The present invention relates to a wind turbine rotor blade. In particular it relates to wind turbine blades having actuators to deflect devices for modifying the aerodynamic surface and camber of the blade in order to alleviate loads acting on the wind turbine rotor.

Modern wind turbines are controlled during operation in order to optimise the performance of the wind turbine in different operating conditions. The different operating conditions can arise from changes in wind speed and wind gusts which are local fast variations in wind speed. It is well known to regulate the speed of rotation of the rotor of a horizontal axis wind turbine by pitching the blades of the rotor. This is typically achieved by turning the blades about their longitudinal axis to influence the aerodynamic angle of attack of the rotor blades, this is the method used in pitch controlled wind turbine and active stall controlled wind turbines.

Wind turbines are subjected to loads of a highly variable nature due to the wind conditions. In modern wind turbines, as the rotor is typically able to control its pitch angle, the pitch can be used not only for controlling the speed of the rotor, but also for reducing the variations in load on the blades. However, due to the large length of modern wind turbine blades and the associated high inertia of the masses to be rotated about a pitch axis, the blade pitch mechanisms are not ideal for reacting rapidly to variations in wind speed which occur over a short time frame. In addition the length of wind turbine blades is increasing with new technology and the blades are becoming more flexible due to their greater length. Consequently, with the length of wind turbine blades increasing, when the blades are pitched there is a longer time lag for the pitch to change at the tip where the main loads are on the blades. Furthermore, controlling the loads on the blades with the use of a pitch system can be problematic as the blade pitch bearings may become damaged with constant use.

It is possible to regulate the loads acting on the blades of a wind turbine rotor with devices which modify the aerodynamic surface or shape of the blades such as by deformable trailing edges or adjustable flaps which can include trailing edge flaps, ailerons, spoilers, slats and gurney flaps. Such aerodynamic devices are advantageous because they allow a faster response time due to their relatively low inertia as they are small compared to the size of the entire wind turbine blade. One such example of a wind turbine blade which has a deformable trailing edge is described in WO2008/132235. However, it is necessary to find a suitable actuator to move the flaps which can withstand the harsh operating conditions experienced by wind turbines.

According to the present invention there is provided a wind turbine rotor blade comprising: a blade body; a flap for modifying the aerodynamic surface of the rotor blade, a part of which forms a part of a trailing edge of the rotor blade, the flap being deflectable relative to the blade body;

an actuation device for deflecting the flap from a first position to a second position; the actuation device comprising a linear motor having a stationary part connected to the blade body and a translating part for movement along a straight or curved path relative to the stationary part, the translating part being connected to the flap, and the actuation device is located inside the rotor blade;

wherein the actuation device deflects the flap when the translating part moves relative to the stationary part.

A linear motor is a particularly suitable actuator for use in a wind turbine blade because it has a high level of reliability. Having a high level of reliability is advantageous for use in a wind turbine generator because it is often difficult to service components in wind turbines due to the harsh and remote conditions in which the wind turbine may operate. Furthermore, a linear motor provides a compact actuator that is capable of rapid motion. A flap on a wind turbine rotor blade may be operated at high frequencies so the provision of a device capable of rapid motion is desirable. It is possible to have a high degree of control over a linear motor, such as the speed of translation and the distance of the translation, this allows a high level of accuracy with which the flap can be controlled; for example, a very precise flap deflection can be set.

In addition, the linear motor system uses Lorenz force for actuation and there is no physical contact between motor coil and track (permanent magnets). The alignment is constrained by guide rails and are mounted external to the system. This is advantageous as it allows flexible configuration and maintenance.

Preferably, the actuation device is located adjacent to the flap. A wind turbine rotor blade undergoes significant deformation when it is rotating, these deformations being caused by wind loading and gravity loading. Such deformations are typically referred to as flapwise bending and edgewise bending in the wind turbine industry. By locating the actuation device adjacent to the flap is advantageous because it avoids any negative effects that may occur if the actuator is placed remotely from the flap. For instance, it avoids the need for any connecting rods or such like that extend from the actuator to the flap and which would be subject to deformation when the wind turbine is in use.

Preferably, the flap comprises a trailing edge and a front end opposite the flap trailing edge, and the front end of the flap is pivotally connected to the blade body. By "pivotally" is meant that the flap can pivot or rotate relative to the blade body. This may be provided by a simple hinge or bearing, or the flap may be constructed from a deformable rubber material that can deflect relative to the blade body. Alternatively, the flap may be formed as a deformable trailing edge. The flap is substantially rectangular in shape when viewed from above, and the opposite edge to the trailing edge, in the upwind direction, is defined as the front end of the flap. This front end may be pivotally connected to the blade body so that it can rotate relative to the blade body. The connection to the blade body may be a hinge or bearing for example. The front end of the flap defines a surface in the thickness direction and the hinge or bearing may be located at any height along the thickness of the front end. In another example, the flap may be formed from a flexible material such as a thermoplastic or composite where an upper surface of the flap is fixed to an upper surface of the blade body, and a lower surface of the flap can slide relative to a lower surface of the blade body.

The flap may be separated from the actuation device in a chordwise direction of the rotor blade, the flap being connected to the translating part of the actuation device via a connection arm, the connection arm being disposed in the chordwise direction of the rotor blade; a first end of the connection arm is attached to the translating part of the actuation device and a second end of the connection arm is attached to the front end of the flap such that movement of the connection arm in a direction su bstantially corresponding to the thickness of the rotor blade causes the flap to pivot about its front end.

Preferably, the flap has a flap length in the longitudinal direction of the rotor blade, and the linear motor is located within the rotor blade, in an area bounded at least partly by the flap length. The "longitudinal direction" may also be referred to as the "spanwise" direction, that is, it is the direction from a root end of the rotor blade to a tip end of the rotor blade. By having the linear motor disposed in a region bounded by the flap length means that the linear motor is adjacent to the flap and is not remote from the flap. The actuation device is thus compact. The thickness of a rotor blade is the distance between the suction surface and the pressure surface of the airfoil profile that makes up the rotor blade.

The wind turbine rotor blade may further comprise a guide for guiding the connection arm. The connection arm may follow a certain path in a direction substantially corresponding to the thickness of the rotor blade, and the use of a guide will retain the connecting arm to follow the correct track.

The actuation device may be an arc shaped linear motor; and the stationary part comprises one of a magnet or an armature and the translating part is the other of the magnet or the armature; the translating part moves within a guide defined by the stationary part in a direction substantially corresponding to the thickness of the rotor blade. The arc shaped motor may be an arc brushless motor. The use of an arc shaped linear motor allows for a compact actuation device which can deliver precise angular positioning of the flap at high speed. The linear motor may be disposed such that the translating part moves along an axis substantially parallel to the longitudinal axis of the rotor blade.

The linear motor may be disposed such that the translating part moves along an axis substantially parallel to the chordwise direction of the rotor blade.

The wind turbine rotor blade may further comprise guide means fixed to the translating part; wherein the first end of the connection arm is connected to the guide means and the guide means are arranged such that movement of the translating part causes movement of the connection arm in a direction substantially corresponding to the thickness of the rotor blade.

The guide means may comprise a slot or projection in which the first end of the connection arm is configured to slide, the slot or projection extending along an axis which is inclined at an angle relative to the movement of the translating part.

The rotor blade may have a plurality of flaps and each flap may be actuated by a separate actuation device. In the longitudinal direction of the rotor blade, a plurality of flaps may be provided which can all be actuated separately. This provides a high degree of control as each flap can be deflected individually to reduce the loads experienced in the region of that flap.

The rotor blade may have a plurality of flaps and the plurality of flaps are actuated by a single actuation device. This will reduce costs associated with the actuation device as only one is needed to control a plurality of flaps.

According to a second aspect of the present invention there is provided a wind turbine generator having a rotor blade according to any one of the preceding claims. The wind turbine generator may be a three bladed horizontal axis wind turbine, where the rotor blades are mounted to a hub on a nacelle, supported by a tower.

The invention will now be described by way of examples with reference to the accompanying drawings in which:

Figure 1 illustrates a cross section of a wind turbine rotor blade according to the present invention.

Figure 2 illustrates a perspective view of a section of a wind turbine rotor blade according to the present invention.

Figure 3 illustrates a perspective view of a first example of a linear motor actuator according to the present invention.

Figure 4 illustrates a perspective view of a second example of a linear motor actuator according to the present invention.

Figure 5 illustrates a perspective view of a counter balance system according to the present invention. Figure 6 illustrates a perspective view of a third example of a linear motor actuator according to the present invention, where the upper skin of the rotor blade is not shown for clarity.

Figure 7 illustrates a cross section of the third example of a wind turbine rotor blade according to the present invention.

Figure 1 shows a cross-section of a wind turbine rotor blade 10. The blade comprises a blade body 1 1 and a flap 12. By "flap" is meant a moveable control surface that alters the aerodynamic profile of the airfoil section of the rotor blade 10. The rotor blade 10 has a leading edge 13 and a trailing edge 14, an upper skin 15 which forms the suction surface of the rotor blade and a lower skin 16 which forms the pressure surface of the rotor blade. The flap 12 deflects towards the suction side or the pressure side as indicated by the double headed arrow in Figure 1 . A spar 17, which extends from a root end of the rotor blade to a tip end of the rotor blade is provided which provides the primary strengthening structure of the rotor blade 10. A trailing edge spar 18 which also extends from the root end to the tip end is provided near the trailing edge 14 to provide an additional strengthening structure in order to support the flap 12. The spars 17 and 18 form part of the blade body 1 1. In an alternative example, the trailing edge spar 18 is only provided in the region of the flap 12 to provide additional strength in that region, rather than extending from the root end to the tip end.

Figure 2 shows a partial section of a rotor blade 10. As can be seen, the flap 12 forms part of the trailing edge 14.

Figure 3 shows a first example of an actuator system for causing the flap 12 to deflect. The flap 12 has a front end 19 opposite the trailing edge of the flap, the front end 19 being in the upwind direction relative to the trailing edge of the flap. The flap 12 is mounted to the trailing edge spar 18 (not shown in Figure 3 for clarity) so that it can pivot about the front end 19.

An actuator designated as 20 comprises a linear electric motor orientated in the chordwise direction of the rotor blade 10, that is in a direction between the leading edge and the trailing edge. The linear motor comprises a track which is formed from two arrays of stationary permanent magnets 21 a and 21 b orientated either side and surrounding a core 22 formed from a conductive coil. When a current is applied to the core 22 it will undergo reciprocating movement between the magnet arrays 21 a and 21 b in a chordwise direction as shown by the double headed arrow in Figure 3. The direction of movement and the speed of movement can be controlled by the current that is applied to the core 22. When the coil 22 moves in a chordwise direction, the flap 12 is caused to deflect as explained below.

Mounted rigidly to the core 22 is a block 23 which slides in a chordwise direction on a rail 24. The stationary parts of the linear motor 20, that is the track and the rail 24 are rigidly mounted (by means not shown) to the blade body 1 1 , and in this example to the spar 17.

The block 23, which in use translates in the chordwise direction of the rotor blade

10, has at an end a guide 25 which is mounted at an acute angle to the chordwise direction as shown in Figure 3. The guide 25 is rigidly mounted to the block 23.

Two connecting arms 26a and 26b, which are spaced in the longitudinal direction of the rotor blade 10, extend in a chordwise direction from the front end 19 of the flap 12.

By causing these connecting arms 26a and 26b to pivot about the front end 19 of the flap

12, the flap deflects as shown in Figure 1 . The connecting arm 26a is forced to pivot about front end 19 by the guide 25 such that the connecting arm moves substantially in the thickness direction of the rotor blade 10, that is in a direction between the upper skin

15 and the lower skin 16.

A boss 27 connects the guide 25 to the connecting arm 26a. The boss 27 comprises a slot 28 which is shaped to receive the guide 25 as shown in Figure 3. the boss 27 also comprises a circular protrusion 29 which is free to rotate in a corresponding hole in the connecting arm 26a. As is apparent from Figure 3, when the core 22 moves in the chordwise direction indicated by the double headed arrow, the connecting arm 26a is forced upwards and downwards in the thickness direction, and this causes the flap 12 to pivot about front end 19.

An array of rollers 30 is provided at the end of the connecting arm 26a and 26b, opposite the flap 12, which surround a guide 31 to guide the arc like movement of the connecting arm 26a.

A beam 32 extends from the front end 19 in a chordwise direction towards the leading edge. This is arranged so that it will hit a brake unit 33 to limit the movement of the flap 12.

In this example, the actuator 20 which is formed of a linear motor is orientated in the chordwise direction of the rotor blade. This means that the linear motor does not suffer from any centrifugal effects as the rotor rotates about a hub of the wind turbine.

Figure 4 shows, in a second example, an actuator 20 which comprises a linear motor which is orientated in the longitudinal direction of the rotor blade 1 0. The component parts of the linear motor are not described here but they comprise a stationary core 40 and a moving track 41.

The moving track 41 of the linear motor translates in a reciprocating direction indicated by the double headed arrow in Figure 4, that is a reciprocating movement in the longitudinal direction of the rotor blade 10. A guide 42 fixed to the moving track 41 is provided with a slot 43 which extends at an acute angle relative to the longitudinal direction of the rotor blade 10. The slot 43 receives the first end of a connecting arm 44 and the first end of the connecting arm 44 is arranged so that it will slide in the slot 43. The connecting arm 44 is fixed at a second end to the front end 19 of the flap 12. The connecting arm 44 pivots about the front end 19 and, as is apparent from Figure 4, when the guide 42 moves in the longitudinal direction of the rotor blade 10, the connecting arm 44 is forced up and down in the thickness direction of the rotor blade 10. This causes the flap 12 to pivot about the front end 19 because the flap 12 is fixed to the connecting arm 44.

During operation of the wind turbine, each rotor blade 10 rotates about the hub, and the actuator 20 in the second example may be subjected to a centrifugal force of between 10G to 20G for a typical megawatt wind turbine generator. This centrifugal force will try to force the moving track 41 in the longitudinal direction of the rotor blade towards the tip end. Figure 5 shows how a counter balance system 50 is constructed to avoid these high G forces. The moving track 41 of the actuator 20 is connected to a counter weight 51 via a series of pu lleys 52 and tensioners 53. A cable 54 connects counterweight 51 and the moving track 41. The counterweight 51 has approximately the same mass as the moving track 41 and moves in the opposite direction to the moving track and thus cancels out the centrifugal force acting on the moving track 41 . The pulleys 52 and the tensioners 53 are fixed to the blade body 1 1 when the counter balance system 50 is installed in a wind turbine blade 10.

Figures 6 and 7 show, in a third example, an actuator 20 which comprises an arc brushless motor. The actuator 20 in this third example comprises four arrays of permanent magnets, 61 a, 61 b, 62a and 62b. As shown in Figures 6, the magnet arrays form a track in the shape of an arc extending in the thickness direction of the rotor blade 10. A coil 63 formed of a conductive material is arranged between the magnets 61 a and 61 b and is configured to move in the arc shape defined by the magnets 61 a and 61 b. The magnet arrays 62a and 62b arrays are spaced from the magnet arrays 61 a, 61 b in the longitudinal direction of the rotor blade 10 and also surround a coil 64. The magnets in this example are permanent magnets and may be constructed from neodymium coated with nickel. The magnet arrays are mounted to the spar 17 by means not shown.

In operation, the coils 63 and 64 are energised and so move in the arc shape defined by the magnet arrays 61 a, 61 b, 62a, 62b. Connected to and fixed between the coils 63 and 64 is a connecting arm 65. At the other end of the connecting arm 65 is fixed the front end 19 of the flap 12, which is pivoted about a position on the trailing edge spar 18. Movement of the coils 63 and 64 causes the connecting arm 65 to reciprocate in the thickness direction of the rotor blade 10 such that flap 12 pivots about the trailing edge spar 18.

In the three examples described above, the actuator 20 may be constructed so that either the magnets are stationary and the conductive coil moves, or the magnets move and the conductive coil is stationary. Power may be provided to the conductive coils by means of a cable from the root end of the rotor blade 10, with a power and control unit being mounted in the nacelle or the hub of the wind turbine.

As shown in Figure 2, a single flap 12 is provided at the trailing edge of the rotor blade 10. However, a plurality of flaps may be provided along the trailing edge. These may be actuated by a single actuator in a group, or each individual flap may have its own associated actuator.

A control unit (not shown) is provided in the rotor blade 10 to measure the aerodynamic loads on the blades, for instance by way of pressure taps or strain gauges (not shown). The control unit will then calculate how the flap 12, or flaps, should be deflected to reduce the loads experienced on the blade 10 and then send a signal to the actuator 20 to control the flap 12 or flaps. The control unit may also be provided in the hub or nacelle of the wind turbine.