System and method for controlling a wind turbine based on a collective pitch offset

Abstract

A system and method are provided for controlling a wind turbine based on a collective pitch offset. Accordingly, a wind condition acting on a rotor of the wind turbine is determined, and a first collective pitch angle for a plurality of rotor blades is set, and the wind turbine is operated. A thrust of the rotor is determined based at least in part on the wind condition, and an actual collective pitch angle is calculated. A collective pitch offset is determined based on a difference between the first collective pitch angle and the actual collective pitch angle. The collective pitch offset is integrated with at least one pitch set point command. The at least one pitch set point command is transmitted to a pitch control mechanism of the wind turbine.

Description

Technical Field

[0001] The present disclosure relates generally to wind turbines, and more particularly to systems and methods for controlling wind turbines based on a collective pitch offset. Background Art

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

[0003] During operation, the speed of the wind that powers the wind turbine may change. Therefore, the wind turbine may adjust the pitch of individual rotor blades about a pitch axis, for example, by a pitch adjustment mechanism. During normal operation, the pitch adjustment mechanism receives pitch commands from a turbine controller. For wind speeds below a rated threshold of the wind turbine, the turbine controller may calculate the desired pitch of the individual rotor blades in order to maximize the power generated at a given wind speed. For wind speeds above the rated threshold of the wind turbine, the turbine controller may calculate the desired pitch of the individual rotor blades in order to reduce thrust generation below a specified design limit.

[0004] In order to ensure accurate calculation of the pitch command, the pitch of the individual rotor blades must be zeroed. One method of zeroing the rotor blades is by establishing a blade zero pitch position based on a mechanical reference at the blade root. However, this method is expensive, and experience has shown that the accuracy of the mechanical reference may not be suitable to ensure a true zero pitch position. In addition, the rotor blades may be manufactured with aerodynamic twist, which may also deviate from the nominal design value. Thus, there may be a difference between the pitch angle sensed by the turbine controller and the actual or effective pitch angle of any individual rotor blade.

[0005] Thus, the turbine controller may combine the sensed pitch angles for the rotor blades into a collective pitch angle for the rotor and utilize the collective pitch angle to calculate a pitch command. However, because there may be a difference or offset between the actual and sensed collective pitch angles, the resulting pitch command may cause the wind turbine to operate in a suboptimal configuration for a given wind speed.

[0006] Accordingly, the art is continually seeking new and improved systems and methods that address the foregoing problems.Accordingly, the present disclosure is directed to systems and methods for controlling wind turbines based on a collective pitch offset. Summary of the invention

[0007] 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.

[0008] In one aspect, the present disclosure is directed to a method for controlling a wind turbine based on a collective pitch offset. The method may include determining a wind condition at a wind turbine via a controller. The method may also include setting a first collective pitch angle for a plurality of rotor blades mounted to a rotatable hub of a rotor of the wind turbine. The method may include operating a wind turbine with a plurality of rotor blades at a first collective pitch angle. In addition, the method may include determining a thrust of the rotor via a controller at least partially based on the wind condition. The method may also include calculating an actual collective pitch angle for a plurality of rotor blades via a controller at least partially based on the thrust. In addition, the method may include determining a collective pitch offset via a controller based on a difference between the first collective pitch angle and the actual collective pitch angle. In addition, the method may include integrating the collective pitch offset with at least one pitch set point command. Moreover, the method may also include transmitting the integrated pitch set point command to a pitch control mechanism of the wind turbine via a controller.

[0009] In an embodiment, determining the thrust of the rotor may include measuring at least one of a bending strain of the tower or a deflection of the tower via one or more sensors. The determining may also include calculating the thrust from at least one of the bending strain or the deflection.

[0010] In an embodiment, calculating the actual collective pitch angle may include calculating a thrust coefficient based on the thrust of the rotor. The calculation may also include calculating a terminal speed ratio for the rotor under wind conditions, and deriving the actual collective pitch angle for the thrust coefficient at the terminal speed ratio based on an aerodynamic performance map of the rotor. In additional embodiments, the method may also include calculating a pitch set point command that optimizes the thrust or power coefficient under wind conditions, wherein the wind conditions may be less than a threshold.

[0011] In an embodiment, determining the collective pitch offset is performed at least one of constantly, at predetermined intervals, or in response to a specified sensor input.

[0012] In an embodiment, the collective pitch offset is determined after at least one of blade installation or pitch control mechanism installation.The method may further comprise integrating pitch control mechanism feedback with the collective pitch offset in order to calibrate the controller.

[0013] In further embodiments, the method may include performing a system check with the controller to check for a pitch system fault. The method may include ignoring the collective pitch excursion when the pitch system fault is detected. Additionally, the method may include generating at least one of a maintenance signal or a turbine shutdown signal when the pitch system fault is detected.

[0014] In an embodiment, the controller may include at least one of a turbine controller or a separate controller module communicatively coupled to the turbine controller.In further embodiments, the method may include comparing the collective pitch excursion to a collective pitch excursion limit, and generating an output signal to trigger a maintenance event when the collective pitch excursion limit is exceeded.

[0015] In additional embodiments, the method may further include calculating a pitch setpoint command that limits thrust production in wind conditions, where the wind conditions may be greater than a threshold value.

[0016] In another aspect, the present disclosure is directed to a system for controlling a wind turbine. The system may include a pitch system for establishing a first collective pitch angle for a plurality of rotor blades mounted to a rotatable hub of a rotor of the wind turbine. The pitch system may also include a pitch controller. The system may also include at least one first sensor configured to monitor wind conditions at the wind turbine, and at least one second sensor for monitoring a load condition of the wind turbine. In addition, the system may include a turbine controller communicatively coupled to the first sensor and the second sensor and the pitch controller. The controller may include at least one processor configured to perform a plurality of operations. The plurality of operations may include, for example, setting a first collective pitch angle for a plurality of rotor blades. The plurality of operations may also include determining a thrust of the rotor based at least in part on the wind conditions. The plurality of operations may also include calculating an actual collective pitch angle for a plurality of rotor blades based at least in part on the thrust. In addition, the plurality of operations may include determining a collective pitch offset based on a difference between the first collective pitch angle and the actual collective pitch angle. The plurality of operations may also include integrating the collective pitch offset with a pitch set point command. Additionally, the plurality of operations may include transmitting the integrated pitch set point command to a pitch control mechanism of the wind turbine.It should be understood that the system may also include any of the additional steps and / or features described herein.

[0017] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] A full and complete disclosure of the invention including the best mode thereof to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0019] Figure 1 A perspective view showing one embodiment of a wind turbine according to the present disclosure;

[0020] Figure 2 showing a perspective interior view of a nacelle of a wind turbine according to one embodiment of the present disclosure;

[0021] Figure 3 A schematic diagram showing one embodiment of a system for controlling a wind turbine according to the present disclosure;

[0022] Figure 4 A schematic diagram illustrating another embodiment of a system for controlling a wind turbine, particularly illustrating a controller communicatively coupled to a turbine controller according to the present disclosure;

[0023] Figure 5 shows one embodiment of an aerodynamic performance diagram, in particular showing an optimum set point curve for a rotor of a wind turbine as a function of the tip speed ratio and the collective pitch angle overlaid with a thrust coefficient diagram according to the present disclosure;

[0024] Figure 6 shows one embodiment of an aerodynamic performance diagram, in particular showing an optimum set point curve for a rotor of a wind turbine as a function of the tip speed ratio and the collective pitch angle overlaid with a power coefficient diagram according to the present disclosure;

[0025] Figure 7 a graph showing one embodiment of wind turbine power output (y-axis) versus wind speed (x-axis), particularly showing wind speed thresholds according to the present disclosure; and

[0026] Figure 8 A flow chart showing one embodiment of a method for controlling a wind turbine based on a collective pitch offset according to the present disclosure.

[0027] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. DETAILED DESCRIPTION

[0028] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are shown in the drawings. Each example is provided as an explanation of the present invention, not a limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, the features shown or described as part of an embodiment may be used with another embodiment to produce further embodiments. Therefore, it is intended that the present invention includes such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0029] As used herein, the terms “first,” “second,” and “third” are used interchangeably to distinguish one component from another and are not intended to indicate the position or importance of individual components.

[0030] Unless otherwise specified herein, the terms "coupled," "fixed," "attached to," and the like refer to both direct coupling, fixing, or attachment as well as indirect coupling, fixing, or attachment through one or more intermediate members or features.

[0031] As used herein throughout the specification and claims, approximating language is used to modify any quantitative representation that is permissibly variable without resulting in a change in the basic function to which it relates. Thus, a value modified by one or more terms such as "about," "approximately," and "substantially" is not limited to the precise value specified. In at least some cases, approximate language may correspond to the precision of an instrument used to measure a value, or the precision of a method or machine used to construct or manufacture a component and / or system. For example, approximate language may refer to within a 10 percent margin.

[0032] Here and throughout the specification and claims, range limitations are combined and interchangeable, and such ranges are identified and include all subranges contained therein (unless context or language indicates otherwise). For example, all ranges disclosed herein include the endpoints, and the endpoints are independently combinable with each other.

[0033] In general, the present disclosure is directed to systems and methods for controlling a wind turbine based on a collective pitch offset. In particular, the present disclosure may include systems and methods that may facilitate detecting a difference between a perceived collective pitch of a rotor of a wind turbine and an actual collective pitch of the rotor of the wind turbine based in part on thrust generated from the rotor. The collective pitch offset may be calculated by a control system of the wind turbine or introduced into a control system of the wind turbine to account for the difference between the perceived collective pitch of the rotor and the actual collective pitch. Utilizing the collective pitch offset may facilitate a wind turbine controller to operate the wind turbine at a maximum efficiency point for a given wind speed. Utilizing the collective pitch offset may also facilitate safe operation of the wind turbine whenever the wind speed exceeds a rated wind speed for the turbine.

[0034] Now refer to the figure, Figure 1A perspective view of one embodiment of a wind turbine 100 according to the present disclosure is shown. As shown, wind turbine 100 generally includes a tower 102 extending from a support surface 104, a nacelle 106 mounted on tower 102 including a housing 160, and a rotor 108 coupled to nacelle 106. Rotor 108 includes a rotatable hub 110 and at least one rotor blade 112 coupled to hub 110 and extending outwardly from hub 110. For example, in the illustrated embodiment, rotor 108 includes three rotor blades 112. However, in alternative embodiments, rotor 108 may include more or less than three rotor blades 112. Each rotor blade 112 may be spaced about hub 110 to facilitate rotating rotor 108 so that kinetic energy can be converted from the wind into usable mechanical energy and subsequently into electrical energy. For example, hub 110 may be rotatably coupled to a generator 118 ( Figure 2 ), to allow the generation of electrical energy.

[0035] Wind turbine 100 may also include controller 202 ( Figure 3 ). In an embodiment, the controller 202 may be a wind turbine controller 204 centralized within the nacelle 106. However, in other embodiments, the controller 202 may be located within any other component of the wind turbine 100 or at a location outside the wind turbine. In addition, the controller 202 may be communicatively coupled to any number of components of the wind turbine 100 in order to control the components. Thus, the controller 202 may include a computer or other suitable processing unit. Therefore, in several embodiments, the controller 202 may include suitable computer-readable instructions that, when implemented, configure the controller 202 to perform a variety of different functions, such as receiving, transmitting and / or executing wind turbine control signals.

[0036] Now refer to Figure 2 , showing Figure 1 106 of a wind turbine 100. As shown, a generator 118 may be coupled to the rotor 108 for generating electrical power from the rotational energy generated by the rotor 108. For example, as shown in the illustrated embodiment, the rotor 108 may include a rotor shaft 122 coupled to the hub 110 for rotation therewith. The rotor shaft 122 may be rotatably supported by a main bearing 144. The rotor shaft 122 may in turn be rotatably coupled to a generator shaft 124 of the generator 118 through a gearbox 126, which is connected to a base support frame 136 through one or more torque arms 142. As generally understood, the rotor shaft 122 may provide a low-speed, high-torque input to the gearbox 126 in response to the rotation of the rotor blades 112 and the hub 110. The gearbox 126 may then be configured to convert the low-speed, high-torque input into a high-speed, low-torque output to drive the generator shaft 124 and thus the generator 118.

[0037] Each rotor blade 112 may also include a pitch control mechanism 120 configured to rotate each rotor blade 112 about its pitch axis 116. The pitch control mechanism 120 may include a pitch controller 150 configured to receive at least one pitch set point command from the controller 202. In addition, each pitch control mechanism 120 may include a pitch drive motor 128 (e.g., any suitable electric, hydraulic, or pneumatic motor), a pitch drive gearbox 130, and a pitch drive pinion 132. In such embodiments, the pitch drive motor 128 may be coupled to the pitch drive gearbox 130 such that the pitch drive motor 128 imparts mechanical force to the pitch drive gearbox 130. Similarly, the pitch drive gearbox 130 may be coupled to the pitch drive pinion 132 for rotation therewith. The pitch drive pinion 132 may in turn rotationally engage a pitch bearing 134 coupled between the hub 110 and the corresponding rotor blade 112, such that rotation of the pitch drive pinion 132 causes rotation of the pitch bearing 134. Thus, in such embodiments, rotation of the pitch drive motor 128 drives the pitch drive gearbox 130 and the pitch drive pinion 132, thereby rotating the pitch bearing 134 and the rotor blade(s) 112 about the pitch axis 116. Similarly, the wind turbine 100 may include one or more yaw drive mechanisms 138 communicatively coupled to the controller 202, wherein each yaw drive mechanism 138 is configured to change the angle of the nacelle 106 relative to the wind (e.g., by engaging a yaw bearing 140 of the wind turbine 100).

[0038] Rotation of each rotor blade 112 about its pitch axis 116 by its respective pitch control mechanism 120 may establish a pitch angle for each of the rotor blades 112. In an embodiment, the pitch angle may be an angular deviation from a zero pitch position. For example, the zero pitch position may be established during blade installation by a mechanical reference at a protrusion or blade root that relies on triggering a limit switch to automate the calibration process. The controller 202 may track the pitch angle of the rotor blade(s) 112 based on the accumulated deviation from the zero pitch position. Thus, the controller 202 may transmit a pitch set point command(s) to the pitch control mechanism 120, instructing the rotor blade(s) 112 to rotate by a specified number of degrees relative to the perceived pitch angle of the rotor blade(s) 112 (as interpreted by a motor mounted encoder).

[0039] In an embodiment, the sensed pitch angle of each of rotor blades 112 may be combined to produce a first collective pitch angle of rotor 108. For example, if controller 202 senses that each of rotor blades 112 is pitched 5 degrees from a zero pitch position, the first collective pitch angle of rotor 108 will be 5 degrees. Thus, controller 202 may set the first collective pitch angle for multiple rotor blades 112 by transmitting pitch setpoint command(s) to pitch control mechanism 120 instructing each of rotor blades 112 to rotate a specified number of degrees.

[0040] Still refer to Figure 2 , one or more sensors 214, 216, 218 may be provided on the wind turbine 100 to monitor the performance of the wind turbine 100 and / or environmental conditions affecting the wind turbine 100. It should also be appreciated that, as used herein, the term "monitoring" and variations thereof indicate that the various sensors of the wind turbine 100 may be configured to provide direct measurements of monitored parameters or indirect measurements of such parameters. Thus, the sensors described herein may, for example, be used to generate signals related to the monitored parameters, which signals may then be used by the controller 202 to determine conditions.

[0041] Now refer to Figure 3 and Figure 4 , presents a schematic diagram of multiple embodiments of a system 200 for controlling a wind turbine 100 according to the present disclosure. As shown, in accordance with the present disclosure, suitable components may be included within a controller 202. As shown, the controller 202 may include one or more processors 206 and associated (one or more) memory devices 208, which are configured to perform a variety of computer-implemented functions (e.g., perform methods, steps, calculations, etc., and store relevant data as disclosed herein). In addition, the controller 202 may also include a communication module 210 to facilitate communication between the controller 202 and various components of the wind turbine 100. Moreover, the communication module 210 may include a sensor interface 212 (e.g., one or more analog-to-digital converters) to allow signals transmitted from one or more sensors 214, 216, 218 to be converted into signals that can be understood and processed by the processor 206. It should be appreciated that the sensors 214, 216, 218 may be communicatively coupled to the communication module 210 using any suitable means. For example, as Figure 3 As shown in FIG. 2 , the sensors 214, 216, 218 are coupled to the sensor interface 212 via a wired connection. However, in other embodiments, the sensors 214, 216, 218 may be coupled to the sensor interface 212 via a wireless connection (such as by using any suitable wireless communication protocol known in the art).

[0042] As used herein, the term "processor" refers not only to integrated circuits that are considered in the art to be included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. In addition, the memory device(s) 208 may generally include memory elements including, but not limited to, computer readable media (e.g., random access memory (RAM)), computer readable non-volatile media (e.g., flash memory), floppy disks, compact disk-read only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements. Such memory device(s) 208 may generally be configured to store suitable computer readable instructions that, when executed by the processor(s) 206, configure the controller 202 to perform various functions including, but not limited to, calculating a collective pitch offset, and using the collective pitch offset in the control of the turbine 100 as described herein, and various other suitable computer-implemented functions.

[0043] like Figure 1-4 1 , the system 200 may include at least one first sensor 214 configured to monitor wind conditions at the wind turbine or acting on the rotor 108. The first sensor(s) 214 may be, for example, a wind vane, anemometer, lidar sensor, or other suitable sensor. The wind conditions may include and the first sensor(s) 214 may be configured to measure wind speed, wind direction, wind shear, gusts, and / or wind turn. In at least one embodiment, the first sensor(s) 214 may be mounted to the nacelle 106 at a downwind position of the rotor 108. In an alternative embodiment, the first sensor(s) 214 may be coupled to the rotor 108 or integrated with the rotor 108. It should be appreciated that the first sensor(s) 214 may include a network of sensors and may be located remote from the wind turbine 100.

[0044] In an embodiment, the system 200 may include at least one second sensor 216 configured to monitor a load condition of the wind turbine 100. For example, Figure 1 As shown in FIG. 1 , a load condition may be a thrust (R ) developed by rotor 108 in response to wind conditions acting thereon. T For example, in an embodiment, the controller 202 may calculate the thrust (R ) based on a signal related to blade root strain received from (one or more) second sensors 216 coupled to the rotor 108 . T ).

[0045] In embodiments where it may be desirable to monitor thrust (R) without employing sensing techniques involving rotor 108 T )), the second sensor(s) 216 may measure the motion of the tower 102. In such cases, the measurement of the motion or deflection of the tower 102 may be used as an acceptable substitute for the thrust measurement made at the rotor 108. For example, the second sensor(s) 216 may be a tower base strain sensor coupled to the tower 102 and measuring its bending moment. The controller 202 may be configured to convert the measurement of the tower strain at one or more locations into thrust (R) for a given wind speed. T Controller 202 may integrate wind condition data from first sensor(s) 214 and tower strain data from second sensor(s) 216 with estimates of mechanical loads to calculate the thrust (R ) generated by rotor 108 under the wind conditions. T ).

[0046] In additional embodiments, the second sensor(s) 216 may be an accelerometer or inclinometer that measures acceleration or angular deflection of the tower top. The second sensor(s) 216 may be a sound detection and ranging (SODAR) sensor, a light detection and ranging (LIDAR) sensor, an optical sensor, or a position sensor for nacelle 106 position tracking, such as GPS. The second sensor(s) 216 may also include a combination of sensors. For example, a GPS signal may be augmented by real-time kinematics (RTK) displayed onboard or received from a public server and / or a gyroscope and / or accelerometer. The second sensor(s) 216 may provide the controller 202 with a measurement of the deflection of the tower 102. The controller 202 may integrate the wind condition data from the first sensor(s) 214 and the tower deflection data from the second sensor(s) 216 with an estimate of the mechanical load to calculate the thrust (R) generated by the rotor 108 under the wind conditions. T ).

[0047] It should be appreciated that the second sensor(s) 216 may be coupled to the tower 102, the nacelle 106, and / or the rotor 108. The second sensor(s) 216 may also include a network of sensors and may be located remotely from the wind turbine 100. It should also be appreciated that the second sensor(s) 216 may include a combination of sensors discussed herein. For example, the second sensor(s) 216 may include both a tower base strain sensor and a tower deflection sensor. The controller 202 may then calculate the thrust (R) based on at least one of the bending strain or the deflection. T). It should be further appreciated that increasing the number and type of second sensors 216 may result in more accurate or precise thrust calculations from controller 202. Controller 202 may utilize the calculated thrust to calculate a thrust coefficient (C T ).

[0048] Still refer to Figure 2-4 The system 200 may also include at least one third sensor 218 configured to monitor environmental conditions or operating conditions of the wind turbine 100. For example, the third sensor(s) 218 ​​may be a power sensor configured to monitor the power output of the generator 118. The controller 202 may use the measured power output of the generator 118 to calculate the power coefficient (C P ).

[0049] In an embodiment, the third sensor(s) 218 ​​may also include a proximity sensor, an inductive sensor, a micro inertial measurement unit (MIMU), a pressure sensor, an accelerometer, a SODAR sensor, a LIDAR sensor, an optical sensor, or a similar sensor. The third sensor(s) 218 ​​may, for example, be configured to provide the controller 202 with measurements related to air temperature, component temperature, air pressure, and / or rotational speed of the rotor blade(s) 112. The controller 202 may, for example, utilize signals from the third sensor(s) 218 ​​to calculate a tip speed ratio (TSR) for the rotor 108 under wind conditions monitored by the first sensor(s) 214. It should be appreciated that the third sensor(s) 218 ​​may be coupled to the tower 102, the nacelle 106, and / or the rotor 108. The third sensor(s) 218 ​​may also include a network of sensors and may be located remotely from the wind turbine 100.

[0050] According to the present disclosure, such as Figure 3 and Figure 4 The controller 202 of the system 200 depicted in FIG. 2 may be configured to calculate the thrust (R T ) to calculate the actual collective pitch angle for the rotor 108. For example, in an embodiment, the collective pitch offset module 220 may derive the actual thrust coefficient (C ) at the terminal speed ratio (TSR) based on the aerodynamic performance map of the rotor 108. T Alternatively, in an embodiment, the collective pitch offset module 220 may derive the actual power coefficient (C P )’s actual collective pitch angle. Figure 5 and Figure 6, a graphical representation of an aerodynamic performance map for rotor 108 is presented in . However, it should be appreciated that the graphical representation is presented herein to aid understanding, but the collective pitch offset module 220 may perform derivations by employing other suitable functions and / or lookup tables. Similarly, it should be appreciated that the term “plotting” may include any calculation, extrapolation, derivation, graphing, or other computational steps performed by the collective pitch offset module 220.

[0051] like Figure 5 As depicted in the figure, the aerodynamic performance characteristics of the rotor 108 can be understood through testing and / or modeling. In particular, the pitch set point curve (PC) can be plotted as a function of the terminal speed ratio (TSR) and the pitch angle. The pitch set point curve (PC) can be overlaid to represent the nominal thrust coefficient (C Tn ) value. Tn ) values ​​may be based on testing and / or modeling of the rotor 108. Based on the aerodynamic characteristics of the rotor 108, the pitch set point curve (PC) may represent an optimal operating point (expressed as coordinates (TSR, pitch)) for the rotor 108 in response to a given wind condition. Based on these characteristics, at a particular terminal speed ratio (TSR), the wind turbine 100 may be operated at a pitch corresponding to an operating point located on the pitch set point curve (PC) at maximum efficiency. In other words, determining the intersection between the line representing the terminal speed ratio (TSR) and the pitch set point curve (PC) will produce an optimal collective pitch angle for the rotor 108 when producing a desired amount of thrust.

[0052] In an embodiment, the controller 202 may be based on the thrust (R T ) to calculate the thrust coefficient (C T ), which in turn may be calculated based on at least one of the bending strain or tower deflection as monitored by the second sensor(s) 216. The thrust coefficient (C T ) can be plotted on an aerodynamic performance diagram (e.g. Figure 5 ) at the calculated terminal speed ratio (TSR). The corresponding pitch angle may thus be the actual collective pitch angle of the rotors 108. In other words, by measuring the thrust (R) generated by the rotors 108 under the measured wind conditions T ), the controller 202 may be able to deduce the actual collective pitch angle of the rotors 108 based on the known aerodynamic performance characteristics of the rotors 108.

[0053] like Figure 5 As further described in , based on the thrust (R T ) is the calculated thrust coefficient (C T) may not be on the pitch set point curve (PC). Such a displacement from the pitch set point curve (PC) may indicate that the rotor 108 may not be pitched optimally for the wind conditions. For example, a displacement from the pitch set point curve (PC) may indicate that the angle of attack of (one or more) rotor blades 112 may be too high or too low for the wind speed. This, in turn, may indicate that the wind turbine 100 is operating in an inefficient or potentially destructive manner.

[0054] It should be appreciated that the actual collective pitch angle may be a combination of the individual pitch angles of each of the rotor blades 112 and may be different from the first collective pitch angle sensed by the controller 202. For example, in an embodiment, the controller 202 may sense that each rotor blade 112 has a pitch angle of 5 degrees relative to the zero pitch position. However, due to aerodynamic twisting of each of the rotor blades 112 and / or variations in the zero pitch position, the first blade may actually have a pitch angle of 7 degrees, the second blade may actually have a pitch angle of 5 degrees, and the third blade may have a pitch angle of 6 degrees. In such an embodiment, the actual collective pitch angle of the rotor 108 will be 6 degrees. The actual collective pitch angle may be indicated by a greater or lesser thrust than would otherwise be expected for the rotor 108 at the first collective pitch angle and the calculated terminal speed ratio (TSR).

[0055] Similar to the previous Figure 5 The discussion, Figure 6 A pitch set point curve (PC) is plotted as a function of the terminal speed ratio (TSR) and the pitch angle. The pitch set point curve (PC) can be overlaid to represent the nominal power coefficient (C Pn ) value. Nominal power factor (C Pn ) value may be based on testing and / or modeling of the wind turbine 100 and may be down from a peak value. Based on the aerodynamic characteristics of the rotor 108, the pitch set point curve (PC) may represent an optimal operating point (expressed as coordinates (TSR, pitch)) for the rotor 108 in response to a given wind condition. Based on these characteristics, at a particular terminal speed ratio (TSR), the wind turbine 100 may be operated at a pitch corresponding to an operating point located on the power curve (PC) at maximum efficiency. In other words, it is determined that the intersection between the line representing the terminal speed ratio (TSR) and the power curve (PC) will produce an optimal collective pitch angle for the rotor 108 when the wind turbine produces a desired amount of power.

[0056] In an embodiment, the controller 202 may calculate the power coefficient (C ) for the operating rotor 108 based on the power output of the generator 118. P ). Power coefficient (C P ) can be plotted on an aerodynamic performance diagram (e.g. Figure 6) at the calculated terminal speed ratio (TSR). The corresponding pitch angle may therefore be the actual collective pitch angle of the rotors 108. In other words, by measuring the power generated by the wind turbine 100 under the measured wind conditions, the controller 202 may be able to deduce the actual collective pitch angle of the rotors 108 based on the known aerodynamic performance characteristics of the rotors 108.

[0057] Back reference Figure 3 , the collective pitch offset module 220 may be a component of the wind turbine controller 204. Alternatively, as Figure 4 As shown in FIG. 2 , collective pitch offset module 220 may be a component of separate controller 202. In such embodiments, utilizing separate controller 202 may facilitate determining the collective pitch angle without requiring access to software and / or hardware of wind turbine controller 204.

[0058] In addition, in an embodiment, the collective pitch offset module 220 may be configured to perform one or more suitable data processing techniques or algorithms. The techniques or algorithms may allow the controller 202 or the wind turbine controller 204 to accurately and efficiently analyze the sensor data from the sensors 214, 216, 218. The analysis may allow the controller 202 or the wind turbine controller 204 to calculate the actual collective pitch angle for the plurality of rotor blades based at least in part on the thrust. In addition, the collective pitch offset module 220 may apply corrections or adjustments to the received data based on the sensor type, sensor resolution, and / or other parameters associated with the wind conditions or the operation of the wind turbine 100. In one case, for example, the collective pitch offset module 220 may filter the data to remove outliers by implementing the subroutines or intermediate calculations required to calculate the collective pitch angle and / or by performing any other desired data processing related techniques or algorithms.

[0059] With particular reference Figure 3-6 , the system 200 may calculate an actual collective pitch angle for the plurality of rotor blades 112 as described herein. The system 200 may also determine a collective pitch offset based on a difference between the first collective pitch angle and the actual collective pitch angle. The collective pitch offset may be used as at least one of a damping factor, an amplification factor, or a calibration factor.

[0060] In an embodiment, a collective pitch offset may be introduced at a suitable location in the system 200 to enable efficient operation of the wind turbine 100. For example, in an embodiment, the collective pitch offset may be integrated with at least one pitch set point command by the turbine controller 204. The integrated pitch set point command(s) may then be transmitted to the pitch control mechanism 120 of the wind turbine 100. In another embodiment, the collective pitch offset module 220 may be communicatively coupled to the pitch control mechanism 120 and may insert the collective pitch offset into the signal between the pitch control mechanism 120 and the turbine controller 204. It should be appreciated that in such embodiments, changes to the signal to or from the pitch control mechanism 120 may not be detectable by the wind turbine controller 204. In yet another embodiment, the collective pitch offset may be provided to the wind turbine controller 204 in the form of a calibration signal and may be used by the wind turbine controller 204 to calculate a new perceived collective zero pitch position for the rotor 108.

[0061] In an embodiment, the controller 202 may determine the collective pitch offset continuously, at predetermined intervals, and / or in response to a specified sensor input. For example, in an embodiment, the controller 202 may determine the collective pitch offset after the blades are installed and / or the pitch control mechanism 120 is installed. In such embodiments, the collective pitch offset may be used to recalibrate the wind turbine controller 204 and / or the pitch control mechanism 120. In additional embodiments, the controller 202 may continuously monitor the actual collective pitch angle and integrate the collective pitch offset into the pitch set point command. In another embodiment, the controller 202 may calculate the actual collective pitch offset at predetermined intervals (e.g., daily, weekly, monthly, etc.). In yet another additional embodiment, receiving a fault signal from a sensor (such as an indication related to an unexpected output of a generator) may trigger the controller 202 to calculate the collective pitch angle of the rotor 108.

[0062] In an embodiment, system 200 may be configured to perform a system check using controller 202 to detect a fault in pitch control mechanism 120. If a fault is detected in pitch control mechanism 120, controller 202 may be configured to ignore the collective pitch excursion and generate at least one of maintenance signal 222 or a turbine shutdown signal.

[0063] Now refer to Figure 7 , shows an exemplary graph of one embodiment of wind turbine power output (y-axis) versus wind speed (x-axis) according to the present disclosure. Figure 7 As depicted in FIG. 1 , as wind speed increases, the power generated by wind turbine 100 also generally increases. E), the correlation between wind speed and power generation may be relatively linear. In this region, the controller 202 may calculate (one or more) pitch set point commands that seek to achieve a desired wind speed by setting a wind speed that falls within Figure 5 and Figure 6 The collective pitch angle on the pitch set point curve (PC) depicted in FIG. 1 is used to optimize power production. Thus, when the wind condition is less than the efficiency threshold (T E ), the controller 202 may calculate (one or more) pitch setpoint commands that optimize the thrust coefficient under the wind conditions. It should be appreciated that integrating the collective pitch offset into the (one or more) pitch setpoint commands will facilitate operating the rotor 108 at a collective pitch angle that falls on the pitch setpoint curve.

[0064] Still refer to Figure 7 , as the wind speed increases, it can approach the rated threshold (T R When the wind speed reaches and / or exceeds the rated threshold (T R ), controller 202 may calculate (one or more) pitch setpoint commands that set up rotor 108 at a pitch angle that limits the amount of power generated by wind turbine 100. Integrating the collective pitch offset into the (one or more) pitch setpoint commands may ensure that the actual collective pitch angle does not cause power generation to exceed a rated threshold (T R ) or operate in an unnecessarily restricted manner below a threshold (e.g., the collective pitch angle produces less power than allowed for the wind speed).

[0065] At the efficiency threshold (T E ) and the rated threshold (T R ), the controller 202 may also calculate a pitch set point command that optimizes efficiency while preventing the wind turbine from exceeding a thrust threshold or mechanical load limit. It should be appreciated that employing the systems and methods disclosed herein may allow for direct feedback of rotor thrust and mechanical load management to reach design limits with improved operational certainty. It should be further appreciated that without the systems and methods described herein, the controller 202 may establish (one or more) pitch set point commands for this operating region, which results in loads that deviate from expected loads on the wind turbine. Higher than expected loads may result in damage to the wind turbine, while lower than expected loads may result in suboptimal power generation.

[0066] Now refer to Figure 8 , a flow chart of one embodiment of a method 300 for controlling a wind turbine based on a collective pitch offset is shown. The method 300 may be used, for example, as described above with reference to Figure 1-7 For purposes of illustration and discussion, Figure 8The steps are depicted as being performed in a particular order. Using the disclosure provided herein, one of ordinary skill in the art will appreciate that the various steps of method 300 or any of the methods disclosed herein may be adjusted, modified, rearranged, performed simultaneously, or modified in various ways without departing from the scope of the present disclosure.

[0067] As shown at (302), method 300 may include determining, via a controller, a wind condition acting on a rotor of a wind turbine. As shown at (304), method 300 may include setting a first collective pitch angle for a plurality of rotor blades. Additionally, as shown at (306), method 300 may include operating a wind turbine with a plurality of rotor blades at a first collective pitch angle. As shown at (308), method 300 may include determining, via the controller, a thrust of the rotor based at least in part on the wind condition(s). As shown at (310), method 300 may also include calculating, via the controller, an actual collective pitch angle for the plurality of rotor blades based at least in part on the thrust. Additionally, as shown at (312), method 300 may also include determining, via the controller, a collective pitch offset based on a difference between the first collective pitch angle and an actual collective pitch angle. As shown at (314), method 300 may also include integrating the collective pitch offset with at least one pitch set point command. As shown at ( 316 ), method 300 may further include transmitting the integrated pitch setpoint command to a pitch control mechanism of the wind turbine via the controller.

[0068] In additional embodiments, in accordance with the present disclosure, method 300 may further include integrating pitch control mechanism feedback with the collective pitch offset in order to calibrate the controller.

[0069] In additional embodiments, according to the present disclosure, method 300 may further include comparing the collective pitch excursion to a collective pitch excursion limit, and generating an output signal to trigger a maintenance event when the collective pitch excursion limit is exceeded.

[0070] In addition, the technician will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described and other known equivalents for each such method and feature can be mixed and matched by a person of ordinary skill in the art to construct additional systems and techniques according to the principles of the disclosure. Of course, it is to be understood that not necessarily all such goals or advantages described above can be realized according to any specific embodiment. Therefore, for example, it will be appreciated by those skilled in the art that the systems and techniques described herein can be embodied or performed in a manner that realizes or optimizes an advantage or a group of advantages as taught herein, without necessarily realizing other goals or advantages as taught or suggested herein.

[0071] 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 device or system and performing any combined 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. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

[0072] The present invention provides a method for controlling a wind turbine based on a collective pitch offset, the method comprising: determining a wind condition at a wind turbine via a controller; setting a first collective pitch angle for a plurality of rotor blades mounted to a rotatable hub of a rotor of the wind turbine; operating the wind turbine with the plurality of rotor blades at the first collective pitch angle; determining a thrust of the rotor via the controller at least partially based on the wind condition; calculating an actual collective pitch angle for the plurality of rotor blades based at least partially on the thrust via the controller; determining a collective pitch offset via the controller based on a difference between the first collective pitch angle and an actual collective pitch angle; integrating the collective pitch offset with at least one pitch set point command; and transmitting the integrated at least one pitch set point command to a pitch control mechanism of the wind turbine via the controller.

[0073] Optionally, determining the thrust of the rotor further comprises: measuring at least one of a bending strain of the tower or a deflection of the tower via one or more sensors; and calculating the thrust based on at least one of the bending strain or the deflection.

[0074] Optionally, calculating the actual collective pitch angle comprises: calculating a thrust coefficient based on the thrust of the rotor; calculating a terminal speed ratio for the rotor under wind conditions; and deriving the actual collective pitch angle for the thrust coefficient at the terminal speed ratio based on an aerodynamic performance map of the rotor.

[0075] Optionally, the method further comprises calculating at least one pitch set point command that optimizes the thrust coefficient in a wind condition, wherein the wind condition is less than a threshold value.

[0076] Optionally, determining the collective pitch offset is performed at least one of constantly, at predetermined intervals, or in response to a specified sensor input.

[0077] Optionally, determining the collective pitch offset is performed after at least one of blade installation or pitch control mechanism installation, the method further comprising integrating pitch control mechanism feedback with the collective pitch offset to calibrate the controller.

[0078] Optionally, the method further comprises: performing a system check with the controller to check for a pitch control mechanism fault; ignoring the collective pitch excursion when a pitch control mechanism fault is detected; and generating at least one of a maintenance signal or a turbine shutdown signal when a pitch control mechanism fault is detected.

[0079] Optionally, the controller comprises at least one of a turbine controller or a separate controller module communicatively coupled to the turbine controller.

[0080] Optionally, the method further comprises: comparing the collective pitch excursion to a collective pitch excursion limit; and generating an output signal to trigger a maintenance event when the collective pitch excursion limit is exceeded.

[0081] Optionally, the method further comprises calculating at least one pitch set point command for limiting thrust production in wind conditions, wherein the wind conditions are greater than a threshold value.

[0082] The present invention provides a system for controlling a wind turbine, the system comprising: a pitch control mechanism for establishing a first collective pitch angle for a plurality of rotor blades mounted to a rotatable hub of a rotor of the wind turbine, the pitch control mechanism comprising a pitch controller; at least one first sensor, the at least one first sensor configured for monitoring wind conditions at the wind turbine; at least one second sensor, the at least one second sensor configured for monitoring load conditions of the wind turbine; a turbine controller, the turbine controller communicatively coupled to the at least one first sensor and the at least one second sensor and the pitch controller, the controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations comprising: setting a first collective pitch angle for the plurality of rotor blades; determining a thrust of the rotor based at least in part on the wind conditions; calculating an actual collective pitch angle for the plurality of rotor blades based at least in part on the thrust; determining a collective pitch offset based on a difference between the first collective pitch angle and the actual collective pitch angle; integrating the collective pitch offset with at least one pitch set point command; and transmitting the integrated at least one pitch set point command to the pitch control mechanism of the wind turbine.

[0083] Optionally, the at least one second sensor comprises at least one of a tower base strain sensor or a tower deflection sensor, and wherein determining the thrust of the rotor further comprises: measuring at least one of a bending strain of the tower or a deflection of the tower via the at least one second sensor; and calculating the thrust based on at least one of the bending strain or the deflection.

[0084] Optionally, the plurality of operations further comprises: calculating a thrust coefficient based on the thrust of the rotor; calculating a terminal speed ratio for the rotor under wind conditions; and deriving an actual collective pitch angle for the thrust coefficient at the terminal speed ratio based on an aerodynamic performance map of the rotor.

[0085] Optionally, determining the collective pitch offset is performed at least one of constantly, at predetermined intervals, or in response to a specified sensor input.

[0086] Optionally, determining the collective pitch offset is performed after at least one of blade installation or pitch control mechanism installation, the plurality of operations further comprising integrating pitch control mechanism feedback with the collective pitch offset to calibrate the controller.

[0087] Optionally, the plurality of operations further comprises: performing a system check with the controller to check for a pitch control mechanism fault; ignoring a collective pitch excursion when a pitch control mechanism fault is detected; and generating at least one of a maintenance signal or a turbine shutdown signal when a pitch control mechanism fault is detected.

[0088] Optionally, the controller comprises at least one of a turbine controller or a separate controller module communicatively coupled to the turbine controller.

[0089] Optionally, the at least one pitch setpoint command is calculated to optimize the thrust coefficient in wind conditions, wherein the wind conditions are less than a threshold value.

[0090] Optionally, at least one pitch setpoint command is calculated to limit thrust production in wind conditions, wherein the wind conditions are greater than a threshold value.

[0091] Optionally, the plurality of operations further comprises: comparing the collective pitch offset to a collective pitch offset limit; and generating an output signal to trigger a maintenance event when the collective pitch offset limit is exceeded.

Claims

1. A method for controlling a wind turbine based on a collective pitch offset, the method comprising: determining, via a controller, wind conditions at the wind turbine; setting a first collective pitch angle for a plurality of rotor blades mounted to a rotatable hub of a rotor of the wind turbine; operating the wind turbine with the plurality of rotor blades at the first collective pitch angle; determining, via the controller, a thrust of the rotor based at least in part on the wind conditions; calculating, via the controller, an actual collective pitch angle for the plurality of rotor blades based at least in part on the thrust; determining, via the controller, the collective pitch offset based on a difference between the first collective pitch angle and the actual collective pitch angle; integrating the collective pitch offset with at least one pitch setpoint command; as well as The integrated at least one pitch set point command is transmitted via the controller to a pitch control mechanism of the wind turbine.

2. The method according to claim 1, characterized in that Determining the thrust of the rotor further includes: measuring at least one of a bending strain of a wind turbine tower or a deflection of the tower via one or more sensors; and The thrust is calculated based on at least one of the bending strain or the deflection.

3. The method according to claim 1, characterized in that Calculating the actual collective pitch angle includes: calculating a thrust coefficient based on the thrust of the rotor; calculating a tip speed ratio for the rotor under the wind conditions; and The actual collective pitch angle for the thrust coefficient at the terminal speed ratio is derived based on an aerodynamic performance map of the rotor.

4. The method according to claim 3, characterized in that The method further includes calculating the at least one pitch setpoint command that optimizes the thrust coefficient under the wind conditions, wherein the wind conditions are less than a threshold value.

5. The method according to claim 1, characterized in that Determining the collective pitch offset is performed at least one of constantly, at predetermined intervals, or in response to a specified sensor input.

6. The method according to claim 1, characterized in that Determining the collective pitch offset is performed after at least one of blade installation or pitch control mechanism installation, the method further comprising: Pitch control mechanism feedback is integrated with the collective pitch offset to calibrate the controller.

7. The method according to claim 1, characterized in that The method further comprises: performing a system check using the controller to check for pitch control mechanism failure; Ignoring the collective pitch excursion when a failure of the pitch control mechanism is detected; and At least one of a maintenance signal or a turbine shutdown signal is generated when a failure of the pitch control mechanism is detected.

8. The method according to claim 1, characterized in that The controller includes at least one of a turbine controller or a separate controller module communicatively coupled to the turbine controller.

9. The method according to claim 8, characterized in that The method further comprises: comparing the collective pitch offset to a collective pitch offset limit; and An output signal is generated to trigger a maintenance event when the collective pitch excursion limit is exceeded.

10. The method according to claim 1, characterized in that The method further includes calculating the at least one pitch setpoint command that limits thrust production in the wind condition, wherein the wind condition is greater than a threshold value.

11. A system for controlling a wind turbine, the system comprising: a pitch control mechanism for establishing a first collective pitch angle for a plurality of rotor blades mounted to a rotatable hub of a rotor of the wind turbine, the pitch control mechanism comprising a pitch controller; at least one first sensor configured to monitor wind conditions at the wind turbine; at least one second sensor configured to monitor a load condition of the wind turbine; a turbine controller communicatively coupled to the at least one first sensor and the at least one second sensor and the pitch controller, the controller comprising at least one processor configured to perform a plurality of operations comprising: setting the first collective pitch angle for the plurality of rotor blades; determining a thrust of the rotor based at least in part on the wind conditions; calculating an actual collective pitch angle for the plurality of rotor blades based at least in part on the thrust; determining a collective pitch offset based on a difference between the first collective pitch angle and the actual collective pitch angle; integrating the collective pitch offset with at least one pitch setpoint command; and The integrated at least one pitch set point command is transmitted to a pitch control mechanism of the wind turbine.

12. The system according to claim 11, characterized in that The at least one second sensor comprises at least one of a tower base strain sensor or a tower deflection sensor, and wherein determining the thrust of the rotor further comprises: measuring, via the at least one second sensor, at least one of a bending strain of a wind turbine tower or a deflection of the tower; and The thrust is calculated based on at least one of the bending strain or the deflection.

13. The system according to claim 11, characterized in that The plurality of operations also include: calculating a thrust coefficient based on the thrust of the rotor; calculating a tip speed ratio for the rotor under the wind conditions; and The actual collective pitch angle for the thrust coefficient at the terminal speed ratio is derived based on an aerodynamic performance map of the rotor.

14. The system according to claim 11, characterized in that Determining the collective pitch offset is performed at least one of constantly, at predetermined intervals, or in response to a specified sensor input.

15. The system according to claim 11, characterized in that Determining the collective pitch offset is performed after at least one of blade installation or pitch control mechanism installation, the plurality of operations further comprising: Pitch control mechanism feedback is integrated with the collective pitch offset to calibrate the controller.

16. The system according to claim 11, characterized in that The plurality of operations also include: performing a system check using the controller to check for pitch control mechanism failure; Ignoring the collective pitch excursion when a failure of the pitch control mechanism is detected; and At least one of a maintenance signal or a turbine shutdown signal is generated when a failure of the pitch control mechanism is detected.

17. The system according to claim 11, characterized in that The controller includes at least one of a turbine controller or a separate controller module communicatively coupled to the turbine controller.

18. The system according to claim 13, characterized in that The at least one pitch setpoint command is calculated to optimize the thrust coefficient in the wind condition, wherein the wind condition is less than a threshold value.

19. The system according to claim 11, characterized in that The at least one pitch setpoint command is calculated to limit thrust production in the wind conditions, wherein the wind conditions are greater than a threshold value.

20. The system according to claim 11, characterized in that The plurality of operations also include: comparing the collective pitch offset to a collective pitch offset limit; and An output signal is generated to trigger a maintenance event when the collective pitch excursion limit is exceeded.

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