Patent Publication Number: US-2022216734-A1

Title: Wireless charging system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/096397, filed on Jun. 16, 2020, which claims priority to Chinese Patent Application No. 201910913196.6, filed on Sep. 25, 2019. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of wireless charging technologies, and in particular, to a wireless charging system. 
     BACKGROUND 
     Currently, charging an electronic device by using a wireless charging technology becomes increasingly popular. A device that implements the wireless charging technology is referred to as a wireless charger. The wireless charger may include two transmit plates, and the electronic device may include two receive plates. After the two transmit plates are placed directly opposite to the two receive plates, the two transmit plates and the two receive plates can implement electric field coupling. 
     When the wireless charger is used to charge the electronic device, the two transmit plates in the wireless charger generate an electric field, and the two receive plates in the electronic device generate an alternating current under the action of the electric field, thereby implementing charging of the electronic device. However, in this case, the two transmit plates need to be placed directly opposite to the two receive plates, and the two transmit plates need to be very close to the two receive plates to implement charging. Consequently, application of the wireless charging technology is greatly limited. 
     SUMMARY 
     This application provides a wireless charging system, to improve flexibility of wireless charging. The technical solutions are as follows: 
     According to one aspect, a wireless charging system is provided, where the system includes: a transmit apparatus and a receive apparatus. 
     The transmit apparatus includes an inverter circuit and two transmit electrodes, an input terminal of the inverter circuit is connected to a direct-current power supply, and two output terminals of the inverter circuit are connected to the two transmit electrodes respectively; the receive apparatus includes two receive electrodes and a rectifier circuit, two input terminals of the rectifier circuit are connected to the two receive electrodes respectively, and an output terminal of the rectifier circuit is connected to a load; and one transmit electrode of the two transmit electrodes is coupled to one receive electrode of the two receive electrodes through a first transmission medium, where electric conductivity of the first transmission medium is greater than electric conductivity of air. 
     The inverter circuit converts, into an alternating current, a direct current input by the direct-current power supply and then outputs the alternating current to the two transmit electrodes, so that the two transmit electrodes generate an electric field. The two receive electrodes generate an alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit; and the rectifier circuit converts the input alternating current into a direct current and outputs the direct current to the load, so as to supply power to the load. 
     It should be noted that the first transmission medium may be metal or a non-metallic dielectric serving as a power transmission medium. For example, the first transmission medium may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     It should be noted that transmission power between the transmit apparatus and the receive apparatus is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus, and input voltage of the receive apparatus, and therefore increasing the equivalent coupling capacitance between the transmit electrode and the receive electrode can effectively increase the transmission power between the transmit apparatus and the receive apparatus, so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the one transmit electrode of the two transmit electrodes can be coupled to the one receive electrode of the two receive electrodes through the first transmission medium. Because the electric conductivity of the first transmission medium is greater than the electric conductivity of the air, that is, the first transmission medium has higher electric conductivity, the equivalent coupling capacitance between the transmit electrode and the receive electrode can be increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     The other transmit electrode of the two transmit electrodes is coupled to the other receive electrode of the two receive electrodes through the air; or the other transmit electrode of the two transmit electrodes is coupled to the other receive electrode of the two receive electrodes through a second transmission medium, where electric conductivity of the second transmission medium is greater than the electric conductivity of the air. 
     It should be noted that, the second transmission medium may be metal or a non-metallic dielectric serving as a power transmission medium. For example, the second transmission medium may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     It should be noted that transmission power between the transmit apparatus and the receive apparatus is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus, and input voltage of the receive apparatus, and therefore increasing the equivalent coupling capacitance between the transmit electrode and the receive electrode can effectively increase the transmission power between the transmit apparatus and the receive apparatus, so as to implement wireless charging over a relatively long distance. In this way, when the one transmit electrode of the two transmit electrodes is coupled to the one receive electrode of the two receive electrodes through the first transmission medium, and the other transmit electrode of the two transmit electrodes is coupled to the other receive electrode of the two receive electrodes through the second transmission medium, because both the electric conductivity of the first transmission medium and the electric conductivity of the second transmission medium are greater than the electric conductivity of the air, that is, both the first transmission medium and the second transmission medium have higher electric conductivity, the equivalent coupling capacitance between the two transmit electrodes and the two receive electrodes can be significantly increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     Further, the transmit apparatus further includes a first compensation circuit, and the first compensation circuit is connected between the inverter circuit and the two transmit electrodes. The receive apparatus further includes a second compensation circuit, and the second compensation circuit is connected between the two receive electrodes and the rectifier circuit. 
     In this embodiment of this application, the first compensation circuit is configured to compensate for capacitive reactance between the transmit apparatus and the receive apparatus. The second compensation circuit is configured to compensate for capacitive reactance between the receive apparatus and the transmit apparatus. The first compensation circuit can reduce a reactive power loss in the transmit apparatus, and the second compensation circuit can reduce a reactive power loss in the receive apparatus, thereby improving power transmission efficiency. 
     Further, the first compensation circuit is further configured to increase voltage of an alternating current output by the inverter circuit. The second compensation circuit is further configured to decrease voltage of an alternating current generated in the two receive electrodes. 
     It should be noted that transmission power between the transmit apparatus and the receive apparatus is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus, and input voltage of the receive apparatus, and therefore increasing the output voltage of the transmit apparatus and the input voltage of the receive apparatus can effectively increase the transmission power between the transmit apparatus and the receive apparatus, so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the first compensation circuit can increase the voltage of the alternating current output by the inverter circuit; and in this way, a relatively strong electric field can be formed around the two transmit electrodes, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     Optionally, the one transmit electrode comes into contact with the first transmission medium, or a distance between the one transmit electrode and the first transmission medium is greater than 0 and less than a first distance. The one receive electrode comes into contact with the first transmission medium, or a distance between the one receive electrode and the first transmission medium is greater than 0 and less than a second distance. 
     Optionally, the one transmit electrode is at least a portion of a metal structural part of a wireless charging transmit device in which the transmit apparatus is located, or the one transmit electrode is located on an inner side of a housing of the wireless charging transmit device. The one receive electrode is at least a portion of a metal structural part of a wireless charging receive device in which the receive apparatus is located, or the one receive electrode is located on an inner side of a housing of the wireless charging receive device. 
     According to one aspect, a wireless charging system is provided, where the system includes: a transmit apparatus and a receive apparatus. 
     The transmit apparatus includes an inverter circuit and one transmit electrode, an input terminal of the inverter circuit is connected to a direct-current power supply, one output terminal of the inverter circuit is connected to the transmit electrode, and the other output terminal of the inverter circuit is connected to an output terminal of the transmit apparatus. The receive apparatus includes one receive electrode and a rectifier circuit, one input terminal of the rectifier circuit is connected to the receive electrode, the other input terminal of the rectifier circuit is connected to an input terminal of the receive apparatus, and an output terminal of the rectifier circuit is connected to a load. The transmit electrode is coupled to the receive electrode through a power transmission medium, where electric conductivity of the power transmission medium is greater than electric conductivity of air. 
     The inverter circuit converts, into an alternating current, a direct current input by the direct-current power supply and then outputs the alternating current through the two output terminals of the inverter circuit, so that the transmit electrode and the output terminal of the transmit apparatus generate an electric field. The receive electrode and the input terminal of the receive apparatus generate an alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit; and the rectifier circuit converts the input alternating current into a direct current and outputs the direct current to the load, so as to supply power to the load. 
     It should be noted that the power transmission medium may be metal or a non-metallic dielectric. For example, the power transmission medium may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     It should be noted that transmission power between the transmit apparatus and the receive apparatus is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus, and input voltage of the receive apparatus, and therefore increasing the equivalent coupling capacitance between the transmit electrode and the receive electrode can effectively increase the transmission power between the transmit apparatus and the receive apparatus, so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the transmit electrode can be coupled to the receive electrode through the power transmission medium. Because the electric conductivity of the power transmission medium is greater than the electric conductivity of the air, that is, the power transmission medium has higher electric conductivity, the equivalent coupling capacitance between the transmit electrode and the receive electrode can be increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     In addition, in this embodiment of this application, the transmit apparatus needs to include only one transmit electrode, and the receive apparatus needs to include only one receive electrode, to implement wireless charging for the receive apparatus by the transmit apparatus, thereby effectively reducing costs, volumes, and weight of the transmit apparatus and the receive apparatus and further improving flexibility of wireless charging. 
     Further, the transmit apparatus further includes a first compensation circuit, and the first compensation circuit is connected between the inverter circuit and the transmit electrode, and is connected between the invert circuit and the output terminal of the transmit apparatus. The receive apparatus further includes a second compensation circuit, and the second compensation circuit is connected between the receive electrode and the rectifier circuit, and is connected between the input terminal of the receive apparatus and the rectifier circuit. 
     In this embodiment of this application, the first compensation circuit is configured to compensate for capacitive reactance between the transmit apparatus and the receive apparatus. The second compensation circuit is configured to compensate for capacitive reactance between the receive apparatus and the transmit apparatus. The first compensation circuit can reduce a reactive power loss in the transmit apparatus, and the second compensation circuit can reduce a reactive power loss in the receive apparatus, thereby improving power transmission efficiency. 
     Further, the first compensation circuit is further configured to increase voltage of an alternating current output by the inverter circuit. The second compensation circuit is further configured to decrease voltage of an alternating current generated in the receive electrode and the input terminal of the receive apparatus. 
     It should be noted that transmission power between the transmit apparatus and the receive apparatus is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus, and input voltage of the receive apparatus, and therefore increasing the output voltage of the transmit apparatus and the input voltage of the receive apparatus can effectively increase the transmission power between the transmit apparatus and the receive apparatus, so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the first compensation circuit can increase the voltage of the alternating current output by the inverter circuit; and in this way, a relatively strong electric field can be formed around the transmit electrode and the output terminal of the transmit apparatus, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     Optionally, the transmit electrode comes into contact with the power transmission medium, or a distance between the transmit electrode and the power transmission medium is greater than 0 and less than a first distance. The receive electrode comes into contact with the power transmission medium, or a distance between the receive electrode and the power transmission medium is greater than 0 and less than a second distance. 
     Optionally, the transmit electrode is at least a portion of a metal structural part of a wireless charging transmit device in which the transmit apparatus is located, or the transmit electrode is located on an inner side of a housing of the wireless charging transmit device. The receive electrode is at least a portion of a metal structural part of a wireless charging receive device in which the receive apparatus is located, or the receive electrode is located on an inner side of a housing of the wireless charging receive device. 
     According to one aspect, a wireless charging system is provided, where the system includes: a transmit apparatus and a receive apparatus. 
     The transmit apparatus includes an inverter circuit and two transmit electrodes, an input terminal of the inverter circuit is connected to a direct-current power supply, and two output terminals of the inverter circuit are connected to the two transmit electrodes respectively; and the two transmit electrodes are coupled through a power transmission medium, where electric conductivity of the power transmission medium is greater than electric conductivity of air. The receive apparatus includes a receive coil and a rectifier circuit, an input terminal of the rectifier circuit is connected to the receive coil, and an output terminal of the rectifier circuit is connected to a load. 
     The inverter circuit converts, into an alternating current, a direct current input by the direct-current power supply and then outputs the alternating current to the two transmit electrodes, so that an alternating current is generated in the power transmission medium between the two transmit electrodes. The alternating current in the power transmission medium excites a magnetic field. The receive coil generates an alternating current under the action of the magnetic field and transmits the generated alternating current to the rectifier circuit; and the rectifier circuit converts the input alternating current into a direct current and outputs the direct current to the load, so as to supply power to the load. 
     It should be noted that the power transmission medium may be metal or a non-metallic dielectric. For example, the power transmission medium may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     In this embodiment of this application, the two transmit electrodes in the transmit apparatus may be coupled through the power transmission medium whose electric conductivity is greater than the electric conductivity of the air; and in this way, an alternating current may be generated in the power transmission medium, and the alternating current can excite the magnetic field. The alternating current is generated in the receive coil of the receive apparatus through electromagnetic induction, to implement wireless charging, thereby improving flexibility of wireless charging. 
     Further, the transmit apparatus further includes a first compensation circuit, and the first compensation circuit is connected between the inverter circuit and the two transmit electrodes. The receive apparatus further includes a second compensation circuit, and the second compensation circuit is connected between the receive coil and the rectifier circuit. 
     In this embodiment of this application, the first compensation circuit is configured to compensate for capacitive reactance between the two transmit electrodes. The second compensation circuit is configured to compensate for inductive reactance of the receive coil. The first compensation circuit can reduce a reactive power loss in the transmit apparatus, and the second compensation circuit can reduce a reactive power loss in the receive apparatus, thereby improving power transmission efficiency. 
     Optionally, at least one transmit electrode of the two transmit electrodes comes into contact with the power transmission medium; or a distance between at least one transmit electrode of the two transmit electrodes and the power transmission medium is greater than 0 and less than a reference distance; or one transmit electrode of the two transmit electrodes comes into contact with the power transmission medium, and a distance between the other transmit electrode and the power transmission medium is greater than 0 and less than a reference distance. 
     Optionally, at least one transmit electrode of the two transmit electrodes is at least a portion of a metal structural part of a wireless charging transmit device in which the transmit apparatus is located; or at least one transmit electrode of the two transmit electrodes is located on an inner side of a housing of the wireless charging transmit device; or one transmit electrode of the two transmit electrodes is at least a portion of a metal structural part of the wireless charging transmit device, and the other transmit electrode is located on an inner side of a housing of the wireless charging transmit device. 
     The technical solutions provided in this application can bring at least the following beneficial effects: 
     The wireless charging system includes the transmit apparatus and the receive apparatus. The transmit apparatus includes the inverter circuit and the two transmit electrodes. The receive apparatus includes the two receive electrodes and the rectifier circuit. The inverter circuit converts, into the alternating current, the direct current input by the direct-current power supply and then outputs the alternating current to the two transmit electrodes, so that the two transmit electrodes generate the electric field. The two receive electrodes generate the alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit; and the rectifier circuit converts the input alternating current into the direct current and outputs the direct current to the load, so as to supply power to the load. Because the one transmit electrode of the two transmit electrodes is coupled to the one receive electrode of the two receive electrodes through the first transmission medium whose electric conductivity is greater than the electric conductivity of the air, the equivalent coupling capacitance between the transmit electrode and the receive electrode can be increased, thereby effectively increasing the wireless charging transmission distance and improving flexibility of wireless charging. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic structural diagram of a first wireless charging system according to an embodiment of this application; 
         FIG. 2  is a schematic structural diagram of a second wireless charging system according to an embodiment of this application; 
         FIG. 3  is a schematic structural diagram of an LC resonance boost circuit according to an embodiment of this application; 
         FIG. 4  is a schematic structural diagram of a planar spiral boost coil according to an embodiment of this application; 
         FIG. 5  is a schematic structural diagram of an LC resonance buck circuit according to an embodiment of this application; 
         FIG. 6  is a schematic structural diagram of a planar spiral buck coil according to an embodiment of this application; 
         FIG. 7  is a schematic structural diagram of a third wireless charging system according to an embodiment of this application; 
         FIG. 8  is a schematic structural diagram of a fourth wireless charging system according to an embodiment of this application; 
         FIG. 9  is a schematic structural diagram of a fifth wireless charging system according to an embodiment of this application; 
         FIG. 10  is a schematic structural diagram of a sixth wireless charging system according to an embodiment of this application; 
         FIG. 11  is a schematic structural diagram of a seventh wireless charging system according to an embodiment of this application; 
         FIG. 12  is a schematic diagram of a first type of wireless charging according to an embodiment of this application; 
         FIG. 13  is a schematic diagram of an internal structure of a first apparatus according to an embodiment of this application; 
         FIG. 14  is a schematic diagram of a second type of wireless charging according to an embodiment of this application; 
         FIG. 15  is a schematic diagram of an internal structure of a second apparatus according to an embodiment of this application; 
         FIG. 16  is a schematic diagram of a third type of wireless charging according to an embodiment of this application; 
         FIG. 17  is a schematic diagram of an internal structure of a third apparatus according to an embodiment of this application; 
         FIG. 18  is a schematic diagram of a fourth type of wireless charging according to an embodiment of this application; 
         FIG. 19  is a schematic diagram of an internal structure of a fourth apparatus according to an embodiment of this application; 
         FIG. 20  is a schematic diagram of a fifth type of wireless charging according to an embodiment of this application; 
         FIG. 21  is a schematic diagram of an internal structure of a fifth apparatus according to an embodiment of this application; 
         FIG. 22  is a schematic diagram of a sixth type of wireless charging according to an embodiment of this application; 
         FIG. 23  is a schematic diagram of an internal structure of a sixth apparatus according to an embodiment of this application; 
         FIG. 24  is a schematic diagram of a seventh type of wireless charging according to an embodiment of this application; 
         FIG. 25  is a schematic diagram of an internal structure of a seventh apparatus according to an embodiment of this application; 
         FIG. 26  is a schematic diagram of an eighth type of wireless charging according to an embodiment of this application; 
         FIG. 27  is a schematic diagram of a ninth type of wireless charging according to an embodiment of this application; 
         FIG. 28  is a schematic diagram of an internal structure of an eighth apparatus according to an embodiment of this application; 
         FIG. 29  is a schematic diagram of a tenth type of wireless charging according to an embodiment of this application; 
         FIG. 30  is a schematic diagram of an eleventh type of wireless charging according to an embodiment of this application; and 
         FIG. 31  is a schematic diagram of a twelfth type of wireless charging according to an embodiment of this application. 
     
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
       10 : transmit apparatus,  101 : direct-current power supply,  102 : inverter circuit,  103 : transmit electrode,  104 : transmit electrode,  105 : first compensation circuit,  20 : receive apparatus,  201 : rectifier circuit,  202 : load,  203 : receive electrode,  204 : receive electrode,  205 : second compensation circuit,  206 : receive coil,  30 : first transmission medium,  40 : second transmission medium,  50 : power transmission medium, P 1 : output terminal of a transmit apparatus, and P 2 : input terminal of a receive apparatus; and 
       60 : mobile phone,  601 : internal circuit of a transmit apparatus,  61 : smart watch,  611 : internal circuit of a receive apparatus,  62 : user,  63 : smart ring,  631 : internal circuit of a receive apparatus,  64 : electronic device,  641 : internal circuit of a receive apparatus,  65 : ground,  70 : power transmit apparatus,  701 : internal circuit of a transmit apparatus,  71 : smoke sensor,  711 : internal circuit of a receive apparatus,  72 : roof,  73 : monitor,  731 : internal circuit of a receive apparatus,  74 : electronic device,  741 : internal circuit of a receive apparatus, and  75 : metal layer. 
     DESCRIPTION OF EMBODIMENTS 
     To make the objectives, technical solutions, and advantages of this application clearer, the following further describes the implementations of this application in detail with reference to the accompanying drawings. 
     Before detailed illustration of the embodiments of this application, application scenarios of the embodiments of this application are first described. 
     In a wireless charging scenario, a transmission distance is a key parameter that affects user experience. Currently, an electronic device needs to be directly opposite to and keep very close to a wireless charging pad before getting charged, which significantly limits application of a wireless charging technology. Therefore, the embodiments of this application provide a wireless charging system that is applicable to a wireless charging scenario with a power transmission medium (such as metal or a non-metallic dielectric) whose electric conductivity is greater than electric conductivity of air. For example, the wireless charging system is applicable to scenarios such as wireless charging for a wearable device, wireless charging for a monitoring device and a sensor in a building, and wireless charging for a desktop electronic device. The wireless charging system provided in the embodiments of this application can freely and flexibly implement wireless charging in a relatively large space, thereby broadening the application of the wireless charging technology. 
       FIG. 1  is a schematic structural diagram of a wireless charging system according to an embodiment of this application. Referring to  FIG. 1 , the system includes a transmit apparatus  10  and a receive apparatus  20 . 
     The transmit apparatus  10  includes an inverter circuit  102  and two transmit electrodes ( 103  and  104  shown in the figure), an input terminal of the inverter circuit  102  is connected to a direct-current power supply  101 , and two output terminals of the inverter circuit  102  are connected to the two transmit electrodes respectively. The receive apparatus  20  includes two receive electrodes ( 203  and  204  shown in the figure) and a rectifier circuit  201 , two input terminals of the rectifier circuit  201  are connected to the two receive electrodes respectively, and an output terminal of the rectifier circuit  201  is connected to a load  202 . One transmit electrode  103  in the two transmit electrodes is coupled to one receive electrode  203  of the two receive electrodes through a first transmission medium  30 , where electric conductivity of the first transmission medium  30  is greater than electric conductivity of air. 
     The inverter circuit  102  converts, into an alternating current, a direct current input by the direct-current power supply  101  and then outputs the alternating current to the two transmit electrodes, so that the two transmit electrodes generate an electric field. The two receive electrodes generate an alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit  201 ; and the rectifier circuit  201  converts the input alternating current into a direct current and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     It should be noted that the transmit apparatus  10  belongs to a wireless charging transmit device, and the receive apparatus  20  belongs to a wireless charging receive device. The wireless charging transmit device is configured to charge the wireless charging receive device. The wireless charging transmit device and the wireless charging receive device may be various types of electronic devices. That is, the transmit apparatus  10  and the receive apparatus  20  may be disposed in various types of electronic devices. For example, the transmit apparatus  10  and the receive apparatus  20  may be disposed in electronic devices such as a handheld electronic device, a wearable electronic device, a desktop electronic device, or a wall-mounted electronic device. These electronic devices may include a mobile phone, a smart watch, a smart ring, a mobile power pack, a computer, a monitoring device, a sensor, and the like. 
     In addition, the direct-current power supply  101  may provide power. For example, the direct-current power supply  101  may be an independently disposed power module, or may be a battery of the wireless charging transmit device, or the like. This is not limited in this embodiment of this application. The load  202  may receive the power. For example, the load  202  may be a light emitting diode (LED) lamp, a chip, a battery of the wireless charging receive device, or the like. This is not limited in this embodiment of this application. 
     In addition, the first transmission medium  30  may be metal or a non-metallic dielectric serving as a power transmission medium. For example, the first transmission medium  30  may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     It should be noted that the inverter circuit  102  is configured to convert a direct current into an alternating current, and may also be referred to as a direct current-alternating current conversion circuit. The rectifier circuit  201  is configured to convert an alternating current into a direct current, and may also be referred to as an alternating current-direct current conversion circuit. The inverter circuit  102  converts, into the alternating current, the direct current input by the direct-current power supply  101  and then outputs the alternating current to the two transmit electrodes. In this case, voltage is generated between the two transmit electrodes, to form an electric field around the two transmit electrodes. Inducting voltage is generated between the two receive electrodes under the action of the electric field; and in this way, the alternating current is generated between the two receive electrodes. The rectifier circuit  201  converts the alternating current in the two receive electrodes into a direct current and then outputs the direct current to the load  202 , so as to supply power to the load  202 , thereby implementing wireless charging for the receive apparatus  20  by the transmit apparatus  10 . 
     It should be noted that, in a possible implementation, the inverter circuit  102  may convert, into a high-frequency alternating current, the direct current input by the direct-current power supply  101  and then output the high-frequency alternating current to the two transmit electrodes. In this way, the two transmit electrodes generate a high-frequency electric field. The two receive electrodes generate a high-frequency alternating current under the action of the high-frequency electric field; and the rectifier circuit  201  may convert the high-frequency alternating current into a direct current applicable to the load  202  and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     In addition, locations of the two transmit electrodes may be set based on use requirements. To improve power transmission efficiency, a coupling degree between the two transmit electrodes should be minimized, so as to minimize a directly-opposite area of the two transmit electrodes. For example, the two transmit electrodes may be respectively disposed at a rear housing and a frame of the wireless charging transmit device. Similarly, locations of the two receive electrodes may be set based on use requirements. To improve power transmission efficiency, a coupling degree between the two receive electrodes should be minimized, so as to minimize a directly-opposite area of the two receive electrodes. For example, the two receive electrodes may be respectively disposed at a rear housing and a frame of the wireless charging receive device. 
     In addition, when the wireless charging system in this embodiment of this application is actually used, a ground point may not be disposed. That is, the wireless charging system may be an integral suspended structure. In addition, to implement charging, the two transmit electrodes in the transmit apparatus  10  do not need to be placed directly opposite to the two receive electrodes in the receive apparatus  20 , thereby improving flexibility of wireless charging. 
     It should be noted that transmission power between the transmit apparatus  10  and the receive apparatus  20  is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus  10 , and input voltage of the receive apparatus  20 , and therefore increasing the equivalent coupling capacitance between the transmit electrode and the receive electrode can effectively increase the transmission power between the transmit apparatus  10  and the receive apparatus  20 , so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the one transmit electrode  103  of the two transmit electrodes can be coupled to the one receive electrode  203  of the two receive electrodes through the first transmission medium  30 . Because the electric conductivity of the first transmission medium  30  is greater than the electric conductivity of the air, that is, the first transmission medium  30  has higher electric conductivity, the equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203  can be increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     Further, referring to  FIG. 2 , the transmit apparatus  10  may further include a first compensation circuit  105 , the first compensation circuit  105  is connected between the inverter circuit  102  and the two transmit electrodes, and the first compensation circuit  105  and a second compensation circuit  205  are configured to compensate for capacitive reactance between the transmit apparatus  10  and the receive apparatus  20 . Further, referring to  FIG. 2 , the receive apparatus  20  may further include the second compensation circuit  205 , the second compensation circuit  205  is connected between the two receive electrodes and the rectifier circuit  201 , and the second compensation circuit  205  is configured to compensate for capacitive reactance between the receive apparatus  20  and the transmit apparatus  10 . 
     It should be noted that two input terminals of the first compensation circuit  105  are connected to two output terminals of the inverter circuit  102  respectively, and the two output terminals of the first compensation circuit  105  are connected to the two transmit electrodes respectively. Two input terminals of the second compensation circuit  205  are connected to two receive electrodes respectively, and the two output terminals of the second compensation circuit  205  are connected to the two input terminals of the rectifier circuit  201  respectively. The first compensation circuit  105  can reduce a reactive power loss in the transmit apparatus  10 , and the second compensation circuit  205  can reduce a reactive power loss in the receive apparatus  20 , thereby improving power transmission efficiency. 
     Further, the first compensation circuit  105  can also increase voltage of an alternating current output by the inverter circuit  102  to increase output voltage of the transmit apparatus  10 , thereby further increasing input voltage of the receive apparatus  20 . In this case, voltage of an alternating current generated in the two receive electrodes is relatively high, and therefore the second compensation circuit  205  may further decrease the voltage of the alternating current generated in the two receive electrodes. 
     For example, after the inverter circuit  102  converts, into a high-frequency low-voltage alternating current, the direct current input by the direct-current power supply  101 , the first compensation circuit  105  can convert the high-frequency low-voltage alternating current into a high-frequency high-voltage alternating current and then apply the high-frequency high-voltage alternating current to the two transmit electrodes to generate a high-frequency electric field. In this case, the two receive electrodes generate a high-frequency high-voltage alternating current under the action of the high-frequency electric field, the second compensation circuit  205  converts the high-frequency high-voltage alternating current into a high-frequency low-voltage alternating current, and the rectifier circuit  201  converts the high-frequency low-voltage alternating current into a direct current applicable to the load  202  and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     It should be noted that the first compensation circuit  105  may be a boost circuit or a boost apparatus when the first compensation circuit  105  can also increase the voltage of the alternating current output by the inverter circuit  102 . For example, the first compensation circuit  105  may be an LC (inductor-capacitor) resonance boost circuit, a planar spiral boost coil, a transformer, or the like. This is not limited in this embodiment of this application. The second compensation circuit  205  may be a buck circuit or a buck apparatus when the second compensation circuit  205  can also decrease the voltage of the alternating current generated in the two receive electrodes. For example, the second compensation circuit  205  may be an LC resonance buck circuit, a planar spiral buck coil, a transformer, or the like. This is not limited in this embodiment of this application. 
     For example, the first compensation circuit  105  may be an LC resonance boost circuit shown in  FIG. 3 , C 1  and C 2  are compensation capacitors, L 1  and L 2  are compensation inductors, a terminal A and a terminal B are two input terminals of the first compensation circuit  105 , and a terminal C and a terminal D are two output terminals of the first compensation circuit  105 . Alternatively, the first compensation circuit  105  may be a planar spiral boost coil shown in  FIG. 4 , the terminal A and the terminal B are connected to a primary coil at an outermost turn, Cs is a series compensation capacitor of the primary coil, the terminal C and the terminal D are connected to a multi-turn secondary coil, Cp is a parallel compensation capacitor of the secondary coil, the terminal A and the terminal B are the two input terminals of the first compensation circuit  105 , and the terminal C and the terminal D are two output terminals of the first compensation circuit  105 . 
     For another example, the second compensation circuit  205  may be an LC resonance buck circuit shown in  FIG. 5 , C 1  and C 2  are compensation capacitors, L 1  and L 2  are compensation inductors, a terminal A and a terminal B are two input terminals of the second compensation circuit  205 , and a terminal C and a terminal D are two output terminals of the second compensation circuit  205 . Alternatively, the second compensation circuit  205  may be a planar spiral buck coil shown in  FIG. 6 , the terminal A and the terminal B are connected to a multi-turn secondary coil, Cp is a parallel compensation capacitor of the secondary coil, the terminal C and the terminal D are connected to a primary coil at an outermost turn, Cs is a series compensation capacitor of the primary coil, the terminal A and the terminal B are the two input terminals of the second compensation circuit  205 , and the terminal C and the terminal D are two output terminals of the second compensation circuit  205 . 
     It should be noted that transmission power between the transmit apparatus  10  and the receive apparatus  20  is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus  10 , and input voltage of the receive apparatus  20 , and therefore increasing the output voltage of the transmit apparatus  10  and the input voltage of the receive apparatus  20  can effectively increase the transmission power between the transmit apparatus  10  and the receive apparatus  20 , so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the first compensation circuit  105  can increase the voltage of the alternating current output by the inverter circuit  102 . In this way, a relatively strong electric field can be formed around the two transmit electrodes, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     Referring to  FIG. 1 , the other transmit electrode  104  of the two transmit electrodes is coupled to the other receive electrode  204  in the two receive electrodes through the air; or referring to  FIG. 7 , the other transmit electrode  104  of the two transmit electrodes is coupled to the other receive electrode  204  in the two receive electrodes through a second transmission medium  40 , where electric conductivity of the second transmission medium  40  is greater than the electric conductivity of the air. 
     It should be noted that, the second transmission medium  40  may be metal or a non-metallic dielectric serving as a power transmission medium. For example, the second transmission medium  40  may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. The second transmission medium  40  may be the same as or different from the first transmission medium  30 . 
     In addition, both the one transmit electrode  103  of the two transmit electrodes and the one receive electrode  203  of the two receive electrodes are coupled to the first transmission medium  30 , to form a power transmission path. Both the other transmit electrode  104  of the two transmit electrodes and the other receive electrode  204  in the two receive electrodes are coupled to the air or the second transmission medium  40 , to form another power transmission path. The two power transmission paths form a power loop. In this case, after the two transmit electrodes generate the electric field, inducting voltage is generated between the two receive electrodes due to the electric field, so as to generate the alternating current between the two receive electrodes. 
     It should be noted that transmission power between the transmit apparatus  10  and the receive apparatus  20  is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode and the receive electrode, output voltage of the transmit apparatus  10 , and input voltage of the receive apparatus  20 , and therefore increasing the equivalent coupling capacitance between the transmit electrode and the receive electrode can effectively increase the transmission power between the transmit apparatus  10  and the receive apparatus  20 , so as to implement wireless charging over a relatively long distance. In this way, when the one transmit electrode  103  of the two transmit electrodes is coupled to the one receive electrode  203  of the two receive electrodes through the first transmission medium  30 , and the other transmit electrode  104  of the two transmit electrodes is coupled to the other receive electrode  204  in the two receive electrodes through the second transmission medium  40 , because both the electric conductivity of the first transmission medium  30  and the electric conductivity of the second transmission medium  40  are greater than the electric conductivity of the air, that is, both the first transmission medium  30  and the second transmission medium  40  have higher electric conductivity, the equivalent coupling capacitance between the two transmit electrodes and the two receive electrodes can be significantly increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     It should be noted that the one transmit electrode  103  of the two transmit electrodes may come into direct contact with the first transmission medium  30 . Alternatively, the transmit electrode  103  may not come into contact with the first transmission medium  30 . That is, there may be some distance between the transmit electrode  103  and the first transmission medium  30 . Specifically, the distance between the transmit electrode  103  and the first transmission medium  30  may be greater than 0 and less than a first distance, and the first distance may be preset. When the transmit electrode  103  does not come into contact with the first transmission medium  30 , there may be another object between the transmit electrode  103  and the first transmission medium  30 . For example, there may be an insulating material between the transmit electrode  103  and the first transmission medium  30 . This is not limited in this embodiment of this application. 
     The transmit electrode  103  may be made of metal such as iron, aluminum, copper, or alloy. In actual application, the transmit electrode  103  may be an independently disposed component. Alternatively, the transmit electrode  103  may be at least a portion of a metal structural part of the wireless charging transmit device. In this case, the transmit electrode  103  may come into direct contact with the first transmission medium  30 . Certainly, the transmit electrode  103  may alternatively not come into contact with the first transmission medium  30 , and the metal structural part may be a metal housing, a metal frame, or the like. Alternatively, the transmit electrode  103  may be located on an inner side of a housing of the wireless charging transmit device. In this case, the housing of the wireless charging transmit device is located between the transmit electrode  103  and the first transmission medium  30 . The housing may be made of an insulating material, metal, or the like. 
     Similarly, the one receive electrode  203  of the two receive electrodes may come into direct contact with the first transmission medium  30 . Alternatively, the receive electrode  203  may not come into contact with the first transmission medium  30 . That is, there may be some distance between the receive electrode  203  and the first transmission medium  30 . Specifically, the distance between the receive electrode  203  and the first transmission medium  30  may be greater than 0 and less than a second distance, and the second distance may be preset. When the receive electrode  203  does not come into contact with the first transmission medium  30 , there may be another object between the receive electrode  203  and the first transmission medium  30 . For example, there may be an insulating material between the receive electrode  203  and the first transmission medium  30 . This is not limited in this embodiment of this application. 
     The receive electrode  203  may be made of metal such as iron, aluminum, copper, or alloy. In actual application, the receive electrode  203  may be an independently disposed component. Alternatively, the receive electrode  203  may be at least a portion of a metal structural part of the wireless charging receive device. In this case, the receive electrode  203  may come into direct contact with the first transmission medium  30 . Certainly, the receive electrode  203  may alternatively not come into contact with the first transmission medium  30 , and the metal structural part may be a metal housing, a metal frame, or the like. Alternatively, the receive electrode  203  may be located on an inner side of a housing of the wireless charging receive device. In this case, the housing of the wireless charging receive device is located between the receive electrode  203  and the first transmission medium  30 . The housing may be made of an insulating material, metal, or the like. 
     Similarly, when the other transmit electrode  104  of the two transmit electrodes is coupled to the other receive electrode  204  in the two receive electrodes through the second transmission medium  40 , the other transmit electrode  104  may or may not come into contact with the second transmission medium  40 , and the other receive electrode  204  may or may not come into contact with the second transmission medium  40 . A structure between the other transmit electrode  104 , the second transmission medium  40 , and the other receive electrode  204  is similar to a structure between the one transmit electrode  103 , the first transmission medium  30 , and the one receive electrode  203 . Details are not described again in this embodiment of this application. 
     In this embodiment of this application, the wireless charging system includes the transmit apparatus  10  and the receive apparatus  20 . The transmit apparatus  10  includes an inverter circuit  102  and two transmit electrodes. The receive apparatus  20  includes two receive electrodes and a rectifier circuit  201 . The inverter circuit  102  converts, into an alternating current, a direct current input by the direct-current power supply  101  and then outputs the alternating current to the two transmit electrodes, so that the two transmit electrodes generate an electric field. The two receive electrodes generate an alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit  201 ; and the rectifier circuit  201  converts the input alternating current into a direct current and outputs the direct current to the load  202 , so as to supply power to the load  202 . Because the one transmit electrode  103  of the two transmit electrodes is coupled to the one receive electrode  203  of the two receive electrodes through the first transmission medium  30  whose electric conductivity is greater than the electric conductivity of the air, the equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203  can be increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
       FIG. 8  is a schematic structural diagram of a wireless charging system according to an embodiment of this application. Referring to  FIG. 8 , the system includes a transmit apparatus  10  and a receive apparatus  20 . 
     The transmit apparatus  10  includes an inverter circuit  102  and one transmit electrode  103 , an input terminal of the inverter circuit  102  is connected to a direct-current power supply  101 , one output terminal of the inverter circuit  102  is connected to the transmit electrode  103 , and the other output terminal of the inverter circuit  102  is connected to an output terminal P 1  of the transmit apparatus  10 . The receive apparatus  20  includes one receive electrode  203  and a rectifier circuit  201 . One input terminal of the rectifier circuit  201  is connected to the receive electrode  203 , the other input terminal of the rectifier circuit  201  is connected to an input terminal P 2  of the receive apparatus  20 , and an output terminal of the rectifier circuit  201  is connected to a load  202 . The transmit electrode  103  is coupled to the receive electrode  203  through a power transmission medium  50 , where electric conductivity of the power transmission medium  50  is greater than electric conductivity of air. 
     The inverter circuit  102  converts, into an alternating current, a direct current input by the direct-current power supply  101  and then outputs the alternating current through the two output terminals of the inverter circuit  102 , so that the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10  generate an electric field. The receive electrode  203  and the input terminal P 2  of the receive apparatus  20  generate an alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit  201 ; and the rectifier circuit  201  converts the input alternating current into a direct current and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     It should be noted that the transmit apparatus  10  belongs to a wireless charging transmit device, and the receive apparatus  20  belongs to a wireless charging receive device. The wireless charging transmit device is configured to charge the wireless charging receive device. The wireless charging transmit device and the wireless charging receive device may be various types of electronic devices. That is, the transmit apparatus  10  and the receive apparatus  20  may be disposed in various types of electronic devices. For example, the transmit apparatus  10  and the receive apparatus  20  may be disposed in electronic devices such as a handheld electronic device, a wearable electronic device, a desktop electronic device, or a wall-mounted electronic device. These electronic devices may include a mobile phone, a smart watch, a smart ring, a mobile power pack, a computer, a monitoring device, a sensor, and the like. 
     In addition, the direct-current power supply  101  may provide power. For example, the direct-current power supply  101  may be an independently disposed power module, or may be a battery of the wireless charging transmit device, or the like. This is not limited in this embodiment of this application. The load  202  may receive the power. For example, the load  202  may be an LED lamp, a chip, a battery of the wireless charging receive device, or the like. This is not limited in this embodiment of this application. 
     In addition, the power transmission medium  50  may be metal or a non-metallic dielectric. For example, the power transmission medium  50  may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     It should be noted that the inverter circuit  102  is configured to convert a direct current into an alternating current, and may also be referred to as a direct current-alternating current conversion circuit. The rectifier circuit  201  is configured to convert an alternating current into a direct current, and may also be referred to as an alternating current-direct current conversion circuit. The inverter circuit  102  converts, into the alternating current, the direct current input by the direct-current power supply  101  and then outputs the alternating current through the two output terminals of the inverter circuit  102 . In this case, voltage is generated between the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10 , to form an electric field around the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10 . Inducting voltage is generated between the receive electrode  203  and the input terminal P 2  of the receive apparatus  20  under the action of the electric field; and in this way, the alternating current is generated between the receive electrode  203  and the input terminal P 2  of the receive apparatus  20 . The rectifier circuit  201  converts the alternating current in the receive electrode  203  and the input terminal P 2  of the receive apparatus  20  into a direct current and then outputs the direct current to the load  202 , so as to supply power to the load  202 , thereby implementing wireless charging for the receive apparatus  20  by the transmit apparatus  10 . 
     It should be noted that, in a possible implementation, the inverter circuit  102  may convert, into a high-frequency alternating current, the direct current input by the direct-current power supply  101  and then output the high-frequency alternating current through the two output terminals of the inverter circuit  102 . In this way, the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10  generate a high-frequency electric field. The receive electrode  203  and the input terminal P 2  of the receive apparatus  20  generate a high-frequency alternating current under the action of the high-frequency electric field; and the rectifier circuit  201  may convert the high-frequency alternating current into a direct current applicable to the load  202  and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     In addition, when the wireless charging system in this embodiment of this application is actually used, a ground point may not be disposed. That is, the wireless charging system may be an integral suspended structure. In addition, to implement charging, the transmit electrode  103  in the transmit apparatus  10  does not need to be placed directly opposite to the receive electrode  203  in the receive apparatus  20 , thereby improving flexibility of wireless charging. 
     It should be noted that, both the transmit electrode  103  and the receive electrode  203  are coupled to the power transmission medium  50 , to form a power transmission path. Both the output terminal P 1  of the transmit apparatus  10  and the input terminal P 2  of the receive apparatus  20  are coupled to the air, to form another power transmission path. The two power transmission paths form a power loop. In this case, after the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10  generate the electric field, inducting voltage is generated between the receive electrode  203  and the input terminal P 2  of the receive apparatus  20  due to the electric field, so as to generate the alternating current between the receive electrode  203  and the input terminal P 2  of the receive apparatus  20 . 
     It should be noted that transmission power between the transmit apparatus  10  and the receive apparatus  20  is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203 , output voltage of the transmit apparatus  10 , and input voltage of the receive apparatus  20 , and therefore increasing the equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203  can effectively increase the transmission power between the transmit apparatus  10  and the receive apparatus  20 , so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the transmit electrode  103  can be coupled to the receive electrode  203  through the power transmission medium  50 . Because the electric conductivity of the power transmission medium  50  is greater than the electric conductivity of the air, that is, the power transmission medium  50  has higher electric conductivity, the equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203  can be increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     In addition, in this embodiment of this application, the transmit apparatus  10  needs to include only one transmit electrode  103 , and the receive apparatus  20  needs to include only one receive electrode  203 , to implement wireless charging for the receive apparatus  20  by the transmit apparatus  10 , thereby effectively reducing costs, volumes, and weight of the transmit apparatus  10  and the receive apparatus  20  and further improving flexibility of wireless charging. 
     Further, referring to  FIG. 9 , the transmit apparatus  10  may further include a first compensation circuit  105 , the first compensation circuit  105  is connected between the inverter circuit  102  and the transmit electrode  103 , and is connected between the inverter circuit  102  and the output terminal P 1  of the transmit apparatus  10 , and the first compensation circuit  105  is configured to compensate for capacitive reactance between the transmit apparatus  10  and the receive apparatus  20 . Further, referring to  FIG. 9 , the receive apparatus  20  may further include a second compensation circuit  205 , the second compensation circuit  205  is connected between the receive electrode  203  and the rectifier circuit  201 , and is connected between the input terminal P 2  of the receive apparatus  20  and the rectifier circuit  201 , and the second compensation circuit  205  is configured to compensate for capacitive reactance between the receive apparatus  20  and the transmit apparatus  10 . 
     It should be noted that two input terminals of the first compensation circuit  105  are connected to two output terminals of the inverter circuit  102  respectively, one output terminal of the first compensation circuit  105  is connected to the transmit electrode  103 , and the other output terminal of the first compensation circuit  105  is connected to the output terminal P 1  of the transmit apparatus  10 . One input terminal of the second compensation circuit  205  is connected to the receive electrode  203 , and the other input terminal of the second compensation circuit  205  is connected to the input terminal P 2  of the receive apparatus  20 , and the two output terminals of the second compensation circuit  205  are connected to the two input terminals of the rectifier circuit  201  respectively. The first compensation circuit  105  can reduce a reactive power loss in the transmit apparatus  10 , and the second compensation circuit  205  can reduce a reactive power loss in the receive apparatus  20 , thereby improving power transmission efficiency. 
     Further, the first compensation circuit  105  can also increase voltage of an alternating current output by the inverter circuit  102  to increase output voltage of the transmit apparatus  10 , thereby further increasing input voltage of the receive apparatus  20 . In this case, voltage of an alternating current generated in the receive electrode  203  and the input terminal P 2  of the receive apparatus  20  is relatively high, and therefore the second compensation circuit  205  may further decrease the voltage of the alternating current generated in the receive electrode  203  and the input terminal P 2  of the receive apparatus  20 . 
     For example, after the inverter circuit  102  converts, into a high-frequency low-voltage alternating current, the direct current input by the direct-current power supply  101 , the first compensation circuit  105  can convert the high-frequency low-voltage alternating current into a high-frequency high-voltage alternating current and then apply the high-frequency high-voltage alternating current to the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10  to generate a high-frequency electric field. In this case, the receive electrode  203  and the input terminal P 2  of the receive apparatus  20  generate a high-frequency high-voltage alternating current under the action of the high-frequency electric field, the second compensation circuit  205  converts the high-frequency high-voltage alternating current into a high-frequency low-voltage alternating current, and the rectifier circuit  201  converts the high-frequency low-voltage alternating current into a direct current applicable to the load  202  and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     It should be noted that the first compensation circuit  105  may be a boost circuit or a boost apparatus when the first compensation circuit  105  can also increase the voltage of the alternating current output by the inverter circuit  102 . For example, the first compensation circuit  105  may be an LC resonance boost circuit, a planar spiral boost coil, a transformer, or the like. This is not limited in this embodiment of this application. The second compensation circuit  205  may be a buck circuit or a buck apparatus when the second compensation circuit  205  can also decrease the voltage of the alternating current generated in the receive electrode  203  and the input terminal P 2  of the receive apparatus  20 . For example, the second compensation circuit  205  may be an LC resonance buck circuit, a planar spiral buck coil, a transformer, or the like. This is not limited in this embodiment of this application. 
     For example, the first compensation circuit  105  may be an LC resonance boost circuit shown in  FIG. 3 , C 1  and C 2  are compensation capacitors, L 1  and L 2  are compensation inductors, a terminal A and a terminal B are two input terminals of the first compensation circuit  105 , and a terminal C and a terminal D are two output terminals of the first compensation circuit  105 . Alternatively, the first compensation circuit  105  may be a planar spiral boost coil shown in  FIG. 4 , the terminal A and the terminal B are connected to a primary coil at an outermost turn, Cs is a series compensation capacitor of the primary coil, the terminal C and the terminal D are connected to a multi-turn secondary coil, Cp is a parallel compensation capacitor of the secondary coil, the terminal A and the terminal B are the two input terminals of the first compensation circuit  105 , and the terminal C and the terminal D are two output terminals of the first compensation circuit  105 . 
     For another example, the second compensation circuit  205  may be an LC resonance buck circuit shown in  FIG. 5 , C 1  and C 2  are compensation capacitors, L 1  and L 2  are compensation inductors, a terminal A and a terminal B are two input terminals of the second compensation circuit  205 , and a terminal C and a terminal D are two output terminals of the second compensation circuit  205 . Alternatively, the second compensation circuit  205  may be a planar spiral buck coil shown in  FIG. 6 , the terminal A and the terminal B are connected to a multi-turn secondary coil, Cp is a parallel compensation capacitor of the secondary coil, the terminal C and the terminal D are connected to a primary coil at an outermost turn, Cs is a series compensation capacitor of the primary coil, the terminal A and the terminal B are the two input terminals of the second compensation circuit  205 , and the terminal C and the terminal D are two output terminals of the second compensation circuit  205 . 
     It should be noted that transmission power between the transmit apparatus  10  and the receive apparatus  20  is directly proportional to an operating frequency of a system, equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203 , output voltage of the transmit apparatus  10 , and input voltage of the receive apparatus  20 , and therefore increasing the output voltage of the transmit apparatus  10  and the input voltage of the receive apparatus  20  can effectively increase the transmission power between the transmit apparatus  10  and the receive apparatus  20 , so as to implement wireless charging over a relatively long distance. In this embodiment of this application, the first compensation circuit  105  can increase the voltage of the alternating current output by the inverter circuit  102 . In this way, a relatively strong electric field can be formed around the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10 , thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
     It should be noted that the transmit electrode  103  may come into direct contact with the power transmission medium  50 . Alternatively, the transmit electrode  103  may not come into contact with the power transmission medium  50 . That is, there may be some distance between the transmit electrode  103  and the power transmission medium  50 . Specifically, the distance between the transmit electrode  103  and the power transmission medium  50  may be greater than 0 and less than a first distance, and the first distance may be preset. When the transmit electrode  103  does not come into contact with the power transmission medium  50 , there may be another object between the transmit electrode  103  and the power transmission medium  50 . For example, there may be an insulating material between the transmit electrode  103  and the power transmission medium  50 . This is not limited in this embodiment of this application. 
     The transmit electrode  103  may be made of metal such as iron, aluminum, copper, or alloy. In actual application, the transmit electrode  103  may be an independently disposed component. Alternatively, the transmit electrode  103  may be at least a portion of a metal structural part of the wireless charging transmit device. In this case, the transmit electrode  103  may come into direct contact with the power transmission medium  50 . Certainly, the transmit electrode  103  may alternatively not come into contact with the power transmission medium  50 , and the metal structural part may be a metal housing, a metal frame, or the like. Alternatively, the transmit electrode  103  may be located on an inner side of a housing of the wireless charging transmit device. In this case, the housing of the wireless charging transmit device is located between the transmit electrode  103  and the power transmission medium  50 . The housing may be made of an insulating material, metal, or the like. 
     Similarly, the receive electrode  203  may come into direct contact with the power transmission medium  50 . Alternatively, the receive electrode  203  may not come into contact with the power transmission medium  50 . That is, there may be some distance between the receive electrode  203  and the power transmission medium  50 . Specifically, the distance between the receive electrode  203  and the power transmission medium  50  may be greater than 0 and less than a second distance, and the second distance may be preset. When the receive electrode  203  does not come into contact with the power transmission medium  50 , there may be another object between the receive electrode  203  and the power transmission medium  50 . For example, there may be an insulating material between the receive electrode  203  and the power transmission medium  50 . This is not limited in this embodiment of this application. 
     The receive electrode  203  may be made of metal such as iron, aluminum, copper, or alloy. In actual application, the receive electrode  203  may be an independently disposed component. Alternatively, the receive electrode  203  may be at least a portion of a metal structural part of the wireless charging receive device. In this case, the receive electrode  203  may come into direct contact with the power transmission medium  50 . Certainly, the receive electrode  203  may alternatively not come into contact with the power transmission medium  50 , and the metal structural part may be a metal housing, a metal frame, or the like. Alternatively, the receive electrode  203  may be located on an inner side of a housing of the wireless charging receive device. In this case, the housing of the wireless charging receive device is located between the receive electrode  203  and the power transmission medium  50 . The housing may be made of an insulating material, metal, or the like. 
     In this embodiment of this application, the wireless charging system includes the transmit apparatus  10  and the receive apparatus  20 . The transmit apparatus  10  includes the inverter circuit  102  and the one transmit electrode  103 . The receive apparatus  20  includes the one receive electrode  203  and the rectifier circuit  201 . The inverter circuit  102  converts, into an alternating current, the direct current input by the direct-current power supply  101  and then outputs the alternating current through the two output terminals of the inverter circuit  102 , so that the transmit electrode  103  and the output terminal P 1  of the transmit apparatus  10  generate an electric field. The receive electrode  203  and the input terminal P 2  of the receive apparatus  20  generate an alternating current under the action of the electric field and transmit the generated alternating current to the rectifier circuit  201 ; and the rectifier circuit  201  converts the input alternating current into a direct current and outputs the direct current to the load  202 , so as to supply power to the load  202 . Because the transmit electrode  103  is coupled to the receive electrode  203  through the power transmission medium  50  whose electric conductivity is greater than the electric conductivity of the air, the equivalent coupling capacitance between the transmit electrode  103  and the receive electrode  203  can be increased, thereby effectively increasing a wireless charging transmission distance and improving flexibility of wireless charging. 
       FIG. 10  is a schematic structural diagram of a wireless charging system according to an embodiment of this application. Referring to  FIG. 10 , the system includes a transmit apparatus  10  and a receive apparatus  20 . 
     The transmit apparatus  10  includes an inverter circuit  102  and two transmit electrodes ( 103  and  104  shown in the figure). An input terminal of the inverter circuit  102  is connected to a direct-current power supply  101 , and two output terminals of the inverter circuit  102  are connected to the two transmit electrodes respectively. The two transmit electrodes are coupled through a power transmission medium  50 , where electric conductivity of the power transmission medium  50  is greater than electric conductivity of air. The receive apparatus  20  includes a receive coil  206  and a rectifier circuit  201 , an input terminal of the rectifier circuit  201  is connected to the receive coil  206 , and an output terminal of the rectifier circuit  201  is connected to a load  202 . 
     The inverter circuit  102  converts, into an alternating current, a direct current input by the direct-current power supply  101  and then outputs the alternating current to the two transmit electrodes, so that an alternating current is generated in the power transmission medium  50  between the two transmit electrodes. The alternating current in the power transmission medium  50  excites a magnetic field. The receive coil  206  generates an alternating current under the action of the magnetic field and transmits the generated alternating current to the rectifier circuit  201 ; and the rectifier circuit  201  converts the input alternating current into a direct current and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     It should be noted that the transmit apparatus  10  belongs to a wireless charging transmit device, and the receive apparatus  20  belongs to a wireless charging receive device. The wireless charging transmit device is configured to charge the wireless charging receive device. The wireless charging transmit device and the wireless charging receive device may be various types of electronic devices. That is, the transmit apparatus  10  and the receive apparatus  20  may be disposed in various types of electronic devices. For example, the transmit apparatus  10  and the receive apparatus  20  may be disposed in electronic devices such as a handheld electronic device, a wearable electronic device, a desktop electronic device, or a wall-mounted electronic device. These electronic devices may include a mobile phone, a smart watch, a smart ring, a mobile power pack, a computer, a monitoring device, a sensor, and the like. 
     In addition, the direct-current power supply  101  may provide power. For example, the direct-current power supply  101  may be an independently disposed power module, or may be a battery of the wireless charging transmit device, or the like. This is not limited in this embodiment of this application. The load  202  may receive the power. For example, the load  202  may be an LED lamp, a chip, a battery of the wireless charging receive device, or the like. This is not limited in this embodiment of this application. 
     In addition, the power transmission medium  50  may be metal or a non-metallic dielectric. For example, the power transmission medium  50  may be metal such as iron, aluminum, copper, an alloy material, a metal pipe, a metal housing of a device, a metal structure of a building, or a ground grid, or may be a non-metallic dielectric such as a human body, an animal, soil, earth, or seawater provided that electric conductivity of the metal or the non-metallic dielectric is greater than the electric conductivity of the air. 
     It should be noted that the inverter circuit  102  is configured to convert a direct current into an alternating current, and may also be referred to as a direct current-alternating current conversion circuit. The rectifier circuit  201  is configured to convert an alternating current into a direct current, and may also be referred to as an alternating current-direct current conversion circuit. The inverter circuit  102  converts, into the alternating current, the direct current input by the direct-current power supply  101  and then outputs the alternating current to the two transmit electrodes. In this case, voltage is generated between the two transmit electrodes. Because electric conductivity of the power transmission medium  50  between the two transmit electrodes is greater than electric conductivity of air, an alternating current is generated in the power transmission medium  50 , and the alternating current excites a magnetic field around the power transmission medium  50 . An alternating current is induced in the receive coil  206  under the action of the magnetic field. The rectifier circuit  201  may convert the alternating current in the receive coil  206  into a direct current and then outputs the direct current to the load  202 , so as to supply power to the load  202 , thereby implementing wireless charging for the receive apparatus  20  by the transmit apparatus  10 . 
     It should be noted that, in a possible implementation, the inverter circuit  102  may convert, into a high-frequency alternating current, the direct current input by the direct-current power supply  101  and then output the high-frequency alternating current to the two transmit electrodes. In this way, a high-frequency alternating current is generated in the power transmission medium  50  between the two transmit electrodes, and the high-frequency alternating current excites a high-frequency magnetic field. The receive coil  206  generates a high-frequency alternating current under the action of the high-frequency magnetic field; and the rectifier circuit  201  may convert the high-frequency alternating current into a direct current applicable to the load  202  and outputs the direct current to the load  202 , so as to supply power to the load  202 . 
     In addition, when the wireless charging system in this embodiment of this application is actually used, a ground point may not be disposed. That is, the wireless charging system may be an integral suspended structure, thereby improving flexibility of wireless charging. 
     It should be noted that, in this embodiment of this application, the two transmit electrodes in the transmit apparatus  10  may be coupled through the power transmission medium  50  whose electric conductivity is greater than the electric conductivity of the air; and in this way, an alternating current may be generated in the power transmission medium  50 , and the alternating current can excite the magnetic field. The alternating current is generated in the receive coil  206  of the receive apparatus  20  through electromagnetic induction, to implement wireless charging, thereby improving flexibility of wireless charging. 
     Further, referring to  FIG. 11 , the transmit apparatus  10  may further include a first compensation circuit  105 , the first compensation circuit  105  is connected between the inverter circuit  102  and the two transmit electrodes, and is configured to compensate for capacitive reactance between the two transmit electrodes. Further, referring to  FIG. 11 , the receive apparatus  20  may further include a second compensation circuit  205 , the second compensation circuit  205  is connected between the receive coil  206  and the rectifier circuit  201 , and is configured to compensate for inductive reactance of the receive coil  206 . 
     It should be noted that two input terminals of the first compensation circuit  105  are connected to two output terminals of the inverter circuit  102  respectively, and the two output terminals of the first compensation circuit  105  are connected to the two transmit electrodes respectively. Two input terminals of the second compensation circuit  205  are connected to the receive coil  206 , and the two output terminals of the second compensation circuit  205  are connected to the two input terminals of the rectifier circuit  201  respectively. The first compensation circuit  105  can reduce a reactive power loss in the transmit apparatus  10 , and the second compensation circuit  205  can reduce a reactive power loss in the receive apparatus  20 , thereby improving power transmission efficiency. 
     In addition, the receive coil  206  may be formed by winding a conducting wire such as a copper wire or a litz wire. In addition, a magnetic conductive plate may be placed below the receive coil  206 . The magnetic conductive plate has a magnetic conductive function, and can increase magnetic flux received by the receive coil  206 . The magnetic conductive plate may be made of at least one magnetic material, such as ferrite, amorphous, or nano-crystal. This is not limited in this embodiment of this application. The second compensation circuit  205  may be implemented by connecting a single capacitor or a plurality of capacitors to an inductor in series or in parallel. 
     It should be noted that, for either of the two transmit electrodes, such as the transmit electrode  103  or the transmit electrode  104 , the transmit electrode may come into direct contact with the power transmission medium  50 . Alternatively, the transmit electrode may not come into contact with the power transmission medium  50 . That is, there may be some distance between the transmit electrode and the power transmission medium  50 . Specifically, the distance between the transmit electrode and the power transmission medium  50  may be greater than 0 and less than a reference distance, and the reference distance may be preset. When the transmit electrode does not come into contact with the power transmission medium  50 , there may be another object between the transmit electrode and the power transmission medium  50 . For example, there may be an insulating material between the transmit electrode and the power transmission medium  50 . This is not limited in this embodiment of this application. 
     In other words, at least one transmit electrode of the two transmit electrodes may come into contact with the power transmission medium  50 ; or a distance between at least one transmit electrode of the two transmit electrodes and the power transmission medium  50  may be greater than 0 and less than a reference distance; or one transmit electrode  103  in the two transmit electrodes may come into contact with the power transmission medium  50 , and a distance between the other transmit electrode  104  and the power transmission medium  50  may be greater than 0 and less than the reference distance. 
     Both the transmit electrode  103  and the transmit electrode  104  may be made of metal such as iron, aluminum, copper, or alloy. In actual application, at least one transmit electrode of the two transmit electrodes may be an independently disposed component. Alternatively, at least one transmit electrode of the two transmit electrodes may be at least a portion of a metal structural part of the wireless charging transmit device. In this case, the at least one transmit electrode may come into direct contact with the power transmission medium  50 . Certainly, the at least one transmit electrode may alternatively not come into contact with the power transmission medium  50 , and the metal structural part may be a metal frame, a metal housing, or the like. Alternatively, at least one transmit electrode of the two transmit electrodes may be located on an inner side of a housing of the wireless charging transmit device. In this case, the housing of the wireless charging transmit device is located between the at least one transmit electrode and the power transmission medium  50 . The housing may be made of an insulating material, metal, or the like. Alternatively, the transmit electrode  103  in the two transmit electrodes may be at least a portion of the metal structural part of the wireless charging transmit device, and the other transmit electrode  104  may be located on an inner side of the housing of the wireless charging transmit device. 
     In this embodiment of this application, the wireless charging system includes the transmit apparatus  10  and the receive apparatus  20 . The transmit apparatus  10  includes the inverter circuit  102  and the two transmit electrodes. The receive apparatus  20  includes the receive coil  206  and the rectifier circuit  201 . The inverter circuit  102  converts, into an alternating current, a direct current input by the direct-current power supply  101  and then outputs the alternating current to the two transmit electrodes. Because the two transmit electrodes are coupled through the power transmission medium  50  whose electric conductivity is greater than the electric conductivity of the air; and in this way, an alternating current is generated in the power transmission medium  50  between the two transmit electrodes, and the alternating current in the power transmission medium  50  excites the magnetic field. The receive coil  206  generates an alternating current under the action of the magnetic field, and transmits the generated alternating current to the rectifier circuit  201 . The rectifier circuit  201  converts the input alternating current into a direct current and then outputs the direct current to the load  202 , so as to supply power to the load  202 , thereby implementing wireless charging for the receive apparatus  20  by the transmit apparatus  10 , thereby improving flexibility of wireless charging. 
     For ease of understanding, the foregoing wireless charging system is described by using an example with reference to a specific application scenario. 
     A first possible application scenario is as follows: 
       FIG. 12  and  FIG. 13  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a handheld mobile phone  60  is used to wirelessly charge a smart watch  61  worn on a wrist. 
       FIG. 12  is a schematic diagram of wireless charging. As shown in  FIG. 12 , the mobile phone  60  is a transmit apparatus  10 , and may include an internal circuit  601  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  601  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smart watch  61  is a receive apparatus  20 , and may include an internal circuit  611  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  611  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When a user  62  holds the mobile phone  60  and wears the smart watch  61  on the wrist, the transmit electrode  103  and the receive electrode  203  are coupled through a body of the user  62 , to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
       FIG. 13  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 13 , the transmit electrode  103  in the mobile phone  60  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on a surface of the mobile phone  60 , corresponding to a contact location between the mobile phone  60  and a palm. To increase a coupling degree between the transmit electrode  103  and the palm, a directly-opposite area between the transmit electrode  103  and the palm can be maximized by setting an area and a shape of the transmit electrode  103 . The transmit electrode  103  may not need to come into direct contact with the body of the user  62 . To be specific, an insulating material may be added between the transmit electrode  103  and the body of the user  62 , or the transmit electrode  103  may be spaced some distance apart from the body of the user  62 . The transmit electrode  104  and the transmit electrode  103  in the mobile phone  60  may be made of a same material or different materials, and the transmit electrode  104  may be disposed inside or on the surface of the mobile phone  60 . To enhance a coupling degree between the transmit electrode  104  and the receive electrode  204 , an area of the transmit electrode  104  should be maximized, and a directly-opposite area between the transmit electrode  104  and the transmit electrode  103  should be reduced, so as to reduce a coupling degree between the transmit electrode  104  and the transmit electrode  103 . 
     The receive electrode  203  in the smart watch  61  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on a bottom cover surface of the smart watch  61 , corresponding to a contact location between the smart watch  61  and the wrist. Certainly, the receive electrode  203  may alternatively be directly at least a portion of a metal frame or metal bottom cover of the smart watch  61  that comes into contact with the wrist. To increase a coupling degree between the receive electrode  203  and the wrist, a directly-opposite area between the receive electrode  203  and the wrist can be maximized by setting an area and a shape of the receive electrode  203 . The receive electrode  203  may not need to come into direct contact with the body of the user  62 . To be specific, an insulating material may be added between the receive electrode  203  and the body of the user  62 , or the receive electrode  203  may be spaced some distance apart from the body of the user  62 . The receive electrode  204  and the receive electrode  203  in the smart watch  61  may be made of a same material or different materials, and the receive electrode  204  may be disposed inside or on the surface of the smart watch  61 . Certainly, the receive electrode  204  may alternatively be directly at least a portion of the metal watch face. To enhance a coupling degree between the receive electrode  204  and the transmit electrode  104 , an area of the receive electrode  204  should be maximized, and a directly-opposite area between the receive electrode  204  and the receive electrode  203  should be reduced, so as to reduce a coupling degree between the receive electrode  204  and the receive electrode  203 . 
     A second possible application scenario is as follows: 
       FIG. 14  and  FIG. 15  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a handheld mobile phone  60  is used to wirelessly charge a smart ring  63  worn on a finger. 
       FIG. 14  is a schematic diagram of wireless charging. As shown in  FIG. 14 , the mobile phone  60  is a transmit apparatus  10 , and may include an internal circuit  601  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  601  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smart ring  63  is a receive apparatus  20 , and may include an internal circuit  631  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  631  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When a user  62  holds the mobile phone  60  and wears the smart ring  63  on the finger, the transmit electrode  103  and the receive electrode  203  establish coupling through a body of the user  62 , to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
       FIG. 15  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 15 , a structure of a mobile phone  60  is similar to the structure of the mobile phone  60  in the foregoing first possible application scenario. Details are not described again in this embodiment of this application. 
     A receive electrode  203  in a smart ring  63  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on an inner surface of the smart ring  63 , corresponding to a contact location between the smart ring  63  and a finger. To increase a coupling degree between the receive electrode  203  and the finger, a directly-opposite area between the receive electrode  203  and the finger can be maximized by setting an area and a shape of the receive electrode  203 . The receive electrode  203  may not need to come into direct contact with the body of the user  62 . To be specific, an insulating material may be added between the receive electrode  203  and the body of the user  62 , or the receive electrode  203  may be spaced some distance apart from the body of the user  62 . The receive electrode  204  and the receive electrode  203  in the smart ring  63  may be made of a same material or different materials, and the receive electrode  204  may be disposed inside or on an outer surface of the smart ring  63 . To enhance a coupling degree between the receive electrode  204  and the transmit electrode  104 , an area of the receive electrode  204  should be maximized, and a directly-opposite area between the receive electrode  204  and the receive electrode  203  should be reduced, so as to reduce a coupling degree between the receive electrode  204  and the receive electrode  203 . 
     A third possible application scenario is as follows: 
       FIG. 16  and  FIG. 17  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a handheld mobile phone  60  is used to wirelessly charge a smart watch  61  worn on a wrist. 
     A difference from the foregoing first possible application scenario lies in that a thumb and an index finger of the other hand come in contact with the transmit electrode  104  and the receive electrode  204  respectively, thereby increasing a coupling degree between the transmit apparatus  10  and the receive apparatus  20 . 
       FIG. 16  is a schematic diagram of wireless charging. As shown in  FIG. 16 , the mobile phone  60  is a transmit apparatus  10 , and may include an internal circuit  601  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  601  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smart watch  61  is a receive apparatus  20 , and may include an internal circuit  611  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  611  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When a user  62  holds the mobile phone  60  and wears the smart watch  61  on the wrist, the transmit electrode  103  and the receive electrode  203  are coupled through a body of the user  62 , to form a power transmission path. The transmit electrode  104  comes in contact with the receive electrode  204  through the thumb and index finger of the other hand, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
       FIG. 17  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 17 , the transmit electrode  103  in the mobile phone  60  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on a surface of the mobile phone  60 , corresponding to a contact location between the mobile phone  60  and a palm. To increase a coupling degree between the transmit electrode  103  and the palm, a directly-opposite area between the transmit electrode  103  and the palm can be maximized by setting an area and a shape of the transmit electrode  103 . The transmit electrode  103  may not need to come into direct contact with the body of the user  62 . To be specific, an insulating material may be added between the transmit electrode  103  and the body of the user  62 , or the transmit electrode  103  may be spaced some distance apart from the body of the user  62 . The transmit electrode  104  and the transmit electrode  103  in the mobile phone  60  may be made of a same material or different materials, and the transmit electrode  104  may be disposed inside or on the surface of the mobile phone  60 . A location of the transmit electrode  104  should facilitate an operation by the index finger of the other hand. To increase a coupling degree between the transmit electrode  104  and the index finger, a directly-opposite area between the transmit electrode  104  and the index finger can be maximized by setting an area and a shape of the transmit electrode  104 . The transmit electrode  104  may not need to come into direct contact with the index finger of the user  62 . To be specific, an insulating material may be added between the transmit electrode  104  and the index finger of the user  62 , or the transmit electrode  104  may be spaced some distance apart from the index finger of the user  62 . 
     The receive electrode  203  in the smart watch  61  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on a bottom cover surface of the smart watch  61 , corresponding to a contact location between the smart watch  61  and the wrist. Certainly, the receive electrode  203  may alternatively be directly at least a portion of a metal frame or a metal bottom cover of the smart watch  61  that comes into contact with the wrist. To increase a coupling degree between the receive electrode  203  and the wrist, a directly-opposite area between the receive electrode  203  and the wrist can be maximized by setting an area and a shape of the receive electrode  203 . The receive electrode  203  may not need to come into direct contact with the body of the user  62 . To be specific, an insulating material may be added between the receive electrode  203  and the body of the user  62 , or the receive electrode  203  may be spaced some distance apart from the body of the user  62 . The receive electrode  204  and the receive electrode  203  in the smart watch  61  may be made of a same material or different materials, and the receive electrode  204  may be disposed at a watch face or a watch band of the smart watch  61 . A location of the receive electrode  204  should facilitate an operation by the thumb of the other hand. To increase a coupling degree between the receive electrode  204  and the thumb, a directly-opposite area between the receive electrode  204  and the thumb can be increased by setting an area and a shape of the receive electrode  204 . The receive electrode  204  may not need to come into direct contact with the thumb of the user  62 . To be specific, an insulating material may be added between the receive electrode  204  and the thumb of the user  62 , or the receive electrode  204  may be spaced some distance apart from the thumb of the user  62 . 
     It should be noted that when the transmit electrode  104  comes in contact with the receive electrode  204  through other parts of a user body to improve the coupling degree between the transmit apparatus  10  and the receive apparatus  20 , the other parts of the user body may not be limited to the thumb or the index finger of the other hand of the body, or may be other two fingers (such as the thumb and a little finger) or other parts of the body (such as the palm and a middle finger). This is not limited in this embodiment of this application. 
     A fourth possible application scenario is as follows: 
       FIG. 18  and  FIG. 19  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a handheld mobile phone  60  is used to wirelessly charge a handheld electronic device  64  on the other side of a body. 
       FIG. 18  is a schematic diagram of wireless charging. As shown in  FIG. 18 , the mobile phone  60  is a transmit apparatus  10 , and may include an internal circuit  601  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  601  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The handheld electronic device  64  on the other side of the body is a receive apparatus  20 , and may include an internal circuit  641  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  641  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When a user  62  holds the mobile phone  60  and holds the electronic device  64  on the other side of the body, the transmit electrode  103  and the receive electrode  203  are coupled through the body of the user  62 , to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the ground  65  or a grounding metal object, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
       FIG. 19  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 19 , structures of a mobile phone  60  and an electronic device  64  are similar to the structure of the mobile phone  60  in the foregoing several possible application scenarios. Details are not described again in this embodiment of this application. 
     A fifth possible application scenario is as follows: 
       FIG. 20  and  FIG. 21  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a handheld grounding mobile phone  60  is used to wirelessly charge a handheld electronic device  64  on the other side of a body. 
       FIG. 20  is a schematic diagram of wireless charging.  FIG. 21  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 20  and  FIG. 21 , the mobile phone  60  and the electronic device  64  have structures, principles, and working scenarios similar to those of the mobile phone  60  and the electronic device  64  in the fourth possible application scenario. A difference lies in that grounding of the mobile phone  60  is implemented by using a charging cable or a data line, to increase a coupling degree between a transmit electrode  104  and the ground  65  or a grounding metal object, thereby further improving efficiency of wireless power transmission. 
     A sixth possible application scenario is as follows: 
       FIG. 22  and  FIG. 23  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 10 , which is specifically an application scenario in which a handheld mobile phone  60  is used to wirelessly charge a smart ring  63  worn on a finger. 
       FIG. 22  is a schematic diagram of wireless charging. As shown in  FIG. 22 , the mobile phone  60  is a transmit apparatus  10 , and may include an internal circuit  601  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  601  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smart ring  63  is a receive apparatus  20 , and may include an internal circuit  631  of the receive apparatus and a receive coil  206 . The internal circuit  631  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When a user  62  holds the mobile phone  60  and wears the smart ring  63  on a finger, a palm comes in contact with the transmit electrode  103  and a finger comes in contact with the transmit electrode  104 . The finger and the palm are connected to the transmit electrode  103  and the transmit electrode  104  respectively, to form a current path. A current in the finger excites a magnetic field. The receive coil  206  in the smart ring  63  generates an alternating current under the action of the magnetic field, so as to implement wireless power transmission. 
       FIG. 23  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 23 , a structure of a mobile phone  60  is similar to the structure of the mobile phone  60  in the foregoing several possible application scenarios. A difference lies in that locations of a transmit electrode  103  and a transmit electrode  104  in the mobile phone  60  should facilitate an operation of the palm and the finger wearing the smart ring  63  to come in contact with the transmit electrode  103  and the transmit electrode  104  respectively. 
     The receive coil  206  in the smart ring  63  may be at least a portion of a ring of the smart ring  63 , and the receive coil  206  may be formed by winding a conducting wire such as a copper wire or a litz wire. 
     A seventh possible application scenario is as follows: 
       FIG. 24  and  FIG. 25  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 10 , which is specifically an application scenario in which a handheld mobile phone  60  is used to wirelessly charge a smart watch  61  worn on a wrist. 
       FIG. 24  is a schematic diagram of wireless charging. As shown in  FIG. 24 , the mobile phone  60  is a transmit apparatus  10 , and may include an internal circuit  601  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  601  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smart watch  61  is a receive apparatus  20 , and may include an internal circuit  611  of the receive apparatus and a receive coil  206 . The internal circuit  611  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When a user  62  holds the mobile phone  60  and wears the smart watch  61  on the wrist, an index finger of the other hand comes in contact with the transmit electrode  103  and a thumb of the other hand comes in contact with an arm on a side of the smart watch  61  away from the mobile phone  60 . The transmit electrode  103  and the transmit electrode  104  form a current path through a body of the user  62 . A current in the arm excites a magnetic field. The receive coil  206  in the smart watch  61  generates an alternating current under the action of the magnetic field, so as to implement wireless power transmission. 
       FIG. 25  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 25 , a structure of a mobile phone  60  is similar to the structure of the mobile phone  60  in the foregoing several possible application scenarios. A difference lies in that a location of a transmit electrode  103  in the mobile phone  60  should facilitate an operation by an index finger of the other hand. 
     The receive coil  206  in the smart watch  61  may be at least a portion of a watch band of the smart watch  61 , and the receive coil  206  may be formed by winding a conducting wire such as a copper wire or a litz wire. 
     It should be noted that the sixth possible application scenario can be combined with the seventh possible application scenario.  FIG. 26  is a schematic diagram of wireless charging by combining the sixth possible application scenario and the seventh possible application scenario. 
     An eighth possible application scenario is as follows: 
       FIG. 27  and  FIG. 28  are schematic diagrams of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a power transmit apparatus  70  hung on a roof is used to wirelessly charge a smoke sensor  71  or monitor  73  hung on the roof 
       FIG. 27  is a schematic diagram of wireless charging. As shown in  FIG. 27 , the power transmit apparatus  70  is a transmit apparatus  10 , and may include an internal circuit  701  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  701  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smoke sensor  71  is a receive apparatus  20 , and may include an internal circuit  711  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  711  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When the power transmit apparatus  70  and the smoke sensor  71  are hung on a roof  72  with a steel structure (such as a steel bar or a steel frame), the transmit electrode  103  and the receive electrode  203  are coupled through the steel structure of the roof  72 , to form an energy transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
       FIG. 28  is a schematic diagram of an internal structure of an apparatus. As shown in  FIG. 28 , the transmit electrode  103  in the power transmit apparatus  70  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on a surface of the power transmit apparatus  70 , corresponding to a contact part between the power transmit apparatus  70  and the roof  72 . To increase a coupling degree between the transmit electrode  103  and the steel structure of the roof  72 , a directly-opposite area between the transmit electrode  103  and the steel structure of the roof  72  can be maximized by setting an area and a shape of the transmit electrode  103 . The transmit electrode  103  may not need to be directly connected electrically to the steel structure of the roof  72 . To be specific, an insulating material may be added between the transmit electrode  103  and the steel structure of the roof  72 , or the transmit electrode  103  may be spaced some distance apart from the steel structure of the roof  72 . The transmit electrode  104  and the transmit electrode  103  in the power transmit apparatus  70  may be made of a same material or different materials, and the transmit electrode  104  may be disposed inside or on a surface of the power transmit apparatus  70  on a side away from the roof  72 . To enhance a coupling degree between the transmit electrode  104  and the receive electrode  204 , an area of the transmit electrode  104  should be maximized, and a directly-opposite area between the transmit electrode  104  and the transmit electrode  103  should be reduced, so as to reduce a coupling degree between the transmit electrode  104  and the transmit electrode  103 . 
     The receive electrode  203  in the smoke sensor  71  may be metal foil, metal mesh, or the like, and is disposed at a location, inside or on a surface of the power transmit apparatus  70 , corresponding to a contact part between the smoke sensor  71  and the roof  72 . To increase a coupling degree between the receive electrode  203  and the steel structure of the roof  72 , a directly-opposite area between the receive electrode  203  and the steel structure of the roof  72  can be maximized by setting an area and a shape of the receive electrode  203 . The receive electrode  203  may not need to be directly connected electrically to the steel structure of the roof  72 . To be specific, an insulating material may be added between the receive electrode  203  and the steel structure of the roof  72 , or the receive electrode  203  may be spaced some distance apart from the steel structure of the roof  72 . The receive electrode  204  and the receive electrode  203  in the smoke sensor  71  may be made of a same material or different materials, and the receive electrode  204  may be disposed inside or on a surface of the smoke sensor  71  on a side away from the roof  72 . To enhance a coupling degree between the receive electrode  204  and the transmit electrode  104 , an area of the receive electrode  204  should be maximized, and a directly-opposite area between the receive electrode  204  and the receive electrode  203  should be reduced, so as to reduce a coupling degree between the receive electrode  204  and the receive electrode  203 . 
     It should be noted that a principle and a structure for wirelessly charging the monitor  73  hung on the roof by the power transmit apparatus  70  are similar to the principle and the structure for wirelessly charging the smoke sensor  71  by the power transmit apparatus  70 . Details are not described again in this embodiment of this application. 
     A ninth possible application scenario is as follows: 
       FIG. 29  is a schematic diagram of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a power transmit apparatus  70  placed on a desk is used to wirelessly charge an electronic device  74  placed on a desk. 
       FIG. 29  is a schematic diagram of wireless charging. As shown in  FIG. 29 , the power transmit apparatus  70  is a transmit apparatus  10 , and may include an internal circuit  701  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  701  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The electronic device  74  is a receive apparatus  20 , and may include an internal circuit  741  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  741  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     In a possible case, a top surface of a desk may be covered with a metal layer  75 . When the power transmit apparatus  70  and the electronic device  74  are placed on the desk covered with the metal layer  75 , the transmit electrode  103  and the receive electrode  203  are coupled through the metal layer  75 , to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. It should be noted that the power transmit apparatus  70  may alternatively be disposed in a portable computer, so as to wirelessly charge the electronic device  74  on the desk by using the portable computer. 
     In another possible case, an area of a transmit electrode  103  of the power transmit apparatus  70  may be increased, and then the electronic device  74  on the desk is directly placed on the transmit electrode  103  of the power transmit apparatus  70 . In this case, the top surface of the desk does not need to be covered with the metal layer  75 . Instead, the transmit electrode  103  may also be used as a first transmission medium  30 , to directly implement coupling of the transmit electrode  103  and the receive electrode  203 . In this case, the transmit electrode  103  and the receive electrode  203  are directly coupled, to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
     A tenth possible application scenario is as follows: 
       FIG. 30  is a schematic diagram of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a charging pad  80  is used to wirelessly charge an electronic device  74  placed on a desk. 
       FIG. 30  is a schematic diagram of wireless charging. As shown in  FIG. 30 , the charging pad  80  is a transmit apparatus  10 , and may include an internal circuit  801  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  801  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The electronic device  74  is a receive apparatus  20 , and may include an internal circuit  741  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  741  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When the electronic device  74  is placed on the transmit electrode  103  of the charging pad  80 , compared with that in  FIG. 1 , the transmit electrode  103  of the charging pad  80  with a relatively large area can also be used as a first transmission medium  30 . When there is an insulating material between the transmit electrode  103  and the receive electrode  203 , coupling is implemented through air, or when there is no insulating material between the transmit electrode  103  and the receive electrode  203 , the transmit electrode  103  and the receive electrode  203  are directly connected electrically, to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
     The transmit electrode  104  and the transmit electrode  103  may be metal foil, metal mesh, or the like. The transmit electrode  104  and the transmit electrode  103  may be stacked, to obtain a largest effective charging area. The transmit electrode  104  and the transmit electrode  103  may alternatively be placed in parallel without overlapping, to reduce a directly-opposite area between the transmit electrode  104  and the transmit electrode  103 , thereby reducing a coupling degree between the transmit electrode  104  and the transmit electrode  103 . 
     An eleventh possible application scenario is as follows: 
       FIG. 31  is a schematic diagram of an application scenario of the wireless charging system provided in the embodiment of  FIG. 1 , which is specifically an application scenario in which a mobile phone  90  is used to wirelessly charge a smart watch  76 . 
       FIG. 31  is a schematic diagram of wireless charging. As shown in  FIG. 31 , the mobile phone  90  is a transmit apparatus  10 , and may include an internal circuit  901  of the transmit apparatus, a transmit electrode  103 , and a transmit electrode  104 . The internal circuit  901  of the transmit apparatus may include a direct-current power supply  101  and an inverter circuit  102 , and may further include a first compensation circuit  105 . The smart watch  76  is a receive apparatus  20 , and may include an internal circuit  761  of the receive apparatus, a receive electrode  203 , and a receive electrode  204 . The internal circuit  761  of the receive apparatus may include a rectifier circuit  201  and a load  202 , and may further include a second compensation circuit  205 . 
     When the smart watch  76  is placed on the transmit electrode  103  of the mobile phone  90 , compared with that in  FIG. 1 , the transmit electrode  103  of the mobile phone  90  can also be used as a first transmission medium  30 . When there is an insulating material between the transmit electrode  103  and the receive electrode  203 , coupling is implemented through air, or when there is no insulating material between the transmit electrode  103  and the receive electrode  203 , the transmit electrode  103  and the receive electrode  203  are directly connected electrically, to form a power transmission path. The transmit electrode  104  and the receive electrode  204  are coupled through the air, to form another power transmission path. The two power transmission paths form a power loop, so as to implement wireless power transmission. 
     It should be noted that the smart watch  76  may be placed on the transmit electrode  103  of the mobile phone  90 , or may be placed on the transmit electrode  104  of the mobile phone  90 , thereby implementing a relatively large effective charging area. 
     The transmit electrode  104  and the transmit electrode  103  may be metal foil, metal mesh, or the like. The transmit electrode  104  and the transmit electrode  103  may be stacked, to obtain a largest effective charging area. The transmit electrode  104  and the transmit electrode  103  may alternatively be placed in parallel without overlapping, to reduce a directly-opposite area between the transmit electrode  104  and the transmit electrode  103 , thereby reducing a coupling degree between the transmit electrode  104  and the transmit electrode  103 . 
     It should be noted that in the embodiments of this application, the foregoing eleven possible application scenarios are used only as examples for description. In actual application, the wireless charging system provided in the embodiments of this application may also be applied to other scenarios requiring wireless charging, thereby implementing good spatial flexibility for wireless charging. 
     The foregoing descriptions are merely embodiments of this application, but are not intended to limit this application. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of this application should fall within the protection scope of this application.