CONTROL SYSTEM FOR STABILIZING A FLOATING WIND TURBINE

Abstract

A control system for stabilizing a floating wind turbine is provided. The control system includes a measuring device configured for measuring a wind field and a wave field, a determining device wherein the determining device is configured for determining an excitation frequency spectrum of the floating wind turbine on the basis of the measured wind field and/or the wave field and/or a current floater pitch angle of the floating wind turbine, and wherein the determining device is further configured for determining a balanced state of the floating wind turbine, wherein in the balanced state a natural frequency is outside of the excitation frequency spectrum and/or the current floater pitch angle is equal to a pre-defined floater pitch angle. The control system further includes an adjustment device which is configured for manipulating the current floater pitch and/or the natural frequency until the balanced state is met.

Claims

1. A control system stabilizing a floating wind turbine, the control system comprising: a measuring device configured for measuring a wind field and/or a wave field; a determining device, configured for determining an excitation frequency spectrum of the floating wind turbine on a basis of the wind field and/or the wave field and/or a current floater pitch angle of the floating wind turbine, further wherein the determining device is further configured for determining a balanced state of the floating wind turbine, and in the balanced state, a natural frequency outside of the excitation frequency spectrum and/or the current floater pitch angle is equal to a pre-defined floater pitch angle; and an adjustment device which is configured for manipulating the current floater pitch angle and/or the natural frequency until the balanced state is met.

2. The control system according to claim 1, wherein the measuring device is configured for measuring the wind field acting on a blade of the floating wind turbine, and/or the measured wave field acting on a floating foundation of the floating wind turbine.

3. The control system according to claim 1, wherein the measuring device comprises a wave buoy, a light detection and ranging device, a radio detection and ranging device, an accelerometer.

4. The control system according to claim 1, wherein the measuring device comprises an accelerometer, an inclinometer, or a strain gauge attached to a mooring line of the floating wind turbine.

5. The control system according to claim 1, wherein the adjustment device is configured for manipulating the current floater pitch angle and/or the natural frequency by a pitch, a roll, a yaw, a surge, a sway or a heave of the floating wind turbine.

6. The control system according to claim 1, wherein the adjustment device is configured for manipulating the current floater pitch angle and/or the natural frequency by manipulating a mass, a buoyancy, or a draught of the floating wind turbine.

7. The control system according to claim 1, wherein the adjustment device comprises a mooring line actuator or a ballast tan with a water pump.

8. The control system according to claim 1, wherein the determining device is configured for determining an excitation frequency spectrum the floating wind turbine on the basis of the wind field and/or the wave field by using a dependency of the excitation frequency spectrum and the wind field and/or the wave field.

9. The control system according to claim 1, wherein the determining device is configured for determining a current floater pitch angle of the floating wind turbine on the basis of the wind field and/or the wave field by using a dependency of the floater pitch angle and the wind field and/or the wave field.

10. A floating wind turbine comprising a wind rotor comprising a blade; a tower; a floating foundation; and a control system according to claim 1.

11. A method for stabilizing a floating wind turbine, the method comprising: measuring a wind field and/or a wave field; determining an excitation frequency spectrum of the floating wind turbine on a basis of the wind field and/or the wave field and/or a current floater pitch angle of the floating wind turbine; determining a balanced state of the floating wind turbine, wherein in the balanced state the natural frequency is outside of the excitation frequency spectrum and/or the current floater pitch angle is equal to a pre-defined floater pitch angle; and manipulating the current floater pitch angle and/or the natural frequency until the balanced state is met.

Description

BRIEF DESCRIPTION

[0073] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0074] FIG. 1 shows a floating wind turbine according to an exemplary embodiment of the present invention;

[0075] FIG. 2 shows a floating wind turbine according to a further exemplary embodiment of the present invention in an unbalanced state;

[0076] FIG. 3 shows a floating wind turbine according to a further exemplary embodiment of the present invention in a balanced state;

[0077] FIG. 4 shows a floating wind turbine according to a further exemplary embodiment of the present invention in a further unbalanced state;

[0078] FIG. 5 shows a diagram of a frequency distribution of the floating wind turbine according to an exemplary embodiment of the invention in the unbalanced state of FIG. 4;

[0079] FIG. 6 shows a floating wind turbine according to a further exemplary embodiment of the present invention in a further balanced state; and

[0080] FIG. 7 shows a diagram of a frequency distribution of the floating wind turbine according to an exemplary embodiment of the invention in the balanced state of FIG. 6.

DETAILED DESCRIPTION

[0081] The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements or features are provided with the same reference signs or with reference signs, which are different from the corresponding reference signs only within the first digit. To avoid unnecessary repetitions elements or features which have already been elucidated with respect to a previously described embodiment are not elucidated again at a later position of the description.

[0082] FIG. 1 shows a floating wind turbine 100 according to an exemplary embodiment of the present invention. The floating wind turbine 100 comprises three blades 140 attached to a hub mounted to a nacelle 160, a tower 130 and a floating foundation 120. The floating wind turbine 100 further comprises a plurality of mooring lines. Only a first mooring line 151 and a second mooring line 154 are shown in FIG. 1 for clarity reasons. The first mooring line 151 is fixed to the floating foundation 120 by a first mooring line fixation 152 and to a sea floor 113 by a second mooring line fixation 153. Further, the second mooring line 154 is fixed to the floating foundation 120 by a further first mooring line fixation 155 and to a sea floor 113 by a further second mooring line fixation 156.

[0083] The floating foundation 120 is fixed by the first mooring line 151 and the second mooring line 152 in such a manner that the floating foundation 120 is dunked into sea water 114 under the sea surface 112. Therefore, the floating foundation 120 is held under water by the mooring lines and the self-weight. A wind 111 acts on the three blades 140 of the floating wind turbine 100 such that electrical energy may be generated by the floating wind turbine 100.

[0084] The floating wind turbine 100 floats in the sea water 114 and is held in position by the mooring lines, exemplarily illustrated by the first mooring line 151 and the second mooring line 154 in FIG. 1. The floating wind turbine 100 has six individual degrees of freedom in which the floating wind turbine 100 may move. Namely, three translations surge 103, sway 102 and heave 101, and three rotations roll 106, pitch 105 and yaw 104.

[0085] FIG. 2 shows a floating wind turbine 200 according to a further exemplary embodiment of the present invention in an unbalanced state.

[0086] The floating wind turbine 200 is tilted around the floater pitch 105 such that an offset 231 in the floater pitch angle occurs. The floating foundation 220, the rotor and the tower 230 are tilted around the floater pitch 105 due to the wind 211 acting onto the three blades 240.

[0087] A weight of the nacelle 260 together with forces due to the wind field 211 acting on the blades 240 compose a weight force 234. The weight force 234 comprises a first force component 232 and a second force component 233. The first force component 232 is parallel to an extension direction of the tower 230 and the second force component 233 is perpendicular to the first force component.

[0088] Therefore, in the unbalanced state as illustrated in FIG. 2 shearing forces are acting on a connection of the nacelle 260 and the tower 230 due to the offset 231.

[0089] FIG. 3 shows a floating wind turbine 300 according to a further exemplary embodiment of the present invention in a balanced state.

[0090] The floating wind turbine 300 comprises a nacelle 360, a tower 330 and a floating foundation 320. A measuring device 371 is configured for measuring the wind field 311 and a determining device 373 is configured for determining that the current floater pitch angle as shown in FIG. 2 has an offset 231 (illustrated in FIG. 2) relative to the pre-defined floater pitch angle. Subsequently an adjustment device 372 formed as a mooring line actuator manipulates the first mooring line 351 such that a length of the mooring line 351 in the balanced state as shown in FIG. 3 is shorter than a length of the mooring line 251 in the unbalanced state as shown in FIG. 2.

[0091] As a result, in the balanced state the weight force 334 extends in the same direction as a first force component 332 parallel to the extension direction of the tower 330. Therefore, in the balanced state as shown in FIG. 3, no shearing forces due to self-weight are acting on a connection of the nacelle 360 and the tower 330.

[0092] FIG. 4 shows a floating wind turbine 400 according to a further exemplary embodiment of the present invention in a further unbalanced state.

[0093] The floating wind turbine 400 comprises a nacelle 460, a tower 430 and a floating foundation 420 and is floatingly anchored to a sea floor 413 by mooring lines, exemplarily illustrated as a first mooring line 451 and a second mooring line 454 in FIG. 4. A first measuring device 471 formed as a light detection and ranging device (LIDAR) is mounted to the nacelle and measures a wave field 418 and a second measuring device 471 formed as an accelerometer is mounted to the tower 430. Furthermore, a determining device 473 is mounted to the floating foundation 420. The determining device 473 determines an excitation frequency spectrum of the floating wind turbine 400. Two adjustment devices 472 formed as water tanks are mounted to the floating foundation 420.

[0094] FIG. 5 shows a diagram of a frequency distribution of the floating wind turbine 400 according to an exemplary embodiment of the invention in the unbalanced state of FIG. 4.

[0095] In the diagram shown in FIG. 5 a graph is plotted showing power on the ordinate 582 and frequency on the abscissa 581. An excitation frequency spectrum 591 of the floating wind turbine 400 determined by the determining device 473 is shown in FIG. 5. A natural frequency 592 of the floating wind turbine 400 is also be shown in the diagram.

[0096] As illustrated in FIG. 5 the natural frequency 592 of the floating wind turbine 400 is inside the excitation frequency spectrum 591 of the load of the wind field 411 and the wave field 418. Therefore, the diagram in FIG. 5 illustrates the further unbalanced state of the floating wind turbine 400 (shown in FIG. 4).

[0097] FIG. 6 shows a floating wind turbine 600 according to a further exemplary embodiment of the present invention in a further balanced state.

[0098] Compared to the floating wind turbine 400 as shown in FIG. 4, the two adjustment devices formed as two water tanks 672 are filled with sea water. Therefore, the weight of the floating wind turbine 600 rises and the floating wind turbine 600 sinks deeper into the sea water and hence nearer to a sea floor 613. Therefore, the natural frequency of the floating wind turbine 600 shifts such that the natural frequency is outside of the excitation frequency spectrum of the load of the wind field 611 and the wave field 618.

[0099] FIG. 7 shows a diagram of a frequency distribution of the floating wind turbine according to an exemplary embodiment of the invention in the balanced state of FIG. 6.

[0100] In the diagram shown in FIG. 7 a graph is plotted showing power on the ordinate 782 and frequency on the abscissa 781. An excitation frequency spectrum 791 of the floating wind turbine 600 determined by the determining device 473 is shown in FIG. 7. A natural frequency 792 of the floating wind turbine 600 is also be shown in the diagram as a dashed line. Additionally, the natural frequency 592 is also shown in the diagram as a continuous line. The natural frequency 792 is outside the excitation frequency spectrum 791. A displacement 793 illustrates the difference between the natural frequency 592 in an unbalanced state and the natural frequency 792 in a balanced state.

[0101] Although the present invention has been disclosed in the form of preferred 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.

[0102] 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.