System and method for monitoring the health of rotor blades of a wind turbine

Abstract

A method for monitoring at least one rotor blade of a wind turbine includes implementing, via a controller, a control scheme for monitoring blade damage of the at least one rotor blade. The control scheme includes monitoring at least one electrical condition of a pitch system of the wind turbine. The method further includes transforming the (plural) electrical conditions of the pitch system into a frequency domain. Additionally, the method includes determining one or more peaks of the frequency domain around a frequency component associated with a natural frequency of the rotor blade. Additionally, the method includes determining a frequency deviation between the one or more peaks of the frequency domain and the frequency component associated with the natural frequency of the rotor blade. Accordingly, a frequency deviation outside a predetermined frequency range indicates an abnormality of the rotor blade. Thus, the method includes implementing a control action when the frequency deviation is outside the predetermined frequency range.

Description

Technical Field

[0001] The present disclosure generally relates to wind turbines and, more particularly, to systems and methods for monitoring the health of rotor blades of a wind turbine, such as using pitch motor current. Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have received increasing attention in this regard. Modern wind turbines typically include a tower, a generator, an optional gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind using known airfoil principles and transfer the kinetic energy by rotational energy to rotate a shaft that couples the rotor blades to a gearbox or, if no gearbox is used, directly to a generator. The generator then converts the mechanical energy into electrical energy, which can be deployed to the utility grid.

[0003] During operation of a wind turbine, its components are subjected to various loads. If the load exceeds the design threshold, the components are at risk of damage and / or failure. For example, rotor blade damage and / or failure is a common occurrence in wind turbines, which is very costly and can result in significant downtime. In addition, blade damage can also cause damage or destruction of the tower, resulting in even more costs and downtime.

[0004] Techniques used in the current market focus on blade inspection, such as image capture and drone inspection to detect blade damage. However, such methods cannot be used to detect hidden blade cracks. Other methods for detecting blade damage may include fiber optic sensing or paired antennas, but such systems are very expensive.

[0005] Accordingly, improved systems and methods for monitoring the health of rotor blades of a wind turbine at minimal hardware cost would be welcome in the art to provide early warnings about the condition of the blades. Thus, the repair and maintenance process can be greatly improved, and downtime and associated losses can be minimized. Summary of the Invention

[0006] Aspects and advantages of the present invention will be set forth in part in the description which follows, or may be obvious from the description, or may be learned by practice of the invention.

[0007] In one aspect, the present disclosure relates to a method for monitoring at least one rotor blade of a wind turbine. The method includes implementing, via a controller, a control scheme for monitoring blade damage of the at least one rotor blade. The control scheme includes monitoring at least one electrical condition of a pitch system of the wind turbine. The method further includes transforming the (plural) electrical conditions of the pitch system into a frequency domain. Additionally, the method includes determining one or more peaks of the frequency domain around a frequency component associated with a natural frequency of the rotor blade. Additionally, the method includes determining a frequency deviation between the one or more peaks of the frequency domain and the frequency component associated with the natural frequency of the rotor blade. Accordingly, a frequency deviation outside a predetermined frequency range indicates an abnormal rotor blade. Thus, the method includes implementing a control action when the frequency deviation is outside the predetermined frequency range.

[0008] In another aspect, the present disclosure relates to a wind turbine. The wind turbine includes a tower, a nacelle mounted on top of the tower, a rotor having a rotatable hub and at least one rotor blade communicatively coupled to a pitch system, and a controller configured to perform a plurality of operations for controlling the wind turbine. For example, the plurality of operations may include implementing a control scheme for monitoring blade damage of the at least one rotor blade. The control scheme includes: monitoring at least one electrical condition of the pitch system; transforming the (plural) electrical conditions of the pitch system into a frequency domain; determining one or more peaks of the frequency domain around a frequency component associated with a natural frequency of the rotor blade; determining a frequency deviation between the one or more peaks of the frequency domain and the frequency component associated with the natural frequency of the rotor blade, wherein a frequency deviation outside a predetermined frequency range indicates an abnormal rotor blade; and implementing a control action when the frequency deviation is outside the predetermined frequency range. It should be understood that the wind turbine may further include any one or a combination of features and / or embodiments described herein.

[0009] In yet another aspect, the present disclosure relates to a method for monitoring a rotor blade of a wind turbine. The method includes monitoring, via a controller of the wind turbine, a power output of the wind turbine. When the power output is higher than a power threshold, the method includes implementing, via the controller, a control scheme for monitoring blade damage of the rotor blade. The control scheme includes: monitoring at least one electrical condition of a pitch system of the wind turbine; transforming the at least one electrical condition of the pitch system into a frequency domain; determining, via the controller, whether the at least one electrical condition in the frequency domain has reduced a predetermined amount around a frequency component associated with a natural frequency of the rotor blade, wherein the at least one electrical condition reducing the predetermined amount around the frequency component associated with the natural frequency of the rotor blade indicates an abnormal rotor blade; and implementing a control action when the at least one electrical condition is outside a predetermined range. It should be understood that the method may further include any one of the combinations of features and / or embodiments described herein.

[0010] These and other features, aspects, and advantages of the present invention will be further supported and described with reference to the following description and the 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

[0011] A complete and enabling disclosure of the present invention, including the best mode thereof, for the ordinary skilled person in the art, is set forth in the specification, which makes reference to the accompanying drawings, in which:

[0012] Figure 1 FIG. illustrates a perspective view of an embodiment of a wind turbine in accordance with the present disclosure;

[0013] Figure 2 FIG. Figure 1 illustrates an internal perspective view of an embodiment of the nacelle of the wind turbine shown in ;

[0014] Figure 3 FIG. Figure 1 illustrates a perspective view of an embodiment of one of the rotor blades of the wind turbine shown in ;

[0015] Figure 4 FIG. illustrates a block diagram of an embodiment of a three-axis pitch system in accordance with the present disclosure;

[0016] Figure 5 FIG. illustrates a graph of an embodiment of the relationship between pitch angle (y-axis) and time (x-axis) for DC offset, 1P pitch, and 2P pitch for three rotor blades during individual pitch pitch operation in accordance with the present disclosure;

[0017] Figure 6 FIG. illustrates a schematic diagram of an embodiment of a controller for a bearing assembly in accordance with the present disclosure;

[0018] Figures 7A to 7B FIG. illustrates a flowchart of an embodiment of a method for monitoring a rotor blade of a wind turbine in accordance with the present disclosure;

[0019] Figure 8 FIG. illustrates a graph of an embodiment of pitch current in the frequency domain in accordance with the present disclosure;

[0020] Figure 9 FIG. illustrates a graph of an embodiment of the relationship between modal frequency (y-axis) and added mass (x-axis) in accordance with the present disclosure; and

[0021] Figure 10 FIG. illustrates a flowchart of another embodiment of a method for monitoring a rotor blade of a wind turbine in accordance with the present disclosure. DETAILED DESCRIPTION

[0022] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present invention and not limitation thereof. 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 or spirit of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield yet a further embodiment. Accordingly, it is intended that the present invention cover such modifications and variations and their equivalents as fall within the scope of the appended claims.

[0023] For many wind turbines, when the power generated by the corresponding wind exceeds a threshold, certain control algorithms are implemented to reduce the tension on the rotor blades and the tower during operation. For a wind turbine operating under such conditions, each axis is commanded at different pitch angles at different rotor positions, including 1P pitch, 2P pitch, and DC offset commands (see Figure 5 ), as well as some other common offset terms. 1P pitch indicates that the blade pitches once per revolution, while 2P pitch indicates that the blade pitches twice per revolution. The commanded values are updated online based on real-time measurements from proximity probes installed on the wind turbine. Note that although each blade can be pitched individually using different control commands, their AC command components (e.g., 1P and 2P commands) remain balanced, having the same magnitude but offset by 120 degrees. Additionally, during such control algorithms, both the commanded DC and AC components can be directly observed from measurements in the pitch drive system, such as the pitch motor current components, pitch speed, and pitch angle for each axis. Furthermore, among all AC oscillations, 1P and 2P pitch oscillations are typically the most significant because these components are externally commanded by the controller.

[0024] However, when the rotor blades are controlled under such control algorithms, there may be another AC oscillation that can be detected in drivetrain measurements, some of which are directly related to the blade natural / modal frequencies. Based on physics, changes in the blade natural / modal frequencies reflect changes in blade stiffness or mass. If ice accumulates on any of the rotor blades, the equivalent mass of the blade also increases, and the natural / modal frequencies will decrease. On the other hand, if blade structural damage occurs on any of the rotor blades, the blade stiffness decreases, and the natural / modal frequencies will also decrease. Therefore, a decrease in the blade natural frequency can be used as a direct indicator of blade anomalies. Additional weather sensors can also be used to distinguish between blade icing events and blade structural damage.

[0025] Accordingly, the present disclosure relates to a system and method for monitoring blade health using pitch motor current. More specifically, the present disclosure observes blade natural / modal frequency related components in the pitch motor current (e.g., armature current for a DC motor, and torque related current components for an AC motor (e.g., q-axis current for a field oriented controlled AC motor), or direct torque measurements) to provide a blade health index by monitoring natural / modal frequency deviations. Thus, the present disclosure provides early detection of wind turbine blade anomalies (e.g., blade structural damage and / or blade icing events).

[0026] Referring now to the drawings, Figure 1 FIG. 1 illustrates a side view of one embodiment of a wind turbine 10. As shown, the wind turbine 10 generally includes a tower 12 extending from a support surface 14 (e.g., the ground, a concrete pad, or any other suitable support surface). Accordingly, it should be understood that the wind turbine 10 described herein can be an onshore or an offshore wind turbine. In addition, the wind turbine 10 may further include 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 the hub 20 and extending outwardly therefrom. 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 fewer than three rotor blades 22. Each rotor blade 22 may be spaced about the hub 20 to facilitate rotation of the rotor 18 such that kinetic energy can be converted from wind energy into useful mechanical energy and subsequently into electrical energy. For example, the hub 20 may be rotatably coupled to a generator 25 ( Figure 2 ) positioned within the nacelle 16 to permit generation of electrical power.

[0027] Referring now to Figure 2 FIG. 2, a simplified internal view of one embodiment of the nacelle 16 of the wind turbine 10 shown in Figure 1 FIG. 1 is illustrated. As shown, the generator 25 may be disposed within the nacelle 16 and supported on top of a floor 36. Generally, the generator 25 may be coupled to the rotor 18 for generating electrical power from the rotational energy generated by the rotor 18. For example, as shown in the illustrated embodiment, the rotor 18 may include a rotor shaft 26 coupled to the hub 20 for rotation therewith. The rotor shaft 26 may in turn be rotatably coupled to a generator shaft 28 of the generator 25 via a gearbox 30. As is commonly understood, in response to rotation of the rotor blades 22 and the hub 20, the rotor shaft 26 may provide a low-speed, high-torque input to the gearbox 30. The gearbox 30 may then be configured to convert the low-speed, high-torque input into a high-speed, low-torque output to drive the generator shaft 28 and thus the generator 25.

[0028] The wind turbine 10 may also include a turbine controller 32 centralized within the nacelle 16. Additionally, as shown, the turbine controller 32 is housed within a control cabinet 34. Further, the turbine controller 32 may be communicatively coupled to any number of components of the wind turbine 10 to control the operation of such components and / or effectuate various corrective actions as described herein.

[0029] Reference Figure 2 and Figure 4 , a typical pitch system 70 has three axis units driven by a pitch drive mechanism 38 configured to rotate each rotor blade 22 about its respective pitch axis 40 via a pitch bearing 42, thereby allowing adjustment of the orientation of each blade 22 relative to the direction of the wind. Each pitch drive mechanism 38 includes a pitch motor 58 and is regulated by its own axis controller 32 such that the rotor blades 22 may be pitched individually during normal operation. It should be understood that the pitch motor 58 may be a direct current (DC) motor or an alternating current (AC) motor. Thus, when the power generated by the corresponding wind exceeds a threshold, individual pitch control is applied to reduce the tension on the rotor blades 22 and the tower 12 during operation. For a wind turbine under individual pitch control operation, as Figure 5 shown, during individual pitch operation, each axis 40 is commanded at a different pitch angle at different rotor positions, including 1P pitch, 2P pitch, and DC offset commands, as well as some other common offset terms. 1P pitch indicates that the rotor blade 22 is pitched once per revolution, while 2P pitch indicates that the rotor blade 22 is pitched twice per revolution. The commanded values are updated online based on real-time measurements from proximity probes mounted on the wind turbine 10. In some embodiments, although each rotor blade 22 is pitched individually with different load commands, their AC command components (e.g., 1P and 2P commands) remain balanced, having the same AC magnitude but offset by 120 degrees.

[0030] Similarly, the wind turbine 10 may include one or more yaw drive mechanisms 44 communicatively coupled to the turbine controller 32, where each yaw drive mechanism 44 is configured to change the angle of the nacelle 16 relative to the wind (e.g., by engaging a yaw bearing 46 of the wind turbine 10).

[0031] Now reference Figure 3 , according to aspects of the present subject matter, illustrated are Figure 1 and Figure 2Perspective view of one of the rotor blades 22 shown in the figure. As shown, the rotor blade 22 includes a blade root 23 configured to mount the rotor blade 22 to the hub 20 and a blade tip 24 disposed opposite the blade root 23. The body 27 of the rotor blade 22 can extend longitudinally between the blade root 23 and the blade tip 24 and can generally serve as the outer shell of the rotor blade 22. As generally understood, the body 27 can define an aerodynamic profile (e.g., by defining an airfoil-shaped cross-section, such as a symmetric or arcuate airfoil-shaped cross-section) to enable the rotor blade 22 to capture kinetic energy from the wind using known aerodynamic principles. Thus, the body 27 can generally include a pressure side 29 and a suction side 31 that extend between a leading edge 33 and a trailing edge 35. Additionally, the rotor blade 22 can have a span 37 and a chord 39, where the span 37 defines the total length of the body 27 between the blade root 23 and the blade tip 24, and the chord 39 defines the total length of the body 27 between the leading edge 33 and the trailing edge 35. As generally understood, as the body 27 extends from the blade root 23 to the blade tip 24, the chord 39 can vary in length relative to the span 37.

[0032] In addition, as shown, the rotor blade 22 can also include a plurality of T-bolts or root attachment assemblies 41 for coupling the blade root 23 to the hub 20 of the wind turbine 10. Generally, each root attachment assembly 41 can include a barrel nut 43 mounted within a portion of the blade root 23 and a root bolt 45 coupled to the barrel nut 43 and extending from the barrel nut 42 so as to project outwardly from a root end 47 of the blade root 23. By projecting outwardly from the root end 47, the root bolt 45 can generally be used to couple the blade root 23 to the hub 20 (e.g., via one of the pitch bearings 42).

[0033] As Figure 6 shown, the controller 32 can include one or more processors 82 and associated memory devices 84 configured to perform various computer-implemented functions (e.g., execute the methods, steps, calculations, etc. disclosed herein and store related data). Additionally, the controller 32 can also include a communication module 86 to facilitate communication between the controller 32 and various sensors 76, 78. Further, the communication module 86 can include a sensor interface 88 (e.g., one or more analog-to-digital converters) to allow signals transmitted from the sensors 76, 78 to be converted into signals that can be understood and processed by the processor 82. It should be appreciated that the sensors 76, 78 can be communicatively coupled to the communication module 86 using any suitable means. For example, as Figure 6As shown, sensors 76, 78 may be coupled to sensor interface 88 via a wired connection. However, in other embodiments, sensors 76, 78 may be coupled to sensor interface 88 via a wireless connection, such as by using any suitable wireless communication protocol known in the art. Accordingly, processors 82 may be configured to receive one or more signals from sensors 76, 78. In addition, controller 32 and sensors 76, 78 may also be an integrated package product.

[0034] As used herein, the term "processor" refers not only to integrated circuits known in the art as being included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Processors 82 may also be configured to compute advanced control algorithms and communicate various Ethernet or serial-based protocols (Modbus, OPC, CAN, etc.) as well as classical analog or digital signals. Additionally, memory devices 84 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 disc read-only memory (CD-ROM), magneto-optical disk (MOD), digital versatile disk (DVD), and / or other suitable memory elements. Such memory devices 84 may generally be configured to store suitable computer-readable instructions that, when implemented by processors 82, configure controller 32 to perform the various functions described herein.

[0035] In additional embodiments, sensors 76, 78 described herein may include any one or combination of the following sensors: electrical sensors, meteorological sensors (such as sensors capable of measuring temperature, humidity, air pressure, wind speed and direction, precipitation, and precipitation type), proximity sensors, inductive sensors, micro inertial measurement units (MIMU), pressure or load sensors, accelerometers, acoustic detection and ranging (SODAR) sensors, light detection and ranging (LIDAR) sensors, optical sensors, or the like.

[0036] Now referring to Figures 7A to 7B , a flowchart of one embodiment of a method 100 for monitoring at least one rotor blade 22 of a wind turbine 10 is illustrated. In some embodiments, controller 32 is configured to perform such operations. Generally, method 100 will be described herein with reference to wind turbine 10 and controller 32 illustrated in Figures 1 to 6 . However, it should be appreciated that the disclosed method 100 may be implemented using a wind turbine having any other suitable configuration. Additionally, although for purposes of illustration and discussion, Figures 7A to 7Bdepicts steps performed in a particular order, however, the methods discussed herein are not limited to any particular order or arrangement. Using the disclosures provided herein, those skilled in the art will recognize that, without departing from the scope of the present disclosure, the various steps of the methods disclosed herein can be omitted, rearranged, combined, and / or modified in various ways.

[0037] As shown at (102), method 100 may include a data acquisition step, where controller 32 collects various electrical conditions. In other words, controller 32 is configured to monitor at least one electrical condition of pitch system 70. In an embodiment, method 100 may include online monitoring of the (multiple) electrical conditions of pitch system 70. Additionally, in such an embodiment, the (multiple) electrical conditions may include at least one of pitch motor current, pitch motor voltage, or pitch motor torque. More specifically, as shown in the illustrated embodiment, the pitch motor current may include the armature current for a DC motor (e.g., I arm,I (t), I arm,II (t), I arm,III (t)), the torque-related current component for an AC motor, or the like or a combination thereof.

[0038] As shown at (104), method 100 may further include monitoring at least one operating parameter of wind turbine 10. For example, in an embodiment, the (multiple) operating parameters may include at least one of power output, wind speed, rotor speed, generator speed, or generator torque. Accordingly, in an embodiment, method 100 may implement blade damage control scheme 108 only when the (multiple) operating parameters exceed an operating threshold. In other words, controller 32 may implement control scheme 108 only when the power output exceeds a certain power threshold (as shown at (106)).

[0039] Thus, as shown at (110), control scheme 108 may include transforming the (multiple) electrical conditions of pitch system 70 into the frequency domain. For example, as Figure 8 shown, graph 150 of an embodiment of pitch motor current 152 in the frequency domain according to the present disclosure is illustrated. Thus, as shown, control scheme 108 may include determining one or more peaks 154 of the frequency domain around a frequency component related to the natural frequency of the (multiple) rotor blades 22. As used herein, by way of example, the frequency component related to the natural frequency of the (multiple) rotor blades 22 may directly include the natural frequency of rotor blades 22 or include the natural frequency of the (multiple) rotor blades 22 modulated by the control scheme. Additionally, it should be understood that the natural frequency of the (multiple) rotor blades 22 may be affected by temperature and / or operating conditions.

[0040] More specifically, as shown at (112), method 100 may include at a given blade natural frequency 156 (also asFigure 7A As shown at (114), F b,nat ) search for actual local peaks around, which can be modulated by 1P, 2P, etc. Thus, as shown at (116), control scheme 108 may include obtaining the frequency for the searched local peaks (e.g., f pk,b,nat,I , f pk,b,nat,II , f pk,b,nat,III ). As shown at (118), control scheme 108 may include determining the frequency deviation (i.e., calculating the difference) between one or more local peaks of the frequency domain and the frequency components related to the natural frequency of the (multiple) rotor blades 22. For example, as shown in the figure, the following equations (1)-(3) can be used to calculate the frequency deviation for each rotor blade 22 of the wind turbine 10:

[0041] Δf pk,b,nat,I = f pk,b,nat,I - f b,nat Equation (1)

[0042] Δf pk,b,nat,II = f pk,b,nat,II - f b,nat Equation (2)

[0043] Δf pk,b,nat,III = f pk,b,nat,III - f b,nat Equation (3)

[0044] Accordingly, a frequency deviation outside a predetermined frequency range may indicate that the rotor blade is damaged or ice has formed on the (multiple) rotor blades 22. In addition, as shown at (115), method 100 may further include monitoring the deviation related to the blade natural frequency (e.g., using temperature correction at selected and aggregated operating points). Thus, still referring to Figure 7B , as shown at (120), method 100 may then include determining whether one or more of the frequency deviations of the multiple rotor blades 22 are greater than a frequency threshold. If not, method 100 ends at (122) without a blade natural frequency deviation. On the contrary, if one or more of the frequency deviations are greater than the frequency threshold, as shown at (124), method 100 continues to determine which axis has the largest frequency deviation. In some embodiments, the effects of temperature and / or operating conditions on the natural frequency of the (multiple) rotor blades 22 may be monitored such that the extracted frequency deviations can be compensated by those normal operating conditions to reduce false alarms.

[0045] As shown at (126), method 100 may also include measuring at least one environmental parameter at wind turbine 10. In such an embodiment, for example, the environmental parameter(s) at wind turbine 10 may include at least one of, for example, temperature, humidity, pressure, wind speed, wind direction, precipitation, or a combination thereof. The reason for this measurement is that a change in the natural frequency of rotor blade 22 reflects a change in its blade stiffness or blade mass. Accordingly, when ice accretion is occurring on rotor blade 22, the blade mass increases and the natural frequency of rotor blade 22 also decreases. For example, as Figure 9 shown therein, graph 170 of an embodiment is illustrated showing the relationship of the natural / modal frequency (y-axis) according to the present disclosure versus the increasing mass (x-axis) of rotor blade 22 for a first mode frequency 172, a second mode frequency 174, a third mode frequency 176, and a fourth mode frequency 178. As shown at 0 kilograms (kg), no ice is present. However, as ice accretes on rotor blade 22, each of the mode frequencies 172, 174, 176, 178 decreases. Conversely, when rotor blade 22 is damaged, the blade stiffness decreases, but the natural frequency of rotor blade 22 also decreases. Thus, controller 32 may determine whether ice accretion is occurring on rotor blade(s) 22 based on the environmental parameter(s).

[0046] Returning to Figure 7B , if ice accretion is present, then as shown at (128) and (132), method 100 may include implementing a control action when the frequency deviation is outside a predetermined frequency range. Similarly, as shown at (130) and (132), if the blade is damaged (or there is any other anomaly in the frequency deviation(s)), then method 100 may also include implementing a control action when the frequency deviation is outside a predetermined frequency range. In several embodiments, the control action may include, for example, generating an alert, scheduling a maintenance action, pitching one or more of rotor blades 22, shutting down the rotor blades, derating wind turbine 10, ramping up wind turbine 10, de-icing (e.g., heating) rotor blade 22, or replacing one or more of rotor blades 22.

[0047] Now referring to Figure 10 , a flowchart of an embodiment of method 200 for monitoring rotor blade 22 of wind turbine 10 is illustrated. In some embodiments, controller 32 is configured to perform such operations. Generally, method 200 will be described herein with reference to Figures 1 to 6 wind turbine 10 and controller 32 illustrated therein. However, it should be appreciated that the disclosed method 200 may be implemented using a wind turbine having any other suitable configuration. Additionally, although for purposes of illustration and discussion, Figure 10depicts steps performed in a particular order, but the methods discussed herein are not limited to any particular order or arrangement. Using the disclosures provided herein, one of ordinary skill in the art will recognize that various steps of the methods disclosed herein can be omitted, rearranged, combined, and / or modified in various ways without departing from the scope of the present disclosure.

[0048] As shown at (202), method 200 may include monitoring the power output of wind turbine 10. When the power output is above a power threshold, as shown at (204), method 200 includes implementing control scheme 206 for monitoring blade damage of (a plurality of) rotor blades 22. As shown at (208), control scheme 206 may include monitoring at least one electrical condition of pitch system 70 of wind turbine 10 (such as any of the electrical conditions described herein). As shown at (210), method 200 may include converting the (a plurality of) electrical conditions of pitch system 70 into the frequency domain. As shown at (212), method 200 may include determining whether the (a plurality of) electrical conditions in the frequency domain decrease by a predetermined amount around a frequency component associated with the natural frequency of (a plurality of) rotor blades 22, wherein the (a plurality of) electrical conditions decreasing by a predetermined amount around a frequency component associated with the natural frequency of (a plurality of) rotor blades 22 indicates an abnormal rotor blade, such as blade damage or blade icing. As shown at (214), method 200 may include implementing a control action when the (a plurality of) electrical conditions are outside a predetermined range.

[0049] Additional aspects of the present invention are provided by the subject matter of the following clauses:

[0050] Clause 1. A method for monitoring at least one rotor blade of a wind turbine, the method comprising:

[0051] Implementing, via a controller, a control scheme for monitoring blade damage of the at least one rotor blade, the control scheme comprising:

[0052] Monitoring at least one electrical condition of a pitch system of the wind turbine;

[0053] Converting the at least one electrical condition of the pitch system into the frequency domain;

[0054] Determining one or more peaks of the frequency domain around a frequency component associated with the natural frequency of the rotor blade;

[0055] Determining a frequency deviation between the one or more peaks of the frequency domain and the frequency component associated with the natural frequency of the rotor blade, wherein a frequency deviation outside a predetermined frequency range indicates an abnormal rotor blade; and

[0056] Implement a control action when the frequency deviation is outside the predetermined frequency range.

[0057] Clause 2. The method according to clause 1, further comprising monitoring at least one operating parameter of the wind turbine and implementing the control scheme only when the at least one operating parameter exceeds an operating threshold.

[0058] Clause 3. The method according to clause 2, wherein the at least one operating parameter comprises at least one of power output, wind speed, rotor speed, generator speed or generator torque.

[0059] Clause 4. The method according to any one of the preceding clauses, wherein the at least one electrical condition comprises at least one of pitch motor current, pitch motor voltage or pitch motor torque.

[0060] Clause 5. The method according to clause 4, wherein the pitch motor current comprises one or more of armature current for a DC motor or torque-related current component for an AC motor.

[0061] Clause 6. The method according to any one of the preceding clauses, further comprising measuring at least one environmental parameter at the wind turbine and determining whether ice accumulation is occurring on the rotor blade based on the at least one environmental parameter.

[0062] Clause 7. The method according to clause 6, wherein the at least one environmental parameter at the wind turbine comprises at least one of temperature, humidity, pressure, wind speed, wind direction, precipitation or a combination thereof.

[0063] Clause 8. The method according to clause 6, wherein a change in the natural frequency of the rotor blade reflects a change in blade stiffness or blade mass of the rotor blade, and wherein when ice accumulation is occurring on the rotor blade, the blade mass increases and the natural frequency of the rotor blade decreases, and wherein when the rotor blade is damaged, the blade stiffness decreases and the natural frequency of the rotor blade decreases.

[0064] Clause 9. The method according to any one of the preceding clauses, further comprising online monitoring of the at least one electrical condition of the pitch system of the wind turbine.

[0065] Clause 10. The method according to any one of the preceding clauses, further comprising:

[0066] Implementing the control scheme for a plurality of rotor blades of the wind turbine to determine a frequency deviation for each of the plurality of rotor blades; and

[0067] Implement the control action when one or more of the frequency deviations of the plurality of rotor blades are greater than a frequency threshold.

[0068] Clause 11. The method according to any one of the preceding clauses, wherein the control action further comprises generating an alarm, scheduling a maintenance action, pitching the rotor blade, shutting down the rotor blade, derating the wind turbine, ramping up the wind turbine, de-icing the rotor blade or replacing the rotor blade.

[0069] Clause 12. A wind turbine, comprising:

[0070] A tower;

[0071] A nacelle mounted on top of the tower;

[0072] A rotor comprising a rotatable hub and at least one rotor blade communicatively coupled to a pitch system; and

[0073] A controller configured to perform a plurality of operations for controlling the wind turbine, the plurality of operations comprising:

[0074] Implement a control scheme for monitoring blade damage of the at least one rotor blade, the control scheme comprising:

[0075] Monitoring at least one electrical condition of the pitch system;

[0076] Converting the at least one electrical condition of the pitch system into the frequency domain;

[0077] Determining one or more peaks in the frequency domain around a frequency component related to the natural frequency of the rotor blade;

[0078] Determining a frequency deviation between the one or more peaks in the frequency domain and the frequency component related to the natural frequency of the rotor blade, wherein a frequency deviation outside a predetermined frequency range indicates an abnormal rotor blade; and

[0079] Implementing a control action when the frequency deviation is outside the predetermined frequency range.

[0080] Clause 13. The wind turbine according to clause 12, wherein the plurality of operations further comprises monitoring at least one operating parameter of the wind turbine and implementing the control scheme only when the at least one operating parameter exceeds an operating threshold, the at least one operating parameter comprising at least one of power output, wind speed, rotor speed, generator speed or generator torque.

[0081] Clause 14. The wind turbine according to clauses 12 to 13, wherein the at least one electrical condition includes at least one of a pitch motor current, a pitch motor voltage, or a pitch motor torque, and wherein the pitch motor current includes one or more of an armature current for a DC motor or a torque-related current component for an AC motor.

[0082] Clause 15. The wind turbine according to clauses 12 to 14, further comprising at least one sensor for measuring at least one environmental parameter at the wind turbine, and the plurality of operations further comprising determining whether ice accumulation is occurring on the rotor blade based on the at least one environmental parameter.

[0083] Clause 16. The wind turbine according to clause 15, wherein the at least one environmental parameter at the wind turbine includes at least one of temperature, humidity, pressure, wind speed, wind direction, precipitation, or a combination thereof.

[0084] Clause 17. The wind turbine according to clause 15, wherein a change in the natural frequency of the rotor blade reflects a change in the blade stiffness or the blade mass of the rotor blade, and wherein when ice accumulation is occurring on the rotor blade, the blade mass increases and the natural frequency of the rotor blade decreases, and wherein when the rotor blade is damaged, the blade stiffness decreases and the natural frequency of the rotor blade decreases.

[0085] Clause 18. The wind turbine according to clauses 12 to 17, wherein the plurality of operations further comprises online monitoring of the at least one electrical condition of the pitch wind turbine of the rotor blade.

[0086] Clause 19. The wind turbine according to clauses 12 to 18, wherein the control actions further comprise generating an alarm, scheduling a maintenance action, pitching the rotor blade, closing the rotor blade, derating the wind turbine, ramping up the wind turbine, de-icing the rotor blade, or replacing the rotor blade.

[0087] Clause 20. A method for monitoring a rotor blade of a wind turbine, the method comprising:

[0088] Monitoring the power output of the wind turbine via a controller of the wind turbine;

[0089] When the power output is higher than a power threshold, implementing, via the controller, a control scheme for monitoring blade damage of the rotor blade, the control scheme comprising:

[0090] Monitoring at least one electrical condition of a pitch system of the wind turbine;

[0091] Convert the at least one electrical condition of the pitch system into the frequency domain;

[0092] Determine, via the controller, whether the at least one electrical condition in the frequency domain reduces a predetermined amount around a frequency component associated with the natural frequency of the rotor blade, wherein the reduction of the at least one electrical condition by the predetermined amount around the frequency component associated with the natural frequency of the rotor blade indicates an abnormality of the rotor blade; and

[0093] Implement a control action when the at least one electrical condition is outside the predetermined range.

[0094] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any incorporated method. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. If these other examples include structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that have insubstantial differences from the literal language of the claims, then these other examples are intended to be within the scope of the claims.

Claims

1. A method for monitoring at least one rotor blade of a wind turbine, the method comprising: Implement a control scheme for monitoring blade damage of the at least one rotor blade via a controller, the control scheme comprising: Monitoring the pitch motor current of the pitch system of the wind turbine; Converting the pitch motor current of the pitch system into the frequency domain; Monitoring local peaks of one or more blade natural frequency-related components in the frequency domain of the pitch motor current, the one or more blade natural frequency-related components including armature current for a DC motor or torque-related current components for an AC motor; Determining a natural frequency deviation by determining a difference between the local peak and a given natural frequency of the rotor blade, wherein a frequency deviation outside a predetermined frequency range indicates an abnormality of the rotor blade; and Implementing a control action when the frequency deviation is outside the predetermined frequency range.

2. The method according to claim 1, further comprising monitoring at least one operating parameter of the wind turbine and implementing the control scheme only when the at least one operating parameter exceeds an operating threshold.

3. The method according to claim 2, wherein, The at least one operating parameter includes at least one of power output, wind speed, rotor speed, generator speed, or generator torque.

4. The method according to claim 1, further comprising determining whether ice accumulation is occurring on the rotor blade based on one or more environmental parameters.

5. The method according to claim 4, wherein, One or more environmental parameters at the wind turbine include at least one of temperature, humidity, pressure, wind speed, wind direction, precipitation, or a combination thereof.

6. The method according to claim 1, further comprising: Implement the control scheme for a plurality of rotor blades of the wind turbine to determine a frequency deviation for each of the plurality of rotor blades; and Implement the control action when one or more of the frequency deviations of the plurality of rotor blades are greater than a frequency threshold.

7. The method according to claim 1, wherein, The control action further includes generating an alarm, scheduling a maintenance action, pitching the rotor blade, shutting down the rotor blade, derating the wind turbine, ramping up the wind turbine, de-icing the rotor blade, or replacing the rotor blade.

8. A wind turbine, comprising: Tower; Nacelle, which is mounted on top of the tower; Rotor, which includes a rotatable hub and at least one rotor blade communicatively coupled to a pitch system; and Controller, which is configured to perform a plurality of operations for controlling the wind turbine, the plurality of operations including: Implement a control scheme for monitoring blade damage of the at least one rotor blade, the control scheme comprising: Monitoring the pitch motor current of the pitch system; Converting the pitch motor current of the pitch system into the frequency domain; Monitoring local peaks of one or more blade natural frequency-related components in the frequency domain of the pitch motor current, the one or more blade natural frequency-related components including armature current for a DC motor or torque-related current components for an AC motor; Determining a natural frequency deviation by determining a difference between the local peak and a given natural frequency of the rotor blade, wherein a frequency deviation outside a predetermined frequency range indicates an abnormality of the rotor blade; and Implementing a control action when the frequency deviation is outside the predetermined frequency range.

9. The wind turbine according to claim 8, wherein, The plurality of operations further includes monitoring at least one operating parameter of the wind turbine and implementing the control scheme only when the at least one operating parameter exceeds an operating threshold, the at least one operating parameter includes at least one of power output, wind speed, rotor speed, generator speed, or generator torque.

10. The wind turbine according to claim 8, further comprising at least one sensor for measuring at least one environmental parameter, the plurality of operations further comprising determining whether ice accumulation is occurring on the rotor blade based on the at least one environmental parameter.

11. The wind turbine according to claim 10, wherein, The at least one environmental parameter includes at least one of temperature, humidity, pressure, wind speed, wind direction, precipitation, or a combination thereof.

12. The wind turbine according to claim 8, wherein, The control actions further include generating an alarm, scheduling maintenance actions, pitching the rotor blade, closing the rotor blade, derating the wind turbine, ramping up the wind turbine, de-icing the rotor blade, or replacing the rotor blade.

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