FLAP CONTROL FOR WIND TURBINE BLADES
A wind turbine blade has one or more trailing edge flaps. An actuator mechanism for the flaps comprises a shaft extending along the blade length driven by a motor arrangement toward the blade root. The flap is connected to the shaft through a linkage so that rotation of the shaft pivots the flap about a hinge line. The linkage may be non-rigid and coupled to the shaft through a roller, or rigid and coupled to the shaft through a crank arm mounted on the shaft. An offset actuation mechanism is provided for imparting movement to the linkage in addition to movement due to rotation of the shaft.
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This invention relates to wind turbines, and in particular, to the control of flaps on wind turbine blades.
It is known to incorporate control surfaces into wind turbine blades, and a number of proposals have been made for actuating those control surfaces in response to various conditions.
US-A-2003/0123973 (Murakami) discloses a rotor for a wind turbine, the blades of which have extendible auxiliary blades at the blade tips, together with a plurality of extendible vanes on the leading and trailing blade edges. The leading and trailing edge vanes are controlled by hydraulic or electric actuators arranged along the length of the blade.
DE-A-2922885 (Rath) discloses a trailing edge flap arrangement for a wind turbine blade in which the flap is actuated either by hydraulic cylinders or by a connecting rod actuated by an electric motor. The flaps are at the blade tips and the actuators are arranged proximate the flaps.
These actuating arrangements are unsatisfactory as they require a large number of moving parts to be arranged within the wind turbine blade away from the nacelle. Wind turbines are often located in remote and inaccessible locations, for example, offshore, and it is desirable that maintenance is as limited and as straightforward as possible. The arrangements of US 2003/0123973 and DE-A-2922885 do not meet with these requirements. In each case, complex actuators are arranged along the blade at positions remote from blade access points at the root of the blade. This makes access difficult and time consuming and may even require removal of the blade which is impractical. Wind turbine blades may be over 40 m in length and taper towards the tip. It is highly undesirable to have to access components in the interior of the blade towards the tip.
The invention aims to address the disadvantages of the prior art discussed above.
According to the invention, there is provided a wind turbine blade comprising at least one control flap on an edge of the blade, and an actuation mechanism for controlling movement of the flap, the actuation mechanism comprising an actuator shaft extending along at least a portion of the length of the blade, an actuator coupled to the shaft to rotate the shaft, the actuator being arranged towards the root end of the blade, a linkage coupled between the flap and the actuator shaft, whereby rotary movement of the shaft moves the flap, and an offset actuation mechanism for imparting movement to the linkage in addition to movement due to rotation of the shaft.
Embodiments of the invention have the advantage that the actuator, which may be an electric, an hydraulic motor or similar, is arranged towards the root of the blade where it is easily accessible and may be serviced as part of a scheduled maintenance visit. Moreover, the actuation mechanism may be very simple reducing the need for maintenance and increasing reliability. The offset mechanism has the advantage of imparting a high frequency movement to one or more flaps in addition to a lower frequency movement imparted by rotation of the shaft.
In a preferred embodiment, the linkage may be a rigid rod which may be attached to the rotatable shaft through a crank arm mounted on the shaft for rotation therewith.
The offset mechanism may comprise an L-shaped crank mounted for rotation about the shaft and to which the rigid rod linkage is attached, wherein the linkage comprises a rigid rod coupled at one end thereof to a first end of an L-shaped crank mounted for rotation about the shaft, the L-shaped crank being coupled to a crank arm mounted on the shaft for rotation therewith through an offset actuator, whereby actuation of the offset actuator moves the L-shaped crank with respect to the shaft to provide an offset movement to the flap.
Preferably the offset actuator is a piezo-electric stack and excitation of the piezo-electric stack moves the L-shaped crank with respect to the shaft to provide an offset movement to the shaft.
In a preferred embodiment the linkage is a control wire. The control wire may be coupled to the actuator shaft through a roller fixed to the shaft for rotation therewith. A plurality of rollers may be arranged on the shaft, each receiving a control wire for a flap. This has the advantage that the diameter of each roller may be chosen so that rotation of the shaft causes the correct amount of movement of the flap.
Where the linkage is a control wire, the offset mechanism may comprise a control wire coupled to the shaft through a roller, and the offset movement mechanism comprises a motor and gear mechanism for rotating the roller with respect to the shaft.
Preferably, the flap is pivotable about a hinge line wherein rotary movement of the shaft causes the linkage to pivot the flap about the hinge line.
Preferably, a spring is arranged between the flap and the wind turbine blade whereby the flap is biased towards an extended position. This has the advantage that the flap is biased towards a failsafe position.
Preferably, the blade comprises a plurality of flaps, for example, along the trailing edge of the blade, wherein each flap is pivotable by rotation of the shaft through a respective linkage.
Preferably, the linkage comprises a first linkage and a second linkage and the flap is pivotable about a mid-point, wherein the first linkage is attached to the flap at a point above the midpoint and the second linkage is attached to the flap at a point below the midpoint, and wherein the first and second linkages are coupled to the shaft through a double arm crank fixed to the shaft for rotation therewith.
This arrangement is advantageous as it enables the flap to be controlled when it is pivoted about a hinge line at the mid-point of the flap enabling the flap to move towards both the suction and pressure sides of the blade.
Preferably, the actuator shaft extends substantially along a structural member of the blade such as a spar or beam. Alternatively, the actuator mechanism and the shaft may be formed as a unit detachable from the blade. This arrangement has the advantage that the whole actuator mechanism may be detached from the blade so facilitating maintenance.
The invention also resides in a wind turbine having a plurality of blades each having an actuation mechanism as described above.
Embodiments of the invention will now be described by way of example only, and with reference to the accompanying drawings, in which:
The following description relates to control of one or more trailing edge flaps on a wind turbine blade. The term “flap” refers to a movable surface of the wind turbine blade which will modify the aerodynamic profile of the wind turbine blade. However, the invention is not limited to trailing edge flaps but is also applicable to the actuation of leading edge devices (typically slots or slats) and other control surfaces arranged along the blade edges as opposed to the tip only. The following description is limited to trailing edge flaps for simplicity. Moreover, the embodiments to be described are not limited to any particular number of flaps, wherever located, and may be used to actuate a single flap or two or more flaps arranged along the leading or trailing edge of a blade.
When designing a flap system for a wind turbine it is highly desirable to move the vulnerable parts, such as the actuators, from the outer parts of the blades to the roots so that they can be serviced as part of the normal service visits and accessed through the hub. Components located towards the blade tips are hard to access in situ and may require the blades to be removed.
The blade 10 comprises an upper surface 12 and a lower surface 14, commonly referred to as the suction surface and the pressure surface, each made from a lightweight composite material by well known techniques. A strengthening spar 16 or beam extends along the length of the blade, as can be seen from
As shown in
In the embodiment of
As can best be seen from
A control linkage comprising a control wire 38 is attached to the shaft at one end and to the flap 26 at its other end. As shown in
The actuator may, for example, be a hydraulic or electric motor.
In order to deploy the flaps, the actuator(s) may only need to rotate the torsion shaft through a portion of a rotation, for example, ⅓ of a turn.
The actuator shaft 32 is preferably torsionally stiff but otherwise non-stiff enabling it to follow blade movement over the lifetime of the blade which may be 20 years or more. The shaft is preferably made from a composite material.
Thus, in the embodiment described, rotary movement of the shaft by the actuator causes movement of the flap. In particular, shaft rotation causes the flap to pivot about the hinge line.
As mentioned previously, in the embodiment of
In the preceding embodiments, the flaps have been hinged about a hinge line on the suction surface of the blade and flap.
Alternatively, the coupling wires of
This embodiment has the advantage of reduced slack in the system, but the torsion arm, being the distance between the pull point on the flap and the hinge is halved.
In the embodiments of
In the embodiment of
In
Thus, this embodiment provides an offset to the movement provided by rotation of the shaft and the crank arm (or roller). It will be appreciated that separate L-shaped cranks and piezo-electric stacks may be provided for each flap and, as the stacks are controlled individually, the fast moving offset movement may be applied separately to each flap.
The arrangement of
As with the previous embodiment, the fast movement motor may be individual to each flap enabling the offset movement to be applied to each flap individually. The extent of movement provided by the shaft rotation is indicated by double headed arrow 90 and that provided by the offset motor and gear is indicated by double headed arrow 92. The speed of actuation may be increased by using spiral splines on the shaft combined with axial movement of the shaft.
Embodiments of the invention have the advantage of providing a simple control mechanism for the flap or flaps on a wind turbine blade, for example, on the trailing edge. The use of a motor actuated shaft enables the motor to be located towards the root of the blade making inspection and maintenance easy and locates the motor relatively close to the turbine controller in the turbine nacelle which is desirable. Moreover, some embodiments of the invention enable movement to be imparted to multiple flaps through a single motor and also additional offset movements to be imparted to individual flaps to provide higher frequency movement.
Claims
1. A wind turbine blade comprising at least one control flap on an edge of the blade, and an actuation mechanism for controlling movement of the flap, the actuation mechanism comprising an actuator shaft extending along at least a portion of the length of the blade, an actuator coupled to the shaft to rotate the shaft, the actuator being arranged towards the root end of the blade, a linkage coupled between the flap and the actuator shaft, whereby rotary movement of the shaft moves the flap, and an offset actuation mechanism for imparting movement to the linkage in addition to movement due to rotation of the shaft.
2. The wind turbine blade according to claim 1, wherein the linkage comprises a rigid rod coupled at one end thereof to a first end of an L-shaped crank mounted for rotation about the shaft, the L-shaped crank being coupled to a crank arm mounted on the shaft for rotation therewith through an offset actuator, whereby actuation of the offset actuator moves the L-shaped crank with respect to the shaft to provide an offset movement to the flap.
3. The wind turbine blade according to claim 2, wherein the offset actuator is a piezo-electric stack and excitation of the piezo-electric stack moves the L-shaped crank with respect to the shaft to provide an offset movement to the shaft.
4. The wind turbine blade according to claim 1, wherein the linkage comprises a control wire coupled to the shaft through a roller, and the offset movement mechanism comprises a motor and gear mechanism for rotating the roller with respect to the shaft.
5. The wind turbine blade according to claim 1, wherein the flap is pivotable about a hinge line and wherein rotary movement of the shaft causes the linkage to pivot the flap about the hinge line.
6. The wind turbine blade according to claim 2, wherein the rigid rod is attached to the rotatable shaft through a crank arm mounted on the shaft for rotation therewith.
7. The wind turbine blade according to claim 4, wherein the control wire is coupled to the actuator shaft through a roller fixed to the shaft for rotation therewith.
8. The wind turbine blade according to claim 1 wherein the linkage comprises a first linkage and a second linkage and the flap is pivotable about a mid-point, wherein the first linkage is attached to the flap at a point above the midpoint and the second linkage is attached to the flap at a point below the midpoint, and wherein the first and second linkages are coupled to the shaft through a double arm crank fixed to the shaft for rotation therewith.
9. The wind turbine blade according to claim 1 comprising a spring arranged between the flap and the blade, the spring biasing the flap towards an extended position.
10. The wind turbine blade according to claim 1, comprising a plurality of control flaps, each control flap being movable by rotation of the shaft through a respective linkage.
11. The wind turbine blade according to claim 1, wherein the actuator shaft extends substantially along a structural member of the blade.
12. wind turbine blade according to claim 1, wherein the actuation mechanism and the flap are formed as a unit detachable from the blade.
13. A wind turbine having a rotor comprising a plurality of rotor blades, each rotor blade comprising at least one control flap on an edge of the blade, and an actuation mechanism for controlling movement of the flap, the actuation mechanism comprising an actuator shaft extending along at least a portion of the length of the blade, an actuator coupled to the shaft to rotate the shaft, the actuator being arranged towards the root end of the blade, a linkage coupled between the flap and the actuator shaft, whereby rotary movement of the shaft moves the flap, and an offset actuation mechanism for imparting movement to the linkage in addition to movement due to rotation of the shaft.
Type: Application
Filed: Nov 23, 2010
Publication Date: Oct 25, 2012
Applicant: VESTAS WIND SYSTEMS A/S (Aarhus N)
Inventor: Carsten Hein Westergaard (Houston, TX)
Application Number: 13/511,909
International Classification: F04D 29/36 (20060101);