Light-weight unmanned aerial vehicle wireless charging magnetic coupling mechanism with low stray magnetic field

Abstract

The invention relates to unmanned aerial vehicle wireless charging, in particular to a low stray magnetic field lightweight unmanned aerial vehicle wireless charging magnetic coupling mechanism, a transmitting coil of a transmitting end is in a centrosymmetric ring shape, the transmitting coil is composed of an even number of coil units, currents of two wire segments belonging to adjacent coil units on an inner ring are the same, and the current flow directions are opposite along the inner ring. And a group of receiving coils of the receiving end consists of a coil alpha and a coil beta, the coil alpha and the coil beta are orthogonally combined and placed, and each of the coil alpha and the coil beta is formed by connecting N identical square solenoid coils in series. The problem of magnetic field interference of a stray magnetic field generated by the transmitting coil on related components of the unmanned aerial vehicle in the prior art is solved, and meanwhile light weight of the receiving coil carried on the side of the unmanned aerial vehicle and efficient coupling of the whole magnetic coupling mechanism are achieved.

Description

Technical Field

[0001] This disclosure relates to wireless charging for drones, and more particularly to a lightweight wireless charging magnetic coupling mechanism for drones with low stray magnetic field. Background Technology

[0002] With the rapid development of the "low-altitude economy," rotary-wing drones have been widely used in many industries and fields such as unmanned inspection, terrain exploration, military reconnaissance, and agricultural and forestry plant protection. The endurance of drones is limited by battery capacity, requiring timely recharging. For unmanned and periodic applications, wireless power transfer technology, which transmits power without physical contact, offers advantages such as safety and convenience, efficiently solving the power replenishment problem for drones and providing strong support for their sustained operation in unmanned scenarios. The magnetic coupling mechanism, as a key component of wireless power transfer technology, plays a crucial role in the overall transmission performance of the wireless charging system. In drone wireless charging systems, drone landings may experience some positional deviation, requiring the designed magnetic coupling mechanism to have a certain degree of resistance to misalignment. The drone fuselage and external equipment contain electrical components, and stray magnetic fields generated by the transmitting coil may adversely affect the normal operation of the drone; therefore, suppressing stray magnetic fields is also essential. On the drone side, the drone's payload is limited and affected by the shape of the drone's landing gear. The magnetic coupling mechanism at the receiving end should have lightweight characteristics and good shape adaptability. Otherwise, the magnetic coupling mechanism will occupy extra weight, which will significantly reduce the drone's range or the battery capacity it can support. Summary of the Invention

[0003] For multi-rotor UAVs with pole-mounted / I-type landing gear structures, this disclosure presents a magnetic coupling mechanism for wireless charging of UAVs. This mechanism solves the problem of stray magnetic fields generated by the transmitting coil interfering with the magnetic field of UAV components in existing technologies. It also achieves lightweight design of the receiving coil mounted on the UAV side and efficient coupling of the magnetic coupling mechanism as a whole.

[0004] A wireless charging magnetic coupling mechanism for unmanned aerial vehicles (UAVs) includes a receiver and a transmitter. The receiver coil consists of coil α and coil β, which are orthogonally arranged. Both coil α and coil β are composed of N identical solenoid coils connected in series, where N is a preset value. The transmitter coil of the transmitter is a centrally symmetrical ring, consisting of an even number of coil units. When energized, the conductor segments belonging to different coil units on the inner ring experience the same current magnitude but flow in opposite directions along the inner ring, resulting in extremely low stray magnetic field in the central region of the transmitter coil.

[0005] The beneficial technical effects of the present invention are as follows: (1) The magnetic coupling mechanism of the proposed UAV wireless charging system has the characteristic of naturally suppressing stray magnetic fields in the central region, which is especially suitable for wireless charging of pole-mounted UAVs. Without the need to add a magnetic shielding structure to the UAV airborne side or add an additional suppression coil to the transmitting coil, the influence of stray magnetic fields of the transmitting coil on the UAV fuselage and external equipment such as the gimbal can be effectively solved. (2) The magnetic coupling mechanism of the proposed UAV wireless charging system achieves efficient magnetic flux utilization of the transmitting coil through a unique coil design and winding method. At the receiving end, the receiving coil can still achieve high coupling performance without the need to install magnetic materials, effectively reducing the weight of the UAV airborne side and realizing the lightweight design of the magnetic coupling mechanism. Attached Figure Description

[0006] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0007] Figure 1 A 3D schematic diagram of a drone docking above a wireless charging magnetic coupling mechanism.

[0008] Figure 2 This is a schematic diagram of the transmitter end of the magnetic coupling mechanism.

[0009] Figure 3 This is a schematic diagram showing the magnetic field distribution characteristics of the transmitting coil.

[0010] Figure 4 This is a schematic diagram of an orthogonal receiving coil.

[0011] Figure 5 The circuit topology for a wireless charging system for drones.

[0012] Figure 6 This is a schematic diagram of the planar magnetic induction intensity distribution of the transmitting coil.

[0013] Figure 7 This is a schematic diagram showing the characteristics and distribution of the magnetic field lines of the transmitting coil.

[0014] Figure 8 This is a schematic diagram of the magnetic induction intensity distribution of the transmitting coil (top) and the monopole circular coil (bottom) in one embodiment.

[0015] Figure 9 This is a schematic diagram of the variation curve of the rotation offset coupling coefficient. Detailed Implementation

[0016] In existing technologies, the suppression of stray magnetic fields generated by the transmitting coil mainly employs methods such as placing shielding material at the receiving end and adding an active shielding coil to the transmitting coil. The former increases the airborne load and installation difficulty, while the latter reduces coupling performance and increases coil losses to some extent. Therefore, this invention proposes a transmitting coil with low stray magnetic field characteristics that does not require an additional shielding coil. The coil is centrally symmetrical and ring-shaped, with an even number of coil units. When energized, the current magnitude of two conductor segments belonging to adjacent coil units on the inner ring is the same, and the current flow direction is opposite along the inner ring, resulting in extremely low stray magnetic fields in the central region of the transmitting coil. The ring in this application is curved, and the edges can be straight segments or curved segments. The opposite current flow direction along the inner ring means that the current flow direction of one conductor segment is clockwise, and the current flow direction of the other conductor segment is counterclockwise. The ring can be a straight-edged ring or a curved-edged ring.

[0017] To improve the coupling performance of the magnetic coupling mechanism, magnetic materials need to be placed at the receiving end. However, these magnetic materials not only increase the weight on the airborne side but are also prone to breakage during drone landing. Therefore, this invention improves the coupling performance by optimizing the design of the transmitting coil and the magnetic field distribution in the magnetic coupling mechanism without using magnetic materials at the receiving end, thus achieving a lightweight design for the receiving coil.

[0018] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0019] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation", "connection" and "joining" should be interpreted broadly, for example, as fixed connection, detachable connection, or integral connection; those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0020] The following description, in conjunction with the accompanying drawings, clearly and completely describes how the technical solution of this case is implemented. Obviously, the described embodiments are only a part of the embodiments of this case, and not all of them. Based on the embodiments in this case, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0021] like Figure 1The diagram shows a four-legged stand-up drone and its wireless charging magnetic coupling mechanism. This mechanism includes a ferrite core at the transmitter, an insulating plate, a transmitting coil, and a receiver, which consists of four sets of receiving coils located at the bottom of the drone's landing gear. The magnetic core is located under the insulating plate, and the transmitting coils are located on the insulating plate.

[0022] See Figure 2 At the transmitting end, the transmitting coil has an overall shape of a regular octagonal planar coil structure, consisting of inner and outer frames formed by two concentric regular octagons with different outer diameters. The vertices of the outer octagonal frame are connected one-to-one with the corresponding vertices of the inner octagonal frame by straight line segments, thus dividing the entire coil area into eight identical trapezoidal coil units. These eight trapezoidal coil units are distributed with rotational symmetry around the coil center (O). Each coil unit contains a magnetic core, and all magnetic cores are uniformly arranged and rotated around the center of the transmitting coil. Note that a regular octagon is a shape similarity, not necessarily eight mathematically identical straight line segments.

[0023] When the eight trapezoidal coil units are in operation: By utilizing the fact that the currents in the conductor segments belonging to different coil units on the inner ring are of the same magnitude but different directions, the stray magnetic field in the central region of the transmitting coil is extremely low. For a single trapezoidal coil unit, the vertical component of the magnetic field generated by each unit above itself has the same direction as the vertical components of the magnetic fields generated by the adjacent coil units on either side above themselves; the horizontal component of the magnetic field generated by each unit above its common edge with the adjacent coil unit has the same direction as the horizontal component of the magnetic field generated by the adjacent coil units at the same location (above the aforementioned common edge). The common edge is the tightly adjacent, connected portion of the coil between two adjacent units. See also... Figure 3 The schematic magnetic field distribution is characterized by its ability to achieve magnetic flux convergence and improve the coupling capability of the magnetic coupling mechanism.

[0024] The transmitting coil that generates this magnetic field characteristic can be composed of eight independent trapezoidal coil units connected together. In this way, the coil unit includes a coil and an inverter circuit, and these eight coil units can be powered by eight transmitting power supplies (inverters). In this case, the number of operating coil units can be configured according to requirements to meet different power charging needs.

[0025] The transmitting coil can also be formed by winding a single wire. In this method, eight trapezoidal coil units are integrated, with each unit consisting of a single wound coil. The winding directions of adjacent trapezoidal coil units are opposite. Starting from any one trapezoidal coil unit, its winding direction alternates with that of its adjacent units. Specifically, if each trapezoidal coil unit is numbered clockwise, odd-numbered units are wound clockwise, while even-numbered units are wound counterclockwise.

[0026] The specific method for fabricating a transmitting coil using a single wire is as follows: Based on the dimensions of the UAV and the predetermined coil size parameters, starting from any trapezoidal coil unit, wind several turns from the outside to the inside of any vertex of the outer octagon in the same winding direction. When reaching the next vertex of the outer octagon, begin winding the next trapezoidal coil unit, winding in the opposite direction to the previous trapezoidal coil unit from the outside to the inside until reaching the next vertex of the outer octagon. Repeat the above steps until all eight trapezoidal coil units are wound. The leads of the transmitting coil can be drawn from any two adjacent trapezoidal coil units, depending on the actual design requirements.

[0027] According to the winding method described, when the transmitting coil is energized, the currents in adjacent trapezoidal coil units on the same side (non-common side) flow in opposite directions, while the currents on the common side flow in the same direction. (See [reference]). Figure 3 In Therefore, the magnetic fields generated by adjacent coil units in the transmitting coil are in opposite directions, and at the junction of adjacent coil units, the magnetic field transitions from vertical to horizontal.

[0028] Meanwhile, since the transmitting coil consists of eight trapezoidal coil units, and each adjacent trapezoidal coil unit is wound in opposite directions, the current flows in opposite directions on adjacent sides of the inner octagon that makes up the transmitting coil. These eight segments can be regarded as wire segments with current of the same magnitude but different directions. According to Ampere's law, the magnetic field generated by these wire segments in the central region can be effectively canceled out, resulting in extremely low stray magnetic field in the central region of the transmitting coil, effectively solving the adverse effects of stray magnetic field on the UAV equipment.

[0029] like Figure 4 As shown, at the receiving end, a set of receiving coils consists of coil α and coil β. Coil α or coil β is composed of N solenoid coils connected in series, where N is a preset value, such as N=4. The solenoids can be square or circular. Each solenoid coil connected in series is square. Based on the characteristics of the magnetic field generated by the transmitting coil, coil α and coil β receive the vertical and horizontal magnetic flux generated by the transmitting coil, respectively. Therefore, the four solenoid coils of coil α or coil β are orthogonally combined in pairs according to the series sequence and installed sequentially at the bottom of the UAV landing gear. During installation, coil α and coil β are designed to form an orthogonal combination to the greatest extent possible.

[0030] After the drone lands, if the receiving coils on the four poles are located within their respective coil units, coil α primarily receives the vertical magnetic field generated by its own coil unit. If the drone lands at the junction of adjacent coil units, coil β primarily receives the horizontal magnetic field generated by these two adjacent transmitting coils. If the drone lands in the region where the magnetic field of the transmitting coil transitions from vertical to horizontal, coils α and β are responsible for receiving the vertical and horizontal components of the magnetic field, respectively. Since coils α and β are orthogonal, the cross-coupling between them is very small and can be ignored. This design enables a 360-degree rotational offset capability of the magnetic coupling mechanism in the drone wireless charging system.

[0031] Based on the orthogonal receiving coil, the magnetic flux generated by the transmitting coil, which is predominantly vertical, is received only through coil α. In the blank spaces of the trapezoidal coil units, each trapezoidal coil unit can provide a stable deflection region of approximately 30 degrees, and the entire transmitting coil can provide a stable deflection region of 240 degrees. The receiving coil can maintain stable mutual inductance and reliable power transfer when landing in these regions. For UAVs with higher lightweight requirements, the scheme deploying only coil α can provide a more lightweight airborne solution.

[0032] The design process of the magnetic coupling mechanism in this invention primarily involves determining the installation position of the receiving coil based on the dimensions of the UAV. This determines the dimensions of the magnetic coupling mechanism's facing position. The outer and inner diameters and number of turns of the transmitting coil, as well as the dimensions and number of turns of the receiving coil, are then determined based on offset and coupling performance requirements. The conductor used in the magnetic coupling mechanism of this invention is Litz wire. The specifications of the Litz wire are selected based on the effective current values ​​of the transmitting and receiving coils obtained from the system's operating power and circuit topology, with a certain margin in place.

[0033] To more clearly explain the design process of the magnetic coupling mechanism proposed in this invention and to verify its advantages such as high coupling and lightweight design, the following invention examples are provided: The transmitting coil has an outer diameter of 400mm, an inner diameter of 160mm, and 6 turns, with Litz wire specifications of 0.1mm × 350 strands; the transmitting end magnetic core consists of eight PC95 ferrite magnetic strips evenly arranged around the center of the transmitting coil, with each strip having a length, width, and height of 200mm, 50mm, and 5mm, respectively. Coil α has dimensions of 20mm × 20mm × 18mm, 8 turns, and Litz wire specifications of 0.1mm × 200 strands; coil β has dimensions of 18mm × 18mm × 18mm, 8 turns, and Litz wire specifications of 0.1mm × 200 strands. There is no strict and precise constraint on the relationship between the core length and the height of the trapezoidal coil unit. The core length is greater than the height of the trapezoidal coil unit. The core can increase the flux path of leakage flux, shorten the coupling flux path, and improve the coupling performance.

[0034] In view of the characteristics of the magnetic coupling mechanism proposed in this invention, the following is adopted: Figure 5 The circuit topology shown. U IN The system input DC voltage is provided, and Q1~Q2 are four MOSFET devices that make up the full-bridge inverter circuit. The compensation topology adopts an LCC-P resonant compensation network. For transmitting end resonant compensation inductor, and This is a capacitor for compensating for the resonant signal at the transmitter. and This is the resonant compensation capacitor at the receiving end. For the self-inductance of the transmitting coil, and These are the self-inductances of the receiving coil α and coil β, respectively. and These are the mutual inductances between the transmitting coil and coils α and β, respectively. It is the mutual inductance between coil α and coil β. The receiving end uses uncontrolled full-bridge rectification. - The diodes are connected in parallel after the coils α and β are rectified. For output filter inductance, It is the equivalent load. This is the output voltage.

[0035] When the compensation network is designed to resonate at angular frequency ω, the parameters of the resonant compensation network should satisfy the following equation:

[0036] This is the reflection impedance of the receiving circuit at the transmitting end, and its amplitude expression is as follows:

[0037] The excitation current at the transmitting end can be obtained from the fundamental wave analysis method as follows:

[0038] The receiver is connected in parallel with a rectifier, and the output current is:

[0039] To verify the relevant characteristics of the magnetic coupling mechanism proposed in this invention, a magnetic coupling mechanism model was established in finite element simulation software, and the magnetic field distribution characteristics of the transmitting coil and the anti-rotation offset capability of the magnetic coupling mechanism were simulated and verified.

[0040] Figure 6 and Figure 7The magnetic flux density amplitude distribution map and magnetic flux density vector map at a vertical height of 3cm from the transmitting coil are obtained through finite element simulation. It can be seen that the magnetic flux density is very low in a certain area around the center above the coil, and the areas with higher magnetic flux density are mainly distributed near each trapezoidal coil unit. The direction of the vertical component of the magnetic flux density is alternately opposite in adjacent trapezoidal coil units. At the junction of the coils, the magnetic field lines transition horizontally from one trapezoidal coil unit to the other trapezoidal coil unit.

[0041] To more intuitively demonstrate the superior performance of this invention in suppressing stray magnetic fields, stray magnetic field distribution diagrams of the transmitting coil proposed in this invention and a conventional monopole circular coil were obtained through simulation software. To ensure the reasonableness of the comparison, the two coils maintained the same maximum outer diameter, current excitation magnitude, and self-inductance value, only changing the shape of the transmitting coil.

[0042] Figure 8 The stray magnetic field distribution diagrams for the two types of coils were obtained using finite element simulation software. The diagrams indicate the magnetic field levels of the two coils at distances of 10cm and 30cm above the coil center. The magnetic induction intensities at 10cm for the present invention and the conventional monopole coil are 23.76μT and 196.13μT, respectively; and at 30cm, they are 5.84μT and 46.28μT, respectively. Compared to the conventional monopole coil, the present invention reduces stray magnetic field suppression at 10cm by approximately 88%, demonstrating the significant effect of the present invention's transmitting coil on suppressing stray magnetic fields on the fuselage.

[0043] For the orthogonal coil used in the magnetic coupling mechanism of this invention, it is necessary to ensure that the receiving coil has good coupling capability at any position when the UAV deflects during landing. Therefore, anti-rotation offset test was carried out on the orthogonal coil used in this invention.

[0044] Figure 9 This diagram shows the coupling coefficient variation curves of the receiving coils at different deflection angles under the simulated rotational deviation of a drone. Starting from the centers of four trapezoidal coil units, the magnetic coupling mechanism of this invention features a centrally symmetrical transmitting coil. Taking the center of the transmitting coil as the origin and considering its characteristics, the rotation angle interval is 4.5°, and the selected deflection angle range is between -22.5° and 22.5° from the starting position. The coupling coefficients between coils α and β and the transmitting coil in the diagram are complementary at different deflection angles, enabling efficient charging of the drone during a 360° rotational deviation.

[0045] The above describes a transmitting coil with an inner and outer octagonal frame for a four-legged stand-alone drone. However, the inner and outer polygonal frames are not limited to regular octagons; an even number of sides, greater than or equal to 4, is sufficient to achieve the technical solution of this application. Therefore, the inner and outer polygonal frames can also be regular hexagons, regular decagons, or other regular polygons. Furthermore, the proposed magnetic coupling mechanism can also be applied to other types of drones and suitable mobile or non-mobile devices. In addition, the conductor segments of the transmitting coil can be curved. When the conductor segments are curved, the inner and outer polygonal frames of the transmitting coil are curvilinear. When constructing a charging device, there can be one or multiple transmitting coils.

[0046] While ensuring the entire transmitting coil is centrally symmetrical, the partitions formed by connecting the vertices of the inner and outer polygons are not limited to isosceles trapezoids. When the number of sides of the inner and outer polygons is different or the vertices are not connected in a corresponding manner, other shapes of partitions may be formed. As long as the adjacent partitions are kept in opposite directions, a similar effect can be produced.

[0047] There are many ways to wind the transmitting coil. This invention only selects one winding method, and the actual winding method may be different.

[0048] In summary, the wireless charging transmitting coil provided by this invention, while ensuring the coupling performance required for wireless charging of flying devices such as drones, naturally suppresses stray magnetic fields at the center due to its unique geometric structure and winding method. This characteristic is not the result of adding an additional magnetic shielding structure or suppressing the coil, but rather an inherent property naturally derived from the basic design principles of the coil.

[0049] Specifically, when the coil is energized, the reverse current configuration of adjacent coil units due to opposite wire windings, combined with the octagonal symmetrical structure, causes the magnetic field components in the central region of the transmitting coil to exhibit a self-cancelling effect. This effect significantly reduces the stray magnetic field strength in the central region of the transmitting coil without adding any additional design complexity, effectively reducing the risk of electromagnetic interference. This stray magnetic field suppression effect is achieved simultaneously with the optimization of the wireless charging performance of the transmitting coil, rather than as an independent design goal, and it does not change with variations in the transmitting coil parameters.

[0050] Furthermore, this invention, through an octagonal partitioned structure and alternating winding method, forms a high-density magnetic flux region at the intended location of the receiver. Because the magnetic field generated by the transmitting coil has excellent directionality and concentration, the receiving coil can capture sufficient magnetic flux without the need for magnetic materials for flux guidance. This allows the receiver to completely eliminate the need for traditional ferrite magnetic materials, reducing weight, material costs, and manufacturing complexity. Simultaneously, it avoids the eddy current losses and heat generation problems associated with magnetic materials at high frequencies. This design enables the wireless charging system to be better suited for weight-sensitive mobile devices such as drones, meeting strict weight limitations without sacrificing charging performance.

[0051] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein. The scope of the invention is defined by the appended claims.

Claims

1. A transmitter for a wireless charging magnetic coupling mechanism for unmanned aerial vehicles (UAVs), characterized in that: The transmitting coil at the transmitting end is a centrally symmetrical ring, and the transmitting coil is composed of an even number of coil units; When energized, the two conductor segments belonging to adjacent coil units on the inner ring have the same current magnitude but opposite current flow directions along the inner ring.

2. The transmitter according to claim 1, characterized in that: The vertical component of the magnetic field generated by each coil unit above it has the same direction as the vertical component of the magnetic field generated by the adjacent transmitting coils at the same position; the horizontal component of the magnetic field above the common edge of each coil unit and the adjacent coil unit has the same direction as the horizontal component of the magnetic field generated by the adjacent transmitting coils at the same position.

3. The transmitter according to claim 1, characterized in that: All coil units are wound from a single wire, with adjacent coil units wound in opposite directions.

4. The transmitter according to claim 1, characterized in that: The coil unit is in the shape of an isosceles trapezoid.

5. The transmitter according to claim 1, characterized in that: Each coil unit has a magnetic core, and all the magnetic cores are evenly arranged and rotated around the center of the transmitting coil.

6. The transmitting end according to claim 5, characterized in that: There is an insulating plate between the coil unit and the magnetic core. The magnetic core is located under the insulating plate, and the coil unit is located on the insulating plate.

7. A receiver for a wireless charging magnetic coupling mechanism for unmanned aerial vehicles, characterized in that: The receiving coil at the receiving end consists of coil α and coil β, which are placed orthogonally. Both coil α and coil β are composed of N identical solenoid coils connected in series, where N is a preset value. Alternatively, the receiving coil at the receiving end may consist of coil α.

8. A wireless charging magnetic coupling mechanism for unmanned aerial vehicles, characterized in that: The magnetic coupling mechanism includes the transmitter as described in any one of claims 1-6 and the receiver as described in claim 7.

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