Method for lubricating pitch bearing of wind turbine

Abstract

The present disclosure relates to a method for lubricating a pitch bearing of a wind turbine, in particular to a method (100, 200) for lubricating a pitch bearing (72) connecting a blade (22) and a hub (20) of a wind turbine (10). A method (100) includes determining (110) that lubrication is to be performed on a pitch bearing (72); determining (120) an upper limit for a thrust gradient, the thrust gradient being a derivative of thrust with respect to time; determining (130) a pitch rate for lubricating the pitch bearing (72) based at least in part on an upper limit for the thrust gradient, and pitch (140) the wind turbine blade (22) at the determined pitch rate to lubricate the pitch bearing (72) such that the upper limit for the thrust gradient is not exceeded.

Description

Technical Field

[0001] The present disclosure relates to a method for lubricating a pitch bearing of a wind turbine. The present disclosure also relates to a wind turbine controller and to a wind turbine configured to implement such a method. 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 generates 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] Wind turbine blades are usually coupled to the hub via a pitch bearing. The pitch bearing typically includes an inner race and an outer race, and usually a plurality of rolling or roller elements between the inner race and the outer race. The wind turbine blade may be attached to the inner race or the outer race, and the hub may be attached to the other of the inner race and the outer race. The attachment may be performed, for example, with nuts and bolts.

[0005] When the pitch bearing race is rotated relative to the other bearing race, for example using an electric or hydraulic pitch actuator, the blade can be rotated relative to the hub about its longitudinal axis. For example, the blade attached to the inner race of the bearing can be rotated relative to the hub. Rotating the wind turbine blades in this way may generally be referred to as "pitching" the blades. In an (electro)mechanical pitch system, a pinion gear may mesh with a ring gear, typically provided on the bearing race to which the blade is attached, in order to start the wind turbine blades rotating. In a hydraulic pitch system, a hydraulic piston may move the blades.

[0006] Pitch bearings are typically subject to high loads and oscillations. If the lubricant is not evenly distributed in the pitch bearing, this may lead to wear and damage of the bearing races and / or the roller elements between them. Grease lubricants are usually used. The lubricant needs to be well distributed and reach all relevant parts and elements of the bearing. It may be necessary to pitch the blades to promote even distribution of the lubricant, especially if the pitch angle of the blades has not been changed during a long period of time or if the pitch angle is changed by small amounts (e.g. less than 1° (degree)) multiple times.

[0007] At below nominal wind speeds, for example between 11 m / s and 13 m / s, the power produced is less than nominal (i.e., rated, maximum) power, and the pitch angle generally remains at the same position at or near a default position, typically at or near 0°. Since the pitch angle may be constant, may vary by small amounts over extended periods of time, or such that movement may not be sufficient to distribute lubricant when operating below nominal wind speeds, it may be necessary to pitch the blades specifically to distribute lubricant. For example, the main controller of the wind turbine may be configured to instruct the blades to pitch by X° every Y hours.

[0008] In conditions above nominal wind speed, the power produced is nominal power (usually until the cut-out wind speed is reached), and the pitch angle of the blades is usually varied to control the loads acting on the blades and the wind turbine. Since the blades are pitched frequently or continuously, the lubricant lubricating the pitch bearings tends to be well distributed in this condition. If it is determined that the lubricant is not sufficiently well distributed, in some examples, the blades may be pitched to redistribute the lubricant specifically in this condition.

[0009] The speed at which the pitch change is performed is relevant. If the pitch change for lubricating the pitch bearing is performed too quickly, the load on the blades may be too high. However, if the pitch change for lubricating the pitch bearing is performed relatively slowly, the power generation may be significantly reduced.

[0010] An object of the present disclosure is to optimize the balance between the loads acting on the blades and the energy generation during pitching to lubricate the pitch bearing. Summary of the invention

[0011] In one aspect of the present disclosure, a method for lubricating a pitch bearing connecting a blade and a hub of a wind turbine is provided. The method includes determining that lubrication is to be applied to the pitch bearing. The method also includes determining an upper limit for a load gradient, the load gradient being a derivative of a load with respect to time. The method also includes determining a pitch rate for lubricating the pitch bearing based at least in part on the upper limit for the load gradient. The method also includes pitching a wind turbine blade at the determined pitch rate to lubricate the pitch bearing so that the upper limit for the load gradient is not exceeded.

[0012] According to this aspect, an upper limit for the load gradient is determined, and the pitch rate is determined based at least in part on the determined upper limit. In this way, pitching for lubricating the pitch bearing, for example for distributing lubricant along the interface between the inner race and the outer race of the pitch bearing, can be performed as quickly as possible without subjecting the wind turbine blade to higher than acceptable loads. Unnecessary power generation losses can be avoided, while fatigue loads can be maintained at acceptable levels.

[0013] In another aspect of the present disclosure, a wind turbine controller is provided. The wind turbine controller includes a processor and a memory. The memory includes instructions that, when executed by the processor, cause the processor to determine that lubrication of a pitch bearing is necessary, determine an upper limit for a load gradient, the load gradient being a derivative of thrust with respect to time, and determine a pitch rate for lubricating a pitch bearing connecting a blade and a hub of the wind turbine based on the upper limit for the load gradient, so that the upper limit for the load gradient is not exceeded when pitching.

[0014] In another aspect of the present disclosure, a wind turbine is provided. The wind turbine comprises a tower, a nacelle on top of the tower, and a rotor connected to the nacelle. The rotor comprises a hub and a plurality of blades connected to the hub via a pitch bearing. The wind turbine also comprises a wind turbine controller of the aforementioned aspect.

[0015] In another aspect of the present disclosure, a method is provided. The method includes determining that a pitch bearing connecting a blade and a hub of a wind turbine requires lubrication, determining a prevailing wind speed, determining a change in thrust relative to a pitch angle based on the prevailing wind speed, determining a pitch rate for lubricating the pitch bearing based on the change in thrust relative to the pitch angle and a maximum limit for a thrust gradient, the thrust gradient being a derivative of the thrust with respect to time, and pitching the wind turbine blades at the determined pitch rate to lubricate the pitch bearing such that the maximum limit for the thrust gradient is not exceeded.

[0016] The aerodynamic thrust on the rotor of a wind turbine is a load indicative of fatigue loads on the wind turbine. According to this aspect, the thrust gradient is kept below an acceptable limit to optimize annual energy production while maintaining fatigue loads at an acceptable level.

[0017] Technical Solution 1. A method (100) for lubricating a pitch bearing (72) connecting a wind turbine blade (22) and a hub (20) of a wind turbine (10), the method comprising:

[0018] Determining (110) that lubrication of the pitch bearing (72) is to be performed;

[0019] determining (120) an upper limit for a load gradient, the load gradient being a derivative of the load with respect to time;

[0020] determining (130) a pitch rate for lubricating the pitch bearing (72) based at least in part on the upper limit for the load gradient; and

[0021] The wind turbine blade (22) is pitched (140) at the pitch rate determined to lubricate the pitch bearing (72) such that the upper limit for the load gradient is not exceeded.

[0022] Technical Solution 2. The method according to Technical Solution 1, wherein the upper limit for the load gradient is predefined.

[0023] Technical Solution 3. A method according to Technical Solution 1 or 2, wherein the pitch rate is determined based on the prevailing wind conditions.

[0024] Technical Solution 4. A method according to Technical Solution 3, wherein the dominant wind condition includes a dominant wind speed.

[0025] Technical Solution 5. A method according to Technical Solution 4, wherein the dominant wind conditions also include one or more of the following: turbulence intensity, wind direction, wind shear and / or wind turning.

[0026] Technical Solution 6. A method according to any one of Technical Solutions 3-5, wherein determining the pitch rate includes determining the change in the load relative to the pitch angle for the determined prevailing wind condition.

[0027] Technical Solution 7. A method according to Technical Solution 6, wherein determining the pitch rate further comprises dividing the upper limit for the load gradient for the prevailing wind speed to determine the change in the load relative to the pitch angle.

[0028] Technical Solution 8. A method according to Technical Solution 6 or 7, wherein data of the load as a function of the pitch angle and as a function of the wind speed are known in advance.

[0029] Technical Solution 9. A method according to any one of Technical Solutions 1-8, wherein the load is an aerodynamic thrust on a rotor of the wind turbine.

[0030] Technical Solution 10. The method according to any one of Technical Solutions 1-8 further includes maintaining the determined pitch rate constant during a complete pitch maneuver for lubricating the pitch bearing (72).

[0031] Technical solution 11. A method according to any one of technical solutions 1-9, wherein determining (110) that lubrication is to be performed on the pitch bearing (72) includes determining that a predefined time period has passed or determining that the blade (22) has not rotated a predetermined amount during the predefined time period.

[0032] Technical Solution 12. A method according to any one of Technical Solutions 1-11, wherein the pitch bearing (72) is lubricated in less than five minutes, and in particular in less than two minutes.

[0033] Technical Solution 13. A wind turbine controller (36), comprising a processor and a memory, wherein the memory comprises instructions which, when executed by the processor, cause the processor to implement a method according to any one of Technical Solutions 1-12.

[0034] Technical solution 14. A wind turbine (10), comprising a tower (15), a nacelle (16) on top of the tower (15), and a rotor (18) connected to the nacelle (16), wherein the rotor (18) comprises a hub (20) and a plurality of blades (22) connected to the hub (20) via a pitch bearing (72), and the wind turbine (10) further comprises a wind turbine controller (36) according to Technical Solution 13.

[0035] Technical Solution 15. A wind turbine according to Technical Solution 14, wherein the wind turbine (10) is an offshore wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 illustrates a perspective view of one example of a wind turbine;

[0037] Figure 2 Graphics Figure 1 A simplified interior view of an example of a nacelle of a wind turbine;

[0038] Figure 3 A flow chart showing an example of a method for lubricating a pitch bearing connecting a blade and a hub of a wind turbine;

[0039] Figure 4 An example of a simulation showing thrust as a function of wind speed;

[0040] Figure 5 An example showing a simulation of thrust gradient as a function of wind speed; and

[0041] Figure 6 A flow chart showing another example of a method for lubricating a pitch bearing. DETAILED DESCRIPTION

[0042] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. Each example is provided as an explanation of the present disclosure rather than 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 embodiment may be used together with another embodiment to produce yet another embodiment. 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.

[0043] Figure 1 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 an alternative embodiment, rotor 18 includes more or less than three rotor blades 22. Tower 15 may be fabricated from tubular steel to define a cavity (not shown) between support system 14 and nacelle 16. Figure 1 ). In an alternative embodiment, 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.

[0044] 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 The loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer region 26 .

[0045] In an example, rotor blades 22 may have a length 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 wind direction 28, rotor 18 rotates about 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.

[0046] In addition, the pitch angle of rotor blades 22 (e.g., the angle that determines the orientation of rotor blades 22 relative to the wind direction) may be varied by pitch system 32 to control the load and power generated by 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 may specifically vary the pitch angle of rotor blades 22 such that the angle of attack of (portions of) the rotor blades is reduced, which may facilitate reducing the rotational speed of rotor 18 and / or facilitating stalling of rotor 18.

[0047] In this example, blade pitch of each rotor blade 22 is individually controlled by wind turbine controller 36 or pitch control system 80. Alternatively, blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0048] Furthermore, in this example, as wind direction 28 changes, the yaw orientation of nacelle 16 may be rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0049] 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 control system distributed 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 one or more processors configured to perform one or more steps of the method described herein. In addition, many other components described herein include one or more processors. The wind turbine controller 36 may also include a memory, such as one or more storage devices. As used herein, a memory may include (multiple) storage elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), a floppy disk, a compact disk read-only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disk (DVD), and / or other suitable storage elements.

[0050] Figure 2 1 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 the relatively slow rotational motion of the rotor 18 and the main shaft 44 into a relatively fast rotational motion of the high-speed shaft 48. The high-speed shaft 48 is connected to the generator 42 by means of the coupling 50 to generate electrical energy. Furthermore, a transformer 90 and / or suitable electronics, switches and / or inverters may be arranged in the nacelle 16 in order to convert the electrical energy generated by the generator 42, for example, with a voltage between 400 V and 1000 V, into electrical energy with a medium voltage (e.g., 10-35 kV). An offshore wind turbine may have a generator voltage, for example, between 650 V and 3500 V, and a transformer voltage, for example, between 30 kV and 70 kV. The electrical energy is conducted from the nacelle 16 to the tower 15 via a power cable.

[0051] In some examples, the wind turbine 10 may include one or more shaft sensors 51. The shaft sensors may be configured to monitor at least one of the torque load acting on the main shaft 44 and / or the high-speed shaft 48 and the rotational speed of the shafts 44, 48. In some examples, the wind turbine 10 may include one or more generator sensors 53. The generator sensor may be configured to monitor at least one of the rotational speed of the generator 42 and the generator torque. The shaft sensor 51 and / or the generator sensor 53 may include, for example, one or more torque sensors (e.g., strain gauges or pressure sensors), optical sensors, accelerometers, magnetic sensors, speed sensors, and micro inertial measurement units (MIMUs).

[0052] The gearbox 46, the generator 42 and the transformer 90 may be supported by a 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 via one or more torque arms 103. In this example, the nacelle 16 also includes a front main support bearing 60 and a rear main support bearing 62. Furthermore, the generator 42 may be mounted to the main frame 52 via 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 source of noise emission.

[0053] Optionally, main frame 52 is configured to carry all loads caused by the weight of components of rotor 18 and nacelle 16 and by wind and rotational loads, and further configured to introduce these loads into tower 15 of wind turbine 10. Rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and any associated fastening, supporting, and / or fixing devices (including but not limited to support member 52 and front and rear support bearings 60, 62) are sometimes referred to as drive train 64.

[0054] 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 typically have a much larger diameter than the generators used in wind turbines with a gearbox 46 to provide a similar amount of power as a wind turbine with a gearbox.

[0055] The nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 , and thereby also the rotor 18 , about the yaw axis 38 to control the viewing angle of the rotor blades 22 relative to the wind direction 28 .

[0056] 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 wind turbine controller 36 with information that may include wind direction 28 and / or wind speed.

[0057] 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.

[0058] 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 134 ), 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.

[0059] Pitch drive system 68 is coupled to wind turbine controller 36 for adjusting the pitch angle of rotor blades 22 upon receipt of 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.

[0060] Pitch assembly 66 may also include one or more pitch control systems 80 for controlling pitch drive system 68 according to control signals from wind turbine controller 36 in the event of certain priority conditions and / or during overspeed of rotor 18. In this example, pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a corresponding pitch drive system 68 for controlling pitch drive system 68 independently of wind turbine controller 36. In this example, pitch control system 80 is coupled to pitch drive system 68 and sensor 70. During normal operation of wind turbine 10, wind turbine controller 36 may control pitch drive system 68 to adjust the pitch angle of rotor blades 22.

[0061] According to one embodiment, a power generator 84, for example including a battery and a capacitor, is disposed 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 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.

[0062] 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 an alternative embodiment, the components are positioned relative to an outer surface of hub 20 and may be coupled directly or indirectly to the outer surface.

[0063] 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.

[0064] In one aspect of the present disclosure, a method 100 is provided for lubricating a pitch bearing 72 connecting a blade 22 and a hub 20 of a wind turbine 10. The method 100 includes: Figure 3 The method includes, at box 110, determining that lubrication is to be performed on the pitch bearing. The method also includes, at box 120, determining an upper limit of a load gradient, the load gradient being the derivative of the load with respect to time. In this specific example, the load gradient is a thrust gradient, i.e., a change in aerodynamic thrust with respect to time.

[0065] The method also includes, at block 130, determining a pitch rate for lubricating the pitch bearing 72 based at least in part on the upper limit for the load gradient. The method also includes, at block 140, pitching the wind turbine blade 22 at the determined pitch rate to lubricate the pitch bearing 72 such that the upper limit for the load gradient is not exceeded.

[0066] In this way, the maximum change in load over time can be determined and used as an upper limit, and the pitch rate can be determined to avoid exceeding the upper limit. Thus, the distribution of lubricant in the pitch bearing by pitching the wind turbine blades can be performed as quickly as possible, thereby reducing potential power losses, while controlling the load on the blades of the wind turbine.

[0067] Determining the upper limit for the load gradient may include consulting a data structure, such as consulting a lookup table, or receiving the upper limit from another controller, component or system, among others. The upper limit may be predefined and stored, for example, in a data structure, such that determining the upper limit includes accessing the data structure. A suitable value for the upper limit may be based, for example, on the size of the wind turbine blades or the location of the wind turbine, as this may affect the load applied to the wind turbine.

[0068] In some examples, an upper limit may be calculated. For example, a wind turbine controller may determine a first upper limit, and then determine the actual limit as a percentage of the first upper limit. Fatigue, damage, and other parameters experienced by the wind turbine blades may affect the percentage applied. In some examples, the upper limit of the load gradient may change during the life of the wind turbine.

[0069] The order of steps illustrated in this figure should not be considered limiting. For example, the step of determining 110 that lubrication of pitch bearing 72 is to be performed (i.e., is deemed beneficial or necessary) may be performed before determining the pitch rate at box 130, and in some examples, may also be performed before determining the upper limit of the thrust gradient at box 120. In other examples, the step of determining the upper limit at box 120 may be performed before the step at box 110.

[0070] Determining that lubrication is to be applied to the pitch bearing may be performed in several ways. In some examples, determining that lubricating the pitch bearing is necessary (or beneficial) may include determining that the pitch bearing 72 has not been lubricated during a (first) predefined time period. In some of these examples, the method may include determining that the (first) predefined time period has passed. For example, the frequency of pitching the blade 22 to lubricate the pitch bearing race may be predefined. In some examples, the controller 36 may be configured to lubricate the pitch bearing race periodically. The memory of the wind turbine controller may include stored instructions indicating that the blade 22 of the wind turbine may be pitched X° every Y hours. In such cases, the time at which the pitch bearing 72 is lubricated is predefined. Therefore, if a predefined specific time period has passed, the pitch rate for lubricating the pitch bearing 72 may be determined. That is, after Y hours, the blade may be pitched X° at a determined pitch rate. And after another Y hours, the blade may be pitched X° again at the same or different pitch rate. Pitching X° may, for example, take tens of seconds or minutes.

[0071] Determining that lubrication is to be applied to the pitch bearing may include determining that the pitch bearing 72 has not been lubricated during a second predefined time period that is different from the first predefined time period. For example, the method may also include determining that the second predefined time period has elapsed. The wind turbine controller 36 may be configured to initiate lubrication of the pitch bearing after a specific first time period and after another specific second time period. For example, the wind turbine controller may be configured to pitch the blades by X° every Y hours and to pitch the same blades by W° every Z hours, where X is different from W and Y is different from Z. For example, the blades may be pitched by a small number of degrees at short time intervals, and the blades may also be pitched by a large or larger number of degrees at long or longer time intervals.

[0072] Determining that lubrication is to be applied to the pitch bearing may include determining that blade 22 has not rotated a predefined amount during a predefined time period. For example, determining that blade 22 has not rotated at all or has not rotated above a threshold value during a (first) predefined time period. If blade 22 should pitch X° every Y hours (e.g., pitch X° in the same direction), but this has not yet been achieved, then a pitch rate for lubricating pitch bearing 72 may be determined.

[0073] Additionally or alternatively, wind turbine 10 may include one or more sensors that may be used to obtain information related to lubrication of pitch bearing 72 and to check whether a pitch change for lubricating the pitch bearing is required. For example, if a need to lubricate pitch bearing 72 is detected before a predefined time period has expired, the pitch rate may be determined without waiting for the predefined time period to elapse.

[0074] Determining that lubrication is to be applied to the pitch bearing may include determining that the prevailing wind speed is below the nominal wind speed. For wind speeds above the nominal wind speed, the blades 22 of the wind turbine 10 may be pitched frequently, and lubricant may not need to be redistributed between the outer bearing race and the inner bearing race of the pitch bearing 72. Therefore, in some examples, if the prevailing wind speed is below the nominal (i.e., rated) wind speed, only the pitch rate may be determined 130. The wind turbine controller may be configured to have a first operating or control mode for wind speeds below the nominal wind speed, in which the pitch rate may be determined 130, and a second operating or control mode (different from the first mode) for wind speeds above the nominal wind speed, in which the pitch rate is not determined 130.

[0075] The pitch rate may be determined at box 130 based on the prevailing wind conditions, in particular the prevailing wind speed. Determining the prevailing wind speed may include measuring or estimating the prevailing wind speed. After detecting that lubrication of the pitch bearing is necessary, the wind speed may be determined (immediately). Thus, in some examples, the need to lubricate the pitch bearing may be detected, then the prevailing wind speed may be measured, for example, and a suitable pitch rate may be determined. In some examples, the wind speed may be determined based on the rotor speed, the pitch angle, etc. In other examples, an anemometer or LIDAR may be used to determine the prevailing wind speed. Other wind conditions that may be considered include turbulence levels, such as turbulence intensity. Other wind conditions that may be considered may include wind direction (changes), wind shear, and wind steering.

[0076] The data of load as a function of pitch angle and as a function of wind speed may be known in advance. Figure 4 The data shown in may be predefined. In the following examples, aerodynamic thrust will be used as an example of load. In other examples, other loads may be used, such as tower or blade bending loads.

[0077] Figure 4 An example of a simulation of thrust (in kN (kilonewtons)) as a function of wind speed (in m / s (meters per second)) is shown. In this figure the minimum, maximum and average values ​​of the thrust for a given wind speed can be seen. In some examples, the thrust gradient may be considered to depend not only on the wind speed, but also on turbulence, for example. Turbulence may lead to different values ​​of thrust for the same average wind speed. For example, a specific wind profile with a specific average wind speed may be introduced. Since the instantaneous wind speed is not constant during all simulations, a dispersion of thrust values ​​is introduced.

[0078] exist Figure 4 In the example of FIG. 1 , it is assumed that the rotor 18 of the wind turbine 10 faces the wind for all wind speeds. A dispersion in the incident wind direction may also be introduced in the simulation so that the calculated thrust value also takes into account that the direction of the incoming wind may not be constant during the simulation. Figure 4 As can be seen in , the thrust, ie the axial force exerted by the wind on the rotor of the wind turbine, is greatest when the wind turbine is operating near the rated (nominal) wind speed.

[0079] Such simulations may be performed in advance, i.e., before operating the wind turbine. Its data may be stored, for example, in a memory of a wind turbine controller (e.g., main wind turbine controller 36) before the wind turbine is installed. In a further example, a remote operation center may store such data, or a SCADA system may store such data. During operation, the wind turbine may access this information.

[0080] Figure 5An example of a simulation showing the variation of thrust with respect to pitch angle (in kN / °) as a function of wind speed (in m / s) is shown. Specifically, Figure 5 Show Figure 4 The pitch derivative of the thrust of the example. Therefore, Figure 5 Shows the maximum, minimum, and average values ​​of how much thrust changes per degree of pitch change at a specific wind speed.

[0081] In absolute value, at lower wind speeds, the thrust gradient is generally lower. Therefore, at low wind speeds, the expected load on the blades when pitching is lower, and the pitching can be performed faster. At higher wind speeds, the absolute value of the thrust gradient is generally higher. Therefore, at high wind speeds, the expected load on the blades when pitching is higher, and the pitching can be performed slower to avoid excessive loads on the blades.

[0082] In some examples, data on the change in thrust relative to the pitch angle as a function of wind speed may be known in advance. Figure 5 The data shown in may be predefined, for example, because simulations may have been performed beforehand. The simulations may be performed using known mathematical models. Figure 4 The data shown in or except Figure 4 In addition to the data shown in Figure 5 The data may be stored in a memory of a wind turbine controller (eg, main wind turbine controller 36) before installing the wind turbine. Similar to before, such data may be stored in a SCADA system or in a remote location, such as a remote operation center.

[0083] During operation, the wind turbine may access this information. The predefined data (eg, thrust or change in thrust relative to pitch angle as a function of wind speed) may be stored in any suitable manner. In some examples, a lookup table may be used.

[0084] The above data may be derived using mathematical equations and mathematical models known in the art for determining (eg, calculating or simulating) thrust as a function of wind speed or the change in thrust relative to pitch angle as a function of wind speed.

[0085] Thus, when determining to redistribute the distribution of lubricant in the pitch bearing, the prevailing wind conditions may be determined (e.g., measured), and the change in thrust relative to the pitch angle for the prevailing wind speed may be determined using (predefined) data of the change in thrust (or other load) relative to the pitch angle for those wind conditions. In some cases, the wind conditions may simply refer to the wind speed, and in other cases, the wind conditions may be more complex, including one or more of the following: air density, wind direction, wind turning, wind shear, turbulence, temperature, or other.

[0086] The upper limit of the thrust gradient (eg in kN / s) may be divided by the determined value of the change in thrust relative to the pitch angle (eg in kN / °) to obtain a value for the pitch rate (eg in ° / s).

[0087] In some examples, an average of the change in thrust relative to pitch for a determined (eg, measured) prevailing wind speed may be used to determine the pitch rate at block 130 .

[0088] Determining the pitch rate may be performed in several ways. In some examples, determining the pitch rate may include using predefined data for thrust and predefined data for a change in thrust relative to a pitch angle. For example, wind turbine controller 36 may consult a lookup table or any other suitable data structure to determine a change in thrust relative to a pitch angle. In other examples, the data for thrust and the data for a change in thrust relative to a pitch angle may not be predefined and may be calculated or estimated each time such information may be useful or necessary. To this end, a suitable mathematical equation may be used.

[0089] In some examples, at block 120, the pitch rate determined may be maximum for a previously determined upper limit for the thrust gradient. That is, the highest possible pitch rate may be determined for the thrust limit. In this way, pitching may be performed as quickly as possible without exceeding the previously determined thrust limit.

[0090] In other examples, the pitch rate determined need not be the maximum for the thrust gradient limitation. For example, a pitch rate may be determined that is not the fastest possible pitch rate for the thrust limit setting.

[0091] In some examples, the determined pitch rate may be higher than a lower limit for the pitch rate. The lower limit for the pitch rate may be predefined, i.e., known in advance, such that the determined pitch rate is sufficiently high. For example, for different wind speeds (e.g., for different average wind speeds), a predefined lower limit for the pitch rate may be provided. For all some of these wind speeds, the lower limit may be different. In some examples, for at least some of the wind speeds, the lower limit may be the same. One or more lower limits for the pitch rate may be stored in a memory of wind turbine controller 36.

[0092] In other examples, a lower limit for the pitch rate may be implicit, in the sense that the determined pitch rate may not be reduced below a certain value when a compromise between maximizing power production and minimizing loads on the wind turbine during pitching can be achieved. Very low or too low pitch rates may be excluded.

[0093] The determined pitch rate may be maintained during a complete pitch maneuver for lubricating the pitch bearing. Pitching for lubricating the pitch bearing typically requires only a small amount of time, such as less than 5 minutes, or even less than 2 minutes, and maintaining the determined pitch rate may provide an effective and safe lubrication maneuver for the pitch bearing. The lubrication operation may include one or more than one lubrication stroke. The lubrication stroke may include pitching in a first direction and then pitching back in the opposite direction.

[0094] In other examples, the method may further include varying the pitch rate during lubrication of the pitch bearing. This option may be implemented depending on, for example, the expected duration of the pitch maneuver for lubricating the pitch bearing, or if gusts or other significant changes in wind conditions are expected or experienced.

[0095] The method may be applied to all blades 22 of wind turbine 10 simultaneously, for example, in some examples, all blades 22 may be pitched simultaneously for lubricating corresponding pitch bearings. The duration of the lubrication maneuver and the determined pitch rate may also be the same for all blades of the wind turbine.

[0096] According to another aspect of the present disclosure, a wind turbine controller 36 is provided. The wind turbine controller includes a processor and a memory. The memory includes instructions that, when executed by the processor, cause the processor to: determine an upper limit for a load gradient, the load gradient being a derivative of thrust with respect to time, determine a pitch rate for lubricating a pitch bearing connecting a blade and a hub of the wind turbine based on the upper limit of the load gradient, and pitch the wind turbine blades at the determined pitch rate to lubricate the pitch bearing so that the upper limit of the load gradient is not exceeded.

[0097] The memory may generally be configured to store suitable computer-readable instructions that, when executed by the processor, configure wind turbine controller 36 to appropriately perform or trigger the performance of various steps disclosed herein, such as steps with respect to method 100. The memory may also be configured to store data, such as predefined data or data from measurements and / or calculations.

[0098] The wind turbine controller 36 may also include a communication module. The communication module may facilitate communication between the controller 36 and various components of the wind turbine 10. For example, the communication module may be used as an interface to enable the turbine controller 36 to transmit control signals to the pitch drive system 66 to control the pitch angle of the rotor blades 22. The communication module may be configured to communicatively connect the controller 36 to other elements of the wind turbine 10. The connection may be implemented via a wired connection and / or via a wireless connection, such as by using any suitable wireless communication protocol known in the art. In addition, the communication module may include a sensor interface, such as one or more analog-to-digital converters, so that signals transmitted from one or more sensors (e.g., a wind speed sensor) can be converted into signals that can be understood and processed by the processor.

[0099] The controller 36 may be configured to perform one or more of the steps and actions noted in the method 100 (and also noted below in the method 200 ).

[0100] According to a further aspect of the present disclosure, there is provided a wind turbine 10. The wind turbine comprises a tower 15, a nacelle 16 on top of the tower 15, a rotor 18 connected to the nacelle 16, the rotor comprising a hub 20 and a plurality of blades 22 connected to the hub via pitch bearings, and a wind turbine controller 36 of the foregoing aspects.

[0101] In some examples, the wind turbine may be an offshore wind turbine. Power generation of an offshore wind turbine may not be stopped in order to perform the lubrication maneuver, and thus the above method may be particularly beneficial for offshore wind turbines. Although the above method may of course be performed by an onshore wind turbine.

[0102] According to another aspect of the present disclosure, a method 200 is provided. The method 200 includes: Figure 6 For example, the details and explanations of the previous aspects of method 100 may be combined and applied to this aspect, and vice versa.

[0103] The method includes: at box 210, determining that a pitch bearing 72 connecting a blade 22 and a hub 20 of the wind turbine 10 requires lubrication; at box 220, determining a prevailing wind speed; at box 230, determining a change in thrust relative to a pitch angle based on the prevailing wind speed; at box 240, determining a pitch rate for lubricating the pitch bearing 72 based on the change in thrust relative to the pitch angle and a maximum limit of a thrust gradient, the thrust gradient being a derivative of the thrust with respect to time; and at box 250, pitching the wind turbine blades 22 at the determined pitch rate for lubricating the pitch bearing such that the maximum limit of the thrust gradient is not overcome.

[0104] Determining that pitch bearing 72 requires lubrication may include determining that pitch bearing 72 has not been lubricated during a predefined period of time.

[0105] The pitch rate may be held constant until lubrication of the pitch bearing is complete. Determining the pitch rate may include dividing the maximum limit for the thrust gradient by the change in thrust relative to the pitch angle. In some examples, additional safety factors or load factors may be considered.

[0106] The data of thrust as a function of wind speed and the data of the variation of thrust with respect to the pitch angle as a function of wind speed may be predefined as explained above.

[0107] The written description uses examples to disclose the present teachings, including the best mode, 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 method. The patentable scope is defined by the claims and may include other examples that occur to a person skilled in the art. If such other examples include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ substantially from the literal language of the claims, such other examples are intended to be within the scope of the claims. A person of ordinary skill in the art may mix and match aspects from the various embodiments described and other known equivalents of each such aspect to construct additional embodiments 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 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 lubricating a pitch bearing (72) connecting a wind turbine blade (22) and a hub (20) of a wind turbine (10), the method comprising: Determining (110) that lubrication of the pitch bearing (72) is to be performed; determining (120) an upper limit for a load gradient, the load gradient being a derivative of the load with respect to time; determining (130) a pitch rate for lubricating the pitch bearing (72) based at least in part on the upper limit for the load gradient; as well as The wind turbine blade (22) is pitched (140) at the pitch rate determined to lubricate the pitch bearing (72) such that the upper limit for the load gradient is not exceeded.

2. The method according to claim 1, wherein: The upper limit for the load gradient is predefined.

3. The method according to claim 1 or 2, wherein: The pitch rate is determined based on the prevailing wind conditions.

4. The method according to claim 3, wherein: The prevailing wind condition includes a prevailing wind speed.

5. The method according to claim 4, wherein: The prevailing wind conditions may also include one or more of: turbulence intensity, wind direction, wind shear and / or wind turning.

6. The method according to any one of claims 3 to 5, wherein: Determining the pitch rate includes determining a change in the load with respect to a pitch angle for the determined prevailing wind condition.

7. The method according to claim 6, wherein: Determining the pitch rate further includes dividing the upper limit for the load gradient for the prevailing wind speed by the determined change in the load with respect to pitch angle.

8. The method according to claim 6 or 7, wherein: The data of the load as a function of the pitch angle and as a function of the wind speed are known in advance.

9. The method according to any one of claims 1 to 8, wherein: The load is the aerodynamic thrust on the rotor of the wind turbine.

10. The method according to any of claims 1-8, further comprising maintaining the determined pitch rate constant during a complete pitch maneuver for lubricating the pitch bearing (72).

Images