Wind turbine and method for noise reduction for a wind turbine

Abstract

Wind turbine comprising a tower (2) bearing a nacelle (5) and a rotor (3) with a plurality of rotor blades (4) and an active noise reduction device (7), wherein the active noise reduction device (7) comprises at least one actuator (8), at least one unsteady pressure sensor (9) adapted to produce an output signal corresponding to a turbulent flow condition during operation of the rotor blade (4), at least one noise sensor (10) adapted to produce an output signal corresponding to a noise generated by the rotor blade (4) at the location of the noise sensor (10), and a control unit (11), wherein the unsteady pressure sensor (9) and the actuator (8) are arranged on at least one of the rotor blades (4) and the noise sensor (10) is arranged at the nacelle (5) and/or at the tower (2), wherein the control unit (11) is adapted to control the actuator (8) in dependence of the output signals of the unsteady pressure sensor (9) and the noise sensor (10) to emit an anti-noise signal at least partly reducing the noise generated by the rotor blade (4).

Claims

1. A turbine comprising: a tower bearing a nacelle and a rotor with a plurality of rotor blades; and an active noise reduction device, wherein the active noise reduction device comprises: at least one actuator, at least one unsteady pressure sensor adapted to produce an output signal corresponding to a turbulent flow condition during operation of a rotor blade, at least one noise sensor adapted to produce an output signal corresponding to a noise generated by the rotor blade at a location of the noise sensor, and a control unit, wherein the unsteady pressure sensor and the actuator are arranged on at least one rotor blade of the plurality of rotor blades and the noise sensor is arranged at the nacelle and/or at the tower, wherein the control unit is adapted to control the actuator in dependence of the output signals of the unsteady pressure sensor and the noise sensor to emit an anti-noise signal at least partly reducing the noise generated by the rotor blade.

2. The wind turbine according to claim 1, wherein the unsteady pressure sensor and the actuator are arranged in at least one arrangement portion of a shell of the rotor blade, further wherein the noise sensor is arranged on an outside of the nacelle and/or on an outside of the tower in an opposing portion that opposes the arrangement portion of the rotor blade at least partly when the rotor blade is aligned in a downward direction parallel to the tower.

3. The wind turbine according to claim 1, wherein the active noise reduction device comprises a plurality of noise sensors, wherein the noise sensors are arranged annularly around an outer circumference of the tower.

4. The wind turbine according to claim 1, wherein the unsteady pressure sensor and/or the actuator are arranged in a tip region of the rotor blade and/or that the unsteady pressure sensor is arranged on a trailing edge of the rotor blade.

5. The wind turbine according to claim 1, wherein the actuator comprises a loudspeaker and/or that the unsteady pressure sensor comprise a pressure transducer, and/or that the noise sensor comprises a pressure transducer, in particular a microphone.

6. The wind turbine according to claim 1, wherein the control unit is adapted to apply at least one filter function to the output signal of the unsteady pressure sensor for determining an input signal for the actuator to emit the anti-noise signal, further wherein the control unit is adapted to adjust the filter function in dependence of the output signal of the noise sensor in an adaptive feedforward control.

7. The wind turbine according to claim 6, wherein the control unit comprises or is connected to a rotor orientation sensor determining the relative position between the plurality of rotor blades and the tower during an operation of the wind turbine, further wherein the control unit is adapted to adjust the filter function in a period of time in which the at least one rotor blade is at least temporarily in a downward direction parallel to the tower.

8. The wind turbine according to claim 1, wherein on each of the plurality of rotor blades at least one actuator and at least one unsteady pressure sensor are arranged, further wherein the control unit is adapted to use a separate filter function for each of the plurality of rotor blades and to adjust the separate filter functions each in a period of time in which the corresponding rotor blade is at least temporarily in a downward direction or a nearly downward direction parallel to the tower.

9. The wind turbine according to claim 1, wherein the control unit is adapted to use an adaptive filter of a filtered-x least mean squares (FxLMS) algorithm as the filter function.

10. The wind turbine according to claim 1, wherein the at least one rotor blade comprises a trailing edge with a passive noise reduction device.

11. A method for noise reduction for a wind turbine comprising a tower bearing a nacelle and a rotor with a plurality of rotor blades and an active noise reduction device, wherein the active noise reduction device comprises at least one actuator, at least one unsteady pressure sensor adapted to produce an output signal corresponding to a turbulent flow condition during operation of a rotor blade, at least one noise sensor adapted to produce an output signal corresponding to a noise generated by the rotor blade at a location of the noise sensor, and a control unit, wherein the unsteady pressure sensor and the actuator are arranged on at least one rotor blade of the plurality of rotor blades and the noise sensor is arranged at the nacelle and/or at the tower, wherein the control unit controls the actuator in dependence of the output signals of the unsteady pressure sensor and the noise sensor to emit an anti-noise signal at least partly reducing the noise generated by the rotor blade.

12. The method according to claim 11, wherein the control unit applies at least one filter function to the output signal of the at least one unsteady pressure sensor for determining an input signal for the actuator to emit the anti-noise signal, further wherein the control unit adjusts the filter function in dependence of the output signal of the noise sensor in an adaptive feedforward control.

13. The method according to claim 12, wherein the control unit comprises or is connected to a rotor orientation sensor determining the relative position between the plurality of rotor blades and the tower during an operation of the wind turbine, further wherein the control unit adjusts the filter function in a period of time in which the at least one rotor blade is at least temporarily in a downward direction or a nearly downward direction parallel to the tower.

14. The method according to claim 12, wherein on each of the plurality of rotor blades at least one actuator and at least one unsteady pressure sensor are arranged, further wherein the control unit uses a separate filter function for each of the plurality of rotor blades and adjusts the separate filter functions each in a period of time in which the corresponding rotor blade is at least temporarily in a downward direction or a nearly downward direction parallel to the tower.

15. The method according to claim 12, wherein the control unit uses an adaptive filter of a filtered-x least mean squares (FxLMS) algorithm as the filter function.

16. The wind turbine according to claim 1, wherein the at least one noise sensor measures the noise by the rotor blade closest to the tower.

17. The method according to claim 11, wherein the at least one noise sensor measures the noise by the rotor blade closest to the tower.

Description

BRIEF DESCRIPTION

(1) Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. The drawings, however, are only principle sketches designed solely for the purpose of illustration and do not limit the invention. The drawings show:

(2) FIG. 1 an embodiment of a wind turbine according to the invention,

(3) FIG. 2 a detail of a rotor blade of a wind turbine according to the invention,

(4) FIG. 3 a control unit of a wind turbine according to the invention adapted to be used in an embodiment of a method according to the invention, and

(5) FIG. 4 a block diagram of a control system used in a wind turbine according to the invention and in an embodiment of a method for noise reduction of a wind turbine according to the invention.

DETAILED DESCRIPTION

(6) In FIG. 1, a wind turbine 1 is shown. The wind turbine 1 comprises a tower 2, which bears a rotor 3 with a plurality of rotor blades 4. The rotor 3 is mounted to a nacelle 5 of the tower 2. The rotor blades 4 of the rotor 3 are connected to a hub 6 of the rotor 3, wherein the rotor 3 and hence the rotor blades 4 rotate during operation of the wind turbine 1.

(7) The wind turbine 1 comprises an active noise reduction device 7, wherein the active noise reduction device 7 comprises at least one actuator 8, a plurality of unsteady pressure sensors 9, a plurality of noise sensors 10, and a control unit 11. The actuator 8 as well as the unsteady pressure sensors 9 are arranged on and/or affixed to at least one of the rotor blades 4 of the wind turbine 1. In particular, at least one actuator 8 and at least one unsteady pressure sensor 9 are arranged on each of the rotor blades 4.

(8) The noise sensors 10 are arranged at the tower 2, in particular at a tower segment of the tower 2 supporting the nacelle 5 of the tower 2. The noise sensors 10 are arranged annularly around the tower 2. Additionally or alternatively, the noise sensors 10, or some of the noise sensors 10, respectively, may be arranged at the nacelle 5, in particular at a backside of the nacelle 5. The control unit 11 is connected to the actuators 8, the unsteady pressure sensors 9, and to the noise sensors 10 via at least one wireless connection and/or via at least one cable connection (not shown).

(9) The actuator 8 and the plurality of unsteady pressure sensors 9 are arranged in an arrangement portion 12 of a shell 13 of the rotor blade 4, wherein the unsteady pressure sensors 9 are arranged close to a trailing edge 14 of the rotor blade 4. The arrangement portion 12, in which the actuator 8 and the unsteady pressure sensors 9 are arranged, is located in the tip region of the rotor blade 4, wherein the tip region and hence the arrangement portion 12 covers in particular 10% to 30%, preferably 20%, of the length of the rotor blade 4 from the tip.

(10) The noise sensors 10 at the tower 2 are arranged in an opposing portion 15, wherein the opposing portion 15 is located opposed to the arrangement portion 12 at the rotor blade 4 in a situation, in which the rotor blade 4 is arranged parallel to the tower 2 of the wind turbine 1 as depicted. In other words, both the arrangement portion 14 and the opposing portion 15 have the same distance to a ground 16, on which the wind turbine 1 is erected, when the rotor blade is aligned parallel to the tower 2 in a downward direction towards the ground 16.

(11) The wind turbine 1 further comprises at least one orientation sensor 17 for determination of the relative position between the rotor blades 4 and the tower 2 during an operation of the wind turbine 1. The at least one orientation sensor 17 is connected to the control unit 11. In an alternative, also the control unit 11 may be arranged for instance in a rotor blade 4 of the wind turbine 1, wherein the control unit 11 may comprise a rotor orientation sensor 17. The rotor orientation sensor 17 arranged in the rotor blade 4 of the wind turbine 1 may be in particular a gravity sensor 18. In addition or as an alternative, a rotary encoder 19 provided as a part of a rotor 20 of a generator 21 of the wind turbine 1 arranged inside the nacelle 5 may be used as orientation sensor 17.

(12) In FIG. 2, the arrangement of the unsteady pressure sensors 9 on the rotor blade 4 is shown in more detail depicting a segment of the rotor blade 4 within the tip region of the rotor blade 4, or the arrangement portion 12, respectively. The unsteady pressure sensors 9 are arranged close to the trailing edge 14 of the rotor blade 4. The trailing edge 14 comprises a passive noise reduction device 22, which is provided as a serrated trailing edge profile 23 comprising a plurality of teeth arranged along the trailing edge 14 of the rotor blade 4. Also the actuators 8 are arranged on the shell 13, wherein the actuators 8 are provided as loudspeakers for emittance of an acoustic anti-noise signal. Each of the actuators 8 may comprise an amplifier for amplifying an anti-noise signal generated by the control unit 11.

(13) During operation of the wind turbine 1, noise is generated in particular at the trailing edge 14 of the rotor blades 4 by a turbulent flow condition caused by the air or the wind, respectively, streaming along the profile of the rotor blade 4 as indicated by the arrow 24. In order to reduce the noise emitted by the rotor blade 4 in a far-field or in a vicinity of the wind turbine 1, respectively, the actuators 8 are used to create an anti-noise signal at least partly reducing the noise created by the rotor blade 4 during operation of the wind turbine 1.

(14) As it is depicted in FIG. 3, the control unit 11 receives the output signals of the unsteady pressure sensors 9 arranged at the rotor blade 4. In addition, the control unit 11 receives the output signals of the noise sensors 10 located at the tower 2 and/or at the nacelle 5 of the wind turbine 1. The control unit 11 is adapted to control the actuators 8 in dependence of the output signals of the unsteady pressure sensors 9 and the noise sensors 10 to emit an anti-noise signal at least partly reducing the noise generated by the rotor blade 4. Therefore, the control unit 11 is adapted to use at least one transfer function describing a relation between the output signal of the unsteady pressure sensors 9 and a far-field noise for determination of the anti-noise signal, which is emitted by the actuators 8. Furthermore, the control unit 11 is adapted to apply a filter function to the output signals of the unsteady pressure sensors 9 to obtain an input signal for the actuators 8. The actuators 8 emit the anti-noise signal based on the input signal from the control unit 11.

(15) The control unit 11 is adapted to adjust the filter function in dependence of the output signals of the noise sensor 10 so that in particular a correction of the filter function may occur in case that the noise generated by the rotor 4 is measured at the locations of the noise sensors 10 at the tower 2 of the wind turbine 1.

(16) In order to account for the rotating parts of the active noise reduction device 7, in particular the actuators 8 and the unsteady pressure sensors 9, the control unit 11 is adapted to adjust the filter function in a period of time in which the at least one rotor blade 4 is at least temporarily in a downward or nearly downward direction parallel to the tower 2. Therefore, the control unit 11 is connected to the orientation sensor 17. The control unit 11 may use the filter function in an adaptive feedforward control. The control unit 11 uses in particular a separate filter function for each of the rotor blades 4, so that the noise generated by each of the rotor blades 4 may be reduced individually. The control unit 11 adapts the filter function for each of the rotor blades 4 at or around the point in time, in which the corresponding rotor blade is aligned parallel to the tower 2.

(17) In FIG. 4, a block diagram 25 of a feedforward control algorithm used in the control unit 11 is shown. In the block diagram 25, the vector x represents the surface pressures measured by the plurality of unsteady pressure sensors 9. Block 26 describes adaptive control filters as vector w used as a filter function in order to determine a vector of control signals y sent to the actuators 8.

(18) Block 27 describes the physical relationship G between the actuators 8 and the noise sensors 10 located at the tower 2 of the wind turbine 1 in form of an actuator transfer function. The actuator transfer function describes for instance the relation between the input signal of the at least one actuator 8 and a far-field noise generated in a region of interest in the vicinity of the wind turbine 1, in which a noise emitted by the wind turbine shall be reduced.

(19) The filter function relates the output signals x from the at least one unsteady pressure sensor to the signals sent to the at least one actuator. The filter function is implemented for example as a weighted linear combination of stored signal samples from the at least one unsteady pressure sensors. This is expressed mathematically as follows:
y.sub.m(n)=x(n)w.sub.m(n).
Here, y.sub.m(n) is a vector of signal sent to the actuators 8 expressed in discrete time n, m is an index between 1 and M, where M is the number of actuators 8, x is a horizontal vector containing previously recorded samples of the signals from the unsteady pressure sensors 9, and w is the filter function expressed as a vertical vector of equal length to x containing weighting scalars.

(20) The filter function w of block 27 may be calculated by using the measured relationship between the unsteady pressure described by the output signals of the unsteady pressure sensors 9 and the far-field noise measured by the far-filed noise sensors 10. The filter function is dependent on the relationship between the unsteady pressure signals of the unsteady noise sensors 9 and the far-field sound, though it is not necessary to calculate this relationship in the form of a transfer function at any point due to the usage of the adaptive filter function.

(21) In the summation node 28, the anti-noise signal generated by the actuators 8 merges with the noise n.sub.a generated at the rotor blade 4. The remaining error noise signal e measured at the noise sensors 10 is the output signal of the noise sensors 10 and describes the remaining noise generated from the rotor blade 4 and is fed into summation node 29. There, the error noise signal e is added to or subtracted from an expected noise level determined using a model of the noise system Ĝ in block 30 and the measured surface pressures x. The output of node 29 is used to adapt the adaptive filters W in block 26 in order to reduce the error noise signal e measured at the noise sensors 10.

(22) The model of the system Ĝ in block 30 describes for instance propagation paths between the actuators 8 as secondary sources and the noise sensors 10. The adaption of the filter function or the adaptive filter w, respectively, occurs in dependence of an expected noise level at the position of the noise sensors 10 in the current state of operation and the actual error noise signal e measured at the position of the noise sensors 10. An adaption of the adaptive filters w in block 26 occurs in particular when the measured error noise signal e deviates from the expected noise level determined using the model Ĝ in block 30. The depicted block diagram 25 is an example of a filtered-x least mean squares (FxLMS) algorithm.

(23) Both the unsteady pressure sensors 9 and the noise sensors 10 may be provided as unsteady pressure transducers, in particular as microphones. The adaption of the filters w in block 26 occurs, as previously described, in a period of time, in which a rotor blade 4 is arranged parallel to the tower 2 and hence in a situation in which the unsteady pressure sensors 9 are located close to the noise sensors 10. The adaption of the filters w in block 26 allows to take into account effects like the current flow condition of the fluid flowing along the rotor blade 4 as well as degradation effects occurring slowly during operation of the wind turbine 1, for instance degradation of the trailing edge 14 of the rotor blades 4 and/or degradation of the unsteady pressure sensors 9. The adaptive filter w in block 26 may alternatively be adapted in order to minimize the noise at the location of the noise sensors 10, for example in a mean squared pressure sense. Minimizing the noise level itself can be accomplished by for example a gradient-based minimization algorithm to adapt the filter function with no need for a model Ĝ of the expected noise level.

(24) Although the present invention has been described in detail with reference to the preferred embodiment, the present invention is not limited by the disclosed examples from which the skilled person is able to derive other variations without departing from the scope of the invention.