A multi-mode active balancing method and system for series lithium battery based on multi-inductor layered topology, and a computer readable storage medium

Abstract

The embodiment of the application discloses a multi-mode active equalization solution based on a multi-inductance layered topology, a multi-path equalization topology framework is designed to construct a parallel energy transmission channel, breaking through the limitation of single current path of traditional single inductance topology; combined with a multi-mode equalization control strategy, four equalization modes of inter-single body (battery monomer-battery monomer), inter-global (battery group whole monomer) and inter-group (battery small group-battery small group) are dynamically switched according to real-time SOC, the equalization speed is accelerated, the equalization efficiency is improved, and the equalization time is reduced.

Description

Technical Field

[0001] This invention relates to the field of battery balancing technology, and in particular to a multi-mode active balancing method for series lithium battery packs based on a multi-inductor hierarchical topology. Background Technology

[0002] Driven by both surging global energy demand and the low-carbon transition, electric vehicles and energy storage power stations are rapidly developing as core carriers of the new energy strategy. Lithium-ion batteries, due to their small size, high efficiency, and low pollution, are widely used in electric vehicles and energy storage power stations. Because individual lithium-ion batteries have low voltages, multiple batteries are typically connected in series to form battery packs to meet the voltage requirements of electrical equipment. However, inconsistencies in parameters such as voltage and capacity can occur during the use of lithium-ion batteries, leading to uneven aging rates within the same battery pack. This inconsistency can cause performance problems in individual batteries to spread throughout the entire battery pack, reducing overall performance and lifespan, and even posing safety hazards. Therefore, passive or active balancing control technologies are needed to maintain similar states among the batteries in the battery pack.

[0003] Currently, passive balancing technology uses high-energy-dissipating cells with resistive energy dissipation for balancing. While inexpensive, it suffers from low balancing efficiency and significant energy loss, failing to meet high energy efficiency requirements. Active balancing technology transfers energy through energy storage elements to achieve peak shaving and valley filling, but its performance is highly dependent on topology design: capacitor-based topologies, while simple in structure, are limited by the voltage difference driving mechanism, making it difficult to control the balancing rate and accuracy; flyback transformer solutions, while offering electrical isolation advantages, face challenges such as fixed winding parameters and difficulties in topology reconfiguration. In contrast, inductive balancing topologies achieve controllable energy transfer through inductor charging and discharging, exhibiting significant advantages in flexibility and scalability.

[0004] In terms of designing active balancing topology types, existing research mainly focuses on optimizing a single balancing mode (overall-to-single / single-to-overall / direct-to-single / adjacent-to-single), which has poor balancing flexibility, long balancing time, and low balancing efficiency. Summary of the Invention

[0005] In view of this, the present invention proposes a multi-inductor hierarchical topology and multi-mode active balancing control strategy, that is, to build parallel balancing channels through a hierarchical architecture to break through the bottleneck of traditional single inductor path blocking; and to design a balancing mode switching algorithm based on SOC difference threshold to realize four balancing modes: direct single cell-to-single cell, battery group-to-battery group, battery group-to-single cell, and single cell-to-battery group-to-battery group.

[0006] The first aspect of this invention provides a multi-mode active balancing method for series lithium battery packs based on a multi-inductor hierarchical topology. The series lithium battery packs are denoted as B1~B8, with B1~B4 forming battery group 1 and B5~B8 forming battery group 2. The multi-inductor hierarchical topology includes the series lithium battery packs, intra-group balancing inductors L1~L2, inter-group balancing inductors L3~L5, MOSFETs M1-M20, diodes D1-D20, and solid-state relays K1-K7. The method includes four balancing modes: balancing mode 1 is direct cell-to-cell, balancing mode 2 is battery pack-to-cell, balancing mode 3 is cell-to-battery pack, and balancing mode 4 is battery group-to-battery group. The method is characterized by the following steps: Step 1: Determine whether the battery pack is charging or discharging. If the battery pack is discharging, proceed to Step 2; if the battery pack is charging, proceed to Step 3. Step 2: Calculate the average SOC and minimum SOC for each battery group, denoted as SOC. AVG and SOC MIN Determine the SOC of each battery group AVG With SOC MIN If the difference is greater than the threshold for enabling Balanced Mode 2, then enable Balanced Mode 2; otherwise, proceed to step 4. Step 3: Calculate the average SOC and maximum SOC for each battery group, denoted as SOC. AVG and SOC MAX Determine the SOC of each battery group MAX With SOC AVG If the difference is greater than the threshold for enabling Balanced Mode 3, then enable Balanced Mode 3; otherwise, proceed to step 4. Step 4: Determine the SOC range of each battery group. The SOC range is the difference between the maximum SOC and the minimum SOC in the battery group. Compare the SOC range with the set threshold for activating Balance Mode 1. If the SOC range is greater than the threshold for activating Balance Mode 1, then activate Balance Mode 1. If the SOC range of both battery groups is less than or equal to the threshold for activating Balance Mode 1, then proceed to step 5. Step 5: Calculate the difference in average SOC between the two battery groups. If the difference is greater than the threshold for activating Equalization Mode 4, then activate Equalization Mode 4 to perform equalization; otherwise, the equalization process ends.

[0007] As a further limitation of the present invention, the invention is characterized in that: in the multi-inductor hierarchical topology, L1 and L2 are the intra-group balancing inductors of battery group 1 and battery group 2, respectively, and L3-L5 are the inter-group balancing inductors of battery groups; the MOS transistor, the diode, and the solid-state relay are used to control the triggering of different balancing modes.

[0008] As a further limitation of the present invention, the equalization mode 1 is used to achieve equalization among different battery cells within a battery group; the equalization mode 1 includes three modes: energy storage mode, energy release mode, and static mode; in the energy storage mode, the battery with the highest SOC in the group charges the equalization inductor within the group; in the energy release mode, the equalization inductor within the group charges the battery with the lowest SOC in the group; in the static mode, the inductor current drops to zero and all MOSFETs are in the off state.

[0009] As a further limitation of the present invention, the balancing mode 2 is used to achieve balancing of the battery pack as a whole with the individual battery cells.

[0010] As a further limitation of the present invention, the balancing mode 3 is used to achieve balancing of the battery cells on the battery pack as a whole.

[0011] As a further limitation of the present invention, it is characterized in that the balancing mode 4 is performed between the two battery groups.

[0012] A second aspect of the present invention provides a multi-mode active balancing device for a series lithium battery pack based on a multi-inductor hierarchical topology, the device being used to implement the method steps of any one of claims 1-6.

[0013] A third aspect of the present invention provides a computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program that can be executed by a processor to implement the method as described in any one of claims 1-6.

[0014] Compared with existing technologies, this invention has at least the following beneficial effects: Addressing the technical problem of low balancing efficiency in series-connected lithium batteries, this invention proposes a multi-mode active balancing solution based on a multi-inductor hierarchical topology. By designing a multi-path balancing topology architecture and constructing parallel energy transmission channels, it overcomes the limitation of a single current path in traditional single-inductor topologies. Combined with a multi-mode balancing control strategy, it dynamically switches between individual cells (cell-to-cell) and between the entire battery pack based on real-time SOC. It offers four equalization modes: single cell, inter-cell (cell group - cell group), which accelerates equalization speed, improves equalization efficiency, and reduces equalization time. Attached Figure Description

[0015] The above and other objects, features and advantages of the present invention will become clearer from the description of embodiments of the invention with reference to the accompanying drawings, which will be described in detail in specific embodiments.

[0016] Figure 1 This invention provides an active balancing topology for a multi-inductor-based hierarchical series battery pack.

[0017] Figure 2a -i is a schematic diagram of different equalization modes provided in the embodiments of the present invention.

[0018] Figure 3 The multi-mode active balancing control strategy provided in the embodiments of the present invention.

[0019] Figure 4a -d represents the experimental verification results of the active balancing control strategy provided in the embodiments of the present invention. Detailed Implementation

[0020] The present application is described below based on embodiments, but it is not limited to these embodiments. In the detailed description of the present application below, certain specific details are described in detail. Those skilled in the art can fully understand the present application without these details. To avoid obscuring the substance of the present application, well-known methods, processes, flows, elements, and circuits are not described in detail.

[0021] Furthermore, those skilled in the art should understand that the accompanying drawings provided herein are for illustrative purposes only and are not necessarily drawn to scale.

[0022] Unless the context explicitly requires it, words such as "including" or "contains" throughout the application should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to".

[0023] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0024] The first aspect of this invention provides a multi-mode active balancing method for series lithium battery packs based on a multi-inductor hierarchical topology. The series lithium battery packs are denoted as B1~B8, with B1~B4 forming battery group 1 and B5~B8 forming battery group 2. The multi-inductor hierarchical topology includes the series lithium battery packs, intra-group balancing inductors L1~L2, inter-group balancing inductors L3~L5, MOSFETs M1-M20, diodes D1-D20, and solid-state relays K1-K7. The method includes four balancing modes: balancing mode 1 is direct cell-to-cell, balancing mode 2 is battery pack-to-cell, balancing mode 3 is cell-to-battery pack, and balancing mode 4 is battery group-to-battery group. The method is characterized by the following steps: Step 1: Determine whether the battery pack is charging or discharging. If the battery pack is discharging, proceed to Step 2; if the battery pack is charging, proceed to Step 3. Step 2: Calculate the average SOC and minimum SOC for each battery group, denoted as SOC. AVG and SOC MIN Determine the SOC of each battery group AVG With SOC MIN If the difference is greater than the threshold for enabling Balanced Mode 2, then enable Balanced Mode 2; otherwise, proceed to step 4. Step 3: Calculate the average SOC and maximum SOC for each battery group, denoted as SOC. AVG and SOC MAX Determine the SOC of each battery group MAX With SOC AVG If the difference is greater than the threshold for enabling Balanced Mode 3, then enable Balanced Mode 3; otherwise, proceed to step 4. Step 4: Determine the SOC range of each battery group. The SOC range is the difference between the maximum SOC and the minimum SOC in the battery group. Compare the SOC range with the set threshold for activating Balance Mode 1. If the SOC range is greater than the threshold for activating Balance Mode 1, then activate Balance Mode 1. If the SOC range of both battery groups is less than or equal to the threshold for activating Balance Mode 1, then proceed to step 5. Step 5: Calculate the difference in average SOC between the two battery groups. If the difference is greater than the threshold for activating Equalization Mode 4, then activate Equalization Mode 4 to perform equalization; otherwise, the equalization process ends.

[0025] As a further limitation of the present invention, the invention is characterized in that: in the multi-inductor hierarchical topology, L1 and L2 are the intra-group balancing inductors of battery group 1 and battery group 2, respectively, and L3-L5 are the inter-group balancing inductors of battery groups; the MOS transistor, the diode, and the solid-state relay are used to control the triggering of different balancing modes.

[0026] As a further limitation of the present invention, the equalization mode 1 is used to achieve equalization among different battery cells within a battery group; the equalization mode 1 includes three modes: energy storage mode, energy release mode, and static mode; in the energy storage mode, the battery with the highest SOC in the group charges the equalization inductor within the group; in the energy release mode, the equalization inductor within the group charges the battery with the lowest SOC in the group; in the static mode, the inductor current drops to zero and all MOSFETs are in the off state.

[0027] As a further limitation of the present invention, the balancing mode 2 is used to achieve balancing of the battery pack as a whole with the individual battery cells.

[0028] As a further limitation of the present invention, the balancing mode 3 is used to achieve balancing of the battery cells on the battery pack as a whole.

[0029] As a further limitation of the present invention, it is characterized in that the balancing mode 4 is performed between the two battery groups.

[0030] In this invention, an active balancing system is designed using a battery pack consisting of eight lithium batteries as an example. The eight lithium batteries are divided into two battery groups: B1-B4 form battery group 1, and B5-B8 form battery group 2. The designed active balancing topology is as follows: Figure 1 As shown.

[0031] In the active balancing topology, the inductor, as a key energy storage component, uses pulse width modulation (PWM) technology to control the switching states of MOSFETs and solid-state relays. By utilizing the mechanism of mutual conversion between electrical energy and magnetic energy, it accurately and efficiently completes the energy transfer between lithium batteries, ensuring the stable performance and reliable safety of the entire lithium battery pack.

[0032] By employing different switching transistors and relay control strategies, direct cell-to-cell, battery pack-to-cell, cell-to-battery pack, and battery group-to-battery group balancing can be achieved. Correspondingly, this balancing topology has four balancing modes.

[0033] (1) Equilibrium Mode 1: Direct Monomer-Monomer Assume that in battery group 1, the battery with the highest SOC is B1 and the battery with the lowest SOC is B4. In battery group 2, the battery with the highest SOC is B8 and the battery with the lowest SOC is B7.

[0034] The active topology balancing process can be divided into the following three modes: 1) Energy storage mode: Close MOSFETs M1, M7, M14, and M20 and solid-state relays K1 and K4. B1, D1, M1, K1, L1, D7, and M7, and B8, D14, M14, K4, L2, D20, and M20 respectively form two current loops, such as... Figure 2a As shown. B1 and B8 start charging L1 and L2 respectively. The current in the two circuits increases linearly from zero. The electrical energy is converted into magnetic field energy through inductor excitation and stored in the two inductors. The circuit current i(t) in the energy storage mode is shown in formula (1).

[0035] (1) In the formula: V i --Voltage of the discharging battery T -- Equilibrium period D -- MOS conduction duty cycle When t=DT, the loop current reaches its maximum value I. max .

[0036] (2) 2) Energy release mode: like Figure 2b As shown, at time DT, M1, M7, and M20 are off, while M5, M9, M18, and M14 are on. The inductor current of L1 freewheels through M5, D5, M9, and D9, and energy is transferred to B4, causing the inductor current to gradually decrease.

[0037] The formula for inductor current in the energy release mode is: (3) In the formula: V j --Voltage of the rechargeable battery When t=t off At that time, t off At the end of the energy release mode, all the energy in the inductor is released, and the inductor current drops to 0.

[0038] The principle of battery pack 2 in the equilibrium energy release mode is similar to that of battery pack 1.

[0039] 3) Static mode When the inductor current drops to zero and all MOSFETs are off, the equalization topology is in a current-free static mode because there is no connected energy transfer path in the circuit, until the control signal of the next equalization cycle triggers a new energy transfer process.

[0040] The inductor current variation curve in equalization mode 1 is as follows: Figure 2c As shown.

[0041] (2) Balanced mode 2: Battery pack as a whole - individual cells In actual operation scenarios of lithium battery packs, inconsistencies are usually caused by individual extreme single cells. Assuming the battery pack is in the process of discharging, the state of charge (SOC) of B6 is much lower than that of other cells. If the balancing speed of B6 is not accelerated, B6 is prone to over-discharge.

[0042] The equalization circuit of this invention operates in discontinuous conduction mode and needs to satisfy: (4) (5) According to equation (5), as the number of discharged batteries increases, the value of D must be reduced to ensure that the balancing circuit operates in discontinuous conduction mode. Correspondingly, the amount of electricity released by a single lithium battery in one balancing cycle decreases. However, due to the increase in the number of lithium batteries in the balancing discharge, the overall discharge capacity increases, and the amount of electricity charged into the balancing charging lithium batteries increases, thereby accelerating the balancing speed. Furthermore, the more batteries in the battery pack and the smaller the value of D, the faster the SOC of the balancing charging battery increases.

[0043] In Equalization Mode 2, the equalization process is also divided into energy storage mode, energy release mode, and static mode. In energy storage mode, M1, M20, K3, and K5 are closed, and the eight lithium batteries discharge as a whole. In energy release mode, M13, M17, and K5 are closed, transferring energy to B6. A schematic diagram of the equalization process is shown below. Figure 2d As shown, the red curve represents the energy storage mode current path, and the green curve represents the energy release mode current path.

[0044] The current waveform of inductor L3 in the active balancing topology is as follows: Figure 2e As shown, the balancing system is currently in a battery pack-to-cell balancing state. Due to the large number of cells participating in the balancing discharge, the duty cycle D decreases accordingly. This parameter change causes the inductor current waveform to exhibit a short rise time, thus maintaining the balancing discharge current of the eight lithium batteries at a low level. In contrast, the fall time of the inductor current waveform is significantly prolonged, allowing B6 to obtain a larger balancing charging current. In this way, during the overall discharge process of the battery pack, the discharge current of B6 can be effectively reduced, thereby slowing down its SOC decline rate and preventing it from falling into an over-discharge state.

[0045] (3) Balanced mode 3: single cell - battery pack as a whole If, during the charging process, the SOC of B1 is much higher than that of other batteries, and the balancing speed of B1 is not accelerated, B1 is prone to overcharging.

[0046] Similarly, according to equation (5), it can be deduced that as the number of rechargeable batteries increases, the D value needs to be increased so that the amount of electricity released by the equalized discharge lithium battery in one equalization cycle increases.

[0047] In equalization mode 3, the equalization process is also divided into energy storage mode, energy release mode, and static mode. In the energy storage mode, M1, M7, K3, K2, and K6 are closed. In the energy release mode, M6, M15, K2, and K6 are closed to transfer energy to the battery pack. A schematic diagram of the equalization process is shown below. Figure 2f As shown, the red curve represents the energy storage mode current path, and the green curve represents the energy release mode current path.

[0048] The inductor current variation curve in equalization mode 3 is as follows: Figure 2g As shown in the waveform diagram, the equalization charging current of each lithium battery is relatively small in this equalization mode, while the equalization discharging current of battery cell B1 is relatively large. This helps to reduce the charging current of B1, thereby effectively avoiding overcharging.

[0049] (4) Balancing Mode 4: Battery Group - Battery Group After the individual cells within each of the two battery groups have been balanced, the balancing process between the battery groups is initiated. The two battery groups are treated as two separate cells for overall balancing. First, K2, K3, and K7 are closed. In the energy storage mode, M1 and M10 are closed, and in the energy release mode, M16 and M15 are closed. A schematic diagram of the balancing process is shown below. Figure 2h As shown, the red curve represents the equalization discharge current path of battery pack 1, and the green curve represents the equalization charging current path of battery pack 2. The inductor current variation curve for equalization mode 4 is shown below. Figure 2i As shown.

[0050] Active balancing variables are core parameters used to quantify the differences between individual cells in a battery pack, trigger balancing actions, and optimize energy transfer strategies. Appropriate balancing variables can accurately reflect the inconsistencies among lithium batteries in a lithium battery pack and precisely identify the cells requiring balancing, thereby achieving efficient energy transfer and ensuring consistency among the individual cells. Furthermore, suitable balancing variables help optimize balancing control strategies, reduce unnecessary balancing operations, and thus lower energy losses during the balancing process. The open-circuit voltage, operating voltage, and state of charge (SOC) of a lithium battery can all reflect inconsistencies within the lithium battery pack. Given that the fundamental goal of active lithium battery balancing is to ensure consistent SOC among lithium batteries operating in series, this embodiment of the invention selects SOC as the balancing variable, which most accurately guarantees consistent SOC among the lithium batteries after balancing.

[0051] To formulate a balanced control strategy, it is necessary to further determine the start and stop threshold conditions for active balancing. When the SOC inconsistency between individual lithium batteries is less than or equal to the set balancing threshold, it indicates that the consistency between individual batteries is good, and active balancing is not required. When the inconsistency between individual lithium batteries exceeds the set threshold, it indicates that active balancing is needed to improve the consistency of lithium batteries.

[0052] SOC range is one of the quantitative indicators for judging the consistency of SOC in lithium batteries. SOC range characterizes the difference in SOC between the highest and lowest SOC lithium batteries in a lithium battery group, as shown in Equation 6. Compared to variance, which requires statistical analysis of the overall SOC dispersion of the lithium battery group, range focuses on the inconsistencies between extreme lithium batteries. Using range as an evaluation criterion can quickly identify inconsistent and abnormal individual cells. Furthermore, range calculation is simple, avoiding the computational burden caused by complex mathematical operations. Therefore, in this embodiment of the invention, the SOC range R of each lithium battery in the lithium battery group is selected as the condition for enabling or disabling equalization mode 1.

[0053] (6) In the formula: SOC MAX --Maximum SOC value in lithium battery group SOC MIN --Minimum SOC value in lithium battery group Balanced Mode 2 selects the average state of charge (SOC) of the battery pack. AVG With the minimum state of charge (SOC) in the battery pack MIN The difference serves as the activation threshold. The maximum state of charge (SOC) value in the battery pack. MAX With SOC AVG The difference is used as the threshold for activating equilibrium mode 3. Equilibrium mode 4 between lithium battery groups uses the difference in the average SOC of each lithium battery in the two lithium battery groups as the equilibrium activation / deactivation condition.

[0054] The process of the multi-mode active balancing control strategy is as follows: Figure 3 As shown. The specific steps are as follows: Step 1: Determine whether the battery pack is charging or discharging. If the battery pack is discharging, proceed to Step 2; if the battery pack is charging, proceed to Step 3. Step 2: Calculate the average SOC and minimum SOC for each battery group, denoted as SOC. AVG and SOC MIN Determine the SOC of each battery group AVG With SOC MINIf the difference is greater than the threshold for enabling Balanced Mode 2, then enable Balanced Mode 2; otherwise, proceed to step 4. Step 3: Calculate the average SOC and maximum SOC for each battery group, denoted as SOC. AVG and SOC MAX Determine the SOC of each battery group MAX With SOC AVG If the difference is greater than the threshold for enabling Balanced Mode 3, then enable Balanced Mode 3; otherwise, proceed to step 4. Step 4: Determine the SOC range of each battery group. The SOC range is the difference between the maximum SOC and the minimum SOC in the battery group. Compare the SOC range with the set threshold for activating Balance Mode 1. If the SOC range is greater than the threshold for activating Balance Mode 1, then activate Balance Mode 1. If the SOC range of both battery groups is less than or equal to the threshold for activating Balance Mode 1, then proceed to step 5. Step 5: Calculate the difference in average SOC between the two battery groups. If the difference is greater than the threshold for activating Equalization Mode 4, then activate Equalization Mode 4 to perform equalization; otherwise, the equalization process ends.

[0055] An active balancing system was built using Matlab / Simulink software for simulation to verify the previously designed active balancing topology and balancing control strategy.

[0056] Discharge process equalization verification: The initial SOCs of the eight lithium-ion batteries in the series-connected battery pack were set to 33%, 33.5%, 32.5%, 32%, 34%, 24%, 28.6%, and 31%, respectively, and the battery pack discharge current was 1A. The SOC change curves of the eight lithium-ion batteries during the equalization process are shown below. Figure 4a As shown.

[0057] At the start of balancing, because B6's SOC is relatively low compared to other batteries, it is prone to over-discharge during battery pack discharge. Therefore, during the 0s-500s period, the active balancing system operates in balancing mode 2. Due to the presence of balancing charge and discharge current, B6's SOC decreases less rapidly than the other batteries. During the 500s-640s period, the SOC... AVGSince the SOC difference between battery group 1 and battery group B6 is less than the threshold for balancing mode 2, both battery groups perform intra-group balancing separately. Between 640s and 1280s, by 640s, the SOC within battery group 1 has reached consistency, and battery group 2 performs intra-group balancing independently. After 1280s, balancing mode 4 is activated to begin balancing between the two battery groups. Balancing ends at 1500s, with the SOCs of the eight lithium batteries being 10.04%, 10.08%, 9.63%, 9.58%, 9.58%, 9.11%, 9.08%, and 9.56%, respectively.

[0058] Figure 4b The figure shows the SOC variation curves of eight lithium-ion batteries using a traditional single-inductor-based active balancing scheme. Experimental results show that this scheme requires 2040 seconds to achieve battery balancing. At the end of balancing, the SOCs of the eight lithium-ion batteries are 2.43%, 2.44%, 2.44%, 2.43%, 2.44%, 1.44%, 1.44%, and 2.44%, respectively, indicating that over-discharge is imminent.

[0059] Comparison of the two sets of experimental data shows that the equalization scheme designed in this invention can significantly improve the equalization speed of the battery pack, and the equalization time is reduced by 26% compared with the traditional single-inductor active equalization scheme, which can effectively avoid the occurrence of over-discharge.

[0060] Charging process equalization verification: The initial SOC of the lithium battery was set to 79%, 80%, 78.5%, 77.5%, 81%, 89%, 80.5%, and 79.5%, with a total charging current of 1A. The SOC change curve of the lithium battery during the equalization process is shown below. Figure 4c As shown.

[0061] When equalization is activated, because the B6 SOC is relatively high compared to other batteries, it is prone to overcharging during battery pack charging. Therefore, from 0s to 610s, the active equalization system operates in equalization mode 3. From 610s to 930s, equalization is performed within each battery group. After 930s, equalization mode 4 is activated to equalize between the two battery groups until equalization ends at 1100s. The SOCs of the eight lithium batteries are 95.44%, 95.44%, 95.07%, 94.94%, 95.8%, 95.99%, 95.49%, and 95.49%, respectively.

[0062] Figure 4d The figure shows the SOC variation curves of 8 lithium batteries using a traditional equalization scheme. This scheme requires 1320 seconds to achieve equalization among the batteries, and the SOCs of the 8 lithium batteries are 98.23%, 98.33%, 98.23%, 98.24%, 99.23%, 99.23%, 98.83%, and 98.23%, respectively.

[0063] Comparison of the two sets of experimental data shows that the equalization time during charging is reduced by 17% compared to the traditional equalization scheme, which can effectively avoid overcharging.

[0064] A second aspect of the present invention provides a multi-mode active balancing device for a series lithium battery pack based on a multi-inductor hierarchical topology, the device being used to implement the method steps of any one of claims 1-6.

[0065] A third aspect of the present invention provides a computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program that can be executed by a processor to implement the method as described in any one of claims 1-6.

[0066] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A multi-mode active balancing method for series lithium battery packs based on a multi-inductor hierarchical topology, wherein the series lithium battery packs are denoted as B1~B8, and B1~B4 constitute battery group 1, and B5~B8 constitute battery group 2; the multi-inductor hierarchical topology includes the series lithium battery packs, intra-group balancing inductors L1~L2, inter-group balancing inductors L3~L5, MOSFETs M1-M20, diodes D1-D20, and solid-state relays K1-K7; the method includes four balancing modes, wherein balancing mode 1 is direct cell-to-cell, balancing mode 2 is battery pack-to-cell, balancing mode 3 is cell-to-battery pack, and balancing mode 4 is battery group-to-battery group, characterized in that... Includes the following steps: Step 1: Determine whether the battery pack is charging or discharging. If the battery pack is discharging, proceed to Step 2; if the battery pack is charging, proceed to Step 3. Step 2: Calculate the average SOC and minimum SOC for each battery group, denoted as SOC. AVG and SOC MIN Determine the SOC of each battery group AVG With SOC MIN If the difference is greater than the threshold for enabling Balanced Mode 2, then Balanced Mode 2 is enabled. Conversely, proceed to step 4; Step 3: Calculate the average SOC and maximum SOC for each battery group, denoted as SOC. AVG and SOC MAX Determine the SOC of each battery group MAX With SOC AVG If the difference is greater than the threshold for enabling Balanced Mode 3, then Balanced Mode 3 is enabled. Conversely, proceed to step 4; Step 4: Determine the SOC range of each battery group. The SOC range is the difference between the maximum SOC and the minimum SOC in the battery group. Compare the SOC range with the set threshold for activating Balance Mode 1. If the SOC range is greater than the threshold for activating Balance Mode 1, then activate Balance Mode 1. If the SOC range of both battery groups is less than or equal to the threshold for activating Balance Mode 1, then proceed to step 5. Step 5: Calculate the difference in average SOC between the two battery groups. If the difference is greater than the threshold for activating Equalization Mode 4, then activate Equalization Mode 4 to perform equalization; otherwise, the equalization process ends.

2. The method according to claim 1, characterized in that: In the multi-inductor hierarchical topology, L1 and L2 are the intra-group balancing inductors of battery group 1 and battery group 2, respectively, and L3-L5 are the inter-group balancing inductors of battery groups; the MOSFET, the diode, and the solid-state relay are used to control the triggering of different balancing modes.

3. The method according to claim 1, characterized in that, The equalization mode 1 is used to achieve equalization among different battery cells within the battery group; the equalization mode 1 includes three modes: energy storage mode, energy release mode, and rest mode; in the energy storage mode, the battery with the highest SOC in the group charges the equalization inductor in the group; in the energy release mode, the equalization inductor in the group charges the battery with the lowest SOC in the group; in the rest mode, the inductor current drops to zero and all MOSFETs are in the off state.

4. The method according to claim 1, characterized in that, The equalization mode 2 is used to achieve equalization of the battery pack as a whole with respect to individual battery cells.

5. The method according to claim 1, characterized in that, The equalization mode 3 is used to achieve equalization of the battery cells to the overall battery pack.

6. The method according to claim 1, characterized in that, In the equalization mode 4, equalization is performed between the two battery groups.

7. A multi-mode active balancing device for a series lithium battery pack based on a multi-inductor hierarchical topology, the device being used to implement the steps of the method described in any one of claims 1-6.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that can be executed by a processor to implement the method as described in any one of claims 1-6.

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