Wind turbine operation

Abstract

The present disclosure relates to a method for determining a thrust limit of a wind turbine and a method for operating a wind turbine. The method includes determining an operational state of a blade load monitoring system of the wind turbine. The method further includes adjusting a thrust threshold of the wind turbine based at least in part on the operational state of the blade monitoring system. The method also includes operating the wind turbine such that a thrust load on a rotor of the wind turbine is maintained at or below the adjusted thrust threshold. A control system suitable for maintaining a thrust load at or below the thrust threshold, as well as a wind turbine including such a control system, are also provided.

Description

[Technical Field]

[0001] The present disclosure relates to wind turbines and methods and systems for operating wind turbines. More particularly, the present disclosure relates to methods and systems for determining the operating state of a blade load measurement system and adjusting the operation of the wind turbine based on the operating state of the blades. The present disclosure also relates to a method for determining an adjusted thrust threshold for use in operating a wind turbine. [Background technology]

[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 disposed on the tower. The rotor, which typically comprises a hub and a number of blades, rotates under the influence of wind on the blades. The rotation typically generates torque that is transmitted through the rotor shaft to a generator, either directly ("direct drive" or gearless) or through the use of a gearbox. In this way, the generator produces electricity that can be supplied to the power grid.

[0003] Offshore wind turbines have gained great popularity in recent years due to a combination of factors: the offshore environment provides a consistent and strong wind resource, which is beneficial for generating electricity from wind; wind speeds are generally higher and more stable offshore compared to onshore, resulting in higher energy output; furthermore, the offshore environment, without onshore constraints, allows for the construction of larger turbines, as they can be spaced farther apart, taller, and have longer blades; this can result in higher energy output per turbine and therefore more efficient use of the wind resource.

[0004] However, offshore wind turbine sites also present several challenges and problems due to the harsh and remote nature of the offshore environment. In some cases, access to the turbines can be difficult and time-consuming, requiring maintenance personnel to travel to the turbines by boat or helicopter. This can be further complicated by weather conditions, making safe access to the turbines difficult for extended periods of time.

[0005] Additionally, turbine components and systems may be exposed to extreme weather conditions, which can lead to accelerated wear and tear and increase the likelihood of component failure, which can lead to increased turbine downtime and reduced energy output.

[0006] Additionally, the installation and commissioning of offshore wind turbines can take longer than onshore wind turbines. Special vessels are required to lift the nacelle, rotor, and rotor blades, which may not be possible in all wind conditions. This can result in long wind farm installation times. Commissioning of wind turbines can also take longer than onshore wind turbines, as personnel must travel to the farm for testing and inspection. Commissioning can include testing of wind turbine power generation, verification of protection systems, power measurement tests, and many mechanical tests. Some of the tests may only be performed in certain wind conditions, which can delay the commissioning process.

[0007] A wind turbine may have multiple sensor systems that aid or are essential to the safe and efficient operation of the wind turbine, for example, load sensors and accelerometers may be used throughout the wind turbine to detect abnormal or unsafe conditions.

[0008] Load sensors may be located on or with the blades, for example, to measure the load on the blades. The input of such load sensors may be used directly as an input in the operation of the wind turbine. For example, blade load measurements may be used to keep the operational load under control, especially taking into account fatigue load accumulation and taking into account maximum allowable loads. For example, in cases of high turbulence, it is known to modify the operational thrust limit of a wind turbine. In practice, the operating parameters of the wind turbine may be changed, for example, pitching the blades and reducing rotor speed and output power to keep the thrust of the wind turbine at the operational thrust limit.

[0009] As mentioned above, load sensors may be located with the blades, particularly near the blade root. The sensors may be positioned to measure both edgewise and flapwise loads. The sensors used to determine blade loads may also be located elsewhere, for example, in the hub or main rotor shaft, or with the pitch bearings or main bearings.

[0010] In some cases, commissioning and calibration of blade load monitoring systems for offshore wind turbines can be a complicated process due to the difficult conditions of the offshore environment, such as high winds and waves, which can complicate access. Furthermore, proper calibration of the blade load monitoring system may require specific wind conditions, for example, relatively low wind speeds.

[0011] Delays in the calibration of blade monitoring systems can lead to annual energy losses for wind turbines. Because the systems are used to optimize turbine performance as well as to protect against critical loads, wind turbines with inoperable blade monitoring systems cannot operate. Similarly, blade monitoring systems can become unreliable after a period of operation due to wear and tear. If this is detected, wind turbine operation can be stopped.

[0012] The present disclosure provides methods and systems that at least partially overcome some of the aforementioned drawbacks associated with blade load monitoring systems. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 116126 Summary of the Invention

[0014] In one aspect of the disclosure, a method for determining a thrust threshold for a wind turbine is provided, the method including determining an operating state of a blade load monitoring system for the wind turbine, and determining a thrust threshold for the wind turbine based at least in part on the operating state of the blade monitoring system and wind turbulence.

[0015] According to this aspect, appropriate operating parameters for safe and efficient operation of the wind turbine can be provided even if the blade load monitoring system is not operational, not yet calibrated, or not operating properly. Rather than not operating the wind turbine at all, appropriate thrust thresholds are provided based on whether the blade load monitoring system is operational.

[0016] In a further aspect of the present disclosure, there is provided a method for operating a wind turbine, the method including determining an operational state of a blade load monitoring system of the wind turbine and determining a thrust threshold for the wind turbine based at least in part on the operational state of the blade monitoring system, the method then further including operating the wind turbine such that a thrust load on a rotor of the wind turbine is less than or equal to the determined thrust threshold.

[0017] This aspect allows the wind turbine to operate in scenarios where a blade load monitoring system is not available. This may be particularly relevant for offshore wind turbines, where long delays in commissioning blade monitoring systems due to intense weather conditions may frequently occur. Therefore, the method enables operation of the wind turbine at improved annual energy production output compared to other prior art approaches. Furthermore, it has been found that operation at maximum thrust levels can be more efficient and increase annual energy production compared to operation with setpoint reduction ("downrating" the wind turbine).

[0018] In yet another aspect of the present disclosure, there is provided a wind turbine comprising: a wind turbine tower; a rotor including one or more blades mounted atop the tower; a blade load monitoring system for determining a load on the blade; and a control system configured to determine an operational state of the blade load monitoring system, determine a thrust threshold for the wind turbine based at least in part on the operational state of the blade monitoring system, and operate the wind turbine such that a thrust load on the rotor of the wind turbine is at or below the determined thrust threshold.

[0019] Throughout this disclosure, the term "turbulence intensity" may be understood as the standard deviation of wind speed relative to the mean value of the wind speed. Turbulence intensity may refer to a percentage or a decimal number less than one. The standard deviation of wind speed and the mean value of wind speed may be determined over a certain time interval. Such a time interval may be, for example, 10 minutes.

[0020] Throughout this disclosure, the thrust load of a wind turbine may be considered to be the axial force exerted by the wind on the rotor of the wind turbine, and the thrust threshold may be considered to be the maximum level of thrust allowed during operation.

[0021] Additional objects, advantages and features of the embodiments of the present disclosure will become apparent to those skilled in the art upon examination of the description or may be learned by practice. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram illustrating a perspective view of an example wind turbine. [Figure 2] 1 illustrates an example of a hub and nacelle of a wind turbine. [Figure 3] FIG. 1 illustrates a flowchart of an example method for determining a thrust threshold. [Figure 4] FIG. 1 shows a flow chart of an example of a method for operating a wind turbine. [Figure 5] FIG. 10 shows a flowchart of a further example of a method for operating a wind turbine. [Figure 6] FIG. 10 shows a flowchart of yet another example of a method for operating a wind turbine. [Figure 7] 1 is a schematic diagram of a control system for controlling the operation of a wind turbine; [Figure 8] FIG. 1 illustrates an example of a power output curve for a wind turbine operating at an original thrust threshold and an adapted threshold. DETAILED DESCRIPTION OF THE INVENTION

[0023] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation, not limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the teachings of the present disclosure. For example, features illustrated or described as part of any embodiment may be used in another embodiment to yield yet a further embodiment. Accordingly, the present disclosure is intended to cover such modifications and variations as come within the scope of the appended claims and their equivalents.

[0024] FIG. 1 is a perspective view of an example 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 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 and extending outward from hub 20. In this example, rotor 18 has three rotor blades 22. In alternative embodiments, rotor 18 includes more or fewer than three rotor blades 22. Tower 15 may be fabricated from tubular steel to define a cavity (not shown in FIG. 1 ) between support system 14 and nacelle 16. In alternative embodiments, tower 15 is any suitable type of tower having any suitable height. According to alternatives, the tower may be a hybrid tower comprising a concrete section and a tubular steel section, or the tower may be a partial or full lattice tower.

[0025] The rotor blades 22 are spaced about the hub 20 to facilitate rotation of the rotor 18 so that kinetic energy can be converted from the wind into usable mechanical energy and subsequently electrical energy. The rotor blades 22 are fitted to the hub 20 by coupling blade root portions 24 to the hub 20 at a plurality of load transfer areas 26. The load transfer areas 26 may include hub load transfer areas and blade load transfer areas (both not shown in FIG. 1 ). Loads conducted to the rotor blades 22 are transferred to the hub 20 via the load transfer areas 26.

[0026] In examples, rotor blades 22 may have lengths ranging from about 15 meters (m) to about 90 m 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 lengths of 20 m or less, or lengths of 37 m, 48.7 m, 50.2 m, 52.2 m, or greater than 91 m. When wind strikes rotor blades 22 from wind direction 28, rotor 18 rotates about rotor axis 30. As rotor blades 22 rotate and experience centrifugal forces, rotor blades 22 also experience various forces and moments. Thus, rotor blades 22 may deflect and / or rotate from a neutral or unbiased position to a biased position.

[0027] Furthermore, 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, may be varied by the pitch system 32 to adjust the angular position of at least one rotor blade 22 relative to the wind vector, thereby controlling the load and the power generated by the wind turbine 10. A pitch axis 34 of the rotor blade 22 is also shown. During operation of the wind turbine 10, the pitch system 32 may particularly vary the pitch angle of the rotor blades 22 such that the angle of attack of (some of) the rotor blades is reduced, thereby facilitating a reduction in rotational speed and / or facilitating a stall of the rotor 18.

[0028] In this example, the blade pitch of each rotor blade 22 is individually controlled by wind turbine controls 36 or by pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0029] Further, in this example, as wind direction 28 changes, the yaw direction of nacelle 16 may be rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0030] In this example, wind turbine controls 36 are shown as being centralized within nacelle 16, but wind turbine controls 36 may be distributed throughout wind turbine 10, on support system 14, within a wind farm, and / or at a remote control center. Wind turbine controls 36 include a processor 40 configured to perform the methods and / or steps described herein. Additionally, many of the other components described herein include a processor.

[0031] As used herein, the term "processor" is not limited to integrated circuits referred to 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 further include memory, input channels, and / or output channels.

[0032] 2 is an enlarged cross-sectional view of a portion of wind turbine 10. In this example, wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to nacelle 16. More specifically, a hub 20 of rotor 18 is rotatably coupled to a generator 42 disposed within nacelle 16 by a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In this example, main shaft 44 is disposed at least partially coaxially with a longitudinal axis (not shown) of nacelle 16. Rotation of main shaft 44 drives gearbox 46, which then drives high-speed shaft 48 by converting the relatively slow rotational motion of rotor 18 and main shaft 44 into relatively fast rotational motion of high-speed shaft 48. The latter is connected to generator 42 for generating electrical energy with the aid of coupling 50. Additionally, a transformer 90 and / or appropriate electronics, switches, and / or inverters may be disposed in the nacelle 16 to convert the electrical energy generated by the generator 42 having a voltage of 400V to 1000V into electrical energy having a medium voltage (10 to 35 kV). The electrical energy is conducted from the nacelle 16 to the tower 15 via a power cable.

[0033] The gearbox 46, generator 42, and transformer 90 may be supported by a main support structure frame of the nacelle 16, which may optionally be embodied as a main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 by one or more torque arms 103. In this example, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Furthermore, the generator 42 may be attached to the main frame 52 by an isolation support means 54, particularly to prevent vibrations of the generator 42 from being transmitted to the main frame 52 and thereby becoming a source of noise emissions.

[0034] Optionally, main frame 52 is configured to carry the entire loads caused by the weight of rotor 18 and nacelle 16 components, as well as wind and rotational loads, and to transmit these loads to 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 securing devices, including, but not limited to, supports 52, forward support bearing 60, and aft support bearing 62, may be referred to as drive train 64.

[0035] In some examples, the wind turbine may be a direct drive wind turbine without a gearbox 46. The generators 42 operate at the same rotational speed as the rotor 18 in direct drive wind turbines. Therefore, they generally have a much larger diameter than the generators used in wind turbines with gearboxes 46 to provide a similar amount of power as wind turbines with gearboxes.

[0036] Nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate nacelle 16 , and thus rotor 18 , about yaw axis 38 to control the orientation of rotor blades 22 relative to wind direction 28 .

[0037] To properly position the nacelle 16 relative to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system 58, which may include a wind vane and an anemometer. The meteorological measurement system 58 may provide information, which may include the wind direction 28 and / or wind speed, to the wind turbine control 36. In this example, the pitch system 32 is at least partially disposed within the hub 20 as a pitch assembly 66. The 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 respective rotor blade 22 (shown in FIG. 1 ) to modulate the pitch angle of the rotor blade 22 along the pitch axis 34. Only one of the three pitch drive systems 68 is shown in FIG. 2 .

[0038] In this example, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and each rotor blade 22 (shown in FIG. 1 ) to rotate each rotor blade 22 about pitch axis 34. Pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. Pitch drive motor 74 is coupled to pitch drive gearbox 76 such that pitch drive motor 74 imparts mechanical force to pitch drive gearbox 76. Pitch drive gearbox 76 is coupled to pitch drive pinion 78 such that pitch drive pinion 78 is rotated by pitch drive gearbox 76. Pitch bearing 72 is coupled to pitch drive pinion 78 such that rotation of pitch drive pinion 78 causes rotation of pitch bearing 72.

[0039] Pitch drive system 68 is coupled to wind turbine control 36 to adjust the pitch angle of rotor blades 22 upon receiving one or more signals from wind turbine control 36. In this example, pitch drive motor 74 is any suitable motor driven by an electrical and / or hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components, such as, but not limited to, hydraulic cylinders, springs, and / or servo mechanisms. In certain embodiments, pitch drive motor 74 is driven by energy extracted from the rotational inertia of hub 20 and / or from a stored energy source (not shown) that provides energy to components of wind turbine 10.

[0040] Pitch assembly 66 may also include one or more pitch control systems 80 for controlling pitch drive systems 68 according to control signals from wind turbine controls 36 for certain priority situations and / or during overspeed of rotor 18. In this example, pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to each pitch drive system 68 for controlling pitch drive systems 68 independently from wind turbine controls 36. In this example, pitch control system 80 is coupled to pitch drive systems 68 and sensors 70. During normal operation of wind turbine 10, wind turbine controls 36 may control pitch drive systems 68 to adjust the pitch angle of rotor blades 22.

[0041] According to one embodiment, power generator 84, comprising, for example, a battery and an electrical capacitor, is disposed at or within hub 20 and is coupled to sensors 70, pitch control system 80, and pitch drive system 68 to provide a source of electrical power to these components. In this example, power generator 84 provides a continuous source of electrical power to pitch assembly 66 during operation of wind turbine 10. In an alternative embodiment, power generator 84 provides power to pitch assembly 66 only during a power loss event of wind turbine 10. A power loss event may include a loss or degradation of the electrical grid, a malfunction of the electrical system of wind turbine 10, and / or a failure of wind turbine control 36. During a power loss event, power generator 84 operates to provide electrical power to pitch assembly 66 so that pitch assembly 66 can operate during the power loss event.

[0042] In this example, pitch drive system 68, sensor 70, pitch control system 80, cables, and power generator 84 are each disposed within a cavity 86 defined by an interior surface 88 of hub 20. In alternative embodiments, the components may be disposed relative to and directly or indirectly coupled to an outer roof surface of hub 20.

[0043] 3 illustrates a flowchart of an example method 200 for determining a thrust threshold for a wind turbine. The method includes determining an operational state of a blade load monitoring system for the wind turbine, at block 210. The method further includes determining a thrust threshold for the wind turbine, at block 220, based at least in part on the operational state of the blade monitoring system and on wind turbulence.

[0044] The operational state of a blade load monitoring system may be either "normal" or "operational," or it may be "abnormal" or "inoperable." The state "normal" may refer to a state in which the sensor has been calibrated, commissioned, and is considered to be operating correctly. If the sensor has not yet been calibrated (i.e., before commissioning), or if deviations from normal function are observed during operation, the state may change to "abnormal" or "inoperable," meaning that even if measurements are obtained, they are unreliable and monitoring of critical loads cannot be relied upon such sensors when they are not sufficiently reliable.

[0045] In some examples, the method 200 for determining a thrust threshold may include determining a turbulence intensity at or near the wind turbine and determining a thrust threshold based at least in part on the determined turbulence intensity.

[0046] In some examples, the method may further include determining a wind speed at or near the wind turbine and determining a thrust threshold based at least in part on the determined wind speed. For example, known wind speed measurement systems, including an anemometer, a hot wire anemometer, a pitot tube, a mechanical anemometer, a SODAR, a LIDAR, or other suitable systems, may be used to determine wind speed fluctuations over a specific interval. Furthermore, the average wind speed and wind speed fluctuations may be estimated based on signals of any suitable sample length, e.g., 2 minutes, 5 minutes, 10 minutes, or any other long or short time period. Furthermore, the signal acquisition rate may be adapted to wind characteristics, e.g., average wind speed values. The acquisition rate may vary, for example, from 10 Hz to 10 KHz, depending on the measurement technology used and the computing power of the system responsible for calculating the wind parameters. The average wind speed, as well as the standard deviation of the wind speed relative to the average, may be determined, which is an indicator of the intensity of turbulence. In an example, the adjusted thrust threshold may be based in part on wind turbulence. For example, the adjusted thrust threshold may be based at least in part on the turbulence intensity of the wind.

[0047] In normal operation of a wind turbine, thrust loads can be particularly high near the wind turbine's nominal wind speed. However, high turbulence results in high thrust loads. A combination of both wind speed and turbulence intensity may be considered to determine the thrust threshold.

[0048] In some examples, the method may include determining a plurality of first thrust thresholds for the operational blade load monitoring system and a plurality of second thrust thresholds for the inoperative blade load monitoring system. The method may then include selecting a thrust threshold from the plurality of first and second thrust thresholds.

[0049] There may be multiple predetermined thrust thresholds for combinations of ranges or "bins" of wind speeds and ranges or "bins" of turbulence intensity. Determining the appropriate thrust threshold may then include selecting one of the predetermined thresholds.

[0050] Purely by way of example, for a wind speed range of 10-12 m / s and a turbulence intensity of 20-22%, a thrust threshold level of X may be defined for a wind turbine with an operational and well-functioning blade load monitoring system. For the same wind speed range and turbulence intensity, a thrust threshold of X-3% may be defined.

[0051] Similarly, for example, for a wind speed range of 16-18 m / s and a turbulence intensity of 18-20%, a thrust threshold of Y may be defined for a wind turbine with an operational and well-functioning blade load monitoring system. For the same wind speed and turbulence intensity combination with a malfunctioning blade load monitoring system, a thrust threshold of Y-5% may be defined. For the same wind speed but a turbulence intensity of 24-28%, a thrust threshold of Y-10% may be defined, in one example.

[0052] Figure 4 schematically illustrates a method 300 for operating a wind turbine 10 according to an example of the present disclosure. The method 300 of Figure 4 includes, at block 310, determining an operational state of a blade load monitoring system of the wind turbine 10. The method 300 also includes, at block 320, determining a thrust threshold for the wind turbine 10 based at least in part on the operational state of the blade monitoring system. Further, the method 300 includes, at block 330, operating the wind turbine 10 such that a thrust load on the rotor 18 of the wind turbine 10 is maintained at or below the adjusted thrust threshold.

[0053] As previously described, method 300 can determine the operational status of the blade load monitoring system, for example, the blade load monitoring system may determine that communication with the wind turbine control system is insufficient, or that a sensor of the blade load monitoring system is not calibrated, is not operational, or may provide sensor fault detection, among other things. Thus, method 300 can adjust the thrust threshold of wind turbine 10 accordingly to provide structural protection to wind turbine components. Furthermore, method 300 allows the wind turbine to operate even before the blade monitoring system has been commissioned, for example, due to inaccessibility due to severe weather conditions. This can significantly increase the annual energy production of the wind turbine without compromising the safe operation of the wind turbine.

[0054] In an example, the method may include establishing a lower thrust threshold when the blade monitoring system is inactive or unreliable.

[0055] In an example, operating the wind turbine such that the thrust load on the wind turbine rotor is less than or equal to the determined thrust threshold in block 330 includes modifying the pitch angle of the wind turbine blades. In a further example, a generator torque or other actuator may be used, for example, to reduce the speed of rotation of the wind turbine and / or reduce the aerodynamic torque of the wind turbine rotor.

[0056] Figure 5 illustrates another example of a method of operating a wind turbine according to an example of the present disclosure. The method of operating a wind turbine 300 may include the same steps as those illustrated in Figure 4, namely, determining an operating state of a blade load monitoring system at block 310 and determining a thrust threshold at block 320 based at least in part on the operating state.

[0057] The method 300 may further include, at block 340, determining a turbulence intensity at or near the wind turbine and determining a thrust threshold based at least in part on the determined turbulence intensity.

[0058] The method 300 may further include, at block 350, determining a wind speed at or near the wind turbine and determining a thrust threshold based at least in part on the determined wind speed.

[0059] Although steps 340, 350, and 320 are shown in a particular order, it will be apparent that this order may be changed, and the method shown in Figure 4 (and the methods shown in other figures) may be performed continuously and / or repeated at predetermined intervals.

[0060] 6 illustrates yet another example of a method for operating a wind turbine. In yet another example, a method 300 for operating a wind turbine may include, at block 360, determining a changed operating state of a blade load monitoring system of the wind turbine and determining an adjusted thrust threshold for the wind turbine based at least in part on the changed operating state of the blade monitoring system. The method may then further include, at block 380, operating the wind turbine such that a thrust load on a rotor of the wind turbine is less than or equal to the adjusted thrust threshold.

[0061] In an example, adjusting the thrust threshold of a wind turbine includes reducing the thrust threshold when the blade monitoring system is inactive or unreliable. As previously mentioned, this may be due to, for example, a faulty sensor or blade monitoring system. The thrust threshold may also be reduced for any other technical reason related to the blade monitoring system.

[0062] FIG. 7 shows a schematic diagram of a wind turbine 10 comprising a rotor 18 including one or more blades 20, a blade load monitoring system 150, and a control system 400.

[0063] The control system 400 is configured to determine an operating state of the blade load monitoring system 150, determine a thrust threshold for the wind turbine 10 based at least in part on the operating state of the blade monitoring system 150, and operate the wind turbine 10 such that the thrust load on the wind turbine rotor is at or below the determined thrust threshold.

[0064] In an example, wind turbine 10 may include one or more pitch systems for rotating the blades along their longitudinal axes, and the control system is configured to control the pitch systems to maintain a thrust load below a determined thrust threshold.

[0065] Additionally, the thrust threshold adjusted by the control system 400 may be based in part on wind turbulence, and more specifically, wind turbulence intensity. In an example, the wind turbine may include one or more systems for measuring wind speed, and the control system may be further configured to determine turbulence intensity based on the measured wind speed.

[0066] In some examples, wind parameters such as wind turbulence intensity may be estimated by a wind module 140 located on the wind turbine 10, which may be in data communication with the control system 400. The data may be communicated by cable or wirelessly.

[0067] In other examples, the wind module 140 may be located at a location remote from the wind turbine 10, for example, the wind module 140 may provide wind parameters to multiple control systems 400 of each wind turbine 10.

[0068] In an example, control system 400 may be further configured to reduce the thrust threshold when one or more blade load monitoring systems 150 are inoperative. For example, control system 400 may reduce the thrust threshold of wind turbine 10 when a single blade load monitoring system 150 has not been calibrated or when one or more blade load monitoring systems 150 have not yet been commissioned. Other technical reasons that cause a blade load monitoring system 150 to be inoperative or to fail may also cause control system 400 to reduce the thrust threshold of wind turbine 10.

[0069] Figure 8 shows an example of a power curve for a wind turbine operating at the original thrust threshold and the adapted threshold. The power curve for a wind turbine represents the output power of the wind turbine as a function of hub height wind speed.

[0070] 8 shows three power curves. Power curve 250 may correspond to normal operation, i.e., the power curve of a normally functioning blade load monitoring system. Two further power curves 260, 270 are shown for operation of a wind turbine with a non-functional blade load monitoring system for different turbulence levels: power curve 260 for a first turbulence intensity level and power curve 270 for a high turbulence intensity.

[0071] The aerodynamic thrust of a wind turbine rotor is known to be high in a range of wind speeds near the power knee (a range of wind speeds near the nominal wind speed where the rotor rotational speed may be at or near nominal).

[0072] A method of operating a wind turbine may include determining a plurality of first thrust thresholds for an operable blade load monitoring system and for a predetermined combination of wind speed ranges and turbulence intensity ranges, and a plurality of second thrust thresholds for an inoperable blade load monitoring system and for a predetermined combination of wind speed ranges and turbulence intensity ranges.

[0073] Such a method may further include determining a turbulence intensity at or near the wind turbine, determining a wind speed at or near the wind turbine, and selecting a thrust threshold from first and second thrust thresholds based on the determined turbulence intensity, the determined wind speed, and an operating condition of the blade load monitoring system.

[0074] That is, several thrust thresholds may be predefined, and an appropriate thrust threshold may be selected from the plurality of predefined thresholds depending on wind conditions and the operating state of the blade load monitoring system.

[0075] In some examples, the first and second thrust thresholds may be the same for a range of wind speeds from the cut-in wind speed to the first wind speed. CUT-IN is the wind speed at which the wind turbine can generate electricity. As can be seen in the example of Figure 8, up to a first wind speed V1, the risk of high blade load is relatively low, so that no specific countermeasures are required even if the blade load monitoring system malfunctions.

[0076] In an example, the second thrust threshold may be 3-12% lower for each wind turbine intensity range for a wind speed range from the first wind speed V1 to the second wind speed V2.

[0077] The first wind speed V1 may be below the nominal wind speed of the wind turbine, for example, about 10 m / s, and the second wind speed V2 may be above the nominal wind speed of the wind turbine, for example, about 15 m / s. At high wind speeds, the wind turbine blades may be pitched to maintain a constant rotational speed and a constant (nominal) power output, and thrust may be reduced to a level where normal operation may be possible even with a malfunctioning blade load monitoring system.

[0078] This specification uses examples to disclose the present teachings, including preferred embodiments, and also enables one of ordinary skill in the art to practice the teachings, including making and using any device or system and performing any incorporated methods. The patentable scope is defined by the claims and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have 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. Those skilled in the art will be able to mix and match aspects from the various embodiments described above, as well as other known equivalents for each such aspect, to construct further embodiments and techniques consistent with the principles of the present application. Where reference signs relating to the drawings are placed within parentheses in the claims, these reference signs are merely to enhance the clarity of the claims and should not be construed as limiting the scope of the claims. [Explanation of symbols]

[0079] 10. Wind Turbines 12 Ground 14 Support System 15 Tower 16 Nacelle 18 rotors 20 Hub 22 rotor blades 24 Blade base 26 Load Transfer Area 28 Wind direction 30 rotor shaft 32 Pitch System 34 Pitch axis 36 Wind turbine control unit 38 Yaw axis 40 processors 42 Generator 44 Main shaft 46 Gearbox 48 High Speed ​​Shaft 50 Coupling 52 Mainframe 54 Separation support means 56 Yaw drive mechanism 58 Weather Measurement System 60 Main front support bearing 62 Main rear support bearing 64 Drivetrain 66 Pitch Assembly 68 Pitch Drive System 70 sensors 72 Pitch bearing 74 Pitch drive motor 76 Pitch drive gearbox 78 Pitch drive pinion 80 Pitch Control System 84 Electric Power Generator 86 Cavity 88 Inner 90 Transformer 103 Torque arm 140 Wind Module 150 Blade Load Monitoring System 200 ways 250 power curve 260 Power Curve 270 Power Curve 300 ways 400 Control System

Claims

1. 1. A method (200) for determining a thrust threshold of a wind turbine (10), said method (200) comprising: determining (210) the operational status of a blade load monitoring system (150) of the wind turbine (10); determining (220) a thrust threshold for the wind turbine (10) based at least in part on the operating conditions of the blade monitoring system (150) and wind turbulence; A method (200) comprising:

2. 10. The method of claim 1, further comprising determining a level of turbulence at or near the wind turbine and determining the thrust threshold based at least in part on the determined level of turbulence.

3. The method (200) of claim 2, wherein the level of turbulence is turbulence intensity.

4. 4. The method (200) of any one of claims 1 to 3, further comprising determining (350) a wind speed at or near the wind turbine (10) and determining (320) the thrust threshold based at least in part on the determined wind speed.

5. determining a plurality of first thrust thresholds for an operable blade load monitoring system; determining a plurality of second thrust thresholds for an inoperative blade load monitoring system; selecting a thrust threshold from the plurality of first and second thrust thresholds; The method (200) of any one of claims 1 to 4, comprising:

6. The plurality of first thresholds are provided for predetermined combinations of wind speed ranges and turbulence intensity ranges, and the plurality of second thresholds are provided for the same predetermined combinations of wind speed ranges and turbulence intensity ranges, and the method (200) comprises: determining (340) turbulence intensity at or near the wind turbine (10); determining (350) wind speed at or near the wind turbine (10); selecting a thrust threshold from the first and second thrust thresholds based on the determined turbulence intensity, the determined wind speed, and the operating state of the blade load monitoring system (150); The method (200) of claim 5, further comprising:

7. The first and second thrust thresholds are set to a value ranging from a cut-in wind speed to a first wind speed (V １ 7. The method (200) of claim 6, wherein the wind speed is the same for a range of wind speeds up to .

8. The second thrust threshold is １ ) to the second wind speed (V ２ 8. The method (200) of claim 7, wherein the wind turbine intensity range is 3-12% lower for a wind speed range up to 100 kW.

9. The first wind speed (V １ ) is below the nominal wind speed of the wind turbine (10), and the second wind speed (V ２ 9. The method (200) of claim 8, wherein the wind speed is greater than the nominal wind speed of the wind turbine (10).

10. 10. A method (300) for operating a wind turbine (10), the method (300) comprising determining a thrust threshold for the wind turbine (10) according to any one of claims 1 to 9, and further comprising operating the wind turbine (10) such that a thrust load on a rotor (18) of the wind turbine (10) is less than or equal to the determined thrust threshold.

11. 11. The method (300) of claim 10, wherein operating (330) the wind turbine (10) such that the thrust load on the rotor (18) of the wind turbine (10) is less than or equal to the determined thrust threshold comprises modifying a pitch angle of one or more wind turbine blades.

12. The method (300) of claim 10 or 11, wherein the wind turbine (10) is operated before calibrating the blade load monitoring system (150).

13. determining (360) a changed operating state of a blade load monitoring system (150) of the wind turbine (10); determining (370) an adjusted thrust threshold for the wind turbine (10) based at least in part on the changed operating state of the blade monitoring system (150); and operating (380) the wind turbine (10) such that a thrust load on the rotor (18) of the wind turbine (10) is equal to or less than the adjusted thrust threshold; The method (300) of any one of claims 10 to 12, further comprising:

14. A wind turbine (10), comprising: a wind turbine tower (15); a rotor (18) including one or more blades (20) attached to the top of the tower (15); a blade load monitoring system (150) for determining the load on said blade (20); A control system (400) configured to carry out the method (200, 300) of any one of claims 1 to 13; A wind turbine (10) comprising:

15. The wind turbine (10) of claim 14, wherein the wind turbine (10) is an offshore wind turbine.

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