Patent Publication Number: US-2022216723-A1

Title: Charging system and electric vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 202110083917.2, filed on Jan. 21, 2021, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     This application relates to the field of new energy vehicle technologies, and in particular, to a charging system and an electric vehicle. 
     BACKGROUND 
     With development of new energy technologies, electric vehicles have received increasingly more attention. A power battery is disposed in the electric vehicle, and the power battery can receive and store electric energy provided by a charging pile, and in a traveling process of the electric vehicle, the power battery releases the stored electric energy to drive the electric vehicle to travel. 
     To improve a charging speed of the electric vehicle, increasingly more electric vehicles use an 800 V high-voltage power battery. A maximum battery voltage of the power battery is 800 V, and a charging voltage required by the power battery may exceed 800 V. However, currently, most fast direct current charging piles in the market have an output voltage of 500 V. These charging piles cannot directly charge the 800 V high-voltage power battery. As a result, the electric vehicle equipped with the high-voltage power battery faces a difficulty of being charged, which is not conducive to improvement in user experience. 
     Therefore, currently, a charging solution to the electric vehicle needs to be studied. 
     SUMMARY 
     In view of this, the application provides a charging system and an electric vehicle. When a power supply voltage is less than a minimum charging voltage of a power battery, the electric vehicle can still support the power supply voltage in charging the power battery. 
     According to a first aspect, the application provides a charging system, including a motor control unit MCU and a first inductor. The MCU includes N bridge arms, and N is an integer greater than or equal to one. High-potential ends of the N bridge arms are connected to a first power supply end and a first battery end of the charging system, the first power supply end may be connected to a positive electrode of a direct current power supply, the first battery end may be connected to a positive electrode of a power battery, the direct current power supply may output a power supply voltage, and the power battery may receive a first output voltage of the charging system. Low-potential ends of the N bridge arms are connected to a second battery end of the charging system, and the second battery end may be connected to a negative electrode of the power battery. One end of the first inductor is connected to a second power supply end, the other end of the first inductor is connected to a middle point of a first bridge arm, the second power supply end may be connected to a negative electrode of the direct current power supply, and the first bridge arm is any of the N bridge arms. The N bridge arms in the MCU and the first inductor constitute a voltage conversion circuit. When the power supply voltage is less than a minimum charging voltage of the power battery, the MCU may perform boost conversion on the power supply voltage by using the voltage conversion circuit, and output the power supply voltage obtained after boost conversion to the power battery as the first output voltage, where the first output voltage is not less than the minimum charging voltage. 
     In conclusion, in the application, the MCU is multiplexed to implement a charging system. When the power supply voltage is less than the minimum charging voltage of the power battery, the charging system may perform boost conversion on the power supply voltage to obtain the first output voltage that is not less than the minimum charging voltage. In this case, the first output voltage can be adapted to the power battery, so as to charge the power battery. In addition, in the application, the common MCU in an electric vehicle is multiplexed, which helps reduce space occupied by the charging system and costs of the charging system. 
     For example, the first aspect of the application provides the following examples for description. 
     Example 1 
     The first bridge arm includes a first switch transistor and a second switch transistor. A first electrode of the first switch transistor is separately connected to the first battery end and the first power supply end, a second electrode of the first switch transistor is connected to a first electrode of the second switch transistor, and the middle point of the first bridge arm is located between the first switch transistor and the second switch transistor. When the power supply voltage is less than the minimum charging voltage, the MCU may turn on the first switch transistor, so that the first inductor is charged; and the MCU turns off the first switch transistor, so that the first inductor discharges electricity. 
     When the MCU turns on the first switch transistor, current is output from the positive electrode of the direct current power supply, and reaches the first inductor after passing through the first switch transistor, so that the first inductor is charged. When the MCU turns off the first switch transistor, the first inductor starts to discharge electricity. The current is output from an end that is of the first inductor and that is close to the second power supply end, and flows back to an end that is of the first inductor and that is close to the second switch transistor after being transmitted by the direct current power supply, the power battery, and a diode in the second switch transistor. In this process, the direct current power supply and the first inductor are connected in series to discharge electricity, and the first output voltage is the sum of the power supply voltage and a voltage of the first inductor. Apparently, the first output voltage is greater than the power supply voltage, and therefore, boost conversion can be implemented. 
     It can be understood that the power supply voltage provided by the direct current power supply may fall within a charging voltage range of the power battery, that is, the power supply voltage is adapted to the power battery. To be compatible with this scenario, the charging system in the application may include a first switch. A first end of the first switch is connected to the second battery end, and a second end of the first switch is connected to the second power supply end. The MCU may turn on the first switch when the power supply voltage falls within the charging voltage range of the power battery, and turn off the first switch when the power supply voltage is beyond the charging voltage range of the power battery. 
     When the first switch is turned on, the power battery can be directly connected to the direct current power supply. Therefore, the power battery can directly receive the power supply voltage provided by the direct current power supply to complete charging. Therefore, the first switch may be turned on when the power supply voltage falls within the charging voltage range of the power battery. When the first switch is turned off, the MCU may convert the power supply voltage, and provide the converted power supply voltage to the power battery as the first output voltage. Therefore, the first switch may be turned off when the power supply voltage is beyond the charging voltage range of the power battery. 
     To adapt to a high power scenario, the charging system may include N first inductors and N third switches. One end of each of the N third switches is connected to the second power supply end, the other end of each of the N third switches is connected to one end of each of the N first inductors in a one-to-one correspondence, and the other end of each of the N first inductors is connected to the N bridge arms in a one-to-one correspondence. The N third switches may be turned on when the power supply voltage is received, and may be turned off when receiving of the power supply voltage is stopped. 
     When the N third switches are turned on, charging and discharging of the N first inductors may be separately controlled by using the N bridge arms. In other words, the N first inductors may be connected in parallel to transmit power, so as to adapt to the high power scenario. When receiving of the power supply voltage is stopped, the N third switches are turned off, so that the N first inductors are disconnected from each other, thereby helping reduce impact of the N first inductors on an inverter function of the MCU. 
     Example 2 
     It is foreseeable that in some scenarios, the power supply voltage may be greater than a maximum charging voltage of the power battery. In view of this, in the application, when the power supply voltage is greater than the maximum charging voltage of the power battery, the MCU may perform buck conversion on the power supply voltage by using the voltage conversion circuit, and output the power supply voltage obtained after buck conversion to the power battery as the first output voltage, where the first output voltage is not greater than the maximum charging voltage. In this case, the electric vehicle can receive a relatively large power supply voltage. After the power supply voltage is converted, the converted power supply voltage charges the power battery, thereby helping improve charging convenience. 
     For example, the first bridge arm includes a first switch transistor and a second switch transistor. A first electrode of the first switch transistor is separately connected to the first battery end and the first power supply end, a second electrode of the first switch transistor is connected to a first electrode of the second switch transistor, and the middle point of the first bridge arm is located between the first switch transistor and the second switch transistor. The charging system may include a first switch and a second switch. A first end of the first switch is connected to the second battery end, a second end of the first switch is connected to the second power supply end, a first end of the second switch is connected to the first battery end, a second end of the second switch is connected to one end of the first inductor, and a third end of the second switch is connected to the first power supply end. 
     Based on the charging system, when the power supply voltage is greater than the maximum charging voltage, the MCU may turn on the first switch, and turn on the first end and the second end of the second switch; the MCU turns on the first switch transistor, so that the first inductor is charged; and the MCU turns off the first switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the first switch transistor, the first inductor can be charged. In this case, the first output voltage is a voltage difference obtained after a voltage of the first inductor is subtracted from the power supply voltage. After the MCU turns off the first switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the voltage of the first inductor. It can be learned that the first output voltage is always less than the power supply voltage. Therefore, the charging system can perform buck conversion on the power supply voltage. 
     It should be noted that the charging system provided in Example 2 may also perform boost conversion on the power supply voltage. For example, the charging system may include a third switch. A first end of the third switch is connected to one end of the first inductor, and a second end of the third switch is connected to the second power supply end. When the power supply voltage is less than the minimum charging voltage, the MCU may turn on the first end and the third end of the second switch, turn on the third switch, and turn off the first switch; the MCU turns on the first switch transistor, so that the first inductor is charged; and the MCU turns off the first switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the first switch transistor, the first inductor can be charged. After the MCU turns off the first switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the sum of the voltage of the first inductor and the power supply voltage. It can be learned that the first output voltage is greater than the power supply voltage. Therefore, the charging system can perform boost conversion on the power supply voltage. 
     In addition, the charging system provided in Example 2 may also perform buck-boost conversion on the power supply voltage. For example, the charging system may include a third switch. A first end of the third switch is connected to one end of the first inductor, and a second end of the third switch is connected to the second power supply end. The MCU may turn on the first end and the second end of the second switch, and turn on the third switch; the MCU turns on the first switch transistor, so that the first inductor is charged; and the MCU turns off the first switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the first switch transistor, the first inductor can be charged. After the MCU turns off the first switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the voltage of the first inductor. The voltage of the first inductor depends on charging duration of the first inductor. Therefore, the first output voltage can be adjusted by adjusting the charging duration of the first inductor. The first output voltage may be greater than the power supply voltage (boost conversion), or may be less than the power supply voltage (buck conversion). 
     It can be understood that the charging system provided in Example 2 in the application may also be compatible with a scenario in which the power supply voltage matches the power battery. For example, when the power supply voltage falls within a charging voltage range of the power battery, the MCU may turn on the first end and the third end of the second switch, and turn on the first switch. In this case, the power battery is directly connected to the direct current power supply, and can directly receive the power supply voltage to complete charging. 
     According to a second aspect, the application provides a charging system, mainly including a motor control unit MCU and a first inductor. The MCU includes N bridge arms, and N is an integer greater than or equal to one. High-potential ends of the N bridge arms in the MCU are connected to a first power supply end and a first battery end of the charging system, the first power supply end may be connected to a positive electrode of a direct current load, the first battery end may be connected to a positive electrode of a power battery, the direct current load may receive a second output voltage of the charging system, and the power battery may output a battery voltage to the charging system. Low-potential ends of the N bridge arms in the MCU are connected to a second battery end of the charging system, and the second battery end may be connected to a negative electrode of the power battery. One end of the first inductor is connected to a second power supply end, the other end of the first inductor is connected to a first bridge arm, the second power supply end may be connected to a negative electrode of the direct current load, and the first bridge arm is any of the N bridge arms. The first bridge arm and the first inductor constitute a voltage conversion circuit. When the battery voltage is greater than a maximum working voltage of the direct current load, the MCU may perform buck conversion on the battery voltage by using the voltage conversion circuit, and output the battery voltage obtained after buck conversion to the direct current load as the second output voltage, where the second output voltage is not greater than the maximum working voltage. 
     In conclusion, in the application, the MCU is multiplexed to implement a charging system. When the battery voltage is greater than the maximum working voltage of the direct current load, the charging system may perform buck conversion on the battery voltage to obtain the second output voltage that is not greater than the maximum working voltage. In this way, the second output voltage can be adapted to the direct current load, so as to provide power to the direct current load. In addition, in the application, the common MCU in an electric vehicle is multiplexed, which helps reduce space occupied by the charging system and costs of the charging system. 
     For example, the second aspect of the application provides the following examples for description. 
     Example 1 
     For example, the first bridge arm includes a first switch transistor and a second switch transistor. A first electrode of the first switch transistor is separately connected to the first battery end and the first power supply end, a second electrode of the first switch transistor is connected to a first electrode of the second switch transistor, and the middle point of the first bridge arm is located between the first switch transistor and the second switch transistor. When the battery voltage is greater than the maximum working voltage, the MCU may turn on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. In this case, the second output voltage is a voltage difference obtained after a voltage of the first inductor is subtracted from the battery voltage. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the voltage of the first inductor. It can be learned that the first output voltage is always less than the battery voltage. Therefore, the charging system provided in Example 1 in the application can implement buck conversion on the battery voltage. 
     It can be understood that the battery voltage of the power battery may be adapted to the direct current load. To be compatible with this scenario, the charging system may include a first switch. A first end of the first switch is connected to the second battery end, and a second end of the first switch is connected to the second power supply end. The MCU may turn on the first switch when the battery voltage falls within a working voltage range of the direct current load, and turn off the first switch when the battery voltage is beyond the working voltage range of the direct current load. 
     When the first switch is turned on, the power battery can be directly connected to the direct current load, and can directly provide power to the direct current load. When the first switch is turned off, the MCU may convert the battery voltage, and provide the converted battery voltage to the direct current load as the second output voltage. 
     To adapt to a high power scenario, the charging system may include N first inductors and N third switches. One end of each of the N third switches is connected to the second power supply end, the other end of each of the N third switches is connected to one end of each of the N first inductors in a one-to-one correspondence, and the other end of each of the N first inductors is connected to the N bridge arms in a one-to-one correspondence. The N third switches may be turned on when the second output voltage is output, and may be turned off when outputting of the second output voltage is stopped. 
     When the N third switches are turned on, charging and discharging of the N first inductors may be separately controlled by using the N bridge arms. In other words, the N first inductors may be connected in parallel to transmit power, so as to adapt to the high power scenario. When receiving of the power supply voltage is stopped, the N third switches are turned off, so that the N first inductors are disconnected from each other, thereby helping reduce impact of the N first inductors on an inverter function of the MCU. 
     Example 2 
     It is foreseeable that in some scenarios, the battery voltage may be less than a minimum working voltage of the direct current load. In view of this, in the application, when the battery voltage is less than the minimum working voltage of the direct current load, the MCU may perform boost conversion on the battery voltage by using the voltage conversion circuit, and output the battery voltage obtained after boost conversion to the direct current load as the second output voltage, where the second output voltage is not less than the minimum working voltage. 
     For example, the first bridge arm in the MCU includes a first switch transistor and a second switch transistor. A first electrode of the first switch transistor is separately connected to the first battery end and the first power supply end, a second electrode of the first switch transistor is connected to a first electrode of the second switch transistor, and the middle point of the first bridge arm is located between the first switch transistor and the second switch transistor. The charging system may include a first switch and a second switch. A first end of the first switch is connected to the second battery end, a second end of the first switch is connected to the second power supply end, a first end of the second switch is connected to the first battery end, a second end of the second switch is connected to one end of the first inductor, and a third end of the second switch is connected to the first power supply end. 
     Based on the charging system, when the battery voltage is less than the minimum working voltage, the MCU may turn on the first switch, and turn on the first end and the second end of the second switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the second output voltage is the sum of the battery voltage and a voltage of the first inductor. It can be learned that the second output voltage is greater than the battery voltage. Therefore, the charging system can perform boost conversion on the battery voltage. 
     It should be noted that the charging system provided in Example 2 may also perform buck conversion on the battery voltage. For example, the charging system may include a third switch. A first end of the third switch is connected to one end of the first inductor, and a second end of the third switch is connected to the second power supply end. When the battery voltage is greater than the maximum working voltage, the MCU may turn on the first end and the third end of the second switch, turn on the third switch, and turn off the first switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. In this case, the second output voltage is a voltage difference obtained after the voltage of the first inductor is subtracted from the battery voltage. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the second output voltage is the voltage of the first inductor. It can be learned that the second output voltage is always less than the battery voltage. Therefore, the charging system can perform buck conversion on the battery voltage. 
     In addition, the charging system provided in Example 2 may also perform buck-boost conversion on the battery voltage. For example, the charging system may include a third switch. A first end of the third switch is connected to one end of the first inductor, and a second end of the third switch is connected to the second power supply end. The MCU may turn on the first end and the second end of the second switch, and turn on the third switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the second output voltage is the voltage of the first inductor. The voltage of the first inductor depends on charging duration of the first inductor. Therefore, the second output voltage can be adjusted by adjusting the charging duration of the first inductor. The second output voltage may be greater than the battery voltage (boost conversion), or may be less than the battery voltage (buck conversion). 
     It can be understood that the charging system provided in Example 2 in the application may also be compatible with a scenario in which the battery voltage matches the direct current load. For example, when the battery voltage falls within a working voltage range of the power battery, the MCU may turn on the first end and the third end of the second switch, and turn on the first switch. In this case, the power battery is directly connected to the direct current load, and can directly provide power to the direct current load. 
     According to a third aspect, the application provides a charging system, mainly including a motor control unit MCU and a first inductor. The MCU includes N bridge arms, and N is an integer greater than or equal to one. High-potential ends of the N bridge arms are connected to a first battery end of the charging system, the first battery end may be connected to a positive electrode of a power battery, and the power battery may receive a first output voltage of the charging system. Low-potential ends of the N bridge arms are connected to a second battery end and a second power supply end of the charging system, the second battery end may be connected to a negative electrode of the power battery, the second power supply end may be connected to a negative electrode of a direct current power supply, and the direct current power supply may output a power supply voltage. One end of the first inductor is connected to a first power supply end, the other end of the first inductor is connected to a middle point of a first bridge arm, the first power supply end may be connected to a positive electrode of the direct current power supply, and the first bridge arm is any of the N bridge arms. The first bridge arm and the first inductor constitute a voltage conversion circuit. When the power supply voltage is less than a minimum charging voltage of the power battery, the MCU may perform boost conversion on the power supply voltage by using the voltage conversion circuit, and output the power supply voltage obtained after boost conversion to the power battery as the first output voltage, where the first output voltage is not less than the minimum charging voltage. When the power supply voltage is greater than a maximum charging voltage of the power battery, the MCU performs buck conversion on the power supply voltage by using the voltage conversion circuit, and outputs the power supply voltage obtained after buck conversion to the power battery as the first output voltage, where the first output voltage is not greater than the minimum charging voltage. 
     For example, the first bridge arm includes a first switch transistor and a second switch transistor. A first electrode of the first switch transistor is separately connected to the first battery end and the first power supply end, a second electrode of the first switch transistor is connected to a first electrode of the second switch transistor, and the middle point of the first bridge arm is located between the first switch transistor and the second switch transistor. The charging system includes a sixth switch and a fifth switch. A first end of the fifth switch is connected to the second battery end, a second end of the fifth switch is connected to the low-potential ends of the N bridge arms, a third end of the fifth switch is connected to one end of the first inductor, a first end of the sixth switch is connected to the first battery end, and a second end of the sixth switch is connected to the first power supply end. 
     When the power supply voltage is greater than the maximum charging voltage, the MCU may turn on the sixth switch, and turn on the first end and the third end of the fifth switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. In this case, the second output voltage is a voltage difference obtained after a voltage of the first inductor is subtracted from the battery voltage. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the voltage of the first inductor. It can be learned that the first output voltage is always less than the power supply voltage. Therefore, the charging system can perform buck conversion on the power supply voltage. 
     It should be noted that the charging system provided in the third aspect of the application may also perform boost conversion on the power supply voltage. For example, the charging system may include a fourth switch. A first end of the fourth switch is connected to one end of the first inductor, and a second end of the fourth switch is connected to the first power supply end. When the power supply voltage is less than the minimum charging voltage, the MCU may turn on the first end and the second end of the fifth switch, turn on the fourth switch, and turn off the sixth switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the sum of the voltage of the first inductor and the power supply voltage. It can be learned that the first output voltage is greater than the power supply voltage. Therefore, the charging system can perform boost conversion on the power supply voltage. 
     In addition, the charging system provided in the third aspect of the application may also perform buck-boost conversion on the power supply voltage. For example, the charging system may include a fourth switch. A first end of the fourth switch is connected to one end of the first inductor, and a second end of the fourth switch is connected to the first power supply end. The MCU may turn on the first end and the third end of the fifth switch, and turn on the fourth switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the second switch transistor, the first inductor can be charged. After the MCU turns off the second switch transistor, the first inductor can discharge electricity. In this case, the first output voltage is the voltage of the first inductor. The voltage of the first inductor depends on charging duration of the first inductor. Therefore, the first output voltage can be adjusted by adjusting the charging duration of the first inductor. The first output voltage may be greater than the power supply voltage (boost conversion), or may be less than the power supply voltage (buck conversion). 
     It can be understood that the charging system provided the third aspect of the application may also be compatible with a scenario in which the power supply voltage matches the power battery. For example, when the power supply voltage falls within a charging voltage range of the power battery, the MCU may turn on the first end and the second end of the fifth switch, and turn on the sixth switch. In this case, the power battery is directly connected to the direct current power supply, and can directly receive the power supply voltage to complete charging. 
     According to a fourth aspect, the application provides a charging system, mainly including a motor control unit MCU and a first inductor. The MCU includes N bridge arms, and N is an integer greater than or equal to one. High-potential ends of the N bridge arms are connected to a first battery end of the charging system, the first battery end may be connected to a positive electrode of a power battery, and the power battery may output a battery voltage to the charging system. Low-potential ends of the N bridge arms are connected to a second battery end and a second power supply end of the charging system, the second battery end may be connected to a negative electrode of the power battery, the second power supply end may be connected to a negative electrode of a direct current load, and the direct current load may receive a second output voltage of the charging system. One end of the first inductor is connected to a first power supply end, the other end of the first inductor is connected to a middle point of a first bridge arm, the first power supply end may be connected to a positive electrode of the direct current load, and the first bridge arm is any of the N bridge arms. The first bridge arm and the first inductor may constitute a voltage conversion circuit. When the battery voltage is greater than a maximum working voltage of the direct current load, the MCU may perform buck conversion on the battery voltage by using the voltage conversion circuit, and output the battery voltage obtained after buck conversion to the direct current load as the second output voltage, where the second output voltage is not greater than the maximum working voltage. When the battery voltage is less than a minimum working voltage of the direct current load, the MCU performs boost conversion on the battery voltage by using the voltage conversion circuit, and outputs the battery voltage obtained after boost conversion to the direct current load as the second output voltage, where the second output voltage is not less than the minimum working voltage. 
     For example, the first bridge arm in the MCU includes a first switch transistor and a second switch transistor. A first electrode of the first switch transistor is separately connected to the first battery end and the first power supply end, a second electrode of the first switch transistor is connected to a first electrode of the second switch transistor, and the middle point is located between the first switch transistor and the second switch transistor. The charging system includes a sixth switch and a fifth switch. A first end of the fifth switch is connected to the second battery end, a second end of the fifth switch is connected to the low-potential ends of the N bridge arms, a third end of the fifth switch is connected to one end of the first inductor, a first end of the sixth switch is connected to the first battery end, and a second end of the sixth switch is connected to the first power supply end. 
     Based on the charging system, when the battery voltage is less than the minimum working voltage, the MCU may turn on the sixth switch, and turn on the first end and the third end of the fifth switch; the MCU turns on the first switch transistor, so that the first inductor is charged; and the MCU turns off the first switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the first switch transistor, the first inductor can be charged. After the MCU turns off the first switch transistor, the first inductor can discharge electricity. In this case, the second output voltage is the sum of the battery voltage and a voltage of the first inductor. It can be learned that the second output voltage is greater than the battery voltage. Therefore, the charging system can perform boost conversion on the battery voltage. 
     It should be noted that the charging system provided in the fourth aspect of the application may also perform buck conversion on the battery voltage. For example, the charging system may include a fourth switch. A first end of the fourth switch is connected to one end of the first inductor, and a second end of the fourth switch is connected to the first power supply end. When the battery voltage is greater than the maximum working voltage, the MCU may turn on the first end and the second end of the fifth switch, turn on the fourth switch, and turn off the sixth switch; the MCU turns on the second switch transistor, so that the first inductor is charged; and the MCU turns off the second switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the first switch transistor, the first inductor can be charged. In this case, the second output voltage is a voltage difference obtained after the voltage of the first inductor is subtracted from the battery voltage. After the MCU turns off the first switch transistor, the first inductor can discharge electricity. In this case, the second output voltage is the voltage of the first inductor. It can be learned that the second output voltage is always less than the battery voltage. Therefore, the charging system can perform buck conversion on the battery voltage. 
     In addition, the charging system provided in the fourth aspect of the application may also perform buck-boost conversion on the battery voltage. For example, the charging system may include a fourth switch. A first end of the fourth switch is connected to one end of the first inductor, and a second end of the fourth switch is connected to the first power supply end. The MCU may turn on the first end and the third end of the fifth switch, and turn on the fourth switch; the MCU turns on the first switch transistor, so that the first inductor is charged; and the MCU turns off the first switch transistor, so that the first inductor discharges electricity. 
     After the MCU turns on the first switch transistor, the first inductor can be charged. After the MCU turns off the first switch transistor, the first inductor can discharge electricity. In this case, the second output voltage is the voltage of the first inductor. The voltage of the first inductor depends on charging duration of the first inductor. Therefore, the second output voltage can be adjusted by adjusting the charging duration of the first inductor. The second output voltage may be greater than the battery voltage (boost conversion), or may be less than the battery voltage (buck conversion). 
     It can be understood that the charging system provided in the fourth aspect of the application may also be compatible with a scenario in which the battery voltage matches the direct current load. For example, when the battery voltage falls within a working voltage range of the direct current load, the MCU may turn on the first end and the second end of the fifth switch, and turn on the sixth switch. In this case, the power battery is directly connected to the direct current load, and can directly provide power to the direct current load. 
     According to a fifth aspect, the application provides an electric vehicle, mainly including a power battery and the charging system provided in any one of the first aspect to the fourth aspect, where the charging system can charge the power battery. 
     These aspects or other aspects of the application are more readily apparent from the following description of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a charging scenario of an electric vehicle; 
         FIG. 2  is a schematic diagram of an electrical drive system; 
         FIG. 3  is a schematic diagram of a charging system according to an embodiment of the application; 
         FIG. 4  shows a first boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 5  shows a second boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 6  is a schematic diagram of a charging system according to an embodiment of the application; 
         FIG. 7  is a schematic diagram of a charging system according to an embodiment of the application; 
         FIG. 8  shows a first buck conversion state of a charging system according to an embodiment of the application; 
         FIG. 9  shows a second buck conversion state of a charging system according to an embodiment of the application; 
         FIG. 10  is a schematic diagram of a charging system according to an embodiment of the application; 
         FIG. 11  shows a first switch state of a charging system according to an embodiment of the application; 
         FIG. 12  shows a third buck conversion state of a charging system according to an embodiment of the application; 
         FIG. 13  shows a fourth buck conversion state of a charging system according to an embodiment of this application; 
         FIG. 14  shows a second switch state of a charging system according to an embodiment of the application; 
         FIG. 15  shows a third switch state of a charging system according to an embodiment of the application; 
         FIG. 16  shows a first buck-boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 17  shows a second buck-boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 18  shows a third boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 19  shows a fourth boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 20  shows a third buck-boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 21  shows a fourth buck-boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 22  is a schematic diagram of another charging system according to an embodiment of this application; 
         FIG. 23  shows a fourth switch state of a charging system according to an embodiment of the application; 
         FIG. 24  shows a fifth buck conversion state of a charging system according to an embodiment of the application; 
         FIG. 25  shows a sixth buck conversion state of a charging system according to an embodiment of the application; 
         FIG. 26  shows a fifth switch state of a charging system according to an embodiment of the application; 
         FIG. 27  shows a sixth switch state of a charging system according to an embodiment of the application; 
         FIG. 28  shows a fifth buck-boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 29  shows a sixth buck-boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 30  shows a fifth boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 31  shows a sixth boost conversion state of a charging system according to an embodiment of the application; 
         FIG. 32  shows a seventh buck-boost conversion state of a charging system according to an embodiment of the application; and 
         FIG. 33  shows an eighth buck-boost conversion state of a charging system according to an embodiment of the application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To make objectives, technical solutions, and advantages of the application more clearly, the following describes this application in detail with reference to the accompanying drawings. An operation method in a method embodiment may also be applied to an apparatus embodiment or a system embodiment. It should be noted that in the description of this application, “at least one” means one or more, and “a plurality of” means two or more. In view of this, “a plurality of” may also be understood as “at least two” in the embodiments of the present disclosure. “And/or” describes an association relationship between associated objects and represents that three relationships may exist. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists. In addition, unless otherwise specified, the character “I” usually indicates an “or” relationship between the associated objects. In addition, it should be understood that, in the description of this application, terms “first”, “second”, and the like are only used for a purpose of distinguishing between descriptions, but cannot be understood as an indication or implication of relative importance, and cannot be understood as an indication or implication of a sequence. 
     The following clearly describes the technical solutions in the embodiments of the application with reference to the accompanying drawings in the embodiments of the application. 
     An electric vehicle, which may also be referred to as a new energy vehicle, is a vehicle driven by electric energy. As shown in  FIG. 1 , an electric vehicle  10  mainly includes a power battery  12 , a motor  13 , and a wheel  14 . The power battery  12  is a battery with a large capacity and high power. When the electric vehicle  10  travels, the power battery  12  may provide power to the motor  13  by using a motor control unit (MCU)  111 . The motor  13  converts electric energy provided by the power battery  12  into mechanical energy, to drive the wheel  14  to rotate, so that the vehicle travels. 
     When the electric vehicle  10  is charged, a charging pile  20  usually may be used to charge the electric vehicle  10 . As shown in  FIG. 1 , the charging pile  20  mainly includes a power supply circuit  21  and a charging gun  22 . One end of the power supply circuit  21  is connected to a power frequency grid  30 , and the other end of the power supply circuit  21  is connected to the charging gun  22  through a cable. Currently, most charging piles  20  are direct current charging piles, and the power supply circuit  21  may convert alternating current provided by the power frequency grid  30  into direct current. An operator may insert the charging gun  22  into a charging socket of the electric vehicle  10 , so that the charging gun  22  is connected to the power battery  12  in the electric vehicle  10 , and then the power supply circuit  21  of the charging pile  20  can charge the power battery  12  by using the charging gun  22 . 
     An output voltage of the charging pile  20  may be understood as a power supply voltage received by the electric vehicle  10 . In a fast direct current charging scenario, the power supply voltage received by the electric vehicle  10  falls within a charging voltage range of the power battery  12 , and the power battery  12  can directly use the output voltage of the charging pile  20  to complete charging. 
     A lower limit of the charging voltage range of the power battery  12  is a minimum charging voltage, and the minimum charging voltage may be understood as a minimum charging voltage value that can be adapted to the power battery  12 . An upper limit of the charging voltage range of the power battery  12  is a maximum charging voltage, and the maximum charging voltage may be understood as a maximum charging voltage value that can be adapted to the power battery  12 . 
     Currently, to improve a charging speed of the electric vehicle  10 , a voltage level of the power battery  12  gradually increases from current 500 V to 800 V. Using the power battery  12  of an 800 V voltage level as an example, a battery voltage of the power battery  12  can reach 800 V, and a required charging voltage is usually not less than 800 V. However, currently, voltage levels of charging piles  20  that support fast direct current charging in the market are usually 500 V, that is, maximum output voltages of most charging piles  20  that support fast direct current charging are 500 V. As a result, many electric vehicles  10  equipped with a high-voltage power battery face a difficulty of being charged. 
     In view of this, the embodiments of the application provide a charging system  11 , and the charging system  11  is connected to the power battery  12 . When charging the electric vehicle  10 , the charging system  11  may receive a power supply voltage. When the power supply voltage is less than the minimum charging voltage of the power battery  12 , the charging system  11  may perform boost conversion on the power supply voltage, and provide the power supply voltage obtained after boost conversion to the power battery  12  as a first output voltage. 
     In the foregoing example, the output voltage of the charging pile  20  is 500 V, that is, the power supply voltage received by the charging system  11  is 500 V. Assuming that a charging voltage that can be adapted to the power battery  12  is 960 V, the charging system  11  may convert the power supply voltage into 960 V through boosting, to provide a 960 V first output voltage to the power battery  12 , so that the power battery  12  can use the first output voltage to complete charging. 
     It should be noted that to reduce space occupied by the charging system  11  in the electric vehicle  10  and control costs of the charging system  11 , the charging system  11  an embodiment of the application may be implemented based on the MCU  111  in the electric vehicle  10 . The MCU  111  and the motor  13  are generally integrated into an electrical drive system. In other words, the charging system  11  in an embodiment of the application may be implemented by improving a conventional electrical drive system. 
     The motor  13  converts electric energy into mechanical energy based on an electromagnetic induction effect. Therefore, a motor winding is disposed in the motor  13 . Currently, there are three or six motor windings in the motor  13 . A three-phase motor is used as an example. As shown in  FIG. 2 , the MCU  111  includes three bridge arms, the motor  13  includes three motor windings (N 1  to N 3 ), and the three bridge arms in the MCU  111  are respectively connected to the three motor windings in the motor  13  in a one-to-one correspondence. 
     A first bridge arm includes a switch transistor T 1  and a switch transistor T 2 . A first electrode of the switch transistor T 1  is configured to connect to a positive electrode of the power battery  12 , a second electrode of the switch transistor T 1  is connected to a first electrode of the switch transistor T 2 , and a second electrode of the switch transistor T 2  is configured to connect to a negative electrode of the power battery  12 . A middle point of the first bridge arm is a point connecting the switch transistor T 1  and the switch transistor T 2 . The middle point of the first bridge arm is connected to one end of the motor winding N 1 . 
     A second bridge arm includes a switch transistor T 3  and a switch transistor T 4 . A first electrode of the switch transistor T 3  is configured to connect to the positive electrode of the power battery  12 , a second electrode of the switch transistor T 3  is connected to a first electrode of the switch transistor T 4 , and a second electrode of the switch transistor T 4  is configured to connect to the negative electrode of the power battery  12 . A middle point of the second bridge arm is a point connecting the switch transistor T 3  and the switch transistor T 4 . The middle point of the second bridge arm is connected to one end of the motor winding N 2 . 
     A third bridge arm includes a switch transistor T 5  and a switch transistor T 6 . A first electrode of the switch transistor T 5  is configured to connect to the positive electrode of the power battery  12 , a second electrode of the switch transistor T 5  is connected to a first electrode of the switch transistor T 6 , and a second electrode of the switch transistor T 6  is configured to connect to the negative electrode of the power battery  12 . A middle point of the third bridge arm is a point connecting the switch transistor T 5  and the switch transistor T 6 . The middle point of the third bridge arm is connected to one end of the motor winding N 3 , and the other ends of the three motor windings are connected to each other. 
     The MCU  111  includes a control board (not shown in the figure). The control board is separately connected to control electrodes of the switch transistor T 1  to the switch transistor T 6 , to separately control on and off of the switch transistor T 1  to the switch transistor T 6 , so that the three bridge arms can convert the battery voltage that is output by the power battery  12  into three-phase alternating current. Each bridge arm corresponds to one phase of the three-phase alternating current. The MCU  111  outputs the three-phase alternating current to the motor  13 , so that the motor windings N 1  to N 3  generate a space rotational magnetic field, so as to drive a motor rotor to rotate, thereby converting electric energy into mechanical energy. 
     It should be noted that the switch transistor in an embodiment of the application may be one or more of a plurality of types of switch transistors such as a relay, a metal oxide semiconductor field effect transistor (MOSFET), a bipolar junction transistor (BJT), or an insulated gate bipolar transistor (IGBT), which are not enumerated one by one in an embodiment of the application. Each switch transistor may include a first electrode, a second electrode, and a control electrode. The control electrode is configured to control on or off of the switch transistor. When the switch transistor is turned on, current may be transmitted between the first electrode and the second electrode of the switch transistor. When the switch transistor is turned off, the current cannot be transmitted between the first electrode and the second electrode of the switch transistor. The IGBT is used as an example. In an embodiment of the application, the first electrode of the switch transistor may be a collector electrode, the second electrode of the switch transistor may be an emitter electrode, and the control electrode of the switch transistor may be a gate electrode. 
     Generally, as shown in  FIG. 2 , a switch K 2  and a switch K 5  may be disposed between the power battery  12  and the MCU  111 . For example, the switch K 2  and the switch K 5  may be relays. The switch K 2  and the switch K 5  may be integrated with the power battery  12  in a battery pack, or may be independently disposed. This is not limited in an embodiment of the application. 
     One end of the switch K 2  is connected to an anode of the power battery  12 , and the other end of the switch K 2  is connected to high-potential ends of the three bridge arms. One end of the switch K 5  is connected to a cathode of the power battery  12 , and the other end of the switch K 5  is connected to low-potential ends of the three bridge arms. When the switch K 2  and the switch K 5  are turned on, the power battery  12  can provide power to the MCU  111 . When the switch K 2  and the switch K 5  are turned off, the power battery  12  stops providing power to the MCU  111 . 
     It can be learned from the foregoing description of the MCU  111  and the motor  13  that the MCU  111  includes N bridge arms, and N is an integer greater than or equal to one. It can be understood that when the electric vehicle  10  is charged, the electric vehicle  10  usually does not need to be moved. In other words, in this case, the MCU  111  does not need to provide the three-phase current to the motor  13 . Therefore, in an embodiment of the application, the power battery  12  can be charged based on the N bridge arms in the MCU without affecting a traveling function of the electric vehicle  10 . 
     Next, the charging system  11  provided in an embodiment of the application is described by using the following examples. 
     Embodiment 1 
     For example, a charging system  11  provided in an embodiment of the application includes an MCU  111  and a motor  13 . The MCU  111  includes N bridge arms, the motor  13  includes N motor windings, the N bridge arms are respectively connected to the N motor windings in a one-to-one correspondence, and N is an integer greater than or equal to one. 
     For example, N=3. As shown in  FIG. 3 , the charging system  11  includes the MCU  111  and the motor  13 . A first battery end of the charging system  11  is connected to a positive electrode of the power battery  12 , a second battery end of the charging system  11  is connected to a negative electrode of the power battery  12 , a first power supply end of the charging system  11  is connected to a positive electrode of a direct current power supply, and a second power supply end of the charging system is connected to a negative electrode of the direct current power supply. 
     The direct current power supply may be a charging pile, another electric vehicle, or the like. This is not limited in an embodiment of the application. The direct current power supply can output a power supply voltage. The charging system  11  receives the power supply voltage by using the first power supply end and the second power supply end, converts the power supply voltage into a first output voltage adapted to the power battery  12 , and outputs the first output voltage to the power battery  12  by using the first battery end and the second battery end. The power battery  12  can receive the first output voltage provided by the charging system  11  to complete charging. 
     As shown in  FIG. 3 , the MCU  111  includes three bridge arms. In an embodiment of the application, high-potential ends of the three bridge arms in MCU  111  are connected to the first power supply end, and low-potential ends of the three bridge arms are connected to the second battery end of the charging system  11 . The charging system  11  includes an inductor L 1 . One end of the inductor L 1  is connected to the second power supply end, and the other end of the inductor L 1  is connected to a middle point of any bridge arm in the MCU  111 . In the example shown in  FIG. 3 , the other end of the inductor L 1  is connected to a middle point of a bridge arm  2  in which a switch transistor T 3  and a switch transistor T 4  are located. 
     In this case, the three bridge arms in the MCU  111  and the inductor L 1  may constitute a voltage conversion circuit, so that the MCU  111  can control on and off of each of switch transistors T 1  to T 6 , and the voltage conversion circuit converts the power supply voltage. 
     Therefore, when the power supply voltage is less than the minimum charging voltage of the power battery  12 , the MCU  111  may perform boost conversion on the power supply voltage by using the voltage conversion circuit, and output the power supply voltage obtained after boost conversion to the power battery as the first output voltage, where the first output voltage is not less than the minimum charging voltage of the power battery  12 . 
     For example, the power supply voltage is 500 V, and the minimum charging voltage of the power battery  12  is 960 V. The MCU  111  may convert the power supply voltage into 960 V or above 960 V through boosting to provide an adaptive first output voltage to the power battery  12 , so that the power battery  12  can complete charging. 
     Generally, as shown in  FIG. 3 , the charging system  11  includes a switch K 3  and a switch K 4 . The switch K 3  and the switch K 4  may also be referred to as fast contactors. One end of the switch K 3  is connected to a point connecting motor windings N 1  to N 3 , and the other end of the switch K 3  is connected to the second power supply end. One end of the switch K 4  is connected to the high-potential ends of the three bridge arms, and the other end of the switch K 4  is connected to the first power supply end. When the switch K 3  and the switch K 4  are turned on, the direct current power supply can provide power to the charging system  11 . When the switch K 3  and the switch K 4  are turned off, the direct current power supply can stop providing power to the charging system  11 . 
     Next, the bridge arm  2  including the switch transistor T 3  and the switch transistor T 4  is used as an example to illustrate a boost conversion process. The middle point of the bridge arm  2  is a point connecting the switch transistor T 3  and the switch transistor T 4 . One end of the inductor L 1  is connected to the second power supply end, and the other end of the inductor L 1  is connected to the middle point of the bridge arm  2 . When boost conversion is performed on the power supply voltage, the following two stages are mainly included. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  may turn on the switch transistor T 3  to charge the inductor L 1 . It can be understood that in this case, the switch transistor T 4  is turned off. As shown in  FIG. 4 , current is output from the positive electrode of the direct current power supply, and flows back to the negative electrode of the direct current power supply after being transmitted by the switch transistor T 3  and the inductor L 1 , so as to form a charging loop to charge the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  may turn off the switch transistor T 3 , and the inductor L 1  cannot continue to receive the current through the switch transistor T 3 . The inductor L 1  starts to discharge electricity due to a freewheeling feature of the inductor. As shown in  FIG. 5 , the current is output from an end that is of the inductor L 1  and that is close to the second power supply end, and flows back to an end that is of the inductor L 1  and that is close to the switch transistor T 4  after being transmitted by the direct current power supply, the power battery  12 , and a diode in the switch transistor T 4 . In this process, the first output voltage of the charging system  11  is the sum of the power supply voltage of the direct current power supply and a voltage of the inductor L 1 . Apparently, the first output voltage is greater than the power supply voltage of the direct current power supply, so that boost conversion is implemented. 
     It can be understood that when power of the direct current power supply is relatively large, the MCU  111  may also synchronously control a plurality of bridge arms to perform boost conversion. For example, as shown in  FIG. 6 , the MCU  111  includes three inductors (inductors L 1 - 1  to L 1 - 3 ) and three switches K 3  (a switch K 3 - 1  to a switch K 3 - 3 ). One end of each of the switches K 3 - 1  to K 3 - 3  is connected to the second power supply end, and the other end of each of the switches K 3 - 1  to K 3 - 3  is connected to one end of each of the three inductors (the inductors L 1 - 1  to L 1 - 3 ) in a one-to-one correspondence. The switch K 3 - 1  is connected to one end of the inductor L 1 - 1 , the switch K 3 - 2  is connected to one end of the inductor L 1 - 2 , and the switch K 3 - 3  is connected to one end of the inductor L 1 - 3 . 
     The three inductors are respectively connected to middle points of the three bridge arms in the MCU  111  in a one-to-one correspondence. One end of the inductor L 1 - 1  is connected to the second power supply end of the charging system  11 , and the other end of the inductor L 1 - 1  is connected to a middle point between the switch transistor T 1  and the switch transistor T 2 . One end of the inductor L 1 - 2  is connected to the second power supply end of the charging system  11 , and the other end of the inductor L 1 - 2  is connected to a middle point between the switch transistor T 3  and the switch transistor T 4 . One end of the inductor L 1 - 3  is connected to the second power supply end of the charging system  11 , and the other end of the inductor L 1 - 3  is connected to a middle point between the switch transistor T 5  and the switch transistor T 6 . 
     When charging the power battery  12 , the MCU  111  may turn on the switch K 3 - 1  to the switch K 3 - 3 . The MCU  111  may synchronously control on and off of the switch transistor T 1 , the switch transistor T 3 , and the switch transistor T 5 , so that the inductor L 1 - 1  to the inductor L 1 - 3  are simultaneously charged and simultaneously discharge electricity. This case is equivalent to that the three inductors work in parallel to support voltage conversion in a high power scenario. After stopping charging the power battery  12 , the MCU  111  may turn off the switch K 3 - 1  to the switch K 3 - 3 . In this case, the inductor L 1 - 1  to the inductor L 1 - 3  are disconnected from each other, so that impact of the inductor L 1 - 1  to the inductor L 1 - 3  on an inversion process of the MCU  111  can be reduced. 
     In conclusion, the charging system  11  in an embodiment of the application may perform boost conversion on the power supply voltage of the direct current power supply to charge the high-voltage power battery  12 , thereby helping improve convenience of charging the high-voltage power battery  12 . In addition, in an embodiment of the application, the charging system  11  is implemented by multiplexing the N bridge arms in the MCU  111 , thereby helping reduce space occupied by the charging system  11  and costs of the charging system  11 . 
     It can be understood that the power supply voltage provided by the direct current power supply may be adapted to the power battery  12 . For example, the charging voltage range of the power battery  12  is 700 V to 1000 V, and the power supply voltage of the direct current power supply (charging pile) is 800 V. In this case, boost conversion does not need to be performed on the power supply voltage. 
     To be compatible with this scenario, as shown in  FIG. 7 , the charging system  11  provided in an embodiment of the application may include a switch K 1 . A first end of the switch K 1  is connected to the second battery end, and a second end of the switch K 1  is connected to the second power supply end. The MCU  111  may control on and off of the switch K 1 . The MCU  111  may turn on the switch K 1  when the power supply voltage falls within the charging voltage range of the power battery  12 , and turn off the switch K 1  when the power supply voltage is beyond the charging voltage range of the power battery  12 . 
     A scenario in which the power supply voltage falls within the charging voltage range of the power battery  12  may be a scenario in which the power supply voltage is equal to the minimum charging voltage of the power battery  12 , may be a scenario in which the power supply voltage is equal to the maximum charging voltage of the power battery  12 , or may be a scenario in which the power supply voltage is greater than the minimum charging voltage of the power battery  12  and is less than the maximum charging voltage of the power battery  12 . A scenario in which the power supply voltage is beyond the charging voltage range of the power battery  12  may be a scenario in which the power supply voltage is less than the minimum charging voltage of the power battery  12 , or may be a scenario in which the power supply voltage is greater than the maximum charging voltage of the power battery  12 . 
     As shown in  FIG. 7 , when the power battery  12  is charged, the switch K 5  is turned on by default. When the switch K 1  is turned on, the power battery  12  can be directly connected to the direct current power supply, and therefore can directly receive the power supply voltage provided by the direct current power supply to complete charging. Therefore, the MCU  111  may turn on the switch K 1  when the power supply voltage falls within the charging voltage range of the power battery  12 . 
     When the switch K 1  is turned off, the charging system  11  shown in  FIG. 7  is equivalent to the charging system  11  shown in  FIG. 3 , and the MCU  111  may perform boost conversion on the power supply voltage. Details are not described again. 
     In an embodiment, as shown in  FIG. 3 , the charging system  11  may include a filter capacitor C 1 . One end of the filter capacitor C 1  is connected to the first battery end, and the other end of the filter capacitor C 1  is connected to the second battery end. When the power battery  12  is charged, the filter capacitor C 1  may filter the first output voltage. 
     Similarly, as shown in  FIG. 3 , the charging system  11  may include a filter capacitor C 2 . One end of the filter capacitor C 2  is connected to the first power supply end, and the other end of the filter capacitor C 2  is connected to the second power supply end. When the power battery  12  is charged, the filter capacitor C 2  may filter the received power supply voltage. 
     Embodiment 2 
     With development of charging and discharging technologies of the electric vehicle  10 , increasingly more electric vehicles  10  can also support a discharging function, that is, the electric vehicle  10  provides power to a direct current load. In some scenarios, the direct current load may be another electric vehicle. For example, as shown in  FIG. 3 , the first power supply end of the charging system  11  may be connected to a positive electrode of the direct current load, and the second power supply end of the charging system  11  may be connected to a negative electrode of the direct current load. 
     The power battery  12  may output the battery voltage to the charging system  11 . When the battery voltage of the power battery  12  is greater than a maximum working voltage of the direct current load, the charging system  11  may perform buck conversion on the battery voltage to obtain a second output voltage that is adapted to the direct current load, and output the second output voltage to the direct current load by using the first power supply end and the second power supply end. When the direct current load is another electric vehicle, a working voltage range of the direct current load may be understood as a charging voltage range of a power battery in the another electric vehicle. 
     A lower limit of the working voltage range of the direct current load is a minimum working voltage, and the minimum working voltage may be understood as a minimum working voltage value that can be adapted to the direct current load. An upper limit of the working voltage range of the direct current load is the maximum working voltage, and the maximum working voltage may be understood as a maximum working voltage value that can be adapted to the direct current load. 
     For example, if the battery voltage of the power battery  12  is 800 V and the working voltage range of the direct current load is 400 V to 600 V, the MCU  111  may perform buck conversion on the battery voltage to obtain the second output voltage falling within the working voltage range. The charging system  11  outputs the second output voltage to the direct current load to provide an adaptive working voltage to the direct current load. 
     Next, the bridge arm  2  including the switch transistor T 3  and the switch transistor T 4  in  FIG. 3  is used as an example to illustrate a buck conversion process. It can be understood that in this case, the switches K 2  to K 5  are turned on, and details are not described again. When buck conversion is performed on the battery voltage, the following two stages are mainly included. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 4 . In this case, the switch transistor T 3  remains off. As shown in  FIG. 8 , current is output from the positive electrode of the power battery  12 , and flows back to the negative electrode of the power battery  12  after being transmitted by the direct current load, the inductor L 1 , and the switch transistor T 4 . In this stage, the inductor L 1  is charged. The second output voltage that is output by the charging system  11  is a difference obtained after a voltage of the inductor L 1  is subtracted from the battery voltage. Apparently, the second output voltage is less than the battery voltage. Therefore, the charging system  11  can implement buck conversion on the battery voltage. 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  may turn off the switch transistor T 4 , and the charging loop of the inductor L 1  is turned off. The inductor L 1  starts to discharge electricity due to a freewheeling feature of the inductor. As shown in  FIG. 9 , the current is output from an end that is of the inductor L 1  and that is close to the switch transistor T 3 , and flows back to an end that is of the inductor L 1  and that is close to the second power supply end after being transmitted by a diode in the switch transistor T 3  and the direct current load. In this process, the second output voltage of the charging system  11  is the voltage of the inductor L 1 . Apparently, the voltage of the inductor L 1  is less than the battery voltage. Therefore, the charging system  11  can implement buck conversion on the battery voltage. 
     It can be understood that in the charging system  11  shown in  FIG. 6 , the MCU  111  may also synchronously control a plurality of bridge arms to perform boost conversion. For example, the MCU  111  may synchronously control on and off of the switch transistor T 2 , the switch transistor T 4 , and the switch transistor T 6 , so that the inductor L 1 - 1  to the inductor L 1 - 3  are simultaneously charged and simultaneously discharge electricity. This case is equivalent to that the three inductors work in parallel to support voltage conversion in a high power scenario. 
     It should be noted that the charging system  11  shown in  FIG. 7  is also applicable to buck conversion on the battery voltage. When the battery voltage falls within the working voltage range of the direct current load, the MCU  111  may turn on the switch K 1 , so that the power battery  12  directly provides power to the direct current load. When the battery voltage is beyond the working voltage range of the direct current load, the MCU  111  may turn off the switch K 1 , so that the MCU  111  can perform voltage conversion on the battery voltage. Details are not described again. 
     A scenario in which the battery voltage falls within the working voltage range of the direct current load may be a scenario in which the battery voltage is equal to the minimum working voltage of the direct current load, may be a scenario in which the battery voltage is equal to the maximum working voltage of the direct current load, or may be a scenario in which the battery voltage is greater than the minimum working voltage of the direct current load and is less than the maximum working voltage of the direct current load. A scenario in which the battery voltage is beyond the working voltage range of the direct current load may be a scenario in which the battery voltage is less than the minimum working voltage of the direct current load, or may be a scenario in which the battery voltage is greater than the maximum working voltage of the direct current load. 
     Embodiment 3 
     As mentioned above, not only a low-voltage charging pile but also a high-voltage charging pile exists in the market. Not only a high-voltage power battery but also a low-voltage power battery may be configured in the electric vehicle  10 . Therefore, it is also a common scenario in which a high-voltage charging pile charges a low-voltage power battery. 
     In view of this, an embodiment of the application provides a charging system  11 . A connection relationship between the charging system  11  and each of a direct current power supply and the power battery  12  is the same as that in the foregoing embodiment. Details are not described again. When a power supply voltage of the direct current power supply is greater than the maximum charging voltage of the power battery  12 , the charging system  11  may perform buck conversion on the power supply voltage. When the power supply voltage of the direct current power supply is less than the minimum charging voltage of the power battery  12 , the charging system  11  may perform boost conversion on the power supply voltage. Therefore, the charging system  11  can provide the power battery  12  with a first output voltage adapted to the power battery  12 . 
     For example, as shown in  FIG. 10 , the charging system  11  in an embodiment of the application may include an MCU  111  and an inductor L 1 . A connection relationship between the inductor L 1  and the N bridge arms in the MCU  111  is not described again. In addition, the charging system  11  may include a switch K 1  and a switch K 2 . A first end of the switch K 1  is connected to a second battery end of the charging system  11 , and a second end of the switch K 1  is connected to a second power supply end. The switch K 2  is a single-pole double-throw switch. A first end of the switch K 2  is connected to a first battery end, a second end a of the switch K 2  is connected to one end of the inductor L 1 , and a third end b of the switch K 2  is connected to a first power supply end. 
     It should be noted that the switch K 2  and the power battery  12  may be independently disposed. In this case, the first end of the switch K 2  may be understood as the first battery end of the charging system  11 . It can be understood that the switch K 2  and the power battery  12  may be integrated into a power battery pack. In this case, it can be considered that the charging system  11  provided in an embodiment of the application includes two first battery ends, where one first battery end is connected to the second end a of the switch K 2 , and the other first battery end is connected to the third end b of the switch K 2 . 
     Next, buck conversion and boost conversion on the power supply voltage are separately described by using  FIG. 10  as an example. 
     I. Buck Conversion 
     In a buck conversion process, the MCU  111  may turn on the switch K 1 , and turn on the first end and the second end a of the switch K 2 . A circuit state may be shown in  FIG. 11 . It should be noted that in some scenarios, a switch K 3  to a switch K 5  may be disposed in the charging system  11 . In this case, the switch K 4  and the switch K 5  should remain on, and the switch K 3  should remain off. Based on the circuit state shown in  FIG. 11  and using a bridge arm  2  including a switch transistor T 3  and a switch transistor T 4  as an example, the buck conversion process mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 3 , so that the inductor L 1  is charged. As shown in  FIG. 12 , current is output from a positive electrode of the direct current power supply, and flows back to a negative electrode of the direct current power supply after being transmitted by the switch transistor T 3 , the inductor L 1 , the switch K 2 , and the power battery  12 , so as to form a charging loop to charge the inductor L 1 . In this process, the first output voltage of the charging system  11  is a difference obtained after a voltage of the inductor L 1  is subtracted from the power supply voltage. Apparently, the first output voltage is less than the power supply voltage. Therefore, the charging system  11  can implement buck conversion. 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 3 , so that the inductor L 1  discharges electricity. After the MCU  111  turns off the switch transistor T 3 , the charging loop is turned off. The inductor L 1  discharges electricity due to a freewheeling feature of the inductor. As shown in  FIG. 13 , the current is output from an end that is of the inductor L 1  and that is close to the second power supply end, and flows back to an end that is of the inductor L 1  and that is close to the switch transistor T 4  after being transmitted by the switch K 2 , the power battery  12 , and a diode in the switch transistor T 4 . In this process, the first output voltage of the charging system  11  is the voltage of the inductor L 1 . Apparently, the first output voltage is less than the power supply voltage. Therefore, the charging system  11  can implement buck conversion on the power supply voltage. 
     II. Boost Conversion 
     As shown in  FIG. 10 , the charging system  11  may include a switch K 3 . A first end of the switch K 3  is connected to a point connecting motor windings N 1  to N 3 , and a second end of the switch K 3  is connected to the second power supply end. In a boost conversion process, the MCU  111  may turn on the first end and the third end b of the switch K 2 , turn on the switch K 3 , and turn off the switch K 1 . A circuit state may be shown in  FIG. 14 . It can be learned from  FIG. 14  that the circuit state in this case is equivalent to the charging system  11  shown in  FIG. 3 . Therefore, reference may be made to the boost conversion process provided in Embodiment 1. Details are not described again. 
     In addition, the charging system  11  shown in  FIG. 10  may support voltage conversion in a buck-boost mode on the power supply voltage. 
     III. Buck-Boost 
     When buck-boost conversion is performed on the power supply voltage, the MCU  111  may turn on the first end and the second end a of the switch K 2 , and turn on the switch K 3 . A circuit state may be shown in  FIG. 15 . Based on the circuit state shown in  FIG. 15 , the buck-boost conversion mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 3 , so that the inductor L 1  is charged. As shown in  FIG. 16 , current is output from a positive electrode of the direct current power supply, and flows back to a negative electrode of the direct current power supply after being transmitted by the switch transistor T 3  and the inductor L 1 , so as to form a charging loop of the inductor L 1  to charge the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 3 , so that the inductor L 1  discharges electricity. As shown in  FIG. 17 , the current is output from an end that is of the inductor L 1  and that is close to the second power supply end, and flows back to an end that is of the inductor L 1  and that is close to the switch transistor T 4  after being transmitted by the switch K 2 , the power battery  12 , and a diode in the switch transistor T 4 . It can be learned that the first output voltage of the charging system  11  is equal to the voltage of the inductor L 1 . The MCU  111  can control the voltage of the inductor L 1  by controlling charging time of the inductor L 1  in stage 1, so as to control the first output voltage. The first output voltage may be greater than the power supply voltage, or may be less than the power supply voltage. 
     Similar to Embodiment 1, when the power supply voltage of the direct current power supply falls within the charging voltage range of the power battery  12 , the MCU  111  may turn on the first end and the third end b of the switch K 2 , and turn on the switch K 1 , so that the power battery  12  can directly receive the power supply voltage to complete charging. For implementation, refer to Embodiment 1. Details are not described again. 
     Embodiment 4 
     It should be noted that the charging system  11  shown in  FIG. 10  may also support a discharging function of the electric vehicle  10 . When the electric vehicle  10  discharges electricity, a connection relationship between the charging system  11  and each of the power battery  12  and a direct current load is similar to that in Embodiment 2. Details are not described again. 
     Different from Embodiment 2, the charging system  11  provided in  FIG. 10  not only can perform buck conversion on a battery voltage, but also can perform boost conversion on the battery voltage, so that both a battery voltage that is output by a high-voltage power battery and a battery voltage that is output by a low-voltage power battery can be adapted to the direct current load in different working voltage ranges. 
     Next, boost conversion and buck conversion on the battery voltage are separately described by using  FIG. 10  as an example. 
     I. Boost Conversion 
     In a boost conversion process, the MCU  111  may turn on the switch K 1 , and turn on the first end and the second end a of the switch K 2 . A circuit state may be shown in  FIG. 11 . Based on the circuit state shown in  FIG. 11  and using a bridge arm  2  including a switch transistor T 3  and a switch transistor T 4  as an example, the boost conversion process mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 4 , so that the inductor L 1  is charged. As shown in  FIG. 18 , current is output from a positive electrode of the power battery  12 , and flows back to a negative electrode of the power battery  12  after being transmitted by the switch K 2 , the inductor L 1 , and the switch transistor T 4 , so as to form a charging loop to charge the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 4 , so that the inductor L 1  discharges electricity. After the MCU  111  turns off the switch transistor T 4 , the charging loop is turned off. The inductor L 1  discharges electricity due to a freewheeling feature of the inductor. As shown in  FIG. 19 , the current is output from the positive electrode of the power battery  12 , and flows back to the negative electrode of the power battery  12  after being transmitted by the switch K 2 , the inductor L 1 , a diode in the switch transistor T 3 , and the direct current load. In this process, a second output voltage of the charging system  11  is the sum of the battery voltage of the power battery  12  and the voltage of the inductor L 1 . Apparently, the second output voltage is greater than the battery voltage. Therefore, the charging system  11  can implement boost conversion on the battery voltage. 
     II. Buck Conversion 
     As shown in  FIG. 10 , the charging system  11  may include a switch K 3 . A first end of the switch K 3  is connected to a point connecting motor windings N 1  to N 3 , and a second end of the switch K 3  is connected to the second power supply end. In a buck conversion process, the MCU  111  may turn on the first end and the third end b of the switch K 2 , turn on the switch K 3 , and turn off the switch K 1 . A circuit state may be shown in  FIG. 14 . It can be learned from  FIG. 14  that the circuit state in this case is equivalent to the charging system  11  shown in  FIG. 3 . Therefore, reference may be made to the buck conversion process provided in Embodiment 2. Details are not described again. 
     In addition, the charging system  11  shown in  FIG. 10  may support voltage conversion in a buck-boost mode on the battery voltage. 
     III. Buck-Boost 
     When buck-boost conversion is performed on the battery voltage, the MCU  111  may turn on the first end and the second end a of the switch K 2 , and turn on the switch K 3 . A circuit state may be shown in  FIG. 15 . Based on the circuit state shown in  FIG. 15 , the buck-boost conversion mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 4 , so that the inductor L 1  is charged. As shown in  FIG. 20 , current is output from a positive electrode of the power battery  12 , and flows back to a negative electrode of the power battery  12  after being transmitted by the switch K 2 , the inductor L 1 , and the switch transistor T 4 , so as to form a charging loop of the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 4 , so that the inductor L 1  discharges electricity. As shown in  FIG. 21 , the current is output from an end that is of the inductor L 1  and that is close to the switch transistor T 3 , and flows back to an end that is of the inductor L 1  and that is close to the second power supply end after being transmitted by a diode in the switch transistor T 3  and the direct current load. It can be learned that the second output voltage of the charging system  11  is equal to the voltage of the inductor L 1 . The MCU  111  can control the voltage of the inductor L 1  by controlling charging time of the inductor L 1  in stage 1, so as to control the second output voltage. The second output voltage may be greater than the battery voltage, or may be less than the battery voltage. 
     Similar to Embodiment 2, when the battery voltage of the power battery  12  falls within the working voltage range of the direct current load, the MCU  111  may turn on the first end and the third end b of the switch K 2 , and turn on the switch K 1 , so that the power battery  12  can directly provide power to the direct current load. For implementation, refer to Embodiment 2. Details are not described again. 
     Embodiment 5 
     In Embodiment 3 and Embodiment 4, the inductor L 1  is connected to the second power supply end. Based on a similar concept, the inductor L 1  may also be connected to the first power supply end. In this case, the charging system  11  may be shown in  FIG. 22 . 
     The charging system  11  includes a switch K 5  and a switch K 6 . The switch K 5  is a single-pole double-throw switch, a first end of the switch K 5  is connected to the second battery end, a second end a of the switch K 5  is connected to low-potential ends of the N bridge arms, a third end b of the switch K 5  is connected to one end of the inductor L 1 , a second end of the switch K 6  is connected to the second power supply end, a first end of the switch K 6  is connected to the first battery end, and the second end of the switch K 6  is connected to the first power supply end. 
     It should be noted that the switch K 5  and the power battery  12  may be independently disposed. In this case, the first end of the switch K 5  may be understood as the second battery end of the charging system  11 . It can be understood that the switch K 5  and the power battery  12  may be integrated into a power battery pack. In this case, it can be considered that the charging system  11  provided in an embodiment of the application includes two second battery ends, where one second battery end is connected to the second end a of the switch K 5 , and the other second battery end is connected to the third end b of the switch K 5 . 
     Next, buck conversion and boost conversion on the power supply voltage are separately described by using  FIG. 22  as an example. 
     I. Buck Conversion 
     When the power supply voltage is greater than the maximum charging voltage, the MCU  111  may perform buck conversion on the power supply voltage. In a buck conversion process, the MCU  111  may turn on the switch K 6 , and turn on the first end and the third end b of the switch K 5 . A circuit state may be shown in  FIG. 23 . It should be noted that in some scenarios, a switch K 2  to a switch K 4  may be disposed in the charging system  11 . In this case, the switch K 2  and the switch K 3  should remain on, and the switch K 4  should remain off. Based on the circuit state shown in  FIG. 23  and using a bridge arm  2  including a switch transistor T 3  and a switch transistor T 4  as an example, the buck conversion process mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 4 , so that the inductor L 1  is charged. As shown in  FIG. 24 , current is output from a positive electrode of the direct current power supply, and flows back to a negative electrode of the direct current power supply after being transmitted by the power battery  12 , the switch K 5 , the inductor L 1 , and the switch transistor T 4 , so as to form a charging loop to charge the inductor L 1 . In this process, the first output voltage of the charging system  11  is a difference obtained after a voltage of the inductor L 1  is subtracted from the power supply voltage. Apparently, the first output voltage is less than the power supply voltage. Therefore, the charging system  11  can implement buck conversion. 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 4 , so that the inductor L 1  discharges electricity; and turns off a second switch transistor, so that the inductor L 1  discharges electricity. After the MCU  111  turns off the switch transistor T 4 , the charging loop is turned off. The inductor L 1  discharges electricity due to a freewheeling feature of the inductor. As shown in  FIG. 25 , the current is output from an end that is of the inductor L 1  and that is close to the switch transistor T 3 , and flows back to an end that is of the inductor L 1  and that is close to the first power supply end after being transmitted by a diode in the switch transistor T 3 , the power battery  12 , and the switch K 5 . In this process, the first output voltage of the charging system  11  is the voltage of the inductor L 1 . Apparently, the first output voltage is less than the power supply voltage. Therefore, the charging system  11  can implement buck conversion on the power supply voltage. 
     II. Boost Conversion 
     As shown in  FIG. 22 , the charging system  11  may include a switch K 4 . A first end of the switch K 4  is connected to a point connecting the N motor windings, and a second end of the switch K 4  is connected to the first power supply end. In a boost conversion process, the MCU  111  may turn on the first end and the second end of the switch K 5 , turn on the switch K 4 , and turn off the switch K 6 . A circuit state may be shown in  FIG. 26 . It can be learned from  FIG. 26  that the circuit state in this case is equivalent to the charging system  11  shown in  FIG. 3 . Therefore, reference may be made to the boost conversion process provided in Embodiment 1. Details are not described again. 
     In addition, the charging system  11  shown in  FIG. 22  may support voltage conversion in a buck-boost mode on the power supply voltage. 
     III. Buck-Boost 
     When buck-boost conversion is performed on the power supply voltage, the MCU  111  may turn on the first end and the third end b of the switch K 5 , and turn on the switch K 4 . A circuit state may be shown in  FIG. 27 . Based on the circuit state shown in  FIG. 27 , the buck-boost conversion mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 4 , so that the inductor L 1  is charged. As shown in  FIG. 28 , current is output from a positive electrode of the direct current power supply, and flows back to a negative electrode of the direct current power supply after being transmitted by the inductor L 1  and the switch transistor T 4 , so as to form a charging loop of the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 3 , so that the inductor L 1  discharges electricity. As shown in  FIG. 29 , the current is output from an end that is of the inductor L 1  and that is close to the switch transistor T 3 , and flows back to an end that is of the inductor L 1  and that is close to the first power supply end after being transmitted by a diode in the switch transistor T 3 , the power battery  12 , and the switch K 5 . It can be learned that the first output voltage of the charging system  11  is equal to the voltage of the inductor L 1 . The MCU  111  can control the voltage of the inductor L 1  by controlling charging time of the inductor L 1  in stage 1, so as to control the first output voltage. The first output voltage may be greater than the power supply voltage, or may be less than the power supply voltage. 
     Similar to Embodiment 1, when the power supply voltage of the direct current power supply falls within the charging voltage range of the power battery  12 , the MCU  111  may turn on the first end and the second end a of the switch K 5 , and turn on the switch K 6 , so that the power battery  12  can directly receive the power supply voltage to complete charging. For implementation, refer to Embodiment 1. Details are not described again. 
     Embodiment 6 
     It should be noted that the charging system  11  shown in  FIG. 22  also not only can perform buck conversion on a battery voltage, but also can perform boost conversion on the battery voltage, so that both a battery voltage that is output by a high-voltage power battery and a battery voltage that is output by a low-voltage power battery can be adapted to the direct current load in different working voltage ranges. 
     Next, boost conversion and buck conversion on the battery voltage are separately described by using  FIG. 22  as an example. 
     I. Boost Conversion 
     In a boost conversion process, the MCU  111  may turn on the switch K 6 , and turn on the first end and the third end b of the switch K 5 . A circuit state may be shown in  FIG. 23 . Based on the circuit state shown in  FIG. 23  and using a bridge arm  2  including a switch transistor T 3  and a switch transistor T 4  as an example, the boost conversion process mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 3 , so that the inductor L 1  is charged. As shown in  FIG. 30 , current is output from a positive electrode of the power battery  12 , and flows back to a negative electrode of the power battery  12  after being transmitted by the switch transistor T 3 , the inductor L 1 , and the switch K 5 , so as to form a charging loop to charge the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 3 , so that the inductor L 1  discharges electricity. After the MCU  111  turns off the switch transistor T 3 , the charging loop is turned off. The inductor L 1  discharges electricity due to a freewheeling feature of the inductor. As shown in  FIG. 32 , the current is output from the positive electrode of the power battery  12 , and flows back to the negative electrode of the power battery  12  after being transmitted by the direct current load, a diode in the switch transistor T 4 , the inductor L 1 , and the switch transistor T 5 . In this process, a second output voltage of the charging system  11  is the sum of the battery voltage of the power battery  12  and the voltage of the inductor L 1 . Apparently, the second output voltage is greater than the battery voltage. Therefore, the charging system  11  can implement boost conversion on the battery voltage. 
     II. Buck Conversion 
     As shown in  FIG. 22 , the charging system  11  may include a switch K 4 . A first end of the switch K 4  is connected to a point connecting the N motor windings, and a second end of the switch K 4  is connected to the first power supply end. In a buck conversion process, the MCU  111  may turn on the first end and the second end a of the switch K 5 , turn on the switch K 4 , and turn off the switch K 6 . A circuit state may be shown in  FIG. 26 . It can be learned from  FIG. 26  that the circuit state in this case is equivalent to the charging system  11  shown in  FIG. 3 . Therefore, reference may be made to the buck conversion process provided in Embodiment 2. Details are not described again. 
     In addition, the charging system  11  shown in  FIG. 22  may also support voltage conversion in a buck-boost mode on the battery voltage. 
     III. Buck-Boost 
     When buck-boost conversion is performed on the battery voltage, the MCU  111  may turn on the first end and the third end b of the switch K 5 , and turn on the switch K 4 . A circuit state may be shown in  FIG. 27 . Based on the circuit state shown in  FIG. 27 , the buck-boost conversion mainly includes the following two stages. 
     Stage 1: The inductor L 1  is charged. 
     The MCU  111  turns on the switch transistor T 3 , so that the inductor L 1  is charged. As shown in  FIG. 32 , current is output from a positive electrode of the power battery  12 , and flows back to a negative electrode of the power battery  12  after being transmitted by the switch transistor T 3 , the inductor L 1 , and the switch K 5 , so as to form a charging loop of the inductor L 1 . 
     Stage 2: The inductor L 1  discharges electricity. 
     The MCU  111  turns off the switch transistor T 3 , so that the inductor L 1  discharges electricity. As shown in  FIG. 33 , the current is output from an end that is of the inductor L 1  and that is close to the first power supply end, and flows back to an end that is of the inductor L 1  and that is close to the switch transistor T 4  after being transmitted by the direct current load and a diode in the switch transistor T 4 . It can be learned that the second output voltage of the charging system  11  is equal to the voltage of the inductor L 1 . The MCU  111  can control the voltage of the inductor L 1  by controlling charging time of the inductor L 1  in stage 1, so as to control the second output voltage. The second output voltage may be greater than the battery voltage, or may be less than the battery voltage. 
     Similar to Embodiment 2, when the battery voltage of the power battery  12  falls within the working voltage range of the direct current load, the MCU  111  may turn on the first end and the second end a of the switch K 5 , and turn on the switch K 6 , so that the power battery  12  can directly provide power to the direct current load. For implementation, refer to Embodiment 2. Details are not described again. 
     It is clear that one of ordinary skilled in the art can make various modifications and variations to this application without departing from the scope of this application. This application is intended to cover these modifications and variations of this application provided that they fall within the scope of the claims of the application and their equivalent technologies.