Wireless charging system for unmanned aerial vehicles

Abstract

The invention relates to a wireless energy transmission system suitable for installation on high-voltage transmission lines for the purpose of charging the batteries of unmanned aerial vehicles (UAVs). A wireless charging system for UAVs uses a high-voltage transmission line fastened to pylons. Mounted on each pylon is a crossarm, and mounted on each crossarm is a bracket. Suspended from the bracket and connected successively one above another are insulators, and suspended from the bottom insulator is a high-voltage transmission line. Mounted on the line itself is a single-phase autotransformer, an output of which is connected to an input of a diode bridge with a filter capacitor, an output of which is connected to a full-bridge inverter that converts direct current into high-frequency alternating current. Mounted on each insulator is an intermediate transformer in the form of a planar coil with a film capacitor that transmits a high-frequency induced current to an upper receiving coil mounted on a UAV. The receiving coil has a circuit in the form of a diode bridge with an LC resonator, which is coupled to a rechargeable battery of the UAV. The UAV is designed to be capable of landing on a platform attached to the bracket. The invention makes it possible to transmit energy to a UAV without the use of wires.

Description

[0001] WIRELESS CHARGING SYSTEM FOR UNMANNED AERIAL VEHICLES

[0002] FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0003] The claimed system relates to a wireless power transmission (WPT) system suitable for installation on high-voltage transmission lines (HVTL) to power the BILA battery.

[0004] TECHNOLOGY MATURITY LEVEL (ANALOGUE CHARACTERISTICS, PROTOTYPE CHARACTERISTICS)

[0005] To date, WPT technology embedded in string insulators is still in its early stages and is not yet commercially available or widely implemented in practical applications. The industry still requires further refinement, standardization and validation before it reaches a mature commercial stage.

[0006] In order for this technology to reach maturity, several challenges need to be addressed. These challenges include efficient power transmission over long distances and minimizing energy loss due to the large amount of induced eddy currents within the metal parts of the string insulator. Continuous research and efforts have been made to improve the technology, optimize power transmission efficiency, and eliminate any technical issues or limitations.

[0007] This application discusses a domino resonant inductive power transmission system (DR-IPT) embedded in glass disc type insulators (MIC designation: U70B / 146). Therefore, this method is used to transmit the power of the transmission line from the conductor to the top of the tower until the drone can simply fly over it, which can convert the low-frequency 50 Hz AC transmission signal into a high-frequency signal for the resonant WPT.

[0008] A comprehensive numerical (constrained) optimization was proposed to optimize the full independent design parameters (IDP) of DR-IPT (real-class) embedded systems. Existing prototypes have limited functionality focused on verifying the fundamental principles and basic power transmission capabilities.

[0009] The initial prototype was developed to demonstrate the feasibility of WPT using the domino method and embedding it into isolators. We successfully embedded the WPT system inside a string insulator. We thoroughly tested the entire procedure, which includes both the embedded WPT technology and the drone charging process. As a result, our invention demonstrated a functional and viable proof of concept, showing that the WPT system can efficiently transfer energy to charge a drone while mounted on a string insulator. Future developments may focus on scalability considerations, exploring ways to implement the technology in various practical scenarios, and optimizing it for mass production and deployment.

[0010] Future developments may focus on scalability considerations, exploring ways to implement the technology in various practical scenarios, and optimizing it for mass production and deployment.

[0011] PURPOSE OF THE INVENTION

[0012] Unmanned aerial vehicles (UAVs) have recently become popular for various applications around the world. The use of UAVs for various tasks will save huge amounts of energy, reduce labor costs, replace manual human monitoring with machine monitoring, and even facilitate access to hard-to-reach areas such as toxic environments. However, the most significant application of UAVs in the very near future may be in law enforcement.

[0013] Drones can simply act as police assistants and inspect the situation throughout the city and suburbs. Sending information to the police monitoring center using Skynet (4G / 5G) will be one of the future tasks for drones. However, the battery capacity of a medium-sized drone limits its flight range and duration, especially when the drone wants to send and receive data. Therefore, to encourage the use of drones for routine monitoring operations, it is essential to improve the power supply system of drones and solve the charging problem.

[0014] A major technical problem currently faced by modern unmanned aerial vehicles is insufficient battery capacity. Available methods for increasing the flight time of an unmanned aerial vehicle can be divided into two categories: (i) increasing the battery capacity; and (ii) periodically charging the battery from an external power source. Current battery material manufacturing technologies offer limited options for increasing battery capacity. In particular, the battery may be excessively large or heavy, or the material from which the battery is made may be too expensive to be used.In this application, a new domino-structured wireless charging system (WCS) is designed, implemented and embedded into isolators, allowing a UAV to safely approach a power transmission or distribution line and wirelessly charge its battery energy storage system (BESS) from always-on power when required.

[0015] MAIN STRENGTHS OF THE INVENTION

[0016] The flight time of a typical small-sized unmanned aerial vehicle that can be used for monitoring does not exceed 30-40 minutes. In practice, there are two options for increasing the flight time. The first is to increase the battery capacity, which is a very limited option given the current state of battery material manufacturing technology. More precisely, the battery may be too large for the drone to fly, or the material from which the battery is made may be too expensive to deploy. The second option for extending the service life of the unmanned aerial vehicle is to periodically charge the battery from an external power source, such as 1-installation of a solar photovoltaic array, II-laser radiation, 111-takeoff by a gust of wind, IV-wireless charging, V-fuel cells, and VI-installation of the drone over a high-voltage grid, a power line.

[0017] A closer look at existing methods shows that most of them are seriously limited in terms of applicability.

[0018] The installation of a photovoltaic cell on an unmanned aerial vehicle, presented in US 2018 / 0029477 A1, is considered a mature and well-developed technology. Its design principles are well known, and the flight time of this approach is impressive - more than 24 hours of continuous flight. However, this method has several accompanying features that limit its scope of application. Specifically, the biggest drawback is the fact that this method can only be implemented on unmanned aerial vehicle models with a certain architecture. For example, in fixed wings models with a fixed wings architecture, which has a sufficient wingspan to install solar cells. This, in turn, means that multi-rotor drones, which are widely used today, will not be able to benefit from it.In addition, solar cells can only power the drone or charge its battery in the presence of the sun, which means that it is important to include an auxiliary propulsion system in case of insufficient solar radiation or no sun in cloudy weather or in the evening. This, on the other hand, will increase the weight of the drone and the power required to propel it, and in turn, will also reduce the flight duration. Moreover, the fixed-wing architecture is inferior to multi-rotor drones in terms of maintaining the drone's position. In other words, a fixed-wing drone must always move forward to be able to fly, while multi-rotor drones can perform horizontal flights and maintain a stable position.This exercise is very important for some of the proposed applications, especially for surveillance, monitoring and police assistance, where the drone needs to not only fly over an area of ​​interest, but also perform stationary flights at a specific location and for a specific period of time.

[0019] The patent for laser irradiation, presented in US 2016 / 0079810 A1, is one of the widely used methods for increasing the flight endurance of an unmanned aerial vehicle and is called laser irradiation. It uses lasers to transmit energy from a power source to a drone equipped with a specially designed small photovoltaic cell. Once the drone’s battery is depleted, it must return back to a mobile power source, which is usually located near the mission site. A laser transmitter mounted on the power source directs energy to the drone, which flies around it until the battery is fully charged and then resumes its work. Laser irradiation is a way to increase mission endurance, which is relatively often used in military surveillance and reconnaissance missions.The disadvantage is that the power source must be mobile and always close to the drone. In addition, the use of lasers is limited in some places and can pose a danger to surrounding cars, buildings, and living beings. We can emphasize that the main advantage of this technology is its high reliability, due to the fact that the power source is always relatively close to the drone and the charging process is very efficient. However, transporting a mobile supply unit operated by a group of specially trained people with a drone significantly limits the possibility of its deployment. In fact, this approach should only be used in cases where it is dangerous for people to work, such as military operations or rescue operations in disaster areas, etc.Moreover, laser radiation is closely associated with the use of high-intensity beams that are harmful to unprotected objects, including people.

[0020] Drones that operate in gust hover mode use airflow to adjust the position of their wings and body. Due to the variable nature of wind resources, this technique is not always available. Additionally, a drone in gust hover mode must always follow a specific trajectory to obtain energy, which in turn means that it will not be suitable for certain missions, especially those that involve long-term horizontal flight.

[0021] Therefore, this application develops a new technology for transmitting energy from the power line to the drone in flight, the energy source in this technology is permanently present and fixed to the high-voltage line poles. The problem associated with the weight of the implementation of the photovoltaic grid has been successfully solved. In addition, the drone is not limited by the location of its energy source and has increased maneuverability. In this application, the WPT method provides at least 40W of power, enough to charge a normal DJI Air 2S mini drone during flight.

[0022] TECHNICAL DESCRIPTION

[0023] In a WPT system, the transmitter converts electrical energy from the source into a time-varying electromagnetic field, which is then transmitted to the receiver through a transmission medium to the receiver, which converts the electromagnetic field back into electrical current.

[0024] In practice, the effective WPT distance using the inductive power transfer (IPT) method does not exceed a few centimeters, and the efficiency depends heavily on the distance between the transmitter and receiver. Specifically, the closer the primary winding is to the secondary, the more efficient the transmission. Even very small deviations or skews of the receiver relative to the transmitter or vice versa will significantly reduce the transmission efficiency. Domino wireless charging (DWCS) is used to solve the problems associated with long-distance travel (see Fig. 11, Fig. 12).

[0025] For this purpose, a single-phase high-frequency (HF) and full-bridge inverter 55 (Fig. 19) excites a transmitter coil 56, which is built into the lowermost insulator, with HF voltage. An alternating current will flow in the transmitter coil and arrange a time-varying electromagnetic field for transmitting charging power to the upper part of the transmitter pole 46. The receiving coil is installed on the landing pad of the unmanned aerial vehicle 59 and is connected to an output full-bridge diode rectifier 60 and its LC filter 61 for supplying charging energy from the electromagnetic field to the battery 62 of the unmanned aerial vehicle.

[0026] A stable and constant DC input voltage 54 can be supplied to an input inverter 55 by means of a special current transformer 53 (installed on one phase of the transmission line). A rectangular modulation is used to switch the MOSFETs of the input inverter 55. The same duty cycle (50%) is taken into account for the pairs of inverter switches. The DR-IPT system includes compensation circuits, Fig. 19, to make the magnetic coils (with an air core) used operate at a high self-resonant frequency (85 kHz in this application) and to compensate for the reactive part of their own resistance. Series monoresonant compensation circuits, Fig. 6, have become widespread, since they have fewer passive elements. In addition, the compensation process for a coil would not depend on changes in the mutual resistances between the corresponding coil and other coils.

[0027] It is assumed that the output diode rectifier 60 provides the maximum charging power, which corresponds to the end of the battery charging mode with constant current and the beginning of the charging zone with constant voltage. The waveform of the input voltage of the rectifier device can also be considered rectangular.

[0028] For the design and optimization process, the main technical characteristics and design goals of the system are first defined. Then, the particle swarm optimization (PSO) algorithm generates initial (string) vectors of random particles, where the size of each particle is equal to the number of IDPs. The number of random particles is equal to the assumed population size for the PSO algorithms. In addition, for each particle in the generated population, the embedded DR-IPT is analyzed to indicate the value of the dependent design parameters (DDPs) and evaluate the objective function and constraints of the optimization problem.

[0029] The DR-IPT specifications consist of the number of turns of 14 flat spiral coils, the inner diameter of 12, the number of strands, and the natural resonant frequency. To address supply chain issues, identical geometry of the magnetic coils is assumed. The PSO procedure will continue to search for the minimum values ​​for the objective function and satisfy the given constraints by assigning an appropriate velocity to the initially generated particles and updating their values ​​accordingly. The PSO cycle will terminate if the maximum number of iterations is reached.

[0030] Note that first, the proposed IDP design process should be performed without the presence of external metallic objects (EMO) or insulators to determine the basic geometry. Then, a 3D finite element analysis (FEA) should be performed to obtain numerical models of the inductance and resistance changes in the presence of EMO. Finally, the IDP method should be performed again to achieve practical / optimal IDPS.

[0031] BRIEF DESCRIPTION OF DRAWINGS

[0032] Fig. 1 shows a crossbar of a transmission tower that supports high-voltage lines through a string insulator. Fig. 2a and 2b show an example of insulating strings made of porcelain and glass, respectively.

[0033] The cross-section of a single glass insulator is shown in Fig. 3. The properties of the material used in the insulator are presented in Table I.

[0034] TABLE I. MATERIAL USED IN ONE INSULATOR GLASS (FIG. 3)

[0035] Fig. 4 shows a top view of a flat spiral coil.

[0036] Fig. 5 shows a cross-section of the proposed insulator with the possibility of embedding flat spiral turns into its skirt.

[0037] Fig. 6 shows the LC circuit resonator.

[0038] Fig. 7 shows a three-dimensional cross-section of the proposed insulator with built-in flat spiral coils and a compensating capacitor.

[0039] Fig. 8 and 9 compare the proposed insulator with the existing one in terms of skirt structure and creepage distance.

[0040] Fig. 10a and 10b compare two types of skirt configuration in glass and porcelain insulators.

[0041] Fig. 11 shows a WPT system with an air core in the form of a domino.

[0042] Fig. 12 shows a three-dimensional cross-sectional view of the said domino WPT system of Fig. 11 embedded in insulators.

[0043] Fig. 13 shows an example of a high voltage overhead power line and a domino wireless charging system (DWCS) for an unmanned aerial vehicle.

[0044] Fig. 14 shows a close-up view of the installed DWCS for the unmanned aerial vehicle on one of the cross branches of the overhead high-voltage power line. The mini-unmanned aerial vehicle with a designed landing skid for transporting a flat spiral coil is shown in Fig. 15.

[0045] Fig. 16 shows the experimental setup of a laboratory-made WCS.

[0046] Fig. 17 shows a mini-drone (DJI Air 2S) with a designed landing skid, flat spiral and power electronic circuit.

[0047] Fig. 18 shows a flat spiral coil installed under a glass disk-type insulator.

[0048] Fig. 19 shows the equivalent circuit of DR-IPT together with EMOS at the base frequency.

[0049] DESCRIPTION OF THE IMPLEMENTATION OF THE INVENTION

[0050] In this application, a WCS based on DR-IPT system and series compensators for charging batteries of unmanned aerial vehicles is proposed, designed and implemented.

[0051] Fig. 1 shows a crossbar 1 of a power transmission line. The cross bracket supports high-voltage power transmission lines 2 with the help of a string insulator 3. The main task of the string insulator is to provide insulation and maintain a safe distance between the connection point of the high-voltage power transmission line 4 and the support bracket 5, which is grounded. The electrical distance between these two points is directly proportional to the voltage level transmitted by the power transmission lines. For example, at a voltage level of 63 kV, the required distance is more than 60 cm.

[0052] The string insulator itself consists of a number of interconnected disc insulators, which can be made of either glass (see Fig. 2a) or porcelain (see Fig. 2b). In the construction of a single insulator, some parts are necessary for the purposes of electrical insulation 9, 10, 11. While some other parts are necessary to ensure the required mechanical strength and are made of metals that are good conductors 6, 7, 8. For effective transmission of 63 kV voltage, at least five disc insulators must be connected.

[0053] Harvesting energy from the magnetic field surrounding a power line is a promising method for providing reliable and uninterruptible power to online monitoring equipment. However, safe transmission of this energy is vital. Typically, the collected energy is transmitted wirelessly. Disc insulators are a good option for installing flat spiral coils. Fig. 4 shows a flat spiral turn. We have selected the coil so that the insulating skirt 10 completely covers the surface of the coil. Thus, to achieve this goal, it is essential to consider the inner 12 and outer 13 diameters, as well as the number of turns 14 in the coil design.

[0054] The concept of placing the coil in a silicone rubber type insulator has been well documented in US Patent No. 2018 / 0323653, although it does not specifically recommend its use on glass or porcelain insulators. Another important aspect of this technology to consider is the mechanical isolation of the coils from the insulators, and the fact that they do not have any electrical connections, so the embedded coils do not cause any problems with the functionality of the insulators.

[0055] It is not recommended to install a flat spiral coil on an existing porcelain or glass insulator. Therefore, to successfully implement a coil on an insulator, it is necessary to reconfigure the design of the insulators. Therefore, we have proposed a new structure in Fig. 5. As shown in the figure, the design provides an empty space for placing the coil inside the skirt. Thus, the protrusions 15 under the skirt, designed to increase the crawling distance, are separated from its surface 16, which leads to the creation of a depression due to a downward displacement. A flat surface 17 is required to facilitate a secure placement of the coil 19. In addition, several tiny holes 18 are made along the four sides of the insulator to ensure air circulation inside and direct any generated heat to the outside.

[0056] To ensure efficient wireless energy transmission, the flat spiral coil is connected to a specially selected compensating capacitor 20 in such a way that resonant conditions are created on the coil 21 (see Fig. 6) and all reactive components of the coil impedance are dropped. Therefore, the space created in the skirt 22 must be large enough to accommodate the resonant capacitor in addition to the coil itself.

[0057] In Fig. 7 a three-dimensional cross-section of the proposed insulator is shown, showing the placement of the coil 24 and the compensating capacitor 23 inside the skirt 25. In addition, the inserted holes 26a and 27a are visible in the drawing. In the proposed design, it is important to emphasize that the creepage distance has been increased. Comparing the existing insulator and the proposed side view in Fig. 8 and 9, we can notice that the creepage distance 28, 30 increases. In addition, it is worth noting that the length of the ball pin or the overall height 29, 31 of the insulators in the new design remains unchanged. Comparing Fig. 8 and 9, it seems that moving the teeth of the skirt downwards without changing the height of the ball pin may lead to a decrease in the maneuverability of fixing the locking pin when connecting two insulators. However, when comparing the two standard insulators in Fig.10a and c it becomes obvious that the ball pin of one insulator projects completely 32 from the lower surface of the skirt, while the tip of the other ball pin is flush 33 with the lower surface of the skirt. Therefore, in the new design there will be no problems with the assembly and disassembly of the insulators relative to each other.

[0058] The efficiency of the wireless power technology with conventional resonant coupling is inversely related to the distance between the transmitting and receiving coils. In other words, the greater the transmission distance, the lower the efficiency of power transmission. To overcome this limitation, a series of intermediate coils 36a, 36b and 36c of repeated transmission can be used between the transmitter 34 and the last built-in coil 35. This, in turn, will allow us to divide the total transmission distance into smaller air gaps and provide a higher overall energy transfer efficiency - up to 95 percent.

[0059] The interconnected insulators allow us to install a domino structure of coils on them. Such an arrangement ensures safe transmission of energy from the transmission line to a protected point above the tower. As mentioned earlier, at least five of the proposed disk insulators must be connected for efficient transmission of 63 kV (see Fig. 7). Fig. 12 shows flat spiral coils built into the proposed insulator. In order to ensure efficient wireless transmission of power from the transmitter 37 to the last built-in coil in the insulator 38 through the domino structure links 39a, 39b, 39c, each coil is connected to a specially selected compensating capacitor in such a way as to create resonant conditions on the transmission path and disconnect all reactive components of each coil, the coil resistance.

[0060] In Fig. 13 an example of a high-voltage transmission tower 41 is shown. These towers support a plurality of high-voltage transmission lines 42. Each support consists of six crossbars 40 and insulating strings 43a, 43b respectively. The installation of the structure shown in Fig. 12 is possible on any of the new towers. In this work, the main load for receiving the transmitted power is an unmanned aerial vehicle 44 in flight, which can safely approach the top of the nearest transmission pole, land on an electrically neutral site and charge its BESS with WPT from the transmission line and current transformer 45.

[0061] Fig. 14 shows the implementation of the proposed WCS UAV on a high-voltage tower. A single-phase current transformer 48, which is supposed to convert the magnetic field into a useful source of system energy, is installed on the high-voltage line next to the string insulator 49. The domino structure ensures safe transmission of energy from the power line to a protected point above the tower. Thus, unmanned aerial vehicles can safely approach the top of the tower and even land during their missions, maintaining a sufficient distance from the high-voltage wires. As can be seen, the unmanned aerial vehicle carries another flat spiral coil 46, which works as the last coil in the energy transmission chain. And receives its energy from the last coil built into the highest insulator.

[0062] Fig. 15 shows how the coil 51 is mounted on the drone. For this purpose, we have designed and manufactured a lightweight landing platform 52, which not only carries the coil, but also facilitates the landing of the drone on the tower. The receiving coil and the uncontrolled rectifier should be built under the landing platform of the mini-drone as additional equipment, while the aligned transmitting coil should be located next to the inverter. The point of introduction of the charging panel is also shown in the figure.

[0063] Fig. 16 shows the experimental setup manufactured in laboratory conditions. The entire procedure for introducing and transmitting energy from the source to the unmanned aerial vehicle is described in the following stages:

[0064] Firstly, the AC / DC power converter is designed to convert the AC signal into a DC signal. Since most commercial power lines around the world operate at 50 or 60 Hz, the frequency parameter cannot significantly improve the performance of the conductor in terms of quality. Therefore, the AC signal must be converted into a DC signal. For this purpose, an autotransformer is used to provide the required voltage and current for the full-bridge diode rectifier and CLC filter. The DC input voltage can be adjusted to the desired value by fine-tuning the autotransformer connected to the power grid.

[0065] The DC signal is then converted to an AC signal at any desired high frequency (85 kHz). A full-bridge inverter is built and a small single-board computer (Raspberry Pi 4 Model B) is used to program the microcontroller to generate PWM signals for the inverter.

[0066] After converting the low frequency AC signal to a high frequency AC signal, a well-designed DR-IPT system is used to transmit power to the UAV wirelessly. The resonant WPT approach can potentially transmit power to multiple receivers tuned to the resonant frequency, and similarly, such receivers can receive power from multiple sources. Therefore, by taking advantage of this capability and implementing DWPT, the signal can be transmitted over a longer distance to reach the top of the transmission line tower.

[0067] To implement the DWPT system, the magnetic coils are wound using Litz wires with AWG 38 gauges. In the experimental setup, it is necessary to have a flat surface structure or frame to support the resonator coils. To implement this case, a suitable robust frame is used Fig. 18 (plexiglass plates) to fix the coils to the high-voltage insulators. Each resonator coil is located under the insulator plates, see resonator coils in Fig. 18. The base of the insulator is connected to the power transmission conductor, while its other end is fixed to the tower bracket.

[0068] To ensure efficient power transfer through the channels of the domino structure, the transmitting coils are connected to specially selected capacitors in such a way that resonant conditions are created on each coil and all reactive components of the coil impedance are reduced. Compensating capacitors are made by connecting film capacitors in series and parallel to provide the required capacity and rated voltage.

[0069] To test the developed WPT system in real conditions, the DJI Air 2S UAV platform was used (see Fig. 17). The developed coil and related circuits are embedded in the power supply circuit of the UAV. The output rectifier and LC filter are handmade and connected to a 4200 mAh three-cell battery. The UAV is tested by flying over a laboratory-scale high-voltage power plant (Fig. 16) and measuring the charging current and time.

Claims

Invention formula 1. A wireless charging system for unmanned aerial vehicles using a high-voltage transmission line consists of a plurality of high-voltage transmission lines supported by supports, with six crossbars installed on each support, a bracket installed on each crossbar, with five insulators suspended on each of the brackets, the insulators are connected in series one above the other, a high-voltage line is suspended at the bottom of the last insulator, with a single-phase current autotransformer installed on the line itself, the output of which is connected to the input of a diode bridge with a filter capacitor, the output of which is connected to a full-bridge inverter that converts direct current to high-frequency alternating current, with an intermediate transformer in the form of a flat coil with a film capacitor installed on each insulator,which transmits a high-frequency inductive current with the required capacity and nominal voltage to the upper receiving coil, which is installed on the unmanned aerial vehicle, wherein the receiving coil has a circuit in the form of a diode bridge with an LC resonator, which is connected to the battery of the unmanned aerial vehicle, and the unmanned aerial vehicle is also designed with the possibility of landing on a platform attached to a bracket to provide wireless charging.

2. The wireless charging system according to claim 1 is characterized in that the insulator has an empty space for placing a flat coil, and also along four sides of the insulator there are several tiny holes to ensure air circulation inside and direct any generated heat outward.

3. The wireless charging system according to paragraph 1 is characterized in that after converting the low-frequency alternating current signal into a high-frequency alternating current signal, a DR-IPT system is used to transmit power to the unmanned aerial vehicle via a wireless network.

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