Wind turbine wake loss control using detected downstream wake loss as function of wind direction

Abstract

The invention relates to controlling a wind turbine having a predefined wake control strategy for controlling the wind turbine to perform a wake control action according to a wind direction, and for adjusting its generated wake in a wind direction predicted that would result in a wake loss at another downstream wind turbine. The invention includes receiving, from a further wind turbine, a wind direction determined to cause a defined wake condition at the further wind turbine, and determining a difference between a wind direction predicted to cause the defined wake condition at the further wind turbine and the received wind direction determined to cause the defined wake condition. The invention includes determining an adjusted wake control strategy according to a wind direction offset based on the determined difference, the adjusted wake control strategy being used to control the wind turbine to perform a wake control action of the predefined strategy.

Description

Technical Field

[0001] The present invention relates to controlling wind turbines of a wind park comprising a plurality of wind turbines. In particular, the present invention relates to controlling the wind turbines according to a wake loss control strategy to control the wake generated by the wind turbines, the wake loss control strategy being determined based on wake losses experienced at other wind turbines of the plurality of wind turbines (e.g., downstream of the wind turbine) as a function of wind direction. Background Art

[0002] Wind turbines are used to capture energy from the wind as it flows past the wind turbines and to generate power from the captured energy, for example to supply an electrical grid. Typically, several wind turbines are located relatively close to each other in a geographic area, where such a group of wind turbines may be collectively referred to as forming a wind park or wind farm.

[0003] The amount of wind energy that can be captured by a wind turbine varies depending on various environmental factors, such as wind speed and wind direction. For example, a wind turbine can generally be most efficient in capturing wind energy when the turbine's rotor or nacelle faces directly into the direction of the incoming wind, i.e., when the wind turbine is aligned with the wind.

[0004] When wind flows over a wind turbine, a wake in the form of a disturbed flow is generated downstream of the wind turbine. That is, the wind flow downstream of the wind turbine is disturbed or disturbed relative to the upstream of the wind turbine. This disturbance may result in a reduction in the wind flow speed and / or an increase in the wind flow turbulence. Each of these results in a reduction in the amount of available energy that can be captured from the wind.

[0005] In a wind park, the wake generated by a first upstream wind turbine may impact a second downstream wind turbine, thereby causing the power generation efficiency of the downstream wind turbine to decrease relative to a situation where there is no upstream wind turbine, i.e., relative to a situation where there is no wake effect caused by the upstream turbine. This may be referred to as a wake loss experienced by the downstream wind turbine.

[0006] It is known to perform so-called wake steering of wind turbines to steer the wake generated by an upstream turbine away from a downstream turbine. This may involve controlling the misalignment of the upstream turbine relative to the incoming wind. While this may reduce the energy capture efficiency of the upstream turbine, an increase in the energy capture efficiency of the downstream turbine may result in an overall increase in the energy capture efficiency of the wind park.

[0007] Known methods for performing wake steering may be disadvantageous because wake steering is not performed when required, wake steering is performed when not required, and / or wake steering is performed incorrectly such that a reduction in wake effects experienced by downstream turbines is not properly achieved. These disadvantages may result from one or more of: inaccurate detection of wind turbine nacelle position or relative wind speed; inaccurate information regarding the relative positioning of wind turbines in a wind park; and / or variations in the generated wake caused by other factors such as terrain or other obstructions, wind conditions, etc. The resulting effect may be a reduction in the overall energy capture efficiency of the wind park.

[0008] The present invention is proposed against this background. Summary of the invention

[0009] According to one aspect of the present invention, a method for controlling wind turbines of a wind park including a plurality of wind turbines is provided. The method includes retrieving a predefined wake loss control strategy for the wind turbine, the predefined wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions according to a wind direction near the wind turbine, the predefined wake control strategy being used to control the operation of the wind turbine to adjust the wake generated by the wind turbine in a wind direction predicted to cause a wake loss at another wind turbine among the plurality of wind turbines. The method includes receiving a signal from another wind turbine, the signal indicating a wind direction determined to cause a defined wake condition or state at another wind turbine. The method includes determining a difference between a wind direction predicted to cause a defined wake condition at another wind turbine and a received wind direction determined to cause a defined wake condition. The method includes determining an adjusted wake loss control strategy based on a wind direction offset based on (by the determined difference), the adjusted wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions of a predefined wake loss control strategy. The method may include controlling the wind turbine according to the adjusted wake loss control strategy.

[0010] The defined wake condition may be a full wake condition.

[0011] The received wind direction may be a wind direction in which the further wind turbine is in the centre of a wake generated by the wind turbine.

[0012] Determining an adjusted wake loss control strategy may include offsetting a predefined wind direction at which the wake loss control strategy is activated based on the determined difference.

[0013] The method may include, at the further wind turbine: determining a wind direction resulting in a defined wake condition at the further wind turbine; and transmitting a signal to the wind turbine indicative of the wind direction determined to result in the defined wake condition at the further wind turbine.

[0014] A wind direction that results in a defined wake condition at another wind turbine when the wind turbine does not perform one or more wake loss control actions may be determined.

[0015] The wind direction resulting in a defined wake condition at the further wind turbines may be determined during a training period in which a plurality of wind turbines of the wind park are operated for a plurality of different wind directions.

[0016] Determining the wind direction resulting in the defined wake condition may include, for a plurality of different wind directions: receiving sensor signals from one or more sensors of the further wind turbine; and determining a parameter indicative of a load imbalance on a rotor of the further wind turbine based on the received sensor signals.

[0017] The sensor signals from the one or more sensors may be blade load signals from one or more blade load sensors of a rotor blade of the further wind turbine.The parameter may be a yaw moment of the rotor of the further wind turbine determined based on the received blade load signals.

[0018] When activating an adapted wake loss control strategy at a wind turbine to perform one or more wake loss control actions, the method may include iteratively performing the following steps:

[0019] At the further wind turbine:

[0020] monitoring a parameter indicative of a load imbalance based on sensor signals from the one or more sensors; and

[0021] transmitting a signal indicative of the monitored parameter to the wind turbine; and

[0022] At the wind turbine:

[0023] receiving a signal indicative of a monitored parameter from the additional wind turbine;

[0024] determining, based on the received monitoring parameters, a further wind direction offset for reducing a load imbalance on a rotor of the further wind turbine;

[0025] A further adjusted wake loss control strategy is determined according to the wind direction offset based on the determined difference and the additional wind direction offset, wherein the further adjusted wake loss control strategy is used to control the wind turbine to perform the predefined wake loss control strategy.

[0026] one or more wake loss control actions of the strategy; and

[0027] The wind turbine is controlled according to the further adjusted wake loss control strategy.

[0028] Controlling a wind turbine according to an adjusted wake loss control strategy may include: receiving a measured wind direction near the wind turbine from one or more wind direction sensors of the wind turbine or wind park; and activating the adjusted wake loss control strategy to perform one or more wake loss control actions if the measured wind direction offset based on the determined difference is within a predefined range of wake loss control activation wind directions.

[0029] The one or more wake loss control actions may include at least one of: performing yaw control to rotate a nacelle and a rotor of the wind turbine relative to a tower of the wind turbine about a yaw angle to adjust the direction of a wake generated by the wind turbine; performing pitch control to generate a pitch moment about a pitch axis to adjust the direction of a wake generated by the wind turbine; performing collective pitch control of rotor blades of the wind turbine; and performing individual pitch control of rotor blades of the wind turbine.

[0030] According to another aspect of the present invention, there is provided a non-transitory computer-readable storage medium storing therein instructions which, when executed by one or more computer processors, cause the one or more computer processors to perform the method defined above.

[0031] According to another aspect of the present invention, a controller for controlling a wind turbine of a wind park including a plurality of wind turbines is provided. The controller is configured to retrieve a predefined wake loss control strategy for the wind turbine, the predefined wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions according to a wind direction near the wind turbine, the predefined loss control strategy being used to control the operation of the wind turbine to adjust the wake generated by the wind turbine in a wind direction predicted to cause a wake loss at another wind turbine among the plurality of wind turbines. The controller is configured to receive a signal from the other wind turbine, the signal indicating the wind direction determined to cause a wake loss at the other wind turbine. The controller is configured to determine a difference between the wind direction predicted to cause a wake loss and the received wind direction determined to cause a wake loss. The controller is configured to determine an adjusted wake loss control strategy according to a wind direction offset based on the determined difference, the adjusted wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions of the predefined wake loss control strategy. The controller is configured to control the wind turbine according to the adjusted wake loss control strategy.

[0032] According to another aspect of the invention, there is provided a control system for a wind park as defined above, the control system comprising a plurality of wind turbines, the plurality of wind turbines comprising the wind turbine and the further wind turbine. The control system comprises a controller as described above. The control system comprises a further controller for controlling the further wind turbine, the further controller being configured to: determine a wind direction causing wake losses at the further wind turbine; and transmit a signal to the wind turbine indicating the wind direction determined to cause wake losses at the further wind turbine.

[0033] According to an aspect of the invention, there is provided a wind turbine comprising a controller as defined above.

[0034] According to another aspect of the present invention, a wind farm comprising the control system described above is provided.

[0035] According to one aspect of the present invention, a method for controlling wind turbines of a wind park including a plurality of wind turbines is provided. The method includes retrieving a predefined wake loss control strategy for the wind turbine, the predefined wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions according to a wind direction near the wind turbine, the predefined wake loss control strategy being used to control the operation of the wind turbine to adjust the wake generated by the wind turbine in a wind direction predicted to cause a wake loss at another wind turbine among the plurality of wind turbines. The method includes receiving a signal indicating a current wake condition (e.g., a full wake condition) at another wind turbine from another wind turbine. The method includes receiving a signal indicating a current wind direction near the wind turbine. The method includes determining a difference between a wind direction predicted to cause a current wake condition at another wind turbine and a current wind direction corresponding to a defined wake condition. The method includes determining an adjusted wake loss control strategy according to a wind direction offset based on the determined difference, the adjusted wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions of a predefined wake loss control strategy. The method includes controlling the wind turbine according to the adjusted wake loss control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Examples of the present invention will now be described with reference to the accompanying drawings, in which:

[0037] Figure 1 schematically illustrates a wind park including a plurality of wind turbines according to an aspect of the present invention;

[0038] Figure 2 (a) Schematic diagram of the wind turbine when it is aligned with the incoming wind direction. Figure 1 a wake generated downstream of one of the wind turbines, and Figure 2 (b) Schematically illustrates the Figure 2 (a) The wake generated when the wind turbine is misaligned with respect to the direction of the incoming wind;

[0039] Figure 3 yes Figure 1 An illustrative graph of estimated yaw moment versus absolute wind direction for one of the wind turbines in FIG. Figure 1 downstream of another wind turbine among the wind turbines, the other wind turbine generating a wake downstream thereof;

[0040] Figure 4 Schematic diagram of the process upstream of Figure 1 The effect of the wake generated by one wind turbine on another wind turbine Figure 1 one of the downstream wind turbines, wherein: Figure 4 (a) shows the downstream wind turbine in full wake conditions; Figure 4 (b) shows the downstream wind turbine in a left half-plane wake condition; and, (c) shows the downstream wind turbine in a right half-plane wake condition;

[0041] Figure 5 According to one aspect of the present invention, Figure 1 a schematic diagram of a controller of one of the wind turbines generating a wake downstream thereof; and

[0042] Figure 6 According to one aspect of the present invention, Figure 5 The controller performs the steps of the method. DETAILED DESCRIPTION

[0043] The present invention provides a method and system for monitoring wake losses at one or more downstream wind turbines relative to upstream wind turbines in a wind park, and controlling the upstream wind turbines based on the monitored wake losses at these downstream turbines, for example by performing wake steering of the upstream turbines. In particular, the effects of the wake generated by the upstream wind turbines on the downstream wind turbines, for example, the loads experienced by one or more components of the downstream turbines under certain wind conditions (particularly, for certain wind directions), are monitored, and appropriate control of the upstream turbines can be performed to mitigate these effects for certain wind directions, for example in a manner that maximizes the power output of the wind park as a whole. This is in contrast to some known wake steering methods, in which only the wind conditions at the (upstream) wind turbine to be controlled, or only the wind conditions at one or more downstream turbines, are considered when determining how to control the wind turbines.

[0044] Figure 1 A schematic diagram of a wind park or wind farm 10 including a plurality of wind turbines 12 is shown. Each wind turbine 12 includes a tower 121, a nacelle disposed at the apex or top of the tower, and a rotor operably coupled to a generator housed inside the nacelle. In addition to the generator, the nacelle also houses other components required to convert wind energy into electrical energy and various components required to operate, control and optimize the performance of the wind turbine 12. The rotor of the wind turbine 12 includes a central hub and three rotor blades 122 protruding outwardly from the central hub.

[0045] Each wind turbine 12 includes a control system or controller ( Figure 1 Controllers may be placed inside the nacelle, in the tower, or distributed at multiple locations inside (or outside) the turbine 12 and communicatively connected to each other. In addition, the wind park 10 may include a (central) controller communicatively connected to the wind turbine controllers.

[0046] The rotor blades 122 are pitch adjustable. The rotor blades 122 may be adjusted according to a collective pitch setting, wherein each blade is set to the same pitch value. In addition, the rotor blades 122 may be adjusted according to an individual pitch setting, wherein each blade 122 may be provided with an individual pitch set point. The control system / controller of the respective wind turbine 12 may determine the collective pitch setting and / or the individual pitch setting and output / transmit a control signal to an appropriate actuator of the wind turbine 12 to actuate a pitch bearing of the wind turbine 12, thereby controlling the pitch angle of the rotor blades 122 according to the determined pitch setting.

[0047] Each wind turbine 12 may be configured to adjust a yaw angle, for example, relative to the wind in the vicinity of the respective wind turbine 12. Specifically, each turbine 12 may include a yaw system between a tower 121 and a nacelle that allows rotational movement of the nacelle (and attached components, including the rotor and rotor blades 122) relative to the tower in order to adjust the yaw angle of the wind turbine 12 relative to the wind, i.e., rotation about the tower axis of the turbine 12. A control system / controller of the respective wind turbine 12 may determine a desired yaw angle of the wind turbine 12, and output a control signal to control a yaw drive mechanism of the turbine 12 to rotate the nacelle relative to the tower 121 via a yaw bearing according to the desired yaw angle.

[0048] Wake steering can also be achieved by pitch moment control, wherein a pitch moment is generated on the rotor by means of individual pitch changes, which can direct the wake in the vertical direction.

[0049] Each of the wind turbines 12 in the wind park 10 is configured to capture energy from the wind flowing through and convert the captured wind energy into power to be provided to a power grid, for example. It is generally desirable to maximize the amount of wind energy captured by the wind turbines in order to maximize the amount of power generated by the turbines. Each wind turbine 12 monitors wind conditions in its vicinity and appropriately controls / adjusts one or more components of the wind turbine 12 based on the monitored wind conditions to maximize the captured wind energy. Each wind turbine 12 may include one or more sensors for measuring one or more aspects of wind conditions in the vicinity of the turbine 12, such as wind speed, wind direction, etc. For example, each turbine 12 may include one or more accelerometers (e.g., located in the nacelle) for this purpose.

[0050] Each wind turbine 12 may be controlled to balance maximizing the energy captured / power production of the turbine with (minimizing) the loads experienced by one or more components of the turbine 12. If the loads experienced by a wind turbine component (e.g., extreme or fatigue loads) are too high, this may result in a shortened life or even failure of the component. Each turbine 12 may include sensors for monitoring the loads of different wind turbine components. For example, each turbine 12 may include a blade load sensor placed at or near the root end of each blade 122 in such a way that the sensor detects the load in the blade 122. Depending on the placement and type of the sensor, the load may be detected in the flapping (flapping) direction (in-plane / out-of-plane) or the edge (edgewise) direction (in-plane). For example, such a sensor may be a strain gauge sensor or an optical Bragg sensor.

[0051] Typically, in order to maximize the amount of energy that a wind turbine captures from the wind, the wind turbine may be controlled to align with the incoming wind direction. That is, the wind turbine may be controlled so that the rotor or nacelle points directly into the incoming or oncoming wind. The difference between the wind direction and the nacelle / rotor direction (i.e., the situation where the wind turbine is not aligned with the wind direction) may be referred to as yaw error.

[0052] Figure 1 The direction 14 of the wind flow in the wind park 10 is schematically illustrated. When the wind flows through the first turbine 12a in the wind park 10, a wake is generated downstream of the wind turbine 12a. This means that the wind flow downstream of the wind turbine 12a is disturbed or turbulent relative to the wind turbine 12a upstream, resulting in a reduction in wind flow speed and / or an increase in wind flow turbulence.

[0053] Depending on the positioning of the other wind turbines 12b in the wind park 10 relative to the (first) wind turbine 12a, the wind flow past one or more of the other wind turbines 12b may include a wake effect caused by the wind flow past the first wind turbine 12a. The wind turbine that generates / causes the wake may be referred to as an upstream or upwind wind turbine 12a, and the one or more wind turbines that experience the effects of the generated wake may be referred to as a downstream or downwind wind turbine 12b.

[0054] Due to the effect of the wake from the upstream wind turbine on the downstream wind turbine, the upstream wind turbine tends to produce more energy than the downstream wind turbine. In particular, the wake effect from the upstream wind turbine causes a reduction in wind speed and an increase in turbulence near the downstream wind turbine relative to the upstream wind turbine. It is known to control the upstream wind turbine to adjust the generated wake in a manner intended to reduce the effect of the wake on one or more wind turbines downstream of the upstream wind turbine. In particular, for example, a so-called wake steering can be performed to change the direction of the generated wake. This can be performed by misaligning the upstream wind turbine with respect to the incoming wind direction.

[0055] Figure 2 Schematically illustrates how the generated wake can be adjusted using wake steering. In particular, Figure 2 (a) shows a situation where the upstream wind turbine 12a is aligned with the incoming wind direction 14. In this case, it can be seen that the wake 20 generated downstream of the upstream wind turbine 12a is directed toward another wind turbine 12b downstream of the upstream wind turbine 12a. When the downstream wind turbine 12b experiences the effects of the generated wake 20, this reduces the amount of wind energy that can be captured by the downstream wind turbine 12b. Figure 2 (b) shows a situation where the upstream wind turbine 12a is not aligned with respect to the incoming wind direction 14, e.g. Figure 2 (a) The yaw angle of the upstream wind turbine 12a is adjusted. It can be seen that this changes the direction of the generated wake 20 so that the downstream wind turbine 12b does not experience the effects of the generated wake 20, or at least experiences a reduced effect thereof.

[0056] Known methods for performing wake steering may be based on monitored wind conditions in the vicinity of an (upstream) wind turbine to be controlled, and on retrievable information about the layout of the wind park (i.e. the positioning of the wind turbines relative to each other in the wind park). For example, for a specific measured (or otherwise determined, e.g. estimated) wind direction in the vicinity of an upstream wind turbine to be controlled, it may be predicted that a wake in a certain direction is generated downstream of the wind turbine, e.g. when the wind turbine is aligned with the wind direction. If the predicted wake direction is such that its effects are expected (based on wind park layout information) to be experienced by further wind turbines downstream of the upstream wind turbine, one or more wake control actions, e.g. wake steering, of the upstream wind turbine may be performed to adjust the direction of the wake generated by that wind turbine.

[0057] However, such known methods may not always be able to accurately predict when the generated wake effect will be experienced by the downstream wind turbine and be harmful to the amount of wind energy that can be captured by the downstream turbine. This may be for several reasons. For example, the layout of the wind park available to the upstream wind turbine may be inaccurate, that is, the relative positioning of the wind turbines in the wind park may be inaccurate, so that the generated wind flow is incorrectly predicted when it is directed toward one or more downstream turbines. Moreover, other aspects of the main wind conditions, such as wind speed, turbulence level, wind shear / steering, atmospheric stability, can affect the wake generated downstream of the wind turbine and how it develops. In addition, different aspects of the wind park (for example, terrain and / or vegetation between different turbines) can affect the development and path of the wake. The wind direction measurement results used to determine and adjust the wake and / or the positioning (for example, yaw angle) of the rotor or nacelle of the upstream turbine may be inaccurate (for example, if the sensor used to measure these quantities is faulty or incorrectly calibrated), which may also cause the difference between the actual wake effect and the predicted wake effect downstream.

[0058] The present invention is advantageous because it provides a method and controller / system for reducing wake losses (i.e., reductions in wind energy capture efficiency or capability) suffered or experienced by wind turbines in a wind park in a manner that can increase or maximize overall wind energy capture in a wind park comprising a plurality of wind turbines. In particular, this is achieved by monitoring the (actual) effects of wakes generated by upstream wind turbines on one or more downstream wind turbines, and using these monitored effects from the downstream turbines to determine how to control the upstream turbines to reduce the wake losses experienced at the downstream turbines.

[0059] The present invention specifically uses the monitored downstream wake effects to offset the (measured or estimated) wind direction at which a control strategy for addressing wake losses (e.g., performing wake steering) is activated at an upstream wind turbine. Specifically, this modifies / adjusts the control strategy of the upstream wind turbine to account for the error or difference between the wind conditions that were expected or predicted to cause wake losses at the downstream wind turbine and the wind conditions that actually caused the wake losses.

[0060] Return to reference Figure 1 and Figure 2 , the controller of the upstream wind turbine 12a can be configured to implement a predefined wake loss control strategy based on the wind direction near the wind turbine 12a. The predefined wake loss control strategy may involve the controller performing one or more control actions to reduce or mitigate the wake loss experienced by one or more of the downstream wind turbines 12b under a specific monitored wind direction that is predicted or expected to cause downstream wake loss. For example, the control action may include yaw angle control of the upstream turbine 12a to redirect the downstream wake away from the downstream turbine 12b. The predefined control strategy can be activated to perform control actions, such as wake steering, within a predefined range or interval (wake sector) of the monitored wind direction that is believed to cause downstream wake loss. On the other hand, if the monitored wind direction is outside the predefined range, the predefined control strategy can be deactivated so that the control action to mitigate the wake loss is not performed. When the predefined control strategy is not activated (deactivated), the upstream wind turbine 12a can be controlled according to the standard control strategy, for example, to maximize its power generation by aligning the wind turbine 12a with the incoming wind direction 14. The predefined wake loss control strategy (ie, which control actions to perform for which wind conditions) may be determined offline based on historical or experimental data or in any other suitable manner (eg, including machine learning methods) such that it is known a priori.

[0061] In addition to wind direction, the predefined strategy may also take into account (i.e., be a function of) other wind conditions such as wind speed. For example, even if the wind direction is such that the downstream turbine is predicted to be in the generated wake, if the wind speed is relatively high - in particular significantly above the rated wind speed - it may not be worthwhile to perform a wake turn of the upstream turbine, since the downstream turbine is still producing rated power.

[0062] In order to determine the actual position or direction of the wake generated by the upstream wind turbine 12a, one or more aspects of the operation of the downstream wind turbine 12b are monitored. For example, the loads experienced by the rotor blades 122 of the downstream wind turbine 12b may be monitored as a means for detecting wake effects or wake losses experienced by the downstream wind turbine 12b, e.g., blade loads may increase when the wind turbine is operating in a wake.

[0063] In some examples, a parameter indicative of a load imbalance on a downstream turbine rotor may be determined and used as an indicator of wake losses. In one such example, an estimated or measured rotor tilt or yaw moment, for example based on blade load sensor signals, may be used to detect wake losses. If there are other factors that affect the imbalance of the rotor loads, these factors may be removed or compensated for before performing subsequent analysis. For example, if the wind turbine has individual pitch control (IPC) enabled, the (measured) rotor yaw moment may be compensated to account for the correction of the imbalance performed by the IPC.

[0064] Figure 3 An illustrative graph 30 is shown of the rotor yaw moment of the downstream wind turbine 12b (along the y-axis, for example in kNm) versus the absolute wind direction (along the x-axis, in degrees), which allows detection of the wake condition in which the turbine 12b is operating. Figure 4 , the rotor yawing moment allows determining whether the downstream wind turbine 12b is in a so-called full wake condition, a left half plane wake condition, a right half plane wake condition, somewhere between these defined wake conditions or outside these wake conditions.

[0065] Figure 4 (a) schematically illustrates a downstream wind turbine 12b in a full wake condition. In particular, in a full wake condition, the downstream wind turbine 12b is fully within the wake 20 generated by the upstream wind turbine 12a. When this is the case, the wake-induced blade loading effects at the downstream turbine 12b may be substantially balanced (equal) between the left and right sides / half of the rotor plane, such that the yaw moment experienced by the rotor of the downstream turbine 12b is substantially zero, corresponding to Figure 3 The complete wake condition point 301 in FIG.

[0066] Figure 4 (b) schematically illustrates a downstream wind turbine 12b in a left half plane wake condition. In particular, in a left half plane wake condition, (only) the left half of the rotor plane of the downstream turbine 12b (e.g. defined as the swept area of ​​the rotor blades 122 of the turbine 12b) is in (or experiences the influence of) the wake 20 generated by the upstream wind turbine 12a. When this is the case, this may result in a maximum imbalance level / amount of blade loading between the left and right halves of the rotor plane, such that the magnitude of the yaw moment experienced by the rotor of the downstream turbine 12b is at its maximum. This corresponds to Figure 3 The left half plane wake condition point 302 in FIG.

[0067] Figure 4(c) schematically illustrates a downstream wind turbine 12b in a right half plane wake condition. This corresponds to a left half plane wake condition, except that (only) the right half of the rotor plane is in the wake 20 generated by the upstream wind turbine 12a. This corresponds to Figure 3 The right half plane wake condition point 303 in .

[0068] Combination Figure 4 refer to Figure 3 , it will be appreciated that the points 304, 305 of the estimated yaw moment graph 30 correspond to wind directions where the downstream turbine 12b is just outside the wake 20 generated by the upstream turbine 12a, i.e., points where the generated wake does not affect the estimated or measured yaw moment. It may be desirable for the wake loss control strategy of the upstream turbine 12a to be activated / deactivated at wind directions 304, 305; however, the activation / deactivation wind direction may be set at any suitable wind direction based on the estimated yaw moment. For example, it may be desirable for the downstream turbine to be sufficiently in the generated wake before activating the upstream control strategy to mitigate the effects of the downstream wake losses. It may also be desirable to activate and deactivate the wake loss control strategy at different wind directions, i.e., to introduce hysteresis into the control strategy. This may prevent repeated activation and deactivation cycles of the control strategy, and may also prevent deactivation of the control strategy from causing an increase in the yaw moment at the downstream turbine (as the wake may move back in the direction of the downstream turbine).

[0069] Although described above with reference to monitoring parameters indicative of load imbalance (particularly rotor yawing moment) to determine the wind direction leading to a defined wake condition, it will be appreciated that different parameters of the wind turbine may be considered for this purpose. For example, parameters indicative of turbulence, certain frequency components in the fore-aft acceleration of the wind turbine (e.g., 3P components), pitch / yaw controller pitch actuation (at 1P), lateral acceleration of the wind turbine tower or nacelle, and / or blade edge or flapping moment acceleration / variations may be used.

[0070] In order to determine the (actual) wind direction at which the downstream wind turbine 12b is in or experiences a specific or defined wake condition, a training period of wind turbine operation may be conducted, wherein the wind turbine 12 is operated for a plurality of different wind directions. During the training period, the wind turbine 12 may be operated according to a standard control strategy, e.g., to maximize power production. In particular, the upstream wind turbine 12a may not perform any wake steering or other wake loss control actions during the training period.

[0071] During the training period, the downstream wind turbine 12b (e.g., a controller of the downstream turbine 12b) may monitor wind direction, for example using suitable sensors, and monitor parameters indicative of wake losses, such as an estimated yaw moment in each wind direction (e.g., based on blade load sensor signals). The downstream turbine 12b may use this to determine an absolute wind direction corresponding to the downstream turbine 12b being in or experiencing a particular or defined wake condition (typically a full wake condition).

[0072] Another training period of implementing one or more wake control actions by the upstream wind turbine 12a may then be performed, for example to ensure that the desired effect of reducing wake losses is achieved at the downstream turbine 12b.

[0073] In one example, the downstream turbine 12b determines the wind direction in which the turbine 12b is in a full wake condition, such as corresponding to Figure 3 301 in the wake center. This can be determined, for example, by considering the rotor yaw moments for (slightly) smaller and larger wind directions than the wind direction that appears to correspond to the center 301, or by observing that a positive yaw moment is followed by a (unique) pattern of zero yaw moment and negative yaw moment. The wake center will also correspond to lower power production, and therefore other sensor data indicative of downstream wind turbine operation can be used to determine where the wind direction corresponding to the wake center 301 is.

[0074] The determined wind direction(s) corresponding to one (or each) defined wake condition (e.g., full wake condition) may be communicated from the downstream wind turbine 12b to the upstream wind turbine 12a. The upstream wind turbine 12a then uses the determined wind direction to adjust the wake loss control strategy of the upstream turbine 12a to better mitigate the downstream wake loss effects of the wake generated by the upstream turbine 12a, as described below.

[0075] Figure 5Elements of a controller 50 of an upstream wind turbine 12a are schematically illustrated. For example, the controller 50 may be located in a nacelle of the turbine 12a. The controller 50 includes one or more computer processors 501 and may include a data storage device or memory 502. The controller 50 is configured to receive an input signal 504, for example, via an input of the controller 50. The input signal 504 may include a signal indicating the above-mentioned determined wind direction from one or more of the downstream wind turbines 12b. The controller 50 is configured to output / transmit a control signal 505 via an output of the controller 50. The output signal 505 may include a correction amount to be applied to a predefined wake control action / strategy (e.g., wake steering). The output signal 505 may include one or more control signals for controlling the operation of the wind turbine 12a (e.g., for controlling a pitch actuator to adjust the rotor blade pitch according to a determined pitch reference value, and / or for controlling the rotor or generator speed according to a determined speed reference).

[0076] The controller 50 described may be in the form of any suitable computing device, such as one or more functional units or modules implemented on one or more computer processors. Such functional units may be provided by suitable software running on any suitable computing substrate using conventional or custom processors and memory. One or more functional units may use a common computing substrate (e.g., they may run on the same server) or a separate substrate, or one or both may themselves be distributed among multiple computing devices. The computer memory may store instructions for executing the method performed by the controller, and the processor may execute the stored instructions to perform the method.

[0077] Figure 6 The steps of a method 60 for controlling a wind turbine 12a performed by a controller 50 according to an example of the present invention are summarized. However, it will be understood that Figure 6 One or more of the method steps shown in and / or some or all other steps that may form part of the overall method in some examples may be performed remotely from the upstream wind turbine 12a, for example, by a controller of one or more of the downstream wind turbines 12b and / or by a controller of the wind park 10.

[0078] At step 601 of method 60, a predefined wake control strategy for an upstream wind turbine 12a of a wind park 10 is retrieved, for example, from a data storage 502. The predefined wake control strategy is used to control the upstream wind turbine 12a to perform a wake control action according to a wind direction near the wind turbine 12a. Typically, the wind direction used here is an absolute wind direction (rather than a relative wind direction). In particular, the predefined wake control strategy is used to control the operation of the upstream wind turbine 12a to adjust the wake generated by the wind turbine 12a in a wind direction that is predicted, expected, or estimated to generate a wake at one or more additional wind turbines 12b of the wind park 10 downstream or downwind of the upstream wind turbine 12a.

[0079] As described above, the predefined wake loss control strategy may be activated for certain wind directions, i.e., for wind directions that are predicted to result in wake losses being experienced at one or more of the downstream turbines 12b (without activation of wake loss control) (and optionally other wind conditions, such as wind speed). In particular, a particular wind direction may be predicted or expected to result in a defined wake condition downstream (in the predefined wake loss control strategy). Thus, the predefined strategy may take into account the relative positioning (e.g., GPS positioning) of the downstream turbine 12b with respect to the upstream turbine 12a.

[0080] The predefined wake loss control strategy may involve controlling the upstream turbine 12a to change from operating according to a (standard) control strategy to optimize power production at the upstream turbine 12a (optionally while minimizing component loads, or keeping component loads within allowable limits) to operating taking into account how the wake generated by the upstream turbine 12a is expected to affect operation at one or more of the downstream turbines 12b. For example, operation according to the standard control strategy may involve aligning (the nacelle and / or rotor of) the upstream wind turbine 12a with the incoming wind direction in order to maximize wind energy capture. On the other hand, operation according to the predefined wake loss control strategy may involve misaligning the upstream wind turbine 12a with respect to the incoming wind direction for certain wind directions that are expected to cause wake losses at one or more downstream turbines 12b, so as to redirect the generated wake in a manner that reduces wake losses at said downstream turbines 12b.

[0081] At step 602 of the method 60, the controller 50 receives a signal 504 indicative of a wind direction determined to result in a defined wake condition at one or more (additional) wind turbines 12b of the wind park 10 downstream of the upstream wind turbine 12a. In the depicted example, the signal 504 is received by the controller 50 of the upstream turbine 12a from (the controller of) the or each downstream wind turbine 12b.

[0082] As described above, the downstream turbine 12b can determine the wind direction that caused the defined wake condition during the training period, for example, by monitoring / analyzing one or more parameters indicating wake losses (e.g., estimated rotor yaw moment) for different wind directions. In either case, the determination of the wind direction that caused or corresponds to the defined wake condition can be performed when the upstream wind turbine 12a does not perform one or more wake loss control actions. Wind direction measurements or estimates for this purpose can be made at the upstream turbine 12a, the downstream turbine 12b, or at the level of the wind park 10.

[0083] At step 603 of method 60, the controller 50 determines (at the upstream wind turbine 12a) a difference between a wind direction predicted or expected to result in a defined wake condition at one or more of the downstream (additional) wind turbines 12b and a wind direction received from the downstream wind turbine 12b that is determined to result in a defined wake condition. The defined wake condition may be a full wake condition at the downstream turbine 12b, or any other suitable wake condition (e.g., as described above). For example, the determined wind direction may be a wind direction where one of the downstream wind turbines 12b is at the center of a wake generated by the upstream wind turbine 12a.

[0084] Although in the described example, the wind direction determined to result in the defined wake condition is transmitted from the downstream (further) wind turbine 12b to the controller 50 of the upstream turbine 12a, in a different example, the downstream turbine 12b may simply transmit an indication of the (current) wake condition at the downstream turbine 12a (rather than the wind direction indicating the wake condition). The indication may be in the form of acquired sensor data for determining a parameter indicative of wake losses (e.g., rotor yaw moment). The upstream turbine controller 50 may then determine the difference between the wind direction expected to result in the current wake condition and the current (measured) wind direction corresponding to the current wake condition (an indication of which is received from the downstream turbine 12b).

[0085] At step 604 of method 60, the controller 50 determines an adjusted or modified wake loss control strategy based on the wind direction offset based on the determined difference, and the adjusted or modified wake loss control strategy is used to control the upstream wind turbine 12a to perform one or more wake loss control actions of the predefined wake loss control strategy. That is, the wind direction in which the wake loss control action is performed or implemented is offset to the center of the wake loss controller, that is, to account for any errors in the sensor data or other data used by the controller to perform wake loss control, such as wake model data used to set / determine predefined control actions / settings. This can be considered to be that the wake loss control strategy is a function of relative wind direction (e.g., relative to the downstream full wake condition position), rather than a function of absolute wind direction. The method currently described is agnostic to the source of such errors; instead, the method is intended to identify and correct errors regardless of their source.

[0086] The wake loss control action of the adjusted wake loss control strategy is the same as the wake loss control action in the predefined wake loss control strategy; however, the wind direction in which a given control action is implemented in the adjusted strategy is offset from the wind direction in which a given control action is implemented in the predefined strategy by the above-determined difference. For example, determining the adjusted strategy may include offsetting the wind direction at which the predefined wake control strategy is activated (e.g., to perform a wake turn) by the determined difference. It is contemplated that in some examples, the offset need not correspond precisely to the determined difference, but will simply be determined based on the determined difference, for example, the offset may be less than the determined difference. The offset may also be determined or set based on one or more additional operating variables (e.g., wind speed, turbulence intensity, etc.).

[0087] At step 605 of method 60, the controller 50 controls the upstream wind turbine 12a according to the adjusted wake loss control strategy. This may include receiving a measured wind direction near the upstream wind turbine 12a. Then, if the measured wind direction offset based on the determined difference is within a predefined range of wake control activation wind directions, an adjusted wake control strategy for performing one or more control actions may be activated. For example, in one illustrative example, the range of wind directions may correspond to Figure 3 304 and 305 in the range between the wind direction; however, it will be appreciated that a different range may be selected as appropriate. The control action performed may vary depending on the position of the wind direction within the predefined range. For example, gain scheduling may be used based on wind direction and / or other parameters such as wind speed.

[0088] The control action may include any suitable manner of controlling the operation of the upstream wind turbine 12a to control / adjust the wake generated downstream thereof. For example, the control action may include performing yaw control to rotate the nacelle and rotor of the upstream wind turbine 12a about a yaw angle relative to the wind turbine tower to adjust the (lateral) direction of the wake generated by the upstream wind turbine 12a. The control action may also include performing tilt moment control to generate a tilt moment about a tilt axis relative to the tower, for example to direct the generated wake toward the ground. The control action may also include performing collective and / or individual pitch control of the wind turbine rotor blades 122 in a manner that changes the generated wake as desired.

[0089] The wake loss control strategy may be configured to perform control actions based on current wind conditions (including wind direction) that adjust the operation of the upstream wind turbine 12a so as to reduce wake losses at one or more downstream turbines 12b in a manner that results in an overall increase in power production by the wind park 10. In particular, the control actions may be aimed at minimizing the effects of wakes generated at the downstream turbines, for example to achieve a substantially zero rotor yaw moment (unless this corresponds to the center of the wake).

[0090] The steps of the described method may be repeated to iteratively update or further adjust the wake loss control strategy. For example, if the source of the wake loss controller error is related to a faulty sensor that provides wind direction measurements that become more inaccurate over time, then the offset applied to the wind direction used to implement the wake loss control strategy may need to be updated to ensure continued optimization / maximization of power production at the wind park. Thus, the described method may be repeated at any suitable time interval.

[0091] Many modifications may be made to the examples described without departing from the scope of the appended claims.

[0092] In the described example, the (upstream) wind turbine to be controlled receives data indicating wake conditions for a certain wind direction from a single downstream wind turbine. However, it will be appreciated that the upstream wind turbine may receive wake condition data from multiple downstream wind turbines in the wind park. The data may be combined to determine the appropriate wake steering control of the upstream wind turbine that results in the maximum increase in energy capture efficiency of the wind park as a whole.

[0093] In the described example, the controller of the (upstream) wind turbine to be controlled determines the wind direction offset (e.g., the full wake direction offset) to determine the adjusted wake control strategy. However, it will be appreciated that the determination may be performed by the controller of the downstream wind turbine (or one of the wind turbines) after the upstream controller and then transmitted to the (controller of) the upstream wind turbine. Alternatively, the determination may be made, for example, by the controller of the wind park and then transmitted to the upstream wind turbine.

[0094] In some examples, the wind direction offset can be used for fault detection purposes. For example, if multiple wind turbines each determine that a given turbine is offset from a predefined setting, the position coordinates associated with the given turbine (as constructed) may be different from the actual position coordinates (as fixed / designed). In other examples, if the determined / detected full wake position changes over time, then: if the change is relatively sudden, this may indicate that the parameters of the turbine were not properly processed during maintenance; and if the change is relatively gradual, this may indicate that (growing) vegetation is changing the flow in the wind park.

Claims

1. A method for controlling wind turbines of a wind park comprising a plurality of wind turbines, the method comprising: retrieving a predefined wake loss control strategy for the wind turbine, the predefined wake loss control strategy for controlling the wind turbine to perform one or more wake loss control actions based on a wind direction near the wind turbine, the predefined wake loss control strategy for controlling operation of the wind turbine to adjust a wake generated by the wind turbine in a wind direction predicted to cause wake losses at another wind turbine of the plurality of wind turbines; receiving a signal from the further wind turbine, the signal indicating a wind direction determined to result in a defined wake condition at the further wind turbine; determining a difference between a wind direction predicted to result in the defined wake condition at the further wind turbine and a received wind direction determined to result in the defined wake condition; determining an adjusted wake loss control strategy according to the wind direction offset based on the determined difference, the adjusted wake loss control strategy being used to control the wind turbine to perform the one or more wake loss control actions of the predefined wake loss control strategy; and The wind turbine is controlled according to the adjusted wake loss control strategy.

2. The method according to claim 1, wherein: The defined wake condition is a full wake condition.

3. The method according to claim 1 or claim 2, wherein: The received wind direction is the wind direction in which the further wind turbine is in the centre of the wake generated by the wind turbine.

4. A method according to any preceding claim, wherein: Determining the adjusted wake loss control strategy includes offsetting the wind direction at which the predefined wake loss control strategy is activated based on the determined difference.

5. A method according to any preceding claim, the method comprising, at the further wind turbine: determining a wind direction causing the defined wake condition at the further wind turbine; and transmitting a signal to the wind turbine indicative of the wind direction determined to cause the defined wake condition at the further wind turbine.

6. The method according to claim 5, wherein: A wind direction causing the defined wake condition at the other wind turbine is determined when the wind turbine is not performing the one or more wake loss control actions.

7. The method according to claim 5 or claim 6, wherein: The wind direction resulting in the defined wake condition at the further wind turbine is determined during a training period in which a plurality of wind turbines of the wind park are operated for a plurality of different wind directions.

8. The method according to any one of claims 5 to 7, wherein: Determining the wind direction causing the defined wake condition comprises, for a plurality of different wind directions: receiving sensor signals from one or more sensors of the further wind turbines; And, determining a parameter indicative of a load imbalance on the rotor of the further wind turbine based on the received sensor signal.

9. The method according to claim 8, wherein: The sensor signals from the one or more sensors are blade load signals from one or more blade load sensors of rotor blades of the further wind turbine, and wherein the parameter is a yaw moment of the rotor of the further wind turbine determined based on the received blade load signals.

10. The method according to claim 8 or claim 9, wherein: When the adapted wake loss control strategy is activated at the wind turbine to perform the one or more wake loss control actions, the method comprises iteratively performing the following steps: At the further wind turbine: monitoring a parameter indicative of a load imbalance based on sensor signals from the one or more sensors; and transmitting a signal indicative of the monitored parameter to the wind turbine; as well as At the wind turbine: receiving a signal indicative of a monitored parameter from the additional wind turbine; determining, based on the received monitoring parameters, a further wind direction offset for reducing a load imbalance on a rotor of the further wind turbine; determining a further adjusted wake loss control strategy according to the wind direction offset based on the determined difference and the further wind direction offset, the further adjusted wake loss control strategy being used to control the wind turbine to perform one or more wake loss control actions of the predefined wake control strategy; and The wind turbine is controlled according to the further adjusted wake loss control strategy.

11. A method according to any preceding claim, wherein: Controlling the wind turbine according to the adjusted wake loss control strategy includes: receiving a measured wind direction in the vicinity of the wind turbine from one or more wind direction sensors of the wind turbine or wind park; and If the measured wind direction offset based on the determined difference is within a predefined range of wake loss control activation wind directions, the adjusted wake loss control strategy is activated to perform the one or more control actions.

12. A method according to any preceding claim, wherein: The one or more wake loss control actions include at least one of the following: performing yaw control to rotate a nacelle and a rotor of the wind turbine relative to a tower of the wind turbine about a yaw angle to adjust a direction of a wake generated by the wind turbine; performing pitch control to generate a pitch moment about a pitch axis to adjust the direction of a wake generated by the wind turbine; performing collective pitch control of rotor blades of said wind turbine; as well as Individual pitch control of the rotor blades is performed.

13. A controller for controlling a wind turbine of a wind park comprising a plurality of wind turbines, the controller being configured to: retrieving a predefined wake loss control strategy for the wind turbine, the predefined wake loss control strategy for controlling the wind turbine to perform one or more wake loss control actions based on a wind direction near the wind turbine, the predefined wake loss control strategy for controlling operation of the wind turbine to adjust a wake generated by the wind turbine in a wind direction predicted to cause wake losses at another wind turbine of the plurality of wind turbines; receiving a signal from the further wind turbine, the signal indicating a wind direction determined to cause wake losses at the further wind turbine; determining a difference between a wind direction predicted to cause a wake loss and a received wind direction determined to cause a wake loss; determining an adjusted wake loss control strategy according to the wind direction offset based on the determined difference, wherein the adjusted wake loss control strategy is used to control the wind turbine to perform one or more wake loss control actions of the predefined wake loss control strategy; and The wind turbine is controlled according to the adjusted wake loss control strategy.

14. A control system for a wind farm according to claim 13, the control system comprising: The controller according to claim 13; as well as a further controller for controlling the further wind turbine, the further controller being configured to: determining a wind direction causing wake losses at the additional wind turbine; as well as A signal indicative of a wind direction determined to cause wake losses at the further wind turbine is transmitted to the wind turbine.

15. A wind turbine comprising a controller according to claim 13, or a wind park comprising a control system according to claim 14.

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