Control of a wind energy park comprising airborne wind energy

Abstract

The invention relates to a method for controlling the operation of a number of airborne wind energy systems arranged in a wind energy park, where each airborne wind energy system comprising a wind engaging member being coupled to a ground station via a cable. The method comprises the determination of an operational parameter of each of the airborne wind energy systems, such as the flight trajectory, the cable tension, or the power production. A first airborne wind energy system is controlled according to a fault control mode if its operational parameter deviates more than a predetermined threshold parameter from the operation parameters of the other airborne wind energy system. The method further comprises operating one or more neighbouring airborne wind energy systems according to a safe control mode.

Claims

1. A method for controlling the operation of a number of airborne wind energy systems arranged in a wind energy park, each airborne wind energy system comprising a wind engaging member being coupled to a ground station via a cable, the method comprising: determining an operational parameter of each of the number of airborne wind energy systems, determining a deviation between the operational parameter of a first airborne wind energy system and the operational parameters of the other airborne wind energy systems, controlling the operation of the first airborne wind energy system according to a normal control mode if the deviation is smaller than a predetermined threshold parameter, controlling the operation of the first airborne wind energy system according to a fault control mode if the deviation is larger than or equal to the predetermined threshold parameter, and determining a wind direction and controlling the operation of one or more of the other airborne wind energy systems in a downwind direction to the first airborne wind energy system according to a safe control mode if the first airborne wind energy system is in a fault control mode.

2. The method according to claim 1, wherein the safe control mode is initiated prior to initiating the fault control mode.

3. The method according to claim 1, wherein the wind direction is determined from an angle of the cable.

4. The method according to claim 1, further comprising controlling the operation of all neighboring airborne wind energy systems to the first airborne wind energy system according to the safe control mode if the first airborne wind energy system is in a fault control mode.

5. The method according to claim 1, wherein the operational parameter comprises one of: power production, flight speed, a tension in the cable, a cable extraction and/or retraction speed, an angle of the cable, and flight position.

6. The method according to claim 1, wherein the operational parameter is determined without GPS signal.

7. The method according to claim 5, wherein at least one of the speed and the flight position is determined by determining a position of a point on the cable.

8. The method according to claim 7, wherein the point is at a connection between the cable and the first airborne wind energy system.

9. The method according to claim 1, wherein the operational parameter is determined over a predetermined time or time interval.

10. The method according to claim 1, wherein the fault control mode comprises retracting the wind engaging member to the ground station of the airborne wind energy system or to a lower height.

11. The method according to claim 1, wherein the fault control mode comprises releasing the wind engaging member from the cable between the wind engaging member and the ground station.

12. The method according to claim 11 wherein the fault control mode further comprises steering the wind engaging member to the ground.

13. The method according to claim 1, wherein the fault control mode comprises sending out warning and/or tracking signals from the wind engaging member, the warning and/or tracking signals comprising any of audio, visual, and radio signals.

14. The method according to claim 1, wherein the fault control mode includes sending a request for service.

15. The method according to claim 1, wherein the fault control mode comprises maintaining the wind engaging member at essentially the same height and operating the airborne wind energy system in a no-power production mode.

16. The method according to claim 1, wherein the safe control mode comprises retracting the wind engaging member to the ground station of the airborne wind energy system.

17. The method according to claim 1, wherein the safe control mode comprises steering the wind engaging member in a direction away from the wind engaging member of the first airborne wind energy system.

18. The method according to claim 1, wherein the safe control mode comprises steering the wind engaging member to a height above the height of the wind engaging member of the first airborne wind energy system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in further detail with reference to the accompanying drawings in which

(2) FIGS. 1-2 and 4 are perspective views of three airborne wind energy systems for use in a wind energy park according to an embodiment of the invention,

(3) FIGS. 3A and 3B illustrate the power generation phase and the recovery phase of an airborne wind energy system according to embodiments of the invention,

(4) FIGS. 5-7 illustrate a wind energy park with a number of airborne wind energy systems according to embodiments of the invention,

(5) FIGS. 8-9 illustrate the operation of airborne wind energy systems in a wind energy park (as seen in a perspective view) and according to embodiments of the invention, and

(6) FIGS. 10-13 illustrate a method of controlling the airborne wind energy systems in a park according to embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) FIGS. 1, 2, and 5 are perspective views of three airborne wind energy systems 100 for use in a wind energy park operated according to embodiments of the invention. The airborne wind energy systems 100 all comprise a wind engaging member 101 catching and moved by the wind and connected to a ground station 103 via one or more cables 105.

(8) In the airborne wind energy system 100 of FIG. 1, the wind engaging member 101 is in the form of a kite 102 connected to a winch system (not shown) in the ground station 103 via two cables 105. The operation of the kite 102 can thereby be fully or partly controlled by operation of the cables and the winch system.

(9) In the airborne wind energy system 100 of FIG. 2, the wind engaging member 101 is also in the form of a kite 102. In this system, the kite is connected to a control unit 300 via steering lines 301 and to a winch system (not shown) in the ground station 103 via a cable 105. The operation of the kite 102 can thereby be fully or partly controlled by the operation of the steering lines 301 by the control unit in addition to the extraction and retraction of the cable 105 controlled from the winch system.

(10) For both airborne wind energy systems of FIGS. 1 and 2, the extraction of the one or more cables 105 from the winch system generates mechanical energy which is transferred via the winch system to a generator positioned on the ground station 104. The generator is in turn electrically coupled to a power transmission line and to a power grid and/or power storage optionally via a converter and/or transformer.

(11) FIGS. 3A and B illustrate the operation of the kite 102 and with typical flight trajectories 400 indicated. Typically, the kite operation comprises a power generation phase of upwards movement 410 of the kite where the kite 102 may extract the cable(s) 105. Here, the wind acting on the kite 102 and the tensioning forces in the cable(s) 105 and any steering lines 301 causes it to move along a flight trajectory having the shape of an upwards spinning figure eight 401 or circle 501. Such typical flight path during power generation is also indicated in FIG. 1 by the dotted line. Subsequently, the kite 102 is retracted while moving along a substantially linear path 420. During this recovery phase wherein the kite 102 is retracted, energy may be consumed. However, the energy consumed is expected to be less than the energy being generated during the upwards spinning movement of the kite 102. Upon reaching a minimum height, the kite is operated to enter a new power generation phase. Typically, the kite 102 may be extracted by the wind to a maximum height in the range of 600-1000 m depending on the type of kite, and is retracted to a minimum height in the range of 50-150 m. Typically, the recovery phase takes up in the order of 10-30% of the time of a total cycle of a power generation phase followed by a recovery phase.

(12) In the airborne wind energy system 100 of FIG. 4, the wind engaging member 101 is in the form of a glider 200, also sometimes referred to as a Makani. The glider 200 is provided with a number of rotors 201, each being capable of extracting energy from the wind and generating electrical energy. The glider 200 is connected to the ground by means of one or more cables 105. FIG. 4 further illustrates the operation of the glider 200. It can be seen that the wind acts on the glider 200 and causes it to move along a substantially circular movement pattern, as indicated by the dotted line. This movement of the glider 200 causes rotation of the rotors 201 and thereby electrical energy is generated.

(13) The electrical energy is transferred to a suitable electrical component, e.g. a transformer or a converter unit, arranged at the ground station 104 via the cable 105 which comprises an electrically conductive cable 202.

(14) FIGS. 5 and 6 illustrate operation of airborne wind energy systems 100 in a wind energy park 500 according to an embodiment of the invention and as seen from a side and in a top view, respectively. A number of airborne wind energy systems 100 are shown in the figures, each comprising a wind engaging member 101 connected to ground stations 104 via cables 105. The wind engaging members are here shown as all being kites 102 of the same type. However, in an embodiment, an energy park may be equipped with different types of airborne wind energy systems such as for example a kite next to a glider, all gliders 200 etc. The airborne wind energy systems 100 may be directly or indirectly connected optionally via one or more central control units (not shown) which in part or completely contribute to the controlling of the airborne wind energy systems.

(15) The kites or gliders 101 are able to move along specified movement paths or flight trajectories generating mechanical energy, e.g. as described above with reference to FIGS. 3AB and 4.

(16) It can be seen that the kites or gliders 101 are in different positions along their movement patterns or flight trajectories and thereby need not stand precisely in the wind direction (indicated by the arrow 501). Thus, the kites and/or gliders 101 need not to operate in a synchronous manner. It should also be noted that the direction of the wind at the positions of the wind engaging members 101 may be the same or may vary for one reason because of the height variations between the kites and/or gliders at a specific time.

(17) FIG. 7 illustrates a wind energy park 500 with a number of airborne wind energy systems 100. The wind engaging members 101 of each airborne wind energy systems 100 are generally in different positions in their respective flight trajectories, some of them in the power generation phase and others being retracted in their recovery phase. The average or mean positions of each wind engaging member 101 are indicated in the figure, further illustrating that the mean position of the wind engaging member 700 of the airborne wind energy systems 701 clearly deviates from the mean position of some or all of the other wind engaging members 101.

(18) According to an embodiment of the invention an operational parameter of each of the number of airborne wind energy systems is determined and the operation parameter of a first airborne wind energy system is compared to the determined operational parameters of the others. If there is no significant difference, i.e. the deviation is smaller than a predetermined threshold parameter, the first airborne wind energy system is continued to be operated as normal, i.e. according to a normal control mode. However, if the deviation is larger than or equal to the predetermined threshold parameter, the operation of the first airborne wind energy system is changed and the first airborne wind energy system is operated according to a fault control mode.

(19) Such faulty or deviating behaviour could as an example be due to wear on some of the components, a broken steering line, some malfunction in the control unit operating the steering lines or in the winch system, a tear or hole in the wind engaging member or the like.

(20) By the comparison of operational parameters between the different airborne wind energy systems in the park, any abnormal or deviating behaviour of any one of the airborne wind energy systems may be identified earlier and with a higher certainty. Hereby appropriate can be taken earlier to restore the normal operation of the faulty airborne wind energy system potentially avoiding more serious errors or damage to the airborne wind energy system itself and prevent it from causing any damage to the other airborne wind energy systems in the park.

(21) As illustrated in the embodiment illustrated in FIG. 7, the operational parameter may comprise the flight position of each of the flight engaging members. The flight position may be determined as a position of the kite (or glider) relative to its ground station and/or some other fixed point, and may be determined at one or more predefined heights or as a mean position over some time such as over the time of one flight cycle and/or some predefined time interval during a power generation phase.

(22) The abnormal behaviour of the first airborne wind energy system may additionally or alternatively be determined by determining the deviation of one or more of the power production, the flight speed, a tension in the cable, a cable extraction and/or retraction speed, and/or an angle of the cable and comparing it to the same type of operational parameters determined on the other airborne wind energy systems in the energy park.

(23) FIGS. 8 and 9 illustrate a method of controlling the airborne wind energy systems in a park according to an embodiment of the invention. The figures show three airborne wind energy systems in a wind energy park as seen in a perspective front view from the above a little upstream with respect to an overall direction of the wind 501. Here, the airborne wind energy system 700 has been determined to deviate in behaviour from the other airborne wind energy systems 100 and is therefore operated according to a fault control mode which here comprises retracting the wind engaging member of the faulty airborne wind energy system 700. This is indicated by the arrow 800.

(24) In the situation illustrated in FIG. 9, the operation of the airborne wind energy system 900 neighbouring to the faulty airborne wind energy system 700 showing the deviating operational parameter, is furthermore changed from its normal operation mode and into being operated in a safe control mode. The safe control mode is primarily aimed to avoid any risk of collision between the two gliders and in order to clear the airspace for the faulty glider which is being retracted. The safe control mode her comprises steering the kite or glider 101 away from the faulty airborne wind energy system 700 as illustrated by the arrow 901. This may involve steering the wind engaging member 900 up to a higher height, in a sideway direction away from the faulty airborne wind energy system 700, and/or retracting this otherwise normal kite or glider to a lower height above the ground.

(25) FIGS. 10-13 illustrate a wind energy park 500 comprising a number of airborne wind energy systems 100 of which a first airborne wind energy system 700 has been detected to be faulty for example by producing a power deviating significantly from the others, showing significantly higher or lower tension loads in the cable 105 or by a deviating flight trajectory to other airborne wind energy systems being operated similarly. The first airborne wind energy system 700 is therefore operated according a fault control mode which in this embodiment comprises releasing or cutting the cable 105 breaking the connection between the ground station 104 and the wind engaging member 101. The wind engaging member 101 of the faulty or deviating airborne wind energy system 700 is thereby allowed to fall, glide or to be steered to the ground.

(26) In FIG. 10 showing a part of a wind energy park 500 in a front view, airborne wind energy systems 900 in a downwind direction to the first airborne wind energy system 700 with the released wind engaging member 101 are operated in a safe control mode comprising retracting their wind engaging members 101 as indicated by the arrows 1001. Preferably, the safe control mode of the airborne wind energy systems 900 is initiated before the fault control mode of the deviating first airborne wind energy system 700. In this way the airspace is cleared for the wind engaging member of the first airborne wind energy system 700 to be taken or guided down even if the wind engaging member drifts by the wind over a considerable distance.

(27) FIG. 12 illustrates more of the airborne wind energy systems 100 in the wind energy park 500 of FIG. 10 and as seen from above. The figure further shows how a belt or a clearance have been made for the wind engaging member of the first deviating airborne wind energy system 700 to fall down or drift down. As also shown in FIG. 10, some airborne wind energy systems 900 in the downwind direction 501 have been retracted 1001, and their neighbouring airborne wind energy systems 910 on both sides operated according a second safe control mode wherein their wind engaging members are steered in directions (illustrated by arrows 901) away from the crashing or landing path of the first airborne wind energy system 700. The airborne wind energy systems marked with ‘v’s are continued to be operated according to a normal control mode.

(28) FIGS. 11 and 13 illustrate another embodiment of the invention. Here, the airborne wind energy systems 900 are operated according to a safe control mode comprising directing their wind engaging members 101 in directions 901 away from the downwind direction 501 of the first airborne wind energy system 700 with a deviating behaviour.