Patent Publication Number: US-2019176652-A1

Title: Electric vehicle, multifunctional car charger for electric vehicle, and control method thereof

Description:
FIELD 
     The present invention relates to the field of electric vehicle technologies and, in particular, to a multifunctional car charger for an electric vehicle, an electric vehicle, and a control method of a multifunctional car charger for an electric vehicle. 
     BACKGROUND 
     Electric vehicles are gradually favored by consumers because of their advantages such as energy saving and environmental friendliness. 
     At present, the car charger in an electric vehicle generally only has the function of charging the power battery, and the function is relatively simple. The implementation of other charging and powering functions of electric vehicles (such as charging for low-voltage batteries, etc.) requires additional circuits and interfaces, which undoubtedly increases the volume and weight of electric vehicle electrical equipment and increases design and manufacturing costs. 
     SUMMARY 
     The present disclosure aims to solve at least one of the technical problems in the above-mentioned technology to some extent. Accordingly, the present disclosure is first directed to a multifunctional car charger for an electric vehicle, which is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. 
     The present disclosure is secondly directed to an electric vehicle. 
     The present disclosure is thirdly directed to a control method of a multifunctional car charger for an electric vehicle. 
     To achieve the above objects, an embodiment of the first aspect of the present disclosure provides a multifunctional car charger for an electric vehicle, including: a bidirectional AC/DC conversion circuit, where an alternating-current end of the bidirectional AC/DC conversion circuit is configured for coupling to a power grid; a first DC/DC conversion circuit, where a first direct-current end of the first DC/DC conversion circuit is connected to a direct-current end of the bidirectional AC/DC conversion circuit, and a second direct-current end of the first DC/DC conversion circuit is configured for coupling to a power battery of the electric vehicle; a second DC/DC conversion circuit, where a first direct-current end of the second DC/DC conversion circuit is separately connected to a direct-current end of the bidirectional AC/DC conversion circuit and the first direct-current end of the first DC/DC conversion circuit, and a second direct-current end of the second DC/DC conversion circuit is configured for coupling to a low-voltage battery of the electric vehicle; a sampling circuit, where the sampling circuit is configured to sample a voltage and a current of the power grid, a voltage of the direct-current end of the bidirectional AC/DC conversion circuit, a voltage and a current of the power battery and a voltage and a current of the low-voltage battery separately; and a control module, in which a first control circuit for controlling the bidirectional AC/DC conversion circuit, a second control circuit for controlling the first DC/DC conversion circuit and a third control circuit for controlling the second DC/DC conversion circuit are integrated, where the control module is configured to correspondingly control the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit through the first control circuit, the second control circuit and the third control circuit according to the voltage and the current of the power grid, the voltage of the direct-current end of the bidirectional AC/DC conversion circuit, the voltage and the current of the power battery and the voltage and the current of the low-voltage battery that are sampled by the sampling circuit, to realize any one of a power battery charging function, a low-voltage battery charging function, a power battery alternating-current inversion function, a low-voltage battery alternating-current inversion function and a power battery low-voltage loaded output function. 
     According to the multifunctional car charger for an electric vehicle of the embodiments of the present disclosure, the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are integrated, related voltage and current parameters in the car charger circuit are sampled by the sampling circuit, and the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled by the control module according to the related voltage and current parameters to realize multiple functions. In this way, through the highly integrated design, some circuits and ports can be multiplexed under different functions, so that the multifunctional car charger is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. In addition, based on the above design, the charging and discharging efficiency can be improved, the charging power can be expanded conveniently, the reliability can be improved, and the service life can be prolonged. 
     To achieve the above objects, an embodiment of the second aspect of the present disclosure provides an electric vehicle, including the multifunctional car charger for an electric vehicle provided by the embodiment of the first aspect of the present disclosure. 
     According to the electric vehicle of the embodiments of the present disclosure, the car charger has a highly integrated design, so that some circuits and ports can be multiplexed under different functions, so that the car charger is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. 
     To achieve the above objects, an embodiment of the third aspect of the present disclosure provides a control method of a multifunctional car charger for an electric vehicle, where the multifunctional car charger for an electric vehicle includes a bidirectional AC/DC conversion circuit, a first DC/DC conversion circuit and a second DC/DC conversion circuit, an alternating-current end of the bidirectional AC/DC conversion circuit is configured for coupling to a power grid, a first direct-current end of the first DC/DC conversion circuit is connected to a direct-current end of the bidirectional AC/DC conversion circuit, a second direct-current end of the first DC/DC conversion circuit is configured for coupling to a power battery of the electric vehicle, a first direct-current end of the second DC/DC conversion circuit is separately connected to a direct-current end of the bidirectional AC/DC conversion circuit and the first direct-current end of the first DC/DC conversion circuit, and a second direct-current end of the second DC/DC conversion circuit is configured for coupling to a low-voltage battery of the electric vehicle, the method including the following steps: sampling a voltage and a current of the power grid, a voltage of the direct-current end of the bidirectional AC/DC conversion circuit, a voltage and a current of the power battery and a voltage and a current of the low-voltage battery separately; and controlling the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit according to the voltage and the current of the power grid, the voltage of the direct-current end of the bidirectional AC/DC conversion circuit, the voltage and the current of the power battery and the voltage and the current of the low-voltage battery that are sampled, to realize any one of a power battery charging function, a low-voltage battery charging function, a power battery alternating-current inversion function, a low-voltage battery alternating-current inversion function and a power battery low-voltage loaded output function. 
     According to the control method of the multifunctional car charger for an electric vehicle of the embodiments of the present disclosure, the car charger integrates the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit, related voltage and current parameters in the car charger circuit are sampled, and the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled according to the related voltage and current parameters to realize multiple functions. In this way, through the highly integrated design, some circuits and ports can be multiplexed under different functions, so that the car charger is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. In addition, based on the above control method, the charging and discharging efficiency of the car charger can be improved, the charging power can be expanded conveniently, the reliability of the car charger can be improved, and the service life of the car charger can be prolonged. 
     The additional aspects and advantages of the present disclosure will be set forth in part in the description which follows, parts of which will become apparent from the description below, or will be understood by the practice of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a multifunctional car charger for an electric vehicle according to an embodiment of the present disclosure; 
         FIG. 2  is a circuit diagram of a multifunctional car charger for an electric vehicle according to one embodiment of the present disclosure; 
         FIG. 3  is a structure diagram of a sampling circuit and a control module of a multifunctional car charger for an electric vehicle according to one embodiment of the present disclosure; 
         FIG. 4  is a block diagram of an electric vehicle according to an embodiment of the present disclosure; 
         FIG. 5  is a flow chart of a control method of a multifunctional car charger for an electric vehicle according to an embodiment of the present disclosure; and 
         FIG. 6  is a flow chart of a control method of a multifunctional car charger for an electric vehicle according to one specific embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes in detail embodiments of the present disclosure. Examples of the embodiments are shown in the accompanying drawings, where reference signs that are the same or similar throughout the specification 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, which are used only to explain the present disclosure, and cannot be construed as a limitation to the present disclosure. 
     Hereinafter, an electric vehicle, a multifunctional car charger for an electric vehicle and a control method thereof provided by the embodiments of the present disclosure will be described with reference to the accompanying drawings. 
       FIG. 1  is a block diagram of a multifunctional car charger for an electric vehicle according to an embodiment of the present disclosure. 
     As shown in  FIG. 1 , the multifunctional car charger for an electric vehicle of an embodiment of the present disclosure includes a bidirectional AC/DC conversion circuit  10 , a first DC/DC conversion circuit  20 , a second DC/DC conversion circuit  30 , a sampling circuit  40  and a control module  50 . 
     Referring to  FIG. 2 , an alternating-current end of the bidirectional AC/DC conversion circuit  10  is configured for coupling to a power grid, i.e. an AC power source. A first direct-current end of the first DC/DC conversion circuit  20  is coupled to a direct-current end of the bidirectional AC/DC conversion circuit  10 , and a second direct-current end of the first DC/DC conversion circuit  20  is configured for coupling to a power battery of the electric vehicle. A first direct-current end of the second DC/DC conversion circuit  30  is coupled to a direct-current end of the bidirectional AC/DC conversion circuit  10  and also coupled to the first direct-current end of the first DC/DC conversion circuit  20 , and a second direct-current end of the second DC/DC conversion circuit  30  is configured for coupling to a low-voltage battery of the electric vehicle. 
     Referring to  FIG. 2 , the bidirectional AC/DC conversion circuit  10  may include a first bridge circuit, and the first bridge circuit includes a first bridge arm and a second bridge arm connected in parallel. The first bridge arm includes a first switch transistor Q 1  and a second switch transistor Q 2  connected in series as a source and a drain. The second bridge arm includes a third switch transistor Q 3  and a fourth switch transistor Q 4  connected in series as a source and a drain. A node A 1  between the first switch transistor Q 1  and the second switch transistor Q 2  and a node B 1  between the third switch transistor Q 3  and the fourth switch transistor Q 4  serve as the alternating-current ends of the bidirectional AC/DC conversion circuit  10 , and two end nodes E 1  and D 1  of the first bridge arm and the second bridge arm connected in parallel serve as the direct-current ends of the bidirectional AC/DC conversion circuit  10 . The bidirectional AC/DC conversion circuit  10  may further include a first capacitor C 1  connected in parallel to the AC power source and a first inductor L 1  connected in series in the path formed by the nodes A 1  and B 1  and the first capacitor C 1 , so that filtering can be performed by the first capacitor C 1  and the first inductor L 1 . 
     Referring to  FIG. 2 , the first DC/DC conversion circuit  20  may include a second bridge circuit, a first transformer T 1  and a third bridge circuit connected in cascade. The second bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel. The third bridge arm includes a fifth switch transistor Q 5  and a sixth switch transistor Q 6  connected in series as a source and a drain. The fourth bridge arm includes a seventh switch transistor Q 7  and an eighth switch transistor Q 8  connected in series as a source and a drain. Two ends A 2  and B 2  of the third bridge arm and the fourth bridge arm connected in parallel serve as the first direct-current ends of the first DC/DC conversion circuit  20 . A second capacitor C 2  is also connected between the nodes E 1  and D 1  of the first bridge circuit (and also between the nodes A 2  and B 2  of the second bridge circuit). A node E 2  between the fifth switch transistor Q 5  and the sixth switch transistor Q 6  is connected to a first terminal on the first side of the transformer T 1  through a second inductor Lr 1 , and a node D 2  between the seventh switch transistor Q 7  and the eighth switch transistor Q 8  is connected to a second terminal on the first side of the transformer T 1  through a third capacitor Cr 1 . The third bridge circuit includes a fifth bridge arm and a sixth bridge arm connected in parallel. The fifth bridge arm includes a ninth switch transistor Q 9  and a tenth switch transistor Q 10  connected in series as a source and a drain. The sixth bridge arm includes an eleventh switch transistor Q 11  and a twelfth switch transistor Q 12  connected in series as a source and a drain. Two ends E 3  and D 3  of the fifth bridge arm and the sixth bridge arm connected in parallel serve as the second direct-current ends of the first DC/DC conversion circuit  20 . A node A 3  between the ninth switch transistor Q 9  and the tenth switch transistor Q 10  is connected to a third terminal of the second side of the transformer T 1 , and a node B 3  between the eleventh switch transistor Q 11  and the twelfth switch transistor Q 12  is connected to a fourth terminal on the second side of the transformer T 1 . In one embodiment of the present disclosure, a fourth capacitor C 3  connected in parallel to the power battery may also be included at the second direct-current end of the first DC/DC conversion circuit  20 . 
     Referring to  FIG. 2 , the second DC/DC conversion circuit  30  may include a fourth bridge circuit, a second transformer T 2  and a fifth bridge circuit connected in cascade. The fourth bridge circuit includes a seventh bridge arm and an eighth bridge arm connected in parallel. The seventh bridge arm includes a thirteenth switch transistor Q 13  and a fourteenth switch transistor Q 14  connected in series as a source and a drain. The eighth bridge arm includes a fifteenth switch transistor Q 15  and a sixteenth switch transistor Q 16  connected in series as a source and a drain. Two ends A 4  and B 4  of the seventh bridge arm and the eighth bridge arm connected in parallel serve as the first direct-current ends of the second DC/DC conversion circuit  30 . A node E 4  between the thirteenth switch transistor Q 13  and the fourteenth switch transistor Q 14  is connected to a fifth terminal of the first side of the transformer T 2  through a third inductor Lr 2 , and a node D 4  between the fifteenth switch transistor Q 15  and the sixteenth switch transistor Q 16  is connected to a sixth terminal of the first side of the transformer T 2  through a fifth capacitor Cr 2 . The fifth bridge circuit includes a seventeenth switch transistor Q 17  and an eighteenth switch transistor Q 18  connected in series as a source and a drain, one end of the seventeenth switch transistor Q 17  is connected to a seventh terminal of the second side of the transformer T 2 , one end of the eighteenth switch transistor Q 18  is connected to an eighth terminal of the second side of the transformer T 2 , the other end of the seventeenth switch transistor Q 17  and the other end of the eighteenth switch transistor Q 18  are commonly connected to a node D 5 , and D 5  and a ninth terminal (node E 5 ) on the second side of the transformer T 2  form the second direct-current ends of the second DC/DC conversion circuit  30  to obtain a divided voltage output. In one embodiment of the present disclosure, filtering may also be performed at the second direct-current end of the second DC/DC conversion circuit  30  by a filter circuit including a fourth inductor Lr 3  and a sixth capacitor C 4 . 
     As shown in  FIG. 3 , the sampling circuit  40  can be integrated in the control module  50 . Referring to  FIG. 2  and  FIG. 3 , the sampling circuit  40  may be configured to sample a voltage Uac and a current Iac of a power grid, a voltage of the direct-current end of the bidirectional AC/DC conversion circuit  10 , a voltage Uhbt and a current Ihbt of the power battery and a voltage Ulbt and a current Ilbt of the low-voltage battery separately. 
     A first control circuit for controlling the bidirectional AC/DC conversion circuit  10 , a second control circuit for controlling the first DC/DC conversion circuit  20  and a third control circuit for controlling the second DC/DC conversion circuit  30  are integrated in the control module  50 , and the control module  50  is configured to correspondingly control the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  through the first control circuit, the second control circuit and the third control circuit according to the voltage Iac and the current Iac of the power grid, the voltage Udc of the direct-current end of the bidirectional AC/DC conversion circuit  10 , the voltage Uhbt and the current Ihbt of the power battery and the voltage Ulbt and the current Ilbt of the low-voltage battery that are sampled by the sampling circuit  40 . Specifically, for example, pulse-width modulation signals PWM 1  to PWM 6  can be output to the control electrodes (gates) of the switch transistors Q 1 -Q 18  to control the on/off of the switch transistors, thereby realizing any one of a power battery charging function, a low-voltage battery charging function, a power battery alternating-current inversion function, a low-voltage battery alternating-current inversion function and a power battery low-voltage loaded output function. 
     In one embodiment of the present disclosure, the control module  50  is configured to correspondingly control the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  through the first control circuit, the second control circuit and the third control circuit according to the voltage Uac and the current Iac of the power grid, the voltage Udc of the direct-current end of the bidirectional AC/DC conversion circuit  10 , the voltage Uhbt and the current Ihbt of the power battery and the voltage Ulbt and the current Ilbt of the low-voltage battery that are sampled by the sampling circuit  40 , to realize the power battery charging function and the low-voltage battery charging function, or the power battery alternating-current inversion function and the power battery low-voltage loaded output function, or the power battery alternating-current inversion function and the low-voltage battery alternating-current inversion function. 
     In an embodiment of the present disclosure, the first switch transistor Q 1  to the eighteenth switch transistor Q 18  may be all insulated gate bipolar transistors (IGBTs) or metal-oxide-semiconductor field effect transistors (MOSFETs). Between the source and the drain of each of the switch transistors Q 1  to Q 18 , a diode and a capacitor may be connected in parallel. The first switch transistor Q 1  to the eighteenth switch transistor Q 18  in  FIG. 2  may be correspondingly controlled by the PWM 1 -PWM 6  signals output by the control module  50  in  FIG. 3  respectively. For a specific correspondence, refer to  FIG. 2  and  FIG. 3 , and details are not described herein. Referring to  FIG. 2 , the second bridge circuit, the third bridge circuit and the fourth bridge circuit may respectively adopt the manner that two switch transistors are synchronously turned on, which can reduce the conduction loss. 
     In one embodiment of the present disclosure, when the multifunctional car charger is in a charging state, if the level of the low-voltage battery is less than a first preset value, the control module  50  controls the bidirectional AC/DC conversion circuit  10  and the second DC/DC conversion circuit  30  to charge the low-voltage battery; and if the level of the low-voltage battery is greater than or equal to the first preset value, and when the power battery is in a not fully-charged state, the control module  50  controls the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  to respectively supply power to a low-voltage load of the electric vehicle and charge the power battery. When the multifunctional car charger is in a charging state, the control module  50  further determines whether the power battery and the low-voltage battery are abnormal, and controls the multifunctional car charger to stop charging when the power battery and the low-voltage battery are abnormal. 
     In one embodiment of the present disclosure, when the multifunctional car charger is in a discharging state, the control module  50  determines whether the electric vehicle is in a running state, if the electric vehicle is in the running state, the control module  50  controls the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  to supply power to the low-voltage load of the electric vehicle through the power battery, and controls the bidirectional AC/DC conversion circuit  10  to operate when receiving an alternating-current discharge demand instruction such that the power battery performs alternating-current discharge simultaneously through the first DC/DC conversion circuit  20  and the bidirectional AC/DC conversion circuit  10 . 
     When the multifunctional car charger is in the discharging state and the electric vehicle is in a stop state, and if the control module  50  receives the alternating-current discharge demand instruction, whether the level of the low-voltage battery is less than the first preset value is determined, if the level of the low-voltage battery is less than the first preset value, the control module  50  controls the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  to charge the low-voltage battery through the power battery, and controls the bidirectional AC/DC conversion circuit  10  to operate such that the power battery performs alternating-current discharge simultaneously through the first DC/DC conversion circuit  20  and the bidirectional AC/DC conversion circuit  10 ; and if the level of the low-voltage battery is greater than or equal to the first preset value, the control module controls the first DC/DC conversion circuit  20 , the second DC/DC conversion circuit  30  and the bidirectional AC/DC conversion circuit  10  such that the power battery and the low-voltage battery simultaneously perform alternating-current discharge. 
     It should be noted that the power of the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  also needs to meet specific charging and discharging demands. Specifically, when the multifunctional car charger is in a charging state, for example, the rated power of the bidirectional AC/DC conversion circuit  10  is Pw, the rated power of the first DC/DC conversion circuit  20  is Pd 1  and the rated power of the second DC/DC conversion circuit  30  is Pd 2 , and it is assumed that the conversion efficiency of the circuit is approximately 1, then, when the high-voltage battery (power battery) and the low-voltage battery are simultaneously charged, the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  can be controlled to operate simultaneously, at this time, Pw=Pd 1 +Pd 2 . When only the high-voltage battery is charged, the bidirectional AC/DC conversion circuit  10  and the first DC/DC conversion circuit  20  are controlled to operate, and the second DC/DC conversion circuit  30  does not operate, Pw=Pd 1 . When only the low-voltage battery is charged, the bidirectional AC/DC conversion circuit  10  and the second DC/DC conversion circuit  30  are controlled to operate, and the first DC/DC conversion circuit  20  does not operate, Pw=Pd 2 . 
     When the multifunctional car charger is in a discharging state, for example, the rated power of the bidirectional AC/DC conversion circuit  10  is Pw 0 , the rated power of the first DC/DC conversion circuit  20  is Pd 10  and the rated power of the second DC/DC conversion circuit  30  is Pd 20 , and it is assumed that the conversion efficiency of the circuit is approximately 1, then, when the electric vehicle is in a stop state, alternating-current discharge is performed and the low voltage battery is not under voltage, the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  simultaneously operate, Pw 0 =Pd 10 +Pd 20 , and at this time, the power of the alternating-current discharge can reach the maximum value. When the electric vehicle is in a stop state, alternating-current discharge is performed and the low-voltage battery is under voltage, the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  simultaneously operate, and the low-voltage battery is charged and absorbs power, Pw 0 =Pd 10 −Pd 20 . During the running of the vehicle, the vehicle low-voltage battery and the low-voltage load power supply should be first ensured, and if there is a discharge demand, the order of starting is determined according to the obtained power battery, low-voltage battery, power grid and control signal information. When the electric vehicle is in a running state and alternating-current discharge is performed, the bidirectional AC/DC conversion circuit  10 , the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  simultaneously operate, Pw 0 =Pd 10 −Pd 20 . When the electric vehicle is in the running state and alternating-current discharge is not performed, only the first DC/DC conversion circuit  20  and the second DC/DC conversion circuit  30  operate, Pd 10 =Pd 20 . 
     According to the multifunctional car charger for an electric vehicle of the embodiment of the present disclosure, the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are integrated, related voltage and current parameters in the car charger circuit are sampled by the sampling circuit, and the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled by the control module according to the related voltage and current parameters to realize multiple functions. In this way, through the highly integrated design, some circuits and ports can be multiplexed under different functions, so that the car charger is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. In addition, based on the above design, the charging and discharging efficiency of the car charger can be improved, the charging power can be expanded conveniently, the reliability of the car charger can be improved, and the service life of the car charger can be prolonged. 
     Corresponding to the above embodiments, the present disclosure further provides an electric vehicle. 
     As shown in  FIG. 4 , the electric vehicle  200  of the embodiment of the present disclosure includes the multifunctional car charger  100  for an electric vehicle provided by the above embodiment of the present disclosure. For more specific implementations, refer to the above embodiments. To avoid redundancy, details are not described herein again. 
     According to the electric vehicle of the embodiment of the present disclosure, the car charger has a highly integrated design, so that some circuits and ports can be multiplexed under different functions, so that the car charger is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. 
     Corresponding to the above embodiments, the present disclosure also provides a control method of a multifunctional car charger for an electric vehicle. 
     The multifunctional car charger for an electric vehicle includes a bidirectional AC/DC conversion circuit, a first DC/DC conversion circuit and a second DC/DC conversion circuit, an alternating-current end of the bidirectional AC/DC conversion circuit is configured for coupling to a power grid, a first direct-current end of the first DC/DC conversion circuit is coupled to a direct-current end of the bidirectional AC/DC conversion circuit, a second direct-current end of the first DC/DC conversion circuit is configured for coupling to a power battery of the electric vehicle, a first direct-current end of the second DC/DC conversion circuit is separately coupled to a direct-current end of the bidirectional AC/DC conversion circuit and the first direct-current end of the first DC/DC conversion circuit, and a second direct-current end of the second DC/DC conversion circuit is configured for coupling to a low-voltage battery of the electric vehicle. For a more specific circuit coupling manner, refer to  FIG. 2  and the above embodiments, and details are not described herein. 
     As shown in  FIG. 5 , the control method of the multifunctional car charger for an electric vehicle of the embodiment of the present disclosure includes the following steps: 
     S 1 : A voltage and a current of the power grid, a voltage of the direct-current end of the bidirectional AC/DC conversion circuit, a voltage and a current of the power battery and a voltage and a current of the low-voltage battery are sampled respectively. 
     S 2 : The bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled according to the voltage and the current of the power grid, the voltage of the direct-current end of the bidirectional AC/DC conversion circuit, the voltage and the current of the power battery and the voltage and the current of the low-voltage battery that are sampled, to realize any one of a power battery charging function, a low-voltage battery charging function, a power battery alternating-current inversion function, a low-voltage battery alternating-current inversion function and a power battery low-voltage loaded output function. 
     In one embodiment of the present disclosure, the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit may also be controlled according to the voltage and the current of the power grid, the voltage of the direct-current end of the bidirectional AC/DC conversion circuit, the voltage and the current of the power battery and the voltage and the current of the low-voltage battery that are sampled, to realize the power battery charging function and the low-voltage battery charging function, or the power battery alternating-current inversion function and the power battery low-voltage loaded output function, or the power battery alternating-current inversion function and the low-voltage battery alternating-current inversion function. 
     In one embodiment of the present disclosure, when the multifunctional car charger is in a charging state, and if the level of the low-voltage battery is less than a first preset value, the bidirectional AC/DC conversion circuit and the second DC/DC conversion circuit are controlled to charge the low-voltage battery; and if the level of the low-voltage battery is greater than or equal to the first preset value, and when the power battery is in a not fully-charged state, the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled to respectively supply power to a low-voltage load of the electric vehicle and charge the power battery. 
     In one embodiment of the present disclosure, when the multifunctional car charger is in a charging state, whether the power battery and the low-voltage battery are abnormal is further determined, and the multifunctional car charger is controlled to stop charging when the power battery and the low-voltage battery are abnormal. 
     In one embodiment of the present disclosure, when the multifunctional car charger is in a discharging state, whether the electric vehicle is in a running state is further determined, if the electric vehicle is in the running state, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled to supply power to the low-voltage load of the electric vehicle through the power battery, and the bidirectional AC/DC conversion circuit is controlled to operate when receiving an alternating-current discharge demand instruction such that the power battery performs alternating-current discharge simultaneously through the first DC/DC conversion circuit and the bidirectional AC/DC conversion circuit. 
     When the multifunctional car charger is in the discharging state and the electric vehicle is in a stop state, and if the alternating-current discharge demand instruction is received, whether the level of the low-voltage battery is less than the first preset value is determined, if the level of the low-voltage battery is less than the first preset value, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled to charge the low-voltage battery through the power battery, and the bidirectional AC/DC conversion circuit is controlled to operate such that the power battery performs alternating-current discharge simultaneously through the first DC/DC conversion circuit and the bidirectional AC/DC conversion circuit; and if the level of the low-voltage battery is greater than or equal to the first preset value, the first DC/DC conversion circuit, the second DC/DC conversion circuit and the bidirectional AC/DC conversion circuit are controlled such that the power battery and the low-voltage battery simultaneously perform alternating-current discharge. 
     In one specific embodiment of the present disclosure, as shown in  FIG. 6 , the control method of the multifunctional car charger for an electric vehicle may include the following steps: 
     S 501 : Acquire a charging gun signal, a vehicle gear signal and a CAN signal, so as to determine whether charging is performed, whether the electric vehicle is in the running state and the like subsequently. 
     S 502 : Power the low-voltage load and the control circuit. 
     S 503 : Determine whether the multifunctional car charger is in a charging state or a discharging state. If it is in the charging state, go to step S 504 ; and if it is in the discharging state, go to step S 511 . 
     S 504 : Acquire information of the power battery and the low-voltage battery, and determine whether the power battery and the low-voltage battery are abnormal. If yes, go to step S 505 ; and if no, go to step S 506 . 
     S 505 : Stop charging. 
     S 506 : Determine whether the low-voltage battery is seriously under voltage. In the embodiment of the present disclosure, if the level of the low-voltage battery is less than the first preset value, it can be determined that the low-voltage battery is seriously under voltage. If yes, go to step S 508 ; and if no, go to step S 507 . 
     S 507 : Determine whether the power battery is fully-charged. If yes, go to step S 505 ; and if no, go to step S 510 . 
     S 508 : Start the bidirectional AC/DC conversion circuit and the second DC/DC conversion circuit to operate so as to charge the low-voltage battery, and go to step S 509 . 
     S 509 : Determine whether the level of the low-voltage battery is normal, that is, whether the level of the battery is sufficient. If yes, go to step S 507 ; and if no, go back to step S 508  to continue charging the low-voltage battery. 
     S 510 : Start the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit to operate so as to respectively supply power to a low-voltage load of the electric vehicle and charge the power battery. When the power is supplied to the low-voltage load, it is possible to go back to step S 509  to determine whether the level of the low-voltage battery is normal, and go to step S 508  to charge the low-voltage battery when the level of the low-voltage battery is insufficient. In addition, in the process of supplying power to the low-voltage load of the electric vehicle and charging the power battery, it is possible to go to step S 504  in real time to determine whether the power battery and the low-voltage battery are abnormal. 
     S 511 : Determine whether the electric vehicle is running. If yes, go to step S 512 ; and if no, go to step S 515 . 
     S 512 : Start the first DC/DC conversion circuit and the second DC/DC conversion circuit to operate so as to supply power to the low-voltage load of the electric vehicle through the power battery, and go to step S 513 . 
     S 513 : Determine whether there is an alternating-current discharge demand. If yes, go to step S 514 ; and if no, go back to step S 512 . 
     S 514 : Start the bidirectional AC/DC conversion circuit to operate such that the power battery performs alternating-current discharge through the first DC/DC conversion circuit and the bidirectional AC/DC conversion circuit. 
     S 515 : Determine that there is an alternating-current discharge demand. When the electric vehicle is not running, the discharge process is generally alternating-current discharge. 
     S 516 : Determine whether the low-voltage battery is seriously under voltage. If yes, go to step S 517 ; and if no, go to step S 518 . 
     S 517 : Start the first DC/DC conversion circuit and the second DC/DC conversion circuit to operate so as to charge the low-voltage battery through the power battery. At the same time, go to step S 514  to perform alternating-current discharge. 
     S 518 : Start the first DC/DC conversion circuit, the second DC/DC conversion circuit and the bidirectional AC/DC conversion circuit such that the power battery and the low-voltage battery simultaneously perform alternating-current discharge. At this time, the power of the alternating-current discharge can reach the maximum value. 
     According to the control method of the multifunctional car charger for an electric vehicle of the embodiment of the present disclosure, the car charger integrates the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit, related voltage and current parameters in the car charger circuit are sampled, and the bidirectional AC/DC conversion circuit, the first DC/DC conversion circuit and the second DC/DC conversion circuit are controlled according to the related voltage and current parameters to realize multiple functions. In this way, through the highly integrated design, some circuits and ports can be multiplexed under different functions, so that the car charger is small in volume and weight, low in cost and capable of conveniently realizing multiple functions. In addition, based on the above control method, the charging and discharging efficiency of the car charger can be improved, the charging power can be expanded conveniently, the reliability of the car charger can be improved, and the service life of the car charger can be prolonged. 
     In the description of various embodiments, the term “coupling” is used. Coupling represents the interlinkage between two originally separate circuits or between two originally separate portions of a circuit, which may be direct or indirect. “Coupling” allows energy or signals to be transferred from one circuit to another or from one portion of the circuit to another. In this way, “coupling” in the present application will include, but is not limited to, a physical electrical connection and a communication linkage in the form of signal transmission. Specifically, for two equivalent two-port networks, the coupling between the ports of the two two-port networks may be that two terminals on one side of the first two-port network are electrically connected to two terminals on one side of the second two-port network respectively. 
     In the descriptions of the present disclosure, it should be understood that orientations or position relationships indicated by terms such as “central”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “on”, “under”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise” and “counterclockwise” are orientations or position relationships indicated based on the accompanying drawings, and are used only for ease of describing the present disclosure and of simplified descriptions rather than for indicating or implying that an apparatus or a component needs to have a particular orientation or needs to be constructed or operated in a particular orientation, and therefore, cannot be construed as a limitation to the present disclosure. 
     In addition, terms “first” and “second” are used only for describing objectives, and shall not be construed as indicating or implying relative importance or implying a quantity of indicated technical features. Therefore, a feature restricted by “first ” or “second” may explicitly indicate or implicitly include at least one of such features. In the descriptions of the present disclosure, unless otherwise specified, “multiple” means two or more than two. 
     In the present disclosure, unless otherwise explicitly specified and defined, the terms “mounting”, “linking”, “connection”, “fixing” and the like shall be understood broadly, and may be, for example, a fixed connection, a detachable connection or integration; may be a mechanical connection or an electrical connection; or may be a direct connection, an indirect connection through an intermediate medium, or an internal communication between two components or interaction between two components, unless otherwise explicitly defined. A person of ordinary skill in the art can understand specific meanings of the foregoing terms in the present disclosure according to a specific situation. 
     In the present disclosure, unless otherwise explicitly specified and defined, the first feature “on” or “under” the second feature may refers to a direct contact between the first and second features, or an indirect contact between the first and second features through an intermediate medium. Moreover, the first feature “over”, “above” and “on the top of” the second feature may refers to that the first feature is directly above or obliquely above the second feature, or merely that the level of the first feature level is higher than that of the second feature. The first feature “under”, “below” and “on the bottom of” the second feature may refers to that the first feature is directly below or obliquely below the second feature, or merely that the level of the first feature is lower than that of the second feature. 
     In the description of this specification, the description with reference to the terms “one embodiment”, “some embodiments”, “example”, “specific example”, or “some examples” and the like means that specific features, structures, materials, or characteristics described in connection with the embodiments or examples are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms is not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, various embodiments or examples described in this specification, as well as features of various embodiments or examples, may be combined and associated by those skilled in the art without contradicting each other. 
     While the embodiments of the present disclosure have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limiting the present disclosure. Changes, modifications, replacements and variations of the above embodiments may be made by those skilled in the art within the scope of the present disclosure.