A dual battery coupling system and SOC balancing control method

Abstract

The present invention relates to a dual-battery coupling system and a SOC balancing control method. The system comprises: a battery A and a battery B for providing electric energy; a bidirectional DC-DC converter for balancing the charge states of the battery A and the battery B; the bidirectional DC-DC converter comprises: an inductor L for filtering noise and interference; an IGBT Q1 with damping and an IGBT Q2 with damping for balancing the charge states of the battery A and the battery B; the present invention improves the stability and reliability of the system by adding an IGBT with damping to the system, and switches the working state of the dual batteries by adjusting the bidirectional DC-DC converter according to the SOC deviation of the dual batteries, and then realizes the balancing control of the SOC of the dual batteries under different working conditions, thereby avoiding overcharging and overdischarging of the batteries and extending the battery service life.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a dual-battery coupling system and a SOC balancing control method. Background Art

[0002] With the continuous development of new energy vehicles, consumers have higher and higher requirements for the range of new energy passenger vehicles. One way to solve the range problem of new energy passenger vehicles is to increase the capacity of power batteries by continuously increasing battery cell packs, which leads to the increasing size of power battery packs. Due to the limited space in passenger cars, the power batteries have to be arranged separately, so more and more new energy vehicles adopt dual battery pack solutions.

[0003] In the prior art, the main dual-battery arrangement scheme adopted is direct parallel connection. This scheme directly connects two groups of power batteries into the busbar, does not control the dual power battery groups, and charges and discharges the dual battery groups at the same time. However, due to the different internal resistances of different power battery groups, the state of charge (SOC) is also different, which leads to differences in the service life of the two groups of power batteries and even accelerates the attenuation of the power battery capacity. Summary of the invention

[0004] The purpose of the present invention is to provide a dual-battery coupling system and a SOC balancing control method, which improves the stability and reliability of the system by adding an IGBT with damping in the system, and realizes the switching of the dual-battery working state by adjusting the bidirectional DC-DC converter according to the dual-battery SOC deviation, and then realizes the balancing control of the dual-battery SOC under different working conditions, thereby avoiding overcharging and over-discharging of the battery and extending the battery life.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A dual battery coupling system, comprising:

[0007] Battery A and battery B are used to provide electrical energy;

[0008] A bidirectional DC-DC converter, used to balance the charge states of the battery A and the battery B;

[0009] The bidirectional DC-DC converter comprises:

[0010] Inductor L, used to filter out noise and interference;

[0011] The damped IGBT Q1 and the damped IGBT Q2 are used to balance the charge states of the battery A and the battery B;

[0012] Among them, the negative electrode of the battery A is connected in parallel with the emitter of the damped IGBT Q2 and the negative electrode of the battery B, the positive electrode of the battery A is connected in parallel with one end of the inductor L, the positive electrode of the battery B is connected in parallel with the collector of the damped IGBT Q1, the negative electrode of the battery B is connected in parallel with the emitter of the damped IGBT Q2, and the other end of the inductor L is electrically connected to the emitter of the IGBT Q1 and the collector of the damped IGBT Q2, respectively.

[0013] Optionally, the system further comprises:

[0014] Switch K1 and switch K2 are used to control the connection and disconnection of the battery A and the battery B;

[0015] Load, used to consume electrical energy;

[0016] Among them, one end of the switch K1 is electrically connected to the positive electrode of the battery A and one end of the inductor L respectively, the other end of the switch K1 is electrically connected to one end of the switch K2 and one end of the load respectively, one end of the switch K2 is also connected to one end of the load, the other end of the switch K2 is electrically connected to the collector of the damped IGBT Q1 and the positive electrode of the battery B respectively, and the other end of the load is electrically connected to the negative electrode of the battery B, the emitter of the damped IGBT Q2, and the negative electrode of the battery A respectively.

[0017] To achieve the above object, the present invention provides a SOC balancing control method for a dual-battery coupling system, comprising:

[0018] Determine a SOC deviation standard of battery A and battery B, and adjust the working state of the bidirectional DC-DC converter according to the SOC deviation standard;

[0019] Based on the adjusted working state of the bidirectional DC-DC converter, balancing control is performed on the SOC of the battery A and the battery B in different modes;

[0020] Among them, the different modes include: braking energy recovery mode and dual battery discharge mode.

[0021] Optionally, determining the SOC deviation standard of the battery A and the battery B includes:

[0022] According to the size of the deviation, there are three deviation standards, including small deviation, medium deviation and large deviation, wherein the small deviation is smaller than the medium deviation, and the medium deviation is smaller than the large deviation.

[0023] Optionally, performing balanced control on the SOC of the battery A and the battery B in the braking energy recovery mode includes:

[0024] The absolute value of the SOC deviation between the battery A and the battery B is obtained. When the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, the battery A and the battery B are charged, and the bidirectional DC-DC converter does not work. When the absolute value is greater than the small deviation and less than or equal to the large deviation, the SOC of the battery A and the SOC of the battery B are compared, the switch of the battery with a higher SOC is closed, and the switch of the battery with a lower SOC is opened, and the bidirectional DC-DC converter is adjusted to charge the battery with a higher SOC less and charge the battery with a lower SOC more. When the absolute value is greater than the large deviation, the SOC of the battery A and the SOC of the battery B are compared, and the bidirectional DC-DC converter is adjusted to not charge or charge less the battery with a higher SOC, and charge the battery with a lower SOC.

[0025] Optionally, performing balancing control on the SOC of the battery A and the battery B in the dual-battery discharge mode includes:

[0026] A total power requirement assessment standard for the battery A and the battery B is preset, the total power requirement of the battery A and the battery B is obtained, and it is determined whether the total power requirement of the battery A and the battery B is greater than the total power requirement assessment standard. When the total power requirement of the battery A and the battery B is greater than the total power requirement assessment standard, then when the total power requirement of the battery A and the battery B is larger, the SOCs of the battery A and the battery B are balanced and controlled. When the total power requirement of the battery A and the battery B is less than or equal to the total power requirement assessment standard, then when the total power requirement of the battery A and the battery B is smaller, the SOCs of the battery A and the battery B are balanced and controlled.

[0027] Optionally, when the total required power of the battery A and the battery B is small, performing balanced control on the SOCs of the battery A and the battery B includes:

[0028] The absolute value of the SOC deviation between the battery A and the battery B is obtained. When |ΔSOC|≤Δs1 and the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, the battery A and the battery B are discharged, and the bidirectional DC-DC converter does not work. When the absolute value is greater than the small deviation and less than or equal to the medium deviation, the SOC of the battery A and the SOC of the battery B are compared, the switch of the battery with a higher SOC is opened, and the switch of the battery with a lower SOC is closed, and the bidirectional DC-DC converter is adjusted. The battery with a high SOC is discharged more, and the battery with a low SOC is discharged less; when the absolute value is greater than the medium deviation and less than or equal to the large deviation, the SOC of the battery A is compared with the SOC of the battery B, and the bidirectional DC-DC converter is adjusted to discharge the battery with a high SOC and not discharge the battery with a low SOC; when the absolute value is greater than the large deviation, the SOC of the battery A is compared with the SOC of the battery B, and the bidirectional DC-DC converter is adjusted to discharge the battery with a high SOC and charge the battery with a low SOC.

[0029] Optionally, when the total required power of the battery A and the battery B is relatively large, performing balanced control on the SOCs of the battery A and the battery B includes:

[0030] The absolute value of the SOC deviation between the battery A and the battery B is obtained. When the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, the battery A and the battery B are discharged, and the bidirectional DC-DC converter does not work. When the absolute value is greater than the small deviation and less than or equal to the large deviation, the SOC of the battery A and the SOC of the battery B are compared, the switch of the battery with a high SOC is opened, and the switch of the battery with a low SOC is closed, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge more and the battery with a low SOC discharge less. When the absolute value is greater than the large deviation, the SOC of the battery A and the SOC of the battery B are compared, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge, and the battery with a low SOC not discharge or discharge less.

[0031] The beneficial effects of the present invention are:

[0032] The present invention improves the stability and reliability of the system by adding an IGBT with damping in the system, and switches the working state of the dual batteries by adjusting the bidirectional DC-DC converter according to the SOC deviation of the dual batteries, thereby realizing balanced control of the SOC of the dual batteries under different working conditions, thereby avoiding overcharging and over-discharging of the batteries and extending the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 A schematic diagram of a dual-battery coupling system according to an embodiment of the present invention;

[0035] Figure 2 A quadrant diagram of the power decoupling distribution relationship of dual power batteries according to an embodiment of the present invention;

[0036] Figure 3 Schematic diagram of a SOC balancing control method for a dual-battery coupling system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] The invention discloses a dual-battery coupling system, comprising: a battery A and a battery B for providing electric energy; a bidirectional DC-DC converter for realizing balanced charge states of the battery A and the battery B; the bidirectional DC-DC converter comprises: an inductor L for filtering noise and interference; an IGBT Q1 with damping and an IGBT Q2 with damping for realizing balanced charge states of the battery A and the battery B; wherein the negative electrode of the battery A is respectively connected in parallel with the emitter of the IGBT Q2 with damping and the negative electrode of the battery B, the positive electrode of the battery A is connected in parallel with one end of the inductor L, the positive electrode of the battery B is connected in parallel with the collector of the IGBT Q1 with damping, the negative electrode of the battery B is connected in parallel with the emitter of the IGBT Q2 with damping, and the other end of the inductor L is respectively electrically connected with the emitter of the IGBT Q1 and the collector of the IGBT Q2 with damping.

[0040] The system further includes: a switch K1 and a switch K2, which are used to control the connection and disconnection of battery A and battery B; and a load, which is used to consume electric energy; wherein one end of the switch K1 is electrically connected to the positive electrode of battery A and one end of the inductor L, respectively, and the other end of the switch K1 is electrically connected to one end of the switch K2 and one end of the load, respectively, and one end of the switch K2 is also connected to one end of the load, and the other end of the switch K2 is electrically connected to the collector of the damped IGBT Q1 and the positive electrode of battery B, respectively, and the other end of the load is electrically connected to the negative electrode of battery B, the emitter of the damped IGBT Q2, and the negative electrode of battery A, respectively, specifically:

[0041] like Figure 1 As shown, the present invention provides a dual-battery coupling system, including a switch K1, a switch K2, an IGBT Q1 with a damping, an IGBT Q2 with a damping, a battery A, a battery B, a load C and an inductor L, the positive electrode of the battery A is connected in parallel with the switch K1 and the inductor L, the negative electrode of the battery A is connected in parallel with the IGBT Q2 with a damping, the battery B and the load C, the positive electrode of the battery B is connected in parallel with the switch K2 and the IGBT Q1 with a damping, and the IGBT Q1 with a damping and the IGBT Q2 with a damping are both electrically connected to the other end of the inductor L, the other ends of the switch K1 and the switch K2 are both electrically connected to the other end of the load C, the emitter of the IGBT Q1 with a damping is electrically connected to one end of the inductor L, the collector of the IGBT Q1 with a damping is electrically connected to the positive electrode of the battery B, the emitter of the IGBT Q2 with a damping is electrically connected to the negative electrode of the battery A, and the IGBT Q1 with a damping is electrically connected to the negative electrode of the battery A. The collector of Q2 is electrically connected to one end of the inductor L. Switches K1 and K2 are used to control the connection and disconnection of the dual batteries A and B. By controlling the damped IGBTs Q1 and Q2 through the drive circuit to switch the switch states, the charge states of the dual batteries A and B can be balanced. The inductor L is used to filter out noise and interference.

[0042] The present invention also discloses a SOC balancing control method for a dual-battery coupling system, including: determining the SOC deviation standard of battery A and battery B, and adjusting the working state of a bidirectional DC-DC converter according to the SOC deviation standard; based on the adjusted working state of the bidirectional DC-DC converter, balancing control is performed on the SOC of battery A and battery B in different modes; wherein the different modes include: a braking energy recovery mode and a dual-battery discharge mode.

[0043] Determining the SOC deviation standards of battery A and battery B includes: dividing into three deviation standards according to the deviation size, including small deviation, medium deviation and large deviation, wherein the small deviation is smaller than the medium deviation and smaller than the large deviation, specifically:

[0044] like Figure 2-3As shown, an embodiment of the present invention provides: a SOC balancing control method for a dual-battery coupling system, including step 1, determining an SOC deviation standard; step 2, SOC balancing control in a braking energy recovery mode; step 3, SOC balancing control in a dual-battery discharge mode, as shown in Table 1, which is a dual power battery power decoupling distribution relationship table;

[0045] In the above step 1, three deviation standards of the dual battery SOC are determined according to the performance of the dual battery, which are a small deviation Δs1, a medium deviation Δs2 and a large deviation Δs3.

[0046] The SOCs of the two batteries are different, and the terminal voltages of the batteries are also different. The greater the SOC deviation, the greater the voltage difference between the two batteries. Therefore, the working modes of battery A and battery B are affected by the SOC deviation. When the SOC deviation is small, the working modes of battery A and battery B can be consistent. When the SOC deviation is too large, the large SOC battery charges the small SOC battery, which cannot meet the high power requirements of the vehicle and reduces the vehicle's power. When the dual battery deviation is less than 5%, the dual battery working modes can remain consistent, so ΔS1=5%, and the SOC is 100%-50% which is the common working range of the battery. Therefore, the medium deviation ΔS2=50%, and the battery SOC is less than 30%. In order to protect the battery, the battery is prohibited from discharging. Therefore, the large deviation ΔS3=70%.

[0047] The balanced control of the SOC of battery A and battery B in the braking energy recovery mode includes: obtaining the absolute value of the SOC deviation of battery A and battery B, when the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, battery A and battery B are charged, and the bidirectional DC-DC converter does not work; when the absolute value is greater than the small deviation and less than or equal to the large deviation, the SOC of battery A and the SOC of battery B are compared, the switch of the battery with a high SOC is closed, the switch of the battery with a low SOC is opened, and the bidirectional DC-DC converter is adjusted to charge the battery with a high SOC less and charge the battery with a low SOC more; when the absolute value is greater than the large deviation, the SOC of battery A and the SOC of battery B are compared, and the bidirectional DC-DC converter is adjusted to charge the battery with a high SOC less or less, and charge the battery with a low SOC, specifically:

[0048] In the braking energy recovery mode, the total power demanded by the battery is negative. According to the dual-battery SOC deviation, the working state of the bidirectional DC-DC converter is adjusted to achieve balanced control of the dual-battery SOC, specifically: the absolute value of the SOC deviation |ΔSOC| of battery A and battery B is monitored online. When |ΔSOC|≤Δs1, the dual-battery switches are closed and charged at the same time. At this time, the bidirectional DC-DC converter does not work; when Δs1<|ΔSOC|≤Δs3, the switch of the battery with a high SOC is closed, and the switch of the battery with a low SOC is opened. At this time, the bidirectional DC-DC converter is adjusted to charge the battery with a high SOC less and charge the battery with a low SOC more; when |ΔSOC|>Δs3, the bidirectional DC-DC converter is adjusted so that the battery with a high SOC is not charged / charged less, and the battery with a low SOC is charged.

[0049] The SOC balancing control of the battery A and the battery B in the dual-battery discharge mode includes: presetting the total power demand assessment standard of the battery A and the battery B, obtaining the total power demand of the battery A and the battery B, judging whether the total power demand of the battery A and the battery B is greater than the total power demand assessment standard, when the total power demand of the battery A and the battery B is greater than the total power demand assessment standard, then the SOC of the battery A and the battery B is balanced when the total power demand of the battery A and the battery B is large, and when the total power demand of the battery A and the battery B is less than or equal to the total power demand assessment standard, then the SOC of the battery A and the battery B is balanced when the total power demand of the battery A and the battery B is small, specifically:

[0050] In the dual-battery discharge mode, the total power demand of the battery is positive. According to the total power demand of the dual batteries and the SOC deviation, the working state of the bidirectional DC-DC converter is adjusted to achieve balanced control of the dual-battery SOC. The total power demand of the dual batteries specifically includes the following two situations: one is the situation where the total power demand of the dual batteries is small, that is, p≤p B1max , the second is the case where the total power demand of the dual batteries is large, that is, p>p B1max , where p B1max It is the standard for assessing the total power requirement of the preset dual batteries.

[0051] The balanced control of the SOC of battery A and battery B includes: obtaining the absolute value of the SOC deviation of battery A and battery B, when |ΔSOC|≤Δs1, and the absolute value is less than or equal to the small deviation, then the switch K1 and the switch K2 are closed, battery A and battery B are discharged, and the bidirectional DC-DC converter does not work; when the absolute value is greater than the small deviation and less than or equal to the medium deviation, the SOC of battery A and the SOC of battery B are compared, the switch of the battery with a high SOC is opened, and the switch of the battery with a low SOC is closed, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge more and the battery with a low SOC discharge less; when the absolute value is greater than the medium deviation and less than or equal to the large deviation, the SOC of battery A and the SOC of battery B are compared, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge and the battery with a low SOC not discharge; when the absolute value is greater than the large deviation, the SOC of battery A and the SOC of battery B are compared, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge and the battery with a low SOC charge, specifically:

[0052] When the total power demand of the dual batteries is small, when |ΔSOC|≤Δs1, the dual battery switches are closed and discharged at the same time. At this time, the bidirectional DC-DC converter does not work; when Δs1<|ΔSOC|≤Δs2, the switch of the battery with a high SOC is opened, and the switch of the battery with a low SOC is closed. At this time, the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge more and the battery with a low SOC discharge less; when Δs2<|ΔSOC|≤Δs3, the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge and the battery with a low SOC not discharge; when |ΔSOC|>Δs3, the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge and the battery with a low SOC charge.

[0053] In the case where the total power demand of battery A and battery B is large, the SOC of battery A and battery B is balanced and controlled, including: obtaining the absolute value of the SOC deviation of battery A and battery B, when the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, battery A and battery B are discharged, and the bidirectional DC-DC converter does not work; when the absolute value is greater than the small deviation and less than or equal to the large deviation, the SOC of battery A and the SOC of battery B are compared, the switch of the battery with a high SOC is opened, the switch of the battery with a low SOC is closed, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge more and the battery with a low SOC discharge less; when the absolute value is greater than the large deviation, the SOC of battery A and the SOC of battery B are compared, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge, and the battery with a low SOC not discharge or discharge less, specifically:

[0054] When the total power demand of the dual batteries is large, when |ΔSOC|≤Δs1, the dual battery switches are closed and discharged at the same time. At this time, the bidirectional DC-DC converter does not work; when Δs1<|ΔSOC|≤Δs3, the switch of the battery with a high SOC is opened, and the switch of the battery with a low SOC is closed. At this time, the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge more and the battery with a low SOC discharge less; when |ΔSOC|>Δs3, the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge, and the battery with a low SOC not discharge or discharge less.

[0055] Table 1

[0056]

[0057]

[0058] Based on the above, the advantage of the present invention is that when the present invention is used, the dual batteries A and B can be flexibly connected and disconnected through the control of switches K1 and K2, so that the system can distribute and adjust energy according to actual needs, and has the advantage of high flexibility; the flow of energy can be effectively controlled through the damped IGBTs Q1 and Q2, and energy recovery and reuse can be achieved, thereby improving the energy utilization efficiency; by controlling the switching state of the damped IGBTs Q1 and Q2, the charge state of the dual batteries A and B can be balanced, overcharging and over-discharging can be avoided, and the battery life can be extended; and the damped IGBTs Q1 and Q2 can effectively suppress the occurrence of dangerous conditions such as overcurrent and overvoltage, thereby ensuring the safe operation of the system; the inductor L can effectively filter out noise and interference, thereby improving the stability of the system.

[0059] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A dual battery coupling system, characterized in that: include: Battery A and battery B are used to provide electrical energy; A bidirectional DC-DC converter, used to balance the charge states of the battery A and the battery B; The bidirectional DC-DC converter comprises: Inductor L, used to filter out noise and interference; The damped IGBT Q1 and the damped IGBT Q2 are used to balance the charge states of the battery A and the battery B; The negative electrode of the battery A is connected in parallel with the emitter of the damped IGBT Q2 and the negative electrode of the battery B, respectively; the positive electrode of the battery A is connected in parallel with one end of the inductor L; the positive electrode of the battery B is connected in parallel with the collector of the damped IGBT Q1; the negative electrode of the battery B is connected in parallel with the emitter of the damped IGBT Q2; and the other end of the inductor L is electrically connected with the emitter of the IGBT Q1 and the collector of the damped IGBT Q2, respectively; The system also includes: Switch K1 and switch K2 are used to control the connection and disconnection of the battery A and the battery B; Load, used to consume electrical energy; Among them, one end of the switch K1 is electrically connected to the positive electrode of the battery A and one end of the inductor L respectively, the other end of the switch K1 is electrically connected to one end of the switch K2 and one end of the load respectively, one end of the switch K2 is also connected to one end of the load, the other end of the switch K2 is electrically connected to the collector of the damped IGBT Q1 and the positive electrode of the battery B respectively, and the other end of the load is electrically connected to the negative electrode of the battery B, the emitter of the damped IGBT Q2, and the negative electrode of the battery A respectively.

2. The SOC balancing control method of the dual battery coupling system according to claim 1, characterized in that: include: Determine a SOC deviation standard of battery A and battery B, and adjust the working state of the bidirectional DC-DC converter according to the SOC deviation standard; Based on the adjusted working state of the bidirectional DC-DC converter, balancing control is performed on the SOC of the battery A and the battery B in different modes; Among them, the different modes include: braking energy recovery mode and dual battery discharge mode.

3. The SOC balance control method according to claim 2, characterized in that: Determining the SOC deviation standard of the battery A and the battery B includes: According to the size of the deviation, there are three deviation standards, including small deviation, medium deviation and large deviation, wherein the small deviation is smaller than the medium deviation, and the medium deviation is smaller than the large deviation.

4. The SOC balance control method according to claim 3, characterized in that: The SOC balancing control of the battery A and the battery B in the braking energy recovery mode includes: The absolute value of the SOC deviation between the battery A and the battery B is obtained. When the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, the battery A and the battery B are charged, and the bidirectional DC-DC converter does not work. When the absolute value is greater than the small deviation and less than or equal to the large deviation, the SOC of the battery A and the SOC of the battery B are compared, the switch of the battery with a higher SOC is closed, and the switch of the battery with a lower SOC is opened, and the bidirectional DC-DC converter is adjusted to charge the battery with a higher SOC less and charge the battery with a lower SOC more. When the absolute value is greater than the large deviation, the SOC of the battery A and the SOC of the battery B are compared, and the bidirectional DC-DC converter is adjusted to not charge or charge less the battery with a higher SOC, and charge the battery with a lower SOC.

5. The SOC balance control method according to claim 3, characterized in that: The SOC balancing control of the battery A and the battery B in the dual-battery discharge mode includes: A total power requirement assessment standard for the battery A and the battery B is preset, the total power requirement of the battery A and the battery B is obtained, and it is determined whether the total power requirement of the battery A and the battery B is greater than the total power requirement assessment standard. When the total power requirement of the battery A and the battery B is greater than the total power requirement assessment standard, then when the total power requirement of the battery A and the battery B is larger, the SOCs of the battery A and the battery B are balanced and controlled. When the total power requirement of the battery A and the battery B is less than or equal to the total power requirement assessment standard, then when the total power requirement of the battery A and the battery B is smaller, the SOCs of the battery A and the battery B are balanced and controlled.

6. The SOC balance control method according to claim 5, characterized in that: When the total required power of the battery A and the battery B is small, performing balanced control on the SOCs of the battery A and the battery B includes: The absolute value of the SOC deviation between the battery A and the battery B is obtained. When |ΔSOC|≤ΔS1 and the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, the battery A and the battery B are discharged, and the bidirectional DC-DC converter does not work. When the absolute value is greater than the small deviation and less than or equal to the medium deviation, the SOC of the battery A and the SOC of the battery B are compared, the switch of the battery with a higher SOC is opened, and the switch of the battery with a lower SOC is closed, and the bidirectional DC-DC converter is adjusted. The battery with a high SOC is discharged more, and the battery with a low SOC is discharged less; when the absolute value is greater than the medium deviation and less than or equal to the large deviation, the SOC of the battery A is compared with the SOC of the battery B, and the bidirectional DC-DC converter is adjusted to discharge the battery with a high SOC and not discharge the battery with a low SOC; when the absolute value is greater than the large deviation, the SOC of the battery A is compared with the SOC of the battery B, and the bidirectional DC-DC converter is adjusted to discharge the battery with a high SOC and charge the battery with a low SOC.

7. The SOC balance control method according to claim 5, characterized in that: When the total power demand of the battery A and the battery B is relatively large, performing balanced control on the SOCs of the battery A and the battery B includes: The absolute value of the SOC deviation between the battery A and the battery B is obtained. When the absolute value is less than or equal to the small deviation, the switch K1 and the switch K2 are closed, the battery A and the battery B are discharged, and the bidirectional DC-DC converter does not work. When the absolute value is greater than the small deviation and less than or equal to the large deviation, the SOC of the battery A and the SOC of the battery B are compared, the switch of the battery with a high SOC is opened, and the switch of the battery with a low SOC is closed, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge more and the battery with a low SOC discharge less. When the absolute value is greater than the large deviation, the SOC of the battery A and the SOC of the battery B are compared, and the bidirectional DC-DC converter is adjusted to make the battery with a high SOC discharge, and the battery with a low SOC not discharge or discharge less.

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