GB2583973A

GB2583973A - Tethers

Info

Publication number: GB2583973A
Application number: GB1906979.8A
Authority: GB
Inventors: Copley Garth; John Humprhies Howard
Original assignee: Uavtek Ltd
Current assignee: Uavtek Ltd
Priority date: 2019-05-17
Filing date: 2019-05-17
Publication date: 2020-11-18
Anticipated expiration: 2039-05-17
Also published as: GB201906979D0; GB2583973B

Abstract

A tether (110) for a vehicle (102), such as an unmanned vehicle (102), comprises a power unit (104); a vehicle unit (108) arranged to be located on the unmanned vehicle (102); and a tether cable (106) extending between the power unit (104) and the vehicle unit (108). The vehicle unit (108) is arranged to receive power from the tether cable (106) and to adjust voltage of the received power to a suitable level for use by the vehicle (102). The tether cable (106) has a voltage of between 70 V and 250 V and is arranged to supply power to the unmanned vehicle (102). The unmanned vehicle (102) may be an unmanned aerial vehicle (102). The cable may comprise two silver coated cores, with a core diameter of between 1.5mm and 3mm.

Description

TETHERS

The invention relates to tethers for vehicles, in particular unmanned vehicles, and to vehicles including such a tether. In particular, but not exclusively, the invention may relate to a tether for an Unmanned Aerial Vehicle (UAV). The tether may provide power for movement of the vehicle, and/or for auxiliary vehicle systems.

Tethers are arranged to supply power to a vehicle. Tethers may be of particular utility for powering unmanned vehicles, but the skilled person would appreciate that they may also be of use for manned vehicles in some situations (e.g. for a manned repair pod or robot for a submarine, space station or the likes). Tethers are discussed herein primarily in relation to unmanned vehicles, but the skilled person would appreciate that they may be used more widely.

Tethers may be used to allow an unmanned vehicle to remain in operation for longer than would be possible using an in-built power supply (e.g. due to battery capacity limitations), and optionally to remain in operation continually. A tether cable connects a ground station power supply (which may be a mains supply) to the vehicle, and power is transmitted along the cable.

As compared to children's toy remote-control vehicles, commercial/industrial and military unmanned vehicles have much higher power demands and often also require longer ranges (and so longer cables). Tether cable voltage, power drop, and voltage drop may therefore present issues.

The skilled person would appreciate that high voltages are generally selected to minimise power drop along relatively long cables, as power lost in a cable depends on cable length, cable size and resistance per unit length, and the current through the cable, so having a lower-current, higher-voltage allows more power to be transmitted with lower losses. However, these high voltages can present a safety risk. In current commercially available UAV tether systems, the voltage used exceeds normal safety standards, with some systems having a voltage as high as 1000 V (direct current -DC).

These high voltages may present risks to personnel in the area, as well as exceeding voltage limitations for compliance with UK and EU regulations of tools and equipment for use in an external environment. In addition, UAV power requirements can fluctuate widely, for example changing from around 1 kW to 1.8 kW within a fraction of a second. Maintaining a stable power supply to a UAV with a lower voltage may therefore be particularly difficult due to voltage fluctuation leading to the power output not being smooth. UAV power demands may be particularly high for rotorcraft-type UAVs.

Whilst there is a clear desire for a lower voltage tether capable of transmitting sufficient power, such a tether has not previously been made and has been widely regarded as impossible to make.

According to a first aspect of the invention, there is provided a tether for a vehicle, the tether comprising: a tether cable; a power unit arranged to supply power to the tether cable; and a vehicle unit arranged to be located on the vehicle, to receive power from the tether cable and to adjust voltage of the received power to a suitable level for use by the vehicle. The tether cable extends between the power unit and the vehicle unit, and has a voltage of between 70 V and 250 V. The tether cable may have a length of at least 10 m, and preferably at least 25 m.

The tether may be arranged to supply a continuous power of at least 0.8 kW to the vehicle.

The tether cable may have a voltage of 110 V or below. The tether cable voltage may be an AC voltage or a DC voltage. The tether cable may have a voltage of 75 V or below. The voltage may be a DC voltage.

In embodiments in which the tether cable has an AC voltage (i.e. in which power is transmitted to the vehicle unit with an AC voltage), the vehicle unit may comprise an AC to DC converter arranged to convert the AC tether voltage to DC for use onboard the vehicle.

The vehicle unit may be a solid state vehicle unit having no moving parts. For example, even when the vehicle unit comprises one or more converters, no fan, pump or other moving-part cooling system may be provided. Passive cooling may instead be relied upon, so optionally reducing parasitic system power loads and/or vehicle unit weight, The tether cable may be a two-core cable. One or both cores may be made of copper. One or both cores may have a diameter of between 1.5 mm and 3.0 mm, and optionally around 1.75 mm, 2 mm, or 2.5 mm. One or both cores of the tether cable may be coated with a layer of a more conductive metal such as silver.

Each core of the tether cable may be coated or surrounded with a resilient material. The resilient material may be electrically insulating, and may be polytetrafluoroethylene (PTFE). A further layer of a resilient material may be provided around the two coated corcs. The same resilient material may be used for the further layer as for the core coatings. PTFE tape may be used.

The tether cable may have a weight per unit length of less than 0.06 kg/m. The tether cable may have a weight per unit length of: (i) 0.02 kg/m, and may be arranged to carry power of 0.8 kW or more; (ii) 0.03 kg/m, and may be arranged to carry power of 1.6 kW or more; or (iii) 0.05 kg/m, and may be arranged to cam; power of 2.4 kW or more.

The power unit may be arranged to be connected to a mains power supply. In embodiments in which the tether cable is arranged to carry AC power, the power unit may be or comprise a plug arranged to be plugged into a mains socket.

The tether voltage may be a DC voltage. The power unit may be arranged to sense current drawn through the tether cable and to adjust the voltage to account for voltage drop along the cable accordingly. The power unit may comprise one or more converters and one or more tuning circuits to perform the adjustment. The adjustment may be performed automatically in response to a sensed change in current drawn by the vehicle. The power unit may comprise a tuning circuit arranged to automatically adjust power output to the tether cable based on the sensed current.

The vehicle unit may be arranged to step down the tether cable voltage to a voltage suitable for use by the vehicle. The voltage suitable for use by the vehicle may bc less than or equal to 48 V. The voltage suitable for use by the vehicle may be greater than or equal to 24 V. In AC and/or DC transmission embodiments, the vehicle unit may comprise one or more, and optionally a plurality of, converters. Each converter may have a tuning circuit arranged to automatically adjust output of the corresponding converter based on the output voltage of the corresponding converter. The tuning circuits or the converters may be coupled together and arranged to automatically perform load balancing between the converters.

The vehicle unit may comprise one or more converters arranged to adjust voltage of the received power to a suitable level for use by the vehicle, and a tuning circuit arranged to sense an output voltage from each converter and to tune the converters so as to balance load between the converters and provide a desired amount of power to the vehicle.

The power unit may comprise a control interface arranged to allow commands for the vehicle to be entered, and a powerline adaptor arranged to transmit entered commands to the vehicle via the tether cable. Additionally or alternatively, the vehicle unit may comprise a powerline adaptor arranged to transmit data from the vehicle to the power unit via the tether cable.

The vehicle may comprise a battery; the vehicle unit may be arranged to supply power to the battery of the vehicle.

The tether may be a tether for an unmanned vehicle, and optionally may be an Unmanned Aerial Vehicle (UAV) tether. The tether may be arranged to supply a continuous power of at least 0.8 kW, at least 1.6 kW, at least 1.8 kW, or optionally of at least 2.5 kW, to the UAV. The vehicle unit may be arranged to be cooled by airflow generated by one or more rotors of the UAV -no cooling system may be provided as part of the vehicle unit in such embodiments. On or more converters of heat sinks of the vehicle unit may be positioned so as to take advantage of available air flows in operation for passive cooling.

According to a second aspect of the invention, there is provided a tether for a vehicle, the tether comprising: a tether cable; a power unit arranged to supply power to the tether cable: and a vehicle unit arranged to be located on the vehicle and to receive power from the tether cable. The tether cable extends between the power unit and the vehicle unit. The vehicle unit comprises one or more converters arranged to adjust voltage of the received power to a suitable level for use by the vehicle, and a tuning circuit arranged to sense an output voltage from each converter and to tune the converters so as to balance load between the converters and provide a desired amount of power to the vehicle.

In embodiments in which the tether carries DC power, for example, the power unit may comprise one or more converters and a tuning circuit arranged to sense an output current from each converter and to tune the converters so as to balance load between the converters and provide a desired voltage to the vehicle unit.

The tether may be as described in the first aspect.

According to a third aspect of the invention, there is provided a vehicle system comprising: a vehicle; and a tether comprising a tether cable, a power unit arranged to supply power to the tether cable, and a vehicle unit arranged to be located on the vehicle, to receive power from the tether cable and to adjust voltage of the received power to a suitable level for use by the vehicle. The tether cable extends between the power unit and the vehicle unit, and has a voltage of between TO V and 250 V. According to a fourth aspect of the invention, there is provided a vehicle system comprising: a vehicle; and a tether comprising a tether cable, a power unit arranged to supply power to the tether cable, and a vehicle unit arranged to be located on the vehicle and to receive power from the tether cable. The tether cable extends between the power unit and the vehicle unit. The vehicle unit comprises one or more converters arranged to adjust voltage of the received power to a suitable level for use by thc vehicle and a tuning circuit arranged to sense an output voltage from each converter and to tune the converters so as to balance load between the converters and provide a desired amount of power to the vehicle.

In embodiments in which the tether carries DC power, the power unit may comprise one or more converters and a tuning circuit arranged to sense an output current from each converter and to tune the converters so as to balance load between the converters and provide a desired voltage to the vehicle.

The tether of the third and/or fourth aspect may be as described in the first and/or second aspect The vehicle of the third and/or fourth aspect may be an unmanned vehicle, and more particularly may be a UAV. The UAV may be a rotorcraft comprising one or more rotors. Airflow generated by the one or more rotors of the UAV may be arranged to provide the only cooling to the vehicle unit (and in particular to any converters of the vehicle unit).

According to a fifth aspect of the invention, there is provided a tether for a vehicle, the tether comprising: a tether cable, the tether cable being a two-core copper cable, each copper core having a diameter of between 1.5 mm and 3.0 mm and being coated with a layer of silver; a power unit arranged to supply power to the tether cable: and a vehicle unit arranged to be located on the vehicle, to receive power from the tether cable and to adjust voltage of the received power to a suitable level for use by the vehicle, and wherein the tether cable extends between the power unit and the vehicle unit.

Each copper core of the tether cable may have a diameter of 1.75 mm, 2 mm, or 2.5 mm. Each core may be coated with a resilient material, and a further layer of a resilient material may be provided around the two coated cores. The tether cable may have a weight per unit length of less than 0.06 kg/m.

The tether may be as described with respect to any preceding aspect.

According to a sixth aspect of the invention, there is provided a vehicle system comprising: a vehicle; and a tether comprising a tether cable, the tether comprising: a tether cable, the tether cable being a two-core copper cable, each copper core having a diameter of between 1.5 mm and 3.0 mm and being coated with a layer of silver, a power unit arranged to supply power to the tether cable, and a vehicle unit arranged to be located on the vehicle, to receive power from the tether cable and to adjust voltage of the received power to a suitable level for use by the vehicle, and wherein the tether cable extends between the power unit and the vehicle unit.

The tether of the sixth aspect may be as described in any preceding aspect.

The vehicle of the sixth aspect may be an unmanned vehicle, and more particularly may be a UAV. The UAV may be a rotorcraft comprising one or more rotors. Airflow generated by the one or more rotors of the UAV may be arranged to provide the only cooling to the vehicle unit (and in particular to any converters of the vehicle unit).

Features described in relation to one of the above aspects of the invention may be applied, mutatis mutandis, to the other aspect of the invention. Further, the features described may be applied to the or each aspect in any combination.

There now follows by way of example only a detailed description of embodiments of the present invention with reference to the accompanying drawings in which: Figure 1 shows an unmanned vehicle with a tether; Figure 2 shows the tether of Figure 1; Figure 3 shows an AC unmanned vehicle system; Figure 4A schematically represents the AC system vehicle unit of the system of Figure 3; Figure 4B schematically represents the AC system power unit of the system of Figure 3; Figure 5 shows a DC unmanned vehicle system; Figure 6 schematically represents the DC system vehicle unit of the system of Figure 5; Figure 7 schematically represents a DC system power unit of the DC unmanned vehicle system of Figure 5; and Figure 8 shows a cross-section of a cable of various embodiments; Figure 9 shows a circuit diagram for a vehicle unit tuning circuit including a DC-DC converter, which may be used in various embodiments; Figure 10 shows a circuit diagram illustrating the connection of a plurality of DC-DC converters, each with a tuning circuit as shown in Figure 9; Figure 11 shows a circuit diagram for a power unit tuning circuit of various embodiments; Figure 12 shows how a vehicle unit of an embodiment may be mounted within a UAV.

In the figures, like reference numerals are used for like or corresponding components.

The invention is described herein primarily in relation to unmanned aerial vehicle (UAV) applications. However, the skilled person would appreciate that tethers 110 may be used for other manned or unmanned vehicles 102, such as ground-based vehicles (e.g. surveying or mine-disposal robots) or water-based vehicles (such as boats and submersibles).

Unmanned vehicles 102 may be of particular utility in regions where manned access is either unsafe (e.g. disposal of mines, improvised explosive devices and the likes, inspecting nuclear reactor cores, contaminated sites and the likes, and/or obtaining aerial images in regions where there is a significant chance of an aircraft being damaged, e.g. due to terrain or hostile action), or unduly expensive (e.g. due to manned helicopter flight being more expensive than a drone), or difficult (e.g. using a small unmanned vehicle to traverse narrow spaces).

The system 100 shown in Figure 1 comprises a UAV 102 and a tether 110. In the embodiment being described, the UAV 102 is a quadcopter (quadrotor) UAV (with four rotors 112 providing lift). The skilled person would appreciate that different rotorcraft or fixed-wing UAVs 102 may be used in other UAV embodiments, and that non-flying unmanned vehicles, or a manned vehicle of any form, may be used in alternative embodiments.

The tether 110 comprises a power unit 104. The power unit 104 is arranged to provide power for use on the UAV 102. The power unit 104 is arranged to power the UAV 102 in the embodiment being described -providing both motive power and power for auxiliary systems such as sensors. In alternative embodiments, auxiliary system power may be provided by a dedicated battery, for example, with the power unit 104 providing motive power only.

The power unit 104 may be referred to as a ground unit or ground station 104 (especially for UAV or unmanned water-craft applications). The power unit 104 may be referred to as a stationary unit, as, whilst it may be moved and may be portable, the unmanned vehicle 102 is arranged to move relative to the power unit 104. The power unit 104 is arranged to be located separately from the vehicle 102 / not to be on the vehicle 102.

The tether 110 comprises a tether cable 106. The tether cable 106 is arranged to carry power from the power unit 104 to the UAV 102.

The power unit 104 may include a source of power (e.g, a battery or generator), or may be connected to a separate source of power 101 (e.g. a battery, generator or mains supply). In some embodiments in which the power unit 104 is arranged to be connected to a separate source of power 101, the power unit 104 may simply consist of, or comprise, a plug or other connector suitable for connection to the power source 101.

In the embodiment being described, the power unit 104 is arranged to be connected to a mains power supply (e.g. 220-240 V AC at 50 Hz) or to a generator (e.g. a 3 kW generator). The power unit 104 can therefore provide continuous power (for as long as the mains supply and/or generator is functioning). The tether 110 may therefore provide a continuous power supply to the UAV 102.

In alternative or additional embodiments, the power unit 104 may comprise one or more batteries. In embodiments in which the power unit 104 is connected to a mains supply or generator, the batteries may provide back-up power in case of a failure and/or when disconnecting and reconnecting the power unit 104. In embodiments in which the power unit 104 is not connected to a mains supply or generator, the batteries may provide all the power for the UAV 102. The skilled person would appreciate that UAV payload capacity is generally limited, and that a much larger battery bank may be provided in the power unit 104 than could be carried by the UAV 102. Battery-based embodiments may therefore be of particular utility for aerial vehicle applications, although similar considerations may apply to land-based and/or water-based vehicles.

In the embodiment being described, the power unit 104 is modular -one or more modules may be selected and connected together depending on the power required for the UAV 102.

In embodiments in which the tether cable 106 is arranged to carry DC power, each module of the power unit 104 may comprise a power supply 10 la, 10 lb and a tuning circuit 130, as described 40 below.

Each power supply 101a, 101b may comprise an integrated AC to DC or DC to DC converter. The power unit tuning circuit 130 may be arranged to tune the converter based on the current being drawn by the UAV 102. The tuning may compensate for voltage drop along the tether cable 106.

In alternative embodiments, the power unit 104 may not comprise one or more power supplies 101a, 10 lb, but may instead comprise one or more tuning circuits 130a arranged to be connected to an external power supply 101 comprising a converter, or to a converter which is in turn arranged to be connected to an external source of power 101.

In embodiments in which the tether cable 106 is arranged to carry AC power, no conversion or tuning may be performed in the power unit 104 in some embodiments. The power unit 104 may simply be a plug, optionally containing a fuse or other emergency circuit breaker Illa, 111b.

In the embodiment being described, each power unit module 101a, 101b is arranged to provide 800 W. The smallest power unit 104 is therefore capable of providing a continuous power of up to 800W. Two units may be combined to provide a power of 1600 W. three for 2400W, four for 3200 W, or five for 4000 W, for example. The maximum continuous power output is therefore scalable in multiples of 800 W. In other embodiments, the power of a single module may differ, or the power unit 104 may not be modular. The skilled person would appreciate that a modular design may facilitate tailoring a tether 110 to customer needs.

The gap in the tether cable 106 marked X in Figure 2 is shown to indicate that cable length may be much longer than illustrated, and may vary. In the embodiment being described, the tether cable 106 is 70 in long. In various embodiments; the cable may be at least 5 in; 10 m, 20 in, 25 m, 30 m, 50 in, m or 90 in in length.

In the embodiment being described, the tether cable 106 comprises a two-core cable. The two cores 106a, 106b are equivalent and each made of a first metal or metal alloy, having a first conductivity. Each core 106a, 106b comprises a bundle of stranded wire. In the embodiment being described, each core 106a, 106b has a core diameter of between 1 mm and 3 mm, optionally between 2.4 mm and 2.8 mm, and optionally of 2.5 mm. The core may be composed of multiple strands twisted together, for example each with a 0.5 mm diameter. Strand diameter may vary in other embodiments. In the embodiment being described, the tether cable 106 is a two-core copper cable. Each core 106a, 106b has a diameter of between 1.5 mm and 3.0 mm. In the embodiment being described, three different cables 106 are provided; the cables 106 may be interchanged for different uses (e.g. for different vehicles, or for different used of the same vehicle). In the embodiment being described, the three cabled 106 are: * a lightweight cable 106, with each core 106a, 106b having a diameter of 1.75 mm; * a midweight cable 106, with each core 106a, 106b having a diameter of 2 min; and * a heavier cable 106, with each core 106a, 1064) having a diameter o12.5 mm.

In the embodiment being described, the cable 106 connected as part of the tether 110 is the heavier cable 106. The tether cable 106 weighs between 45 g and 65 g per metre, and more particularly 0.05 kg (50 g) per metre. In alternative embodiments, the tether cable 106 may bc lighter or heavier -the skilled person would appreciate that a larger (and therefore heavier) cable 106 may be better able to transport a higher power, and that unmanned vehicles requiring less power (e.g. lower weight UAVs) may be provided with a lighter cable, so reducing payload/power demand as compared to a heavier cable.

In the embodiment being described, the tether cable 106 is arranged to carry a continuous power of around 2.4 kW, and to handle peaks of up to 2.8 kW. In alternative embodiments, such as embodiments using a mid-weight cable 106 as described above, the tether cable 106 may be arranged to carry a continuous power of around 1.6 kW, and to handle peaks of up to 2.0 kW. In such embodiments, a lighter cable 106 may be used -e.g. around 0.03 kg/metre. In alternative embodiments, such as embodiments using a lightweight cable 106 as described above, the tether cable 106 may be arranged to carry a continuous power of around 0.8 kW, and to handle peaks of up to 1.6 kW. In such embodiments, a lighter cable 106 may be used -e.g. around 0.02 kg/metre.

The skilled person would appreciate that a heavier cable 106 may be used for a lower power, but that using a minimum cable size/weight for the desired power may improve performance (e.g. by reducing the cable weight to be carried or moved by the unmanned vehicle 102, which may be of particular importance for a UAV; which is likely to have a limited payload capacity).

In the embodiment being described, each copper core of the tether cable 106 is coated with a second, higher-conductivity, metal such as silver or gold or another precious metal, and in particular is coated with silver in the embodiment being described. In the embodiment being described, each copper core 106a, 106b is electroplated with the second metal. The layer of the higher-conductivity metal may reduce the resistance of the tether cable 106. The higher-conductivity metal may also be less reactive than copper (e.g. with water and/or salts such as sodium chloride). The metal coating on each copper core 106 may improve damage resistance, especially if a water-proof outer coating 103, 105 fails.

The metal coating may protect the copper core 106a,b and reduce corrosion, keeping the resistance of the tether cable 106 relatively low, which may improve power usage. The coating may allow a thinner copper core 106a,b to be used without increasing the power loss.

In the embodiment being described, 20g of the coating metal is used per kg of the copper core.

The two-core cable 106 of the embodiment being described may have a lower resistance per unit length than prior art tether cables, so facilitating the transmission of lower voltage, higher current power (reducing the voltage drop).

In the embodiment being described, each silver-coated copper core 106a, b is coated in a resilient and electrically insulating material, such as a polymeric material, forming a layer 105a, b of the resilient material around the core. Polytetrafluoroethylene (PTFE) is the selected polymeric material in the embodiment being described; in other embodiments, other polymers with similar properties (in terms of toughness, electrical insulation, and/or temperature resistance) may be used.

In the embodiment being described, the two-core cable 106 is coated in a resilient and electrically insulating material, such as a polymeric material 103, and in particular in Polytetrafluoroetlwlene (PTFE).

More particularly, each core 106a, 106b may be wrapped in PTFE tape. Each core 106a, 106b may be surrounded by PTFE with a thickness of between 0.1 and 0.3 nun, and optionally between 0.15 and 0.2 mm. The wrapped cores 106a, 106b may then be optionally twisted together, and wrapped in PTFE tape. One or more; and optionally two or more; layers of PTFE tape may be wrapped around each core 106a, 106b.

In the embodiments being described, the PTFE coatings around each core 106a, 106b, and around both cores, each have a thickness of less than 0.5 mm, and more particularly less than 230 Rm, less than 100 tun or less than 50 gm. The layer thickness may be greater than 30 gm. Thc skilled person would appreciate that use of as thin a layer as possible may minimise cable weight and improve flexibility, but that a minimum thickness may be desirable for insulation and protection.

Each core 106a, 106b of the tether cable 106 is therefore coated with/surrounded by a layer of a resilient material 105a, 105b, and a further layer 103 of a resilient material is provided around the two coated cores 106a, 106b, holding the two cores together to form a single cable 106. The further layer 103 is made of the same resilient material as the core coatings 105a, 105b in the embodiment being described, but may be made of a different resilient material in other embodiments.

The tether cable 106 is therefore double-insulated, with each wire coated, and a second coating surrounding the dual wires, A PTFE coating was found to provide a higher strength (for its weight) than any other suitable material rated for the power to be transferred.

As opposed to prior art systems which often use a cable not rated for the voltage/power it is intended to carry, the tether cable 106 as described for this embodiment is rated for the power, has a weight even a UAV 102 can carry, and is rated for use at temperatures of up to 600C. The skilled person would appreciate that cable temperature can rise in use -the relatively high temperature rating may improve safety and durability, for example reducing or avoiding the risk that a coiled up portion of a cable 106 on a reel in use might melt.

In alternative embodiments, a fibre optic cable may be used However, the skilled person would appreciate that a metal-based cable 106 may be lower cost, and may,: improve ease of repair. In particular, a damaged fibre optic tether cable may; need to be replaced entirely, whereas a damaged portion of a metal cable may be cut out and the cut ends attached, forming a shorter but useable tether cable. The tether cable 106 of the embodiment being described may therefore be field-repairable. The skilled person would appreciate that tether cables 106 can be relatively easily damaged, e.g. by pinching in a vehicle or building door or snagged on rough terrain, and that ease of repair may therefore be an important factor. In addition, use of a fibre optic cable may add weight, potentially leading to different performance characteristics and a lower maximum payload.

The tether 110 comprises a vehicle unit 108. The vehicle unit 108 is located on the UAV 102 In the embodiment being described, the vehicle unit 108 is detachably mounted on the UAV. In alternative embodiments, the vehicle unit 108 11113V be integrally formed with the UAV 102.

The tether cable 106 extends between the power unit 104 and the vehicle unit 108, and transmits power from the power unit 104 to the vehicle unit 108. The tether 110 is therefore used to provide power to the UAV 102 The tether 110 is used to provide up to 2.5 kW of power to the quadcoptcr UAV 102 of the embodiment being described. The skilled person would appreciate that power demands are generally lower for ground-or water-based unmanned vehicles than for UAVs. The UAV power levels described herein may therefore represent an extreme case of tether power demand.

In the embodiment being described, the tether voltage is less than 250 V, less than 245 V, less than 240 V. and in particular less than or equal to 110 V. Lowering the voltage as compared to prior art tethers may improve safety. Keeping the voltage to 110 V or below, and optionally to 75 V or below, may facilitate compliance with Health. Safety and Environmental (HSE) guidance and regulations.

In the embodiment being described, the tether voltage is greater than or equal to 70 V. and more particularly greater than or equal to 75 V. The skilled person would appreciate that the tether technology 110 described herein may not be relevant to lower voltage/power requirement applications such as toys, for which a simple wire and battery pack or the likes may be useable.

In the embodiment being described, the tether cable 106 is detachably connected to both the power unit 104 and the vehicle unit 108 such that the cable 106 can be disconnected and replaced. The cable 106 being detachable may facilitate replacement in case of damage. Each end of the cable 106 may therefore comprise a connector arranged to allow the cable 106 to be attached to the vehicle unit 108 and power unit 104. In the embodiment being described, the connectors are identical such that the tether cable 106 may be connected either way round. In alternative embodiments, the connectors may not be identical and each cud of the tether cable 106 may be connectable to only one of the vehicle unit 108 and the power unit 104.

Additionally or alternatively, the cable 106 being detachable may facilitate selection of a suitable tether cable 106 for a particular UAV 102, or particular use of a given UAV. For example, a thinner cable 106 / a cable 106 with a lower weight per unit length may be used for a lower-power UAV 102 or lower-power utilisation of a given UAV. The thinner cable 106 may be sufficient to supply the lower power and may additionally reduce the load on the UAV (less cable weight to carry). Similarly, a longer or shorter tether cable 106 may be selected depending on an intended range of the unmanned vehicle 102. In alternative embodiments, the cable 106 may not be detachable from either or both of the power unit 104 and the vehicle unit 108.

In the embodiment being described, the vehicle unit 108 is arranged to adjust the power received via the tether cable 106 to make it suitable for use on the UAV 102. The adjustment includes stepping down the voltage to a suitable level (e.g. 14 V, 22 V. 24 V. or 48 V for various UAVs). Stepping down the voltage generally causes sonic energy to be released as heat -in the embodiment being described, the rotors 112 of the UAV 102 provide a flow of air which cools the vehicle unit 108, and no additional, active cooling is needed. The positioning of the vehicle unit 108, and or of vents in a body of the UAV 102, may be selected to facilitate passive cooling. No fan or other cooling system is therefore provided in or for the vehicle unit 108 of the embodiment being described. Embodiments without an (active) cooling system may have lower auxiliary power requirements due to not needing to supply power to a fan or the likes. Further, the lack of an active cooling system may reduce payload mass, so reducing UAV power requirements -the reduced power demand may facilitate providing a lower voltage tether. In other embodiments, an active cooling system may be provided.

One such passive cooling embodiment is shown in Figure 12, The UAV 102 has six rotors I 12 spaced around its fuselage. The centre of gravity 113 of the UAV is marked with a circle -the centre of gravity is located at least substantially centrally with respect to the rotors 112. The vehicle unit 108 is located towards the rear of the UAV 102, adjacent two rotors 112. A payload such as a camera is located near the front of the UAV 102 in this embodiment, so balancing the weight and maintaining a central centre of gravity 113. In embodiments in which the payload is differently located (e.g. towards the back), the vehicle unit 108 may similarly be differently located (e.g. towards the front) to maintain a more even weight distribution. Locating the vehicle unit 108 near one or more rotors 112 of the UAV may facilitate passive cooling of the vehicle unit 108. In particular, one or more heat sinks 108a-c may be located on external faccs of the vehicle unit 108 to increase airflow over the heat sinks, and therefore to increase the level of passive cooling provided. In alternative or additional embodiments, the vehicle unit 108 may be centrally located with respect to the UAV 102 -one or more vents may be used to direct airflow from the rotors 112 across the vehicle unit 108 for cooling in such embodiments. The amount of heat released generally depends on the power being transferred -UAVs 102 -and in particular copter-type UAVs -may have higher power requirements than other kinds of unmanned vehicles. Cooling may therefore not be an issue for other unmanned vehicle types.

For ground-based vehicles, the vehicle unit 108 may be integrated into a frame of the vehicle, allowing heat to dissipate into the vehicle. Cooling/heat distribution may therefore again be achieved without introducing any (additional) moving parts. For high energy-drain ground-based vehicles in hot climates, or other unmanned vehicle situations in which heat loss is more of an issue, a fan or the likes may be added for additional cooling if desired.

In various embodiments, DC (direct current) or AC (alternating current) power may be transmitted along the tether cable 106. In the vehicle unit 108, an AC to DC converter (a rectifier) 109a and/or a DC to DC converter 109b may be provided accordingly, to provide power to the UAV 102 at a suitable voltage (noting that current UAVs generally take DC power).

In the embodiments being described, the converter(s) 109a, 109b are selected to be lightweight, for example, in the AC embodiments being described, the rectifier 109a weighs around just 350 g per 700 W to be handled, with a standard unit weighing 1 kg and outputting 2 kW constant power (2.8 kW peak). In alternative embodiments, e.g. for land-based unmanned vehicles for which payload may be less limited, the converter selected may not be a lightweight converter.

In the embodiments being described, the converter 109a, 109b is solid-state, having no moving parts (e.g. no fan or other moving part cooling system). Further, the converter comprises one or more heat sinks 108a-c arranged to be cooled by airflow from the UAV rotor blades -there may therefore be no moving parts associated with the converter, which may reduce a potential number of points of failure and/or reduce weight. The heat sinks 108a-c may be positioned within the UAV so as to facilitate passive cooling -for example being near and below one or more rotors 112 of the UAV 102.

In the embodiments being described, the heat sinks 108a-c are ultra-lightweight heat sinks, selected from the range of available heat sinks for their low weights. The use of lightweight heat sinks I08a-c may facilitate maintaining a central centre of gravity 113 for the UAV 102, especially in embodiments with a non-central mounting of the vehicle unit 108 on the UAV 102, as well as reducing the weight to be carried by the UAV 102. In alternative embodiments, e.g. for land-based unmanned vehicles for which payload may be less limited, the heat sink(s) selected may not be as light.

In embodiments in which the tether cable 106 carries DC power, the vehicle unit 108 comprises a DC-DC converter 109.

In embodiments in which the tether cable 106 carries AC power, the vehicle unit 108 comprises an AC-DC converter I09a and optionally also a DC-DC converter 109b.

In the embodiments being described, the overall DC-DC converter 109 is modular, with multiple DC-DC converter modules 109b (which may also be referred to as DC-DC converters 109b) connected in parallel (three modules are shown in Figures 4A and 6). More or fewer modules 109b may be added in other embodiments to facilitate making more power available. In embodiments in which scalability and interchangeability of parts is deemed less important, the converter may not be modular.

In embodiments with multiple DC-DC converter modules 109b, each DC-DC converter module 109b comprises a DC-DC converter 200 and a tuning circuit 250, as shown in Figure 9. The tuning circuits 250 of each DC-DC conversion module 109b are arranged to be interconnected as shown in Figure 10, so as to balance load between the different converters 200. The tuning circuit(s) 250 may therefore be thought of as multiple interconnected tuning circuits 250, one for each converter, or as a single tuning circuit with a repeating module for each converter wired thereto. Each converter 200 may be or comprise an off-the-shelf product, e.g. a standard DC-DC converter chip such as XP Power QSB60048S28.

The tuning circuits 250, described in more detail below, are arranged to tune the output of the converters 200 based on the output voltage to the UAV 102, adjusting for fluctuations in power demand.

In embodiments with a single AC-DC or DC-DC converter, a tuning circuit 250 is arranged to tune the output of the converter 200 based on the output voltage to the UAV 102, adjusting for fluctuations in power demand. There is no load balancing between converters in embodiments with a single converter.

The transmission of AC power by the tether cable 106 may risk the generation of more radio-frequency (RF) interference (also known as electromagnetic interference -EMI) than DC power, but may improve safety (as the possibility of a user getting an electric shock from the cable 106 causing the user to spasm and be unable to release the cable is reduced or eliminated) and/or may improve ease of fault management (e.g. by facilitating the use of standard Residual Current Devices (RCDs) as a fuse or the likes).

The use of DC power may reduce or eliminate interference, but may present an increased safety risk and/or more difficulty in implementation (e.g. due to voltage drop).

Embodiments using AC power and DC power are described below by way of example: AC Power Transmission Figure 3 illustrates an AC tether system 100 including a tether 110 connected to a six rotor drone 102. The skilled person would appreciate that different numbers of rotors are shown in different embodiments merely by way of example.

In the embodiment being described with respect to Figure 3, the power unit 104 is arranged to be plugged into an AC mains supply of 240 V. The UAV 102 is therefore plugged into the mains supply via the tether 110. This input voltage of 240 V is stepped down to 110 V AC in the power unit 104 for transmission through the tether cable 106 (AC to AC conversion).

In alternative AC power embodiments, a different mains or generator supply may be used or batteries or the likes may be used. In AC transmission embodiments in which the power input to the power unit 104 is DC power, DC to AC conversion is performed to provide AC power for transmission over the tether cable 106.

In some embodiments, the power supply from the mains or a generator may be at the desired tether voltage (i.e. 110 V in the embodiment shown). In such embodiments, no step up or step down of the voltage may be needed, and there may be no power management performed by the power unit 104. No ground-based voltage regulation or conversion may be performed -all power management may be performed on the unmanned vehicle 102 (e.g. converting the 110 V AC to a lower voltage DC). In such embodiments with no power-management performed by the power unit 104, the power unit 104 may simply be or comprise a plug or other connector arranged to connect the tether cable 106 to the power supply, optionally including a fuse, circuit breaker or the likes. In some embodiments, the tether cable 106 may be permanently connected to a generator or the likes -the generator may be classed as a part of the power unit 104 in such embodiments. The UAV 102 may therefore be flown directly on generator power.

The power unit 104 of the embodiment being described is shown in Figure 4B. An input Residual Current Device (RCD) 111a receives AC power from a power source such as a generator 101 or the likes. The power is then relayed to an output Residual Current Circuit Device (RCCD) 11 lb, which provides power to the tether cable 106.

The input RCD 111a is arranged to protect the power unit 104 from any power surge, voltage spike or the likes from the power source 101. The RCD 111a is arranged to trip if the current on the live or neutral line exceeds a specified value.

The output RCCD 1 1 lb is arranged to protect the power unit 104 from any power surge, voltage spike or the likes from the tether cable 106, and to protect the tether cable 106 (and therefore the vehicle unit 108 and vehicle 102) from any power surge, voltage spike or the likes from the power unit 104 or power source 101. The RCCD 111b is arranged to trip if a difference in current between lines exceeds a specified value -the different acronyms are used for clarity. In alternative embodiments, only one RCD or RCCD, or no RCDs or RCCDs, may be provided.

The power unit 104 also comprises a control interface 122, processing circuitry 121 and data module 120a, as discussed in more detail below. The data module 120a may also be referred to as a powerline adapter I 20a. In alternative embodiments, no such components may be provided, and/or different data transfer components may be provided.

The control interface 122 is arranged to communicate with the processing circuitry 121 -the communications are two-way such that a user can enter commands via the control interface 122, and get a response or other data via the control interface 122, in additional or alternative embodiments, an output means (e.g. a display) separate from the control interface may be provided. The processing circuitry may be provided by an in-built computer, chip or the likes.

The processing circuitry 121 is arranged to communicate with the data module I 20a. The data module I20a is arranged to encode commands provided by the processing circuitry 121 for transmission over the tether cable 106. In the embodiment being described, an output signal from the data module 102 is combined with the power leaving the output RCCD 111b so that the power and command can be transmitted via the tether cable 106.

The skilled person would appreciate that a 110 V AC system 100 may be used on a commercial basis and within EU and UK USE guidelines, unlike higher-voltage known systems. The system 100 may therefore be used on building sites and the likes whilst still complying with health and safety legislation. The system 100 with a 110 V input voltage as well as a 110 V tether voltage may be safer to use in an outside environment as no element of the system exceeds 110 V. The tether cable 106 of the 110 V AC tether voltage embodiments being described is a light weight high conductivity, dual core copper cable as described above.

In the embodiment being described, the tether 110 comprises a spool or reel 107. The spool 107 is arranged to have a length of the tether cable 106 wrapped around it, and to allow the cable 106 to be unwound when the unmanned vehicle 102 moves further away and to be wound back on when the unmanned vehicle moves closer. In various embodiments, the reel 107 may be powered or freely moving. In other embodiments, no reel 107 may be provided, or the reel may be incorporated into the power unit 104. In some embodiments, a reel 107 may (additionally or alternatively) be incorporated into the unmanned vehicle -this skilled person would appreciate that for UAVs 102, minimising weight may bc prioritised and so locating the reel 107 separately from the vehicle 102 may be preferable, whereas for a ground vehicle or the likes, weight (and bulk) may be less of an issue and locating the reel 107 on the vehicle 'nay be preferable. The reel 10'7 may be integral with the power unit 104 in some embodiments.

When the 110 V AC power is received by the vehicle unit 108, the voltage is stepped down to a working voltage of the UAV (22.2 V in the embodiment being described).

In the embodiment being described, the UAV 102 takes a DC voltage -the received power is therefore converted from AC to DC (bridge rectified, in the embodiment being described). In this embodiment, bridge rectification is performed before stepping down the voltage, and a DC-DC converter (and more particularly a modular DC-DC converter including three individual DC-DC converters 109b) is used for the step down.

A schematic view of a vehicle unit 108 of this embodiment is shown in Figure 4A. The vehicle unit 108 comprises a bridge rectifier 109a arranged to receive the (AC) power from the tether cable 106 and to convert this to DC. A single rectifier 109a is used in the embodiment being described; one or more additional rectifiers 109a may be added in other embodiments, for example in higher power embodiments. The DC output is then split between a plurality of DC to DC converters 109b, as is described in more detail below. Three converters 109b are shown in the embodiment being described -in alternative embodiments, a different number of converters may be used; for example from 2 to 10 converters. The converters 109b adjust the voltage to be suitable for use by the UAV 102. The converters 1091), 200 each have a tuning circuit 250 arranged to tune the output of the converters 200 based on the output voltage to the UAV 102, adjusting for fluctuations in power demand and balancing load between converters. The vehicle unit tuning circuit 250 is as described in more detail below, and is different from the power unit inning circuit 130.

The output from the converters 109b is then provided to a diode 109c. The single output from the diode 109c is then provided for use by the UAV 102. The diode 109c is arranged to act as a check valve; preventing back-flow of current.

In the embodiment being described, the vehicle unit 108 of the AC system additionally includes a data module 120b (which may also be referred to as a powcrline adapter). The data module 120b is arranged to receive the input power/signal from the tether cable 106, and to decode the command encoded by the data module 120a of the power unit 104 The command may then be transmitted to a control system of the UAV 102.

In the embodiment being described, the data module 120b is additionally arranged to encode data from one or more sensors of the UAV 102 for transmission to the power unit 104 along the tether cable 106. The data module 120a of the power unit 104 may decode the received signal to obtain the data, which then may be passed to the processing circuity 121 and stored, processed, and/or displayed to a user, as desired. The skilled person would appreciate that commands are simply one form of data, and that the two data modules 120a,b may therefore be equivalent.

In alternative embodiments, no such data module 120b may be provided, and/or alternative communication components may be included.

DC Power In the embodiment being described with respect to Figures 5 to 7, the power unit 104 is plugged into a 3 kW, 1-10V AC generator 101. This input AC voltage is then converted to DC and stepped down to 75 V DC for transmission through the tether cable 106. Ground-based voltage conversion is therefore performed by the power unit 104.

Current UK regulations class systems at 110 V or below as extra low voltage, but only systems at 75 V or below are classed as extra low voltage under European regulations -DC power systems operating at both 110 V DC and 75 V DC were tested, and the 75 V DC embodiment is described in greater detail herein.

In alternative embodiments, a mains supply may be used in place of a generator 101, or a different generator supply may be used, or batteries or the likes may be used. If the power input to the power unit 104 is AC power, AC to DC conversion is performed to provide DC power for transmission over the tether cable 106. In the embodiment being described, two AC to DC converters are used in the power unit 104, connected in series (with separate ground connections).

In the embodiment being described, one of the two AC-DC converters has a tuning circuit 130 connected to it and arranged to tune the converter based on the current being drawn through the tether by the UAV 102. The other AC-DC converter may be set to a maximum level and not tuned. One AC-DC converter may therefore still be available if the power unit tuning circuit 130 failed. There would therefore still be some power as the failure would not shut off both converters.

The tuning circuit 130 may help to reduce or avoid low voltages or power spikes -the skilled person would appreciate that stable power may be especially critical for UAVs 102, as opposed to ground-or water-based unmanned vehicles, as a drop in power can cause a UAV 102 to drop out of the air, potentially damaging or destroying the UAV. The tuning circuit 130 regulates the power output from the converter to which it is attached, and may therefore alternatively be referred to as a power regulator 130.

The tuning circuit 130 tunes the outputs from the DC power supplies 101a, 101b, for example to increase the voltage on the tether cable 106 to compensate for voltage drop over the length of the tether cable 106.

Figure 11 shows a circuit diagram for the tuning circuit 130 of the embodiment being described. The tuning circuit 130 is described in more detail below.

The tether cable 106 of the 75 V DC tether voltage embodiment being described is a light weight, high conductivity dual core copper cable as described above.

The skilled person would appreciate that a 75 V system 100 is classed as an Extra Low Voltage system according to European Union definitions -thc lower voltage may improve safety and may facilitate compliance with safety legislation.

In the embodiment being described, significant voltage drop occurs along the tether cable 106 due to its length, despite the relatively low resistance. Voltage drop depends on current; the power unit 104 of the embodiment being described therefore comprises one or more sensors arranged to detect current drawn through the tether cable 106. The power unit 104 is arranged to sense the current draw and to sense or calculate a voltage drop across the tether cable 106. The tuning circuit 130 of the power unit 104 of the embodiment being described is arranged to adjust the voltage based on the detected current so as to maintain a voltage of 75 V DC for the vehicle unit 108 (at the vehicle end of the tether 106). The power regulator/tuning circuit 130 is arranged to step up the voltage if the current increases enough that voltage drop would increase enough to cause the input voltage to the vehicle unit 108 to fall below 75 V. and to step down the voltage is the current decreases enough that voltage drop would decrease enough to cause the input voltage to the vehicle unit 108 to climb above 75 V. The power unit 104 may therefore be described as providing a self-tuning output voltage; controlling the output provided to the tether cable 106.

A tolerance may be set around the 75 V set value (e.g. plus or minus 3%), such that the input voltage to the vehicle unit 108 is maintained within the tolerance range of the set value. The set value may be different from 75 V. and/or the tolerance may be different from 3%, in alternative embodiments.

The power regulator 130 is arranged to adjust the voltage to compensate for the voltage drop, so ensuring that the UAV 102 receives its required voltage.

When the 75 V DC power is received by the vehicle unit 108, the voltage is stepped down to a working voltage of the UAV (22.2 V or 24 V in the embodiments being described). The vehicle unit 108 comprises a DC to DC converter 109b to step down the voltage The power unit 104 shown in Figure 7 further comprises a wireless router 140. The wireless router 140 is arranged to transmit data between a control station or interface (not shown) in communication with, or provided as part of, the power unit 104 and the UAV 102.

A schematic view of a vehicle unit 108 of this embodiment is shown in Figure 6.

In the embodiment being described, the UAV 102 takes a DC voltage and is supplied with a DC voltage, so no AC-DC or DC-AC conversion is performed by the vehicle unit 108. The vehicle unit 108 therefore does not comprise a bridge rectifier or equivalent, unlike the vehicle unit 108 of the AC transmission system.

The DC input from the tether cable 106 is split between a plurality of DC to DC converters 109b, as is described in more detail below. Three converters 109b are shown in the embodiment being described -in alternative embodiments, a different number of converters may be used; for example from 2 to 10 converters. The converters 109b adjust the voltage to be suitable for use by the UAV 102, Tuning circuits 250 of the vehicle unit 108 on the UAV regulate the power output from the vehicle unit 108 to match the UAV's rated voltage.

The output from the converters 109b is then provided to a diode 109c. The single output from the diode 109c is then provided for use by the UAV 102.

The vehicle unit 108 does not comprise a data module in the embodiment being described. In other DC embodiments, data modules similar to those for the AC systcm may be provided, as described below.

Converter Tuning In the embodiments being described, one or more AC to DC and/or DC to DC converters are included in the vehicle unit 108, to provide power to the UAV 102 at an appropriate DC voltage. The vehicle unit tuning circuit(s) 250 may be arranged to automatically regulate the vehicle unit output based on the voltage output to the UAV 102, In DC tether transmission embodiments, a single converter, optionally with a tuning circuit, 130, may be provided in the power unit 104. The converter may be an AC to DC converter (for an AC power source) or a DC to DC converter (for a DC power source). Multiple converters may be provided in the power unit 104 in some embodiments. One or more of the converters may have a corresponding tuning circuit 130. The power unit tuning circuit(s) 130 may be arranged to automatically regulate the power unit output based on the current being drawn by the UAV 102, through the tether cable 10. In AC tether transmission embodiments, no tuning (and optionally no conversion) may be performed in the power unit 104. All of the tuning and conversion may be performed by the vehicle unit 108 in such embodiments.

* Vehicle Unit In the embodiments being described, for both AC and DC tether transmission, the converter 109b on board the vehicle 102 (as a part of the vehicle unit 108) is a modular converter, comprising a plurality of individual DC to DC (and/or AC to DC) converters coupled together to perform the desired overall conversion. Each individual converter 109b may be an off-the-shelf converter. Each individual DC to DC or AC to DC converter may be provided with a tuning circuit 130 to tune its output based on the power draw of the UAV 102, and more specifically based on the output voltage to the UAV 102. A circuit diagram for a DC-DC converter 109a,b of an embodiment is shown in Figure 9. The outputs of a plurality of DC-DC converters 109b are joined together to provide the desired power, for example as shown in Figure 10.

As the output of each DC-DC converter can generally be tuned within a range (e.g. 45 -160 V), the outputs of each can be varied as appropriate to share the load between the plurality of DC-DC converter units whilst also providing the desired output power. For example, two or three separate DC-DC converters 200 may be used (or more in other embodiments). Each separate DC-DC converter 200 is a standard, off-the-shelf, product in the embodiment being described, selected due to its suitability for the desired voltage input and output. Bespoke DC-DC converter chips or the likes may be used in other embodiments.

An AC to DC converter 109a may be tuned in the same way as the DC to DC converters 1091), for example when adjusting a bridge-rectified AC input to a vehicle unit 108 (the AC to DC converter 109a comprising a rectifier and the tuning being performed thereafter). The skilled person would appreciate that, by contrast, an AC to AC converter generally cannot take a wide spread of input voltages so is less easy to tune in this manner.

The vehicle unit 108 further comprises a tuning circuit 250 associated with each DC-DC converter 10911; the tuning circuits 250 are coupled together as shown in Figure 10 and arranged to share current between the plurality of individual converters in such a way that each converter 109b, 200 can provide an at least approximately equal amount of power. Current sharing may reduce or avoid the risk of any one converter 109b, 200 working harder than the others and over-heating.

The vehicle unit tuning circuits 250 are arranged to bc connected to, and to tune, each converter unit 109b. The tuning circuits 250 are arranged to allow the voltage of each converter unit 109b to be adjusted automatically during operation based on the current. A converter unit 109a,b may be thought of as the combination of a converter 200 and its associated tuning circuitry 250.

In the embodiment being described, each converter 200 has its own tuning circuit 250 and is tuned separately from the other converter(s), but with the tuning taking account of the power split between the converters. The outputs are then combined to provide power to the UAV 102. The skilled person would appreciate that if all the units 109a,b are drawing the same current then the units would all provide the same voltage. If one unit 109b draws more current, the voltage changes. The tuning circuits 250 are arranged to maintain the same voltage out of each DC-DC converter.

The tuning circuit 250 may be designed to control a voltage ramping rate within a se( range; if the voltage changes too quickly, a spike may cause the UAV 102 or the converter 200 to shut off, potentially causing a crash. By contrast, if the voltage changes too slowly, the vehicle module 108 may not be able to provide sufficient power for the UAV 102, potentially causing the converters 109b to trip and/or UAV rotors to slow or stop -this again could result in a crash.

The skilled person would appreciate that DC to DC converters 200 may trip and reset when a maximum voltage is reached or exceeded, not just simply stop increasing in voltage -the sudden tripping may be catastrophic for a UAV 102 in flight. The tuning circuit 250 may be designed to reduce or avoid the chance of this happening.

In the embodiment being described, the tuning circuit 250 is arranged to include a DC-DC converter 200, for example an operational amplifier such as a THS428-1DBVTG4 Texas Instruments High Speed Operational Amplifier.

In the embodiment being described, the tuning circuit 250 comprises a voltage sensing module 251 arranged to detect an output voltage being provided to the UAV 102 and to provide feedback to allow the converter 200 to be adjusted accordingly. The voltage sensing module 251 is connected to a voltage output pin (+Voin,(3)) of the converter 200, and also to a sense pin (the positive sense pin, + SENSE) of the converter 200. The voltage sensing module 251 provides a signal voltage based on the output voltage to the sense pin of the converter 200. A voltage sensing module 251 may be selected for a particular embodiment based on the voltage range and output, as converters may only accept an input of within a certain range. In the embodiment being described, the voltage sensing module 251 used is provided as part of a vibration damping plate from Unmanned Tech (see Mips yytlyjit immanneylt c Imp c odik/i2te, /5:tit v ra t grj?ja bi); in alternative or additional embodiments a different voltage sensing module 251 may be used, and the voltage sensing module 251 may optionally be provided as a separate component.

In the embodiment being described, the tuning circuit 250 comprises a variable resistor 252 connected between a second sense pin (the negative sense pin, -SENSE) of the converter 200 and the TRIM pin of the converter 200. A second voltage output pin (-V0ur(3)), paired to the first mentioned above, is also connected to the variable resistor loop 252. The resistance of the variable resistor 252 is arranged to be automatically adjusted based on the signal voltage provided by the voltage sensing module 251, as relayed via the sense pins (+SENSE, -SENSE) so as to tune the converter 200.

A 0-10 ki2 variable resistor 252 is used in the embodiment being described; other variable resistors may be used in other embodiments as suited for the converter 200 and power profile in use.

The skilled person would appreciate that in prior art uses of converters 200 a fixed value resistor is normally used in place of the variable resistor 252 described herein; the fixed value being selected by a user. By contrast, in the tuning circuit 250 being described, the variable resistor 252 and voltage sensing module 251 are arranged to provide automated tuning of the converter 200.

The tuning circuit 250 of the embodiment being described further comprises two capacitors 253, 254. The first capacitor 253 is wired across the positive and negative voltage input pins (-'-VIN, -VIN) and arranged to smooth a fluctuating input power. The second capacitor 254 is wired across the positive and negative voltage output pins (+V0ur(l-3), -Vour(1-3)) and arranged to smooth the output power.

Both capacitors 253, 254 are 470 RP' capacitors in the embodiment being described; other capacitors may be used in other embodiments, for example as appropriate for a different converter 200.

In the embodiment being described, the capacitors 253, 254 were selected for their physical size, and their residual Equivalent Series Resistance (ESR). The skilled person would appreciate that the space available may be hunted within a UAV, and that the largest capacitor(s) that would fit may therefore be selected. A smaller capacitor may not provide as large a smoothing effect. In other embodiments, a larger capacitor, or more capacitors, may be used, or a smaller capacitor may be used (depending on available space and desired level of smoothing).

The tuning circuit 250 of the embodiment being described further comprises a resistor 255 wired between the circuit loop of the first capacitor 253 and the +ON/OFF pin of the convener 200 This arrangement is provided to turn on the tuning circuit 250 and associated converters 200. The voltage is reduced and a "high" signal is sent to turn it on. In alternative embodiments, a switch could be fitted to turn the tuning circuit 250 and associated converters 200 on and off manually. In the embodiment being described, this functionality is instead provided as a part of the circuit so that an incoming voltage can be detected and used to automatically switch the units on.

A 30 resistor 255 is used in the embodiment being described; other resistors may be used in other embodiments as suited for the converter 200 and power profile in use. The resistor 225 reduces the voltage on the line. The resistances of all resistors in the tuning circuit 250 may need to be adjusted for different selected components and/or power profiles. *

Power Unit In the power unit 104 shown in Figure 7, two or more power supplies 101a, 101b are present, each power supply 101a, 101b being or comprising a converter.

A tuning circuit 130 different from that of the vehicle unit 108, but arranged to provide a corresponding function, is provided. As for the vehicle unit 108, in the power unit 104, a tuning circuit may be provided for each converter 101 in a modular fashion, and these may be linked together.

The tuning circuit 130 in the power unit 104 is arranged to measure the current passing through the converter 10 la, 10 lb (the current being drawn by the UAV 102) and to tune the output voltage up or down depending on the current, adjusting the voltage back towards its set, desired value. The tuning circuit 130 in the power unit 104 therefore senses current, as opposed to voltage being sensed for the tuning circuit 250 of the vehicle unit 108.

If the voltage across one converter 101a, 101b is higher than that across the other converter(s), it will produce more load, and may overheat. If one converter 101a, 101b is producing more power than the other(s), the tuning circuit 130 will read the current and tune the voltage depending on what is needed.

The tuning circuit 130 of the embodiment being described is shown in Figure 11.

The tuning circuit 130 of the embodiment being described comprise an operational amplifier (OpAmp) 131, and more specifically a THS4281DBVTG4 Texas Instruments High Speed Operational Amplifier chip The skilled person would appreciate that alternative chips 131 may be used in other embodiments. The OpAmp 131 amplifies the signal for current sensor described below as the larger signal facilitates providing all the current needed whilst only time part of the sensing ability of the apparatus. In particular; the range is 0-100 Amps for the embodiment being described, but tuning is only performed at 5-30 Amps.

A sensing pin on the converter chip 131 is used to sense the current through that converter; that value is used to tune the voltage output from that converter accordingly. In particular, a current sensor (not shown) is positioned on a main powerline from the power supply 101 to the UAV 102, and a signal voltage from that current sensor is provided, at a position marked X in Figure 11, to a SENSE pin on the chip 131. The current sensor is selected for the ability to handle the maximum current and more (a tolerance is provided to handle spikes in current) and still to provide the required signal. In the embodiment being described, the current sensor is selected to have a 0-100 Amp range, and to provide 0-5 V signal. Any suitable commercially available current sensor may be selected accordingly.

The current sensor outputs a signal voltage (which may be referred to as a tuning voltage) to tune the relevant converter 101 in the power unit 104 on the ground. A separate current sensor may be provided for each converter 101.

At a 0 amp current draw, the current sensor of the tuning circuit 130 produces a 0 V signal voltage, increasing to 5 V for a current draw of 13 amps. If the current draw increases above 13 A, the voltage is maintained at 5 V. At higher currents, voltage on the tether may start to drop (voltage drop effects being dependent on current), but the tuning circuit 130 may be arranged to allow power to be supplied to the UAV 102 at the correct voltage for current draws of up to 18 A. The DC to DC converters in the vehicle unit 108 may be arranged to maintain the appropriate output voltage for the UAV provided that the input voltage does not drop below 45 V. The DC to DC converters may be able to perform across a relatively wide range of voltages; for example from 45 V to 160 V. The skilled person would appreciate that differently-rated converters may be selected depending on the expected vehicle power demands.

A user may use a plug rated for 16 A with the power unit to allow for more power to be provided than would be possible with a plug rated for only 13 A. A mains power supply/ can spike to currents over 13 A. If a signal voltage greater than 5 V were provided during a power spike, the De to DC converters on the UAV, and the AC to DC converter(s) on the ground, (for a DC tether cable plugged into an AC supply) may trip and cut the power. The maximum signal voltage front the tuning circuit 130 may therefore be regulated to avoid a power drop. Two variable resistors 134 are provided in the tuning circuit 130 to allow the converter 101 to be tuned according to the signal voltage. One of the variable resistors 134 (the first) is wired between the input from the current sensor (X) and the SENSE pin, and the second between a positive terminal (+12 V in the embodiment being described) of an auxiliary power supply and the SENSE pin. The first variable resistor 134 is arranged to change the sense current sharing. The second variable resistor 134 is arranged to change the base output voltage when the tuning circuit 130 is set up. The skilled person would appreciate that manufacturing differences between converters may cause differences in resistance, and that the variable resistors 134 may be used to adjust for these differences. For example, some converters 101 may have a 23.97 0, resistance and some a 24.01 Q resistance, so the variable resistors 134 can be used to adjust to a 24.00 Q resistance for each; the converters 101 therefore all have the same effective initial resistance, and can be tuned from the same point Each variable resistor 134 is a 0-10 1(51 variable resistor in the embodiment being described; alternative variable resistors may be used in other embodiments as appropriate, for example based on expected converter variability. In still further alternative embodiments, only one variable resistor may be used (e.g, no tuning of the base output voltage) or more than two variable resistors may be used, or a different feedback and adjustment system not using one or more variable resistors may be used.

In the embodiment being described, a signal voltage is input to a sense pin on all AC to DC and DC to DC converters to be tuned. As opposed to providing a constant voltage signal to the pin, the signal voltage changes dynamically and automatically, in response to current fluctuations, so tuning the chip 131.

In the embodiment being described, the tuning circuit 130 comprises a voltage regulator 132 connected to an auxiliary power supply (a +12V auxiliary power supply in the embodiment being described). The voltage regulator 132 is arranged to reduce the voltage from the auxiliary power supply (to 0.5 V in the embodiment being described) and to provide low-level power to the circuit 130.

The voltage regulator 132 is chosen for the range required and the output signal, as different DC to DC converters 131 may require different specifications. The auxiliary power supply may be or comprise a 12 V battery, or an AC to DC converter or mains regulator to provide a 12 V supply. In the embodiment being described, the voltage regulator 132 used is provided as part of a vibration damping plate from Unmanned Tech (see tjttp5://w)yyy.0 q d te,c h Opp. ... kfp ro.464/55jja: . b rat' o dAmpinicpjatecw(1h-Aly0; in alternative or additional embodiments a different voltage regulator 132 may be used, and the voltage regulator 132 may optionally be provided as a separate component.

The provision of a 0.5 V base voltage to the tuning circuit 130 may facilitate start-up, as the circuit 130 may not function at 0 V and may otherwise take a few seconds to start up. In other embodiments, no auxiliary power supply or voltage regulator 132 may be provided.

In the embodiment being described, the tuning circuit 130 comprises a diode 133 between the voltage regulator 132 and the rest of the tuning circuit 130. The diode 133 may be arranged to prevent back-flow of power to the auxiliary power supply, and is a Zener diode in the embodiment being described. The diode 133 may facilitate providing 0.5 V for the tuning circuit 130 and converters 101 to start up whilst preventing that signal from going back into the tuning circuit 130. The skilled person would appreciate that, at 0 V, the tuning circuit 130 and converters 101 would take a few seconds to start up, whereas maintaining a 0.5 V signal facilitates immediate/rapid start-up.

In the embodiment being described, the tuning circuit 130 comprises a resistance 135 wired between two pins of the converter chip 131. The resistance 135 is used to control an amp ramping rate of the chip 131. Which pins are used may vary dependent on chip architecture, as would be understood by the skilled person (a smaller resistor provides a smaller amp ramping rate, whereas a higher resistance resistor provides a higher amp ramping rate).

The resistance 135 comprises two 2.2 ki/ resistors wired in series in the embodiment being described, for a total resistance of 4A kfl -a different resistance, and/or more or fewer individual resistors, may be used as appropriate in other embodiments.

In the embodiment being described, the tuning circuit 130 comprises a resistance 136 wired between a pin of thc converter chip 131 and the negative terminal of the auxiliary power supply. The resistance 136 is arranged to provide a supply at a voltage lower than 12 V supply. Which pin of the converter chip 131 is used may depend on chip architecture and so vary for different chips 131; using the positive voltage input pin would reduce the voltage the chip 131 sees -the maximum output the tuning circuit 130 can provide may be the voltage on this pin. The resistance 136 comprises a 4.7 resistor in the embodiment being described -a different resistance, and/or more individual resistors, may be used as appropriate in other embodiments depending on the desired voltage.

One or more tuning circuits 130 may therefore be used in the power unit 104 to tune one or more converters, e.g. an AC to DC converter, present there; for example to increase the voltage on the tether cable 106 to compensate for voltage drop over the length of the tether cable 106.

Data Transfer In the embodiments being described, the tether cable 106 is arranged to transfer data between the unmanned vehicle 102 and the power unit 104, as well as transmitting power from the power unit 104 to the unmanned vehicle 102. The skilled person would appreciate that transferring the data via the cable 106 may reduce the chance of data being monitored, intercepted, or otherwise used by a third party as compared to wireless data transfer. In the embodiment being described, a data transfer rate of 1 Gbps (Gigabit per second) is achieved.

The data to be transferred may be sensor data captured by sensors of the unmanned vehicle 102; e.g. photo or video data, thermal imaging, vehicle performance measures, and/or the likes.

The vehicle unit 108 of the embodiments being described comprises a data transmission module 120b arranged to encode the data for transmission along the tether cable 106.

In the embodiments being described in which AC power is transmitted along the cable 106, data are transferred using powerline adapters 120a, 120b (collectivelv/geneally indicated by reference 120) for data over AC transmission, the powerline adapters being one example of a data transmission module. In the embodiments being described, the powerline adapter 120b is lightweight, which may be of particular benefit in UAV applications.

In the embodiments being described in which DC power is transit tted along the cable 106, data are transferred using DC switching voltage data transfer modules.

The skilled person would appreciate that suitable powerline adapters 120a, 120b (alternatively referred to as data modules or data transfer modules) known in the art may be selected according to the tether cable voltage, length and other parameters, for example a Meanwell power supply with a maximum output of 38 V is used in the embodiment being described.

In the embodiments being described, the vehicle unit 108 comprises a data transmission module 120b designed to be fully integrated into the vehicle unit 108. In particular, in AC tether voltage embodiments, a powerline adaptor 120b is wired directly into the vehicle unit 108, so becoming a part of the tether 110.

In the embodiments being described, the powerline adapter 120b is connected in parallel to the main powerlinc within the vehicle unit 108, which may reduce interference with the main power draw.

The vehicle unit 108 is also arranged to provide a 110 V AC buffer to provide power to the powerline adapter 120b if the current draw causes voltage drop meaning the tether 110 would not work and/or that connection dropouts or slow data transfer may occur.

In the embodiments being described, the power unit 104 (which may be described as a ground unit 104, especially in UAV applications) comprises a data module 120a arranged to receive the data and to decode the AC signal. The data module 120a may also be referred to as a powerline adapter 102a.

In the embodiments being described, the data module 120a, 120b is arranged to provide an RJ45 (or other Ethernet) data connection and a WiFi connection. Other connection and connector types may be used in other embodiments. In alternative embodiments, no Ethernet and/or WiFi connection may be provided -this may reduce the chance of interference or remote tampering.

The power unit 104 of the embodiments being described comprises a screen or other output device 122 arranged to display the received data (e.g. a video display of data captured by a vehicle-mounted camera, a graph of measured levels of radioactivity, and/or a marker on a map indicating precise vehicle location).

The power unit 104 of the embodiments being described comprises a port (e.g. a USB port or SD card slot) or other data transfer means (e.g. wired or wireless connection) arranged to allow the data transferred from the unmanned vehicle 102 to be extracted/downloaded.

Command Transfer In the embodiments being described with respect to Figures 1 to 7, the power unit 104 additionally comprises a control interface 122. The control interface 122 may be used to enter commands for the unmanned vehicle 102. Commands may include control of vehicle movement, and/or of vehicle sensors or data capture (e.g. turning camera, starting and stopping filming, or the likes).

In various embodiments, the control interface 122 may be or comprise a push-button interface and/or a graphical or text user interface. The control interface may be provided by a (separable or integrated) portable computer, or the likes connected to the tether 110.

In the embodiments being described, the commands are relayed to the unmanned vehicle 102 via the tether cable 106. The commands may be encoded and transmitted in an equivalent manner to the data transferred from the unmanned vehicle 102 to the power unit 104, as described above. The skilled person would appreciate that commands may be thought of as a class of data and that the same approach to transmission may be applied.

In the embodiments being described, the power unit 104 comprises a command transmission module 120, which may be equivalent to the data transmission module 120 of the vehicle unit 104. The command transmission module and the data transmission module may both be referred to as data modules 120. The command transmission module 120 is designed to be fully integrated into the power unit 104. In particular, in AC tether voltage embodiments, a powerline adaptor is wired directly into the power unit 104, so becoming a part of the tether 110.

In the embodiments being described, the powerline adapter 120 is connected in parallel to the main powerline within the power unit 104, which may reduce interference with the main power draw. The power unit 104 is also arranged to provide a 110 V AC buffer to provide power to the powerline adapter 120 if the current draw causes voltage drop meaning the tether 110 would not work and/or that connection dropouts or slow data transfer may occur.

The control interface 122 of the embodiments being described comprises buttons which are arranged to trigger the sending of control signals to the UAV 102 when used, for example via an integrated computer or other processing circuitry or the likes.

The system 100 may therefore be fully self-contained; no other control interface may be required for the system 100 to work. The unmanned vehicle 102 may therefore be fully powered and controlled via the tether 110.

In the embodiments being described, an autopilot system of the UAV 102 and the ground control system, provided by the power unit 104 comprising a command transmission module 120a, are arranged to use compatible interfaces, for example an IP interface, so the data and/or commands can be sent directly between the UAV 102 and the power unit 104..

The skilled person would appreciate that transferring thc commands via the cable 106 may improve security, for example by reducing the chance of third party interference. In the embodiments being described, all UAV functionality may be controlled via the control interface 122 -no other RF device or the likes may be needed.

In various embodiments, zero, one, or both of data transfer on the tether cable 106 and command transfer on the tether cable 106 may be implemented.

Switching In the embodiments described above, the tether 110 is used in conjunction with an on-vehicle battery (which may form part of the vehicle unit 108 or may be an integral part of the unmanned vehicle 102 to which the vehicle unit 108 is connected). The tether 110 is used to charge the battery. Power draw from the unmanned vehicle 102 may vary over time during vehicle operation -e.g. increasing to cover spikes in load when combatting downthrust from a helicopter flying overhead for a UAV 102, moving against the current for a boat, or against the wind, or moving uphill or moving a load.

In prior art systems without tuning circuits 130, 250, more power would be taken from the battery to cover increased loads, causing the voltage of the battery to drop and the unregulated converters responding to the battery voltage drop could cause the battery to demand a huge amount of power to replace the power used. A resultant voltage spike could reset the converters, causing an oscillation. A relay switch may be used in such systems to help to manage changing power demands and converter re-settings, for example located between the main converter supply and a back-up battery such that if the supply failed the relay would switch to the battery. In many UAV embodiments, in particular helicopter-type UAVs 102, relay switching speed may be too slow to maintain power to the UAV 02, potentially causing the UAV to fall due to a temporary power interruption. Such prior art UAVs may therefore have to land to re-set the converters, so interrupting a mission.

In embodiments with tuning circuits 130, 250, the tuning circuits 130, 250 tune the converters, preventing the instant demand and matching the battery voltage -demand may therefore be slowly increased, resulting in a more gentle change than the spike observed in prior art systems. The more gradual change does not reset the converters, and a voltage oscillation is not set up. The tuning circuit 250 of the vehicle unit 108 may control the current draw, allowing the tether 110 to operate in harmony with the battery -a relay switch may therefore not be necessary.

Using the tuned tether 110 to charge the battery and the battery to power the UAV 102 may therefore facilitate power management as compared to embodiments in which a relay switch is used to switch between use of the tether supply and use of a separate onboard battery. The avoidance of switching may improve reliability by reducing or avoiding the risk of a power cut-out if the switching timing is not sufficiently accurate. In particular, switching speed limitations for the low voltage/high current arrangement may lead to power loss issues in some embodiments using a relay switch (the relay may be too slow, leading to brown-outs, and/or to autopilot systems and motors resetting).

Further, in tether systems in which a relay switch is used, once the power supply has been switched across to the onboard battery from the tether 110 (e.g. to cover a spike in power draw) it may not be possible to switch back without landing the UAV 102 / accessing the unmanned vehicle and resetting it. In the embodiments being described, no relay switch is present in the vehicle unit 108. In alternative embodiments, a tether 110 of an embodiment may be used with a more traditional relay switch circuit on the unmanned vehicle 102.

Overview Tethers 110 of various embodiments balance power output, cable weight, vehicle unit weight and vehicle power demand profile to achieve suitable performance. In various embodiments, the vehicle unit 108 comprises an integrated battery which is arranged to be permanently available to the vehicle 102 and which may assist in providing sufficient power to meet fluctuating demands whilst keeping the power supplied by the tether cable 106 smoother.

The skilled person would appreciate that using previously available tether technologies at a lower voltage of e.g. 250 V or below has been unsuccessful as such a tether is unable to provide the required power to keep a UAV 102 in the air (for example) due to the voltage drop when the current increases.

Use of a dual-core tether cable 106 as described herein allowed for a 75 V power supply (without tuning), but the maximum amount of power deliverable was low, limiting take-off height and weight for a U A V. The usc of a tuning circuit 130 as described herein facilitated provision of the required power whilst overcoming the voltage drop, Even with tuning, fluctuations in the power input to the system 100 could still present issues for power supply smoothness and stability in some embodiments. The skilled person would appreciate that fluctuations in the power input to the system 100 may be insignificant when using, for example, a mains supply, but may have a significant effect when using other supplies, such as a generator. In various embodiments, a battery was incorporated into the vehicle unit 108 to facilitate handling a fluctuating power supply. The battery can therefore take over if the tether power input falls, and may absorb and provide power as nccdcd to maintain a steady supply.

Claims

CLAIMS1. A tether (110) for a vehicle (102), the tether (110) comprising: a tether cable (106); a power unit (104) arranged to supply power to the tether cable (106); and a vehicle unit (108) arranged to be located on the vehicle (102), to receive power from the tether cable (106) and to adjust voltage of the received power to a suitable level for use by the vehicle (102); wherein the tether cable (106) extends between the power unit (104) and the vehicle unit (108), and has a voltage of between 70 V and 250 V.
2. The tether (110) of Claim 1, wherein the tether cable (106) has a length of at least 10 m, and preferably at least 25 in.
3. The tether (110) of Claim 1 or Claim 2, wherein the tether (110) is arranged to supply a continuous power of at least 0.8 kW to the vehicle (102).
4. The tether (110) of any preceding claim, wherein the tether cable (106) has a voltage of 110 V or below, and wherein optionally the voltage is an AC voltage.
5. The tether (110) of any preceding claim, wherein the tether cable (106) has a voltage of 75 V or below, and wherein optionally the voltage is a DC voltage.
6. The tether (110) of any preceding claim, wherein the tether cable (106) has an AC voltage and the vehicle unit (108) comprises an AC to DC converter arranged to convert the AC tether voltage to DC for use onboard the vehicle (102).
7. The tether (110) of any preceding claim, wherein the vehicle unit (108) is a solid state vehicle unit (108) having no moving parts, and optionally wherein the vehicle unit (108) is arranged to be cooled by airflow generated by one or more rotors of the UAV (102); and no cooling system is provided as part of the vehicle unit (108).
8. The tether (110) of any preceding claim, wherein the tether cable (106) is a two-core copper cable, each copper core (106a. 106b) having a diameter of between 1.5 nun and 10 mm, and optionally around 1.75 mm, 2 mm, or 2.5 mm, and wherein optionally each core (106a, 106b) of the tether cable (106) is coated with a layer of silver.
9. The tether (110) of Claim 8 wherein each core (106a; 106b) of the tether cable (106) is coated with a resilient material (105a; 105b); and wherein a further layer (103) of a resilient material is provided around the two coated cores (106a, 106b).
10. The tether (110) of any preceding claim, wherein the tether cable (106) has a weight per unit length of less than 0.06 kg/m, and optionally of: (1) 0.02 kg/m, and is arranged to carry power of 0.8 kW or more; (ii) 0.03 kg/m, and is arranged to carry power of 1.6 kW or more; or (iii) 0.05 kg/m, and is arranged to carty power of 2.4 kW or more.
11. The tether (110) of any preceding claim, wherein the power unit (104) is arranged to be connected to a mains power supply.
12. The tether (110) of any preceding claim, wherein the vehicle unit (108) is arranged to step down the tether cable voltage to a voltage suitable for use by the vehicle (102), and wherein optionally the voltage suitable for use by the vehicle (102) is less than or equal to 48 V.
13. The tether (110) of any preceding claim, wherein the tether voltage is a DC voltage, and wherein the power unit (104) is arranged to sense current drawn through the tether cable (106) and to adjust the voltage to account for voltage drop along the cable (106) accordingly.
14. The tether (110) of claim 13 wherein the power unit (104) comprises a tuning circuit (130) arranged to automatically adjust power output to the tether cable (106) based on the sensed current.
15. The tether (110) of any preceding claim wherein the vehicle unit (108) comprises a plurality of converters (200), and wherein each converter (200) has a tuning circuit (250) arranged to automatically adjust output of the corresponding converter (200) based on the output voltage.
16. The tether (110) of Claim 15 wherein the tuning circuits (250) of the converters (200) are coupled together and arranged to automatically perform load balancing between the converters (200).
17. The tether (110) of any preceding claim, wherein the tether (110) is a tether for an unmanned vehicle, and optionally is an Unmanned Aerial Vehicle (UAV) tether.
18 A vehicle system (100) comprising: a vehicle (102); and a tether (110) comprising a tether cable (106); a power unit (104) arranged to supply power to the tether cable (106); and a vehicle unit (108) arranged to be located on the vehicle (102), to receive power from the tether cable (106) and to adjust voltage of the received power to a suitable level for use by the vehicle (102); wherein the tether cable (106) extends between the power unit (104) and the vehicle unit (108), and has a voltage of between 70 V and 250 V.
19. The vehicle system (100) of Claim 18 wherein the tether (110) is as described in any of Claims 1 to 17
20. Thc vehicle system (100) of Claim 18 or Claim 19 wherein the vehicle is an unmanned vehicle (102); and optionally is a UAV (102).
21. The vehicle system (100) of Claim 20 wherein the UAV (102) is a rotorcraft comprising one or more rotors, and airflow generated by the one or more rotors of the UAV (102) is arranged to provide the only cooling to the vehicle unit (108).
22. A tether (110) for a vehicle (102), the tether (110) comprising: a tether cable (106), the tether cable (106) being a two-core copper cable, each copper core (106a, 106b) having a diameter of between 1.5 mm and 3.0 mm and being coated with a layer of silver; a power unit (104) arranged to supply power to the tether cable (106); and a vehicle unit (108) arranged to be located on the vehicle (102), to receive power from the tether cable (106) and to adjust voltage of the received power to a suitable level for use by the vehicle (102), and wherein the tether cable (106) extends between the power unit (104) and the vehicle unit (108).
23. The tether (110) of claim 22. wherein each copper core (106a. 106b) has a diameter of 1.75 mm, 2 mm, or 2.5 mm.
24. The tether (110) of Claim 22 or Claim 23 wherein each core (106a, 106b) of the tether cable (106) is coated with a resilient material (105a, 105b), and wherein a further layer (103) of a resilient material is provided around the two coated cores (106a, 1061)).
25. The tether (110) of any of Claims 22 to 24, wherein the tether cable (106) has a weight per unit length of less than 0.06 kg/m.