WO2012083961A1

WO2012083961A1 - Wind turbine blades

Info

Publication number: WO2012083961A1
Application number: PCT/DK2011/050500
Authority: WO
Inventors: Yun Chong Gabriel Chang; Chee Kang Lim; Wuh Ken Loh
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2010-12-20
Filing date: 2011-12-19
Publication date: 2012-06-28
Anticipated expiration: 2013-06-20
Also published as: GB201021535D0

Abstract

A rotor blade of a wind turbine is provided with a flap 9 which is movable between first and second configurations so as to change the aerodynamic surface shape of the rotor blade. The flap 9 is attached to the distal end of a push-pull control cable 11, and an actuator 15 remotely situated from the flap 9 is connected to the proximal end of the push-pull control cable 11, such that the flap 9 can be moved by energising the actuator 15 Means are provided for sensing the movement of the cable so as to determine the configuration of the flap 9. In one embodiment, the flap 9 is controlled using four respective push-pull control cables 11 attached to the flap 9 at different positions and controlled by a single actuator 15.

Description

WIND TURBINE BLADES

The present invention relates to rotor blades for wind turbines, and more particularly to such rotor blades having an aerodynamic surface or shape which can be reconfigured.

A typical wind turbine is illustrated in Figure 1. The wind turbine 1 comprises a tower 2, a nacelle 3 mounted at top of the tower 2 and a rotor 4 operatively coupled to a generator 5 within the nacelle 3. The wind turbine 1 converts kinetic energy of the wind into electrical energy. In addition to the generator 5, the nacelle 3 houses the various components required to convert the wind energy into electrical energy and also the various components required to operate and optimize the performance of the wind turbine 1. The tower 2 supports the load presented by the nacelle 3, the rotor 4 and other wind turbine components within the nacelle 3. The rotor 4 includes a central hub 6 and three elongate rotor blades 7a, 7b, 7c of approximately planar configuration which extend radially outward from the central hub 6. In operation, the blades 7a, 7b, 7c are configured to interact with the passing air flow to produce lift that causes the central hub 6 to rotate about its longitudinal axis. Wind exceeding a minimum level will activate the rotor 4 and allow it to rotate within a plane substantially perpendicular to the direction of the wind. The rotation is converted to electric power by the generator 5 and is usually supplied to the utility grid.

It is necessary to control the operation of wind turbines so as to optimise performance over a wide range of wind speeds and power demand, including local fluctuations in wind speed, known as wind gusts. It is also desirable to be able to control each blade independently so as to balance the loads.

A known method of controlling the operation of wind turbines is to pitch the blades. However, with particularly long blades, such as in excess of 60 metres, it is not possible to pitch the blades sufficiently quickly to compensate for wind gusts.

As an alternative to pitching the blades, it is possible simply to change the aerodynamic surface shape over at least a part of the length of the blade. The shape can be changed by the provision of adjustable flaps, such as trailing edge flaps, leading edge flaps, slats or spoilers. An advantage of such an arrangement is a faster response to changing conditions than can be achieved with pitching of the blades mentioned above. One problem with conventional trailing edge flaps is the need to transmit the necessary electric power quickly to such flaps from the hub, which, in turn requires the use of power cables. However, the use of electrical cables is undesirable due to the adverse influence of lightning.

It would therefore be desirable to provide arrangements which overcome, or at least mitigate the above problems. Thus, in accordance with a first aspect of the present invention there is provided a wind turbine blade comprising: a flap arranged to move between first and second configurations; a push-pull control cable attached at a first end to the flap; and means for actuating the second end of the control cable, thereby to move the flap between said first and second configurations.

Push-pull control cables, such as those provided by Tuthill Controls Group, are readily available and can be retrofitted into existing wind turbine rotor blades in order to put the present invention into practice. Push-pull control cables provide a simple and reliable means of transmitting motion and forces and are similar in structure and function to well-known Bowden cables.

By using a push-pull control cable to reconfigure the flap, there is no need for an electrical cable to extend the full length of the rotor blade, since the second end of the control cable, and hence the actuating means, can be located remote from the flap, and could even be located within the rotor hub. Furthermore, push-pull control cables are flexible, and it is therefore possible to reconfigure the flap by arranging the actuating means at any convenient angle relative to the flap, since there is no requirement for the actuating means to operate along the direction of movement of the flap.

The term "flap" is intended to refer to any device which may be used to alter the aerodynamic profile of an airfoil section of the rotor blade. For example, the flap may be a trailing edge flap, a leading edge flap a slat or a spoiler. The flap may be hinged relative to the wind turbine blade or may be formed as a deformable trailing edge. The actuating means may comprise one or more of a pneumatic actuator, a hydraulic actuator, a piezoelectric actuator and an electric actuator, such as a linear motor or any combination of actuator type, such as electro-hydraulic actuator, pneumatic-servo actuator or servo actuators.

The rotor blade preferably also comprises means for sensing the configuration of the flap.

It would be possible to sense the configuration of the flap directly from a control signal applied to the actuating means. However, such a determination would not be reliable in the event of a malfunction of the actuating means.

The sensing means is therefore preferably arranged to sense the configuration of the flap by sensing the position, i.e. degree of extension or retraction, of the push-pull control cable.

The rotor blade may comprise a plurality of push-pull control cables, the first end of each of which is connected to the flap at different respective positions, and wherein the actuating means comprises a single actuator for actuating the second end of each of the plurality of control cables. Such an arrangement enables a greater degree of precision of movement of the flap.

The flap is preferably a trailing edge flap. The flap may be a deformable trailing edge flap.

The first end of push-pull control cable may be attached to a suction skin of the flap. Alternatively, the first end of push-pull control cable may be attached to a pressure skin of the flap.

The present invention extends to a wind turbine comprising at least one wind turbine blade as claimed in any preceding claim.

In accordance with a further aspect of the present invention there is provided a method of moving a flap of a wind turbine blade between two different configurations, the method comprising: attaching a first end of a push-pull control cable to the flap; and actuating the second end of the cable, thereby to cause the first end of the cable to move the wind turbine flap.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates the main structural components of a wind turbine;

Figure 2 illustrates a rotor blade of a wind turbine showing the position of a flap;

Figure 3 is a schematic diagram illustrating a preferred embodiment of the present invention;

Figure 4 illustrates schematically an arrangement for sensing the configuration of the flap;

Figures 5(a) and 5(b) illustrate schematically the sensing arrangement in the two configurations of the flap; and Figure 6 illustrates an arrangement in which four push-pull control cables are used to control the configuration of the flap.

Figures 7(a) and 7(b) illustrate a deformable trailing edge flap. Figure 2 illustrates a rotor blade 7 having a blade body 8 with a leading edge 8a and a trailing edge 8b to which is attached three movable flaps 9. The angle of the flaps 9 relative to the blade body 8 are controlled by the combination of an actuator and push- pull control cable (not shown) both located within the blade body 8. Figure 3 shows a partial cross section through the blade body 8 and the flap 9. Referring to Figure 3, a push-pull control cable 1 1 comprises an inner flexible rod 12 movable longitudinally within an outer flexible sheath 13. The two ends of the outer sheath 13 are rigidly attached to the blade body 8 (by means not shown), and the proximal end 14 of the flexible rod 12 is attached to an actuator 15. The distal end 16 of the flexible rod 12 is attached to the flap 9 via a mechanical coupling 17. In this example, the push-pull control cable 11 extends in a substantially chordwise direction, that is in a direction between the leading edge 8a and the trailing edge 8b. The proximal end 14 of the flexible rod 12 is the end disposed nearest to the leading edge 8a, and the distal end 16 of the flexible rod 12 is the end disposed nearest to trailing edge 8b. In the preferred embodiment the actuator 15 is a pneumatic actuator, but may alternatively be a hydraulic actuator, a piezoelectric actuator or an electric actuator, such as a linear motor. The actuator is anchored to an internal spar (not shown) located within the blade body 8. In operation, the actuator 15 is energised so as to cause the inner flexible rod 12 to move within the outer sheath 13 from a first position to a second position. The movement of the actuator 15 is indicated by the double headed straight arrow on the left hand side of the Figure. This, in turn, causes the flap 9 to pivot from a first angle to a second angle. The flap 9 pivots about hinge 10 in the directions indicated by the double headed curved arrow on the right hand side of the Figure. In operation, when the push-pull control cable 1 1 is "pulled" by the actuator 15, the flap 9 is caused to rotate downwards as per the orientation of Figure 3. When the push-pull control cable 1 1 is "pushed" by the actuator 15, the flap 9 is caused to rotate upwards as per the orientation of Figure 3. A push-pull control cable is highly reliable, which is important in the wind turbine industry, since wind turbines are often situated in remote locations and in harsh weather environments. The provision of reliable components therefore results in lower servicing requirements. The actuator 15 may be located in the hub remote from the flap 9. Locating the actuator 15 in the hub provides the advantage that, should the actuator require servicing or replacement, it is more convenient to access the actuator, than if it were located in the blade 8. Furthermore, by selecting an electrically non-conductive push-pull control cable 1 1 , this results in a reduced risk of lighting strike on the blade, as compared with arrangements in which the electrical controls to actuate the flap 9 are provided within the blade 8. In other examples, the actuator 15 may be located in the blade root end region, or anywhere along the blade which is remote from the flap.

Referring to the schematic of Figure 4, the position of the inner rod 12 is sensed using a displacement cable 18 which is attached to the actuator 15 and which moves with the inner rod 12 of the push-pull control cable 1 1. The displacement cable 18 is provided with indicia 19 along its length which are sensed by a position transducer 20. The indicia 19 are preferably markings which can be sensed optically, in which case the position transducer 20 comprises the combination of a light source and photodetector. However, the indicia 19 may alternatively by magnetic markings, in which case the position transducer 20 comprises a magnetic sensor. As a further alternative, the position transducer 20 could comprise a potentiometer. Although it is preferred that the position transducer 20 is arranged to provide an output signal which is linearly dependent on the position of the inner rod 12, a non-linear dependency of the output signal on the position of the inner rod would still enable an accurate determination of the displacement of the inner rod 12 to be made, provided a calibration is made in order to determine the dependency.

Figures 5(a) and 5(b) illustrate schematically the positions of the displacement cable 18 with the flap 9 in the two configurations. In Figure 5(a) the flap 9 is at an angle of 10° facing rearwardly from the general angle of the blade body 8, and the displacement cable 18 is in its retracted position. In Figure 5(b) the flap 9 is at an angle of 10° facing forwardly of the general angle of the blade body 8, and the displacement cable 18 is in its extended position.

Figure 6 illustrates an arrangement in which four push-pull cables 1 1 (a), 1 1 (b), 11 (c), 1 1 (d) are used to control the configuration of the flap 9, and wherein a single actuator 15 is connected to the proximal ends of the four push-pull cables 1 1 (a), 11 (b), 1 1 (c), 1 1 (d). The distal ends of the four push-pull cables 11 (a), 1 1 (b), 11 (c), 1 1 (d) are connected to the flap 9 at different respective positions, thereby providing a greater degree of control of the movement of the flap 9 than could be achieved with a single push-pull cable. Figures 7(a) and 7(b) illustrate an example with a deformable trailing edge type flap. In this example the flap comprises a pressure skin 31 and a suction skin 32 which are deformable when the push-pull cable 11 is actuated. The pressure skin 31 and the suction skin 32 may be formed from an elastomeric skin such as a compliant silicone skin, or a composite such as a compliant carbon fibre reinforced plastic (CFRP) material or a compliant glass fibre reinforced plastic (GFRP). Disposed between the flap's pressure skin 31 , the suction skin 31 is a spar 33 which acts as an additional stiffening mechanism in the trailing edge region of the blade 7.

The push-pull cable 11 passes through an aperture in the spar 33 and its distal end is connected to an inner surface of the suction skin 32 near to the trailing edge. By connecting the distal end of the push-pull cable 11 directly to the suction skin 32 allows the flap to be deformed in a curved manner as shown in Figure 7(b) where the push-pull cable 11 has been retracted. The skilled person will appreciate that the push-pull cable 1 1 can also be connected to the pressure skin 31. The pressure skin 31 and the suction skin 31 may also be tailored in their composite structure to control how the flap 9 deforms and the shape in which the flap 9 deforms.

In other examples, not included in the scope of the present invention, the push-pull cable is replaced with a cable which is only pulled or pushed. The return movement is provided by a return biasing mechanism such as a spring or another actuator.

Although preferred embodiments of the present invention have been described above, it will be apparent to the person skilled in the art that many variations may be made to these without departing from the scope of the present invention, which is defined solely by the claims appended hereto.

Claims

A rotor blade for a wind turbine, the rotor blade comprising:

a flap arranged to move between first and second configurations;

a push-pull control cable attached at a first end to the flap; and

means for actuating the second end of the control cable, thereby to move the flap between said first and second configurations.

A rotor blade as claimed in claim 1 , wherein the actuating means comprises one or more of a pneumatic actuator, a hydraulic actuator, a piezoelectric actuator and an electric actuator.

A rotor blade as claimed in claim 1 or claim 2, further comprising means for sensing the configuration of the flap.

A rotor blade as claimed in claim 3, wherein the sensing means is arranged to sense the configuration of the flap by sensing the position of the push-pull control cable.

A rotor blade as claimed in any preceding claim, and comprising a plurality of push-pull control cables, the first end of each of which is connected to the flap, and wherein the actuating means comprising a single actuator for actuating the second end of each of the plurality of control cables.

A rotor blade as claimed in any preceding claim, wherein the flap is a trailing edge flap.

A rotor blade as claimed in any preceding claim, wherein the flap is a deformable trailing edge flap.

A rotor blade as claimed in any preceding claim, wherein the first end of push-pull control cable is attached to a suction skin of the flap.

A rotor blade as claimed in any of claims 1 to 7, wherein the first end of push-pull control cable is attached to a pressure skin of the flap. A wind turbine comprising a rotor blade as claimed in any preceding claim.

A method of moving a flap of a wind turbine rotor blade between two different configurations, the method comprising:

attaching a first end of a push-pull control cable to the flap; and

actuating the second end of the cable, thereby to cause the first end of the cable to move the flap.