Low-stray magnetic field voltage equalization full decoupling magnetic coupling structure and design method

Abstract

The application discloses a low-stray magnetic field voltage balancing full decoupling type magnetic coupling structure and a design method, relates to the technical field of wireless charging, and provides a low-stray magnetic field voltage balancing full decoupling type magnetic coupling structure, which comprises a primary side structure and a secondary side structure, wherein the primary side structure and the secondary side structure are both multilayer overlapping structures; and a low-stray magnetic field voltage balancing full decoupling type magnetic coupling structure design method is also provided, which comprises the following steps: S1, selecting a three-phase model; S2, full decoupling magnetic coupling structure design; S3, low-voltage stress design; and S4, magnetic coupling structure winding stacking. The application provides a low-stray magnetic field voltage balancing full decoupling type magnetic coupling structure and a design method, which effectively combines a voltage balancing split coil scheme and a full decoupling structure, and can effectively reduce stray magnetic fields and the safety of a wireless system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wireless charging, and particularly relates to a voltage balancing full decoupling type magnetic coupling structure with low stray magnetic field and a design method. BACKGROUND

[0002] Wireless power transfer technology has been widely applied in various fields such as industry, consumer products and electric vehicles. With the continuous development of industry, the global research attention on high-density and high-power wireless power transfer systems is increasingly close. With the development of wireless power transfer systems, environmental adaptability is also challenged by the influence of stray magnetic field. At present, the research on the problem of stray magnetic field in high-power wireless charging system mainly focuses on the design of magnetic coupling structure of single-phase system. Most of the research adopts low magnetic resistance material to realize the passive shielding technology of space magnetic field convergence and shielding layer. In addition, active or passive shielding coils are placed near the coupling structure to adjust the stray magnetic field, so as to ensure the low stray magnetic field characteristics of the wireless charging system. Multi-phase wireless power transfer system, especially 3-phase system with strong transmission capacity, has become one of the potential solutions to overcome the challenges related to wireless power transfer system [T. Feng, Y. Sun, Z. Zuo, Z. Wang and X. Dai, "Magnetic field analysis and excitation currents optimization for an omnidirectional WPT system based on three-phase tubular coils," IEEE Trans. Ind. Appl., vol. 58, no. 1, pp. 1268-1278, Jan.-Feb. 2022.]

[0003] The current research on 3-phase wireless power transfer system is mainly focused on electric vehicles. Most of the researches utilize the rotating magnetic field characteristics of 3-phase system to design dynamic wireless charging system [B. Song, B. Du, S. Cui, Y. Li and C. Zhu, "Mechanism analysis of output fluctuation in a three-phase dynamic wireless charging system," IEEE Trans. Ind. Electron., vol. 69, no. 3, pp. 2252-2264, March 2022]. Some other researches achieve the structured design of 3-phase transmission / single-phase reception through independently decoupled 3-phase magnetic structure. Due to the constant current characteristics of LCC network and the stability of high-order resonance compensation, 3-phase DLCC network has a wider application prospect. At present, due to the complexity of 3-phase DLCC network compared with single-phase DLCC, the research on 3-phase DLCC network is less, mainly focusing on basic topology design and prototype construction [J. Pries, G. J.-Su, V. Galigekere and O. Onar, "Phase shift control of a three-phase inverter for balanced secondary currents in misaligned three-phase inductive power transfer systems," 2020 IEEE PELS Workshop Emerg. Technol.: Wirel. Power Transf., Seoul, Korea (South), 2020, pp. 10-15].

[0004] Therefore, for the characteristics of 3-phase DLCC resonance network, a magnetic coupling structure design scheme of full decoupling, low stray magnetic field and low voltage balanced split coil is proposed, which can effectively solve the shortcomings of the existing research on magnetic coupling structure design. Improve the large power wireless charging system is applicable.

[0005] The main factors affecting the efficiency of wireless charging system are the loss of resonance inductance, resonance capacitance and power transfer coil. The coupling coefficient is affected by the distance between the primary and secondary power transfer coils and their spatial facing area, which is usually a fixed value in the design of wireless charging system. Therefore, the only effective way to reduce system loss is to increase the self-inductance value of the power transfer coil.

[0006] However, increasing the inductance of the wireless charging system by increasing the power transmission coil can reduce the loss of the system, but also brings significant system insulation withstand voltage safety risk, which produces a contradiction between the efficiency and safety of the wireless charging system. SUMMARY

[0007] The purpose of the present application is to provide a low-stray magnetic field voltage balancing full decoupling type magnetic coupling structure and design method, which realizes the effective combination of voltage balancing coil splitting scheme and low-stray magnetic field full decoupling structure, and improves the overall safety of the wireless charging system.

[0008] In one aspect, according to an embodiment of the present application, a low-stray magnetic field voltage balancing full decoupling type magnetic coupling structure is provided, comprising a primary side structure and a secondary side structure, wherein the primary side structure and the secondary side structure are both multi-layer overlapping structures; the primary side structure comprises a primary side aluminum plate shielding layer located at the lowermost position, a primary side ferrite magnetic core fixedly arranged above the primary side aluminum plate shielding layer, and a primary side single-pole coil L A , a primary side double-pole coil L B , and a primary side double-pole coil L C are sequentially and fixedly overlapped below the primary side ferrite magnetic core; the secondary side structure comprises a secondary side aluminum plate shielding layer located at the uppermost position, wherein a secondary side ferrite magnetic core is fixedly arranged below the secondary side aluminum plate shielding layer; a secondary side single-pole coil L a , a secondary side double-pole coil L c , and a secondary side double-pole coil L b are sequentially and fixedly overlapped below the secondary side ferrite magnetic core.

[0009] According to an aspect of an embodiment of the present application, the primary side single-pole coil L A , the primary side double-pole coil L B , and the primary side double-pole coil L C are three-layer stacked coil structures, wherein the primary side single-pole coil L A is configured to generate a magnetic field along the Z-axis, the primary side double-pole coil L B is configured to generate a magnetic field along the Y-axis, and the primary side double-pole coil L C is configured to generate a magnetic field along the X-axis, thereby realizing full decoupling of the coils through mutually perpendicular magnetic field directions.

[0010] According to an aspect of an embodiment of the present application, the secondary side single-pole coil L a , the secondary side double-pole coil L c , and the secondary side double-pole coil L b are symmetrically designed with the primary side three-layer stacked coil structure, wherein the positions of the secondary side double-pole coil L c and the secondary side double-pole coil L b are exchanged relative to the positions of the primary side double-pole coil L B and the primary side double-pole coil L C .

[0011] According to an aspect of the embodiment of the present application, the primary single coil L A , the primary bipolar coil L B , the primary bipolar coil L C , and the secondary single coil L a , the secondary bipolar coil L b , the secondary bipolar coil L c are series transmission coils in L-C…L-C mode, which are a plurality of series of sub-coils, and a series resonant capacitor between adjacent sub-coils.

[0012] According to an aspect of the embodiment of the present application, the series transmission coil adopts a winding mode of a plurality of split sub-coils wound in a parallel same spiral manner, the effective length and the magnetic path area of each split sub-coil are equal, and the capacitance values of each series resonant capacitor in each group of series transmission coils are equal.

[0013] On the other hand, the embodiment of the present application proposes a voltage balancing full decoupling type magnetic coupling structure design method with low stray magnetic field, which is used for designing the above magnetic coupling structure, and includes the following steps: S1: selecting a three-phase model; selecting a Y-Y type three-phase DLCC resonant network as a basic architecture; S2: full decoupling magnetic coupling structure design; selecting a three-layer stacked structure for the design of the coupling mechanism, winding the power transmission coil into a single coil and a bipolar coil, adjusting the distribution position of the three-layer stacked coil to realize the perpendicularity of the magnetic field directions of the three, and completing the full decoupling design of the coil; S3: low voltage stress design; for the power transmission coil of the three-layer stacked structure, the structure of each layer of power transmission coil is split; the power transmission coil is split and replaced by a plurality of series of power transmission coils, and the corresponding series resonant capacitor also needs to be additionally matched with the split series resonant capacitor, forming a series transmission coil in L-C…L-C mode, so as to effectively reduce the voltage stress; S4: magnetic coupling structure winding and stacking; S401: coil balancing winding, for each layer of power transmission coil, a balancing winding mode is selected, so that the effective length and the magnetic path area of each split power transmission coil of each layer are equal; S402: coil full decoupling stacking, for the shape and current direction of each layer of power coil, the placement position of each layer of power coil is set, so as to realize that the magnetic field directions of the three layers of power coils are kept perpendicular to each other, and realize the full decoupling of the coil; S403: symmetric configuration of the magnetic coupling structure, the primary / secondary side of the magnetic coupling structure is symmetrically laid out, especially the positions of the two bipolar coils in the primary / secondary side are exchanged, so as to ensure the consistency of the mutual inductance distance of the two groups of mutual inductance bipolar coils in the primary / secondary side.

[0014] According to an aspect of the embodiment of the present application, the step S2 comprises the following steps: S201, setting the basic shielding size and the air gap of the power transmission structure, and symmetrically designing the primary side and the secondary side of the magnetic coupling structure to keep the winding width of each phase coil of the three-phase system consistent; S202, analyzing the relationship between the power transmission coil width and the coupling coefficient, drawing a quality factor characteristic curve, and selecting the optimal coil width value.

[0015] According to an aspect of the embodiment of the present application, the step S3 comprises the following steps: S301, setting the split quantity of the basic power transmission coil and the series resonance capacitor, and forming a multi-section L-C…L-C mode series transmission coil; S302, balancing the specifications of each split power transmission coil, so that the length and area of each split power transmission coil are equal; and calculating the capacitance value of the split resonance capacitor to be replaced, wherein the capacitance values of the split resonance capacitors are equal.

[0016] According to an aspect of the embodiment of the present application, in the step S302, the capacitance value of the split resonance capacitor is calculated by the following formula:

[0017]

[0018] In the formula, n represents one phase of the three phases A, B and C, C n is the capacitance value of the resonance capacitor before splitting, C n-1 , C n-2 , C n-3 , C n-4 is the capacitance value of each split resonance capacitor.

[0019] In summary, the beneficial technical effects of the present application are:

[0020] The full decoupling magnetic structure of the present application is superior to the single-phase system in reducing the stray magnetic field distribution, and effectively reduces the stray magnetic field of the magnetic structure. The voltage balancing split coil scheme is effectively combined with the full decoupling structure, which improves the overall safety of the wireless charging system, and provides theoretical guidance for constructing a more effective and safer electric vehicle wireless charging system.

[0021] The design method of the voltage balancing coil of the full decoupling magnetic coupling structure analyzes and determines the low stray magnetic field stress characteristics of the full decoupling magnetic coupling structure; the inductance full balancing-voltage full balancing magnetic coupling structure design is realized through the cross arrangement; the low voltage balancing split coil scheme is effectively combined with the full decoupling structure, which improves the overall safety of the wireless charging system. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The figure is a schematic diagram of the three-phase wireless charging system structure of the present application;

[0023] Figure 2 Schematic diagram of Y-Y connection scheme for three-phase DLCC network of the present invention;

[0024] Figure 3 Schematic diagram of Y-Y connection scheme operation mode for three-phase DLCC network of the present invention;

[0025] Figure 4 Schematic diagram of 3D model for fully decoupled magnetic structure of the present invention;

[0026] Figure 5 (a) Schematic diagram of stray magnetic field analysis model for fully decoupled structure of the present invention, Figure 5 (b) Schematic diagram of stray magnetic field analysis model for single pole structure;

[0027] Figure 6 (a) Schematic diagram of 3D model for single pole A phase split coil of the present invention, Figure 6 (b) Schematic diagram of 3D model for bipolar B phase split coil, Figure 6 (c) Schematic diagram of 3D model for bipolar C phase split coil;

[0028] Figure 7 (a) Schematic diagram of voltage stress analysis for unsplit power transfer coil and resonant capacitor of the present invention, Figure 7 (b) Schematic diagram of voltage stress analysis for split power transfer coil and resonant capacitor;

[0029] Figure 8 (a) Schematic diagram of relationship between power transfer coil width and coupling coefficient for three-phase system of the present invention, Figure 8 (b) Schematic diagram of relationship between power transfer coil width and quality factor for three-phase system;

[0030] Figure 9 (a) Stray magnetic field distribution characteristics for fully decoupled primary side rated current and secondary side open circuit of the present invention, Figure 9 (b) Stray magnetic field distribution characteristics for single pole structure primary side rated current and secondary side open circuit;

[0031] Figure 10 (a) Magnetic flux density and phase distribution characteristics curve for three-phase fully decoupled magnetic structure of the present invention, Figure 10 (b) Magnetic flux density and phase distribution characteristics curve for single-phase single pole magnetic structure, Figure 10 (c) Magnetic flux density and phase distribution characteristics curve for three-phase fully decoupled magnetic structure split along X, Y, Z axis, Figure 10 (d) Magnetic flux density and phase distribution characteristics curve for three-phase fully decoupled magnetic structure characteristics, Figure 10 (e) Magnetic flux density and phase distribution characteristics curve for three-phase fully decoupled magnetic structure characteristics, Figure 10(f) is a three-phase full decoupling type the magnetic flux density and phase distribution characteristic curve;

[0032] Figure 11 (a) is a simulation analysis schematic diagram of the influence between the three-phase full decoupling structure of the present application and human beings; Figure 11 (b) is a simulation analysis schematic diagram of the influence between the single-phase single-pole structure and human beings;

[0033] Figure 12 (a) is a stray magnetic field distribution diagram of the three-phase full decoupling structure of the present application, Figure 12 (b) is a stray magnetic field distribution diagram of the single-phase single-pole structure;

[0034] Figure 13 (a) is a magnetic flux density and phase distribution characteristic curve at different distances of the three-phase full decoupling structure of the present application, Figure 13 (b) is a magnetic flux density and phase distribution characteristic curve at different distances of the single-phase single-pole structure;

[0035] Figure 14 is an inductance distribution characteristic diagram of the balanced split coil based on finite element simulation of the present application;

[0036] Figure 15 (a) is a simulation analysis schematic diagram of the influence between the voltage balanced split coil of the three-phase full decoupling structure of the present application and human beings; Figure 15 (b) is a simulation analysis schematic diagram of the influence between the voltage balanced split coil of the single-phase single-pole structure and human beings. DETAILED DESCRIPTION

[0037] The features and exemplary embodiments of various aspects of the present application will be described in detail below, in order to make the purposes, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, but not to limit the present application. The present application can be implemented without some of these specific details by those skilled in the art. The following description of the embodiments is only to provide a better understanding of the present application by showing examples of the present application.

[0038] It is to be understood that the terminology "first" and "second", and the like, used throughout this disclosure are only used to differentiate one from another entity or action, and do not imply any actual relationship or order between these entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0039] In the embodiments of the present application, the same reference signs represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of the present application shown in the drawings, and the overall thickness, length, width, and other dimensions of the integrated device are only exemplary and should not constitute any limitation on the present application.

[0040] "Multiple" appearing in the present application means two or more (including two).

[0041] In the present application, the drawings are Figure 1 The drawings are Figure 3 The following analysis is made for the three-phase DLCC resonant network:

[0042] 1.1 Analysis of characteristics of three-phase DLCC network

[0043] The three-phase wireless charging system has fewer switching tubes while maintaining a large transmission power capability and achieving a lower stray magnetic field, and is more suitable for medium and high power wireless charging systems. The three-phase wireless charging system is composed of a three-phase high-frequency inverter, a full-decoupling resonant compensation structure, and a three-phase high-frequency rectifier, and the overall architecture is as shown in Figure 1

[0044] Based on the high-stability DLCC resonant network architecture, the characteristics of the type resonant network are explored, and the coupling characteristics of the three-phase energy transmission coil are analyzed. The type resonant network architecture that can be independently operated in single phase is determined, and further analysis of the loss composition of the resonant compensation network, the voltage stress characteristics of the key devices, and the design requirements of the full-decoupling magnetic coupling structure are made to achieve conversion to compatible operation state of single-phase DLCC, and improve the interoperability of the wireless charging system.

[0045] 1.2 Analysis of three-phase DLCC resonant network ​

[0046] In the three-phase DLCC network, the capacitances and inductances can be connected in delta or Y type. However, the delta connection of the three-phase DLCC network cannot achieve complete decoupling in the three-phase system, limiting the single-phase independent operation characteristics of the three-phase wireless charging system and reducing the reliability of the three-phase system. By Y connecting the energy transmission coil and the resonance capacitance, the three-phase system meets the condition of single-phase independent operation. In the design, the bus capacitance is split as the neutral point of the three-phase system, and the structure is as shown in Figure 2 .

[0047] In Figure 2 the Y-Y connection scheme described for the three-phase DLCC network, U in is the DC bus voltage, where U a-in , U b-in and U c-in are the vector forms of the fundamental components of the inverter output voltage, whose effective values are U a-in , U b-in and U c-in , respectively. N is the neutral point of the inverter. The vector forms of the fundamental components of the three-phase rectifier output voltage are U a-out , U b-out and U c-out , respectively, whose effective values are U a-out , U b-out and U c-out , respectively. L A , L B and L C are the Y-connected power transmission coils; C A , C B and C C are the resonance compensation capacitances in series with the power transmission coils. L p1 , L p2 , L p3 , C p1 , C p2 and C p3 are the resonance inductances and Y-connected resonance capacitances. L a , L b and L c are the Y-connected receiving coils; C a , C b and C c are the resonance compensation capacitances in series with the receiving coils. L s1 , L s2 , L s3 , C s1 , C s2 and C s3 are the resonance inductances and corresponding Y-connected resonance capacitances at the receiving end. Since the power transmission coils and the receiving coils are placed in the same magnetic field space and belong to a semi-open magnetic circuit, LA L B L C L a L b L c There is mutual inductance coupling between L

[0048]

[0049] In equation (1), L T = L(1:3,1:3) represents the inductance matrix of the power transmitting coil, including self-inductance and mutual inductance. Similarly, L R = L(4:6,4:6) represents the inductance matrix of the power receiving coil. M T-R = M(1:3,4:6) and M R-T = M(4:6,1:3) represent the mutual inductance matrix between the transmitting coil and the receiving coil. The main power transmission in the mutual inductance matrix is contributed by M Aa , M Bb , and M Cc . The existence of additional mutual inductance increases the complexity of system parameter design and reduces stability. To simplify the analysis process, in the following parameter calculation, the mutual inductance between the main power transmission coils of the magnetic coupling structure is mainly concerned. That is, the cross-coupling coefficient is ignored, and by implementing the design of a fully decoupled magnetic structure, only the main mutual inductance M Aa , M Bb , and M Cc for power transmission are concerned. To simplify the analysis process of the three-phase DLCC network, when considering the parameter design scheme of phase A in the three-phase wireless charging system, we have:

[0050]

[0051]

[0052] The currents of phase A are the primary side resonant inductor current I a-in , the energy transmission coil current I A-P , and I a-s , and the secondary side resonant inductor current I a-out :

[0053]

[0054]

[0055]

[0056]

[0057] where ω0 is the system operating angular frequency; and j is the imaginary part.

[0058] U a-in =U b-in =U c-in =U in , whose output current I out is:

[0059]

[0060] where π is the ratio of a circle.

[0061] To facilitate the development of the prototype and the selection of devices, I a-out =I b-out =I c-out . The phase shield scheme can be used to achieve high-efficiency multi-stage constant current operation as shown in Figure 3

[0062] 1.3 Analysis of voltage stress and loss of three-phase DLCC resonant network

[0063] When the primary / secondary side works at the resonant frequency (the system has zero phase angle (ZPA) and zero voltage switching (ZVS) characteristics). The main factors affecting the efficiency of the wireless charging system are the resonant inductance, resonant capacitance and power transmission coil loss. Further, the power transmission coil loss P loss has a significant impact on the transmission efficiency of the wireless charging system:

[0064] P loss = P Aloss + P Bloss + P Closs (9)

[0065] In equation (9), P Aloss , P Bloss , P Closs represent the losses of A, B, and C phase transmission coils respectively. To simplify the analysis, only P Aloss is discussed:

[0066]

[0067] Let the primary / secondary side be completely symmetrical (L A = L a = L Y , L p1 = L s1 = L1, U a-in = U a-out = U a ). Then:

[0068]

[0069] L A ​L a With C A ,C a The voltage of is:

[0070]

[0071]

[0072] wherein K Aa is a coupling coefficient.

[0073] As can be seen from equation (11), when U a-in , U a-out and I out remain constant, the loss is mainly affected by the coupling coefficient and the self-inductance of the power transmission coil. Among them, the coupling coefficient is affected by the distance between the primary and secondary sides of the power transmission coil and their spatially opposite areas, which is usually a fixed value in the design of a wireless charging system. Therefore, the only effective way to reduce system loss is to increase the self-inductance of the power transmission coil. As can be seen from equations (12) and (13), increasing the self-inductance of the power transmission coil will increase the terminal voltage of the transmission coil and the resonant capacitor, thereby increasing the insulation withstand safety risk level of the system. The Litz wire used for the transmission coil of the wireless charging system has a turn-to-turn insulation voltage of 2kV. In order to achieve strong insulation between turns, physical methods such as multi-layer insulation wire are usually used. However, these methods increase the design cost and generate high voltage at both ends of the coil, thereby increasing the insulation withstand safety risk of the system.

[0074] In addition, due to its material and current characteristics, the resonant capacitor in the DLCC network is usually composed of multi-layer ceramic chip capacitors (MLCC) of C0G and NPO, and the maximum withstand voltage of these capacitors does not exceed 3kV. If the voltage of the resonant capacitor is too high, the risk of capacitor voltage breakdown and ground discharge will increase. In a humid environment, serious accidents such as PCB board discharge to power ground and air may occur. Therefore, although increasing the inductance of the wireless charging system by increasing the power transmission coil can reduce the loss of the system, it also brings significant system insulation withstand safety risk, which creates a contradiction between the efficiency and safety of the wireless charging system. Although increasing the inductance of the coupling structure can fundamentally improve the system efficiency, it may also lead to an increase in the voltage stress of the resonant elements in the resonant system. High voltage stress of the resonant elements may cause the high-efficiency coupling structure to run at risk significantly increased in humid, explosive, and other conditions, thereby increasing the operating cost of the wireless charging system and reducing its safety.

[0075] In summary, in view of the above conflict between system loss and system operating cost and safety of the magnetic coupling structure system, the present application proposes a low-stray magnetic field voltage balancing full decoupling magnetic coupling structure, and combines Figures 1-14Further description is made.

[0076] In one aspect, the following is described in combination with Figures 4 to 7 The low-stray magnetic field voltage-balanced full-decoupling magnetic coupling structure of the embodiment of the present application is described in detail.

[0077] Referring to the accompanying Figure 4 A low-stray magnetic field voltage-balanced full-decoupling magnetic coupling structure includes a primary side structure and a secondary side structure, wherein the primary side structure and the secondary side structure are both multi-layer overlapping structures.

[0078] The primary side structure includes a primary side aluminum plate shielding layer at the bottom, a primary side ferrite magnetic core is fixedly arranged above the primary side aluminum plate shielding layer, a primary side single-pole coil L A , a primary side bipolar coil L B , and a primary side bipolar coil L C are sequentially and fixedly overlapped above the primary side ferrite magnetic core.

[0079] The secondary side structure includes a secondary side aluminum plate shielding layer at the top, wherein a secondary side ferrite magnetic core is fixedly arranged below the secondary side aluminum plate shielding layer; a secondary side single-pole coil L a , a secondary side bipolar coil L c , and a secondary side bipolar coil L b are sequentially and fixedly overlapped below the secondary side ferrite magnetic core.

[0080] Further including an FR-4 electric field shielding layer, which is arranged between the primary side single-pole coil L A , the primary side bipolar coil L B , and the primary side bipolar coil L C , and the secondary side single-pole coil L a , the secondary side bipolar coil L b , and the secondary side bipolar coil L c .

[0081] Referring to the accompanying Figure 5 The primary side single-pole coil L A , the primary side bipolar coil L B , and the primary side bipolar coil L C are three-layer stacked coil structures, wherein the primary side single-pole coil L A is configured to generate a magnetic field along the Z-axis, the primary side bipolar coil L B is configured to generate a magnetic field along the Y-axis, and the primary side bipolar coil L C is configured to generate a magnetic field along the X-axis, thereby realizing full decoupling of the coils through mutually perpendicular magnetic field directions.

[0082] It is worth noting that, since the primary side single-pole coil L A is a single-pole coil structure, it itself generates a magnetic field along the Z-axis. Figure 5The magnetic field along the Z-axis direction shown in the bottom layer of the primary side bipolar coil L B and the primary side bipolar coil L C is a bipolar coil structure, which generates a magnetic field as shown in Figure 5 The magnetic field direction generated by the second layer and the third layer is affected by the current flow direction in the bipolar coil. The second layer generates a magnetic field along the Y-axis direction in the horizontal direction, and the third layer generates a magnetic field along the X-axis direction in the horizontal direction, so that the three layers of magnetic field directions are perpendicular to each other to achieve full decoupling of the three-layer stacked structure.

[0083] Referring to the accompanying drawings Figure 4 and the accompanying drawings Figure 5 , the secondary side bipolar coil L a , the secondary side bipolar coil L c , the secondary side bipolar coil L b is symmetrically designed with the primary side three-layer stacked coil structure, wherein the position of the secondary side bipolar coil L c and the secondary side bipolar coil L b is exchanged with the position of the primary side bipolar coil L B and the primary side bipolar coil L C .

[0084] Through the symmetric design of the primary and secondary side structures, the size specifications of the primary and secondary sides are ensured to be consistent, further ensuring the consistency of the primary and secondary side magnetic field ranges, thereby effectively reducing the stray magnetic field. In addition, by exchanging the positions of the secondary side bipolar coil L c and the secondary side bipolar coil L b , the relative distance between the secondary side bipolar coil L b and the primary side bipolar coil L B is ensured to be consistent with the relative distance between the secondary side bipolar coil L c and the primary side bipolar coil L C , ensuring that the coupling coefficient of transmitting and receiving the Y-axis magnetic field is relatively consistent with the coupling coefficient of transmitting and receiving the X-axis magnetic field.

[0085] Referring to the accompanying drawings Figure 6 and the accompanying drawings Figure 7 , the primary side bipolar coil L A , the primary side bipolar coil L B , the primary side bipolar coil L C and the secondary side bipolar coil L a , the secondary side bipolar coil L b , the secondary side bipolar coil L c are series transmission coils in L-C…L-C mode. The series transmission coil is a plurality of split coils arranged in series, and a series resonance capacitor is arranged between adjacent split coils. The split coils after splitting are wound in a parallel spiral winding manner. The effective length and magnetic path area of each split coil after splitting are equal, and the capacitance values of the series resonance capacitors in each group of series transmission coils are equal.

[0086] The primary single-pole coil L A is taken as an example for detailed splitting description, referring to Figure 5 The single-pole coil winding method of (a), the primary single-pole coil L A is divided into four sub-coils L A-1 , L A-2 , L A-3 and L A-4 , and L A-1 =L A-2 =L A-3 =L A-4 On the basis of ensuring the lengths of the four sub-coils, a multi-coil stranded spiral winding mode is adopted to form a rectangular hollow coil structure, which can effectively ensure that the effective lengths and magnetic path areas of the split sub-coils are equal, the mutual inductive coupling between the four sub-coils is maximized, and the voltage balance of the split sub-coils is ensured.

[0087] In a wireless charging system, a resonant capacitor usually uses an MLCC made of C0G and NPO materials. To simplify the design process, the resonant capacitor can be set as C A-1 =C A-2 =C A-3 =C A-4 =4C A , where C A is the capacitance value of the resonant capacitor before splitting, and C A-1 , C A-2 , C A-3 , C A-4 are the capacitance values of the resonant capacitors in series after splitting of the sub-coils.

[0088] Where the voltage balance splitting schemes of the bipolar coil are shown in (b) and (c), respectively, and the splitting scheme of the bipolar coil also ensures that the lengths and winding areas of the coils are equal through multi-coil stranded spiral winding, thereby realizing L B-1 =L B-2 =L B-3 =L B-4 , L C-1 =L C-2 =L C-3 =L C-4 .

[0089] On the other hand, the voltage balance full decoupling type magnetic coupling structure design method of a low-stray magnetic field according to the embodiments of the present application is described in detail below. Figures 4 to 15

[0090] A voltage balance full decoupling type magnetic coupling structure design method of a low-stray magnetic field, comprising the following steps:

[0091] S1: Select a three-phase model;​

[0092] A YY-type three-phase DLCC resonant network is selected as the basic architecture; the YY connection of the three-phase DLCC network can realize MCC operation by using a fully decoupled structural design scheme.

[0093] like Figure 2 The YY-connected three-phase DLCC network shown has a multi-level constant current characteristic. This resonant network makes the wireless charging system flexible and efficient.

[0094] S2: Fully decoupled magnetic coupling structure design;

[0095] like Figure 4 and Figure 5 As shown in Figure (a), a three-layer stacked structure is selected for the design of the coupling mechanism. The power transmission coil is wound into a monopolar coil and a bipolar coil. The distribution positions of the three-layer stacked coils are adjusted to ensure that the magnetic field directions of the three are perpendicular to each other, completing the full decoupling design of the coil.

[0096] In the embodiment of the present application, the primary unipolar coil L A , primary bipolar coil L B and the primary bipolar coil L C It is a three-layer stacked coil structure, in which the primary monopolar coil L A It is configured to generate a magnetic field along the Z axis, and the primary bipolar coil L B Configured to generate a magnetic field along the Y axis, the primary bipolar coil L C It is configured to generate a magnetic field along the X axis, and achieve full decoupling of the coils through mutually perpendicular magnetic field directions. c and the secondary bipolar coil L b The position relative to the primary bipolar coil L B and the primary bipolar coil L C The positions are swapped to ensure that the coupling coefficient between the transmission and reception of the Y-axis magnetic field is relatively consistent with the coupling coefficient between the transmission and reception of the X-axis magnetic field.

[0097] S201, setting the basic shielding size and the air gap of the power transmission structure, and symmetrically designing the primary and secondary sides of the magnetic coupling structure to maintain the same winding width of each phase coil of the three-phase system.

[0098] In the embodiment of the present application, an aluminum shielding layer with a size of 420mm×420mm×1mm and a ferrite shielding layer with a size of 400mm×400mm×3mm are used, the air gap between the energy transmission coils is 150mm, and the coil width of each phase coil in the three-phase system remains consistent.

[0099] S202 , analyzing the relationship between the power transmission coil width and the coupling coefficient, drawing a quality factor characteristic curve, and selecting an optimal coil width value.

[0100] As Figure 8 (a) and 8(b) show, the relationship between the coil width and the coupling coefficient of the transmission coil and the relationship between the coil width and the quality factor are analyzed using the finite element method in a three-phase system.

[0101] According to the above relationship analysis, it can be known that the coupling coefficient of the power transmission coil is affected by the coil width; at the same time, the coil width further affects the quality factor of the coil. When the width is not greater than 55 mm, the wider the coil width, the more the number of turns, and the greater the quality factor and the coupling coefficient; when the coil width increases to a certain extent, the coupling coefficient and the quality factor of the DD coil both show a downward trend.

[0102] In the design of this paper, considering the above characteristics and the actual winding difficulty, the coil width is taken as 60 mm. Therefore, the design parameters are shown in Table I.

[0103] Table I Design parameters of three-phase DLCC resonant network

[0104]

[0105] After the coil width is determined as 60 mm, the stray magnetic field distribution characteristics of the power transmission coil are affected by the size, flow direction, phase, etc. of the current flowing through the coil. In the traditional three-phase wireless charging system, the phase difference of A, B, and C is set to 120°, and under this characteristic, if the three-phase system is completely symmetrical, the neutral point current is zero. In the case of zero neutral point current, the working pressure of the system split capacitor is reduced, ensuring the safety of the system.

[0106] According to formula (14), when the three-phase DLCC network is full-power operation, it can be known that the stray magnetic field of P point outside the coil is mainly composed of the vector superposition of the magnetic field B A generated by L A-p , the magnetic field B B generated by L B-p , and the magnetic field B C generated by L C-p . In addition, the magnetic field of P point is affected by the coil current and the distance factor. Therefore, a stray magnetic field comparison analysis model as shown in the figure can be established.

[0107]

[0108] At this time, the stray magnetic field B of P point can be further vectorially decomposed, that is, B A-P , B B-P , and B C-Pare decomposed along X, Y and Z axis vectors respectively, and then the fully decoupled X, Y, Z axis magnetic field vectors are superimposed. When only considering the magnetic field B generated by the single pole coil at P point unipolar-p , it can be decomposed into B x , B y and B z . Since there is a 120° phase difference between I A-p , I B-p and I C-p , a mutual offset magnetic field can be generated. In a single phase system, the external stray magnetic field B unipolar is affected by the peak current, and there is no offset effect of the magnetic field. In the case of transmitting the same power, the average value of the current of the single phase system will be greater than that of the three phase system, so it is necessary to analyze the stray magnetic field of the single phase system in order to analyze the stray magnetic field distribution characteristics caused by the magnetic coupling mechanism of the single phase system and the three phase system. However, due to the limitation of the magnetic coupling mechanism of the wireless charging system which belongs to a space semi-open magnetic circuit, it is impossible to completely explain the distribution characteristics of the stray magnetic field by formula. In order to analyze the stray magnetic field distribution characteristics between the three phase magnetic coupling mechanism and the single phase magnetic coupling mechanism, let the rated current flow through the primary side transmitting coil of the three phase system and the primary side single pole coil of the single phase system, and keep the secondary side receiving coil open, and then use the finite element analysis software to calculate the peak distribution characteristics of the stray magnetic field, as shown in Figure 9

[0109] It can be seen from Figure 9 that the stray magnetic field of the three phase fully decoupled structure is smaller than that of the single phase single pole structure in the case of transmitting the same power. Further, in order to illustrate the characteristics of the stray magnetic field with the change of phase, it is assumed that P point is located at a distance of 500 mm from the transmission platform, and the maximum magnetic induction intensity is B 500 . At this time, the peak value of the stray magnetic field of the three phase fully decoupled structure is 0.5 B 500 . The peak value of the stray magnetic field of the single pole structure at this point B unipolar-p is 15.38 μT. Further, the magnetic field at P point is decomposed as shown in Figure 10 (a). As shown in Figure 10 (b), the magnetic field B unipolar-p of the single pole structure can be decomposed into B x , B y and B z , and B z occupies the main component of B unipolar-p . B A-p , B B-p and B C-p decomposed from are further decomposed along X, Y and Z axes, and plotted as shown in Figure 10 (c) toFigure 10 (f) is the superposition diagram of the magnetic flux distribution characteristics shown.

[0110] Through analysis Figure 10 (c) to Figure 10 (f) shows the phase and peak characteristics. It can be seen that in the three-phase system coil A, the main stray magnetic flux at 500mm is distributed along the Z axis. yes For the coil B in the three-phase system, the bipolar structure can generate a horizontal magnetic field along the Y axis, which constitutes Since the distance between point P and the outside and inside of coil C is close to the same, the magnetic field component generated by coil C at this position is relatively low. Figure 10 (b) It can be seen that the stray magnetic field generated by the fully decoupled magnetic structure proposed in this chapter at a distance of 500mm from the transmission coil is much lower than that of the monopole magnetic structure used in the single-phase system. The research on stray magnetic fields should focus on the impact of stray magnetic fields on the human body. Therefore, when the fully decoupled structure used in the three-phase system and the monopole structure used in the single-phase system are both working normally, when a human leg model is added at a distance of 500mm from the transmission coil, the distribution characteristics of the stray magnetic field are as follows: Figure 11 shown.

[0111] Through Figure 11 Analysis shows that the stray magnetic field of the wireless charging system is mainly concentrated near the feet of the magnetic coupling structure. The maximum stray magnetic field B of the three-phase fully decoupled structure max The stray magnetic field of the single-phase single-pole structure is 22.881μT under the same power condition, while the stray magnetic field of the single-phase single-pole structure is 27.543μT. That is, the three-phase wireless charging system with full decoupling capability can significantly reduce the impact of the stray magnetic field on the position of the human leg. In order to further illustrate the characteristics of the stray magnetic field distribution, the spatial distribution model of the stray magnetic field is drawn in the space area 500mm outside the magnetic structure, as shown in the figure. Figure 12 shown.

[0112] exist Figure 12 In-depth research on its stray magnetic field shows that the stray magnetic field of the three-phase system at point P is 15.34uT, while the stray magnetic field of the single-phase monopole coil structure is 21.52uT. In order to further demonstrate the stray magnetic field distribution characteristics of the wireless charging system, the stray magnetic field at 500mm and 250mm away from the transmission coil is plotted as a function of phase. Figure 13 shown.

[0113] Depend on Figure 13It can be seen that the stray magnetic field of the three-phase full decoupling structure is significantly lower than that of the single-phase single-pole structure. At the center point 500 mm away from the stray magnetic field, the stray magnetic field can be reduced by 28.7%. At a distance of 250 mm, the stray magnetic field of the three-phase system is 19.3% lower than that of the single-phase system. Through the above analysis, it can be seen that the stray magnetic field of the three-phase full decoupling magnetic structure proposed in this chapter is significantly lower than that of the single-pole single-phase structure, and the constraint rate of the stray magnetic field changes with the spatial position.

[0114] In summary, the three-phase full decoupling magnetic structure proposed in this chapter has certain advantages in terms of stray magnetic field distribution characteristics.

[0115] S3: Low voltage stress design;

[0116] Based on the contradictory characteristics of loss and voltage stress, a balanced split transmission coil and resonant capacitor connection scheme with low voltage stress characteristics is proposed, which can reduce the voltage stress of the resonant network and enhance the safety of the system. However, the split design of the three-phase full decoupling magnetic structure will face problems such as mutual coupling of split coils, voltage balance between coils, etc.

[0117] For the power transmission coil of the three-layer stacked structure, each layer of the power transmission coil is split; the power transmission coil is replaced by a plurality of series power transmission coils, and the corresponding series resonant capacitor also needs to be additionally matched with the split series resonant capacitor, forming an L-C…L-C mode series transmission coil to effectively reduce the voltage stress.

[0118] S301, set the split number of the basic power transmission coil and the series resonant capacitor, form a plurality of L-C…L-C mode series transmission coils;

[0119] In the embodiments of the present application, the power transmission coil L A and the resonant capacitor C A are taken as examples for analysis and description.

[0120] The voltage stress characteristics of the power transmission coil L A and the resonant capacitor C A are analyzed, and it can be seen that the voltage stress is as shown in Figure 7 . In this case, the terminal voltage of the power transmission coil is affected by the inductance value, and after balancing through the resonant capacitor, the terminal voltage is equal to the voltage of the resonant capacitor C p . Since the highest voltage stress is high, there is a safety risk of insulation withstand voltage in the operation of inductance and resonant capacitor. Accordingly, a power transmission coil and resonant capacitor connection structure with low voltage stress characteristics as shown in Figure 7 is designed.

[0121] In this connection structure, the traditional power transmission coil L A is replaced by four series-connected coils as shown in Figure 7 . This structure can minimize the voltage stress of the system. In addition, the series resonant capacitor is also split into L-C…L-C mode, which can further reduce the voltage stress inside the system. This connection method makes full use of the voltage stress characteristics of inductors and resonant capacitors, reduces the voltage stress of the system by splitting, and enhances the safety of the system. Since L A is split into L A-1 , L A-2 , L A-3 and L A-4 , and the system adopts a semi-open design, mutual cross-coupling occurs between L A-1 , L A-2 , L A-3 and L A-4 . The relationship is described in (15).

[0122]

[0123] The voltage of the transmission coil depends on the splitting method, and to achieve voltage balance, L A-1 must be equal to L A-2 , L A-3 must be equal to L A-4 . Therefore, the voltage balance splitting coil method is shown in Figure 6 (a), which uses cross-winding to ensure that the length and effective area of the split transmission coil are consistent. The voltage balance splitting scheme for the bipolar structure is shown in Figure 6 (b) and Figure 6 (c), respectively. The split scheme for the bipolar structure also ensures that the length and winding area of the coil are equal through cross-winding, thereby achieving L B-1 , L B-2 , L B-3 and L B-4 , L C-1 , L C-2 , L C-3 and L C-4 .

[0124] S302, balance the specifications of each split power transmission coil, so that the length and area of each split power transmission coil are equal; and calculate the capacitance value of the split resonant capacitor to be replaced, wherein the capacitance values of the split resonant capacitors are equal. The capacitance value of the split resonant capacitor is determined using the following formula:

[0125]

[0126] In equation (16), n represents one of the three phases A, B and C.n C n-1 C n-2 C n-3 C n-4 C

[0127] In the embodiments of the present application, the power transmission coil L A and the resonance capacitor C A are analyzed and described by taking the A-phase as an example.

[0128] When the power transmission coil is split into L A-1 , L A-2 , L A-3 and L A-4 , the series capacitance C A also needs to be adjusted. According to equation (2), the resonance capacitance is:

[0129]

[0130] In a wireless charging system, the resonance capacitor usually uses an MLCC made of C0G and NPO materials. To simplify the design process, the capacitance values of the split resonance capacitors can be set to be equal, so that C A-1 =C A-2 =C A-3 =C A-4 =4C A . By analyzing equations (12), (13), (15) and (17), it can be concluded that Figure 7 (b) The inductance and capacitance split design scheme can effectively reduce the voltage stress across the inductance and capacitance. Further comparison with Figure 7 (a) can find that using the L-C...L-C configuration after splitting can reduce the total internal voltage and the size of the end voltage and floating ground voltage of the individual resonator.

[0131] S303, the inductance matrix of the split three-phase power transmission coil is simulated and verified, and the balance characteristics of each split power transmission coil are determined.

[0132] Further verification of the rationality of the split design scheme shown in Figure 6 is performed by using finite element simulation software to obtain the inductance distribution characteristic diagram of the split structure, as shown in Figure 14 .

[0133] According to the A-phase balance split parameters shown in Figure 14 and equation (15), it can be known that the single-pole coil balance split scheme is effective, and the scheme shows good self-inductance balance and equivalent inductance balance. The balance at this point is defined as: (maximum value-minimum value) / average value. Similarly, the inductance balance of the bipolar coil is also good. This shows that the coil structure does not affect the balance split strategy.

[0134] S304, the coupling coefficient of the split three-phase power transmission coil is simulated and verified, and the coupling effect of each split power transmission coil is determined.

[0135] In the three-phase full-decoupling magnetic structure of the embodiment of the present application, to verify whether the split scheme affects the coupling effect, the split coils are unified, and the inductance matrix as described in Table II is constructed. As can be known from the analysis of Table II, in the three-phase voltage balance split scheme, the main coupling coefficient of the energy transmission coil is large. And in the inductance matrix, the cross coupling coefficient is relatively small, that is, the cross coupling effect of the voltage balance split scheme can be ignored.

[0136] Table II Coupling coefficients of the magnetic structure under the split scheme based on finite element simulation

[0137]

[0138] At this time, the stray magnetic field distribution of the voltage balance split coil is as shown in Figure 15 .

[0139] As can be known from the comparison of Figure 15 and Figure 11 , the stray magnetic field distribution characteristics of the split coil scheme and the traditional winding scheme remain almost unchanged. Therefore, the magnetic structure with low stray magnetic field characteristics and low voltage stress can coexist. In other words, by combining the split coil winding scheme and the three-phase full-decoupling structure design scheme, a wireless charging system design with high safety, low voltage stress and low stray magnetic field characteristics is realized.

[0140] S4: winding and stacking of the magnetic coupling structure;

[0141] S401: coil balancing winding, for each layer of power transmission coil, a balancing winding mode is selected to make the effective length and magnetic path area of each split power transmission coil of each layer equal;

[0142] In the embodiment of the present application, the primary single coil L A is taken as an example for detailed split description, referring to the single coil winding method of Figure 5 (a), the primary single coil L A is divided into four sub-coils L A-1 , L A-2 , L A-3 and L A-4 , and L A-1 =L A-2 =L A-3 =L A-4On the basis of ensuring the consistent length of the four sub-coils, the rectangular hollow coil structure is formed by adopting the multi-coil stranded spiral winding mode, which can effectively ensure that the effective length and magnetic path area of the split sub-coil are equal, the mutual inductive coupling between the four sub-coils is as much as possible, and the voltage balance of the split coil is ensured.

[0143] S402: full decoupling of the coil stack, for the shape and current direction of each layer of power coil, the placement position of each layer of power coil is set to realize that the magnetic field directions of the three layers of power coils are perpendicular to each other, and full decoupling of the coil is realized;

[0144] In the embodiments of the present application, referring to the accompanying Figure 4 and the accompanying Figure 5 , the primary single coil L A , the primary double coil L B and the primary double coil L C are three-layer stacked coil structures, wherein the primary single coil L A is configured to generate a magnetic field along the Z-axis, and the primary double coil L B is configured to generate a magnetic field along the Y-axis, and the primary double coil L C is configured to generate a magnetic field along the X-axis, and full decoupling of the coil is realized by the mutually perpendicular magnetic field directions.

[0145] S403: symmetric configuration of the magnetic coupling structure, the primary / secondary side of the magnetic coupling structure is symmetrically laid out, especially the positions of the two double coils in the primary / secondary side are exchanged, to ensure the consistency of the mutual inductive distance of the two groups of mutual inductive double coils in the primary / secondary side.

[0146] In the embodiments of the present application, the secondary single coil L a , the secondary double coil L c , the secondary double coil L b are symmetrically designed with the three-layer primary coil structure, wherein the positions of the secondary double coil L c and the secondary double coil L b are exchanged relative to the positions of the primary double coil L B and the primary double coil L C .

[0147] The above is only the preferred specific embodiments of the present application, and is not limited to the protection scope of the present application, therefore: all equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A low-stray magnetic field voltage-balanced full-decoupled magnetic coupling structure for wireless power transfer, characterized in that: The primary side structure and the secondary side structure are both multi-layer overlapping structures; The primary side structure comprises a primary side aluminum plate shielding layer at the bottom, a primary side ferrite magnetic core is fixedly arranged above the primary side aluminum plate shielding layer, a primary side single pole coil L is fixedly arranged above the primary side ferrite magnetic core in sequence A , a primary side double pole coil L B , a primary side double pole coil L C ; The secondary side structure comprises a secondary side aluminum plate shielding layer located at the uppermost position, wherein a secondary side ferrite magnetic core is fixedly arranged below the secondary side aluminum plate shielding layer; a secondary side single-pole coil L is fixedly arranged below the secondary side ferrite magnetic core in sequence and overlaps a , a secondary side double-pole coil L c , a secondary side double-pole coil L b ; Primary side single pole coil L A , primary side double pole coil L B , and primary side double pole coil L C is a three-layer stacked coil structure, wherein the primary side single pole coil L A is configured to generate a magnetic field along the Z axis, while the primary side double pole coil L B is configured to generate a magnetic field along the Y axis, and the primary side double pole coil L C is configured to generate a magnetic field along the X axis, so as to realize full decoupling of the coils through mutually perpendicular magnetic field directions; Primary coil L a , secondary bipolar coil L c , secondary bipolar coil L b is designed symmetrically with the primary three-layer stacked coil structure, wherein the positions of the secondary bipolar coil L c and the secondary bipolar coil L b are exchanged with the primary bipolar coil L B and the primary bipolar coil L C .

2. The voltage-balanced, fully decoupled magnetic coupling structure of claim 1, wherein: The primary single-coil L A The primary bipolar coil L B The primary bipolar coil L C The secondary single-coil L a The secondary bipolar coil L b The secondary bipolar coil L c All of the primary and secondary bipolar coils L are series transmission coils of L-C…L-C mode, which are multiple sub-coils arranged in series and have series resonance capacitors between adjacent sub-coils.

3. The voltage-balanced, fully decoupled magnetic coupling structure of claim 2, wherein: The series transmission coils adopt a winding mode of parallel strand spiral winding, the effective length and the magnetic path area of each split sub-coil are equal, and the capacitance values of the series resonant capacitors in each group of series transmission coils are equal.

4. A design method of a low-stray magnetic field voltage-balanced full-decoupled magnetic coupling structure, applied to the low-stray magnetic field voltage-balanced full-decoupled magnetic coupling structure design of any one of claims 1-3, characterized in that: The method comprises the following steps: S1: selecting a three-phase model; Selecting a Y-Y type three-phase DLCC resonant network as the basic architecture; S2: full decoupling magnetic coupling structure design; Selecting a three-layer stack structure for the design of the coupling mechanism, winding the power transmission coil into a monopole coil and a dipole coil, adjusting the distribution position of the three-layer stack coil to realize the perpendicularity of the magnetic field directions of the three, and completing the full decoupling design of the coil; S3: low voltage stress design; For the power transmission coil of the three-layer stack structure, each layer of the power transmission coil is split; The power transmission coil is split and replaced by a plurality of series power transmission coils, and the corresponding series resonant capacitors also need to be additionally matched with the split series resonant capacitors to form a series transmission coil in the L-C…L-C mode, so as to effectively reduce the voltage stress; S4: magnetic coupling structure winding stack; S401: coil balancing winding, for each layer of the power transmission coil, a balancing winding mode is selected to make the effective length and the magnetic path area of each split power transmission coil equal; S402: coil full decoupling stack, for the shape and current direction of each layer of the power coil, the placement position of each layer of the power coil is set to realize the perpendicularity of the magnetic field directions of the three layers of the power coil, and the full decoupling of the coil is realized; S403: symmetric configuration of the magnetic coupling structure, the primary side and the secondary side of the magnetic coupling structure are symmetrically arranged, the positions of the two dipole coils between the primary side and the secondary side are exchanged, and the mutual inductance consistency of the two groups of mutual inductance dipole coils of the primary side and the secondary side is ensured.

5. The method of claim 4, wherein the method further comprises: The step S2 comprises the following steps: S201: setting the basic shielding size and the air gap of the power transmission structure, and symmetrically designing the primary side and the secondary side of the magnetic coupling structure to keep the winding width of each phase coil of the three-phase system consistent; S202: analyzing the relationship between the power transmission coil width and the coupling coefficient, drawing a quality factor characteristic curve, and selecting the best coil width value.

6. The method of claim 4, wherein the method is characterized by: The step S3 comprises the following steps: S301: setting the split number of the basic power transmission coil and the series resonant capacitor to form a series transmission coil in the L-C…L-C mode; S302: balancing the specifications of each split power transmission coil to make the length and area of each split power transmission coil equal, and calculating the capacitance value of the split resonant capacitor to be replaced, wherein the capacitance values of the split resonant capacitors are equal.

7. The method of claim 6, wherein the method further comprises: determining a magnetic field of the magnetic coupling structure; and determining a magnetic field of the magnetic coupling structure with the voltage balancing circuitry. In the S302 step, the capacitance value of the split resonant capacitor is calculated by the following formula: In the formula, n represents one of the three phases of A, B, and C, C n is the capacitance value of the split front resonant capacitor n-1 is the capacitance value of the split front resonant capacitor n-2 is the capacitance value of the split front resonant capacitor n-3 is the capacitance value of the split front resonant capacitor n-4 is the capacitance value of each split resonant capacitor.

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