WO2017085501A1

WO2017085501A1 - Docking system

Info

Publication number: WO2017085501A1
Application number: PCT/GB2016/053599
Authority: WO
Inventors: George TATESON
Original assignee: Kite Power Solutions Limited
Priority date: 2015-11-19
Filing date: 2016-11-18
Publication date: 2017-05-26
Also published as: GB201520413D0

Abstract

A docking system for a tethered airborne device having a main line and a nose line, the docking system comprising: a ground station comprising a docking structure; a nose line capture apparatus movable from a first position to a second position; wherein the nose line capture apparatus is configured to couple to the nose line at the first position when the airborne device is a predetermined distance from the ground station and wherein the nose line capture apparatus is subsequently movable to a second position corresponding to a docking position of the airborne device with respect to the docking structure.

Description

Docking system

Field

The present invention relates to a docking system for a tethered airborne device.

Background

People have tried to harness wind energy for thousands of years. Lately, with fossil fuels running out, techniques for converting energy in the wind to other forms of energy and, in particular, electrical energy have become more popular. It is known to use wind turbines to extract the energy from the wind. It is also known to use kites to extract energy from the wind. Kites can fly at high altitudes where wind speeds are more reliable than the wind speed at the height of the hub of a wind turbine. The hub height of a wind turbine maybe at 8o or loom whereas kites can be flown at a typical height of 400 to 700m or even higher. With kite-based power generating systems, the majority of the mass is kept near to ground or water level at a base station, thereby minimising bending moments and reducing the mass of the airborne equipment considerably. Repair and service of the equipment is easier since the bulk of the equipment is at low- level. At sea, the ground based equipment can be mounted on towable barges or buoys allowing retrieval to harbour for major repair or service.

A system for the extraction of power from the wind using a kite typically includes a kite connected to a base station using a tether. An important aspect in kite power systems is to provide a system that allows for the launch and capture of tethered airborne device such as kites in an efficient way to maximise the time that the devices are airborne.

Summary

According to a first aspect of the invention there is provided a docking system for a tethered airborne device having a main line and a nose line, the docking system comprising: a ground station comprising a docking structure; a nose line capture apparatus movable from a first position to a second position; wherein the nose line capture apparatus is configured to couple to the nose line at the first position when the airborne device is a predetermined distance from the ground station and wherein the nose line capture apparatus is subsequently movable to a second position

corresponding to a docking position of the airborne device with respect to the docking structure. The system may further comprise a shuttle located at a point on the main line and a nose line holding arrangement proximate the free end of the main line, wherein the nose line comprises a substantially taut section extending coextensively with the main line between the shuttle and the nose line holding arrangement.

The shuttle may be arranged to hold the coextensive section of the nose line proximate thereto to provide a separation between the nose line and the main line. The nose line holding arrangement may comprise a retractor having a tensile biasing device and a retractor line attached at one end thereof to an upper portion of the coextensive section of the nose line and attached at a second end thereof to the tensile biasing device. The first position of the nose line capture apparatus may be proximate a section of the nose line to be captured and wherein the nose line capture apparatus is configured to pull at least part of the nose line over the structure to the second position.

The system may further comprise a captive pulley located proximate the top of the structure, the captive pulley being arranged to allow the nose line capture apparatus to pass therethrough.

The system may further comprise a nose line winch and wherein the nose line capture apparatus is attached to a capture apparatus line forming a closed loop between the nose line winch and the top of the structure and, wherein the nose line winch is configured to move the nose line capture apparatus from the first position to the second position.

The capture apparatus line may comprise an upper section extending from the nose line capture apparatus to the nose line winch via the top of the structure and a lower section comprising two lengths of line extending respectively either side of the main line from the nose line capture apparatus to the nose line winch.

The system may further comprise a control module for controlling the nose line winch to move the nose line capture apparatus from the first position to the second position. At least part of the main line may have a faired profile.

The system may further comprise a main line winch for winding the main line thereon. The nose line may be arranged so that a section thereof is windable on to the main line winch.

The system may further comprise an alignment head arranged to align the section of nose line to be captured with the nose line capture apparatus.

The alignment head may be arranged to allow a shuttle to pass therethrough. The docking structure may be a docking mast. According to a second aspect of the invention there is provided a method of docking a tethered airborne device having a main line and a nose line to a ground station comprising a docking structure, the method comprising: providing a nose line capture apparatus at a first position; causing the nose line capture apparatus to couple to the nose line at the first position when the airborne device is a predetermined distance from the ground station; and moving the nose line capture apparatus to a second position corresponding to a docking position of the airborne device with respect to the docking structure.

Brief description of the drawings

Embodiments of the invention will be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 is a schematic view of three stages of a docking process; Figure 2 shows a main line winch;

Figure 3 is a close-up view of a kite and length of main line and nose line; Figure 4 is a close-up view of a retractor;

Figure 5 is a close-up view of a shuttle and length of main line; Figures 6A and 6B show a nose line capture device in use; Figure 7 is a close-up view of the nose line during capture;

Figure 8 is a view of the kite during the final stages of docking; and Figure 9 is a close-up view of Figure 8. Detailed description

Embodiments of the invention provide a docking arrangement for a kite power generation system.

Figure 1 shows a kite system 100 at various stages of the docking process according to an embodiment of the present invention. A kite 101 is attached, via a main line 102, to a base station 103. The base station 103 maybe located on land or at sea on a suitable platform 104. The base station 103 comprises a main line winch 105 to which the main line 102 is attached and a docking mast 106. The kite 101 comprises a wing 107, bridles 108 and a nose line 109. The bridles 108 extend from the wing 101 to a pod 110 located at the end of the main line 102. The nose line 109 extends from the wing 107 to a shuttle 111 which is located at a fixed point on the main line 102. The nose line 109 provides a connection to the wing 107 of the kite 101. As the kite 101 approaches the mast 106, the nose line 109 is captured so that the kite 101 is pulled towards the mast 106 for docking. In order that the kite 101 can be docked safely and reliably it is important that the nose line 109 is captured early in the docking approach while the kite 101 is in more stable flight; this gives more time for the nose line capture system to work and allows for docking aborts and re-attempts, if required. In order that the nose line 109 is captured early it is provided with a significant length, typically at least 100 metres.

Figure 2 shows the main line winch 105 in more detail. The main line winch 105 comprises a drum 150 which is used for storing the main line 102. Furthermore, the main line winch 105 is also part of the power generation system for transferring mechanical energy into electrical energy or usable power. As the kite 101 travels away from the winch 105 using its prescribed path, the length of main line 102 is pulled off the winch drum, thereby causing the drum to rotate. The rotation of the drum is used to drive an alternator, generator or pumping apparatus that may be mounted on to the drum via a gearbox or alternatively a hydraulic transmission system could be used so that the generator or other power generating apparatus or pumping apparatus can be mounted remotely.

At the end of the power-generating cycle, the main line winch 105 is reversed to wind in the main line 102 and the kite 101 is flown out of the power generating window or feathered in some way, such as by reducing the angle of attack (pitching forwards), so as to reduce the kite's drag. Winding in the main line 102 can be performed in a number of different ways, such as: using the electrical generating equipment as a motor and running it in reverse, having a second motor gearbox arrangement on the opposite end of the drum that is used for winding the tether back in, reversing the hydraulic transmission while providing hydraulic fluid at pressure from an accumulator or another power source.

The main line winch 105 comprises an alignment apparatus 151. The alignment apparatus 151 comprises a guide head 152 which follows the unwound length of main line 102 and guides the main line 102 onto the drum 150. The guide head 152 is housed between respective curved tracks 153, 154. The curved tracks 153, 154 curve around the drum 150 to follow a path which forms a section of an orbital path around the drum 150. The guide head 152 can thus move along a curved path around the drum 150 to maintain elevational alignment between the guide head 152, the main line 102 and the kite 101.

The guide head 152 may be provided with an aperture through which the main line 102 is threaded, dimensioned so as to hold the main line 102 securely in place while allowing the main line 102, part of the nose line 109 and the shuttle 111 to feed through in either direction depending on whether the main line 102 is being wound or unwound. The guide head 152 may be arranged so that it forces the shuttle 111 to pass therethrough in a specific orientation in order to present the nose line 109 to the nose line capture apparatus.

The alignment of the main line winch 105 in the azimuthal direction may be performed using a controller to control a turntable on which the main line winch 105 may be located. The controller may be programmed with the predetermined flight path of the kite 101 so that the rotation of the turntable respective to the vertical axis can be varied to comply with the kite flight path, for example a figure of eight or a continuous loop. The controller sends control signals to the motor to ensure alignment of the winch with the tether. Furthermore, the wing 107 may be provided with a GPS receiver to enable the position of the wing 107 to be determined. The wing 107 may also be provided with kite speed and air pressure sensors. Positioning information, kite speed and air pressure data may be transmitted to the controller. Moreover, the guide head 152 may be provided with a sensor to detect the elevation of the guide head which can provide an indication of the elevational and azimuthal position of the wing 107.

Servo mechanisms may also be used to compensate automatically for any deviations in the flight path of the kite.

As stated above, the shuttle 111 is fixed to the main line 102. The position of the shuttle 111 on the main line 102 is selected so that as the main line 102 is being wound in, the shuttle 111 and base of the nose line 109 approach the guide head 152 and the main line winch 105 so that the nose line 109 can be captured. This is typically when the kite 101 is approximately 150 metres from the base station 103.

Referring to Figure 3, the nose line 109 comprises a relatively taut lower section 109a and a relatively loose upper section 109b. Prior to capture, the taut section 109a forms a lower section of the nose line 109 and extends from the shuttle 111 towards a retractor 113. The lower section 109a is substantially coextensive with the length of the main line 102 extending from the shuttle 111 towards the pod 110. The loose section 109b forms an upper section of the nose line 109. The loose section 109b extends from the wing 107 towards the retractor 113.

Referring to Figure 4, the retractor 113 comprises a housing 113a in which is stored a length of retractor line 114 attached to the retractor 113 at one end. The retractor line is attached to the nose line 109 at the other end. The retractor 113 comprises a motorised drum that may be controlled so that the retractor line 114 is held under a constant retracting tension. Alternatively, the retractor 113 may comprise a spring-loaded pulley. The tension on the retracting line 113 serves to pull the attachment point between the retractor line 114 and the nose line 109 towards the retractor 113. Prior to capture of the nose line 109, the attachment point between the retractor line 114 and the nose line 109 is proximate the retractor 113. As such, the lower section of the nose line 109 is kept taut. Maintaining a taut lower section of nose line 109 is advantageous since it prevents this section from becoming tangled with the main line 102 or from becoming loose which would make it difficult for the nose line 109 to be captured. Maintaining a loose upper section is advantageous since it prevents the nose line 109 interfering with the control of the kite 101. However, the length of the loose section 109b is selected to be sufficiently short so that it does not flap excessively and interfere with the aerodynamic profile of the kite.

Referring to Figure 5, the shuttle 111 is configured to provide a separation between the main line 102 and the nose line 109 in the vicinity of the shuttle 111. Providing a separation between the main line 102 and the nose line 109 is advantageous since it facilitates capture of the nose line 109. The shuttle 111 may be formed from a compressible material such as memory foam. The shuttle 111 maybe provided with a leaf spring. As the shuttle 111 is wound onto the main line drum 150 along with the main line 102, the shuttle and nose line 109 are compressed, thereby allowing them to be stored on the main line winch 105. The main line 102 may then be unwound during a subsequent launch of the kite 101. The memory foam and leaf spring expand as the shuttle 111 is unwound from the main line winch 105. The main line 102 may have a faired profile so that the shuttle 111 is wound on to the main line winch 105 in the correct orientation.

The main line 102 may be formed from any suitable material known in the art such as PBO (poly(p-phenylene-2,6-benzobisoxazole or Zylon(RTM) or linear carbon.

However, in some embodiments the main line 102 is formed from an ultrahigh molecular weight polyethylene (UHMWP) material such as Dyneema. Main lines made from Dyneema have high yield strengths and are therefore durable, having extended lifetimes.

The kite system 100 also comprises a nose line capture apparatus such as a nose line capture device 115 (shown in Figures 6A and 6B) and a capture apparatus winch 116 located at the base of the mast 106. The nose line capture device 115 is connected to a capture apparatus line 117. An upper portion 117a of the capture apparatus line 117 extends as a single line connected to an upper part of the nose line capture device 115. The upper portion 117a extends from an upper part of the nose line capture device 115 upwardly towards the top of the mast 106. The upper portion extends over the top of mast 106 and over a pulley 118 situated near to the top of the mast 106. The upper portion 117a extends downwardly from the top to the base of the mast 106, where it meets the capture apparatus winch 116. A lower portion 117b of the capture apparatus line 117 comprises two lengths of line, arranged either side of the main line 102. The lower portion 117b extends downwardly from the nose line capture device 115 under the main line 102 and meets the capture apparatus winch 116. As such, the capture apparatus line 117 forms a closed loop extending from the capture apparatus winch 116 up to the top of the mast 106 and returning down the mast 106 and back to the capture apparatus winch 116. The capture apparatus winch 116 is coupled to a motor and a controller so that the capture apparatus winch 116 may be rotated. Rotation of the capture apparatus winch 116 causes the nose line capture device 115 to move from a first position where the nose line capture device 115 picks up the portion of nose line 109 near to the shuttle and a second position where the nose line capture device 115 is pulled over the pulley 118 at the top of the mast 106.

The nose line capture device 115 comprises first and second pulley halves 120a, 120b, which, when closed (as shown in Figure 6B), form a pulley 120. As such, the first and second pulley halves 120a, 120b are movable from an open position to a closed position. Prior to capture of the lower section of the nose line 109, the pulley 120 is open. The nose line capture device 115 is then positioned sufficiently close to the nose line 109 so that the nose line 109 can be captured. The pulley halves 120a, 120b are actuated via a motor or other suitable actuation device so that the nose line 109 is held between the pulley 120 and the block 121 of the nose line capture device 115. The nose line winch 116 is then operated so that the nose line capture device 115 is moved upwards towards the top of the mast 106 pulling the nose line 109 therewith. An advantage of the pulley 120 is that it provides a low friction surface against which the nose line 109 moves as the capture device 115 is moved upwards.

Various alternatives to the nose line capture device 115 shown in Figure 6 may be provided in alternative embodiments. In general, the nose line capture device is arranged to allow the nose line to be captured from above and to be pulled over the top of the mast. The arrangement is also configured to allow the nose line to be easily releasable. In the embodiment shown in Figure 6, the nose line may be released by opening the pulley 120.

Referring again to Figure 1, the position of the kite 101 is shown at three successive points A, B, C during the docking process. At position A, the kite is at an early retract phase. This corresponds to a stage at which retraction is initiated following the power generation phase. When the kite 101 is at this position the controller controls the kite to commence docking. In response thereto, the main line winch 105 is switched to a winding phase and the main line 102 is wound in and the kite 101 approaches the base station 103.

The main line 102 retracts until the shuttle 111 approaches the main line winch 105, as shown at Figure lB. The nose line winch 116 controls the position of the nose line capture device 115 so that the nose line capture device 115 is sufficiently close to the nose line 109 so that the nose line 109 can be captured, as shown in Figure 7.

As the shuttle 111 approaches the guide head 152 of the main winch 105, retraction of the main line 102 pauses and the shuttle 111 is forced into a specific orientation in which it presents a small loop of nose line which can be reliably collected by the nose line capture device 115.

The pulley halves 120a, 120b are then actuated. The nose line 109 is then held between the block 121 and the pulley 120. As such, the nose line capture device 115 becomes coupled to the nose line 109. The section of the nose line 109 between the nose line capture device 115 and the retractor 113 is held taut by the attachment between the nose line 109 and the retractor line 114 which is itself held under tension by the retractor 113. This helps to keep the nose line in position and avoids it becoming tangled.

The main line winch 105 continues to retract and stores excess nose line and main line on the drum 150.

The nose line winch 116 is then activated in response to an automated signal from the controller to cause the capture apparatus line 117 to pull the nose line capture device 115 upwards and over the top of the captive pulley 118 located near to the top of the mast 106. This is shown in Figure lC and in Figures 8 and 9. The nose line capture device 115 pulls a length of nose line 109 over the captive pulley 118. The force exerted on the nose line 109 by the nose line capture device 115 causes a length of the retractor line 114 to be extended from the retractor 113. The unwinding of the retractor line 114 may be passive. However, in some embodiments, a motorised retractor is configured to actively unwind a length of retractor line 114. As the nose line capture device 115 is pulled over the top of the mast 106, a portion of the nose line 109 as well as a length of the retractor line 114 proximate the attachment point X between the nose line 109 and the retractor line 114 are also pulled over the top of the mast 106. The nose line winch 116 pulls the nose line capture device 115 to a predefined position which corresponds to the docking position of the kite 101 with respect to the docking mast 106. In Figures 1, 8 and 9, the representation of the various lines has been simplified and the lines have been spaced out and represented schematically by different line patterns. The main line 102 is represented by a thick solid line. The nose line 109 is represented by a dashed and dotted line. The retractor line 114 is represented by a dashed line. The capture apparatus line 117 is represented by a dotted line.

The main line winch 105 continues to retract the main line 102 to be wound on to the drum 150. The length of main line 102 between the main line winch 105 and the pod 110 shortens. The nose line winch 116 continues to pull the nose line capture device 115 to pull the wing 107 up against the upper portion of the mast 106. The length of the nose line 109 also shortens by substantially identical amounts, pulling the kite to the mast and recovering main line. The retraction of the main line 102 and the retraction of the nose line 109 are coordinated so that the top of the kite is pulled against the mast 106 at the same time as the bottom of the kite is pulled in close to the main line winch 105.

As will be apparent from the above description, the configuration of the base station 103 having a docking mast 106 allows for the kite 101 to dock with the ground station 103 as the main line 102 is wound in onto the drum of the main line winch 105.

Providing a docking system having a mast and a nose line capture apparatus allows for the kite to be captured quickly and efficiently and also reduces the risk of damaging the kite.

The loose section 109b of the nose line 109 may be secured at the lower end thereof by the retractor 113, as explained above. Alternatively, a winch or an elastic arrangement may be provided in the wing 107 to control the nose line 109 so that the length of loose section 109b is kept under control to avoid interfering with the aerodynamic profile of the kite.

Embodiments described herein have referred to kites. Such kites may be rigid, soft or hybrid kites. However, it should be understood that alternative tethered airborne devices could be used such as rigid wings or blimps. Embodiments described herein relate to ground stations having a docking mast. However, it should be borne in mind that alternative docking structures may be employed instead that are provided with an elevated point to allow capture of the tethered airborne device. For example, a docking tower could be provided instead of a mast.

The embodiments described above are intended to be illustrative examples. It should be borne in mind that numerous alternative examples also fall within the scope of the invention which is defined by the claims appended hereto.

Claims

1. A docking system for a tethered airborne device having a main line and a nose line, the docking system comprising:

a ground station comprising a docking structure;

a nose line capture apparatus movable from a first position to a second position; wherein the nose line capture apparatus is configured to couple to the nose line at the first position when the airborne device is a predetermined distance from the ground station and wherein the nose line capture apparatus is subsequently movable to a second position corresponding to a docking position of the airborne device with respect to the docking structure.

2. The system of claim l, further comprising a shuttle located at a point on the main line and a nose line holding arrangement proximate the free end of the main line, wherein the nose line comprises a substantially taut section extending coextensively with the main line between the shuttle and the nose line holding arrangement.

3. The system of claim 2, wherein the shuttle is arranged to hold the coextensive section of the nose line proximate thereto to provide a separation between the nose line and the main line.

4. The system of either claim 2 or claim 3, wherein the nose line holding arrangement comprises a retractor having a tensile biasing device and a retractor line attached at one end thereof to an upper portion of the coextensive section of the nose line and attached at a second end thereof to the tensile biasing device.

5. The system of any preceding claim, wherein the first position of the nose line capture apparatus is proximate a section of the nose line to be captured and wherein the nose line capture apparatus is configured to pull at least part of the nose line over the structure to the second position.

6. The system of claim 5, further comprising a captive pulley located proximate the top of the structure, the captive pulley being arranged to allow the nose line capture apparatus to pass therethrough.

7. The system of any preceding claim, further comprising a nose line winch and wherein the nose line capture apparatus is attached to a capture apparatus line forming a closed loop between the nose line winch and the top of the structure and, wherein the nose line winch is configured to move the nose line capture apparatus from the first position to the second position.

8. The system of claim 7, wherein the capture apparatus line comprises an upper section extending from the nose line capture apparatus to the nose line winch via the top of the structure and a lower section comprising two lengths of line extending respectively either side of the main line from the nose line capture apparatus to the nose line winch.

9. The system of either claim 7 or claim 8, further comprising a control module for controlling the nose line winch to move the nose line capture apparatus from the first position to the second position.

10. The system of any preceding claim, wherein at least part of the main line has a faired profile.

11. The system of any preceding claim, further comprising a main line winch for winding the main line thereon.

12. The system of claim 11, wherein the nose line is arranged so that a section thereof is windable on to the main line winch.

13. The system of any preceding claim, further comprising an alignment head arranged to align the section of nose line to be captured with the nose line capture apparatus.

14. The system of claim 13, wherein the alignment head is arranged to allow a shuttle to pass therethrough.

15. The system of any preceding claim, wherein the docking structure is a docking mast.

16. A method of docking a tethered airborne device having a main line and a nose line to a ground station comprising a docking structure, the method comprising:

providing a nose line capture apparatus at a first position;

causing the nose line capture apparatus to couple to the nose line at the first position when the airborne device is a predetermined distance from the ground station; and

moving the nose line capture apparatus to a second position corresponding to a docking position of the airborne device with respect to the docking structure.