WO2018206065A1

WO2018206065A1 - Individual pitch control with hub sensor

Info

Publication number: WO2018206065A1
Application number: PCT/DK2018/050096
Authority: WO
Inventors: Michael Friedrich
Original assignee: Envision Energy (Denmark) Aps
Priority date: 2017-05-10
Filing date: 2018-05-07
Publication date: 2018-11-15
Also published as: DK179515B1; DK201770330A1

Abstract

A system for load control of a wind turbine is disclosed. The wind turbine comprises a nacelle having a main structure, a rotor, which rotor comprises at least two rotor blades, each mounted to a rotor hub via a root end of the rotor blade. The rotor hub is connected with a rotatable main shaft which is supported in a bearing structure which can be of any bearing configuration. The rotatable main shaft is connected with a generator for producing electricity. The system further comprises displacement sensors arranged for detecting a displacement. One or more sensors to detect axial displacement are arranged at the root end of the rotor blade in order to detect changes in the axial distance between the root end of the rotor blade and a reference surface on a reference part being fixed to the main structure. The changes in axial distance indicate unwanted loads on the rotor. The system comprises a control circuit coupled with the one or more sensors to mitigate load causing the axial displacement.

Description

Individual pitch control with hub sensor Field of the Invention

The present invention relates generally to the field of wind turbines, and more particu- larly to a control system for load control of a wind turbine through the use of displacement sensors being a part of the control system.

System for load control of a wind turbine comprising a nacelle having a main structure, a rotor, which rotor comprises at least two rotor blades, each mounted to a rotor hub via a root end of the rotor blade, which rotor hub is connected with a moment bearing structure or a main shaft which is supported in a bearing structure, which bearing structure is arranged for transferring the load on the rotor towards the main structure of the nacelle, which system further comprises displacement sensors arranged for detecting a displacement.

Preferably the wind turbine is arranged for individual pitch control.

Moreover the invention relates to the use of such system for determining blade root deflection or the blade root bending. It is clear that it is not a main shaft deflection which is determined with the system.

The present invention relates to a low wind turbines. These wind turbines will have a large rotor diameter and accordingly high loads are generated. Individual pitch control (IPC) is used in these wind turbines.

However, the system can also be used for large rotors, large rating turbines, set up in high wind sites.

This requires measurements of the loads on the individual rotor blades. Background of the Invention

Rotor blades are the primary elements of wind turbines for converting wind energy into electrical energy. The rotor blades have the cross-sectional profile of an airfoil such that, during operation, air flows over the rotor blade producing a pressure differ- ence between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the rotor blade. The lift force generates torque on a main shaft. The main shaft is connected with a generator for producing electricity.

A system for load control is known which includes detectors to measure the deflection of the main shaft in a wind turbine. Such detectors are used for a measurement of the deflection of the main shaft. Examples are disclosed in US 2004/0151575 Al and US 20090129924 Al .

In Direct Drive wind turbines, such measurement is not possible as such wind turbines would have the generator arranged directly on the hub or shaft of the rotor. Thus, it will not have a main shaft where the deflection measurement can be conducted. The shaft of the rotor is supported in a main bearing which absorbs the bending and lateral forces from the rotor.

A system is known which makes use of strain gauge sensors arranged in the rotor blade. An example is disclosed in WO 2005/071382 A l , This system has the advantage that the measurements will provide an exact value for the load on each rotor blade. However, this system is complicated and therefore also expensive.

US 2004/0151577 discloses a system for load control and of the type mentioned byway of introduction. This system comprises displacement sensors to detect axial displacement. There is no disclosure of arranging the sensors at the root end of a blade.

There exists a need for a svstem for load control of a wind turbine, whether or not it is a Direct Drive wind turbine, and usable for any bearing configuration which makes it possible to obtain a measurement for each individual rotor blade and which may be technical simple and which provides for an individual pitch control. Object of the Invention

It is the object of the present invention to obtain a system for load control of a wind turbine which has the advantage that it may be used for individual pitch control and which may be produced in a mechanical simple way at low cost. It is a further object that the system may be used in wind turbines having different bearing structure for the shaft of the rotor.

Description of the Invention

This object is obtained with a system for load control of a wind turbine of the type mentioned in the introductory paragraph and being peculiar in that one or more sen- sors to detect axial displacement between the blade root and the main structure are arranged at the root end of the rotor blade in order to detect changes in the axial dis- tance between the root end of the rotor blade and a reference surface on a reference part being fixed to the main structure, which changes in axial distance indicate unwanted loads on the rotor and that said system comprises a control circuit coupled with the one or more sensors to mitigate load causing the axial displacement.

The object is also obtained with the use of a system according to the invention for determining blade root deflection.

The present invention makes use of one or more sensors which may be denoted as hub sensors for determining blade root deflection.

The unwanted loads on the rotor may be asymmetrical loads.

One or more sensors are arranged in connection with each of the rotor blades in close proximity of the end of a rotor blade. One or more sensors are arranged in a position opposite to a reference surface which is arranged on a part being fixed to the main structure. Seeing that the main structure will be very stiff and seeing that a load on a rotor blade provided with said one or more sensors would cause a deflection and, accordingly, also a change in the axial distance between the blade root and the main structure the signal from the sensor may be used in a control circuit in order to mitigate load causing the actual change in the distance between the blade root and the main structure. It is possible to mitigate load causing the axial displacement in different ways. If it is a pitch regulated wind turbine the control circuit will be coupled to a pitch regulation in order to mitigate load. It is possible to effect an individual pitch control, and accordingly, it is also possible to effect an individual pitch regulation of the associated rotor blade. The hub sensor is used for detecting the change in distance which is an expression for the deflection and which is also an expression for the load on the rotor blade.

With this invention, it is possible to obtain a construction which is technically simple and still gives a secure basis for the control in order to mitigate load. There is no need to have any sensors arranged in the rotor blade. Moreover, when measuring at the hub of the root end of the rotor blade and the fixed main structure it is possible to make use of the system in connection with any bearing structure for the rotor shaft. There is no need for having a main shaft with more main bearings and it is possible to make use of the system in a Direct Drive wind turbine in which a main bearing is used for the rotor shaft.

The measurements of the loads on the individual rotor blades are effected through measurements and control of the tilt/yaw moments of the hub. According to a further embodiment the system according to the present invention is peculiar in that the one or more sensors are included in but not limited to: light emitting sensors, ultrasonic sensors, laser sensors and/or inductive sensors.

The system is not sensible to the type of sensor chosen. Accordingly, it is possible to choose any sensor which will be suitable for detecting an axial displacement.

According to a further embodiment the system according to the present invention is peculiar in that the rotor blades are mounted to the rotor hub via a pitch bearing and that the mitigation of loads is effected by controlling pitch of one or more rotor blades. When using the system in a pitch regulated wind turbine it is possible to effect the mitigation of load by controlling the pitch of one or more rotor blades.

According to a further embodiment the system according to the present invention is peculiar in that said reference part being fixed to the main structure is an outer or inner ring of a moment bearing being part of the bearing structure or a ring attached to the main structure or the main structure itself.

The reference part used should be fixed to the main structure in order to have secure reference surface.

Preferably, the outer or the inner ring of the bearing being a part of the bearing structure is used. Preferably, the ring is a stiffening ring attached to the bearing in the main bearing. Alternatively the reference part may be a part of the main structure itself. Hereby, a secure measurement of the change in the axial distance between the blade root and the main structure - and thus the deflection - is obtained.

According to a further embodiment the system according to the present invention is peculiar in that the one or more sensors are attached to the pitch bearing via a bracket. When a pitch regulated wind turbine is used the sensor will, in a very simple way, be connected via a bracket which is attached to the pitch bearing.

The connection to the pitch bearing ensures that a secure signal for blade deflection is obtained.

According to a further embodiment the system according to the present invention is peculiar in that said bracket is attached to the pitch bearing by the standard bolts used for fastening the pitch bearing to the rotor hub. Attaching a bracket to the pitch bearing by the standard bolt is a technically simple solution, which does not require any machining of any part of the rotor hub or rotor blade. In practice it has shown that the length of the bolts would be sufficient to arrange the bracket on the bolts and after that connecting the nuts.

According to a further embodiment the system according to the present invention is peculiar in that the sensor is mounted displaceable in the bracket so that the distance from the sensor to the reference surface may be adjusted.

Even though the system may be calibrated with the sensor in a given position, it is preferred that the sensor is mounted displaceable in the bracket in order to adjust the distance between the sensor and the reference surface. Such displacement can be ef- fected by providing the sensor with a thread and connect the sensor with the bracket with two nuts which are arranged on each side of the bracket in order to adjust the sensor. Other adjustment structures could also be used. Moreover, it is also preferred that the bracket comprises elongated holes, making it possible to displace the sensors in a direction which is parallel with the reference surface, in order to have the correct positioning of the sensor relating to a reference surface. In this respect it should be remembered that the sensor will rotate together with the hub, whereas the reference surface would stand still.

According to a further embodiment the system according to the present invention is peculiar in that it comprises means to provide individual pitch control (IPC) working continuously. The system could be arranged for different working conditions. However, it is preferred that the control system comprises means making it possible to have a continuously individual pitch control. Hereby, it is possible to mitigate load continuously.

According to a further embodiment the system according to the present invention is peculiar in that said bearing structure comprises a rotor bearing in form of a moment bearing.

As mentioned earlier it is possible to use the system in connection with different bearing structures. In the specific embodiment, the bearing structure is provided in form of a moment bearing or main bearing which would absorb the bending and lateral forces from the rotor. In such bearing structure, it is not possible to detect lateral deflection of a main shaft and accordingly, the system would be especially suitable for use in such wind turbine structure. This structure is used in Direct Drive wind turbines.

Description of the Drawing

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Fig. 1 shows perspective view of a wind turbine, Fig. 2 shows a cross section of a wind turbine nacelle and rotor hub,

Fig. 3 shows a perspective view of the bracket to which a sensor is mounted, Fig. 4 shows a partial perspective view of the bracket and with the sensor in a position opposite a reference surface,

Fig. 5 shows a partial perspective view of the bracket mounted on the pitch bearing and

Fig. 6 shows a partial view corresponding to Fig. 5 but seen from another angle.

Detailed Description of the Invention

In the following text the figures will be described one by one, and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

Position number list

1 Wind turbine

2 Wind turbine tower

3 Nacelle

4 Wind turbine blade having a root end 4a

5 Rotor hub

6 Generator unit

7 Main shaft

8 First end, rotor end

9 Second end, generator end

10 Mounting flange

11 Main bearing unit

12 Mainframe

13 First opening, rotor opening

14 Supporting bearing unit

15 Flange tube

16 Torque dampening unit

17 Central axis 18 Bracket

19 First part of bracket

20 Mounting holes for fixing bracket to pitch bearing

21 Intermediate part of bracket

22 Second part of bracket

23 Mounting holes for fixing mounting plate

24 Bolt for fixing mounting plate to bracket

25 Mounting plate

26 Sensor

27 Reference surface

28 Bearing unit

29 Stiffening ring of bearing in bearing unit

30 Bolt for stiffening ring

31 Bolt for pitch bearing

32 Pitch bearing

33 Axial distance

Fig. 1 shows an exemplary embodiment of a wind turbine 1 comprising a wind turbine tower 2, a nacelle 3 arranged on top of the wind turbine tower 2, and a rotor rotatably connected to the nacelle 3, e.g. a generator unit (not shown). The rotor comprises at least two wind turbine blades 4, here three are shown, mounted to a rotor hub 5. Each of the wind turbine blades comprises a root end 4a. A pitch bearing 32 is provided for connecting the blade 4 with the rotor hub 5. Fig. 2 shows a cross-section of the nacelle 3 and rotor where the nacelle cover housing is removed. The rotor hub 5 is connected to at least one/first generator unit 6 via a rotatable main shaft 7. The main shaft 6 has a first/rotor end 8 and a second/generator end 9. In this embodiment, the main shaft 6 has a constant diameter along the longitudinal length of the shaft as shown in fig. 2. The first end 8 is connected to a mounting flange 10 of the rotor hub 5. The second end 9 is connected to the generator unit 6, e.g. to a generator shaft thereof.

The rotor hub 5 is further connected to a main bearing unit 11, e.g. via another mounting flange as shown in fig. 2. The main bearing unit 1 1 comprises a first bearing part 11a and a second bearing part 1 lb. The first bearing part 11a is connected to a mainframe 12 of the nacelle 3. The second bearing part 1 lb is connected to the rotor hub 5. The main bearing unit 11 is arranged in a first/rotor opening 13 of the mainframe 12. The generator unit 6 is resting on the main shaft 6 via at least one supporting bearing unit 14, thus no support on the mainframe 12 is needed. The generator unit 6 is further placed at a predetermined distance, e.g. between 2 to 8 metres, from the main bearing unit 11 so that the bending moment of the generator unit 6 is used to counteract the bending moment of the rotor.

The generator unit 6 is further connected to a flange tube 15 at one end, e.g. a generator end. The flange tube 15 is at the other end, e.g. the rotor end, connected to at least one torque dampening unit 16. The flange tube 15 is configured to transfer the generator torque and other torque forces from the generator unit 6 to the torque dampening unit 16. The torque dampening unit 16 is arranged on a seat located on the mainframe 12. The torque dampening unit 16 and thus the seat are further aligned with the wind turbine tower 2, e.g. positioned over the central axis 17 of the wind turbine tower 2, to provide an optimal transfer of forces to the wind turbine tower 2. The main shaft 7 is arranged inside the flange tube 15 and extends through openings in the flange tube to allow for connection to the generator unit 6 and the rotor hub 5. The flange tube 15 has a cone-shaped structure where the diameter of the generator end is larger than the diameter of the rotor end. The main shaft 7 is supported in a bearing unit 28 in form of a main bearing. The main bearing absorbs all bending and lateral forces from the rotor.

Fig. 3 shows a bracket 18 which is used for mounting a sensor 26 to the pitch bearing as explained later. The bracket 18 consists of a first part 19 being a plane part provided with mounted holes 20 which are used for fixing the bracket to the pitch bearing on the rotor hub. The bracket has an intermediate part 21 consisting of two angled portions and a second part 22 of the bracket which is arranged on an angle being arranged in a plane substantially perpendicular to the plane of the first part of the bracket. The second part of the bracket 22 is provided with mounting holes 23 for fixing a mounting plate 25. The mounting holes 23 are elongated in order to make it possible to dis- place the mounting plate 25 and the sensor 26 arranged therein along the surface of the second part 22 of the bracket. Bolts 24 are used for fixing the mounting plate 25 to the bracket 18. The sensor 26 is displaceable substantially perpendicular to the plane of the mounting plate 25. In the illustration this is not illustrated in detail. However, it is possible to provide the sensor with a thread and provide a nut on each side of the mounting plate in order to arrange the sensor in any position desired in relation to the mounting plate 25. Hereby, the sensor 26 could be adjusted in relation to a reference surface 27 (illus- trated in fig. 4).

Fig. 4 is a partial perspective view of the bracket 18. It is seen that the bracket 18 is connected to the rotor hub 5 on the left hand side in such a way that the sensor 26 is arranged opposite the reference surface 27 which is arranged on a part of the bearing unit 28. The reference surface 27 is provided on a stiffening ring 29 of the bearing in the bearing unit. Hereby, the reference surface 27 is fixed in relation to the main structure of the nacelle.

Bolts 30 are used for attaching the stiffening ring 29 to the bearing structure.

Fig. 5 illustrates in more detail how the bracket 18 is connected to the pitch bearing 32. Bolts 31 which are used for attaching the pitch bearing 32 is also used for attaching the bracket 18. One can see that the end of the thread extends slightly above the used nut in a position where the bracket is mounted whereas the thread has a longer extension on the remaining part of the bolts 31.

This is a very simple and secure way of attaching the bracket and the sensor 26 connected therewith.

Fig. 6 has a picture corresponding to the one illustrated in figure 5, however, seen un- der an angle being substantially perpendicular compared to the thread in figure 5.

Figure 6 illustrates the mounting of the bracket 18 having the first part 19 and the second part 22 arranged substantially perpendicular to each other. The bracket has such configuration that the second part 22 of the bracket will be orientated substantially parallel to the reference surface 27 of the stiffening ring 29. An axial distance 33 is illustrated as a distance between the sensor 26 and the reference surface 27. This sensor is used for detecting changes in this axial distance 33.

The measurement is used in a control circuit (not illustrated) which is used to mitigate load when the changes in axial distance indicates unwanted load on the rotor.

It is noted that the embodiments illustrated above are examples, and that modifications are possible. It is also possible to combine the features from different embodiments.

Claims

1. System for load control of a wind turbine (1) comprising a nacelle (3) having a main structure, a rotor, which rotor comprises at least two rotor blades (4), each mounted to a rotor hub (5) via a root end (4a) of the rotor blade, which rotor hub (5) is connected with a moment bearing structure or a main shaft (7) which is supported in a bearing structure (11), which bearing structure is arranged for transferring the load on the rotor towards the main structure (12) of the nacelle (3), which system further comprises displacement sensors (26) arranged for detecting a displacement, characterised in that one or more sensors (26) to detect axial displacement between the blade root (4a) and the main structure (12) are arranged at the root end (4a) of the rotor blade in order to detect changes in the axial distance (33) between the root end (4a) of the rotor blade and a reference surface (27) on a reference part (29) being fixed to the main structure (12), which changes in axial distance indicate unwanted loads on the rotor and that said system comprises a control circuit coupled with the one or more sensors (26) to mitigate load causing the axial displacement,

2. System according to claim 1, characterised in that the one or more sensors (26) are included in but not limited to: light emitting sensors, ultrasonic sensors, laser sensors and/or inductive sensors.

3. System according to claim 1 or 2, characterised in that the rotor blades (4) are mounted to the rotor hub (5) via a pitch bearing (32) and that the mitigation of loads is effected by controlling pitch of one or more rotor blades (4).

4. System according to any one of the preceding claims, characterised in that said reference part being fixed to the main structure (12) is an outer or inner ring of a moment bearing (28) being part of the bearing structure or a ring (29) attached to the main structure or the main structure itself.

5. System according to claim 3 or 4, characterised in that the one or more sensor (26) are attached to the pitch bearing (32) via a bracket (18).

6. System according to claim 5, characterised in that said bracket (18) is attached to the pitch bearing (32) by the standard bolts (31) used for fastening the pitch bearing (32) to the rotor hub (5).

7. System according to claim 5 or 6, characterised in that the sensor (26) is mounted displaceable in the bracket (18) so that the distance from the sensor to the reference surface (27) may be adjusted.

8. System according to any one of the claims 3 - 7, characterised in that it comprises means to provide individual pitch control (IPC) working continuously.

9. System according to any one of the preceding claims, characterised in that said bearing structure comprises a rotor bearing (11) in form of a moment bearing.

10. Use of a system according to any one of the preceding claims for determining blade root deflection.