Battery pack active balancing method and system

Abstract

The present invention discloses a battery pack active balancing method and system, which includes a plurality of serially connected battery modules, and each battery module includes a plurality of serially connected battery cells; between the battery modules, switches are used to control the connection and disconnection of the battery modules; between the battery cells within each battery module, switches are also used to control the connection and disconnection of the battery cells. The present invention adopts a two-layer topological structure based on flexible reconstruction, divides the battery pack into multiple battery modules, and the series connection modes of the multiple battery cells between the battery modules and within the battery modules are the same, and both are connected and disconnected through single-pole double-throw switches, so as to isolate faulty cells or modules in the later stage without affecting the balancing function; it provides a hardware basis for improving the balancing timeliness and balancing consistency.

Description

Technical Field

[0001] The present invention relates to the technical field of battery equalization, and specifically to an active equalization method and system for a battery pack. Background Art

[0002] Factors such as battery material limitations, production process, and environmental condition changes can lead to inconsistencies in the battery pack. Using inconsistent battery monomers will cause energy changes between the individual batteries, resulting in local overcharging or over-discharging, which has an adverse impact on system performance and increases safety risks. To solve this problem, equalization technology has developed to the level of balancing cell energy. It effectively extends the service life of the battery pack and improves the overall performance of the system.

[0003] Currently, the method of improving the energy consistency of the battery pack mainly adopts active equalization technology. This method uses energy storage devices such as inductors and transformers to promote energy transfer between battery monomers, so that the charge states of each battery monomer tend to be balanced. By improving the consistency of the battery pack, this method can enable each monomer to reach the cut-off discharge condition as much as possible at the same time, thereby improving the capacity utilization rate of the battery pack. This active equalization technology helps to extend the service life of the battery pack and improve its overall performance. However, in order to achieve efficient and rapid equalization management, a complex equalization circuit needs to be designed. This not only increases the design cost but also increases the complexity of control. In addition, most of the existing active equalization schemes are proposed for fixed-topology battery systems and cannot handle the equalization scenarios of faulty batteries. Additionally, in actual vehicles, the battery pack usually consists of thousands of batteries connected in series or in parallel. With the substantial increase in the number of batteries, the problem of inconsistency between the batteries in the battery pack will become more prominent, and the requirements for the equalization mechanism will also be higher. Due to the limitations of its adjustment ability, the traditional single-stage equalization mechanism will become slower in equalization speed and the equalization effect will also be greatly reduced when dealing with a large number of batteries. Although the existing two-stage equalization mechanism is superior to the single-stage equalization mechanism to a certain extent, its efficiency still needs to be improved when facing a large-scale battery pack. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to quickly and effectively actively equalize the battery energy when facing thousands of batteries and when a single battery may be faulty.

[0005] The present invention solves the above technical problem through the following technical means:

[0006] A battery pack, including a plurality of battery modules connected in series, and each battery module includes a plurality of battery monomers connected in series; between the battery modules, switches are used to control the connection and disconnection of the battery module; between the battery monomers in each battery module, switches are also used to control the connection and disconnection of the battery monomer.

[0007] As an optimization of the above solution, the switch is a single-pole double-throw switch.

[0008] The present invention also provides a method for active balancing of battery pack consistency, which is applied to the above battery pack, and is characterized by including the following steps:

[0009] S1. Collect the state of charge of all battery cells in the battery pack;

[0010] S2. Equivalent the connection topology of a single battery module and the connection topology of a battery pack composed of multiple battery modules to a directed graph, and calculate the edge weights of the directed graph;

[0011] S3. Based on the state of charge SOC of all monomers in the battery pack and the edge weights of the directed graph, select the shortest path and the longest path of energy flow between and within the battery modules based on the graph theory traversal algorithm;

[0012] S4. Determine the selected battery cells or battery modules in the two stages of balancing, and realize the active balancing of the battery pack by controlling the action of the switch network;

[0013] S5. Repeat the above S1-S4 until the SOC between all battery cells and battery modules in the battery pack reaches consistency.

[0014] As an optimization of the above solution, the edge weights of the directed graph in step S2 w i，j The calculation formula is as follows:

[0015]

[0016] Wherein, α represents the weight value, n represents from node i to node j the number of switches experienced, q represents the energy loss fraction of a single switch, r i represents the energy fraction of a single cell or module;

[0017]

[0018] Wherein, x i is the difference between the current state of the SOC battery system of the i-th single cell or module and its fully charged state.

[0019] As an optimization of the above solution, the method for calculating the energy path of a battery cell or battery module is:

[0020] Step 1: Determine the starting vertex of the directed graph V 0 and V n+1, representing the positive and negative electrodes of the battery pack respectively; put the starting vertex V 0 into the stack;

[0021] Step 2: Access the starting vertex V0 at the top of the stack;

[0022] Step 3: Identify the adjacent nodes that have not been traversed and place them in the stack;

[0023] Step 4: If there are no adjacent nodes that have not been traversed, pop the node from the stack and repeat Step 3;

[0024] Step 5: The target node V n+1 is popped from the stack;

[0025] Step 6: All nodes adjacent to the node V n have been traversed, and it is popped from the stack;

[0026] Step 7: The node V i directly accesses the target node V n+1 ; where i represents the i th node;

[0027] Step 8: The target node V n+1 is popped from the stack;

[0028] Step 9: All nodes adjacent to the node V i have been traversed, and it is popped from the stack;

[0029] Step 10: Repeat Steps 7 - 9 to traverse all paths;

[0030] Finally, filter out the longest and shortest energy paths.

[0031] As an optimization of the above solution, output a logic control signal to the switching network for the selected shortest energy path solution. Through the control of the switching network, realize the series recombination of the battery pack and charge the balancing inductor; output a logic control signal to the switching network for the selected longest energy path solution. Through the control of the switching network, realize the series recombination of the battery pack, and charge the selected battery by the balancing inductor.

[0032] The present invention also provides a battery pack consistency active balancing system, which is characterized in that it includes:

[0033] Charged data acquisition module: acquire the state of charge of all battery cells in the battery pack;

[0034] Directed graph construction module: equivalent the connection topology of a single battery module and the connection topology of a battery pack composed of multiple battery modules to a directed graph, and calculate the edge weights of the directed graph;

[0035] Energy path calculation module: based on the state of charge SOC of all cells in the battery pack and the edge weights of the directed graph, select the shortest path and the longest path of energy flow between and within the battery modules based on the graph theory traversal algorithm;

[0036] Active balancing module: determine the selected battery cells or battery modules in two stages of balancing, and realize the active balancing of the battery pack by controlling the action of the switching network; perform cyclic operations until the SOCs of all battery cells and between battery modules in the battery pack reach consistency.

[0037] As an optimization of the above solution, the edge weights of the directed graph w i，j The calculation formula is as follows:

[0038]

[0039] Among them, α represents the weight value, n represents the number of switches experienced from node i to node j the number of switches experienced, q represents the energy loss fraction of a single switch, r i represents the energy fraction of a single cell or module;

[0040]

[0041] Among them, x i is the difference between the current state of the SOC battery system of the i-th single cell or module and its fully charged state.

[0042] As an optimization of the above solution, the method for calculating the energy path of a battery cell or battery module is:

[0043] Step 1: Determine the starting vertex V 0 and V n+1 , respectively representing the positive and negative poles of the battery pack; put the starting vertex V 0 into the stack;

[0044] Step 2: Access the starting vertex V0 at the top of the stack;

[0045] Step 3: Identify adjacent nodes that have not been traversed and place them on the stack;

[0046] Step 4: If there are no adjacent nodes that have not been traversed, pop the node from the stack and repeat Step 3;

[0047] Step 5: The target node V n+1 is popped from the stack;

[0048] Step 6: All nodes adjacent to the node V n have been traversed, and it is popped from the stack;

[0049] Step 7: The node V i directly accesses the target node V n+1 ; where i represents the i th node;

[0050] Step 8: The target node V n+1 is popped from the stack;

[0051] Step 9: All nodes adjacent to the node V i have been traversed, and it is popped from the stack;

[0052] Step 10: Repeat Steps 7 - 9 to traverse all paths;

[0053] Finally, filter out the longest and shortest energy paths.

[0054] As an optimization of the above solution, a logic control signal is output to the switch network for the selected shortest energy path solution. Through the control of the switch network, series recombination of the battery pack is achieved, and the equalizing inductor is charged; a logic control signal is output to the switch network for the selected longest energy path solution. Through the control of the switch network, series recombination of the battery pack is achieved, and the selected battery is charged by the equalizing inductor.

[0055] The advantages of the present invention are as follows:

[0056] The present invention adopts a two - layer topological structure based on flexible reconstruction, divides the battery pack into multiple battery modules, and the series connection methods of multiple battery cells between and within the battery modules are the same. They are all switched in and out through single - pole double - throw switches, which is used to isolate faulty single cells or modules without affecting the balancing function in the later stage, providing a hardware basis for improving the equalization timeliness and equalization consistency.

[0057] The method of the present invention can achieve active balancing and fault isolation within and between modules during the operation of the battery pack. Even if a fault occurs in the battery cells of the battery pack, the present invention can cut off the faulty battery through a switch without affecting the overall balancing and operation of the battery pack.

[0058] The switch network reconstruction technology of the present invention can not only achieve energy transfer between battery monomers, but also optimize the energy flow of the entire battery pack, reducing the time and energy loss during the balancing process. This mechanism plays a key role in improving the overall consistency of the battery pack, especially in the application of larger battery packs. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a flowchart of the active balancing method for a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0060] Figure 2 is a schematic diagram of the topology of a battery pack according to an embodiment of the present invention;

[0061] Figure 3 is a stack building schematic diagram of Step 1 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0062] Figure 4 is a stack building schematic diagram of Step 2 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0063] Figure 5 is a stack building schematic diagram of Step 3 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0064] Figure 6 is a stack building schematic diagram of Step 4 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0065] Figure 7 is a stack building schematic diagram of Step 5 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0066] Figure 8 is a stack building schematic diagram of Step 6 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0067] Figure 9 is a stack building schematic diagram of Step 7 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0068] Figure 10 is a stack building schematic diagram of Step 8 for solving the "energy path" of a battery pack based on a graph theory traversal algorithm according to an embodiment of the present invention;

[0069] Figure 11 It is the schematic diagram of stack building in Step 9 for solving the "energy path" of the battery pack based on the graph theory traversal algorithm in the embodiment of the present invention;

[0070] Figure 12 It is the schematic diagram of stack building in Step 10 for solving the "energy path" of the battery pack based on the graph theory traversal algorithm in the embodiment of the present invention;

[0071] Figure 13 It is the SOC curve graph of the battery in the embodiment of the present invention.

[0072] Figure 14 It is the SOC curve graph of the battery in the comparative experiment embodiment. Detailed implementation manners

[0073] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0074] This embodiment proposes a battery pack consistency active balancing scheme based on the graph theory traversal algorithm, as Figure 1 , including the following steps:

[0075] Step 1: Collect the state of charge of all single cells in the battery pack.

[0076] The state of charge (SOC) is obtained by the ampere-hour integration method.

[0077] Step 2: Topologically equivalent the battery pack to a directed graph, and use an adjacency matrix to represent the edge weights of the directed graph:

[0078]

[0079] The battery pack is in a series structure as Figure 2 shown, the battery pack contains n battery modules, and each battery module M i ( i = 1, 2,..., n ) is controlled by a single-pole double-throw switch Kn to cut in and out of the module. The battery cells inside the module have the same connection topology. Each battery module contains m battery cells. The n th module, each battery cell B n，i ( i= 1, 2, …, m is controlled by a single-pole double-throw switch k n，m to cut in and cut out the monomer.

[0080] The switch action logic principle is as follows:

[0081]

[0082]

[0083] Among them, K i and k n，i respectively represent the states of the single-pole double-throw switches between modules and between monomers within a module. Logic 1 indicates that the switch cuts the module or monomer into the circuit, and logic 0 indicates that the switch cuts the module or monomer out of the circuit.

[0084] w i，j ( i = 0, 1, 2, …, n ; j = 1, 2, …, n + 1) is the edge weight of the directed graph, ∞ represents no energy flow between nodes, and the edge weight w i，j is calculated as follows:

[0085]

[0086] Among them, α represents the weight value, n represents the number of switches experienced from node i to node j q represents the energy loss fraction of a single switch, r i represents the energy fraction of the monomer or module.

[0087] Among them, the method for calculating the energy fraction of the monomer or module is:

[0088]

[0089] Among them, x i is the difference between the current state of the SOC battery system of the i-th monomer or module and its fully charged state.

[0090] Step 3: Based on the state of charge SOC of all monomers in the battery pack and the edge weight values of the directed graph, select the shortest path and the longest path of the energy flow of the battery system using a graph theory traversal algorithm. Specifically, use the algorithm to solve from node V ​All "energy paths" from 0 to V n+1 where an "energy path" refers to the path from the negative electrode to the positive electrode of the battery pack. The specific steps are as follows:

[0091] Step 1: Determine the starting vertex of the directed graph V 0 and V n+1 represent the positive and negative electrodes of the battery pack respectively, as Figure 3 shown.

[0092] Step 2: Visit the starting vertex V0 at the top of the stack, as Figure 4 shown.

[0093] Step 3: Identify the adjacent nodes that have not been traversed and place them in the stack, as Figure 5 shown.

[0094] Step 4: If there are no adjacent nodes that have not been traversed, pop the node from the stack and repeat Step 3, as Figure 6 shown.

[0095] Step 5: The target node V n+1 is popped from the stack, as Figure 7 shown.

[0096] Step 6: All nodes adjacent to the node V n have been traversed, and it is popped from the stack, as Figure 8 shown.

[0097] Step 7: The node V i directly accesses the target node V n+1 , i indicating the i th node, as Figure 9 shown, V i being V 3.

[0098] Step 8: The target node V n+1 is popped from the stack, as Figure 10 shown.

[0099] Step 9: All nodes adjacent to the node V i have been traversed, and it is popped from the stack, as Figure 11 shown.

[0100] Step 10: Repeat Steps 7 - 9 to traverse all paths, as Figure 12 shown.

[0101] Based on the calculated energy flow paths, screen the shortest and longest "energy paths" that meet the application requirements: Specifically, screen the "energy path" solutions, and select the shortest and longest "energy path" solutions; the shortest "energy path" is used to determine the battery for charging the balancing inductor, and the longest "energy path" is used to determine the battery to be charged by the balancing inductor;

[0102] Step 4: Determine the selected battery cells for the two stages of balancing, and achieve active balancing of the battery pack by controlling the operation of the switch network. Specifically, output a logic control signal to the switch network for the screened shortest "energy path" solution, and through the control of the switch network, achieve series recombination of the battery pack and charge the balancing inductor; output a logic control signal to the switch network for the screened longest "energy path" solution, and through the control of the switch network, achieve series recombination of the battery pack, and the balancing inductor charges the selected battery. The switch network is realized by the series - parallel connection of relays or Mos transistors, as Figure 2 shown.

[0103] Step 5: Repeat all the above steps until the SOC of all battery cells and modules in the battery pack reaches consistency.

[0104] The technical solution of the present invention will be further elaborated below with a specific application example.

[0105] Carry out an equalization experiment verification on a series battery pack containing 36 battery cells. These 36 batteries are divided into 6 modules, with 6 battery cells in each module. The initial voltages of the batteries are shown in Table 1 below.

[0106] Table 1

[0107]

[0108] Through the graph - theory traversal algorithm, find the shortest and longest "energy paths", and determine the battery cells or modules for charging the balancing inductor and the battery cells or modules to be charged by the balancing inductor. Figure 13 Shows the change of the battery pack SOC under the equalization of this solution. It can be seen that this solution can achieve the consistency of SOC between modules and within modules. Figure 14The single-layer active balancing effect is demonstrated. From the overall convergence trend, the proposed two-stage active balancing speed is significantly faster than the single-stage balancing scheme. At 10,000 s, the SOC range of the battery pack of the traditional scheme is 0.193. For the proposed active balancing scheme, the SOCs of the battery pack are basically converged together, and the SOC range is 0.0254, which is about 86.839% lower than that of the traditional one. In terms of the balancing time, at 14,400 s for the traditional balancing scheme, the SOC range of the battery pack is 0.1609. For the proposed balancing scheme, the SOC range converges to 0.1609 at 3,412 s. Compared with the traditional scheme, the balancing time is shortened by 10,988 s.

[0109] Although this experiment is only carried out on a battery pack of 36 batteries, through in-depth analysis of the experimental results, the differences in time and effect between the proposed technology in this application and the existing single-stage and two-stage balancing mechanisms for thousands of batteries in actual vehicles can be reasonably deduced. In comparison, the two-stage balancing mechanism of this application has stronger adaptability and high efficiency. In terms of the balancing time, due to its unique two-stage collaborative working mode, it can balance and adjust a large number of batteries in a shorter time. As the number of batteries increases, this time advantage may become more obvious. For example, assuming that the balancing time has a certain linear relationship with the number of batteries (the actual situation may be more complex), then when dealing with thousands of batteries, the balancing mechanism of this application may shorten the balancing time by several times or even dozens of times compared with the traditional single-stage balancing mechanism. In terms of the balancing effect, the two-stage balancing mechanism of this application can more accurately adjust the SOC of each battery, significantly improving the consistency of the batteries in the battery pack. For actual vehicles, this means that the overall performance of the battery pack is optimized, the service life of the batteries is extended, and at the same time, the cruising range and safety of the vehicle are improved.

[0110] In summary, this embodiment proposes an active balancing scheme for battery pack consistency based on the graph theory traversal algorithm. The proposed scheme adopts a two-layer topology structure based on flexible reconstruction, which can isolate faulty single cells or modules without affecting the balancing function; the graph theory is used to improve the convenience of the balancing process. The proposed scheme can achieve double-layer active balancing between modules and within modules, and has better balancing performance compared with the single-stage balancing scheme.

[0111] By adopting the two-layer topology structure and the graph theory traversal algorithm, this embodiment can perform efficient active balancing inside and outside the module. This method adapts to the balancing requirements of large-scale battery packs through flexible topology reconstruction, significantly improving the balancing speed and accuracy. Compared with the existing single-stage balancing scheme, the differences in balancing time and effect of this embodiment are more significant, especially in the actual application of dealing with thousands of batteries, which can shorten the balancing time and greatly improve the balancing effect.

[0112] In this embodiment, the switching network realizes the series and parallel reconstruction of the battery pack through relays or MOS transistors, and uses the graph theory traversal algorithm to optimize the energy flow. The battery cells and modules control the energy transfer and balancing through single-pole double-throw switches and cut out the faulty circuits through switches. The operation of the switches is controlled by the SOC state of the battery pack to achieve the balancing inside and outside the battery modules.

[0113] The switching network in this embodiment not only helps to realize the energy transfer between battery cells, but also can optimize the energy flow of the entire battery pack. By optimizing the energy path through graph theory, the time and energy losses during the balancing process are reduced. This mechanism plays a key role in improving the overall consistency of the battery pack, especially in the application of larger battery packs.

[0114] In addition, in the existing active balancing mechanism, the topology of the battery pack is fixed, and the energy interaction between batteries is realized through a large number of capacitor and inductor hardware circuits outside the circuit. Once a certain battery fails, since the faulty battery cannot be isolated and cut out, the entire battery system needs to stop running. However, although a large number of switches are used in this embodiment, the cost of the switches is significantly lower than that of capacitors and inductors. And whether a single cell in the battery module fails or a certain battery module fails, the faulty single cell or module can be cut out through the switching network without affecting the overall operation of the system, ensuring the continuation of the primary and secondary balancing.

[0115] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An active equalization method for battery pack consistency, characterized in that, The battery pack includes multiple battery modules connected in series, and each battery module includes multiple battery cells connected in series; the connection and disconnection of each battery module are controlled by a switch; the connection and disconnection of the battery cells within each battery module are also controlled by a switch; The active balancing method for the battery pack consistency includes: S1. Collect the state of charge of all battery cells in the battery pack; S2. Equivalent the connection topology of a single battery module and the connection topology of the battery pack composed of multiple battery modules to a directed graph, and calculate the edge weights of the directed graph; S3. Based on the state of charge SOC of all cells in the battery pack and the edge weights of the directed graph, select the shortest energy path and the longest energy path for the energy flow between and within the battery modules based on the graph theory traversal algorithm; S4. Based on the shortest energy path and the longest energy path, determine the selected battery cells or battery modules in the two stages of balancing, and realize the series recombination of the battery pack by controlling the switch action to achieve the active balancing of the battery pack; S5. Repeat the above S1 - S4 until the SOC of all battery cells and between battery modules in the battery pack reaches consistency.

2. The active balancing method for battery pack consistency according to claim 1, wherein The switch is a single - pole double - throw switch.

3. The active balancing method for battery pack consistency according to claim 1, characterized in that The directed graph edge weights in the step S2 w i，j The calculation formula is as follows: Among them, α represents the weight value, n represents the number of switches experienced from node i to node j The number of switches experienced, q represents the energy loss fraction of a single switch, r i represents the energy fraction of a single cell or module; wherein, x i is the difference between the current state of the SOC battery pack of the i th monomer or module and its fully charged state.

4. The battery pack consistency active balancing method according to any one of claims 1 to 3, characterized in that The method for calculating the energy path of a battery cell or a battery module is: Step 1: Determine the starting vertex of the directed graph V 0 and V n+1 , respectively represent the positive and negative electrodes of the battery pack; Put the starting vertex V 0 into the stack; Step 2: Access the starting vertex V0 at the top of the stack; Step 3: Identify the unvisited adjacent nodes and place them in the stack; Step 4: If there are no unvisited adjacent nodes, pop the node from the stack and repeat Step 3; Step 5: Target node V n+1 is popped from the stack; Step 6: All the nodes adjacent to the node V n have been traversed and are popped from the stack; Step 7: Node V i Directly access the target node V n+1 ; where i represents the i th node; Step 8: Target node V n+1 is popped from the stack; Step 9: All the nodes adjacent to the node V i have been traversed, and it is popped from the stack; Step 10: Repeat Step 7 - 9 to traverse all paths; Finally, filter out the longest and shortest energy paths.

5. The active balancing method for battery pack consistency according to claim 4, characterized in that, Output a logic control signal to the switch network for the selected shortest energy path scheme. Through the control of the switch network, realize the series recombination of the battery pack and charge the balancing inductor; output a logic control signal to the switch network for the selected longest energy path scheme. Through the control of the switch network, realize the series recombination of the battery pack, and charge the selected battery by the balancing inductor.

6. Battery pack consistency active balancing system, characterized in that The battery pack includes multiple battery modules connected in series, and each battery module includes multiple battery cells connected in series; the connection and disconnection of each battery module are controlled by a switch; the connection and disconnection of the battery cells within each battery module are also controlled by a switch; The active balancing method for the battery pack consistency includes: State - of - charge data acquisition module: Collect the state of charge of all battery cells in the battery pack; Directed - graph construction module: Equivalent the connection topology of a single battery module and the connection topology of the battery pack composed of multiple battery modules to a directed graph, and calculate the edge weights of the directed graph; Energy - path calculation module: Based on the state of charge SOC of all cells in the battery pack and the edge weights of the directed graph, select the shortest energy path and the longest energy path for the energy flow between and within the battery modules based on the graph theory traversal algorithm; Active balancing module: Based on the shortest energy path and the longest energy path, determine the selected battery cells or battery modules to be balanced in two stages, and achieve active balancing of the battery pack by controlling the switch actions; perform cyclic operations until the SOCs among all battery cells and battery modules in the battery pack reach consistency.

7. The active balancing system for battery pack consistency according to claim 6, characterized in that, The edge weights of the directed graph w i，j The calculation formula is as follows: Among them, α represents the weight value, n represents the number of switches experienced from the node i to the node j The number of switches experienced, q represents the energy loss fraction of a single switch, r i represents the energy fraction of a single cell or module; Among them, x i is the difference between the current state of the SOC battery system of the i th monomer or module and its fully charged state.

8. The battery pack consistency active equalization system according to claim 6 or 7, characterized in that The method for calculating the energy path of battery cells or battery modules is as follows: Step 1: Determine the starting vertex of the directed graph V 0 and V n+1 , respectively represent the positive and negative electrodes of the battery pack; Put the starting vertex V 0 into the stack; Step 2: Access the starting vertex V0 at the top of the stack; Step 3: Identify the unvisited adjacent nodes and place them in the stack; Step 4: If there are no unvisited adjacent nodes, pop the node from the stack and repeat Step 3; Step 5: Target Node V n+1 is popped from the stack; Step 6: All nodes adjacent to the node V n have been traversed and popped from the stack; Step 7: Node V i Directly access the target node V n+1 ; where i represents the i th node; Step 8: Target Node V n+1 is popped from the stack; Step 9: All the nodes adjacent to the node V i have been traversed and it is popped from the stack; Step 10: Repeat Steps 7 - 9 to traverse all paths; Finally, filter out the longest and shortest energy paths.

9. The battery pack consistency active equalization system according to claim 8, wherein Output a logic control signal to the switch network for the selected shortest energy path scheme. Through the control of the switch network, achieve series recombination of the battery pack and charge the balancing inductor; output a logic control signal to the switch network for the selected longest energy path scheme. Through the control of the switch network, achieve series recombination of the battery pack, and charge the selected battery with the balancing inductor.

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