Patent Description:
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 modem wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes a rotor assembly coupled to the gearbox and to the generator. The rotor assembly and the gearbox are mounted on a bedplate support frame located within the nacelle. The one or more rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy and the electrical energy may be transmitted to a converter and/or a transformer housed within the tower and subsequently deployed to a utility grid. Modern wind power generation systems typically take the form of a wind farm having multiple such wind turbine generators that are operable to supply power to a transmission system providing power to a power grid.

Capturing the kinetic energy of the wind generally includes yawing the nacelle of the wind turbine into the wind. Typically, when the wind turbine is operating below rated power, the wind turbine may produce a maximal amount of power for given environmental conditions when the nacelle and the wind are aligned in parallel. Accordingly, when the wind and the nacelle are misaligned so that the wind's vector intersects the axis of the nacelle, the power production of the wind turbine may be less than the maximal amount.

In order to facilitate the maximal power production of the wind turbine for a given environmental condition, wind turbines are typically equipped with a wind vane or other sensor which may detect the direction of the wind. This information may be utilized to yaw the nacelle in order to bring the nacelle into alignment with the wind. However, this information may lack the desired level of accuracy. For example, the wind vane may be misaligned during installation or following a maintenance procedure.

Additionally, the wind vane may typically be mounted downwind of the rotor. Thus, the interaction of the rotor and the wind may induce a wind direction change downwind of the rotor. Accordingly, the wind vane may be intentionally misaligned and/or a biasing value may be applied to its output. However, the misalignment/biasing may be based on nominal design calculations and may not reflect differences in the rotor and/or other factors. As such, the degree of misalignment/biasing may not result in the desired level of accuracy.

In view of the aforementioned, the art is continuously seeking new and improved systems and methods for controlling a wind turbine of a wind farm which align the nacelle in parallel with the wind direction. An example of prior art is given by <CIT>.

In one aspect, the present disclosure is directed to a method according to claim <NUM> for controlling a wind turbine of a plurality of wind turbines of a wind farm. The method may include determining, via the controller, a performance differential for the wind turbine for multiple sampling intervals of a yaw event. The performance differential may be indicative of a ratio of the monitored performance parameter to an estimated performance parameter for the wind turbine. The method may also include determining, via the controller, a trendline for the wind turbine correlating the performance differential to a deviation of a wind direction at each of the multiple sampling intervals from a first yaw angle for the yaw event. Additionally, the method may include determining, via the controller, a yaw angle offset based on a difference between an angle associated with a vertex of the trendline and the first yaw angle. Also, the method may include adjusting, via the controller, a second yaw angle of the wind turbine based at least in part on the yaw angle offset.

In an embodiment, the method may include receiving, via the controller, an indication of the performance parameter for each wind turbine of a designated subset of the plurality of wind turbines at each of the multiple sampling intervals. The method may also include modeling, via the controller, an estimated performance parameter for the wind turbine at each of the multiple sampling intervals based on the received indications of the performance parameter of each wind turbine of the designated subset.

In an additional embodiment, the method may include receiving, via the controller, an indication of a monitored wind direction from an environmental sensor of the wind turbine at each of the multiple sampling intervals of the yaw event. The method may also include receiving, via the controller, an indication of a yaw setpoint from at least a portion of the plurality of wind turbines at least once per yaw event. The method may also include determining, via the controller, a median yaw setpoint based on the received indications. The median yaw setpoint may be indicative of a yaw-event wind direction. The yaw-event wind direction may be the wind direction in axial alignment with the wind turbine for the yaw event. Additionally, the method may include determining, via the controller, a difference between the monitored wind direction at each of the multiple sampling intervals and the first yaw angle. The difference may correspond to the deviation of the wind direction at each of the multiple sampling intervals from the yaw-event wind direction. Further, the method may include determining, via the controller, a performance-parameter-correlation distribution relative to the deviation of the wind direction from the first yaw angle for the yaw event.

In yet a further embodiment, the method may include defining at least a first and a second yaw sector. The method may also include determining a first yaw angle offset for the wind turbine when the wind turbine is in the first yaw sector. Additionally the method may include determining a second yaw angle offset for the wind turbine when the wind turbine is in the second yaw sector. The second yaw angle offset being different than the first yaw angle offset.

In an embodiment, the yaw event may be defined by a period between subsequent yaw setpoint commands received from the controller. The yaw event may include at least five sampling intervals.

In an additional embodiment, the yaw event may have a duration of <NUM> seconds. Additionally, each sampling interval may occur once every <NUM> seconds over the duration of the yaw event.

In a further embodiment, the method may be repeated for each yaw event occurring over a sampling period of at least one month.

In yet a further embodiment, adjusting the yaw angle of the wind turbine may include aligning or recalibrating an environmental sensor of the wind turbine.

In an embodiment, the adjusting of the yaw angle of the wind turbine may be accomplished following the installation of the wind turbine or the environmental sensor and/or a maintenance or service activity.

In a further embodiment, the method may include establishing an alignment test interval for the wind turbine. The method may also include determining the yaw angle offset in accordance with a test schedule as defined by the alignment test interval in order to detect a drift in the alignment of the environmental sensor or the wind turbine.

In yet a further embodiment, the performance parameter may be a power output.

In an embodiment, the performance parameter may be a first performance parameter. The method may also include determining, via the controller, a second performance differential for the wind turbine at each of the multiple sampling intervals of the yaw event. The second performance differential may be indicative of a ratio of a monitored second performance parameter to an estimated second performance parameter for the wind turbine. Additionally, the trendline may be a three-dimensional trendline correlating the first performance differential and the second performance differential to the deviation of the wind direction at each of the multiple sampling intervals from the first yaw angle.

In an additional embodiment, the second performance parameter may include a tip speed ratio, a pitch setpoint, a yawing moment, wind speed, turbulence intensity and/or a bending moment.

In another aspect, the present disclosure is directed to a system according to claim <NUM> for controlling a wind turbine of the plurality of wind turbines of a wind farm. The system may include a yaw drive mechanism for yawing the wind turbine and a controller communicatively coupled to the plurality wind turbines. The controller may include at least one processor configured to perform a plurality of operations. The plurality of operations may include any of the methods, steps and/or/or features described herein.

Generally, the present disclosure is directed to systems and methods for controlling a wind turbine that may be part of a wind farm. In particular, the present disclosure may include systems and methods which facilitate the establishment of a yaw angle offset in order to adjust a yaw angle of the wind turbine. More specifically, the present disclosure may include estimating a performance parameter for a subject wind turbine of the wind farm based on performance parameters of a designated subset of wind turbines of the wind farm at multiple sampling intervals. This estimated performance parameter may be correlated with a monitored performance parameter for the subject wind turbine. Accordingly, a ratio of the monitored performance parameter to the estimated performance parameter may be calculated to determine a performance differential.

The wind turbines of the wind farm may receive yaw setpoint commands at a yaw event. The yaw setpoint commands may orient the axis of the wind turbines parallel to the wind direction. Due, at least in part, to the amount of power consumed in yawing the nacelle of the wind turbine, the yaw event may be a fixed period of time, such as <NUM> seconds. Accordingly, the wind direction may deviate from the direction parallel to the axis of the wind turbine during the yaw event and become misaligned with the wind turbine. However, the deviations of the wind from the axially aligned orientation may be recorded by the wind turbine at a number of sampling intervals during the yaw event. For example, each yaw event may include at least five sampling intervals.

Thus, a controller may correlate the performance differential to the deviations in wind direction at each sampling interval during the yaw event. Using such correlations, the controller may determine a trendline for the wind turbine. The trendline may reflect variations in the ratio between the monitored performance and the estimated performance based on the perceived wind direction. A vertex of the trendline may indicate a perceived wind direction at which the monitored performance parameter most closely coincides with the estimated performance parameter maxima. If the wind turbine is properly aligned to the wind direction, the vertex may occur at the first yaw angle.

The vertex occurring at the first yaw angle may be due to the fact that the designated subset of wind turbines may maximize their respective performance parameters, and therefore the estimated performance parameter, when aligned with the wind at the yaw angle for the yaw event. As such, a vertex of the trendline which is offset from the first yaw angle may indicate a misalignment of the wind turbine to the wind. In other words, the shifted vertex may indicate that when the controller of the wind turbine perceives that the wind turbine is parallel to the wind, the wind turbine may actually be offset by a number of degrees from aerodynamic alignment with the wind, which may be the yaw angle at which optimal power may be produced. Therefore, when the wind is perceived to deviate from the reciprocal of the yaw angle, the wind may actually come into parallel alignment with the axis of the wind turbine. This may result in the wind turbine having a performance parameter most closely correlated to the estimated performance parameter.

The difference in degrees between the perceived wind angle associated with the vertex and the first yaw angle may represent a yaw angle offset. The yaw angle offset may be utilized to adjust the yaw angle of the wind turbine. This adjustment may occur, for example, when the wind turbine or the environmental sensor are installed, maintained, or serviced. For example, the adjustment may include biasing the sensor measurement of the installed anemometer or wind vane or physically rotating the sensor achieve the yaw angle offset determined using the systems and methods described herein.

It should be appreciated that utilizing the designated subset of wind turbines to develop the estimated performance parameter may preclude a requirement that the wind velocity be measured. This may reduce the sensor requirements, and therefore costs, for the wind farm. For example, the utilization of the estimated performance parameter instead of wind speed may eliminate a requirement for a meteorological mast, a lidar, or other sensor system disposed within the wind farm.

It should further be appreciated that the utilization of the performance differential as opposed to a direct measurement of the performance parameter may reduce the number of variables which must be accounted for by the control system. For example, calculations based on the power output of the wind turbine may be subject to fluctuations in wind velocity. This may, thus, require the monitoring of wind velocity and make it more difficult to determine whether the power variations at the multitude of sampling intervals for the yaw event are due to the deviation of the wind direction or due to deviations in wind velocity.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> according to the present disclosure. As shown, the wind turbine <NUM> generally includes a tower <NUM> extending from a support surface <NUM>, a nacelle <NUM>, mounted on the tower <NUM>, and a rotor <NUM> coupled to the nacelle <NUM>. The rotor <NUM> includes a rotatable hub <NUM> and at least one rotor blade <NUM> coupled to and extending outwardly from the hub <NUM>. For example, in the illustrated embodiment, the rotor <NUM> includes three rotor blades <NUM>. However, in an alternative embodiment, the rotor <NUM> may include more or less than three rotor blades <NUM>. Each rotor blade <NUM> may be spaced about the hub <NUM> to facilitate rotating the rotor <NUM> to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub <NUM> may be rotatably coupled to an electric generator <NUM> (<FIG>) positioned within the nacelle <NUM> to permit electrical energy to be produced.

The wind turbine <NUM> may also include a controller <NUM> configured as a turbine controller centralized within the nacelle <NUM>. However, in other embodiments, the controller <NUM> may be located within any other component of the wind turbine <NUM> or at a location outside the wind turbine. Further, the controller <NUM> may be communicatively coupled to any number of the components of the wind turbine <NUM> in order to control the components. As such, the controller <NUM> may include a computer or other suitable processing unit. Thus, in several embodiments, the controller <NUM> may include suitable computer-readable instructions that, when implemented, configure the controller <NUM> to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals.

Referring now to <FIG>, a simplified, internal view of one embodiment of the nacelle <NUM> of the wind turbine <NUM> shown in <FIG> is illustrated. As shown, the generator <NUM> may be coupled to the rotor <NUM> for producing electrical power from the rotational energy generated by the rotor <NUM>. For example, as shown in the illustrated embodiment, the rotor <NUM> may include a rotor shaft <NUM> coupled to the hub <NUM> for rotation therewith. The rotor shaft <NUM> may be rotatably supported by a main bearing <NUM>. The rotor shaft <NUM> may, in turn, be rotatably coupled to a high-speed shaft <NUM> of the generator <NUM> through a gearbox <NUM> connected to a bedplate support frame <NUM>. As is generally understood, the rotor shaft <NUM> may provide a low-speed, high-torque input to the gearbox <NUM> in response to rotation of the rotor blades <NUM> and the hub <NUM>. The gearbox <NUM> may then be configured to convert the low-speed, high-torque input to a high-speed, low-torque output to drive the high-speed shaft <NUM> and, thus, the generator <NUM>.

Each rotor blade <NUM> may also include a pitch control mechanism <NUM> configured to rotate each rotor blade <NUM> about its pitch axis <NUM>. The pitch control mechanism <NUM> may include a pitch controller <NUM> configured to receive at least one pitch setpoint command from the controller <NUM>. Further, each pitch control mechanism <NUM> may include a pitch drive motor <NUM>, a pitch drive gearbox <NUM>, and a pitch drive pinion <NUM>. In such embodiments, the pitch drive motor <NUM> may be coupled to the pitch drive gearbox <NUM> so that the pitch drive motor <NUM> imparts mechanical force to the pitch drive gearbox <NUM>. Similarly, the pitch drive gearbox <NUM> may be coupled to the pitch drive pinion <NUM> for rotation therewith. The pitch drive pinion <NUM> may, in turn, be in rotational engagement with a pitch bearing <NUM> coupled between the hub <NUM> and a corresponding rotor blade <NUM> such that rotation of the pitch drive pinion <NUM> causes rotation of the pitch bearing <NUM>. Thus, in such embodiments, rotation of the pitch drive motor <NUM> drives the pitch drive gearbox <NUM> and the pitch drive pinion <NUM>, thereby rotating the pitch bearing <NUM> and the rotor blade(s) <NUM> about the pitch axis <NUM>.

Similarly, the wind turbine <NUM> may include one or more yaw drive mechanisms <NUM> communicatively coupled to the controller <NUM>, with each yaw drive mechanism(s) <NUM> being configured to change the angle of the nacelle <NUM> relative to the wind (e.g., by engaging a yaw bearing <NUM> of the wind turbine <NUM>). It should be appreciated that the controller <NUM> may direct the yawing of the nacelle <NUM> and/or the pitching of the rotor blades <NUM> so as to aerodynamically orient the wind turbine <NUM> relative to a wind(W) acting on the wind turbine <NUM>, thereby facilitating power production.

Referring now to <FIG>, a schematic view of a wind farm <NUM> according to the present disclosure is illustrated. As shown, the wind from <NUM> may include a plurality of the wind turbines <NUM> described herein and the controller <NUM> configured as a farm controller. For example, as shown in the illustrated embodiment, the wind farm <NUM> may include twelve wind turbines <NUM>. However, in other embodiments, the wind farm <NUM> may include any other number of wind turbines <NUM>, such as less than twelve wind turbines <NUM> or greater than twelve wind turbines <NUM>. In one embodiment, the controller(s) <NUM> may be communicatively coupled via a wired connection, such as by connecting the controller(s) through suitable communicative links <NUM> (e.g., a suitable cable). Alternatively, the controller(s) may be communicatively coupled through a wireless connection, such as by using any suitable wireless communications protocol known in the art.

In several embodiments, the wind farm <NUM> may include a plurality of environmental sensors <NUM> for monitoring a wind profile of the wind (W) affecting the wind farm <NUM>, and thereby the wind turbines <NUM>. The environmental sensor <NUM> may be configured for gathering data indicative of at least one environmental condition. The environmental sensor <NUM> may be operably coupled to the controller <NUM>. Thus, in an embodiment, the environmental sensor(s) <NUM> may, for example, be a wind vane, an anemometer, a lidar sensor, thermometer, barometer, or other suitable sensor. The data gathered by the environmental sensor(s) <NUM> may include measures of wind direction, wind speed, wind shear, wind gust, wind veer, atmospheric pressure, pressure gradient and/or temperature. In at least one embodiment, the environmental sensor(s) <NUM> may be mounted to the nacelle <NUM> at a location downwind of the rotor <NUM>. It should be appreciated that the environmental sensor(s) <NUM> may include a network of sensors and may be positioned away from the turbine(s) <NUM>. It should be appreciated that environmental conditions may vary significantly across a wind farm <NUM>. Thus, the environmental sensor(s) <NUM> may allow for the local environmental conditions at each wind turbine <NUM> to be monitored individually by the respective turbine controllers and collectively by the farm controller. However, it should be appreciated that the utilization of the systems and methods disclosed herein may preclude a requirement for the environmental sensor(s) <NUM> to monitor certain environmental conditions, such as wind speed, in order to determine a yaw offset for the wind turbine <NUM>.

Referring now to <FIG>, wherein various aspects of multiple embodiments of a system <NUM> for controlling the wind turbine <NUM> according to the present disclosure are presented. As shown particularly in <FIG>, a schematic diagram of one embodiment of suitable components that may be included within the controller <NUM> is illustrated. For example, as shown, the controller <NUM> may include one or more processor(s) <NUM> and associated memory device(s) <NUM> configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and the like and storing relevant data as disclosed herein). Additionally, the controller <NUM> may also include a communications module <NUM> to facilitate communications between the controller <NUM> and the wind turbines <NUM>, and components thereof. Further, the communications module <NUM> may include a sensor interface <NUM> (e.g., one or more analog-to-digital converters) to permit signals transmitted from one or more sensors, such as the environmental sensor(s) <NUM> to be converted into signals that can be understood and processed by the processors <NUM>. It should be appreciated that the sensors may be communicatively coupled to the communications module <NUM> using any suitable means. For example, as shown in <FIG>, the sensors may be coupled to the sensor interface <NUM> via a wired connection. However, in other embodiments, the sensors may be coupled to the sensor interface <NUM> via a wireless connection, such as by using any suitable wireless communications protocol known in the art. Additionally, the communications module <NUM> may also be operably coupled to an operating state control module <NUM> configured to change at least one wind turbine operating state.

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) <NUM> may generally comprise memory element(s) including, but not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) <NUM> may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) <NUM>, configure the controller <NUM> to perform various functions including, but not limited to, controlling the wind turbine <NUM> of the plurality of wind turbines <NUM> of the wind farm <NUM> as described herein, as well as various other suitable computer-implemented functions.

Referring particularly to <FIG>, in an embodiment, the controller <NUM> of the system <NUM> may be configured to receive a monitored performance parameter <NUM> and an estimated performance parameter <NUM> for the wind turbine <NUM> at multiple sampling intervals <NUM> of a yaw event <NUM>. Based on the performance parameters <NUM>, <NUM>, the controller <NUM> may determine a performance differential <NUM> for the wind turbine <NUM> at the multiple sampling intervals <NUM>. The performance differential <NUM> may be indicative of a ratio of, or difference, between, the monitored performance parameter <NUM> to the estimated performance parameter <NUM>. For example, the controller <NUM> may determine the percentage of the estimated performance parameter <NUM> actually produced/developed by the wind turbine at the corresponding sampling interval <NUM>.

The performance parameter may, in an embodiment, be a performance parameter of the wind turbine <NUM> which is subject to monitoring. For example, in an embodiment, the performance parameter may comprise the power outputs of the wind turbines <NUM> of the wind farm <NUM>. In an additional embodiment, the performance parameter may be a tip speed ratio, a pitch setpoint, a yawing moment, and/or a bending moment. It should be appreciated that the utilization of the power production of the wind turbines <NUM> of the wind farm <NUM> may be particularly advantageous in that the measurement of the power output is employed in multiple control schemes relating to the control of the wind turbines <NUM> and/or the wind farm <NUM>. Therefore, indications of the power production of the wind turbines <NUM> may be reliable and may be readily available to the controller <NUM>.

In an embodiment, the yaw event <NUM> may be defined by a period between subsequent yaw setpoint commands received from the controller <NUM>. For example, because of the power consumption associated with the activation of the yaw drive mechanism <NUM>, yaw setpoint commands <NUM> may be transmitted by the controller <NUM> at a set interval. In an embodiment, this interval may have a duration of <NUM> seconds. Accordingly, the wind turbine <NUM> may receive the yaw setpoint command <NUM> and the nacelle <NUM> may be rotated into aerodynamic alignment with the wind (W) (e.g., aligning the axis (A) of the wind turbine <NUM> parallel to the wind (W)) at a first yaw angle <NUM>. In such an embodiment, the rotation of the nacelle <NUM> may remain unchanged at the first yaw angle <NUM> during the yaw event <NUM> (e.g. <NUM> seconds) regardless of deviations of the wind away from aerodynamic alignment.

In an embodiment, the period between subsequent yaw setpoint commands <NUM> may include multiple sampling intervals <NUM>. At each sampling interval <NUM>, the controller <NUM> may receive indications corresponding to the performance of the wind turbine <NUM> in response to the environmental conditions. For example, at each sampling interval <NUM> of the multiple sampling intervals, the controller <NUM> may receive the monitored performance parameter <NUM>, the estimated performance parameter <NUM>, and/or a monitored wind direction <NUM>. In an embodiment, each yaw event <NUM> may include at least five sampling intervals <NUM>. For example, in an embodiment each sampling interval <NUM> may occur once every <NUM> seconds over the duration of the yaw event <NUM>. Accordingly, in such an embodiment, the controller <NUM> may be updated six times in between yawing events. Therefore, variations in the wind direction may be detected but not reacted to. Thus, the collection of the parameters at each sampling interval <NUM> during the corresponding yaw event <NUM> may serve as a test sequence for the controller <NUM> without necessitating a deviation from normal wind turbine <NUM> operations.

In an embodiment, the method disclosed herein may be repeated for each yaw event <NUM> occurring over a sampling period <NUM>. The sampling period <NUM> may have a duration of at least one month (e.g. <NUM> days)). In an additional embodiment, the sampling period <NUM> may be greater than five months (e.g. six months). In an embodiment wherein the sampling period <NUM> is greater than five months, the system <NUM> may include more than <NUM>,<NUM> sampling intervals <NUM> per wind turbine <NUM>. It should be appreciated that the more than <NUM>,<NUM> sampling intervals <NUM> may permit the accurate detection of patterns and/or deviations from patterns which may not be accurately discernible at a lower number of sampling intervals.

As depicted graphically in <FIG>, in an embodiment, the controller <NUM> may determine a trendline <NUM> for the wind turbine <NUM>, which correlates the performance differential <NUM> to a deviation of the wind direction <NUM> at each of the multiple sampling intervals <NUM>. The deviation of the wind direction <NUM> may be a deviation relative to a first yaw angle <NUM>. The first yaw angle <NUM> may correspond to a wind direction which is parallel to the axis (A) of the wind turbine <NUM> for the yaw event <NUM>. For example, the first yaw angle <NUM> may be the angle to which the nacelle is yawed in response to the yaw setpoint command <NUM> at the origination of the yaw event <NUM>. In other words, the reciprocal of the first yaw angle may be the direction of the wind (W) at the initiation of the yaw event <NUM>. It should be appreciated that the trendline <NUM> may, in an embodiment, be determined by the controller <NUM> via a polynomial expression.

Referring still to <FIG>, the controller <NUM> may, in an embodiment, utilize the trendline <NUM> to determine a yaw angle offset <NUM>. The yaw angle offset <NUM> may be a difference between an angle <NUM> associated with the vertex <NUM> of the trendline <NUM> and the first yaw angle <NUM>. In an embodiment, such as depicted by the dashed trendline (TLi), wherein the vertex <NUM> aligns with the first yaw angle <NUM>, the yaw angle offset <NUM> may be zero degrees.

It should be appreciated that the vertex <NUM> may correspond to the wind direction wherein the correlation between the monitored performance parameter <NUM> and the estimated performance parameter <NUM> is maximal. Accordingly, the vertex <NUM> may indicate an aerodynamic alignment of the nacelle <NUM> to the wind (W). For example, the vertex <NUM> may, in an embodiment, depict the angle of the nacelle <NUM> relative to the wind (W) at which the wind turbine <NUM> is producing the full estimated performance parameter <NUM> (e.g., is actually producing the estimated amount of power).

As depicted in <FIG>, in an embodiment, the controller <NUM> of the system <NUM> may be configured to adjust a second yaw angle <NUM> of the wind turbine <NUM> based, at least in part, on the yaw angle offset <NUM>. The second yaw angle <NUM> may correspond to the angle to which the nacelle <NUM> is yawed in response to a yaw setpoint command <NUM> incorporating the yaw angle offset <NUM>. In an embodiment, the adjustment of the second yaw angle <NUM> may correspond to the introduction of a biasing value to the controller <NUM>. In a further embodiment, the adjustment may correspond to an aligning or recalibration of the environmental sensor(s) <NUM> of the wind turbine <NUM>. The adjustment may, in an embodiment, be accomplished following the installation of the wind turbine <NUM> or the environmental sensor <NUM>. In an additional embodiment, the adjustment may be accomplished following a maintenance or service activity on the wind turbine <NUM>. For example, the adjustment may include physically rotating the wind direction sensor and/or introducing a biasing factor into the control system for the wind turbine <NUM>.

In an additional embodiment, adjusting the second yaw angle <NUM> of the wind turbine <NUM> may include establishing an alignment test interval for the wind turbine <NUM>. The alignment test interval may define a test schedule for the wind turbine <NUM>. Accordingly, the yaw angle offset may be determined in accordance with the test schedule in order to detect a drift in the alignment of the environmental sensor(s) <NUM> and/or the wind turbine <NUM>.

In an embodiment, the controller <NUM> may designate a subset <NUM> of the plurality of wind turbines <NUM>. The controller <NUM> may then receive an indication of the performance parameter <NUM> for each wind turbine of the designated subset <NUM> at each of the multiple sampling intervals <NUM>. In at least one embodiment, the controller <NUM> may select the designated subset <NUM> of the plurality of wind turbines <NUM> based on a power production profile for each of the designated wind turbines <NUM>. For example, in an embodiment, the designated subset <NUM> may be the wind turbine(s) <NUM> having a demonstrated affinity for power generation under the prevailing conditions. Alternatively, the designated subset <NUM> may have an average power generation capability relative to the plurality of wind turbines <NUM>. It should be appreciated that selecting a designated subset <NUM> having an average, or below average power generation capability for the prevailing conditions, may ensure that a power generation level from the designated subset <NUM> is foreseeably achievable by other wind turbines <NUM> of the wind farm <NUM>.

In an additional embodiment, the designated subset <NUM> may include wind turbines <NUM> positioned in particularly advantageous or disadvantaged locations relative to the wind (W) affecting the wind farm <NUM>. For example, the designated subset <NUM> may include wind turbine(s) <NUM> located at the point of greatest elevation of the wind farm <NUM> and/or along a portion of the perimeter of the wind farm <NUM> upwind of other wind turbines <NUM>. Alternatively, the designated subset <NUM> may be in a disadvantaged position, such as in a wind shadow, or other region of disturbed wind flow. Selecting wind turbines <NUM> which are in a disadvantaged position may result in the designated subset <NUM> having a power generation capability which is foreseeably achievable by other wind turbines <NUM> in more advantageous positions.

In an embodiment, the controller <NUM> may model an expected performance parameter <NUM> for the wind turbine <NUM> at each of the multiple sampling intervals <NUM> based on the received indications of the performance parameter <NUM> of each wind turbine <NUM> of the designated subset <NUM>. The expected performance parameter <NUM> may correspond to the estimated performance parameter <NUM> and may, therefore, indicate the anticipated/predicted performance parameter for the specific sampling interval <NUM> given the wind (W). Additionally, the controller <NUM> may monitor the actual performance parameter for the wind turbine <NUM> at each of the multiple sampling intervals <NUM>. It should be appreciated that the modelling may be accomplished using known techniques in the art, such as ensemble forecasting.

Referring still to <FIG>, in an embodiment, in order to determine the trendline <NUM>, the controller <NUM> may receive an indication of the monitored wind direction <NUM> from the environmental sensor <NUM> of the wind turbine <NUM> at each of the multiple sampling intervals <NUM> of the yaw event <NUM>. For example, during the period between yaw setpoint commands <NUM>, wherein the nacelle <NUM> may be stationary, the environmental sensor <NUM> may detect wind shifts or oscillations relative to the first yaw angle <NUM>. Being in the period between yaw setpoint commands <NUM>, the controller <NUM> may record these observations without reacting to the change in wind direction by commanding a yawing action from the yaw drive mechanism <NUM>.

In an embodiment, the first yaw angle <NUM> may be determined by the controller <NUM> without a direct measurement of the wind direction. Accordingly, in an embodiment, the controller <NUM> may receive an indication of the yaw setpoint <NUM> from at least a portion of the plurality of wind turbines <NUM> at least once per yaw event <NUM>. For example, in an embodiment, the controller <NUM> may receive an indication of the yaw direction of each wind turbine <NUM> of the wind farm <NUM> relative to a cardinal direction (N). In an embodiment, the controller <NUM> may determine a median yaw setpoint <NUM> based on the received indications of the yaw setpoints <NUM>. The median yaw setpoint <NUM> may be indicative of a yaw-event wind direction, which may be the wind direction in axial alignment (e.g. aerodynamic alignment) with the wind turbine <NUM> for the yaw event <NUM>. It should be appreciated that determining the first yaw angle <NUM> via the meeting yaw setpoint <NUM> and without a direct measurement of the wind direction may preclude errors which may be associated with the alignment/response of any individual wind turbine <NUM>.

The yaw-event wind direction may be considered the prevailing wind direction for the yaw event and may remain unchanged between subsequent yaw setpoint commands <NUM>. Therefore, any wind shift away from the yaw-event wind direction may be considered to be a deviation of the wind direction <NUM>. Accordingly, controller <NUM> may, at <NUM>, determine a difference between the monitored wind direction <NUM> at each of the multiple sampling intervals <NUM> and the first yaw angle <NUM>. The difference may correspond to the deviation of the wind direction <NUM> at each of the multiple sampling intervals <NUM> from the yaw event wind direction/first yaw angle <NUM>. Accordingly, in an embodiment, the controller <NUM> may determine a performance-parameter-correlation distribution <NUM> relative to the deviation of the wind direction <NUM> from the first yaw angle <NUM> for the yaw event <NUM>. The performance-parameter-correlation distribution <NUM> may serve as a foundation for determining the trendline <NUM>.

In an embodiment, the accuracy of the yaw angle offset <NUM> may be increased by the utilization of a second performance parameter in addition to the performance parameter <NUM>, <NUM> discussed above. Accordingly, in an embodiment, the controller may determine a second performance differential <NUM> for the wind turbine <NUM> at each of the multiple sampling intervals <NUM>. The second performance differential <NUM> may be indicative of a ratio of a monitored second performance parameter to an estimated second performance parameter for the wind turbine <NUM>. The inclusion of the second performance parameter may transform the trendline <NUM> into a three-dimensional trendline correlating the first performance differential <NUM> and the second performance differential <NUM> to the deviation of the wind direction <NUM>, at each of the multiple sampling intervals <NUM>, from the first yaw angle <NUM>. In an embodiment, the second performance parameter may include a tip speed ratio, a pitch setpoint, a yawing moment, wind speed, turbulence intensity, and/or a bending moment. , It should be appreciated that more than two performance parameters may be utilized to further increase the fidelity of the yaw angle offset <NUM>.

Referring particularly to <FIG>, as depicted at <NUM>, in an embodiment, the system <NUM> may define at least a first and a second yaw sector <NUM>, <NUM>. In an embodiment, additional yaw sectors <NUM> may be defined as desired. Each of the yaw sectors <NUM>, <NUM>, <NUM> may be defined by an arc of rotation of the nacelle <NUM> relative to a cardinal direction (N).

In an embodiment, the system <NUM> may determine/define a first yaw angle offset <NUM> for the wind turbine <NUM> when the wind turbine <NUM> is in the first yaw sector <NUM>. Additionally, the system <NUM> may determine/define a second yaw angle offset <NUM> for the wind turbine <NUM> when the wind turbine <NUM> is in the second yaw sector <NUM>. In an embodiment, the second yaw angle offset <NUM> may be different than the first yaw angle offset <NUM>. For example, the second yaw angle offset <NUM> may be greater than the first yaw angle offset <NUM> an embodiment. It should be appreciated that the utilization of multiple yaw angle offsets in distinct yaw sectors may be necessitated by the layout of the wind farm <NUM> (e.g. the presence of wake effects from neighboring wind turbines <NUM>) and/or the topography of the wind farm. Thus, the utilization of multiple yaw angle offsets may permit the system <NUM> to tailor the adjustment of the second yaw angle <NUM> in consideration of topography, wake effects, and/or other site conditions.

Claim 1:
A method for controlling a wind turbine of a wind farm (<NUM>) having a plurality of wind turbines (<NUM>), the method comprising:
determining, via a controller (<NUM>), a performance differential (<NUM>) for the wind turbine (<NUM>) for multiple sampling intervals (<NUM>) of a yaw event (<NUM>), the performance differential (<NUM>) being indicative of a ratio of a monitored performance parameter (<NUM>) to an estimated performance parameter (<NUM>) for the wind turbine (<NUM>), the estimated performance parameter (<NUM>) for the wind turbine (<NUM>) being estimated based on performance parameters of a designated subset (<NUM>) of wind turbines of the wind farm (<NUM>) at the multiple sampling intervals (<NUM>);
determining, via the controller (<NUM>), a trendline for the wind turbine (<NUM>) correlating the performance differential (<NUM>) to a deviation of a wind direction (W, <NUM>) at each of the multiple sampling intervals (<NUM>) from a first yaw angle (<NUM>) for the yaw event (<NUM>);
determining, via the controller (<NUM>), a yaw angle offset (<NUM>) based on a difference between an angle associated with a vertex of the trendline and the first yaw angle (<NUM>); and
adjusting, via the controller (<NUM>), a second yaw angle of the wind turbine (<NUM>) based, at least in part, on the yaw angle offset (<NUM>).