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 modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.

In many wind turbines, the generator may be electrically coupled to a bi-directional power converter that includes a rotor-side converter joined to a line-side converter via a regulated DC link. Such wind turbine power systems are generally referred to as a doubly-fed induction generator (DFIG). DFIG operation is typically characterized in that the rotor circuit is supplied with current from a current-regulated power converter. As such, the wind turbine produces variable mechanical torque due to variable wind speeds and the power converter ensures this torque is converted into an electrical output at the same frequency of the grid.

During operation, wind impacts the rotor blades and the blades transform wind energy into a mechanical rotational torque that drives a low-speed shaft. The low-speed shaft is configured to drive the gearbox that subsequently steps up the low rotational speed of the low-speed shaft to drive a high-speed shaft at an increased rotational speed. The high-speed shaft is generally coupled to the generator so as to rotatably drive a generator rotor. As such, a rotating magnetic field may be induced by the generator rotor and a voltage may be induced within a generator stator. Rotational energy is converted into electrical energy through electromagnetic fields coupling the rotor and the stator, which is supplied to a power grid via a grid breaker. Thus, the main transformer steps up the voltage amplitude of the electrical power such that the transformed electrical power may be further transmitted to the power grid.

For some wind turbines, it is desirable to modify the torque command of the power converter during operation of the wind turbine as each rotor blade aligns with and passes the tower. This modification, however, can tend to cause undesirable low-frequency voltage variations on the power grid. Such variations are often referred to as flicker. Thus, the term "flicker" as used herein generally refers to variations in current or voltage on the power grid that are perceptible at certain frequencies (e.g. from about <NUM> Hertz (Hz) to about <NUM>). Additionally, when the wind turbines are assembled as a wind farm, the flicker of the individual wind turbines, or a portion thereof, may be unintentionally synchronized resulting in an output flicker in the output of the wind farm. Oftentimes, grid requirements prohibit connection to the power grid if flicker is present in a certain amount.

In view of the aforementioned, the art is continuously seeking new and improved systems and methods for managing flicker generated by wind farm.

The paper "<NPL>) explains how significant electrical power fluctuations in the range of seconds may be generated by most oscillating wave energy converters without significant amounts of energy storage capacity. Because of these fluctuations, a wave farm may have a negative impact on the power quality of the local grid to which it is connected. The paper details a case study on the impact of a wave farm on the distribution grid around the national wave test site of Ireland with respect to voltage and power fluctuations, as well as regarding flicker levels.

Further, the paper "<NPL>) details how the flicker emission produced by the turbine due to rapid changes in wind speed results in fluctuating power, which can lead to voltage fluctuations at the point-of-common-coupling (PCC). The accuracy of the measuring methods is an essential part of the assessment of power quality in the grid-connected wind turbine. This paper introduces the innovative procedure of flicker measurement model of grid-connected wind turbines and deals with the verification test of the measurement procedure for the flicker.

The invention is defined by a method for managing output flicker of a wind farm connected to a power grid with the steps of independent claim <NUM> and by a system for managing output flicker generated by a wind farm with the technical features of independent claim <NUM>.

In a further embodiment, the wind farm may also include at least one output sensor operably coupled to the farm controller at a point of interconnect (POI) with the power grid. Additionally, detecting the parameter(s) indicative of the output flicker may also include monitoring via the output sensor(s) a frequency and amplitude of variations in current or voltage of the output of the wind farm at the point of interconnect with the power grid. The frequency and amplitude of the variations may be indicative of output flicker in the output of the wind turbine(s). The method may also include detecting, with the farm controller, an approach of the output of the output sensor(s) to a flicker threshold for the wind farm.

In yet a further embodiment, the wind farm may include at least one environmental sensor operably coupled to the farm controller. Additionally, detecting the parameter(s) indicative of the output flicker may include monitoring, via the environmental sensor(s), at least one environmental parameter indicative of an environmental condition affecting the wind farm. The method may also include correlating, with the farm controller, the environmental parameter(s) to indicate an of a level of output flicker as detected by the output sensor(s) at the monitored environmental condition.

In an embodiment, the method may include determining, with the farm controller, an output flicker potential for the wind farm based at least in part on the correlation and a forecasted environmental condition.

In an additional embodiment, generating the command offset may include generating the command offset when at least one of the output flicker potential or the output of the output sensor(s) approaches or exceeds the flicker threshold for the wind farm.

In a further embodiment, the method may include determining an impact on the level of output flicker resulting from the changing of the operating parameter of the wind turbine(s) based on the command offset. The method may also include correlating, with the farm controller, the impact with the environmental condition affecting the wind farm. Further, the method may include assigning a synchronicity-impact score to the wind turbine(s) based on the computed correlation for the detected environmental condition. Additionally, the method may include selecting the wind turbine(s) from the plurality of wind turbines to receive the command offset based, at least partially, on the synchronicity-impact score.

In yet a further embodiment, detecting the parameter(s) indicative of the output flicker may include receiving, with the farm controller, a timing signal from the two wind turbines. The timing signal may be indicative of a rotor position for each of the wind turbines. The method may include determining, with the farm controller, a degree of synchronicity amongst the two wind turbines of the plurality of wind turbines based on the respective timing signals. Additionally, the method may include determining, with the farm controller, a difference between the degree of synchronicity and a synchronicity threshold corresponding to an output flicker threshold.

In an embodiment, determining the degree of synchronicity among the plurality of wind turbines may include establishing, with the farm controller, a plurality of time slices. The method may also include determining, with the farm controller, a standard deviation for the timing signals across the time slices. The standard deviation for the timing signals may be indicative of the degree of synchronicity amongst the plurality of wind turbines.

In an additional embodiment, the two wind turbines of the plurality of wind turbines may include at least a first sub-grouping of wind turbines and a second sub-grouping of wind turbines. The timing signal may be indicative of a combined timing of the first and second sub-groupings of wind turbines respectively.

In a further embodiment, changing the operating parameter of the wind turbine(s) based on the command offset may include changing an operating parameter corresponding to at least one of generator torque, power output, rotor speed, or mechanical loading of the wind turbine(s).

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 of the invention as defined by the appended claims.

The term "coupled" refers to both direct coupling, as well as indirect coupling, through one or more intermediate components or features, unless otherwise specified herein.

Generally, the present disclosure is directed to systems and methods for controlling a wind farm connected to power grid. In particular, the present invention includes a system and method which facilitate managing flicker occurring in the power grid generated by the wind farm. The flicker is be an output flicker resulting in the output of the wind farm resulting from the unintentional alignment/synchronization of the flicker that may be present in the outputs of the individual wind turbines of the wind farm. Accordingly, the farm controller detects a parameter of the wind farm, the indicative of a synchronized flicker of two or more wind turbines of the wind farm. In the various embodiments, the parameter may, for example, include measurements of the flicker, weather conditions, rotor position timing signals, learned wind turbine behaviors, and/or the wind turbine operational state.

In response to detecting the parameter, the farm controller generates a command offset for at least one of the wind turbines. The command offset may temporarily alter an operating state or parameter of the wind turbine. For example, when the rotors of two wind turbines pass through the six o'clock position at the same time, any flicker in the output of the wind turbines may be synchronized. Upon detecting such a state, the farm controller may direct one of the wind turbines to momentarily change its rotational speed so that the rotors of the two wind turbines pass through the six o'clock position at different instants. In other words, under the present disclosure, one of the wind turbines may, essentially, "skip a beat" so that the rotor positions, or other aspect of the turbines, are de-synchronized. Even though the individual wind turbines may produce an output having flicker, by de-synchronizing the flickers, the combined output of the wind farm delivered to the power grid may not flicker.

Referring now to the drawings, <FIG> illustrates a perspective view of one embodiment of a wind turbine <NUM> according to the present disclosure. 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 (not shown) 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 <NUM>. The controller <NUM> may be 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 <NUM>. 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 turbine 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.

Still referring to <FIG>, one or more sensors <NUM>, <NUM> may be provided on the wind turbine <NUM> to monitor the performance of the wind turbine <NUM> and/or environmental conditions affecting the wind turbine <NUM>. It should also be appreciated that, as used herein, the term "monitor" and variations thereof indicates that the various sensors of the wind turbine <NUM> may be configured to provide a direct measurement of the parameters being monitored or an indirect measurement of such parameters. Thus, the sensors described herein may, for example, be used to generate signals relating to the parameter being monitored, which can then be utilized by the controller <NUM> to determine the condition of the wind turbine <NUM>. For example, as shown, each of the wind turbines <NUM> may include an environmental sensor <NUM> 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 speed, wind direction, wind shear, wind gust, wind veer, atmospheric pressure, 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>. The environmental sensor(s) <NUM> may, in alternative embodiments, be coupled to, or integrated with, 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 wind turbines <NUM>.

In addition to the environmental sensor(s) <NUM>, the wind turbines <NUM> may also include one or more asset condition sensors <NUM>. The asset condition sensor(s) <NUM> may, for example, be configured to monitor electrical properties of the output of the generator of each of the wind turbines <NUM>, such as current sensors, voltage sensors temperature sensors, or power sensors that monitor power output directly based on current and voltage measurements. In at least one embodiment, the asset condition sensor(s) <NUM> may include any other sensors that may be utilized to monitor the operating state of the wind turbines <NUM>, such as rotor position and/or rotor timing.

Referring now to <FIG>, a schematic view of a wind farm <NUM> controlled according to the system and method of the present disclosure is illustrated. As shown, in an embodiment, the wind farm <NUM> may include a plurality of wind turbines <NUM> described herein and a controller <NUM>. The controller <NUM> may be configured as a farm controller <NUM>. 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 turbine controller(s) <NUM> of the wind turbine(s) <NUM> may be communicatively coupled to the farm controller <NUM> through a wired connection, such as by connecting the controller(s) <NUM> through suitable communicative links <NUM> (e.g., a suitable cable). Alternatively, the controller(s) <NUM> may be communicatively coupled to the farm controller <NUM> through a wireless connection, such as by using any suitable wireless communications protocol known in the art. In addition, the farm controller <NUM> may be generally configured similar to the controller <NUM> for each of the individual wind turbines <NUM> within the wind farm <NUM>.

In an embodiment, the farm controller <NUM> may also be operably coupled to at least one output sensor <NUM> at a point of interconnect with the power grid. The output sensor(s) <NUM> may be configured to monitor the output of the wind farm <NUM> in order to detect indications of output flicker in the output.

Referring now to <FIG>, schematic diagrams of multiple embodiments of a system <NUM> for managing flicker generated by the wind farm <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 various components of the wind turbines <NUM>. 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 <NUM>, <NUM>, <NUM> to be converted into signals that can be understood and processed by the processors <NUM>. It should be appreciated that the sensors <NUM>, <NUM>, <NUM> may be communicatively coupled to the communications module <NUM> using any suitable means. For example, as shown in <FIG>, the sensors <NUM>, <NUM>, <NUM> are coupled to the sensor interface <NUM> via a wired connection. However, in other embodiments, the sensors <NUM>, <NUM>, <NUM> 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/operating parameter.

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, detecting at least one parameter indicative of an output flicker, generating a command offset for a wind turbine, and changing an operating parameter of the wind turbine based on the command offset in order to de-synchronize the synchronized flicker in the output signals of the wind turbines, as described herein, as well as various other suitable computer-implemented functions.

Referring particularly to <FIG>, according to the invention, the farm controller <NUM> of the system <NUM> is configured to detect at least one parameter <NUM> of the wind farm <NUM> indicative of an output flicker occurring in the power grid and generated by at least two of the wind turbines <NUM>. In an embodiment, the parameter(s) <NUM> may be indicated by output sensor data <NUM>, the environmental sensor data <NUM>, and/or a timing signal <NUM>. In an embodiment, the parameter(s) <NUM> may include measurements of the flicker in the output of the wind farm <NUM> as indicated by variations in current and/or voltage, which may be indicative of synchronized flicker. In an additional embodiment, the parameter(s) <NUM> may include data indicative of an environmental condition affecting the wind turbines <NUM>. In a further embodiment, the parameter(s) <NUM> may include rotor positions of the rotors <NUM> of the wind turbines <NUM> as indicated by the timing signal <NUM>. Additionally, in an embodiment, the parameter(s) <NUM> may be a learned wind turbine behavior wherein historical environmental conditions that resulted in flicker may be correlated to determine an output flicker potential corresponding to a weather forecast. In yet a further embodiment, the parameter(s) <NUM> may correspond to an operational state of the wind farm. For example, in an embodiment, the presence of synchronized flicker may be presumed whenever the wind farm <NUM> is in operation and, therefore, the control logic of the system <NUM> may be utilized to de-synchronize the output of each wind turbine <NUM> of the wind farm <NUM>.

It should be appreciated that the flicker generated by the wind farm <NUM> is the result of the synchronization of flicker present in the output of at least a portion of the plurality of wind turbines <NUM> of the wind farm <NUM>. For example, <FIG> depicts an embodiment wherein the output signal of a first wind turbine <NUM>, a second wind turbine <NUM>, and a third wind turbine <NUM> may be characterized by frequency and amplitude variations in current/voltage, which may be synchronized. In such an embodiment, when the outputs of the three wind turbines <NUM> are combined at the POI, the resultant output of the wind farm <NUM> may reflect the combined, synchronized flicker of the wind turbines <NUM>, as indicated by the plot <NUM>. In an embodiment, plot <NUM>, may reflect flicker in the output of the wind farm <NUM> as seen by the power grid, and which may be delivered to a power grid consumer. However, as depicted by <FIG>, in an embodiment, the system <NUM> may be employed to change an operating parameter of at least one wind turbine <NUM> in order to de-synchronize the synchronized flicker in the output signals. For example due to the changing of an operating parameter, the output signals of the first, second, and third wind turbines <NUM>, <NUM>, <NUM> may be characterized by frequency and amplitude variations in current/voltage which are de-synchronized relative to one another as depicted in <FIG>. The combination of the de-synchronized output signals may result in an output signal of the wind farm <NUM> having an absence of flicker as depicted by plot <NUM>.

It should be further appreciated that being de-synchronized, the frequency and amplitude variations (e.g., flicker) in the output signal of a wind turbine <NUM> may be essentially masked by the frequency and amplitude variations in the output signal of another wind turbine <NUM> of the wind farm <NUM>. Therefore, while flicker may, in an embodiment, be detectable in the outputs of the individual wind turbines <NUM>, the combination of the de-synchronized outputs, as reflected by the output of the wind farm <NUM>, may be a stable/constant output as perceived by a power grid consumer.

Referring again to <FIG>, the farm controller <NUM> of the system <NUM> is configured to generate a command offset <NUM> for at least one wind turbine <NUM> upon detecting the parameter(s) <NUM> indicative of the synchronized flicker of the outputs of at least two wind turbines <NUM>. The command offset <NUM> facilitates the de-synchronization of the synchronized flicker in order to develop a wind farm <NUM> output which does not demonstrate the characteristics of flicker.

In an embodiment, the command offset, at <NUM>, is employed by the system <NUM> to change an operating parameter of the wind turbine(s) <NUM> so as to de-synchronize the synchronized flicker in the output signals of the at least two wind turbines at <NUM>. In an embodiment, changing the operating parameter of the wind turbine(s) <NUM> based on the command offset <NUM> may include changing an operating parameter corresponding to a generator torque, power output, rotors speed, and/or mechanical loading of the wind turbine(s) <NUM>. For example, in an embodiment, the command offset may be merged with a setpoint command for the wind turbine(s) <NUM> to generate a modified setpoint command. The modified setpoint command may, in an embodiment, be transmitted to the wind turbine(s) <NUM> in order to adjust the operating state of the wind turbine(s) <NUM>. In an embodiment, the system <NUM> may follow the transmission of the modified setpoint command with the transmission of an unmodified setpoint command thereby returning the wind turbine(s) <NUM> to the original operating state but without the previously detected synchronized flicker. For instance, in an embodiment, the torque set point of the generator may be temporarily increased, resulting in an alteration of the frequency and/or amplitude of variations in the output current/voltage of the wind turbine(s) <NUM>, before returning to a previous established optimal torque setpoint for the given operating state of the wind turbine(s) <NUM>.

According to the invention, generating the command offset <NUM> includes the generation of a random biasing value <NUM> by the farm controller <NUM>. The random biasing value <NUM> may be a random value introduced into a control logic of the wind turbine(s) <NUM> to temporarily bias a setpoint of the wind turbine(s) <NUM>. For example, as shown at <NUM>, in an embodiment, the farm controller <NUM> may be configured to introduce the biasing value <NUM> into a speed feedback loop of the turbine controller(s) <NUM> of the wind turbine(s) <NUM> to develop a variable rotor speed <NUM> for the wind turbine(s) <NUM>. In an embodiment, the random biasing value <NUM> may include different variables introduced to different wind turbines <NUM> of the wind farm <NUM>. In an additional embodiment, the random biasing value <NUM> may be a single value introduced to a random selection of wind turbines <NUM> of the wind farm <NUM> at a first instant, and a different random selection of wind turbines <NUM> at a second instant.

In an embodiment, as depicted in <FIG>, the farm controller <NUM> of the system <NUM> may be configured to receive output sensor data <NUM> from the output sensor(s) <NUM>. Accordingly, the output sensor(s) <NUM> may, at <NUM>, be utilized to monitor the frequency and amplitude of variations in current and/or voltage of the output of the wind farm <NUM> at the POI. In an embodiment, the frequency and/or amplitude of the variations in the output of the wind farm <NUM> may be indicative of the synchronization of the flicker present in the output of various wind turbines <NUM> of the wind farm <NUM>. As depicted at <NUM>, in an embodiment, the farm controller <NUM> may compare the monitored variations in current and/or voltage to a flicker threshold <NUM>. Accordingly, the farm controller <NUM> may, at <NUM>, detect an approach of the output of the output sensor(s) <NUM> to the flicker threshold <NUM> for the wind farm <NUM>. In an embodiment wherein the farm controller <NUM> determines, at <NUM>, a level of flicker which approaches or exceeds the flicker threshold <NUM>, the farm controller <NUM> may generate the command offset <NUM>.

In an embodiment, detecting the parameter(s) <NUM> indicative of output flicker may include monitoring environmental sensor data <NUM>. The environmental sensor data <NUM> may be at least one environmental parameter <NUM> indicative of an environmental condition affecting the wind farm <NUM>. In an embodiment, the farm controller <NUM> may, at <NUM>, correlate the environmental parameter(s) <NUM> to an indication of a level of output flicker. For example, the farm controller <NUM> may, in an embodiment, correlate the environmental parameter(s) <NUM> to the level of output flicker detected by the output sensor(s) <NUM> at the monitored environmental condition.

In an embodiment, the correlation of the environmental conditions to the level of output flicker may be accomplished over a specified period in order to establish a historical data set of correlations based on the observed relationship between the environmental conditions and the resultant level of output flicker. Accordingly, in an embodiment, the farm controller <NUM> of the system <NUM> may be configured to receive an environmental condition forecast <NUM>. Based at least in part on the environmental condition forecast <NUM> and the correlation between the environmental parameter(s) <NUM>/level of output flicker correlation, the farm controller <NUM> may determine an output flicker potential <NUM>. It should be appreciated that the output flicker potential <NUM> may represent the degree of synchronized flicker which may be anticipated when the wind farm is affected by the forecasted environmental conditions.

As depicted at <NUM>, in an embodiment, the farm controller <NUM> may be configured to compare the output flicker potential <NUM> to the flicker threshold <NUM> in order to detect, at <NUM>, an approach of the flicker potential <NUM> to the flicker threshold <NUM>. In an embodiment wherein the output flicker potential <NUM> approaches or exceeds the flicker threshold <NUM> for the wind farm <NUM>, the farm controller <NUM> may generate the command offset <NUM>. For example, the farm controller <NUM> may receive a weather forecast and may determine the anticipated level of output flicker under the forecast conditions. This anticipated level may, in an embodiment, be compared to the flicker threshold <NUM>. When the anticipated level of output flicker meets or exceeds the flicker threshold <NUM>, the farm controller <NUM> may prospectively generate the command offset <NUM> so as to preclude the development of an unacceptable level of output flicker in the output of the wind farm <NUM>. Accordingly, it should be appreciated that the farm controller <NUM> may, in an embodiment generate the command offset <NUM> when the output flicker potential <NUM> and/or the output of the output sensor(s) <NUM> approaches or exceeds the flicker threshold <NUM> for the wind farm <NUM>.

In an embodiment, the farm controller <NUM> of the system <NUM> may be configured to execute a feedback loop wherein the de-synchronization efficacy of the various wind turbines <NUM> of the wind farm <NUM> may be determined for various environmental conditions. Accordingly, the farm controller <NUM> may determine an impact <NUM> on the level of output flicker resulting from the changing of the operating parameter, at <NUM>, of the wind turbine(s) <NUM> based on the command offset <NUM>. As depicted at <NUM>, the farm controller <NUM> may correlate the impact <NUM> with the environmental condition affecting the wind turbine <NUM> as indicated by the environmental parameter(s) <NUM>. In an embodiment, the farm controller <NUM> may assign a synchronicity-impact score <NUM> to the wind turbine(s) <NUM> based on the computed correlation for the detected environmental condition. Based, at least partially, on the synchronicity-impact score <NUM>, the farm controller <NUM> may, at <NUM>, select the wind turbine(s) <NUM> from the plurality of wind turbines <NUM> to receive the command offset <NUM>. In an embodiment, the feedback loop may be executed each time the command offset <NUM> is generated in response to the detection of the parameter(s) <NUM> indicative of output flicker, over a specified number of command cycles, and/or a specified period. Accordingly, a historical data set of correlations between the environmental parameter(s) <NUM> (e.g., weather conditions) and the de-synchronization efficacy of the wind turbine(s) <NUM>. It should be appreciated that the farm controller <NUM> may utilize the historical data set, at least in part, to select the wind turbine(s) <NUM> from the plurality of wind turbines <NUM> which may be most effective at de-synchronizing the synchronized flicker output either prospectively or reactively.

In an embodiment, the detection of the parameter(s) <NUM> indicative of the output flicker may be based, at least in part, on the rotor positions of at least two wind turbines <NUM>. As such, in an embodiment, the farm controller <NUM> of the system <NUM> may be configured to receive a timing signal <NUM> from at least two wind turbines <NUM> of the wind farm <NUM>. The timing signal <NUM> may be indicative of the rotor position for the rotors <NUM> for each of the wind turbines <NUM>. For example, the rotor position may indicate that a rotor blade <NUM> of each respective rotor <NUM> may be passing the tower <NUM> at the same instant, thereby indicating that the rotation of the respective rotors <NUM> may be synchronized. Based on the respective timing signals <NUM>, the farm controller <NUM> may, in an embodiment, determine a degree of synchronicity <NUM> amongst the wind turbines <NUM>.

It should be appreciated that in an embodiment, the at least two wind turbines <NUM> may be at least a first sub-grouping <NUM> of wind turbines <NUM> and a second sub-grouping <NUM> of wind turbines <NUM>. In such an embodiment, the timing signals <NUM> of the individual wind turbines <NUM> of the respective sub-groupings <NUM>, <NUM> may be consolidated into a single timing signal <NUM> for each of the sub-groupings <NUM>, <NUM>. Accordingly, in an embodiment, the timing signals <NUM> received by the farm controller <NUM> may correspond to a consolidated timing signal for the first sub-grouping <NUM> and a consolidated timing signal for the second sub-grouping <NUM>.

In an embodiment, determining the degree of synchronicity <NUM>, may include establishing a plurality of time slices <NUM> with the farm controller <NUM>. The farm controller <NUM> may then determine a standard deviation <NUM> for the timing signal <NUM> across the time slices. The standard deviation <NUM> may be indicative of the degree of synchronicity <NUM> amongst the wind turbines <NUM>. It should be appreciated that the lower the standard deviation <NUM>, the greater the degree of synchronicity <NUM> amongst the wind turbines <NUM>, with the opposite being also true.

The farm controller <NUM> may, in an embodiment, determine, at <NUM>, a difference between the degree of synchronicity <NUM> and a synchronicity threshold <NUM>. The synchronicity threshold <NUM> may correspond to the flicker threshold <NUM> such that an approach to the synchronicity threshold <NUM> may indicate an approach of the output flicker in the output of the wind farm <NUM> to the flicker threshold <NUM>. It should be appreciated that the utilization of the degree of synchronicity <NUM> to detect an approach of the level of flicker to the flicker threshold <NUM> may preclude the requirement to monitor the output of the wind farm <NUM> and/or the environmental parameter(s) <NUM>, or may be employed in conjunction with the monitoring of the output and/or the environmental parameter(s) <NUM>.

It should be appreciated that the various embodiments disclosed herein relating to the detection of the parameter(s) <NUM> indicative of the output flicker, the generation of the command offset <NUM>, and the changing of an operating parameter may be combined in various combinations and/or employed individually to facilitate the managing of flicker in the output of the wind farm <NUM> by the system <NUM>.

Claim 1:
A method for managing output flicker of a wind farm (<NUM>) connected to a power grid, the wind farm (<NUM>) comprising a plurality of wind turbines (<NUM>), the method comprising:
detecting, with a controller (<NUM>), at least one parameter of the wind farm (<NUM>) indicative of output flicker resulting from a synchronized flicker from at least two wind turbines (<NUM>) of the plurality of wind turbines (<NUM>);
upon detecting the at least one parameter, generating a command offset (<NUM>) for at least one wind turbine (<NUM>) of the at least two wind turbines (<NUM>), generating the command offset (<NUM>) comprising generating a random biasing value (<NUM>); and
changing an operating parameter of the at least one wind turbine (<NUM>) based on the command offset (<NUM>) so as to de-synchronize the synchronized flicker in output signals of the at least two wind turbines (<NUM>),
wherein the random biasing value (<NUM>) is introduced into a speed feedback loop of a turbine controller (<NUM>) to develop a variable rotor speed for the at least one wind turbine (<NUM>).