Control system for stabilizing a floating wind turbine

Abstract

A control system (170) for stabilizing a floating wind turbine (100) is described. The control system (170) includes: detection means (271, 272, 273, 274) configured to monitor an offset (231) from a predetermined floating body pitch angle (393) of the floating wind turbine (100) and / or an offset from a predetermined floating body yaw angle of the floating wind turbine (100), wherein the detection means (271, 272, 273, 274) is further configured to monitor an oscillatory motion (396) of the floating body pitch angle (392) and / or an oscillatory motion of the floating body yaw angle, wherein the predetermined floating body pitch angle (393) and the predetermined floating body yaw angle define a predetermined equilibrium state of the floating wind turbine (100), and wherein thresholds (394, 395) of the oscillatory motion (396) of the floating body pitch angle (392) and the oscillatory motion of the floating body yaw angle further define the predetermined equilibrium state of the floating wind turbine (100); and actuation means (281, 282) configured to manipulate the floating body pitch angle (392) and / or the floating body yaw angle until the predetermined equilibrium state is satisfied, wherein the actuation means (281, 282) is further configured to manipulate the oscillatory motion (396) of the floating body pitch angle (392) and / or the oscillatory motion of the floating body yaw angle until the predetermined equilibrium state of the floating wind turbine (100) is satisfied. In addition, a floating wind turbine (100) is described. Further, a method for stabilizing a floating wind turbine (100) is described.

Description

Technical Field

[0001] The present invention relates to a control system for stabilizing a floating wind turbine. Furthermore, the present invention relates to a floating wind turbine and a method for stabilizing a floating wind turbine. Background Art

[0002] In the technical field of floating wind turbines, it is known that, compared with conventional wind turbines, floating wind turbines may undergo additional motions due to additional degrees of freedom. Such additional motions may cause severe loads on the floating wind turbine and a decrease in annual power production. For example, if the floating body pitches, the shear force at the interface between the tower and the nacelle may increase due to the increased gravitational load. In addition, for the spar floater concept of a floating wind turbine, conventional closed-loop speed-pitch control of the drivetrain may lead to instability of the pitch motion of the floating body. This may be due to the interference of the pitch motion of the floating body and the natural frequency of the control system adding negative damping to the floating wind turbine system. Another challenge for current floating wind turbines may be the possible large motions of the floating foundation. For example, the rotation of the floating foundation in yaw may cause severe loads on the mooring cable system. However, the vertical motion in heave may also cause severe loads. In addition, there may be a potential risk that vibrations induced by vortex shedding may occur at specific wave frequencies, which may lead to induced structural vibrations.

[0003] The pitch motion of the floating body may further introduce challenges in current estimations, such as determining the rotational speed based on other components in the hub acceleration and tower acceleration. For example, the heave motion may interfere with the accelerometers and gyroscopes, resulting in incorrect estimations after being used in the controller.

[0004] Therefore, in current floating wind turbines, the instability of the pitch motion of the floating body is solved by adding an additional reference speed signal to the speed-pitch control in such a way that the controller reference does not interfere with the floating wind turbine system. The input comes from a gyroscope or accelerometer that measures the tilt angle of the floating wind turbine or measures the tower acceleration.

[0005] Other current academic solutions are to detune the speed-pitch controller to reduce the bandwidth (frequency) so that it does not respond to the pitch frequency of the floating body. However, this is accompanied by poor rotational speed tracking ability. Detuning may be a trade-off between stability and control performance. Yaw motion control has also been implemented to avoid excessive yaw motion in the spar floater concept.

[0006] Accordingly, there may be a need to provide an active system that can actively change the global system behavior of a floating wind turbine such that control of the floating wind turbine can be provided in a safe and optimal manner. Accordingly, the translation and / or rotation of the floating wind turbine during operation is restricted and accordingly stabilized. Additionally, power production can be increased. Additionally, the loads acting on the floating wind turbine can be reduced and, accordingly, the durability of the floating wind turbine can be increased. Summary of the Invention

[0007] This need can be met by the subject matter of the present invention.

[0008] According to a first aspect of the present invention, there is provided a control system for stabilizing a floating wind turbine. The control system includes detection means configured to monitor an offset from a predetermined floating body pitch angle of the floating wind turbine and / or an offset from a predetermined floating body yaw angle of the floating wind turbine, wherein the detection means is further configured to monitor an oscillatory movement of the floating body pitch angle and / or an oscillatory movement of the floating body yaw angle, wherein the predetermined floating body pitch angle and the predetermined floating body yaw angle define a predetermined equilibrium state of the floating wind turbine, and wherein a threshold of the oscillatory movement of the floating body pitch angle and a threshold of the oscillatory movement of the floating body yaw angle further define the predetermined equilibrium state of the floating wind turbine; actuation means configured to manipulate the floating body pitch angle and / or the floating body yaw angle until the predetermined equilibrium state is satisfied, wherein the actuation means is further configured to manipulate the oscillatory movement of the floating body pitch angle and / or the oscillatory movement of the floating body yaw angle until the predetermined equilibrium state of the floating wind turbine is satisfied.

[0009] The described control system is based on the concept that a control system can be provided that can stabilize the undesired translation and / or rotation and / or oscillatory movement of a floating wind turbine. Accordingly, the floating wind turbine can be manipulated in a safe and optimal manner while having increased power production and reduced loads on the substructure of the floating wind turbine.

[0010] This can result in increased annual power production of the wind farm and reduced loads on the floating wind turbine.

[0011] A floating wind turbine includes a movable floating foundation. By the movement of the floating foundation, the floating wind turbine mounted on the floating foundation moves accordingly. The movement of the floating foundation or the corresponding movement of the floating wind turbine can be divided into six individual degrees of freedom, namely three translations: surge, sway, and heave, and three rotations: roll, pitch, and yaw.

[0012] In addition, naturally irregular wind loads, wave loads, and / or current loads, as well as aerodynamic, structural, and / or hydrodynamic loads, and control drives all contribute to complex dynamic behavior.

[0013] Due to the naming similarity between the pitch of the blade and the pitch of the floating foundation, in this application, the pitch of the floating body and the pitch of the blade are clearly distinguished by differentiating them. The pitch of the floating body represents the rotation of the floating foundation around its rotation point, and the pitch of the blade represents the controlled pitch change of the blade. Similarly, the yaw of the floating body represents the rotation of the floating foundation around its vertical axis (heave), and the yaw of the turbine represents the rotation of the nacelle.

[0014] Setting the detection device as a single-piece detection device provides the possibility of using one device to detect the deviation from a predetermined pitch angle of the floating body, the deviation from a predetermined yaw angle of the floating body, and the oscillatory motion of the pitch angle of the floating body and the oscillatory motion of the yaw angle of the floating body. Therefore, a cost-effective way can be provided for monitoring whether a floating wind turbine is operating in a predetermined equilibrium state.

[0015] Setting the detection device as a multi-part detection device provides the possibility of separately detecting the value of the pitch angle of the floating body and / or the value of the yaw angle of the floating body, and the oscillatory motion of the pitch angle of the floating body and / or the oscillatory motion of the yaw angle of the floating body at different positions on the floating wind turbine, so that detection is possible even at exposed positions. Therefore, an accurate detection of whether a floating wind turbine is operating in a predetermined equilibrium state can be provided.

[0016] Setting the actuation device as a single-piece actuation device provides the possibility of actuating multiple floating wind turbines one by one or all at once using a single actuation device. Therefore, a low-maintenance actuation device can be provided.

[0017] Setting the actuation device as a multi-part actuation device provides the possibility of separately and accurately actuating each floating wind turbine. Therefore, a time-efficient actuation can be provided.

[0018] The predetermined pitch angle of the floating body according to the present invention can represent the pitch angle of the floating body corresponding to the vertical alignment of the floating wind turbine. This vertical alignment can also represent an alignment slightly deviated from the vertical to ensure that the rotor of the floating wind turbine is optimally positioned relative to the incoming wind field, and at the same time, the shear force acting on the connection between the nacelle and the tower is deviated into the tower.

[0019] The predetermined yaw angle of the floating body according to the present invention can represent the following yaw angle of the floating body, that is, the yaw angle of the floating body is adjusted so that the rotor of the floating wind turbine is aligned perpendicular to the wind direction of the incoming wind field.

[0020] According to the present invention, the oscillatory motion of the pitch angle of the floating body can represent the instability of the floating wind turbine, which can be regarded as an oscillation around the pitch angle of the floating body. This oscillation can oscillate at the same frequency as the natural pitch frequency of the floating body.

[0021] According to the present invention, the oscillatory motion of the yaw angle of the floating body can represent the instability of the floating wind turbine, which can be regarded as an oscillation around the yaw angle of the floating body. This oscillation can oscillate at the same frequency as the natural yaw frequency of the floating body.

[0022] The threshold value of the oscillatory motion of the pitch angle of the floating body according to the present invention can represent a value characterizing the amount of oscillation that is still acceptable for the floating wind turbine. However, if the oscillatory motion of the pitch angle of the floating body exceeds this threshold value, the oscillatory motion of the pitch angle of the floating body may be harmful to the floating wind turbine and / or to the fixed structure of the floating wind turbine.

[0023] The threshold value of the oscillatory motion of the yaw angle of the floating body according to the present application can represent a value characterizing the amount of oscillation that is still acceptable for the floating wind turbine. However, if the oscillatory motion of the yaw angle of the floating body exceeds this threshold value, the oscillatory motion of the yaw angle of the floating body may be harmful to the floating wind turbine and / or to the fixed structure of the floating wind turbine.

[0024] The predetermined equilibrium state according to the present invention can represent the following state, that is: wherein, the rotor of the floating wind turbine is aligned perpendicular to the wind direction of the incoming wind field, and the minimum load acts on the connection between the nacelle and the tower of the floating wind turbine. In addition, in this predetermined equilibrium state, any occurring oscillatory motion of the pitch angle of the floating body and / or the yaw angle of the floating body is small and does not exceed the threshold value of the oscillatory motion of the pitch angle of the floating body and / or the threshold value of the oscillatory motion of the pitch angle of the floating body.

[0025] The detection device can detect when a given threshold value of the oscillatory motion of the pitch angle of the floating body and / or a given threshold value of the oscillatory motion of the yaw angle of the floating body is exceeded, and thus activate the corresponding actuating device.

[0026] The detection device can continuously monitor the oscillatory motion of the pitch angle of the floating body and / or the yaw angle of the floating body. Therefore, together with the actuating device, the detection device can ensure that instability does not occur.

[0027] According to an exemplary embodiment, in this predetermined equilibrium state, the offset from the predetermined pitch angle of the floating body is in the range of -10° to +10°, particularly -5° to +5°, more particularly -2° to +2°, and even more particularly 0°.

[0028] Offset from a predetermined pitch angle of the floating body is limited within a certain range in a predetermined equilibrium state, particularly within a range of -10° to +10°, more particularly within a range of -5° to +5%, even more particularly within a range of -2° to +2°, and even more particularly 0°, which can provide the following possibility: a compromise between reduced loads acting on the substructure of the floating wind turbine and increased power production can be achieved. In particular, due to the fact that a certain alignment of the floating wind turbine relative to the incoming wind field is possible.

[0029] An offset of zero from the predetermined pitch angle of the floating body can provide the following possibility: precise alignment with the predetermined equilibrium state can be satisfied.

[0030] According to an exemplary embodiment of the present invention, in this predetermined equilibrium state, the offset from the predetermined yaw angle of the floating body is within a range of -10° to +10°, particularly -5° to +5°, more particularly -2° to +2°, and even more particularly 0°.

[0031] Offset from a predetermined yaw angle of the floating body is limited within a certain range in a predetermined equilibrium state, particularly within a range of -10° to +10°, more particularly within a range of -5° to +5%, even more particularly within a range of -2° to +2°, and even more particularly 0°, which can provide the following possibility: a compromise between reduced loads acting on the substructure of the floating wind turbine and increased power production can be achieved. In particular, due to the fact that a certain alignment of the floating wind turbine relative to the incoming wind field is possible.

[0032] An offset of zero from the predetermined yaw angle of the floating body can provide the following possibility: precise alignment with the predetermined equilibrium state can be satisfied.

[0033] According to an exemplary embodiment of the present invention, in this predetermined equilibrium state, the offset from the predetermined pitch angle of the floating body is zero and / or the offset from the predetermined yaw angle of the floating body is zero.

[0034] According to an exemplary embodiment of the present invention, the threshold value of the oscillatory motion of the pitch angle of the floating body and / or the threshold value of the oscillatory motion of the yaw angle of the floating body are within a range of -5° to +5°, particularly -2° to +2°, and more particularly 0°.

[0035] Limiting the threshold value of the oscillatory motion of the pitch angle of the floating body within a range of -5° to +5%, particularly within a range of -2° to +2°, in a predetermined equilibrium state can provide the following possibility: large oscillatory behavior in the floating wind turbine system can be suppressed. In particular, if the threshold value can be 0°, no oscillatory motion occurs in the floating wind turbine.

[0036] Limiting the threshold of the oscillatory motion of the yaw angle of the floating body in a predetermined equilibrium state to a range of -5° to +5%, in particular in the range of -2° to +2°, provides the possibility of suppressing large oscillatory behavior in a floating wind turbine system. In particular, if the threshold can be 0°, no oscillatory motion occurs in the floating wind turbine.

[0037] According to another embodiment of the present invention, the detection device is mounted on a substructure of the floating wind turbine, in particular on the nacelle, blades, tower and / or floating foundation.

[0038] The substructure of the floating wind turbine can represent the nacelle, blades, tower and / or floating foundation of the floating wind turbine.

[0039] Mounting the detection device on a substructure of the floating wind turbine provides the possibility of providing a quick detection based on the detection value of the offset from the predetermined yaw angle of the floating body and / or the detection value of the offset from the predetermined pitch angle of the floating body. Additionally or alternatively, a quick detection based on the detection value of the oscillatory motion of the pitch angle of the floating body and / or the detection value of the oscillatory motion of the yaw angle of the floating body can be provided.

[0040] Mounting a corresponding detection device at more than one substructure of the floating wind turbine provides the possibility of providing an accurate detection of the value of the offset from the predetermined yaw angle and / or the predetermined pitch angle of the floating body and the value of the oscillatory motion of the pitch angle of the floating body and / or the value of the oscillatory motion of the yaw angle of the floating body.

[0041] The substructure to which the detection device is mounted can be selected based on which substructure indicates the measured yaw angle and / or pitch angle of the floating body and / or the oscillatory motion of the pitch angle of the floating body and / or the oscillatory motion of the yaw angle of the floating body.

[0042] Alternatively, the substructure to which the detection device is mounted can be selected based on which is the optimal position for the selected detection device. For example, a blade load sensor can preferably be mounted on the blade and thus on the rotor of the floating wind turbine.

[0043] According to another exemplary embodiment, the detection device includes at least one of the group consisting of: a spinner pressure sensor, a wind speed sensor, a wind direction sensor, a blade load sensor.

[0044] By measuring the pressure difference that varies according to the rotor azimuth angle, the spinner pressure sensor can detect the offset from the predetermined yaw angle of the floating body, the offset from the predetermined pitch angle of the floating body, the oscillatory motion of the pitch angle of the floating body and / or the oscillatory motion of the yaw angle of the floating body.

[0045] The use of a hub cover pressure sensor provides the possibility that an already integrated sensor can additionally provide values of an offset from a predetermined pitch angle of the floating body and / or an offset from a predetermined yaw angle of the floating body and / or an oscillatory movement of the pitch angle of the floating body and / or an oscillatory movement of the yaw angle of the floating body.

[0046] A wind speed sensor can detect an offset from a predetermined pitch angle of the floating body and / or an oscillatory movement of the pitch angle of the floating body by measuring a change in the wind speed caused by the movement of the turbine nacelle.

[0047] The use of a wind speed sensor provides the possibility that an already integrated sensor can additionally provide values of an offset from a predetermined pitch angle of the floating body and / or an oscillatory movement of the pitch angle of the floating body.

[0048] A wind direction sensor can detect an offset from a predetermined pitch angle of the floating body and / or an oscillatory movement of the pitch angle of the floating body by measuring the incoming wind direction at a specific substructure of the floating wind turbine.

[0049] The use of a wind direction sensor provides the possibility that an already integrated sensor can additionally provide values of an offset from a predetermined pitch angle of the floating body and / or an oscillatory movement of the pitch angle of the floating body.

[0050] A blade load sensor can detect an offset from a predetermined pitch angle of the floating body and / or an oscillatory movement of the pitch angle of the floating body and / or an offset from a predetermined yaw angle of the floating body and / or an oscillatory movement of the yaw angle of the floating body by measuring blade loads that vary depending on a specific alignment of the blades relative to the incoming wind field and / or the inclination of the floating wind turbine.

[0051] The use of a blade load sensor provides the possibility that a mapping of yaw misalignment / oscillation and / or pitch misalignment / oscillation of the floating body can be provided. Thus, precise detection of an offset from a predetermined pitch angle and / or a predetermined yaw angle of the floating body and the occurrence of an oscillatory movement of the pitch angle of the floating body and / or an oscillatory movement of the yaw angle of the floating body can be provided.

[0052] According to another exemplary embodiment of the present invention, a detection device is mounted to a fixed structure to which the floating wind turbine is mounted, in particular to a mooring cable of the fixed structure.

[0053] The fixed structure of the floating wind turbine can represent a part of the floating wind turbine that holds the floating wind turbine in place and through which alignment of the floating wind turbine in each of the six degrees of freedom is made possible.

[0054] Mounting a detection device to a mooring cable of a floating wind turbine provides the possibility of detecting an offset from a predetermined floating body pitch angle and / or a predetermined floating body yaw angle at additional locations on the floating wind turbine system. Additionally, it also provides the possibility of detecting an oscillatory movement of the floating body pitch angle and / or an oscillatory movement of the floating body yaw angle at additional locations on the floating wind turbine system.

[0055] According to an exemplary embodiment of the present invention, the detection device includes a strain gauge.

[0056] The strain gauge can detect an offset from a predetermined floating body pitch angle, an offset from a predetermined floating body yaw angle, an oscillatory movement of the floating body pitch angle, and / or an oscillatory movement of the floating body yaw angle. In particular, by mounting a strain gauge to each mooring cable that holds the floating wind turbine in place, a deviation from a predetermined equilibrium state can be detected.

[0057] Using a strain gauge mounted to a mooring cable provides the possibility of detecting a deviation from a predetermined equilibrium state more detailedly and quickly.

[0058] According to an exemplary embodiment of the present invention, the detection device includes a sensor configured to detect an operating mode of the floating wind turbine.

[0059] The operating mode of the floating wind turbine can indicate whether the floating wind turbine is in operation, idle, or in service. The operating mode may affect the behavior of the floating wind turbine. Additionally, if the floating wind turbine is idle, an increase in power production may not be important, and a reduction in the loads on the substructure of the floating wind turbine may be more important. If the floating wind turbine is in service / operation, an increase in power production may be more important. Additionally, for an operating floating wind turbine, a reduction in the offset from a predetermined floating body pitch angle and / or a predetermined floating body yaw angle and a reduction in the oscillatory movement of the floating body pitch angle and / or the floating body yaw angle may be more important.

[0060] Detecting the operating mode of the floating wind turbine provides the possibility of accurately and precisely determining a predetermined equilibrium state.

[0061] According to an exemplary embodiment of the present invention, the actuating device includes an adjustable spoiler on the nacelle and / or an active blade attachment.

[0062] The adjustable spoiler can represent an airfoil that can be adjusted according to the oncoming wind field detected by the detection device on the blade.

[0063] Adjusting the airfoil provides the possibility that the contact surfaces of the nacelle and / or the blade and / or the tower can be enlarged such that higher drag loads act on the nacelle and / or the blade and / or the tower. Accordingly, the offset and / or oscillatory movement of the floating body pitch angle and / or the floating body yaw angle can be adapted.

[0064] The active blade add-on can be, for example, an add-on that can be actively adjusted or activated according to a given condition, i.e., the active blade add-on acts according to an input from a controller unit.

[0065] According to an exemplary embodiment of the invention, the actuation device includes a mooring cable actuator.

[0066] Attaching a mooring cable actuator to each mooring cable that holds the floating wind turbine in place provides the possibility of repositioning the floating wind turbine along each or a combination of surge, sway, heave, roll, pitch, and yaw. Additionally, the mooring cable actuator can provide the possibility of influencing the overall system behavior, such as the natural frequency of the floating wind turbine, and thus influencing the oscillatory movement of the floating body pitch angle and / or the floating body yaw angle. The mooring cable actuator can be installed in the floating foundation such that the mooring cable actuator can actively adjust the length of a mooring cable.

[0067] According to an exemplary embodiment of the invention, the actuation device includes an adjustable damper configured to damp the vibrations of the floating wind turbine.

[0068] The vibrations of the floating wind turbine can cause translational and / or rotational movements of the floating wind turbine, which may result in an offset from a predetermined floating body pitch angle and / or a predetermined floating body yaw angle.

[0069] The adjustable damper can be configured such that the translational and / or rotational movements can be reduced and, in the best case, completely suppressed.

[0070] Additionally, the adjustable damper can influence the oscillatory movement of the floating body pitch angle and / or the floating body yaw angle by influencing the damping of the vibrations of the floating wind turbine.

[0071] According to an exemplary embodiment of the invention, the actuation device includes a liquid damper, a mass damper, and / or a vortex-induced vibration brake.

[0072] A liquid damper may comprise a container which can be filled or emptied of liquid depending on the desired damping. The damping may directly depend on the mass of the liquid present in the liquid damper. Preferably, the liquid damper may work together with the seawater present around the floating wind turbine. The container may be fixed to the floating foundation. Furthermore, the liquid damper may offer the possibility of having an actuation device that is easy and inexpensive to operate.

[0073] A mass damper may be adjustable such that the weight of the mass damper is changed according to the desired amount of damping. Furthermore, the mass damper may offer the possibility of having a simple actuation device.

[0074] A vortex-induced vibration brake may offer the possibility of preventing the floating wind turbine from locking into the vortex-induced vibration locking frequency.

[0075] According to another aspect of the present invention, there is provided a floating wind turbine. The floating wind turbine comprises: (a) a wind rotor including blades; (b) a tower to which the wind rotor is mounted; (c) a floating foundation to which the tower is mounted; and (d) the above-described control system.

[0076] Furthermore, the described system is based on the concept that a control system can be provided which can stabilize the undesired translational and / or rotational and / or oscillatory movements of the floating wind turbine. Thus, the floating wind turbine can be operated in a safe and optimal manner while having increased power production and reduced loads on the substructure of the floating wind turbine.

[0077] According to another aspect of the present invention, there is provided a method for stabilizing a floating wind turbine. The method comprises: (a) monitoring the deviation from a predetermined floating body pitch angle of the floating wind turbine and / or the deviation from a predetermined floating body yaw angle of the floating wind turbine; (b) monitoring the oscillatory movement of the floating body pitch angle and / or the oscillatory movement of the floating body yaw angle, wherein the predetermined floating body pitch angle and the predetermined floating body yaw angle define a predetermined equilibrium state of the floating wind turbine, and wherein a threshold value of the oscillatory movement of the floating body pitch angle and a threshold value of the oscillatory movement of the floating body yaw angle further define the predetermined equilibrium state of the floating wind turbine; (c) manipulating the floating body pitch angle and / or the floating body yaw angle until the predetermined equilibrium state is satisfied; and (d) manipulating the oscillatory movement of the floating body pitch angle and / or the oscillatory movement of the floating body yaw angle until the predetermined equilibrium state of the floating wind turbine is satisfied.

[0078] Furthermore, the described method is based on the idea that a control system can be provided that can stabilize unwanted translational and / or rotational and / or oscillatory movements of a floating wind turbine. Thus, the floating wind turbine can be maneuvered in a safe and optimal manner while having increased power production and reduced loads on the substructures of the floating wind turbine.

[0079] Some exemplary embodiments of the present invention are described below.

[0080] According to an exemplary embodiment of the present invention, in terms of a control system utilizing various sensors and / or actuators, the misalignment of the floating body's pitch and / or the misalignment of the floating body's yaw during operation can be solved in different ways.

[0081] By using another or additional sensor, an improved estimation of the tilt and / or rotation in the pitch, roll, or yaw of the floating body can be made. Exemplary sensors that can be added to improve the information relative to a conventional wind turbine can be one of the following.

[0082] A nacelle pressure sensor can indicate yaw misalignment. The nacelle pressure sensor can be extended to indicate the pitch offset of the floating body (i.e., the tilt of the structure of the floating wind turbine). The nacelle pressure sensor can measure the pressure difference that can change according to the rotor azimuth angle. Thus, an estimation of the imbalance resulting from yaw misalignment and also from tilt can be detected. Thereby, the sensor can be used to estimate the pressure difference in the vertical direction indicating the tilt of the hub, which means an offset from a predetermined floating body pitch angle.

[0083] An anemometer can indicate a higher or lower wind speed that can be observed when the floating wind turbine hub moves due to an offset from a predetermined floating body pitch angle. The anemometer can utilize this difference in wind speed.

[0084] A wind direction sensor can indicate the wind direction that manifests not only in the horizontal direction but also in the vertical direction. Thus, the wind direction can directly indicate the tilt of the floating wind turbine caused by an offset from a predetermined floating body pitch angle.

[0085] A blade load sensor can indicate an estimated floating body pitch misalignment and / or an estimated floating body yaw misalignment. This is due to the fact that, for example, a floating body yaw misalignment or a floating body pitch misalignment can be regarded as an imbalance in the measured blade loads. Thus, the change in the load measurement can be mapped to the floating body yaw misalignment and / or the floating body pitch misalignment, or the corresponding offset from a predetermined floating body pitch angle and / or the offset from a predetermined floating body yaw angle.

[0086] A strain gauge on a mooring cable can be used to map the strain measured in the strain gauge to an estimation of the offset from a predetermined floating body pitch angle. The higher the strain, the greater the offset from the predetermined floating body pitch angle.

[0087] Hub pressure sensors, wind speed sensors, and / or wind direction sensors may already be implemented in floating wind turbines. Therefore, additional sensors may not be required.

[0088] The above sensors may define a way to improve the estimation of the offset from a predetermined floating body pitch angle and / or the offset from a predetermined floating body yaw angle. Due to the improved information, the already built-in control system can be used to more easily limit the undesired rotation of the floating body.

[0089] Exemplary actuators are described below, which may be more cost-effective and may provide an additional layer of safety to control floating wind turbines.

[0090] Active blade add-ons can be used to implement positive damping in a floating wind turbine system, thereby eliminating the negative damping from the speed-pitch controller and thus minimizing the translation and / or rotation of the floating wind turbine.

[0091] A spoiler on top of the nacelle can be used to implement positive damping in a floating wind turbine system, thereby eliminating the negative damping from the speed-pitch controller and thus minimizing the translation and / or rotation of the floating wind turbine.

[0092] Vortex-induced vibration brakes can be used on floating wind turbines to prevent locking into the vortex-induced vibration lock-in frequency.

[0093] Passive liquid dampers can be installed inside the floating foundation to add additional damping to the floating wind turbine system and thus minimize the translation and / or rotation of the floating wind turbine.

[0094] Mooring cable actuators can be installed inside the floating foundation and used to balance the rotational offset by increasing or decreasing the length of one of the mooring cables.

[0095] According to an exemplary embodiment of the present invention, a floating wind turbine can be stabilized during operation, idle, and / or service. When the floating wind turbine is idle or under maintenance, the floating wind turbine should be controlled in such a way that there is no potential risk of substances or personnel that may occur due to stabilizing the floating wind turbine and may limit all translational and rotational movements. This may result in a potentially larger inspection window.

[0096] The present invention can provide the possibility of using different sensor and actuator solutions to control a floating wind turbine in an optimal and safe manner. Combinations of sensors and actuators that may not necessarily be found in standard wind turbine constructions can be used.

[0097] Restricting or stabilizing the translation and / or rotation of a floating wind turbine during operation can be highly beneficial. During operation, unwanted translation or rotation can lead to reduced power production, increased loads, and unnecessary controller actuations and / or critical oscillations of the floating wind turbine.

[0098] It should be noted that embodiments of the present invention have been described with reference to different topics. However, those skilled in the art will appreciate from the above and the following description that, unless otherwise stated, any combination between features related to different topics, in addition to any combination of features belonging to one type of topic, is also considered to be disclosed by this document.

[0099] The aspects of the present invention defined above, as well as additional aspects, are apparent from and will be elucidated by the examples of the embodiments described hereinafter. The present invention will be described in more detail hereinafter with reference to the examples of the embodiments, but the present invention is not limited to the examples of these embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1 A floating wind turbine according to an exemplary embodiment of the present invention in a predetermined equilibrium state is shown.

[0101] Figure 2 A floating wind turbine according to another exemplary embodiment of the present invention in an unbalanced state is shown.

[0102] Figure 3 A schematic diagram showing the offset and oscillatory motion of the pitch angle of the floating body is shown. DETAILED DESCRIPTION

[0103] The illustrations in the drawings are schematic. It should be noted that in different drawings, similar or identical elements or features are provided with the same reference numerals, or with reference numerals that differ only in the first digit from the corresponding reference numerals. To avoid unnecessary repetition, elements or features that have been described with respect to previously described embodiments will not be described again at a later position in this specification.

[0104] Figure 1 A floating wind turbine 100 according to an exemplary embodiment of the present invention in a predetermined equilibrium state is shown. The floating wind turbine 100 includes three blades 140, a tower 130, and a floating foundation 120 mounted to a nacelle 160. The floating wind turbine 100 further includes a fixed structure 150 that includes a plurality of mooring cables. For clarity, Figure 1Only the first mooring cable 151 and the second mooring cable 154 are shown. The first mooring cable 151 is fixed to the floating foundation 120 through the first mooring cable fixing member 152 and fixed to the sea ground 113 through the second mooring cable fixing member 153. In addition, the second mooring cable 154 is fixed to the floating foundation 120 through another first mooring cable fixing member 155 and fixed to the sea floor 113 through another second mooring cable fixing member 156.

[0105] The floating foundation 120 is fixed by the first mooring cable 151 and the second mooring cable 152 in such a way that the floating foundation 120 is immersed in the sea water 114 below the sea surface 112. Therefore, the floating foundation 120 is held underwater by the first mooring cable 151 and the second mooring cable 154. The oncoming wind field 111 acts on the three blades 140 of the floating wind turbine 100, enabling the floating wind turbine 100 to generate electrical energy.

[0106] The floating wind turbine 100 floats in the sea water 114 and is held in place by mooring cables, which are exemplarily illustrated by Figure 1 the first mooring cable 151 and the second mooring cable 154 in. The floating wind turbine 100 has six separate degrees of freedom by which the floating wind turbine 100 can move. That is, three translations, surge 103, sway 102, and heave 101, and three rotations, roll 106, pitch 105, and yaw 104. In addition, the floating wind turbine 100 is stabilized by a control system 170 installed on the floating foundation 120. As Figure 1 shown in, the alignment of the floating wind turbine 100 can illustrate a predetermined equilibrium state.

[0107] Figure 2 Shown is a floating wind turbine 100 according to another exemplary embodiment of the present invention in an unbalanced state.

[0108] The floating wind turbine 100 is tilted about the pitch 105 of the floating body, such that an offset 231 relative to a predetermined floating body pitch angle occurs. Additionally, the floating wind turbine 100 is tilted about the yaw 104, such that an offset relative to a predetermined floating body yaw angle occurs. Due to the force of the oncoming wind field 111 acting on the three blades 140 of the floating wind turbine 100, the floating wind turbine 100 is tilted with an offset 231 relative to the predetermined floating body pitch angle and the said offset relative to the predetermined floating body yaw angle.

[0109] The weight of the nacelle 160 together with the forces caused by the incoming wind field 111 acting on the three blades 140 constitutes the gravity 134. The gravity 234 includes a first force component 232 and a second force component 233. The first force component 232 is parallel to the extension direction of the tower 230, and the second force component 233 is perpendicular to the first force component 232.

[0110] Therefore, in the unbalanced state as shown in Figure 2 , due to the offset 131 about the pitch 105 and the offset about the yaw 106, shear forces act on the connection between the nacelle 160 and the tower 130.

[0111] The offset 231 about the floating body pitch 105 and the offset about the floating body yaw 106 are detected by the blade load sensors 271, the wind speed sensors 272, and the wind direction sensors 273, each of which is mounted on one of the blades 140 or the nacelle 160. Additionally, the strain gauges 274 contribute to detecting the offset 231 about the floating body pitch 105 and the offset about the floating body yaw 106.

[0112] Then, the floating wind turbine 100 will be brought back to the predetermined balanced state as shown in Figure 1 by the mooring cable actuator 281.

[0113] Figure 3 A schematic diagram showing the offset 397 and the oscillatory motion 396 of the floating body pitch angle 392 is shown. The floating body pitch angle is plotted on the vertical axis 391. The floating body pitch angle 392 can be, for example, 5°. The predetermined floating body pitch angle 393 can be, for example, 0°. Therefore, the offset 397 can be 5°. As shown in Figure 3 , the upper threshold 394 is set to +3°, and the lower threshold 395 is set to -3°. As can be seen in Figure 3 , the oscillatory motion 396 of the floating body pitch angle 392 is within the upper threshold 394 and the lower threshold 395.

[0114] It should be noted that the term "comprising" does not exclude other elements or steps, and the use of the words "a", "an", or "one" does not exclude a plurality. Additionally, elements described in connection with different embodiments can also be combined.

Claims

1. A control system (170) for stabilizing a floating wind turbine (100), the control system (170) comprises: detection means (271, 272, 273, 274) configured to monitor an offset (231) from a predetermined pitch angle (393) of a floating body of the floating wind turbine (100) and an offset from a predetermined yaw angle of the floating body of the floating wind turbine (100), wherein the detection means (271, 272, 273, 274) is further configured to monitor an oscillatory motion (396) of the pitch angle (392) of the floating body and an oscillatory motion of the yaw angle of the floating body, wherein the predetermined pitch angle (393) of the floating body and the predetermined yaw angle of the floating body define a predetermined equilibrium state of the floating wind turbine (100), wherein thresholds (394, 395) of the oscillatory motion (396) of the pitch angle (392) of the floating body and the oscillatory motion of the yaw angle of the floating body further define the predetermined equilibrium state of the floating wind turbine (100), actuation means (281, 282) configured to manipulate the pitch angle (392) of the floating body and the yaw angle of the floating body until the predetermined equilibrium state is satisfied, wherein the actuation means (281, 282) is further configured to manipulate the oscillatory motion (396) of the pitch angle (392) of the floating body and the oscillatory motion of the yaw angle of the floating body until the predetermined equilibrium state of the floating wind turbine (100) is satisfied.

2. The control system (170) according to claim 1, wherein, in the predetermined equilibrium state, the offset (231) from the predetermined pitch angle (393) of the floating body is in the range of -10° to +10°.

3. The control system (170) according to claim 1, wherein, in the predetermined equilibrium state, the offset (231) from the predetermined pitch angle (393) of the floating body is in the range of -5° to +5°.

4. The control system (170) according to claim 1, wherein, in the predetermined equilibrium state, the offset (231) from the predetermined pitch angle (393) of the floating body is in the range of -2° to +2°.

5. The control system (170) according to claim 1, wherein, in the predetermined equilibrium state, the offset (231) from the predetermined pitch angle (393) of the floating body is 0°.

6. The control system (170) according to any one of claims 1 to 5, wherein, in the predetermined equilibrium state, the offset from the predetermined yaw angle of the floating body is in the range of -10° to +10°.

7. The control system (170) according to any one of claims 1 to 5, wherein, in the predetermined equilibrium state, the offset from the predetermined yaw angle of the floating body is in the range of -5° to +5°.

8. The control system (170) according to any one of claims 1 to 5, wherein, In the said predetermined equilibrium state, the offset from the said predetermined yaw angle of the floating body is within the range of -2° to +2°.

9. The control system (170) according to any one of claims 1 to 5, wherein, in the said predetermined equilibrium state, the offset from the said predetermined yaw angle of the floating body is 0°.

10. The control system (170) according to any one of claims 1 to 5, wherein, the threshold of the oscillatory motion (396) of the pitch angle (392) of the floating body and / or the threshold of the oscillatory motion of the yaw angle of the floating body are within the range of -5° to +5°.

11. The control system (170) according to any one of claims 1 to 5, wherein, the threshold of the oscillatory motion (396) of the pitch angle (392) of the floating body and / or the threshold of the oscillatory motion of the yaw angle of the floating body are within the range of -2° to +2°.

12. The control system (170) according to any one of claims 1 to 5, wherein, the threshold of the oscillatory motion (396) of the pitch angle (392) of the floating body and / or the threshold of the oscillatory motion of the yaw angle of the floating body is 0°.

13. The control system (170) according to any one of claims 1 to 5, wherein, the detection devices (271, 272, 273, 274) are mounted to the substructures (120, 130, 140, 160) of the floating wind turbine (100).

14. The control system (170) according to any one of claims 1 to 5, wherein, the detection devices (271, 272, 273, 274) are mounted to the nacelle (160), the blades (140), the tower (130) and / or the floating foundation (120).

15. The control system (170) according to any one of claims 1 to 5, wherein, the detection devices (271, 272, 273, 274) include at least one of the group consisting of: a hub cover pressure sensor, an airspeed sensor (272), a wind direction sensor (273), a blade load sensor (271).

16. The control system (170) according to any one of claims 1 to 5, wherein, the detection devices (271, 272, 273, 274) are mounted to the fixed structure to which the floating wind turbine (100) is mounted.

17. The control system (170) according to claim 16, wherein, the detection devices (271, 272, 273, 274) are mounted to the mooring cables (151, 154) of the fixed structure.

18. The control system (170) according to any one of claims 1 to 5, wherein, the detection devices (271, 272, 273, 274) include strain gauges (274).

19. The control system (170) according to any one of claims 1 to 5, wherein, The detection devices (271, 272, 273, 274) include sensors configured to detect the operating mode of the floating wind turbine (100).

20. The control system (170) according to any one of claims 1 to 5, wherein, the actuation devices (281, 282) include adjustable spoilers and / or active blade attachments on the nacelle.

21. The control system (170) according to any one of claims 1 to 5, wherein, the actuation devices (281, 282) include a mooring cable actuator (281).

22. The control system (170) according to any one of claims 1 to 5, wherein, the actuation devices (281, 282) include adjustable dampers configured to damp the vibrations of the floating wind turbine (100).

23. The control system (170) according to any one of claims 1 to 5, wherein, the actuation devices (281, 282) include liquid dampers, mass dampers, and / or vortex-induced vibration brakes.

24. A floating wind turbine (100), comprising: a wind rotor including blades (140), a tower (130) to which the wind rotor is mounted, a floating foundation (120) to which the tower (130) is mounted, and the control system (170) according to any one of claims 1 to 23.

25. A method for stabilizing a floating wind turbine (100), the method comprising: monitoring an offset (231) from a predetermined floating body pitch angle (393) of the floating wind turbine (100) and an offset from a predetermined floating body yaw angle of the floating wind turbine (100), monitoring an oscillatory motion (396) of the floating body pitch angle (392) and an oscillatory motion of the floating body yaw angle, wherein the predetermined floating body pitch angle (393) and the predetermined floating body yaw angle define a predetermined equilibrium state of the floating wind turbine (100), wherein thresholds (394, 395) of the oscillatory motion (396) of the floating body pitch angle (392) and the oscillatory motion of the floating body yaw angle further define the predetermined equilibrium state of the floating wind turbine (100), manipulating the floating body pitch angle (392) and the floating body yaw angle until the predetermined equilibrium state is satisfied, manipulating the oscillatory motion (396) of the floating body pitch angle (392) and the oscillatory motion of the floating body yaw angle until the predetermined equilibrium state of the floating wind turbine (100) is satisfied.

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