A magnetically coupled resonant wireless energy transmission system based on a class E power amplifier and a four-coil structure

Abstract

The invention discloses a magnetic coupling resonant wireless energy transmission system based on a class E power amplifier and a four-coil structure, comprising a gate drive signal source (1), a power tube (2), a drain DC input (3), a parallel capacitor and an LC resonant circuit (4), a second-level coil (5), a third-level coil (6), a receiving coil (7) and an output load (8); the gate drive signal source (1) is connected to the gate of the power tube (2), the drain DC input (3) is connected to the drain of the power tube (2), the drain output of the power tube (2) is transmitted to the second-level coil (5) via the parallel capacitor and the LC resonant circuit (4), the second-level coil (5) is transmitted to the third-level coil (6), the third-level coil (6) is transmitted to the receiving coil (7), and the receiving coil (7) is connected to the output load (8). The invention has a simplified structure, high transmission efficiency and low cost.

Description

Technical Field

[0001] The present invention belongs to the field of wireless energy transmission, and in particular relates to a magnetically coupled resonant wireless energy transmission system based on a class E power amplifier and a four-coil structure. Background Art

[0002] Magnetic coupling resonant wireless power transmission technology is one of the three major wireless power transmission technologies and is also one of the hot topics currently being studied by scholars at home and abroad. However, the power of wireless power transmission is still not large, and increasing the transmission power requires the high efficiency of the overall system as a prerequisite.

[0003] Improving the overall system efficiency currently mainly involves the following aspects: (1) improving power supply efficiency; (2) accurate load matching; (3) reducing coil parasitic parameters; and (4) high robustness of the resonant frequency.

[0004] However, there are few studies on magnetically coupled resonant wireless energy transmission systems that start from the perspective of power supply and coil integration, and reduce system losses by simplifying the overall system structure. This can not only reduce the intermediate losses of the system and improve the overall efficiency, but also reduce the system structure and reduce costs. The present invention aims to provide a magnetically coupled resonant wireless energy transmission system that combines a class E power amplifier with a four-coil structure. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned problems and shortcomings and to propose a magnetically coupled resonant wireless energy transmission system based on a class E power amplifier and a four-coil structure, which does not require a special impedance matching circuit, simplifies the system structure, reduces costs, and improves output power and transmission efficiency.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a magnetic coupling resonant wireless energy transmission system based on a class E power amplifier and a four-coil structure, comprising a gate drive signal source (1), a power tube (2), a drain DC input (3), a parallel capacitor and an LC resonant circuit (4), a second coil (5), a third coil (6), a receiving coil (7) and an output load (8);

[0007] The gate drive signal source (1) is connected to the gate of the power tube (2), the drain DC input (3) is connected to the drain of the power tube (2), the drain output of the power tube (2) is transmitted to the second coil (5) via the parallel capacitor and the LC resonant circuit (4), the second coil (5) is transmitted to the third coil (6), the third coil (6) is transmitted to the receiving coil (7), and the receiving coil (7) is connected to the output load (8).

[0008] To further improve the above technical solution, the drain DC input (3) is composed of a capacitor C5, a DC voltage source V1 and a choke coil RFL, the negative electrode of the DC voltage source V1 is connected in series with the capacitor C5 to ground, and the positive electrode of the DC voltage source V1 is connected in series with the choke coil RFL to connect to the drain of the power tube (2).

[0009] Furthermore, the parallel capacitor and LC resonant circuit (4) is composed of a parallel capacitor C0, a resonant inductor L1 and a resonant capacitor C1, the parallel capacitor C0 is connected in parallel between the drain and source of the power tube (2), the source of the power tube (2) is grounded, and the resonant inductor L1 and the resonant capacitor C1 are connected in series at both ends of the parallel capacitor C0.

[0010] Furthermore, the second coil (5) is formed by a series connection of an inductor L2 and a capacitor C2.

[0011] Furthermore, the third coil (6) is formed by a series connection of an inductor L3 and a capacitor C3.

[0012] Furthermore, the receiving coil (7) is formed by connecting an inductor L4 and a capacitor L4 in series, and the inductor L4, the capacitor L4 and the output load (8) form a closed loop.

[0013] The beneficial effects of the present invention are as follows: the present invention uses the resonant inductor of the Class E power amplifier as the primary coil, couples the energy of the primary coil to the secondary coil by magnetic coupling resonance, couples the second coil to the third coil, couples the third coil to the receiving coil, and transmits the energy to the output load. The overall system structure is simpler than the traditional structure, which is beneficial to improving system efficiency and reducing overall cost. The present invention changes the input impedance of the four-coil structure to the Class E power amplifier by adjusting the distance between the primary coil and the second coil, the third coil and the receiving coil, thereby achieving the purpose of load matching. There is no need to rely on a matching circuit to achieve load matching, thereby simplifying the system structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a structural block diagram of the wireless energy transmission system based on a class E power amplifier and a four-coil structure according to the present invention;

[0015] Figure 2 for Figure 1 Circuit diagram of

[0016] Figure 3 for Figure 2 Equivalent circuit diagram of

[0017] Figure 4 for Figure 3 The relationship between the load current phase φ of the class E power amplifier and the load (input impedance Rin) change;

[0018] Figure 5 for Figure 3 The efficiency η of the class E power amplifier E and power Po E Relationship diagram with changes in load (input impedance Rin);

[0019] Figure 6 for Figure 3 The relationship between the equivalent input impedance Rin of the four-coil structure and the number of coil turns N and the coil radius r;

[0020] Figure 7 The relationship diagram of the overall system output power Po of the present invention as the number of coil turns N and the coil radius r changes;

[0021] Figure 8 is a graph showing the relationship between the efficiency η of the overall system of the present invention and the number of coil turns N and the coil radius r;

[0022] Fig. 9 The relationship diagram of the overall system output power Po of the present invention as a function of the distance d12 between the primary coil and the second coil and the distance d34 between the third coil and the receiving coil;

[0023] Fig.10 Graph showing the relationship between the efficiency η of the overall system of the present invention and the distance d12 between the primary coil and the secondary coil and the distance d34 between the tertiary coil and the receiving coil.

[0024] In the figure, 1. Gate drive signal source; 2. Power tube; 3. Drain DC input; 4. Parallel capacitor and LC resonant circuit; 5. Second-stage coil; 6. Third-stage coil; 7. Receiving coil; 8. Output load. DETAILED DESCRIPTION

[0025] In order to make the content of the invention clearer, the specific implementation of the invention is further described in detail below in conjunction with the accompanying drawings. It should be noted that for the purpose of clarity, the representation and description of components that are not related to the invention and are known to those of ordinary skill in the art are omitted in the drawings and descriptions.

[0026] Embodiment 1:

[0027] The resonant frequency of the LC resonant circuit of the class E power amplifier is the same as the self-resonant frequency of the coil, so the LC resonant circuit of the class E power amplifier can be used as the primary coil of the four-coil structure at the same time; however, it is necessary to design the coil parameters so that the resonant inductance value of the class E power amplifier is consistent with the primary coil inductance value of the four-coil structure, and through the precise design of other parameters, the equivalent input impedance of the four-coil structure is equal to the ideal load impedance of the class E power amplifier, thereby simplifying the system structure on the basis of ensuring the transmission power and efficiency of the overall system.

[0028] 1. Class E power amplifier design

[0029] The structure of the class E power amplifier adopts a typical class E power amplifier with parallel capacitors. In order to achieve the maximum efficiency output, it must meet the following ZVS and ZDS conditions at the operating frequency: ZVS (zero-voltage switching): when the switch changes from the off state to the on state, the collector or drain voltage of the power tube is equal to 0; ZDS (zero-derivative switching): when the switch changes from the off state to the on state, the collector or drain voltage derivative of the power tube is equal to 0.

[0030] The class E power amplifier comprises a gate drive signal source (1), a power tube (2), a drain DC input (3) and a parallel capacitor and LC resonant circuit (4); the gate drive signal source (1) is connected to the gate of the power tube (2); the drain DC input (3) is composed of a DC voltage source V1, a capacitor C5 and a choke coil RFL, the negative electrode of the DC voltage source V1 is connected in series with the capacitor C5 to ground, and the positive electrode of the DC voltage source V1 is connected in series with the choke coil RFL to the drain of the power tube (2); the parallel capacitor and LC resonant circuit (4) is composed of a parallel capacitor C0, a resonant inductor L1 and a resonant capacitor C1, the parallel capacitor C0 is connected in parallel between the drain and source of the power tube (2), the source of the power tube (2) is grounded, and the resonant inductor L1 and the resonant capacitor C1 are connected in series to both ends of the parallel capacitor C0.

[0031] The main components of the Class E power amplifier are: DC voltage source V1, power tube Q1, choke coil RFL, parallel capacitor C0, resonant inductor L1 and resonant capacitor C1.

[0032] The specific design steps are as follows:

[0033] (1) After determining the DC voltage source V1, operating frequency f, and quality factor Q L Based on the output power Po, the parameters of the resonant inductor L1, the resonant capacitor C1 and the parallel capacitor C0 of the class E power amplifier are designed according to the design indicators;

[0034] For a class E power amplifier with a duty cycle of 0.5, its parameters are obtained by the following formula;

[0035]

[0036]

[0037]

[0038]

[0039] Where: R is the ideal load impedance of the class E power amplifier, L1 is the resonant inductor, C1 is the resonant capacitor, C0 is the parallel capacitor, V1 is the DC voltage source, Po is the output power, Q L is the quality factor and f is the operating frequency.

[0040] (2) When analyzing the transmission characteristics of the four-coil structure, the front-end power supply needs to be equivalent to a constant voltage source or current source with an internal resistance Rs. The optimal operating conditions of the single-frequency class E power amplifier need to be analyzed under a certain duty cycle, operating frequency, output power and load resistance. However, in the wireless energy transmission system, it is necessary to analyze the operating characteristics of the class E power amplifier under different equivalent input impedances Rin, so it is necessary to analyze the load characteristics of the class E power amplifier. Therefore, according to the duty cycle, determine the effect of the load (i.e., input impedance Rin) change on the efficiency η E And output power Po E The impact of

[0041] When the duty cycle of the gate drive signal of the power tube (2) is 0.5, the following relationship can be obtained:

[0042]

[0043]

[0044]

[0045] Where: X = ωL1-1 / ωC1, φ is the load current phase, Io is the output current, I D is the DC input current, Us is the output voltage; ω is the operating angular frequency, C0 is the parallel capacitor, L1 is the resonant inductor, C1 is the resonant capacitor, Rin is the input impedance, and V1 is the DC voltage source.

[0046] (3) The efficiency η of the class E power amplifier E and the output voltage Us is expressed as a function of the load (input impedance Rin);

[0047]

[0048]

[0049]

[0050] Where: η E is the efficiency of the class E power amplifier, Pton is the conduction loss of the power tube (2); r DS is the on-resistance of the power tube (2), r Lis the equivalent series resistance of the resonant inductor L1, tf is the fall time of the power tube (2), I D is the DC input current, Io is the output current, φ is the load current phase, C0 is the parallel capacitance, and ω is the operating angular frequency.

[0051] 2. Design of four-coil structure

[0052] The four-coil structure of the present invention uses the resonant inductor L1 of the class E power amplifier as the primary coil of the magnetic coupling resonance system, i.e., the excitation coil, without using an additional load matching circuit, and simplifies the system structure as much as possible to improve the overall efficiency. The four-coil structure has a variety of different resonance compensation structures, and the present invention adopts the ss compensation structure.

[0053] The design of the four-coil structure is based on the mutual inductance principle, and the four-coil structure is equivalent to four LC series resonant circuits. The resonant circuit includes an LC resonant circuit of an E-class power amplifier, a second-level coil (5), a third-level coil (6), a receiving coil (7) and an output load (8); the LC resonant circuit of the E-class power amplifier is used as an excitation coil, which is composed of a resonant inductor L1 and a resonant capacitor C1 connected in series, and is coupled to the second-level coil (5) through mutual inductance; the second-level coil (5) is used as an energy transmitting coil, which is composed of an inductor L2 and a capacitor C2 connected in series, and is coupled to the third-level coil (6) through mutual inductance; the third-level coil (6) is an energy receiving coil, which is composed of an inductor L3 and a capacitor C3 connected in series, and is coupled to the load coil (7) through mutual inductance; the load coil (7) is composed of an inductor L4 and a capacitor C4 connected in series, and the load coil (7) and the output load (8) are connected in series to form a closed loop.

[0054] The main components of the four-coil structure are: excitation coil L1, energy transmitting coil L2, energy receiving coil L3, load coil L4, output load RL, tuning capacitors C2, C3 and C4.

[0055] The specific design steps are as follows:

[0056] (1) Based on Figure 3 The circuit schematic shown lists the equivalent KVL equation and solves the mutual inductance between the coils at each level;

[0057] The equivalent KVL equation is:

[0058]

[0059] Where: Z2=R2+jωL2+1 / jωC2, ​​Z3=R3+jωL3+1 / jωC3, Z4=R4+jωL4+1 / jωC4; ω is the operating angular frequency, M 12 、M 23 and M 34are the mutual inductances among the four coils, R2, R3 and R4 are the equivalent series resistances of the energy transmitting coil L2, the energy receiving coil L3 and the load coil L4 respectively, RL is the output load, I1, I2, I3 and I4 are the currents in the four-coil loops respectively, and Us is the output voltage of the class E power amplifier.

[0060] In order to ensure the transmission efficiency of the four-coil structure and reduce the reactive power loss of the system, all coils except the excitation coil are in a resonant state. ( Z 2) =Im ( Z 3) =Im ( Z 4) =0, that is, Z2=R2, Z3=R3, Z4=R4; since the excitation coil is the resonant inductor L1 of the class E power amplifier, according to the working characteristics of the class E power amplifier, there is no reactive loss when the ZVS condition is met.

[0061] (2) According to formula (11), we can further deduce:

[0062]

[0063] Where: Poc is the output power of the four-coil structure, η c is the efficiency of the four-coil structure, Rin is the input impedance; M 12 、M 23 and M 34 are the mutual inductance between adjacent coils, R L is the output load, Us is the output voltage of the class E power amplifier, ω is the operating angular frequency, R2, R3 and R4 are the equivalent series resistances of the energy transmitting coil L2, the energy receiving coil L3 and the load coil L4 respectively.

[0064] (3) According to the relationship between the mutual inductance M, coil parameters and operating frequency f, the relationship between the output power Poc and coil parameters of the four-coil structure can be obtained;

[0065] The mutual inductance M between the coils is obtained by Newman's formula:

[0066]

[0067] Where: N1 and N2 are the number of turns of the two adjacent coils, μ0 is the vacuum permeability, r1 and r2 are the radii of the two coils, θ and Φ are the angles within the two coils, and d is the interaxial distance between the two coils.

[0068] Since the resonant coil has skin effect and proximity effect at high frequency, the proximity effect has a greater impact on the coil internal resistance. In order to reduce its impact on the equivalent internal resistance of the coil, the coil is wound with a hollow copper tube and a winding method with turn spacing is used. The approximate calculation formula for the spiral coil loss resistance is as follows:

[0069]

[0070] Where: ω is the operating angular frequency, μ0 is the vacuum magnetic permeability, σ is the electrical conductivity, N is the number of coil turns, r is the coil radius, and a is the wire radius.

[0071] The coils involved in the present invention are all coaxial spiral coils with equal radius r, wherein the number of turns of the energy transmitting coil L2 and the energy receiving coil L3 are equal, and the load coil L4 is a single-turn coil. When designing a wireless energy transmission system, the output power Po required for the design, the transmission distance d23 between the energy transmitting coil L2 and the energy receiving coil L3, and the system operating angular frequency ω, etc., will be given; according to the power and frequency required for the work, the design of the class E power amplifier can be completed, the specific parameters of the resonant inductor L1 can be obtained, and the number of turns of the resonant inductor L1 can be obtained according to the following formula:

[0072]

[0073] Where: μ rc is the relative magnetic permeability of the core, μ0 is the magnetic permeability of vacuum, r is the radius of the coil, N is the number of turns of the coil; lc=Na+(N-1), a is the radius of the wire, and s is the turn spacing.

[0074] (4) Combined with the changes in the input impedance Rin of the four-coil structure on the load current phase φ, output power Po and efficiency η of the class E power amplifier, the overall system design is completed;

[0075] When analyzing the overall system transmission efficiency, the number of coil turns N and the coil radius r are selected as the basic design variables, and the function Rin(N,r) of the equivalent input impedance Rin with respect to N and r can be obtained, and then the efficiency η can be obtained. c Function η about N,r c (N,r), and the output power Po and system efficiency η are expressed as functions Po(N,r) and η(N,r) about N,r. The relationship between N,r and the overall transmission efficiency and power of the system can be clearly analyzed. The overall power Po and efficiency η of the system are:

[0076]

[0077] 3. Overall design of wireless energy transmission system based on Class E power amplifier and four-coil structure

[0078] In order to accurately and vividly describe the relationship between the efficiency η and power Po of the wireless energy transmission system based on the class E power amplifier and the four-coil structure of the present invention and the coil radius r and the number of coil turns N, as well as the overall design process of the system, the system is designed and analyzed by combining simulation software with numerical calculation software. The design indicators of the system are shown in Table 1;

[0079] project parameter unit Operating frequency f 3 MHZ Transmission distance d 0.4 m Output power Po 40 w System efficiency η 90％ -- <![CDATA[Output load R L > 50 Ω

[0080] Table 1

[0081] (1) Design of Class E Power Amplifier

[0082] The class E power amplifier uses IRF200b211. According to formulas (1) to (4) and the design parameters in Table 1, the quality factor QL=7 and the DC voltage V1=40V are selected. The parameters of the class E power amplifier are shown in Table 2.

[0083] project parameter unit <![CDATA[Resonant inductor L1]]> 8.65 μH <![CDATA[Resonant capacitor C1]]> 393 pF <![CDATA[Parallel capacitor C0]]> 422 pF <![CDATA[DC voltage source V1]]> 40 V <![CDATA[Ideal load R opt > 23 Ω

[0084] Table 2

[0085] From equations (5) to (10), it can be concluded that when the load (input impedance Rin) of the class E power amplifier changes, the load current phase φ and efficiency η E And output power Po E The law of change is as follows: Figure 4 and Figure 5 shown by Figure 4 It can be seen that the change of the load (input impedance Rin) of the Class E power amplifier has little effect on the phase angle of the load current. When the input impedance Rin changes in the range of 1Ω-100Ω, the phase of the load current is basically maintained at -0.56 radians. Figure 5 It can be seen that the efficiency η of the class E power amplifier is E And output power Po E The input impedance Rin changes significantly, but the efficiency η E And output power Po E The maximum value is not reached at the same load impedance Rin. This is because when the load impedance Rin is not the optimal load impedance, the class E power amplifier does not operate under the optimal ZVS condition, and the voltage across the power tube is not 0 when the power tube is turned off, resulting in a large power but insufficient efficiency for the class E power amplifier.

[0086] (2) Four-coil structural parameter design

[0087] When designing the number of coil turns N and the coil radius r, according to the input impedance Rin and the ideal load Ropt, the spacing d12 between the excitation coil L1 and the energy transmitting coil L2, and the spacing d34 between the energy receiving coil L3 and the load coil L4 are set to an initial value of 15 cm, so that the input impedance Rin includes the ideal load R in a certain range. opt (23Ω). According to formulas (12) to (14), the variation law of input impedance Rin with respect to coil turns N and coil radius r is as follows: Figure 6 As shown in the figure, in order to facilitate the analysis of the resonant inductor L1 of the class E power amplifier, the number of turns is taken as an integer, and the inductance value is fine-tuned by adjusting the turn spacing. Figure 6 It can be seen that the equivalent input impedance Rin is distributed in a step-like manner. This is because the number of turns of the excitation coil is rounded. The inductance of the excitation coil is determined by the resonant inductance L1 of the class E power amplifier. Therefore, when the radius of the coil changes, the number of turns of the excitation coil can be derived according to formula (15) as follows:

[0088]

[0089] Where: L1 is the resonant inductance of the class E power amplifier, that is, the inductance of the primary coil, r is the coil radius, μ rc is the relative magnetic permeability of the core, μ0 is the vacuum magnetic permeability; lc is the length of the core, lc=Na+(N-1)s, N is the number of coil turns, a is the wire radius, and s is the turn spacing. When the coil radius r gradually increases, in order to ensure the inductance of the primary coil, the number of coil turns will decrease step by step, and the mutual inductance M 12 The size of is proportional to the number of turns of the coil (as can be seen from Newman's formula), so the step-by-step reduction of the number of turns of the primary coil leads to the mutual inductance M 12 The input impedance is greatly reduced and the size of M 12 It is proportional to the square of the input impedance, so the input impedance will be greatly reduced when the number of turns of the primary coil decreases in a step-by-step manner. After the number of turns stabilizes, the mutual inductance gradually increases with the increase of the coil radius, and the equivalent input impedance gradually increases.

[0090] In the overall trend, the input impedance Rin increases with the increase of the radius, and there is an optimal radius and number of turns, which makes the input impedance Rin close to the ideal load impedance, so that the system can reach the best working state. However, the specific value of the number of turns and radius is not obvious, and needs to be further determined by the relationship between the overall system power Po and efficiency η and the number of coil turns N and the coil radius r. The change law of the overall system power Po and efficiency η with respect to the number of coil turns N and the coil radius r is as follows Figure 7 and 8 shown.

[0091] Depend on Figure 7 and8 It can be seen that when the coil radius r and the number of coil turns N change, the output voltage of the power supply is also stepped due to the step-like distribution of the input impedance Rin. Therefore, when the equivalent input impedance Rin increases with the coil radius r and the number of turns N, on the one hand, the power Po and efficiency η of the system are greater when the equivalent input impedance Rin is closer to the optimal load impedance. On the other hand, when the number of turns of the primary coil is rounded to an integer, the number of turns will decrease when the radius increases to a certain extent, resulting in the mutual inductance M. 12 The input impedance Rin is greatly reduced, causing the output voltage to change. Under the influence of these two factors, the overall power Po and efficiency η of the system are stepped and have multiple peaks, but the overall trend has a maximum value. Through simulation analysis, it is found that the optimal number of coil turns N = 10 and the coil radius r = 0.2m; although there are peaks in power Po and efficiency η, the maximum efficiency of the system at this time is less than 90%, and the maximum power is only 31W, which does not reach the ideal working state. This is because d 12 and d 34 The initial value is set, so that the adjustment range of the equivalent input impedance Rin is limited, which requires d 12 and d 34 As the basic design variables, the system parameters are designed. The overall system power Po and efficiency η are related to d 12 and d 34 The changing rules of Fig. 9 The and 10 are shown.

[0092] Depend on Fig. 9 and 10 It can be seen that there is an optimal distance d between the excitation coil L1 and the energy transmitting coil L2 12 The distance d between the energy receiving coil L3 and the loading coil L4 34 , so that the power Po and efficiency η of the overall system are optimal, and the optimal distance d between the excitation coil L1 and the energy transmitting coil L2 12 The optimal distance d between the energy receiving coil L3 and the loading coil L4 is 0.17m. 34 The system has a maximum efficiency of 93% and an ideal output power of 38W.

[0093] The main design parameters of the four-coil structure are shown in Table 3.

[0094] project parameter unit Number of turns of energy transmitting coil and energy receiving coil N 10 Turn Coil radius r 0.2 m <![CDATA[Number of turns N1 of the excitation coil]]> 3 Turn <![CDATA[Distance d between the excitation coil and the energy transmitting coil 12 > 0.16 m <![CDATA[Distance d between the energy receiving coil and the load coil 34 > 0.17 m

[0095] Table 3

[0096] The above only expresses the implementation methods of the invention, which are described in a more specific and detailed manner, but cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the invention, which all belong to the protection scope of the invention. Therefore, the protection scope of the invention patent shall be based on the attached claims.

Claims

1. A magnetically coupled resonant wireless energy transmission system based on a class E power amplifier and a four-coil structure, characterized in that: It comprises a gate drive signal source (1), a power tube (2), a drain DC input (3), a parallel capacitor and an LC resonant circuit (4), a second coil (5), a third coil (6), a receiving coil (7) and an output load (8); the gate drive signal source (1) is connected to the gate of the power tube (2), the drain DC input (3) is connected to the drain of the power tube (2), the drain output of the power tube (2) is transmitted to the second coil (5) via the parallel capacitor and the LC resonant circuit (4), the second coil (5) is transmitted to the third coil (6), the third coil (6) is transmitted to the receiving coil (7), and the receiving coil (7) is connected to the output load (8); the drain DC input (3) is composed of a capacitor C5, a DC voltage source V1 and a choke coil RFL, the negative electrode of the DC voltage source V1 is connected in series with the capacitor C5 to ground, and the positive electrode of the DC voltage source V1 is connected in series with the choke coil RFL to the drain of the power tube (2); The parallel capacitor and LC resonant circuit (4) is composed of a parallel capacitor C0, a resonant inductor L1 and a resonant capacitor C1. The parallel capacitor C0 is connected in parallel between the drain and source of the power tube (2). The source of the power tube (2) is grounded. The resonant inductor L1 and the resonant capacitor C1 are connected in series to the two ends of the parallel capacitor C0. The second coil (5) is composed of an inductor L2 and a capacitor C2 connected in series. The third coil (6) is composed of an inductor L3 and a capacitor C3 connected in series. The receiving coil (7) is composed of an inductor L4 and a capacitor L4 connected in series. The inductor L4, the capacitor L4 and the output load (8) form a closed loop. The LC resonant circuit of the class E power amplifier is used as the primary coil of the four-coil structure at the same time. The class E power amplifier and the coil structure are adjusted so that the resonant inductance value of the class E power amplifier is consistent with the primary coil inductance value of the four-coil structure, and the equivalent input impedance of the four-coil structure is equal to the ideal load impedance of the class E power amplifier. The coils are all wound with hollow copper tubes and use a winding method with turn spacing. The coils are all coaxial spiral coils with equal radius r. The number of turns of the energy transmitting coil L2 and the energy receiving coil L3 is equal, and the load coil L4 is a single-turn coil; Design of Class E power amplifier: On the basis of determining the DC voltage source V1, the operating frequency f, the quality factor QL and the output power Po, according to the design indicators, the resonant inductor L1, the resonant capacitor C1 and the parallel capacitor C0 of the Class E power amplifier are designed, and the influence of the load change on the efficiency ηΕ and the output power PoE is determined according to the duty cycle; Design of four-coil structure: List the equivalent KVL equation, solve the mutual inductance between the coils at each level, calculate the relationship between the output power Poc of the four-coil structure, the efficiency ηc of the four-coil structure and the input impedance, and according to the relationship between the mutual inductance M and the coil parameters and the operating frequency f, the relationship between the output power Poc of the four-coil structure and the coil parameters is obtained, and the overall design of the system is completed by combining the input impedance Rin of the four-coil structure with the load current phase φ, output power Po and efficiency η of the Class E power amplifier; When the coil radius r and the number of coil turns N change, due to the step-like distribution of the input impedance Rin, the output voltage of the power supply also presents a step-like shape. Therefore, in the process in which the equivalent input impedance Rin increases with the coil radius r and the number of turns N, on the one hand, the power Po and efficiency η of the system increase when the equivalent input impedance Rin is closer to the optimal load impedance. On the other hand, since the number of turns of the primary coil is rounded to an integer, the number of turns will decrease when the radius increases to a certain extent, resulting in a significant reduction in the mutual inductance M12, causing the input impedance Rin to suddenly change and the output voltage to change accordingly. Under the influence of these two factors, the overall power Po and efficiency η of the system present a step-like shape with multiple peaks, but the overall trend has a maximum value. The optimal radius and number of turns are confirmed by the change law of the overall system power Po and efficiency η with respect to the number of coil turns N and the coil radius r, and the optimal distance d12 between the excitation coil L1 and the energy transmitting coil L2 and the distance d34 between the energy receiving coil L3 and the load coil L4 are confirmed by the change law of the overall system power Po and efficiency η with respect to d12 and d34.

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