System and method for mitigating damage to rotor blades of a wind turbine

Abstract

A method for mitigating damage to a rotor blade among a plurality of rotor blades of a wind turbine includes receiving a plurality of acceleration signals from the plurality of rotor blades in at least one direction. The method also includes generating a spectral density for each of the plurality of acceleration signals. In addition, the method includes determining a blade energy for each of the plurality of rotor blades based on the spectral density for each of the plurality of acceleration signals for at least one predetermined frequency range. Moreover, the method includes comparing the blade energies to at least one of each other or a predetermined damage threshold. In addition, the method includes performing a control action when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceeds a predetermined damage threshold.

Description

Technical Field

[0001] The present disclosure relates generally to wind turbines, and more particularly to systems and methods for mitigating damage to rotor blades of wind turbines. Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and in this regard, wind turbines are gaining more and more attention. Modern wind turbines typically include a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes a rotor assembly coupled to the gearbox and the generator. The rotor assembly and the gearbox are mounted on a bedplate support frame located within the nacelle. More specifically, in many wind turbines, the gearbox is mounted to the bedplate via one or more torque arms or arms. One or more rotor blades obtain the kinetic energy of the wind using the known airfoil principle. The rotor blades transmit kinetic energy in the form of rotational energy so as to rotate the shaft that couples the rotor blades to the gearbox (or directly to the generator if a gearbox is not used). The generator then converts the mechanical energy into electrical energy, which can be deployed to the utility grid.

[0003] During the life cycle of a rotor blade, the rotor blade may be subjected to various conditions that cause blade damage. For example, during wind turbine operation, the rotor blade may be overloaded due to various operating and / or environmental conditions, and / or the rotor blade may include various stress points due to manufacturing defects. Regardless of what causes the damage, local stress concentrations may form cracks, which may quickly propagate and eventually lead to blade failure. In the worst case, catastrophic blade failure may require replacement of the tower or even the entire wind turbine.

[0004] In view of the foregoing, the art is continually seeking new and improved systems and methods for detecting and mitigating rotor blade damage. Summary of the invention

[0005] Aspects and advantages of the invention will be set forth in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0006] In one aspect, the present disclosure relates to a method for mitigating damage to a rotor blade among a plurality of rotor blades of a wind turbine. The method includes receiving, via a controller, a plurality of acceleration signals from a plurality of rotor blades in at least one direction. The method also includes generating, via the controller, a spectral density for each of the plurality of acceleration signals. In addition, the method includes determining, via the controller, a blade energy of each of a plurality of rotor blades based on the spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range. Moreover, the method includes comparing the blade energies to at least one of each other or a predetermined damage threshold. In addition, the method includes performing a control action when one or more blade energies differ from each other by a predetermined amount or when one or more blade energies exceed a predetermined damage threshold.

[0007] In one embodiment, for example, the plurality of acceleration signals may be generated by respective pitch systems of the plurality of rotor blades. In another embodiment, the direction may include a Z direction with respect to gravity.

[0008] In a further embodiment, the method may include determining at least one predetermined frequency range based on a power output of the wind turbine, a rotor blade type, a wind turbine type, and / or an angle of one or more of the plurality of rotor blades. Thus, as the power output increases, the predetermined damage threshold increases.

[0009] In further embodiments, determining the blade energy of each of the plurality of rotor blades may include determining an area under a curve of a spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range.

[0010] More specifically, in one embodiment, the predetermined frequency range may include a plurality of predetermined frequency ranges. For example, in such embodiments, the plurality of predetermined frequency ranges may include a first frequency range from about 25 Hertz (Hz) to about 30 Hz and a second frequency range from about 35 Hz to about 40 Hz. In such embodiments, determining the area under a curve of the spectral density for each of the plurality of acceleration signals for the plurality of predetermined frequency ranges may include determining the area under a curve of the spectral density for the logarithm of each of the plurality of acceleration signals for the plurality of predetermined frequency ranges.

[0011] In yet another embodiment, the method may include determining an area under a curve of the spectral density for a logarithm of each of the plurality of acceleration signals for a plurality of predetermined frequency ranges using Simpson's rule.

[0012] In yet another embodiment, the method may include determining an area under a curve of the spectral density for each of the plurality of acceleration signals for a predetermined frequency range for a training period to determine a healthy blade threshold as a baseline for each of the plurality of rotor blades.

[0013] In certain embodiments, determining the blade energy of each of the plurality of rotor blades based on the spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range may include determining a maximum value and a minimum value of an area under a curve of the spectral density for each of the plurality of acceleration signals for at least one predetermined frequency range, and determining a difference between the maximum value and the minimum value of each of the plurality of acceleration signals.

[0014] In such embodiments, comparing the blade energies to at least one of each other or a predetermined damage threshold may include comparing each of the differences between a maximum value and a minimum value of each of the plurality of acceleration signals to the predetermined damage threshold.

[0015] In another embodiment, the spectral density of each of the plurality of acceleration signals may correspond to a power spectral density.Thus, in certain embodiments, the method may include that determining the power spectral density of each of the plurality of acceleration signals further includes utilizing a Welch method.

[0016] In particular embodiments, the control action may include, for example, generating an alarm or notification signal, shutting down the wind turbine, and / or de-rating the wind turbine.

[0017] On the other hand, the present disclosure relates to a system for mitigating damage to a rotor blade among a plurality of rotor blades of a wind turbine. The system includes a pitch system communicatively coupled to each of the plurality of rotor blades. Each pitch system may generate a plurality of acceleration signals. The system also includes a controller including at least one processor. The processor is configured to perform a plurality of operations, including but not limited to receiving a plurality of acceleration signals from the pitch system, determining a blade energy of each of the plurality of rotor blades based on the plurality of acceleration signals for at least one predetermined frequency range, comparing the blade energies with each other or at least one of a predetermined damage threshold, and performing a control action when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceed a predetermined damage threshold.

[0018] Technical Solution 1. A method for reducing damage to a rotor blade among a plurality of rotor blades of a wind turbine, the method comprising:

[0019] receiving, via a controller, a plurality of acceleration signals from the plurality of rotor blades in at least one direction;

[0020] generating, via the controller, a spectral density for each of the plurality of acceleration signals;

[0021] determining, via the controller, a blade energy of each of the plurality of rotor blades based on a spectral density of each of a plurality of acceleration signals for at least one predetermined frequency range;

[0022] comparing the blade energies to at least one of each other or a predetermined damage threshold; and

[0023] A control action is performed when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceeds the predetermined damage threshold.

[0024] Technical Solution 2. The method according to any of the foregoing technical solutions, wherein the plurality of acceleration signals are generated by corresponding pitch systems of the plurality of rotor blades.

[0025] Technical Solution 3. The method according to any of the foregoing technical solutions, wherein the at least one direction includes a Z direction in terms of gravity.

[0026] Technical Solution 4. A method according to any of the preceding technical solutions, wherein the method further comprises determining the at least one predetermined frequency range based on the power output of the wind turbine, the rotor blade type, the wind turbine type and / or the angle of one or more of the plurality of rotor blades, wherein as the power output increases, the predetermined damage threshold increases.

[0027] Technical Solution 5. The method according to any of the foregoing technical solutions, wherein determining the blade energy of each of the plurality of rotor blades further comprises determining an area under a curve of the spectral density for each of the plurality of acceleration signals in the at least one predetermined frequency range.

[0028] Technical Solution 6. The method according to any of the foregoing technical solutions, wherein the at least one predetermined frequency range includes a plurality of predetermined frequency ranges.

[0029] Technical Solution 7. The method according to any of the preceding technical solutions, wherein the plurality of predetermined frequency ranges include from about 25 Hertz (Hz) to about 30 Hz or from about 35 Hz to about 40 Hz.

[0030] Technical Solution 8. A method according to any of the aforementioned technical solutions, wherein determining the area under the curve of the spectral density for each of the multiple acceleration signals in the multiple predetermined frequency ranges also includes determining the area under the curve of the spectral density for the logarithm of each of the multiple acceleration signals in the multiple predetermined frequency ranges.

[0031] Technical Solution 9. The method according to any of the foregoing technical solutions, wherein the method further comprises: using Simpson's rule to determine the area under the curve of the spectral density for the logarithm of each of the plurality of acceleration signals in the plurality of predetermined frequency ranges.

[0032] Technical Solution 10. A method according to any of the foregoing technical solutions, wherein the method further comprises: determining the area under the curve of the spectral density for each of the multiple acceleration signals in the predetermined frequency range for a training time period so as to determine a healthy blade threshold as a baseline for each of the multiple rotor blades.

[0033] Technical Solution 11. The method according to any of the above technical solutions, wherein determining the blade energy of each of the plurality of rotor blades based on the spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range further comprises:

[0034] determining a maximum value and a minimum value of an area under a curve of the spectral density for each of the plurality of acceleration signals of the at least one predetermined frequency range; and

[0035] A difference between a maximum value and a minimum value of each of the plurality of acceleration signals is determined.

[0036] Technical Solution 12. A method according to any of the foregoing technical solutions, wherein comparing the blade energy with each other or at least one of predetermined damage thresholds further comprises: comparing each of the differences between the maximum value and the minimum value of each of the multiple acceleration signals with the predetermined damage threshold.

[0037] Technical Solution 13. The method according to any of the foregoing technical solutions, wherein the spectral density of each of the multiple acceleration signals includes a power spectral density.

[0038] Technical Solution 14. The method according to any of the foregoing technical solutions, wherein determining the power spectral density of each of the plurality of acceleration signals further comprises utilizing a Welch method.

[0039] Technical Solution 15. The method according to any of the preceding technical solutions, wherein the control action comprises at least one of the following: generating an alarm or notification signal, shutting down the wind turbine, and / or de-rating the wind turbine.

[0040] Technical Solution 16. A system for mitigating damage to a rotor blade among a plurality of rotor blades of a wind turbine, the system comprising:

[0041] a pitch system communicatively coupled to each of the plurality of rotor blades, each of the pitch systems generating a plurality of acceleration signals; and,

[0042] A controller including at least one processor, the at least one processor performing a plurality of operations, the plurality of operations comprising:

[0043] receiving the plurality of acceleration signals from the pitch system;

[0044] determining a blade energy of each of the plurality of rotor blades based on the plurality of acceleration signals for at least one predetermined frequency range;

[0045] comparing the blade energies to at least one of each other or a predetermined damage threshold; and

[0046] A control action is performed when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceeds the predetermined damage threshold.

[0047] Technical Solution 17. A system according to any of the foregoing technical solutions, wherein the method further comprises determining at least one predetermined frequency range based on the power output of the wind turbine, the rotor blade type, the wind turbine type and / or the angle of one or more of the plurality of rotor blades, wherein the predetermined damage threshold increases as the power output increases.

[0048] Technical Solution 18. A system according to any of the preceding technical solutions, wherein the plurality of operations further comprises generating a power spectral density for each of the plurality of acceleration signals.

[0049] Technical Solution 19. A system according to any of the preceding technical solutions, wherein determining the blade energy of each of the plurality of rotor blades further comprises determining an area under a curve of the power spectral density for each of the plurality of acceleration signals in the at least one predetermined frequency range.

[0050] Technical solution 20. The system according to any of the above technical solutions, wherein determining the blade energy of each of the plurality of rotor blades based on the power spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range further comprises:

[0051] determining a maximum value and a minimum value of an area under a curve of the spectral density for each of the plurality of acceleration signals of the at least one predetermined frequency range;

[0052] determining a difference between a maximum value and a minimum value of each of the plurality of acceleration signals; and

[0053] Each of the differences between the maximum value and the minimum value of each of the plurality of acceleration signals is compared with the predetermined damage threshold.

[0054] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and together with the description serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] A complete and open disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0056] Figure 1 shows a perspective view of a wind turbine according to one embodiment of the present disclosure;

[0057] Figure 2 shows a perspective interior view of a nacelle of a wind turbine according to one embodiment of the present disclosure;

[0058] Figure 3 A schematic diagram illustrating one embodiment of suitable components that may be included in a wind turbine controller according to the present disclosure;

[0059] Figure 4 A schematic diagram showing an embodiment of a pitch system of a wind turbine according to the present disclosure is shown;

[0060] Figure 5 A flow chart illustrating one embodiment of a method for mitigating damage to a rotor blade among a plurality of rotor blades of a wind turbine according to the present disclosure;

[0061] Figure 6 A graph showing one embodiment of acceleration (y-axis) of a rotor blade versus time (x-axis) according to the present disclosure;

[0062] Figure 7 shows a graph of power spectral density (y-axis) versus frequency (x-axis) for a wind turbine having healthy rotor blades in accordance with the present disclosure; and

[0063] Figure 8 Shown is a graph of power spectral density (y-axis) versus frequency (x-axis) for a wind turbine having at least one unhealthy rotor blade in accordance with the present disclosure. DETAILED DESCRIPTION

[0064] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are shown in the accompanying drawings. Each example is provided by way of illustration of the present invention without limiting the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope of the present invention. For example, a feature shown or described as a part of an embodiment may be used together with another embodiment to produce a further embodiment. Therefore, it is expected that the present invention covers such modifications and variations within the scope of the appended claims and their equivalents.

[0065] Now referring to the accompanying drawings, Figure 1A perspective view of one embodiment of a wind turbine 10 according to the present disclosure is shown. As shown, the wind turbine 10 includes a tower 12 extending from a supporting surface 14, a nacelle 16 mounted on the tower 12, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 20 coupled to the hub 20 and extending outwardly from the hub 22. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in alternative embodiments, the rotor 18 may include more or less than three rotor blades 22. Each rotor blade 22 may be spaced around the hub 20 to facilitate rotating the rotor 18 so that kinetic energy can be converted from the wind into usable mechanical energy and subsequently converted into electrical energy. For example, the hub 20 may be rotatably coupled to a generator 24 ( Figure 2 ), to allow the generation of electrical energy.

[0066] View now Figure 2 , a simplified internal view of one embodiment of a nacelle 16 of a wind turbine 10 is shown. As shown, a generator 24 may be disposed within the nacelle 16. Generally, the generator 24 may be coupled to the rotor 18 of the wind turbine 10 for generating electrical power from the rotational energy generated by the rotor 18. For example, the rotor 18 may include a main shaft 40 that is coupled to the hub 20 for rotation therewith. The generator 24 may then be coupled to the main shaft 40 such that rotation of the main shaft 40 drives the generator 24. For example, in the illustrated embodiment, the generator 24 includes a generator shaft 42 that is rotatably coupled to the main shaft 40 via a gearbox 44. However, in other embodiments, it should be appreciated that the generator shaft 42 may be directly rotatably coupled to the main shaft 40. Alternatively, the generator 24 may be directly rotatably coupled to the main shaft 40.

[0067] It should be appreciated that the main shaft 40 may generally be supported within the nacelle 16 by a support frame or bedplate 46 positioned atop the wind turbine tower 12. For example, the main shaft 40 may be supported by the bedplate 46 via a pair of pillow blocks mounted thereto.

[0068] like Figure 1 and Figure 2 As shown in FIG. 1 , the wind turbine 10 may also include a turbine control system or turbine controller 26 within the nacelle 16. For example, Figure 2 , the turbine controller 26 is disposed within a control cabinet 52 mounted to a portion of the nacelle 16. However, it should be appreciated that the turbine controller 26 may be disposed at any location on or in the wind turbine 10, at any location on the support surface 14, or generally at any other location. The turbine controller 26 may generally be configured to control various operating modes (e.g., startup or shutdown procedures) and / or components of the wind turbine 10.

[0069] like Figure 2 and Figure 4As shown in , the wind turbine 10 may also include a pitch system 50, which includes a pitch adjustment mechanism 32 for each rotor blade 22, the pitch adjustment mechanism being configured to rotate each rotor blade 22 about its pitch axis 34. In addition, each pitch adjustment mechanism 32 may include a pitch drive motor 33 (e.g., any suitable electric, hydraulic, or pneumatic motor), a pitch drive gearbox 35, and a pitch drive pinion 37. In such embodiments, the pitch drive motor 33 may be coupled to the pitch drive gearbox 35 so that the pitch drive motor 33 imparts mechanical force to the pitch drive gearbox 35. Similarly, the pitch drive gearbox 35 may be coupled to the pitch drive pinion 37 to rotate therewith. The pitch drive pinion 37, in turn, may be rotationally engaged with a pitch bearing 54 coupled between the hub 20 and the corresponding rotor blade 22, such that rotation of the pitch drive pinion 37 causes rotation of the pitch bearing 54. Thus, in such embodiments, rotation of the pitch drive motor 33 drives the pitch drive gearbox 35 and the pitch drive pinion 37, thereby rotating the pitch bearing 54 and the rotor blades 22 about the pitch axis 34. Similarly, the wind turbine 10 may include one or more yaw drive mechanisms 38 communicatively coupled to the controller 26, wherein each yaw drive mechanism 38 is configured to change the angle of the nacelle 16 relative to the wind (e.g., by engaging a yaw bearing 56 of the wind turbine 10).

[0070] In addition, as shown in the figure, the turbine controller 26 can also be controlled by a separate or integrated pitch controller 30 ( Figure 1 and Figure 4 ) is communicatively coupled to each pitch adjustment mechanism 32 of wind turbine 10 for controlling and / or changing the pitch angle of each corresponding rotor blade 22 (ie, the angle that determines the projection of rotor blade 22 relative to direction 28 of the wind).

[0071] In addition, if Figure 2 As shown in , one or more sensors 57, 58 may be provided on the wind turbine 10. More specifically, as shown, the blade sensor 57 may be configured with respect to one or more of the rotor blades 22 to monitor the rotor blades 22. In addition, as shown, a wind sensor 58 may be provided on the wind turbine 10. For example, the wind sensor 58 may be a wind vane and anemometer, a LIDAR sensor, or other suitable sensor that measures wind speed and / or direction. As such, the sensors 57, 58 may further communicate with the controller 26 and may provide relevant information to the controller 26.

[0072] It should also be appreciated that the term "monitoring" and variations thereof as used herein indicate that the various sensors of wind turbine 10 may be configured to provide direct measurements of monitored parameters and / or indirect measurements of such parameters. Thus, for example, the sensors described herein may be used to generate signals regarding monitored parameters, which may then be used by controller 26 to determine a condition.

[0073] View now Figure 3 , shows a block diagram of one embodiment of suitable components that may be included in the controller 26 (or pitch controller 30) according to the present disclosure. As shown, the controller 26, 30 may include one or more processors 60 and associated memory devices 62, which are configured to perform a variety of computer-executable functions (e.g., executing methods, steps, calculations, etc., and storing relevant data as disclosed herein). In addition, the controller 26, 30 may also include a communication module 64 to facilitate communication between the controller 26, 30 and various components of the wind turbine 10. In addition, the communication module 64 may include a sensor interface 66 (e.g., one or more analog-to-digital converters) to allow signals transmitted from one or more sensors 57, 58 to be converted into signals that can be understood and processed by the processor 60. It should be appreciated that the sensors 57, 58 may be communicatively coupled to the communication module 64 using any suitable means. For example, Figure 3 As shown in FIG. 6 , the sensors 57 , 58 are coupled to the sensor interface 66 via a wired connection. However, in other embodiments, the sensors 57 , 58 may be coupled to the sensor interface 66 via a wireless connection, such as by using any suitable wireless communication protocol known in the art.

[0074] As used herein, the term "processor" refers not only to what is known in the art as an integrated circuit included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. In addition, the memory device 62 may generally include memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk read-only memories (CD-ROMs), magneto-optical disks (MODs), digital versatile disks (DVDs), and / or other suitable memory elements. This memory device 62 may generally be configured to store suitable computer-readable instructions, which, when implemented by the processor 60, configure the controllers 26, 30 to perform various functions, including but not limited to transmitting suitable control signals to implement corrective actions in response to distance signals exceeding predetermined thresholds as described herein, as well as various other suitable computer-implemented functions.

[0075] View now Figure 4 , a schematic diagram of one embodiment of an overall pitch system 50 for wind turbine 10 is shown. More specifically, as shown, pitch system 50 may include multiple pitch drive mechanisms 32, i.e., one for each pitch axis 34. Furthermore, as shown, each pitch drive mechanism may be communicatively coupled to power grid 45. Thus, during normal operation of wind turbine 10, pitch drive motor 33 may be driven by power grid 45.

[0076] More precisely, if Figure 5 , a flow chart of one embodiment of a method 100 for mitigating damage to a rotor blade in a plurality of rotor blades of a wind turbine is shown. The method 100 may be implemented using, for example, the method described above with reference to Figure 1-Figure 4 The discussed wind turbine 10 is implemented with a controller 26 , rotor blades 22 , and a pitch system 50 . Figure 5 The steps are depicted as being performed in a particular order for purposes of illustration and discussion. One of ordinary skill in the art using the disclosure provided herein will appreciate that the various steps of method 100, or any other method disclosed herein, may be adjusted, modified, rearranged, performed simultaneously, or modified in various ways without departing from the scope of the present disclosure.

[0077] As shown at (102), the method 100 includes receiving a plurality of acceleration signals from the plurality of rotor blades 22 in at least one direction (e.g., an X direction, a Y direction, and a gravity-related Z direction). For example, in one embodiment, the plurality of acceleration signals may be generated by a pitch system 50 of the plurality of rotor blades 22. Figure 6 A graph 70 of one embodiment of acceleration (y-axis) versus time (x-axis) of a rotor blade 22 according to the present disclosure is shown. More specifically, as shown, acceleration signals 72, 72, 76 for one of the rotor blades 22 in the X-direction, the Y-direction, and the Z-direction with respect to gravity are shown. Thus, the pitch controller 30 and / or the turbine controller 26 may receive this signal from each rotor blade 22 and use the Z-direction acceleration signal 76 from each rotor blade 22 for further processing as described herein. Thus, by using the Z-direction acceleration signal from each rotor blade 22 (which is typically already collected by the pitch system 50), no additional sensors may be required, thereby simplifying the system described herein.

[0078] Look back Figure 5 As shown at (104), method 100 includes generating a spectral density for each of the plurality of acceleration signals. For example, the spectral density of each of the plurality of acceleration signals may correspond to a power spectral density, which describes the distribution of power in the frequency components of each acceleration signal.

[0079] As shown at (106), the method 100 includes determining a blade energy of each of the plurality of rotor blades 22 based on a power spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range. For example, in certain embodiments, the controller 26, 30 may determine the power spectral density of each acceleration signal using the Welch method. As described herein, the Welch method generally refers to a method for spectral density estimation and encompasses its definition as understood by a person of ordinary skill in the art.

[0080] More specifically, in certain embodiments, the controller 26, 30 may determine the blade energy of each of the plurality of rotor blades 22 by determining the area under a curve of the power spectral density of each of the plurality of acceleration signals for a predetermined frequency range. Additionally, the controller 26, 30 may determine the predetermined frequency range based on the power output of the wind turbine 10, the rotor blade type / manufacturer, the wind turbine type / manufacturer, and / or the angle of one or more of the plurality of rotor blades 22.

[0081] In yet another embodiment, the controller 26, 30 may determine a plurality of predetermined frequency ranges. For example, in such an embodiment, the plurality of predetermined frequency ranges may include a first frequency range from about 25 Hertz (Hz) to about 30 Hz and a second frequency range from about 35 Hz to about 40 Hz.

[0082] In such embodiments, the controller 26, 30 may determine the area under the curve of the power spectral density of each acceleration signal by determining the area under the curve of the power spectral density of the logarithm of each acceleration signal. In certain embodiments, the controller 26, 30 may determine the area under the curve of the power spectral density for the logarithm of each acceleration signal using Simpson's rule. As described herein, Simpson's rule generally refers to a method for numerical integration and encompasses definitions understood by those of ordinary skill in the art.

[0083] In certain embodiments, the controller 26 , 30 may determine the blade energy of each of the plurality of rotor blades 22 based on the power spectral density of each acceleration signal for at least one predetermined frequency range by determining maximum and minimum values ​​of the area under a curve of the power spectral density of each acceleration signal and determining a difference between the maximum and minimum values ​​of each acceleration signal.

[0084] Look back Figure 5 As shown at (108), method 100 includes comparing the blade energies to each other and / or to a predetermined damage threshold. In certain embodiments, as the power output increases, the predetermined damage threshold may also increase. In such embodiments, for example, controller 26, 30 may compare each difference between the maximum and minimum values ​​of each acceleration signal to each other and / or to a predetermined damage threshold.

[0085] In a further embodiment, the method 100 may include determining an area under a curve of the spectral density for each of a plurality of acceleration signals for a predetermined frequency range for a training time period in order to determine a healthy blade threshold as a baseline for each of the plurality of rotor blades 22. For example, comparing the blade energy (e.g., area under the curve over a frequency range) of one blade to another blade allows for immediate detection of blade damage. However, using the rotor blade area under the curve for a learned frequency range may also reveal anomalies over a period of time. Thus, if the blade energy for that frequency range increases over time, damage to that particular rotor blade is likely to have occurred. The analysis may begin by using a training time period during which rotor blade health is determined as a baseline. In the event that multiple blade damage occurs, comparisons over time may be important to capture such damage events.

[0086] Reference Figure 7 and Figure 8 The blade energy detection method according to the present disclosure can be better understood. As shown in the figure, Figure 7 80 shows a graph of power spectral density (y-axis) versus frequency (x-axis) for a wind turbine having healthy rotor blades according to the present disclosure, and Figure 8 A graph 90 of power spectral density (y-axis) versus frequency (x-axis) of an unhealthy rotor blade according to the present disclosure is shown. More specifically, Figure 7 Two exemplary first predetermined frequency ranges 85 and second predetermined frequency ranges 87 are highlighted, wherein the logarithms of the power spectral densities 82, 84, 86 of the three rotor blades 22 (eg, the area under the curve for each of the three rotor blades 22) are substantially equal within the two predetermined frequency ranges 85, 87. Figure 8 Two exemplary first predetermined frequency ranges 95 and second predetermined frequency ranges 97 are highlighted, wherein within the first predetermined frequency range 95 the logarithm of the power spectral density 94 of one of the rotor blades 22 is greater than the power spectral densities 92 , 96 of the other two rotor blades 22 (e.g., the area under the curve for each of the three rotor blades 22 ).

[0087] Look back Figure 5 As shown at (110), method 100 may include performing a control action when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceeds a predetermined damage threshold. For example, in certain embodiments, the control action may include, for example, generating an alarm or notification signal, shutting down the wind turbine, and / or de-rating the wind turbine 10. In this way, maintenance and / or repair actions may be performed on the damaged rotor blade as needed.

[0088] In addition, the skilled person will recognize the interchangeability of various features of different embodiments. Similarly, the various method steps and features described, as well as other known equivalents of each such method and feature, can be mixed and matched by one of ordinary skill in the art to construct additional systems and techniques in accordance with the principles of the disclosure. Of course, it will be understood that all such objects or advantages described herein may not necessarily be achieved according to any particular embodiment. Thus, for example, one of ordinary skill in the art will recognize that the systems and techniques described herein may be embodied or performed in a manner that achieves or optimizes one advantage or combination of advantages as taught herein without achieving other objects or advantages as taught or suggested herein.

[0089] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

1. A method for mitigating damage to a rotor blade of a plurality of rotor blades of a wind turbine, the method comprising: receiving, via a controller, a plurality of acceleration signals generated by respective pitch systems of the plurality of rotor blades from the plurality of rotor blades in at least one direction; generating, via the controller, a power spectral density for each of the plurality of acceleration signals; determining, via the controller, a blade energy of each of the plurality of rotor blades based on a power spectral density of each of a plurality of acceleration signals for at least one predetermined frequency range; comparing the blade energies to at least one of each other or a predetermined damage threshold; as well as A control action is performed when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceeds the predetermined damage threshold.

2. The method according to claim 1, characterized in that The at least one direction includes a Z direction with respect to gravity.

3. The method according to claim 1, characterized in that The method further includes determining the at least one predetermined frequency range based on a power output of the wind turbine, a rotor blade type, a wind turbine type, and / or an angle of one or more of the plurality of rotor blades, wherein the predetermined damage threshold increases as the power output increases.

4. The method according to claim 1, characterized in that: Determining a blade energy for each of the plurality of rotor blades further includes determining an area under a curve of the power spectral density for each of the plurality of acceleration signals for the at least one predetermined frequency range.

5. The method according to claim 4, characterized in that The at least one predetermined frequency range comprises a plurality of predetermined frequency ranges.

6. The method according to claim 5, characterized in that The plurality of predetermined frequency ranges include from 25 Hertz (Hz) to 30 Hz or from 35 Hz to 40 Hz.

7. The method according to claim 5, characterized in that Determining an area under a curve of the power spectral density for each of the plurality of acceleration signals for the plurality of predetermined frequency ranges further comprises determining an area under a curve of the power spectral density for a logarithm of each of the plurality of acceleration signals for the plurality of predetermined frequency ranges.

8. The method according to claim 7, characterized in that The method further includes determining an area under a curve of the power spectral density for a logarithm of each of the plurality of acceleration signals for the plurality of predetermined frequency ranges using Simpson's rule.

9. The method according to claim 4, characterized in that The method further includes determining an area under a curve of the power spectral density for each of the plurality of acceleration signals for the predetermined frequency range for a training period to determine a healthy blade threshold as a baseline for each of the plurality of rotor blades.

10. The method according to claim 4, characterized in that Determining a blade energy of each of the plurality of rotor blades based on a power spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range further comprises: determining a maximum value and a minimum value of an area under a curve of the power spectral density for each of the plurality of acceleration signals of the at least one predetermined frequency range; and A difference between a maximum value and a minimum value of each of the plurality of acceleration signals is determined.

11. The method according to claim 10, characterized in that Comparing the blade energies to at least one of each other or a predetermined damage threshold further includes comparing each of the differences between a maximum value and a minimum value of each of the plurality of acceleration signals to the predetermined damage threshold.

12. The method according to claim 4, characterized in that Determining a power spectral density of each of the plurality of acceleration signals further includes utilizing a Welch method.

13. The method according to claim 1, characterized in that The control action includes at least one of: generating an alarm or notification signal, shutting down the wind turbine, and / or de-rating the wind turbine.

14. A system for mitigating damage to a rotor blade of a plurality of rotor blades of a wind turbine, the system comprising: a pitch system communicatively coupled to each of the plurality of rotor blades, each of the pitch systems generating a plurality of acceleration signals; as well as, A controller including at least one processor, the at least one processor performing a plurality of operations, the plurality of operations comprising: receiving the plurality of acceleration signals from the pitch system; generating, via the controller, a power spectral density for each of the plurality of acceleration signals; determining a blade energy of each of the plurality of rotor blades based on the plurality of acceleration signals for at least one predetermined frequency range; comparing the blade energies to at least one of each other or a predetermined damage threshold; and A control action is performed when one or more of the blade energies differ from each other by a predetermined amount or one or more of the blade energies exceeds the predetermined damage threshold.

15. The system according to claim 14, characterized in that The system further includes determining the at least one predetermined frequency range based on a power output of the wind turbine, a rotor blade type, a wind turbine type, and / or an angle of one or more of the plurality of rotor blades, wherein the predetermined damage threshold increases as the power output increases.

16. The system according to claim 14, characterized in that Determining a blade energy for each of the plurality of rotor blades further includes determining an area under a curve of the power spectral density for each of the plurality of acceleration signals for the at least one predetermined frequency range.

17. The system according to claim 16, characterized in that Determining a blade energy of each of the plurality of rotor blades based on a power spectral density of each of the plurality of acceleration signals for at least one predetermined frequency range further comprises: determining a maximum value and a minimum value of an area under a curve of the power spectral density for each of the plurality of acceleration signals of the at least one predetermined frequency range; determining a difference between a maximum value and a minimum value of each of the plurality of acceleration signals; and Each of the differences between the maximum value and the minimum value of each of the plurality of acceleration signals is compared with the predetermined damage threshold.

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