Method for controlling wind turbine during yaw operation

Abstract

The present disclosure relates to a method (100, 200, 300) for controlling a wind turbine (10) during yaw operation. The disclosure further relates to a control system (92) for a wind turbine and a wind turbine (10). A method for operating a wind turbine (10) during yaw operation includes operating one or more yaw drivers (35) to rotate a nacelle (16) relative to a tower (15). In addition, the method includes predicting an end of the yaw operation, and in response to predicting the end of the yaw operation, actuating the hydraulic brake (94) prior to the predicted end.

Description

Technical Field

[0001] The present disclosure relates to wind turbines, and more particularly, to yaw systems and methods for controlling yaw systems. Background Art

[0002] Modern wind turbines are commonly used to supply electricity to an electricity grid. Such wind turbines generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, begins to rotate under the influence of the wind on the blades. The rotation generates a torque which is generally transmitted to a generator via a rotor shaft directly ("direct drive" or "gearless") or by using a gearbox. In this way, the generator generates electricity which can be supplied to an electricity grid.

[0003] The wind turbine hub may be rotatably coupled to the front of the nacelle. The wind turbine hub may be connected to the rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of the wind turbine tower that may house and protect the gearbox (if present) and the generator (if not placed outside the nacelle), and depending on the wind turbine, may house and protect additional components such as a power converter and auxiliary systems.

[0004] A wind turbine typically comprises a yaw system for rotating the rotor and the nacelle relative to the tower about a longitudinal axis of the tower.

[0005] During power generation operation, the wind direction may change. When the wind turbine rotor is misaligned with respect to the wind direction, the yaw system rotates the nacelle around the longitudinal axis of the tower to achieve alignment with the wind. It can be determined that the nacelle and the rotor are no longer aligned with the prevailing wind direction based on, for example, a weather vane mounted on the nacelle. However, other methods based on measuring loads and / or oscillations are also known. In general, if the prevailing wind direction deviates from the rotor and nacelle orientation by more than a predefined threshold value (e.g., 5°, 7°, or 10° or more) for at least a predetermined time period, the yaw system may be enabled. The predetermined time period may be 1 minute, 5 minutes, 10 minutes, or longer. For example, a second to minute average, such as a 3 second, 10 second, 1 minute, or 5 minute average, may be determined to calculate the direction of the prevailing wind speed.

[0006] In addition to power generation, other operating modes may also involve rotation of the nacelle around the longitudinal axis of the tower. A non-limiting example is a cable untwisting operation. The wind turbine includes cables (power cables and / or other cables) that may be fixed at their ends, for example from a component in the nacelle to some other component at a certain point in the tower. As a result of the previously mentioned rotation during the power generation operation, the cables may become twisted. Typically, there is a twisting limit, beyond which the cable may be damaged. Before such a limit is reached, the cables need to be untwisted. To this end, the untwisting operation of the wind turbine may include stopping the wind turbine and yaw the nacelle until a predetermined orientation is reached in which the cables are substantially untwisted.

[0007] The yaw system generally performs this rotation of the nacelle with the aid of a yaw drive comprising a plurality of motors, such as electric motors or hydraulic motors, with a suitable gearbox for driving a gear (pinion) meshing with a ring gear or a toothed ring attached to the nacelle or the wind turbine tower. Thus, the nacelle can be rotated about the longitudinal axis of the tower in or away from the wind direction. The rotatable connection between the wind turbine tower and the nacelle is called a yaw bearing. The yaw bearing can be of roller type or sliding type.

[0008] Typically, when the rotor is positioned according to a desired orientation (e.g. aligned with the wind direction in the case of power generation operation), the yaw system maintains the orientation with the aid of brakes (e.g. motor brakes of the yaw motor and / or hydraulic brake calipers). These brakes can be activated and deactivated by the wind turbine control system.

[0009] In particular, it is known that wind turbine controllers activate and deactivate different components in a defined sequence when a desired orientation is reached during yaw operation. Thus, once the desired orientation is reached, a stop command is provided to the motor and a command is sent to activate a yaw braking system, such as a hydraulic brake. Furthermore, it is known to send a command to a motor brake of the yaw motor to also block the motor after a certain period of time.

[0010] It has surprisingly been found that in some situations, in particular in high and / or gusty winds, the aforementioned operation may lead to misalignment and premature wear and cracking of the yaw system.

[0011] The present disclosure seeks to provide an improved method of operating a wind turbine and a wind turbine that at least partially mitigates one or more of the aforementioned problems. Summary of the invention

[0012] In one aspect of the present disclosure, a method for operating a wind turbine during a yaw operation is provided. The method includes operating one or more yaw drives to rotate a nacelle relative to a tower. The method also includes predicting an end of the yaw operation, and in response to predicting an end of the yaw operation, actuating a hydraulic brake before the predicted end.

[0013] According to this aspect, the yaw operation sequence is such that actuation of the hydraulic brake is performed in response to predicting the end of the yaw operation rather than at or after the end. That is, the operating state of the hydraulic brake is changed in response to predicting the end of the yaw operation. The actuation is performed in anticipation of the predicted end so that a suitable braking torque is applied when the time for the end of the yaw operation is reached. The braking torque mitigates potential slippage of the nacelle when the yaw operation stops, which potential slippage can cause uncontrolled movement of the nacelle. With this operation, the risk of damage, failure or premature wear of wind turbine components is mitigated.

[0014] In a further aspect of the present disclosure, another example of a method for operating a wind turbine during a yaw maneuver is provided. The method includes operating one or more yaw drives to rotate the nacelle relative to the tower. The method includes predicting an end of the yaw maneuver and actuating the hydraulic brake prior to the predicted end such that a braking torque applied by the hydraulic brake at the predicted end of the yaw maneuver is at least 60%, particularly at least 70%, and more particularly at least 80% of its rated value.

[0015] In a further aspect of the present disclosure, a control system for a wind turbine is provided. The control system is configured to perform a method according to any example of the aforementioned aspects. The control system is configured to instruct one or more yaw drives to rotate a nacelle of the wind turbine relative to a tower during a yaw operation, and predict an end of the yaw operation. The control system is further configured to control actuation of a hydraulic brake prior to the predicted end in response to predicting the end of the yaw operation.

[0016] In another aspect of the present disclosure, a wind turbine is provided. The wind turbine includes a tower, a nacelle rotatably mounted on the tower, and a yaw system for rotating the nacelle relative to the tower around a longitudinal axis of the tower. In addition, the wind turbine includes a control system according to the previous example of the present disclosure.

[0017] Technical solution 1. A method for controlling a wind turbine during a yaw operation, the wind turbine comprising a nacelle, a tower and a yaw system for rotating the nacelle relative to the tower about a longitudinal axis of the tower, the yaw system comprising a hydraulic brake and one or more yaw drives, the method comprising:

[0018] operating the yaw drive to rotate the nacelle relative to the tower;

[0019] predicting an end of the yaw maneuver;

[0020] In response to predicting the end of the yaw maneuver, the hydraulic brake is actuated prior to the predicted end.

[0021] Technical Solution 2. A method according to Technical Solution 1, wherein predicting the end of the yaw operation includes predicting a time for completing the yaw operation and / or a nacelle orientation relative to the tower for completing the yaw operation.

[0022] Technical Solution 3. A method according to Technical Solution 1 or 2, wherein the hydraulic brake has a rated braking torque, and wherein the braking torque applied by the hydraulic brake at the predicted end is at least 60%, particularly at least 70%, and more particularly at least 80% of its rated braking torque.

[0023] Technical solution 4. A method according to any of the foregoing technical solutions, wherein the pressure of the hydraulic brake reaches a predetermined percentage of its rated pressure within the hydraulic brake pressure rise time, in particular 80%, and wherein actuating the hydraulic brake before the predicted end includes actuating the hydraulic brake based on the hydraulic brake pressure rise time.

[0024] Technical Solution 5. A method according to Technical Solution 4, wherein actuating the hydraulic brake based on the hydraulic brake pressure rise time includes actuating when the remaining time until the predicted end is substantially equal to the hydraulic brake pressure rise time.

[0025] Technical Solution 6. A method according to any of the preceding technical solutions, wherein predicting the end of the yaw operation comprises predicting a time when the nacelle will reach a predetermined orientation relative to the tower.

[0026] Technical Solution 7. A method according to any one of Technical Solutions 1 to 5, wherein predicting the end of the yaw operation includes predicting the time when the error between the orientation of the nacelle and the prevailing wind direction is equal to or lower than a threshold and / or the orientation of the nacelle relative to the tower.

[0027] Technical Solution 8. A method according to Technical Solution 7, wherein the time when the error between the orientation of the nacelle and the prevailing wind direction is equal to or lower than a threshold and / or the orientation of the nacelle relative to the tower is predicted based on the actual wind direction, the actual orientation of the nacelle relative to the tower and the rotation speed of the nacelle.

[0028] Technical Solution 9. A method according to any one of Technical Solutions 1-8, wherein the yaw drive includes a yaw motor, and wherein the yaw motor includes a motor brake, and the method further includes stopping the yaw motor when the predicted end is reached.

[0029] Technical Solution 10. The method according to Technical Solution 9 includes activating the motor brake after stopping the yaw motor.

[0030] Technical solution 11. A method according to Technical solution 10, wherein the motor brake is enabled after reaching the predicted end and / or after a predetermined delay after stopping the yaw motor.

[0031] Technical Solution 12. The method according to Technical Solution 10 further includes determining a cabin speed and activating the motor brake when the cabin speed reaches a predetermined minimum speed threshold.

[0032] Technical Solution 13. The method according to Technical Solution 10 further includes determining a cabin speed and / or a cabin acceleration, and enabling the motor brake when the cabin speed reaches a predetermined maximum speed threshold and / or when the acceleration reaches a predetermined maximum acceleration threshold.

[0033] Technical Solution 14. A control system for a wind turbine, characterized in that the control system is configured to execute the method according to any one of Technical Solutions 1-13.

[0034] Technical solution 15. A wind turbine comprising a tower, a nacelle rotatably mounted on the tower, and a yaw system for rotating the nacelle relative to the tower around a longitudinal axis of the tower, and a control system according to Technical solution 14. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 illustrates a perspective view of one example of a wind turbine;

[0036] Figure 2 Graphics Figure 1 A simplified interior view of an example of a nacelle of a wind turbine;

[0037] Figure 3 schematically illustrates an example of a yaw system;

[0038] Figure 4 A flow chart showing an example of a method for controlling a wind turbine during a yaw operation.

[0039] Figure 5 The operation of a yaw system during a yaw maneuver according to an example is schematically illustrated.

[0040] Figure 6 A flow chart showing another example of a method for controlling a yaw motor brake during yaw operation of a wind turbine.

[0041] Figure 7 The operation of a yaw system during a yaw maneuver according to another example is schematically illustrated.

[0042] Figure 8 A flow chart showing a further example of a method for controlling a yaw motor brake during yaw operation of a wind turbine.

[0043] Fig. 9 The operation of a yaw system during a yaw maneuver according to a further example is schematically illustrated.

[0044] Fig.10 The operation of a yaw system according to the prior art during a yaw maneuver is schematically illustrated. DETAILED DESCRIPTION

[0045] Reference will now be made in detail to the embodiments, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation only and not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present disclosure. For example, a feature illustrated or described as part of one example may be used together with another example to produce yet another additional example. Therefore, the present disclosure is intended to cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0046] Figure 1 is a perspective view of an example of a wind turbine 10. In this example, the wind turbine 10 is a horizontal-axis wind turbine. Alternatively, the wind turbine 10 may be a vertical-axis wind turbine. In this example, the wind turbine 10 includes a tower 15 extending from a support system 14 on the ground 12, a nacelle 16 mounted on the tower 15, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to the hub 20 and extending outwardly from the hub 20. In this example, the rotor 18 has three rotor blades 22. In alternative embodiments, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be made of tubular steel to define a cavity ( Figure 1 1 ). In alternative embodiments, the tower 15 is any suitable type of tower having any suitable height. According to an alternative, the tower may be a hybrid tower including a portion made of concrete and a tubular steel portion. Furthermore, the tower may be a partial lattice tower or a full lattice tower.

[0047] Rotor blades 22 are spaced about hub 20 to facilitate rotating rotor 18 to enable kinetic energy to be converted from the wind into usable mechanical energy and subsequently into electrical energy. Rotor blades 22 are mated to hub 20 by coupling blade root regions 24 to hub 20 at a plurality of load transfer regions 26. Load transfer regions 26 may have hub load transfer regions and blade load transfer regions (neither of which is present at the hub). Figure 1 ). Loads induced to rotor blades 22 are transferred to hub 20 via load transfer regions 26 .

[0048] In an example, rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 m or longer. Rotor blades 22 may have any suitable length that enables wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include 20 m or less, 37 m, 48.7 m, 50.2 m, 52.2 m, or a length greater than 91 m. When wind strikes rotor blades 22 from a wind direction 28, rotor 18 rotates about rotor axis 30. When rotor blades 22 rotate and are subjected to centrifugal forces, rotor blades 22 are also subjected to various forces and moments. As such, rotor blades 22 may deflect and / or rotate from a neutral or non-deflected position to a deflected position.

[0049] In addition, the pitch angle of rotor blades 22 (i.e., the angle that determines the orientation of rotor blades 22 relative to the wind direction) can be changed by pitch system 32 to control the load and power output of wind turbine 10 by adjusting the angular position of at least one rotor blade 22 relative to the wind vector. A pitch axis 34 is shown for rotor blades 22. During operation of wind turbine 10, pitch system 32 can specifically change the pitch angle of rotor blades 22 such that the angle of attack of (portions of) the rotor blades is reduced, which facilitates reducing the rotational speed and / or facilitating stalling of rotor 18.

[0050] In this example, the blade pitch of each rotor blade 22 is individually controlled by wind turbine controller 36 or pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0051] Furthermore, in this example, as wind direction 28 changes, nacelle 16 may be rotated about the longitudinal axis of the tower (ie, about yaw axis 38 ) to position rotor blades 22 relative to wind direction 28 .

[0052] In this example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed system throughout the wind turbine 10, on the support system 14, within the wind farm, and / or at a remote control center. The wind turbine controller 36 may include a processor 40 configured to perform some of the methods and / or steps described herein. In addition, many other components described herein include processors.

[0053] As used herein, the term "processor" is not limited to the integrated circuits known in the art as computers, but broadly refers to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that the processor and / or control system may also include memory, input channels, and / or output channels.

[0054] The control system 36 may also include a memory, such as one or more memory devices. The memory may include (one or more) memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk-read only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements. (One or more) such memory devices may generally be configured to store suitable computer-readable instructions that, when implemented by (one or more) processors 40, configure the controller 36 to perform or trigger the execution of various steps disclosed herein. The memory may also be configured to store data, such as data from measurements and / or calculations.

[0055] Figure 21 is an enlarged cross-sectional view of a portion of a wind turbine 10. In this example, the wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to the nacelle 16. More specifically, the hub 20 of the rotor 18 is rotatably coupled to a generator 42 positioned within the nacelle 16 via a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In this example, the main shaft 44 is at least partially disposed coaxially with a longitudinal axis (not shown) of the nacelle 16. The rotation of the main shaft 44 drives the gearbox 46, which in turn drives the high-speed shaft 48 by converting relatively slow rotational movement of the rotor 18 and the main shaft 44 into relatively fast rotational movement of the high-speed shaft 48. The high-speed shaft 48 is connected to the generator 42 by means of a coupling 50 for generating electrical energy. In addition, a transformer 90 and / or suitable electronic devices, switches and / or inverters may be arranged in the nacelle 16 to transform the electrical energy generated by the generator 42 having a voltage between 400 V and 1000 V into electrical energy having a medium voltage (e.g., 10-35 kV). The electrical energy is conducted from the nacelle 16 to the tower 15 via power cables.

[0056] The gearbox 46, the generator 42, and the transformer 90 may be supported by the main support structural frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 by one or more torque arms 55. In this example, the nacelle 16 also includes a front main support bearing 60 and a rear main support bearing 62. In addition, the generator 42 may be mounted to the main frame 52 by a separate support device 54, in particular in order to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thereby causing a noise emission source.

[0057] Optionally, the main frame 52 is configured to carry all loads caused by the weight of the components of the rotor 18 and the nacelle 16 and by wind and rotational loads, and is further configured to introduce these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, the generator 42, the gearbox 46, the high speed shaft 48, the coupling 50, and any associated fastening, support and / or fixing equipment (including but not limited to the support 52 and the front support bearing 60 and the rear support bearing 62) are sometimes referred to as the drive train 64.

[0058] In some examples, the wind turbine may be a direct drive wind turbine without a gearbox 46. In a direct drive wind turbine, the generator 42 operates at the same rotational speed as the rotor 18. Therefore, they generally have a much larger diameter than the generators used in wind turbines with a gearbox 46 for providing a similar amount of power compared to a wind turbine with a gearbox.

[0059] The nacelle 16 may also include a yaw system including a yaw bearing (in Figure 21 and 2. The yaw bearing has two bearing members configured to rotate relative to one another (not visible in FIG. 1 ). The tower 15 is coupled to one of the bearing members, and the bedplate or support frame 52 of the nacelle 16 is coupled to the other bearing member.

[0060] The yaw system may include ring gear 21 and yaw drive mechanism 56 that may be used to rotate nacelle 16 , and thereby also rotor 18 , about the longitudinal axis of the tower (ie, about yaw axis 38 ) to control the viewing angle of rotor blades 22 relative to wind direction 28 .

[0061] The yaw drive mechanism 56 may include a plurality of yaw drives 35 having a motor 33, a gearbox 37, and a pinion 39 for engaging with the ring gear 21 for rotating one of the bearing members relative to the other. The ring gear 21 may include a plurality of teeth that engage with the teeth of the pinion 39. Figure 2 In the example of , the yaw drive 35 and the ring gear 21 are placed outside the outer diameter of the tower. The teeth of the ring gear are oriented outwards, but in other examples, the ring gear and the yaw drive may be arranged at the interior of the tower.

[0062] In some examples, one of the yaw drives may be a "master drive" and the other drives may be "slave drives" that follow the instructions of the master drive or adapt their operation to suit the master drive.

[0063] The turbine controller 36 may be communicatively coupled to the yaw drive mechanism 56 of the wind turbine 10 for controlling and / or changing the yaw direction of the nacelle 16 relative to the wind direction 28. As the wind direction 28 changes, the wind turbine controller 36 may be configured to control the yaw angle of the nacelle 16 about the longitudinal axis of the tower or the yaw axis 38 to position the rotor blades 22 and, therefore, the rotor 18 relative to the wind direction 28, thereby controlling the loads acting on the wind turbine 10. For example, the turbine controller 36 may be configured to transmit a control signal or command to the yaw drive mechanism 56 of the wind turbine 10 via a yaw controller or direct transmission so that the nacelle 16 may rotate about the longitudinal axis of the tower or the yaw axis 38 via a yaw bearing.

[0064] To properly position nacelle 16 relative to wind direction 28, nacelle 16 may also include at least one meteorological measurement system, which may include a wind vane and anemometer. Meteorological measurement system 58 may provide information to wind turbine controller 36, which may include wind direction 28 and / or wind speed.

[0065] In this example, pitch system 32 is arranged at least in part as a pitch assembly 66 in hub 20. Pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a corresponding rotor blade 22 (at Figure 1), for modulating the pitch angle of rotor blades 22 along pitch axis 34. Figure 2 Only one of three pitch drive systems 68 is shown.

[0066] In this example, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and a corresponding rotor blade 22 (at Figure 1 34 ), for rotating the corresponding rotor blade 22 about the pitch axis 34. The pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. The pitch drive motor 74 is coupled to the pitch drive gearbox 76 so that the pitch drive motor 74 applies a mechanical force to the pitch drive gearbox 76. The pitch drive gearbox 76 is coupled to the pitch drive pinion 78 so that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. The pitch bearing 72 is coupled to the pitch drive pinion 78 so that rotation of the pitch drive pinion 78 causes rotation of the pitch bearing 72.

[0067] Pitch drive system 68 is coupled to wind turbine controller 36 for adjusting the pitch angle of rotor blades 22 upon receiving one or more signals from wind turbine controller 36. In this example, pitch drive motor 74 is any suitable motor driven by electrical power and / or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, pitch assembly 66 may include any suitable structure, construction, arrangement, and / or components, such as, but not limited to, a hydraulic cylinder, a spring, and / or a servo mechanism. In certain embodiments, pitch drive motor 74 is driven by energy extracted from the rotational inertia of hub 20 and / or a stored energy source (not shown) that supplies energy to components of wind turbine 10.

[0068] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive system 68 according to control signals from the wind turbine controller 36 in the event of certain priority situations and / or during overspeed of the rotor 18. In this example, the pitch assembly 66 includes at least one pitch control system 80 that is communicatively coupled to a corresponding pitch drive system 68 for controlling the pitch drive system 68 independently of the wind turbine controller 36. In this example, the pitch control system 80 is coupled to the pitch drive system 68 and the sensor 70. During normal operation of the wind turbine 10, the wind turbine controller 36 may control the pitch drive system 68 to adjust the pitch angle of the rotor blades 22.

[0069] According to an embodiment, a power generator 84, for example including a battery and a capacitor, is arranged at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and the pitch drive system 68 to provide a power source to these components. In this example, the power generator 84 provides a continuous power source to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, the power generator 84 provides power to the pitch assembly 66 only during an electrical power loss event of the wind turbine 10. The electrical power loss event may include a grid loss or voltage drop (dip), a fault in the electrical system of the wind turbine 10, and / or a failure of the wind turbine controller 36. During the electrical power loss event, the power generator 84 operates to provide electrical power to the pitch assembly 66 so that the pitch assembly 66 can operate during the electrical power loss event.

[0070] In this example, pitch drive system 68, sensor 70, pitch control system 80, cables, and power generator 84 are each positioned within a cavity 86 defined by an inner surface 88 of hub 20. In alternative embodiments, the components are positioned relative to an outer surface of hub 20 and may be coupled directly or indirectly to the outer surface.

[0071] Figure 3 Part of a yaw system according to one example is illustrated. The yaw system includes a yaw bearing 98 having a first bearing member 95 coupled to the tower 15 and a second bearing member 96 coupled to the main frame 52 of the nacelle. The yaw system includes a ring gear 21, which in this example is coupled to the first bearing member 95. Other configurations are also possible, such as, for example, the ring gear 21 may be coupled to the tower 15. The yaw system includes a yaw drive 35, and in this example, the yaw drive 35 includes a motor 33, a gearbox 37, and a pinion 39 for meshing with the ring gear 21. Rotation of the motor may cause the pinion to rotate relative to the ring gear 21. As mentioned, in this example, the ring gear 21 is coupled to the first bearing member 95, and thus the first bearing member 95 may rotate relative to the second bearing member 96 coupled to the main frame 52. Although only a single yaw drive is shown, it should be clear that multiple yaw drives may be provided around the circumference of the tower, each yaw drive having its motor, gearbox, and pinion.

[0072] The ring gear 21 may include a plurality of teeth that engage with the teeth of the pinion 39. In this example, the yaw drive 35 and the ring gear 21 are placed outside the outer diameter of the tower. The teeth of the ring gear 21 are oriented outwardly. However, in other examples, the ring gear 21 and the yaw drive 35 may be placed inside the tower.

[0073] Figure 3The yaw system further includes a brake disc 93 and a hydraulic brake unit 94 configured to apply a braking force on the brake disc 93 for braking the rotation of the first bearing member 95 relative to the second bearing member 96. Although only a single hydraulic brake unit is shown, a plurality of brake units may be provided along the circumference of the tower.

[0074] exist Figure 3 , the brake disc 93 is connected to the tower 15. In other examples, the brake disc 93 may be integrally formed with the tower 15. The hydraulic brake unit 94 may include a brake caliper attached to the support frame 52, and may engage the brake disc 93 to prevent the rotation of the nacelle 16 relative to the tower 15. In order to activate the brake unit 94, i.e., engage the brake disc 93, the hydraulic brake unit 94 may include an active hydraulic system to control the pressure of the brake caliper on the brake disc 93.

[0075] In some examples, actuation of the brake unit 94 may be controlled by the controller 92. In some examples, the controller 92 may be embodied in a wind turbine controller. The controller 92 may enable or disable the brake unit 94, or the controller 92 may actuate the brake unit 94 to control the pressure of the hydraulic system in order to control the braking torque applied by the brake unit 94 when engaging the brake disc 93. In particular, during rotation of the nacelle, a moderate braking torque (e.g., in the range of 20-40%, depending on the design and operating mode) may be applied to provide some damping 16, and actuation may be required to increase the braking torque applied by the brake unit 94 to stop the yaw operation.

[0076] In some examples, the motor 33 may include a motor brake 91. The motor brake 91 may be disposed inside a housing of the motor 33, and the motor brake 91 may be arranged to prevent rotation of the motor 33. The motor brake 91 may include a friction brake in which a friction disk is fixed to a rotatable shaft of the electric motor 33. The friction disk may be configured to engage a non-rotating surface, thereby applying a braking torque on the system.

[0077] Figure 3 Also illustrated in FIG. 9 is a control system 92 configured to control the yaw system according to an algorithm. In this example, a stand-alone control system 92 is depicted. However, it is understood that control of the yaw system may be implemented in any controller including, for example, the wind turbine controller 36.

[0078] Figure 3 The yaw system of includes a roller bearing type bearing 98. However, other types of bearings, such as plain yaw bearings, are well known in the art and may also be used in other examples.

[0079] Figure 3The motor shown in the figure can be directly connected to the power supply source, or the motor can be connected to the power supply source via a vertical frequency driver VFD (not shown in the figure). The use of such a VFD is well known in the art, so no further details are provided herein.

[0080] Fig.10 The time evolution of a yaw maneuver according to a method of the prior art is depicted. In particular, the behavior of the system at the end of the yaw maneuver is depicted. Line 901 shows the yaw control command, which at t END The hydraulic brake 94 (whose evolution is represented by line 904) changes from a high level to a low level at t to indicate the end condition for the yaw operation. Line 902 shows the state of the yaw motor 33, which is stopped at the end of the yaw operation so that no driving torque is applied to rotate the nacelle relative to the tower. ... END 904 , the hydraulic brakes 94 may be activated when the yaw maneuver is complete to help stop the rotation by applying a corresponding braking torque. Finally, after a certain unavoidable delay, the motor brakes 91 are also activated after the yaw maneuver is complete. The actuation of the hydraulic brakes 94 represented in line 904 may not necessarily involve "activation" of the hydraulic brakes 94 (i.e., "turning on" the brakes). In some applications, the hydraulic brakes 94 may already be applying a moderate braking torque during the yaw maneuver, so that the transition in line 904 will represent a change in the operating state of the hydraulic brakes 94 (but not necessarily activation) to increase their braking torque.

[0081] As mentioned in the introduction, it has been found that this prior art approach can lead to misalignment and premature wear of the yaw system. It has been observed that misalignment causes an increased number of yaw operations for the wind turbine and in some cases it requires shutting down the wind turbine, which increases economic costs and further increases wear of components.

[0082] After careful analysis, the inventors identified a problem at the end of the yaw operation. The yaw motor 33 is END t is deactivated, so that it is no longer possible to control the nacelle 16 via the motor 33. On the other hand, it has been found that even if the hydraulic brake 94 is END 16 is activated, there is also a period during which the braking capacity of the hydraulic brakes 94 is insufficient to control the movement of the nacelle 16. During this time frame, the nacelle 16 is still subject to certain loads, such as wind loads, and the nacelle 16 may slip, especially in the case of high wind loads due to, for example, the presence of high prevailing wind speeds or gusts. The inventors have found that such slipping may result in uncontrolled nacelle acceleration.

[0083] As a result of this movement of the nacelle 16, the yaw speed (line 905) may be subject to changes as determined by t ENDThe uncontrolled deviation is represented by the dashed line 905. It has been found that these nacelle accelerations can cause the nacelle to END Further movement thereafter may result in significant yaw misalignment or in significant wear or damage to wind turbine components such as components of the yaw system itself or even other components of the wind turbine (in the case of very high slip), resulting in mechanical loads exceeding the design loads. As an example, the motor brake 91 may be applied at t MOT is actuated at t, but depending on the prevailing conditions, MOT The yaw speed may be too great, which may cause premature wear of the motor brake 91.

[0084] Based on these observations, the inventors have developed a new control method for yaw maneuvers as explained below.

[0085] In an example of the present disclosure, a method 100 for controlling a wind turbine 10 during yaw operation is provided. The method 100 includes: Figure 4 The method includes operating the yaw drive 35 to rotate the nacelle 16 relative to the tower 15 at box 110. The method further includes predicting the end of the yaw operation at box 120. Box 130 of the method includes, in response to predicting the end of the yaw operation in box 120, actuating the hydraulic brake 94 before the predicted end.

[0086] It should be noted that actuating the hydraulic brake may result in the activation of the hydraulic brake or in a modification of the operating conditions of the hydraulic brake. As mentioned previously, it is known from examples of the prior art that during yaw maneuvers a certain braking torque may be applied by the hydraulic brake to provide a certain damping. Thus, it is known to operate the hydraulic brake at 20-40% of the rated torque of the hydraulic brake when yawed during power generation, so that damping is achieved in some prior designs. In such a case, the actuation of the hydraulic brake according to the present disclosure, which is performed in response to predicting the end of the yaw maneuver itself, will result in a change in the braking torque, and more specifically in an increase in the braking torque to be higher than the braking torque applied during the yaw rotation.

[0087] In some other operating modes, namely when yaw for cable untwisting, lower values ​​(or even 0%) may be used during yaw.In those cases, actuation according to this aspect may result in activation of the hydraulic brakes.

[0088] The specific value depends on certain design details of the yaw system in the wind turbine. For example, a yaw system comprising sliding bearings can achieve a sufficient level of damping during the power generation mode with less pressure (or even no pressure) on the hydraulic brakes than a yaw system comprising ball bearings.

[0089] Now refer to Figure 5 To explain this example of the present disclosure, Figure 5 The time evolution of the yaw operation according to the method 100 and the evolution of the nacelle rotation speed during the yaw operation are illustrated. Line 101 shows a yaw control command for starting the yaw operation (by switching from low to high in the diagram) or for indicating that an end condition for the yaw operation has been reached, in which case the yaw control signal switches from high to low. The command is provided by the controller 92, which controls the yaw operation of the wind turbine and can be a stand-alone controller or a controller implemented in the wind turbine controller 36.

[0090] Line 102 shows the state of the yaw motor 33. When the yaw control signal switches from low to high, the yaw motor 33 is enabled, so that a driving torque is applied by the yaw drive 35 to actively rotate the nacelle 16 relative to the tower 15 and initiate a yaw operation. Line 103 shows the behavior of the motor brake 91, which is also deactivated when the yaw system receives an indication to initiate a yaw operation to allow the yaw operation to occur. The evolution 104 of the hydraulic brake 94 is also illustrated in this example, and when the yaw operation is started, the pressure of the hydraulic brake 94 is reduced, so that the braking torque applied by the hydraulic brake 94 is reduced. Finally, 105 schematically represents the yaw speed, i.e. the rotation speed of the nacelle 16 when the nacelle 16 rotates about the longitudinal axis of the tower 15. As expected, the activation of the yaw control signal 101 causes the yaw speed 104 to increase for a short period of time until a stable speed for the yaw operation is reached.

[0091] According to this example of the disclosure, the end of the yaw maneuver is predicted during the yaw maneuver.A high frequency may be used for the prediction, which in a specific example comprises a cycle time for the prediction of between 20-100 ms and more particularly 40 ms during the yaw maneuver.

[0092] exist Figure 5 In the example shown in , the end of the yaw maneuver occurs at time t END According to this example of the method, and more particularly according to frame 130 of method 100, the hydraulic brake 94 is applied at an earlier time t HYD As shown in curve 104, the braking torque increases at the early stage and the braking torque increases at time t END A significant braking torque is achieved at T. HYD According to this example, the braking torque caused by the early activation of the hydraulic brake 94 reduces the potential slip of the nacelle 16 that occurs during the completion of the yaw maneuver.

[0093] In an example of a method for operating a wind turbine, predicting the end of a yaw maneuver includes predicting a time for completing the yaw maneuver and / or predicting an orientation of the nacelle 16 relative to the tower 15 for completing the yaw maneuver. In particular, as described in further detail below with respect to some specific examples, different methods may be used for predicting the end of the yaw maneuver, which may depend on, for example, the cause of the yaw maneuver. In some cases, the end of the yaw maneuver may be better defined by a specific time before which the yaw maneuver is expected to end (or a time remaining relative to a current time) or by a specific orientation that the nacelle 16 is expected to exhibit at the end of the yaw maneuver.

[0094] In an example of the method, the hydraulic brake 94 is characterized by a rated braking torque. The method comprises applying the brake in a manner and at a time t HYD The hydraulic brake 94 is actuated at t END The braking torque applied is at least 60%, particularly 70% or more particularly at least 80% of the rated value. As the value of the braking torque increases, the potential slip of the nacelle is further reduced, and therefore, the potential risk of damage or failure of wind turbine components is further mitigated.

[0095] In another example of a method for operating a wind turbine during a yaw operation, the evolution of the pressure of the hydraulic brake 94 is considered. Thus, the hydraulic brake 94 can be defined by the time required for its pressure to reach a predetermined value from the start of the operating situation (i.e., the hydraulic brake pressure rise time). In particular, the predetermined value may refer to a percentage of the hydraulic pressure rated value, such as, for example, 80%, 90% or 100% of the rated value. Thus, in this example, before the predicted end time (i.e., at t END Before) in t HYD Actuating the hydraulic brake 94 at the predicted time t may include actuating the hydraulic brake 94 based on the hydraulic brake pressure rise time. In a more specific example, actuating the hydraulic brake 94 based on the hydraulic brake pressure rise time includes actuating the brake 94 when the remaining time until the end of the prediction is substantially equal to the hydraulic brake pressure rise time. In other words, at the predicted time t END When t HYD , so that t END -t HYD is substantially equal to the hydraulic brake pressure rise time. In the case of this example, the hydraulic brake 94 is applied at t END The braking torque applied is close to the value expected for the predetermined value of the hydraulic pressure, which may be, for example, 80%, 90% or 100% of the rated value of the hydraulic pressure. This will result in a high braking torque being applied, so that the nacelle 16 slip and the associated risks are highly mitigated.

[0096] The hydraulic brake pressure rise time may be determined as the time required for the pressure to reach a predetermined value (e.g., a percentage of a rated value) when starting from a value of pressure corresponding to operation of the hydraulic brake 94 during a yaw operation. In some examples, the hydraulic brake 94 may be deactivated during a rotation. However, in some other cases, the hydraulic brake 94 may apply a moderate braking torque, such as 40% of its rated value, for damping purposes. In the former case, the hydraulic pressure rise time will correspond to the time required to increase the pressure from 0% of a predetermined value (e.g., a percentage of a rated value) to a predetermined value, while in the latter case, the hydraulic pressure rise time will correspond to the time required to increase the pressure from 40% of the rated value to the predetermined value.

[0097] In an example of a method for operating a wind turbine, predicting the end of a yaw maneuver includes predicting a time when the nacelle 16 will reach a predetermined orientation relative to the tower 15. This may be the case for some yaw maneuvers involving deterministic yaw movements, such as, for example, movements associated with a cable untwist operation, in which a final orientation of the nacelle 16 relative to the tower 15 is predetermined based on the arrangement of the cables relative to the tower 15. In such a case, the orientation of the nacelle 16 at the end of the yaw maneuver may be known, but the time required to reach that position may need to be predicted, as this may depend on different designs and / or prevailing operating conditions.

[0098] In yet another further example, predicting the end of the yaw operation includes predicting the time when the error between the orientation of the nacelle 16 and the prevailing wind direction 28 is equal to or below a threshold and / or the orientation of the nacelle 16 relative to the tower 15. This may be the case in certain operating modes involving non-deterministic movement of the nacelle 16, such as the power generation mode. Indeed, it is known that, especially during the power generation mode, the goal is to align the rotor 18 of the wind turbine 10 with the prevailing wind direction. However, the wind direction 28 is constantly changing, and thus the changing yaw error is defined in real time as the difference between the wind direction 28 and the actual orientation of the nacelle 16.

[0099] The wind direction 28 may be measured with a wind vane, estimated from load measurements, or obtained in other ways known in the art. Since the wind direction 28 may change rapidly, an average value obtained, for example, over a ten minute period may be used. In order to ensure optimal energy capture from the wind and proper load control, a yaw error threshold value that may not be exceeded may be defined. In particular, a yaw error threshold value may be defined for the activation of the yaw system. In the event that the determined yaw error exceeds the threshold value, activation of the yaw system may be performed in order to reduce the misalignment. Similarly, the yaw error threshold value may be used to indicate the end of the yaw operation after the orientation of the nacelle 16 reduces the misalignment of the nacelle 16 relative to the wind direction 28 to a sufficiently low value. In some examples, a hysteresis may be provided so that the value of the yaw error threshold value for activating the yaw system is greater than the value of the yaw error threshold value for indicating an end condition.

[0100] In some examples, actual wind direction 28, actual orientation of nacelle 16 relative to tower 15, and rotation speed of nacelle 16 may be used to predict an end time when the yaw operation ends or an orientation of the nacelle relative to tower 15. In particular, actual wind direction 28 and actual orientation of nacelle 16 may be used to derive an actual yaw error. The evolution of the yaw error over time may then be used to predict a time and / or a corresponding orientation of nacelle 16 when the yaw error satisfies a threshold condition to end the yaw operation.

[0101] In another example of a method for operating a wind turbine during yaw operation, a yaw drive 35 comprises at least one motor 33, at least one motor 33 being driven at t END By stopping motor 33, no driving torque is applied to nacelle 16, so that the movement of nacelle 16 is determined by the braking torque applied by the braking system and by the load acting on wind turbine 10. In some examples, at least one motor 33 may be turned off at t END After a certain delay, it is closed. This delay can be useful to provide some additional time for the hydraulic brake 94 to build up its pressure and braking torque. However, this delay can be kept short to prevent any significant yaw deviation relative to the initial intended orientation.

[0102] In still other examples, the yaw drive 35 includes one or more yaw motors 33, and one or more yaw motors 33 include a motor brake 91. In those examples, the motor brake 91 can be activated at the end time t of the yaw operation. END After that, it is enabled after stopping the yaw motor 33. This behavior is also shown in Figure 5 middle, Figure 5 Depict the motor brake at t MOTThe activation of the motor brake 91 may be triggered differently according to different examples. The motor brake may include some friction elements that may wear out prematurely if the activation of the motor brake 91 occurs when the rotation speed is high. For this reason, it may be preferred to activate the motor brake 91 once the rotation speed has been significantly reduced. In this sense, examples of the present invention may include activating the motor brake 91 after a predetermined delay after the end of the yaw maneuver. In this case, t MOT and t END can be separated by some predetermined time delay, which can be selected based on the following estimation: at least under some conditions, at time t MOT The rotation speed is sufficiently low or even zero.

[0103] Figure 6 A flow chart of an example of another method 200 for controlling a wind turbine 10 during a yaw operation and more particularly for controlling a yaw motor 33 and a motor brake 91 during the end of a yaw operation is shown. In the method, the activation of the yaw motor brake 91 is not based on some predetermined time, but on the speed of the nacelle 16. The method comprises receiving an indication of the end of a yaw rotation operation at box 210. The indication may be generated by the controller 92 and this may be based on different criteria depending on the operating mode as explained above. Box 220 comprises stopping the yaw motor 33 so that the drive torque is no longer provided in an active manner. Box 230 comprises determining the nacelle speed, while box 240 comprises checking whether the nacelle speed has reached a predetermined minimum speed threshold (v MIN ). When the speed of the nacelle 16 is higher than v MIN , the method remains at box 240. Box 250 corresponds to the situation when the speed of the nacelle 16 reaches the minimum speed threshold, in which case the motor brake 91 is activated.

[0104] To further illustrate the method, Figure 7 Schematically shown are the evolution of a yaw control command 201, a yaw motor state 202, a yaw motor brake state 203, a yaw speed 204 of the nacelle during operation, and a change in the yaw orientation 205 of the nacelle 16 relative to the tower 15 during operation. Figure 5 As already explained, the yaw speed 204 increases when the yaw operation is enabled until a stable yaw speed is reached. The yaw operation is initiated at t END According to this example, the yaw motor 33 is stopped, as also indicated by the corresponding transition from high to low in the curve 202. The nacelle speed is then determined. Figure 7Two different scenarios are presented in , which result in different evolutions of the nacelle speed. Thus, both curves 204a and 204b exhibit the expected behavior during the braking process, ie the speed of the nacelle 16 decreases, but at different rates.

[0105] As mentioned previously, it may be preferred to activate the motor brake 91 at low speeds to prevent premature wear of the friction components. For this reason, the minimum speed threshold v is predetermined. MIN , the purpose of which is to maintain the wear of the motor brake within acceptable design parameters. In this particular example, curve 204a presents a curve where the nacelle speed is at t END Therefore, in this case, the activation time (t MOT_a ) is very close to the end time t for the yaw operation END .

[0106] On the other hand, curve 204b presents a scenario in which the deceleration of the nacelle takes more time so that the nacelle speed remains above the minimum threshold for a longer time. In this second case, the motor brake 91 is applied until t MOT_b is enabled. Note that this also has an impact on the final orientation of the nacelle. Therefore, curves 205a and 205b show the evolution of the yaw position after the end of the yaw maneuver. It can be observed how the yaw deviation is lower (205a) in the case where the nacelle speed reaches the minimum threshold for a short period of time, while in the scenario where the speed of the nacelle 16 remains above the minimum threshold for enabling the motor brake 91 for a longer time, a larger deviation in the yaw position can be observed (205b). The change from one scenario to another may depend on different factors, including but not limited to the prevailing wind conditions during the stopping sequence or the braking torque applied by other braking mechanisms that may be present in the wind turbine 10.

[0107] Figure 8 A flow chart of yet another additional example of a method 300 for controlling a wind turbine 10 during a yaw operation, and more particularly for operating a yaw motor 33 and a motor brake 91 during the end of a yaw operation, is shown. A box 310 is included, similar to box 210 of method 200, which includes receiving an indication of the end of a yaw rotation operation. Box 320 includes stopping the yaw motor 33. Box 330 includes determining a yaw speed of the nacelle and / or a yaw acceleration of the nacelle, and box 340 includes comparing those determined variables to some predetermined maximum thresholds. If the determined yaw speed or the determined yaw acceleration exceeds the respective predetermined threshold, the method continues to box 350, which includes activating the motor brake 91 so that further movement of the nacelle 16 is limited.

[0108] In this further example of a method for operating a wind turbine (which also consists of Fig. 9 In the example (schematically illustrating the time evolution of different elements in ), a different behavior compared to the previous example is considered. In particular, Fig. 9 The curves marked with "a" or "b" in FIG. 1 depict different scenarios in which the nacelle 16 does not decelerate as typically expected at the end of the yaw maneuver. Instead, in these examples, the nacelle 16 experiences an increased speed (304a) or acceleration (305b) after the yaw maneuver ends and the yaw motor 33 stops. Thus, the solid line (corresponding to the first "a" scenario) shows a scenario in which the nacelle speed 304a reaches a certain predetermined maximum threshold v MAX The dashed line (corresponding to the second "b" scenario) shows a situation in which a sudden increase in acceleration is observed at the end of the yaw maneuver, which causes the nacelle acceleration (305b) to reach a predetermined maximum threshold a MAX .

[0109] Different physical situations may lead to such behavior, including but not limited to very high gusts occurring at the time or failure of other braking mechanisms in the wind turbine 10, such as, for example, the hydraulic brake 94. In such a situation, this additional example shows the activation of the motor brake 91 even though the rotational speed is high. As mentioned previously, this is not a preferred operating mode for the motor brake 91, because operation at high speeds may induce significant wear or damage on the friction system of the motor brake 91. However, this example addresses certain scenarios in which the motor brake 91 may be used as a safety system for the wind turbine 10.

[0110] Fig. 9 The evolution of the yaw position 306 in the two scenarios mentioned above is also depicted. This schematically illustrates how the orientation of the nacelle 16 relative to the tower 15 exhibits some loss of control caused by extreme speed and / or acceleration. However, the magnitude of the loss of control is contained by activation of the motor brake 91.

[0111] even though Fig. 9 Examples involving methods for operating wind turbine 10 in which both nacelle speed and nacelle acceleration may be considered also include additional examples that may include using only speed or only acceleration to detect operating conditions where motor brake 91 may be activated as a safety mechanism.

[0112] The nacelle speed and the nacelle acceleration may relate to different directions of rotation of the nacelle 16 relative to the tower 15. In particular, the direction of the rotation may depend on the predicted time t at which the yaw maneuver is to be terminated. ENDThe load then acting on the wind turbine 10. In the above mentioned variants of the methods 200 and 300, the respective thresholds of the nacelle speed and the nacelle acceleration for activating the motor brake 91 may depend on the rotation direction of the nacelle 16 and more particularly on the rotation direction at t END Whether the rotation experienced afterwards is in the same direction as the rotation during the yaw maneuver.

[0113] Notice, Figure 5 , Figure 7 and Fig. 9 The evolution of the different quantities presented in and more particularly the evolution of the nacelle speed, nacelle acceleration and nacelle orientation are provided only for illustrative purposes to aid the understanding of these methods, but they should not be understood as accurately representing the operation of the nacelle.

[0114] The details and explanations of methods 100 , 200 , and 300 may be combined with and applied to each other.

[0115] According to another aspect of the present disclosure, a controller 92 is provided. The controller 92 is configured to perform a method of operating a wind turbine during yaw operation as described throughout the present disclosure or any equivalent examples (including combinations). The controller 92 may be implemented as a stand-alone controller to control the yaw system, or the controller 92 may be implemented as part of the wind turbine controller 36.

[0116] The controller 92 may be configured to receive a plurality of signals 501 , such as signals indicating wind direction 28 , orientation of the nacelle 16 relative to the tower 15 , nacelle speed, nacelle acceleration, etc. The controller 92 may use this information to derive a plurality of signals 502 to control the yaw system, including generating yaw control commands ( 101 , 201 , 301 ) and controlling the hydraulic brake 94 , the yaw motor 33 , or the motor brake 91 .

[0117] According to another aspect of the present disclosure, a wind turbine 10 is provided that includes a tower 15, a nacelle 16 rotatably mounted on top of the tower 15, a wind turbine rotor 18 including a plurality of wind turbine blades 22, and a yaw system. The wind turbine includes a controller 92 configured to perform a method as described throughout the present disclosure or any equivalent example (including combinations). In some examples, the wind turbine 10 may include a yaw system having a variable frequency drive (VFD) to control a yaw motor 33. The use of such a VFD may provide additional control capabilities to yaw operations.

[0118] This written description uses examples to disclose the present teachings, and also enables any person skilled in the art to practice the present teachings, including making and using any device or system and performing any incorporated method. The scope of patentability is defined by the claims, and may include other examples that occur to those skilled in the art. If such other examples have structural elements that are not different from the literal language of the claims, or if such other examples include equivalent structural elements that are not substantially different from the literal language of the claims, such other examples are intended to be within the scope of the claims. Aspects from the various examples described and other known equivalents for each such aspect may be mixed and matched by a person of ordinary skill in the art to construct additional examples and techniques according to the principles of the present application. If reference marks associated with the drawings are placed in brackets in the claims, they are merely used to attempt to increase the understandability of the claim and should not be interpreted as limiting the scope of the claim.

Claims

1. A method (100) for controlling a wind turbine (10) during a yaw operation, the wind turbine (10) comprising a nacelle (16), a tower (15) and a yaw system for rotating the nacelle (16) relative to the tower (15) about a longitudinal axis of the tower (15), the yaw system comprising a hydraulic brake (94) and one or more yaw drives (35), the method comprising: operating the yaw drive to rotate the nacelle (16) relative to the tower (15); predicting an end of the yaw maneuver; In response to predicting the end of the yaw maneuver, the hydraulic brake (94) is actuated prior to the predicted end.

2. The method according to claim 1, wherein: Predicting the end of the yaw maneuver includes predicting a time for completing the yaw maneuver and / or an orientation of the nacelle relative to the tower (15) for completing the yaw maneuver.

3. The method according to claim 1 or 2, wherein: The hydraulic brake (94) has a rated braking torque, and wherein the braking torque applied by the hydraulic brake (94) at the predicted end is at least 60%, particularly at least 70% and more particularly at least 80% of its rated braking torque.

4. A method according to any preceding claim, wherein: The pressure of the hydraulic brake (94) reaches a predetermined percentage, particularly 80%, of its rated pressure within a hydraulic brake pressure rise time, and wherein actuating the hydraulic brake (94) before the predicted end includes actuating the hydraulic brake (94) based on the hydraulic brake pressure rise time.

5. The method according to claim 4, wherein: Actuating the hydraulic brake (94) based on the hydraulic brake pressure rise time includes actuating when a remaining time until the predicted end is substantially equal to the hydraulic brake pressure rise time.

6. A method according to any preceding claim, wherein: Predicting the end of the yaw maneuver includes predicting when the nacelle (16) will reach a predetermined orientation relative to the tower (15).

7. The method according to any one of claims 1 to 5, wherein: Predicting the end of the yaw maneuver includes predicting a time when an error between the orientation of the nacelle and a prevailing wind direction (28) is equal to or below a threshold and / or the orientation of the nacelle relative to the tower (15).

8. The method according to claim 7, wherein: The invention relates to predicting the time when the error between the orientation of the nacelle (16) and the prevailing wind direction (28) is equal to or lower than a threshold value and / or the orientation of the nacelle relative to the tower (15) based on the actual wind direction (28), the actual orientation of the nacelle (16) relative to the tower (15) and the rotation speed of the nacelle (16).

9. The method according to any one of claims 1 to 8, wherein: The yaw drive (35) comprises a yaw motor (33), and wherein the yaw motor (33) comprises a motor brake (91), the method further comprising stopping the yaw motor (33) when the predicted end is reached.

10. The method of claim 9, comprising activating the motor brake (91) after stopping the yaw motor (33).

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