FIELD
[0001] The present disclosure relates in general to wind turbines, and more
particularly to systems and methods for mitigating damage in a rotor blade of a wind
turbine.
BACKGROUND
[0002] Wind power is considered one of the cleanest, most environmentally
friendly energy sources presently available, and wind turbines have gained increased
attention in this regard. A modern wind turbine typically includes 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 to 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. The one or more rotor blades capture kinetic
energy of wind using known airfoil principles. The rotor blades transmit the kinetic
energy in the form of rotational energy so as to turn a shaft coupling the rotor blades
to a gearbox, or if a gearbox is not used, directly to the generator. The generator then
converts the mechanical energy to electrical energy that may be deployed to a utility
grid.
[0003] During their lifecycle, the rotor blades may be subjected to various
conditions that cause blade damage. For example, during wind turbine operation, the
rotor blades may be excessively loaded due to various operating and/or environmental
conditions and/or the rotor blades may include various stress points due to
manufacturing defects. Regardless of what causes the damage, localized stress
concentrations may develop into cracks, which can spread quickly and eventually lead
to blade failure. In a worst-case scenario, a catastrophic blade failure may necessitate
the tower, or even the entire wind turbine, to be replaced.
[0004] In view of the aforementioned, the art is continuously seeking new and
improved systems and methods for detecting and mitigating rotor blade damage.
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BRIEF DESCRIPTION
[0005] Aspects and advantages of the invention will be set forth in part 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 is directed to a method for mitigating
damage in a rotor blade of a plurality of rotor blades of a wind turbine. The method
includes receiving, via a controller, a plurality of acceleration signals from the
plurality of the 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. Further, the method includes determining, via the controller,
blade energies for each of the plurality of rotor blades based on the spectral densities
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 implementing a control action when one or more of the blade energies vary
from each other by a predetermined amount or one or more of the blade energies
exceed the 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(s) may include a Z-direction in terms of gravity.
[0008] In further embodiments, the method may include determining the at least
one predetermined frequency range based on a power output of the wind turbine, rotor
blade type, wind turbine type, and/or an angle of one or more of the plurality of rotor
blades. As such, as the power output increases, the predetermined damage threshold
increases.
[0009] In additional embodiments, determining the blade energies for each of the
plurality of rotor blades may include determining an area under a curve of the spectral
densities for each of the plurality of acceleration signals for the at least one
predetermined frequency range.
[0010] More specifically, in one embodiment, the predetermined frequency
range(s) may include a plurality of predetermined frequency ranges. For example, in
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such embodiments, the plurality of predetermined frequency ranges may include a
first frequency range of 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 the curve of the spectral densities for each of the plurality of
acceleration signals for the plurality of predetermined frequency ranges may include
determining the area under the curve of the spectral densities for a 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 the area
under the curve of the spectral densities for the logarithm of each of the plurality of
acceleration signals for the plurality of predetermined frequency ranges using
Simpson’s rule.
[0012] In still another embodiment, the method may include determining the area
under the curve of the spectral densities for each of the plurality of acceleration
signals for the predetermined frequency range for a training time period so as to
determine a healthy blade threshold as a baseline for each of the plurality of rotor
blades.
[0013] In certain embodiments, determining the blade energies for each of the
plurality of rotor blades based on the spectral densities for 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 the area under the curve of
the spectral densities for each of the plurality of acceleration signals for the at least
one predetermined frequency range and determining a difference between the
maximum value and the minimum value for 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 the maximum value and the minimum value for each of the
plurality of acceleration signals to the predetermined damage threshold.
[0015] In another embodiment, the spectral density for each of the plurality of
acceleration signals may correspond to a power spectral density. Therefore, in certain
embodiments, the method may include determining the power spectral density for
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each of the plurality of acceleration signals further comprises utilizing Welch’s
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
derating the wind turbine.
[0017] In another aspect, the present disclosure is directed to a system for
mitigating damage in a rotor blade of 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 of the pitch systems may generate a plurality of acceleration
signals. The system further includes a controller comprising at least one processor.
The processor(s) is configured to perform a plurality of operations, including but not
limited to receiving the plurality of acceleration signals from the pitch systems,
determining blade energies for each of the plurality of rotor blades based 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
implementing a control action when one or more of the blade energies vary from each
other by a predetermined amount or one or more of the blade energies exceeds the
predetermined damage threshold.
[0018] 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 invention and,
together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] A full and enabling disclosure of the present invention, including the best
mode thereof, directed to one of ordinary skill in the art, is set forth in the
specification, which makes reference to the appended figures, in which:
[0020] FIG. 1 illustrates a perspective view of a wind turbine according to one
embodiment of the present disclosure;
[0021] FIG. 2 illustrates a perspective, internal view of a nacelle of a wind turbine
according to one embodiment of the present disclosure;
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[0022] FIG. 3 illustrates a schematic diagram of one embodiment of suitable
components that may be included in a wind turbine controller according to the present
disclosure;
[0023] FIG. 4 illustrates a schematic diagram of one embodiment of a pitch
system of a wind turbine according to the present disclosure;
[0024] FIG. 5 illustrates a flow diagram of one embodiment of a method for
mitigating damage in a rotor blade of a plurality of rotor blades of a wind turbine
according to the present disclosure;
[0025] FIG. 6 illustrates a graph of one embodiment of acceleration (y-axis)
versus time (x-axis) for a rotor blade according to the present disclosure;
[0026] FIG. 7 illustrates 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
[0027] FIG. 8 illustrates a graph of power spectral density (y-axis) versus
frequency (x-axis) for a wind turbine having at least one unhealthy rotor blade
according to the present disclosure.
DETAILED DESCRIPTION
[0028] Reference now will be made in detail to embodiments of the invention,
one or more examples of which are illustrated in the drawings. Each example is
provided by way of explanation of the invention, not limitation of the invention. In
fact, it will be apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing from the scope of
the invention. For instance, features illustrated or described as part of one
embodiment can be used with another embodiment to yield a still further
embodiment. Thus, it is intended that the present invention covers such modifications
and variations as come within the scope of the appended claims and their equivalents.
[0029] Referring now to the drawings, FIG. 1 illustrates perspective view of one
embodiment of a wind turbine 10 according to the present disclosure. As shown, the
wind turbine 10 includes a tower 12 extending from a support 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 22 coupled to and extending
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outwardly from the hub 20. For example, in the illustrated embodiment, the rotor 18
includes three rotor blades 22. However, in an alternative embodiment, the rotor 18
may include more or less than three rotor blades 22. Each rotor blade 22 may be
spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to
be transferred from the wind into usable mechanical energy, and subsequently,
electrical energy. For instance, the hub 20 may be rotatably coupled to an electric
generator 24 (FIG. 2) positioned within the nacelle 16 to permit electrical energy to be
produced.
[0030] Referring now to FIG. 2, a simplified, internal view of one embodiment of
the nacelle 16 of the wind turbine 10 is illustrated. As shown, a generator 24 may be
disposed within the nacelle 16. In general, 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 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 instance, in the illustrated embodiment, the generator 24 includes a
generator shaft 42 rotatably coupled to the main shaft 40 through a gearbox 44.
However, in other embodiments, it should be appreciated that the generator shaft 42
may be rotatably coupled directly to the main shaft 40. Alternatively, the generator
24 may be directly rotatably coupled to the main shaft 40.
[0031] 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 to the bedplate 46.
[0032] As shown in FIGS. 1 and 2, the wind turbine 10 may also include a turbine
control system or a turbine controller 26 within the nacelle 16. For example, as
shown in FIG. 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 the various operating modes
(e.g., start-up or shut-down sequences) and/or components of the wind turbine 10.
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[0033] As shown in FIGS. 2 and 4, the wind turbine 10 may further a pitch system
50 that includes a pitch adjustment mechanism 32 for each of the rotor blades 22 that
is configured to rotate each rotor blade 22 about its pitch axis 34. Further, 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 for rotation therewith. The pitch drive pinion 37 may, in turn,
be in rotational engagement with a pitch bearing 54 coupled between the hub 20 and a
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 blade 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, with each yaw drive mechanism(s) 38
being 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).
[0034] Further, as shown, the turbine controller 26 may also be communicatively
coupled to each pitch adjustment mechanism 32 of the wind turbine 10 through a
separate or integral pitch controller 30 (FIGS. 1 and 4) for controlling and/or altering
the pitch angle of each respective rotor blade 22 (i.e., an angle that determines a
perspective of the rotor blades 22 with respect to the direction 28 of the wind).
[0035] In addition, as shown in FIG. 2, one or more sensors 57, 58 may be
provided on the wind turbine 10. More specifically, as shown, a blade sensor 57 may
be configured with one or more of the rotor blades 22 to monitor the rotor blades 22.
Further, as shown, a wind sensor 58 may be provided on the wind turbine 10. For
example, the wind sensor 58 may a wind vane, and anemometer, a LIDAR sensor, or
another suitable sensor that measures wind speed and/or direction. As such, the
sensors 57, 58 may further be in communication with the controller 26, and may
provide related information to the controller 26.
[0036] It should also be appreciated that, as used herein, the term “monitor” and
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variations thereof indicates that the various sensors of the wind turbine 10 may be
configured to provide a direct measurement of the parameters being monitored and/or
an indirect measurement of such parameters. Thus, the sensors described herein may,
for example, be used to generate signals relating to the parameter being monitored,
which can then be utilized by the controller 26 to determine the condition.
[0037] Referring now to FIG. 3, there is illustrated a block diagram of one
embodiment of suitable components that may be included within the controller 26 (or
the pitch controller 30) according to the present disclosure. As shown, the
controller(s) 26, 30 may include one or more processor(s) 60 and associated memory
device(s) 62 configured to perform a variety of computer-implemented functions
(e.g., performing the methods, steps, calculations and the like and storing relevant
data as disclosed herein). Additionally, the controller(s) 26, 30 may also include a
communications module 64 to facilitate communications between the controller(s) 26,
30 and the various components of the wind turbine 10. Further, the communications
module 64 may include a sensor interface 66 (e.g., one or more analog-to-digital
converters) to permit signals transmitted from one or more sensors 57, 58 to be
converted into signals that can be understood and processed by the processors 60. It
should be appreciated that the sensors 57, 58 may be communicatively coupled to the
communications module 64 using any suitable means. For example, as shown in FIG.
3, 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
communications protocol known in the art.
[0038] As used herein, the term “processor” refers not only to integrated circuits
referred to in the art as being included in a computer, but also refers to a controller, a
microcontroller, a microcomputer, a programmable logic controller (PLC), an
application specific integrated circuit, and other programmable circuits. Additionally,
the memory device(s) 62 may generally comprise memory element(s) including, but
not limited to, computer readable medium (e.g., random access memory (RAM)),
computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a
compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital
versatile disc (DVD) and/or other suitable memory elements. Such memory device(s)
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62 may generally be configured to store suitable computer-readable instructions that,
when implemented by the processor(s) 60, configure the controller(s) 26, 30 to
perform various functions including, but not limited to, transmitting suitable control
signals to implement corrective action(s) in response to a distance signal exceeding a
predetermined threshold as described herein, as well as various other suitable
computer-implemented functions.
[0039] Referring now to FIG. 4, a schematic diagram of one embodiment the
overall pitch system 50 for the wind turbine 10 is illustrated. More specifically, as
shown, the pitch system 50 may include a plurality of pitch drive mechanisms 32, i.e.
one for each pitch axis 34. Further, as shown, each of the pitch drive mechanisms
may be communicatively coupled to the power grid 45. Thus, during normal
operation of the wind turbine 10, the pitch drive motors 33 may be driven by the
power grid 45.
[0040] More specifically, as shown in FIG. 5, a flow diagram of one embodiment
of a method 100 for mitigating damage in a rotor blade of a plurality of rotor blades of
a wind turbine is illustrated. The method 100 may be implemented using, for
instance, the wind turbine 10 and controller 26, the rotor blades 22, and the pitch
system 50 discussed above with reference to FIGS. 1-4. FIG. 5 depicts steps
performed in a particular order for purposes of illustration and discussion. Those of
ordinary skill in the art, using the disclosures provided herein, will understand that
various steps of the method 100 or any of the other methods disclosed herein may be
adapted, modified, rearranged, performed simultaneously or modified in various ways
without deviating from the scope of the present disclosure.
[0041] As shown at (102), the method 100 includes receiving a plurality of
acceleration signals from the plurality of the rotor blades 22 in at least one direction
(e.g. the X-, Y-, and Z- directions in terms of gravity). For example, in one
embodiment, the plurality of acceleration signals may be generated by the pitch
system 50 of the plurality of rotor blades 22. FIG. 6 illustrates a graph 70 of one
embodiment of acceleration (y-axis) versus time (x-axis) for a rotor blade 22
according to the present disclosure. More specifically, as shown, the acceleration
signals 72, 72, 76 for one of the rotor blade 22 in the X-, Y-, and Z- directions in
terms of gravity are illustrated. Thus, the pitch controller 30 and/or the turbine
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controller 26 may receive such signals from each of the rotor blades 22 and use the Zdirection acceleration signals 76 from each rotor blade 22 for further processing as
described herein. Therefore, by using the Z-direction acceleration signals from each
rotor blade 22 (which are generally already collected by the pitch system 50),
additional sensors may not be required, thereby simplifying the system described
herein.
[0042] Referring back to FIG. 5, as shown at (104), the method 100 includes
generating a spectral density for each of the plurality of acceleration signals. For
example, the spectral density for each of the plurality of acceleration signals may
correspond to a power spectral density, which describes the distribution of power into
frequency components of each acceleration signal.
[0043] As shown at (106), the method 100 includes determining blade energies
for each of the plurality of rotor blades 22 based on the power spectral densities for
each of the plurality of acceleration signals for at least one predetermined frequency
range. For example, in certain embodiments, the controller(s) 26, 30 may determine
the power spectral density for each of the acceleration signals using Welch’s method.
As described herein, Welch’s method generally refers to a method for spectral density
estimation and encompasses its definition understood by those having ordinary skill in
art.
[0044] More specifically, in certain embodiments, the controller(s) 26, 30 may
determine the blade energies for each of the plurality of rotor blades 22 by
determining an area under a curve of the power spectral densities for each of the
plurality of acceleration signals for the predetermined frequency range(s). In
addition, the controller(s) 26, 30 may determine the predetermined frequency range(s)
based on a power output of the wind turbine 10, rotor blade type/manufacturer, wind
turbine type/manufacturer, and/or an angle of one or more of the plurality of rotor
blades 22.
[0045] In yet another embodiment, the controller(s) 26, 30 may determine a
plurality of predetermined frequency ranges. For example, in such embodiments, the
plurality of predetermined frequency ranges may include a first frequency range of
from about 25 Hertz (Hz) to about 30 Hz and a second frequency range from about 35
Hz to about 40 Hz.
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[0046] In such embodiments, the controller(s) 26, 30 may determine the area
under the curve of the power spectral densities for each of the acceleration signals by
determining the area under the curve of the power spectral densities for a logarithm of
each of the acceleration signals. In particular embodiments, the controller(s) 26, 30
may determine the area under the curve of the power spectral densities for the
logarithm of each of the acceleration signals using Simpson’s rule. As described
herein, Simpson’s rule generally refers to a method for numerical integration and
encompasses its definition understood by those having ordinary skill in art.
[0047] In certain embodiments, the controller(s) 26, 30 may determine the blade
energies for each of the plurality of rotor blades 22 based on the power spectral
densities for each of the acceleration signals for at least one predetermined frequency
range by determining a maximum value and a minimum value of the area under the
curve of the power spectral densities for each of the acceleration signals and
determining a difference between the maximum value and the minimum value for
each of the acceleration signals.
[0048] Referring back to FIG. 5, as shown at (108), the 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, the
controller(s) 26, 30 may compare each of the differences between the maximum value
and the minimum value for each of the acceleration signals to each other and/or to a
predetermined damage threshold.
[0049] In further embodiments, the method 100 may include determining the area
under the curve of the spectral densities for each of the plurality of acceleration
signals for the predetermined frequency range for a training time period so as to
determine a healthy blade threshold as a baseline for each of the plurality of rotor
blades 22. For example, comparison of blade energy (e.g. the area under the curve for
a frequency range) for one blade to another allows for immediate detection of blade
damage. However, using the rotor blade’s area under the curve for a learned
frequency ranges may also show anomalies over time. As such, if the blade energy
for that frequency range increases over time, it is likely damage that damage to that
particular rotor blade has occurred. This analysis may start by using the training time
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period where the rotor blade is determined as healthy as a baseline. In cases where
damage on multiple blades occurs, the comparison over time may be important to
capture such damage events.
[0050] Blade energy detection methods according to the present disclosure can be
better understood with reference to FIGS. 7 and 8. As shown, FIG. 7 illustrates a
graph 80 of power spectral density (y-axis) versus frequency (x-axis) for a wind
turbine having healthy rotor blades according to the present disclosure, whereas FIG.
8 illustrates a graph 90 of power spectral density (y-axis) versus frequency (x-axis)
for an unhealthy rotor blade according to the present disclosure. More particularly,
FIG. 7 highlights two example first and second predetermined frequency ranges 85,
87, wherein, within the two predetermined frequency ranges 85, 87, the logarithm of
the power spectral densities 82, 84, 86 for the three rotor blades 22 (e.g. the area
under the curve of each of the three rotor blades 22) is approximately equal. In
contrast, FIG. 8 highlights two example first and second predetermined frequency
ranges 95, 97, wherein, within the first predetermined frequency range 95, the
logarithm of the power spectral density 94 for one of the rotor blades 22 is greater
than the power spectral densities 92, 96 for the other two rotor blades 22 (e.g. the area
under the curve of each of the three rotor blades 22).
[0051] Referring back to FIG. 5, as shown at (110), the method 100 may include
implementing a control action when one or more of the blade energies vary from each
other by a predetermined amount or one or more of the blade energies exceed the
predetermined damage threshold. For example, in particular embodiments, the
control action may include, for example, generating an alarm or notification signal,
shutting down the wind turbine, and/or derating the wind turbine 10. As such, a
maintenance and/or repair action may be performed on the damaged rotor blade as
needed.
[0052] Furthermore, the skilled artisan will recognize the interchangeability of
various features from different embodiments. Similarly, the various method steps and
features described, as well as other known equivalents for each such methods and
feature, can be mixed and matched by one of ordinary skill in this art to construct
additional systems and techniques in accordance with principles of this disclosure. Of
course, it is to be understood that not necessarily all such objects or advantages
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14
described above may be achieved in accordance with any particular embodiment.
Thus, for example, those skilled in the art will recognize that the systems and
techniques described herein may be embodied or carried out in a manner that achieves
or optimizes one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught or suggested
herein.
[0053] 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 languages
of the claims.
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Claims:
1. A method for mitigating damage in 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 from the plurality
of the rotor blades in at least one direction;
generating, via the controller, a spectral density for each of the plurality of
acceleration signals;
determining, via the controller, blade energies for each of the plurality of rotor
blades based on the spectral densities for each of 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,
implementing a control action when one or more of the blade energies vary
from each other by a predetermined amount or one or more of the blade energies
exceed the predetermined damage threshold.
2. The method of claim 1, wherein the plurality of acceleration signals is
generated by respective pitch systems of the plurality of rotor blades.
3. The method of any of the preceding claims, wherein the at least one
direction comprises a Z-direction in terms of gravity.
4. The method of any of the preceding claims, further comprising
determining the at least one predetermined frequency range based on a power output
of the wind turbine, rotor blade type, wind turbine type, and/or an angle of one or
more of the plurality of rotor blades, wherein as the power output increases, the
predetermined damage threshold increases.
5. The method of any of the preceding claims, wherein determining the
blade energies for each of the plurality of rotor blades further comprises determining
an area under a curve of the spectral densities for each of the plurality of acceleration
signals for the at least one predetermined frequency range.
6. The method of claim 5, wherein the at least one predetermined
frequency range comprises a plurality of predetermined frequency ranges.
7. The method of claim 6, wherein the plurality of predetermined
frequency ranges comprises from about 25 Hertz (Hz) to about 30 Hz or from about
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35 Hz to about 40 Hz.
8. The method of claim 6, wherein determining the area under the curve
of the spectral densities for each of the plurality of acceleration signals for the
plurality of predetermined frequency ranges further comprises determining the area
under the curve of the spectral densities for a logarithm of each of the plurality of
acceleration signals for the plurality of predetermined frequency ranges.
9. The method of claim 8, further comprising determining the area under
the curve of the spectral densities for the logarithm of each of the plurality of
acceleration signals for the plurality of predetermined frequency ranges using
Simpson’s rule.
10. The method of claim 5, further comprising determining the area under
the curve of the spectral densities for each of the plurality of acceleration signals for
the predetermined frequency range for a training time period so as to determine a
healthy blade threshold as a baseline for each of the plurality of rotor blades.
11. The method of claim 5, wherein determining the blade energies for
each of the plurality of rotor blades based on the spectral densities for 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 the area under the
curve of the spectral densities for each of the plurality of acceleration signals for the
at least one predetermined frequency range; and,
determining a difference between the maximum value and the minimum value
for each of the plurality of acceleration signals.
12. The method of claim 11, wherein comparing the blade energies to at
least one of each other or a predetermined damage threshold further comprises
comparing each of the differences between the maximum value and the minimum
value for each of the plurality of acceleration signals to the predetermined damage
threshold.
13. The method of claim 5, wherein the spectral density for each of the
plurality of acceleration signals comprises a power spectral density, wherein
determining the power spectral density for each of the plurality of acceleration signals
further comprises utilizing Welch’s method.
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14. The method of claim 1, wherein the control action comprises at least
one of generating an alarm or notification signal, shutting down the wind turbine,
and/or derating the wind turbine.
15. A system for mitigating damage in 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; and,
a controller comprising 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 systems;
determining blade energies for each of the plurality of rotor blades
based 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,
implementing a control action when one or more of the blade energies
vary from each other by a predetermined amount or one or more of the blade
energies exceed the predetermined damage threshold.