MEASUREMENT ARRANGEMENT FOR A WIND TURBINE

Abstract

A measuring arrangement for a wind power installation for determining a thrust force of the rotor. A measuring device detects a first bending moment of the tower at a first height and a second bending moment of the tower at a second height, which is different from the first height. The first and second bending moments are in this case made up in each case of a natural moment component, a pitching moment component and a thrust force component. A thrust force determining unit determines a thrust force of the rotor based on a comparison of the at least first and second bending moments, so that the natural moment component and the pitching moment component cancel one another out.

Claims

1. A measuring arrangement of a wind power installation having a tower and an aerodynamic rotor with at least one rotor blade, the measuring arrangement comprising: a measuring device configured to detect a first bending moment of the tower at a first height and a second bending moment of the tower at a second height, wherein the second height is different from the first height, each of the first and second bending moments being made up of: a natural moment component, a pitching moment component, and a thrust force moment component; and a processor configured to: compare the first and second bending moments to determine a first comparison value; determine a thrust force of the aerodynamic rotor based on the first comparison value determined based on a comparison of the at least first and second bending moments, the first comparison value being independent of the natural moment component and the pitching moment component.

2. The measuring arrangement as claimed in claim 1, wherein the measuring device having a first sensor for detecting the first bending moment of the tower at the first height and a second sensor for detecting the second bending moment of the tower at the second height.

3. The measuring arrangement as claimed in claim 2, wherein the first sensor is arranged directly under a nacelle of the wind power installation, and wherein the second sensor is arranged proximate a foot of the wind power installation.

4. The measuring arrangement as claimed in claim 2, wherein the first and second sensors include strain gauges.

5. The measuring arrangement as claimed in claim 1, wherein the first comparison value is a difference between the first and second bending moments.

6. The measuring arrangement as claimed in claim 5, wherein the thrust force is based on the first comparison value and a difference in height between the first and second heights.

7. The measuring arrangement as claimed in claim 2, wherein the measuring device has at least a third sensor for detecting a third bending moment of the tower at a third height, the third height being between the first and second heights.

8. The measuring arrangement as claimed in claim 7, wherein the processor is configured to determine at least a second and a third comparison value, the second comparison value being formed as a difference between the first and third bending moments the third comparison value being formed as a difference between the third and second bending moments.

9. The measuring arrangement as claimed in claim 8, wherein the processor is configured to determine a first thrust value based on the first comparison value on a difference in height between the first and second heights, a second thrust value based on the second comparison value and a difference in height between the first and third heights, and a third thrust force based on the third comparison value and a difference in height between the third and second heights.

10. The measuring arrangement as claimed in claim 9, wherein the processor is configured to determine the thrust force of the rotor as a mean value of at least two of the first, second and third thrust forces, or the processor is configured to determine the thrust force of the rotor as a weighted combination of the first, second and third thrust forces, weights of the combination being based on a measure of the accuracy of the first, second and third thrust forces.

11. A wind power installation with the measuring arrangement as claimed in claim 1, the wind power installation being configured to be operated in dependence on the determined thrust force.

12. A wind farm for generating electricity, the wind farm having: at least one wind power installation as claimed in claim 11; a processor configured to determine a turbulence of at least one wind power installation based on the thrust force of the aerodynamic rotor of the at least one wind power installation; and a wind farm controller configured to control the at least one wind power installation.

13. A method for determining a thrust force of an aerodynamic rotor of a wind power installation, the method comprising: detecting a first bending moment of a tower of the wind power installation at a first height and detecting a second bending moment of the tower at a second height, wherein the second height is different from the first height, the first and second bending moments, each including: a natural moment component, a pitching moment component and a thrust force moment component; comparing the first and second bending moments to determine a first comparison value; and determining a thrust force based on the first comparison value, the first comparison value being independent of the natural moment component and the pitching moment component.

14. A method for operating a wind power installation, wherein the wind power installation is operated using the thrust force as determined in the method as claimed in claim 13.

15. A method for operating a wind farm, the method comprising: determining a turbulence of at least one wind power installation based on a thrust force of the rotor of the at least one wind power installation; and controlling the wind power installations of the wind farm by reducing an output of the at least one wind power installation of the wind farm so that effects of the turbulence of the at least one wind power installation on other wind power installations of the wind farm are reduced.

16. The wind farm as claimed in claim 14, wherein the wind farm controller is configured to cause the at least one wind power installation to reduce its output so that effects of the turbulence of the at least one wind power installation on other wind power installations of the wind farm is reduced.

17. The measuring arrangement as claimed in claim 2 wherein the strain gauges of the first and second sensors are full strain gauge bridges.

18. The measuring arrangement as claimed in claim 6, wherein the thrust force is a ratio of the first comparison value and the difference in height.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0044] The present invention is now explained in more detail below by way of example on the basis of exemplary embodiments with reference to the accompanying figures.

[0045] FIG. 1 shows a schematic view of a wind power installation having a measuring arrangement.

[0046] FIG. 2 shows a schematic view of the composition of bending moments acting on a wind power installation.

DETAILED DESCRIPTION

[0047] FIG. 1 shows a wind power installation 100 with a tower 102 and a nacelle 104. Arranged on the nacelle 104 is an aerodynamic rotor 106 with rotor blades 108 and a spinner 110. During operation, the rotor 106 is set in a rotational motion by the wind and thereby drives a generator in the nacelle 104.

[0048] Also arranged on the tower 102 of the wind power installation 100 is a measuring device, the measuring device having a first sensor 112, a second sensor 114 and a third sensor 116. The first, second and third sensors 112, 114, 116 are designed in each case for determining the bending moment of the tower 102 of the wind power installation 100 at the respective height.

[0049] In this exemplary embodiment, the first, second and third sensors 112, 114, 116 are formed by in each case by at least two full strain gauge bridges. In this case, the full strain gauge bridges are configured in such a way that a measuring grid foil with a thin resistance wire is applied to the surface of the tower 102, it being possible by means of a Wheatstone bridge circuit, in particular in the embodiment of a full bridge, for changes in the length of the resistance wire to be measured as changes in the resistance of the resistance wire. Such strain measuring sensors make it possible even to determine very small changes, in particular bends, of the carrier, that is to say here the tower 102 of the wind power installation 100, with great accuracy.

[0050] FIG. 2 schematically shows which components make up a determined bending moment of the tower 102 of the wind power installation 100. The mass of the nacelle 104 produces a force of weight 202, which acts on the center of gravity 201 of the nacelle 104. Since the weight of the rotor blades 108 shifts the center of gravity in the direction of the rotor 106, the center of gravity 201 of the nacelle 104 generally lies outside a vertical center axis 120 of the tower 102 in the horizontal direction. As a result, the mass of the nacelle 104 causes a natural moment on the tower 102 of the wind power installation 100. This natural moment is determined from the force of weight 102 that acts on the nacelle 104, and the distance 203 between the center of gravity 201 of the nacelle 104 and the center axis 120 of the tower 102. The following formula is obtained for the natural moment:

M.sub.nat=FgI.sub.2,

[0051] where M.sub.nat is the natural moment of the nacelle 104, Fg is the force of weight 202 that acts on the nacelle 104 and I.sub.2 is the distance 203 between the center of gravity 201 of the nacelle 104 and the center axis 120 of the tower 102. It should be taken into account that the natural moment of the nacelle 104 acts constantly over the entire height H of the tower 102.

[0052] A pitching moment 210 also acts on the tower 102 of the wind power installation 100. The pitching moment 210 is caused by the different wind speeds in the rotor area that is flowed through. Thus, the wind speed generally increases from the bottom upward over the described rotor area, that is to say that a rotor blade 108 that is located above the nacelle 104 is exposed to a higher wind speed than a rotor blade 108 that is under the nacelle 104. The forces occurring as a result on the rotor blades 108 produce a pitching moment 210, the loading of the pitching moment 210 likewise remaining the same over the entire height H of the tower 102.

[0053] A thrust force 220 also acts on the rotor 106 in the direction of the wind, the thrust force 220 being applied directly at the center of gravity 201 of the rotor 106. This has the consequence that the thrust force 220 exerts a bending moment via the tower 102 as a lever on the tower 102. In particular, the bending moment of the thrust force 220 is dependent on the height H of the tower 102 and thereby obeys the law:

M.sub.thrust=F.sub.thrustH,

[0054] where F.sub.thrust is the thrust force 220, M.sub.thrust is the bending moment based on the thrust force 220 and H is the height of the tower 102 of the wind power installation 100.

[0055] The diagram 300 schematically shows once again the value of the bending moment with the height of the wind power installation 100. In this case, the bending moment is plotted on the x axis and the height of the wind power installation is plotted on the y axis. It can be seen from the schematic progression of the bending moment that the bending moment at each height is made up of three moment components, to be specific the natural moment component 301, the pitching moment component 302 and the thrust force moment component 303. Since, as explained above, the natural moment component 301 and the pitching moment component 302 are constant over the height H of the tower 102, only the thrust force moment component 303 exhibits a progression, which is dependent on the height H of the tower 102, in particular proportional to the height H of the tower 102. It follows from this that, when a bending moment at the height H2 is subtracted from a bending moment at the height H1, the natural moment component 301 and the pitching moment component 302, which are constant over the height, and consequently equal in both bending moments, cancel one another out. What remains is an element of the thrust force moment component 303.

[0056] Since the thrust force moment component 303 is directly proportional to the height H of the tower 102, it is generally possible by means of the formula:

F.sub.thrust=(B1B2)/(H1H2)

to calculate the thrust force 2201 that acts on the rotor 106, where B1 is a first bending moment, B2 is a second bending moment and H1 is a first height and H2 is a second height of the respective bending moment.

[0057] Based on the above findings concerning the composition of the bending moments that act on the tower 102 of the wind power installation 100, it is therefore possible by means of measuring the bending moments at least two heights H1, H2 to determine the thrust force 220 that acts on the rotor 106.

[0058] In the embodiment shown here, the bending moment is determined by means of the first sensor 112, the second sensor 114 and the third sensor 116 respectively at a first height H1, a second height H2 and a third height H3. It is consequently possible by

V1=B2B1

to determine a first comparison value V1, where V1 is the first comparison value, B1 is the bending moment, which is measured by the first sensor 112, and B2 is the second bending moment, which is measured by the second sensor 114. Furthermore, it is possible by

V2=B3B1,

V3=B2B3,

to determine a second and a third comparison value, where V2 is the second comparison value, V3 is the third comparison value and B3 is the bending moment, which is measured by the third sensor 116.

[0059] As emerges from the schematic representation 300 and has been explained above, all three comparison values only contain elements of the thrust force moment component 303. It can likewise be seen from the schematic representation 300 that the thrust force component 303 decreases constantly with the height. It follows from this that, with correct measurement of the bending moment, the second and third bending moments are equal, so it should therefore be that V2=V3. Since, in this exemplary embodiment, the third sensor 116 is provided midway between the first sensor 112 and the second sensor 114, it is also the case that the second comparison value and the third comparison value should be exactly half the first comparison value. If the calculated comparison values deviate too much from these stated conditions during the operation of the wind power installation, this is an indication that the function of at least one of the sensors is faulty. In particular, a safety margin within which correct functioning of the sensors is ensured can be fixed.

[0060] As explained above, a first, second and third thrust force of the rotor 106 can be calculated by

F.sub.thrust1=V1(H1H2),

F.sub.thrust2=V2/(H2H3),

F.sub.thrust3=V3/(H1H3)

where H1 is the height at which the first sensor 112 measures the bending moment, H2 is the height at which the second sensor 114 measures the bending moment and H3 is the height at which the third sensor 116 measures the bending moment.

[0061] Allowing for the measuring accuracy, consequently all three calculated thrust forces should be equal. For determining the thrust force 220 of the rotor 106 while allowing for the measuring accuracy of the various sensors, the three thrust forces calculated above may be used in the following formula:

[00001]$F_{\mathrm{thrust}}=\underset{i}{.Math.}.Math.W_i{F}_{\mathrm{thrust},i}$

where i ranges from 1 to 3 in this exemplary embodiment and Wi are weights that replicate the accuracy of the respective measured values. For the weights Wi it is also the case that the sum of all the weights must correspond to one. The weights Wi may for example be dependent on the difference in height, which is entered into the respective calculation of the thrust force. In this case, a greater difference in height is indicative of a more accurate calculation of the thrust force than a smaller difference in height. Furthermore, the weights Wi may comprise information about known measuring accuracies of the sensors used at individual heights. In this way explained above, a particularly accurate determination of the thrust force 220 that acts on the rotor 106 is possible.

[0062] This makes it possible to determine the turbulence in the wake of the rotor 106 based on the thrust force 220 determined of the rotor 106. In particular, the thrust coefficient of the rotor 106 can be determined from the measured thrust force 220. It applies here that: the higher the value of the thrust coefficient, the more turbulences are produced in the wake by the rotating rotor 106.

[0063] As a result of this direct relationship, the control of the wind power installation 100 based on the thrust force 220 or the thrust force coefficient brings about a direct control of the turbulence that is produced in the wake by the rotor 106.

[0064] If the wind power installation 100 is in a wind farm, the wind power installation 100 can be operated in such a way that, based on the determination of the thrust force 220, the turbulences are reduced in such a way that the other wind power installations of the wind farm are not influenced over and above a certain amount. In particular, when there are critical thrust forces, the wind power installation 100 can be operated in a reduced-output mode. This makes it possible to integrate more wind power installations per unit area into the wind farm at the planning stage, without compromising safety and while at the same time increasing the energy yield.

[0065] In the embodiment described above, the measuring arrangement comprises three sensors. In another embodiment, the measuring arrangement may however also have two sensors or more than three sensors.

[0066] In the embodiment described above, full strain gauge bridges are used as sensors. In another embodiment, however, other sensors that are designed for determining bending moments of the tower of the wind power installation may also be used, for example optical strain sensors.