Patent Publication Number: US-2020303926-A1

Title: Car charger and vehicle

Description:
BACKGROUND 
     Technical Field 
     The present invention relates to the field of vehicle technologies and, in particular, to a car charger and a vehicle having the car charger. 
     Related Art 
     There are various car chargers such as unidirectional and bidirectional car chargers. In the related art, as shown in  FIG. 1 , a unidirectional isolated car charger is illustrated. The car charger includes a rectifier bridge circuit  1 ′, a power factor correction circuit  2 ′, a direct current (DC)/DC isolated converter  3 ′, a control circuit  4 ′ and a control circuit  5 ′. The car charger intelligently implements charging of an energy storage device, that is, a battery. The rectifier bridge circuit  1 ′ converts an external alternating current (AC) into a DC current (half wave). The power factor correction circuit  2 ′ includes a power transistor Q 5 ′, an inductor L 1 ′, a diode D 1 ′ and a filter capacitor C 1 ′. The control circuit  4 ′ collects an AC input voltage VL/VN and a current iq of the power transistor Q 5 ′, obtains a pulse width modulation (PWM) wave (PWM 1 ′) with an appropriate duty cycle through calculation, controls the power transistor Q 5 ′, and makes the AC input current synchronized with the input voltage, thereby improving an AC terminal power factor. The DC/DC isolated converter  3 ′ includes power transistors Q 1 ′, Q 2 ′, Q 3 ′ and Q 4 ′, a transformer T 1 ′, a rectifier bridge circuit  6 ′ and a filter capacitor C 2 ′. The control circuit  5 ′ collects a DC output voltage Vdc and a DC current Idc, obtains a PWM wave (PWM 2 ′) with an appropriate duty cycle through calculation, controls turning on or off of the power transistors Q 1 ′, Q 2 ′, Q 3 ′ and Q 4 ′, stabilizes an output DC voltage by using the transformer T 1 ′ and rectifier bridge circuit  6 ′, and changes an energy storage device such as a high-voltage battery. 
     As shown in  FIG. 2 ,  FIG. 2  is a circuit diagram of a bidirectional non-isolated car charger in the related art. The car charger includes a bidirectional converter circuit  10 ′ (PWM rectifier circuit) including four power controllable switch transistors, a boost circuit and a filter capacitor. During charging, the converter circuit  10 ′ is used as a controllable DC circuit, an AC current is connected to a controllable rectifier circuit, and a control module  20 ′ performs Sinusoidal PWM (SPWM) control on power transistors Q 10 ′ to Q 40 ′ to output a DC current (half wave) and is connected to a high voltage battery pack. During discharging, the converter circuit  10 ′ is used as an inverter circuit, and the high voltage battery pack is connected to the inverter circuit and outputs an AC current to a load of an AC terminal for use. 
     However, the unidirectional isolated car charger has a complex topology and a large quantity of power devices, and needs to be controlled at multiple levels, leading to high costs and low efficiency. A diode of a rectifier bridge, a controllable switch transistor of the power factor correction circuit, a controllable switch transistor of a DC/DC converter and an isolated rectifier circuit all have controllable switch losses, making an energy storage device incapable of outputting an AC current externally. 
     Although the bidirectional non-isolated car charger has a simple structure and relatively low costs, there are many problems due to its non-isolated system. For example, limited by a limit of an AC peak voltage, when an output voltage is lower than the AC peak value voltage, charging cannot be directly performed by using a circuit. Further, as a DC voltage increases, a loss of a power transistor controllable switch increases, efficiency decreases, and heat dissipation becomes more difficult. The power transistor needs to withstand higher voltage stress while satisfying power. The voltage stress refers to a ratio of an actual voltage to a device specification value. Higher voltage stress indicates a greater pressure withstood by the power transistor. 
     Further, in the non-isolated system, the AC and DC are switched by the controllable switch transistor. A high common-mode voltage on the AC side is difficult to eliminate and there is a great potential safety hazard. A current discharged by the DC side to the ground is finally fed back to a power grid through an AC line. When a product is working, an AC leakage current detection value is relatively large, which easily triggers leakage protection. 
     SUMMARY 
     An objective of the present invention is to at least resolve one of the technical problems in the related art to some extent. 
     Therefore, the present invention needs to provide a car charger. The car charger can implement bidirectional electric energy transmission and it is safer to use an isolated design. 
     The present invention further provides a vehicle having the car charger. 
     To resolve the foregoing problem, according to one aspect, this application provides a car charger. The car charger includes: a bidirectional converter module, where a first end of the bidirectional converter module is connected to one end of an AC terminal, and a second end of the bidirectional converter module is connected to the other end of the AC terminal; a bidirectional DC/DC conversion module, where the bidirectional DC/DC conversion module includes: a first DC conversion unit, where a first end of the first DC conversion unit is connected to a third end of the bidirectional converter module, and a second end of the first DC conversion unit is connected to a fourth end of the bidirectional converter module; a transformer unit, where a first end of the transformer unit is connected to a third end of the first DC conversion unit, and a second end of the transformer unit is connected to a fourth end of the first DC conversion unit; and a second DC conversion unit, where a first end of the second DC conversion unit is connected to a third end of the transformer unit, a second end of the second DC conversion unit is connected to a fourth end of the transformer unit, a third end of the second DC conversion unit is connected to one end of an energy storage device, and a fourth end of the second DC conversion unit is connected to another end of the energy storage device; a collection module, where the collection module collects an output of the AC terminal, a rectified output of the bidirectional converter module, and an output of the second DC conversion unit, and collects an output of the energy storage device, an output of the first DC conversion unit, and an inverter output of the bidirectional converter module; and a control module, where the control module controls the bidirectional converter module, the first DC conversion unit, and the second DC conversion unit according to the data collected by the collection module, so that the energy storage device performs charging or discharging. 
     The car charger of the present invention can implement bidirectional flow of energy and improve efficiency based on a combination of the bidirectional converter module and the bidirectional DC/DC conversion module. The bidirectional DC/DC conversion module uses the transformer unit for isolation, so that a common-mode voltage on the AC side can be reduced to isolate the AC side from the DC side, thereby improving safety and reducing conducted radiation. A DC voltage has a wide application range. 
     Based on the foregoing car charger, according to another aspect, the present invention further provides a vehicle. The vehicle includes the car charger described above. 
     By using the car charger according to the foregoing aspect, the vehicle can implement bidirectional energy transmission, isolate the AC side from the DC side, reduce the common-mode voltage on the AC side, and improve safety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a circuit of a unidirectional isolated car charger in the related art; 
         FIG. 2  shows a bidirectional non-isolated car charger in the related art; 
         FIG. 3  is a block diagram of a car charger according to an embodiment of the present invention; 
         FIG. 4  is a schematic circuit diagram of a car charger according to an embodiment of the present invention; and 
         FIG. 5  is a block diagram of a vehicle according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes in detail embodiments of the present invention. Examples of the embodiments are shown in the accompanying drawings, where reference signs that are the same or similar from beginning to end represent same or similar components or components that have same or similar functions. The following embodiments described with reference to the accompanying drawings are exemplary, and are intended to describe the present invention and cannot be construed as a limitation to the present invention. 
     The following describes a car charger provided in the embodiments of the present invention with reference to the accompanying drawings. 
       FIG. 3  is a block diagram of a car charger according to an embodiment of the present invention. As shown in  FIG. 3 , the car charger  100  includes a bidirectional converter module  10 , a bidirectional DC/DC conversion module  20 , a collection module  30 , and a control module  40 . 
     A first end a 11  of the bidirectional converter module  10  is connected to one end of an AC terminal. A second end a 12  of the bidirectional converter module  10  is connected to the other end of the AC terminal. The bidirectional DC/DC conversion module  20  includes a first DC conversion unit  201 , a transformer unit  202 , and a second DC conversion unit  203 . 
     A first end b 11  of the first DC conversion unit  201  is connected to a third end a 13  of the bidirectional converter module  10 . A second end b 12  of the first DC conversion unit  201  is connected to a fourth end a 14  of the bidirectional converter module  10 . A first end c 11  of the transformer unit  202  is connected to a third end b 13  of the first DC conversion unit  201 . A second end c 12  of the transformer unit  202  is connected to a fourth end b 14  of the first DC conversion unit  201 . A first end d 11  of the second DC conversion unit  203  is connected to a third end c 13  of the transformer unit  202 . A second end d 12  of the second DC conversion unit  203  is connected to a fourth end c 14  of the transformer unit  202 . A third end d 13  of the second DC conversion unit  203  is connected to one end of an energy storage device such as a high-voltage battery. A fourth end d 14  of the second DC conversion unit  203  is connected to another end of the energy storage device. 
     The collection module  30  collects an output such as an output current signal and current and voltage signals of the AC terminal, a rectified output of the bidirectional converter module  10 , and an output of the second DC conversion unit  203 , and collects an output of the energy storage device, an output of the first DC conversion unit  201 , and an inverter output of the bidirectional converter module  10 . 
     The control module  40  controls the bidirectional converter module  10 , the first DC conversion unit  201 , and the second DC conversion unit  203  according to the data collected by the collection module  30 , so that the energy storage device performs charging or discharging to implement bidirectional electric power transmission. 
     The car charger  100  in this embodiment of the present invention obtains a bidirectional isolated converter circuit by combining the bidirectional converter module  10  such as a bidirectional PWM rectifier circuit and an isolated bidirectional DC/DC conversion module  20 . “Bidirectional” herein may be referred as being capable of implementing both rectification and inversion. 
     Specifically, during charging of the energy storage device such as a high voltage battery pack, the bidirectional converter module  10  is used as a rectifier circuit and the bidirectional DC/DC conversion module  20  is used as an inverter-transformer transmission-rectifier circuit. 
     The first DC conversion unit  201  performs inversion control, the transformer unit  202  provides an isolation function to isolate the AC side from the DC side, and the second DC conversion unit  203  performs rectification control. An AC current is connected to the bidirectional converter module  10  as an input end. The control module  40  performs calculation according to the data collected by the collection module  30  and performs SPWM control on the bidirectional converter module  10 , to output a DC current such as a half wave DC current. After an output DC voltage is stabilized, the control module  40  controls the first DC conversion unit  201  to convert the DC current into an AC current, controls the transformer unit  202  to transmit energy, then rectifies the AC current into a DC current by using the second DC conversion unit  203 , and connects the DC current to the energy storage device such as a high voltage battery pack, to implement a charging function of the energy storage device. 
     During discharging of the energy storage device, the bidirectional converter module  10  such as a PWM rectifier circuit is used as an inverter circuit, and the bidirectional DC/DC conversion unit  20  is also used as an inverter-transformer transmission-rectifier circuit. The energy storage device such as a high voltage battery pack is used as an input end and connected to the second DC conversion unit  203 . The second DC conversion unit  203  converts a DC current output by the high voltage battery pack into an AC current. The transformer unit  202  transmits energy. Then the first DC conversion unit  201  rectifies the AC current into a DC current and outputs the DC current into the bidirectional converter module  10 . The bidirectional converter module  10  converts the DC current into an AC current, for use by a load of the AC terminal, thereby implementing a discharging function of the energy storage device. 
     It can be seen that the car charger  100  of this embodiment of the present invention uses the bidirectional converter module  10  and the bidirectional DC/DC conversion module  20 , to implement bidirectional energy transmission. The AC current can be used to charge the energy storage device and the energy storage device can perform outputting to provide power for an AC load of the AC terminal. An isolation design of using the transformer unit  202  in the bidirectional DC/DC conversion module  20  can reduce a common-mode voltage on the AC side and isolate the AC side from the DC side, thereby improving safety. The transformer unit  202  is used to increase or reduce a voltage, and a DC voltage has a wide application range, thereby reducing conducted radiation. 
     The following further describes the modules of the car charger  100  of this embodiment of the present invention with reference to  FIG. 4 . 
     The bidirectional converter module  10  may be a controllable bidirectional PWM rectifier circuit. The bidirectional converter module  10  includes a first controllable switch transistor Q 1 , a second controllable switch transistor Q 2 , a third controllable switch transistor Q 3 , and a fourth controllable switch transistor Q 4 . 
     A control end  01  of the first controllable switch transistor Q 1  is connected to the control module  40 . A control end  02  of the second controllable switch transistor Q 2  is connected to the control module  40 . A first end  21  of the second controllable switch transistor Q 2  is connected to a second end  12  of the first controllable switch transistor Q 1 . There is a first node D 1  between the first end  21  of the second controllable switch transistor Q 2  and the second end  12  of the first controllable switch transistor Q 1 . The first node D 1  is connected to one end of the AC terminal. A control end  03  of the third controllable switch transistor Q 3  is connected to the control module  40 . A first end  31  of the third controllable switch transistor Q 3  is connected to a first end  11  of the first controllable switch transistor Q 1  and the first DC conversion unit  201 . A control end  04  of the fourth controllable switch transistor Q 4  is connected to the control module  40 . A first end  41  of the fourth controllable switch transistor Q 4  is connected to a second end  32  of the third controllable switch transistor Q 3 . There is a second node D 2  between the first end  41  of the fourth controllable switch transistor Q 4  and the second end  32  of the third controllable switch transistor Q 3 . The second node D 2  is connected to the other end of the AC terminal. A second end  42  of the fourth controllable switch transistor Q 4  is connected to a second end  22  of the second controllable switch transistor Q 2  and the first DC conversion unit  201 . 
     During outputting of the AC terminal, that is, during charging of the energy storage device, the control module  40  controls the first controllable switch transistor Q 1 , the second controllable switch transistor Q 2 , the third controllable switch transistor Q 3  and the fourth controllable switch transistor Q 4  according to an AC voltage and an AC current output by the AC terminal and a rectified output voltage of the bidirectional converter module  10 . The bidirectional converter module  10  implements a rectification function. 
     During discharging of the energy storage device, the control module  40  controls the first controllable switch transistor Q 1 , the second controllable switch transistor Q 2 , the third controllable switch transistor Q 3 , and the fourth controllable switch transistor Q 4  according to an AC voltage of the inverter output of the bidirectional converter module  10 . The bidirectional converter module  10  implements an inversion function. 
     As shown in  FIG. 4 , the bidirectional converter module  10  further includes a filter unit  1010 . The filter unit  1010  includes a first inductor L 1 , a second inductor L 2 , and a first capacitor C 1 . A first end of the first inductor L 1  is connected to one end of the AC terminal. A second end of the first inductor L 1  is connected to the first node D 1 . A first end of the second inductor L 2  is connected to the other end of the AC terminal. A second end of the second inductor L 2  is connected to the second node D 2 . A first end of the first capacitor C 1  is connected to the first end of the first inductor L 1  and one end of the AC terminal. A second end of the first capacitor C 1  is connected to the first end of the second inductor L 2  and the other end of the AC terminal. 
     The first DC conversion unit  201  includes a fifth controllable switch transistor Q 5 , a sixth controllable switch transistor Q 6 , a seventh controllable switch transistor Q 7 , and an eighth controllable switch transistor Q 8 . 
     A control end  05  of the fifth controllable switch transistor Q 5  is connected to the control module  40 . A first end  51  of the fifth controllable switch transistor Q 5  is connected to the first end  31  of the third controllable switch transistor Q 3 . A control end  06  of the sixth controllable switch transistor Q 6  is connected to the control module  40 . A first end  61  of the sixth controllable switch transistor Q 6  is connected to a second end  52  of the fifth controllable switch transistor Q 5 . There is a third node D 3  between the first end  61  of the sixth controllable switch transistor Q 6  and a second end  52  of the fifth controllable switch transistor Q 5 . A second end  62  of the sixth controllable switch transistor Q 6  is connected to the second end  42  of the fourth controllable switch transistor Q 4 . A control end  07  of the seventh controllable switch transistor Q 7  is connected to the control module  40 . A first end  71  of the seventh controllable switch transistor Q 7  is connected to the first end  51  of the fifth controllable switch transistor Q 5 . A control end  08  of the eighth controllable switch transistor Q 8  is connected to the control module  40 . A first end  81  of the eighth controllable switch transistor Q 8  is connected to a second end  72  of the seventh controllable switch transistor Q 7 . There is a fourth node D 4  between the first end  81  of the eighth controllable switch transistor Q 8  and a second end  72  of the seventh controllable switch transistor Q 7 . A second end  82  of the eighth controllable switch transistor Q 8  is connected to the second end  62  of the sixth controllable switch transistor Q 6 . 
     The second DC conversion unit  203  includes a ninth controllable switch transistor Q 9 , a tenth controllable switch transistor Q 10 , an eleventh controllable switch transistor Q 11 , and a twelfth controllable switch transistor Q 12 . 
     A control end  09  of the ninth controllable switch transistor Q 9  is connected to the control module  40 . A control end  010  of the tenth controllable switch transistor Q 10  is connected to the control module  40 . A first end  101  of the tenth controllable switch transistor Q 10  is connected to a second end  92  of the ninth controllable switch transistor Q 9 . There is a fifth node D 5  between the first end  101  of the tenth controllable switch transistor Q 10  and the second end  92  of the ninth controllable switch transistor Q 9 . A control end  011  of the eleventh controllable switch transistor Q 11  is connected to the control module  40 . A first end  111  of the eleventh controllable switch transistor Q 11  is connected to a first end  91  of the ninth controllable switch transistor Q 9  and one end of the energy storage device. A control end  012  of the twelfth controllable switch transistor Q 12  is connected to the control module  40 . A first end  121  of the twelfth controllable switch transistor Q 12  is connected to a second end  112  of the eleventh controllable switch transistor Q 11 . There is a sixth node D 6  between the first end  121  of the twelfth controllable switch transistor Q 12  and a second end  112  of the eleventh controllable switch transistor Q 11 . A second end  122  of the twelfth controllable switch transistor Q 12  is connected to a second end  102  of the tenth controllable switch transistor Q 10  and another end of the energy storage device. In this embodiment of the present invention, the second DC conversion unit  203  substitutes a controllable switch for a diode, so that transmission efficiency can be improved. 
     The transformer unit  202  includes a high frequency transformer. Different from the related art in which a bidirectional isolated AC/DC circuit function is implemented by using a circuit combining an industrial frequency transformer and a bidirectional rectifier, where the industrial frequency transformer is difficult to implement in vehicle, in this embodiment of the present invention, the high frequency transformer is used to implement high frequency isolated transmission, and bidirectional energy transmission can also be implemented. 
     The high frequency transformer includes a first coil T 11  and a second coil T 22 . A first end of the first coil T 11  is connected to the third node D 3  by using a third inductor L 3 . A second end of the first coil T 11  is connected to the fourth node D 4  by using a second capacitor C 2 . A first end of the second coil T 22  is connected to the fifth node D 5  by using a third capacitor C 3 . A second end of the second coil T 22  is connected to the sixth node D 6 . The high frequency transformer is used to isolate energy on the AC side from that on the DC side, improve safety, and implement bidirectional energy transmission. The high frequency transformer is used to increase and reduce a voltage, and the DC voltage has a wide application range. 
     During outputting of the AC terminal, that is, during charging of the energy storage device, the control module  40  performs inversion control on the fifth controllable switch transistor Q 5  to the eighth controllable switch transistor Q 8  and performs rectification control on the ninth controllable switch transistor Q 9  to the twelfth controllable switch transistor Q 12  according to a rectified output voltage of the bidirectional converter module  10  and an output current and an output voltage of the second DC conversion unit  203 , to implement a charging function of the energy storage device. 
     During outputting of the energy storage device, the control module  40  performs inversion control on the ninth controllable switch transistor Q 9  to the twelfth controllable switch transistor Q 12  and performs rectification control on the fifth controllable switch transistor Q 5  to the eighth controllable switch transistor Q 8  according to a voltage and a current output by the energy storage device and a voltage output by the first DC conversion unit  201 , to convert a DC current to an AC current by using the bidirectional converter module  10  and provide the AC current to a load of the AC terminal for use, thereby implementing discharging of the energy storage device. 
     As shown in  FIG. 4 , the car charger  100  further includes a switch module  50 . The switch module  50  includes a first switch S 1 , a second switch S 2 , a third switch S 3 , and a first resistor R 1 . A first end of the first switch S 1  is connected to one end of the AC terminal. A second end of the first switch S 1  is connected to the first end of the first inductor L 1 . A first end of the second switch S 2  is connected to the other end of the AC terminal. A second end of the second switch S 2  is connected to the first end of the second inductor L 2 . A first end of the third switch S 3  is connected to one end of the AC terminal and the first end of the first switch S 1 . A first end of the first resistor R 1  is connected to a second end of the third switch S 3 . A second end of the first resistor R 1  is connected to the second end of the first switch S 1 . 
     The car charger  100  further includes a fourth capacitor C 4  and a fifth capacitor C 5 . There is a seventh node D 7  between the first end  31  of the third controllable switch transistor Q 3  and the first end  51  of the fifth controllable switch transistor Q 5 . A first end of the fourth capacitor C 4  is connected to the seventh node D 7 . There is an eighth node D 8  between the second end  42  of the fourth controllable switch transistor Q 4  and the second end  62  of the sixth controllable switch transistor Q 6 . A second end of the fourth capacitor C 4  is connected to the eighth node D 8 . The first end of the fifth capacitor C 5  is connected to one end of the energy storage device. A second end of the fifth capacitor C 5  is connected to another end of the energy storage device. 
     Referring to  FIG. 4 , the control module  40  includes a control module  1  and a control module  2 , and the collection module  30  includes a sampling circuit  1  and a sampling circuit  2 . 
     During charging of the energy storage device such as a high voltage battery pack, the second switch S 2  and the third switch S 3  are first controlled to be turned on. The sampling circuit  1  collects an AC voltage Vac, an AC current Iac and an output DC voltage Vdc 1  of the bidirectional converter module  10 . The control module  1  outputs a PWM signal such as PWM  1  and PWM  2  after calculation. Controllable rectification is performed on the first controllable switch transistor Q 1  to the fourth controllable switch transistor Q 4  sequentially, and the DC voltage Vdc 1  is output as a feedback, to implement AC-DC conversion and constant-voltage outputting. In addition, the AC current is synchronized with the AC voltage and a power factor is close to 1. 
     The fourth capacitor C 4  performs filtering. After the voltage Vdc 1  is constant, the sampling circuit  2  collects the voltage Vdc 1 , a DC output, that is, a battery voltage Vdc 2  and a DC output current Idc 2 . The control module  2  outputs a PWM signal after calculation, performs inversion control on the fifth controllable switch transistor Q 5  to the eighth controllable switch transistor Q 8  sequentially, and continues to perform synchronized rectification control on the ninth controllable switch transistor Q 9  to the twelfth controllable switch transistor Q 12 , to implement DC-DC conversion. In this way, charging power can be adjusted according to the current Idc 2  that is fed back. 
     The high frequency transformer is used to isolate energy on the AC side from that on the DC side, so that a design of the high frequency transformer can be adjusted according to a range of the DC voltage for matching. 
     During discharging of the energy storage device, the energy storage device such as a high voltage battery pack is used as an input end. The sampling circuit  2  collects Vdc 1 , the battery voltage Vdc 2  and a battery output current Idc 2 . The control module  2  outputs a PWM signal after calculation, performs inversion control on the ninth controllable switch transistor Q 9  to the twelfth controllable switch transistor Q 12  sequentially, performs synchronized rectification control on the fifth controllable switch transistor Q 5  to the eighth controllable switch transistor Q 8 , and outputs the DC voltage Vdc 1  as a feedback, to implement AC-DC conversion and constant-voltage outputting. 
     After the voltage Vdc 1  is constant, Vdc 1  is used as an input end. The sampling circuit  1  collects an AC voltage Vac as a feedback. The control module  1  outputs an SPWM waveform signal according to a sine law, controls the first controllable switch transistor Q 1  to the fourth controllable switch transistor Q 4 , so that the AC terminal outputs an AC current at an appropriate voltage, and provides power for a load of the AC terminal, to implement inversion. 
     Thus, the car charger  100  of this embodiment of the present invention can implement bidirectional flow of energy and improve efficiency based on a combination of the bidirectional converter module  10  and the bidirectional DC/DC conversion module  20 . The bidirectional DC/DC conversion module  20  uses the transformer unit  202  for isolation, so that a common-mode voltage on the AC side can be reduced to isolate the AC side from the DC side, thereby improving safety and reducing conducted radiation. A DC voltage has a wide application range. 
     Based on the car charger  100  of the embodiment according to the foregoing aspect, according to another aspect, an embodiment of the present invention provides a vehicle. 
       FIG. 5  is a block diagram of a vehicle according to an embodiment of the present invention. As shown in  FIG. 5 , the vehicle  1000  includes the car charger  100  of the embodiment according to the foregoing aspect. 
     By using the car charger  100  according to the foregoing aspect, the vehicle  1000  can implement bidirectional energy transmission, isolate the AC side from the DC side, reduce the common-mode voltage on the AC side, and improve safety. 
     It should be noted that in the descriptions of this specification, a description of a reference term such as “an embodiment”, “some embodiments”, “an example”, “a specific example”, or “some examples” means that a specific feature, structure, material, or characteristic that is described with reference to the embodiment or the example is included in at least one embodiment or example of the present invention. In the specification, the foregoing exemplary expressions of the terms are not necessarily with respect to a same embodiment or example. In addition, the described specific features, structures, materials, or characteristics may be combined in a proper manner in any one or more of the embodiments or examples. In addition, a person skilled in the art may integrate or combine different embodiments or examples and characteristics of different embodiments or examples described in the specification, as long as they do not conflict each other. 
     Although the embodiments of the present invention are shown and described above, it can be understood that, the foregoing embodiments are exemplary, and cannot be construed as a limitation to the present invention. Within the scope of the present invention, a person of ordinary skill in the art may make changes, modifications, replacement, and variations to the foregoing embodiments.