METHOD FOR DETERMINING A SPATIAL ARRANGEMENT OF A FLOATING WIND TURBINE RELATIVE TO ITS ENVIRONMENT

Abstract

A sensor system for a floating wind turbine is provided. The sensor system includes a wind sensor configured to provide a wind sensor signal indicative of a wind flow; and a processing unit configured to receive the wind sensor signal and to determine, based on the wind sensor signal, information indicative of a spatial arrangement of a floating base of the floating wind turbine relative to an environment of the floating wind turbine. Furthermore, a corresponding floating wind turbine and method of operating a floating wind turbine are provided.

Claims

1. A sensor system for a floating wind turbine, the sensor system comprising a wind sensor configured to provide a wind sensor signal indicative of a wind flow; and a processing unit configured to receive the wind sensor signal and to determine, based on the wind sensor signal, information indicative of a spatial arrangement of a floating base of the floating wind turbine relative to an environment of the floating wind turbine.

2. The sensor system according to claim 1, wherein the information is indicative of a rotation of the floating base relative to the environment.

3. The sensor system according to claim 1, wherein the wind sensor signal provided by the wind sensor is used for determining further information indicative of an orientation of a wind rotor of the floating wind turbine relative to a tower and/or the floating base of the floating wind turbine.

4. The sensor system according to claim 1, wherein the wind sensor is configured to measure the wind flow at at least two measurement points and/or in at least two measurement directions.

5. The sensor system according to claim 4, wherein the processing unit is further configured to determine a wind shear based on the wind sensor signal indicative of the wind flow at the at least two measurement points and wherein the processing unit determines the information based on the wind shear.

6. The sensor system according to claim 1, wherein the wind sensor signal is indicative of a vertical angle of the wind flow.

7. The sensor system according to claim 1, wherein the information is indicative of an oscillating motion of the floating base relative to the environment.

8. The sensor system according to claim 1, wherein the information is indicative of a rotational offset of the floating base relative to the environment.

9. The sensor system according to claim 1, wherein the processing unit is further configured to determine whether the spatial arrangement of the floating base satisfies a threshold criterion.

10. The sensor system according to claim 1, wherein the information is determined based on the assumption that a wind direction of the wind flow is horizontal.

11. The sensor system according to claim 1, wherein the information is indicative of a wind direction relative to a reference direction, wherein the reference direction is defined relative to the floating wind turbine.

12. A floating wind turbine comprising the sensor system according to claim 1.

13. The floating wind turbine according to claim 12, further comprising a control system; wherein the information is indicative of a wind direction relative to a reference direction, wherein the reference direction is defined relative to the floating wind turbine; and wherein the control system is configured to rotate the floating wind turbine such that the reference direction is aligned with the wind direction.

14. A method of operating a floating wind turbine comprising: providing, by a wind sensor, a wind sensor signal indicative of a wind flow; receiving, by a processing unit, the wind sensor signal; and determining, by the processing unit and based on the wind sensor signal, information indicative of a spatial arrangement of a floating base of the floating wind turbine relative to an environment of the floating wind turbine.

Description

BRIEF DESCRIPTION

[0070] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0071] FIG. 1 shows a floating wind turbine with a sensor system according to an exemplary embodiment of the invention;

[0072] FIG. 2 shows the floating wind turbine of FIG. 1 aligned with a wind flow; and

[0073] FIG. 3 shows the floating wind turbine of FIG. 1 misaligned with a wind flow.

DETAILED DESCRIPTION

[0074] Before, referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the invention have been developed.

[0075] Rigid body rotations of a floating wind turbine may be determined and used as input for control and monitoring systems, using wind sensors applicable to other/existing wind turbine applications. The floating wind turbine floats in the water and is held in position by the mooring lines. The floating wind turbine has six individual degrees of freedom in which the floating wind turbine may move, namely three translations, i.e., floater surge, floater sway and floater heave, and three rotations, i.e., floater roll, floater pitch and floater yaw.

[0076] The degrees of freedom may depend on a given reference coordinate system. Internally for controlling purposes, they may be defined globally with respect to the rotor plane. Thus, surge may be in the direction orthogonal to the rotor plane, while floater roll is the rotation around the surge axis, comparable to tower fore-aft. Sway may be orthogonal on the surge direction and floater pitch is a rotation around the sway axis, comparable to tower side-side. Heave may be pointing upwards along the tower, while yaw is the rotation around the heave axis. Floater yaw and nacelle yaw may coincide but may also be distinguished.

[0077] According to an embodiment, a method exploits wind sensors, in particular wind direction from wind sensors, to determine rotation information of a floating wind turbine. Instead of costing in additional sensors to determine rotation information explicitly, the idea is to use wind sensors that are used, or can be used, for other/existing functionalities. These sensors may therefore be present without any additional cost or complexity.

[0078] The measurement concept is to use a wind sensor to determine the wind direction relative to a reference line and translate that into a rotation information value.

[0079] As a wind sensor, a nacelle-mounted lidar may be used. A nacelle-mounted lidar normally measures wind speed and possibly relative wind direction. In some configurations, it comes with additional measures and derived features. A lidar typically uses several scanning points, and it may be necessary to average over multiple scanning points for robustness.

[0080] The lidar may measure the wind direction in more dimensions. For estimating floater pitch, the wind inflow angle is measured. For determining floater roll, the wind direction in 3D may be measured to have information available to measure the roll angle relative to a reference. Floater yaw angle is measured at the relative wind direction and covers both floater yaw orientation and nacelle or conventional yaw orientation. Normally, the relative wind direction is used to yaw the nacelle into the wind.

[0081] As a wind sensor, a nacelle-mounted ultrasonic sensor may be used. A nacelle-mounted ultrasonic sensor may normally measure wind speed and relative wind direction. An ultrasonic sensor may have to be flipped by 90 degree to measure wind direction relative to a reference line or direction, e.g., a horizontal line at 0 degree floater pitch.

[0082] In general, processing, such as filtering, may be applied to compensate a non-horizontal wind inflow. This is less likely offshore, where floating turbines are installed. Filtering may be applied to clean the signal.

[0083] When the floater rotation has been determined, it can be used by the control and monitoring system. For example, it can be used to ensure that the controller or a control system attenuate the mean floater pitch angle or that the control system does not react to any oscillating floater pitch angles. Monitoring systems may curtail or shutdown a turbine if the floater pitch angle exceeds a threshold.

[0084] An advantage of the above-described approach is to exploit existing sensors to determine information that is useful in a control system of a floating turbine. As a further advantage, wind direction information can be exploited to determine floater rotation, e.g., floater pitch or floater roll. Floater yaw relates to yaw control and may be addressed already via yaw error control, i.e., aligning turbine nacelle into the wind, though the platform yaw needs to be controlled also. Finally, identical sensors may be used for onshore wind turbines, offshore fixed foundation wind turbines and offshore floating foundations wind turbines. To use similar hardware with only software changes is a cost/complexity advantage.

[0085] FIG. 1 shows a floating wind turbine 100 with a sensor system. The floating wind turbine 100 comprises a wind rotor 140, a nacelle 150, a tower 130, and a floating base 120. The tower 130 is mounted on the floating base 120. The floating base 120 floats in the sea water 109 at or below a sea surface 107. The floating base 120 is anchored to the sea floor 108 by two mooring lines 121. The mooring line 121 is fixed to the floating base 120 by a first mooring line fixation 122 and to the sea floor 108 by a second mooring line fixation 123.

[0086] Compared with a conventional non-floating wind turbine, the floating wind turbine 100, in particular the floating base 120 of the floating wind turbine 100, has six additional degrees of freedom, in which the floating wind turbine 100 may move. The additional degrees of freedom are three translational degrees of freedom, namely floater surge 103, floater sway 102 and floater heave 101, and three rotational degrees of freedom, namely floater roll 106, floater pitch 105 and floater yaw 104.

[0087] Floater surge 103 is horizontal and in direction orthogonal to the rotor plane, while floater roll 106 regards rotation around the floater surge axis 103. Floater sway 102 is horizontal and in direction orthogonal to floater surge 103, while floater pitch 105 regards rotation around the floater sway axis 102. Floater heave 101 points upwards along the tower 130, while floater yaw 104 regards rotation around the floater heave axis 101.

[0088] The sensor system comprises a wind sensor 160, which is mounted on the nacelle 150. The wind sensor 160 is configured to provide a wind sensor signal indicative of a wind flow 110. The sensor system 160 further comprises a processing unit 170, which is arranged in the nacelle 150. The processing unit 170 is configured to receive the wind sensor signal and to determine, based on the wind sensor signal, information indicative of a spatial arrangement of the floating base 120 relative to an environment of the floating wind turbine 100, for example relative to the sea floor 108. The spatial arrangement can be described in terms of the mentioned six additional degrees of freedom.

[0089] FIG. 2 shows the floating wind turbine 100 of FIG. 1, wherein floater pitch 105 of the floating wind turbine 100 is determined by comparing a wind direction 211 measured by the nacelle-mounted wind sensor 160 with a reference direction 213. The wind direction 211 is but need not be parallel to a wave direction 214 of the sea water 109. The reference direction 213 is defined with respect to a reference line 212, which is defined relative to the tower 130 of the wind turbine 100. The reference line 212 lies in a plane orthogonal to a central axis of the tower 130 of the wind turbine 100 pointing in the direction, in which the wind rotor 140 is oriented. Alternatively, the reference line 212 may be defined orthogonal to the wind rotor plane. The reference direction 213 is parallel to the reference line 212 and points towards the wind turbine 100. In FIG. 2, the reference direction 213 is aligned with the wind direction 211, both directions 211, 213 are parallel and point towards the wind turbine 100. This information regarding the alignment of wind direction 211 and reference direction 213 may indicate that a floater pitch angle α (not shown) of the floater pitch 105 is zero degrees.

[0090] FIG. 3 shows the floating wind turbine 100 of FIG. 1, wherein floater pitch 105 of the floating wind turbine 100 is determined by comparing a wind direction 211 measured by the nacelle-mounted wind sensor 160 with a reference direction 213. The reference direction 213 is defined in the same way as described with respect to FIG. 2. In FIG. 3, the reference direction 213 is misaligned with the wind direction 211, it deviates from the wind direction 211 by a reference angle of β degrees. If the wind turbine 100 tilts towards the wind and/or in direction of the wind rotor 140, β may be defined to be negative. If the wind turbine 100 tilts away from the wind and/or in direction opposite to the orientation of the wind rotor 140, β may be defined to be positive. According to these definitions, β is negative in FIG. 3, e.g., −15 degrees. The floater pitch angle α is defined as the angle between a horizontal direction 315 orthogonal to floater sway 102 and a direction 316, which is orthogonal to floater sway 102 and orthogonal to a central axis 131 of the tower 130. If the wind turbine 100 tilts towards the wind and/or in direction of the wind rotor 140, the floater pitch angle α may be defined to be negative. If the wind turbine 100 tilts away from the wind and/or in direction opposite to the orientation of the wind rotor 140, the floater pitch angle α may be defined to be positive. In FIG. 3, a equals β. Thus, the information regarding the misalignment between wind direction 211 and reference direction 213 by the reference angle β is indicative of a floater pitch angle α of the same amount.

[0091] 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.

[0092] 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.