PARALLEL CHARGING METHOD FOR ELECTRIC VEHICLES

Abstract

Abstract PARALLEL BATTERY CHARGING METHOD FOR ELECTRIC VEHICLES The parallel battery charging method for electric vehicles is implemented in a parallel battery charging system. The system used by electric vehicles includes a number of battery modules and a control unit. The control unit is active when the electric vehicle is connected to the charger, and then the control unit receives the voltage values ​​​​from a number of battery modules, the control unit determines whether the voltage difference between a number of battery modules is greater than a preset voltage value. When the voltage difference is greater than the preset voltage value, the control unit controls the battery module among a number of battery modules that has a lower voltage value to charge, and when the voltage difference is smaller than the preset voltage value, the control unit controls the number of battery modules to be charged together.

Description

1. Field of Invention Engineering The present invention relates to electric vehicle batteries, in particular a method of parallel charging batteries for electric vehicles. 2. Description of the Related Invention Currently, rechargeable batteries are widely used as power sources for electric motorcycles. To increase the capacity of a single battery, a multi-battery power supply system has been developed for electric motorcycles, where multiple batteries are usually connected in series or parallel to form a battery pack to increase the maximum range of the electric motorcycle. The battery pack inside the electric motorcycle can be directly charged as a whole through a dedicated charging cable, or removed from the electric motorcycle to charge each battery individually; when users use the charging cable to charge the battery, if the individual voltages of the batteries connected in series in the battery pack are not balanced, some batteries may have completed charging early while others are still charging. Regarding the shortcomings of series battery charging technology, Republic of China Patent Application No. 109106621 discloses a Charging Balance Device System and Method for Multi-cell Battery Pack having a rounding structure, which disconnects the parallel switch in the switching circuit for the fully charged battery through the controller, and then turns on the bypass switch in the switching circuit, so as to exclude the fully charged battery from the charging circuit while the remaining batteries can be charged stably and continuously. The above technique may have the following problems: 1. When the parallel switch in the switching circuit is suddenly disconnected, the overall charging voltage will drop which causes unstable charging. 2. If the parallel switch and bypass switch in the switch circuit do not work, there will be a risk of damage to the battery in the switch circuit due to a short circuit. BRIEF DESCRIPTION OF THE INVENTION Problems to be solved with this invention: Currently, electric vehicles use serially connected batteries. To exclude a fully charged battery from the charging circuit, the series switch in the switching circuit for the fully charged battery must be disconnected, which tends to cause a sudden drop in the charging circuit's charging voltage and affect the stability of the battery charging process. In addition, if the parallel switch in the switching circuit fails, there is a risk of damage to the battery in the switching circuit due to a short circuit. To address the above problems, the present invention discloses a method for parallel charging batteries for electric vehicles. Technical Means for Solving Problems: The present invention discloses a method for parallel charging batteries for an electric vehicle. According to one embodiment of the present invention, the electric vehicle includes a plurality of battery modules and a control unit, the battery modules include a battery core module, a charging switch and a discharging switch, and the plurality of battery modules are connected in parallel and the control unit is electrically connected to the plurality of battery modules; when the electric vehicle is connected to a charger, the control unit receives an enable-trigger signal sent from the charger to execute the method for parallel charging the batteries, and the method includes: the control unit receives individual voltage values ​​from a number of battery modules; a control unit that determines whether the voltage difference between a number of battery modules is greater than a predetermined voltage value; when the voltage difference is greater than the preset voltage value, the control unit controls a number of battery modules that have a lower voltage value to be charged; when the voltage difference is less than the preset voltage value, the control unit controls a number of battery modules to be charged together. According to another embodiment of the present invention, an electric vehicle includes a first battery module, a second battery module and a control unit, the first battery module includes a first battery core module, a first charging switch and a first discharging switch; the second battery module includes a second battery core module, a second charging switch and a second discharging switch; the first battery module and the second battery module are connected in parallel, and the control unit is electrically connected to the first battery module and the second battery module; when the electric vehicle is connected to a charger, the control unit receives an enable-trigger signal transmitted from the charger to execute a method of parallel charging the batteries, and the method includes: the control unit receives the first voltage value from the first battery module and the second voltage value from the second battery module; control unit that calculates the voltage difference between the first voltage value and the second voltage value; the control unit determines whether the voltage difference is greater than the preset voltage value; when the voltage difference is greater than the preset voltage value, the control unit controls one of the first battery modules and the second battery module which has a lower voltage value to charge; when the voltage difference is less than the preset voltage value, the control unit controls the first battery module and the second battery module to charge together. Benefits of this invention: The parallel battery charging method for electric vehicles of the present invention determines the voltage difference between the battery modules, and during the charging process, no battery module is disconnected from the charging circuit; as a result, the charger can produce a stable output voltage. Each battery module includes a charge switch and a discharge switch that both operate in the same direction to prevent current from flowing towards each other when charging the battery module. In addition, because the charging is done in parallel, the charging and discharging rates (C-rates) of the battery modules are each served by the charger, thereby reducing the temperature of the battery modules during charging, which extends the service life of the battery modules. SHORT DESCRIPTION OF THE IMAGE Figure 1: Circuit block diagram of a battery parallel charging system for implementing a first embodiment of the present invention; Figure 2: Flow diagram of a first embodiment of a method for parallel charging batteries for electric vehicles of the present invention; Figure 3: Circuit block diagram of the second battery module on charging in the first embodiment of the present invention; Figure 4: Block diagram of the simultaneous charging circuit of the first battery module and the second battery module in the first embodiment of the present invention; Figure 5: Circuit block diagram of a battery parallel charging system for implementing the second embodiment of the present invention; And Figure 6: Flow diagram of the second embodiment of the method of parallel charging electric vehicle batteries of the present invention. Complete Description of the Invention In the following, the technical solution in the embodiments of this invention will be explained clearly and completely by referring to the drawings in the embodiments of this invention. Obviously, the embodiments described are only some of, not all, embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by a person skilled in the art without creative effort will fall within the scope of protection of this invention. The present invention discloses a method of parallel charging of batteries for electric vehicles that can be implemented according to the battery parallel charging system depicted in Figure 1. The battery parallel charging system is configured in an electric vehicle. In a first embodiment of the battery parallel charging system of the present invention, a first battery module 10, a second battery module 20 and a control unit 30 are included. The first battery module 10 and the second battery module 20 are connected in parallel, and receive power provided by the charger 50 through the charging cable for charging. The control unit 30 has a communication control unit 31 and a receiver module 32, the communication control unit 31 is connected to the first battery module 10 and the second battery module 20 for communication, the receiver module 32 may, but is not limited to, a wake-up circuit, and is connected to the charger 50 for communication.When the control unit 30 wakes up by receiving the signal sent from the charger 50 via the receiver module. 32, the control unit 30 may receive battery information sent by the first battery module 10 and the second battery module 20 through the communication control unit 31, or issue commands to control the first battery module 10 and the second battery module 20. The first battery module 10 includes a first battery core module 11 and a first battery management system (BMS for short) 12. The first battery core module 11 may comprise one battery core or multiple battery cores. The first battery management system 12 may be implemented on a circuit board as an information management core of the first battery core module 11 that performs charge and discharge operation management for the first battery core module 11, and monitors power information and temperature information of the first battery core module 11. The first battery management system 12 is connected to the charger 50, the first battery core module 11 and the control unit 30, and includes a first interface communication 13, a first charging switch 14 and a first discharge switch 15. The first interface communication 13 is connected to the communication control unit 31, receives control commands from the control unit 30, or transmits battery information from the first battery module 10 to the control unit 30. Specifically, the first battery management system 12 and the control unit 30 communicate with the first interface communication 13 through the communication control unit 31, wherein, the first communication module 13 and the communication control unit 31 may support a Controller Area Network (CAN or CAN bus) protocol, or other wired / wireless interface communication. The first charging switch 14 and the first discharging switch 15 are unidirectional switches, such as metal oxide semiconductor field effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs). For example, the first charging switch 14 and the first discharging switch 15 are respectively taken as MOSFETs for the following explanation: a parasitic diode is located between the source and drain of the MOSFET. The charger 50, the first charging switch 14, and the first discharging switch 15 are connected in series with the first battery core module 11, and the first charging switch 14 and the first discharging switch 15 are connected in reverse, so that the cathodes of each parasitic diode are connected. The first charging switch 14 and the first discharging switch 15 can be turned on or off according to the control unit 30, and the charger 50 can charge the first battery core module 11 by changing the state of the first charging switch 14 and the first discharging switch 15. The second battery module 20 also includes a second battery core module 21 and a second battery management system 22. The second battery management system 22 has a second communication interface 23, a second charging switch 24 and a second discharging switch 25, wherein the second communication interface 23 also communicates with a communication control unit 31 of the control unit 30. Since the circuit structure of the second battery module 20 is the same as that of the first battery module 10, the circuit structure of the second battery module 20 is not repeated herein. A first embodiment of the battery parallel charging method for electric vehicles of the present invention can be implemented by connecting the above-mentioned battery parallel charging system to a charger 50. Specifically, the charger 50 has a communication charging unit 51 and a wake-up module 52. When the battery parallel charging system is connected to the charger 50, the communication charging unit 51 is connected and communicated with the communication control unit 31, and the wake-up module 52 is connected and communicated with the receiver module 32. Let the charger 50 send a trigger-activate signal T1 to the receiver module 32 through the wake-up module 52, and the receiver module 32 receives the trigger-activate signal T1, thereby, the control unit 30 triggers to wake up and execute the battery parallel charging method, wherein the trigger-activate signal T1 can be a power signal. Please refer to Figure 2: the battery parallel charging method includes the following steps: The present invention discloses a method of parallel charging of batteries for electric vehicles that can be implemented according to the battery parallel charging system depicted in FIG. 1. The battery parallel charging system is configured in an electric vehicle. In a first embodiment of the battery parallel charging system of the present invention, a first battery module 10, a second battery module 20 and a control unit 30 are included. The first battery module 10 and the second battery module 20 are connected in parallel, and receive power provided by the charger 50 through the charging cable for charging. The control unit 30 has a communication control unit 31 and a receiver module 32, the communication control unit 31 is connected to the first battery module 10 and the second battery module 20 for communication, the receiver module 32 may, but is not limited to, a wake-up circuit, and is connected to the charger 50 for communication.When the control unit 30 wakes up by receiving a signal sent from the charger 50 through the receiver module 32, the control unit 30 can receive battery information sent by the first battery module 10 and the second battery module 20 through the communication control unit 31, or issue commands to control the first battery module 10 and the second battery module 20. The first battery module 10 includes a first battery core module 11 and a first battery management system (BMS for short) 12. The first battery core module 11 may comprise one battery core or multiple battery cores. The first battery management system 12 may be implemented on a circuit board as an information management core of the first battery core module 11 that performs charge and discharge operation management for the first battery core module 11, and monitors power information and temperature information of the first battery core module 11. The first battery management system 12 is connected to the charger 50, the first battery core module 11 and the control unit 30, and includes a first interface communication 13, a first charging switch 14 and a first discharge switch 15. The first interface communication 13 is connected to the communication control unit 31, receives control commands from the control unit 30, or transmits battery information from the first battery module 10 to the control unit 30. Specifically, the first battery management system 12 and the control unit 30 communicate with the first interface communication 13 through the communication control unit 31, wherein, the first communication module 13 and the communication control unit 31 may support a Controller Area Network (CAN or CAN bus) protocol, or other wired / wireless interface communication. The first charging switch 14 and the first discharging switch 15 are unidirectional switches, such as metal oxide semiconductor field effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs). For example, the first charging switch 14 and the first discharging switch 15 are respectively taken as MOSFETs for the following explanation: a parasitic diode is located between the source and drain of the MOSFET. The charger 50, the first charging switch 14, and the first discharging switch 15 are connected in series with the first battery core module 11, and the first charging switch 14 and the first discharging switch 15 are connected in reverse, so that the cathodes of each parasitic diode are connected. The first charging switch 14 and the first discharging switch 15 can be turned on or off according to the control unit 30, and the charger 50 can charge the first battery core module 11 by changing the state of the first charging switch 14 and the first discharging switch 15. The second battery module 20 also includes a second battery core module 21 and a second battery management system 22. The second battery management system 22 has a second communication interface 23, a second charging switch 24 and a second discharging switch 25, wherein the second communication interface 23 also communicates with a communication control unit 31 of the control unit 30. Since the circuit structure of the second battery module 20 is the same as that of the first battery module 10, the circuit structure of the second battery module 20 is not repeated herein. A first embodiment of the battery parallel charging method for electric vehicles of the present invention can be implemented by connecting the above-mentioned battery parallel charging system to a charger 50. Specifically, the charger 50 has a communication charging unit 51 and a wake-up module 52. When the battery parallel charging system is connected to the charger 50, the communication charging unit 51 is connected and communicated with the communication control unit 31, and the wake-up module 52 is connected and communicated with the receiver module 32. Let the charger 50 send a trigger-activate signal T1 to the receiver module 32 through the wake-up module 52, and the receiver module 32 receives the trigger-activate signal T1, thereby, the control unit 30 triggers to wake up and execute the battery parallel charging method, wherein the trigger-activate signal T1 can be a power signal. Please refer to Figure 2: the battery parallel charging method includes the following steps: S10: the control unit 30 receives the first voltage value from the first battery module 10 and the second voltage value from the second battery module 20. The control unit 30 triggers to wake up the first battery module 10 and the second battery module 20 through the communication control unit 31, so that the first battery module 10 transmits the first voltage value to the communication control unit 31 through the first communication interface 13, and the second battery module 20 transmits the second voltage value to the communication control unit 31 through the second communication interface 23. S11: control unit 30 calculates the voltage difference according to the first voltage value and the second voltage value. S12: determine whether the voltage difference is greater than the preset voltage value. S13: When the voltage difference is greater than the preset voltage value, the first battery module 10 or the second battery module 20 having a lower voltage value is controlled to charge. For example, as shown in FIG. 3, the second battery module 20 has a lower voltage value, and the control unit 30 controls the first battery management system 12 and the second battery management system 22 through the communication control unit 31, to turn on the first charging switch 14, the second charging switch 24 and the second discharge switch 25, so that the charger 50 generates a larger second charging current I2 to charge the second battery module 20 first, and the first battery module 10 has only a small first charging current I1 input because only the first charging switch 14 is turned on. The first charging current I1 is input to the first battery module 10 through the parasitic diode of the first discharge switch 15.Where the total charging current issued by the charger 50 is the sum of the first charging current I1 and the second charging current I2. As the second battery module 20 is gradually charged, the voltage value of the second battery module 20 gradually increases, so the second charging current I2 gradually decreases, and the first charging current I1 input to the first battery module 10 gradually increases. When the first charging current I1 will exceed the maximum current value that the parasitic diode can withstand, it indicates that the voltage difference between the first battery module 10 and the second battery module 20 will be smaller than the preset voltage value. It should be noted that during the above charging process, because the first discharge switch 15 is turned off, the current of the first battery module 10 which has a higher voltage can be prevented from flowing to the second battery module 20 which has a lower voltage, thereby preventing damage to the second battery module 20. S14: When the voltage difference is less than the preset voltage value, the first battery module 10 and the second battery module 20 are controlled to be charged together. As shown in Figure 4, the control unit controls the first battery management system 12 and the second battery management system 22 through the communication control unit 31, so that the first charge switch 14, the first discharge switch 15, the second charge switch 24 and the second discharge switch 25 are turned on, and the first battery module 10 and the second battery module 20 receive the first charge current I1 and the second charge current I2 respectively to be charged together, wherein the first charge current I1 and the second charge current I2 vary respectively with respect to the change of the voltage value of the first battery module 10 and the second battery module 20. When the voltage value of the first battery module 10 and the second battery module 20 are the same, the first charge current I1 is equal to the second charge current I2.In one embodiment of the present invention, when the first battery module 10 and the second battery module 20 are charged together, the control unit 30 communicates with the communication charging unit 51 through the communication control unit 31 to make the charger 50 increase the total charging current output. A second embodiment of the battery parallel charging method for an electric vehicle of the present invention may be implemented by a second embodiment of a battery parallel charging system based on the circuit structure of a first embodiment of a battery parallel charging system and additionally comprising a plurality of battery modules each having a charging switch and a discharging switch. In the following, a parallel battery charging system having three such battery modules is taken as an example for explanation. As illustrated in Figure 5, the third battery module 40 also includes a third battery core module 41 and a third battery management system 42, and the third battery management system 42 has a third communication interface 43, a third charging switch 44 and a third discharging switch 45, wherein the third communication interface 43 also connects and communicates with the communication control unit 31 of the control unit 30; since the circuit structure of the third battery module 30 is the same as that of the first battery module 10, the circuit structure of the third battery module 30 is not repeated herein. When the second embodiment of the battery parallel charging system is connected to the charger 50, the control unit 30 triggers to wake up and execute the second embodiment of the battery parallel charging method; please refer to Figure 6, and the method includes the following steps: S20: The control unit 30 receives the voltage values ​​of the first battery module 10, the second battery module 20 and the third battery module 40. Since the method used by the control unit 30 to receive the voltage values ​​is the same as the method of step S10 for the first embodiment, further details of this method are not repeated here. S21: The control unit 30 determines whether the voltage difference among a plurality of battery modules is greater than a preset voltage value. In particular, the control unit 30 may determine that among the first battery module 10, the second battery module 20 and the third battery module 40, the battery module having the minimum voltage value is used as the reference battery module; for example, the third battery module 40 is the reference battery pack.The control unit (30) respectively calculates the voltage difference between the reference battery module and the other battery module, and judges whether the voltage difference is greater than a preset voltage value, wherein the voltage difference between the reference battery module and the first battery module 10 is a first voltage difference, the voltage difference between the reference battery module and the second battery module 20 is a second voltage difference; the preset voltage value is the same as the first embodiment, and the preset voltage value is related to the maximum current value maintained by each parasitic diode. S22: When the voltage difference is greater than the preset voltage value, the control unit (30) controls the battery module having the lower voltage value among the plurality of battery modules to be charged, as mentioned above, that is, when the first voltage difference and the second voltage difference are respectively greater than the preset voltage value, the control unit (30) controls to charge the reference battery module. Since the charging method mentioned above is the same as the first embodiment, further details of the method are not repeated herein. S23: When the voltage difference is less than the preset voltage value, the control unit 30 controls a plurality of battery modules to be charged together. Cooperating with the above example, for example, at least one of the first voltage difference and the second voltage difference is less than the preset voltage value, the control unit 30 controls the battery modules whose voltage difference is less than the preset voltage value to be charged together with the reference battery module. For example, the second voltage difference is less than the preset voltage value, the control unit 30 controls the second battery regulating system 22 and the third battery regulating system 42 through the communication control unit 31, so that the second battery module 20 and the third battery module 40 are charged together. The parallel battery charging method for electric vehicles of the present invention aims to charge electric vehicles with a charger through a dedicated charging cable. Determine a reference battery module having the smallest voltage value among a plurality of battery modules. Calculate the respective voltage differences between each battery module and the reference battery module. When each voltage difference is greater than a preset voltage value, charge only the reference battery module by controlling the charging switch, the discharge switch of the reference battery module and the charging switches of other battery modules to be turned on, so as to prevent current from other battery modules from flowing to the reference battery module. When at least one voltage difference is smaller than the preset voltage value, the battery module corresponding to at least one voltage difference is charged together with the reference battery module by controlling the charging switch, the discharge switch of the reference battery module shall be turned on, and charge the battery module corresponding to at least one voltage difference; as a result, the battery modules with voltage difference can be charged together, and thus the voltage of all battery modules can be uniform. The above is a preferred embodiment of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, certain improvements and refinements of the present invention can still be made, which are still considered to be within the scope of protection of the present invention. Although many of the characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is for illustrative purposes only. Changes may be made in details, particularly in the shape, size and arrangement of parts in the principles of the invention as fully as indicated by the broad general meaning of the terms in which the appended claims are set forth. The parallel battery charging method for electric vehicles of the present invention aims to charge electric vehicles with a charger through a dedicated charging cable. Determine the reference battery module having the smallest voltage value among a plurality of battery modules. Calculate the respective voltage differences between each battery module and the reference battery module. When each voltage difference is greater than a preset voltage value, charge only the reference battery module by controlling the charging switch, the discharge switch of the reference battery module and the charging switches of other battery modules to be turned on, so as to prevent current from other battery modules from flowing to the reference battery module.When at least one voltage difference is smaller than the preset voltage value, the battery module corresponding to at least one voltage difference is charged together with the reference battery module by controlling the charging switch, the discharge switch of the reference battery module shall be turned on, and charge the battery module corresponding to at least one voltage difference; as a result, the battery modules with voltage difference can be charged together, and thus the voltage of all battery modules can be uniform. The above is a preferred embodiment of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, certain improvements and refinements of the present invention can still be made, which are still considered to be within the scope of protection of the present invention. Although many of the characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is for illustrative purposes only. Changes may be made in details, particularly in the shape, size and arrangement of parts in the principles of the invention as fully as indicated by the broad general meaning of the terms in which the appended claims are set forth. The parallel battery charging method for electric vehicles of the present invention aims to charge electric vehicles with a charger through a dedicated charging cable. Determine the reference battery module having the smallest voltage value among a plurality of battery modules. Calculate the respective voltage differences between each battery module and the reference battery module. When each voltage difference is greater than a preset voltage value, charge only the reference battery module by controlling the charging switch, the discharge switch of the reference battery module and the charging switches of other battery modules to be turned on, so as to prevent current from other battery modules from flowing to the reference battery module.When at least one voltage difference is smaller than the preset voltage value, the battery module corresponding to at least one voltage difference is charged together with the reference battery module by controlling the charging switch, the discharge switch of the reference battery module shall be turned on, and charge the battery module corresponding to at least one voltage difference; as a result, the battery modules with voltage difference can be charged together, and thus the voltage of all battery modules can be uniform. The above is a preferred embodiment of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, certain improvements and refinements of the present invention can still be made, which are still considered to be within the scope of protection of the present invention. Although many of the characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is for illustrative purposes only. Changes may be made in details, particularly in the shape, size and arrangement of parts in the principles of the invention as fully as indicated by the broad general meaning of the terms in which the appended claims are set forth. The parallel battery charging method for electric vehicles of the present invention aims to charge electric vehicles with a charger through a dedicated charging cable. Determine the reference battery module having the smallest voltage value among a plurality of battery modules. Calculate the respective voltage differences between each battery module and the reference battery module. When each voltage difference is greater than a preset voltage value, charge only the reference battery module by controlling the charging switch, the discharge switch of the reference battery module and the charging switches of other battery modules to be turned on, so as to prevent current from other battery modules from flowing to the reference battery module.When at least one voltage difference is smaller than the preset voltage value, the battery module corresponding to at least one voltage difference is charged together with the reference battery module by controlling the charging switch, the discharge switch of the reference battery module shall be turned on, and charge the battery module corresponding to at least one voltage difference; as a result, the battery modules with voltage difference can be charged together, and thus the voltage of all battery modules can be uniform. The above is a preferred embodiment of the present invention. It should be noted that for those skilled in the art, without departing from the principles of the present invention, certain improvements and refinements of the present invention can still be made, which are still considered to be within the scope of protection of the present invention. Although many of the characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is for illustrative purposes only. Changes may be made in details, particularly in the shape, size and arrangement of parts in the principles of the invention as fully as indicated by the broad general meaning of the terms in which the appended claims are set forth.

Claims

1. A battery parallel charging method for an electric vehicle, the electric vehicle including a plurality of battery modules and a control unit (30), the battery modules including a battery core module, a charging switch and a discharging switch, the plurality of battery modules being connected in parallel, and the control unit (30) being electrically connected to the plurality of battery modules; characterized in that, when the electric vehicle is connected to a charger (50), the control unit (30) receives an enable-trigger signal sent from the charger (50) to execute the battery parallel charging method, and the method includes: the control unit (30) receiving respective voltage values ​​of the plurality of battery modules; the control unit (30) determining whether the voltage difference among the plurality of battery modules is greater than a pre-set voltage value;when the voltage difference is greater than the preset voltage value, the control unit (30) controls a plurality of battery modules having a lower voltage value to be charged; when the voltage difference is less than the preset voltage value, the control unit (30) controls a plurality of battery modules to be charged together.; 2. A method of parallel charging a battery for an electric vehicle, the electric vehicle includes a first battery module (10), a second battery module (20) and a control unit (30), the first battery module (10) includes a first battery core module (11), a first charging switch (14) and a first discharge switch (15); the second battery module (20) includes a second battery core module (21), a second charging switch (24) and a second discharge switch (25); the first battery module (10) and the second battery module (20) are connected in parallel, and the control unit (30) is electrically connected to the first battery module (10) and the second battery module (20);characterized in that, when the electric vehicle is connected to the charger (50), the control unit (30) receives an enable-trigger signal transmitted from the charger (50) to execute a battery parallel charging method, and the method includes: the control unit (30) receives a first voltage value from the first battery module (10) and a second voltage value from the second battery module (20); the control unit (30) calculates a voltage difference between the first voltage value and the second voltage value; the control unit (30) determines whether the voltage difference is greater than a preset voltage value; when the voltage difference is greater than the preset voltage value, the control unit (30) controls one of the first battery module (10) and the second battery module (20) having a lower voltage value to charge; when the voltage difference is less than the preset voltage value, the control unit (30) controls the first battery module (10) and the second battery module (20) to charge together.; 3. A method of parallel battery charging for an electric vehicle as claimed in claim 1 or 2, wherein the control unit (30) includes a receiver module, the charger (50) includes an activation module (52), the charger (50) transmits an activation-trigger signal to the receiver module through the wake-up module (52), and the activation-trigger signal is a power signal.

4. A method of parallel charging a battery for an electric vehicle as claimed in claim 3, wherein, the receiver module is an activation circuit, and the activation circuit wakes up the control unit (30) according to the trigger-on-signal rising.

5. A method of parallel battery charging for an electric vehicle as claimed in claim 2, wherein, the first battery module (10) includes a first battery regulation system (12), the second battery module (20) includes a second battery regulation system (22), and the control unit (30) includes a communication control unit (31), wherein, through the communication control unit (31), the control unit (30) communicates with the first battery regulation system (12) and the second battery regulation system (22) respectively to receive a first voltage value and a second voltage value.

6. A method of parallel charging a battery for an electric vehicle as claimed in claim 5, wherein, the charger (50) further includes a communication charging unit (51), and the communication charging unit (51) communicates with the communication control unit (31).

7. A method of parallel battery charging for an electric vehicle as claimed in claim 6, wherein, when the first battery module (10) and the second battery module (20) are charged together, the control unit (30) causes the charger (50) to increase the total charging current output through the communication charging unit (51).

8. A method of parallel battery charging for an electric vehicle as claimed in claim 2, wherein, when the voltage difference is greater than a predetermined voltage value, the control unit (30) turns on the charging switch and the discharging switch of the first battery module (10) and the second battery module (20) with a lower voltage value, and turns on the charging switch of the first battery module (10) and the second battery module (20) with a higher voltage value.

9. A method of parallel battery charging for an electric vehicle as claimed in claim 2, wherein, when the voltage difference is less than a predetermined voltage value, the control unit (30) turns on the second charging switch (24) and the second discharging switch (25), and turns on the first charging switch (14) and the first discharging switch (15) to charge simultaneously.

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