Anti-offset magnetic coupling mechanism for wireless charging system of unmanned aerial vehicle

Abstract

The invention provides an anti-offset magnetic coupling mechanism for a wireless charging system of an unmanned aerial vehicle, the magnetic coupling mechanism comprises a transmitting end arranged on a landing platform and a receiving end mounted on the unmanned aerial vehicle, and a transmitting coil is a double-layer circular coil wound at gradient intervals; an axial magnetic field which is uniformly distributed is formed through a non-uniform distribution structure of coil turn spacing; the receiving end is composed of four sets of same magnetic core-coil structures, each set is composed of a lightweight cylindrical novel soft magnetic composite material magnetic core and an externally-wound solenoid coil of a vertical landing gear of the unmanned aerial vehicle, the magnetic cores are located in the vertical landing gear of the unmanned aerial vehicle, and the coils of the four magnetic core-coil structures are closely wound in the axial direction of the outer surface of the landing gear and connected in series. And coil and magnetic core parameters are designed by using an evolutionary algorithm. The problems that in a traditional scheme, the anti-offset capacity is weak, the magnetic core weight is large, and the receiving end is not matched with the special-shaped structure of the unmanned aerial vehicle are solved, and the method is suitable for unmanned aerial vehicle wireless charging scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless charging, and particularly relates to an anti-offset magnetic coupling mechanism for an unmanned aerial vehicle (UAV) wireless charging system. Background Art

[0002] With the needs of practical applications, UAVs have been widely used in many fields such as substation inspections, military reconnaissance, and agriculture. However, UAVs face the problem of insufficient endurance. The limited capacity of the battery cannot support long-term flight, which severely restricts the working efficiency of UAVs. Carrying large-volume batteries will increase the load burden of UAVs, while traditional wired charging will increase labor costs. Wireless charging technology has the advantages of safety, reliability, and convenience, and can effectively improve the endurance of UAVs. The magnetic coupling mechanism is a key part of wireless charging technology, and its design plays an important role in the overall transmission performance of the system. In practice, UAVs do not land at an ideal position fixedly, which will cause the receiver of the magnetic coupling mechanism to deviate relative to the transmitter, resulting in a decrease in charging efficiency. Therefore, it is necessary to design an anti-offset magnetic coupling mechanism to improve the charging stability of the system. In addition, considering the load capacity and special-shaped structure of UAVs, the receiver of the magnetic coupling mechanism should be adapted to the UAV structure and reduce the load burden of UAVs to enhance the working efficiency.

[0003] Currently, in order to solve the problems of poor anti-offset performance, large weight, and poor adaptability to the special-shaped structure of UAVs in the wireless charging magnetic coupling mechanism, multiple patents have conducted research and proposed corresponding solutions. For example:

[0004] 1. In the patent with the application number CN202311304275.X and the name "A Magnetic Coupling Mechanism for Anti-Offset Wireless Charging of UAVs", a new magnetic coupling structure of orthogonal double transmitting coils and a cross-shaped ferrite magnetic core is proposed. By regulating the orthogonal coil current to achieve the synthesis of magnetic field vectors, the limitation of the spatial degree of freedom of traditional single coils is broken through. The embedded receiving coil design is adopted to adapt to the lightweight requirements of UAVs. However, this design requires continuously controlling the frequency and phase of the power supply according to the position of the UAV, increasing the complexity of the wireless charging system.

[0005] 2. In the patent with the application number CN202310536516.7 and the name "A Double-U Magnetic Coupling Mechanism for UAV Wireless Charging", a double-U magnetic coupling mechanism for UAV wireless charging is proposed. The transmitting coil is wound on the U-shaped magnetic core, and the receiving coil is wound around the UAV fuselage, which can receive a larger magnetic field area and thus obtain more energy. However, the ability of this magnetic coupling mechanism to cope with the rotational offset of UAVs is not strong. Winding the receiving coil around the fuselage cannot fully adapt to the special-shaped structure of UAVs and will still increase wind resistance.

[0006] In the patent with the application number CN202011335346.9 and the title "A Lightweight Orthogonal Solenoid Magnetic Coupling Mechanism for UAV Wireless Charging", a lightweight orthogonal solenoid magnetic coupling mechanism for UAV wireless charging is proposed. The receiving end is wound around the bottom crossbeam of the UAV bracket, and the transmitting end coils are respectively wound around three magnetic columns of the transmitting core. This design adapts to the special-shaped structure of the UAV and avoids the problem of electromagnetic interference. However, the anti-offset performance of this magnetic coupling mechanism is poor, and the nanocrystalline receiving core will generate relatively large eddy current losses, affecting the power transmission performance.

[0007] In summary, the existing methods have problems such as being unable to fully adapt to the special-shaped structure of the UAV, complex control, and difficulty in using traditional cores. Therefore, there is an urgent need for a new magnetic coupling mechanism for UAV wireless charging systems to solve the problems of poor anti-offset performance, large weight, and weak adaptability to the special-shaped structure of the UAV. Summary of the Invention

[0008] In view of this, the object of the present invention is to address the problems of poor anti-offset performance, large weight of traditional cores, and weak adaptability of the receiving end to the special-shaped structure of the UAV in the magnetic coupling mechanism for UAV wireless charging, and propose an anti-offset magnetic coupling mechanism for UAV wireless charging systems.

[0009] The present invention includes a transmitting end arranged on the landing platform and a receiving end installed on the UAV. The transmitting coil uses a double-layer equal-increase circular coil with a gradient pitch - an equal-increase coil, and a uniformly distributed axial magnetic field is formed through the arrangement of the turn pitch with a dense outer and sparse inner pattern. The transmitting end uses a ferrite core; the receiving end is composed of four identical core-coil structures, which are respectively denoted as the first core-coil structure, the second core-coil structure, the third core-coil structure, and the fourth core-coil structure. Each structure consists of a first receiving core, a second receiving core, a third receiving core, and a fourth receiving core and the solenoid wound around them - the first receiving coil, the second receiving coil, the third receiving coil, and the fourth receiving coil. The four cylindrical receiving cores are respectively installed in the first vertical landing gear of the UAV, the second vertical landing gear of the UAV, the third vertical landing gear of the UAV, and the fourth vertical landing gear of the UAV. The four receiving coils are respectively wound axially and densely along the outer surface of the landing gear and are connected in series.

[0010] To solve the problems of heavy weight, easy damage, and large eddy current loss of traditional magnetic cores, a new type of nanocrystalline soft magnetic composite material is introduced. This material is not easily damaged during jolts, has good toughness, small eddy current loss, and small density, meeting the design requirements of anti-offset and lightweight magnetic cores for the receiving end of drones. Four cylindrical magnetic cores are made from the new type of nanocrystalline soft magnetic composite material; the first vertical landing gear of the drone, the second vertical landing gear of the drone, the third vertical landing gear of the drone, and the fourth vertical landing gear of the drone are arranged at the four corners, and the first receiving magnetic core, the second receiving magnetic core, the third receiving magnetic core, and the fourth receiving magnetic core are respectively installed in the four vertical landing gears of the drone.

[0011] Four solenoid coils are respectively wound around the outside of the vertical landing gears of the drone using Litz wire as receiving coils. The first receiving coil, the second receiving coil, the third receiving coil, and the fourth receiving coil are connected in series. Since the four receiving coils adopt a distributed layout and are far apart, the mutual inductance between them can be ignored, effectively avoiding the mutual influence between multiple receiving ends.

[0012] The design of the transmitting coil is as follows: The coil group formed by closely winding every 3 turns of Litz wire is used as the basic unit. Five coil units are arranged in each layer and a double-layer coil structure is formed through a series connection method. The distance between adjacent coil groups of the transmitting coil increases arithmetically with a fixed tolerance Δp from the outside to the inside, and the fixed tolerance satisfies the relationship:

[0013]

[0014] where Δp is the fixed tolerance, D t is the outer diameter of the transmitting coil, d t is the inner diameter of the transmitting coil, d L is the wire diameter of the Litz wire, N t is the total number of turns of the transmitting coil, G t is the number of coil groups in each layer of the transmitting coil.

[0015] The ferrite magnetic core at the transmitting end is composed of ferrite rods evenly distributed along the circumference.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: By adopting a magnetic core made of a new type of nanocrystalline soft magnetic composite material, the weight of the magnetic core is significantly reduced, meeting the lightweight design requirements of the drone. Due to the soft magnetic characteristics of the new type of nanocrystalline soft magnetic composite material, a magnetic core is introduced at the receiving end, effectively improving the transmission performance compared with the traditional non-magnetic core mechanism. The equal-increasing coils at the transmitting end are used in combination with the distributed receiving structure, significantly improving the charging stability of the drone during horizontal and rotational offsets. Installing the magnetic core inside the landing gear of the drone eliminates the need for additional auxiliary devices, not only matching the special-shaped structure of the drone but also simplifying the overall system design and improving the practicality.

[0017] In summary, through the application of new materials and the structural optimization of the magnetic coupling mechanism, the present invention significantly improves the anti-offset ability of the UAV wireless charging system. Meanwhile, it has the advantages of light weight and adaptability to the special-shaped structure of the UAV, possessing important practical value and promotional significance. Brief Description of the Drawings

[0018] Figure 1 It is the structural diagram of the wireless charging system based on the S-S compensation structure of the present invention;

[0019] Figure 2 It is the structural diagram of the receiving end of the magnetic coupling mechanism of the UAV wireless charging system of the present invention;

[0020] Figure 3 It is the structural diagram of the transmitting end of the magnetic coupling mechanism of the UAV wireless charging system of the present invention;

[0021] Figure 4 It is the overall structural diagram of the magnetic coupling mechanism of the UAV wireless charging system of the present invention;

[0022] Figure 5 It is the multi-objective optimization flow chart of the magnetic coupling mechanism based on the evolutionary algorithm of the present invention;

[0023] Figure 6 It is the cross-sectional magnetic flux distribution diagram of the magnetic coupling mechanism of the UAV wireless charging system of the present invention;

[0024] Figure 7 It is the relationship diagram between the mutual inductance and the x-y plane offset of the UAV wireless charging system of the present invention;

[0025] Figure 8 It is the relationship diagram between the transmission efficiency and the x-y plane offset of the UAV wireless charging system of the present invention;

[0026] Figure 9 It is the mutual inductance simulation result diagram of the UAV wireless charging system of the present invention with different charging heights and rotational offsets.

[0027] Among them, 1-UAV fuselage; 2-first core-coil structure; 2_1, 2_2, 2_2-first landing gear, first receiving core, first receiving coil of the UAV; 3-second core-coil structure; 3_1, 3_2, 3_2-second landing gear, second receiving core, second receiving coil of the UAV; 4-third core-coil structure; 4_1, 4_2, 4_2-third landing gear, third receiving core, fourth receiving coil of the UAV; 5-fourth core-coil structure; 5_1, 5_2, 5_2-fourth landing gear, fourth receiving core, fourth receiving coil of the UAV; 6-transmitting coil; 7-transmitting core. Detailed Embodiment

[0028] The present invention will be further described below with reference to the drawings.

[0029] The structural diagram of the wireless charging system based on the S-S compensation structure is shown in the appendix Figure 1 as follows. The expression for the system resonance condition is:

[0030]

[0031] where ω is the system angular frequency; L t and L r are the inductances of the transmitting coil and the receiving coil respectively; C t and C r are the resonance capacitances of the transmitting coil and the receiving coil respectively.

[0032] The output power P out and efficiency η of the magnetic coupling mechanism can be achieved through the resonance condition:

[0033]

[0034] where U in and U out are the transmitting voltage and receiving voltage of the magnetic coupling mechanism respectively; R eq is the reflected resistance of the diode rectifier; M is the mutual inductance between the transmitting end and the receiving end; R t and R r are the internal resistances of the transmitting coil and the receiving coil respectively.

[0035] The efficiency is determined by the parameters of the magnetic coupling structure itself, and it has a strong correlation with the change of mutual inductance. During the landing process of the UAV, the randomness of the landing point will cause the change of mutual inductance. The anti-offset ability is mainly reflected in the amplitude of the change of mutual inductance with the position offset. Therefore, it is necessary to suppress the change of mutual inductance during the offset process, so as to reduce the influence of the offset on the system performance.

[0036] A new type of nanocrystalline soft magnetic composite material is used to solve the problems of large weight, easy damage and large eddy current loss of the traditional magnetic core. The measured density of this material is 1.26 g / cm 3 , which is lower than that of nanocrystalline strip and ferrite, and can effectively reduce the overall mass of the magnetic core, meeting the lightweight design requirements of the UAV. In terms of electromagnetic characteristics, the high resistivity characteristic of the material can reduce the eddy current loss, which plays a key role in improving the energy transmission efficiency under high-frequency working conditions.

[0037] The parameters of the magnetic coupling mechanism are initially set, as shown in the appendix Figure 2It is a structural diagram of the receiving end of the magnetic coupling mechanism of the UAV wireless charging system. Four cylindrical magnetic cores with a diameter of 14 mm and a length of 55 mm are made of a new type of nanocrystalline soft magnetic composite material, which are respectively denoted as the first receiving magnetic core 2_2, the second receiving magnetic core 3_2, the third receiving magnetic core 4_2, and the fourth receiving magnetic core 5_2. The first vertical landing gear 2_1, the second vertical landing gear 3_1, the third vertical landing gear 4_1, and the fourth vertical landing gear 5_1 of the UAV are arranged at the four corners, and the distance between adjacent landing gears is 140 mm. The four cylindrical magnetic cores are respectively embedded in the four vertical landing gears of the UAV. Four solenoid coils with 20 turns are respectively wound outside the landing gears using Litz wire with a wire diameter of 2.7 mm as receiving coils, which are respectively denoted as the first receiving coil 2_3, the second receiving coil 3_3, the third receiving coil 4_3, and the fourth receiving coil 5_3. The four receiving coils are connected in series, and the outer diameter is 25.2 mm.

[0038] To make the transmitting end generate a uniform axial magnetic field to give enough free movement space for the four receiving coils, keep the efficiency relatively stable, and improve the anti-offset ability of the magnetic coupling mechanism. A circular planar coil with rotational offset is used to effectively prevent the UAV from being affected by different rotational angles of the fuselage when landing. In addition, the traditional circular planar coil is optimized to an equal-increase coil as the transmitting coil 6 of the magnetic coupling mechanism to maintain the mutual inductance stability when the UAV has a horizontal offset. The structural diagram of the transmitting end of the magnetic coupling mechanism of the UAV wireless charging system is as attached Figure 3 shown. The transmitting coil 6 uses an equal-increase coil and adopts a sparse winding method with a dense outer and sparse inner structure. The coil group formed by closely winding 3 turns of Litz wire with a wire diameter of 2.7 mm is used as the basic unit. 5 coil units are arranged in each layer and a complete coil structure with 30 turns in two layers is formed through a series connection method. The outer diameter of the transmitting coil 6 is 400 mm, the inner diameter is 79 mm, and the distance between adjacent coil groups increases arithmetically from the outside to the inside according to a fixed tolerance Δp = 12 mm. The fixed tolerance satisfies the relationship:

[0039]

[0040] where, Δp is the fixed tolerance, D t is the outer diameter of the transmitting coil, d t is the inner diameter of the transmitting coil, d L is the wire diameter of the Litz wire, N t is the total number of turns of the transmitting coil, G t is the number of coil groups in each layer of the transmitting coil.

[0041] The transmitting end magnetic core is composed of 8 ferrite magnetic cores 7 evenly distributed along the circumference. The width, length, and thickness of each magnetic core are 53 mm, 159 mm, and 5 mm respectively. The overall structural diagram of the magnetic coupling mechanism of the UAV wireless charging system is as attached Figure 4 shown.

[0042] The sparse winding method with a dense outer and sparse inner structure of the transmitting coil 6 generates a uniform axial magnetic field, enabling the magnetic coupling mechanism to have anti-offset performance in the horizontal direction. The circular transmitting structure is combined with the symmetric structure of the receiving end, reducing the influence of the rotation angle on the charging performance.

[0043] Table 1 Value ranges of optimization variables

[0044]

[0045] To further improve the system performance, an evolutionary algorithm is used to optimize the fixed tolerance of the transmitting coil, the total number of turns of the receiving coil, and the length of the cylindrical magnetic core. The value ranges of the optimization variables are shown in Table 1. The primary goal of the anti-offset design is to ensure that the mutual inductance is as stable as possible when an offset occurs. The main factor affecting the stability of the mutual inductance is the uniformity of the magnetic field generated by the transmitting coil. Reasonable design of the transmitting coil can make the magnetic field evenly distributed and improve the anti-offset performance. Therefore, the difference in mutual inductance between when there is no offset and when the offset is 70 mm is used as the first objective function. Excessive improvement of the anti-offset performance of the magnetic coupler may affect its power transmission performance. Therefore, the mutual inductance when there is no offset is used as the second objective. A lightweight magnetic coupling mechanism can reduce the load burden of the UAV and improve work efficiency. The weight of the receiving end is used as the third objective function.

[0046] The multi-objective optimization flowchart of the magnetic coupling mechanism based on the evolutionary algorithm is as shown in the appendix Figure 5 First, sensitivity analysis is carried out to evaluate the influence of changes in input parameters on the model output results, effectively reducing the computational complexity and improving the optimization efficiency. The Latin hypercube sampling method is used to generate an initial population of a certain scale, and the values of the optimization objective functions are obtained through finite element simulation to evaluate the results of the sensitivity analysis. Then, the fixed tolerance of the transmitting coil, the total number of turns of the receiving coil, and the length of the cylindrical magnetic core are optimized, and the fitness value of each individual is calculated. The higher the fitness value, the closer the individual is to the optimal solution of the problem. The offspring population is generated through three basic operations: selection, crossover, and mutation. G and G max are the current iteration number and the maximum iteration number respectively. If the maximum iteration number is reached, the calculation is stopped and the Pareto optimal solution set is output.

[0047] The optimization results are normalized and sorted, and the optimal result is selected. The normalization method is shown in the following formula:

[0048]

[0049] Among them, f t is the normalized value of the t-th solution in the Pareto solution set; n obj is the number of optimization objectives; f t (n) is the function value of the n-th optimization objective corresponding to the t-th solution; fmin (n) and f max (n) is the minimum and maximum function values of the nth optimization objective among all solutions; α t is the weight of different objective functions.

[0050] Multiply the result after normalizing the mutual inductance difference and the receiving end weight by a negative sign to keep the evaluation directions of different optimization objectives consistent. The variable values corresponding to the obtained optimal result are: the fixed tolerance of the transmitting coil is 7.5 mm, the total number of turns of the receiving coil is 76 turns, and the length of the cylindrical magnetic core is 70 mm.

[0051] Appendix Figure 6 shows the cross-sectional magnetic flux distribution of the magnetic coupling mechanism of the UAV wireless charging system. The main magnetic flux passes through the bottom of the receiving coil, and there is almost no magnetic flux around the landing gear above the receiving coil, which can significantly reduce the impact of electromagnetic interference problems on the UAV's on-board equipment. Since the four receiving coils adopt a distributed layout and are far apart from each other, the mutual inductance between them is only 28.2 nH, avoiding the influence between multiple receiving ends.

[0052] Appendix Figure 7 and Appendix Figure 8 shows the relationship between the mutual inductance and the system transmission efficiency and the x - y plane offset. The mutual inductance when the system has no offset is 17.81 μH, and the transmission efficiency is 85%, which are increased by 12.93 μH and 27.65% respectively compared with the coreless scheme, effectively improving the transmission performance. When the UAV undergoes a horizontal offset of ±60 mm, the fluctuation of the mutual inductance is 3.45 μH, and the fluctuation of the efficiency is 0.69%, and the mutual inductance can still be maintained at no less than 15.56 μH and the efficiency at 84.47%.

[0053] Considering the hovering height and direction of the UAV during charging, the present invention also examines the influence of the charging height and rotational offset on the mutual inductance. As shown in Appendix Figure 9 , since the ferrite magnetic core is not fully covered, there is a region where the mutual inductance decreases. During the process of the UAV rotating 360°, the mutual inductance changes by 1.08 μH, and the efficiency changes by 0.09%. Its stability stems from the rotationally symmetric magnetic field design of the transmitting coil. During the process of the charging height increasing from 1 mm to 11 mm, the mutual inductance decreases by 2.15 μH, and the efficiency decreases by 0.15%. This magnetic coupling mechanism has a certain charging height fault tolerance while achieving omnidirectional anti-offset.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. An anti-offset magnetic coupling mechanism for a drone wireless charging system, characterized in that: It includes a transmitting end disposed on a landing platform and a receiving end mounted on a drone (1). The transmitting coil (6) is a double-layer equal-increment circular coil wound with a gradient pitch - an equal-increment coil, which forms a uniformly distributed axial magnetic field through the arrangement of turn pitches that are dense on the outside and sparse on the inside. The transmitting end uses a ferrite core (7); the receiving end is composed of four identical core - coil structures, which are respectively denoted as the first core - coil structure (2), the second core - coil structure (3), the third core - coil structure (4), and the fourth core - coil structure (5). Each structure consists of a first receiving core (2_2), a second receiving core (3_2), a third receiving core (4_2), and a fourth receiving core (5_2) and the solenoids wound around them - the first receiving coil (2_3), the second receiving coil (3_3), the third receiving coil (4_3), and the fourth receiving coil (5_3). The four cylindrical receiving cores are respectively installed in the first vertical landing gear (2_1) of the drone, the second vertical landing gear (3_1) of the drone, the third vertical landing gear (4_1) of the drone, and the fourth vertical landing gear (5_1) of the drone. The four receiving coils are respectively wound axially and densely along the outer surface of the landing gear and are connected in series.

2. The anti-offset magnetic coupling mechanism for a drone wireless charging system according to claim 1, characterized in that: To solve the problems of the traditional magnetic core, such as large weight, easy damage, and large eddy current loss, a new type of nanocrystalline soft magnetic composite material is introduced. This material is not easily damaged by bumps, has good toughness, has relatively small eddy current loss, and has a relatively small density, which meets the design requirements of anti - offset and lightweight cores for the receiving end of the drone. The new type of nanocrystalline soft magnetic composite material is made into four cylindrical cores; the first vertical landing gear (2_1) of the drone, the second vertical landing gear (3_1) of the drone, the third vertical landing gear (4_1) of the drone, and the fourth vertical landing gear (5_1) of the drone are arranged at the four corners, and the first receiving core (2_2), the second receiving core (3_2), the third receiving core (4_2), and the fourth receiving core (5_2) are respectively installed in the four vertical landing gears of the drone.

3. The anti-offset magnetic coupling mechanism for a drone wireless charging system according to claim 1, characterized in that: The first receiving coil (2_3), the second receiving coil (3_3), the third receiving coil (4_3), and the fourth receiving coil (5_3) are connected in series. Since the four receiving coils adopt a distributed layout and the spacing is relatively far, the mutual inductance between them can be ignored, effectively avoiding the mutual influence between multiple receiving ends.

4. The anti-offset magnetic coupling mechanism for a drone wireless charging system according to claim 1, characterized in that: The design of the transmitting coil (6) is as follows. The coil group formed by closely winding every 3 turns of Litz wire is used as the basic unit. Five coil units are arranged in each layer and a double - layer coil structure is formed through a series connection method. The spacing between adjacent coil groups of the transmitting coil increases arithmetically with a fixed tolerance Δp from the outside to the inside, and the fixed tolerance satisfies the relationship: where Δp is the fixed tolerance, D t is the outer diameter of the transmitting coil, d t is the inner diameter of the transmitting coil, d L is the diameter of the litz wire, N t is the total number of turns of the transmitting coil, G t is the number of groups of the transmitting coil per layer.

5. The anti-offset magnetic coupling mechanism for a drone wireless charging system according to claim 1, characterized in that: The transmitting - end ferrite core (7) is composed of ferrite rods evenly distributed along the circumference.

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