Wind turbine wake deflection method

Abstract

The invention relates to wake deflection. The second wind turbine is located downstream of the first wind turbine so it may be affected by the wake of the first wind turbine. In the method of the invention, a yaw offset signal is applied to produce a yaw offset between the rotor of the first wind turbine and the wind direction, and the yaw offset signal varies based on a transfer function in response to a change in the wind direction. The transfer function includes a negative offset band, a negative transition, a positive offset band, a positive transition, and a dead zone between the positive transition and the negative transition.

Description

TECHNICAL FIELD

[0001] The present invention relates to a wind turbine wake deflection method, a yaw offset controller configured to control a wind turbine by the method; and a wind turbine comprising the yaw offset controller. BACKGROUND

[0002] US2021 / 207580 A1 discloses a known method of controlling a first wind turbine of a plurality of wind turbines in a wind farm. A second wind turbine of the plurality of wind turbines can be affected by a wake region induced by the first wind turbine located upstream of the second wind turbine. The method comprises determining a current yaw state; determining a wind condition indicative of a potential wake-induced level at the second wind turbine caused by at least the first wind turbine; and defining a rotor yaw offset angle setpoint for the first wind turbine based on the current yaw state, the wind condition, and at least one yaw angle hysteresis switching threshold. The rotor yaw offset angle setpoint follows a hysteresis, thereby avoiding immediate consecutive switching between a positive yaw offset angle range and a negative yaw offset angle range. SUMMARY

[0003] A first aspect of the invention provides a method of deflecting a wake of a first wind turbine, wherein a second wind turbine is located downstream of the first wind turbine such that the second wind turbine can be affected by the wake of the first wind turbine, the method comprising: applying a yaw offset signal to a yaw control system of the first wind turbine, the yaw offset signal causing the yaw control system to produce a yaw offset between a rotor of the first wind turbine and a wind direction, the yaw offset deflecting the wake away from the second wind turbine; and changing the yaw offset signal in response to a change in the wind direction, wherein the yaw offset signal is changed based on a transfer function, and the transfer function comprises: a negative offset band, wherein the yaw offset signal is negative and decreasing to a minimum value; a negative transition, wherein the yaw offset signal is increasing from the minimum value; a positive offset band, wherein the yaw offset signal is positive and increasing to a maximum value; a positive transition, wherein the yaw offset signal is decreasing from the maximum value; and a deadband located between the positive transition and the negative transition, wherein the yaw offset signal is substantially zero in at least a portion of the deadband, such that in at least a portion of the deadband there is substantially zero offset between the rotor of the first wind turbine and the wind direction.

[0004] Optionally, a rate of change of the transfer function decreases at a lower boundary of the deadband and increases at an upper boundary of the deadband.

[0005] Optionally, the rate of change of the transfer function is greater in the transition than in the deadband.

[0006] Optionally, the rate of change of the transfer function is substantially zero in at least a portion of the deadband.

[0007] Optionally, the rate of change of the transfer function is substantially zero throughout the deadband.

[0008] Optionally, each transition comprises a transition band spanning a range of wind directions.

[0009] Optionally, the yaw offset signal is substantially zero throughout the deadband, such that there is substantially zero offset between the rotor of the first wind turbine and the wind direction throughout the deadband.

[0010] Optionally, the yaw offset signal is below a maximum value throughout the deadband and above a minimum value throughout the deadband.

[0011] Optionally, the method further comprises monitoring wind variability conditions and varying the width of the deadband based on the wind variability conditions.

[0012] Optionally, when the first wind turbine is operating in the deadband, the wake of the first wind turbine affects the second wind turbine.

[0013] Optionally, the deadband spans a full wake direction, wherein the full wake direction is parallel to a heading between the first and second wind turbines.

[0014] Optionally, the deadband spans the full wake direction asymmetrically, the deadband having a greater extent on one side of the full wake direction than on the other side of the full wake direction.

[0015] Optionally, the method further comprises applying an induction control to the first wind turbine in response to the wind turbine entering the deadband, wherein applying the induction control causes the wake to reduce.

[0016] Optionally, applying the induction control comprises changing at least one of a pitch angle and / or a tip speed ratio of one or more blades of the rotor. The induction control can be performed by adjusting the pitch angle and the tip speed ratio in combination to achieve a minimum thrust coefficient (Ct) while reducing the impact on the power coefficient (Cp).

[0017] Optionally, the transfer function further comprises: a negative cut-off band between the negative offset band and the negative transition, wherein the yaw offset signal is substantially equal to the minimum value throughout the negative offset cut-off band; and a positive cut-off band between the positive offset band and the positive transition, wherein the yaw offset signal is substantially equal to the maximum value throughout the positive offset cut-off band.

[0018] A further aspect of the invention provides a yaw offset controller configured to control a first wind turbine by a method according to the first aspect.

[0019] A further aspect of the invention provides a wind turbine comprising: a rotor; a yaw control system; and a yaw offset controller according to the preceding aspect. BRIEF DESCRIPTION OF DRAWINGS

[0020] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 A wind turbine is shown.

[0021] Figure 2A The control system of the wind turbine is shown; Figure 2B The various components of the yaw offset controller are shown; Figure 3 The transfer function shown is not part of this invention; Figure 4 The running state at the first point of the transfer function is shown; Figure 5 This indicates the second point of the transfer function; Figure 6 The operating status at the second point is shown; Figure 7 This indicates the third point of the transfer function; Figure 8 The operating status at point three is shown; Figure 9 This indicates the fourth point of the transfer function; Figure 10 The operating status at point four is shown; Figure 11 The transfer function according to the first embodiment of the present invention is shown; Figure 12 Instructions Figure 11 The first point of the transfer function; Figure 13 It shows Figure 12 The operating status at the first point; Figure 14 Instructions Figure 11 The second point of the transfer function; Figure 15 It shows Figure 14 The operating status at the second point; Figure 16 Instructions Figure 11 The third point of the transfer function is located in the direction of the entire wake; Figure 17 It shows Figure 16 The operating status at the third point; Figure 18 Instructions Figure 11 The fourth point of the transfer function; Figure 19 It shows Figure 18 The operating status at the fourth point; Figure 20 Instructions Figure 11The fifth point of the transfer function; Figure 21 It shows Figure 20 The operating status at point five; Figure 22 The transfer function according to the second embodiment of the present invention is shown; Figure 23 The transfer function according to the third embodiment of the present invention is shown; Figure 24 The transfer function according to the fourth embodiment of the present invention is shown; Figure 25 The transfer function, which is not part of this invention, is shown, having a series of operating states; and Figure 26 The transfer function according to the present invention is shown, having a series of operating states. Detailed Implementation

[0022] Figure 1 A first wind turbine 1 is shown in a schematic perspective view. The wind turbine 1 includes a tower 2 and a rotor-nacelle assembly (RNA) located on top of the tower 2. The RNA includes a nacelle 3 and a rotor 4, which is operatively coupled to a generator housed inside the nacelle 3. In addition to the generator, the nacelle 3 also houses various components required for converting wind energy into electrical energy, as well as various components required for operating and controlling the wind turbine 1.

[0023] The rotor 4 includes a central hub and multiple blades 5 projecting outward from the central hub. In the wind turbine 1 shown, the rotor 4 includes three blades 5, but the number can vary.

[0024] Figure 2A The implementation of the control system 20 and the components of the wind turbine 1 are schematically shown. The rotor is mechanically connected to the generator 7 via a gearbox 9 (there is no gearbox in a direct-drive system). The electrical energy generated by the generator 7 is injected into the power grid 24 via a converter 25. The generator 7 and converter 25 can be based on a full-size converter (FSC) architecture or a doubly fed induction generator (DFIG) architecture, but other types may also be used.

[0025] Control system 20 includes multiple elements, including at least one main controller 10 with a processor and memory, enabling the processor to perform computational tasks based on instructions stored in the memory. Typically, the main controller 10 ensures that the wind turbine produces the requested power output level during operation. This is achieved by adjusting the blade pitch angles and / or the power extraction of the converter 25. To this end, control system 20 includes a pitch system using a pitch reference signal 28, which includes a pitch controller 27, and a power system using a power reference signal 26, which includes a power controller 29. The rotor blades 5 can be pitched via a pitch mechanism. The rotor includes individual pitch systems capable of individually pitching the rotor blades 5, and may include a common pitch system that simultaneously adjusts all pitch angles on all rotor blades. Control system 20 or its elements may be connected to a power plant controller (not shown) or other control systems to receive externally provided instructions.

[0026] The wind turbine 1 includes a yaw control system 31 configured to rotate RNA 3, 4 about a vertical yaw axis to control the yaw angle of the rotor 4. The yaw control system 31 includes various components, including a yaw motor. The control system 20 includes a yaw offset controller 30 configured to generate a yaw offset signal 32 input to the yaw control system 31.

[0027] The yaw offset controller 30 is configured to control the wind turbine 1 by changing the yaw offset signal 32 in response to changes in wind direction. The yaw offset signal 32 can be changed based on a transfer function stored in the memory of the yaw offset controller 30. Various possible transfer functions will be explained in more detail below.

[0028] Figure 2B A schematic overview of the components of the yaw offset controller 30 and a portion of the yaw control system 31 is provided. The yaw offset controller 30 includes a sensor and processing unit 80 and a yaw offset control module 81; the yaw control system 31 includes an upwind yaw control module 82.

[0029] Sensor 80 receives wind and calibrated cabin heading as input; and outputs wind direction and wind speed to modules 81 and 82.

[0030] The yaw offset control module 81 outputs the yaw offset signal 32 to the upwind yaw control module 82. The yaw offset signal 32 is based on the wind direction and the aforementioned transfer function, which can be stored by the yaw offset module 81 in the form of a lookup table or in any other way.

[0031] The upwind yaw control module 82 outputs a yaw motor activation signal to the yaw motor based on the yaw offset signal 32 (which gives the target yaw offset) and the wind direction and wind speed.

[0032] Figure 3 A first example of a transfer function that can be used by the yaw offset controller 30 is given. Figure 3 The transfer function is not part of this invention and is for reference only.

[0033] like Figure 4 As shown, the second wind turbine 40 is located downstream of the first wind turbine 1, making it susceptible to the influence of the wake 41 of the first wind turbine 1. The direction between turbines 1 and 40 is indicated by heading 14. When wind 13 is parallel to heading 14, the wind direction is referred to as the full wake wind direction. The wind direction in... Figures 3-26 In Chinese, it is usually represented by W.

[0034] Figure 4 It shows Figure 3 The transfer function is defined at point 1a of the wind turbine 1, 40, where the wind direction and yaw angle are calculated. For this wind direction +α, the yaw offset signal 32 is set to zero, therefore the rotor shaft 12 is parallel to the wind 13. The wind direction +α is defined here as the angle of the wind 13 relative to the heading 14. Figures 3-26 In this context, yaw offset is usually represented by Y, and yaw offset is usually represented by YOS.

[0035] Since the wind direction + α is a relatively large angle, Figure 4 Under normal operating conditions, the wake 41 will not significantly affect the second wind turbine 40.

[0036] As the wind direction decreases from +α, thus getting closer to the full wake wind direction, the transfer function causes the applied yaw offset to gradually increase until... Figure 5 and Figure 6 The maximum value is reached at point 2a. For this wind direction +β, the yaw offset signal 32 is at its maximum value +θ, therefore the rotor shaft forms an angle of +θ with the wind, as shown. Figure 6 As shown. Due to the wake deflection caused by yaw deviation, in Figure 6 Under normal operating conditions, the wake 41 will not significantly affect the second wind turbine 40.

[0037] As the wind direction decreases from +β, the transfer function becomes flat until... Figure 7 and Figure 8 Point 3a is shown, where wind 13 is in the full wake direction.

[0038] For this part of the transfer function, the yaw offset signal 32 remains at its maximum value of +θ, therefore the rotor shaft maintains an angle of +θ with the wind, as shown below. Figure 8 As shown. At point 3a, the wake 41 may affect the second wind turbine 40, such as... Figure 8 As shown.

[0039] Next, the transfer function has a step transition, which jumps from point 3a to...Figure 9 Point 4a is shown. The yaw offset signal 32 jumps to the minimum angle -θ, therefore the rotor shaft forms an angle of -θ with the wind direction, as shown. Figure 10 As shown. At point 4a, the wake 41 may affect the second wind turbine 40, as... Figure 10 As shown.

[0040] Figure 3 The remainder of the transfer function will not be described further, as the transfer function is symmetric.

[0041] In an embodiment of the present invention, the yaw offset signal 32 can be based on Figure 11 The transfer function shown is used to change the yaw offset controller 30’s memory, which is stored in the form of a lookup table or in any other way.

[0042] Figure 11 The transfer function comprises various bands (i.e., the portion of the transfer function that spans the wind direction range) and two step transitions (i.e., the portion of the transfer function that does not span the wind direction range). Specifically, the transfer function includes: a negative offset band 50a, in which the yaw offset signal is negative and decreases to a minimum value of -θ as the wind direction amplitude decreases (i.e., as the wind direction more closely aligns with the full wake direction); a negative step transition 51a, in which the yaw offset signal increases from its minimum value; a positive offset band 50b, in which the yaw offset signal is positive and increases to a maximum value of +θ as the wind direction amplitude decreases (i.e., as the wind direction more closely aligns with the full wake direction); a positive step transition 51b, in which the yaw offset signal decreases from its maximum value; and a dead zone 52 located between the positive and negative step transitions.

[0043] The yaw offset signal can be lower than the maximum value +θ throughout the entire dead zone 52 and higher than the minimum value -θ throughout the entire dead zone 52.

[0044] A negative cutoff band 53a can be provided between the negative offset band 50a and the negative transition section 51a. The yaw offset signal can be substantially equal to the minimum value -θ throughout the entire negative offset cutoff band 53a.

[0045] Similarly, a positive cutoff band 53b can be provided between the positive offset band 50b and the positive transition section 51b. The yaw offset signal can be substantially equal to the maximum value + θ throughout the entire positive offset cutoff band 53b.

[0046] Cut off bands 53a and 53b to avoid applying excessive yaw offset.

[0047] Figure 11 transfer function and Figure 3 The transfer functions are the same, except that there is a dead zone of 52. Figure 12The first point 1b at the upper end of dead zone 52 is indicated. For this wind direction +δ1, the yaw offset signal 32 is at its maximum value +θ, therefore the rotor shaft forms an angle of +θ with the wind direction, as shown below. Figure 13 As shown. At this first point 1b, the wake 41 may affect the second wind turbine 40, such as... Figure 13 As shown, but to a lesser extent. Figure 8 .

[0048] exist Figure 14 At point 2b, as shown, the yaw offset signal 32 jumps to zero, therefore the rotor shaft of the first wind turbine 1 is essentially offset from the wind (i.e., the rotor shaft is parallel to the wind). At point 2b, the wake 41 may affect the second wind turbine 40, such as... Figure 15 As shown.

[0049] As the wind direction decreases from +δ1, the transfer function becomes flat until... Figure 18 Point 4b is shown. For this part of the transfer function, the yaw offset signal 32 remains zero, so the rotor shaft is parallel to the wind.

[0050] At all points in dead zone 52, wake 41 may affect the second wind turbine 40, especially... Figure 16 At point 3b, this point is... Figure 17 The “full wake” operating state is associated with the second wind turbine 40 being located directly downwind of the first wind turbine 1.

[0051] When the wind direction reaches -δ1, the transfer function is Figure 20 As shown at point 5b, the step drop reaches the minimum value -θ, therefore the wake 41 is deflected away from the second wind turbine 40, as... Figure 21 As shown.

[0052] For wind directions less than -δ1, Figure 11 transfer function and Figure 3 The transfer function is the same as that of the two functions, so these parts of the transfer function will not be described again.

[0053] The transfer function described in this article is based on a sign convention, where counterclockwise is defined as the positive direction of yaw offset, and clockwise is defined as the positive direction of wind direction. Therefore, for example, in... Figure 13 In this configuration, rotor shaft 12 rotates counterclockwise relative to wind 13 to provide a positive yaw offset angle of +θ; wind 13 rotates clockwise relative to heading 14 to provide a positive wind direction of +δ1. Other embodiments of the invention may use different notation conventions.

[0054] Back Figure 11Dead zone 52 provides an inflection point region in the transfer function, similar to an inflection point in a smooth curve, where the rate of change of the transfer function decreases at the lower boundary of the dead zone and then increases at the upper boundary. This inflection point region breaks down... Figure 3 The large step transition between points 3a and 4a in the exemplary transfer function.

[0055] The rate of change is greater in the step transition sections 51a and 51b than in the dead zone 52. For example, the rate of change may be very large (or infinitely large) in the step transition sections 51a and 51b, and essentially zero in all or part of the dead zone.

[0056] When the yaw offset signal is zero in dead zone 52, there is essentially zero offset between the rotor shaft of the first wind turbine and the wind direction. Figure 15 , 17 As shown in Figure 19, the wake 41 is not deflected away from the second wind turbine 40. Consequently, when the first wind turbine 1 operates within the dead zone 52, the wake 41 may affect the second wind turbine. To mitigate this effect, the control system 20 may apply induced control to the first wind turbine 1 in response to the wind turbine entering the dead zone 52. This induced control can result in a reduction in the effect of the wake 41, maintaining it at a relatively low level throughout or in part of the dead zone.

[0057] Induction control may include changing the pitch angle of one or more blades 5 of rotor 4 via pitch reference signal 27, changing the power via power reference signal 26, changing the tip speed ratio, or any other form of induced control.

[0058] Such induced control can provide net power gain and load mitigation effect, or at least reduce the combined power loss of the affected turbine at the expense of load mitigation effect.

[0059] Figure 11 The transfer function can be fixed or can be varied during the operation of the wind turbine 1. For example, the yaw offset controller 30 may optionally monitor wind variability conditions and adjust the width of the dead zone based on these conditions. These wind variability conditions may include atmospheric stability, wind direction variability, turbulence intensity, or any other wind variability index. Low wind variability (associated with high atmospheric stability, low wind direction variability, or low turbulence intensity) may cause the yaw offset controller 30 to narrow the dead zone.

[0060] Figure 22 An example of a transfer function is given, where the width of the dead zone decreases from a dead zone 52 spanning a relatively large range of wind directions (-δ1 to +δ1) to a narrower dead zone 52a spanning a smaller range of wind directions (-δ2 to +δ2).

[0061] Figure 11The transition parts 51a and 51b in the transfer function are step transition parts that do not cross the wind direction range, but Figure 23 An alternative example is given, where each transition section includes transition zones 53a and 53b spanning wind direction ranges 54a and 54b, thus the changes are more gradual. The rate of change of the yaw offset signal in each transition zone 53a and 53b is relatively large (compared to the dead zone), but lower than... Figure 11 The rate of change in the step transition sections 51a and 51b.

[0062] The dead zone can span the entire wake direction. Figure 11 In this case, the dead zone 52 symmetrically spans the entire wake direction, and the extent of the dead zone on one side is the same as the extent on the other side. Figure 24 The alternative dead zone 55 asymmetrically spans the entire wake wind direction, with the dead zone's extent on one side being larger than its extent on the other. In other words, the center of dead zone 55 is offset from the entire wake position.

[0063] In this example, dead zone 55 spans the wind direction range from -δ3 to +δ4, where |δ4| > |δ3|. Therefore, the range of dead zone 55 on the positive side, |δ4|, is greater than the range of dead zone 55 on the negative side, |δ3|.

[0064] This offset dead zone can be used to balance the load and the power gain from wake deflection. For example, if the load is more favorable at a negative yaw offset than at a positive yaw offset, it may be beneficial to place more dead zone on the positive side to help reduce the load, such as... Figure 24 As shown in the example.

[0065] The advantages of dead zones will now be described.

[0066] As mentioned above, Figure 3 The transfer function has a step transition section that jumps from point 3a to point 4a at an angle of 2θ, possibly about 40 degrees. The large size of this step transition section can cause wear on the yaw control system 31, especially if the wind direction changes rapidly back and forth near the full wake wind direction. Figures 11-24 One advantage of all the dead zones described is that they reduce the size of the transition section (halving its size from 2θ to θ), thereby reducing wear on the yaw control system 31.

[0067] Another advantage of dead zones will be referenced Figure 25 The alternative transfer function shown has no dead zone. If the wind direction changes rapidly back and forth near the full wake direction, then... Figure 3 The step transition section will cause the yaw offset signal to switch back and forth rapidly. Figure 25 The transfer function has a more progressive single transition band 60 that spans the wind direction range, thus avoiding the problem of rapid back-and-forth switching of the yaw offset signal.

[0068] Although the yaw control system 31 ideally and precisely follows Figure 25 The transfer function, but the actual yaw offset of the rotor shaft will adopt a range of random operating states centered on the transfer function, such as Figure 25 The crosses and circles in the diagram are shown.

[0069] Some of these operating states include negative yaw offsets associated with negative wind direction (such as...). Figure 25 (as shown in circle 61a in the lower left quadrant) and positive yaw offset associated with the right wind direction (such as...) Figure 25 (As shown in circle 61b in the upper right quadrant). These are acceptable operating conditions because they cause the wake to deflect away from the second wind turbine 40.

[0070] Other operating conditions include positive yaw offsets associated with negative wind direction (such as...). Figure 25 (as shown by cross 62a in the upper left quadrant) and negative yaw offset associated with positive wind direction (such as...) Figure 25 (As shown by cross 62b in the lower right quadrant). These are less acceptable operating conditions because they cause the wake to deflect towards the second wind turbine 40, potentially resulting in net power loss.

[0071] Figure 26 The operating states associated with a transfer function including a dead zone 70 according to an embodiment of the present invention are shown. Figure 25 Similarly, the actual yaw offset of the rotor shaft will adopt an operating state centered on the transfer function, such as... Figure 26 The crosses and circles in the diagram are shown.

[0072] In this case, there are fewer unacceptable operating states in the upper left and lower right quadrants (such as...). Figure 26 (as indicated by the cross in the diagram), and any such operating state has a relatively low yaw offset angle.

[0073] In the embodiments of the invention described above, the transfer function can be stored in the memory of the yaw offset controller 30 of the wind turbine 1. In other embodiments of the invention, the transfer function can be stored remotely at a location far from the wind turbine 1, for example, at a centralized location.

[0074] In the embodiments of the invention described above, the transfer function can be stored in the form of a lookup table, whether at the wind turbine 1 or at a centralized location. In other embodiments of the invention, the transfer function can be obtained through online optimization or similar methods.

[0075] Although the invention has been described with reference to one or more preferred embodiments, it will be understood that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method for deflecting the wake of a first wind turbine, wherein a second wind turbine is located downstream of the first wind turbine, such that the second wind turbine may be affected by the wake of the first wind turbine, the method comprising: A yaw offset signal is applied to the yaw control system of the first wind turbine, the yaw offset signal causing the yaw control system to generate a yaw offset between the rotor of the first wind turbine and the wind direction, the yaw offset deflecting the wake away from the second wind turbine; as well as The yaw offset signal is changed in response to changes in wind direction, wherein the yaw offset signal is changed based on a transfer function, and the transfer function includes: The negative offset band, in which the yaw offset signal is negative and decreases to a minimum value; Negative transition section, in which the yaw offset signal increases from a minimum value; Positive offset band, where the yaw offset signal is positive and increases to its maximum value; Positive transition section, in which the yaw offset signal decreases from its maximum value; and The dead zone is located between the positive transition section and the negative transition section, wherein the yaw offset signal is substantially zero in at least a portion of the dead zone, so that there is substantially zero offset between the rotor of the first wind turbine and the wind direction in at least a portion of the dead zone.

2. The method according to any of the preceding claims, wherein the rate of change of the transfer function is greater in the transition region than in the dead zone.

3. The method according to any of the preceding claims, wherein the rate of change of the transfer function is substantially zero in at least a portion of the dead zone.

4. The method according to any of the preceding claims, wherein each transition section includes a transition zone spanning a range of wind directions.

5. The method according to any of the preceding claims, wherein the yaw offset signal is below the maximum value throughout the dead zone and above the minimum value throughout the dead zone.

6. The method according to any of the preceding claims further includes monitoring wind variability conditions and changing the width of the dead zone based on the wind variability conditions.

7. The method according to any of the preceding claims, wherein when the first wind turbine is operating in the dead zone, the wake affects the second wind turbine.

8. The method according to any of the preceding claims, wherein the dead zone spans the entire wake direction, wherein the entire wake wind direction is parallel to the heading between the first and second wind turbines.

9. The method of claim 8, wherein the dead zone asymmetrically spans the entire wake direction, and the extent of the dead zone on one side of the entire wake direction is greater than the extent on the other side of the entire wake direction.

10. The method according to any of the preceding claims further includes applying induced control to the first wind turbine in response to the wind turbine entering a dead zone, wherein applying the induced control results in a reduction in the wake.

11. The method of claim 10, wherein applying induced control comprises changing at least one of the pitch angle and / or tip speed ratio of one or more blades of the rotor.

12. The method according to any of the preceding claims, wherein the transfer function further comprises: The negative cutoff band is located between the negative offset band and the negative transition zone, where the yaw offset signal is essentially equal to its minimum value throughout the entire negative offset cutoff band; And the positive cutoff band located between the positive offset band and the positive transition zone, where the yaw offset signal is essentially equal to its maximum value throughout the entire positive offset cutoff band.

13. A yaw offset controller configured to control a first wind turbine by means of the method according to any of the preceding claims.

14. A wind turbine, comprising: Rotor; Yaw control system; And the yaw offset controller according to claim 13.

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