An omni-directional wireless power transfer system based on drone applications

Abstract

The application discloses a three-dimensional omnidirectional anti-deviation wireless power transmission system of a UAV, and belongs to the field of wireless power transmission. The system comprises a transmitting end and an airborne receiving end of a UAV. The transmitting end is composed of a direct current source, three groups of single-phase full-bridge inverters, a primary SS compensation network and a triple planar transmitter (TPT). Three nested symmetrical transmitting coils are used for decoupling and generating a three-dimensional composite magnetic field. The airborne receiving end is equipped with double receivers, each of which is provided with two groups of orthogonal receiving coils. Two independent resonant receiving branches are formed by combining the secondary SS compensation. After rectification and filtering, the branches are connected to the battery load of the UAV. When the UAV is spatially deviated or the attitude is deflected, the coupling strength of the two branches is complementary, the rectification is superimposed, the output current fluctuation can be suppressed, the spatial anti-deviation performance is greatly improved, and the wireless charging of the UAV is adapted.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, specifically to a fully automatic charging system for drones that features three-dimensional omnidirectional magnetic field transmission and omnidirectional wireless power transmission. Background Technology

[0002] Wireless power transmission technology relies on electromagnetic coupling to achieve contactless power replenishment, which can eliminate the risks of wear, leakage and corrosion of drone charging interfaces, simplify the onboard charging hardware structure, and reduce operation and maintenance costs. It is the core technology for automatic refueling and unattended charging of drone swarms.

[0003] Existing wireless charging solutions for drones have core technical bottlenecks: during the landing process of drones, there are lateral and attitude deviations. Traditional single-coil and two-dimensional planar multi-coil systems can only maintain stable coupling when the coils are precisely aligned. When there is misalignment in three-dimensional space, the coupling coefficient is greatly reduced, and the output current fluctuates violently, which cannot meet the rigid requirement of constant current charging for lithium batteries.

[0004] In summary, existing wireless charging solutions can only achieve anti-offset transmission in a two-dimensional plane, lack three-dimensional omnidirectional magnetic field coverage, and cannot meet multiple requirements such as constant current output and structural decoupling under symmetrical conditions, thus exhibiting significant technical limitations. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies, which are only compatible with two-dimensional plane offset, lack three-dimensional omnidirectional coupling capability, and generate reactive power loss due to coil cross-coupling. This invention provides an omnidirectional wireless power transmission system based on UAV applications. The invention achieves three-dimensional omnidirectional magnetic field synthesis through a triple planar transmitter (TPT) coil. It achieves structural decoupling of the transmitting and receiving coils under symmetrical conditions by relying on a symmetrical magnetic field structure, which is compatible with the payload limitations of UAVs. The complementary currents of the two orthogonal receiving branches achieve constant current output over a wide spatial range. The SS series topology can stably output constant current without complex control.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: an omnidirectional wireless power transmission system based on UAV applications, comprising a transmitter and an UAV-borne receiver;

[0007] The transmitter includes a DC voltage source, three sets of single-phase full-bridge inverters, three sets of primary SS series compensation networks, and a TPT transmitter; the input terminals of the three sets of full-bridge inverters are connected in parallel with DC voltage sources, and the output terminals of each set of inverters are connected in series with a primary SS compensation network to drive a corresponding set of transmitting coils.

[0008] The UAV onboard receiver includes two sets of secondary SS series compensation networks, two receivers, a rectifier circuit, a filter capacitor, and a UAV battery load. The two receivers are fixedly mounted on the bottom crossbar of the UAV landing gear. Each receiver includes two orthogonally wound receiving coils, which are decoupled from each other based on a symmetrical structure. The rectangular coils of the two receivers are connected in series to form a set of receiving coils. One set of receiving coils has a cross-section parallel to the transmitting plane and is used to pick up the vertical magnetic flux component. The other set of receiving coils has a cross-section perpendicular to the transmitting plane and is used to pick up the horizontal magnetic flux component. The two sets of receiving coils are connected in series with the secondary SS compensation network to form two independent receiving resonant branches. The output of the two receiving resonant branches is connected to the input of the rectifier circuit. The output of the rectifier circuit is connected in parallel with a filter capacitor and then connected to the UAV battery load.

[0009] Three transmitting coils are fed with excitation currents of independent amplitude and phase, which can synthesize arbitrary vector magnetic fields in three-dimensional space. When the UAV undergoes spatial offset or attitude deflection, the two receiving coils correspond to magnetic flux components in different directions. When the coupling of one of them weakens, the output of the corresponding branch of the other increases. After rectification and superposition, the output current fluctuation is reduced.

[0010] As a preferred technical solution of the present invention, all transmitting coils, receiving coils and matching compensation capacitors meet the series resonance condition. The parameters of the compensation capacitor are determined only by the coil self-inductance and the operating frequency, and are independent of the coil mutual inductance and load resistance. No additional re-matching of compensation parameters is required when the coil deviates or the battery voltage changes.

[0011] As a preferred technical solution of the present invention, the three transmitting coils are symmetrically arranged, and the mutual inductance integrals between the coils cancel each other out, thereby achieving structural decoupling under symmetrical conditions, and the three excitation currents can be independently controlled without interfering with each other.

[0012] As a preferred technical solution of the present invention, the AC currents of the two receiving branches are rectified and superimposed to output a DC charging current. Under the condition of UAV deviation, the currents of the two branches complement each other and cancel out the fluctuations, and the output DC current is stable.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. Three-dimensional omnidirectional magnetic field emission with a large spatial fault tolerance range: The three orthogonally nested transmitting coils with a planar two-dimensional layout can synthesize a magnetic field in any direction in space, breaking through the limitation of traditional two-dimensional coils that only resist deviation in a planar manner. Effective coupling can be achieved at any angle of the UAV, reducing the charging dead zone.

[0015] 2. The coils achieve structural decoupling under symmetrical conditions, reducing hardware complexity: The three coils at the transmitting end and the two sets of orthogonal coils at the receiving end achieve pairwise decoupling by canceling each other out with symmetrical magnetic fields. There is no additional reactive power loss, and there is no need to add decoupling control circuits or sampling modules. The system structure is simple and the system complexity is reduced.

[0016] 3. SS series resonant topology, natural constant current output adapted for drone charging: all circuits resonate independently, the compensation capacitor is not affected by offset or load changes; the current of the two receiving branches is complementary under offset conditions, and the total DC current fluctuation after rectification is small, matching the standard working condition of lithium battery first constant current charging and then constant voltage float charging.

[0017] 4. The system has a simple and reliable structure. It can achieve omnidirectional and constant current transmission by relying only on coil topology and resonant topology, making it suitable for unattended automatic charging scenarios for drones. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall circuit topology of the omnidirectional wireless power transmission system according to an embodiment of the present invention.

[0019] Figure 2 This is a simplified structural diagram illustrating the mathematical analysis of the decoupling of the three coils at the transmitter end of the present invention.

[0020] Figure 3 This is a schematic diagram of two-dimensional energy transfer in the XOZ plane under simultaneous excitation by three transmitting coils according to the present invention;

[0021] Figure 4 This is a diagram showing the angle offset mutual inductance results of the wireless power transmission system of the present invention;

[0022] Figure 5 This is a diagram showing the mutual inductance results of the wireless power transmission system of the present invention in the X-axis direction offset.

[0023] Figure 6 This is a diagram showing the mutual inductance results of the wireless power transmission system of the present invention in the Y-axis direction offset. Detailed Implementation

[0024] The technical solution of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. The following embodiments are only some implementation methods of the present invention.

[0025] like Figure 1 As shown, this invention provides a three-dimensional omnidirectional anti-misalignment wireless power transmission system for UAV applications, mainly composed of a transmitter, a wireless power coupling mechanism, an airborne receiver, and a rectifier load circuit. The transmitter includes a DC voltage source. Three sets of single-phase full-bridge inverters , , Three sets of primary SS series compensation capacitors , , and the corresponding transmitting coil , , Three sets of single-phase full-bridge inverters drive their respective transmitting coils to generate high-frequency alternating magnetic fields. The airborne receiver includes two sets of receiving coils. , Two sets of secondary SS series compensation capacitors , Full-bridge rectifier circuit ~ Filter capacitor and drone battery load ,in ~ This represents the equivalent resistance of each coil. (Transmitting coil) ~ With receiving coil , Mutual induction is formed between them. , , , , and This enables wireless power coupling transmission.

[0026] The transmitter consists of three coaxially nested orthogonally arranged transducer coils, each driven by an independent inverter. A primary SS series compensation network generates a high-frequency resonant current. The airborne receiver has two sets of orthogonal receiving coils, each receiving magnetic flux components in different directions. After secondary SS series compensation, rectification, and filtering, the flux is transmitted to the UAV battery load. Outputs DC power.

[0027] like Figure 2 As shown in the simplified structure, the TPT transmitter contains three coaxially nested coils with coincident centers: coil 1 is a large circular monopole coil, and two bipole coils 2 and coil 3 are nested inside each other. In this structure, coils 2 and 3 are symmetrically designed and manufactured, and all three are placed at the same central point. In terms of physical structure, coil 1 consists of a single circular coil, coil 2 consists of two circular coils wound with a single excitation wire (left and right), and coil 3 consists of two circular coils wound with a single excitation wire (top and bottom). The inner diameter of coil 1; , The outer diameters of coils 2 and 3; For transmitting coils 2 and 3 and the center point The distance between them; , , 2L and 2R represent the angles between the x-axis and any point on each coil; 2L and 2R represent the left and right sides of coil 2, respectively; 3U and 3D represent the upper and lower parts of coil 3, respectively. , , These are the current vectors for coils 1, 2, and 3, respectively.

[0028] The spatial coordinates of any point on coil 1, coil 2, and coil 3 can be represented as:

[0029] (1)

[0030] (2)

[0031] (3)

[0032] in The inner diameter of coil 1; , The outer diameters of coils 2 and 3; For transmitting coils 2 and 3 and the center The distance between them; , , These represent the angles between the x-axis and any point on coils 1, 2, and 3, respectively.

[0033] According to the Neumann mutual inductance integral formula (4):

[0034] (4)

[0035] In the formula: For coil With coil Mutual intuition; The vacuum permeability; , coils , Number of turns; For coil A tiny length vector at a certain point on the current path, directed along the direction of the current. For coil A tiny length vector at a certain point on the current path, directed along the direction of the current. Let be the distance between two infinitesimal elements.

[0036] The mutual inductance between the three transmitters can be expressed as:

[0037] (5)

[0038] (6)

[0039] (7)

[0040] (8)

[0041] (9)

[0042] (10)

[0043] (11)

[0044] (12)

[0045] in, , , These represent the number of turns for coils 1, 2, and 3, respectively. The mutual inductance between the left sides of coil 1 and coil 2; The mutual inductance between the right sides of coil 1 and coil 2; The mutual inductance between the upper parts of coil 1 and coil 3; The mutual inductance between the lower portions of coil 1 and coil 3; The mutual inductance between the left side of coil 2 and the upper side of coil 3; The mutual inductance between the left side of coil 2 and the lower side of coil 3; The mutual inductance between the right side of coil 2 and the upper side of coil 3; The mutual inductance between the right side of coil 2 and the lower side of coil 3; The mutual inductance between coil 1 and coil 2; The mutual inductance between coil 1 and coil 3; This refers to the mutual inductance between coil 2 and coil 3.

[0046] The total mutual inductance among transmitting coil 1, transmitting coil 2, and transmitting coil 3 satisfies:

[0047] (13)

[0048] in: The mutual inductance between coil 1 and coil 2; The mutual inductance between coil 1 and coil 3; This refers to the mutual inductance between coil 2 and coil 3.

[0049] According to the mutual inductance formulas (5) to (13) between the three coils, the mutual inductance between the transmitting coil 1, transmitting coil 2 and transmitting coil 3 is obtained. , , All are much less than 0.6 That is, the mutual inductance between each pair satisfies the decoupling requirement, and passive decoupling can be achieved without additional devices.

[0050] A three-dimensional frequency domain electromagnetic simulation model was built using COMSOL Multiphysics 6.3. The receiver was configured with two sets of orthogonally decoupled rectangular pickup coils 4 and 5, which picked up vertical and horizontal magnetic flux respectively. The coils were fitted with solid cuboid magnetic cores, measuring 120mm in length, 20mm in width, and 20mm in height. The solid cores helped to concentrate the magnetic flux and suppress leakage interference. The receiving coils were wound tightly against the magnetic core, with 18 turns each and double-layered winding. The system operated at a frequency of 85kHz, with a vertical transmission distance of 10mm. Transmitting coil parameters: Coil 1 inner diameter... =400mm, number of turns =12, outer diameter of coils 2 and 3 = =160mm, number of turns = =13. Transmitting coils 2 and 3 and the center point Distance between =10mm; both the receiving and transmitting coils have a wire diameter of 2mm; , , The currents are alternating currents with the same frequency but different phases, and the effective value of the current is set to 1A.

[0051] The magnetic flux density generated by a single coil current element at any observation point in space follows the Biot-Savart law (14):

[0052] (14)

[0053] In the formula: The infinitesimal magnetic flux density generated by the current element; This is the excitation current for the transmitting coil; It is a tiny line segment along the direction of the current; The spatial vector pointing from the current element to the observation point; It is the vector magnitude.

[0054] After the three orthogonal transmitting coils are simultaneously supplied with alternating current, the total magnetic flux density at any position in space is the superposition of the three-axis magnetic field vectors, and the three-dimensional magnetic field synthesis satisfies the vector equation system of equation (15):

[0055] (15)

[0056] In the formula: , , These are the components of the total magnetic flux density along the X, Y, and Z axes, respectively. , , The triaxial magnetic flux component generated by the excitation of coil 1; , , The triaxial magnetic flux component generated by the excitation of coil 2; , , This refers to the triaxial magnetic flux component generated by the excitation of coil 3.

[0057] from Figure 3 The schematic diagram of two-dimensional energy transmission in the XOZ plane under simultaneous excitation of three transmitting coils shows that the three coils, based on the vector superposition of formula (15), jointly construct a spatially diffuse composite magnetic field. The magnetic field lines can be uniformly dispersed in multiple directions, including horizontal (X-direction) and vertical (Z-direction), completely breaking away from the limitation that the magnetic field of a single coil is only oriented along the axis.

[0058] In the horizontal X-axis region, the magnetic field energy spreads to the left and right sides over a wide area, and the horizontal magnetic field amplitude remains at a high level. In the vertical Z-axis region, the magnetic field is continuously connected in the up and down direction, forming a stable and continuous high field strength energy transmission channel in the longitudinal direction.

[0059] Combining the decoupling characteristics of equations (1) to (13), the generation law of the single coil magnetic field of equation (14), and the three-dimensional vector synthesis mechanism of equation (15), the XOZ cross-section simulation results intuitively prove that the three orthogonal nested transmitting coil structure can simultaneously construct a continuous and effective magnetic field channel in the horizontal and vertical planes, forming a multi-directional full-coverage energy transmission channel in a large area of ​​space. The system has three-dimensional omnidirectional energy transmission characteristics. The UAV airborne orthogonal receiver can couple and capture effective magnetic flux at any angle and any lateral offset position in space, greatly expanding the system's anti-offset fault tolerance range and solving the technical defects of the traditional two-dimensional coil charging blind zone and severe attenuation of offset coupling.

[0060] To quantitatively verify the omnidirectional and X / Y axis anti-misalignment performance, the mesh of the coils and near-field region was refined to improve the solution accuracy. Three sets of parametric misalignment simulations were completed. Since both the transmitting and receiving coils are symmetrically designed and wound, for ease of explanation, the simulation results only show half a cycle of the receiving coil. Accompanying misalignment diagrams, branch mutual inductance, and total equivalent mutual inductance are also provided. The variation curve and simulation conclusions are as follows:

[0061] 1. Angle deflection simulation: Controlling the winding of the receiving coil Complete continuous scanning from 0° to 180° and extract the mutual inductance curves of each branch and the total mutual inductance. Figure 4The demonstration visually shows that the mutual inductance of the receiving coil is not zero under arbitrary deflection angles. While there are some fluctuations in the total mutual inductance between 0° and 30°, and between 60° and 180°, the total mutual inductance remains high, indicating good coupling stability. A certain level of mutual inductance is maintained even within the 30° to 60° range. Within the entire angle range, the branch mutual inductance increases and decreases, and the total mutual inductance exhibits some periodic fluctuations, with no charging dead zone. Under small-angle deflection, the receiving coil can capture multidimensional magnetic flux, ensuring continuous and efficient system operation.

[0062] 2. X-axis lateral offset simulation: The offset distance range is 0~100mm, and the receiving mechanism scans the entire range of the X-axis. Figure 5 The results visually demonstrate that as the offset increases, the magnetic fields of the three coils complement each other, resulting in a gradual decrease in total mutual inductance. The reference value of mutual inductance is high throughout the entire range, and sufficient coupling strength is maintained even at extreme offsets, thus widening the effective charging range of the X-axis. The magnetic flux pickup is stable under large X-axis offsets, demonstrating excellent anti-offset performance.

[0063] 3. Y-axis lateral offset simulation: The offset distance range is 0~100mm, and the receiving mechanism scans the entire range along the Y-axis. Figure 6 The system demonstrates that the overall mutual inductance of the wireless power transmission system remains stable throughout the entire process, with only a slight attenuation at extreme offsets, while still maintaining sufficient coupling strength. The three coils work together to construct a three-dimensional magnetic field, compensating for the flux loss caused by the offset of a single coil. Even with a large Y-axis offset, the receiving coil can continuously pick up effective flux without a drastic drop in transmission efficiency, demonstrating outstanding Y-axis offset resistance.

[0064] Based on the comprehensive simulation results, the TPT transmitting coil can achieve stable energy transfer in the full circumference from 0° to 180°, and has strong fault tolerance for both X and Y lateral offsets. Regardless of the attitude deflection or large horizontal offset of the UAV, the airborne orthogonal receiving coil can stably capture the magnetic flux, and the system can operate continuously and efficiently, greatly reducing the accuracy requirements for UAV landing alignment and making it suitable for wireless charging scenarios for landing gear.

[0065] The complete system workflow is as follows: The DC power supply powers three sets of full-bridge inverters, which modulate and generate high-frequency AC power to be sent to the transmitting SS resonant branch; the three coils, decoupled based on a symmetrical structure, generate X / Y / Z axial magnetic fields respectively, which are vectored and superimposed to form directional magnetic flux; the two sets of orthogonal receiving coils of the UAV pick up the vertical and horizontal magnetic flux respectively, and the two secondary branches induce high-frequency AC power; during lateral offset, the mutual inductance of the two branches increases and decreases, and the output current is complementary to cancel power fluctuations; the two AC power can be rectified by a bridge rectifier and filtered by a capacitor to output constant DC power, which charges the UAV's lithium battery with constant current.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, and are not intended to limit it; those skilled in the art can modify or make equivalent substitutions to the solution without departing from the core concept of the present invention, and such modifications and substitutions all fall within the protection scope of the claims of the present invention.

Claims

1. An omnidirectional wireless power transmission system for unmanned aerial vehicle (UAV) applications, characterized in that, This includes the transmitter, wireless power transmission mechanism, UAV onboard receiver, wireless power receiving mechanism, rectifier and filter circuit, and UAV battery load, among which: Three sets of primary SS series compensation capacitors , , and the corresponding transmitting coil , , Three sets of single-phase full-bridge inverters drive their respective transmitting coils to generate high-frequency alternating magnetic fields; the airborne receiver includes two sets of receiving coils. , Two sets of secondary SS series compensation capacitors , Full-bridge rectifier circuit ~ Filter capacitor and drone battery load ,in ~ The equivalent resistance of each coil; the transmitting coil ~ With receiving coil , Mutual induction is formed between them. , , , , and ; The wireless power transmission mechanism is equipped with a Triple Planar Transmitter (TPT), which is composed of three coaxially nested orthogonally arranged transmitting coils with coincident centers. Transmitting coil 1 is a unipolar circular coil, while transmitting coils 2 and 3 are symmetrically arranged bipolar coils, with the two bipolar coils nested intersecting inside transmitting coil 1. The three transmitting coils are wound symmetrically, with their central origins coinciding. The spatial coordinates of any point on coils 1, 2, and 3 can be represented as: （1） （2） （3） in The inner diameter of coil 1; , The outer diameters of coils 2 and 3; For transmitting coils 2 and 3 and the center point The distance between them; , , These represent the angles between the x-axis and any point on coils 1, 2, and 3, respectively. The mutual inductance between transmitting coil 1, transmitting coil 2 and transmitting coil 3 satisfies the Neumann mutual inductance integral relation (4): （4） In the formula: For coil With coil Mutual intuition; The vacuum permeability; , coils , Number of turns; For coil A tiny length vector at a certain point on the current path, directed along the direction of the current. For coil A tiny length vector at a certain point on the current path, directed along the direction of the current. The distance between two infinitesimal elements; The mutual inductance between the three transmitting coils can be expressed as: （5） （6） （7） （8） （9） （10） （11） （12） in, , , These represent the number of turns for coils 1, 2, and 3, respectively. The mutual inductance between the left sides of coil 1 and coil 2; The mutual inductance between the right sides of coil 1 and coil 2; The mutual inductance between the upper parts of coil 1 and coil 3; The mutual inductance between the lower portions of coil 1 and coil 3; The mutual inductance between the left side of coil 2 and the upper side of coil 3; The mutual inductance between the left side of coil 2 and the lower side of coil 3; The mutual inductance between the right side of coil 2 and the upper side of coil 3; The mutual inductance between the right side of coil 2 and the lower side of coil 3; The total mutual inductance among transmitting coil 1, transmitting coil 2, and transmitting coil 3 satisfies: （13） in: The mutual inductance between coil 1 and coil 2; The mutual inductance between coil 1 and coil 3; The mutual inductance between coil 2 and coil 3; The mutual inductance between transmitting coil 1, transmitting coil 2 and transmitting coil 3 , , All are much less than 0.6 ; The spatial magnetic field generated by the three transmitting coils satisfies the Biot-Savart law (14), and its magnetic flux density element is expressed as: （14） In the formula: The infinitesimal magnetic flux density generated by the current element; This is the excitation current for the transmitting coil; It is a tiny line segment along the direction of the current; The spatial vector pointing from the current element to the observation point; It is the vector magnitude; The magnetic flux density generated by the three transmitting coils satisfies (15): （15） In the formula: , , These are the components of the total magnetic flux density along the X, Y, and Z axes, respectively. , , The triaxial magnetic flux component generated by the excitation of coil 1; , , The triaxial magnetic flux component generated by the excitation of coil 2; , , The triaxial magnetic flux component generated by the excitation of coil 3; The UAV onboard receiver includes two receivers, which are fixedly mounted on the bottom crossbar of the UAV landing gear. It contains two sets of orthogonally wound receiving coils. Each set of receiving coils consists of two rectangular coils connected in series in the same direction. The cross-section of one set of receiving coils is parallel to the transmitting plane, and the cross-section of the other set of receiving coils is perpendicular to the transmitting plane. The two sets of receiving coils are arranged in an orthogonal structure and are connected in series with corresponding secondary SS series compensation networks to form two resonant branches. All transmitting coils, receiving coils and corresponding compensation capacitors in the wireless power receiving mechanism satisfy the SS series resonance condition. The compensation parameters are determined according to the corresponding coil parameters and the system operating frequency so that the corresponding branch works in the series resonance state. The input terminal of the rectifier and filter circuit is connected to the output terminals of the two receiving resonant branches respectively. The output terminal of the rectifier and filter circuit is connected to the filter capacitor and the drone battery load in sequence. The AC power generated by the two receiving branches is rectified and filtered to output DC power. The receiving coil is fitted with a solid rectangular magnetic core, measuring 120mm in length, 20mm in width, and 20mm in height. The receiving coil is wound tightly against the magnetic core, with 18 turns in each coil, in a double-layer winding. The system operates at a frequency of 85kHz, and the vertical transmission distance is 10mm. Transmitting coil parameters: Coil 1 inner diameter... =400mm, number of turns =12, outer diameter of coils 2 and 3 = =160mm, number of turns = =13; Transmitting coils 2 and 3 and the center of the circle Distance between =10mm; both the receiving and transmitting coils have a wire diameter of 2mm; , , The currents are alternating currents with the same frequency but different phases, and the effective value of the current is set to 1A.

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