Damping vibrations in a wind turbine

Abstract

A method for damping vibration in a wind turbine including aerodynamic devices for influencing the airflow flowing from the leading edge of a rotor blade of the wind turbine to the trailing edge of the rotor blade, each aerodynamic device being movable by an actuator between a first protruded configuration and a second retracted configuration is provided. The method includes measuring vibrations in the wind turbine, if the measured vibrations are greater than a threshold within a predefined frequency band, moving a portion of the aerodynamic devices to the second retracted configuration and continuing to measure vibrations, if the measured vibrations are still greater than a threshold within a frequency band, reducing the pitch angle interval of the blade and continuing to measure vibrations, if the measured vibrations are still greater than a threshold within a frequency band, moving all the aerodynamic devices to the second retracted configuration.

Claims

1. A method for damping vibration in a wind turbine including a plurality of aerodynamic devices for influencing an airflow flowing from a leading edge of a rotor blade of the wind turbine to a trailing edge of the rotor blade, each aerodynamic device being movable by an actuator between a first protruded configuration and a second retracted configuration, the method comprising: measuring vibrations in the wind turbine; if the measured vibrations are greater than a predefined threshold within a predefined frequency band, moving a portion of the aerodynamic devices to the second retracted configuration and continuing to measure vibrations in the wind turbine; if the measured vibrations are still greater than the predefined threshold within the predefined frequency band, reducing a pitch angle interval of the rotor blade and continuing to measure vibrations in the wind turbine; and if the measured vibrations are still greater than the predefined threshold within the predefined frequency band, moving all the aerodynamic devices to the second retracted configuration.

2. The method according to the claim 1, wherein the pitch angle interval of the rotor blade is reduced by increasing a minimum pitch angle of the rotor blade.

3. The method according to the claim 1, wherein the predefined frequency band includes a first blade flap mode.

4. The method according to claim 1, wherein vibrations are measured by means of an acceleration sensor installed on a tower or on a nacelle of the wind turbine or on the rotor blade.

5. The method according to claim 1, wherein vibrations are measured by means of a load sensor installed on a tower or on a nacelle of the wind turbine or on the rotor blade.

6. The wind turbine according to claim 1, wherein the aerodynamic devices are flaps.

7. The wind turbine according to claim 1, wherein the aerodynamic devices are spoilers.

Description

BRIEF DESCRIPTION

(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

(2) FIG. 1 depicts a wind turbine;

(3) FIG. 2 depicts a rotor blade of a wind turbine with an aerodynamic device, which is operatable according to the present invention;

(4) FIG. 3 depicts a first radial section of the rotor blade of FIG. 2; and

(5) FIG. 4 depicts a second radial section of the rotor blade of FIG. 2.

DETAILED DESCRIPTION

(6) The drawings are in schematic form. Similar or identical elements are referenced by the same or different reference signs.

(7) FIG. 1 shows a conventional wind turbine 10 for generating electricity. The wind turbine 10 comprises a tower 11 which is mounted on the ground 16 at one end. At the opposite end of the tower 11 there is mounted a nacelle 12. The nacelle 12 is usually mounted rotatable with regard to the tower 11, which is referred to as comprising a yaw axis substantially perpendicular to the ground 16. The nacelle 12 usually accommodates the generator of the wind turbine and the gear box (if the wind turbine is a geared wind turbine). Furthermore, the wind turbine 10 comprises a hub 13 which is rotatable about a rotor axis Y. When not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotor axis Y.

(8) The hub 13 is often described as being a part of a wind turbine rotor, wherein the wind turbine rotor is capable to rotate about the rotor axis Y and to transfer the rotational energy to an electrical generator (not shown).

(9) The wind turbine 1 further comprises at least one blade 20 (in the embodiment of FIG. 1, the wind rotor comprises three blades 20, of which only two blades 20 are visible) mounted on the hub 13. The blades 4 extend substantially radially with respect to the rotational axis Y.

(10) Each rotor blade 20 is usually mounted pivotable to the hub 13, in order to be pitched about respective pitch axes X. This improves the control of the wind turbine and in particular of the rotor blades by the possibility of modifying the direction at which the wind is hitting the rotor blades 20.

(11) Each rotor blade 20 is mounted to the hub 13 at its root section 21. The root section 21 is opposed to the tip section 22 of the rotor blade.

(12) A pitch actuation system (either electric or hydraulic) is associated to the rotor blades 20 proximal to the respective root sections 21 for regulating the pitch angle of each blade. According to the different possible embodiments of the present invention, one single pitch actuation system may be provided for all rotor blades 20 or a plurality of pitch actuation systems may be provided, each serving one respective blade 20.

(13) The pitch angle of each rotor blade 20 extends between a minimum pitch angle and a maximum pitch angle.

(14) FIG. 2 illustrates the rotor blade 20 comprising an aerodynamic device 30 in the form of an actuated spoiler. Between the root section 21 and the tip section 22 the rotor blade 20 furthermore comprises a plurality of aerofoil sections for generating lift. Each aerofoil section comprises a suction side 25 and a pressure side 26. The aerofoil shape of the aerofoil portion is symbolized by one aerofoil profile which is shown in FIG. 2 and which illustrates the cross-sectional shape of the rotor blade at this spanwise position. Also note that the suction side 25 is divided or separated from the pressure side 26 by a chord line 27 which connects a leading edge 41 with a trailing edge 31 of the rotor blade 20.

(15) The aerodynamic device 30 in FIG. 2 is movable by means of a pressure line 53 connected to a pneumatic actuator 34. According to the embodiment of the attached figures, the pneumatic actuator 34 is realized as a hose. The hose 34 comprises an elastic outer skin, such that it can inflate and deflate reversibly and during many cycles when operated by means of the pressure line 53.

(16) The pressure line 53 is comprised in a pressure supply system 52 and controlled by a control unit 51. The pressure supply system 52 provides pressurized air or other pressurized gas, to the pneumatic actuator 34. In this context, the term “pressurized fluid” not only implies positive pressure but also negative pressure, wherein fluid is sucked (or “drawn”) out of the pneumatic actuator 34. The pressure line 53 could be in practice realized as tubes or pipes which do not significantly change their volume. The control unit 51 is responsible for setting a specific pressure at the pressure supply system 52 which subsequently leads to a certain predetermined pressure at the pneumatic actuator 34. By controlling the pressure of the pressurized air the pneumatic actuator 34 is operated between an inflated and a deflated configuration.

(17) According to different embodiments of the present invention, any of the control unit 51 and the pressure supply system 52 may be located in the root section 21 of the rotor blade 20 or placed elsewhere in the wind turbine, such as e.g. in the hub 13 of the wind turbine 10 or in the nacelle 12 or in the tower 11.

(18) The rotor blade 20 additionally comprises a flow regulating unit 40 comprising multiple pairs of vortex generators.

(19) The flow regulating unit 40 are arranged on the suction side 25 of the blade 20 between the aerodynamic device 30 and the trailing edge 31.

(20) According to other embodiments of the present invention (not shown in the attached figures), the flow regulating unit 40 are arranged on the suction side 25 of the blade 20 between the leading edge 41 and the aerodynamic device 30.

(21) According to other embodiments of the present invention (not shown in the attached figures), the flow regulating unit 40 are not present and only the aerodynamic device 30 is used to regulate the flow on the surface of the blade 20.

(22) According to other embodiments of the present invention (not shown in the attached figures), the blade 20 comprises a plurality of aerodynamic devices 30.

(23) According to other embodiments of the present invention (not shown in the attached figures), the aerodynamic device 30 are configured as a trailing edge flap.

(24) According to other embodiments of the present invention (not shown in the attached figures), the blade 20 may comprise a plurality of aerodynamic devices 30 including flaps and spoilers.

(25) The rotor blade 20 additionally comprises one sensor 54 for measuring vibrations or loads on the rotor blade 20. The sensor 54 is connected to the control unit 51 for transmitting a vibration or load signal.

(26) According to other embodiments of the present invention (not shown in the attached figures), the blade 20 may comprise a plurality of vibration or load sensors 54, distributed along the rotor blade 20.

(27) FIG. 3 shows the aerodynamic device 30 in a first protruded configuration, corresponding to an inflated configuration of the pneumatic actuator 34.

(28) In the first configuration the aerodynamic device 30 deviates the airflow 71 which is flowing from the leading edge 41 to the trailing edge 31 of the rotor blade.

(29) The aerodynamic device 30 in the first protruded configuration induces stall. This is visualized with relatively large vortices 63 downstream of the aerodynamic device 30. A consequence of the induced stall is a decrease in lift of the rotor blade and, consequently, a reduced loading of the rotor blade and related components of the wind turbine.

(30) FIG. 4 shows the aerodynamic device 30 in a second retracted configuration, i.e. moved downwards towards the surface of the rotor blade 20, corresponding to a deflated configuration of the pneumatic actuator 34.

(31) In this second configuration, the airflow 71 flowing across the aerodynamic device 30 remains attached to the surface of the rotor blade 20, thus that no flow separation, i.e. stall, occurs. As a consequence, the lift of the rotor blade increases. Re-energizing vortices 64 are generated in the boundary layer by the vortex generators 40, which have the effect of helping increasing the lift. As a result, the highest lift values can be achieved.

(32) By operating the pneumatic actuator 34 of the aerodynamic device 30 through the pressure line 53, the aerodynamic device 30 can be moved between the first protruded configuration and the second retracted configuration in order to vary the aerodynamic properties of the blade as desired and requested when operating the wind turbine 10.

(33) According to the method of the present invention, when a vibration is detected, which is greater than a predefined threshold within a predefined frequency band, such vibration can be damped by operating the aerodynamic devices 30 alone or in combination with the blade pitch angle.

(34) A vibration of the wind turbine 10 may be detected through the sensors 54 or through other sensors (not shown in the attached figures). For example vibrations may be measured also by means of an acceleration sensor installed on the tower or nacelle.

(35) Particularly, but not exclusively, the present invention permits to damp vibrations around the first blade flap mode.

(36) The method comprises the steps of: measuring vibrations in the wind turbine, if the measured vibrations are greater than a predefined threshold within a predefined frequency band, moving a portion of the aerodynamic devices to the second retracted configuration and continuing to measure vibrations in the wind turbine, if the measured vibrations are still greater than a predefined threshold within a predefined frequency band, reducing the pitch angle interval of the rotor blade and continuing to measure vibrations in the wind turbine, if the measured vibrations are still greater than a predefined threshold within a predefined frequency band, moving all the aerodynamic devices to the second retracted configuration.

(37) The pitch angle interval of the rotor blade is reduced by increasing the minimum pitch angle of the rotor blade.

(38) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(39) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.