Balancing control method for multi-branch battery pack

Abstract

The invention discloses a balance control method for a multi-branch battery pack, the battery pack comprises at least two branches, each branch comprises at least two battery sub-packs which are connected in series, and each battery sub-pack comprises at least one battery cell; the equalization control method comprises the following steps: sorting each battery sub-pack according to the magnitude of the minimum voltage of each battery sub-pack; for each branch, selecting at least two adjacent battery sub-packs in the sorting sequence to form a branch; different branches comprise different battery sub-packs; and when determining that the battery pack has at least one to-be-balanced branch, controlling each to-be-balanced branch to start a passive balancing strategy. The to-be-balanced branch is a branch in which the residual electric quantity of at least one battery cell is greater than the target residual electric quantity corresponding to the branch. The sequence of the battery sub-packs is flexibly adjusted according to the magnitude of the minimum voltage of the battery sub-packs, the minimum voltage difference in each branch is ensured, the balance requirement in each branch is reduced, and the consistency and the balance efficiency of the whole pack are better improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery management, and in particular to a method for controlling a multi-branch battery pack. Background Art

[0002] With the popularity of super-fast charging, pure electric commercial vehicles and low-altitude aircraft have been widely used. Among them, the commercial vehicle battery pack uses standard battery sub-packs, which are connected in series and then in parallel to form a multi-branch battery system. This can ensure that the total power meets the requirements and the total voltage is within a reasonable range to meet the requirements of the entire vehicle.

[0003] A battery subpack includes multiple cells. When the battery management system detects that the voltage difference between cells is too large, the cells need to be balanced to improve the consistency of the entire pack. However, the existing balancing solution has low balancing efficiency. Summary of the invention

[0004] The present invention provides a balancing control method for a multi-branch battery pack to solve the problem of low balancing efficiency and alleviate the balancing requirements within each branch.

[0005] According to one aspect of the present invention, a method for balancing a multi-branch battery pack is provided, wherein the battery pack comprises at least two branches, each of the branches comprises at least two battery sub-packs connected in series, and the battery sub-pack comprises at least one battery cell;

[0006] The balancing control method of the multi-branch battery pack includes:

[0007] sorting the battery sub-packs according to the minimum voltage of the battery sub-packs;

[0008] For each of the branches, at least two battery sub-packs that are adjacent in sorting order are selected to form the branch; and different branches include different battery sub-packs;

[0009] When it is determined that there is at least one branch to be balanced in the battery pack, each branch to be balanced is controlled to start a passive balancing strategy; wherein the branch to be balanced is a branch in which the remaining power of at least one battery cell is greater than the target remaining power corresponding to the branch.

[0010] Optionally, the passive balancing strategy includes:

[0011] For any battery cell to be balanced in a branch to be balanced, the balancing time of the battery cell to be balanced is calculated according to the remaining power of the battery cell to be balanced, the target remaining power corresponding to the branch to which the battery cell to be balanced belongs, the capacity of the battery cell to be balanced, and the balancing current; the battery cell to be balanced is a battery cell whose remaining power is greater than the target remaining power corresponding to the branch to which the battery cell to be balanced belongs;

[0012] Each of the cells to be balanced is controlled to start balancing, and the balancing of any cell to be balanced is stopped after the corresponding balancing time is reached, until all the cells to be balanced reach the corresponding balancing time, and the passive balancing strategy ends.

[0013] Optionally, the balancing control method for the multi-branch battery pack further includes:

[0014] Control each of the to-be-balanced branches to start at least one passive balancing strategy until, for each of the to-be-balanced branches, the remaining power of each battery cell in the to-be-balanced branch is less than or equal to the target remaining power corresponding to the to-be-balanced branch.

[0015] Optionally, for any of the branches to be balanced:

[0016] The target remaining power SOC0 corresponding to the branch to be balanced is SOC1=(SOC1+SOC2) / 2; wherein SOC1 is the average value of the remaining power of each battery cell in the branch to be balanced, and SOC2 is the minimum value of the remaining power of each battery cell in the branch to be balanced.

[0017] Optionally, the balancing time t1 of the battery cell to be balanced satisfies the following formula:

[0018] t1=(SOC3-SOC0)·C1 / I1; wherein SOC3 is the remaining power of the battery cell to be balanced, SOC0 is the target remaining power corresponding to the branch to which the battery cell to be balanced belongs, C1 is the capacity of the battery cell to be balanced, and I1 is the balancing current.

[0019] Optionally, before calculating the balancing time of the battery cells to be balanced according to the remaining power of the battery cells to be balanced, the target remaining power corresponding to the branch to which the battery cells to be balanced belong, the capacity of the battery cells to be balanced, and the balancing current, the method further includes:

[0020] After determining that the battery pack is in a static state for a preset time, obtaining the voltage of each of the battery cells and using it as the open circuit voltage of the battery cell; in the static state, the current of the battery pack is less than or equal to a first current threshold;

[0021] The remaining power of the battery cell is determined according to a preset corresponding relationship and the open circuit voltage of the battery cell; the preset corresponding relationship is a corresponding relationship between the open circuit voltage and the remaining power.

[0022] Optionally, the branches are connected in parallel, and the balancing control method for the multi-branch battery pack further includes:

[0023] Active balancing is performed between the branches through circulating current; wherein the direction of active balancing is that the flow from the branch with high voltage flows to the branch with low voltage.

[0024] Optionally, each of the branches includes a branch relay, and for any of the branches, each battery sub-pack on the branch is connected in series with the branch relay corresponding to the branch;

[0025] The balancing control method of the multi-branch battery pack further includes:

[0026] The branch relays of each branch are controlled to be closed, so that each branch is connected in parallel and active balancing is performed through circulating current; wherein the direction of active balancing is that the voltage from the branch with high voltage flows to the branch with low voltage.

[0027] Optionally, for any of the branches, the branch is connected in series between the main positive relay and the negative positive relay;

[0028] The balancing control method of the multi-branch battery pack further includes:

[0029] When receiving the high voltage instruction, the main positive relay, the negative positive relay, and the branch relays on each branch are controlled to be closed;

[0030] When receiving a lower high voltage instruction, controlling the main positive relay and the negative positive relay to be disconnected;

[0031] The magnitude of the current on each of the branches is obtained, and for any of the branches, when the current on the branch is greater than a second current threshold, the branch relay on the branch is controlled to continue to be closed.

[0032] Optionally, for any of the battery sub-packs, the minimum value of the voltages of the battery cells in the battery sub-pack is used as the minimum voltage of the battery sub-pack.

[0033] The technical solution of the embodiment of the present invention is to select at least two battery sub-packs with adjacent sorting order to form a branch after sorting the battery sub-packs according to the minimum voltage of the battery sub-packs, and different branches include different battery sub-packs. When it is determined that there is at least one branch to be balanced in the battery pack, each branch to be balanced is controlled to start a passive balancing strategy. Before forming a branch, the order of the battery sub-packs is flexibly adjusted according to the size of the minimum voltage of the battery sub-packs to ensure that the voltage difference inside each branch is minimized, reduce the balancing requirements inside each branch, and better improve the consistency and balancing efficiency of the whole pack.

[0034] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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 creative work.

[0036] Figure 1 A schematic diagram of the structure of a battery pack provided in Embodiment 1 of the present invention;

[0037] Figure 2 A flowchart of a method for balancing a multi-branch battery pack provided in Embodiment 1 of the present invention;

[0038] Figure 3 A flowchart of a method for balancing a multi-branch battery pack provided in Embodiment 2 of the present invention;

[0039] Figure 4 A schematic diagram of the structure of a battery pack provided in Embodiment 2 of the present invention;

[0040] Figure 5 A schematic diagram of the structure of a battery pack provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0043] Embodiment 1

[0044] Figure 1Schematic diagram of the structure of a battery pack provided in Embodiment 1 of the present invention Figure 2 Flowchart of an equalization control method for a multi-branch battery pack provided in Embodiment 1 of the present invention. Refer to Figure 1 and Figure 2 , the battery pack includes at least two branches, each branch includes at least two battery sub-packages connected in series, and the battery sub-package includes at least one battery cell;

[0045] The equalization control method for the multi-branch battery pack includes:

[0046] S110: Sort the battery sub-packages according to the magnitudes of the minimum voltages of the respective battery sub-packages.

[0047] In this embodiment, it is exemplarily shown that the battery sub-package includes at least three battery cells, and the battery cells can be connected in series and / or in parallel with each other. For any battery sub-package, the minimum value of the voltages of the battery cells in the battery sub-package is used as the minimum voltage of the battery sub-package. All the battery sub-packages are sorted in ascending or descending order according to the minimum voltages of the battery sub-packages.

[0048] Exemplarily, the battery pack includes eight battery sub-packages, which are sequentially named as the first battery sub-package 111 to the eighth battery sub-package 118 in sequence, and the minimum voltages among the first battery sub-package 111 to the eighth battery sub-package 118 satisfy: U2 < U4 < U6 < U8 < U1 < U3 < U5 < U7, where Ui is the minimum voltage of the i-th battery sub-package.

[0049] S120: For each branch, select at least two adjacent battery sub-packages in the sorting order to form a branch; and the battery sub-packages included in different branches are different.

[0050] Each branch includes at least two battery sub-packs, and the order of the battery sub-packs in the same branch is adjacent. The number of battery sub-packs in each branch may be the same or different. In an optional embodiment, the difference in the number of battery sub-packs between any two branches is less than or equal to 1, so as to minimize the difference between the sum of the voltages of all battery sub-packs between different branches. If the above eight battery sub-packs constitute two branches, the second battery sub-pack 112, the fourth battery sub-pack 114, the sixth battery sub-pack 116 and the eighth battery sub-pack 118 constitute one branch, and the first battery sub-pack 111, the third battery sub-pack 113, the fifth battery sub-pack 115 and the seventh battery sub-pack 117 constitute another branch. For the branch, the order of each battery sub-pack is not limited. If the above eight battery sub-packs constitute three branches, the second battery sub-pack 112, the fourth battery sub-pack 114, and the sixth battery sub-pack 116 constitute the first branch, the eighth battery sub-pack 118, the first battery sub-pack 111, and the third battery sub-pack 113 constitute the second branch, and the remaining fifth battery sub-pack 115 and the seventh battery sub-pack 117 constitute the third branch. In other embodiments, the first branch may include the second battery sub-pack 112 and the fourth battery sub-pack 114, the second branch may include the sixth battery sub-pack 116, the eighth battery sub-pack 118, and the first battery sub-pack 111, and the third branch may include the third battery sub-pack 113, the fifth battery sub-pack 115, and the seventh battery sub-pack 117. In an optional embodiment, the minimum voltage of the first preset battery sub-pack in the mth branch is greater than the maximum voltage of the second preset battery sub-pack in the m-1th branch, and m is an integer greater than or equal to 2. The first preset battery sub-pack is the battery sub-pack with the smallest minimum voltage in the m-th branch, and the second preset battery sub-pack is the battery sub-pack with the largest minimum voltage in the m-1-th branch.

[0051] S130: When it is determined that there is at least one branch to be balanced in the battery pack, control each branch to be balanced to start a passive balancing strategy; wherein the branch to be balanced is a branch in which the remaining power of at least one battery cell is greater than the target remaining power corresponding to the branch.

[0052] Each branch corresponds to a target remaining power. In an optional implementation, for any branch, the average value of the remaining power of each battery cell included in each battery sub-pack in the branch is used as the target remaining power of the branch. Alternatively, the minimum value of the remaining power of each battery cell included in the battery sub-pack in the branch can also be used as the target remaining power of the branch, which is not specifically limited.

[0053] Determine whether there is at least one battery cell in each branch whose remaining power is greater than the target remaining power corresponding to the branch. If so, determine that the branch is a branch to be balanced. For the branch to be balanced, control it to start the passive balancing strategy. The passive balancing strategy is an operation process of reducing the remaining power of the battery cells in the branch to be balanced that is greater than the target remaining power corresponding to the branch, and balances each battery cell by consuming the remaining power of the battery cells. In an optional embodiment, the balancing operation can be to control the battery cells to be balanced with large remaining power to discharge to the battery cells to be balanced with small remaining power, so that the remaining power between each battery cell is similar. Because the remaining power corresponds to the voltage, after the branch to be balanced performs the passive balancing strategy, the remaining power between each battery cell in the branch is similar, so that the voltage difference between each battery cell is reduced, and the consistency of the battery cell voltage is improved.

[0054] In this embodiment, the branches of the battery pack are connected in parallel. Figure 1 Taking the number of branches as 2 and the number of battery sub-packs in each branch as 4 as an example, the number of branches and the number of battery sub-packs in each branch can be configured according to actual needs and are not specifically limited here.

[0055] The technical solution of the embodiment of the present invention is to select at least two battery sub-packs with adjacent sorting order to form a branch after sorting the battery sub-packs according to the minimum voltage of the battery sub-packs, and different branches include different battery sub-packs. When it is determined that there is at least one branch to be balanced in the battery pack, each branch to be balanced is controlled to start a passive balancing strategy. Before forming a branch, the order of the battery sub-packs is flexibly adjusted according to the size of the minimum voltage of the battery sub-packs to ensure that the voltage difference inside each branch is minimized, reduce the balancing requirements inside each branch, and better improve the consistency and balancing efficiency of the whole pack.

[0056] Embodiment 2

[0057] Figure 3 This is a flow chart of a method for balancing a multi-branch battery pack provided in Embodiment 2 of the present invention. This embodiment further refines step S130 of Embodiment 1. Figure 3 As shown, the method includes:

[0058] S131: sorting the battery sub-packs according to the minimum voltage of each battery sub-pack.

[0059] S132: For each branch, select at least two battery sub-packs that are adjacent in sorting order to form a branch; and different branches include different battery sub-packs.

[0060] S133: After determining that the battery pack is in a static state for a preset time, the voltage of each battery cell is obtained and used as the open circuit voltage of the battery cell; in the static state, the current of the battery pack is less than or equal to the first current threshold.

[0061] The first current threshold is the maximum current value that indicates that the battery pack is charged or discharged at low power or not charged or discharged. The current of the battery pack can be the sum of the currents of each branch. When the current of the battery pack is less than or equal to the first current threshold, it is determined that the battery pack is in a static state. The preset duration can be set according to demand, and can be half an hour, 1 hour or 2 hours, etc., without specific limitation.

[0062] After the battery pack has been in a static state for a long time, the voltage of the battery cell approaches the open circuit voltage. Therefore, the voltage across each battery cell in the battery pack after being in a static state for a preset time can be regarded as the open circuit voltage of the battery cell. The open circuit voltage is the potential difference between the positive and negative electrodes of the battery cell when no current flows through it. When the battery cell is not connected to a load, its terminal voltage is the open circuit voltage.

[0063] S134: determining the remaining power of the battery cell according to a preset corresponding relationship and the open circuit voltage of the battery cell; the preset corresponding relationship is a corresponding relationship between the open circuit voltage and the remaining power.

[0064] The preset correspondence may be an OCV table, which includes multiple data groups, each of which includes an open circuit voltage and the remaining power corresponding to the open circuit voltage, and different data groups include different open circuit voltages. After obtaining the open circuit voltage of the battery cell, the remaining power corresponding to the open circuit voltage is determined by looking up a table or by interpolation, thereby obtaining the remaining power of the battery cell.

[0065] S135: For any cell to be balanced in the branch to be balanced, the balancing time of the cell to be balanced is calculated according to the remaining power of the cell to be balanced, the target remaining power corresponding to the branch to which the cell to be balanced belongs, the capacity of the cell to be balanced, and the balancing current. The cell to be balanced is a cell whose remaining power is greater than the target remaining power corresponding to the branch to which the cell to be balanced belongs.

[0066] Optionally, the target remaining power SOC0 corresponding to the branch to be balanced is SOC1=(SOC1+SOC2) / 2; wherein SOC1 is the average value of the remaining power of each battery cell on the branch to be balanced, and SOC2 is the minimum value of the remaining power of each battery cell on the branch to be balanced.

[0067] The target remaining power corresponding to the branch is numerically equal to (SOC1+SOC2) / 2, so that after multiple equalizations, the inconsistency of the cells inside the battery pack can be gradually reduced, and the result of the equalization judgment can be used for a long time without pursuing a single judgment. Directly using the minimum remaining power in the branch as the target remaining power will lead to problems such as too many cells needing to be balanced and too long a single balancing channel balancing time, which can easily cause the slave board temperature of the battery management system to be too high.

[0068] Optionally, the balancing time t1 of the cells to be balanced satisfies:

[0069] t1 = (SOC3 - SOC0) · C1 / I1; wherein SOC3 is the remaining power of the battery cell to be balanced, SOC0 is the target remaining power corresponding to the branch to which the battery cell to be balanced belongs, C1 is the capacity of the battery cell to be balanced, and I1 is the balancing current.

[0070] S136: Control each battery cell to be balanced to start balancing, and stop balancing the battery cell to be balanced after any battery cell to be balanced reaches the corresponding balancing time, until all the battery cells to be balanced reach the corresponding balancing time, and then the passive balancing strategy ends.

[0071] In an optional embodiment, at least one resistor is connected to both ends of each battery cell through a switch, that is, the battery cell, the switch and the resistor can form a loop, and the battery cell, the switch and the resistor form a balancing channel. After the control switch is closed, the remaining power of the battery cell is consumed through the resistor, so that the remaining power of the battery cell to be balanced is close to the target remaining power.

[0072] For a passive equilibrium strategy:

[0073] For any branch to be balanced, the balancing time of each battery cell to be balanced in the branch to be balanced is calculated. The switches corresponding to all the batteries to be balanced in each branch to be balanced can be controlled to be closed at the same time, and all the batteries to be balanced in each branch to be balanced can be controlled to be turned on for balancing at the same time. For any battery cell to be balanced, when its balancing time is reached, the switch corresponding to the battery cell to be balanced is controlled to be turned off to stop the balancing of the battery cell to be balanced. When each battery cell to be balanced in each branch to be balanced reaches its corresponding balancing time, the balancing strategy ends.

[0074] Control each branch to be balanced to start at least one passive balancing strategy, that is, execute S135 and S136 once, until, for each branch to be balanced, the remaining power of each battery cell in the branch to be balanced is less than or equal to the target remaining power corresponding to the branch to be balanced. After ending one passive balancing strategy, re-determine the branch to be balanced, and re-determine the battery cell to be balanced for the branch to be balanced, and then start the next passive balancing strategy.

[0075] Figure 4 A schematic diagram of a battery pack according to the second embodiment of the present invention is shown in FIG. Figure 4 , optionally, the battery pack is connected between the positive output terminal and the negative output terminal of the battery pack through the main positive relay 131 and the negative positive relay 132. The main positive relay 131 and the negative positive relay 132 are both connected to the battery management system 12. In this embodiment, the branches are connected in parallel, and optionally, the branches can be connected in parallel through copper plates. After the branches are connected in parallel through copper plates, the branches are actively balanced through circulating current; wherein, the direction of active balancing is from the branch with high voltage to the branch with low voltage. For the case where the minimum voltage of the first preset battery sub-pack in the mth branch as described in Example 1 is greater than the minimum voltage of the second preset battery sub-pack in the m-1th branch, the mth branch is the branch with high voltage, and the m-1th branch is the branch with low voltage. The branch voltage can be characterized by the voltage of the battery cell with the lowest voltage in the branch. Wherein, m is an integer greater than or equal to 2.

[0076] In this embodiment, the balancing judgment is performed separately on a branch basis, and the principle followed is that the voltage difference of the battery cells inside the branch is passively balanced, and the branches are balanced by parallel circulation, so that the balancing is completed in the shortest time and the capacity of the whole package is increased. At the same time, the balancing pressure of the battery management system can be reduced, and long-term balancing can be avoided, which will cause the temperature of the control board to be too high for a long time.

[0077] Embodiment 3

[0078] Figure 5 This is a schematic diagram of the structure of a battery pack provided by Embodiment 3 of the present invention. Figure 5 As shown, each branch includes a branch relay 133. For any branch, each battery sub-pack on the branch is connected in series with the branch relay 133 corresponding to the branch.

[0079] For the configuration of branch parallel connection through branch relay 133 control, when the battery management system 12 receives the upper high voltage instruction, it controls the main positive relay 131, the negative positive relay 132, and the branch relays 133 on each branch to be closed, so as to realize the parallel connection of each branch, so that each branch is connected in parallel, and active balancing is performed through the circulating current. Among them, the direction of active balancing is that the branch with high voltage flows to the branch with low voltage, and the pressure difference between the branches is eliminated through the circulating current.

[0080] When the battery management system 12 receives the high voltage command, it controls the main positive relay 131 and the negative positive relay 132 to disconnect, and stops the battery pack from outputting voltage. The current on each branch is obtained, and for any branch, when the current on the branch is greater than the second current threshold, the branch relay 133 on the branch is controlled to continue to close.

[0081] When the battery pack is applied to a vehicle, if the whole vehicle requests a high voltage, and if there is still a circulating current between the branches at this time, the battery management system 12 directly disconnects the branch relay 133. On the one hand, the current cut-off affects the life of the relay, and on the other hand, disconnecting the branch relay 133 cannot continue to eliminate the branch pressure difference. For this working condition, when receiving a high voltage instruction and the current of the branch is greater than the second current threshold such as 2A, the battery management system 12 controls the main positive relay 131 and the negative positive relay 132 to disconnect, and still closes the branch relay 13 on the branch. The battery management system 12 stops sending on the CAN network to meet the network management requirements of the whole vehicle. When waiting for the current on the branch to be less than or equal to the second current threshold, the branch relay 133 on the branch is controlled to disconnect. After the branch relays on each branch are disconnected, the battery management system completely enters sleep.

[0082] After the vehicle is under high voltage, the branches to be balanced of the battery pack in the third embodiment can be controlled according to steps S110-S130 for balancing, or the branches to be balanced of the battery pack in the third embodiment can be balanced according to steps S131-S136, which will not be described in detail in this embodiment.

[0083] For the configuration with branch relays, by stopping sending messages, only the branch relays are kept closed to meet the vehicle network management requirements, achieve pseudo-dormant state, and continue to complete branch balancing. When the branch current is less than 2A, the branch relays are disconnected and the battery management system enters sleep completely. When the branch current is small, the branch relays are disconnected to eliminate the voltage difference between branches as much as possible through the circulating current, which is also conducive to extending the life of the branch relays.

[0084] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0085] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for balancing a multi-branch battery pack, characterized in that: The battery pack includes at least two branches, each of which includes at least two battery sub-packs connected in series, and the battery sub-pack includes at least one battery cell; The balancing control method of the multi-branch battery pack includes: sorting the battery sub-packs according to the minimum voltage of the battery sub-packs; For each of the branches, at least two battery sub-packs that are adjacent in sorting order are selected to form the branch; and different branches include different battery sub-packs; When it is determined that there is at least one branch to be balanced in the battery pack, each branch to be balanced is controlled to start a passive balancing strategy; wherein the branch to be balanced is a branch in which the remaining power of at least one battery cell is greater than the target remaining power corresponding to the branch.

2. The balancing control method for a multi-branch battery pack according to claim 1, characterized in that: The passive balancing strategy includes: For any battery cell to be balanced in a branch to be balanced, the balancing time of the battery cell to be balanced is calculated according to the remaining power of the battery cell to be balanced, the target remaining power corresponding to the branch to which the battery cell to be balanced belongs, the capacity of the battery cell to be balanced, and the balancing current; the battery cell to be balanced is a battery cell whose remaining power is greater than the target remaining power corresponding to the branch to which the battery cell to be balanced belongs; Each of the cells to be balanced is controlled to start balancing, and the balancing of any cell to be balanced is stopped after the corresponding balancing time is reached, until all the cells to be balanced reach the corresponding balancing time, and the passive balancing strategy ends.

3. The balancing control method for a multi-branch battery pack according to claim 2, characterized in that: Also includes: Control each of the to-be-balanced branches to start at least one passive balancing strategy until, for each of the to-be-balanced branches, the remaining power of each battery cell in the to-be-balanced branch is less than or equal to the target remaining power corresponding to the to-be-balanced branch.

4. The balancing control method for a multi-branch battery pack according to claim 2, characterized in that: For any of the branches to be balanced: The target remaining power SOC0 corresponding to the branch to be balanced is SOC1=(SOC1+SOC2) / 2; wherein SOC1 is the average value of the remaining power of each battery cell in the branch to be balanced, and SOC2 is the minimum value of the remaining power of each battery cell in the branch to be balanced.

5. The balancing control method for a multi-branch battery pack according to claim 4, characterized in that: The balancing time t1 of the battery cell to be balanced satisfies the following formula: t1=(SOC3-SOC0)·C1 / I1; wherein SOC3 is the remaining power of the battery cell to be balanced, SOC0 is the target remaining power corresponding to the branch to which the battery cell to be balanced belongs, C1 is the capacity of the battery cell to be balanced, and I1 is the balancing current.

6. The balancing control method for a multi-branch battery pack according to any one of claims 2 to 5, characterized in that: Before calculating the balancing time of the battery cell to be balanced according to the remaining power of the battery cell to be balanced, the target remaining power corresponding to the branch to which the battery cell to be balanced belongs, the capacity of the battery cell to be balanced, and the balancing current, the method further includes: After determining that the battery pack is in a static state for a preset time, obtaining the voltage of each of the battery cells and using it as the open circuit voltage of the battery cell; in the static state, the current of the battery pack is less than or equal to a first current threshold; The remaining power of the battery cell is determined according to a preset corresponding relationship and the open circuit voltage of the battery cell; the preset corresponding relationship is a corresponding relationship between the open circuit voltage and the remaining power.

7. The balancing control method for a multi-branch battery pack according to claim 1, characterized in that: Each of the branches is connected in parallel, and the balancing control method of the multi-branch battery pack further includes: Active balancing is performed between the branches through circulating current; wherein the direction of active balancing is that the flow from the branch with high voltage flows to the branch with low voltage.

8. The balancing control method for a multi-branch battery pack according to claim 1, characterized in that: Each of the branches includes a branch relay. For any of the branches, each battery sub-pack on the branch is connected in series with the branch relay corresponding to the branch. The balancing control method of the multi-branch battery pack further includes: The branch relays of each branch are controlled to be closed, so that each branch is connected in parallel and active balancing is performed through circulating current; wherein the direction of active balancing is that the voltage from the branch with high voltage flows to the branch with low voltage.

9. The balancing control method for a multi-branch battery pack according to claim 8, characterized in that: For any of the branches, the branch is connected in series between the main positive relay and the negative positive relay; The balancing control method of the multi-branch battery pack further includes: When receiving the high voltage instruction, the main positive relay, the negative positive relay, and the branch relays on each branch are controlled to be closed; When receiving a lower high voltage instruction, controlling the main positive relay and the negative positive relay to be disconnected; The magnitude of the current on each of the branches is obtained, and for any of the branches, when the current on the branch is greater than a second current threshold, the branch relay on the branch is controlled to continue to be closed.

10. The balancing control method for a multi-branch battery pack according to claim 1, characterized in that: For any of the battery sub-packs, the minimum value of the voltages of the cells in the battery sub-pack is taken as the minimum voltage of the battery sub-pack.

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