DK201470456A1 - System for and Method of reducing Wake Effect of Offshore Wind Turbines - Google Patents

Abstract

The present invention relates to multiple wind turbines where at least one wind turbine has a floating foundation mechanically connected to a nacelle with a rotor with at least two bl ades and where at least one wind turbine is configured to be positioned at a substantially fixed positon and to operate offshore and where at least two wind turbines can be positioned dynamically relative to each other as a function of a wake field of at least one wind turbine upwind of another wind turbine amongst the multiple wind turbines. Further disclosed is a method of dynamically positioning multiple offshore wind turbines relative to each other where at least one wind turbine is placed on a floating foundation, the method comprising acts of providing a positioning force as top force on at least one wind turbine on a floating foundation

Description

System for and Method of Reducing Wake Effect of Offshore Wind Turbines Field of the Invention

The present invention relates to multiple wind turbines where at least one wind turbine has a floating foundation mechanically connected to a nacelle with a rotor with at least two blades and where at least one wind turbine is configured to be positioned at a substantially fixed position and to operate offshore and where at least two wind turbines can be positioned dynamically relative to each other as a function of a wake field of at least one wind turbine upwind of another wind turbine among the multiple wind turbines. Further disclosed is a method of dynamically positioning multiple offshore wind turbines relative to each other where at least one wind turbine is placed on a floating foundation, the method comprising acts of providing a positioning force as a top force on at least one wind turbine on a floating foundation.

The present invention also relates to a method of dynamically positioning multiple offshore wind turbines relative to each other where at least one wind turbine is placed on a floating foundation, the method comprising acts of providing a positioning force as top force on at least one wind turbine. on a floating foundation.

Background of the Invention

Operation of wind turbine parks on land has naturally taken its offset from each wind turbine being in a fixed position and thus, wind turbines in the wind turbine park have fixed positions relative to each other. Until recently this mind frame has been used in or applied to off-shore wind turbine parks, where each turbine has been placed on a foundation solidly placed on the sea floor.

Recently placing wind turbines on floating foundations has gained interest. One reason is the desire to locate wind turbines on deep sea water rather than shallow water, where foundations can be placed on the sea floor.

Deep sea installations rely on floating foundations that are held in place or the same position by anchor arrangements using, for example, cables, chains, ropes rather than rigid structures.

Positioning each wind turbine on a floating foundation requires a complex and strong mooring arrangement to overcome the loads and forces acting on a wind turbine off shore.

Object of the Invention

It is an objective of the invention to overcome limitations of the prior art.

In particular, it is an objective to provide a solution that overcomes the need for a mooring system that must be designed to handle huge loads and provide forces to position a floating foundation with a wind turbine.

Description of the Invention

An objective is achieved by multiple wind turbines where at least one wind turbine has a floating foundation mechanically connected to a nacelle with a rotor with at least two blades and where at least one wind turbine is configured to be positioned at a substantially fixed position and to operate offshore and where at least two wind turbines can be positioned dynamically relative to each other as a function of a wake field of at least one wind turbine upwind of another wind turbine among the multiple wind turbines.

The platform or foundation of the wind turbine is configured to float when the wind turbine is installed for operation at sea and may be made of concrete, steel or combinations thereof. The foundation may be floating with parts above the sea, but the foundation may be configured to be submerged not only partially, but also fully. The foundation's vertical position or degree of being submerged may be controllable.

The floating foundation may be configured to be positioned at a substantially fixed position by a mooring system. It is clear that during operation the floating foundation is essentially in the same position and held there by means of forces acting on the foundation or near the foundation. A wind turbine installed on a floating foundation will follow the position of the floating foundation. In a particular embodiment, the position of a turbine on a foundation may be variable. It is understood that when wind turbines are positioned relative to each other, the position of the foundations may be positioned relative to each other. If such a wind turbine installed on a floating foundation may be considered a single unit.

It is understood that two wind turbines can be shifted or displaced relative to each other. The shift may be in the plane of the sea level. The shift may also include a vertical displacement say by changing the level of submerging of a foundation.

There is a wake or a wake field of wind conditions downstream of a wind turbine that is different than had the wind turbine not been there. A wake field may be the combined contribution of wakes from individual turbines or simply the field from a single turbine.

Information about a wake field may be obtained by means of a model, empirical data, by measurements or combinations thereof.

The wake field may be characterized by data such as wind speed, turbulence measures or similar atmospheric conditions. The wake field data may be a scalar field or a vector field.

The positioning of wind turbines relative to each other is then determined as a function of information about the wake field according to a model or operational needs or limitations.

In a particular embodiment, the positioning of turbines including a two bladed wind turbine such as a partial pitch wind turbine may be such that the direction of the common axis of the blades of the two-bladed turbine is directed into the wind to mitigate loads during harsh weather conditions or simply reduce the loads on the wind turbine structures when the floating foundation is to be repositioned.

In one aspect, a positioning force to dynamically position at least two wind turbines relative to each other, which positioning force includes a top force established in the region of the nacelle of at least one wind turbine on a floating foundation.

Thereby a force is provided on the wind turbine structure which will mitigate through to the floating foundation and result in a force that will shift or reposition the foundation.

During operation and stationary the wind turbine will experience forces on the top part of the wind turbine. It is understood that the top force established in the top part is a force that is generated to intentionally shift, reposition or move the wind turbine to a desired position. This desired position may be a function of the wake field.

The top force is thus provided as a sufficient force that would otherwise have been provided at the foundation by means of a mooring system or an anchor arrangement. A person skilled in the art will appreciate that the top force provided in combination with a bottom force established in the region of the floating foundation of at least one wind turbine will be needed to maintain an operational situation.

In one aspect, a top force is established by introducing an offset or an error to the otherwise intended operational setting of at least one wind turbine.

An intended operation of a turbine will generally focus on maximizing power production while minimizing the loads and forces on mechanical structures of the turbine and supporting structures. The intended operation may also include balancing or compensation of forces to maintain a relative fixed position of the wind turbine. Moreover, the intended operation may further include idle modes and power down modes.

The offset or error to the operational settings is sufficient to result in a force that can overcome frictional forces and result in the foundation moving. The resulting force is a force that would otherwise have been compensated or eliminated.

By introducing an offset or error, the structure of an offset force or error force will be of a size large enough to move the wind turbine on the floating foundation and at the same time as per design so small that it does not require additional modification of the wind turbine or floating foundation. In addition, the top force generated as a result of an introduced error or an offset is generated inherently by the existing design of the wind turbine and floating foundation.

In one aspect, the offset or error to the otherwise intended operational setting of at least one wind turbine is established as an introduced yaw error.

This particular error is readily available and controllable. The yaw control mechanisms of turbines are generally well developed, which allow for an operational implementation. Moreover, the forces resulting from a yaw error or an offset are well suited to generate a positioning force to reposition a foundation. A person skilled in the art will be able to modify yaw control to obtain a desired position force of sufficient value without at the same time causing the wind turbine and / or floating foundation to become mechanically overloaded, unstable or beyond operational limits. A person skilled in the art will appreciate applying or introducing similar error or offset to otherwise intended control settings.

In one aspect, the positioning force may include a bottom force that may be provided by a mooring arrangement. In particular, the bottom force may be provided by a tow arrangement, an anchor arrangement, a thruster arrangement or a combination thereof. Tow or anchor lines may be used to provide the necessary force and to fix a desired position. Again, a person skilled in the art and having the mooring arrangement available will combine the bottom forces with the top forces to obtain the desired resultant forces that will result in the wind turbine and floating foundation being positioned in the desired position. Likewise, the person skilled in the art will appreciate that the bottom forces are kept within the limits of the operation of the wind turbine, the floating foundation and the mooring system. A mooring system or anchor arrangement is disclosed in Danish Patent Application PA 2014 70213. The content of which is incorporated herein by reference.

In one aspect, the anchor arrangement is configured with at least one tow line or anchor line arranged to pull the floating foundation. The anchor lines may be fixed to the sea bed. The tow lines may interconnect one or more floating foundations or other fix points.

The position of a wind turbine or floating foundation may be determined by a positioning system. Such positioning system may be an absolute system such as GPS or a relative system where a position of one wind turbine is determined relative to one or more other wind turbines. A plurality of such positioning systems are readily available.

In addition to a mooring system there may be provided a thruster arrangement on floating foundation. Such a thruster arrangement will provide sufficient thrust or force to position or at least additional force or control so that a floating foundation can be moved or repositioned relative to another floating foundation.

In one aspect, multiple wind turbines further comprise at least one control unit configured to input at least one operational signal from a wake field, processing the at least one operational signal and generating an output signal, which output signal is generated to offset or error the intended operational setting of at least one wind turbine and results in a positioning force that dynamically positions at least two floating foundations relative to each other.

The control unit may estimate the wake field of the multiple wind turbines by measurements of wind conditions, by using tabulated, possible empirical data, or by forecasts. Measurement system may be placed on one or more wind turbine or established as a common system. Likewise, a plurality of models, such as the Jensen model or variations and / or refinements thereof, may be used to estimate the wake field based on the geometry of the arrangement of wind turbines in combination with or taking into account measurements. Anemometers, LiDAR systems or equivalent atmospheric sensing system may be used to acquire the desired wind conditions.

The control system may also acquire and use mechanical and operational parameters such as loads and power generation data.

Additionally, by means of algorithms or look up tables, generating an output that will alter the otherwise intended operational setting by introducing the desired offset or error and provide a corrected set of operational control values.

In one aspect, the control unit is configured to position at least two floating foundations in positions where the effect of the wake field is minimized.

In such implementation the control unit will aim to optimize the position of wind turbines so that the effect of the wake field will be mitigated for the individual wind turbine. A person skilled in the art applying this approach will achieve optimal performance or minimal load on individual turbines.

In one aspect, the control unit is configured to position each wind turbine in relative positions where the effect of the wake field is minimized. A person skilled in the art applying this approach will achieve overall optimal performance or overall minimal load on multiple wind turbines.

In one aspect, the multiple wind turbines further comprise positioning means for determining the relative position of at least two floating foundations.

An objective is achieved by a method of dynamically positioning multiple offshore wind turbines relative to each other where at least one wind turbine is placed on a floating foundation. The method consists of providing a positioning force as a top force on at least one wind turbine on a floating foundation.

In one aspect, the act of providing a positioning force includes an act of introducing an offset or an error to the otherwise intended operational setting of the control of the wind turbine.

In one aspect, the act of introducing an offset or an error to the otherwise intended operational setting of the control of the wind turbine includes an act of introducing a yaw error.

In one aspect, the act of providing a positioning force includes an act of determining the positioning force as a function of a wake field of the multiple wind turbines.

In one aspect, the act of determining the positioning force includes an act of reducing or minimizing the effect of the wake field on the multiple wind turbines.

The methods or acts disclosed may be implemented using the systems disclosed or by other equivalent means. Likewise, the effects or functions of the systems or those derived from the disclosed systems may be implemented as methods or acts.

Description of the Drawings

The invention is described by example only and with reference to the drawings, wherein:

FIG. 1 shows an embodiment of a wind turbine on a floating foundation;

FIG. 2 shows multiple wind turbines with floating foundations where the floating foundations can be positioned relative to each other;

FIG. 3 illustrates a wake field from a single wind turbine and a wake field from multiple wind turbines;

FIG. 4 illustrates multiple wind turbines arranged relative to each other and the resulting wake field;

FIG. 5 illustrates the result of a positioning force established on a downwind wind turbine to position at least two floating foundations relative to each other; FIG. 6 illustrates the result of positioning force established on an upwind wind turbine turning and positioning the upwind wind turbine relative to the downwind wind turbine;

FIG. 7 illustrates the result of a positioning force established to dynamically position at least two floating foundations relative to each other and to fix the position by a mooring arrangement;

FIG. 8 illustrates the result of applying opposite yaw errors to two wind upwind turbines to introduce positioning forces to separate the wake field into two disjoint wakes at the position of a downwind wind turbine;

FIG. 9 illustrates a mooring system with an anchor arrangement and a mooring system with a thruster arrangement;

FIG. 10 illustrates a method of dynamically positioning multiple offshore wind turbines relative to each other; spirit

FIG. 11 illustrates a method of dynamically positioning multiple offshore wind turbines relative to each other by providing a positioning force by introducing an error to the otherwise intended operational control of a wind turbine by an yaw error.

In the following text, the figures will be described one by one and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

Detailed Description of the Invention

The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention as described in the patent claims below.

FIG. 1 illustrates a single wind turbine 12 placed on a floating foundation 14 configured to support a wind turbine 12 with a nacelle 16 on which there is a rotor 18 which in this embodiment has two blades 20. The nacelle 16 is supported by a tower 22 positioned on the floating foundation 14.

The floating foundation 14 and the wind turbine 12 are configured to operate in the wind direction 30.

The wind turbine will generate a wake 100 that will form or contribute to a wake field 110.

The nacelle 16 is configured to yaw 32 and during operation the wind turbine 12 is configured to operate in a intended yaw direction 34 as controlled by a wind turbine generator controller 36. Preferably the yaw 32 is aligned with the wind direction 30. Deviations from the intended yaw direction 34 is a yaw error 40.

FIG. 2 illustrates multiple wind turbines 10 placed offshore and positioned relative to each other. For purposes of definition only two turbines 12A, 12B are shown.

Among the multiple wind turbines 10 each wind turbine 12 has a floating foundation 14 mechanically connected to a nacelle 16 with a rotor 18 with at least two blades 20. In this case both wind turbines 12A, 12B are configured to operate offshore.

In relation to the wind direction 30 the wind turbines 12A, 12B are organized upwind 112 and downwind 114. In such a case the upwind 112 turbine 12A generates the wake 100 and the downwind 114 turbine 12B experiences a wake field 110, which in this case is identical to the wake 100, but generally a sum of contribution from one or more wakes 100.

The two wind turbines 12A, 12B can be positioned dynamically relative to each other as a function of a wake field 110 of at least one wind turbine 12A upwind 112 of another wind turbine 12B among the multiple wind turbines 10.

As an example, the downwind 114 wind turbine 12B is positioned relative to the upwind 112 turbine 12A. To reposition or shift the position the downwind 112 wind turbine 12B may experience an applied or generated positioning force 120. Such positioning force 120 may be in a plane parallel to the sea or vertically.

The positioning force 120 may be applied as a function of the wake field 110 experienced by the downwind 114 wind turbine 12B.

Likewise, a positioning force 120 may be applied to the upwind 112 wind turbine 12A. This will reposition the upwind 112 wind turbine 12A and the wake 100 and as a result change the wake field 110 experienced by the downwind 114 wind turbine 12B.

The positioning force 120 may be applied to the floating foundation 14 or the wind turbine 12.

The positioning force 120 may be applied as a bottom force 124 on the bottom part of the wind turbine 12 or on the floating foundation 14. The positioning force 120 may be applied as a top force 122 on the top part of the wind turbine 12. In particular, the top force 122 may be generated or induced in the region of the nacelle 16. The top force 122 may be generated by the forces resulting from introducing an offset 130 or an error 132 in the setting or operation of the nacelle 16, the rotor 18 or a blade 20. In particular, the top force 122 may be the result of an introduced yaw error 140. As such, the yaw error 140 is an intended error 132 or offset 130.

It is understood that the floating foundation 14 is positioned by a mooring arrangement 150. Likewise, the mooring arrangement 150 contributes to or balances the positioning force 120.

FIG. 3 illustrates excerpts from the Jensen model as a wake 100 model and how a wake field 110 may be understood.

FIG. 3A shows an upwind 112 wind turbine 12A generating a wake 100 and a downwind 114 wind turbine 12B in the wake 100 or wake field 110. According to the Jensen model the wind speed is a field with an ambient wind speed U and a wind speed V0 just behind the upwind 112 wind turbine 12A. A wind speed V experienced in the wake field 110 may be estimated by the Jensen model or any other wake model, prediction or measurement. The wind speed V may depend on a distance X between the upwind 112 and the downwind 114 turbines. Likewise, the extent of a wake 100 may be estimated as a function of distance and relative positions between the upwind 112 and downwind 114 turbines.

As is seen, a different position with a different (more advantageous) wind speed may be advantageous.

FIG. 3B illustrates wakes 100 of multiple wind turbines 12A, ... 12B arranged equidistantly on a line in the wind direction 30 with an upwind 112 and a downwind 114.

From upwind 112 to downwind 114 wind turbine 12A generates a wake 100A, wind turbine 12B generates a wake 100B and so on. Each wind turbine 12 in the arrangement will experience a wake field 110 resulting from contributions of wakes 100A, ... of the wind turbines 12 upwind 112 form each wind turbine 12.

Wind turbine 12C will experience a wake field 110C with a wind speed V2.

As is seen, a different position with a different (more advantageous) wind speed may be advantageous.

FIG. 4 illustrates - again based on the Jensen Model - multiple wind turbines 10 here arranged in a circle. Each wind turbine 12A, ..., 12E with a corresponding wake 100A, ..., 100J and the multiple wind turbines 10 resulting in a wake field 110, which in this case results in four distinct areas: an area type with ambient wind conditions, an area type with wind conditions resulting from a wake from a single turbine, an area type with wind conditions resulting from two wakes, and an area type with wind conditions resulting from three wakes.

As has been seen, a positioning of a wind turbine in a different position with a different (more advantageous) wind speed may be advantageous.

FIG. 5 illustrates the dynamic positioning of a downwind turbine 12B in the wake field 110 resulting from the wake 100 form the upwind 112 wind turbine 12A. In this case a yaw error 140 is introduced in the downwind 114 wind turbine 12B resulting in a positioning force 120 in a direction that relocates, shifts or repositions the down wind 114 wind turbine 12B as a function of the wake field 110 such as the place the wind turbine 12B in wind conditions that are operationally more advantageous than the original position. The wind turbine 12B may experience less forces or generate more power in the new position.

In the illustration the wind turbine 12B appears to be moved completely out of the wake 100 and into the ambient wind conditions. In practice the transition may not be as distinct as illustrated.

FIG. 6 illustrates a situation where with an upwind 112 wind turbine 12A generating a wake 100 which contributes to the wake field 110 seen by the downwind 114 wind turbine 12B. In this case the upwind 112 wind turbine 12A is repositioned to alter the wake field 110 experienced by the downwind 114 wind turbine 12B.

Again the positioning force 120A may be established by contributions from an introduced yaw error 140. In this case the wake 100 may shift or reposition. Furthermore, the wake 100 may also change properties due to the introduced yaw error 140.

FIG. 7 illustrates multiple wind turbines 10 arranged relative to each other in wind field V (X, Y). The wind turbines 10 may share a common control unit 160 configured to input at least one operational signal 162 of a wake field 110 W and or forces L on wind turbines. The control unit 160 is configured for processing the at least one operational signal 162 and generating an output signal 164 which is an offset 130 or an error 132 to the intended operational setting. The output signal 164 is provided to generate a contribution to a positioning force 120 that will reposition a wind turbine 12 as a function of the wake field 110. The control unit 160 may be configured to reduce or minimize loads, increase or optimize power production. or combinations thereof.

The control unit 160 may optimize or improve wind turbines 12 individually or seek to optimize or improve multiple wind turbines 10 collectively.

The control unit 160 may also be configured to position a wind turbine 12 in any position or operational mode.

FIG. 8 illustrates multiple wind turbines 10 with two wind turbines 12A, 12B placed upwind 112 and a third wind turbine 12C placed downwind 114. In figure 8A the two upwind 112 turbines generate a wake field 110 with an overlap of the wake 100A and the wake 100B . A yaw error 140A, 140B may be introduced to each wind turbine 12A, 12B so that each will experience a positioning force 120A, 120B so that the two wind turbines 12A, 12B will separate further from each other in such a way that the third wind turbine 12C will experience a less disturbing wake field 110 than otherwise and as indicated in figure 8A.

FIG. 9 illustrates a mooring arrangement 150 of a floating foundation 14. The mooring arrangement 150 may be an anchor arrangement 154 with tow or anchor lines.

In FIG. 9A there is an anchor arrangement 154 where the anchor lines can be used to position, to fix a position or to reposition the floating foundation 14.

FIG. 9B illustrates an embodiment where there is an additional thruster 156 arrangement.

Multiple wind turbines 10 may be positioned relative to each other by use of a bottom force 124 provided by a tow or anchor arrangement 152.

In either case, the mooring system 150 and / or the thruster arrangement 156 may provide a contribution to a positioning force 120. A person skilled in the art will appreciate that forces should be balanced and combined to maintain a desired position.

Likewise, a person skilled in the art will make use of positioning means 170, which may be based on a GPS 172 type of system. Alternatively, each foundation or wind turbine may have a positioning system based on a relative position to a common reference position.

FIG. 10 illustrates a method 200 of dynamically positioning multiple offshore wind turbines relative to each other where at least one wind turbine is placed on a floating foundation. The method 200 includes an act of providing 210 a positioning force as a top force on at least one wind turbine on a floating foundation.

FIG. 11 illustrates a method 200 with an act of providing 210 a positioning force as a top force and further acts of introducing 220 an offset or an error to the otherwise intended operational setting of the control of the wind turbine. The offset or error may be a yaw error. The method may further comprise an act of determining the positioning force as a function of a wake field.

Claims (15)

1. Multiple wind turbines (10) where at least one wind turbine (12) has a floating foundation (14) mechanically connected to a nacelle (16) with a rotor (18) with at least two blades (20) and where at least one wind turbine (12) is configured to be positioned at a substantially fixed positon and to operate offshore and where at least two wind turbines (12A, 12B) can be positioned dynamically relative to each other as a function of a wake field (110) of at least one wind turbine (12A) upwind (112) of another wind turbine (12B) amongst the multiple wind turbines (10).

2. Multiple wind turbines (10) according to claim 1, wherein a positioning force (120) is provided to dynamically position at least two wind turbines (12A, 12B) relative to each other, which positioning force (120) includes a top force (122) established in the region of the nacelle (12) of at least one wind turbine (12) on a floating foundation (14).

3. Multiple wind turbines (10) according to claim 2, wherein the top force (122) is established by introducing an offset (130) or an error (132) to the otherwise intended operational setting of at least one wind turbine (12).

4. Multiple wind turbines (10) according to claim 3, wherein the offset (130) or the error (132) to the otherwise intended operational setting of at least one wind turbine (12) is established as an introduced yaw error (140).

5. Multiple wind turbines (10) according to any of claim 1 to 4, wherein the positioning force (120) includes a bottom force (124) provided by a mooring arrangement (150).

6. Multiple wind turbines (10) according to claim 5, wherein the bottom force (124) is provided by a tow arrangement (152), an anchor arrangement (154), a thruster arrangement (156) or a combination thereof.

7. Multiple wind turbines (10) according to any of claim 1 to 6, further comprising at least one control unit (160) configured to input at least one operational signal (162) of a wake field (110), processing the at least one operational signal (162) and generating an output signal (164), which output signal (164) is generated to offset (130) or error (132) the intended operational setting of at least one wind turbine (12) and result in a positioning force (120) that dynamically positions at least two floating foundations (14A, 14B) relative to each other.

8. Multiple wind turbines (10) according to claim 7, wherein the control unit (160) is configured to position at least two floating foundations (14A, 14B) in positions where the effect of the wake field (110) is minimized.

9. Multiple wind turbines (10) according to claim 7 or 8, wherein the control unit (160) is configured to position each wind turbine (12) in relative positions where the effect of the wake field (110) is minimized.

10. Multiple wind turbines (10) according to any of claim 1 to 9, further comprising positioning means (170) for determining the relative position of at least two floating foundations (14A, 14B).

11. Method of dynamically positioning multiple offshore wind turbines (200) relative to each other where at least one wind turbine (12) is placed on a floating foundation (14), the method comprising acts of: - providing (210) a positioning force (120) as top force (122) on at least one wind turbine (12) on a floating foundation (14).

12. Method according to claim 11 where the act of providing (210) a positioning force (120) includes an act of: - introducing (220) an offset (130) or an error (132) to the otherwise intended operational setting of the control of the wind turbine (12).

13. Method according to claim 11 where the act of introducing (220) an offset (130) or an error (132) to the otherwise intended operational setting of the control of the wind turbine (12) includes an act of: - introducing a yaw error (140).

14. Method according to any of claim 11 to 13 where the act of providing (210) a positioning force (120) includes an act of: - determining (230) the positioning force (120) as a function of a wake field (110) of the multiple wind turbines (10).

15. Method according to any of claim 11 to 14 where the act of determining (230) the positioning force (120) includes an act of: - reducing or minimizing (240) the effect of the wake field (110) on the multiple wind turbines (10).