CN116231876A - Wireless power transfer system and charging coil selection method for its application - Google Patents

Abstract

The disclosure provides a wireless power transmission system and a charging coil selection method for its application. The system includes a transmitting end and a receiving end; the transmitting end includes a voltage conversion unit, an inverter unit, a filtering unit, a coil selection unit, and at least two transmitting coils; The coil selection unit includes a control module and several switch modules; the receiving end includes a receiving coil, a rectification unit and a communication unit. The wireless power transmission system and the charging coil selection method for its application provided by the present disclosure can realize automatic switching of multiple transmitting coils, effectively improve power transmission efficiency, improve charging freedom, effectively reduce switching loss, and improve transmission efficiency; without additional The circuit and module can realize the intelligent switching of power transmission and coil, ensure the efficiency of power transmission, reduce the weight and cost of wireless power transmission system, and then reduce the weight and cost of related products, which is convenient for the promotion and use of wireless power transmission, and improves user use experience.

Description

Wireless power transfer system and charging coil selection method for its application

technical field

The present disclosure relates to the technical field of wireless power transmission, and in particular to a wireless power transmission system and a charging coil selection method for its application.

Background technique

Wireless power transmission technology, also known as wireless power transmission or non-contact power transmission, refers to the conversion of electric energy into other forms of relay energy (such as electromagnetic field energy, laser, microwave and mechanical waves, etc.) , and then convert the relay energy into electrical energy through the receiver to realize the transmission of wireless energy. Wireless power transmission technology can realize the electrical isolation between the power supply and the load, avoid the generation of arc, and also has the advantages of waterproof and convenient. At present, the magnetic field coupled wireless power transmission technology is common, that is, the magnetic field is coupled from the transmitting coil to the receiving coil through the principle of electromagnetic induction.

The traditional coupled wireless power transmission architecture commonly used at present has low working efficiency in high-frequency wireless charging systems and cannot achieve high-degree-of-freedom power transmission. The transmission distance and output efficiency are greatly limited, the production cost is high, and the use scenarios are limited.

Contents of the invention

The purpose of the present disclosure is to provide a charging coil selection method for a wireless power transmission system and its application, which can solve one or more of the above existing problems.

In the first aspect, a wireless power transmission system is provided, including a transmitting end and a receiving end;

The transmitting end includes a voltage conversion unit, an inverter unit, a filtering unit, a coil selection unit and at least two transmitting coils;

The voltage conversion unit is used to adjust the amplitude of the DC voltage input to the transmitter, and output the initial voltage Vin;

The inverter unit is used to convert the initial voltage Vin into a high-frequency AC voltage, and the inverter unit is a class E inverter composed of switches, capacitors and inductors;

The filter unit is used to filter the high-frequency noise in the high-frequency AC voltage;

The coil selection unit is used to communicate with the receiving end, and select at least one transmitting coil for charging according to the communication result;

The coil selection unit includes a control module and several switch modules, the number of the switch modules is equal to the number of the transmitting coils, one end of the switch module is connected to the output end of the filter unit, the other end is connected in series with a transmitting coil, and the other end of the transmitting coil is grounded;

The signal output terminal of the control module is connected with the signal input terminal of each switch module respectively, which is used to control the on-off of the switch module, and the signal output terminal of the control module is connected with the signal input terminal of the switch in the inverter unit, which is used to control the inverter The on-off of the switch in the unit, the signal output end of the control module is connected with the signal input end of the voltage conversion unit, and is used to control the voltage conversion unit to output the initial voltage Vin; the signal input end of the control module is connected with each transmitting coil respectively, and is used for The communication signal received by the transmitting coil is processed;

The transmitting coil is used to convert the electric energy of high-frequency alternating current into magnetic field energy and transmit it;

The receiving end includes a receiving coil, a rectifying unit and a communication unit;

The receiving coil is used to receive magnetic field energy and convert it into high-frequency alternating current;

The rectifier unit is used to convert high-frequency alternating current into direct current output to supply power to the load;

The communication unit is used for communicating with the transmitter.

In some embodiments, the inverter unit includes an inductor Ldc, a switch Q1, and a capacitor Cpar. One end of the inductor Ldc is connected to the output end of the voltage conversion unit, and the other end is connected to the drain of the switch Q1; the source of the switch Q1 is grounded, and the The gate is connected to the signal output terminal of the coil selection unit, and the capacitor Cpar is connected in parallel with the switch Q1.

In some embodiments, the filter unit includes a capacitor Ct, an inductor Ltf and a capacitor Cf, one end of the capacitor Ct is the input end of the filter unit, the capacitor Ct and the inductor Ltf are connected in series, the inductor Ltf is the output end of the filter unit, and one end of the capacitor Cf is connected The output end of the filter unit, and the other end is grounded.

In some embodiments, the transmitting end further includes several Tx impedance matching units, the number of Tx impedance matching units is equal to the number of transmitting coils, the Tx impedance matching unit includes a first capacitor, and the first capacitor is connected in series between the switch module and the transmitting coil between.

In some embodiments, the receiving end further includes an Rx impedance matching unit, the Rx impedance matching unit includes a second capacitor, one end of the second capacitor is connected to the receiving coil, and the other end of the second capacitor is connected to the input end of the rectification unit.

In some embodiments, the rectification unit includes a rectification bridge and a filter capacitor Cfdc. The rectification bridge is composed of a diode D1, a diode D2, a diode D3, and a diode D4. The AC input terminals of the rectification bridge are respectively connected to the two ends of the receiving coil. A filter capacitor Cfdc is connected between the output terminal and the negative output terminal.

In some embodiments, the signal output terminal of the communication unit is connected to the receiving coil for sending the communication signal to be sent to the receiving coil, and the signal input terminal of the communication unit is connected to the receiving coil for obtaining the communication signal received by the receiving coil and process it.

In the second aspect, a charging coil selection method is provided, which is applied to any of the above wireless power transmission systems, including the following steps,

Step 1: Connect the transmitter to the power supply;

Step 2: the control module controls the voltage conversion unit to output the initial voltage Vin, and enters the pairing mode;

Step 3: The control module turns on one switch module and turns off other switch modules, and at this time, the transmitting coil corresponding to the currently turned on switch module performs energy transmission;

Step 4: After a delay of t1, the control module turns on the switch in the inverter unit;

Step 5: After a delay of t2, the control module sends a contact data packet through the current transmitting coil to determine whether a reply from the receiving end is received. If no reply is received, perform step 6, and if a reply is received, perform step 7;

Step 6: The control module turns off the switch in the inverter unit, after a delay of t3, turns off the currently turned on switch module, turns on the next switch module, and executes steps 4 and 5 until the reply is received, then executes step 7;

Step 7: The control module sends a configuration data packet to the receiving end, and adjusts the amplitude of the initial voltage Vin output by the voltage conversion unit according to the current load state loaded in the received reply, and the sending coil corresponding to the currently opened switch module Perform wireless power transfer.

In some embodiments, after the wireless power transmission starts, step 8 is further included, performing state monitoring on the receiving end.

In some embodiments, step 8 specifically includes:

Step 8.1: Set the count value i=0, and pre-design the upper limit n;

Step 8.2: After a delay of t4, the control module sends a status data packet to the receiving end to determine whether a reply is received, if a reply is received, execute step 8.2, if no reply is received, execute step 8.3;

Step 8.3: Add 1 to the count value i, and judge whether the current i is less than n, if less than n, then perform step 8.2, if not less than n, then perform step 8.4;

Step 8.4: The control module turns off the switch in the inverter unit, and returns to step 1.

The wireless power transmission system and the charging coil selection method for its application provided by the present disclosure combine the multi-coil architecture on the basis of the Class-E architecture, and communicate with the receiving end through the coil selection unit at the transmitting end, and transmit according to the feedback information of the receiving end. The switching of the coil can effectively improve the power transmission efficiency and increase the degree of freedom of charging; the E-class inverter has a simple structure, which can effectively reduce switching losses and improve transmission efficiency; the wireless power transmission system has a simple structure and can realize power without additional circuits and modules. The intelligent switching of transmission and coil ensures the efficiency of power transmission, reduces the weight and cost of the wireless power transmission system, and then reduces the weight and cost of related products, facilitates the promotion and use of wireless power transmission, and improves user experience.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Apparently, the drawings in the following description are some embodiments of the present disclosure. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is a structural block diagram of a wireless power transmission system provided by an embodiment of the present disclosure.

Fig. 2 is a circuit diagram of a transmitting end in a wireless power transmission system provided by an embodiment of the present disclosure.

Fig. 3 is a circuit diagram of a receiving end in a wireless power transmission system provided by an embodiment of the present disclosure.

Fig. 4 is a flowchart of a charging coil selection method provided by another embodiment of the present disclosure.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments It is a part of the embodiments of the present disclosure, but not all of them. Based on the embodiments in the present disclosure, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present disclosure.

Example 1:

In this embodiment, referring to the accompanying drawings 1-3 of the specification, a wireless power transmission system is disclosed, including a transmitting end 1 and a receiving end 2 . The transmitter 1 includes a voltage conversion unit 11 , an inverter unit 12 , a filter unit 13 , a coil selection unit 14 and two transmitter coils 15 .

The voltage conversion unit 11 is used to adjust the amplitude of the DC voltage Vdc input to the transmitter 1 and output an initial voltage Vin. The magnitude of the DC voltage Vdc can be between 5V-100V, and the DC voltage Vdc input to the transmitter 1 can be input to the transmitter through USB or other interfaces conforming to QC, PD and other protocols. The voltage conversion unit 11 can adjust the amplitude of the DC voltage Vdc according to the state of the receiving terminal 2 and output an initial voltage Vin, and the magnitude of the initial voltage Vin can be between 1V-100V. The voltage conversion unit 11 may include a buck-boost converter or a PD protocol chip.

The inverter unit 12 is used to convert the initial voltage Vin into a high-frequency AC voltage, and the inverter unit 12 is a class E inverter composed of switches, capacitors and inductors.

Specifically, the inverter unit 12 includes an inductor Ldc, a switch Q1, and a capacitor Cpar. One end of the inductor Ldc is connected to the output end of the voltage conversion unit 11, and the other end is connected to the drain of the switch Q1. The inductor Ldc converts the initial voltage Vin into a constant current. source; the source of the switch Q1 is grounded, the gate of the switch Q1 is connected to the signal output terminal of the coil selection unit 14, the switch Q1 can be a MOSFET or a GaN semiconductor switch, and the constant current source is converted into a high-frequency alternating current; the capacitor Cpar and the switch Q1 is connected in parallel.

The filtering unit 13 is used for filtering high-frequency noise in the high-frequency alternating current.

Specifically, the filter unit 13 includes a capacitor Ct, an inductor Ltf and a capacitor Cf, one end of the capacitor Ct is the input terminal of the filter unit 13, the capacitor Ct and the inductor Ltf are connected in series, the inductor Ltf is the output terminal of the filter unit 13, and one end of the capacitor Cf is connected The other end of the output end of the filter unit 13 is grounded. The capacitor Ct is a resonant capacitor, which resonates with the inductor Ltf to convert the high-frequency alternating current into a quasi-sine wave; the inductor Ltf is a resonant inductor and filter inductor, and converts the high-frequency alternating current into a quasi-sine wave with the capacitor Ct, and forms a low-pass with the capacitor Cf Filter to filter out high-frequency noise interference.

The coil selection unit 14 is used to communicate with the receiving end 2, and select a transmitting coil 15 for charging according to the communication result.

Coil selection unit 14 comprises control module and switch module, and the quantity of switch module should be equal to the quantity of transmitting coil 15, and in the present embodiment, switch module has two, is marked as switch module S1 and switch module S2 respectively, and switch module S1 Both the switching module S1 and the switching module S2 are composed of two MOSFETs, and the switching module S1 and the switching module S2 are connected in parallel. One end of the switch module is connected to the output end of the filter unit 13 , the other end is connected in series with a transmitting coil 15 , and the other end of the transmitting coil 15 is grounded.

The control module may include a chip Ut1, a regulating circuit Dem1, a regulating circuit Dem2, a driving circuit Gs1, a driving circuit Gs2 and a driving circuit Gq1; wherein, the signal output terminal of the chip Ut1 is directly connected with the signal input terminal of the voltage conversion unit 11 for controlling The voltage conversion unit 11 outputs the initial voltage Vin; the signal output terminal of the chip Ut1 is respectively connected to the signal input terminal of each switch module through the drive circuit Gs1 and the drive circuit Gs2, and is used to control the on-off of the switch module; the signal output terminal of the chip Ut1 The drive circuit Gq1 is connected to the signal input end of the switch in the inverter unit 12 to control the on-off of the switch in the inverter unit 12; the signal input end of the chip Ut1 is connected to each transmitting coil 15 through the adjustment circuit Dem1 and the adjustment circuit Dem2 respectively. connected to process the communication signal received by the transmitting coil 15 .

In an optional embodiment, the information sent from the transmitting end 1 to the receiving end 2 can be realized by changing the switching frequency of the switch Q1, so there is no need to add an adjustment circuit to the control module, thereby simplifying the circuit structure, improving communication efficiency, and reducing cost.

The transmitting end 1 also includes a number of Tx impedance matching units 16, the number of Tx impedance matching units 16 is equal to the number of transmitting coils 15, the Tx impedance matching unit 16 includes a first capacitor, and the first capacitor C1s and the first capacitor C2s are connected in series in the switch Between the module and the transmitting coil 15, the inductive reactance of the transmitting coil 15 is compensated to improve the power output capability of the transmitting coil.

The transmitting coil 15 is used to convert the electric energy of the high-frequency alternating current into magnetic field energy and transmit it. The number of transmitting coils 15 may be more than two, and this embodiment only takes two transmitting coils 15 as an example. Lt1 and Lt2 respectively represent the self-inductance of the two transmitting coils, and C1p and C2p respectively represent the parasitic capacitance of the two transmitting coils.

The receiving end 2 includes a receiving coil 21 , a rectifying unit 22 and a communication unit 23 .

The receiving coil 21 is used to receive magnetic field energy and convert it into high-frequency alternating current, the inductance Lr represents the self-inductance of the receiving coil, and the capacitance Crp represents the parasitic capacitance of the receiving coil.

The rectifier unit 22 is used to convert the high-frequency alternating current into a direct current output to supply power to the load; the rectifier unit 22 includes a rectifier bridge and a filter capacitor Cfdc, and the rectifier bridge is composed of a diode D1, a diode D2, a diode D3 and a diode D4, and the AC input of the rectifier bridge terminals are respectively connected to the two ends of the receiving coil 21, and the filter capacitor Cfdc is connected between the positive output terminal and the negative output terminal of the rectifier bridge. In this embodiment, the load is composed of a charging management circuit and a rechargeable battery Bat, wherein the charging management circuit includes a battery charging management chip Ur2.

The communication unit 23 is used for communicating with the transmitter 1, and includes a chip Ur1, a demodulation circuit Dem3, and a modulation circuit Mod. The signal output end of the chip Ur1 is connected to the receiving coil 21 through the modulation circuit Mod, and is used to send the communication signal to be sent to the receiving coil 21, and the signal input end of the chip Ur1 is connected to the receiving coil 21 through the demodulation circuit Dem3, for obtaining The communication signal received by the receiving coil 21 is processed.

The receiving end 2 further includes an Rx impedance matching unit 24 , the Rx impedance matching unit 24 includes a second capacitor Crs, one end of the second capacitor Crs is connected to the receiving coil 21 , and the other end is connected to the input end of the rectifying unit 22 . The second capacitor Crs compensates the inductive reactance of the receiving coil 21 to improve the output capability of the receiving coil.

The wireless power transmission system provided by the present disclosure combines the multi-coil architecture on the basis of the Class-E architecture, and communicates with the receiving end through the coil selection unit of the transmitting end, and switches the transmitting coil according to the feedback information of the receiving end, effectively improving power transmission. Efficiency, improve charging freedom; E-class inverter has a simple structure, which can effectively reduce switching loss and improve transmission efficiency; the wireless power transmission system has a simple structure, and can realize intelligent switching between power transmission and coils without additional circuits and modules, ensuring The efficiency of power transmission reduces the weight and cost of the wireless power transmission system, thereby reducing the weight and cost of related products, facilitating the promotion and use of wireless power transmission, and improving user experience.

Example 2:

A charging coil selection method, referring to Figure 4 of the specification, applied to any wireless power transmission system in the above product embodiments, including the following steps:

Step 1: Connect the transmitter to the power supply;

Step 2: the control module controls the voltage conversion unit to output the initial voltage Vin, and enters the pairing mode;

Step 3: The control module turns on one switch module and turns off other switch modules, and at this time, the transmitting coil corresponding to the currently turned on switch module performs energy transmission;

Step 4: After a delay of t1, the control module turns on the switch in the inverter unit;

Step 5: After a delay of t2, the control module sends a contact data packet through the current transmitting coil to determine whether a reply from the receiving end is received. If no reply is received, perform step 6, and if a reply is received, perform step 7;

Step 6: The control module turns off the switch in the inverter unit, after a delay of t3, turns off the currently turned on switch module, turns on the next switch module, and executes steps 4 and 5 until the reply is received, then executes step 7;

Step 7: The control module sends a configuration data packet to the receiving end, and adjusts the amplitude of the initial voltage Vin output by the voltage conversion unit according to the current load state loaded in the received reply, and the sending coil corresponding to the currently opened switch module Perform wireless power transfer.

In an optional implementation manner, after starting the wireless power transmission, step 8 is further included, performing state monitoring on the receiving end.

Step 8 may specifically include the following steps:

Step 8.1: Set the count value i=0, and pre-design the upper limit n;

Step 8.2: After a delay of t4, the control module sends a status data packet to the receiving end to determine whether a reply is received, if a reply is received, execute step 8.2, if no reply is received, execute step 8.3;

Step 8.3: Add 1 to the count value i, and judge whether the current i is less than n, if less than n, then perform step 8.2, if not less than n, then perform step 8.4;

Step 8.4: The control module turns off the switch in the inverter unit, and returns to step 1.

Therefore, the wireless power transmission system can adjust the transmitting coil according to the real-time status of the receiving end, further improving the flexibility of wireless charging, meeting the needs of different charging scenarios, and improving the efficiency of power transmission.

The charging coil selection method provided by the present disclosure combines the multi-coil architecture on the basis of the Class-E architecture, communicates with the receiving end through the coil selection unit at the transmitting end, and switches the transmitting coil according to the feedback information of the receiving end, effectively improving power transmission. Efficiency, improve charging freedom; E-class inverter has a simple structure, which can effectively reduce switching loss and improve transmission efficiency; the wireless power transmission system has a simple structure, and can realize intelligent switching between power transmission and coils without additional circuits and modules, ensuring The efficiency of power transmission reduces the weight and cost of the wireless power transmission system, thereby reducing the weight and cost of related products, facilitating the promotion and use of wireless power transmission, and improving user experience.

In the embodiments provided in this application, it should be understood that the disclosed technical content can be realized in other ways. Wherein, the device embodiments described above are only illustrative, for example, the division of the units is only a logical function division, and there may be other division methods in actual implementation, for example, multiple units or components can be combined or can be Integrate into another system, or some features may be ignored, or not implemented.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present disclosure may be integrated into one processing unit, each unit may exist separately physically, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

Therefore, if the integrated unit is realized in the form of a software function unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the essence of the technical solution disclosed in this disclosure or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium. Several instructions are included to make a computer device (which may be a personal computer, server or network device, etc.) execute all or part of the steps of the methods described in the various embodiments of the present disclosure. The aforementioned storage medium includes: various media capable of storing program codes such as U disk, read-only memory, random access memory, removable hard disk, magnetic disk or optical disk.

The above descriptions are only optional implementations of the present disclosure. It should be pointed out that those skilled in the art can make some improvements and modifications without departing from the principle of the present disclosure. These improvements and modifications It should also be regarded as the protection scope of the present disclosure.

Claims (10)

1. A wireless power transfer system, characterized in that,

comprises a transmitting end (1) and a receiving end (2);

the transmitting end (1) comprises a voltage conversion unit (11), an inversion unit (12), a filtering unit (13), a coil selection unit (14) and at least two transmitting coils (15);

the voltage conversion unit (11) is used for adjusting the amplitude of the direct current voltage input into the transmitting end (1) and outputting an initial voltage Vin;

the inverter unit (12) is used for converting an initial voltage Vin into a high-frequency alternating voltage, and the inverter unit (12) is an E-type inverter consisting of a switch, a capacitor and an inductor;

the filtering unit (13) is used for filtering high-frequency noise in the high-frequency alternating voltage;

the coil selection unit (14) is used for communicating with the receiving end (2) and selecting at least one transmitting coil (15) for charging according to a communication result;

the coil selection unit (14) comprises a control module and a plurality of switch modules, the number of the switch modules is equal to that of the transmitting coils (15), one end of each switch module is connected to the output end of the filtering unit (13), the other end of each switch module is connected with one transmitting coil (15) in series, and the other end of each transmitting coil (15) is grounded;

the signal output end of the control module is respectively connected with the signal input end of each switch module and used for controlling the on-off of the switch module, the signal output end of the control module is connected with the signal input end of a switch in the inversion unit (12) and used for controlling the on-off of the switch in the inversion unit (12), and the signal output end of the control module is connected with the signal input end of the voltage conversion unit (11) and used for controlling the voltage conversion unit (11) to output an initial voltage Vin; the signal input end of the control module is respectively connected with each transmitting coil (15) and is used for processing communication signals received by the transmitting coils (15);

the transmitting coil (15) is used for converting the electric energy of the high-frequency alternating current into magnetic field energy and transmitting the magnetic field energy;

the receiving end (2) comprises a receiving coil (21), a rectifying unit (22) and a communication unit (23);

the receiving coil (21) is used for receiving magnetic field energy and converting the magnetic field energy into high-frequency alternating current;

the rectifying unit (22) is used for converting high-frequency alternating current into direct current and outputting the direct current to supply power for a load;

the communication unit (23) is used for communicating with the transmitting end (1).

2. The wireless power transfer system according to claim 1, wherein the inverter unit (12) comprises an inductance Ldc, a switch Q1 and a capacitor Cpar, one end of the inductance Ldc is connected to the output end of the voltage converting unit (11), and the other end is connected to the drain electrode of the switch Q1; the source electrode of the switch Q1 is grounded, the gate electrode of the switch Q1 is connected with the signal output end of the coil selection unit (14), and the capacitor Cpar is connected with the switch Q1 in parallel.

3. The wireless power transmission system according to claim 1, wherein the filter unit (13) includes a capacitor Ct, an inductor Ltf and a capacitor Cf, one end of the capacitor Ct is an input end of the filter unit (13), the capacitor Ct and the inductor Ltf are connected in series, the inductor Ltf is an output end of the filter unit (13), and one end of the capacitor Cf is connected to the output end of the filter unit (13), and the other end is grounded.

4. The wireless power transfer system according to claim 1, wherein the transmitting end (1) further comprises a number of Tx impedance matching units (16), the number of Tx impedance matching units (16) being equal to the number of transmitting coils (15), the Tx impedance matching units (16) comprising a first capacitance, the first capacitance being connected in series between the switching module and the transmitting coils (15).

5. The wireless power transfer system according to claim 1, wherein the receiving terminal (2) further comprises an Rx impedance matching unit (24), the Rx impedance matching unit (24) comprising a second capacitor, one end of the second capacitor being connected to the receiving coil (21), the other end being connected to the input terminal of the rectifying unit (22).

6. The wireless power transmission system according to claim 1, wherein the rectifying unit (22) comprises a rectifying bridge and a filter capacitor Cfdc, the rectifying bridge is composed of a diode D1, a diode D2, a diode D3 and a diode D4, alternating current input ends of the rectifying bridge are respectively connected with two ends of the receiving coil (21), and the filter capacitor Cfdc is connected between an anode output end and a cathode output end of the rectifying bridge.

7. The wireless power transfer system according to claim 1, characterized in that the signal output of the communication unit (23) is connected to the receiving coil (21) for transmitting a communication signal to be transmitted to the receiving coil (21), and the signal input of the communication unit (23) is connected to the receiving coil (21) for obtaining and processing a communication signal received by the receiving coil (21).

8. A charging coil selection method applied to the wireless power transmission system according to any one of claims 1 to 7, characterized by comprising the steps of:

step 1: the transmitting end is connected with a power supply;

step 2: the control module controls the voltage conversion unit to output an initial voltage Vin and enter a pairing mode;

step 3: the control module turns on one switch module and turns off other switch modules, and at the moment, the transmitting coil corresponding to the currently-turned-on switch module transmits energy;

step 4: after the delay t1, the control module turns on a switch in the inversion unit;

step 5: after the time delay t2, the control module sends out a contact data packet through the current transmitting coil, judges whether a reply of the receiving end is received or not, if the reply is not received, the step 6 is executed, and if the reply is received, the step 7 is executed;

step 6: the control module turns off the switch in the inversion unit, turns off the switch module which is turned on at present after a time delay t3, turns on the next switch module, and executes the step 4 and the step 5 until the reply is received, and then executes the step 7;

step 7: the control module sends a configuration data packet to the receiving end, adjusts the amplitude of the initial voltage Vin output by the voltage conversion unit according to the current load state loaded in the received reply, and carries out wireless power transmission by the sending coil corresponding to the currently opened switch module.

9. The method of claim 8, further comprising step 8 of monitoring a status of the receiving terminal after starting the wireless power transmission.

10. The method of claim 8, wherein step 8 specifically comprises:

step 8.1: setting a count value i=0, and presetting an upper limit n of the count value;

step 8.2: after the time delay t4, the control module sends a state data packet to the receiving end, judges whether a reply is received, if the reply is received, executes the step 8.2, and if the reply is not received, executes the step 8.3;

step 8.3: adding 1 to the count value i, judging whether the current i is smaller than n, if so, executing the step 8.2, and if not, executing the step 8.4;

step 8.4: and (3) the control module turns off the switch in the inversion unit and returns to execute the step (1).

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