Patent Publication Number: US-2015086357-A1

Title: Wind turbine and method for adjusting yaw bias in wind turbine

Description:
FIELD OF THE INVENTION 
     The present disclosure relates generally to wind turbines, and more particularly to systems and methods adjusting yaw bias in wind turbines. 
     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, generator, gearbox, nacelle, and a rotor including one or more rotor blades. The rotor blades capture kinetic energy from wind using known foil 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. 
     During operation, the direction of the wind which powers a wind turbine may change. The wind turbine may thus adjust, through for example a yaw adjustment about a longitudinal axis of the tower, to maintain alignment with the wind direction. In many wind turbines, however, a yaw bias exists, such that after yawing the wind turbine is slightly misaligned with the wind direction. Such bias can be caused by, for example, the location of the wind sensor (such as a wind vane or anemometer) behind the blades, because the turbulence from the blades can introduce inaccuracies into the wind sensor readings. Such bias can also be caused by, for example, variations in the hardware utilized to mount the wind sensor to the wind turbine. As a result of such yaw bias, the overall power captured by the wind turbine may be reduced. 
     Various attempts have been made to increase the accuracy if the wind sensors and reduce yaw bias. For example, some past efforts have involved the application of a single blanket yaw correction. This blanket correction has been applied for all operating conditions of the wind turbine. However, the amount of yaw bias can change based on changes in various operating conditions, thus resulting in such blanket correction efforts being inaccurate when the wind turbine is subjected to various operating conditions. Other efforts have involved attempts to correlate yaw bias with wind speed. However, the amount of yaw bias can vary for a particular wind speed based on changes in other operating conditions, thus also resulting in inaccurate yaw bias corrections. 
     Accordingly, improved systems and methods for adjusting yaw bias in wind turbines are desired. In particular, systems and methods which accurately adjust yaw bias for a variety of operating conditions would be advantageous. 
     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 embodiment, the present disclosure is directed to a method for adjusting yaw bias in a wind turbine. The method includes defining an operational condition for the wind turbine, the operational condition including a turbine speed range, a pitch angle range, and a wind speed range. The method further includes operating the wind turbine within the operational condition, adjusting a yaw angle of the wind turbine during operation of the wind turbine, and measuring power output of the wind turbine during operation within the operational condition. 
     In another embodiment, the present disclosure is directed to a method for adjusting yaw bias in a wind turbine. The method includes defining an operational condition for the wind turbine, the operational condition including a wind speed range and a range for at least one other operational parameter. The method further includes operating the wind turbine within the operational condition, adjusting a yaw angle of the wind turbine during operation of the wind turbine, and measuring power output of the wind turbine during operation within the operational condition. 
     In another embodiment, the present disclosure is directed to a wind turbine. The wind turbine includes a tower, a nacelle mounted to the tower, a rotor coupled to the nacelle, the rotor comprising a hub and a plurality of rotor blades, and a generator coupled to the rotor. The wind turbine further includes a controller, the controller operational to adjust a yaw angle of the wind turbine during operation of the wind turbine and measure power output of the wind turbine during operation within an operational condition, the operational condition including a turbine speed range, a pitch angle range, and a wind speed range. 
     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 
       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  is a perspective view of a wind turbine according to one embodiment of the present disclosure; 
         FIG. 2  illustrates a perspective, internal view of a nacelle of a wind turbine according to one embodiment of the present disclosure; 
         FIG. 3  illustrates a top view of a wind turbine according to one embodiment of the present disclosure; 
         FIG. 4  illustrates a plot of power output as a function of yaw angle for an operational condition according to one embodiment of the present disclosure; and 
         FIG. 5  is a flow chart of a method for adjusting yaw bias in a wind turbine according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
       FIG. 1  illustrates perspective view of one embodiment of a wind turbine  10 . 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. 
     As shown, the wind turbine  10  may also include a turbine control system or a turbine controller  26  centralized within the nacelle  16 . However, it should be appreciated that the turbine controller  26  may be disposed at any location on or in the wind turbine  10 , at any location on the support surface  14  or generally at any other location. The turbine controller  26  may generally be configured to control the various operating modes (e.g., start-up or shut-down sequences) and/or components of the wind turbine  10 . For example, the controller  26  may be configured to control the blade pitch or pitch angle of each of the rotor blades  22  (i.e., an angle that determines a perspective of the rotor blades  22  with respect to the direction  28  of the wind) to control the loading on the rotor blades  22  by adjusting an angular position of at least one rotor blade  22  relative to the wind. For instance, the turbine controller  26  may control the pitch angle of the rotor blades  22 , either individually or simultaneously, by transmitting suitable control signals/commands to a pitch controller of the wind turbine  10 , which may be configured to control the operation of a plurality of pitch drives or pitch adjustment mechanisms  32  ( FIG. 2 ) of the wind turbine, or by directly controlling the operation of the plurality of pitch drives or pitch adjustment mechanisms. Specifically, 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  along their pitch axes  34  using the pitch adjustment mechanisms  32 . Further, as the direction  28  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 , via a yaw controller or direct transmission, such that the nacelle  16  may be rotated about the yaw axis  36 . 
     It should be appreciated that the turbine controller  26  and/or the pitch controller  30  may generally comprise a computer or any other suitable processing unit. Thus, in several embodiments, the turbine controller  26  and/or pitch and yaw controllers may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions. 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) of the turbine controller  26  and/or pitch and yaw controllers may generally comprise 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) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the turbine controller  26  and/or pitch and yaw controllers to perform various computer-implemented functions. In addition, the turbine controller  26  and/or pitch and yaw controllers may also include various input/output channels for receiving inputs from sensors and/or other measurement devices and for sending control signals to various components of the wind turbine  10 . 
     Referring now to  FIG. 2 , a simplified, internal view of one embodiment of the nacelle  16  of the wind turbine  10  is illustrated. As shown, a generator  24  may be disposed within the nacelle  16 . In general, the generator  24  may be coupled to the rotor  18  of the wind turbine  10  for generating electrical power from the rotational energy generated by the rotor  18 . For example, the rotor  18  may include a main shaft  40  coupled to the hub  20  for rotation therewith. The generator  24  may then be coupled to the main shaft  40  such that rotation of the main shaft  40  drives the generator  24 . For instance, in the illustrated embodiment, the generator  24  includes a generator shaft  42  rotatably coupled to the main shaft  40  through a gearbox  44 . However, in other embodiments, it should be appreciated that the generator shaft  42  may be rotatably coupled directly to the main shaft  40 . Alternatively, the generator  24  may be directly rotatably coupled to the main shaft  40  (often referred to as a “direct-drive wind turbine”). 
     It should be appreciated that the main shaft  40  may generally be supported within the nacelle by a support frame or bedplate  46  positioned atop the wind turbine tower  12 . For example, the main shaft  40  may be supported by the bedplate  46  via a pair of pillow blocks  48 ,  50  mounted to the bedplate  46 . 
     Additionally, as indicated above, the turbine controller  26  may also be located within the nacelle  16  of the wind turbine  10 . 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, in other embodiments, the turbine controller  26  may be disposed at any other suitable location on and/or within the wind turbine  10  or at any suitable location remote to the wind turbine  10 . Moreover, as described above, 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. For example, the turbine controller  26  may be communicatively coupled to the yaw drive mechanism(s)  38  of the wind turbine  10  for controlling and/or altering the yaw direction of the nacelle  16  relative to the direction  28  ( FIG. 1 ) of the wind. Similarly, the turbine controller  26  may also be communicatively coupled to each pitch adjustment mechanism  32  of the wind turbine  10  (one of which is shown) through the pitch controller  30  for controlling and/or altering the pitch angle of the rotor blades  22  relative to the direction  28  of the wind. For instance, the turbine controller  26  may be configured to transmit a control signal/command to each pitch adjustment mechanism  32  such that one or more actuators (not shown) of the pitch adjustment mechanism  32  may be utilized to rotate the blades  22  relative to the hub  20 . 
     As further shown in  FIG. 2 , a wind sensor  60  may be provided on the wind turbine  10 . The wind sensor  60 , which may for example be a wind vane, and anemometer, and LIDAR sensor, or another suitable sensor, may measure wind speed and direction. The wind sensor  60  may further be in communication with the controller  26 , and may provide such speed and direction information to the controller  26 . For example, yawing of the wind turbine  10  may occur due to sensing of changes in the wind direction  28 , in order to maintain alignment of the wind turbine  10  with the wind direction  28 . 
     Referring now to  FIG. 3 , and as discussed above, a wind turbine  10 , such as the nacelle  16  thereof, may rotate about the yaw axis  36  as required. Yaw axis may generally extend along (and be coaxial with) a longitudinal axis of the tower  12 . In particular, rotation about the yaw axis  36  may occur due to changes in the wind direction  28 , such that the rotor  18  is aligned with the wind direction  28 .  FIG. 3  illustrates a wind directions  28  which is aligned with the rotor  18 , such that a central axis of the rotor  18  and/or a longitudinal axis of the nacelle  16  may for example be generally parallel with the wind direction  28 . 
     In some cases, however, after rotation about the yaw axis  36 , the rotor  18  may remain slightly misaligned with the wind direction  28 , causing a yaw bias which, as discussed above, can reduce the power generated by the wind turbine. For example, misalignments relative to the wind direction  28  are illustrated. Such misalignment may be by any suitable angle, and either to the right or left of the wind direction  28  (in a top view as shown in  FIG. 3 ). As shown, a negative θ indicates a yaw angle θ to the left of the wind direction  28 , while a positive θ indicates a yaw angle θ to the right of the wind direction  28 . 
     Referring now to  FIGS. 4 and 5 , the present disclosure is thus directed to methods for adjusting yaw bias in a wind turbine  10 . Such adjustment may reduce the yaw bias, such that a wind turbine  10  can accurately align with the wind direction  28  and increase the power generated therefrom. 
     A method may include, for example, the step  100  of defining one or more operational conditions  102  for the wind turbine. Such operational conditions  102  may generally be predetermined, and are generally sets of ranges for various operational parameters of the wind turbine  10  during operation thereof. For example, in exemplary embodiments, an operational condition may include one or more operational parameters and ranges thereof, such as in exemplary embodiments turbine speed range, pitch angle range  104 , and wind speed range  106 . The turbine speed range  104  may be the rotor speed range  108  and/or the generator speed range  110 . Other suitable operational parameters include, for example, power output and rotor position. In general, an operational condition  102  may include a wind speed range  106  and at least one other operational parameter and range thereof. 
     Various operational conditions  102  may be predetermined for a wind turbine  10 , and each may include a predetermined range for each operational parameter thereof. For example, one operational condition  102  may be a run-up condition. In one run-up condition, for example, the generator speed may be between approximately 0.4 and approximately 0.7 times a rated generator speed for the wind turbine  10 , the wind speed may be less than 5 meters per second, and the pitch angle range may be variable throughout the allowable range of pitch angles. Another operational condition  102  may be a wind turbine standstill condition. In one turbine standstill condition, for example, the generator speed may be less than approximately 0.07 times a rated generator speed for the wind turbine  10 , the wind speed may be any suitable wind speed, and the pitch angle range may be a constant pitch angle. Other operational conditions may include an idle condition (for example, generator speed approximately 0.7 times a rated generator speed for the wind turbine  10 , wind speed less than 5 meters per second, and pitch angle constant); lower constant speed load condition (for example, generator speed approximately 0.6 times a rated generator speed for the wind turbine  10 , wind speed variable, pitch angle constant); variable speed condition (for example, generator speed between approximately 0.6 and approximately 1.05 times a rated generator speed for the wind turbine  10 , wind speed variable, pitch angle constant); rated turbine speed condition (for example, generator speed approximately 1.05 times a rated generator speed for the wind turbine  10 , wind speed variable, pitch angle constant, such that output power is greater than approximately 800 kilowatts); peak shaver condition (for example, generator speed less than approximately 1.05 times a rated generator speed for the wind turbine  10 , wind speed variable, pitch angle variable, such that output power is greater than approximately 1200 kilowatts); rated power condition (for example, generator speed variable, wind speed variable, pitch angle variable, such that output power is greater than approximately 1600 kilowatts); and/or high wind speed condition (for example, generator speed variable, wind speed greater than 15 meters per second, pitch angle variable). 
     A method may further include, for example, the step  120  of operating the wind turbine  10  within the one or more operational conditions  102 . Such operation may be a constant operation within an operational condition  102 , followed if required by constant operation within another operational condition  102 , or may be intermittent operation within various operational conditions  102  such that, during operation of the wind turbine  10 , the wind turbine  10  is intermittently operated within an operational condition  102 . For example, in some instances, the wind turbine  10  may be operated as in a normal operating scenario, with various operational conditions  102  being met during such operation. In other instances, the wind turbine  10  may be purposefully operated in, for example, a test scenario wherein operational conditions  102  are met. 
     A method may further include, for example, the step  130  of adjusting a yaw angle θ of the wind turbine  10  during operation within the operational condition  102 . In general, it is desirable according to the present disclosure to adjust the yaw angle θ such that the wind turbine  10  is operated at a large range of yaw angles θ for a relatively constant wind direction  28 . Thus, adjustments to the power output of the wind turbine  10  are facilitated during operation within the operational condition. In exemplary embodiments, the yaw angle θ may be adjusted through a full or partial range of yaw angles θ for the wind turbine  10  during operation within the operational condition and for a generally constant wind direction  28 . 
     A method may further include, for example, the step  140  of measuring power output  142  of the wind turbine  10  during operation within the one or more operational conditions  102 . Such measurements of power output  142  may be taken by suitable sensors and communicated to the controller  26 . Further, such measurements  142  may, in the controller  26 , be segmented per operational condition  102  such that a range of power outputs  142  as a function of yaw angle θ for each operational condition  102  is obtained. In exemplary embodiments, measuring of the power output  142  may occur for each operational condition  102  for a predetermined period of time, in order to obtain suitable power output  142  data as a function of yaw angle θ for an operational condition  102 . This predetermined period of time may further occur before any implementation of yaw offset to reduce yaw bias, as discussed below. 
     A method may further include, for example, the step  150  of identifying a yaw error  152  for one or more of the operational conditions  102  based on the measured power output  142 . The yaw error  152  (or yaw bias) is the difference between the desired direction of the wind turbine  10  with respect to a wind direction  28  and the actual direction of the wind turbine  10  with respect to that wind direction. In other words, the yaw error  152  is the yaw angle θ of the wind turbine  10  relative to a wind direction  28  for an operational condition  102 . 
     In exemplary embodiments, the step of identifying the yaw error  152  includes the step  155  of plotting or otherwise associating the power output  142  as a function of the yaw angle θ within one or more operational conditions  102 . For example,  FIG. 4  illustrates one embodiment of a plot of the power output  142  versus the yaw angle θ for an operational condition  102 . The yaw error  152  can be determined through such plotting or otherwise associating because it is generally the yaw angle θ at which the maximum power output  142  occurs for an operational condition  142 . As shown, 0 degrees indicates no yaw relative to a wind direction  28  such that the wind turbine  10  is aligned with the wind turbine  10  for an operational condition  142 . If the wind turbine  10  were actually aligned with the wind direction  28  when it is indicated that the wind turbine  10  is so aligned, the maximum power output  142  would be at such 0 degree alignment. An offset maximum power output  142  indicates a yaw bias, and thus a yaw error  152 . 
     A method may further include, for example, the step  160  of implementing a yaw offset  162  for an associated operational condition  102  based on the yaw error  152 . The yaw offset  162  may generally be a yaw angle opposite to the angle of the yaw error  152 . For example, such implementing step  152  may include instructing the yaw drive mechanism  38  to, when yawing such that the wind turbine  10  is aligned with the wind direction  28 , offset this yaw by the yaw offset  162 . 
     It should be understood that the yaw error  152  and yaw offset  162  are angles that are relative to the alignment of the wind turbine  10  with the wind direction  28 , as discussed above. Further, the yaw error  152  and yaw offset  162  may change for each operational condition  102 , and may thus be implemented separately for each associated operational condition  102  as required. 
     It should further be understood that the various methods steps, including but not limited to steps  130 ,  140 ,  150  and  16  may be performed in exemplary embodiments by the controller  26 . Thus, a wind turbine  10  according to the present disclosure may include a controller  26  that is operational to, for example, adjust a yaw angle θ of the wind turbine  10  during operation of the wind turbine  10  and measure power output  142  of the wind turbine  10  during operation within one or more operational conditions  102 . The controller  26  may further be operational to, for example, identify a yaw error  152  for the operational condition(s)  102  based on the measured power output  142 . Such identification may be performed by, for example, plotting the power output  142  as a function of the yaw angle θ within the operational condition  102 . The controller  26  may further be operational to, for example, implement a yaw offset  162  for the operational condition(s)  102  based on the yaw error  152 . 
     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.