A wireless charging system and method for realizing constant current and constant voltage output based on variable topology

Abstract

This invention discloses a wireless charging system and method for achieving constant current and constant voltage output based on variable topology. The system includes a transmitting section and a receiving section; the transmitting section includes a DC power supply U. D The system consists of a composite high-frequency inverter H, resonant circuit 1, and resonant circuit 2; the receiving section includes resonant circuit 3, rectifier D, and filter capacitor C. F and battery load R B The method includes: after charging is initiated, both Q2 and Q4 are turned on, while Q1 and Q3 operate alternately with a 50% duty cycle, and the system uses a three-coil structure to charge the battery at a constant current. When the load voltage rises to a preset voltage, Q1 turns on, Q2 turns off, and Q3 and Q4 operate alternately with a 50% duty cycle, and the system uses a two-coil structure to charge the battery at a constant voltage. When the battery is fully charged, the system automatically cuts off the inverter's power output and stops charging. Compared to existing similar technologies, this invention requires no additional AC switch or frequency switching control; it has a simple structure, low cost, and convenient control.

Description

Technical Field

[0001] This invention relates to a wireless charging system and method for achieving constant current and constant voltage output based on variable topology, belonging to the field of wireless charging technology. Background Technology

[0002] Traditional power supplies require a charging cable to charge devices. However, this method is susceptible to problems such as complex wiring, aging lines, and electrical sparks caused by plugging and unplugging, significantly reducing the reliability and safety of the power supply. Therefore, finding a more flexible and convenient charging method has become an urgent need. In recent years, Wireless Power Transfer (WPT) systems have attracted widespread attention and research from academia and industry due to their high security, convenient charging, and resistance to environmental influences. Currently, WPT systems have been initially applied in many commercial and industrial sectors, such as electric vehicles, smart homes, medical devices, and consumer electronics.

[0003] To ensure safe charging and maintain battery performance, battery charging typically involves two stages: constant current and constant voltage. Initially, the battery charges in constant current mode. As charging progresses, the battery voltage gradually increases. Once the voltage reaches a preset value, the system switches to constant voltage charging mode. As the battery's equivalent load increases, the charging current gradually decreases. Charging ends when the charging current approaches zero. In other words, a wireless power transfer system should be capable of providing constant current and voltage output.

[0004] Currently, wireless power transfer systems mainly employ the following methods to achieve stable constant current and constant voltage output:

[0005] 1. Phase-shift control: This method is difficult to achieve zero-voltage switching under significant load changes, resulting in a large amount of system losses.

[0006] 2. Variable frequency control: This method may cause frequency bifurcation, reducing the reliability and stability of the system; and it is difficult to make the system work under zero phase angle conditions, introducing reactive circulating current and causing huge losses.

[0007] 3. DC-DC converter control: This method increases the number of components, increases the cost and complexity of the system, and introduces more losses.

[0008] 4. Dual-frequency switching control: In this method, the parameters of the system compensation components are difficult to match, the design is difficult, and it is difficult to limit both the constant current frequency and the constant voltage frequency to the standard specified frequency range.

[0009] 5. Traditional topology switching increases the number of compensation components and additional AC switches, thus increasing the system's cost, weight, and size. Summary of the Invention

[0010] The purpose of this invention is to provide a wireless charging system and method based on variable topology to achieve constant current and constant voltage output, so as to achieve constant current and constant voltage output to meet battery charging requirements. It is easy to control, simple in structure, low in system cost, and stable in operation.

[0011] The objective of this invention can be achieved through the following technical solutions:

[0012] A wireless charging system based on variable topology to achieve constant current and constant voltage output includes a transmitting section and a receiving section; the transmitting section includes a DC voltage source U. D The system consists of: a composite high-frequency inverter H composed of four MOSFETs connected in a T-shape; a resonant circuit 1 composed of coil L1 and capacitor C1; a resonant circuit 2 composed of coil L2 and capacitor C2; a receiving section including a resonant circuit 3 composed of coil L3 and capacitor C3, and a compensation inductor L4 and capacitor C4; a full-bridge rectifier D; and a filter capacitor C. F and battery load R B ;

[0013] The DC voltage source U D Connected to the input terminal of the composite high-frequency inverter H, the composite high-frequency inverter H is composed of 4 MOSFET switching transistors Q1, Q2, Q3 and Q4 connected in a T-type configuration. One end of the resonant circuit 2 is connected to one end of Q2, and the other end of the resonant circuit 2 is connected to the midpoint of Q3 and Q4. One end of the resonant circuit 1 is connected to one end of the resonant circuit 2, and the other end of the resonant circuit 1 is connected to one end of Q4.

[0014] The resonant circuit 3 is connected to the input terminal of the full-bridge rectifier D, and the output terminal of the full-bridge rectifier D is connected to the filter capacitor C. F For battery load R B powered by.

[0015] Furthermore, in the constant current charging mode of the wireless charging topology, Q2 and Q4 in the composite high-frequency inverter H, which consists of four MOSFETs connected in a T-shape, are both turned on, while Q1 and Q3 work alternately with a 50% duty cycle. The system uses a three-coil structure to charge the battery load with constant current. Among them, resonant circuit 2 serves as the transmitting resonant circuit, resonant circuit 1 serves as the relay resonant circuit, and resonant circuit 3 serves as the receiving resonant circuit.

[0016] Furthermore, in the constant voltage charging mode, in the wireless charging topology, Q1 in the composite high-frequency inverter H, which consists of four MOSFETs connected in a T-shape, is turned on, Q2 is turned off, and Q3 and Q4 work alternately with a 50% duty cycle. The system uses a two-coil structure to charge the battery load at a constant voltage. In this system, the resonant circuit 2 is automatically cut off, the resonant circuit 1 serves as the transmitting resonant circuit, and the resonant circuit 3 serves as the receiving resonant circuit.

[0017] The value of the compensation capacitor C1 in the resonant circuit 1 is determined by equation (1):

[0018]

[0019] Where ω is the system's resonant angular frequency;

[0020] The value of the compensation capacitor C2 in the resonant circuit 2 is determined by equation (2):

[0021]

[0022] Among them, M 12 M represents the mutual inductance between coils L1 and L2. 13 M represents the mutual inductance between coils L1 and L3. 23 Here is the mutual inductance value between coil L2 and coil L3;

[0023] The values ​​of the compensation capacitors C3 and C4 in the resonant circuit 3 are determined by equations (3) and (4), respectively:

[0024]

[0025]

[0026] L4 is the compensation inductor on the receiving side of the system;

[0027] During the constant current charging phase of the battery, the system operates with a three-coil structure, and its output current is calculated by equation (5):

[0028]

[0029] Among them, U D This is the DC power supply voltage value.

[0030] During the constant voltage charging phase of the battery, the system operates with a two-coil structure, and its output voltage is calculated by equation (6):

[0031]

[0032] A method for achieving constant current and constant voltage output in a wireless charging system based on variable topology includes the following steps:

[0033] Step 1: After starting charging, Q2 and Q4 are both turned on, and Q1 and Q3 work alternately with a 50% duty cycle. The system uses a three-coil structure to charge the battery load with constant current.

[0034] Step 2: When the load voltage rises to the preset voltage, Q1 turns on, Q2 turns off, and Q3 and Q4 work alternately with a 50% duty cycle. The system uses a two-coil structure to charge the battery load at a constant voltage.

[0035] Step 3: Once the battery is fully charged, the system automatically cuts off the power output of the hybrid inverter and stops charging.

[0036] The beneficial effects of this invention are:

[0037] 1. In this invention, a wireless charging system based on variable topology to achieve constant current and constant voltage output is designed. By controlling the four T-connected MOSFET switches Q1, Q2, Q3 and Q4 in the composite inverter, the switching between three coils and two coils can be realized to meet the charging requirements of the battery with constant current first and then constant voltage. No additional AC switch, corresponding drive circuit and additional compensation components are required. Its circuit structure is simple, low cost, no complicated control strategy, simple, convenient and reliable operation;

[0038] 2. This invention enables the inverter output voltage and current to be basically in phase during constant current and constant voltage output, allowing the inverter to inject almost no reactive power, thus reducing system losses and ensuring high system efficiency.

[0039] 3. This invention can meet the charging requirements of the battery by first maintaining constant current and then constant voltage, and the system always operates at a single frequency point without frequency bifurcation. The system is stable and reliable.

[0040] 4. This invention is suitable for various application scenarios, including low-power consumer electronics and biomedical products, medium-power electric bicycle charging applications, and high-power electric vehicle charging applications. Attached Figure Description

[0041] Figure 1 This is a circuit diagram of a wireless charging system based on variable topology to achieve constant current and constant voltage output according to the present invention.

[0042] Figure 2 This is a system circuit diagram of the present invention operating in constant current output mode.

[0043] Figure 3 This is a simplified circuit diagram of the system of the present invention operating in constant current output mode.

[0044] Figure 4 This is a system circuit diagram of the present invention operating in constant voltage output mode.

[0045] Figure 5 This is a simplified circuit diagram of the system of the present invention operating in constant voltage output mode. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the embodiments described 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.

[0047] Figure 1 The system circuit diagram of the invention shown is as follows:

[0048] The system structure includes: a DC power supply, a composite high-frequency inverter, resonant circuit 1, resonant circuit 2, resonant circuit 3, a rectifier circuit, and a battery load;

[0049] The resonant circuit 1 includes: coil L1 and coil series compensation capacitor C1;

[0050] The resonant circuit 2 includes: coil L2 and coil series compensation capacitor C2;

[0051] The resonant circuit 3 includes: coil L3 and capacitor C3, as well as compensation inductor L4 and capacitor C4;

[0052] The rectifier circuit includes a full-bridge rectifier composed of four diodes (D1, D2, D3, and D4), and a filter capacitor C is connected in parallel at the output of the full-bridge rectifier. F This ensures a stable power supply to the load.

[0053] Working principle: The composite high-frequency inverter inverts the output DC power into high-frequency AC power, which is then wirelessly transmitted from the transmitter to the receiver. After being rectified into DC, it charges the battery load. Initially, during the initial charging phase, Q2 and Q4 are both on, while Q1 and Q3 operate alternately with a 50% duty cycle. The system uses a three-coil structure to charge the battery at a constant current. When the load voltage rises to the preset voltage, Q1 turns on, Q2 turns off, and Q3 and Q4 operate alternately with a 50% duty cycle. The system then uses a two-coil structure to charge the battery at a constant voltage. Once the battery is fully charged, the system automatically cuts off the power output of the composite inverter, stopping the charging process.

[0054] like Figure 2 As shown, in constant current mode, Q2 and Q4 in the composite high-frequency inverter H, which consists of four MOSFETs connected in a T-shape, are both turned on. Q1 and Q3 operate alternately with a 50% duty cycle. The system uses a three-coil structure to charge the battery load with constant current. Resonant circuit 2 serves as the transmitting resonant circuit, resonant circuit 1 as the relay resonant circuit, and resonant circuit 3 as the receiving resonant circuit. The corresponding simplified circuit is shown below. Figure 3 As shown. DC power supply U D and U i The relationship between the output current I and the output current IB The relationship between the loop current I4 and the current I4 can be expressed as:

[0055]

[0056] like Figure 3 As shown, the input voltage U can be listed according to Kirchhoff's Voltage Law (KVL). i The loop relationship expression for the current flowing through the two coils is as follows:

[0057]

[0058] Where I2 represents the current vector of the transmitting circuit, I1 represents the current vector of the relay circuit, I3 represents the current vector of the receiving coil L3, and I4 represents the current vector flowing through R... ac The current vector, j denotes the imaginary unit, U i M represents the square wave voltage output by the composite high-frequency inverter. 12 For the mutual inductance between relay coil L1 and transmitting coil L1, M 13 For the mutual inductance between relay coil L1 and receiving coil L3, M 23 The mutual inductance of transmitting coil L2 and receiving coil L3, where Z1, Z2, and Z3 represent the equivalent reactances, are expressed by the following equations:

[0059]

[0060] Through analysis and calculation, the resonance relationship of the system must satisfy the following conditions:

[0061]

[0062] Combining (2) and (4), we can obtain R. ac The expression for the current across the two ends:

[0063]

[0064] Substituting equation (1) into equation (5) yields the system output current I. B Value:

[0065]

[0066] Observing equation (6), it can be found that the output current I B Its size is independent of the load size, and it can achieve constant current charging.

[0067] At this time, the system's input impedance Z in This can be derived and simplified as follows:

[0068]

[0069] Equation (7) shows that the input impedance Z in The value has no imaginary part and is fully resistive; therefore, the system can perform ZPA operation.

[0070] In summary, when condition (4) is satisfied, the system can achieve constant current output under ZPA operation with a three-coil structure.

[0071] like Figure 4 As shown, in constant voltage mode, switch Q1 is on and Q2 is off. The system uses a two-coil structure to charge the battery load at a constant voltage. Resonant circuit 2 is automatically disconnected, resonant circuit 1 acts as the transmitting resonant circuit, and resonant circuit 3 acts as the receiving resonant circuit. The corresponding simplified circuit is shown below. Figure 5 As shown, the DC power supply U D and U i The relationship between the output voltage U and the output voltage U B The relationship between the loop voltage U4 and the loop voltage U4 can be expressed as:

[0072]

[0073] According to Kirchhoff's Voltage Law (KVL), the input voltage U can be listed. i The expression relating the loop current to the current.

[0074]

[0075] Where I1 represents the current vector in the transmitting circuit, I3 represents the current vector in the receiving coil L3, and I4 represents the current vector flowing through R... ac The current vector, j denotes the imaginary unit, U i M represents the square wave voltage output by the composite high-frequency inverter. 13 This represents the mutual inductance between the transmitting coil L1 and the receiving coil L3.

[0076] Combining (2) and (9), we can obtain R. ac The expression for the current across the two ends:

[0077]

[0078] The voltage of the receiving circuit can be obtained according to equation (10):

[0079]

[0080] Substituting equation (8) into equation (11) yields the output voltage U. B Value:

[0081]

[0082] According to equation (12), the output voltage UB The size of the voltage is independent of the load size, so constant voltage charging can be achieved.

[0083] At this time, the system's input impedance is:

[0084]

[0085] According to equation (13), the system input impedance is purely resistive, which can achieve ZPA.

[0086] In summary, when condition (4) is satisfied, the system can achieve constant voltage output under ZPA operation with a two-coil structure.

[0087] In general, when both control switches Q2 and Q4 are turned on, the system uses a three-coil structure to achieve constant current charging with ZPA operation; when control switch Q1 is turned on and Q2 is turned off, the system uses a two-coil structure to achieve constant voltage charging with ZPA operation.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any simple modifications, equivalent transformations and alterations within the technical solutions and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A wireless charging system for achieving constant current and constant voltage output based on variable topology, characterized in that: It includes a transmitting section and a receiving section; the transmitting section includes a DC voltage source U. D The system consists of: a composite high-frequency inverter H composed of four MOSFETs connected in a T-shape; a resonant circuit 1 composed of coil L1 and capacitor C1; a resonant circuit 2 composed of coil L2 and capacitor C2; a receiving section including a resonant circuit 3 composed of coil L3 and capacitor C3, and a compensation inductor L4 and capacitor C4; a full-bridge rectifier D; and a filter capacitor C. F and battery load R B ; The DC voltage source U D Connected to the input terminal of the composite high-frequency inverter H, which consists of four MOSFET switches Q1, Q2, Q3, and Q4 connected in a T-connection, the DC voltage source U... D The positive terminal of Q1 is connected to the drain of Q1. The source of Q1 is connected in parallel to the source of Q2 and the drain of Q3. The source of Q3 is connected to the drain of Q4. The source of Q4 is connected to the DC voltage source U. D The negative terminal of the capacitor is connected. One end of capacitor C2 is connected to the drain of Q2, and the other end of capacitor C2 is connected to one end of coil L2. The other end of coil L2 is connected to the source of Q3 and the drain of Q4. One end of capacitor C1 is connected to the other end of coil L2, and the other end of capacitor C1 is connected to one end of coil L1. The other end of coil L1 is connected to the DC voltage source U. D The negative electrode; The resonant circuit 3 is connected to the input of a full-bridge rectifier D, the output of which is filtered by a capacitor C F for a battery load R B power supply; The value of the compensation capacitor C1 in the resonant circuit 1 is determined by equation (1): （1）； Where ω is the system's resonant angular frequency; The value of the compensation capacitor C2 in the resonant circuit 2 is determined by equation (2): （2）； where M 12 is the mutual inductance value of coil L1 and coil L2, M 13 is the mutual inductance value of coil L1 and coil L3, M 23 is the mutual inductance value of coil L2 and coil L3; The values ​​of the compensation capacitors C3 and C4 in the resonant circuit 3 are determined by equations (3) and (4), respectively: （3）； （4）； L4 is the compensation inductor on the receiving side of the system; During the constant current charging phase of the battery, the system operates with a three-coil structure, and its output current is calculated by equation (5): （5）； wherein U D is the DC supply voltage value; During the constant voltage charging phase of the battery, the system operates with a two-coil structure, and its output voltage is calculated by equation (6): （6）。 2.The wireless charging system of claim 1, wherein: In the constant current charging mode, Q2 and Q4 in the composite high-frequency inverter H, which consists of four MOSFETs connected in a T-shape, are both turned on. Q1 and Q3 work alternately with a 50% duty cycle. The system uses a three-coil structure to charge the battery load with constant current. Among them, resonant circuit 2 serves as the transmitting resonant circuit, resonant circuit 1 serves as the relay resonant circuit, and resonant circuit 3 serves as the receiving resonant circuit. 3.The wireless charging system of claim 1, wherein: In the constant voltage charging mode, the wireless charging topology consists of a composite high-frequency inverter H composed of four MOSFETs connected in a T-shape. Q1 is turned on, Q2 is turned off, and Q3 and Q4 work alternately with a 50% duty cycle. The system uses a two-coil structure to charge the battery load at a constant voltage. The resonant circuit 2 is automatically cut off, the resonant circuit 1 serves as the transmitting resonant circuit, and the resonant circuit 3 serves as the receiving resonant circuit. 4.The wireless charging system of claim 1, wherein: The wireless charging method for a wireless charging system based on variable topology to achieve constant current and constant voltage output includes the following steps: Step 1: After starting charging, Q2 and Q4 are both turned on, and Q1 and Q3 work alternately with a 50% duty cycle. The system uses a three-coil structure to charge the battery load with constant current. Step 2: When the load voltage rises to the preset voltage, Q1 turns on, Q2 turns off, and Q3 and Q4 work alternately with a 50% duty cycle. The system uses a two-coil structure to charge the battery load at a constant voltage. Step 3: Once the battery is fully charged, the system automatically cuts off the power output of the hybrid inverter and stops charging.

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