WIND TURBINE ROTOR BLADE

Abstract

A wind turbine rotor blade is provided including a deformation arrangement, which deformation arrangement includes a plurality of linear actuators, wherein each linear actuator is arranged at the suction side of the rotor blade, wherein a longitudinal axis of a linear actuator is aligned with a longitudinal axis of the rotor blade, and wherein each linear actuator is realized to alter its length in response to an excitation signal; and an interface configured to receive a corrective control signal and to issue excitation signals to the linear actuators on the basis of the corrective control signal. Also provided is a wind turbine and a method of operating a wind turbine.

Claims

1-15. (canceled)

16. A wind turbine rotor blade comprising: a deformation arrangement, wherein the deformation arrangement comprises: at least one series arrangement of linear actuators, each comprising a plurality of linear actuators, wherein each linear actuator is arranged at a suction side of the wind turbine rotor blade, wherein a longitudinal axis of a linear actuator is aligned with a longitudinal axis of the wind turbine rotor blade, wherein each linear actuator is at least partially embedded in a body of the wind turbine rotor blade and is configured to alter a length in response to an excitation signal; and an interface configured to receive a corrective control signal and to issue excitation signals to the plurality of linear actuators on a basis of the corrective control signal.

17. The wind turbine rotor blade according to claim 16, wherein each linear actuator comprises a rigid outboard end plate and a rigid inboard end plate embedded at least partially in the body of the suction side of the wind turbine rotor blade.

18. The wind turbine rotor blade according to claim 16, wherein components of the deformation arrangement are arranged to counteract a compression of the wind turbine rotor blade in a downwind direction.

19. The wind turbine rotor blade according to claim 16, wherein each linear actuator is any of a piezoelectric motor transducer, a hydraulic cylinder, a pneumatic cylinder, an electro-mechanical actuator.

20. The wind turbine rotor blade according to claim 16, wherein each linear actuator is configured to alter a length by up to 0.1% of a resting length.

21. The wind turbine rotor blade according to claim 20, wherein each linear actuator comprises a stack of piezoelectric cells.

22. The wind turbine rotor blade according to claim 16, wherein the at least one series arrangement comprises at least twenty linear actuators, or at least forty linear actuators.

23. The wind turbine rotor blade according to claim 16, wherein the plurality of linear actuators are located in a vicinity of a rotor blade root region.

24. The wind turbine rotor blade according to claim 16, wherein each linear actuator comprises a number of attachment means for attaching the linear actuator to the body.

25. A wind turbine comprising: a plurality of wind turbine rotor blades according to claim 16; a monitoring arrangement configured to determine a downwind deflection of a rotor blade from wind loading; and an analysis unit configured to determine a corrective deformation of the rotor blade to counteract the downwind deflection and to generate a corresponding corrective control signal to the deformation arrangement of the rotor blade.

26. The wind turbine according to claim 25, configured to determine a corrective deformation for each wind turbine rotor blade independently.

27. The wind turbine according to claim 25, wherein each rotor blade comprises an inherent curvature in an upwind direction.

28. A method of operating a wind turbine according to claim 25, the method comprising: determining a downwind deflection of a rotor blade from wind loading; determining a magnitude of a corrective length to be effected by the deformation arrangement of the rotor blade to counteract the downwind deflection; generating a corrective control signal on a basis of a corrective force magnitude; and issuing the corrective control signal to the deformation arrangement of the rotor blade.

29. The method according to claim 28, wherein the downwind deflection of the rotor blade is determined from a strain sensor arrangement and/or from a wind speed monitoring arrangement.

30. The method according to claim 28, wherein computing the corrective force is carried out when wind speed exceeds a minimum threshold.

Description

BRIEF DESCRIPTION

[0034] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0035] FIG. 1 shows a wind turbine;

[0036] FIG. 2 illustrates deflection of a rotor blade;

[0037] FIG. 3 shows a schematic of a rotor blade according to embodiments of the invention;

[0038] FIG. 4 shows a block diagram of a control arrangement in an embodiment of the wind turbine;

[0039] FIG. 5 shows curves associated with the rotor blade during normal operation, according to embodiments of the present invention;

[0040] FIG. 6 shows curves associated with a conventional rotor blade during normal operation;

[0041] FIG. 7 shows a first embodiment of the rotor blade;

[0042] FIG. 8 shows a second embodiment of the rotor blade;

[0043] FIG. 9 shows an exemplary implementation of a linear actuator in an embodiment of the rotor blade; and

[0044] FIG. 10 shows another exemplary implementation of a linear actuator in an embodiment of the rotor blade.

DETAILED DESCRIPTION

[0045] FIG. 1 shows a wind turbine 2 of the most common type in use at present. The wind turbine 2 has an aerodynamic rotor comprising three rotor blades 20 attached to a hub 21. Rotation of the aerodynamic rotor causes rotation of a generator rotor, so that output power can be exported by the wind turbine 2.

[0046] The rotor blades 20 are shaped to optimize the amount of energy that can be extracted from the wind. To this end, a rotor blade 20 has an airfoil portion over much of its length, and the shape of the rotor blade transitions from a generally circular shape at the root end 20R to the flatter airfoil portion 20A, ultimately tapering to a thin tip 20T. The length of a rotor blade can be in the order of 80 m or more. This type of rotor blade may undergo significant deflection in the downwind direction, as illustrated in FIG. 2, which shows how the rotor blades 20 of such a wind turbine may be deflected by high wind loading in the downwind direction DW, i.e., in the direction of the tower 22. The downwind side DW and upwind side UW of the aerodynamic rotor are indicated. In this exemplary wind turbine, the axis of rotation is tilted upwards by several degrees and the rotor blades are pre-bent as indicated by the ghost outlines that show their resting shape in low wind conditions.

[0047] FIG. 3 shows a schematic of a rotor blade according to embodiments of the invention. The diagram is a view of the rotor blade looking at the trailing edge TE. It shall be noted that the axes are not to the same scale. The diameter at the root end 20R is in the order of 3-4 m (X-axis), and the rotor blade length is in the order of 80-90 m (Y-axis). The pressure side 20P and suction side 20S of the rotor blade 20 are shown as indicated. It shall be assumed that the wind turbine is controlled so that its aerodynamic rotor always faces upwind UW during normal operation.

[0048] The diagram shows a deflection shape (dotted line) to indicate the shape of an equivalent conventional rotor blade 20X under high wind conditions without corrective pitch control. Deflection can be measured from a reference, for example relative to a vertical line extending through 0 of the X-axis. The significant tip-to-tower deflection X of the conventional rotor blade 20X can have undesirable effects such as fatigue loading, tower collision, etc. For this reason, a conventional rotor blade is generally pitched out of the wind to decrease the tip-to-tower deflection X, resulting in a reduction in output power during normal operation. In the inventive rotor blade 20, such extreme downwind deflection is prevented by its deformation arrangement, indicated here schematically to comprise a series of linear actuators 11 embedded at least partially at the suction-side 20S of the rotor blade 20. In this exemplary embodiment, a series of linear actuators is indicated at an inboard blade region. Each linear actuator may comprise a stack of piezo-electric cells, for example. In response to a corrective control signal, the linear actuators extend their lengths to counteract the downwind deflection, assisting the rotor blade 20 to return towards its normal shape, i.e., compression of the suction side is counteracted.

[0049] The corrective control signal 320 for the linear actuators can originate from an actuator control unit 32 as indicated in FIG. 4, which shows a block diagram of a wind turbine control arrangement 3. In this exemplary embodiment, a monitoring arrangement 30 determines the downwind deflection 300 associated with the momentary wind loading on a rotor blade 20. The monitoring arrangement 30 may base its computations on relevant input variables such as wind speed, rotor blade angular position, rotor blade pitch angle etc., which can be supplied by the wind turbine controller WTC. Analysis unit 31 determines the magnitude of the length correction 310 that must be effected by the deformation arrangement 1 (indicated here only schematically) of that rotor blade in order to counteract the suction-side compression of the rotor blade. Analysis unit 31 may be provided with any relevant information such as the rotor azimuth angle, the rotor blade pitch angle, blade loading, a measurement of tip-to-tower clearance etc., which can be supplied by the wind turbine controller WTC. In one example, the monitoring arrangement 30 may determine that the current wind loading would result in a deflection of 3 m relative to a reference. Analysis unit 31, knowing the present state of the deformation arrangement 1, determines the length correction that will be required to counteract the longitudinal compression of the suction-side to avoid severe deflection. The actuator control unit 32 translates the length correction 310 into an appropriate actuator control signal 320 that is then issued to the linear actuators of the deformation arrangement 1 of that rotor blade. In this way, the control arrangement 3 mitigates, prevents or counteracts the downwind deflection of that rotor blade.

[0050] The exemplary control arrangement 3 described above comprises the monitoring arrangement 30, the analysis unit 31, and the actuator control unit 32. One or more components of the control arrangement can be realized locally in a wind turbine or at a remote location.

[0051] The computations described above can be carried out for all three rotor blades collectively, i.e., a single length correction 310 is determined and converted into a corrective actuator control signal 320 that is issued to the deformation arrangements of all three rotor blades. However, since the downwind deflection is affected by wind shear and angular rotor blade position, the downwind deflection 300, corrective lengths 310 and actuator control signals 320 can be computed independently for each rotor blade.

[0052] Since wind loading on the rotor blades will fluctuate, the corrective force magnitude 310 can fluctuate accordingly. This is indicated in FIG. 5, which shows curves for wind load 51, predicted downwind deflection 52, corrective lengths 53 and actual downwind deflection 54 respectively for a rotor blade according to embodiments of the invention. The diagram shows that corrective actuation of the linear actuators counteracts the suction-side compression and prevents significant downwind deflection. This pre-emptive or counter-deformation of the rotor blades means that the wind turbine controller does not need to adjust the pitch angle to avoid rotor blade damage, but can continue to operate at the favorable high-power output. The pitch angle and power output can remain essentially constant. The predicted downwind deflection 52 may correspond to the output of the monitoring arrangement 30, and the corrective lengths 53 may correspond to the output 310 of the analysis unit 31 as explained in FIG. 4 above.

[0053] The conventional approach of adjusting the pitch angle to mitigate downwind deflection is illustrated in FIG. 6, which shows curves for wind load 61, downwind deflection 62, pitch angle correction 63 and power output 64 respectively. The diagram illustrates how downwind deflection can only be avoided by adjusting the rotor blade pitch angle, which in turn results in a decrease in output power.

[0054] FIG. 7 shows a schematic diagram of a possible embodiment of the inventive rotor blade 20, indicating the deformation arrangement 1 in the interior of the rotor blade. The diagram shows a series of linear actuators 11 arranged along an inboard region of the rotor blade 20. Each linear actuator 11 can comprise a stack of piezoelectric motor transducers that act together as a unit. Each linear actuator 11 is at least partially embedded in the suction-side body of the rotor blade. A length correction input 320 is converted to an appropriate excitation signal 100 by an interface module 10. For example, in an arrangement using ten piezoelectric units 11, each comprising a piezoelectric stack, a length correction input 320 corresponding to 3 cm may be converted to a suitable input 100 voltage that causes each of the ten units 11 to extend its length by 3 mm.

[0055] FIG. 8 shows a schematic diagram of another possible embodiment of the inventive rotor blade 20. Here, three series of linear actuators 11 is implemented, and each linear actuator can comprise a stack of piezoelectric motor transducers that act together as a unit. The units 11 may all be identical. Alternatively, each series may comprise units 11 of the same type, but units 11 of one series may differ from the units 11 of the other series.

[0056] FIG. 9 shows a very simplified exemplary embodiment in which a piezoelectric motor transducer 11 is embedded in the suction-side body 20S or shell of the rotor blade. The longitudinal axis 11A of the linear actuator is essentially in line with a longitudinal axis of the rotor blade. The linear actuator 11 has a rigid outboard end plate 11Pout and a rigid inboard end plate 11Pin. These end plates 11Pin, 11Pout are embedded in the suction-side body 20S and serve as anchors. The active portion 11B of the transducer is located between the end plates 11Pin, 11Pout. Depending on the magnitude of the input voltage 100, the active portion 11B of the transducer will extend or contract, as will be known to the skilled person. In this embodiment, the linear actuator is arranged in line with its anchors.

[0057] FIG. 10 shows an alternative arrangement, in which the linear actuator is upwind of its anchors. In such an embodiment, compression of the suction side will extend or stretch the active portion of the linear actuator. Here, the linear actuator is configured with a negative free deflection, i.e., it will contract or reduce its length in response to a suitable input voltage.

[0058] Although the present invention has been disclosed in the form of 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.

[0059] 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.