A multi-branch battery system charging method and vehicle

Abstract

The present invention provides a charging method for a multi-branch battery system and a vehicle, belonging to the technical field of vehicle charging. By calculating in real time the branch SOC of each battery branch and the single-cell SOC of the abnormal single-cell battery with the highest voltage in each battery branch; judging the difference between the branch SOCs of each battery branch, and the difference between the single-cell SOC of the abnormal single-cell battery and the branch SOC of the battery where it is located. After charging for a period of time, if the difference in branch SOC ΔSOC 支路‑支路 between battery branches is higher than the difference in ΔSOC 单体‑支路 between the single-cell SOC of the abnormal single-cell battery and the branch SOC of the battery branch, the BMS adopts a method of stepwise reducing the charging current to reduce the SOC difference between each battery branch, thereby avoiding the single-cell overvoltage phenomenon caused by the abnormal single-cell battery being charged after the end of the charging stage.

Description

Technical Field

[0001] The invention relates to a multi-branch battery system charging method and a vehicle, belonging to the technical field of vehicle charging. Background Art

[0002] As users have higher and higher requirements for the range of electric vehicles, the battery power of electric vehicles is getting higher and higher. However, due to the operating voltage limit of electric vehicles (the operating voltage range of passenger car batteries is generally 300V-500V, and the operating voltage of bus batteries is generally 400-750V), it is necessary to increase the battery capacity to increase the battery power. The current main method to increase battery capacity is to increase the number of batteries in parallel to form a multi-branch battery system, especially buses. Batteries generally use parallel connection.

[0003] However, the inconsistency of the branch connection internal resistance and the battery internal resistance in the parallel battery system will lead to differences in branch currents during the charging and discharging process. In particular, during the charging process, the branch with small internal resistance has a large charging current and a high branch SOC (SOC is the charge capacity of a battery cell or a battery system, which is the ratio of the existing charge of a battery cell or a battery system to the rated charge). This will further cause the branch with a high SOC to discharge to other branches after charging is completed, which may easily cause overcharging of some single cells on the charged branch.

[0004] Currently, many battery manufacturers are not aware of this problem, or a small number of battery manufacturers have found this problem and provided a solution of not fully charging. This solution will cause the vehicle to have a short range and cause customers to have a bad experience. Summary of the invention

[0005] The object of the present invention is to provide a multi-branch battery system charging method and vehicle, which are used to solve the problem that at the end of charging of the multi-branch battery system, a high SOC branch charges a low SOC branch, resulting in overcharging of single cells in the low SOC branch.

[0006] In order to achieve the above object, the present invention provides a charging method for a multi-branch battery system, wherein the multi-branch battery system comprises at least two parallel battery branches, and the charging method comprises the following steps:

[0007] 1) Obtain the branch SOC of each battery branch during charging;

[0008] 2) obtaining a maximum value ΔSOC of a battery branch SOC difference; the battery branch SOC difference is a branch SOC difference between any two battery branches;

[0009] 3) Obtain the single SOC value of the abnormal single cell in the battery branch with the smallest branch SOC during charging: SOC 单; The abnormal single cell is the single cell with the highest single SOC value in the battery branch with the smallest branch SOC;

[0010] 4) If If the value is greater than the first setting value, charging is stopped; If the charging current is less than the first setting value and greater than the second setting value, the charging current is reduced; If it is less than the second set value, charging is normal.

[0011] By calculating the branch SOC of each battery branch and the single cell SOC of the abnormal single cell corresponding to the highest voltage in each battery branch in real time; BMS determines the difference between the branch SOC of each battery branch, the difference between the single cell SOC of the abnormal single cell and the branch SOC of the battery in which it is located in real time. At the beginning of charging, when the single cell SOC of the abnormal single cell is higher than the branch SOC of the battery branch in which it is located, the abnormal single cell is marked to balance it, so that the single cell SOC of the abnormal single 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 is ΔSOC 支路-支路 The difference ΔSOC between the single cell SOC of the abnormal single cell and the branch SOC of the battery branch 单体-支路 When charging, the BMS adopts a step-by-step method to reduce the charging current, so that the SOC difference between the battery branches is reduced, thereby avoiding the single cell overvoltage phenomenon caused by the abnormal single cell being charged after the charging stage.

[0012] Furthermore, in the above method, in step 1), the method for obtaining the branch SOC of each battery branch during charging is: obtaining the branch SOC of each battery branch before charging, the charging current and the charging time of each battery branch during charging, and calculating the branch SOC of the battery branch during charging according to the branch SOC of the battery branch before charging, the charging current and the charging time of the battery branch during charging.

[0013] Furthermore, in the above method; in step 3), the method for obtaining the single cell SOC value of the abnormal single cell in the battery branch where the branch SOC is the smallest during charging is: obtaining the single cell SOC of the abnormal single cell before charging and the charging current and charging time of the battery branch where the abnormal single cell is located during charging, and calculating the single cell SOC of the abnormal single cell in the battery branch during charging based on the single cell SOC of the abnormal single cell before charging and the charging current and charging time of the battery branch where the abnormal single cell is located during charging.

[0014] Furthermore, in the above method; in step 4), the method of reducing the charging current is: dividing the interval less than the first set value and greater than the second set value into at least two charging intervals, namely the first charging interval and the second charging interval;

[0015] The first charging interval: is 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;

[0016] The second charging interval: is 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;

[0017] The first charging current is less than or equal to the second charging current.

[0018] The method of step-by-step reduction of charging current is adopted. In different charging intervals, the battery system sends different charging request currents to the charger, and different charging currents are used to protect the safety of the battery system.

[0019] Further, in the above method; the first charging current is a larger value of a first maximum allowable charging current and a minimum requested current, and the first maximum allowable charging current is a product of a maximum allowable charging current and a first set threshold value;

[0020] The second charging current is a larger value between a second maximum allowable charging current and a minimum requested current, and the second maximum allowable charging current is a product of the maximum allowable charging current and a second set threshold value;

[0021] The first set threshold is smaller than the second set threshold.

[0022] Furthermore, in the above method, the first set threshold and the second set threshold are in the range of 0.25 to 1.

[0023] Furthermore, in the above method, during charging, the abnormal single cells are balanced to reduce their single cell SOC.

[0024] Furthermore, in the above method, the method for balancing the abnormal single cell is: the abnormal single cell is discharged to the balancing circuit connected thereto, and the discharge time is determined according to the single cell SOC of the abnormal single cell and the branch SOC of the battery branch in which it is located.

[0025] Balance abnormal single cells to enhance the protection capability of the battery system during charging.

[0026] The present invention also provides a vehicle, including a multi-branch battery system and a controller, wherein the multi-branch battery system includes at least two parallel battery branches, and the controller connects each battery branch; the controller executes instructions to implement the above-mentioned multi-branch battery system charging method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is an electrical schematic diagram of the charging stage of a multi-branch battery system in the prior art;

[0028] Figure 2 It is an electrical schematic diagram of the circulation stage after the multi-branch battery system is charged in the prior art;

[0029] Figure 3 It is a schematic diagram of the single cell SOC distribution at the end of charging and after the circulation of a multi-branch battery system in the first scenario in the prior art;

[0030] Figure 4 It is a schematic diagram of the single cell SOC distribution at the end of charging and after the circulation of a multi-branch battery system in the second scenario in the prior art;

[0031] Figure 5 It is a schematic diagram of the single cell SOC distribution at the end of charging and after the circulation of a multi-branch battery system in the third scenario in the prior art;

[0032] Figure 6 It is a schematic diagram of the single cell SOC distribution at the end of charging and after the circulation of a multi-branch battery system in the fourth scenario in the prior art;

[0033] Figure 7 It is a schematic diagram of the flow of a multi-branch battery system charging method in an embodiment of the present invention.

[0034] In the figure: 1 is the first battery branch; 2 is the second battery branch; 3 is a single battery cell. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0036] Method Example:

[0037] The multi-branch battery system includes n parallel battery branches, such as the first battery branch 1 and the second battery branch 2. Each battery branch includes a plurality of single cells, such as the single cell 3 in the first battery branch. The same single cell 3 is also used in the remaining battery branches. Figure 1 As shown, the charging current charges each battery branch from the positive charging current and flows out from the negative charging current. During charging, if there is a battery branch whose branch SOC is higher than the branch SOC of other battery branches, such as the first battery branch 1, then after charging is completed, the first battery branch 1 will discharge to other battery branches, such as Figure 2 As shown, this stage is the shelving circulation stage of the multi-branch battery system.

[0038] like Figure 3 , Figure 4 , Figure 5 , Figure 6As shown in the figure, the multi-branch battery system is divided into the following four scenarios at the end of charging and the idle circulation stage:

[0039] Specifically, Figure 3 The first scenario is shown. In this scenario, the branch SOCs of each battery branch are inconsistent during the charging phase, and there are abnormal single cells in each battery branch. The single cell SOC of the abnormal single cell is different from the branch SOC. That is, there are one or more abnormal single cells in the battery branch whose single cell SOC is higher than that of other single cells. However, the difference between the single cell SOC of the abnormal single cell and the branch SOC of the battery branch where it is located is ΔSOC. 单体-支路 , compared with the difference ΔSOC between the branch SOCs of different battery branches 支路-支路 Therefore, in the circulation stage after the charging stage, the battery branch with low branch SOC is charged, so that the branch SOC increases. Correspondingly, the abnormal single cell in the battery branch is also charged, but it will not cause overcharging. Therefore, in the first scenario, the single cell will not experience single cell overvoltage in the circulation stage.

[0040] like Figure 4 The second scenario is shown. In this scenario, the branch SOCs of the battery branches are inconsistent during the charging phase, but the branch internal resistances are consistent and there are no abnormal single cells. Therefore, in the circulation phase after the charging phase, the battery branches with high branch SOCs are discharged and the battery branches with low branch SOCs are charged, and no single cell overvoltage occurs.

[0041] like Figure 5 The third scenario is shown. In this scenario, the branch SOCs of the battery branches are inconsistent during the charging stage, and the battery branches with low branch SOCs have poor consistency, that is, there are abnormal single cells in the battery branches with low branch SOCs, but the single cell SOC of the abnormal single cell is significantly smaller than the branch SOC of the battery branch where it is located, which is manifested as a downward consistency difference. Therefore, in the circulation stage after the charging stage, the battery branches with high branch SOCs are discharged, and the battery branches with low branch SOCs are charged, and no single cell overvoltage phenomenon occurs.

[0042] like Figure 6The fourth scenario is shown. In this scenario, the branch SOCs of each battery branch are inconsistent during the charging stage, and the battery branch with a low branch SOC has a consistency problem, that is, there is an abnormal single cell in the battery branch with a low branch SOC, and the single cell SOC of the abnormal single cell is significantly larger than the branch SOC of the battery branch where it is located, which is manifested as an upward consistency difference. Therefore, in the circulation stage at the end of the charging stage, the battery branch with a high branch SOC is discharged, and the battery branch with a low branch SOC is charged. The abnormal single cell with a high single cell SOC in the battery branch with a low branch SOC will gradually be fully charged and continue to be charged after being fully charged, resulting in a single cell overvoltage phenomenon.

[0043] In response to the possible single cell overvoltage in the multi-branch battery system during the charging stage in the fourth scenario, in this embodiment, the branch SOC of each battery branch and the single cell SOC of the abnormal single cell corresponding to the highest voltage in each battery branch are calculated in real time; the BMS determines in real time the difference between the branch SOCs of each battery branch, and the difference between the single cell SOC of the abnormal single cell and the branch SOC of the battery in which it is located. At the beginning of charging, when the single cell SOC of the abnormal single cell is higher than the branch SOC of the battery branch in which it is located, the abnormal single cell is marked for balancing, so that the single cell SOC of the abnormal single cell is consistent with the branch SOC of the battery branch; after charging for a period of time, if the branch SOC difference ΔSOC between the battery branches is 支路-支路 The difference ΔSOC between the single cell SOC of the abnormal single cell and the branch SOC of the battery branch 单体-支路 When charging, the BMS adopts a step-by-step method to reduce the charging current, so that the SOC difference between the battery branches is reduced, thereby avoiding the single cell overvoltage phenomenon caused by the abnormal single cell being charged after the charging stage.

[0044] In this embodiment, the multi-branch battery system charging method is as follows: Figure 7 As shown, the following steps are included:

[0045] 1) BMS obtains the branch SOC of each battery branch before charging, which are SOC 支1 , SOC 支2 ,…,SOC 支n . Among them, SOC 支1 Corresponding to the first battery branch 1, SOC 支2 Corresponding to the second battery branch 2, SOC 支n The BMS also obtains the SOC values ​​of abnormal cells (i.e., cells with the highest SOC value) in each battery branch before charging, which are SOC 单1max , SOC 单2max , SOC 单n max , where SOC单1max is the single SOC value of the abnormal single cell in the first battery branch 1, SOC 单2max is the single SOC value of the abnormal single cell in the second battery branch 2, SOC 单n max It is the single cell SOC value of the abnormal single cell in the nth battery branch.

[0046] 2) During the charging phase, the BMS collects the charging current of each battery branch in real time, which are I1, I2, ..., I n , where I1 corresponds to the first battery branch 1, I2 corresponds to the second battery branch 2, and I n Corresponding to the nth battery branch.

[0047] 3) Real-time calculation of the SOC value of each battery branch during the charging phase, which are SOC 充1 , SOC 充2 ,…,SOC 充n .

[0048]

[0049] Where Q0 is the rated capacity of the single cell.

[0050] 4) According to the real-time calculated SOC 充1 , SOC 充2 ,…,SOC 充n , and also calculates the difference ΔSOC between the branch SOCs of each battery branch in real time 支路-支路 , the calculation formula is:

[0051] ΔSOC 支路-支路 =max{SOC 充i -SOC 充j}

[0052] In the formula, SOC 充i and SOC 充j is the branch SOC of any two battery branches during the charging stage.

[0053] 5) The SOC values ​​of abnormal cells in each battery branch during the charging phase are calculated in real time, namely SOC 充1max , SOC 充2max ,…,SOC 充nmax .

[0054]

[0055] 6) According to the real-time calculated SOC 充1max , SOC 充2max ,…,SOC 充nmax, and also calculates the remaining charge capacity SOC of abnormal single cells in each battery branch in real time 剩 , respectively SOC 剩1 , SOC 剩2 ,…,SOC 剩n , the calculation formula is:

[0056] SOC 剩n =1-SOC 充n max

[0057] In the formula, SOC 剩n is the remaining charge capacity of the abnormal single cell in the nth battery branch, SOC 充n max It is the single cell SOC value of the abnormal single cell in the nth battery branch.

[0058] 7) According to the calculation results of steps 3) and 5), the difference between the single cell SOC of the abnormal single cell in each battery branch and the branch SOC of the battery branch is calculated in real time.

[0059] 8) Since it takes a long time for the equalization circuit to play the equalization role, the abnormal single cells are equalized only in the charging stage, which still poses a great safety hazard. Therefore, in this embodiment, at the beginning of the charging stage, the BMS determines in real time whether there are abnormal single cells in the battery branch. If there are abnormal single cells, the abnormal single cells are equalized according to the difference between the single cell SOC of the abnormal single cell and the branch SOC of the battery branch where it is located, to ensure consistency in each battery branch, and then send a charging request current to the charger to request charging.

[0060] If max{SOC 充i -SOC 充j}>SOC 充nmax -SOC 充n >0, the BMS controls the abnormal single cell that meets this condition to start balancing, and the abnormal single cell discharges to the balancing circuit, and the balancing ends when the single cell SOC is reduced to a level that is consistent with the branch SOC. The balancing time is set to T = (SOC 充nmax -SOC 充n )*Q0 / I 均衡 , where I 均衡 The value of is determined according to the resistance of the equalization circuit. When the BMS detects that the SOC 充nmax -SOC 充n When ≤0, the control balancing circuit is cut off, ending the balancing of the abnormal single cell.

[0061] 9) In the circulation phase after the charging phase, the battery branch with high SOC (i-th battery branch) discharges to the battery branch with low SOC (j-th battery branch), and the maximum discharge capacity Q 环 =max{SOC 充i -SOC 充j}*Q0*1 / 2; the charging capacity Q required to fully charge the abnormal single cell in the battery branch being charged 剩余 =(1-SOC 充k max )*Q0.

[0062] In the circulation phase after the charging phase, the sufficient but not necessary condition for the abnormal single cell to be charged to single cell overvoltage is: Q 环 >Q 剩余 , that is, it is necessary to satisfy max{SOC 充i -SOC 充j}*Q0*1 / 2>(1-SOC 充j max )*Q0. That is, max{SOC 充i -SOC 充j}>2(1-SOC 充j max ), the abnormal single cell in the jth battery branch may experience single cell overvoltage during the circulation stage.

[0063] Therefore, after the multi-branch battery system enters the charging stage, the charging current entering the multi-branch battery system is controlled. 充i -SOC 充j}≤(1-SOC 充j max ), the BMS controls the charging request current to be max (maximum allowed charging current, minimum requested current) and performs normal charging; if (1-SOC 充j max )<max{SOC 充i -SOC 充j}<1.5*(1-SOC 充j max ), the BMS controls the charging request current to be max(0.5*maximum allowed charging current, minimum requested current); if 1.5*(1-SOC 充j max )≤max{SOC 充i -SOC 充j}<1.8*(1-SOC 充j max ), the BMS controls the charging request current to be max(0.25*maximum allowed charging current, minimum requested current); if 1.8*(1-SOC 充jmax )≤max{SOC 充i -SOC 充j}<2*(1-SOC 充j max ), the BMS controls the charging request current to be the minimum request current; if max{SOC 充i -SOC 充j}≥2.0*(1-SOC 充j max ), BMS requests to stop charging.

[0064] In this embodiment, in order to enhance the safety of the charging stage, the (1-SOC 充j max )<max{SOC 充i -SOC 充j}<1.5*(1-SOC 充j max ), the BMS controls the charging request current to be max(0.5*maximum allowed charging current, minimum requested current), as another implementation; at 1.5*(1-SOC 充j max )≤max{SOC 充i -SOC 充j}<1.8*(1-SOC 充j max ), the BMS controls the charging request current to be max(0.25*maximum allowable charging current, minimum request current). As another embodiment, the interval (1-SOC 充j max )≤max{SOC 充i -SOC 充j}<2*(1-SOC 充j max ) is divided into multiple steps and different step standards are selected. The BMS designs the standard of charging request current accordingly.

[0065] Vehicle Example:

[0066] The vehicle of this embodiment adopts the multi-branch battery system charging method described in the method embodiment, including the following steps:

[0067] 1) Obtain branch SOC of multi-branch battery system before charging stage 支 and the single cell SOC of the abnormal single cell with the largest single cell SOC value in each battery branch;

[0068] 2) Obtain the charging current of each battery branch during the charging stage;

[0069] 3) Calculate the real-time branch SOC of each battery branch and the real-time single cell SOC of abnormal single cells in each battery branch during the charging stage;

[0070] 4) Calculate the difference between the real-time branch SOC of each battery branch, i.e. SOC 充i -SOC 充j ; Calculate the remaining charge capacity required to fully charge the abnormal single cell of each battery branch, that is, 1-SOC 充j max .

[0071] If SOC 充i -SOC 充j >2(1-SOC 充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 method in the charging phase:

[0072] If max{SOC 充i -SOC 充j}≤(1-SOC 充j max ), the BMS controls the charging request current to be max (maximum allowed charging current, minimum requested current) and performs normal charging;

[0073] If (1-SOC 充j max )<max{SOC 充i -SOC 充j}<1.5*(1-SOC 充j max ), then the BMS controls the charging request current to be max(0.5*maximum allowed charging current, minimum request current);

[0074] If 1.5*(1-SOC 充j max )≤max{SOC 充i -SOC 充j}<1.8*(1-SOC 充j max ), then the BMS controls the charging request current to be max(0.25*maximum allowed charging current, minimum request current);

[0075] If 1.8*(1-SOC 充j max )≤max{SOC 充i -SOC 充j}<2*(1-SOC 充j max ), the BMS controls the charging request current to be the minimum request current;

[0076] If max{SOC 充i -SOC 充j}≥2.0*(1-SOC 充j max ), BMS requests to stop charging.

[0077] In addition, the BMS also performs balancing control on abnormal single cells during the charging phase. The control method is as follows:

[0078] If max{SOC 充i -SOC 充j}>SOC 充nmax -SOC 充n >0, the BMS controls the abnormal single cells that meet this condition to start balancing, and the balancing time is set to T = (SOC 充nmax -SOC 充n )*Q0 / I 均衡 , where I 均衡 The value of is determined according to the equalization circuit. Until SOC 充nmax -SOC 充n When ≤0, BMS control balancing is turned off.

[0079] The implementation of each step has been clearly introduced in the method embodiment and will not be repeated here.

Claims

1. A multi-branch battery system charging method, characterized in that: The multi-branch battery system includes at least two parallel battery branches, and the charging method includes the following steps: 1) Obtain the branch SOC of each battery branch during charging; 2) obtaining a maximum value ΔSOC of a battery branch SOC difference; the battery branch SOC difference is a 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 单 ; The abnormal single cell is the single cell with the highest single SOC value in the battery branch with the smallest branch SOC; 4) If If the value is greater than the first setting value, charging is stopped; If the charging current is less than the first setting value and greater than the second setting value, the charging current is reduced; If it is less than the second set value, charging is normal.

2. The multi-branch battery system charging method according to claim 1, characterized in that: In step 1), the method for obtaining the branch SOC of each battery branch during charging is: obtaining the branch SOC of each battery branch before charging, the charging current and charging time of each battery branch during charging, and calculating the branch SOC of the battery branch during charging according to the branch SOC of the battery branch before charging, the charging current and charging time of the battery branch during charging.

3. The multi-branch battery system charging method according to claim 1, characterized in that: In step 3), the method for obtaining the single cell SOC value of the abnormal single cell in the battery branch with the smallest branch SOC during charging is: obtain the single cell SOC of the abnormal single cell before charging and the charging current and charging time of the battery branch where the abnormal single cell is located during charging, and calculate the single cell SOC of the abnormal single cell in the battery branch during charging according to the single cell SOC of the abnormal single cell before charging and the charging current and charging time of the battery branch where the abnormal single cell is located during charging.

4. The multi-branch battery system charging method according to claim 1, characterized in that: In step 4), the method of reducing the charging current is: dividing the interval less than the first set value and greater than the second set value into at least two charging intervals, namely a first charging interval and a second charging interval; The first charging interval: is 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; The second charging interval: is 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.

5. The multi-branch battery system charging method according to claim 4, characterized in that: The first charging current is a larger value between a first maximum allowable charging current and a minimum requested current, and the first maximum allowable charging current is a product of the maximum allowable charging current and a first set threshold value; The second charging current is a larger value between a second maximum allowable charging current and a minimum requested current, and the second maximum allowable charging current is a product of the maximum allowable charging current and a second set threshold value; The first set threshold is smaller than the second set threshold.

6. The multi-branch battery system charging method according to claim 5, characterized in that: The first set threshold and the second set threshold are in the range of 0.25 to 1.

7. The multi-branch battery system charging method according to claim 1, characterized in that: During charging, the abnormal single cells are balanced to reduce the single cell SOC.

8. The multi-branch battery system charging method according to claim 6, characterized in that: The method for balancing the abnormal single cell is: the abnormal single cell is discharged to the balancing circuit connected thereto, and the discharge time is determined according to the single cell SOC of the abnormal single cell and the branch SOC of the battery branch where the abnormal single cell is located.

9. A vehicle, characterized in that: It comprises a multi-branch battery system and a controller, wherein the multi-branch battery system comprises at least two parallel battery branches, and the controller connects the battery branches; the controller executes instructions to implement the multi-branch battery system charging method according to any one of claims 1 to 8.

Images