Operation of wind turbine

Abstract

The invention relates to a method for determining a thrust limit for a wind turbine and a method for operating a wind turbine. A method includes determining an operating state of a blade load monitoring system of a wind turbine. In addition, the method includes adjusting a thrust threshold of the wind turbine based at least in part on the operating condition of the blade monitoring system. Further, the method 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 adapted to maintain a thrust load at or below a thrust threshold and a wind turbine comprising 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 an operational state of a blade load measurement system and adjusting the operation of the wind turbine based on the operational state of the blades. The present disclosure also relates to methods for determining an adjusted thrust threshold for use in operating a wind turbine. Background Art

[0002] Modern wind turbines are commonly used to supply electricity to the power grid. This type of wind turbine generally consists of a tower and a rotor mounted on the tower. The rotor, typically consisting of a hub and a plurality of blades, is set to rotate under the influence of the wind. This rotation generates torque, which is typically transmitted to a generator via the rotor shaft, 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 significant popularity in recent years due to a combination of factors. Offshore environments offer consistent and strong wind resources, which are beneficial for generating electricity from wind power. Wind speeds are generally higher and more sustained offshore compared to onshore winds, resulting in higher energy output. Furthermore, offshore environments allow for the construction of larger turbines, as the lack of land-based constraints allows turbines to be located farther apart, taller, and have longer blades. This results in higher energy output per turbine and, therefore, more efficient use of wind resources.

[0004] However, due to the harsh and remote nature of the offshore environment, offshore wind turbine sites are also associated with several challenges and issues. In some cases, accessing the turbines can be difficult and time-consuming, as maintenance personnel must be transported to the turbines by boat or helicopter. This can be further complicated by weather conditions, making it impossible to safely access the turbines for extended periods of time.

[0005] In addition, the components and systems of the turbine may be exposed to extreme weather conditions, which may cause accelerated wear and tear and may increase the likelihood of component failure. This may result in increased downtime for the turbine and reduced energy output.

[0006] Furthermore, the installation and commissioning of offshore wind turbines can be more time-consuming than for onshore wind turbines. Lifting the nacelle, rotor, and rotor blades requires specialized vessels and may not be possible under all wind conditions. Consequently, the installation of a wind farm can take a long time. Commissioning a wind turbine can also take more time than for onshore wind turbines because personnel may be required to visit the wind farm to perform tests and inspections. Commissioning can include testing the wind turbine's power generation, verifying protection systems, testing power measurements, and numerous mechanical tests. Some of these tests may only be performed under specific wind conditions, which can delay the commissioning process.

[0007] A wind turbine may have a number of sensor systems that contribute to, or are critical 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, for example, abnormal or dangerous conditions.

[0008] For example, load sensors may be arranged on or in conjunction with the blades to measure the loads on the blades. The input from such load sensors can be used directly as input into the operation of the wind turbine. For example, blade load measurements can be used to keep operational loads under control, particularly to account for the accumulation of fatigue loads and also to account for maximum permissible loads. It is known to modify the operational thrust limit of a wind turbine in situations such as high turbulence. In practice, operating parameters of the wind turbine can be altered, for example, blade pitch can be adjusted, rotor speed and output power can be reduced, in order to maintain the thrust of the wind turbine at the operational thrust limit.

[0009] As mentioned, load sensors can be arranged with the blades, in particular near the root of the blades. The sensors can be arranged to measure both the flapwise and the swaywise loads. Sensors for determining the loads on the blades can also be arranged elsewhere, for example in the hub or main rotor shaft, or with the pitch bearing or main bearing.

[0010] In some cases, commissioning and calibrating blade load monitoring systems for offshore wind turbines can be a complex process due to the challenging conditions of the offshore environment, such as high winds and waves that can complicate access. Additionally, proper calibration of blade load monitoring systems can require specific wind conditions, such as relatively low wind speeds.

[0011] Delays in calibrating blade monitoring systems can result in annual energy losses for a wind turbine. Because the system is used not only to optimize turbine performance but also to protect against critical loads, wind turbines with inoperative blade monitoring systems are not permitted to operate. Similarly, blade monitoring systems can become less reliable after a certain period of operation due to wear and tear. When this condition is detected, operation of the wind turbine can be halted.

[0012] The present disclosure provides methods and systems that at least partially overcome some of the aforementioned shortcomings associated with blade load monitoring systems. Summary of the Invention

[0013] In one aspect of the present disclosure, a method for determining a thrust threshold for a wind turbine is provided. The method includes 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 load monitoring system and on wind turbulence.

[0014] According to this aspect, even if the blade load monitoring system is not operating, has not been calibrated, or is not operating properly, appropriate operating parameters for safe and efficient operation of the wind turbine can be provided. Rather than not operating the wind turbine at all, an appropriate thrust threshold is provided based on whether the blade load monitoring system is operating.

[0015] In another aspect of the present disclosure, a method for operating a wind turbine is provided. The method includes 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 load monitoring system. The method then further includes operating the wind turbine such that a thrust load on a rotor of the wind turbine is at or below the determined thrust threshold.

[0016] According to this aspect, a wind turbine can be operated in scenarios where a blade load monitoring system may be unavailable. This may be particularly relevant for offshore wind turbines, where long delays in commissioning blade monitoring systems due to severe weather conditions can often occur. Thus, the method allows the wind turbine to be operated with an increased annual energy production output compared to other prior art methods. Furthermore, it has been found that operation according to a maximum thrust level is more efficient and can increase annual energy production, as compared to operation with a reduced setpoint ("derating" of the wind turbine).

[0017] In yet another aspect of the present disclosure, a wind turbine is provided that includes a wind turbine tower, a rotor including one or more blades mounted on top of the tower, a blade load monitoring system for determining loads on the blades, and a control system. The control system is 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 load monitoring system; and operate the wind turbine so that the thrust load on the rotor of the wind turbine is at or below the determined thrust threshold.

[0018] Throughout this disclosure, the term "turbulence intensity" may be understood as the standard deviation of wind speed from the mean value of wind speed. Turbulence intensity may be quoted as a percentage or as a decimal less than 1. The standard deviation of wind speed and the mean value of wind speed may be determined over a fixed time interval. Such a time interval may be, for example, 10 minutes.

[0019] Throughout this disclosure, the thrust load on a wind turbine may be considered to be the axial force exerted by the wind on the rotor of the wind turbine.The thrust threshold may be considered to be the maximum thrust level allowed in operation.

[0020] Additional objects, advantages, and features of the embodiments of the present disclosure will become apparent to those skilled in the art upon reviewing the description, or may be learned through practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 a perspective view schematically illustrating one example of a wind turbine; Figure 2 illustrates an example of a hub and nacelle of a wind turbine; Figure 3 A flow chart illustrating an example of a method for determining a thrust threshold; Figure 4 A flow chart illustrating an example of a method for operating a wind turbine; Figure 5 a flow chart illustrating a further example of a method for operating a wind turbine; Figure 6 a flow chart illustrating yet another example of a method for operating a wind turbine; Figure 7 a schematic diagram showing a control system for controlling the operation of a wind turbine; and Figure 8 Examples of power output curves for a wind turbine operating at an original thrust threshold and an adapted threshold are shown. DETAILED DESCRIPTION

[0022] 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 by way of illustration and not by way of limitation. Indeed, it will be apparent to those skilled in the art that various modifications and variations may be made in the present disclosure without departing from the scope or spirit of the teachings. For example, features illustrated or described as part of one embodiment may be used in conjunction with another embodiment to produce yet another embodiment. Therefore, it is intended that the present disclosure encompass such modifications and variations as come within the scope of the appended claims and their equivalents.

[0023] Figure 1is a perspective view of an example of a wind turbine 10. In the example, wind turbine 10 is a horizontal axis wind turbine. Alternatively, wind turbine 10 may be a vertical axis wind turbine. In the 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 and extending outward from hub 20. In the example, rotor 18 has three rotor blades 22. In alternative embodiments, rotor 18 includes more or less than three rotor blades 22. Tower 15 may be made of tubular steel to define a cavity (not shown) between support system 14 and nacelle 16. Figure 1 ). In alternative embodiments, tower 15 is any suitable type of tower having any suitable height. Alternatively, the tower may be a hybrid tower comprising a portion made of concrete and a portion made of tubular steel. Furthermore, the tower may be a partial lattice or full lattice tower.

[0024] Rotor blades 22 are spaced about hub 20 to facilitate rotating rotor 18, thereby enabling kinetic energy from the wind to be converted into usable mechanical energy and subsequently into electrical energy. Rotor blades 22 are mated to hub 20 by coupling blade root portions 24 to hub 20 at a plurality of load transfer regions 26. Load transfer regions 26 may include hub load transfer regions and blade load transfer regions (neither of which is present in the hub). Figure 1 ). Loads directed to rotor blades 22 are transferred to hub 20 via load transfer regions 26 .

[0025] In an example, rotor blades 22 may have a length 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 operate as described herein. For example, non-limiting examples of blade lengths include 20 m or less, 37 m, 48.7 m, 50.2 m, 52.2 m, or a length greater than 91 m. As wind strikes rotor blades 22 from a wind direction 28, rotor 18 rotates about rotor axis 30. As rotor blades 22 rotate and are subjected to centrifugal forces, rotor blades 22 are also subjected to various forces and moments. As such, rotor blades 22 may deflect and / or rotate from a neutral or non-deflected position to a deflected position.

[0026] Furthermore, the pitch angle of rotor blades 22 (i.e., the angle that determines the orientation of rotor blades 22 with respect to the wind direction) can 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 can, in particular, vary the pitch angle of rotor blades 22 such that the angle of attack of (portions of) the rotor blades is reduced, which facilitates reducing the rotational speed of rotor 18 and / or facilitating stalling of rotor 18.

[0027] In an example, the blade pitch of each rotor blade 22 is individually controlled by wind turbine controller 36 or by pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0028] Furthermore, in an example, as wind direction 28 changes, the yaw orientation of nacelle 16 may be rotated about yaw axis 38 to position rotor blades 22 with respect to wind direction 28 .

[0029] In the example, the wind turbine controller 36 is shown as being centralized within the nacelle 16; however, the wind turbine controller 36 may be a distributed system located throughout the wind turbine 10, on the support system 14, within the wind farm, and / or at a remote control center. The wind turbine controller 36 includes a processor 40 configured to execute the methods and / or steps described herein. In addition, many of the other components described herein include a processor.

[0030] As used herein, the term "processor" is not limited to integrated circuits, which are known in the art as computers, but broadly refers to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application-specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and / or control system may also include memory, input channels, and / or output channels.

[0031] Figure 21 is an enlarged cross-sectional view of a portion of wind turbine 10. In the example, wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to nacelle 16. More specifically, hub 20 of rotor 18 is rotatably coupled to an electrical generator 42 positioned within nacelle 16 via a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In the 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 in turn drives high-speed shaft 48 by converting the relatively slow rotational motion of rotor 18 and main shaft 44 into a relatively fast rotational motion of high-speed shaft 48. High-speed shaft 48 is connected to generator 42 for generating electrical energy with the aid of coupling 50. Furthermore, a transformer 90 and / or suitable electronic components, switches, and / or inverters may be arranged in the nacelle 16 to transform the electrical energy generated by the generator 42, which has a voltage between 400 V and 1000 V, into electrical energy having a medium voltage (10 KV to 35 KV). The electrical energy is conducted from the nacelle 16 to the tower 15 via power cables.

[0032] The gearbox 46, generator 42, and transformer 90 may be supported by the main support structural 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 via one or more torque arms 103. In the example, the nacelle 16 also includes a main front support bearing 60 and a main rear support bearing 62. In addition, the generator 42 may be mounted to the main frame 52 via a separate support device 54, particularly to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thereby causing a source of noise emission.

[0033] Optionally, main frame 52 is configured to carry all loads caused by the weight of the components of rotor 18 and nacelle 16, as well as wind and rotational loads, and, in addition, 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, support, and / or fixing equipment (including, but not limited to, supports 52 and front and rear support bearings 60, 62) are sometimes referred to as drive train 64.

[0034] 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, these generators generally have a much larger diameter than generators used in wind turbines with a gearbox 46 in order to provide a similar amount of power as compared to wind turbines with a gearbox.

[0035] Nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate nacelle 16 , and thereby rotor 18 , about yaw axis 38 to control the viewing angle of rotor blades 22 with respect to wind direction 28 .

[0036] To properly position the nacelle 16 with respect 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 anemometer. The meteorological measurement system 58 may provide information to the wind turbine controller 36, which may include wind direction 28 and / or wind speed. In an example, the pitch system 32 is at least partially arranged as a pitch assembly 66 in the hub 20. 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 corresponding rotor blade 22 (at Figure 1 ) for adjusting the pitch angle of rotor blades 22 along pitch axis 34. Only one of the three pitch drive systems 68 is in Figure 2 Shown in.

[0037] In the example, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and to a corresponding rotor blade 22 (at Figure 1 34 , for rotating the corresponding rotor blade 22 about the 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 applies a 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.

[0038] Pitch drive system 68 is coupled to wind turbine controller 36 for adjusting the pitch angle of rotor blades 22 upon receiving one or more signals from wind turbine controller 36. In an example, pitch drive motor 74 is any suitable motor driven by electrical power and / or a hydraulic system that enables pitch assembly 66 to operate as described herein. Alternatively, pitch assembly 66 may include any suitable structure, configuration, 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.

[0039] 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 a specific priority condition and / or during an overspeed of rotor 18. In an 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 an example, pitch control system 80 is coupled to pitch drive system 68 and to 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.

[0040] According to an embodiment, a power generator 84, for example, including a battery and a capacitor, is disposed at or within hub 20 and is coupled to sensor 70, pitch control system 80, and pitch drive system 68 to provide a power source to these components. In an example, power generator 84 provides a continuous power source 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 an electrical power loss event of wind turbine 10. An electrical power loss event may include a loss or drop in power grid power, a malfunction in the electrical system of wind turbine 10, and / or a failure of wind turbine controller 36. During an electrical power loss event, power generator 84 operates to provide electrical power to pitch assembly 66 so that pitch assembly 66 can operate during the electrical power loss event.

[0041] In the example, pitch drive system 68, sensor 70, pitch control system 80, cables, and power generator 84 are each positioned within a cavity 86 defined by an inner surface 88 of hub 20. In alternative embodiments, the components are positioned with respect to an outer top surface of hub 20 and may be coupled directly or indirectly thereto.

[0042] Figure 3 A flow chart illustrating an example of a method 200 for determining a thrust threshold for a wind turbine is shown. The method includes determining an operational state of a blade load monitoring system of the wind turbine at block 210. The method further includes determining a thrust threshold for the wind turbine based at least in part on the operational state of the blade load monitoring system and on wind turbulence at block 220.

[0043] The operational state of the blade load monitoring system may be "correct" or "operating," or "incorrect" or "not operating." The "correct" state may refer to a state in which the sensor has been calibrated and commissioned and is assumed to be operating correctly. If the sensor has not yet been calibrated (i.e., before commissioning), or if deviations from normal operation are noted during operation, the state may change to "incorrect" or "not operating": even if measurements are obtained, they are unreliable, and when such sensors are not sufficiently reliable, critical load monitoring cannot be relied upon.

[0044] In some examples, method 200 for determining a thrust threshold may include determining a turbulence intensity at or near a wind turbine and determining a thrust threshold based at least in part on the determined turbulence intensity.

[0045] 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. A known wind speed measurement system (e.g., anemometers, hot-wire anemometers, pitot tubes, mechanical anemometers, sodar, lidar, or other suitable systems) may be used to determine wind speed variations over a specific time interval. Furthermore, average wind speed and wind speed variations may be estimated based on signals of any suitable sample length (e.g., 2 minutes, 5 minutes, 10 minutes, or any other longer or shorter time length). Furthermore, the acquisition rate of the signal may also be adapted to the characteristics of the wind, such as the average wind speed. The acquisition rate may vary from 10 Hz to 10 kHz, depending on, for example, the measurement technology used and the computing power of the system responsible for calculating the wind parameters. An average wind speed and a standard deviation of the wind speed about the average may be determined. This is indicative 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 wind turbulence intensity.

[0046] In normal operation of a wind turbine, thrust loads may be particularly high near the rated wind speed of the wind turbine. However, higher turbulence will result in higher thrust loads. The thrust threshold may be determined taking into account a combination of wind speed and turbulence intensity.

[0047] In some examples, the method may include determining a plurality of first thrust thresholds for an operational blade load monitoring system and a plurality of second thrust thresholds for an inoperative blade load monitoring system. The method may then include selecting a thrust threshold from the plurality of first thrust thresholds and the plurality of second thrust thresholds.

[0048] A plurality of predefined thrust thresholds may be provided for combinations of ranges or “bins” of wind speeds and ranges or “bins” of turbulence intensities. Determining a suitable thrust threshold may then comprise selecting one of the predefined thresholds.

[0049] By way of example only, for a wind speed range of 10 m / s to 12 m / s and a turbulence intensity of 20% to 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.

[0050] Similarly, by way of example, for a wind speed range of 16 m / s to 18 m / s and a turbulence intensity of 18% to 20%, a thrust threshold of Y may be defined for a wind turbine with an operational and properly functioning blade load monitoring system. For the same combination of wind speed and turbulence intensity and a malfunctioning blade load monitoring system, a thrust threshold of Y−5% may be defined. Furthermore, in the example, for the same wind speed but a turbulence intensity of 24% to 28%, a thrust threshold of Y−10% may be defined.

[0051] Figure 4 A method 300 for operating a wind turbine 10 according to examples of the present disclosure is schematically illustrated. Figure 3 The method 300 in FIG. 1 includes determining an operational state of a blade load monitoring system of the wind turbine 10 at block 310. The method 300 also includes determining a thrust threshold value for the wind turbine 10 based at least in part on the operational state of the blade monitoring system at block 320. Furthermore, 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 an adjusted thrust threshold value.

[0052] As previously discussed, method 300 can determine the operational status of the blade load monitoring system. For example, the method can determine that the blade load monitoring system has poor communication with the wind turbine control system. The method can also determine that the blade load monitoring system's sensors are not calibrated or inoperable, or that the method can provide sensor failure detection, etc. Accordingly, method 300 can adjust the thrust thresholds of wind turbine 10 to provide structural protection to wind turbine components accordingly. Furthermore, method 300 allows the wind turbine to be operated even before the blade monitoring system has been commissioned (e.g., due to inaccessibility during severe weather conditions). This can result in a significant increase in the wind turbine's annual energy production without compromising the wind turbine's safe operation.

[0053] In an example, the method may include establishing a lower thrust threshold when the blade monitoring system is inactive or unreliable.

[0054] In an example, operating the wind turbine at block 330 such that the thrust load on the wind turbine's rotor is at or below the determined thrust threshold includes modifying the pitch angle of the wind turbine blades. In other examples, generator torque or other actuators may also be used, for example, to reduce the wind turbine's rotational speed and / or lower the aerodynamic torque on the wind turbine rotor.

[0055] Figure 5 Another example of a method of operating a wind turbine according to an example of the present disclosure is shown. The method 300 of operating a wind turbine may include: Figure 4 , namely, determining an operational state of the blade load monitoring system at block 310 and determining a thrust threshold based at least in part on the operational state at block 320 .

[0056] The method 300 may further include determining a turbulence intensity at or near the wind turbine at block 340 , and determining a thrust threshold based at least in part on the determined turbulence intensity.

[0057] The method 300 may further include determining a wind speed at or near the wind turbine at block 350 , and determining a thrust threshold based at least in part on the determined wind speed.

[0058] Although steps 340, 350, 320 have been indicated in a specific order, it should be clear that this order can be changed. Figure 4 The method illustrated in FIG. 1 (and the methods illustrated in other figures) may be performed continuously and / or may be repeated at a predetermined frequency.

[0059] Figure 6 Still another example of a method for operating a wind turbine is shown. In yet other examples, the method 300 for operating a wind turbine may include determining a changed operational state of a blade load monitoring system of the wind turbine at block 360, and determining an adjusted thrust threshold for the wind turbine based at least in part on the changed operational state of the blade monitoring system at block 370. The method may then further include operating the wind turbine at block 380 such that the thrust load on the rotor of the wind turbine is at or below the adjusted thrust threshold.

[0060] In one example, adjusting the thrust threshold of a wind turbine includes reducing the thrust threshold when the blade monitoring system is inactive or has become unreliable. As previously discussed, this may be due to, for example, a malfunctioning sensor or blade monitoring system. The thrust threshold may also be reduced for any other technical reason associated with the blade monitoring system.

[0061] Figure 7A schematic diagram of a wind turbine 10 is shown, including a rotor 18 including one or more blades 20 , a blade load monitoring system 150 , and a control system 400 .

[0062] Control system 400 is configured to: determine an operational state of blade load monitoring system 150; determine a thrust threshold value for wind turbine 10 based at least in part on the operational state of blade monitoring system 150; and operate wind turbine 10 such that the thrust load on the rotor of the wind turbine is at or below the determined thrust threshold value.

[0063] In an example, wind turbine 10 may include one or more pitch systems for rotating blades along their longitudinal axes, and the control system is configured to control the pitch systems to maintain thrust loads at or below a determined thrust threshold.

[0064] Furthermore, the thrust threshold adjusted by the control system 400 may be based in part on wind turbulence, and more specifically on wind turbulence intensity. In an example, the wind turbine may include one or more systems for measuring wind speed, and wherein the control system is further configured to determine turbulence intensity based on the measured wind speed.

[0065] In some examples, wind parameters such as wind turbulence intensity may be estimated by a wind module 140 located in wind turbine 10, and the wind module 140 may be in data communication with control system 400. The data may be communicated via cables or wirelessly.

[0066] In other examples, wind module 140 may be located at a location remote from wind turbine 10 , for example, where wind module 140 may provide wind parameters to a plurality of control systems 400 of corresponding wind turbines 10 .

[0067] In an example, the control system 400 may be further configured to reduce the thrust threshold when one or more blade load monitoring systems 150 are not operating. For example, when a single blade load monitoring system 150 is not calibrated, or when one or more blade load monitoring systems 150 have not yet been commissioned, the control system 400 may reduce the thrust threshold for the wind turbine 10. Other technical reasons causing the blade load monitoring system(s) 150 to be inoperative or malfunctioning may also cause the control system 400 to reduce the thrust threshold for the wind turbine 10.

[0068] Figure 8 An example of a power (output) curve of a wind turbine operating at an original thrust threshold and an adapted threshold is shown.The power curve of a wind turbine describes the output power of the wind turbine as a function of hub height wind speed.

[0069] Figure 8Three power curves are shown. Power curve 250 may correspond to a power curve for normal operation (i.e., a properly functioning blade load monitoring system). Two further power curves 260, 270 are shown for operation of a wind turbine with a non-operating blade load monitoring system for different turbulence levels, power curve 260 for a first turbulence intensity level and power curve 270 for a higher turbulence intensity.

[0070] It is known that the aerodynamic thrust on a wind turbine rotor is high in the wind speed range around the power break point (the wind speed range close to the rated wind speed at which the rotor rotational speed may be at or near rated).

[0071] A method of operating a wind turbine may include determining a plurality of first thrust thresholds for an operational blade load monitoring system and for predetermined combinations of wind speed ranges and turbulence intensity ranges, and a plurality of second thrust thresholds for predetermined combinations of wind speed ranges and turbulence intensity ranges for an inoperative blade load monitoring system.

[0072] Such a method may further include determining a turbulence intensity at or near the wind turbine and determining a wind speed at or near the wind turbine, and selecting a thrust threshold from a first thrust threshold and a second thrust threshold based on the determined turbulence intensity, the determined wind speed, and an operational state of the blade load monitoring system.

[0073] That is, a plurality of thrust thresholds may be predefined, and a suitable 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.

[0074] In some examples, for a wind speed range from the cut-in wind speed to the first wind speed, the first thrust threshold and the second thrust threshold may be the same. 切入 is the wind speed at which the wind turbine can generate power. Figure 8 As can be seen in the example of , up to a first wind speed V1 , the risk of high blade loads is relatively low, so that even in the event of a malfunction of the blade load monitoring system no specific measures are necessary.

[0075] In an example, for a range of wind speeds from a first wind speed V1 to a second wind speed V2 , the second thrust threshold may be between 3% and 12% lower for each range of wind turbine strengths.

[0076] The first wind speed V1 may be lower than the rated wind speed for the wind turbine, for example, about 10 m / s, and the second wind speed V2 may be higher than the rated wind speed for the wind turbine, for example, about 15 m / s. At higher wind speeds, the wind turbine blades may be pitched to maintain a constant rotational speed and a constant (rated) power output, so that the thrust is reduced to a level that normal operation may be possible even in the event of a malfunction of the blade load monitoring system.

[0077] This written description uses examples to disclose the teachings (including preferred embodiments) and also to enable anyone skilled in the art to practice the teachings (including making and using any device or system and performing any incorporated methods). The scope of patentability is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples have structural elements that are not different from the literal language of the claims, or if such other examples include equivalent structural elements that are not substantially different from the literal language of the claims, then such other examples are intended to be within the scope of the claims. Aspects from the various embodiments described and other known equivalents for each such aspect can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques according to the principles of this application. If reference numerals relating to the drawings are placed in parentheses in the claims, these reference numerals are merely intended to increase the understandability of the claim and should not be construed as limiting the scope of the claim.

Claims

1. A method (200) for determining a thrust threshold of a wind turbine, the method comprising: determining (210) an operational status of a blade load monitoring system of the wind turbine; as well as A thrust threshold for the wind turbine is determined (220) based at least in part on the operational state of the blade monitoring system and on wind turbulence.

2. The method of claim 1, further comprising determining (340) a turbulence level at or near the wind turbine and determining the thrust threshold based at least in part on the determined turbulence level.

3. The method according to claim 2, wherein: The turbulence level is the turbulence intensity.

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

5. The method according to any one of claims 1 to 4, comprising: determining a plurality of first thrust thresholds for an operational blade load monitoring system; determining a plurality of second thrust thresholds for an inoperative blade load monitoring system; as well as A thrust threshold is selected from the plurality of first thrust thresholds and the plurality of second thrust thresholds.

6. The method according to claim 5, wherein: The plurality of first threshold values ​​are provided for predetermined combinations of wind speed ranges and turbulence intensity ranges, and the plurality of second threshold values ​​are provided for the same predetermined combinations of wind speed ranges and turbulence intensity ranges, and the method further comprises: determining a turbulence intensity at or near the wind turbine; determining a wind speed at or near the wind turbine; and A thrust threshold is selected from the first thrust threshold and the second thrust threshold based on the determined turbulence intensity, the determined wind speed, and the operational state of the blade load monitoring system.

7. The method according to claim 6, wherein: For a wind speed range from a cut-in wind speed to a first wind speed (V1), the first thrust threshold and the second thrust threshold are the same.

8. The method according to claim 7, wherein: For a wind speed range from the first wind speed (V1) to a second wind speed (V2), the second thrust threshold is between 3% and 12% lower for each wind turbine strength range.

9. The method according to claim 8, wherein The first wind speed (V1) is lower than a rated wind speed for the wind turbine, and wherein the second wind speed (V2) is higher than the rated wind speed for the wind turbine.

10. A method (300) for operating a wind turbine, the method comprising determining (200) a thrust threshold value for the wind turbine according to any one of claims 1 to 9, and further comprising: The wind turbine is operated (330) such that a thrust load on a rotor of the wind turbine is at or below the determined thrust threshold.

11. The method according to claim 10, wherein: Operating the wind turbine so that the thrust load on the rotor of the wind turbine is at or below the determined thrust threshold includes modifying a pitch angle of one or more wind turbine blades.

12. The method according to claim 10 or 11, wherein: The wind turbine is operated prior to calibrating the blade load monitoring system.

13. The method according to any one of claims 10 to 12, further comprising: determining a changed operational state of a blade load monitoring system of the wind turbine, determining an adjusted thrust threshold for the wind turbine based at least in part on the changed operational state of the blade monitoring system; and operating the wind turbine so that a thrust load on the rotor of the wind turbine is at or below the adjusted thrust threshold.

14. A wind turbine (10), comprising: Wind turbine towers, a rotor comprising one or more blades (20), the rotor mounted on top of the tower; a blade load monitoring system (150) for determining the load on the blade; as well as A control system (400) configured to perform the method according to any one of claims 1-13.

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

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