Method for operating an energy-generation apparatus, control unit for an energy-generation apparatus, energy-generation apparatus, and computer program product
By adjusting the trim angle and retrieval speed of kites based on operating parameters, the method stabilizes flight and reduces retrieval force, improving the efficiency and stability of energy generation systems.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SKYSAILS GROUP GMBH
- Filing Date
- 2026-01-08
- Publication Date
- 2026-07-23
Smart Images
Figure EP2026050270_23072026_PF_FP_ABST
Abstract
Description
[0001] 08.01.2026 / PH
[0002] Method for operating a power generating device, control unit for a power generating device, power generating device, computer program product
[0003]
[0001] The invention relates to a method for operating an energy generation device, a control unit for an energy generation device, an energy generation device and a computer program product.
[0004]
[0002] To generate electrical energy, a kite can exert a pulling force on a tow rope, thus driving a generator via the tow rope. By appropriately adjusting the aerodynamic properties of the kite, the kite system can be moved along flight paths that generate a high pulling force. The flight paths are essentially perpendicular to the tow rope.
[0005]
[0003] The tow rope is extended while electrical energy is generated by the generator; thus, the distance between the kite and the base station increases during this phase. Energy generation is interrupted when the tow rope is extended to its maximum length. The tow rope must then be retrieved, requiring energy, before electrical energy can be generated again. The phase in which electrical energy is generated is called the power phase. The phase in which the tow rope is retrieved is called the retrieval phase. The excess electrical energy between the power phase and the retrieval phase is available for other purposes and can, for example, be fed into a power grid.
[0006]
[0004] For the efficiency of such an energy-generating device, it is advantageous if the tow rope can be retrieved with the least possible force during the retrieval phase. One possible approach is to guide the kite into a position in a transition phase prior to the start of the retrieval phase in which the wind exerts only a small pulling force on the kite, EP 4 174 311 Al. This can, for example, be a position in which the tow rope extends substantially perpendicular to the wind direction. Since electrical energy cannot be generated to any significant extent during the transition phase, such a transition phase reduces the efficiency of the energy-generating device.
[0007]
[0005] The invention is based on the objective of presenting a method for operating an energy generation device, a control unit for an energy generation device, an energy generation device, and a computer program product, with which the aforementioned disadvantages are reduced. This objective is achieved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.
[0008]
[0006] In a method according to the invention for operating an energy generation device, the energy generation device comprises a base station and a kite system. The kite system comprises a kite and a gondola, wherein the kite is connected to the gondola via a line boom and wherein the gondola is connected to the base station via a tow rope. Electrical energy is generated by a pulling force exerted by the tow rope, whereby the kite is alternately brought into a first operating state and a second operating state. In the second operating state, the trim angle of the kite is smaller than in the first operating state. In the second operating state, the kite is brought towards the base station by reeling in the tow rope, the reeling speed being varied depending on an operating parameter of the energy generation device representing the flight state of the kite.
[0009]
[0007] According to the invention, the trim angle of the kite is changed between the first operating state and the second operating state. Starting from a flight state in the power phase, in which the kite exerts a high pulling force on the tow line, a reduction in the trim angle results in a reduced pulling force. However, if the trim angle is reduced too much, this can lead to undesirable downforce in the front kite segment, resulting in a loss of tethering and an unstable flight state of the kite. Therefore, an arbitrary reduction of the trim angle for the purpose of reducing the pulling force is not possible.
[0010]
[0008] The invention proposes influencing the kite's flight state during the retrieval phase by adjusting the retrieval speed of the tow rope. The invention recognizes that increasing the retrieval speed has a stabilizing effect on the kite's flight state. Thus, if, for example, the kite is at risk of becoming unstable, this can be counteracted by increasing the retrieval speed. The kite can be in the first operating state during the power phase and in the second operating state during the retrieval phase.
[0011]
[0009] Since the flow state cannot be directly measured in practice, the invention uses an operating parameter of the kite system to infer the flight state. An operating parameter in this sense is any parameter of the energy generation device that correlates with the kite's flight state. The operating parameter is fed to a control unit of the kite system as an input, for example, in the form of a measured value of the operating parameter. The operating parameter is processed in the control unit to generate a control command for adjusting the retrieval speed. The retrieval speed is adjusted based on the control command. A change in the operating parameter leads to a change in the control command and thus to a change in the retrieval speed.The invention differs from a conventional approach, in which the kite is retrieved at a predetermined retrieval speed regardless of the current flight condition, due to the dependence between the operating parameter and the retrieval speed.
[0012]
[0010] The kite has a leading edge and a trailing edge that are positioned one behind the other in the direction of flight. In flight, the oncoming airflow is separated at the leading edge and rejoined at the trailing edge. There is a profile centerline that extends in a straight line and along the shortest path between the leading and trailing edges of the kite. In the lateral dimension, and thus perpendicular to the direction of the profile centerline, the profile centerline can be located in the middle of the kite, so that the profile centerline is equidistant from both lateral ends of the kite. In its longitudinal direction, the profile centerline has a central point that is equidistant from the leading and trailing edges of the kite. The trim angle is defined as the angle between a trim line and the portion of the profile centerline extending from the central point of the profile centerline to the leading edge of the kite.The trim line runs in a straight line between the center point of the profile's centerline and the connection point between the tow line and the kite system. Decreasing the trim angle shifts the leading edge downwards and / or the trailing edge upwards. Increasing the trim angle shifts the leading edge upwards and / or the trailing edge downwards. The trim angle in the first operating state can, for example, be between 80 and 90 degrees. The trim angle in the second operating state can, for example, be between 20 and 50 degrees.
[0013]
[0011] For high power output, it is advantageous if the kite is guided in such a way that the tow rope is extended as parallel to the wind direction as possible during the power phase. For the retrieval phase, a combination of a short retrieval path and low pulling force is favorable. With conventional methods such as those described in EP 4 174 311 Al, where no change in the trim angle is made, this combination of requirements for the retrieval phase results in the kite being guided far outwards to the edge of the wind window during the retrieval phase. The wind window is defined as a spherical segment extending from the ground station, in particular from an attachment point of the tow rope at the ground station, within which the kite can remain without artificial increase in airflow or its own propulsion. In the method according to the invention, the position of the kite in the second operating state can lie within the wind window and be at a distance from the edge of the wind window.The distance between the center of the wind window and the kite can be less than 80%, preferably less than 50%, and more preferably less than 30% of the distance between the center of the wind window and the edge of the wind window. In this comparison, both distances are measured in the same direction.
[0014]
[0012] The operating parameter used to adjust the retrieval speed in the second operating state can be the pulling force exerted by the kite on the tow rope. If a loss of control is imminent, the lift and thus the pulling force decrease. Increasing the retrieval speed improves the airflow over the kite, thereby increasing the pulling force again. The pulling force can be adjusted to a substantially constant value by decreasing the retrieval speed when the pulling force increases and by increasing the retrieval speed when the pulling force decreases.
[0015]
[0013] The method can be carried out such that a target value for the pulling force is specified. Information about the current value of the pulling force can be supplied to a control unit of the kite system. The control unit can generate a control signal with which an actuator designed to influence the retrieval speed is controlled.
[0016]
[0014] The information about the value of the pulling force can be a force measurement. The kite system can include a force sensor that provides the measurement. The force sensor can be located within the tow rope, which extends between the kite and a component of the base station that holds the tow rope. The force sensor can be a tension sensor that provides a measurement of the tension in the tow rope. The force sensor can be designed to measure the force transmitted via the line boom or a part thereof. The force sensor can be designed to measure the force transmitted via the gondola. If the tow rope is taken in and paid out via a winch, the pulling force can be deduced from the torque acting on the winch. The force measurement can therefore also refer to the torque of the winch.The winch can be controlled in such a way that the pulling force is kept constant when retrieving the kite. The measured torque can be compensated for inertial forces to avoid unwanted fluctuations in the pulling force. The torque of the winch can be deduced from the current data of the frequency converter.
[0015] It is also possible to carry out the method without a direct measurement of the pulling force. Instead of a direct force measurement, one or more operating parameters that are related to the pulling force can be processed. In one embodiment, vibrations occurring within the line boom are recorded and the vibration measurements are processed to adjust the retrieval speed. It has been shown that typical vibration patterns occur when the kite approaches its stability limit.The procedure can be carried out by increasing the retrieval speed until the relevant vibration patterns are measured, and then decreasing the retrieval speed after the vibration patterns appear until they disappear. The retrieval process can be controlled in such a way that the kite is always close to its stability limit. A high retrieval speed shortens the recovery phase, which has a positive effect on the efficiency of the energy generation system.
[0017]
[0016] It is also possible, or alternatively, to infer an approach to the stability limit and thus a change in the currently acting tensile force from suitable measurements of the air pressure. In one embodiment, the absolute pressure in the vicinity of the kite is measured as an operating parameter. This is based on the understanding that the air pressure drops in certain areas around the kite and rises in other areas as the kite approaches the stability limit. Therefore, an approach to the stability limit can be inferred from a measurement of the absolute pressure. In other embodiments, the differential pressure between different points of the flow profile is measured to infer an approach to the stability limit. The proximity to the stability limit can also be inferred from the ratio between dynamic pressure and internal pressure.
[0018]
[0017] Additionally or alternatively, a change in wind conditions can also indicate an approach to the stability limit and thus a change in the currently acting traction force. It can be assumed that the traction force increases with increasing wind speed and decreases with decreasing wind speed. Information about a change in wind conditions can be obtained, for example, by lidar measurement or by ultrasound measurement. The relevant sensors can be attached, for example, to the kite or another component of the kite system. The sensors can be designed to obtain measurements of the wind conditions in the direction of flight. The sensors can be designed to detect turbulence.
[0019]
[0018] Approaching the stability limit often results in a change in the kite's geometric shape due to altered flow conditions. Consequently, a change in the kite's geometric shape can also indicate an approach to the stability limit and thus a change in the currently acting traction force. Information about the kite's geometric shape can be obtained, for example, by evaluating image data or distance data. In one embodiment, the kite system is equipped with one or more image sensors and / or lidar sensors to record this data. An indication of approaching the stability limit can be derived, for example, from deformations appearing in the leading edge of the aerodynamic profile.
[0019] To adjust the trim angle, the kite system can include a trim mechanism designed to change the lengths of lines within the line boom relative to each other. The line boom connects the gondola and the kite via a plurality of lines. The trim angle can be changed by altering the length of the lines running towards the trailing edge of the kite relative to the length of the lines running towards the leading edge of the kite. If the length of the trailing lines is shortened relative to the length of the leading lines, the trim angle of the kite increases. If the length of the trailing lines is increased relative to the length of the leading lines, the trim angle of the kite decreases. There may be a section between the leading and trailing edges where the length of the line boom remains unchanged when the trim angle is adjusted.Depending on practicality, this area can be located closer to the front edge, closer to the rear edge, or approximately halfway between the front and rear edges.
[0020]
[0020] The kite system can include a control mechanism for steering the kite along predetermined flight paths. To change the direction of flight, the length of lines running to the left can be changed relative to the length of lines running to the right of the line boom. The control mechanism can be configured so that steering the direction of flight is possible independently of the trim angle to which the kite is set. The control mechanism can be configured so that the direction of flight can be changed while the trim angle remains unchanged.
[0021]
[0021] The kite system can include an electric machine that is driven by the tow rope during the power phase to generate electrical energy. The kite system can include a winch onto which the tow rope is wound when the tow rope is pulled in and from which the tow rope is unwound when it is released. The winch can be coupled to the electric machine. The electric machine can be designed to operate alternately in generator mode and in motor mode. During the power phase, in which the tow rope is pulled from the winch under the pulling force of the kite, the electric machine can operate in generator mode. The winch can drive the electric machine, thus generating electrical energy.During the retrieval phase, the electric machine can be operated in motor mode, so that the winch is driven by the electric machine and the tow rope is retrieved against the pulling force of the kite.
[0022]
[0022] The base station can be a ground-based base station. It is also possible for the base station to be a floating base station. The base station can be a fixed base station or a mobile base station. The electric motor can be a component of the base station. The winch can be a component of the base station.
[0023]
[0023] The invention also relates to a control unit for an energy generation device, wherein the control unit is designed to alternately bring a kite, which is connected to a base station via a tow rope, into a first operating state and a second operating state. In the second operating state, the trim angle of the kite is smaller than in the first operating state. The control unit is designed to control a tow rope winch such that, in the second operating state, the kite is brought towards the base station by retracting the tow rope, the retraction speed being varied depending on an operating parameter of the energy generation device representing the flight state of the kite.
[0024]
[0024] The control unit can be a single physical unit. It is also possible that the control unit is distributed across various components of the power supply system. The components can be located in different places.
[0025]
[0025] The invention further relates to an energy generation device comprising a base station, a kite system, and a control unit. The kite system comprises a kite and a gondola, wherein the kite is connected to the gondola via a line boom and wherein the gondola is connected to the base station via a tow rope. The control unit is designed as a control unit according to the invention.
[0026]
[0026] The invention also relates to a computer program product or a set of computer program products comprising program parts which, when loaded into a computer or into interconnected computers connected to an energy generation device according to the invention, are designed to carry out the method according to the invention.
[0027]
[0027] The disclosure includes further developments of the control unit and the energy generation device with features that are described in connection with the method according to the invention. The disclosure includes further developments of the method with features that are described in connection with the control unit or the energy generation device according to the invention.
[0028]
[0028] The invention is described below by way of example with reference to the accompanying drawings and advantageous embodiments. Figure 1 shows a schematic representation of an energy generation device according to the invention;
[0029] Fig. 2 : a schematic representation of an operating phase of the energy generation device from Fig. 1 ;
[0030] Fig. 3 : a kite system of an energy generation device according to the invention;
[0031] Fig. 4: the energy balance during an operating cycle of the energy generation device;
[0032] Fig. 5 : a block diagram of one aspect of the inventive energy generation device;
[0033] Fig. 6 : a schematic representation of the kite system from Fig. 3 in the first operating state of the kite;
[0034] Fig. 7: the view according to Fig. 6 in the second operating state of the kite;
[0035] Fig. 8 : an exemplary representation of a disturbance compensated according to the invention.
[0036]
[0029] An energy generation device shown in Fig. 1 is designed to generate electrical energy using a kite system 23. The kite system 23 comprises a kite 14, which is connected to a gondola 25 via a line boom 24. The gondola 25 is connected to a base station 28 via a tow rope 15. The base station 28 includes a winch 16 with which the tow rope 15 can be wound in and unwound.
[0037]
[0030] Coupled with the winch 16 is an electric machine 17, which operates as a generator in a first operating mode and as a motor in a second operating mode. The electric machine is connected via an electrical power train 18, which includes a converter and a transformer, to a public transmission network z 19 and / or a battery buffer, so that either electrical energy generated by the machine 17 can be fed into the transmission network z 19 or the machine 17 can be operated as a motor with electrical energy drawn from the transmission network 19. The device includes a control unit 20, which is designed to control the interaction of the components of the energy generation device.
[0038]
[0031] The control unit 20 includes an antenna 21, enabling the exchange of control signals with the gondola 25 via a radio link 22. In particular, the control unit 20 sends control signals to the gondola 25 to control the flight direction of the kite 14. Using these control signals, the length of the control lines of the boom 24 is changed, thereby influencing the flight direction of the kite 14. Alternatively, the control unit 20 can also be a component of the gondola 25. In this case, signals are transmitted to the ground station to provide setpoints for the operation of the winch 16.
[0039]
[0032] In the embodiment shown in Fig. 2, the kite 14 is guided along a figure-eight pattern oriented essentially perpendicular to the wind direction W. The figure-eight is positioned such that the angle between the wind W and the direction of the tow rope is as small as possible, thus exerting a high force on the kite 14. As the kite 14 follows the flight path, a tensile force is exerted on the tow rope 15, which drives the machine 17 via the winch 16. With the machine 17 operating as a generator in this state, the mechanical energy is converted into electrical energy and fed into the public transmission network 19 via the power train 18. It is also possible to store some of the generated energy in electrical form in an energy storage device of the power train 18.In this way, electrical energy can be generated until the length of the haul rope 15 is exhausted and the haul rope 15 is fully extended from the haul rope winch 16. The haul rope 15 is then retracted using the electric machine 17, which is driven as a motor, before electrical energy can be generated again.
[0040]
[0033] The line boom 24 of the kite system 23 according to the invention comprises, as shown in Fig. 3, a plurality of lines through which tensile forces are transmitted between the kite 14 and the gondola 25. Each line provides a connection between the gondola 25 and an attachment point 27 on the underside of the kite 14. By changing the distance between the gondola 25 and the attachment points 27 relative to each other, which is mediated by different lines, the direction of flight of the kite 14 and / or the trim angle of the kite can be influenced.
[0041]
[0034] In Fig. 4, the generated and consumed electrical energy E is plotted against time T. Phases of an operating cycle 30 in which the electric machine 17 is operated as a generator and in which electrical energy E is generated are referred to as power phases 31. Phases in which the electric machine 17 is operated as a motor and in which electrical energy E is consumed are referred to as recovery phases 32. Transition phases 33 can occur between the power phases 31 and the recovery phases 32. For the efficiency of the device, it is advantageous if the transition phases 33 are as short as possible. The balance of electrical energy E during an operating cycle 30 is the difference between the electrical energy E generated in the power phase 31 and the electrical energy E consumed in the recovery phase 32.
[0035] As shown in Fig.Figures 6 and 7 show that the trim angle 43 of the kite 14 is changed between the power phase 31 and the recovery phase 32. Figure 6 shows the first operating state 41 of the kite 14, which the kite 14 has during the power phase 31 and in which the trim angle 43 is large. The trim angle 43 is measured between a trim line 39 and the forward-pointing section of a profile centerline 40. The trim line 39 extends between a central point 47 of the profile centerline 40 and the attachment point 48 of the tow rope 15 on the gondola 25. The profile of the kite 14 extends between a leading edge 34 and a trailing edge 35. In Figure 6, the profile centerline 40, which forms a connection between the leading edge 34 and the trailing edge 35, is shown.
[0042]
[0036] To transition from the first operating state 41 shown in Fig. 6 to the second operating state 42 shown in Fig. 7, changes are made to the line boom 24 using a trim mechanism 46. Several rear lines 38 leading towards the trailing edge 35 of the kite 14, of which only a single rear line 38 is shown in Fig. 6, are lengthened. Several front lines 36 leading towards the leading edge 34 of the kite 14 are shortened. Lines 37 located in the middle remain unchanged in length or are only slightly altered in length. By lengthening all rearward lines of the line boom 24 and correspondingly shortening all forward-leading lines, the entire kite 14 is pivoted about an axis oriented perpendicular to the plane of the drawing. This results in a reduction of the trim angle 43 between the profile centerline 40 and the trim line 39, see Fig. 7.
[0043]
[0037] In the second operating state 42, the pulling force exerted by the kite 14 on the tow rope 15 is considerably lower than in the first operating state 41. Due to this lower resistance, the kite 14 can be retrieved in the recovery phase 32 with less energy than was generated in the power phase 31.
[0044]
[0038] According to the schematic representation in Fig. 5, the cable winch 16 is equipped with a torque sensor 44. Alternatively, the torque can also be derived from the current data of the frequency converter. In this case, a torque sensor is not required. The torque is proportional to the tensile force exerted by the cable 15, so that the measured values 49 of the torque sensor 44 represent a measure of the tensile force of the cable 15. During the return phase 32, the control unit 20 processes the measured values 49 supplied by the torque sensor 44 in order to control the motor operation of the electric machine 17. For this purpose, the control unit 20 compares the measured value of the torque sensor 44 with a setpoint for the tensile force stored in a memory module 45. If the measured value is lower than the setpoint, the speed at which the electric machine 17 drives the cable winch 16 is increased.If the measured value is higher than the target value, the speed of the electric machine 17 is reduced.
[0045]
[0039] Fig. 8 shows the measured values 49 of the torque D over time T during a section of the retrieval phase. Before time TI, the torque D has a substantially constant value. Between times TI and T2, the torque D decreases due to an unstable flight condition of the kite 14, which is registered by the torque sensor 44. The rotational speed of the winch 16 is increased, so that the torque D increases between times T2 and T3. From time T3 onwards, the kite 14 is again in a stable flight condition, in which the measured values 49 of the torque D remain substantially unchanged. The entire period shown in Fig. 8 lies within a middle section of the retrieval phase. No transitions to previous or subsequent power phases are shown in Fig. 8.
[0046]
[0040] In this way, the retrieval speed of the kite 14 is changed in a closed control loop such that the pulling force exerted on the kite 14 remains essentially constant. This has the particular effect that, in the event of an imminent loss of stability, the retrieval speed is automatically increased, so that the flight state of the kite 14 stabilizes again. This opens up the possibility of operating the kite 14 in an aerodynamic state that would not be stable without the application of the method according to the invention.
Claims
Patent claims 1. Method for operating an energy generating device, wherein the energy generating device comprises a base station (28) and a kite system (23) with a kite (14) and a gondola (25), wherein the kite (14) is connected to the gondola (25) via a line boom (24), wherein the gondola (25) is connected to the base station (28) via a haul rope (15), and wherein electrical energy is generated by a pulling force exerted on the haul rope (15), wherein the kite (14) is alternately brought into a first operating state (41) and a second operating state (42), wherein in the second operating state (42) the trim angle (43) of the kite (14) is smaller than in the first operating state (41).wherein in the second operating state (42 ) the kite ( 14 ) is brought towards the base station (28 ) by retrieving the tow rope ( 15 ) and wherein the retrieval speed is changed depending on an operating parameter (49) of the energy generation device representing the flight state of the kite ( 14 ).
2. Method according to claim 1, wherein the operating parameter of a control unit (20) of the energy generation device is supplied as an input variable.
3. Method according to claim 2, wherein the operating parameter is processed in the control unit (20) to generate a control command for setting the retrieval speed.
4. Method according to any one of claims 1 to 3, wherein the position of the kite (14) in the second operating state (24) is a distance from the edge of the wind window (29).
5. Method according to any one of claims 1 to 4, wherein the operating parameter is the tensile force exerted by the kite (14) on the tow rope (15).
6. Method according to claim 5, wherein the operating parameter is processed in the form of a force measurement value.
7. Method according to claim 6, wherein the energy generating device comprises a cable winch ( 16) for the cable ( 15) and wherein the force measurement refers to a torque acting on the cable winch ( 16 ).
8. Method according to any one of claims 1 to 7, wherein the kite system (23) comprises a trimming mechanism (46) designed to change the length of lines (36) leading to a leading edge (34) of the kite (14) relative to the length of lines (38) leading to a trailing edge (35) of the kite (14) in order to adjust the trim angle (43).
9. Control unit for an energy generation device, wherein the control unit (20) is designed to alternately bring a kite (14) connected to a base station (28) via a tow rope (15) into a first operating state (41) and a second operating state (42), wherein in the second operating state (42) the trim angle (43) of the kite (14) is smaller than in the first operating state (41), wherein the control unit (20) is designed to control a tow rope winch (16) such that in the second operating state (42) the kite (14) is brought towards the base station (28) by retracting the tow rope (15), wherein the retraction speed is varied depending on an operating parameter (49) of the energy generation device representing the flight state of the kite (14). 10.Energy generating device, comprising a base station (28), a kite system (23) and a control unit (20), wherein the kite system (23) comprises a kite (14) and a gondola (25), wherein the kite (14) is connected to the gondola (25) via a line boom (24), wherein the gondola (25) is connected to the base station (28) via a pull rope (15), wherein the control unit is configured according to claim 9.
11. Computer program product or set of computer program products, comprising program parts which, when loaded into a computer or into interconnected computers connected to a device according to claim 10, are designed to carry out the method according to any one of claims 1 to 8.