Patent Publication Number: US-2022224225-A1

Title: Converter and on-board charger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 202110352122.7, filed on Mar. 31, 2021, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     This application relates to the field of power electronics technologies, and in particular, to a converter and an on-board charger. 
     BACKGROUND 
     With development of technologies in the field of new energy, application of new energy vehicles, for example, electric vehicles, is increasingly popular. Because infrastructure for fast direct current charging is incomplete at present, on-board chargers (OBC) are usually configured for new energy vehicles for charging convenience, so that users can charge power batteries through household alternating current power sockets. 
     Because users have increasingly high requirements on a driving mileage of new energy vehicles, capacities of power batteries accordingly become larger, and a higher charging power class of the power batteries is also required. Therefore, an OBC generally has relatively high charging power, to implement fast charging. In addition, the OBC may be further compatible with an inverter function, to implement a vehicle-to-vehicle (V2V) discharging function and a vehicle-to-load (V2L) discharging function. For example, during electricity consumption off-peak hours of a grid, power supply of an on-board storage battery may be implemented by using a charging function, and during electricity consumption peak hours of the grid, electric energy stored in the on-board storage battery may be fed back to the grid by using a discharging function, thereby improving utilization of electric energy of the grid. 
     A surge impact is one of main causes of a failure of an electronic device in the OBC. In surge impacts caused by many factors, surge impacts caused by lightning and a system switching operation have a great impact on operation and life of the electronic device. In this case, a protection device, for example, a surge protection device (SPD) needs to be configured in the OBC, to mutually cooperate with a conventional lightning protection network or an air-terminal system to further protect the OBC. A main function of the SPD is to inhabit an overvoltage and an overcurrent that are on a circuit and that are caused by a surge impact, and limit a voltage and a current of the circuit to a low level, thereby ensuring normal operation of the electronic device on the circuit and implementing protection. 
     Currently, an SPD including diodes is mainly used in an OBC. When surge impact energy is input to the OBC, this part of energy directly flows to a direct current bus through the diodes and is consumed. However, for an OBC for bidirectional charging, when an inverter function of the OBC is enabled, if an alternating current terminal of the OBC is connected to a capacitive load, and when a discharging cycle of the capacitive load is less than a cycle of an alternating current, energy of the capacitive load constitutes a short-circuit path through the OBC. Consequently, electronic devices inside the OBC are at risk. 
     SUMMARY 
     This application provides a converter and an on-board charger, to avoid a short-circuit fault of the converter while inhibiting a surge impact. 
     According to a first aspect, an embodiment of this application provides a converter. The converter may include a power factor correction circuit (PFC circuit), a surge protection circuit, and a switch circuit. 
     The PFC circuit is configured to: convert a first component of a first alternating current received by an alternating current terminal of the PFC circuit into a first direct current, and output the first direct current through a direct current terminal of the PFC circuit, where an absolute value of an instantaneous voltage value of the first component is less than or equal to a preset threshold; and convert a second direct current received by the direct current terminal of the PFC circuit into a second alternating current, and output the second alternating current through the alternating current terminal of the PFC circuit. An alternating current terminal of the surge protection circuit is connected to the alternating current terminal of the PFC circuit, a direct current terminal of the surge protection circuit is connected to a first terminal of the switch circuit, and the surge protection circuit is configured to: convert a second component of the first alternating current into a third direct current, and output the third direct current through the direct current terminal of the surge protection circuit, where an absolute value of an instantaneous voltage value of the second component is greater than the preset threshold. A second terminal of the switch circuit is connected to the direct current terminal of the PFC circuit, and the switch circuit is configured to be turned on when the alternating current terminal of the PFC circuit outputs the first direct current, and to be turned off when the alternating current terminal of the PFC circuit outputs the second alternating current. 
     A voltage value of the first direct current may be equal to a voltage value of the third direct current. Specifically, both the direct current terminal of the PFC circuit and the alternating current terminal of the surge protection circuit may be connected to a charged device (for example, an on-board storage battery), the direct current terminal of the PFC circuit outputs the first direct current, and the direct current terminal of the surge protection circuit outputs the third direct current, to supply power to the charged device. A rated voltage of a power consumption device may be the voltage value of the first direct current. 
     Further, a positive direction and a negative direction of the first direct current may be the same as those of the third direct current. That a positive direction and a negative direction of the first direct current are the same as those of the third direct current may specifically mean that if both the direct current terminal of the PFC circuit and the direct current terminal of the surge protection circuit are connected in parallel to the charged device, in the direct current terminal of the PFC circuit, one terminal that outputs a high electrical level is connected to a positive electrode of the charged device, one terminal that outputs a low electrical level is connected to a negative electrode of the charged device, and a difference between voltages of the high electrical level and the low electrical level is equal to the voltage value of the first direct current; and similarly, in the direct current terminal of the surge protection circuit, one terminal that outputs a high electrical level is connected to the positive electrode of the charged device, one terminal that outputs a low electrical level is connected to the negative electrode of the charged device, and a difference between voltages of the high electrical level and the low electrical level is equal to the voltage value of the third direct current. 
     In the converter provided in the first aspect, when the converter is configured to charge the charged device (for example, the on-board storage battery), if there is no surge impact exists in a circuit, the PFC circuit converts the first alternating current received by the alternating current terminal of the PFC circuit into the first direct current; or if there is a surge impact exists in the circuit, the PFC circuit converts a part, with an instantaneous voltage value less than or equal to the preset threshold, in the first alternating current into the first direct current that is available to a back-end device, and the surge protection circuit converts a part (surge impact energy), with an instantaneous voltage value less than or equal to the preset threshold, in the first alternating current into the third direct current that is available to the back-end device for consumption by the back-end device. This effectively avoids an impact of the surge impact energy on the PFC circuit. In addition, because the switch circuit is connected to a rear terminal of the surge protection circuit, when an inverter function of the converter is enabled, the switch circuit is turned off, and a closed path cannot be formed between a capacitive load connected to the alternating current terminal of the PFC circuit and the surge protection circuit, thereby effectively avoiding a short-circuit failure of the converter. 
     In a possible implementation, the converter provided in this embodiment of this application may further include a controller. 
     The controller is configured to: control the PFC circuit to convert the first component into the first direct current, and convert the second direct current into the second alternating current. 
     According to the solution, under control of the controller, power may be supplied to the charged device through the converter. 
     In a possible implementation, the controller is further configured to control states of the switch circuit. The states include turn-off and turn-on. 
     According to the solution, under control of the controller, the third direct current output by the surge protection circuit may be supplied to the charged device through the switch circuit. 
     To enable the converter to convert different types of alternating currents, in this embodiment of this application, the PFC circuit, the switch circuit, and the surge protection circuit may have different structures. Possible implementations of the PFC circuit, the switch circuit, and the surge protection circuit are as follows. 
     In a possible implementation, the alternating current terminal of the PFC circuit is a three-phase alternating current terminal, and the PFC circuit includes a first bidirectional converter, a second bidirectional converter, and a third bidirectional converter. 
     An alternating current terminal of the first bidirectional converter is a first alternating current terminal of the three-phase alternating current terminal, an alternating current terminal of the second bidirectional converter is a second alternating current terminal of the three-phase alternating current terminal, and an alternating current terminal of the third bidirectional converter is a third alternating current terminal of the three-phase alternating current terminal. The first alternating current terminal, the second alternating current terminal, and the third alternating current terminal constitute the three-phase alternating current terminal. A direct current terminal of the first bidirectional converter, a direct current terminal of the second bidirectional converter, and a direct current terminal of the third bidirectional converter constitute the direct current terminal of the PFC circuit, and the direct current terminal of the PFC circuit is connected to a first direct current bus. 
     According to the solution, when the converter converts a three-phase alternating current, the first bidirectional converter, the second bidirectional converter, and the third bidirectional converter each constitute a single-phase converter, to convert one phase of alternating current in the three-phase alternating current received by the alternating current terminal, so as to implement three-phase rectification. 
     In a possible design, the first bidirectional converter includes: a first inductor, where a first terminal of the first inductor is connected to the first alternating current terminal; a first bidirectional switch, where the first bidirectional switch is connected between a second terminal of the first inductor and a positive terminal of the first direct current bus; and a second bidirectional switch, where the second bidirectional switch is connected between the second terminal of the first inductor and a negative terminal of the first direct current bus. The second bidirectional converter includes: a second inductor, where a first terminal of the second inductor is connected to the second alternating current terminal; a third bidirectional switch, where the third bidirectional switch is connected between a second terminal of the second inductor and the positive terminal of the first direct current bus; and a fourth bidirectional switch, where the fourth bidirectional switch is connected between the second terminal of the second inductor and the negative terminal of the first direct current bus. The third bidirectional converter includes: a third inductor, where a first terminal of the third inductor is connected to the third alternating current terminal; a fifth bidirectional switch, where the fifth bidirectional switch is connected between a second terminal of the third inductor and the positive terminal of the first direct current bus; and a sixth bidirectional switch, where the sixth bidirectional switch is connected between the second terminal of the third inductor and the negative terminal of the first direct current bus. 
     In a possible design, the PFC circuit further includes a seventh bidirectional switch and an eighth bidirectional switch. 
     The seventh bidirectional switch is connected between the positive terminal of the first direct current bus and a first neutral line. The eighth bidirectional switch is connected between the negative terminal of the first direct current bus and the first neutral line. 
     In a possible implementation, the switch circuit includes a first unidirectional switch and a second unidirectional switch. 
     A first electrode of the first unidirectional switch is connected to the direct current terminal of the surge protection circuit, and a second electrode of the first unidirectional switch is connected to the positive terminal of the first direct current bus. A first electrode of the second unidirectional switch is connected to the negative terminal of the first direct current bus, and a second electrode of the second unidirectional switch is connected to the direct current terminal of the surge protection circuit. 
     In a possible implementation, the surge protection circuit includes a first unidirectional converter, a second unidirectional converter, and a third unidirectional converter. 
     An alternating current terminal of the first unidirectional converter is connected to the first alternating current terminal, an alternating current terminal of the second unidirectional converter is connected to the second alternating current terminal, and an alternating current terminal of the third unidirectional converter is connected to the third alternating current terminal. 
     The alternating current terminal of the first unidirectional converter, the alternating current terminal of the second unidirectional converter, and the alternating current terminal of the third unidirectional converter constitute the alternating current terminal of the surge protection circuit. A direct current terminal of the first unidirectional converter, a direct current terminal of the second unidirectional converter, and a direct current terminal of the third unidirectional converter constitute the direct current terminal of the surge protection circuit. 
     According to the solution, a surge voltage exists in an alternating current received by the converter, and the surge voltage in the received alternating current may be converted, by using the surge protection circuit, into a direct current that is available to the charged device. Specifically, the first unidirectional converter, the second unidirectional converter, and the third unidirectional converter each convert one phase of alternating current in the three-phase alternating current, to implement three-phase rectification. 
     In a possible implementation, the first unidirectional converter includes: a first diode, where the first diode is connected between the first alternating current terminal and the first electrode of the first unidirectional switch; and a second diode, where the second diode is connected between the first alternating current terminal and the second electrode of the second unidirectional switch. The second unidirectional converter includes: a third diode, where the third diode is connected between the second alternating current terminal and the first electrode of the first unidirectional switch; and a fourth diode, where the fourth diode is connected between the second alternating current terminal and the second electrode of the second unidirectional switch. The third unidirectional converter includes: a fifth diode, where the fifth diode is connected between the third alternating current terminal and the first electrode of the first unidirectional switch; and a sixth diode, where the sixth diode is connected between the third alternating current terminal and the second electrode of the second unidirectional switch. 
     In a possible implementation, the alternating current terminal of the PFC circuit is a single-phase alternating current terminal, and the PFC circuit includes a fourth bidirectional converter and a fifth bidirectional converter. 
     An alternating current terminal of the fourth bidirectional converter is a fourth alternating current terminal of the single-phase alternating current terminal, and an alternating current terminal of the fifth bidirectional converter is a fifth alternating current terminal of the single-phase alternating current terminal. The fourth alternating current terminal and the fifth alternating current terminal constitute the single-phase alternating current terminal. A direct current terminal of the fourth bidirectional converter and a direct current terminal of the fifth bidirectional converter constitute the direct current terminal of the PFC circuit, and the direct current terminal of the PFC circuit is connected to a second direct current bus. 
     According to the solution, the fourth bidirectional converter may be used to convert a positive half-cycle voltage of a received single-phase alternating current, and the fifth bidirectional converter may be used to convert a negative half-cycle voltage of the single-phase alternating current, so as to implement single-phase rectification. 
     In a possible implementation, the fourth bidirectional converter includes: a fourth inductor, where a first terminal of the fourth inductor is connected to the fourth alternating current terminal; a ninth bidirectional switch, where the ninth bidirectional switch is connected between a second terminal of the fourth inductor and a positive terminal of the second direct current bus; and a tenth bidirectional switch, where the tenth bidirectional switch is connected between the second terminal of the fourth inductor and a negative terminal of the second direct current bus. The fifth bidirectional converter includes: a fifth inductor, where a first terminal of the fifth inductor is connected to the fifth alternating current terminal; an eleventh bidirectional switch, where the eleventh bidirectional switch is connected between a second terminal of the fifth inductor and the positive terminal of the second direct current bus; and a twelfth bidirectional switch, where the twelfth bidirectional switch is connected between the second terminal of the fifth inductor and the negative terminal of the second direct current bus. 
     In a possible implementation, the fourth alternating current terminal is connected to the fifth alternating current terminal, and the PFC circuit further includes a thirteenth bidirectional switch and a fourteenth bidirectional switch. 
     The thirteenth bidirectional switch is connected between the positive terminal of the second direct current bus and a second neutral line. The fourteenth bidirectional switch is connected between the negative terminal of the second direct current bus and the second neutral line. 
     In a possible implementation, the switch circuit includes a third unidirectional switch and a fourth unidirectional switch. 
     A first electrode of the third unidirectional switch is connected to the direct current terminal of the surge protection circuit, and a second electrode of the third unidirectional switch is connected to the positive terminal of the second direct current bus. A first electrode of the fourth unidirectional switch is connected to the negative terminal of the second direct current bus, and a second electrode of the fourth unidirectional switch is connected to the direct current terminal of the surge protection circuit. 
     In a possible implementation, the surge protection circuit includes an H-bridge rectifier circuit including diodes. 
     An intermediate node of a first bridge arm of the H-bridge rectifier circuit is connected to the fourth alternating current terminal, an intermediate node of a second bridge arm of the H-bridge rectifier circuit is connected to the fifth alternating current terminal, both a first terminal of the first bridge arm and a first terminal of the second bridge arm are connected to the first electrode of the third unidirectional switch, and both a second terminal of the first bridge arm and a second terminal of the second bridge arm are connected to the second electrode of the fourth unidirectional switch. 
     According to a second aspect, an embodiment of this application provides an on-board charger. The on-board charger may include a direct current-to-direct current converter circuit (DC/DC converter circuit) and the converter provided in the first aspect and any possible design of the first aspect in the embodiments of this application. 
     The converter is configured to: receive a first alternating current, convert the first alternating current into a first direct current, and output the first direct current to the DC/DC converter circuit; and convert a second direct current output by the DC/DC converter circuit into a second alternating current, and output the second alternating current. The DC/DC converter circuit is connected to the converter, and the DC/DC converter circuit is configured to: convert the first direct current output by the converter into a third direct current, and output the third direct current to a charged device; and convert a fourth direct current output by the charged device into a second direct current, and transmit the second direct current to the converter. 
     Specifically, the charged device may be a power battery. For example, the charged device may be a power battery such as a nickel metal hydride battery, a lithium battery, or a lead-acid battery. 
     In addition, for technical effects brought by any possible design manner in the second aspect, refer to technical effects brought by different design manners in the first aspect. Details are not described herein again. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a waveform of a three-phase alternating current according to an embodiment of this application; 
         FIG. 2  is a schematic diagram of a structure of an alternating current converter according to an embodiment of this application; 
         FIG. 3  is a schematic diagram of a flow direction of a current of an alternating current converter according to an embodiment of this application; 
         FIG. 4  is a schematic diagram  1  of a structure of a converter according to an embodiment of this application; 
         FIG. 5  is a schematic diagram  2  of a structure of a converter according to an embodiment of this application; 
         FIG. 6  is a schematic diagram  3  of a structure of a converter according to an embodiment of this application; 
         FIG. 7  is a schematic diagram  1  of a structure of a PFC circuit according to an embodiment of this application; 
         FIG. 8  is a schematic diagram  2  of a structure of a PFC circuit according to an embodiment of this application; 
         FIG. 9  is a schematic diagram  3  of a structure of a PFC circuit according to an embodiment of this application; 
         FIG. 10  is a schematic diagram  4  of a structure of a PFC circuit according to an embodiment of this application; 
         FIG. 11  is a schematic diagram  5  of a structure of a PFC circuit according to an embodiment of this application; 
         FIG. 12  is a schematic diagram  1  of a structure of a switch circuit according to an embodiment of this application; 
         FIG. 13  is a schematic diagram  2  of a structure of a switch circuit according to an embodiment of this application; 
         FIG. 14  is a schematic diagram  1  of a structure of a surge protection circuit according to an embodiment of this application; 
         FIG. 15  is a schematic diagram  2  of a structure of a surge protection circuit according to an embodiment of this application; 
         FIG. 16  is a schematic diagram  4  of a structure of a converter according to an embodiment of this application; 
         FIG. 17  is a schematic diagram  4  of a structure of a converter according to an embodiment of this application; 
         FIG. 18  is a schematic diagram  5  of a structure of a converter according to an embodiment of this application; 
         FIG. 19  is a schematic diagram  6  of a structure of a converter according to an embodiment of this application; 
         FIG. 20  is a schematic diagram  7  of a structure of a converter according to an embodiment of this application; and 
         FIG. 21  is a schematic diagram of a structure of an on-board charger according to an embodiment of this application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To make objectives, technical solutions, and advantages of this application clearer, the following further describes this application in detail with reference to accompanying drawings. 
     A specific operation method in a method embodiment may also be applied to an apparatus embodiment or a system embodiment. It should be noted that in description of this application, “at least one” means one or more, and “a plurality of” means two or more. In view of this, in embodiments of this application, “a plurality of” may also be understood as “at least two”. The term “and/or” describes an association relationship between associated objects and indicates that three relationships may exist. For example, A and/or B may indicate the following three cases: Only A exists, both A and B exist, and only B exists. In addition, the character “/” generally indicates an “or” relationship between the associated objects, unless otherwise specified. In addition, it should be understood that in the description of this application, terms such as “first” and “second” are merely used for distinguishing and description, but should not be understood as indicating or implying relative importance, or should not be understood as indicating or implying a sequence. 
     It should be noted that the “connection” in embodiments of this application refers to an electric connection, and the connection between two electrical elements may be a direct or indirect connection between the two electrical elements. For example, a connection between A and B may represent that A and B are directly connected to each other, or A and B are indirectly connected to each other by using one or more other electrical elements. For example, the connection between A and B may also represent that A is directly connected to C, C is directly connected to B, and A and B are connected to each other through C. 
     It should be noted that bidirectional switches in the embodiments of this application may be one or more types of a plurality of types of power devices such as a relay, a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar junction transistor (bipolar junction transistor, BJT), an insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT), and a silicon carbide (SiC) transistor. Details are not described in the embodiments of this application again. Each power device may include a first electrode, a second electrode, and a control electrode, where the control electrode is configured to control turn-on or turn-off of the power device. When the power device is turned on, a current may be transmitted between the first electrode and the second electrode of the power device. When the power device is turned off, the current cannot be transmitted between the first electrode and the second electrode of the power device. A MOSFET is used as an example. The control electrode of the power device is a gate; and the first electrode of the power device may be a source of the power device, and the second electrode may be a drain of the power device; or the first electrode may be a drain of the power device, and the second electrode may be a source of the power device. 
     For ease of description, an alternating current converter is described below in the embodiments of this application. It should be noted that the alternating current converter is a converter that can support both alternating current (alternating current, AC)-to-direct current (direct current, DC) conversion (AC/DC) and DC/AC conversion. 
     Currently, common alternating currents mainly include a single-phase alternating current and a three-phase alternating current. The three-phase alternating current is used as an example.  FIG. 1  is a diagram of an example of a voltage waveform of a three-phase alternating current. As shown in  FIG. 1 , the three-phase alternating current mainly includes three single-phase alternating currents among which phase offsets exist, namely, a phase A alternating current, a phase B alternating current, and a phase C alternating current shown in  FIG. 1 . Each single-phase alternating current fluctuates periodically as a sine wave with a same fluctuation amplitude (mostly ±311 V in China) and a same fluctuation frequency (mostly 50 Hz in China). In the three-phase alternating current, a phase difference between each phase of alternating current and the other two phases of alternating current is 120°. For example, at a moment, a phase of the phase A alternating current is 0, a phase of the phase B alternating current is 120°, and a phase of the phase C alternating current is 240° (namely, −) 120°. 
     Both the single-phase alternating current and the three-phase alternating current are commonly used alternating currents in the market. Therefore, the converter that supports both the AC-DC conversion and the DC-AC conversion has a broad application prospect. For example, the converter is used in an on-board charger (OBC) for charging a new energy vehicle. The OBC may convert a voltage of a grid into a charging voltage for a power battery in the new energy vehicle, to charge the power battery, and may feed back electric energy stored in the power battery to the grid or supply the electric energy to an on-board power consumption device.  FIG. 2  is a schematic diagram of an example of a structure of an alternating current converter that supports both AC-DC conversion and DC-AC conversion. 
     As shown in  FIG. 2 , an alternating current power supply is connected to the alternating current converter through a switch. When the switch is turned on, a phase A alternating current, a phase B alternating current, and a phase C alternating current in a three-phase alternating current output by the alternating current power supply each are transmitted to the converter through a corresponding circuit. When a switch circuit is switched from a turn-off state to a turn-on state, a surge voltage may be generated on the circuits, and the surge voltage is output to the converter after being superimposed with the three-phase alternating current. Specifically, the alternating current converter mainly includes two parts. A part on a left side of a dotted line is a surge protection circuit including diodes, and a part on a right side of the dotted line is a power factor correction (power factor correction, PFC) circuit including a switch and an inductor. A surge voltage in an alternating current that can be received by the surge protection circuit is converted into a direct current voltage, and then the direct current voltage is output to a back-end direct current bus including capacitors C 1  and C 2 . The PFC circuit may convert the three-phase alternating current voltage output by the alternating current power supply into a direct current voltage, and output the direct current voltage to the direct current bus. In this case, the alternating current converter is in a rectification state. It should be noted that a rear terminal of the direct current bus may be connected to a charged device (for example, a power battery of a new energy vehicle), to charge the charged device. 
     When the converter is in an inverter state, a left side of the PFC circuit may be connected to a power consumption device. In this case, the PFC circuit may receive a direct current output by the direct current bus, and convert the received direct current into an alternating current, to supply power to the power consumption device. 
     In actual use, for example, the power consumption device is a capacitive load, and the capacitive load has a charging and discharging cycle. When the charging and discharging cycle of the capacitive load is different from a phase offset cycle of the alternating current output by the PFC circuit, a voltage value of the capacitive load may be greater than a voltage output by the PFC circuit. For example, the alternating current converter outputs a single-phase alternating current through ports A 1  and A 2 , and supply power to the capacitive load through switches K 1  and K 2 . In a positive half cycle of the single-phase alternating current, K 1  is one terminal that is of the capacitive load and that receives a high electrical level, and K 2  is one terminal that is of the capacitive load and that receives a low electrical level in this case. When the positive half cycle of the output single-phase alternating current reaches a peak, effective values output by the ports A 1  and A 2  are gradually decreased. If a discharging speed of the capacitive load is less than the cycle of the single-phase alternating current, an electrical level of K 1  is higher than an electrical level of the port A 1 . In this case, the capacitive load is equivalent to a power supply, and K 1  is a positive electrode of the power supply. Refer to  FIG. 3 . A current may return to a negative electrode of the power supply through a diode D 1  and a switch Sa 1 . In this case, the capacitive load and the alternating current converter are short-circuited, causing damage to the alternating current converter and the power consumption device. 
     In view of this, this application provides a converter. In addition to supporting both AC-DC conversion and DC-AC conversion, surge protection can be implemented, a short-circuit failure of a circuit can be effectively avoided, and normal operation of the converter is ensured. 
       FIG. 4  is a schematic diagram of a structure of a converter according to an embodiment of this application. As shown in  FIG. 4 , the converter  400  mainly includes a PFC circuit  401 , a surge protection circuit  402 , and a switch circuit  403 . 
     Specifically, an alternating current terminal of the surge protection circuit  402  is connected to an alternating current terminal of the PFC circuit  401 , a direct current terminal of the surge protection circuit  402  is connected to a first terminal of the switch circuit  403 , and a second terminal of the switch circuit  403  is connected to a direct current terminal of the PFC circuit  401 . 
     The PFC circuit  401  may be configured to: convert a first component of a first alternating current received by the alternating current terminal of the PFC circuit  401  into a first direct current, and output the first direct current through the direct current terminal of the PFC circuit  401 , where an absolute value of an instantaneous voltage value of the first component is less than or equal to a preset threshold; and convert a second direct current received by the direct current terminal of the PFC circuit  401  into a second alternating current, and output the second alternating current through the alternating current terminal of the PFC circuit  401 . The surge protection circuit  402  may be configured to: convert a second component of the first alternating current into a third direct current, and output the third direct current through the direct current terminal of the surge protection circuit  402 , where an absolute value of an instantaneous voltage value of the second component is greater than the preset threshold. The switch circuit  403  may be configured to be turned on when the alternating current terminal of the PFC circuit  401  outputs the first direct current, and to be turned off when the alternating current terminal of the PFC circuit  401  outputs the second alternating current. 
     A voltage value of the first direct current is equal to a voltage value of the third direct current. In this case, the direct current terminal (which outputs the first direct current) of the PFC circuit  401  may be electrically connected to a charged device. The direct current terminal (which outputs the third direct current) of the surge protection circuit  402  may also be electrically connected to the charged device through the switch circuit  403 . To be specific, both the PFC circuit  401  and the surge protection circuit  402  have a voltage conversion function, and respectively rectify the received first component and the received second component. Outputs of the PFC circuit  401  and the surge protection circuit  402  are connected in parallel and are connected to the charged device, to charge the charged device. 
     Further, a positive direction and a negative direction of the first direct current may be the same as those of the third direct current. That a positive direction and a negative direction of the first direct current are the same as those of the third direct current may specifically mean that if the direct current terminal of the PFC circuit  401  is connected to the charged device, one terminal that is in the direct current terminal of the PFC circuit  401  and that outputs a high electrical level is connected to one terminal that is of the charged device and that receives the high electrical level, and one terminal that is in the direct current terminal of the PFC circuit  401  and that outputs a low electrical level is connected to one terminal that is of the charged device and that receives the low electrical level; and similarly, if the direct current terminal of the surge protection circuit  402  is connected to the first terminal of the switch circuit  403 , and the second terminal of the switch circuit  403  is connected to the charged device, when the switch circuit  403  is turned on, one terminal that is in the direct current terminal of the surge protection circuit  402  and that outputs a high electrical level is connected to one terminal that is of the charged device and that receives the high electrical level, and one terminal that is in the direct current terminal of the surge protection circuit  402  and that outputs a low electrical level is connected to one terminal that is of the charged device and that receives the low electrical level. 
     When the converter  400  is configured to charge the charged device, if a surge voltage exists in the first alternating current received by the alternating current terminal of the PFC circuit  401 , the PFC circuit  401  may convert the first component of the first alternating current into the first direct current, and output the first direct current through the direct current terminal of the PFC circuit  401 , and the surge protection circuit  402  converts the second component of the first alternating current received by the alternating current terminal into the third direct current; or if there is no surge voltage exist in the first alternating current received by the alternating current terminal of the PFC circuit  401 , the PFC circuit  401  may directly convert the first alternating current received by the alternating current terminal into the first direct current. The absolute value of the instantaneous voltage value of the first component is less than or equal to the preset threshold, and the absolute value of the instantaneous voltage value of the second component is greater than the preset threshold. The preset threshold may be a peak value of an alternating current output by an alternating current power supply connected to the converter  400 . When the first alternating current includes a surge voltage, the first component and the second component of the first alternating current constitute the first alternating current. 
     Specifically, when the charged device is charged, an equivalent circuit of the converter  400  may be shown in  FIG. 5 . In this case, the alternating current terminal of the PFC circuit  401  and the alternating current terminal of the surge protection circuit  402  are used as an input terminal of the converter  400 , and the direct current terminal of the PFC circuit  401  and the second terminal of the switch circuit  403  are used as an output terminal of the converter  400  after being connected in parallel. In specific implementation, the charged device may be an inverter, a power battery of a new energy vehicle, or another device powered by a direct current. The converter  400  shown in  FIG. 5  may charge the charged device through the alternating current power supply. 
     It should be understood that a voltage fluctuation of a direct current obtained after the converter  400  rectifies the first alternating current is large, and a voltage value of an output direct current is difficult to meet a voltage requirement of the charged device. Therefore, a DC/DC converter circuit may be further connected between the converter  400  and the charged device. The DC/DC converter circuit may perform rectification and voltage adjustment processing on the direct current output by the converter  400 , to output a direct current voltage that is available to the charged device. 
     When the converter  400  is configured to discharge the charged device, the switch circuit  403  is turned off Therefore, the surge protection circuit  402  can perform only unidirectional AC-DC conversion. Therefore, the surge protection circuit  402  does not operate in this case. That is, when the charged device discharges, only a part of circuit in the converter  400  operates. Specifically, the PFC circuit  401  may be configured to convert the second direct current output by the charged device into the second alternating current that is available to a power consumption device. 
     Specifically, when the charged device discharges, an equivalent circuit of the converter  400  may be shown in  FIG. 6 . In this case, the direct current terminal of the PFC circuit  401  is used as an input terminal of the converter  400 , and the alternating current terminal of the PFC circuit  401  is used as an output terminal of the converter. 
     It should be understood that when the charged device discharges, the switch circuit  403  in the converter  400  is turned off. If the power consumption device is a capacitive load, the surge protection circuit  401  and the switch circuit  403  cannot form a closed path. Therefore, a short-circuit fault between the power consumption device and the converter  400  can be effectively avoided, and normal operation of the converter  400  is ensured. 
     In a specific implementation, the electrical device may be an on-board power consumption device, or may be another power battery. The converter  400  shown in  FIG. 6  may be used to supply power to an on-board power consumption device or charge another power battery through a power battery. 
     For example, the power consumption device may be an on-board power consumption device, for example, an induction cooker or a rice cooker, and the charged device may be a power battery. Therefore, when the power battery discharges, a direct current of 90 V to 400 V may be output. After DC/AC conversion is performed, by using the PFC circuit  401 , on the direct current output by the power battery, an alternating current of 220 V is output for use by a device, for example, an induction cooker or a rice cooker. 
     For example, the power consumption device and the charged device may be respectively power batteries on two new energy vehicles, where an electricity quantity of the charged device is greater than an electricity quantity of the power consumption device. In this case, the charged device may charge the power consumption device through the converter  400 . Specifically, when the charged device discharges, a direct current of 90 V to 400 V may be output. After DC/AC conversion is performed, by using the PFC circuit  401 , on the direct current output by the charged device, an alternating current is output, to charge a power battery of the other new energy vehicle. 
     It should be understood that if the direct current output by the charged device is directly inverted by using the PFC circuit  401 , a voltage value of an output alternating current may be difficult to meet a voltage requirement of the power consumption device. Therefore, a DC/DC converter may be included between the converter  400  and the charged device. The DC/DC converter may first adjust the voltage value of the direct current output by the charged device, and send the direct current to the PFC circuit  401  for inversion processing, to output an alternating current voltage that is available to the power consumption device. 
     For ease of description, in this embodiment of this application, a charging process of the converter  400  is referred to as “forward charging”, and a discharging process of the converter  400  is referred to as “reverse discharging”. 
     In actual application, the converter  400  may be fastened onto a new energy vehicle, and the power consumption device may be connected to the converter  400  through a fixed interface on the new energy vehicle. For example, a power plug of a device such as an induction cooker or a rice cooker may be directly plugged into the fixed interface, so that a power battery supplies power to the induction cooker or the rice cooker. In another implementation, the converter  400  may alternatively be disposed into a flexible detachable form. To be specific, a fixed interface is disposed on the new energy vehicle, to connect the converter  400  and the charged device. In this case, the converter  400  may be considered as an apparatus independent of the new energy vehicle. 
     In specific implementation, the PFC circuit  401 , the surge protection circuit  402 , and the switch circuit  403  each may include devices such as a switch, a diode, an inductor, and a capacitor. Operation states of the PFC circuit  401 , the surge protection circuit  402 , and the switch circuit  403  may be implemented by adjusting operation states of these devices (for example, the switch). 
     In this application, a controller may be used to adjust the foregoing operation states. To be specific, the converter  400  may further include a controller, and when the converter  400  is configured to perform “forward charging”, the controller may be configured to control the PFC circuit  401  to convert the first component of the first alternating current into the first direct current, and control an operation state of the switch circuit  403 ; and when the converter  400  is configured to perform “reverse discharging”, the controller may be configured to control the PFC circuit  401  to convert the second direct current received by the direct current terminal into the second alternating current. 
     It should be understood that when the converter  400  is configured to perform “forward charging”, if a device in the surge protection circuit  402  is a switch, the controller may be further configured to control the surge protection circuit  402  to convert the second component of the first alternating current into the third direct current. 
     In specific implementation, the controller may be any one of a micro control unit (MCU), a central processing unit (CPU), or a digital signal processor (DSP). Certainly, a specific form of the controller is not limited to the foregoing examples. 
     The following describes specific structures of the PFC circuit  401 , the surge protection circuit  402 , and the switch circuit  403  in the converter  400 . 
     1. PFC Circuit  401   
     The alternating current terminal of the PFC circuit  401  is connected to the alternating current terminal of the surge protection circuit  402 , the direct current terminal of the PFC circuit  401  is connected to the second terminal of the switch circuit, and the PFC circuit  401  may be configured to: convert the first component of the first alternating current received by the alternating current terminal of the PFC circuit into the first direct current, and output the first direct current through the direct current terminal of the PFC circuit; and convert the second direct current received by the direct current terminal of the PFC circuit into the second alternating current, and output the second alternating current through the alternating current terminal of the PFC circuit. The absolute value of the instantaneous voltage value of the first component is less than or equal to the preset threshold. 
     In actual use, the alternating current terminal of the PFC circuit  401  may be a three-phase alternating current terminal, and is configured to receive a three-phase alternating current. Alternatively, the alternating current terminal of the PFC circuit  401  may be a single-phase alternating current terminal, and is configured to receive a single-phase alternating current. 
     The following describes two cases of the alternating current terminal of the PFC circuit in detail with reference to embodiments. 
     Embodiment 1 
     The alternating current terminal of the PFC circuit  401  is a three-phase alternating current terminal, and is configured to receive a three-phase alternating current. The PFC circuit  401  may include a first bidirectional converter, a second bidirectional converter, and a third bidirectional converter. 
     An alternating current terminal of the first bidirectional converter is a first alternating current terminal of the three-phase alternating current terminal, an alternating current terminal of the second bidirectional converter is a second alternating current terminal of the three-phase alternating current terminal, and an alternating current terminal of the third bidirectional converter is a third alternating current terminal of the three-phase alternating current terminal. The first alternating current terminal, the second alternating current terminal, and the third alternating current terminal constitute the three-phase alternating current terminal. A direct current terminal of the first bidirectional converter, a direct current terminal of the second bidirectional converter, and a direct current terminal of the third bidirectional converter constitute the direct current terminal of the PFC circuit, and the direct current terminal of the PFC circuit is connected to a first direct current bus. 
     A function of disposing the three bidirectional converters is as follows: When the converter  400  is configured to perform “forward charging”, the first bidirectional converter may perform single-phase rectification on a phase A alternating current that is received by the first alternating current terminal and that is in the three-phase alternating current, the second bidirectional converter may perform single-phase rectification on a phase B alternating current that is received by the second alternating current terminal and that is in the three-phase alternating current, and the third bidirectional converter may perform single-phase rectification on a phase C alternating current that is received by the third alternating current terminal and that is in the three-phase alternating current. When the converter  400  is configured to perform “reverse discharging”, the first bidirectional converter may perform inversion processing on a direct current received by the direct current terminal of the PFC circuit  401 , to obtain the phase A alternating current in the three-phase alternating current, and output the phase A alternating current through the first alternating current terminal, the second bidirectional converter may perform inversion processing on the direct current received by the direct current terminal of the PFC circuit, to obtain the phase B alternating current in the three-phase alternating current, and output the phase B alternating current through the second alternating current terminal, and the third bidirectional converter may perform inversion processing on the direct current received by the direct current terminal of the PFC circuit, to obtain the phase C alternating current in the three-phase alternating current, and output the phase C alternating current through the third alternating current terminal, so as to output the second alternating current in a three-phase alternating current form. When the converter  400  is configured to perform “reverse discharging”, the first bidirectional converter may perform inversion processing on a direct current received by the direct current terminal of the PFC circuit  401 , and output an alternating current obtained after inversion processing through the first alternating current terminal, and the second alternating current terminal is connected to a neutral line, so as to output the second alternating current in a single-phase alternating current form. 
     It can be learned that one bidirectional converter constitutes one single-phase converter, and the PFC circuit  401  may implement a Y-type connection by using the three bidirectional converters. 
     In a possible implementation, the PFC circuit  401  may further include a first direct current bus connected to the first bidirectional converter, the second bidirectional converter, and the third bidirectional converter. 
     The following provides a specific structure of the PFC circuit  401 . 
     Specifically, the first unidirectional converter includes: a first inductor, where a first terminal of the first inductor is connected to the first alternating current terminal; a first bidirectional switch, where the first bidirectional switch is connected between a second terminal of the first inductor and a positive terminal of the first direct current bus; and a second bidirectional switch, where the second bidirectional switch is connected between the second terminal of the first inductor and a negative terminal of the first direct current bus. 
     The second bidirectional converter includes: a second inductor, where a first terminal of the second inductor is connected to the second alternating current terminal; a third bidirectional switch, where the third bidirectional switch is connected between a second terminal of the second inductor and the positive terminal of the first direct current bus; and a fourth bidirectional switch, where the fourth bidirectional switch is connected between the second terminal of the second inductor and the negative terminal of the first direct current bus. 
     The third bidirectional converter includes: a third inductor, where a first terminal of the third inductor is connected to the third alternating current terminal; a fifth bidirectional switch, where the fifth bidirectional switch is connected between a second terminal of the third inductor and the positive terminal of the first direct current bus; and a sixth bidirectional switch, where the sixth bidirectional switch is connected between the second terminal of the third inductor and the negative terminal of the first direct current bus. 
     In an example, the bidirectional switch may include a single switch, or may include two power devices connected in reverse series. In other words, the bidirectional switch in this embodiment of this application includes two power devices connected in reverse series, so that a switching feature of the bidirectional switch is implemented by using an inherent anti-parallel diode in the switching transistor. 
     It should be understood that in the first bidirectional converter, the first inductor may be an independent inductor or may be a coupled inductor; similarly, in the second bidirectional converter, the second inductor may be an independent inductor or may be a coupled inductor; and in the third bidirectional converter, the third inductor may be an independent inductor or may be a coupled inductor. 
     In a possible implementation, the PFC circuit  401  may further include a seventh bidirectional switch and an eighth bidirectional switch. The seventh bidirectional switch is connected between the positive terminal of the first direct current bus and a first neutral line. The eighth bidirectional switch is connected between the negative terminal of the first direct current bus and the first neutral line. 
     In actual use, when the PFC circuit  401  is configured to perform “reverse discharging”, if the alternating current terminal of the PFC circuit  401  outputs the second alternating current in the single-phase alternating current, any alternating current terminal in the three-phase alternating current terminal of the PFC circuit  401  and an intermediate node between the seventh bidirectional switch and the eighth bidirectional switch are used as two ports for outputting the single-phase alternating current. 
     For ease of understanding, the following provides two specific examples of the PFC circuit  401 . 
       FIG. 7  is a schematic diagram of a structure of a PFC circuit  401  according to an embodiment of this application. In  FIG. 7 , L 1  may be considered as the first inductor, Sa 1  may be considered as the first bidirectional switch, Sa 2  may be considered as the second bidirectional switch, and L 1 , Sa 1 , and Sa 2  constitute the first bidirectional converter. Similarly, L 2  may be considered as the second inductor, Sb 1  may be considered as the third bidirectional switch, Sb 2  may be considered as the fourth bidirectional switch, and L 2 , Sb 1 , and Sb 2  constitute the second bidirectional converter. L 3  may be considered as the third inductor, Sc 1  may be considered as the fifth bidirectional switch, Sc 2  may be considered as the sixth bidirectional switch, and L 3 , Sc 1 , and Sc 2  constitute the third bidirectional converter. Va may be considered as the first alternating current terminal, Vb may be considered as the second alternating current terminal, Vc may be considered as the third alternating current terminal, and Va, Vb, and Vc may receive the three-phase alternating current. A and B may be considered as two ports of the direct current terminal of the PFC circuit  401 , the port A is connected to the positive terminal of the first direct current bus, and the port B is connected to the negative terminal of the first direct current bus. 
     A connection relationship among the devices in the PFC circuit  401  shown in  FIG. 7  may be as follows: The first terminal of the inductor L 1  is connected to Va, the second terminal of L 1  is separately connected to a first electrode of the bidirectional switch Sa 1  and a second electrode of the bidirectional switch Sa 2 , a second electrode of Sa 1  is connected to the port A, and a first electrode of Sa 2  is connected to the port B. The first terminal of the inductor L 2  is connected to Vb, the second terminal of L 2  is separately connected to a first electrode of the bidirectional switch Sb 1  and a second electrode of the bidirectional switch Sb 2 , a second electrode of Sb 1  is connected to the port A, and a first electrode of Sb 2  is connected to the port B. The first terminal of the inductor L 3  is connected to Vc, the second terminal of L 3  is separately connected to a first electrode of the bidirectional switch Sc 1  and a second electrode of the bidirectional switch Sc 2 , a second electrode of Sc 1  is connected to the port A, and a first electrode of Sc 2  is connected to the port B. 
     When three-phase rectification is implemented by using the PFC circuit  401  shown in  FIG. 7 , Va, Vb, and Vc are used as a three-phase alternating current input terminal, A and B are used as a direct current output terminal, and energy is transmitted from left to right. The first component of the first alternating current input on a left side is converted into the first direct current and then the first direct current is output. When three-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va, Vb, and Vc are used as an alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va, Vb, and Vc. When single-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va and Vb are used as a single-phase alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va and Vb. 
       FIG. 8  is a schematic diagram of a structure of another PFC circuit  401  according to an embodiment of this application. In  FIG. 8 , L 1 , Sa 1 , and Sa 2  constitute the first bidirectional converter; L 2 , Sb 1 , and Sb 2  constitute the second bidirectional converter; and L 3 , Sc 1 , and Sc 2  constitute the third bidirectional converter. Sn 1  may be considered as the seventh bidirectional switch, Sn 2  may be considered as the eighth bidirectional switch, Va may be considered as the first alternating current terminal, Vb may be considered as the second alternating current terminal, and Vc may be considered as the third alternating current terminal. Va, Vb, and Vc may receive the three-phase alternating current. A and B may be considered as two ports of the direct current terminal of the PFC circuit  401 , the port A is connected to the positive terminal of the first direct current bus, the port B is connected to the negative terminal of the first direct current bus, and Vn is connected to a neutral line N 1 . 
     When three-phase rectification is implemented by using the PFC circuit  401  shown in  FIG. 8 , Va, Vb, and Vc are used as a three-phase alternating current input terminal, A and B are used as a direct current output terminal, and energy is transmitted from left to right. The first component of the first alternating current input on a left side is converted into the first direct current and then the first direct current is output. When three-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va, Vb, and Vc are used as an alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va, Vb, and Vc. When single-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va and Vn are used as an alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va and Vn. 
     Embodiment 2 
     The alternating current terminal of the PFC circuit is a single-phase alternating current terminal, and is configured to receive a single-phase alternating current. The PFC circuit  401  includes a fourth bidirectional converter and a fifth bidirectional converter. 
     An alternating current terminal of the fourth bidirectional converter is a fourth alternating current terminal of the single-phase alternating current terminal, and an alternating current terminal of the fifth bidirectional converter is a fifth alternating current terminal of the single-phase alternating current terminal. The fourth alternating current terminal and the fifth alternating current terminal constitute the single-phase alternating current terminal. A direct current terminal of the fourth bidirectional converter and a direct current terminal of the fifth bidirectional converter constitute the direct current terminal of the PFC circuit, and the direct current terminal of the PFC circuit  401  is connected to a second direct current bus. 
     A function of disposing the two bidirectional converters is as follows: When the converter  400  is configured to perform “forward charging”, the fourth alternating current terminal and the fifth alternating current terminal receive the single-phase alternating current, the fourth bidirectional converter may convert a positive half-cycle voltage of the received single-phase alternating current, and similarly, the fifth bidirectional converter may convert a negative half-cycle voltage of the received single-phase alternating current, to implement single-phase rectification. When the converter  400  is configured to perform “reverse discharging”, the fourth bidirectional converter may perform inversion processing on a direct current received by the direct current terminal of the PFC circuit, to obtain a positive half-cycle voltage of the second alternating current, the fifth bidirectional converter may perform inversion processing on the direct current received by the direct current terminal of the PFC circuit, to obtain a negative half-cycle voltage of the second alternating current, and the second alternating current is output through the fourth alternating current terminal and the fifth alternating current terminal, to implement single-phase inversion. The fourth bidirectional converter and the fifth bidirectional converter complementarily operate. To be specific, when the fourth bidirectional converter converts the positive half-cycle voltage of the single-phase alternating current, the fifth bidirectional converter cannot convert the negative half-cycle voltage of the single-phase alternating current. 
     In a possible implementation, the PFC circuit  401  may further include a second direct current bus connected to the fourth bidirectional converter and the fifth bidirectional converter. 
     The following provides a specific structure of the PFC circuit  401 . 
     The fourth unidirectional converter includes: a fourth inductor, where a first terminal of the fourth inductor is connected to the fourth alternating current terminal; a ninth bidirectional switch, where the ninth bidirectional switch is connected between a second terminal of the fourth inductor and a positive terminal of the second direct current bus; and a tenth bidirectional switch, where the tenth bidirectional switch is connected between the second terminal of the fourth inductor and a negative terminal of the second direct current bus. 
     The fifth bidirectional converter includes: a fifth inductor, where a first terminal of the fifth inductor is connected to the fifth alternating current terminal; an eleventh bidirectional switch, where the eleventh bidirectional switch is connected between a second terminal of the fifth inductor and the positive terminal of the second direct current bus; and a twelfth bidirectional switch, where the twelfth bidirectional switch is connected between the second terminal of the fifth inductor and the negative terminal of the second direct current bus. 
     It should be understood that in the fourth bidirectional converter, the fourth inductor may be an independent inductor or may be a coupled inductor; and similarly, in the fifth bidirectional converter, the fifth inductor may be an independent inductor or may be a coupled inductor. 
     In a possible implementation, the PFC circuit  401  may further include a thirteenth bidirectional switch and a fourteenth bidirectional switch. 
     The thirteenth bidirectional switch is connected between the positive terminal of the second direct current bus and a second neutral line. The fourteenth bidirectional switch is connected between the negative terminal of the second direct current bus and the second neutral line. 
     In actual use, when the PFC circuit  401  is configured to perform “reverse discharging”, if the alternating current terminal of the PFC circuit  401  outputs a single-phase alternating current, any alternating current terminal of the single-phase alternating current terminal of the PFC circuit  401  and an intermediate node between the thirteenth bidirectional switch and the fourteenth bidirectional switch are used as two ports for outputting the single-phase alternating current. 
     For ease of understanding, the following provides two specific examples of the PFC circuit. 
       FIG. 9  is a schematic diagram of a structure of a PFC circuit  401  according to an embodiment of this application. In  FIG. 9 , L 4  may be considered as the fourth inductor, S 1  may be considered as the ninth bidirectional switch, S 2  may be considered as the tenth bidirectional switch, and L 4 , S 1 , and S 2  constitute the fourth bidirectional converter. Similarly, L 5  may be considered as the fifth inductor, S 3  may be considered as the eleventh bidirectional switch, S 4  may be considered as the twelfth bidirectional switch, and L 5 , S 3 , and S 4  constitute the fifth bidirectional converter. Va may be considered as the fourth alternating current terminal, Vb may be considered as the fifth alternating current terminal, and Va and Vb may receive the single-phase alternating current. A and B may be considered as two ports of the direct current terminal of the PFC circuit  401 , the port A is connected to the positive terminal of the second direct current bus, and the port B is connected to the negative terminal of the second direct current bus. 
     A connection relationship among the devices in the PFC circuit  401  shown in  FIG. 9  may be as follows: The first terminal of the inductor L 4  is connected to Va, the second terminal of L 4  is separately connected to a first electrode of the bidirectional switch S 1  and a second electrode of the bidirectional switch S 2 , a second electrode of S 1  is connected to the port A, and a first electrode of S 2  is connected to the port B. The first terminal of the inductor L 5  is connected to Vb, the second terminal of L 5  is separately connected to a first electrode of the bidirectional switch S 3  and a second electrode of the bidirectional switch S 4 , a second electrode of S 3  is connected to the port A, and a first electrode of S 4  is connected to the port B. 
     When single-phase rectification is implemented by using the PFC circuit  401  shown in  FIG. 9 , Va and Vb are used as a single-phase alternating current input terminal, A and B are used as a direct current output terminal, energy is transmitted from left to right, and the first component of the first alternating current input on a left side is converted into the first direct current and then the first direct current is output. When single-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va and Vb are used as an alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va and Vb. 
       FIG. 10  is a schematic diagram of a structure of another PFC circuit  401  according to an embodiment of this application. In  FIG. 10 , L 4 , S 1 , and S 2  constitute the fourth bidirectional converter, L 5 , S 3 , and S 4  constitute the fifth bidirectional converter, Sn 3  may be considered as the thirteenth bidirectional switch, Sn 4  may be considered as the fourteenth bidirectional switch, Va may be considered as the fourth alternating current terminal, and Vb may be considered as the fifth alternating current terminal. Va and Vb may receive the single-phase alternating current. A and B may be considered as two ports of the direct current terminal of the PFC circuit  401 , the port A is connected to the positive terminal of the second direct current bus, the port B is connected to the negative terminal of the second direct current bus, and Vn may be considered as a port connected to a neutral line N 2 . 
     When single-phase rectification is implemented by using the PFC circuit  401  shown in  FIG. 10 , Va and Vb are used as a single-phase alternating current input terminal, A and B are used as a direct current output terminal, energy is transmitted from left to right, and the first component of the first alternating current input on a left side is converted into the first direct current and then the first direct current is output. When single-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va and Vn are used as an alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va and Vn. 
     In actual use, to implement precise control on the positive half-cycle voltage and the negative half-cycle voltage, an inductance value of the fifth inductor and an inductance value of the sixth inductor may be different. 
     In a possible manner, the fourth alternating current terminal may be connected to the fifth alternating current terminal. As shown in  FIG. 11 , when single-phase rectification is implemented by using the PFC circuit  401  shown in  FIG. 11 , Va and Vn are used as a single-phase alternating current input terminal, A and B are used as a direct current output terminal, energy is transmitted from left to right, and the first component of the first alternating current input on a left side is converted into the first direct current and then the first direct current is output. When single-phase inversion is implemented, A and B are used as a direct current input terminal, and are configured to receive a direct current output by a direct current bus. Va and Vn are used as an alternating current output terminal, and energy is transmitted from right to left. The second direct current input on a right side is converted into the second alternating current and then the second alternating current is output through Va and Vn. 
     In addition, after using the foregoing structure, the PFC circuit  401  may implement AC/DC conversion and DC/AC conversion, and may further obtain a high power factor and a low current harmonic by controlling on/off of the bidirectional switches in the PFC circuit  401 . 
     Certainly, the foregoing description of the structure of the PFC circuit  401  is merely an example. In actual application, the PFC circuit  401  may alternatively use another structure to implement three-phase rectification and three-phase inversion. 
     2. Switch Circuit  403   
     The first terminal of the switch circuit  403  is connected to the direct current terminal of the surge protection circuit  402 , the second terminal of the switch circuit  403  is connected to the direct current terminal of the PFC circuit  401 , and the switch circuit  403  may be configured to be turned on when the alternating current terminal of the PFC circuit outputs the first direct current, and to be turned off when the alternating current terminal of the PFC circuit outputs the second alternating current. 
     When the alternating current terminal that is of the surge protection circuit  403  and that is connected to the first terminal of the switch circuit  403  is a three-phase alternating current terminal, the switch circuit  403  may include a first unidirectional switch and a second unidirectional switch. 
     Specifically, a first electrode of the first unidirectional switch is connected to the direct current terminal of the surge protection circuit, and a second electrode of the first unidirectional switch is connected to the positive terminal of the first direct current bus; and a first electrode of the second unidirectional switch is connected to the negative terminal of the first direct current bus, and a second electrode of the second unidirectional switch is connected to the direct current terminal of the surge protection circuit. The first electrode of the first unidirectional switch is a positive electrode of the first unidirectional switch, and the second electrode of the first unidirectional switch is a negative electrode of the first unidirectional switch. 
     A function of disposing the first unidirectional switch and the second unidirectional switch is as follows: When the surge protection circuit  401  converts the second component of the first alternating current and outputs the third direct current, the first unidirectional switch and the second unidirectional switch are turned on, and form an electric energy transmission path for the third direct current with the first direct current bus; and when the converter is in inversion, the first unidirectional switch and the second unidirectional switch are turned off, to avoid a short-circuit path between the surge protection circuit  402  and the PFC circuit  401 . 
     When the alternating current terminal that is of the surge protection circuit  403  and that is connected to the first terminal of the switch circuit  403  is a single-phase alternating current terminal, the switch circuit  403  may include a third unidirectional switch and a fourth unidirectional switch. 
     Specifically, a first electrode of the third unidirectional switch is connected to the direct current terminal of the surge protection circuit, and a second electrode of the third unidirectional switch is connected to the positive terminal of the second direct current bus; and a first electrode of the fourth unidirectional switch is connected to the negative terminal of the second direct current bus, and a second electrode of the fourth unidirectional switch is connected to the direct current terminal of the surge protection circuit. 
     It should be noted that a function of disposing the third unidirectional switch and the fourth unidirectional switch is the same as the function of disposing the first unidirectional switch and the second unidirectional switch. Details are not described herein in this application again. 
     With reference to the foregoing structure of the PFC circuit  401 , the following provides two specific examples of the switch circuit  403 . 
       FIG. 12  is a schematic diagram of a structure of a switch circuit  403  according to an embodiment of this application. In  FIG. 12 , SCR 1  may be considered as the first unidirectional switch, and SCR 2  may be considered as the second unidirectional switch. 
     By using the foregoing structure of the switch circuit  403 , when the surge protection circuit  402  implements three-phase rectification, the controller sends a control signal to SCR 1  and SCR 2 , where the control signal is used to control SCR 1  and SCR 2  to be turned on. In this case, the surge protection circuit  402  transmits the third direct current output by the direct current terminal to the first direct current bus through a closed path constituted by SCR 1 , SCR 2 , and the first direct current bus, and energy is transmitted from left to right. When the PFC circuit  401  implements three-phase or single-phase inversion, there is no control signal sent to SCR 1  and SCR 2 . In this case, if the direct current terminal of the surge protection circuit  402  outputs electric energy, the electric energy cannot pass through the PFC circuit. This effectively avoids a short-circuit path between the surge protection circuit  402  and the PFC circuit  401 , thereby avoiding a short-circuit failure of the converter  400 . 
       FIG. 13  is a schematic diagram of a structure of another switch circuit  403  according to an embodiment of this application. In  FIG. 13 , SCR 3  may be considered as the third unidirectional switch, and SCR 4  may be considered as the fourth unidirectional switch. 
     By using the foregoing structure of the switch circuit  403 , when the surge protection circuit implements three-phase rectification, the controller sends a control signal to SCR 3  and SCR 4 , where the control signal is used to control SCR 3  and SCR 4  to be turned on. In this case, the surge protection circuit  402  transmits the third direct current output by the direct current terminal to the second direct current bus through a closed path constituted by SCR 3 , SCR 4 , and the second direct current bus, and energy is transmitted from left to right. When the PFC circuit  401  implements three-phase or single-phase inversion, there is no control signal sent to SCR 3  and SCR 4 . In this case, if the direct current terminal of the surge protection circuit  402  outputs electric energy, the electric energy cannot pass through the PFC circuit. This effectively avoids a short-circuit path between the surge protection circuit  402  and the PFC circuit  401 , thereby avoiding a short-circuit failure of the converter  400 . 
     It should be noted that the unidirectional switch in this embodiment of this application may be a silicon controlled rectifier (silicon controlled rectifier, SCR). When a control electrode of the SCR receives the control signal, a first electrode of the SCR transmits a current to a second electrode. When the SCR does not receive the control signal, the SCR is turned off, and the first electrode of the SCR cannot transmit a current to the second electrode. 
     Certainly, the foregoing description of the structure of the switch circuit  403  is merely an example. In actual application, the switch circuit  403  may use another structure. For example, a bidirectional switch may be used to replace a unidirectional switch, and an electric energy transmission time and an electric energy transmission direction of the switch circuit  401  are controlled by controlling a control signal of the bidirectional switch. 
     3. Surge Protection Circuit  402   
     The alternating current terminal of the surge protection circuit  402  is connected to the alternating current terminal of the PFC circuit  401 , the direct current terminal of the surge protection circuit  402  is connected to the first terminal of the switch circuit  403 , and the surge protection circuit  402  may be configured to: convert the second component of the first alternating current into the third direct current, and output the third direct current through the direct current terminal of the surge protection circuit. The absolute value of the instantaneous voltage value of the second component is greater than the preset threshold. 
     The alternating current terminal of the surge protection circuit  402  may be a three-phase alternating current terminal, and is configured to convert the second component of the first alternating current received by the three-phase alternating current terminal, to obtain the third direct current. Alternatively, the alternating current terminal of the surge protection circuit  402  may be a single-phase alternating current terminal, and is configured to convert the second component of the first alternating current received by the single-phase alternating current terminal, to obtain the third direct current. 
     If the alternating current terminal of the surge protection circuit  402  is a three-phase alternating current terminal, the surge protection circuit  402  may include a first unidirectional converter, a second unidirectional converter, and a third unidirectional converter. 
     An alternating current terminal of the first unidirectional converter is connected to the first alternating current terminal, an alternating current terminal of the second unidirectional converter is connected to the second alternating current terminal, and an alternating current terminal of the third unidirectional converter is connected to the third alternating current terminal. The alternating current terminal of the first unidirectional converter, the alternating current terminal of the second unidirectional converter, and the alternating current terminal of the third unidirectional converter constitute the alternating current terminal of the surge protection circuit  402 , and a direct current terminal of the first unidirectional converter, a direct current terminal of the second unidirectional converter, and a direct current terminal of the third unidirectional converter constitute the direct current terminal of the surge protection circuit  402 . 
     A function of disposing the three unidirectional converters is as follows: When a surge voltage (the second component) exists in the first alternating current received by the three-phase alternating current terminal of the surge protection circuit  402 , the first unidirectional converter may perform single-phase rectification on a phase A alternating current that is received by the first alternating current terminal and that is in the three-phase alternating current, the second unidirectional converter may perform single-phase rectification on a phase B alternating current that is received by the second alternating current terminal and that is in the three-phase alternating current, and the third unidirectional converter may perform single-phase rectification on a phase C alternating current that is received by the third alternating current terminal and that is in the three-phase alternating current. 
     In actual use, because the direct current terminal of the surge protection circuit  402  is connected to the direct current terminal of the PFC circuit  401  through the switch circuit  403 , and the switch circuit  401  is turned off when the PFC circuit performs inversion, the surge protection circuit  402  can implement only AD/DC conversion, and cannot implement DC/AC conversion. 
     The following provides a specific structure of the surge protection circuit. 
     The first unidirectional converter may include a first diode, a second diode, a third diode, a fourth diode, a fifth diode, and a sixth diode. 
     Specifically, the first diode is connected between the first alternating current terminal and the first electrode of the first unidirectional switch; the second diode is connected between the first alternating current terminal and the second electrode of the second unidirectional switch; the third diode is connected between the second alternating current terminal and the first electrode of the first unidirectional switch; the fourth diode is connected between the second alternating current terminal and the second electrode of the second unidirectional switch; the fifth diode is connected between the third alternating current terminal and the first electrode of the first unidirectional switch; and the sixth diode is connected between the third alternating current terminal and the second electrode of the second unidirectional switch. 
     For ease of understanding, the following provides a specific example of the surge protection circuit. 
       FIG. 14  is a schematic diagram of a structure of a surge protection circuit  402  according to an embodiment of this application. In  FIG. 14 , D 1  may be considered as the first diode, D 2  may be considered as the second diode, and D 1  and D 2  constitute the first unidirectional converter. Similarly, D 3  may be considered as the third diode, D 4  may be considered as the fourth diode, and D 3  and D 4  constitute the second unidirectional converter. D 5  may be considered as the fifth diode, D 6  may be considered as the sixth diode, and D 5  and D 6  constitute the third unidirectional converter. Va may be considered as the first alternating current terminal, Vb may be considered as the second alternating current terminal, and Vc may be considered as the third alternating current terminal. C and D may be considered as two ports of the direct current terminal of the surge protection circuit  402 . The port C is connected to the positive terminal of the first direct current bus, and the port D is connected to the negative terminal of the first direct current bus. 
     When three-phase rectification is implemented by using the surge protection circuit  402  shown in  FIG. 14 , Va, Vb, and Vc are used as a three-phase alternating current input terminal, C and D are used as a direct current output terminal, and energy is transmitted from left to right. The second component of the first alternating current input on a left side is converted into the third direct current and then the third direct current is output through the ports C and D. 
     If the alternating current terminal of the surge protection circuit  402  is a single-phase alternating current terminal, the surge protection circuit  402  may include an H-bridge rectifier circuit including diodes. 
     An intermediate node of a first bridge arm of the H-bridge rectifier circuit is connected to the fourth alternating current terminal, an intermediate node of a second bridge arm of the H-bridge rectifier circuit is connected to the fifth alternating current terminal, both a first terminal of the first bridge arm and a first terminal of the second bridge arm are connected to the first electrode of the third unidirectional switch, and both a second terminal of the first bridge arm and a second terminal of the second bridge arm are connected to the second electrode of the fourth unidirectional switch. 
     A function of disposing the H-bridge rectifier circuit is as follows: When a surge voltage (the second component) exists in the first alternating current received by the single-phase alternating current terminal of the surge protection circuit  402 , the first bridge arm of the H-bridge rectifier circuit may convert a positive half-cycle voltage of the second component, and the second bridge arm of the H-bridge rectifier circuit may convert a negative half-cycle voltage of the second component, to implement single-phase rectification of the single-phase alternating current received by the single-phase alternating current terminal. 
     In actual use, because the direct current terminal of the surge protection circuit  402  is connected to the direct current terminal of the PFC circuit  401  through the switch circuit  403 , and the switch circuit  401  is turned off when the PFC circuit performs inversion, the surge protection circuit  402  can implement only AD/DC conversion, and cannot implement DC/AC conversion. 
     To facilitate connection, the following provides a specific example of the surge protection circuit. 
       FIG. 15  is a schematic diagram of a structure of a surge protection circuit  402  according to an embodiment of this application. In  FIG. 15 , the surge protection circuit includes: diodes D 7 , D 8 , D 9 , and D 10 , where D 7 , D 8 , D 9 , and D 10  constitute the H-bridge rectifier circuit. C and D may be considered as two ports of the direct current terminal of the surge protection circuit  402 . The port C is connected to the positive terminal of the second direct current bus, and the port D is connected to the negative terminal of the second direct current bus. 
     When single-phase rectification is implemented by using the surge protection circuit  402  shown in  FIG. 15 , Va and Vb are used as a single-phase alternating current input terminal, C and D are used as a direct current output terminal, and energy is transmitted from left to right. The second component of the first alternating current input on a left side is converted into the third direct current and then the third direct current is output through the ports C and D. 
     Certainly, the foregoing description of the structure of the surge protection circuit  402  is merely an example. In actual application, the surge protection circuit  402  may alternatively use another structure. For example, the surge protection circuit  402  may use a bidirectional switch to replace a diode, and rectification is implemented by controlling a control signal of the bidirectional switch. 
     With reference to the foregoing description, for example, a converter provided in the embodiments of this application may be shown in  FIG. 16 . 
     A PFC circuit includes inductors L 1 , L 2 , and L 3 , and bidirectional switches Sa 1 , Sa 2 , Sb 1 , Sb 2 , Sc 1 , and Sc 2 . L 1 , Sa 1 , and Sa 2  constitute a first bidirectional converter; L 2 , Sb 1 , and Sb 2  constitute a second bidirectional converter; and L 3 , Sc 1 , and Sc 2  constitute a third bidirectional converter. Input phase lines on an alternating current side are respectively connected to the inductors L 1 , L 2  and L 3 . Second electrodes of the bidirectional switches Sa 1 , Sb 1 , and Sc 1  are connected to a positive terminal of a first direct current bus, and second electrodes of the bidirectional switches Sa 2 , Sb 2 , and Sc 2  are connected to a negative terminal of the first direct current bus. A first electrode of Sa 1  is separately connected to the second electrode of Sb 1  and a second terminal of the inductor L 1 , a first electrode of Sb 1  is separately connected to the second electrode of Sb 2  and a second terminal of the inductor L 2 , and a first electrode of Sc 1  is separately connected to the second electrode of Sc 2  and a second terminal of the inductor L 3 . The bidirectional switches are all connected to an external control circuit (or a controller), and the control circuit implements a corresponding function of the PFC circuit by controlling on/off of a switching transistor. 
     A surge protection circuit includes diodes D 1 , D 2 , D 3 , D 4 , D 5 , and D 6 . The diodes D 1  and D 2  constitute a first unidirectional converter, D 3  and D 4  constitute a second unidirectional converter, and D 5  and D 6  constitute a third unidirectional converter. Cathodes of D 1 , D 3 , and D 5  are connected to a switch circuit, and anodes of D 2 , D 4 , and D 6  are connected to the switch circuit. An anode of D 1  is separately connected to a cathode of D 2  and a port Va, an anode of D 3  is separately connected to a cathode of D 4  and Vb, and an anode of D 5  is separately connected to a cathode of D 6  and Vc. 
     The switch circuit includes unidirectional switches SCR 1  and SCR 2 . A first electrode of SCR 1  is connected to the cathodes of D 1 , D 3 , and D 5 , a second electrode of SCR 1  is connected to a positive terminal of a direct current bus, a first electrode of SCR 2  is connected to a negative terminal of the direct current bus, and a second electrode of SCR 2  is connected to the anodes of D 2 , D 4 , and D 6 . 
     When the converter shown in  FIG. 14  implements three-phase rectification, a part of circuit uses diode rectification (the surge protection circuit), and a part of circuit uses bidirectional switch rectification (the PFC circuit). When inversion is implemented, a circuit (the PFC circuit) including bidirectional switches is used to perform inversion. 
     When the converter shown in  FIG. 16  is configured to perform three-phase rectification, Va, Vb, and Vc are used as a three-phase input terminal of the converter, and two terminals connected to the first direct current bus are used as a direct current output terminal of the converter. If a surge voltage (a second component) exists in a first alternating current received by the three-phase alternating current terminal, the PFC circuit converts a first component of the first alternating current into a first direct current, and the surge protection circuit converts the second component of the first alternating current into a third direct current, so that the third direct current is output through the direct current output terminal of the converter. When there is no surge voltage exists in the first alternating current received by the three-phase alternating current terminal, the PFC circuit converts the first alternating current into the first direct current. 
     When the converter shown in  FIG. 16  is configured to perform three-phase inversion or single-phase inversion, SCR 1  and SCR 2  are turned off, the bidirectional switches Sa 1 , Sa 2 , Sb 1 , Sb 2 , Sc 1 , and Sc 2  are complementarily turned on, and energy is transmitted from right to left. In this case, two terminals connected to the first direct current bus are used as a direct current input terminal of the converter, and Va, Vb, and Vc are used as a three-phase alternating current output terminal of the converter (or Va and Vb are used as a single-phase alternating current output terminal of the converter). 
     Because the switch circuit does not operate during single-phase inversion or three-phase inversion, a closed path of the alternating current output terminal cannot be formed between the surge protection circuit and the PFC circuit. Therefore, a short-circuit failure cannot occur in the converter shown in  FIG. 16 . 
     Certainly, the foregoing description of the structure of the converter is merely an example. In actual application, as shown in  FIG. 17 , the PFC circuit may alternatively include a port and a bidirectional switch that are connected to a neutral line. 
     With reference to the foregoing description, for example, another converter provided in the embodiments of this application may be shown in  FIG. 18 . 
     A PFC circuit includes inductors L 4  and L 5  and bidirectional switches S 1 , S 2 , S 3 , and S 4 . L 4 , S 1 , and S 2  constitute a fourth bidirectional converter, and L 5 , S 3 , and S 4  constitute a fifth bidirectional converter. Input phase lines on an alternating current side are respectively connected to the inductors L 4  and L 5 . Second electrodes of the bidirectional switches S 1  and S 3  are connected to a positive terminal of a second direct current bus, and second electrodes of the bidirectional switches S 2  and S 4  are connected to a negative terminal of the second direct current bus. A first electrode of S 1  is separately connected to the second electrode of S 2  and a second terminal of the inductor L 4 . A first electrode of S 3  is separately connected to the second electrode of S 4  and a second terminal of the inductor L 5 . The bidirectional switches are all connected to an external control circuit (or a controller), and the control circuit implements a corresponding function of the PFC circuit by controlling on/off of a switching transistor. 
     A surge protection circuit includes an H-bridge rectifier circuit including diodes D 7 , D 8 , D 9 , and D 10 . Cathodes of D 7  and D 9  are connected to a switch circuit, anodes of D 8  and D 10  are connected to the switch circuit, the cathode of D 7  is separately connected to the anode of D 8  and a port Va, and the cathode of D 9  and the anode of D 8  are connected to a port Vb. 
     The switch circuit includes unidirectional switches SCR 3  and SCR 4 . A first electrode of SCR 3  is separately connected to the cathodes of D 7  and D 9 , a second electrode of SCR 3  is connected to a positive terminal of a direct current bus, a first electrode of SCR 4  is connected to a negative terminal of the direct current bus, and a second electrode of SCR 4  is separately connected to the anodes of D 8  and D 10 . 
     When the converter shown in  FIG. 18  implements single-phase rectification, a part of circuit uses diode rectification (the surge protection circuit), and a part of circuit uses bidirectional switch rectification (the PFC circuit). When inversion is implemented, a circuit (the PFC circuit) including bidirectional switches is used to perform inversion. 
     When the converter shown in  FIG. 18  is configured to perform single-phase rectification, Va and Vb are used as an alternating current input terminal of the converter, and two terminals connected to the direct current bus are used as a direct current output terminal of the converter. If a surge voltage (a second component) exists in a first alternating current received by the single-phase alternating current terminal, the PFC circuit converts a first component of the first alternating current into a first direct current, and the surge protection circuit converts the second component of the first alternating current into a third direct current, so that the third direct current is output through the direct current output terminal of the converter. When there is no surge voltage exists in the first alternating current received by the single-phase alternating current terminal, the PFC circuit converts the first alternating current into the first direct current. 
     When the converter shown in  FIG. 18  is configured to perform single-phase inversion, SCR 3  and SCR 4  are turned off, the bidirectional switches S 1 , S 2 , S 3 , and S 4  are complementarily turned on, and energy is transmitted from right to left. In this case, two terminals connected to the direct current bus are used as a direct current input terminal of the converter, and Va and Vb are used as a single-phase alternating current output terminal of the converter. 
     Because the switch circuit does not operate during single-phase inversion, a closed path of the alternating current output terminal cannot be formed between the surge protection circuit and the PFC circuit. Therefore, a short-circuit failure cannot occur in the converter shown in  FIG. 18 . 
     Certainly, the foregoing description of the structure of the converter is merely an example. In actual application, as shown in  FIG. 19 , the PFC circuit may alternatively include a port and a bidirectional switch that are connected to a neutral line. 
     In implementation, a fourth alternating current terminal and a fifth alternating current terminal that are configured to receive a single-phase alternating current may be connected, as shown in  FIG. 20 . In this case, the fourth alternating current terminal and the port connected to the neutral line receive the single-phase alternating current. 
     Based on a same inventive concept, an embodiment of this application further provides an on-board charger. Refer to  FIG. 21 . The on-board charger  2100  includes the foregoing converter  400  and/or a DC/DC converter circuit  2101 . 
     The converter  400  is configured to: receive a first alternating current, convert the first alternating current into a first direct current, and output the first direct current to the DC/DC converter circuit  2101 ; and convert a second direct current output by the DC/DC converter circuit  2101  into a second alternating current, and output the second alternating current. The DC/DC converter circuit  2101  is connected to the converter  400 . The DC/DC converter circuit  2101  is configured to: convert the first direct current output by the converter  400  into a third direct current, and output the third direct current to a charged device; and convert a fourth direct current output by the charged device into a second direct current, and transmit the second direct current to the converter  400 . 
     Specifically, the charged device may be a power battery. For example, the charged device may be a power battery such as a nickel metal hydride battery, a lithium battery, or a lead-acid battery. When discharging, the charged device may charge a load such as an induction cooker, a rice cooker, a mobile phone, or another terminal. 
     Optionally, the on-board charger  2100  may further include an alternating current power supply. The alternating current power supply is configured to supply power to the converter  400  and the DC/DC converter circuit  2101 , that is, the alternating current power supply may output the first alternating current. 
     Optionally, the on-board charger  2100  further includes a charged device, and the DC/DC converter circuit  2101  is configured to charge the charged device. 
     Optionally, the on-board charger  2100  further includes a power consumption device, and the converter  400  may be configured to supply power to the power consumption device. 
     It should be understood that the solutions provided in this application may be applied to charging and discharging solutions of different vehicles. Specifically, the vehicles include but are not limited to different types of vehicles such as a pure/battery electric vehicle (Pure EV/Battery EV), a hybrid electric vehicle (HEV), and a new energy vehicle. In addition, the apparatus provided in this application is not limited to being applied to the field of vehicles, but may be further applied to the fields such as wind power generation and photovoltaic power generation. 
     The foregoing description is merely specific implementations of this application, but are not intended to limit the protection scope of this application. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in this application shall fall within the protection scope of this application. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.