason, the fans are adjusted so that the fan noise frequency lies within the characteristic frequency range. This broadens the narrow peak of the generator tone at the generator noise frequency, making it perceived as less unpleasant.

[0077] This should be achieved at least up to a maximum fan speed and thus maximum fan noise frequency.

[0078] However, it was also recognized that the speed of each fan must be adjusted to avoid an unfavorable superposition of the amplitude maxima of the fan noise and the generator noise. The resulting noise should therefore not be louder, but broader in its spectrum. This is achieved by avoiding the frequency range into which the fan noise frequency should not fall.

[0079] According to another aspect, the fan speed is specified as a fan speed characteristic curve. The fan speed characteristic curve describes a function of the fan speed as a function of the rotor speed. In particular, the fan speed characteristic curve is designed as a linear characteristic curve.

[0080] At a given rotor speed, the fan speed is then set according to the fan speed characteristic curve. This ensures simple implementation, as the fan speed can be easily adjusted using a characteristic curve without having to explicitly determine the resulting fan noise frequency.

[0081] The fan speed characteristic curve can be determined beforehand. Simulations or experiments are suitable for this purpose. However, the fan speed characteristic curve can also be calculated.

[0082] If the fan speed characteristic curve is set to a linear profile, simple control can be achieved. Furthermore, this has the advantage that, regardless of the rotor speed, the resulting fan noise frequencies can maintain a constant frequency difference from the generator noise frequency, depending on the selected fan speed characteristic curve and its slope.

[0083] The fan speed characteristic curve is linear, in particular, when the fan speed is nL by the with a factor m multiplied rotor speed n R can be calculated, where a constant offset c This can be taken into account. The fan speed could then be calculated, for example, as... n L = m ⋅ n R + c .

[0084] According to another aspect, each fan has its own fan speed characteristic curve. The fan speed characteristic curves of several fans each differ from each other by a predefined speed deviation criterion.

[0085] In particular, it is intended that the fan speed characteristics of several fans are shifted relative to each other by a predefinable differential speed and / or differ from each other by a speed deviation factor in the range of 0.8 to 1.2.

[0086] In order to ensure that each fan produces a fan sound with a different fan sound frequency, a different fan speed characteristic curve is assigned to each fan.

[0087] It is crucial that the resulting fan noise frequencies are sufficiently far apart to avoid superposition, which would increase the noise level. The speed deviation criterion thus ensures that the fan speeds of two fans differ sufficiently to prevent the resulting fan noise frequencies from colliding unfavorably and leading to a higher amplitude.

[0088] The speed deviation criterion can be achieved particularly easily by specifying a differential speed. This differential speed can be determined in advance as the difference between two fan speeds, and it must be set so that the fans optimally mask the generator noise on the one hand, and on the other hand, the fan noise signals do not overlap unfavorably.

[0089] Alternatively or additionally, the speed deviation criterion can also be specified as a speed deviation factor. The fan speed characteristic curve of a first fan then corresponds to the fan speed characteristic curve of a second fan multiplied by the speed deviation factor. The fan speed characteristic curves are then inclined relative to each other.

[0090] The speed deviation criterion can be implemented particularly easily by specifying a power difference. For example, the power of one fan is set 1% lower than that of another fan. Instead of 100% fan power, the fan is then set to 99% of its possible power.

[0091] Alternatively or additionally, it is provided that the fan sound frequency characteristic curves of several fans, each describing a fan sound frequency as a function of the rotor speed, differ from each other by a predefinable frequency deviation criterion.

[0092] In particular, it is provided that the fan sound frequency characteristics of several fans are shifted from each other by a predefinable difference frequency and / or differ from each other by a frequency deviation factor, which can correspond to the speed deviation factor, in the range of 0.8 to 1.2.

[0093] Instead of directly specifying the rotational speed, it is also possible to specify the fan noise frequency that should be set at a given rotor speed. The fan speed characteristic curve is particularly suitable for this purpose, as it assigns a corresponding fan noise frequency to each rotor speed.

[0094] To enable proper masking and avoid unfavorable superposition of the fan noise signals, each fan is assigned a different fan speed characteristic curve. The frequency deviation criterion ensures that the fan noise frequencies do not overlap in such a way as to increase the amplitude of the resulting noise. Furthermore, the masking of the generator noise is also taken into account. This can be achieved directly via the respective fan noise frequency characteristic curves.

[0095] The frequency deviation criterion can be easily implemented by specifying the difference frequency to the fan sound frequency characteristic curves. Each fan sound frequency thus deviates from the sound frequency of the next fan by this difference frequency.

[0096] It was found that a preferred difference frequency lies between 2 Hz and 5 Hz, and is particularly preferably around 3.5 Hz.

[0097] Alternatively or additionally, it is also possible to specify the frequency deviation factor, which indicates how far the fan sound frequency characteristics are shifted relative to each other.

[0098] It is also possible to define both fan speed and fan noise frequency curves for the fans. In this case, the fan speed is primarily set based on the fan speed curve, and the fan noise frequency curves can be used for verification. If it is detected that the resulting fan speed deviates from the corresponding fan noise frequency curve by a predefined value, the system can react accordingly and correct the fan speed according to the fan noise frequency curve.

[0099] According to another aspect, the wind turbine has at least two fans for cooling the nacelle and / or the generator. The fans can be sorted into a fan sequence. The fan speeds or fan speed characteristics are selected according to the fan sequence. Additionally, the fan sequence is changed after a predefined exchange period or depending on another exchange criterion, so that the fan speeds or fan speed characteristics are reselected according to the changed fan sequence.

[0100] The idea is to keep the cooling performance of each fan as consistent as possible. Reducing a fan's speed also reduces its cooling capacity. Therefore, if the fans are operated at different speeds, their cooling performance will vary. One fan will then cool more effectively than another, resulting in uneven cooling and / or uneven wear on the fans.

[0101] It was recognized that it can therefore be useful to swap the fan speeds so that the cooling effect can be distributed more evenly.

[0102] This results in different fans operating at their highest, lowest, and other speeds on a rotating basis. Rotating the fan speeds can also improve fan efficiency.

[0103] The fans can be numbered and sorted according to their order. The fan speeds or characteristic curves can be assigned to specific fans in various ways. One simple implementation is to select the fans according to their order for determining the set fan speed. This assumes that the fans are identical or at least have the same speed ranges.

[0104] After the exchange period has expired, the fans will be re-sorted. This will effectively assign each fan a new fan speed or fan speed characteristic curve.

[0105] Alternatively, the replacement criterion can be predefined. For example, the fan order can be changed if a desired cooling temperature is no longer reached in the area of ​​a particular fan. Another criterion could be the performance of the fans.

[0106] According to another aspect, the wind turbine has at least one other noise source, and this at least one other noise source generates further sound, each with a constant frequency. The fan speed of this at least one fan is adjusted so that the fan's sound frequency deviates from the constant frequency.

[0107] One such noise source is, for example, a transformer in a wind turbine.

[0108] One advantage of this is that the fan noise and the noise from the other noise source do not overlap to such an extent that they increase the amplitude of the overall noise. In other words, the noise from the other source is also masked, which is a positive effect.

[0109] Another advantage is that the sound from the additional noise source already contributes to masking the generator noise. It thus contributes to broadening the generator noise frequency. This can be exploited by adjusting the fan speed while avoiding a constant frequency. The generator frequency can thereby be broadened even further.

[0110] According to the invention, a wind energy plant according to claim 15 is also proposed.

[0111] The wind turbine comprises a nacelle and a generator with a rotor whose speed is adjustable, the rotor having at least one rotor blade. The generator produces sound with at least one characteristic generator sound frequency that depends on the rotor speed.

[0112] The wind turbine has at least one fan for cooling the nacelle and / or the generator. The at least one fan is adjustable in speed and generates sound with a characteristic frequency that depends on the fan speed.

[0113] Preferably, sound emissions can be detected, in particular by a microphone. Detection may be unnecessary if the expected sound emission is known or derivable from the settings of the wind turbine, in particular the generator speed and / or generator power. The wind turbine also has a control module.

[0114] To modify the sound emission, the control module adjusts the fan speed of at least one fan as a function of the rotor speed such that the fan sound frequency deviates from the at least one generator sound frequency. In particular, the fan speed of the at least one fan is adjusted according to the above aspect. The preceding explanations of the method according to the invention apply accordingly to the wind turbine.

[0115] The invention is explained in more detail below by way of example with reference to the accompanying figures. Figure 1 shows a wind turbine in perspective view. Figure 2 This shows an example of a spectrum from a wind turbine at different rotational speeds. Figure 3 shows a speed-dependent generator sound frequency. Figure 4 shows a diagram of several superimposed sound signals.

[0116] Figure 1Figure 1 shows a schematic representation of a wind turbine according to the invention. The wind turbine 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During operation of the wind turbine, the aerodynamic rotor 106 is set into rotation by the wind and thus also rotates an electrodynamic rotor or rotor of a generator, which is directly or indirectly coupled to the aerodynamic rotor 106. The electric generator is arranged in the nacelle 104 and generates electrical energy. The blade angles of the rotor blades 108, which can also be referred to as pitch angles or setting angles, can be changed by pitch motors at the rotor blade roots 109 of the respective rotor blades 108.

[0117] The wind turbine also has four cooling fans for cooling the generator.

[0118] Figure 2 Figure 1 shows a coordinate system in which the sound pressure amplitude of sound signals is represented as a function of frequency. The coordinate system displays seven exemplary spectra (211, 212, 213, 214, 215, 216, 217) of a wind turbine at different rotor speeds.

[0119] In each of the spectra 211, 212, 213, 214, 215, 216, 217, a peak is discernible that stands out noticeably from the surrounding background spectrum. This peak is a design-related generator tone 220, which lies at the generator's sound frequency, and is circled for clarity.

[0120] The further the generator tone 220 stands out from the fundamental frequency, the more unpleasant the sound is perceived. Therefore, the aim is to prevent the amplitude of the peak at the generator sound frequency from being further increased. To achieve this, the fan speed is adjusted so that a dominant tone in the fan's sound has a fan sound frequency that differs from the generator sound frequency. Thus, a frequency range determined by the frequency width of the peak, i.e., the generator tone 220 at the generator sound frequency, is avoided.

[0121] The fan noise is not represented in the coordinate system.

[0122] Figure 3 The diagram shows a coordinate system where frequency in Hz is plotted on the ordinate and rotor speed nR in rpm on the abscissa. An example of a range from 3 rpm to 12 rpm and 0 Hz to 160 Hz is shown.

[0123] A characteristic generator sound frequency 320 is shown. The generator sound frequency increases with increasing rotor speed. A frequency range 330 around the generator sound frequency 320, which should be avoided, is also shown.

[0124] The fans of the wind turbine also generate sound, which is superimposed on the generator sound and each has a characteristic fan sound frequency.

[0125] The fans are adjusted to avoid a critical speed, specifically the speed that would result in fan noise with a frequency equal to the generator's frequency. A target speed range is also defined to ensure the fan noise stays below the target frequency of 330 Hz. Four fan noise frequencies are shown: 341, 342, 343, and 344. Each fan speed is adjusted so that the fan noise frequencies 341, 342, 343, and 344 do not fall within the target frequency range of 330 Hz.

[0126] Furthermore, it was recognized that the fan noise frequencies can also overlap unfavorably. Therefore, the fan speeds are also set so that their noise frequencies (341, 342, 343, 344) differ from each other. A frequency difference is specified for each fan, which two fans must have. This prevents unfavorable overlapping.

[0127] Another aspect that the Figure 3 The purpose of this is to illustrate the masking of the generator tone. The peak that the generator tone exhibits in the spectrum is to be broadened by adjusting the fan speeds so that the fan sound frequencies 341, 342, 343, 344 are close to the generator sound frequency 320.

[0128] The plan also includes adjusting the fan speed so that the fan noise frequencies have a frequency spacing between them. This frequency spacing is chosen to mask the generator tone.

[0129] In Figure 3 The frequency spacing is constant. However, it is also specifically designed to allow the frequency spacing between the fans to be set differently. This allows the fan noise frequencies and the generator noise frequency to be optimally matched.

[0130] The four fan sound frequencies 341, 342, 343, 344 are thus represented in the figure as fan sound frequency characteristic curves that are shifted relative to each other. It is also provided that each fan sound frequency characteristic curve is assigned a corresponding fan speed characteristic curve, which are shifted relative to each other and each reaches a maximum speed. The maximum speeds are also different here and accordingly result in a maximum frequency for the fan sound frequency characteristic curves.

[0131] Figure 3 also shows a pitch width of the generator sound as ERB width, namely a lower ERB limit 351 and an upper ERB limit 352.

[0132] To mask the generator tone with a generator sound frequency of 320 Hz, the fan speeds are set so that the fan sound frequencies lie within the frequency range defined by the tone width, i.e., above the lower ERB limit of 351 Hz and below the upper ERB limit of 352 Hz. This is only possible within certain limits, as the fans have a maximum speed. At this point, the fan is already operating at full power. In the example, this is achieved for the fan with a fan sound frequency of 341 Hz at approximately 8.2 rpm of the rotor speed. Furthermore, the frequency difference between the fan sound frequencies should be maintained.

[0133] Figure 4Figure 1 shows another coordinate system in which the amplitude, namely the sound pressure amplitude, of several sound spectra in dB is plotted against a frequency f in Hz. The simulation depicts the superposition of sound signals from twelve identical fans with sound frequencies of twelve different frequencies, resulting in a single sound signal with sound spectrums 410, 420, 430, 440, 450, and 460. For each of the resulting sound spectra 410, 420, 430, 440, 450, and 460, a different frequency spacing between the fans is chosen to investigate different superpositions. For this purpose, each of the twelve fans is assigned a corresponding (different) rotational speed. However, in the case of the superimposed sound spectrum 410, all fans have the same rotational speed. Alternatively, a fan power rating could be specified instead of a rotational speed. For the sake of simplicity, the generator noise is not considered in this example.

[0134] With the superimposed sound signal with sound spectrum 410, the frequency difference between all fans is zero, meaning all fans operate at the same speed. All twelve fans are therefore set to 100% of their rated speed. With the superimposed sound signal with sound spectrum 420, the speed differs from fan to fan by 0.5%. The frequency difference is thus constant. The frequency difference is also constant with sound spectra 450 and 460. The fan speeds vary by 1% and 2%, respectively, between the fans.

[0135] Sound spectra 430 and 440 show the superimposed sound of the twelve fans, where the frequency differences between different fans vary. The speed difference between the fans is therefore not constant, but varies from fan to fan.

[0136] The resulting sound spectrum 410 should be avoided, as the sound signals from all 12 fans overlap unfavorably, creating the sound with a large peak. The peak has a narrow width and a large amplitude. Both of these characteristics are undesirable.

[0137] A sound signal with a frequency spectrum of 460 should also be avoided. This signal exhibits several peaks in the spectrum, which are perceptible as individual tones and can be perceived as disturbing. A large frequency difference between the fans, which is also consistent across all fans, results in a sound spectrum like that of 460. With such large frequency differences, the fan speed also decreases significantly from fan to fan. This is undesirable because it drastically reduces the average cooling performance of all the fans combined.

[0138] This also highlights another advantage of the variable frequency spacing. The amplitudes of the 430, 440, and 450 frequency spectra differ only slightly. However, the frequency range of the 450 frequency spectrum is noticeably wider than that of the 430 and 440 spectra. Therefore, the fan speed of the slowest fan is higher for the resulting sound with the 430 and 440 spectra than for the resulting sound with the 450 spectrum. Thus, the variable frequency spacing increases the average cooling performance of the fans while maintaining a nearly constant maximum amplitude.

[0139] The goal is therefore to broaden the resulting spectrum across a frequency range to such an extent that a plateau with a low amplitude is established. At the same time, the frequency range of the plateau should remain as small as possible so that the average cooling performance of the fans is only minimally reduced. This is particularly relevant for the resulting sound signals with sound spectra 430 and 440, where the frequency spacing varies individually.

[0140] According to the invention, the following aspects and solutions were particularly identified.

[0141] The invention relates in particular to preventing unfavorable superposition of sound components from different sources of wind turbine components, or to actively masking tonal components by means of one or more sound sources. The sound of the generator and one or more fans was identified as being particularly relevant.

[0142] The invention also relates to an algorithm designed to prevent unfavorable acoustic interference from multiple operating-dependent (speed-dependent) sound sources of a wind turbine. A further function is the targeted masking by "starting up" or "controlling" a specific speed range and / or frequency range of a sound source in order to achieve the best possible "masking" of a tone (usually from the generator).

[0143] The idea is described using the example of a generator and a cooling fan: Due to their design, generators emit a tone that depends on their rotational speed. This is usually the 12th harmonic, as has been observed.

[0144] In a sound measurement according to DIN 61400-11, the tone analysis examines how strongly the tone "stands out" from the rest of the adjacent spectrum. The frequency range in which the analysis takes place depends on the frequency of the tone and is based on psychoacoustic principles.

[0145] At high sound levels relative to the surrounding spectrum, a sound surcharge (KTN > 0) can occur, which can lead to non-compliance with warranties and thus to compensation costs. In the nacelle of the wind turbine, there are now additional sound sources that superimpose on the sound from the generator.

[0146] A cooling unit with four large fans is particularly critical acoustically, as it is located directly at the rear of the nacelle and can radiate unhindered towards the wake of the wind turbine, where the sound is measured according to the standard.

[0147] Like the generator, the fans also have a dominant tone, which is referred to here as the characteristic fan sound frequency or blade pass frequency (BPF). Characteristic fan sound frequency, blade pass frequency, and BPF can therefore be used synonymously or treated similarly. The fan sound frequency is also dependent on the rotational speed.

[0148] The algorithm is designed to prevent the fan noise frequencies from being in the "avoidable range" at any time or at any speed and from overlapping with the generator tone.

[0149] Theoretically, there could also be several avoidable areas, depending on the application.

[0150] Furthermore, all fans should ideally be operated at different speeds. However, the speed difference between the fans should also be variable, so that fan noise frequencies can lie both "above" and "below" the generator tone in the spectrum. More often, however, the fan noise frequencies will be below the generator frequency due to design constraints.

[0151] The harmonics (multiples) of the fan sound frequency, or other possible installation-related dominant frequency ranges of the fan, may also need to be taken into account in the control system, depending on their characteristics, which was recognized according to the invention.

[0152] Furthermore, the "fan index" should change at regular intervals (e.g., every 15 minutes) to ensure more even cooling of the cooling fins or coolant. The fans are essentially swapped between each other. Otherwise, the fluctuating fan speeds would result in uneven airflow across the cooling surface, leading to inconsistent cooling. This approach could also be used for generator fans to achieve more uniform generator cooling, potentially improving efficiency.

[0153] Suitable input parameters for the algorithm include, in particular, parameters selected from the list comprising a number of fans, a number of blades or rotor blades of the fans, an order of harmonics of the generator, a number of slots of the generator, a number of pole pairs of the generator, a pitch width of the generator tone, a speed of the generator, a minimum frequency difference between the fans, and a marker for masking (ON / OFF).

[0154] If the masking marker is set to ON, the fan sounds, i.e., the characteristic fan frequencies, are driven into the close range of the generator sound frequency.

[0155] The target fan speeds are defined as output parameters. The fan speed is then set according to these target speeds.

[0156] The invention also serves the acoustic optimization of a wind turbine. The invention aims to prevent the occurrence of tonal characteristics or the exceeding of guaranteed sound power levels in certain third-octave / octave bands. Exceedances can lead to shutdowns and thus to yield losses. Furthermore, the masking is intended to improve the "sound" and reduce the "nuisance" of the wind turbine, thereby increasing public acceptance.

Claims

1. Method for modifying a sound emission of a wind power installation (100), wherein - the wind power installation comprises a nacelle (104) and a generator with a rotor (106) which is adjustable in terms of its rotational speed, and the rotor has at least one rotor blade, - the generator produces sound with at least one characteristic generator sound frequency which depends on the rotor rotational speed, - the wind power installation has at least one fan for cooling the nacelle and / or generator, - the at least one fan is adjustable in terms of a fan rotational speed, wherein - the at least one fan produces sound with a characteristic fan sound frequency which depends on the fan rotational speed, and - the fan rotational speed of the at least one fan is set in such a way on the basis of the rotor rotational speed that the fan sound frequency deviates from the at least one generator sound frequency, characterized in that - at least one critical fan rotational speed is determined on the basis of the rotor rotational speed as a rotational speed to be avoided by the respective fan, and - the fan rotational speed of each fan is specified in such a way that the at least one critical fan rotational speed is avoided, wherein - the at least one critical fan rotational speed is the same for fans of identical construction, and / or - the at least one critical fan rotational speed corresponds to a fan rotational speed at which the associated fan sound frequency corresponds to the generator sound frequency.

2. Method according to Claim 1, characterized in that a harmonic of a frequency variable of the generator is used as the generator sound frequency, in particular a harmonic of a pole passing frequency which specifies how often a rotor pole passes a reference position, in particular the 12th harmonic of the frequency variable, on which the sound depends, and - a fundamental frequency or harmonic of the sound produced by the fan is used as the fan sound frequency, wherein in particular - the fan sound frequency fL is a blade passing frequency and the fan sound frequency fL is determined on the basis of the fan rotational speed nL and a number of fan rotor blades AL, in particular according to the formula: f L Hz = n L rpm 60 ⋅ A L .

3. Method according to claim 1 or 2, characterized in that - the fan rotational speed of the at least one fan is specified in such a way that the associated fan sound frequency deviates from the generator sound frequency by no more than a specifiable masking deviation, in order to mask the generator sound frequency.

4. Method according to any of the preceding claims, characterized in that - the critical fan rotational speed nL,i is determined for each fan i on the basis of - the rotor rotational speed nR, - a number of pole pairs PG of the generator, - a number or the number of fan rotor blades AL,i of the fan i, and - an order k of the sound produced by the generator, with the order k as characteristic order of the generator, and / or as an order of a harmonic or the harmonic used as the generator sound frequency, wherein - the critical fan rotational speed is determined as n L , i = n R ⋅ k ⋅ P G A L , i .

5. Method according to any of the preceding claims, characterized in that - the wind power installation has a plurality of fans for cooling the nacelle and / or generator, wherein - the fans are each adjustable in terms of their fan rotational speed and each produce sound with a characteristic fan sound frequency which depends on their fan rotational speed, and - each of the fan rotational speeds is set, respectively dependent on the rotor rotational speed, in such a way that its fan sound frequency deviates from the generator sound frequency, and in particular - the fan rotational speeds are set in such a way that their fan sound frequencies also differ from one another.

6. Method according to any of the preceding claims, characterized in that - at least one frequency spacing is specified as the frequency difference respectively between two fan sound frequencies of two fans, and - the fan rotational speeds of the fans are set in such a way on the basis of the frequency spacing that - fan sound frequencies of at least two fans have the frequency spacing from one another.

7. Method according to any of the preceding claims, characterized in that - a frequency spacing or the frequency spacing is variably adjustable as the frequency difference respectively between two fan sound frequencies of two fans, and / or - the frequency spacing among the fans is different from one another, wherein in particular - the frequency spacing is chosen on the basis of at least one weather parameter, from the list comprising - an outside temperature, - a humidity, - an atmospheric pressure, - a rate of precipitation, - a droplet size, - a rate of snowfall and - a wind speed.

8. Method according to any of the preceding claims, characterized in that a frequency spacing or the frequency spacing is variably adjustable as the frequency difference respectively between two fan sound frequencies of two fans, and - the frequency spacing among the fans reduces with increasing distance from the generator sound frequency.

9. Method according to any of the preceding claims, characterized in that a frequency spacing or the frequency spacing is specified as the frequency difference respectively between two fan sound frequencies of two fans, depending on the rotor rotational speed, and - the frequency spacing is specified to be ever smaller, the lower the rotor rotational speed is.

10. Method according to any of the preceding claims, characterized in that - the generator sound frequency has a tone bandwidth, in particular an ERB bandwidth, as characteristic frequency bandwidth, with the tone bandwidth defining a characteristic frequency range around the generator sound frequency, and - a frequency range to be avoided, having an avoidance bandwidth, is determined on the basis of the tone bandwidth, with the avoidance bandwidth defining the frequency range to be avoided as the frequency range around the generator sound frequency and the avoidance bandwidth being smaller than the tone bandwidth, with the result that the frequency range to be avoided is located within the characteristic frequency range, and - the fan rotational speed of each fan is set so that the fan sound frequency is located - outside of the frequency range to be avoided and / or - within the characteristic frequency range.

11. Method according to any of the preceding claims, characterized in that - the fan rotational speed is respectively specified as a fan rotational speed characteristic, wherein - the fan rotational speed characteristic describes a function of the fan rotational speed depending on the rotor rotational speed, wherein in particular - the fan rotational speed characteristic is provided as a linear characteristic.

12. Method according to any of the preceding claims, characterized in that - a dedicated fan rotational speed characteristic is provided for each fan and - the fan rotational speed characteristics of a plurality of fans respectively deviate from one another by a specifiable rotational speed deviation criterion, in particular in that - the fan rotational speed characteristics of a plurality of fans are shifted from one another by a specifiable difference rotational speed and / or deviate from one another by a rotational speed deviation factor ranging between 0.8 and 1.2, and / or in that - fan sound frequency characteristics, which are associated with the fan rotational speed characteristics and each describe a fan sound frequency depending on the rotor rotational speed, of a plurality of fans respectively deviate from one another by a specifiable frequency deviation criterion, in particular in that - the fan sound frequency characteristics of a plurality of fans are shifted from one another by a specifiable difference frequency and / or deviate from one another by a frequency deviation factor, which may correspond to the rotational speed deviation factor, ranging between 0.8 and 1.2.

13. Method according to any of the preceding claims, characterized in that the wind power installation has at least two fans for cooling the nacelle and / or generator, wherein - the fans can be sorted in a fan sequence, - the fan rotational speeds or fan rotational speed characteristics of the fans are selected in accordance with the fan sequence and - the fan sequence is modified in such a way after a specifiable exchange time or on the basis of another exchange criterion that - the fan rotational speeds or fan rotational speed characteristics of the fans are selected anew in accordance with the modified fan sequence.

14. Method according to any of the preceding claims, characterized in that the wind power installation has at least one further source of noise and - the at least one further source of noise produces further sound at in each case a constant frequency, wherein - the fan rotational speed of the at least one fan is set in such a way that the fan sound frequency deviates from the constant frequency.

15. Wind power installation comprising a nacelle and a generator with a rotor which is adjustable in terms of its rotational speed, wherein the rotor has at least one rotor blade, - the generator produces sound with at least one characteristic generator sound frequency which depends on the rotor rotational speed, - the wind power installation has at least one fan for cooling the nacelle and / or generator, - the at least one fan is adjustable in terms of a fan rotational speed, wherein - the at least one fan produces sound with a characteristic fan sound frequency which depends on the fan rotational speed, and - the wind power installation has a control module, and - the control module sets a fan rotational speed of the at least one fan in such a way on the basis of the rotor rotational speed and for the purpose of modifying a sound emission that the fan sound frequency deviates from the at least one generator sound frequency, and - the fan rotational speed of the at least one fan is set in accordance with a method according to any of Claims 1-14, wherein - at least one critical fan rotational speed is determined on the basis of the rotor rotational speed as a rotational speed to be avoided by the respective fan, and - the fan rotational speed of each fan is specified in such a way that the at least one critical fan rotational speed is avoided, wherein - the at least one critical fan rotational speed is the same for fans of identical construction, and / or - the at least one critical fan rotational speed corresponds to a fan rotational speed at which the associated fan sound frequency corresponds to the generator sound frequency.