METHOD FOR MODIFYING A SOUND EMISSION OF A WIND POWER INSTALLATION

Abstract

A method for modifying a sound emission of a wind power installation, wherein the wind power installation comprises a nacelle and a generator with a rotor 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. Tonal sounds in wind power installations, or the perception thereof, are intended to be reduced in particular.

Claims

1. A method for modifying a sound emission of a wind power installation, wherein: the wind power installation comprises a nacelle and a generator with a rotor 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 at least one of the nacelle or generator, a rotational speed of the at least one fan is adjustable, and the at least one fan produces sounds having characteristic fan sound frequencies depending on the fan rotational speed, and the method comprising: setting the fan rotational speed of the at least one fan depending on the rotor rotational speed such that the fan sound frequency deviates from the at least one generator sound frequency.

2. The method according to claim 1, wherein: at least one critical fan rotational speed is determined based on the rotor rotational speed as a rotational speed to be avoided by the at least one fan, the fan rotational speed of each fan is specified in such a way that the at least one critical fan rotational speed is avoided, 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.

3. The method according to claim 1, wherein: a harmonic of a frequency variable of the generator on which the sound depends is used as the generator sound frequency, a fundamental frequency or harmonic of the sound produced by the at least one fan is used as the fan sound frequency, and the fan sound frequency f.sub.L is a blade passing frequency and the fan sound frequency f.sub.L is determined based on the fan rotational speed n.sub.L and a number of fan rotor blades A.sub.L, and according to the formula: $f_L\left[\mathrm{Hz}\right]=n_L\frac{\left[\mathrm{rpm}\right]}{60}.Math.A_L.$

4. The method according to claim 1, wherein the fan rotational speed of the at least one fan is specified in such a way that an associated fan sound frequency deviates from the generator sound frequency by no more than a specifiable masking deviation to mask the generator sound frequency.

5. The method according to claim 1, wherein the critical fan rotational speed n.sub.L,i is determined for each fan i based on: the rotor rotational speed n.sub.R, a number of pole pairs P.sub.G of the generator, a number or the number of fan rotor blades A.sub.L,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: $n_{L,i}=\frac{n_R.Math.k.Math.P_G}{A_{L,i}}.$

6. The method according to claim 1, wherein: the wind power installation has a plurality of fans for cooling the nacelle and generator, wherein: the plurality of fans have adjustable rotational speeds and produce sounds with a characteristic fan sound frequency depending on their respective fan rotational speed, and each of the fan rotational speeds is set, respectively, dependent on the rotor rotational speed, in such a way that the respective fan sound frequency deviates from the generator sound frequency, and the fan rotational speeds are set in such a way that their fan sound frequencies also differ from one another.

7. The method according to claim 1, wherein: the at least one fan is a plurality of fans, a frequency spacing is specified as a frequency difference respectively between two fan sound frequencies of two fans of the plurality of fans, and the fan rotational speeds of the two fans are set such that fan sound frequencies of the two fans have frequency spacing from one another.

8. The method according to claim 1, wherein: the at least one fan is a plurality of fans, a frequency spacing is variably adjustable as the frequency difference respectively between two fan sound frequencies of two fans of the plurality of fans, and/or the frequency spacing among the two fans is different from one another, the frequency spacing is chosen based on at least one weather parameter from a 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.

9. The method according to claim 1, wherein: the at least one fan is a plurality of fans, a frequency spacing is variably adjustable as the frequency difference respectively between two fan sound frequencies of two fans of the plurality of fans, and the frequency spacing between the two fans reduces with increasing distance from the generator sound frequency.

10. The method according to claim 1, wherein: the at least one fan is a plurality of fans, a frequency spacing or the frequency spacing is specified as the frequency difference respectively between two fan sound frequencies of two fans of the plurality of fans depending on the rotor rotational speed, and the frequency spacing is specified to be reduced as the rotor rotation speed is reduced.

11. The method according to claim 1, wherein: the generator sound frequency has a tone bandwidth, 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 based on the tone bandwidth, with the avoidance bandwidth defining a 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 a result that the frequency range to be avoided is located within the characteristic frequency range, and the fan rotational speed of the at least one 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.

12. The method according to claim 1, wherein: the fan rotational speed is specified as a fan rotational speed characteristic, the fan rotational speed characteristic describes a function of the fan rotational speed depending on the rotor rotational speed, and the fan rotational speed characteristic is provided as a linear characteristic.

13. The method according to claim 1, wherein: the at least one fan is a plurality of fans, a dedicated fan rotational speed characteristic is provided for each fan, the fan rotational speed characteristics of the plurality of fans, respectively, deviate from one another by a specifiable rotational speed deviation criterion, 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 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, 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 corresponds to the rotational speed deviation factor, ranging between 0.8 and 1.2.

14. The method according to claim 1, wherein the wind power installation has at least two fans for cooling the nacelle and/or generator, wherein: the at least two fans are arranged in a fan sequence, the fan rotational speeds or fan rotational speed characteristics of the at least two 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 based on 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.

15. The method according to claim 1, wherein the wind power installation generates at least one further noise, and wherein the at least one further noise is a sound with constant frequency, and wherein the fan rotational speed of the at least one fan is set such that the fan sound frequency deviates from the constant frequency.

16. The method according to claim 1, wherein a harmonic of a pole passing frequency of the generator on which the sound depends is used as the generator sound frequency, wherein the harmonic of the pole passing frequency specifies how often a rotor pole passes a reference position.

17. A wind power installation comprising: a nacelle, a generator with a rotor, wherein a rotational speed of the rotor is adjustable, wherein the rotor has at least one rotor blade, and a control module, wherein the generator produces sound with at least one characteristic generator sound frequency depending on a rotor rotational speed, wherein the wind power installation has at least one fan for cooling the nacelle and/or generator, wherein a fan rotational speed of the at least one fan is adjustable, wherein the at least one fan produces sound with a characteristic fan sound frequency which depends on the fan rotational speed, and wherein the control module is configured to set a fan rotational speed of the at least one fan in such a way based on 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.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0114] The invention is explained in more detail hereinbelow by way of example with reference to the accompanying figures.

[0115] FIG. 1 shows a wind power installation in a perspective view.

[0116] FIG. 2 shows, by way of example, a spectrum of a wind power installation at different rotational speeds.

[0117] FIG. 3 shows a rotational speed-dependent generator sound frequency.

[0118] FIG. 4 shows a diagram of a plurality of superposed sound signals.

DETAILED DESCRIPTION

[0119] FIG. 1 shows a schematic illustration of a wind power installation according to an embodiment of the invention. The wind power installation 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 having three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During the operation of the wind power installation, the aerodynamic rotor 106 is set in rotational motion by the wind and thereby also rotates an electrodynamic rotor or armature of a generator, which is coupled directly or indirectly to the aerodynamic rotor 106. The electric generator is arranged in the nacelle 104 and produces electrical energy. The blade angles of the rotor blades 108, which may also be referred to synonymously as the pitch angle or setting angle, can be modified by pitch motors at the rotor blade roots 109 of the respective rotor blades 108.

[0120] The wind power installation also has four heat-exchanger fans for cooling the generator.

[0121] FIG. 2 shows a coordinate system in which respective sound pressure amplitudes of sound signals are depicted as a function of frequency. The coordinate system depicts seven actually recorded spectra 211, 212, 213, 214, 215, 216, 217 of the wind power installation at different rotor rotational speeds by way of example.

[0122] A peak which clearly rises from the surrounding base spectrum is identifiable in each of the spectra 211, 212, 213, 214, 215, 216, 217. The peak is a structure-related generator tone 220, which is located at the generator sound frequency and circled for clarity.

[0123] The more the generator tone 220 rises above the base spectrum, the more unpleasantly the sound is perceived. Consequently, the amplitudes of the peaks of the generator sound frequency should be prevented from being increased even further. To this end, the rotational speed of the fan is set so that a dominant tone in the sound of the fan has a fan sound frequency which differs from the generator sound frequency. Thus, a frequency range is avoided, the latter being determined on the basis of a frequency bandwidth of the peak, which is to say the generator tone 220 at the generator sound frequency.

[0124] The fan sound is not depicted in the coordinate system.

[0125] FIG. 3 shows a coordinate system where the frequency in Hz is plotted on the ordinate and the rotor rotational speed n.sub.R in rpm is plotted on the abscissa. By way of example, a detail from 3 rpm to 12 rpm, and from 0 Hz to 160 Hz, is illustrated.

[0126] A characteristic generator sound frequency 320 is depicted. The generator sound frequency also increases with increasing rotor rotational speed. A frequency range 330 to be avoided around the generator sound frequency 320 is likewise depicted.

[0127] The fans of the wind power installation also produce a sound, which is superposed on the generator sound and which has a characteristic fan sound frequency in each case.

[0128] In this case, the fans are set in such a way in terms of their fan rotational speed that they avoid a critical fan rotational speed, specifically precisely the rotational speed that would lead to a fan sound with a fan sound frequency equal to the generator sound frequency. In the process, a rotational speed range to be avoided is also determined here, so that the fan sound frequency avoids the frequency range 330 to be avoided. Four fan sound frequencies 341, 342, 343, 344 are depicted. Consequently, each fan rotational speed is set so that the fan sound frequencies 341, 342, 343, 344 are not located in the frequency range 330 to be avoided.

[0129] It was also recognized that there can also be a disadvantageous superposition of the fan sound frequencies. The fan rotational speeds are therefore set in such a way that their fan sound frequencies 341, 342, 343, 344 differ from one another. In this case, a frequency spacing which must be observed by two fans is specified for the fans. This avoids a disadvantageous superposition.

[0130] A further aspect intended to be clarified by FIG. 3 lies in the masking of the generator tone. In this case, the peak of the generator tone in the spectrum should be broadened by virtue of the rotational speeds of the fans being set so that the fan sound frequencies 341, 342, 343, 344 are located in the vicinity of the generator sound frequency 320.

[0131] To this end, provision is also made for the rotational speeds of the fans to be set so that the fan sound frequencies are spaced apart by the frequency spacing. Consequently, the frequency spacing is chosen so that the generator tone is masked.

[0132] In this case, the frequency spacing is constant in FIG. 3. However, provision is also made, in particular, for the frequency spacing between the fans to be set differently. As a result, fan sound frequencies and generator sound frequency can be optimally matched to one another.

[0133] Consequently, the four fan sound frequencies 341, 342, 343, 344 are provided in the figure as fan sound frequency characteristics which are shifted relative to one another. Provision is also made for a respective fan rotational speed characteristic to be specified for the fan sound frequency characteristics, the said fan rotational speed characteristics being shifted with respect to one another and each achieving a maximum rotational speed. In this case, the maximum rotational speeds are also different and lead accordingly to a maximum frequency of the fan sound frequency characteristics.

[0134] FIG. 3 also shows a tone bandwidth of the generator sound as an ERB bandwidth, specifically a lower ERB limit 351 and an upper ERB limit 352.

[0135] To mask the generator tone at the generator sound frequency 320, provision is made for the rotational speeds of the fans to be specified so that the fan sound frequencies are located within the frequency range defined by the tone bandwidth, which is to say above the lower ERB limit 351 and below the upper ERB limit 352. This is only possible to a certain extent here since the fans have a maximum rotational speed. Thus, the fan is already operated at full power in that case. In the example, this is reached at a rotor rotational speed of approximately 8.2 rpm for the fan with the fan sound frequency 341. However, the frequency spacing between the fan sound frequencies should continue to be maintained.

[0136] FIG. 4 shows a further coordinate system, in which an amplitude, specifically a sound pressure amplitude, of a plurality of sound spectra in dB is plotted against a frequency f in Hz. Shown is a simulation of a superposition of sound signals at twelve fan sound frequencies from twelve fans of identical construction, to form a resultant sound signal with the sound spectrum 410, 420, 430, 440, 450, 460. A different frequency spacing between the fans is chosen for each of the resultant sound spectra 410, 420, 430, 440, 450, 460, in order to thereby examine different superpositions. To this end, a corresponding (different) rotational speed is specified for each of the twelve fans. However, all fans have the same rotational speed in the case of the superposed sound spectrum 410. Rather than specifying a rotational speed, a respective power of the fan could be specified as an alternative. To simplify the explanation, the generator sound is not taken into account in this example.

[0137] The frequency spacing between all the fans is zero in the case of the superposed sound signal with the sound spectrum 410, which is to say the fans are all operated at the same rotational speed. Thus, all twelve fans are set to 100% of their nominal fan rotational speed. In the superposed sound signal with the sound spectrum 420, the rotational speed respectively differs by 0.5% from fan to fan. The frequency spacing is consequently constant. The frequency spacing is also constant in the case of the sound spectra 450 and 460. In this case, the fan rotational speeds vary by 1% and 2%, respectively, between each of the fans.

[0138] The sound spectra 430, 440 show the superposed sound of the twelve fans, in the case of which the frequency spacings between the various fans differ. Consequently, the rotational speed difference between the fans is not constant but varies from fan to fan.

[0139] The resultant sound spectrum 410 should be avoided since the sound signals of all 12 fans are disadvantageously superposed to form the sound with the sound spectrum 410 with the large peak. The peak has a narrow bandwidth and a large amplitude. Both of these are undesirable.

[0140] A sound signal with the sound spectrum 420 should also be avoided. A plurality of peaks can be identified in the spectrum in this case, the said peaks being perceivable as individual tones and possibly being perceived as annoying. A large frequency spacing between the fans, which is moreover constant between the fans, leads to a sound spectrum like the sound spectrum 460. Consequently, the fan rotational speed also decreases significantly from fan to fan in the case of such large frequency spacings. This is undesirable since this significantly reduces the mean cooling power of the totality of all fans.

[0141] A further advantage of the variable frequency spacing can also be found here. The amplitudes of sound spectra 430, 440 and 450 only differ slightly from one another. However, the frequency range of the sound spectrum 450 is significantly broader than in the case of the sound spectra 430, 440. The fan rotational speed of the slowest fan is consequently higher in the resultant sound with the spectra 430, 440 than in the resultant sound with the spectrum 450. Consequently, as a result of the variable frequency spacing, the mean cooling power of the fans is increased in the case of an otherwise approximately unchanged maximum amplitude.

[0142] Thus, a goal is to broaden the resultant spectrum over a frequency range to such an extent that a plateau with a low amplitude sets in. At the same time, the frequency range of the plateau should remain as small as possible in the process so that the mean cooling power of the fans is only reduced a little. This is especially the case for the resultant sound signals with sound spectra 430 and 440, in which the frequency spacing varies on an individual basis.

[0143] According to the invention, the following aspects and solutions in particular were recognized.

[0144] The invention relates in particular to the prevention of disadvantageous superposition of sound components from different sources of components of the wind power installation, or to an active masking of tonal components by means of one or more sound sources. The sound of the generator and one or more fans was recognized as being particularly relevant.

[0145] The invention also relates to an algorithm which is intended to prevent a disadvantageous acoustic superposition of a plurality of operationally dependent (rotational speed-dependent) sources of sound in a wind power installation. A further function is intended to be the targeted masking by driving or controlling a specific rotational speed range and/or frequency range of a source of sound, in order to obtain the best possible masking of a tone (usually from the generator).

[0146] The concept is described on the basis of an example of generator and heat-exchanger fan.

[0147] Generators emit a tone, which depends on the rotational speed, for structural reasons. It was recognized that this usually is the 12th harmonic.

[0148] In the case of a sound measurement pursuant to DIN 61400-11, there is an investigation within the tone analysis as to the extent to which the tone emerges from the remaining adjacent spectrum. The frequency range in which the analysis takes place depends on the frequency of the tone and is based on psychoacoustic discoveries.

[0149] In the case of high tone levels relative to the surrounding spectrum there may be a tone allowance (KTN>0), which may lead to a non-observance of the guarantees and hence to compensation costs. The nacelle of the wind power installation now contains further additional sources of sound, which are superposed on the sound from the generator.

[0150] A heat exchanger unit with four large fans is particularly critical from an acoustic point of view since it is situated directly on the back side of the nacelle and can emit in unimpeded fashion in the direction of the wake of the wind power installation, in which the sound is measured according to the standard.

[0151] Like the generator, the fans also have a dominant tone, which is referred to here as the characteristic fan sound frequency or blade passing frequency (BPF). Therefore, characteristic fan sound frequency, blade passing frequency and BPF can be used synonymously herein, or treated similarly. The fan sound frequency is also rotational speed dependent.

[0152] The algorithm should prevent the fan sound frequencies of the fans from being in the avoidable region at all times or at all rotational speeds, and from being superposed on the generator tone.

[0153] Depending on the application, it may also theoretically be possible for there to be a plurality of avoidable regions.

[0154] Further, all fans should be operated at differing fan rotational speeds where possible. However, the rotational speed difference between the fans should also be variable such that fan sound frequencies of fans may also be located above and below the generator tone in the spectrum. However, the fan sound frequencies will more frequently be located below the generator sound frequency for structural reasons.

[0155] The harmonics (multiples) of the fan sound frequency, and other possible installation-related dominant frequency ranges of the fan, must also be taken into account as appropriate according to their characteristics in the closed-loop control; this was recognized according to the invention.

[0156] Furthermore, the fan index should change at regular time intervals (e.g., every 15 minutes) so that there is more uniform cooling of cooling ribs or a coolant. As it were, the fans are thus exchanged among one another. Otherwise, the rotational speed shift would lead to differently strong flows through the cooler area, which would not be cooled uniformly as a result. This procedure could likewise be used for the generator fans in order to obtain more uniform cooling of the generator. This might have a positive effect on the efficiency.

[0157] Parameters selected from the following list, in particular, come into question as input parameters for the algorithm, the list comprising a number of fans, a number of blades or rotor blades of the fans, an order of the harmonics of the generator, a number of slots of the generator, a number of pole pairs of the generator, a tone bandwidth of the generator tone, a rotational speed of the generator, a minimal frequency spacing between the fans among themselves, a marker for masking (ON/OFF).

[0158] To the extent the marker for masking is ON, the fan tones, which is to say the characteristic fan frequencies, are driven into the vicinity of the generator sound frequency.

[0159] The target rotational speeds of the fans are determined as output parameters. The fan rotational speed of the fans is set in accordance with the target rotational speed.

[0160] The invention also serves for the acoustic optimization of a wind power installation. The invention is intended to prevent tonal zones from occurring or guaranteed sound power levels from being exceeded in certain one-third octave/octave bands. Such overshoots could lead to deactivations and hence loss of income. Furthermore, the masking should improve the sonority or reduce the annoyance of the wind power installation, in order to increase acceptance.

[0161] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.