Long-distance space-time symmetric wireless power transmission system with multi-coil structure

Abstract

The invention discloses a long-distance space-time symmetric wireless electric energy transmission system with a multi-coil structure, and belongs to the technical field of wireless electric energy transmission. The system comprises a transmitting device, repeating coil circuits and a receiving device, wherein a plurality of groups of repeating coil circuits are arranged between the transmitting device and the receiving device. When the transmitting device is in an associated reference direction, the voltage at the two ends of the full-bridge inverter is opposite to the flowing current, the transmitting device and the power supply are jointly equivalent to a negative resistor-RN, and the resonant capacitors C1s and C1p are connected with the resistor-RN in parallel and then connected with the inductor L1 in series to form an SP structure. Resonant capacitors C5s and C5p of the receiving device are connected with a load RL in parallel and then are connected with an inductor L5 in series to form a PS structure. According to the invention, the energy transmission process is enhanced, the critical coupling condition is reduced, and the system can work in a strong coupling region more easily. In addition, an SP-PS structure is adopted in topology, so that the wide coupling characteristic of the PT system is further enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless power transmission, and in particular to a long-distance parity-time symmetric wireless power transmission system with a multi-coil structure. Background Art

[0002] Wireless power transfer (WPT) shows exciting and promising applications in various fields where physical connection is not allowed. Driven by modern physical concepts and increasing practical needs, the so-called magnetic resonance mechanism of non-radiative WPT technology has been rapidly developed in recent years. However, conventional WPT systems are not robust when the transmitting and receiving coils are misaligned or there is relative motion, resulting in changes in mutual coupling.

[0003] Parity-Time Symmetric (PT-symmetric) is rooted in quantum physics and opens up a different perspective for studying non-Hermitian Hamiltonians. With the development of WPT devices, efficient, long-range, and robust PT-WPT is urgently needed. However, designing a robust long-range PT-WPT system is extremely challenging. Currently, WPT schemes are inherently sensitive to transmission distance and structural perturbations, which is an essential challenge for various application scenarios.

[0004] At present, the research on magnetic resonance PT-WPT system is relatively mature. The PT symmetric WPT system has a real spectrum and can automatically select the operating frequency corresponding to the highest efficiency, thereby ensuring the optimal power transmission over a wide range of transmission distances without any active tuning. High-order PT symmetric systems are expected to achieve robust WPT in a larger longitudinal frequency splitting range and a wider transverse precise PT symmetric region.

[0005] In summary, building a high-order PT-WPT system enables the system to be further optimized in terms of wide coupling range, wide coupling conditions, etc., which is of great significance in the development of this field. Summary of the invention

[0006] 1. Technical problem to be solved by the invention

[0007] Based on non-Hermitian physics and parity-time symmetric wireless power transmission technology (PT-PWT), the present invention designs a long-distance parity-time symmetric wireless power transmission system with a multi-coil structure to solve or improve the following problems:

[0008] (1) Researchers are no longer satisfied with the traditional second-order PT system and are trying to build a high-order PT system to further explore and improve the transmission advantages and inherent characteristics of the original PT system. However, most of the current research is limited to low-order PT systems, and there is a lack of research on high-order PT-WPT. In other words, in current research, there is a lack of a high-order PT-WPT system that can meet longer coupling distances and more stable transmission efficiency.

[0009] (2) The original PT-WPT with the second-order coupled mode equation is well-known for its wide coupling and transmission advantages without active tuning. In current research, scholars are no longer satisfied with the transmission advantages of the original PT-WPT system, that is, the stability of the original PT-WPT no longer meets existing needs.

[0010] (3) In the second-order PT-WPT system, there is a defect that it is highly sensitive to the coupling strength. This requires the system to meet various parameter requirements to achieve wide coupling, and the system needs to eliminate various interferences, resulting in low effective stability of the second-order PT-WPT.

[0011] (4) Most of the current PT systems use the SS topology. However, the SS-type PT-WPT system has high sensitivity and poor stability.

[0012] 2. Technical solution

[0013] In order to achieve the above object, the technical solution provided by the present invention is:

[0014] The present invention discloses a long-distance parity-time symmetric wireless power transmission system with a multi-coil structure, comprising a transmitting device, a relay coil circuit and a receiving device. Two capacitors and a resistor are connected in parallel and then in series with an inductor to form a transmitting device with an SP structure and a receiving device with a PS structure. Multiple groups of relay coil circuits are arranged between the transmitting device and the receiving device.

[0015] Furthermore, the transmitting device includes a power supply, a full-bridge inverter, a resonant capacitor C 1s , C 1p and inductor L1; where, in the associated reference direction, the voltage across the full-bridge inverter and the current flowing through it are opposite, and together with the power supply are equivalent to a negative resistance -R N , resonant capacitor C 1s , C 1p and resistor - R N The parallel connection and the series connection with the inductor L1 form an SP structure.

[0016] Furthermore, the receiving device includes a receiving inductor L5, a resonant capacitor C 5s , C 5p and load R L ; Among them, the resonant capacitor C5s , C 5p and load R L The parallel connection and the series connection with the inductor L5 form a PS structure.

[0017] Furthermore, a total of three groups of relay coil circuits are arranged between the transmitting device and the receiving device.

[0018] Furthermore, in the first relay coil circuit, the inductor L2 and the capacitor C2 form a closed loop, and the inductor L1 and the inductor L2 are adjacent to each other, and there is a mutual inductance M 12 In the second relay coil circuit, the inductor L3 and the capacitor C3 form a closed loop. The inductor L2 and the inductor L3 are adjacent coils, and there is a mutual inductance M 23 In the third relay coil circuit, the inductor L4 and the capacitor C4 form a closed loop. The inductor L3 and the inductor L4 are adjacent coils, and there is a mutual inductance M 34 At the same time, inductor L4 and inductor L5 are adjacent coils, and there is a mutual inductance M 45 .

[0019] Furthermore, the mutual inductance between the transmitting device, the relay coil circuit and the non-adjacent coils in the receiving device is zero.

[0020] Furthermore, there is a coil internal resistance r in the transmitting device, the relay coil circuit and the receiving device. n , n=1,2,3,4,5, the internal resistance of the coil is very small and can be ignored.

[0021] Furthermore, the number of turns of the inductor in the relay coil circuit is greater than the number of turns of the inductor in the transmitting device and the receiving device.

[0022] Furthermore, the distances between the coils in the transmitting device, the relay coil circuit and the receiving device are equal.

[0023] Furthermore, the transmitting device, the relay coil circuit and the coils in the receiving device maintain the same resonant frequency, i.e., ω1=ω2=ω3=ω4=ω5=ω, and the same coupling coefficient, i.e., k 12 =k 23 =k 34 =k 45 =k.

[0024] 3. Beneficial effects

[0025] Compared with the existing known technologies, the technical solution provided by the present invention has the following significant effects:

[0026] (1) The present invention designs a PT-WPT system with a multi-coil structure. By inserting a relay coil between the transmitting coil and the receiving coil, the energy transmission process is not only enhanced, but also the critical coupling condition is reduced, so that the system can work more easily in the strong coupling area. In addition, the SP-PS structure is adopted in the topology, so that the wide coupling characteristics of the PT system are further enhanced.

[0027] (2) The present invention triples the transmission distance of robust wireless power transmission by designing a PT-WPT system with a multi-coil structure. In addition, under the multi-coil structure, the PT-WPT system exhibits stronger transmission stability.

[0028] (3) Compared with the dual-coil PT-WPT system under the same conditions, the present invention has a larger spectrum and a larger frequency selection range in longitudinal frequency splitting. This shows that the present invention has a larger longitudinal frequency splitting area, increases the wide coupling range, and expands the strong coupling area.

[0029] (4) The PT-WPT system of the present invention adopts an improved new SP-PS topology structure, so that the relationship between the dual capacitors on the receiving coil can dynamically adjust the transmission efficiency of the coil, making the transmission efficiency of the coil more flexible and controllable, and has better performance than the active tuning of the original PT-WPT system, and better stability than the traditional PT-WPT systems with SS and PP structures.

[0030] (5) The PT-WPT system with a five-coil structure in the present invention has a real characteristic frequency that is independent of coupling, which means that compared with the two-coil, four-coil, and six-coil PT-WPT systems, the five-coil PT-WPT system with PT symmetry can work efficiently at different distances without frequency tracking. This can be explained by the low sensitivity of the characteristic frequency of the five-coil model used to the coupling strength, which gives the five-coil an advantage in robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 (a) is the splitting diagram of the four-coil PT-WPT system in the strong coupling region; Figure 1 (b) is a comparison diagram of the splitting of the four-coil PT-WPT system in the strong coupling region and the splitting of the two-coil PT-WPT system in the strong coupling region.

[0032] Figure 2 (a) is the splitting diagram of the five-coil PT-WPT system in the strong coupling region; Figure 2 (b) is a comparison diagram of the splitting of the five-coil PT-WPT system in the strong coupling region and the splitting of the two-coil PT-WPT system in the strong coupling region.

[0033] Figure 3(a) is the splitting diagram of the six-coil PT-WPT system in the strong coupling region; Figure 3 (b) is a comparison diagram of the splitting of the six-coil PT-WPT system in the strong coupling region and the splitting of the two-coil PT-WPT system in the strong coupling region.

[0034] Figure 4 This is a comparison chart of the coupling coefficients between the coils of the asymmetric structure and the symmetric structure.

[0035] Figure 5 For the circuit topology of the present invention, the basic SS structure topology is improved and the SP-PS structure topology is designed. It should be additionally explained that because the characteristics of the topology itself cannot show the size of the actual coil, the number of turns of the relay coil is larger than that of the transmitting and receiving coils.

[0036] Figure 6 The equivalent topological diagram of the present invention is shown in FIG. The receiving coil is equivalent to an equivalent circuit with a lower load, so that its intrinsic loss rate is reduced to expand the precise PT symmetry area. DETAILED DESCRIPTION

[0037] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings and embodiments.

[0038] Example 1

[0039] Combination Figure 5 and Figure 6 , a long-distance parity-time symmetric wireless power transmission system with a multi-coil structure in this embodiment includes a transmitting device, a relay coil and a receiving device. Among them:

[0040] The transmitting device described above has a voltage across the full-bridge inverter and a current flowing therethrough in the opposite direction in the associated reference direction, which is equivalent to a negative resistance -R N , used as a power supply to provide input voltage for the system. C 1s , C 1p is the resonant capacitor of the transmitter. L1 is the inductance of the transmitter, and r1 is the resistance of the transmitter. 1s One end is connected to the positive pole of the power supply, and the other end is divided into two branches, one branch is connected to the resonant capacitor C 1p The other branch is connected to one end of the inductor L1, and the other end of the inductor L1 is connected to the resistor r1, the resonant capacitor C 1p The other end of is connected in parallel with the other end of resistor r1 and then connected to the negative pole of the power supply.

[0041] The receiving device includes a receiving inductor L5, a resonant capacitor C 5s , C 5p , resistor r5 and load R LOne end of the receiving inductor L5 is connected to the resonant capacitor C 5s and resonant capacitor C 5p , resonant capacitor C 5s Series load R L After that, with the resonant capacitor C 5p The other end of the receiving inductor L5 is connected in parallel and then connected to the other end of the receiving inductor L5 through the resistor r5.

[0042] Three relay coil circuits are set between the transmitter and the receiver, where L2, L3, and L4 are relay coil inductors, C2, C3, and C4 are relay coil resonant capacitors, and r2, r3, and r4 are relay coil resistances. In the first relay coil circuit, the inductor L2, the capacitor C2, and the resistor r2 form a closed loop, and the inductor L1 and the inductor L2 are adjacent, and there is a mutual inductance M. 12 In the second relay coil circuit, the inductor L3, the capacitor C3 and the resistor r3 form a closed loop. The inductor L2 and the inductor L3 are adjacent coils, and there is a mutual inductance M. 23 In the third relay coil circuit, the inductor L4, the capacitor C4 and the resistor r4 form a closed loop. The inductor L3 and the inductor L4 are adjacent coils, and there is a mutual inductance M. 34 At the same time, inductor L4 and inductor L5 are adjacent coils, and there is a mutual inductance M 45 Since the distance between non-adjacent coils is large, the magnetic field coupling between non-adjacent coils can be ignored, that is, the mutual inductance between non-adjacent coils is 0.

[0043] It is worth mentioning that Figure 5 The r shown n , n=1,2,3,4,5 is the internal resistance of the coil. Since the internal resistance of the coil is too small, it is ignored in the subsequent calculations.

[0044] This embodiment is a PT-WPT system with a five-coil structure. A relay coil is added during transmission, and the distance between each coil is defined as d (cm). The relay coil is located between the transmitting and receiving devices. In order to ensure the maximum transmission efficiency of the system and maintain PT phase symmetry, this embodiment sets the distance d (cm) between each coil to be equal, and the five coils maintain the same resonant frequency, i.e., ω1 = ω2 = ω3 = ω4 = ω5 = ω, and the same coupling coefficient, i.e., k 12 =k 23 =k 34 =k 45 =k.

[0045] It is worth mentioning that because adding a relay coil will lead to a different critical coupling coefficient, the inventors continuously changed the distance between each coil to find the strong coupling area, and finally determined that when the distance between each coil is equal, when the operating frequency of the system meets the natural resonant frequency, the total gain of the system is equal to the total loss, and PT symmetry is achieved. When the system changes in the strong coupling area, robust transmission can be achieved over long distances.

[0046] At the same time, this embodiment further improves the structure of the transmitting device and the receiving device. The parallel connection of two capacitors and a resistor and the series connection of an inductor constitute the transmitting device and the receiving device of SP and PS. When the load resistance R L When the receiving coil is replaced, a smaller equivalent resistance R can be obtained. Leq , which makes the critical coupling coefficient of the SP-PS structure system much smaller than that of the SS structure. Therefore, the compensation network of the SP-PS structure can expand the PT symmetry area of ​​the PT-WPT system, so that the system has better robust transmission characteristics, that is, the transmission efficiency is more stable within the lateral transmission distance.

[0047] Wireless power transmission is increasingly being used, and the principle of even-odd time symmetry has been shown to significantly improve the degree of freedom of WPT systems without increasing control complexity. Currently, with the theoretical support of non-Hermitian physics, researchers have made a lot of achievements in expanding wide coupling conditions and wide coupling range.

[0048] The present invention also aims to achieve technical breakthroughs in two key areas: PT symmetry area, frequency splitting range, and transmission stability. The long-distance wireless power transmission system designed by the present invention has a multi-coil structure, which uses the larger longitudinal frequency splitting range and real characteristic frequency of the multi-coil to increase its stability; the original long-chain structure with SS topology is improved into a PT-WPT system with a PS-SP structure to expand the lateral precise PT symmetry area of ​​the system; within a larger axial transmission distance and lateral misalignment range, the transmission efficiency is more stable, and the transmission distance is tripled compared to the traditional dual-coil PT-WPT system.

[0049] The specific verification is carried out below.

[0050] Since the research on the dual-coil PT-WPT system and the triple-coil PT-WPT system is relatively mature, the research results clearly show that when the parameter conditions are met, the PT-WPT system with dual-coil and triple-coil structures is in the strong coupling region and the system is robust. Therefore, the transmission characteristics of the receiving groups of these two structures will not be explained in detail. Here are the various conditions under the ideal PT system:

[0051] When g = γ, that is, when the gain is equal to the loss

[0052]

[0053] However, in the derivation and calculation of higher-order coupled mode equations, it was found that due to the complex conditions of various data, the condition g=γ could not be deduced, which means that the gain and loss cannot be balanced, that is, the wireless power transmission system of the PT system cannot be realized.

[0054] The present invention uses Hamiltonian to represent the coupled mode and establishes a new equation. First, from the standard second-order demonstration, the time evolution of the resonance amplitude of the transmitting and receiving coils of the standard PT symmetric system is used, and a=[a1 a2] T It can evolve into

[0055] in, is the Hamiltonian function, and in this way, the fourth-order, fifth-order, and sixth-order Hamiltonian equations are constructed.

[0056] In calculations using the new Hamiltonian, we find that the fourth-order equation for g = γ is:

[0057]

[0058] After comparing the frequency splitting formulas of the two-coil PT-WPT system and the four-coil PT-WPT system, it can be found that the minimum longitudinal splitting range of the four-coil PT-WPT system is smaller than the minimum longitudinal splitting range of the two-coil PT-WPT system. Figure 1 .

[0059] The five-coil long-distance PT-WPT system is analyzed. The fifth-order Hamiltonian equation is constructed to obtain the formula of the equivalent system:

[0060]

[0061] in, Represents the resonant angular frequency of the nth LC circuit, γ=γ5+γ Leq , represents the intrinsic loss rate of the nth LC circuit, Indicates the intrinsic loss rate of the load, g = g A -γ1 is the gain of the transmitting coil, represents the total gain of the system, is the coupling coefficient between two adjacent coils.

[0062] Setting k 12 =k 23 =k 34 =k 45 =k, the five coils maintain the same resonant frequency ω1=ω2=ω3=ω4=ω5=ω.

[0063] By solving the characteristic equation, we can obtain:

[0064]

[0065] Let Δω=ω-ω0. Simplifying equation (4) we can get the real part and imaginary part of the equation respectively:

[0066]

[0067] From formula (5), we can further solve:

[0068] When g = γ:

[0069]

[0070] It can be seen from formula (6) that when the gain is equal to the loss, the resonant frequency of the system has a wide coupling characteristic. In addition, a real characteristic frequency that is independent of γ can be obtained, indicating that it is not affected by distance and enhances the stability of the system. Based on formula (6) and the longitudinal frequency splitting range of the five-coil PT-WPT system and the longitudinal frequency splitting range of the two-coil PT-WPT system, the following is drawn: Figure 2 . The critical coupling coefficient is further solved according to the real part equation:

[0071]

[0072] The critical coupling coefficient is called a singular point (EP) in non-Hermitian physics. When a system has a singular point, the topological structure has a topological protection property. According to equations (6) and (7), the PT symmetry condition of the system can be summarized as follows:

[0073]

[0074] Therefore, when the condition of equation (8) is satisfied, the system is in the PT symmetric region. It is worth mentioning that the five-coil PT-WPT system undergoes multiple splits at the singular point and has a wider coupling range, indicating that the five-coil system has a more robust advantage.

[0075] Furthermore, the sixth-order Hamiltonian equation is constructed in the same way and solved (in order to facilitate writing and see the equation more intuitively, ABCEFG is used instead of the equation):

[0076]

[0077] E=-g 4 +g 2 γ 2 -7γ 4

[0078]

[0079] G = g 4 -g 2 γ 2 +7γ 4

[0080]

[0081]

[0082] The frequency splitting range of the six-coil PT-WPT system is obtained from formula (9) and compared with the frequency splitting range of the two-coil PT-WPT system. Figure 3 .

[0083] Depend on Figure 2 It can be seen from equation (6) that compared with four coils and six coils, when the fifth-order PT symmetry is maintained, there is a real characteristic frequency that is independent of coupling, which means that when the distance changes, the frequency does not change, indicating that compared with the two-coil, four-coil or six-coil PT-WPT system, the five-coil system with PT symmetry can work efficiently at different distances without frequency tracking, which means that the coupling characteristics of the nonlinear gain element can be used to achieve stable and efficient power transmission in the strong coupling region. Secondly, from Figure 1 It can be seen from (b) that the minimum longitudinal frequency splitting range of the four-coil PT-WPT system is smaller than that of the two-coil PT-WPT system. Figure 2 The minimum longitudinal frequency splitting range of the five-coil PT-WPT in (b) is larger than that of the two-coil PT-WPT system, which means that the five-coil has a wider coupling range than the four-coil. When the transmitting coil and the receiving coil are misaligned or there is relative motion, the WPT system is still robust and can maintain stable transmission.

[0084] Depend on Figure 3 It is concluded that the longitudinal frequency splitting range and transverse PT symmetry area of ​​the six-coil PT-WPT system are larger than those of the two-coil PT-WPT system. However, the six-coil PT-WPT system will inevitably have a smaller frequency due to the increased loss caused by the increase in the number of relay coils, and the six-coil has a lower ability to actively tune due to the increase in the number of relay coils.

[0085] Furthermore, by changing the number of turns of the excitation coil and redesigning the relay coil, a long-distance PT-WPT system with an asymmetric structure is constructed. At the same time, the value of the resonant capacitor in the relay coil is changed so that the resonant frequencies between the coils are equal, thereby achieving the coupling condition. The above design changes the symmetric structure of the system, so that the wireless power transmission system of the present invention presents an asymmetric structure. The relay coil has a larger number of turns, which is different from the traditional symmetrical structure and can have a higher coupling coefficient under the same conditions. After conducting the experiment and recording the data, the coupling coefficient between them was obtained by Ansys simulation, and then drawn by Origin. Figure 4 A higher coupling coefficient means that it is easier to reach the strong coupling zone, that is, it is easier to reach the PT precise symmetry area to achieve stable wireless power transmission. By improving the structure, the conditions for the strong coupling zone reached by the wireless power transmission system are reduced, allowing the system to more easily achieve robust energy transmission. In summary, the study of the five-coil PT-WPT system is optimal.

[0086] However, from Figure 2 Figure (b) shows that the fifth order is better than the original splitting. c (critical coupling condition) is larger, indicating that it has the characteristics of hysteresis splitting compared with the original PT-WPT.

[0087] In order to solve the delay lag of the five-coil system, the present invention designs a PT-WPT topology diagram with PS-SP structural characteristics and makes the receiving coil equivalent, and draws Figure 5 and Figure 6 .

[0088] The circuit structure of the present invention generally presents an SP-PS structure. In the process of energy transfer, energy is transmitted from the transmitting coil with negative resistance, and the energy is transmitted to the receiving coil with a PS structure through the relay coils, thereby realizing long-distance energy transmission.

[0089] Will Figure 5 The receiving coil is equivalent to a simple inductor and capacitor series topology, and the following formula can be obtained:

[0090]

[0091] Decomposing it into R+jX, the equivalent capacitance and resistance can be obtained as follows:

[0092]

[0093] ΘR L 2 ω 2 c 5p c 5s 2 ,RL 2 ω 2 c 5p 2 c 5s <<c 5p +c 5s ∴c=c 5p +c 5s (13)

[0094]

[0095] It can be seen from formula (14) that the equivalent resistance R of the topological structure proposed in the present invention is Leq Than the original load R L is much smaller, so its intrinsic loss rate γ Leq To reduce it, substitute into equation (7) and get k c It becomes smaller, that is, its critical coupling condition becomes smaller, which means that the present invention can expand the precise PT symmetry area under the condition of the same load resistance, thus compensating for the inherent sensitivity of the original WPT and solving the problem of the small fifth-order lateral PT area.

[0096] Next, a mathematical model is constructed to calculate the output power and transmission efficiency of the SP-PS structure.

[0097] Table 1 Performance comparison between SP-PS structure and SS structure

[0098]

[0099] From Table 1, we know that the transmission efficiency and output power of the SP-PS system are related to α, and α is related to the capacitance of the receiving coil from the derivation of formula (14), that is, the capacitance C on the receiving coil can be changed. 5p and C 5s The fifth-order transmission efficiency can be dynamically changed by adjusting the capacitance distribution ratio of the receiving coil to adapt to different product requirements, so as to freely change and make a trade-off between the transmission distance and the transmission efficiency. When the input voltage and load resistance are constant, a smaller α can extend the transmission distance of the system and increase the output power of the system, but it will also reduce the transmission efficiency. Therefore, we need to design a suitable α value according to different application scenarios in practice, and improve the transmission efficiency as much as possible when the output power and transmission distance meet the product requirements. Compared with the original PT-WPT system, the active tuning advantage of the PS-SP system is stronger.

[0100] From the above, it can be seen that the use of SP-PS compensation network greatly reduces the equivalent load resistance of the system, thereby effectively reducing the critical coupling coefficient k cTherefore, the system shows that the lateral PT precise symmetry area of ​​the system is expanded, the inherent sensitivity of the system is improved, and the system is more stable during the transmission process. And because of the parallel and series combination of capacitors and inductors, it is no longer limited to the current simple circuit that cannot be adjusted. The SP-PS type wireless power transmission system can be adjusted according to the capacitor C 5p , C 5s Dynamically adjust output power and transmission efficiency to facilitate the design and modification of system parameters.

Claims

1. A long-distance parity-time symmetric wireless power transmission system with a multi-coil structure, characterized in that: It includes a transmitting device, a relay coil circuit and a receiving device. Two capacitors and a resistor are connected in parallel and then in series with an inductor to form a transmitting device with an SP structure and a receiving device with a PS structure. Multiple groups of relay coil circuits are arranged between the transmitting device and the receiving device.

2. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 1, characterized in that: The transmitting device includes a power supply, a full-bridge inverter, a resonant capacitor C 1s , C 1p and inductor L1; where, in the associated reference direction, the voltage across the full-bridge inverter and the current flowing through it are opposite, and together with the power supply are equivalent to a negative resistance -R N , resonant capacitor C 1s , C 1p and resistor - R N The parallel connection and the series connection with the inductor L1 form an SP structure.

3. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 2 is characterized in that: The receiving device includes a receiving inductor L5, a resonant capacitor C 5s , C 5p and load R L ; Among them, the resonant capacitor C 5s , C 5p and load R L The parallel connection and the series connection with the inductor L5 form a PS structure.

4. A long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to any one of claims 1 to 3, characterized in that: A total of three groups of relay coil circuits are arranged between the transmitting device and the receiving device.

5. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 4, characterized in that: In the first relay coil circuit, the inductor L2 and the capacitor C2 form a closed loop. The inductor L1 and the inductor L2 are adjacent to each other, and there is a mutual inductance M. 12 In the second relay coil circuit, the inductor L3 and the capacitor C3 form a closed loop. The inductor L2 and the inductor L3 are adjacent coils, and there is a mutual inductance M 23 In the third relay coil circuit, the inductor L4 and the capacitor C4 form a closed loop, and the inductor L3 and the inductor L4 are adjacent coils, and there is a mutual inductance M 34 At the same time, inductor L4 and inductor L5 are adjacent coils, and there is a mutual inductance M 45 .

6. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 5, characterized in that: The mutual inductance between the transmitting device, the relay coil circuit and the non-adjacent coils in the receiving device is zero.

7. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 6, characterized in that: There is a coil internal resistance r in the transmitter, relay coil circuit and receiver. n , n=1,2,3,4,5, the internal resistance of the coil is very small and can be ignored.

8. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 7, characterized in that: The number of turns of the inductor in the relay coil circuit is greater than the number of turns of the inductor in the transmitting device and the receiving device.

9. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 8, characterized in that: The distances between the coils in the transmitting device, the relay coil circuit and the receiving device are equal.

10. The long-distance parity-time symmetric wireless power transmission system with a multi-coil structure according to claim 9, characterized in that: The transmitting device, the relay coil circuit and the receiving device each coil maintain the same resonant frequency, i.e., ω1=ω2=ω3=ω4=ω5=ω, and the same coupling coefficient, i.e., k 12 =k 23 =k 34 =k 45 =k.

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