Unmanned aerial vehicle system with dual UAV control and its operating method

Abstract

The invention is an unmanned aerial vehicle (UAV) system with dual UAV control, the system comprising an UAV having a tethered flight mode, and a tethered power supply unit (11) connected to a tether (10) and to the UAV when the UAV is in its tethered flight mode. The UAV comprises a first flight controller (20) and a first set of rotor units, a second flight controller (30) and a second set of rotor units, as well as an on-board battery (40) with a battery management system (41). The tethered power supply unit (11) comprises a supply voltage output (12) supplying operating voltage for the first flight controller (20) and the first set of rotor units, and a charging current output (13) supplying charging current for the on-board battery (40), the on- board battery (40) supplying operating voltage for the second flight controller (30) and for the second set of rotor units.

Description

[0001] UNMANNED AERIAL VEHICLE SYSTEM WITH DUAL UAV CONTROL AND ITS OPERATING METHOD

[0002] TECHNICAL FIELD

[0003] The invention relates to an unmanned aerial vehicle (UAV) system with dual UAV control, which system comprises an UAV, such as a drone, having a tethered flight mode. The invention also relates to a method for operating the unmanned aerial vehicle system.

[0004] BACKGROUND ART

[0005] UAVs may be utilized for many different purposes, for example for carrying out observation tasks by means of onboard sensors. The acquired data may be transmitted to a ground station. UAVs are usually powered by an onboard battery which is required to supply power for both propulsion, onboard sensors and other electronics.

[0006] A drone controller is usually responsible for carrying out flight operations. It does this by using sensors to measure its own position and orientation in space, and by calculating how to control the actuators to move the drone towards a desired target position, which is determined by an operator or a machine. These computations are usually performed by a processor running autopilot software, which coordinates various subtasks.

[0007] Drones can also pose a direct threat to people and property in the event of a malfunction or disturbances, such as wind or rain, which is a major safety risk. Drone controller failure can result from many sources, all of which will usually result in loss of control of the drone. Examples include a short circuit in the battery, a sensor malfunctioning and giving wrong readings, causing the drone controller to fail to control the actuators properly, or a failure of the actuator or motor itself. In general, civil drones are not immune to this. There are drones in military applications or other safety-critical services that are protected against component failure by multiplying the components.

[0008] Redundant controllers in drones provide a range of advantages, ensuring reliability, safety, and performance, especially in critical applications. Redundant flight controllers enhance the drone's safety by providing a backup in case of failure of the primary controller. If one controller fails due to hardware issues or a software malfunction, the secondary controller can take over, allowing the drone to continue its flight without crashing. This is crucial for commercial, industrial, and military drones where mission success is critical, and failure could lead to significant loss or damage, or in situations where the drone is operating in hard-to-reach areas. Redundant controllers often come with systems for continuous monitoring of both the primary and backup controllers. These systems can detect anomalies or potential issues before they lead to failure, allowing for preventative maintenance and ensuring the drone's systems remain operational.

[0009] UAVs with redundant controllers or components are disclosed e.g. in US 9,828,107 B1 , WO 2022 / 115132 A1 and GB 2613298 A.

[0010] Redundant controllers, however, come with their own set of disadvantages. The integration of multiple controllers increases the overall complexity of the drone’s design and systems. Extra controllers mean additional weight, which can reduce the drone’s overall payload capacity, flight time, and efficiency. This is particularly important in applications where weight is a critical factor, such as for racing drones or drones with small payloads. Furthermore, running multiple controllers requires more power. This can lead to a reduction in battery life, as more energy is consumed to support the redundant systems. This trade-off may be problematic for drones operating in remote areas where recharging or replacing batteries is difficult.

[0011] In case of additional, i.e. dual or redundant flight controllers, the additional power consumption shortens battery life and the maximum mission length for the UAV. One solution to extend mission length is to power the UAVs via a tether deployed from a ground station during their operation. Of course, mission flight area is restricted in such cases based on the length of the filament. Tethered UAVs are disclosed e.g. in US 10,926,890 B2, US 10,703,474 B2, US 11 ,174,021 B2 and CN109835491 A.

[0012] The problem with tethered UAV solutions is that the dynamic thrust needed for UAV maneuvering and counteracting external forces, such as wind and gust, results in power flow peaks which are to be handled by the tethered power supply unit of the UAV. As the tethered power supply units necessarily comprise an electronic converter for converting a tether voltage to the operating voltage of the UAV components, the electronic converter should also be able to handle such power flow peaks. Typical tether voltage levels can be around a few hundred Volts DC to limit power loss on the tether, while UAV components usually need less than one hundred Volts DC.

[0013] Power flow fluctuations can have several negative effects on voltage converters, potentially leading to reduced efficiency, reliability, and longevity. When power fluctuations occur, the voltage converter may work harder to adjust and compensate for the changes, resulting in excessive heat generation. Over time, this increased thermal load can damage internal components, degrade efficiency, and reduce the overall lifespan of the converter. Large fluctuations may push the converter out of its optimal operating range, leading to energy losses as the converter tries to regulate the output. This inefficiency can also cause additional heat buildup. Fluctuating power can subject the internal components of the converter (such as capacitors, inductors, and semiconductors) to stress. This can result in premature wear or even failure of these components. Furthermore, power fluctuations, especially if they result in large surges or drops, can cause the output of the voltage converter to either exceed or fall below the required voltage levels for downstream devices. This can damage sensitive electronics or cause them to operate improperly.

[0014] Such fluctuations are usually handled by temporary power storage solutions in voltage converters. Temporary power storage enables the voltage converter to respond quickly enough to maintain a stable output. Energy storage components (such as batteries or capacitors) provide a buffer, absorbing excess energy during low demand and supplying it during peak demand, thereby smoothing out these transients. Storing energy temporarily allows the converter to operate more efficiently during steady-state conditions, without needing to constantly overproduce energy to account for possible peaks. By only supplying the peak load when necessary, the converter can run closer to its optimal efficiency most of the time.

[0015] However, temporary power storage in voltage converters represent a weight penalty. As higher is the capacity of such temporary power storage, as higher is the additional weight of the tethered power supply unit of the UAV, thereby reducing efficiency of the system.

[0016] A continuing need exists for improvements of unmanned aerial vehicles for a variety of applications. There is a special need for a solution that enables in a tethered flight mode to combine the advantages of battery-powered control and propulsion with tether-powered control and propulsion by dividing these into two separately controllable propulsion.

[0017] DISCLOSURE OF INVENTION

[0018] It is an object of the invention to provide an unmanned aerial vehicle system and a method for its operation that eliminate disadvantages of prior art solutions as much as possible. Another object of the invention is to provide a solution that enables in a tethered flight mode to combine the advantages of battery-powered control and propulsion with tether-powered control and propulsion by dividing these into two separately controllable propulsion. It is a further object of the invention to provide an unmanned aerial vehicle system and a method for its operation that eliminate the need of a large capacity temporal power storage in voltage converters of tethered power supply units, thereby improving efficiency.

[0019] The above and other objects have been achieved by the unmanned aerial vehicle system according to claim 1 , by the method according to claim 9. Preferred embodiments are defined in the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0020] Characteristics, objectives, and advantages of embodiments of the subject matter will become apparent from the following description, which is given solely by way of illustration, is non-limiting, and is to be read with reference to the appended drawings in which

[0021] Fig. 1 schematically illustrates an unmanned aerial vehicle system according to a preferred embodiment of the invention, and

[0022] Fig. 2 schematically illustrates flowcharts of a dual control applicable in the invention.

[0023] MODES FOR CARRYING OUT THE INVENTION

[0024] The subject matter disclosed herein comprises an UAV system with dual UAV control, the system comprising an UAV having a tethered flight mode and a tethered power supply unit. The latter is connected to a tether and to the UAV when the UAV is in its tethered flight mode. Embodiments can include controlled operation of the UAV via the tether, with which power, control and communication signals are transmitted to and from the unmanned aerial vehicle.

[0025] Fig. 1 schematically illustrates an unmanned aerial vehicle system according to an embodiment of the invention. The UAV system has a dual UAV control, as detailed below. The system comprises an UAV having a tethered flight mode and a tethered power supply unit 11. The latter is connected to a tether 10 and to the UAV when the UAV is in its tethered flight mode.

[0026] The tethered power supply unit 11 is a module that receives the tether 10 or cable from a ground station, is attached to the UAV, converts a tether voltage and charges an on-board battery 40. It preferably fits in place of an additional battery.

[0027] The UAV or drone is connected to the ground station by a long tether 10 or cable through which it can receive power and transmit live data from the drone e.g. camera stream and may receive mission tasks or direct maneuvering commands. An additional benefit of this approach is that it guarantees that the communication remains secure, uninterrupted, and resistant to both external interference (jamming) and eavesdropping from remote sources, since it does not rely on radio frequency communication.

[0028] In order to provide the dual control functionality, the UAV comprises a first flight controller 20 and a first set of rotor units, as well as a second flight controller 30 and a second set of rotor units. In the given example there are four rotor units in both sets.

[0029] In the first set of rotor units, each rotor unit comprises an electronic speed controller (ESC) 22 controlled by the first flight controller 20, a motor (not depicted) driven by the ESC 22 and a rotor (not depicted) rotated by the motor. Similarly, in the second set of rotor units, each rotor unit comprises an ESC 32 controlled by the second flight controller 30, a motor driven by the ESC 32 and a rotor rotated by the motor.

[0030] Each ESC 22, 32 is an electronic circuit that connects the respective motor, the respective power supply and the respective flight controller 20, 30. The primary purpose of ESCs 22, 32 is to directly control motor speed and direction.

[0031] The first flight controller 20 communicates with the respective ESCs 22 via a communication line 21 which is preferably a bidirectional and differential line, e.g. a CAN (Controller Area Network) line. Similarly, the second flight controller 30 also communicates with the respective ESCs 32 via a communication line 31 which is preferably a bidirectional and differential line, e.g. a CAN (Controller Area Network) line. The communication lines 21 and 31 are attached to respective ESC communication interfaces 23, 33 and to respective controller communication interfaces.

[0032] Typically, two types of tasks run on the first and second flight controllers 20, 30: one is safety-critical (e.g. reading stability sensor data, control algorithms, actuator control) and the other is all other (e.g. trajectory tracking, communication with ground station, mission task execution). The safety-critical tasks preferably run on a dedicated, separate respective safety processor 25, 35 inside the SoC unit, which are duplicated in themselves. The safety processors 25, 35 preferably also include a sensor handling unit 26, 36, a GNNS (Global Navigation Satellite System) unit 27, 37, and controller communication interfaces 28, 38.

[0033] The tethered power supply unit 11 comprises a supply voltage output 12 supplying operating voltage for the first flight controller 20 and for the ESCs 22 of the first set of rotor units via their respective DC interfaces 24. This feed is depicted with dashed double lines in Fig. 1 .

[0034] The UAV also comprises an on-board battery 40 with a battery management system 41 . The battery management system 41 is also responsible for protecting the battery and the external system. It protects against overvoltage, overcurrent, overcharging, deep discharge and monitors cell voltages. The tethered power supply unit 11 also comprises a charging current output 13 supplying charging current for the on-board battery 40 via its DC interface 42. The on-board battery 40 supplies operating voltage for the second flight controller 30 and for the ESCs 32 of the second set of rotor units via their respective DC interfaces 34. This feed is depicted with dotted double lines in Fig. 1 .

[0035] The two power supplies can be connected via a power distribution unit 70 by means of a manual switch 71 , if required or in an emergency situation, allowing operation from a single power supply, i.e. also without the tethered power supply unit 11. In this case, safety-critical operation is not possible, but in a fault-free state, it is possible to fly with a single power supply. The power distribution unit 70 may also provide signals to the controllers via lines 72 and 73 indicating the presence or absence of correct voltage levels.

[0036] The above separation of voltage supply for the two control / drive part enables in a tethered flight mode to combine the advantages of battery-powered control and propulsion with tether-powered control and propulsion. The division into two separately controllable propulsion enables to achieve a more efficient power distribution, to which the electronic circuits, such as converters, power storage components can be more efficiently dimensioned. Furthermore, the presence of two independent DC power supplies increase safety. In an especially preferred embodiment, in said tethered flight mode the first set of rotor units is controlled by the first flight controller 20 to produce a static thrust which serves to maintain an UAV position or steadily moving the UAV, and the second set of rotor units is controlled by the second flight controller 30 to produce a dynamic thrust that serves to manoeuvre the UAV and / or counteract external forces. In this way, power flow fluctuations can be kept at a minimum on the tethered power supply unit, thereby expanding its lifetime and reducing its weight due to reduced temporal power storage needs.

[0037] In this operational mode, the system offers the option to use the power delivered through the cable to provide static thrust to the machine. This is beneficial because it helps stabilize the power flow by reducing large fluctuations and eliminating local power peaks. By managing these fluctuations, the need for large local energy storage at the electronic converter at the end of the cable is minimized, leading to more efficient power distribution and storage. Essentially, the system can rely on the continuous power from the cable to maintain a stable thrust without overloading the local energy storage.

[0038] At the same time, the dynamic loads required for maneuvering or counteracting external forces, such as wind and gust, are managed by the on-board battery 40. The configuration can be designed so that four motors on one unit handle the primary thrust needed for the system to maintain its position or move steadily, while four motors on the other unit are responsible for the dynamic control, including adjustments for wind resistance or changes in direction. This allows precise control of the drone's movement and stability in varying conditions.

[0039] Moreover, in this mode, the on-board battery 40 is not just supplying dynamic power but can also be charged while the system is operating in the cabled or tethered mode. This is particularly advantageous as it ensures that the on-board battery 40 remains adequately charged for dynamic power needs, thus enabling continuous operation over extended periods without the need for frequent recharging breaks. It is pointed out that charging the on-board battery 40 never results in power load peaks for the tethered power supply unit 11 , so the above-described hybrid powering eliminates power peak loads on the tethered power supply unit 11 entirely. If needed the cable can be ejected from the drone and the converter can bypass the battery to this (cable side) in order to power both sides of the system.

[0040] The tethered power supply unit 11 typically comprises an electronic converter for converting a tether voltage to the operating voltage supplied via the supply voltage output 12. The electronic converter usually comprises a local energy storage unit for stabilizing power flow. The local energy storage may consist only of one or more capacitors, i.e. can be simple and light, due to the reduced temporal power storage needs. More specifically, due to the even energy flow and to the lack of current fluctuation, it is sufficient to put only a few larger capacitors at the output of the power supply. If the motors with dynamic thrust were to be applied to this power supply, they could not be covered by capacitors alone, some kind of battery would have to be added to the converter output to handle these surges. An additional battery would result extra weight and volume, which has been avoided by this inventive embodiment.

[0041] Preferably, the UAV comprises at least one communication line 50, 51 between the first flight controller 20, the second flight controller 30, the tethered power supply unit 11 and the battery management system 41 of the on-board battery 40. The communication lines 50 and 51 are connected to respective communication interfaces of the first and second flight controllers 20, 30, to respective communication interfaces 43, 44 of the battery management system 41 , and to respective communication interfaces 15, 16 of the tethered power supply unit 11. The communication lines 50, 51 are preferably high-speed redundant communication lines, e.g. CAN, ethernet, RS485 or similar lines between components. Further communication lines, like communication line 53 for allowing a direct communication between the first and second flight controllers 20, 30 via their respective communication interfaces 28 and 38 can also be included.

[0042] The tethered power supply unit 11 may further comprise a tether communication connector 14, and the UAV may comprise a tether communication line 53 connected to the tether communication connector 14 and to at least one of the first flight controller 20 and the second flight controller 30. In this way, the UAV can be controlled from the ground station and UAV sensor data can be transmitted to the ground station.

[0043] Preferably, the UAV is formed with a battery insertion opening or cradle, into which the tethered power supply unit 11 is inserted and secured. If the UAV is not in a tethered flight mode, the tethered power supply unit 11 can be replaced by a second battery 60 with a respective battery management system 61 , which is denoted with a double arrow.

[0044] The invention also relates to a method for operating the above-described system. The method comprises the steps of dividing a total thrust to be produced by the rotors into

[0045] - a static thrust serving to maintain an UAV position or steadily moving the UAV, and controlling the first set of rotor units by the first flight controller 20 to produce said static thrust, and

[0046] - a dynamic thrust serving to manoeuvre the UAV and / or counteract external forces, and controlling the second set of rotor units by the second flight controller 30 to produce said dynamic thrust.

[0047] The division of the total thrust is preferably carried out by means of a predetermined threshold change rate of the thrust. The static thrust is then the part of the total thrust the change rate of which is (equal or) below the threshold change rate, while the dynamic thrust is the part of the total thrust the change rate of which is (equal or) above the threshold change rate. In a preferred embodiment the threshold change rate is zero, i.e. the static thrust is the constant part of the total needed thrust. Practically, the division of the static and dynamic parts is carried out with respect to a time window, the time span of which is selected according to the actual circumstances. Preferably, the static thrust is distributed evenly on the first set of rotor units by the first flight controller 20. The step of dividing the total thrust is preferably carried out at the ground station and information relating to the division is communicated with the UAV via the tether 10.

[0048] Alternatively, the step of dividing the total thrust can carried out by

[0049] - the first flight controller 20 and information relating to the division is communicated with the second flight controller 30,

[0050] - the second flight controller 30 and information relating to the division is communicated with the first flight controller 20, or

[0051] - in a cooperation of the first flight controller 20 and of the second flight controller 30.

[0052] As can be seen in Fig. 1 , the concept of the inventive UAV control is based on full redundancy in terms of control and propulsion. The advantage is that although it seems complex, it can be installed even in a very small UAV or drone due to the possibility to realize the control units as SoC (System on a Chip) circuitry, which can perform a number of functions in a small size on a single chip, such as sensor data scanning, environment sensor algorithms execution, Al algorithms execution, perception based localization, sensor signal compression, data encryption, communication management, trajectory planning, running real-time control algorithms, real-time communication with sensors and interferes for stability, which can result in a very small controller card size. The complete system can fit in a drone with a total weight of less than 4kg.

[0053] Fig. 2 schematically illustrates flowcharts of a dual control applicable in the invention. The two independent drone controllers work side by side which is represented by the two flowcharts. During normal operation in steps 100 and 200, the two systems communicate with each other and work together. This is maintained as long as no failure is detected in steps 101 and 201 , and the other controller is working, which is checked in steps 102 and 202. However, if a (critical) failure is detected in steps 101 or 201 in either of them, which means that the stand-alone part cannot guarantee safe operation, the system checks in steps 103 and 203 whether the other controller is working, and if yes, the controller shuts down in steps 104 and 204. After the shutdown of the failed complete unit the functional unit takes over to provide full functionality. Even in the event of a complete failure of one of the components, the system will have sufficient performance and functionality to ensure safe task performance. If the check in steps 102 and 202, or in steps 103 and 203 provides the result that the other controller is not working, the UAV aborts the execution of the task by an emergency landing in step 105 and 205.

[0054] The control can also take the form of a primary-secondary or master-slave scenario. The primary or master set of rotor units is normally controlled by the primary or master controller. The secondary controller controls the secondary drive according to the instructions of the primary controller, while also calculating itself according to its own sensors and algorithms. If it finds a discrepancy or inconsistency, it alerts the primary controller.

[0055] The inventive system can be used e.g. in reconnaissance applications, surveying road sections e.g. to assist rescue services, tracking and monitoring people, disaster management, to assist fire brigades. In addition, it can also provide a practical solution for safety-critical drones, e.g. for home delivery ones.

[0056] The ground station (not depicted) may have a tether rewind system, a landing platform, a communication and data processing system for sending data to and receiving data from the UAV on the tether 10, and a galvanically isolated DC / DC converter converting a ground station voltage level to the tether voltage level for supplying voltage on the tether 10.

[0057] The ground station can be a vehicle, e.g. passenger car, truck, military vehicle, unmanned ground vehicle, watercraft, in which case the galvanically isolated DC / DC converter converts an on-board voltage level to the tether voltage level. A vehicle nominal voltage is typically either 12 V DC or 24 V DC supplied by on-board batteries, while the tether nominal voltage level is preferably within a DC range of 400 V to 600 V, more preferably 500 V DC or 550 V DC, to keep the tether mass and the tether cable heat dissipation on a low level. The tether rewind system may have an automatic tether tensioner system and a winch system comprising a tether force measurement system and a tether angle measurement system. The automatic tether tensioner system and the tether rewind system can be activated either by the ground station or by the UAV.

[0058] The communication and data processing system is preferably a high-speed communication and data processing system which sends / receives data to / from the UAV and has remote connection with other ground stations. The communication is preferably done on a bidirectional fiber optic line of the tether 10.

[0059] This written description uses examples to disclose the subject matter, and also to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Portions of the embodiments of the present invention may be provided as one or more computer- readable programs or code embodied on or in one or more non-transitory media.

Claims

CLAIMS1 . An unmanned aerial vehicle (UAV) system with dual UAV control, the system comprising an UAV having a tethered flight mode, and a tethered power supply unit (11 ) connected to a tether (10) and to the UAV when the UAV is in its tethered flight mode, wherein the UAV comprises- a first flight controller (20) and a first set of rotor units, each rotor unit comprising an electronic speed controller (ESC) (22) controlled by the first flight controller (20), a motor driven by the ESC (22) and a rotor rotated by the motor,- a second flight controller (30) and a second set of rotor units, each rotor unit comprising an ESC (32) controlled by the second flight controller (30), a motor driven by the ESC (32) and a rotor rotated by the motor, and- an on-board battery (40) with a battery management system (41 ), and wherein the tethered power supply unit (11 ) comprises- a supply voltage output (12) supplying operating voltage for the first flight controller (20) and for the ESCs (22) of the first set of rotor units, and- a charging current output (13) supplying charging current for the on-board battery (40), the on-board battery (40) supplying operating voltage for the second flight controller (30) and for the ESCs (32) of the second set of rotor units.

2. The system according to claim 1 , wherein in said tethered flight mode- the first set of rotor units is controlled by the first flight controller (20) to produce a static thrust serving to maintain an UAV position or steadily moving the UAV, and- the second set of rotor units is controlled by the second flight controller (30) to produce a dynamic thrust serving to manoeuvre the UAV and / or counteract external forces.

3. The system according to claim 2, wherein the tethered power supply unit (11 ) comprises an electronic converter for converting a tether voltage to the operating voltage supplied via the supply voltage output (12).

4. The system according to claim 3, wherein the electronic converter comprises a local energy storage unit for stabilizing power flow.

5. The system according to claim 4, wherein the local energy storage consists of one or more capacitors.

6. The system according to any of claims 2 to 5, wherein the UAV comprises at least one communication line (50, 51 ) between the first flight controller (20), the second flight controller (30), the tethered power supply unit (11 ) and the battery management system (41 ) of the on-board battery (40).

7. The system according to any of claims 2 to 6, wherein the tethered power supply unit (11 ) further comprises a tether communication connector (14), and the UAV comprises a tether communication line (53) connected to the tether communication connector (14) and to at least one of the first flight controller (20) and the second flight controller (30).

8. The system according to any of claims 2 to 7, wherein the UAV is formed with a battery insertion opening or cradle, into which the tethered power supply unit (11 ) is inserted and secured.

9. A method for operating a system according to any of claims 2 to 8, comprising the steps of dividing a total thrust to be produced by the rotors into- a static thrust serving to maintain an UAV position or steadily moving the UAV, and controlling the first set of rotor units by the first flight controller (20) to produce said static thrust, and- a dynamic thrust serving to manoeuvre the UAV and / or counteract external forces, and controlling the second set of rotor units by the second flight controller (30) to produce said dynamic thrust.

10. The method according to claim 9, wherein the step of dividing the total thrust is carried out by means of a threshold change rate of the thrust, and the static thrustis the part of the total thrust the change rate of which is below the threshold change rate, while the dynamic thrust is the part of the total thrust the change rate of which is above the threshold change rate.

11. The method according to claim 9, wherein the static thrust is distributed evenly on the first set of rotor units by the first flight controller (20).

12. The method according to claim 9, wherein the step of dividing the total thrust is carried out at a ground station and information relating to the division is communicated with the UAV via the tether (10).

13. The method according to claim 9, wherein the step of dividing the total thrust is carried out by- the first flight controller (20) and information relating to the division is communicated with the second flight controller (30),- the second flight controller (30) and information relating to the division is communicated with the first flight controller (20), or- in a cooperation of the first flight controller (20) and of the second flight controller (30).

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