A Constant Current and Constant Voltage Wireless Charging System and Method Based on a Three-Coil Loosely Coupled Transformer

Abstract

This application belongs to the field of wireless charging technology, specifically relating to a constant current and constant voltage wireless charging system and method based on a three-coil loosely coupled transformer, including an inverter circuit, a primary-side compensation circuit, a resonant circuit, a secondary-side compensation circuit, a rectifier circuit, and a filter capacitor; the resonant circuit has an anti-parallel coil structure, with the third coil located on the secondary side and a single coil on the primary side; its advantages are high misalignment tolerance, load-independent output, and high efficiency.

Description

Technical Field

[0001] This application belongs to the field of wireless charging technology, specifically relating to a constant current and constant voltage wireless charging system and method based on a three-coil loosely coupled transformer. Background Technology

[0002] A major challenge in practical applications of wireless charging systems is the tendency for the receiver to shift horizontally during placement. This affects the coupling coefficient of the wireless charging system, thereby reducing output power and system efficiency. Researchers have conducted extensive investigations to improve the offset characteristics of WPT (Wireless Power Transfer) systems.

[0003] Existing methods for improving offset characteristics mainly include the design of mistuning compensation networks, resonator adjustment, and optimization of compensation topologies. These methods improve the system's offset tolerance to some extent, but often come with problems such as complex control strategies, additional size, and increased cost. Furthermore, although some studies have proposed designs such as dual-D, bipolar and tripolar magnetic pads, and asymmetric magnetic couplers to improve bias performance, these methods are generally only applicable to bias-tolerant operation in a single direction and rarely address the constant output characteristics of the IPT system.

[0004] During charging, the battery's equivalent impedance changes continuously, and coil misalignment reduces the coupling coefficient, leading to a decrease in system efficiency. Therefore, IPT systems need to achieve constant output independent of the load and exhibit strong robustness to coupling changes. To achieve this, various control methods have been proposed, such as phase-shift control, pulse frequency control, frequency control, and hybrid control methods. However, these complex control methods often increase system cost and power loss, and the stability of the control system is also affected by data transmission speed and accuracy.

[0005] Another solution is to use a reconfigurable topology to improve deviation tolerance. While this approach improves output stability to some extent, the use of a large number of components leads to inefficiency. Furthermore, reconfiguration requires detectors and controllers, which remains a challenge for control strategies. Summary of the Invention

[0006] Existing IPT charging systems still have shortcomings in terms of misalignment tolerance, constant output characteristics, and system efficiency. Therefore, developing a wireless charging system with high misalignment tolerance, load-independent output, and high efficiency is particularly important. This invention is proposed against this background, aiming to solve the above problems and meet the practical needs of wireless charging systems for electric bicycles. The technical solution of this application is as follows:

[0007] A constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer includes an inverter circuit, a primary-side compensation circuit, a resonant circuit, a secondary-side compensation circuit, a rectifier circuit, and a filter capacitor.

[0008] The inverter circuit includes switching transistors Q1 and Q2;

[0009] The primary-side compensation circuit includes an inductor L1 and a capacitor C. P1 C f1 The inductor L1 is connected to the capacitor C. P1 C f1 Connection, the capacitor C P1 C f1 In parallel; inductor L1 is connected to switching transistors Q1 and Q2 respectively;

[0010] The resonant circuit includes a loosely coupled transformer, whose secondary coil is connected in series with an auxiliary coil;

[0011] The secondary-side compensation circuit includes inductor L2 and capacitor C. p2 C f2 One end of L2 is connected to capacitor C. p2 C f2 One end is connected to the rectifier circuit via a switching transistor Q5; the capacitor C p2 C f2 Parallel connection, where C f2 With inductor L S Connection, capacitor C p2 Connect to the rectifier circuit;

[0012] The rectifier circuit includes switching transistors Q3 and Q4, and the auxiliary coil L T Connect Q3 and Q4 respectively, with switch Q3 connected to switch Q5 through diode D5;

[0013] The rectifier circuit and the filter capacitor C0 are connected in parallel.

[0014] Preferably, the secondary coil L S and auxiliary coil L T Equivalent to a coil M EQ Equivalent self-induction L' P The calculation is as follows:

[0015] L' P =L P +L T -2M PT ;

[0016] M EQ =M PS -M PT ;

[0017] LP L S and L T It is the inductance of the primary side, secondary side, and auxiliary coil of the loosely coupled transformer; U P U S and I P I S This represents the input and output voltage and current of a loosely coupled transformer; M PT M PS and M TS It is the relevant coupling coefficient of the primary side, secondary side and auxiliary coil of the loosely coupled transformer;

[0018] Under the condition of misalignment, M PS and M PT As they decrease simultaneously, the degree of decrease in the two mutual inductances is expressed by ΔM. PS and ΔM PT The equivalent mutual inductance coefficient is expressed as:

[0019] M' EQ =(M PS -ΔM PS )-(M TS -ΔM TS )

[0020] =M EQ -(ΔM PS -ΔM TS );

[0021] Assume ΔM PS =ΔM PT Then M' EQ =M EQ This indicates that mutual inductance remains stable under misalignment conditions.

[0022] Preferably, when the topology operates in CV mode, switch Q4 is turned on, and Q3 and Q5 are turned off to construct the LCC-S topology, and AC-DC rectification is achieved on the secondary side through a half-bridge rectifier circuit.

[0023] Preferably, when the topology operates in CV mode, the AC input current I... in The formula is:

[0024]

[0025] U AB and I in U represents the AC output voltage and current of the inverter circuit. ab and I ab This represents the AC input voltage and current of the rectifier circuit; U DC and I DC U represents the DC input voltage and current of the inverter circuit.b and I b This indicates the DC output voltage and current of the rectifier circuit;

[0026] The formulas for calculating AC output voltage and voltage gain ratio are as follows:

[0027]

[0028] Z in Input impedance, R ac The equivalent AC resistance of the secondary side, I s Output current;

[0029] The formulas for calculating the current in the primary and secondary coils are:

[0030]

[0031] The formulas for calculating the DC output voltage and current on the secondary side are as follows:

[0032]

[0033] The relationship between primary-side input and output voltage and current is as follows:

[0034]

[0035]

[0036] The formula for calculating the relationship between equivalent AC resistance and DC resistance is:

[0037]

[0038] Preferably, when the topology operates in CV mode, the calculated AC-AC efficiency can be obtained as follows:

[0039]

[0040] The derivation of the optimal equivalent AC resistance is as follows:

[0041]

[0042] R S Primary coil resistance, R p The secondary coil resistance, M is the mutual inductance between the two coils of the loosely coupled transformer; R L1 Let ω be the resistance of inductor L1, and ω0 be the resonant angular frequency.

[0043] Preferably, when the topology operates in CC mode, switches Q3 and Q5 are turned on and Q4 is turned off to construct an LCC-LCC topology. The secondary side achieves AC-DC rectification through a rectifier circuit, enabling reconfigurable topology and CC mode. Current flows through freewheeling switch Q4 and diode D5.

[0044] Preferably, the resonance condition of the LCC-LCC topology is expressed as:

[0045]

[0046] The formulas for calculating AC input and output current are as follows:

[0047]

[0048] The currents on the primary and secondary coils are respectively represented as follows:

[0049]

[0050] The AC output current and voltage are respectively:

[0051]

[0052] The DC output current and voltage are respectively:

[0053]

[0054] The formula for calculating output power is:

[0055]

[0056] Preferably, the calculated AC-AC efficiency is:

[0057]

[0058] The derivation of the optimal equivalent AC resistance is as follows:

[0059]

[0060] A constant current and constant voltage wireless charging method based on a three-coil loosely coupled transformer is disclosed. When operating in CV mode, switch Q4 is turned on, and Q3 and Q5 are turned off to construct an LCC-S topology. The secondary side achieves AC-DC rectification through a half-bridge rectifier circuit. When operating in CC mode, switches Q3 and Q5 are turned on, and Q4 is turned off to construct an LCC-LCC topology. The secondary side achieves AC-DC rectification through a rectifier circuit. The topology and CC mode are reconfigurable, and the current flows through switch Q4 and diode D5.

[0061] Preferably, in CC and CV modes, changes in the self-inductance of the primary coil do not affect the current and voltage gains; the input phase angle increases as the self-inductance decreases, which will cause inductance drift in the system's input impedance, thus enabling switches Q1 and Q2 to operate under ZVS conditions; changes in the self-inductance of the secondary coil on the second side will affect the current gain, and a decrease in the self-inductance will cause capacitance drift in the system's input impedance, thereby affecting the inverter circuit's ability to achieve ZVS; when the input impedance changes due to capacitance, the change in self-inductance of the primary single coil is greater than that of the secondary side.

[0062] Compared with the prior art, the beneficial effects of this application are as follows:

[0063] The wireless charging system proposed in this application achieves significant benefits in terms of improved deviation tolerance, load-independent constant current and constant voltage output, simplified control scheme, and improved power density and efficiency through innovative design and topology improvements. Attached Figure Description

[0064] Figure 1 This is the equivalent circuit of a loosely coupled transformer coil;

[0065] Figure 2 Equivalent models (a) and (b) of loosely coupled transformer coils;

[0066] Figure 3 The circuit diagram of the system;

[0067] Figure 4 The equivalent circuit in CV mode;

[0068] Figure 5 The equivalent resonant network in CV mode;

[0069] Figure 6 This is the equivalent circuit in CC mode;

[0070] Figure 7 The equivalent circuit of the proposed IPT system in CC mode;

[0071] Figure 8 The change in self-inductance of the three-coil structure;

[0072] Figure 9 The curves showing the relationship between normalized current / voltage gain and input phase angle and normalized self-inductance in CC mode;

[0073] Figure 10 The curves showing the relationship between normalized current / voltage gain and input phase angle and normalized self-inductance value in CV mode;

[0074] Figure 11 This is a flowchart of the IPT system. Detailed Implementation

[0075] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0076] A constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer includes an inverter circuit, a primary-side compensation circuit, a resonant circuit, a secondary-side compensation circuit, a rectifier circuit, a filter capacitor, and a load R. L ;

[0077] The inverter circuit includes switching transistors Q1 and Q2;

[0078] The primary-side compensation circuit includes an inductor L1 and a capacitor C. P1 C f1 The inductor L1 is connected to the capacitor C. P1 C f1 Connection, the capacitor C P1 C f1 In parallel; inductor L1 is connected to switching transistors Q1 and Q2 respectively;

[0079] The resonant circuit includes a loosely coupled transformer, whose secondary coil is connected in series with an auxiliary coil;

[0080] The secondary-side compensation circuit includes inductor L2 and capacitor C. p2 C f2 One end of L2 is connected to capacitor C. p2 C f2 One end is connected to the rectifier circuit via a switching transistor Q5; the capacitor C p2 C f2 Parallel connection, where C f2 With inductor L S Connection, capacitor C p2 Connect to the rectifier circuit;

[0081] The rectifier circuit includes switching transistors Q3 and Q4, and the auxiliary coil L T Connect Q3 and Q4 respectively, with switch Q3 connected to switch Q5 through diode D5;

[0082] The rectifier circuit and the filter capacitor C0 are connected in parallel.

[0083] The coil structure described in this article is an anti-parallel connection, with the third coil located on the secondary side and a single coil on the primary side. The equivalent model of the coil is as follows: Figure 1 As shown.

[0084] Secondary coil current I s From the secondary coil L s Inflow, from the third coil L T Outflow L P L S and L T This refers to the inductance of the primary / secondary side and auxiliary coil of the loosely coupled transformer. U P U S and I P I S This represents the input / output voltage and current of the coupler. M PT M PS and M TS These are the relevant coupling coefficients of the primary coil, secondary coil, and auxiliary coil. According to... Figure 2 The M-model and Kirchhoff's laws shown indicate that:

[0085]

[0086] For ease of analysis, the secondary coil L S and auxiliary coil L T It can be equated to a coil M EQ The relationship between self-induction and mutual induction is as follows:

[0087] L' P =L P +L T -2M PT ;

[0088] M EQ =M PS -M PT .

[0089] Under the condition of misalignment, M PS and M PT Both decrease simultaneously. The degree of decrease in the two mutual inductances is expressed by ΔM. PS and ΔM PT The equivalent mutual inductance coefficient can be expressed as:

[0090] M' EQ =(M PS -ΔM PS )-(M TS -ΔM TS )

[0091] =M EQ -(ΔM PS -ΔM TS );

[0092] Assume ΔM PS =ΔM PT Then M'EQ =M EQ This indicates that the mutual inductance remains stable under misalignment conditions, thus improving the anti-misalignment characteristics of the proposed coil. Common resonant network topologies, such as SS, SP, LCL, and LCC, can be applied to the proposed loosely coupled transformer without affecting the output characteristics of the original topology. Under misalignment conditions, the mutual inductance M... PS and M PT Both will decrease. Assume ΔM PS =ΔM PT Then the equivalent mutual inductance coefficient (M) e =M PS -M TS It remains stable. The output of a loosely coupled transformer (LCT) is unaffected by changes in coupling, thus improving deviation tolerance.

[0093] The circuit diagram of the proposed system is as follows: Figure 3 As shown. U AB and I in U represents the AC output voltage and current of the half-bridge inverter. ab and I ab This indicates the AC input voltage and current of the rectifier. U DC and I DC U represents the DC input voltage and current of the half-bridge inverter. b and I b This represents the DC output voltage and current of the rectifier. It is determined by L1 and C. p1 C f1 and L2, C p2 C f2 The high-order compensation network LCC is applied to the primary and secondary sides respectively.

[0094] When the topology operates in CV mode, switch Q4 is on, and Q3 and Q5 are off, forming an LCC-S topology. The secondary side implements an AC-DC rectifier via a half-bridge. Reconfigurable topologies are as follows: Figure 4 As shown, current flows through freewheeling diode Q4 and diode D5. The formula for AC input current based on Kirchhoff's laws is:

[0095]

[0096] The formulas for calculating AC output voltage and voltage gain ratio are:

[0097]

[0098] The formulas for calculating the current in the primary and secondary coils are:

[0099]

[0100] The formulas for calculating DC output voltage and current are as follows:

[0101]

[0102] The relationship between input and output voltage and current is as follows:

[0103] ;

[0104]

[0105] The formula for calculating the relationship between AC resistance and DC resistance is:

[0106]

[0107] The calculated AC-AC efficiency can be derived as follows:

[0108]

[0109] The derivation of the optimal AC resistance is as follows:

[0110]

[0111] When the topology operates in CC mode, switches Q3 and Q5 are turned on, and Q4 is turned off to construct an LCC-LCC topology. The secondary side uses a half-bridge to implement an AC-DC rectifier. See [link to circuit diagram] for the reconfigurable topology and CC mode equivalent circuit. Figure 6 The current flows through the freewheeling diode Q4 and the diode D5.

[0112] The resonance condition of the LCC-LCC topology can be expressed as:

[0113]

[0114] The formulas for calculating AC input and output current are as follows:

[0115]

[0116] The currents on the primary and secondary coils are respectively represented as follows:

[0117]

[0118] The AC output current and voltage are respectively:

[0119]

[0120] The DC output current and voltage are respectively:

[0121]

[0122] The formula for calculating output power is:

[0123]

[0124] The calculated AC-AC efficiency is:

[0125]

[0126] The derivation of the optimal AC resistance is as follows:

[0127]

[0128] like Figure 8 As shown, when the position shifts, the change in self-inductance of the primary-side single coil is greater than that of the secondary-side, especially when the air gap is narrow. From Figure 9 It can be seen that in CC and CV modes, changes in the primary coil's self-inductance do not affect the current and voltage gains. Furthermore, the input phase angle increases as the self-inductance decreases, leading to inductance drift in the system's input impedance, thus enabling the MOSFET to operate under ZVS conditions. However, changes in the secondary coil's self-inductance significantly impact the current and voltage gains. In particular, changes in the secondary coil's self-inductance significantly affect the current gain. Moreover, a decrease in self-inductance causes capacitance drift in the system's input impedance, affecting the inverter's ability to achieve ZVS. Therefore, introducing a third coil on the secondary side is crucial. It not only provides greater flexibility and accuracy for the receiver's compensation network design, enabling the system to more effectively handle changes in self-inductance under various operating conditions and maintain stable current and voltage gains, but also significantly improves the system's offset performance, enhancing the overall circuit's robustness and reliability. The introduction of a third coil on the secondary side is undoubtedly a significant optimization of the original design, laying a solid foundation for the circuit's efficient and stable operation.

[0129] This invention relates to a high-performance wireless charging system, particularly suitable for low-power charging scenarios such as electric bicycles. By introducing a third-coil loosely coupled transformer (LCT) and a reconfigurable topology, the system significantly improves the misalignment performance of the wireless charging system and achieves constant current (CC) and constant voltage (CV) output. The following is a detailed description of the specific implementation of this invention.

[0130] Three-coil loosely coupled transformer (LCT):

[0131] Primary coil (LP): 250mm x 250mm in size, used to receive energy from the power source.

[0132] Secondary coil (LS): 240mm x 240mm in size, used to transfer received energy to the load.

[0133] The third coil (LT): measuring 160mm × 160mm, is located near the secondary coil and is used to improve the system's misalignment performance and mitigate the impact of self-inductance variations on the system's current / voltage gain and input phase angle.

[0134] All coils are wound with more strands of Litz wire to reduce the equivalent series AC resistance and improve energy transfer efficiency. Furthermore, the relative positions of the coils are precisely calculated to ensure effective misalignment tolerance in the x and y directions.

[0135] The reconfigurable topology is integrated into the secondary coil, allowing for automatic adjustment of the charging mode based on charging demand, enabling both CC and CV outputs. The coupler employs an aluminum-free shielding design to suit low-power charging scenarios such as electric bicycles. Its compact structure facilitates installation and maintenance.

[0136] The fabrication method involves first winding a primary, secondary, and tertiary coil using Litz wire according to the design dimensions and winding requirements. During winding, the uniformity and compactness of the coils must be ensured to improve energy transfer efficiency. The wound coils are then assembled into a coupler according to the design requirements. During assembly, the relative positions and spacing between the coils must meet the design requirements to guarantee the system's misalignment tolerance. Next, the reconfigurable topology and related control circuitry are integrated into the secondary coil. During integration, the stability and reliability of the circuit must be ensured to meet practical application requirements.

[0137] Before using the wireless charging system, system initialization is required. Set initial parameter values ​​based on input / output and magnetic coupling parameters, such as operating frequency and maximum offset distance. Then, select the charging mode according to actual needs, i.e., CC mode or CV mode. During selection, ensure the system operates stably and meets the charging requirements of the load. Next, connect the primary coil to the power supply and the secondary coil to the load. After starting the wireless charging system, energy will be transferred to the load through the three-coil LCT. During transmission, the system will automatically adjust the charging mode and parameters according to actual needs to achieve stable energy transfer and efficient charging.

[0138] During the operation of a wireless charging system, real-time monitoring and maintenance are necessary. By monitoring parameters such as the system's input / output voltage and current waveforms, system efficiency, and loss distribution, problems can be identified and resolved promptly, ensuring stable operation and high performance.

[0139] The design flowchart of the entire IPT system is as follows: Figure 10As shown. First, initial parameter values, such as operating frequency and maximum deviation distance, are set based on input / output and magnetic coupling parameters. Second, three coils are designed. Finally, a resonant network and a reconfigurable CC-CV charging topology are designed based on component current and voltage stresses, as well as input / output parameters.

[0140] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer, characterized in that, It includes an inverter circuit, a primary-side compensation circuit, a resonant circuit, a secondary-side compensation circuit, a rectifier circuit, and a filter capacitor; The inverter circuit includes switching transistors Q1 and Q2; The primary-side compensation circuit includes an inductor L1 and a capacitor C. P1 C f1 The inductor L1 is connected to the capacitor C. P1 C f1 Connection, the capacitor C P1 C f1 In parallel; inductor L1 is connected to switching transistors Q1 and Q2 respectively; The resonant circuit includes a loosely coupled transformer, whose secondary coil is connected in series with an auxiliary coil; The secondary-side compensation circuit includes inductor L2 and capacitor C. p2 C f2 One end of L2 is connected to capacitor C. p2 C f2 One end is connected to the rectifier circuit via a switching transistor Q5; the capacitor C p2 C f2 Parallel connection, where C f2 With inductor L S Connection, capacitor C p2 Connect to the rectifier circuit; The rectifier circuit includes switching transistors Q3 and Q4, and the auxiliary coil L T Connect Q3 and Q4 respectively, with switch Q3 connected to switch Q5 through diode D5; The rectifier circuit and the filter capacitor C0 are connected in parallel.

2. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 1, characterized in that, Secondary coil L S and auxiliary coil L T Equivalent to a coil M EQ Equivalent self-induction L' P The calculation is as follows: L' P =L P tL T -2M PT ; M EQ =M PS -M PT ; L P L S and L T It is the inductance of the primary side, secondary side, and auxiliary coil of the loosely coupled transformer; U P U S and I P I S This represents the input and output voltage and current of a loosely coupled transformer; M PT M PS and M TS It is the relevant coupling coefficient of the primary side, secondary side and auxiliary coil of the loosely coupled transformer; Under the condition of misalignment, M PS and M PT As they decrease simultaneously, the degree of decrease in the two mutual inductances is expressed by ΔM. PS and ΔM PT The equivalent mutual inductance coefficient is expressed as: M' EQ =(M PS -ΔM PS )-(M TS -ΔM TS ) = M EQ -(ΔM PS -ΔM TS ); Assume ΔM PS =ΔM PT Then M' EQ =M EQ This indicates that mutual inductance remains stable under misalignment conditions.

3. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 1, characterized in that, When the topology operates in CV mode, switch Q4 is turned on, while Q3 and Q5 are turned off to construct the LCC-S topology. The secondary side achieves AC-DC rectification through a half-bridge rectifier circuit.

4. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 2, characterized in that, When the topology operates in CV mode, the AC input current I in The formula is: U AB and I in U represents the AC output voltage and current of the inverter circuit. ab and I ab This represents the AC input voltage and current of the rectifier circuit; U DC and I DC U represents the DC input voltage and current of the inverter circuit. b and I b This indicates the DC output voltage and current of the rectifier circuit; The formulas for calculating AC output voltage and voltage gain ratio are as follows: Z in Input impedance, R ac The equivalent AC resistance of the secondary side, I s Output current; The formulas for calculating the current in the primary and secondary coils are: The formulas for calculating the DC output voltage and current on the secondary side are as follows: The relationship between primary-side input and output voltage and current is as follows: The formula for calculating the relationship between equivalent AC resistance and DC resistance is:

5. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 3, characterized in that, When the topology operates in CV mode, the calculated AC-AC efficiency can be obtained as follows: The derivation of the optimal equivalent AC resistance is as follows: R S Primary coil resistance, R p The secondary coil resistance, M is the mutual inductance between the two coils of the loosely coupled transformer; R L1 Let ω be the resistance of inductor L1, and ω0 be the resonant angular frequency.

6. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 1, characterized in that, When the topology operates in CC mode, switches Q3 and Q5 are turned on and Q4 is turned off to construct an LCC-LCC topology. The secondary side achieves AC-DC rectification through a rectifier circuit. The topology and CC mode are reconfigurable, and the current flows through the freewheeling switch Q4 and diode D5.

7. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 5, characterized in that, The resonance condition of the LCC-LCC topology is expressed as: The formulas for calculating AC input and output current are as follows: The currents on the primary and secondary coils are respectively represented as follows: The AC output current and voltage are respectively: The DC output current and voltage are respectively: The formula for calculating output power is:

8. The constant current and constant voltage wireless charging system based on a three-coil loosely coupled transformer according to claim 6, characterized in that, The calculated AC-AC efficiency is: The derivation of the optimal equivalent AC resistance is as follows:

9. A constant current and constant voltage wireless charging method based on a three-coil loosely coupled transformer, characterized in that, The constant current and constant voltage wireless charging system using a three-coil loosely coupled transformer as described in any one of claims 1-8, operates in CV mode with switch Q4 turned on and Q3 and Q5 turned off to construct an LCC-S topology, and AC-DC rectification is achieved on the secondary side through a half-bridge rectifier circuit; operates in CC mode with switches Q3 and Q5 turned on and Q4 turned off to construct an LCC-LCC topology, and AC-DC rectification is achieved on the secondary side through a rectifier circuit. The system can reconfigure the topology and CC mode, and the current flows through switch Q4 and diode D5.

10. The constant current and constant voltage wireless charging method based on a three-coil loosely coupled transformer according to claim 9, characterized in that, In CC and CV modes, changes in the self-inductance of the primary coil do not affect the current and voltage gains; the input phase angle increases as the self-inductance decreases, which causes inductance drift in the system's input impedance, allowing switches Q1 and Q2 to operate under ZVS conditions; changes in the self-inductance of the secondary coil on the second side affect the current gain, and a decrease in the self-inductance causes capacitance drift in the system's input impedance, thus affecting the inverter circuit's ability to achieve ZVS; when the input impedance changes due to capacitance, the change in self-inductance of a single coil on the primary side is greater than that on the secondary side.

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