FIELD OF THE INVENTION
The present disclosure relates generally to wind turbines, and more particularly to
systems and methods for optimizing power output in knee region of wind turbine
operation.
BACKGROUND OF THE INVENTION
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 a rotor including one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles and transmit the kinetic energy through rotational energy 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.
In conventional wind turbines, the turbine controller attempts to regulate the power output to not exceed the rated power on a time scale of seconds or faster. Although some turbine components are limited by the short-term power/torque increase, many components are also sized based on long-term average power, e.g. on a time scale of minutes to hours. Limits on grid interconnectivity, Balance of Plant (BOP), etc. are usually long-term limits either on the individual wind turbine or at the wind farm level. Therefore, the power output of the wind turbine may be unnecessarily limited during short periods of turbulent wind where the turbine frequently crosses between below rated and at/above rated operation which typically occurs when wind speeds are near the knee region of the power curve. Accordingly, the present disclosure is directed to systems and methods for optimizing power output in the knee region of wind turbine operation so address the aforementioned issues.
BRIEF DESCRIPTION OF THE INVENTION
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.
In one aspect, the present disclosure is directed to a method for optimizing power output of a wind turbine. The method includes operating, via a controller, the wind turbine based on a power curve having an initial power level configured to generate a rated power. The method also includes monitoring, via the controller, the power output of the wind turbine. Immediately after the power output increases from below the rated power to above the rated power in a knee region of the power curve, the method includes temporarily adjusting, via the controller, the initial power level of the wind turbine to a modified power level for a short-term duration so as to optimize an average power of the wind turbine in turbulent wind near rated wind speeds.
In one embodiment, the method may also include temporarily adjusting at least one of a power set point, a torque set point, or a speed set point of the wind turbine immediately after the power output increases from below the rated power to above the rated power in the knee region of the power curve. In another embodiment, the step of temporarily adjusting the initial power level of the wind turbine to the modified power level may include increasing the initial power level of the wind turbine to an increased power level specified by short-term constraints of the wind turbine. In such embodiments, after temporarily increasing the initial power level to the increased power level, the method may include decreasing the increased power level back to the initial power level over a specified short-term duration. In several embodiments, the increased power level may be greater than a name plate setting of at least one turbine component of the wind turbine.
In alternative embodiments, the step of temporarily adjusting the initial power level of the wind turbine to the modified power level may include decreasing the initial power level of the wind turbine to a decreased power level. In further embodiments, the method may include determining the short-term duration and/or an amplitude of the modified power level based on an amount of time the wind turbine operated below the rated power and/or the power output

prior to reaching the rated power. In additional embodiments, the method may include monitoring, via a long-term power boost monitoring device of the controller, the average power to ensure the average power does not violate the rated power long-term.
In another aspect, the present disclosure is directed to a system for optimizing power output of a wind turbine. The system includes a turbine controller having one or more processors configured to perform one or more operations, including but not limited to operating the wind turbine based on a power curve having an initial power level configured to generate a rated power, monitoring the power output of the wind turbine, and immediately after the power output increases from below the rated power to above the rated power in a knee region of the power curve, temporarily adjusting the initial power level of the wind turbine to a modified power level for a short-term duration so as to optimize an average power of the wind turbine in turbulent wind near rated wind speeds. It should be understood that the system may further include any of the additional features described herein.
In yet another aspect, the present disclosure is directed to a wind turbine. The wind turbine includes a tower, a nacelle mounted on the tower, a rotor coupled to the nacelle and having a rotatable hub with a plurality of rotor blades mounted thereto, and a turbine controller having at least one processor configured to perform one or more operations. The one or more operations include but are not limited to operating the wind turbine based on a power curve having an initial power level configured to generate a rated power, monitoring the power output of the wind turbine, and immediately after the power output increases from below the rated power to above the rated power in a knee region of the power curve, temporarily adjusting the initial power level of the wind turbine to a modified power level for a short-term duration so as to optimize an average power of the wind turbine in turbulent wind near rated wind speeds. It should be understood that the wind turbine may further include any of the additional features described herein. 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 OF THE INVENTION
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:
FIG. 1 illustrates a perspective view of one embodiment of a wind turbine
according to the present disclosure;
FIG. 2 illustrates a perspective, internal view of one embodiment of a nacelle of a
wind turbine according to the present disclosure;
FIG. 3 illustrates a schematic diagram of one embodiment of suitable components
that may be included within a controller of a wind turbine according to the present
disclosure;
FIG. 4 illustrates a graph of one embodiment of a power curve according to the
present disclosure, particularly illustrating the knee region of the power curve;
FIG. 5 illustrates a simplified graph of one embodiment of a power curve
according to the present disclosure, particularly illustrating the short-term boost
and curtailment in power; and
FIG. 6 illustrates a flow diagram of one embodiment of a method for optimizing
power output of a wind turbine according to the present disclosure.
DETAILED DESCRIPTION
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 or spirit 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.
Referring now to the drawings, FIG. 1 illustrates a 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 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. 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, the 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 rotor shaft 40 coupled to the hub 20 for rotation therewith. The generator 24 may then be coupled to the rotor shaft 40 such that rotation of the rotor shaft 40 drives the generator 24. For instance, in the illustrated embodiment, the generator 24 includes a generator shaft 42 rotatably coupled to the rotor 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 rotor shaft 40. Alternatively, the generator 24 may be directly rotatably coupled to the rotor shaft 40 (often referred to as a “direct-drive wind turbine”). It should be appreciated that the rotor 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 rotor shaft 40 may be supported by the bedplate 46 via a pair of pillow blocks 48, 50 mounted to the bedplate 46. Additionally, as shown, the wind turbine 10 may also include a turbine control system or a turbine controller 26 located within the nacelle 16. For example, as shown in the illustrated embodiment, 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. Moreover, as described herein, the turbine controller 26 may also be communicatively coupled to various components of the wind turbine 10 for generally controlling the wind turbine and/or such components, as well as the various operating modes (e.g., start-up or shut-down sequences) of the wind turbine 10.
In addition, as shown, the rotor blades 22 may be rotatably mounted to the hub 20 by one or more pitch bearing(s) (not illustrated) such that the pitch angle may be adjusted by rotating the rotor blades 22 about their pitch axes 34 using the pitch adjustment mechanisms 32. Further, as the direction 28 (FIG. 1) of the wind changes, the turbine controller 26 may be configured to control a yaw direction of the nacelle 16 about a yaw axis 36 to position the rotor blades 22 with respect to the direction 28 of the wind, thereby controlling the loads acting on the wind turbine 10. For example, the turbine controller 26 may be configured to transmit control signals/commands to a yaw drive mechanism 38 (FIG. 2) of the wind turbine 10 such that the nacelle 16 may be rotated about the yaw axis 30. It should be appreciated that the turbine controller 26 may generally include a computer or any other suitable processing unit. Thus, in several embodiments, the turbine controller 26 may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions, as shown in FIG. 3 and discussed herein. 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 of the turbine controller 26 may generally include memory element(s) including, but are 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) 62 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 60, configure the controller 26 to perform various computer-implemented functions including, but not limited to, performing proportional integral derivative (“PID”) control algorithms, including various calculations within one or more PID control loops, and various other suitable computer-implemented functions.
In addition, the turbine controller 26 may also include various input/output channels for receiving inputs from sensors 70, 72, 74 and/or other measurement devices and for sending control signals to various components of the wind turbine 10. For example, example sensors 70, 72, 74 may include wind sensors 70, rotor sensors 72, and/or generator sensors 74. In several embodiments, the sensors 70, 72, 74 may include, for example, Light Detection and Ranging (“LIDAR”) devices, Sonic Detection and Ranging (“SODAR”) devices, anemometers, wind vanes, barometers, and radar devices (such as Doppler radar devices). The present disclosure is further directed to systems and methods for optimizing power output in the knee region of wind turbine operation. In particular, the controller 26 may be utilized to perform such methods. Thus, as shown in FIG. 3, there is illustrated a block diagram of one embodiment of suitable components that may be included within the turbine controller 26 in accordance with aspects of the present subject matter. As shown, the controller 26 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 disclosed herein). Additionally, the controller 26 may

also include a communications module 64 to facilitate communications between the controller 26 and the various components of the wind turbine 10. For instance, the communications module 64 may serve as an interface to permit the turbine controller 26 to transmit control signals to each pitch adjustment mechanism 32 for controlling the pitch angle of the rotor blades 22. Moreover, the communications module 64 may include a sensor interface 66 (e.g., one or more analog-to-digital converters) to permit input signals transmitted from, for example, various sensor, to be converted into signals that can be understood and processed by the processor(s) 60.
Referring now to FIG. 4, one embodiment of a power curve 150 that can be used by the controller 26 to control operation of the wind turbine 10 according to the present disclosure is illustrated. As shown, at low wind speeds, there is insufficient torque exerted by the wind on the rotor blades 22 to make the blades rotate. However, as the wind speed increases, the wind turbine 10 will begin to rotate and generate electrical power. The speed at which the wind turbine 10 first starts to rotate and generate power is called the cut-in wind speed 152. In certain embodiments, the cut-in wind speed 152 may range from about 3 to about 4 meters per second.
As the wind speed rises above the cut-in wind speed 152, the level of electrical output power rises rapidly as shown. However, typically somewhere between about 12 to about 17 meters per second, the power output reaches the limit that the electrical generator is capable of, i.e. the power output reaches the nameplate rating of the generator. This limit to the generator output is generally referred to as the rated power 154. The rated power of a wind turbine is defined as the maximum continuous electrical power output which a wind turbine is designed to achieve under normal operation and external conditions. The wind speed at which rated power is reached is generally referred to as the rated output wind speed 156. In addition, as shown, the region of the power curve 150 in which the power output increases from below the rated power 154 to above the rated power 154 in commonly referred to as a knee region 158 of the power curve 150. At higher wind speeds, the wind turbine 10 is designed to limit the power to this maximum

level (i.e. the rated power) such that no further increase in the power output is achieved. Adjusting the power output can be achieved via a variety of methods including, for example, by adjusting the blade angles and increasing or decreasing the generator speed.
Still referring to FIG. 4, as the wind speed continues to increase above the rated speed 154, the forces on the wind turbine 10 continue to rise and, at some point, there is a risk of damage to the rotor 18. As a result, a braking system (not shown) may be employed to bring the rotor 18 to a standstill. This action is also commonly referred to as the cut-out wind speed 160 and is usually around 25 meters per second.
Referring now to FIG. 5, a simplified graph of one embodiment of a baseline power output 250 compared to a boosted power output 252 according to the present disclosure is illustrated. As shown, the power curve 250 represents the baseline power tracking behavior, whereas power curve 252 represents the power boost after the wind turbine 10 spends time below rated power and curtailment, i.e. if there is risk of the long-term average (e.g. a 10-minute average) exceeding the nameplate rating of the wind turbine 10. Thus, as shown, below the rated power, the short-term power is below the nameplate rating. Above the rated power, the short-term power is at or above the nameplate rating. Thus, referring now to FIG. 6, a flow diagram of one embodiment of a method 100 for optimizing power output of a wind turbine in the knee region 158 of the power curve 150 that can be implemented by the turbine controller 26 is illustrated. In general, the method 100 will be described herein with reference to the wind turbine 10, the turbine controller 26, and the power curve 150 shown in FIGS. 1-5. However, it should be appreciated that the disclosed method 100 may be implemented with wind turbines having any other suitable configurations. In addition, although FIG. 6 depicts steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and/or adapted in various

ways without deviating from the scope of the present disclosure. As shown at (102), the method 100 includes operating the wind turbine 10 based on the power curve 150 having an initial power level configured to generate a rated power (e.g. rated power 154). As shown at (104), the method 100 includes monitoring the power output of the wind turbine 10. Immediately after the power output increases from below the rated power to above the rated power in the knee region 156 of the power curve 150, as shown at (106), the method 100 includes temporarily adjusting the initial power level of the wind turbine 10 to a modified power level for a short-term duration so as to optimize an average power of the wind turbine 10 (e.g. in 10-minute time series) in turbulent wind near rated wind speeds. In one embodiment, the controller 26 may determine and set the short-term duration based on an amount of time the wind turbine 10 operates below the rated power. As such, the short-term duration may be adjusted to optimize the average power of the wind turbine 10. In addition, the method 100 may also include temporarily adjusting a torque set point and/or a speed set point of the wind turbine 10 immediately after the power output increases from below the rated power to above the rated power in the knee region 156 of the power curve 150.
For example, in one embodiment, the controller 26 may be configured to adjust the initial power level of the wind turbine 10 to the modified power level by increasing the initial power level of the wind turbine 10 to an increased power level specified by short-term constraints of the wind turbine 10. In such embodiments, after temporarily increasing the initial power level to the increased power level, the method 100 may include decreasing the increased power level back to the initial power level over a specified short-term duration. In several embodiments, the increased power level may be greater than a name plate setting of at least one turbine component of the wind turbine 10. In addition, if needed, the controller 26 may also be configured to temporarily adjust the initial power level of the wind turbine to the modified power level by decreasing or curtailing the initial power level of the wind turbine 10 to a decreased power level. In additional embodiments, the controller 26 may also include a long-term power

boost monitoring device, e.g. programmed in the processor(s) 60 thereof, which is configured to ensure that the average power stays within limits does not violate the rated power long-term.
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.

We claim:
1. A method for optimizing power output of a wind turbine, the
method comprising:
operating, via a controller, the wind turbine based on a power curve having an initial power level configured to generate a rated power;
monitoring, via the controller, the power output of the wind turbine; and, immediately after the power output increases from below the rated power to a value at or above the rated power in a knee region of the power curve, temporarily adjusting, via the controller, the initial power level of the wind turbine to a modified power level for a short-term duration so as to optimize an average power of the wind turbine in turbulent wind near rated wind speeds.
2. The method as claimed in claim 1, further comprising temporarily adjusting at least one of a power set point, a torque set point, or a speed set point of the wind turbine immediately after the power output increases from below the rated power to above the rated power in the knee region of the power curve.
3. The method as claimed in claim 1, wherein temporarily adjusting the initial power level of the wind turbine to the modified power level further comprising increasing the initial power level of the wind turbine to an increased power level specified by short-term constraints of the wind turbine.
4. The method as claimed in claim 3, further comprising, after temporarily increasing the initial power level to the increased power level, decreasing the increased power level back to the initial power level over a specified short-term duration.
5. The method as claimed in claim 3, wherein the increased power level is greater than a name plate setting of at least one turbine component of the wind turbine.
6. The method as claimed in claim 1, wherein temporarily adjusting the initial power level of the wind turbine to the modified power level further comprising decreasing the initial power level of the wind turbine to a decreased power level.
7. The method as claimed in claim 1, further comprising determining

the short-term duration and/or an amplitude of the modified power level based on an amount of time the wind turbine operated below the rated power and/or the power output prior to reaching the rated power.
8. The method as claimed in claim 1, further comprising monitoring, via a long-term power boost monitoring device of the controller, the average power to ensure the average power does not violate the rated power long-term.
9. A system for optimizing power output of a wind turbine, the system comprising:
a turbine controller comprising one or more processors configured to perform one or more operations, the one or more operations comprising:
operating the wind turbine based on a power curve having an initial power level configured to generate a rated power;
monitoring the power output of the wind turbine; and, immediately after the power output increases from below the rated power to above the rated power in a knee region of the power curve, temporarily adjusting the initial power level of the wind turbine to a modified power level for a short-term duration so as to optimize an average power of the wind turbine in turbulent wind near rated wind speeds.
10. The system as claimed in claim 9, wherein the one or more operations further comprise temporarily adjusting a power set point, a torque set point, or a speed set point of the wind turbine immediately after the power output increases from below the rated power to above the rated power in the knee region of the power curve.
11. The system as claimed in claim 9, wherein temporarily adjusting the initial power level of the wind turbine to the modified power level further comprising increasing the initial power level of the wind turbine to an increased power level specified by short-term constraints of the wind turbine.
12. The system as claimed in claim 11, wherein the one or more operations further comprise, after temporarily increasing the initial power level to the increased power level, decreasing the increased power level back to the initial

power level over a specified short-term duration.
13. The system as claimed in claim 11, wherein the increased power level is greater than a name plate setting of at least one turbine component of the wind turbine.
14. The system as claimed in claim 9, wherein temporarily adjusting the initial power level of the wind turbine to the modified power level further comprising decreasing the initial power level of the wind turbine to a decreased power level.
15. The system as claimed in claim 9, further comprising determining the short-term duration and/or an amplitude of the modified power level based on an amount of time the wind turbine operated below the rated power and/or the power output prior to reaching the rated power.
16. The system as claimed in claim 9, wherein the one or more operations further comprise monitoring, via a long-term power boost monitoring device of the controller, the average power to ensure the average power does not violate the rated power long-term.
17. A wind turbine, comprising:
a tower;
a nacelle mounted on the tower;
a rotor coupled to the nacelle, the rotor comprising a rotatable hub having a plurality of rotor blades mounted thereto; and
a turbine controller comprising at least one processor configured to perform one or more operations, the one or more operations comprising:
operating the wind turbine based on a power curve having an initial power level configured to generate a rated power;
monitoring the power output of the wind turbine; and, immediately after the power output increases from below the rated power to above the rated power in a knee region of the power curve, temporarily adjusting the initial power level of the wind turbine to a modified power level for a short-term duration so as to optimize an average power of the wind turbine in turbulent wind near rated wind

speeds.
18. The wind turbine as claimed in claim 17, wherein the one or more operations further comprise temporarily adjusting a power set point, a torque set point, or a speed set point of the wind turbine immediately after the power output increases from below the rated power to above the rated power in the knee region of the power curve.
19. The wind turbine as claimed in claim 17, wherein temporarily adjusting the initial power level of the wind turbine to the modified power level further comprising increasing the initial power level of the wind turbine to an increased power level specified by short-term constraints of the wind turbine.
20. The wind turbine as claimed in claim 19, wherein the one or more operations further comprise, after temporarily increasing the initial power level to the increased power level, decreasing the increased power level back to the initial power level over a specified short-term duration.