CN115805845A - A multi-branch battery system charging method and vehicle - Google Patents

Abstract

The invention provides a charging method of a multi-branch battery system and a vehicle, and belongs to the technical field of vehicle charging. Calculating branch SOC of each battery branch and monomer SOC of abnormal monomer battery cell corresponding to the highest voltage in each battery branch in real time; and judging the difference between the branch SOC of each battery branch, the difference between the single SOC of the abnormal single battery core and the branch SOC of the battery where the abnormal single battery core is located. After a period of charging, if the branch SOC difference between battery branches is delta SOC _{Branch-branch} Difference delta SOC between monomer SOC higher than abnormal monomer battery cell and branch SOC of battery branch _{Monomer branch} In the process, the BMS adopts a method of reducing charging current in a stepped mode, so that the SOC difference between each battery branch is reduced, and the monomer overvoltage phenomenon caused by charging abnormal monomer battery cores after the charging stage is finished is avoided.

Description

A multi-branch battery system charging method and vehicle

technical field

The invention relates to a multi-branch battery system charging method and a vehicle, belonging to the technical field of vehicle charging.

Background technique

As users have higher and higher requirements for the cruising range of electric vehicles, the batteries equipped with electric vehicles are getting higher and higher, but they are limited by the operating voltage limit of electric vehicles (the operating voltage range of passenger car batteries is generally 300V-500V, passenger cars The working voltage of the battery is generally 400-750V), so it is necessary to increase the battery capacity by increasing the battery capacity. Currently, the main way to increase the battery capacity is to increase the number of parallel connections of batteries to form a multi-branch battery system, especially for passenger cars. Way.

However, the internal resistance of the branch connection in the parallel battery system and the internal resistance of the battery are inconsistent, which will lead to differences in the branch current during the charging and discharging process, especially during the charging process, the charging current of the branch with small internal resistance is large, and the SOC of the branch is high. (SOC is the charging capacity of a battery cell or battery system, and is the ratio of the existing power of a battery cell or battery system to the rated power), which further causes the branch with a high SOC to discharge to other branches after charging, which is likely to cause damage Some single cells on the charging branch have overcharge problems.

At present, many battery manufacturers are not aware of this problem, or a small number of battery manufacturers find out this problem and give a solution that is not enough to charge. This solution will cause the problem of short cruising range of the vehicle, resulting in poor customer experience.

Contents of the invention

The purpose of the present invention is to provide a multi-branch battery system charging method and a vehicle, which are used to solve the problem that when the charging of the multi-branch battery system ends, there is a high SOC branch charging to a low SOC branch, which leads to the charging of the single battery in the low SOC branch. Core overcharge problem.

In order to achieve the above object, the present invention provides a multi-branch battery system charging method, the multi-branch battery system includes at least two parallel battery branches, the charging method includes the following steps:

1) Obtain the branch SOC of each battery branch when charging;

2) Obtain the maximum value ΔSOC of the battery branch SOC difference; the battery branch SOC difference is the branch SOC difference between any two battery branches;

3) Obtain the single SOC value of the abnormal single cell in the battery branch with the smallest branch SOC during charging: SOC _single ; the abnormal single cell has the highest single SOC value in the battery branch with the smallest branch SOC single cell;

大于第一设定值，则停止充电；若

小于第一设定值且大于第二设定值，则减小充电电流；若

小于第二设定值，则正常充电。4) if

is greater than the first set value, stop charging; if

Less than the first set value and greater than the second set value, then reduce the charging current; if

If it is less than the second set value, it will be charged normally.

By calculating the branch SOC of each battery branch in real time and the single SOC of the abnormal single cell corresponding to the highest voltage in each battery branch; the BMS judges the difference between the branch SOCs of each battery branch and the abnormal cell The difference between the single SOC of a cell and the branch SOC of the battery it is in. At the beginning of charging, when the single SOC of the abnormal single cell is higher than the branch SOC of the battery branch where it is located, the abnormal single cell is marked to balance it, so that the abnormal single cell The single SOC of the battery cell is consistent with the branch SOC of the battery branch; after charging for a period of time, if the branch SOC difference between the battery branches ΔSOC _{branch-branch} is higher than that of the abnormal single cell When the difference between the SOC and the branch SOC of the battery branch is ΔSOC _{monomer-branch} , the BMS adopts a stepwise method of reducing the charging current to reduce the SOC difference between the battery branches, thereby avoiding abnormal cells The single overvoltage phenomenon caused by the charging of the battery after the end of the charging phase.

Further, in the above method, in step 1), the method of obtaining the branch SOC of each battery branch during charging is: obtaining the branch SOC of each battery branch before charging, and the charging current of each battery branch during charging and charging time, calculate the branch SOC of the battery branch during charging according to the branch SOC of the battery branch before charging, the charging current of the battery branch during charging, and the charging time.

Further, in the above method; in step 3), the method of obtaining the SOC value of the abnormal single cell in the second battery branch during charging is: obtaining the single SOC and the value of the abnormal single cell before charging. The charging current and charging time of the battery branch where the abnormal single cell is located during charging, according to the SOC of the abnormal single cell before charging and the charging time of the battery branch where the abnormal single cell is located during charging The current and charging time are used to calculate the SOC of the abnormal single cell in the battery branch when charging.

小于第一设定值且大于第二设定值的区间分为至少两个充电区间，分别为第一充电区间和第二充电区间；Further, in the above method; in step 4), the method of reducing the charging current is:

The interval that is less than the first set value and greater than the second set value is divided into at least two charging intervals, namely the first charging interval and the second charging interval;

小于第一设定值且大于第三设定值，控制电池系统在第一充电区间的充电电流为第一充电电流；The first charging interval:

less than the first set value and greater than the third set value, controlling the charging current of the battery system in the first charging interval to be the first charging current;

小于第三设定值且大于第二设定值，控制电池系统在第二充电区间的充电电流为第二充电电流；The second charging interval:

less than the third set value and greater than the second set value, controlling the charging current of the battery system in the second charging interval to be the second charging current;

The first charging current is less than or equal to the second charging current.

The method of reducing the charging current in steps is adopted, and the battery system sends different charging request currents to the charger in different charging intervals, and uses different charging currents to protect the safety of the battery system.

Further, in the above method; the first charging current is the larger value of the first maximum allowable charging current and the minimum request current, and the first maximum allowable charging current is the maximum allowable charging current and the first set threshold the product of

The second charging current is the larger value of the second maximum allowable charging current and the minimum request current, and the second maximum allowable charging current is the product of the maximum allowable charging current and a second set threshold;

The first set threshold is smaller than the second set threshold.

Further, in the above method; the range of the first set threshold and the second set threshold is 0.25-1.

Further, in the above method; when charging, equalize the abnormal single cell, so as to reduce the SOC of the single cell.

Further, in the above method; the method of balancing the abnormal single cell is: discharge the abnormal single cell to the equalization circuit connected to it, and the discharge time is based on the single SOC of the abnormal single cell Determine with the branch SOC of the battery branch where it is located.

Balance the abnormal single cells to enhance the protection ability of the battery system when charging.

The present invention also provides a vehicle, including a multi-branch battery system and a controller, the multi-branch battery system includes at least two parallel battery branches, the controller is connected to each battery branch; the controller executes Instructions to implement the above charging method for a multi-branch battery system.

Description of drawings

FIG. 1 is an electrical schematic diagram of the charging stage of a multi-branch battery system in the prior art;

FIG. 2 is an electrical schematic diagram of the circulation stage after charging of the multi-branch battery system in the prior art;

Fig. 3 is a schematic diagram of the SOC distribution of single cells at the end of charging and after the circulation of the multi-branch battery system in the first scenario in the prior art;

Fig. 4 is a schematic diagram of the SOC distribution of single cells at the end of charging and after the circulation of the multi-branch battery system in the second scenario in the prior art;

Fig. 5 is a schematic diagram of the SOC distribution of single cells at the end of charging and after the circulation of the multi-branch battery system in the third scenario in the prior art;

Fig. 6 is a schematic diagram of the SOC distribution of single cells at the end of charging and after the circulation of the multi-branch battery system in the fourth scenario in the prior art;

FIG. 7 is a schematic flowchart of a method for charging a multi-branch battery system in an embodiment of the present invention.

In the figure: 1 is the first battery branch; 2 is the second battery branch; 3 is the single cell.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Method example:

A multi-branch battery system includes n parallel battery branches, such as the first battery branch 1 and the second battery branch 2, and each battery branch includes several single cells, such as the first battery branch Single cell 3, the same single cell 3 is also used in the other battery branches. In the charging phase of a multi-branch battery system, as shown in Figure 1, the charging current is charged from the charging positive to each battery branch, and flows out from the charging negative. When charging, if there is a battery branch whose SOC is higher than that of other battery branches, such as the first battery branch 1, then after the charging is completed, the first battery branch 1 will send other battery branches circuit discharge, as shown in Figure 2, this stage is the shelving circulation stage of the multi-branch battery system.

As shown in Figure 3, Figure 4, Figure 5, and Figure 6, the multi-branch battery system is divided into the following four scenarios at the end of charging and the stage of shelving circulation:

Specifically, as shown in Figure 3, the first scenario is shown. In this scenario, the branch SOC of each battery branch in the charging stage is inconsistent, and there are abnormal single cells in each battery branch. There is a consistent difference between the SOC of the single cell and the SOC of the branch circuit, that is, there are one or more abnormal single cells in the battery branch whose SOC is higher than that of other single cells, but the cells of the abnormal single cell The difference ΔSOC _{monomer-branch} between the SOC and the branch SOC of the battery branch where it is located is significantly smaller than the difference ΔSOC _{branch-branch} between the branch SOCs of different battery branches. Therefore, in the circulation phase after the end of the charging phase, the battery branch with a low SOC of the branch is charged, which increases the SOC of the branch. Correspondingly, the abnormal single cells in the battery branch are also charged, but it will not cause Overcharge, so in the first scene, the single cell will not have a single overvoltage phenomenon during the circulation phase.

As shown in Figure 4, it is the second scenario. In this scenario, the branch SOC of each battery branch in the charging stage is inconsistent, but the internal resistance of the branch is consistent, and there is no abnormal single cell. Therefore, at the end of the charging stage In the final circulation stage, the battery branch with high branch SOC is discharged, and the battery branch with low SOC is charged, so that there will be no single overvoltage phenomenon.

As shown in Figure 5, the third scenario, in this scenario, the branch SOC of each battery branch in the charging stage is inconsistent, and the battery branch with low branch SOC has the problem of poor consistency, that is, the battery with low branch SOC There are abnormal single cells in the branch, but the single SOC of the abnormal single cell is significantly smaller than the branch SOC of the battery branch where it is located, showing a downward consistency difference. Therefore, in In the circulating current stage after the charging stage, the battery branch with high branch SOC is discharged, and the battery branch with low SOC is charged, so that there will be no single overvoltage phenomenon.

As shown in Figure 6, the fourth scenario, in this scenario, the branch SOC of each battery branch in the charging stage is inconsistent, and the battery branch with low branch SOC has poor consistency, that is, the battery branch with low branch SOC There are abnormal single cells in the battery branch, and the single SOC of the abnormal single cell is significantly larger than the branch SOC of the battery branch where it is located, showing an upward consistency difference. Therefore, in In the circulation phase at the end of the charging phase, the battery branch with high SOC branch is discharged, the battery branch with low SOC is charged, and the abnormal single cell with high SOC in the battery branch with low SOC will be gradually charged. , and continue to be charged after being fully charged, a single overvoltage phenomenon occurs.

In view of the cell overvoltage that may occur in the charging phase of the multi-branch battery system in the fourth scenario, in this embodiment, the branch SOC of each battery branch and the abnormal cell corresponding to the highest voltage in each battery branch are calculated in real time The single SOC of the battery cell; the BMS judges the difference between the branch SOC of each battery branch in real time, the difference between the single SOC of the abnormal single cell and the branch SOC of the battery where it is located. At the beginning of charging, when the single SOC of the abnormal single cell is higher than the branch SOC of the battery branch where it is located, the abnormal single cell is marked to balance it, so that the abnormal single cell The single SOC of the battery cell is consistent with the branch SOC of the battery branch; after charging for a period of time, if the branch SOC difference between the battery branches ΔSOC _{branch-branch} is higher than that of the abnormal single cell When the difference between the SOC and the branch SOC of the battery branch is ΔSOC _{monomer-branch} , the BMS adopts a stepwise method of reducing the charging current to reduce the SOC difference between the battery branches, thereby avoiding abnormal cells The single overvoltage phenomenon caused by the charging of the battery after the end of the charging phase.

In this embodiment, the multi-branch battery system charging method is shown in Figure 7, including the following steps:

1) The BMS obtains the branch SOC of each battery branch before charging, which are SOC _{branch 1} , SOC _{branch 2} , ..., SOC _{branch n} . The SOC _{branch 1} corresponds to the first battery branch 1, the SOC _{branch 2} corresponds to the second battery branch 2, and the SOC _{branch n} corresponds to the nth battery branch. The BMS also obtains the individual SOC values of abnormal single cells (that is, the single cell with the highest single SOC value) in each battery branch before charging, which are SOC _{single 1max} , SOC _{single 2max} , and SOC _{single n max} , among which The SOC _{unit 1max} is the single SOC value of the abnormal single cell in the first battery branch 1, the SOC _{unit 2max} is the single SOC value of the abnormal single cell in the second battery branch 2, and the SOC _{unit n max} is the first Single SOC value of abnormal single cells in n battery branches.

2) The BMS collects the charging current of each battery branch in real time during the charging phase, which are I ₁ , I ₂ , ..., _In , where I ₁ corresponds to the first battery branch 1, and I ₂ corresponds to the second battery branch 2, I _n corresponds to the nth battery branch.

3) Real-time calculation of the branch SOC values of each battery branch in the charging phase, which are respectively SOC _{charge 1} , SOC _{charge 2} , ..., SOC _{charge n} .

…

In the formula, Q ₀ is the rated capacity of a single cell.

4) According to the real-time calculated SOC _{charge 1} , SOC _{charge 2} , ..., SOC _{charge n} , the difference ΔSOC _{branch-branch} between the branch SOCs of each battery branch is also calculated in real time, and the calculation formula is:

ΔSOC _{branch - branch} = max{SOC _{charge i} -SOC _{charge j} }

In the formula, SOC _{charge i} and SOC _{charge j} are the branch SOCs of any two battery branches in the charging phase.

5) The SOC values of the abnormal single cells in each battery branch in the charging phase are also calculated in real time, which are respectively SOC _{charging 1max} , SOC _{charging 2max} , ..., SOC _{charging nmax} .

…

6) According to the real-time calculated SOC _{charge 1max} , SOC _{charge 2max} , ..., SOC _{charge nmax} , _{the remaining} charging capacity SOC of the abnormal single cell in each battery branch is also calculated in real time, which are respectively SOC ₁ and SOC ₂ , ..., SOC _{remaining n} , the calculation formula is:

SOC _{remaining n} ＝1-SOC _{charging n max}

In the formula, SOC _{remaining n} is the remaining charging capacity of the abnormal single cell in the nth battery branch, and SOC _{charge n max} is the single SOC value of the abnormal single cell in the nth battery branch.

7) According to the calculation results of steps 3) and 5), the difference between the SOC of the abnormal single cell in each battery branch and the branch SOC of the battery branch is calculated in real time.

8) Since it takes a long time for the equalization circuit to perform the equalization function, the abnormal single cells are only balanced during the charging stage, and there are still great potential safety hazards. Therefore, in this embodiment, at the beginning of the charging phase, the BMS judges in real time whether there is an abnormal cell in the battery branch. The difference in the SOC of the branch of the battery branch is to balance the abnormal single cells to ensure the consistency in each battery branch, and then send the charging request current to the charger to request charging.

当BMS检测到SOC_充nmax-SOC_充n≤0时，控制均衡电路切断，结束对异常单体电芯的均衡。If max{SOC _{charging i} -SOC _{charging j} }>SOC _{charging nmax} -SOC _{charging n} >0, then the BMS controls the abnormal single cell that meets this condition to start equalization, and the abnormal single cell discharges to the equalization circuit, so that The balance ends when the monomer SOC decreases to a better consistency with the branch SOC. The equalization time is set as T=(SOC _{charging nmax} -SOC _{charging n} )*Q ₀ /I _equalization , where the value of I _equalization is determined according to the resistance value of the equalization circuit,

When the BMS detects that SOC _{charging nmax} -SOC _{charging n} ≤ 0, the control equalization circuit is cut off, and the equalization of abnormal single cells is ended.

9) In the circulation phase after the charging phase, the battery branch with a high branch SOC (the i-th battery branch) discharges to the battery branch with a low branch SOC (the j-th battery branch), and the discharge maximum capacity Q _loop ＝max{SOC _{charging i} -SOC _{charging j} }*Q ₀ *1/2; _{the remaining} charging capacity Q required for the abnormal single cell in the charged battery branch to be fully charged＝(1-SOC _{charging k max} )*Q ₀ .

In the circulation phase after the end of the charging phase, the sufficient and unnecessary condition for the abnormal single cell to be charged to the single overvoltage is: Q _ring > Q _remaining , that is, it needs to satisfy max{SOC _{charge i} -SOC _{charge j} }*Q ₀ *1/2>(1-SOC _{charge j max} )*Q ₀ . That is to say, when max{SOC _{charging i} -SOC _{charging j} }>2(1-SOC _{charging j max} ), the abnormal single cell in the jth battery branch may have a single overvoltage phenomenon during the circulation phase.

Therefore, after the multi-branch battery system enters the charging stage, the charging current entering the multi-branch battery system is controlled. If max{SOC _{charge i} -SOC _{charge j} }≤(1-SOC _{charge j max} ), then the BMS controls The charging request current is max (maximum allowable charging current, minimum request current), and normal charging is performed; if (1-SOC _{charging j max} )<max{SOC _{charging i} -SOC _{charging j} }<1.5*(1-SOC _{charging j max} ), the BMS controls the charging request current to be max(0.5*maximum allowable charging current, minimum request current); if 1.5*(1-SOC _{charging j max} )≤max{SOC _{charging i} -SOC _{charging j} }＜1.8*(1 -SOC _{charging j max} ), then the BMS controls the charging request current to be max(0.25*maximum allowable charging current, minimum request current); if 1.8*(1-SOC _{charging j max} )≤max{SOC _{charging i} -SOC _{charging j} } <2*(1-SOC _{charging j max} ), the BMS controls the charging request current to be the minimum request current; if max{SOC _{charging i} -SOC _{charging j} }≥2.0*(1-SOC _{charging j max} ), the BMS requests to stop Charge.

In this embodiment, in order to enhance the safety of the charging stage, when (1-SOC _{charging j max} )<max{SOC _{charging i} -SOC _{charging j} }<1.5*(1-SOC _{charging j max} ), the BMS controls the charging The request current is max(0.5*maximum allowable charging current, minimum request current), as other implementation; when 1.5*(1-SOC _{charging j max} )≤max{SOC _{charging i} -SOC _{charging j} }<1.8*(1- When the SOC _{is charging j max} ), the BMS controls the charging request current to max (0.25*maximum allowable charging current, minimum request current). As other implementations, it is also possible to divide the interval (1-SOC _{charge j max} )≤max{SOC _{charge i} -SOC _{charge j} }<2*(1-SOC _{charge j max} ) into multiple steps, and select different steps According to the standard, the BMS makes a corresponding design for the standard of the charging request current.

Vehicle Example:

The vehicle in this implementation adopts the multi-branch battery system charging method described in the method embodiment, including the following steps:

1) Obtain the branch SOC _branch of the multi-branch battery system before the charging stage and the single SOC of the abnormal single cell with the largest single SOC value in each battery branch;

2) Obtain the charging current of each battery branch during the charging phase;

3) Calculate the real-time branch SOC of each battery branch and the real-time single SOC of abnormal single cells in each battery branch during the charging phase;

4) Calculate the difference between the real-time branch SOC of each battery branch, that is, SOC _{charge i} -SOC _{charge j} ; calculate the remaining charging capacity required for the abnormal single cell distance of each battery branch to be full, that is, 1- SOC _{charge j max} .

If SOC _{charging i} -SOC _{charging j} > 2 (1-SOC _{charging j max} ), it is considered that in the circulation phase after the charging phase, the abnormal single cell may have overvoltage phenomenon, therefore, the BMS performs the following control during the charging phase method:

If max{SOC _{charging i} -SOC _{charging j} }≤(1-SOC _{charging j max} ), then the BMS controls the charging request current to max (maximum allowable charging current, minimum request current), and performs normal charging;

If (1-SOC _{charging j max} )<max{SOC _{charging i} -SOC _{charging j} }<1.5*(1-SOC _{charging j max} ), then the BMS controls the charging request current to max(0.5*maximum allowable charging current, minimum request current);

If 1.5*(1-SOC _{charging j max} )≤max{SOC _{charging i} -SOC _{charging j} }<1.8*(1-SOC _{charging j max} ), then the BMS controls the charging request current to be max(0.25*maximum allowable charging current, minimum request current);

If 1.8*(1-SOC _{charging j max} )≤max{SOC _{charging i} -SOC _{charging j} }<2*(1-SOC _{charging j max} ), then the BMS controls the charging request current to be the minimum request current;

If max{SOC _{charging i} -SOC _{charging j} }≥2.0*(1-SOC _{charging j max} ), the BMS requests to stop charging.

In addition, the BMS also performs balanced control on abnormal single cells during the charging phase. The control method is as follows:

直到SOC_充nmax-SOC_充n≤0时，BMS控制均衡关闭。If max{SOC _{charging i} -SOC _{charging j} }>SOC _{charging nmax} -SOC _{charging n} >0, then the BMS controls the abnormal single cells that meet this condition to start equalization, and the equalization time is set as T=(SOC _{charging nmax} -SOC _{charging n} )*Q ₀ /I _balance , where the value of I _balance is determined according to the balance circuit,

Until SOC _{charge nmax} -SOC _{charge n} ≤ 0, BMS control balance is turned off.

The implementation of each step has been clearly described in the method embodiments, and will not be repeated here.

Claims (9)

1. A charging method of a multi-branch battery system is characterized in that the multi-branch battery system comprises at least two battery branches which are connected in parallel, and the charging method comprises the following steps:

1) Acquiring branch SOC of each battery branch during charging;

2) Obtaining the maximum value delta SOC of the SOC difference value of the battery branch; the battery branch SOC difference value is a branch SOC difference value between any two battery branches;

3) Acquiring a monomer SOC value of an abnormal monomer battery cell in a battery branch with the minimum branch SOC during charging: SOC _Sheet (ii) a The abnormal single battery cell is the single battery cell with the highest single SOC value in the battery branch with the smallest branch SOC;

4) If it is

If the voltage is larger than the first set value, stopping charging; if it is

If the current is smaller than the first set value and larger than the second set value, the charging current is reduced; if it is

And if the charging voltage is less than the second set value, the charging is normally carried out.

2. The charging method for the multi-branch battery system according to claim 1, wherein in step 1), the method for obtaining the branch SOC of each battery branch during charging is: the branch SOC of each battery branch before charging, the charging current and the charging time of each battery branch during charging are obtained, and the branch SOC of each battery branch during charging is calculated according to the branch SOC of each battery branch before charging, the charging current and the charging time of each battery branch during charging.

3. The charging method for the multi-branch battery system according to claim 1, wherein in step 3), the method for obtaining the cell SOC value of the abnormal cell in the second battery branch during charging includes: acquiring the monomer SOC of the abnormal monomer battery cell before charging and the charging current and the charging time of the battery branch where the abnormal monomer battery cell is located during charging, and calculating the monomer SOC of the abnormal monomer battery cell in the battery branch during charging according to the monomer SOC of the abnormal monomer battery cell before charging and the charging current and the charging time of the battery branch where the abnormal monomer battery cell is located during charging.

4. The multi-branch battery system charging method according to claim 1, wherein in the step 4), the method for reducing the charging current comprises: will be provided with

The interval which is smaller than the first set value and larger than the second set value is divided into at least two charging intervals which are a first charging interval and a second charging interval respectively;

the first charging interval:

the charging current of the battery system in the first charging interval is controlled to be the first charging current when the charging current is smaller than the first set value and larger than the third set value;

the second charging interval:

the charging current of the battery system in the second charging interval is controlled to be a second charging current when the charging current is smaller than the third set value and larger than the second set value;

the first charging current is less than or equal to the second charging current.

5. The multi-branch battery system charging method according to claim 4, wherein the first charging current is a larger value of a first maximum allowable charging current and a minimum request current, the first maximum allowable charging current being a product of the maximum allowable charging current and a first set threshold;

the second charging current is the larger value of a second maximum allowable charging current and a minimum request current, and the second maximum allowable charging current is the product of the maximum allowable charging current and a second set threshold;

the first set threshold is less than a second set threshold.

6. The multi-branch battery system charging method according to claim 5, wherein the first set threshold and the second set threshold range from 0.25 to 1.

7. The charging method for a multi-branch battery system according to claim 1, wherein the abnormal unit cells are equalized to lower the unit SOC thereof during charging.

8. The charging method for the multi-branch battery system according to claim 6, wherein the method for equalizing the abnormal single cells comprises: and discharging to an equalizing circuit connected with the abnormal single battery cell by the abnormal single battery cell, wherein the discharging time is determined according to the single SOC of the abnormal single battery cell and the branch SOC of the battery branch where the abnormal single battery cell is located.

9. A vehicle is characterized by comprising a multi-branch battery system and a controller, wherein the multi-branch battery system comprises at least two battery branches connected in parallel, and the controller is connected with each battery branch; the controller executes instructions to implement the multi-branch battery system charging method of any one of claims 1-8.

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