Method for controlling yaw system of wind turbine

Abstract

The present disclosure relates to a method (100) for operating a yaw system of a wind turbine (10), the yaw system comprising a yaw bearing (98), a ring gear (31) and a plurality of yaw drives (35) comprising a motor (33) with a motor brake (91), a gearbox (37) and a pinion (39) operatively connected with the motor (33). The method (100) includes operating a plurality of yaw drives (35) to rotate the nacelle (16) relative to a tower (15) of the wind turbine (10). The method further includes stopping rotation of the nacelle (16) relative to the tower (15), including closing a motor brake (91) of the yaw drive (35). Further, the method (100) includes balancing loads experienced by a plurality of yaw drivers (35) of the yaw system after the latency time. The disclosure also relates to a control system (92) for a wind turbine (10) configured to perform such a method (100).

Description

Technical Field

[0001] The present disclosure relates to wind turbines, and more particularly to a yaw system and a method for controlling a yaw system of a wind turbine. Background Art

[0002] Modern wind turbines are commonly used to supply electricity to the power grid. This type of wind turbine generally comprises 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 usually transmitted to a generator via the rotor shaft directly ("direct drive" or "gearless") or by using a gearbox. In this way, the generator produces electricity that can be supplied to the power 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 contain and protect the gearbox (if present) and the generator (if not placed outside the nacelle), and depending on the wind turbine, further 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 direction of the wind 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. Typically, the yaw system can be activated if the prevailing wind direction deviates from the rotor and nacelle orientation by more than a predefined threshold (e.g., 5°, 7°, or 10° or more) for at least a predetermined period of time. The predetermined time period may be 1 minute, 5 minutes, 10 minutes or more. For example, an average value from seconds to minutes, such as a 3-second average, a 10-second average, a 1-minute average, or a 5-minute average, can be determined to calculate the direction of the prevailing wind speed.

[0006] Other operating modes may also involve rotation of the nacelle around the longitudinal axis of the tower. One example is a cable untwist 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. Due to the previously mentioned rotation during power generation operation, the cables may become twisted. Typically, there is a twist limit, beyond which the cable may be damaged. Before such a limit is reached, the cable needs to be untwisted. To this end, the untwist operation of the wind turbine may include stopping the wind turbine and yaw the nacelle until a predetermined orientation is reached in which the cable is substantially untwisted.

[0007] Another operating mode that may involve rotation of the nacelle is a yaw rotation during idling (i.e., during a situation where no power is being generated). Thus, even if the wind turbine does not generate any power, it may still be subject to a dominant load induced by the wind, or in the case of an offshore wind turbine, a dominant load induced by waves. The yaw system may be configured to rotate the nacelle to keep the load within a design margin. In some cases, the nacelle may be rotated so that the rotor faces the wind (i.e., upwind orientation) in a manner similar to when the wind turbine is in power generation mode. In some other cases, it may be preferred to yaw the nacelle away from the wind when the wind turbine is in idling mode. This may be the case if, for example, there is a fault and the blades are stuck (the blades cannot be pitched). In addition, some control strategies are known to track the wind direction when the wind turbine is idling, not only for load control, but also for providing better alignment with the wind so as to reduce startup delays when the wind speed increases into the operating range.

[0008] The yaw system typically uses a plurality of yaw drives comprising a plurality of motors (e.g. electric motors or hydraulic motors) to perform the rotation of the nacelle using a suitable gearbox for driving a gear (pinion) which meshes with a ring gear or annulus attached to the nacelle or the wind turbine tower. Thus, the nacelle can be rotated in or out of the wind direction around the longitudinal axis of the tower. 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.

[0009] Typically, when the rotor is positioned according to the desired orientation, a system is used to maintain the state and hold the nacelle in place. Therefore, the yaw system maintains the orientation by using brakes (e.g., hydraulic brake calipers and / or motor brakes of the yaw motor). These brakes can be activated and deactivated by the wind turbine control system. In addition, the pinion of the yaw drive remains engaged with the ring gear or ring gear, so they also help to increase the ability of the wind turbine to maintain the nacelle in place (i.e., with the desired orientation).

[0010] The term "parked wind turbine" or "parked nacelle" may be used to refer to a condition involving maintaining the orientation of the nacelle in a given position. It should be understood that this condition may occur under different operating conditions, including but not limited to power production and idling operation. It is important to note that this condition corresponds to most of the life of a wind turbine.

[0011] It was surprisingly found that in some cases, even if the distribution of the yaw motors is symmetrical, the aforementioned operation of holding the desired orientation may lead to overloading of individual components of the yaw system, and more particularly of the individual yaw drives and the corresponding yaw pinions.

[0012] The present disclosure seeks to provide an improved method for operating a yaw system of a wind turbine, in particular during a yaw stop and during a shutdown condition.The present disclosure also seeks to provide a wind turbine that at least partially reduces the aforementioned problems. Summary of the invention

[0013] In one aspect of the present disclosure, a method for operating a yaw system of a wind turbine is provided. The yaw system includes a yaw bearing, a ring gear, and a plurality of yaw drives. The yaw drive includes a motor with a motor brake, a gearbox, and a pinion operatively connected to the motor. The method includes operating the plurality of yaw drives to rotate a nacelle relative to a tower of the wind turbine. The method also includes stopping the rotation of the nacelle relative to the tower, including stopping the motor and closing the motor brake of the yaw drive. After a waiting time, the method includes balancing a load experienced by the plurality of yaw drives of the yaw system.

[0014] According to this aspect, the yaw operation causes the motor brake to be closed (i.e., activated) to stop the rotation of the nacelle relative to the tower, thereby ending the yaw rotation operation. Stopping the rotation of the nacelle relative to the tower also includes stopping the yaw motor. In some variations of the present disclosure, the motor brake may be closed at the same time as stopping the motor. In other variations, the motor brake may be closed after stopping the motor. In any case, after a waiting time that may be defined from the moment the motor brake is closed, the loads experienced by the multiple yaw drives of the yaw system are balanced.

[0015] Throughout this disclosure, "balancing the load" may be interpreted as reducing an existing imbalance between the loads experienced by the multiple yaw drives. Thus, a more balanced system is achieved after the "balancing the load" action, and the imbalance is reduced. In some cases, this reduction may result in a so-called fully balanced system, in which all yaw drives experience substantially the same load. In other cases, the "balancing the load" action may reduce the differences between the loads experienced by the multiple drives, even though the loads may remain different.

[0016] The inventors have discovered a significant imbalance between the loads borne by the individual yaw drives when the nacelle is stopped (i.e. in a shutdown state). Despite the symmetrical distribution, the load sharing between the yaw drives is uneven, because the pinions of each yaw drive mesh with the ring gear at different positions, so that the pinions are unequally loaded. The inventors have determined that the positions depend on several factors, such as variations in the closing time of the motor brake, individual pinion tooth backlash or yaw motor brake wear. These different positions lead to residual loads that translate into uneven loading of the yaw pinions. The shutdown state occurs during a long period of time and it represents most of the life of the wind turbine, so such uneven loading can lead to loads that exceed the design loads of the respective yaw drives. As a result, components of the yaw drives may become overloaded and damaged.

[0017] It has been found that the load balancing action after stopping the rotation of the nacelle reduces the risk of component loading found previously. It has been found that the load balancing action passively releases the residual load on the plurality of yaw drives. It has been found that the residual load is more evenly distributed between the plurality of yaw drives.

[0018] In examples of the present disclosure, balancing the loads experienced by the plurality of yaw drives may include temporarily reducing braking friction.Thus, by reducing braking friction in the yaw system for a certain period of time, balancing of the loads experienced by the plurality of yaw drives may be achieved.

[0019] In a further example, balancing the loads experienced by the plurality of yaw drives of the yaw system may include opening the motor brake during an opening time and closing the motor brake after the opening time. Thus, the motor brake is opened (i.e. released) during the so-called opening time, after which the motor brake is closed again. In other words, after stopping the rotation of the nacelle, an opening-closing action is performed on the motor brake.

[0020] Throughout this disclosure, an "opening-closing maneuver" may be considered as a temporary (relatively short) opening of the yaw brake (in particular, the motor brake) to subsequently close the brake again. I.e., the brake is released for a short time and then activated again. In particular, the yaw drive is not activated during the opening-closing maneuver, i.e., the motor is not driven to move the position of the nacelle.

[0021] It has been found that an opening-closing action after stopping the rotation of the nacelle (i.e. releasing or lifting the motor brake during the opening time, more specifically during a small amount of time) temporarily reduces the braking friction and passively releases the residual load on the plurality of yaw drives. It has been found that the residual load is more evenly distributed between the plurality of yaw drives, resulting in a more balanced load distribution while reducing the risk of component overloads.

[0022] In another aspect of the present disclosure, another method for operating a yaw system of a wind turbine is provided. The yaw system includes a yaw bearing, a ring gear, a hydraulic brake, and a plurality of yaw drives, the plurality of yaw drives including a motor with a motor brake, a gearbox, and a pinion operatively connected to the motor. As in the previous example, the method includes operating the plurality of yaw drives to rotate the nacelle relative to the tower of the wind turbine. However, in this example, the hydraulic brake is actuated to increase the braking pressure relative to its average value during the rotation of the nacelle. Subsequently, the method includes stopping the rotation of the nacelle relative to the tower, including stopping the motor and closing the motor brake. Subsequently, the motor brake is opened during the opening time, a waiting time after closing the motor brake. Finally, the method includes closing the motor brake again after the opening time.

[0023] According to this aspect of the disclosure, the hydraulic brakes are actuated before the end of the yaw maneuver, so that the brake pressure of the hydraulic brakes increases relative to its average value when rotating the nacelle. The early actuation of the hydraulic brakes occurs at a specific moment before stopping the rotating nacelle, i.e., a determined time before stopping the yaw motor. The determined time may be a predefined amount of time obtained by, for example, simulation, or it may be determined based on operating conditions. Stopping the nacelle also includes turning off the motor brakes, which may occur simultaneously or with some delay relative to the stopping of the yaw motor.

[0024] It is known in the art that the hydraulic brake can be actuated at a certain hydraulic pressure to apply a braking torque during rotation of the nacelle. This braking torque is used to provide damping during yaw operation and typically involves operating the hydraulic brake in the range of 20%-40% of its braking pressure, the specific value depending on different factors such as the yaw bearing type (roller, sliding) or the operating conditions. The inventors have found that by increasing the pressure of the hydraulic brake in advance (i.e. before stopping the rotation of the nacelle by stopping the motor and closing the motor brake), a faster standstill is achieved, which translates into a reduced imbalance in the load borne by the yaw drive. This effect, combined with the opening-closing action of the motor brake already described with respect to the previous aspects, helps to further balance the load between the yaw pinions.

[0025] In yet another aspect of the present disclosure, a control system for a wind turbine is provided. The control system is configured to perform any example of the method according to the aforementioned aspect. For example, the control system is configured to command operation of multiple yaw drives to rotate the nacelle relative to the tower during a yaw operation, and then instruct closing of the motor brake to stop rotating the nacelle. Subsequently, after a waiting time, the control system is configured to command balancing of loads experienced by multiple yaw drives of the yaw system. In an example, the balancing of the loads may involve the control system instructing the opening of the motor brake during an opening time before instructing the closing of the motor brake.

[0026] According to this further aspect of the disclosure, an example of a system that may be arranged in a wind turbine is provided.The control system is capable of implementing a method of controlling a yaw system during a yaw sequence and more specifically during a shutdown state of a wind turbine after ending a yaw operation.

[0027] In yet 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. The wind turbine also includes such a control system.

[0028] Technical solution 1. A method (100) for operating a yaw system of a wind turbine (10), the yaw system comprising a yaw bearing (98), a ring gear (31) and a plurality of yaw drives (35), the plurality of yaw drives (35) comprising a motor (33) with a motor brake (91), a gearbox (37) and a pinion (39) operatively connected to the motor (33), the method comprising: operating the plurality of yaw drives (35) to rotate the nacelle (16) relative to a tower (15) of the wind turbine (10); stopping rotation of the nacelle (16) relative to the tower (15), including closing the motor brake (91) of the yaw drive (35); After the waiting time, the loads experienced by the plurality of yaw drives (35) of the yaw system are balanced.

[0029] Technical solution 2. A method according to Technical solution 1, wherein balancing the load experienced by the plurality of yaw drives (35) of the yaw system comprises temporarily reducing braking friction.

[0030] Technical solution 3. The method according to any one of technical solutions 1 or 2, wherein balancing the loads experienced by the plurality of yaw drives (35) of the yaw system comprises: opening the motor brake (91) during an opening time; and After the opening time, the motor brake is closed.

[0031] Technical Solution 4. A method according to Technical Solution 3, wherein the opening time is predetermined or based on the operating conditions of the wind turbine (10), and specifically, wherein the opening time is between 0.02 seconds and 1 second, more specifically between 0.05 seconds and 0.5 seconds, and even more specifically between 0.2 seconds and 0.4 seconds.

[0032] Technical Solution 5. A method according to any one of the aforementioned technical solutions, wherein the yaw system includes a hydraulic brake (94), and the method includes utilizing the hydraulic brake (94) to substantially maintain the nacelle (16) in an appropriate position during the balancing of the load, and more specifically, wherein balancing the load includes opening the motor brake (91) during an opening time, and utilizing the hydraulic brake (94) to substantially maintain the nacelle (16) in an appropriate position includes maintaining the nacelle (16) in an appropriate position during the opening time of the motor brake (91).

[0033] Technical Solution 6. A method according to any one of the preceding technical solutions, wherein the method is performed when the wind turbine (10) is in a power generation mode.

[0034] Technical Solution 7. A method according to any one of Technical Solutions 1 to 5, wherein the method is performed when the wind turbine (10) is in an idling mode.

[0035] Technical Solution 8. A method according to any one of the aforementioned technical solutions, wherein the waiting time is a predetermined amount of time after the closing of the motor brake (91), and specifically, wherein the waiting time is between 0.5 seconds and 600 seconds, more specifically between 1 second and 10 seconds, and even more specifically between 2 seconds and 4 seconds.

[0036] Technical Solution 9. A method according to any one of Technical Solutions 1 to 7, wherein the waiting time is determined based on the operating conditions of the wind turbine (10), and more specifically, wherein the waiting time is based on at least one of the yaw moment, the rate of change of the yaw moment, the speed of the nacelle (16) around the longitudinal axis of the tower (15), the acceleration of the nacelle (16) around the longitudinal axis of the tower (15), or the imbalance of the load on the pinion (39).

[0037] Technical solution 10. The method according to any one of the preceding technical solutions, comprising repeating the step of balancing the loads experienced by the plurality of yaw drives (35) of the yaw system at least once.

[0038] Technical solution 11. A method according to technical solution 10, wherein repeating the step of balancing the loads experienced by the multiple yaw drives (35) of the yaw system at least once includes repeating the following steps at least once: after a waiting time, opening the motor brake (91) during an opening time, and closing the motor brake (91) after the opening time, and specifically, wherein the same waiting time and the same opening time are used for all repetitions; and more specifically, wherein the number of repetitions is based on one or more operating conditions.

[0039] Technical solution 12. A method according to any one of the aforementioned technical solutions, wherein the yaw system includes a hydraulic brake (94), and the method includes actuating the hydraulic brake (94) before stopping the rotation of the nacelle (16) relative to the tower (15) so as to increase the brake pressure relative to its value during the yaw movement, and more specifically, wherein the hydraulic brake (94) is actuated at a predetermined time before closing the motor brake (91), and the predetermined time is at least 1 second.

[0040] Technical Solution 13. A method according to any one of the aforementioned technical solutions, wherein the yaw drive (35) is divided into a plurality of groups, each group comprising at least one yaw drive (35), and the method comprises performing steps of balancing the loads experienced by the plurality of yaw drives (35) of the yaw system in a sequential manner for different groups of the yaw drives (35).

[0041] Technical solution 14. A control system (92) for a wind turbine (10), characterized in that the control system (92) is configured to execute the method according to any one of Technical Solutions 1 to 13.

[0042] Technical Solution 15. A wind turbine (10), comprising a tower (15), a nacelle (16) rotatably mounted on the tower (15), and a yaw system for rotating the nacelle (16) relative to the tower (15) around the longitudinal axis of the tower (15), and a control system (92) according to Technical Solution 14. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 illustrates a perspective view of one example of a wind turbine;

[0044] Figure 2 Diagram Figure 1 A simplified interior view of an example of a nacelle of a wind turbine;

[0045] Figure 3schematically illustrates an example of a portion of a yaw system according to an example;

[0046] Figure 4 schematically illustrates an example of a yaw system;

[0047] Figure 5 A flow chart showing an example of a method for operating a yaw system of a wind turbine;

[0048] FIG. 6A to FIG. 6D schematically illustrates the evolution of the torque at the yaw drive pinion and the resulting torque imbalance during operation of the yaw system according to an example;

[0049] Figure 7 A flow chart illustrating another example of a method for operating a yaw system of a wind turbine;

[0050] 8A-8B schematically illustrate the evolution of the torque at the yaw drive pinion and the resulting torque imbalance during operation of the yaw system according to the prior art. DETAILED DESCRIPTION

[0051] 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 example. Therefore, it is intended that the present disclosure covers such modifications and variations and their equivalents as fall within the scope of the appended claims.

[0052] Figure 1 is a perspective view of an example of a wind turbine 10. In this example, wind turbine 10 is a horizontal-axis wind turbine. Alternatively, wind turbine 10 may be a vertical-axis wind turbine. In this example, wind turbine 10 includes a tower 15 extending from a support system 14 on the ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 coupled to nacelle 16. Rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to hub 20 and extending outwardly from hub 20. In this example, rotor 18 has three rotor blades 22. In alternative embodiments, rotor 18 includes more or less than three rotor blades 22. Tower 15 may be manufactured from tubular steel to define a cavity (not in the cavity) between support system 14 and nacelle 16. Figure 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.

[0053] Rotor blades 22 are spaced about hub 20 to facilitate rotating rotor 18 to enable kinetic energy to be converted from wind energy 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 ( Figure 1 The loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26 .

[0054] In an example, rotor blades 22 may have a length in the range of from about 15 meters (m) to about 90 meters or more. 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 meters or less, 37 meters, 48.7 meters, 50.2 meters, 52.2 meters, or a length greater than 91 meters. When wind strikes rotor blades 22 from a wind direction 28, rotor 18 rotates around rotor axis 30. When rotor blades 22 are rotated and 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 position or a non-deflected position to a deflected position.

[0055] In addition, the pitch angle of the rotor blades 22 (i.e., the angle that determines the orientation of the rotor blades 22 relative to the wind direction) can be changed by the pitch system 32 to control the load and the power output by the wind turbine 10 by adjusting the angular position of at least one rotor blade 22 relative to the wind vector. A pitch axis 34 of the rotor blade 22 is shown. During operation of the wind turbine 10, the pitch system 32 can specifically change the pitch angle of the rotor blades 22 so that the angle of attack of (portions of) the rotor blades is reduced, which is beneficial to reduce the rotational speed and / or to facilitate the stalling of the rotor 18.

[0056] In this example, the blade pitch of each rotor blade 22 is individually controlled by wind turbine controller 36 or by pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0057] 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 .

[0058] 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 turbines 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.

[0059] As used herein, the term "processor" is not limited to the integrated circuits known in the art as computers, but refers broadly 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.

[0060] The control system 36 may also include memory, such as one or more memory devices. The memory may include (multiple) 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. (Multiple) such memory devices may generally be configured to store suitable computer-readable instructions that, when implemented by (multiple) processors 40, configure the controller 36 to perform the various steps disclosed herein or trigger their execution. The memory may also be configured to store data, such as data from measurements and / or calculations.

[0061] 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 disposed at least partially coaxial 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 the 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 convert 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.

[0062] The gearbox 46, the generator 42 and the transformer 90 may be supported by the main support structural frame of the nacelle 16, which may optionally be implemented 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 breakaway 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 source of noise emission.

[0063] 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 securing devices (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.

[0064] 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 as a wind turbine with a gearbox.

[0065] The nacelle 16 may also include a yaw system including a yaw bearing (in Figure 21 and 2. The yaw bearing has two bearing components configured to rotate relative to one another (not visible in FIG. 1 ). The tower 15 is coupled to one of the bearing components, and the bedplate or support frame 52 of the nacelle 16 is coupled to the other bearing component.

[0066] Yaw system may include ring gear 31 and yaw drive mechanism 56 that may be used to rotate nacelle 16 , and thereby rotor 18 , about a longitudinal axis of the tower (ie, about yaw axis 38 ) to control the viewing angle of rotor blades 22 relative to wind direction 28 .

[0067] The yaw drive mechanism 56 includes a plurality of yaw drives 35 having a motor 33, a gearbox 37, and a pinion 39 for engaging with the ring gear 31 to rotate one of the bearing components relative to another. The ring gear 31 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 31 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 inside the tower.

[0068] In some examples, one of the yaw drives may be a "master drive" and the other drives may be "slave drives" that follow the master drive's instructions or adjust their operation to accommodate the master drive.

[0069] 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. When 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 thus 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.

[0070] 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.

[0071] 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 the rotor blades 22 along the pitch axis 34. Figure 2 Only one of three pitch drive systems 68 is shown.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 power grid loss or voltage drop, 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.

[0076] 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.

[0077] Figure 3 A portion of a yaw system according to an example is illustrated. The yaw system includes a yaw bearing 98 having a first bearing component 95 coupled to the tower 15 and a second bearing component 96 coupled to the main frame 52 of the nacelle 16. The yaw system includes a ring gear 31, which in this example is coupled to the first bearing component 95. Other configurations are possible, such as, for example, the ring gear 31 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 engaging with the ring gear 31, the motor 33 including a motor brake 91. Rotation of the motor 33 causes the pinion 39 to rotate relative to the ring gear 31. As mentioned, in this example, the ring gear 31 is coupled to the first bearing component 95, and thus the first bearing component 95 rotates relative to the second bearing component 96 coupled to the main frame 52. Although in Figure 3 Only a single yaw drive 35 is shown in FIG. 3 , but a plurality of yaw drives 35 may be arranged around the circumference to engage with the ring gear 31 , each yaw drive 35 having its motor 33 , gearbox 37 and pinion 39 .

[0078] The ring gear 31 may include a plurality of teeth that engage with the teeth of the pinion gear 39. In this example, the yaw drive 35 and the ring gear 31 are placed outside the outer diameter of the tower. The teeth of the ring gear 31 are directed outwardly. However, in other examples, the ring gear 31 and the yaw drive 35 may be placed inside the tower.

[0079] The motor brake 91 may be disposed inside the housing of the motor 33, and it may be arranged to prevent rotation of the motor 33. The motor brake 91 may include a friction brake, wherein a friction disk may be secured 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.

[0080] Figure 3 The yaw system of the tower 15 also includes a brake disc 93 and a hydraulic brake 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 94 is shown, multiple brakes 94 may be provided along the periphery of the tower 15 so as to engage the brake disc 93 at different points. 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 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.

[0081] To activate the brake 94 (i.e., engage the brake disc 93), the hydraulic brake 94 may include an active hydraulic system to control the pressure of the brake caliper on the brake disc 93. In some examples, the activation and deactivation of the brake 94 may be controlled by the controller 92. In some examples, the controller 92 may be implemented in the wind turbine controller 36. The controller 92 may not only activate or deactivate the brake 94, but it may also actuate the brake 94 to actively control the pressure of the hydraulic system in order to control the braking torque applied by the brake 94 when engaging the brake disc 93. In particular, a moderate braking torque may be applied during a yaw rotation to provide damping during the rotation of the nacelle 16, and when stopping the rotation of the nacelle 16, actuation may be required to increase the braking torque applied by the brake 94.

[0082] Figure 3 Also illustrated in FIG. 9 is a control system 92 configured to control the yaw system according to a control algorithm. In this example, an independent control system 92 is depicted. However, it should be understood that control of the yaw system may be implemented in any controller, including, for example, the wind turbine controller 36.

[0083] 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 further examples.

[0084] Figure 3 The motor shown in the figure can be directly connected to a power source, or it can be connected to a power source via a variable frequency drive VFD (not shown in the figure). The use of such VFD is well known in the art, so no further details are provided herein.

[0085] Despite Figure 3 A single yaw drive 35 is depicted in FIG, but multiple yaw drives 35 are typically employed. Thus, Figure 4 An example of a yaw system comprising a plurality of yaw drives 35 is schematically illustrated. In this example, four yaw drives 35a-35d may be evenly distributed on the yaw bearing (in Figure 4 As for Figure 3 As indicated, each of those yaw drives 35a-35d comprises a pinion 39a-39d meshing with the ring gear 31. This example will be used hereinafter to explain the present disclosure, but it should be understood that any number of yaw drives may be selected.

[0086] Figures 8A-8B depict the evolution of operating conditions of a yaw system comprising four yaw drives according to a prior art method.The nacelle 16 is not rotating and the braking system is activated, which corresponds to the non-yaw or shutdown state representing most of the life of a wind turbine.

[0087] 8A shows the evolution of the individual torques 139a-139d of each of the four pinions 39a-39d, while FIG8B depicts the evolution of the maximum torque deviation or imbalance 111. In other words, FIG8B represents the maximum torque difference between the torques determined for the pinions 39a-39d at each instant. A balanced yaw system 35 will exhibit a uniform load sharing between all pinions 39a-39d, which will result in substantially the same torques for all pinions 39a-39d and a substantially zero value for the maximum torque deviation 111.

[0088] However, FIG. 8A shows that there is a variable torque at each pinion 39a-39d, so that there is a significant deviation when in the parking state, which includes a high peak pinion load. Even more importantly, the load sharing is clearly uneven, and a significant value is observed for the maximum torque deviation 111 in FIG. 8B. FIGS. 8A and 8B also show the evolution of the control signal for the motor brake 191, which in this case remains at a low (L) value, meaning that the motor brake 91 is closed, i.e., activated. This is the normal state of the motor brake 91 for such a non-yaw state of the wind turbine 10.

[0089] The inventors have identified a problem during the non-yaw (i.e., shutdown) state of the wind turbine 10. The individual arrangement of each pinion 39 relative to the ring gear 31 results in a different engagement position, so that the load sharing during the non-yaw condition is uneven, i.e., the pinions are not loaded equally. Different reasons lead to the different positions, such as, but not limited to, different reaction times of each motor brake 91, uneven wear of components of each motor brake 91, or uneven wear of the individual pinions 39.

[0090] Based on these observations, the inventors developed a new control method for yaw sequences as explained below.

[0091] In an example of the present disclosure, a method 100 is provided for operating a yaw system of a wind turbine 10, the yaw system including a yaw bearing 98, a ring gear 31, and a plurality of yaw drives 35. Each yaw drive 35 includes a motor 33 with a motor brake 91, a gearbox 37, and a pinion 39 operatively connected to the motor 33. The method 100 includes: Figure 5 The method includes: at box 110, operating a plurality of yaw drives to rotate the nacelle relative to a tower of the wind turbine. The method also includes: at box 120, stopping the rotation of the nacelle relative to the tower, including closing a motor brake of the yaw drive. Box 130 of the method includes waiting for a waiting time t W And balance the loads experienced by the multiple yaw drives 35 of the yaw system.

[0092] In examples of the present disclosure, balancing the loads experienced by the plurality of yaw drives may include temporarily reducing braking friction.Thus, by reducing braking friction in the yaw system for a certain period of time, balancing of the loads experienced by the plurality of yaw drives may be achieved.

[0093] In another example, balancing the loads experienced by the plurality of yaw drives of the yaw system may include at the opening time t O During this time, the motor brake is opened and after the opening time, the motor brake is closed.

[0094] Now refer to FIG. 6A to FIG. 6D To explain the examples of the present disclosure, FIG. 6A to FIG. 6D The evolution of the operating conditions of the yaw system comprising four yaw drives is shown. The frame 110 comprising operating the yaw drive 35 to rotate the nacelle 16 is FIG. 6A to FIG. 6D From until time t E The evolution of E corresponds to the end of the yaw maneuver and therefore to the transition to box 120 of the method 100 which comprises stopping the rotation of the nacelle 16. At t E Stopping rotation of nacelle 16 includes stopping yaw motor 33 and, in this example, simultaneously activating yaw motor brake 91 as represented by yaw motor brake control signal 191. In other examples, motor brake 91 may be closed with a delay relative to stopping yaw motor 91.

[0095] Fig. 6A The evolution of the torque 239a-239d of each of the four yaw drives in the example and the evolution of the motor brake control signal 291 are shown.E The evolution of the pinion torque shows relatively modest values ​​and, more importantly, similar values ​​for all pinions, which is an indication of uniform load sharing. In this situation, load balancing can be achieved by the slip of the asynchronous motor or, if present, by controlling the variable frequency drive (VFD) used during operation. Figure 6B The same behavior can be observed. Figure 6B The maximum torque deviation 211 determined from the torque values ​​at each pinion is shown. As expected from the evolution of the individual torques 239a-239b, at t E Previously, a substantially even load sharing was achieved, which translated into a very low value for the maximum torque deviation 211 .

[0096] Block 120 corresponds to stopping the rotation of the nacelle 16, which involves stopping the yaw motor 33 and includes closing the motor brake 91. This Fig. 6A and Figure 6B This is indicated by the transition of the motor brake control signal 291 from a high signal (H) indicating an open state to a low signal (L) indicating a closed state. This transition occurs at time t E As previously indicated, in this example, the motor brake 91 is closed at the same time as the yaw motor 33 stops. In other examples, the motor brake 91 may be closed later than the yaw motor 33 stops.

[0097] After activation of the motor brake 91, a significant deviation in the torque 239a-239d experienced by the pinion can be observed. Figure 6B Even more obvious, Figure 6B The maximum deviation 211 between the determined torques is depicted and clearly shown at t E This behavior is consistent with that observed in the prior art (see FIGS. 8A to 8B ).

[0098] Waiting time t W Present in block 130 of method 100. Block 130 includes balancing the load of the yaw drive 35. FIG. 6A to FIG. 6D In the example shown in FIG. , such a balancing load of the yaw drive 35 is included in the waiting time t W The motor brake 91 is then opened for the opening time t O This is Fig. 6A and Figure 6B The motor brake control signal 291 is kept low (L) (ie, closed) for a duration t W And then transition to high (H) to illustrate. In this example, the waiting time t WIt is defined from the moment when the motor brake 91 is closed, which in this case coincides with the moment when the yaw motor 33 stops. In other examples, t W The start time of t may be defined differently. In particular, some examples may include closing the motor brake 91 after stopping the yaw motor 33. In these examples, t W It may be defined with reference to the torque of stopping the yaw motor 33 or with reference to the torque of closing the motor brake 91. It will be appreciated that the concept and technical effect remain the same, ie a certain time passes until the next action in the sequence occurs.

[0099] As also shown in the figure, in this example, the motor brake 91 is only opened for a certain opening time t O In other words, in this example, the load balancing step in block 130 includes only opening the O During this time, the motor brake 91 is opened. Opening time t O After the end, the motor brake 91 is closed again, that is, the motor brake control signal 291 switches back to the low (L) level. Therefore, during the implementation of the method, the motor brake 91 undergoes an opening-closing action, in which the motor brake 91 is released for a period of time t O .

[0100] exist Fig. 6A and Figure 6B The effect of this opening-closing action on the load sharing in the yaw drive 35 can be seen in FIG. Fig. 6A It is shown that after the opening-closing action is completed, that is, at t O Thereafter, the variability between the pinion torque signals 239a-239d is reduced. In other words, the torque signals 239a-239d determined for different pinions converge to similar values.

[0101] exist Figure 6B The same behavior can also be seen in , which shows a significant reduction in the maximum torque deviation 211 after performing the opening-closing action of the motor brake 91. More specifically, at the opening time t O A rapid decrease in the maximum torque deviation 211 is observed over a period of time until a very low value is observed indicating a substantially uniform load sharing. This observation indicates that by the opening action of the motor brake 91, the residual load at the pinion 91 is released and an improved load sharing is achieved. In other words, the opening-closing action of the motor brake 91 is a load balancing action of the yaw drive. Once released after the opening-closing action of the motor brake 91, the yaw system remains substantially balanced and at time t O Very low values ​​are then observed for the maximum torque deviation 211 .

[0102] In an example of the present disclosure, the yaw system may include a hydraulic brake 94, and the method may further include utilizing the hydraulic brake 94 to substantially maintain the nacelle 16 in position during balancing of the load. More specifically, balancing the load may include opening the hydraulic brake 94 at a time t O During this time, the motor brake 91 is opened, and the nacelle 16 is substantially held in position using the hydraulic brake 94, which may include opening the motor brake 91 during the opening time t O The nacelle 16 is substantially held in position during this period. FIG. 6A to FIG. 6D More specifically, Figure 6C The evolution of the hydraulic pressure 294 of the hydraulic brake 94 during the yaw of the nacelle 16 (ie, at time t E The hydraulic brake 94 may be maintained at a moderate value (e.g., 20%-40% of its rated value) before t E The brakes 14 are actuated at the nacelle 16 to increase their braking torque to support stopping the rotation of the nacelle 16 .

[0103] according to FIG. 6A to FIG. 6D In the example shown in O During the time when the motor brake 91 is opened, the hydraulic brake 94 may be at a sufficiently high pressure, such as 80% of its rated value, to hold the nacelle 16 in the appropriate position. In this example, such use of the hydraulic brake 94 may allow for improved operational stability because it may prevent unwanted movement of the nacelle 15 caused by gusts of wind that occur, for example, during the implementation of the method. This example may be particularly useful for a wind turbine including a yaw system that features a roller-type yaw bearing 98. Alternatively, other examples of the present disclosure may not use the hydraulic brake 94 to hold the position of the nacelle 16 while the motor brake 91 is opened, in which case the inertia of the nacelle 16 itself may be used for this purpose.

[0104] In an example of the present disclosure, the method may be performed when the wind turbine is in "normal operation" (i.e., in power generation mode). In this example, the alignment of the rotor 18 of the wind turbine 10 with the wind direction 28 may be used to optimize power generation. To this end, the nacelle 16 may be rotated relative to the tower 15 until the yaw error (i.e., the difference between the rotor axis 30 and the prevailing wind direction 28) is below a certain threshold.

[0105] Once aligned, the nacelle 16 may be retained by means of a retention system, which includes, among other things, a motor brake 91 of the yaw motor 33 and a pinion 39, which may remain engaged with the ring gear 31. However, different factors, such as varying wind conditions or operating conditions of the wind turbine 10, may induce varying loads and, more specifically, varying moments about the vertical axis 39 of the tower 15. Such moments about the vertical axis 30 of the tower 15 may be referred to as Q moments. Such loads may increase the torque experienced by the yaw pinions 39, and, more specifically, they may lead to an imbalance, wherein the loads in at least some of the pinions 39 may exceed the design value. Thus, a method according to this example may be performed to mitigate the risk of potential damage to yaw system components when in power generation mode.

[0106] In another example of a method according to the present disclosure, the method may be performed when the wind turbine is in an idle mode (i.e., an operating mode in which no power is generated). In this case, the rotor axis 30 does not need to be aligned to optimize power production. However, significant loads may be induced in the wind turbine by the wind or, in the case of an offshore wind turbine, by the waves. For this reason, a yaw system may be used to orient the nacelle 16 according to a preferred orientation.

[0107] In some examples, the orientation may be an orientation aligned and facing the wind (an upwind orientation) or an orientation in which the rotor 18 is aligned at 180° relative to the direction of the incoming wind (i.e., a downwind orientation). In further examples, the loads may be mitigated by rotating the nacelle 16 in a controlled manner to move the rotor 18 away from the wind direction 28. In any case, the position of the nacelle 16 relative to the tower 15 may also be held, and similar to the previous examples, the yaw drive 35 and the yaw system in general may be subject to some loads while the nacelle 16 is held in position. For this reason, an opening-closing action of the motor brake 91 may also be implemented in this case to mitigate the risks associated with high loads and more specifically to improve load sharing between the yaw pinions 39 of the yaw drive 35.

[0108] Fig. 6A and Figure 6B Shown in the waiting time t W The motor brake 91 is then opened. This is indicated by a transition of the motor brake control signal 291 from a low (L) value to a high (H) value. Different criteria may be used to determine the magnitude of the waiting time.

[0109] In examples of the present disclosure, the waiting time may be a predetermined amount of time, for example, a predetermined amount of time from the actuation of the motor brake 91. To this end, simulations and preliminary analysis may be performed to determine the optimal amount of time required to increase the benefits of the method. In particular, the waiting time may be sufficient to allow the yaw system to reach a certain equilibrium after stopping the rotation of the nacelle. As previously described, the equilibrium state may include some unbalanced residual load on the yaw pinion 39, which can then be compensated by the predetermined time t W The motor brake 91 is then opened to release in the opening-closing action.

[0110] In other examples of the present disclosure, an adaptive method may be implemented. To this end, the waiting time may be determined based on operating conditions of the wind turbine and / or based on environmental conditions. The operating conditions may be monitored in real time in order to adapt the method to the prevailing conditions.

[0111] More specifically, examples of the method may include a waiting time that may depend on the yaw moment (Q moment) and / or the rate of change of the yaw moment (yaw moment slope). The yaw moment refers to the moment experienced by the yaw system about the vertical axis of the tower 15, and it represents the moment that the different holding systems (nacelle 16, motor brake 91, the inertia of the pinion gears 39 meshing with the ring gear 31, etc.) may withstand in order to hold the nacelle 16 in the appropriate position. In some cases, the yaw moment may oscillate, more specifically, at a frequency related to the rotation of the rotor 18 and blades 22, which may also cause some of the pinion gears 39 to become periodically overloaded. Therefore, the determination of the yaw moment may provide an indication of potential imbalance and overload conditions. Fig.6D The evolution of the yaw moment 122 during a yaw sequence according to an example is shown.

[0112] In a variation of this example, the rate of change of the yaw moment may determine the waiting time t W Thus, a high rate of change may indicate the approach of a scenario that may lead to overloading or excessive imbalance in the yaw drive 35 (and more particularly in the yaw pinion 39). Therefore, a shorter waiting time t may be used in case of a high rate of change of the yaw moment. W , and the longer waiting time t W May result from a more stable scenario showing less variability in the yaw moment.

[0113] In another example involving a variable (ie, non-predetermined) waiting time, the waiting time may be based on the speed and / or acceleration of the nacelle about the longitudinal axis of the tower. The variables may be detected by appropriate sensors, for example, a yaw rate encoder may be arranged to measure the rotational speed of the nacelle 16, and the waiting time may be determined from this information. EAfter initiating the stop of the nacelle 16 at , it may still take some time before the nacelle 16 stops so that the motor brake 91 can be safely released. In this example, the nacelle speed and / or acceleration can be used to monitor the deceleration of the nacelle 16 after closing the motor brake 91 in order to determine the precise moment when the nacelle 16 is effectively stopped, which represents the earliest time when the motor brake 91 can be opened, or in other words, the earliest waiting time t W As a non-limiting example, this condition may be characterized by the nacelle rotation speed being within ±0.1 degrees / second.

[0114] In yet another example, the waiting time t W The determination of the imbalance of the pinion load may be based on. In this example, torque transducers may be arranged at the yaw drives 35 to measure the torque borne by each of them. In some variants, the torque may be determined in an indirect manner by using a transfer function between the torque and the current consumption as measured in the VFD (if present). Waiting time t W The load on the pinion gears may be directly caused by this. Therefore, the opening-closing action or balancing action of the motor brake 91 can be performed only when necessary, i.e. only when a significant imbalance is detected. To this end, a certain threshold value may be defined for the maximum permissible torque deviation between the yaw pinions 39, so that if the determined maximum torque deviation exceeds the threshold value, an opening of the motor brake 91 for a certain opening time t may be provided. O signal.

[0115] Other examples may include other operating and / or environmental conditions, such as individual yaw motor torque, wear condition of hydraulic brake 94 , wear condition of motor brake 91 , or ambient temperature.

[0116] For those examples where the operating conditions of the wind turbine are to be considered, different methods may be used to determine the waiting time. In particular, a lookup table relating different waiting times to different ranges of the considered operating parameters may be implemented. Alternatively, an analytical function defining a mathematical relationship between the waiting time and the operating parameter may also be used in other variations of these examples.

[0117] In the examples of the present disclosure, the waiting time may be between 0.5 seconds and 600 seconds, specifically between 1 second and 10 seconds, and more specifically between 2 seconds and 4 seconds, starting from the moment the motor brake is closed. Therefore, regardless of the method used to determine the waiting time, i.e., predetermined or based on operating conditions, certain lower and upper limits may be defined for the specific example. On the one hand, a lower limit may be used to ensure that the method is only performed after a certain equilibrium is reached after closing the motor brake 91. On the other hand, an upper limit may be used so that the method can be performed even in those cases where the operating conditions may not be very harsh. Such actuation can be used to release any residual load in the yaw pinion 91 in a preventive manner, even if the prevailing operating conditions may be relatively acceptable.

[0118] In the process including opening the motor brake 91 for the opening time t O In the example, the opening time t can also be selected according to different criteria. O , i.e. the time during which the motor brake 91 is opened. The opening time may be predetermined or it may be based on the operating conditions of the wind turbine. In particular, a lower limit may be defined, which may be sufficient for the yaw system to release the residual load on the yaw pinion 39. The minimum time may depend on different design characteristics, and more specifically it may depend on the reaction time of the motor brake 91. The reaction time of the motor brake 91 may depend on the design of the system, but also on the condition of the motor brake 91, for example the wear of the friction elements or the state of the electrical connections.

[0119] On the other hand, it can also be the opening time t O In particular, at t O The opening of the motor brake 91 during this period means that a smaller braking torque is applied to the nacelle 16 to maintain its position during a certain period of time. Therefore, if a gust of wind occurs, for example, an extended period of time may increase the risk of the nacelle 16 sliding. In order to mitigate this risk, an upper limit may also be defined for the opening time. The upper limit may be predefined, or it may be adjusted according to operating conditions such as yaw moment, nacelle inertia, nacelle rotation speed and / or environmental conditions. Therefore, examples of the present disclosure may include that the opening time may be between 0.02 seconds and 1 second, specifically between 0.05 seconds and 0.5 seconds, and more specifically between 0.2 seconds and 0.4 seconds.

[0120] In an example of the present disclosure, the method may include repeating at least once the step of balancing the loads experienced by multiple yaw drives of the yaw system. More specifically, the example may include repeating at least once the following steps: after a waiting time, opening the motor brake during an opening time, and closing the motor brake after the opening time. In other words, in some examples, multiple opening-closing actions may be performed on the motor brake 91 to more effectively reduce the load imbalance. More specifically, an opening-closing action in this example that is shorter than in the previous example may be preferred. In addition, the specific parameters of each repetition may be adjusted. The example may include using the same waiting time and the same opening time for one or more of the repetitions, but other examples may include using different times for different load balancing actions. The corresponding times may be determined based on some predefined analysis, or they may be determined based on real-time operating conditions of the wind turbine.

[0121] In yet another example involving repeated load balancing actions, the number of repetitions may be based on operating conditions, and more specifically on the yaw moment. According to this example, not only may a waiting time t be selected for (one or more) opening-closing actions W and opening time t O , and in case of multiple actions the number of repetitions can be adjusted according to the observed operating conditions. More specifically, the yaw moment can be monitored and it can be used to define the number of repetitions in such a way that a larger number of repetitions can be performed for high values ​​of the yaw moment. In another example of the present disclosure, the number of repetitions can be adjusted according to the evolution of the yaw moment over a certain time window. Thus, after performing a first opening-closing action, a certain time window, for example between 30 seconds and 60 seconds, can be defined during which, if the yaw moment exceeds a certain threshold, further opening-closing actions can be performed. The process can be repeated as deemed necessary, as defined, for example, by the magnitude of the yaw moment and / or the pinion load imbalance.

[0122] In other examples of the present disclosure, other operating conditions such as yaw pinion torque or imbalance between pinion loads may be used as inputs to determine the number of repetitions.

[0123] The yaw system according to the present disclosure includes a plurality of yaw drives 35 . Figure 3An example of a yaw system comprising four yaw drives 35 is provided in . However, a different number of yaw drives 35, and more specifically a larger number of yaw drives 35, may be used. This may be particularly the case for wind turbines 10 exhibiting a rated power of more than 10 MW, for which more than ten (for example, sixteen) yaw drives 35 may be provided. In an example of the present disclosure, the yaw drives 35 may be divided into a plurality of groups, each group comprising at least one yaw drive 35. The method may then include performing steps of balancing the loads experienced by a plurality of yaw drives of the yaw system in a sequential manner for the yaw drives of the different groups. More specifically, in an example of the present disclosure, the method may include performing the following steps for the grouped yaw drives 35: opening the motor brake 91 during the opening time after the waiting time, and closing the motor brake 91 after the opening time. These steps may be performed in a sequential manner for the different groups. In other words, the method provides a series of opening-closing actions, wherein each load balancing action is performed for the motor brake 91 of a different group of yaw drives 35. This may be particularly useful for very large wind turbines including an increased number of yaw drives 35, in which case coordination may be facilitated by division into different groups. In a variation of this example, each group may include a single yaw drive 35, in which case the motor brakes 91 may be actuated sequentially (i.e., one after the other).

[0124] More specifically, when there are a large number of yaw drives 35, examples of the present disclosure may include forming groups of yaw drives 35 that can be actively tensioned against the bearing 98 in a specific direction. As an example, a first group of yaw drives 35 can be tensioned in a clockwise (CW) direction, while a second group of yaw drives 35 can be tensioned in a counterclockwise (CCW) direction. This can be practiced to reduce the effects of gear backlash, thereby reducing nacelle oscillations and improving directional stability. For each such group of yaw drives 35, the opening-closing action can be performed in a sequential manner.

[0125] like Figure 4 As shown in and as referenced FIG. 6A to FIG. 6D As discussed, the yaw system may include a hydraulic brake 94 to control and / or hold the yaw movement of the nacelle 16. It is known that a certain hydraulic pressure may be applied to the hydraulic brake during yaw of the nacelle 16. Doing so may provide some damping during operation, thereby obtaining a more stable movement. This may be particularly the case when a roller type yaw bearing is employed. Although the braking torque applied may depend on specific design considerations, a braking torque in the range of 20%-40% of the rated value may be applied.

[0126] Another example of a method for controlling a yaw system is provided, the method for a system including a hydraulic brake. The example includes actuating a hydraulic brake 94 to increase the brake pressure relative to its value during the yaw movement before stopping the rotation of the nacelle 16 relative to the tower 15 (including closing the motor brake 91 of the yaw drive 35). Due to this early activation of the hydraulic brake 94, in anticipation of the yaw rotation stopping, the braking torque induced by the hydraulic brake 94 may be increased to a value higher than its value during the yaw operation. Such early activation may result in a faster and more controlled stop of the nacelle 16 after closing the motor brake 91, which may reduce the load imbalance between different yaw drives 35.

[0127] Early activation of the hydraulic brake 94 is interpreted to mean that the hydraulic brake 94 is activated before the start of the yaw stop sequence, i.e., before the stop of the yaw motor 33 and the activation of the motor brake 91. The amount of time of the early activation determines the braking torque applied by the hydraulic brake 94 at the start of the nacelle stop sequence. Thus, in an example of the present disclosure, the hydraulic brake 94 may be actuated a predetermined time before closing the motor brake 91, the predetermined time being at least 1000 ms. The predetermined time may depend on design considerations of the yaw system, and more particularly on design considerations of the hydraulic brake 94 and the associated hydraulic system.

[0128] In a specific example, the predetermined time may be selected to ensure a certain level of brake pressure in the hydraulic brake 94, more specifically, to ensure that the motor brake 91 is at t E At least 80% of the rated brake pressure in the hydraulic brake 94 when it is closed at t, which in the example may also correspond to the time when the yaw motor 33 stops. As already mentioned, in other examples, the motor brake 91 may not be actuated at the same time as the stopping of the yaw motor 33, but later than the stopping of the yaw motor 33. In these examples, t E The moment (of initiating the stop of the rotation of the nacelle) may be defined by the stop of the yaw motor 33, and the timing of the early activation of the hydraulic brake 94 may be defined with reference to the stop of the motor 33 and not with reference to the activation of the motor brake 91. In any case, regardless of the definition, the effect may remain to achieve a braking torque higher than the braking torque applied during normal yaw of the nacelle 16 before initiating the yaw stop sequence.

[0129] Figure 7A flow chart further illustrating a method 200 for controlling a yaw system is provided, wherein the yaw system includes a hydraulic brake 94. The method 200 includes, in box 210, operating a plurality of yaw drives to rotate the nacelle 16 relative to the tower 15 of the wind turbine 10. Then, at box 220, the method includes actuating the hydraulic brake 94 to increase the brake pressure relative to its value during the rotation of the nacelle 16. Subsequently, box 230 of the method includes stopping the rotation of the nacelle 16 relative to the tower 15, including closing the motor brake 91 of the yaw drive 35. Subsequently, after a waiting time, the method includes opening the motor brake 91 during an opening time in box 240 of the method. Finally, box 250 includes closing the motor brake 91 after the opening time.

[0130] In this way, the method includes early activation of hydraulic brake 94 and subsequent opening-closing action of motor brake 91 before stopping the rotation of nacelle 16 to release residual load in yaw drive 35, thereby facilitating sufficient load sharing among multiple yaw pinions 39. In some variations of the method, before stopping the rotation of nacelle 16 (i.e., at t E The time for the early activation of the hydraulic brakes 94 may be predetermined. More specifically, the time may be predetermined by means of simulation and may be selected to ensure a certain braking pressure. In other variations, the time of the expected activation of the hydraulic brakes 94 may be variable and depend on operating conditions such as the prevailing wind speed.

[0131] According to another aspect of the present disclosure, a controller 92 may be provided. The controller 92 may be configured to perform any example or any equivalent example (including combinations) of the method of operating a yaw system as described throughout the present disclosure. The controller 92 may be implemented as a standalone controller to control the yaw system, or it may be implemented as part of the wind turbine controller 36.

[0132] The controller 92 may be configured to receive a plurality of signals 501, such as signals indicating the wind direction 28, the orientation of the nacelle 16 relative to the tower 15, the torque at the pinion 39, the Q torque, the nacelle speed, the nacelle acceleration, etc. The controller 92 may use this information to obtain a plurality of signals 502 to control the yaw system. This may include signals 502 for controlling the yaw motor 33, the motor brake 91 (particularly during an opening-closing action), or the hydraulic brake 94.

[0133] According to another aspect of the present disclosure, a wind turbine 10 may be 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 may include a controller 92 configured to perform a method as described throughout the present disclosure or any equivalent examples (including combinations).

[0134] 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 combined methods. 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 they include equivalent structural elements that are not substantially different from the literal language of the claims, such other examples are intended to fall within the scope of the claims. A person of ordinary skill in the art may mix and match aspects of the various examples described and other known equivalents of each such aspect to construct additional examples and techniques according to the principles of the present application. If the figure marks associated with the drawings are placed in brackets in the claims, they are merely intended to increase the understandability of the claims and should not be interpreted as limiting the scope of the claims.

Claims

1. A method (100) for operating a yaw system of a wind turbine (10), the yaw system comprising a yaw bearing (98), a ring gear (31) and a plurality of yaw drives (35), the plurality of yaw drives (35) comprising a motor (33) with a motor brake (91), a gearbox (37) and a pinion (39) operatively connected to the motor (33), the method comprising: operating the plurality of yaw drives (35) to rotate the nacelle (16) relative to a tower (15) of the wind turbine (10); stopping rotation of the nacelle (16) relative to the tower (15), including closing the motor brake (91) of the yaw drive (35); After the waiting time, the loads experienced by the plurality of yaw drives (35) of the yaw system are balanced.

2. The method according to claim 1, wherein: Balancing loads experienced by the plurality of yaw drives (35) of the yaw system includes temporarily reducing braking friction.

3. The method according to any one of claims 1 or 2, wherein: Balancing the loads experienced by the plurality of yaw drives (35) of the yaw system comprises: opening the motor brake (91) during an opening time; and After the opening time, the motor brake is closed.

4. The method according to claim 3, wherein: The opening time is predetermined or based on operating conditions of the wind turbine (10), and in particular, wherein the opening time is between 0.02 seconds and 1 second, more particularly between 0.05 seconds and 0.5 seconds, and even more particularly between 0.2 seconds and 0.4 seconds.

5. A method according to any one of the preceding claims, wherein: The yaw system comprises a hydraulic brake (94), the method comprising maintaining the nacelle (16) substantially in position using the hydraulic brake (94) during the balancing of the load, and more particularly, wherein balancing the load comprises opening the motor brake (91) during an opening time, and maintaining the nacelle (16) substantially in position using the hydraulic brake (94) comprises maintaining the nacelle (16) substantially in position during the opening time of the motor brake (91).

6. A method according to any one of the preceding claims, wherein: The method is performed when the wind turbine (10) is in a power generation mode.

7. The method according to any one of claims 1 to 5, wherein: The method is performed when the wind turbine (10) is in an idle mode.

8. A method according to any one of the preceding claims, wherein: The waiting time is a predetermined amount of time after the closing of the motor brake (91), and specifically, wherein the waiting time is between 0.5 seconds and 600 seconds, more specifically between 1 second and 10 seconds, and even more specifically between 2 seconds and 4 seconds.

9. The method according to any one of claims 1 to 7, wherein: The waiting time is determined based on operating conditions of the wind turbine (10), and more specifically, wherein the waiting time is based on at least one of a yaw moment, a rate of change of the yaw moment, a speed of the nacelle (16) about the longitudinal axis of the tower (15), an acceleration of the nacelle (16) about the longitudinal axis of the tower (15), or an imbalance of the pinion (39) load.

10. A method according to any one of the preceding claims, comprising repeating the step of balancing the loads experienced by the plurality of yaw drives (35) of the yaw system at least once.

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