A Multi-Threshold Active and Passive Equalization Control Method and System for Lithium Batteries

Abstract

The present invention belongs to the field of battery state of health monitoring, and discloses a multi-threshold active and passive equalization control method and system for lithium batteries. By collecting the current, voltage and SOC data of lithium batteries in real time and combining with a multi-threshold judgment mechanism, this method can more accurately reflect the dynamic changes of the battery pack, trigger equalization operations in a timely manner, and effectively avoid over-equalization or under-equalization problems that may be caused by a single-threshold strategy. At the same time, the intelligent selection of active and passive equalization strategies further improves the equalization efficiency and effect, ensures that the voltage difference and SOC difference between individual batteries in the battery pack are kept within a reasonable range, thereby extending the service life of the battery pack, improving the overall performance, and reducing potential safety hazards. Using this method can provide a strong guarantee for the stable operation of the energy storage system.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery state - of - health monitoring, and particularly relates to a multi - threshold active and passive equalization control method and system for lithium batteries. Background Art

[0002] In an energy storage system, a battery pack formed by connecting multiple single - cell batteries in series or in parallel is usually used to provide the required electrical energy. Due to factors such as differences in the manufacturing process, changes in the usage environment, and the aging of the batteries themselves, the individual single - cell batteries in the battery pack often exhibit varying degrees of performance differences, such as inconsistencies in parameters such as charge capacity, voltage, and internal resistance. Due to the existence of the above - mentioned differences, the overall performance of the battery pack will decline, thereby affecting the service life of the battery pack and even potentially causing safety hazards.

[0003] In response to the above problems, researchers in the current field have proposed battery equalization technologies. Existing equalization technologies can better solve the problem of performance differences among multiple battery units in a battery pack. However, existing equalization technologies have certain limitations, specifically manifested as follows: Existing equalization means usually select a single threshold as the criterion for the equalization strategy. This will lead to the inability to adapt to the dynamic changes of the battery pack. During the use of the battery pack, due to the initial differences between battery cells, different working environments, and the number of usage times, the performance of the battery pack will change. The single - threshold equalization strategy often judges whether equalization is required based on a fixed threshold, which cannot accurately reflect the dynamic changes of the battery pack during actual use. When the performance of the battery pack changes significantly, the single - threshold strategy cannot trigger the equalization operation in a timely manner, resulting in a decline in the performance of the battery pack. Moreover, it is also prone to causing problems of over - equalization or under - equalization: When setting the threshold for the single - threshold equalization strategy, various factors such as the initial differences of battery cells and the working environment often need to be considered. However, since these factors may change during actual use, the set threshold cannot accurately reflect the actual situation of the battery pack. This may lead to triggering over - equalization operations in some cases, wasting energy and accelerating battery aging; while in other cases, it may cause under - equalization, unable to effectively improve the performance of the battery pack.

[0004] It can be seen that existing battery equalization measures, due to the adoption of the single - threshold equalization strategy, cannot adapt to the dynamic changes of the battery pack, thereby resulting in poor equalization effect and low equalization efficiency. Summary of the Invention

[0005] The present invention provides a multi - threshold active and passive equalization control method and system for lithium batteries to solve the technical problem that existing battery equalization measures, due to the adoption of the single - threshold equalization strategy, cannot adapt to the dynamic changes of the battery pack, thereby resulting in poor equalization effect and low equalization efficiency.

[0006] To achieve the above - mentioned purpose, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a multi-threshold active and passive balancing control method for a lithium battery, including:

[0008] Data acquisition process: Collect the current value of the lithium battery and the voltage values corresponding to each single cell in the lithium battery. At the same time, based on the current value of the lithium battery and the voltage values corresponding to each single cell, obtain the SOC corresponding to each single cell;

[0009] First judgment process: Judge the voltage values corresponding to each single cell against the first voltage threshold range respectively, and at the same time judge the SOC corresponding to each single cell against the first SOC threshold range respectively, to obtain a first judgment result;

[0010] The specific steps of the first judgment process are as follows:

[0011] Judge the voltage values corresponding to each single cell against the first voltage threshold range respectively. If the voltage values corresponding to all single cells are within the first voltage threshold range, the first voltage judgment condition is satisfied;

[0012] Judge the SOC corresponding to each single cell against the first SOC threshold range respectively. If the SOC corresponding to all single cells are within the first SOC threshold range, the first SOC judgment condition is satisfied;

[0013] If the first voltage judgment condition or / and the first SOC judgment condition is satisfied, output a passive balancing instruction as the first judgment result;

[0014] Otherwise, output an active balancing instruction as the first judgment result;

[0015] Strategy screening process: Screen an active balancing strategy or a passive balancing strategy based on the first judgment result;

[0016] Balancing process: Use the active balancing strategy or the passive balancing strategy to balance each single cell;

[0017] Circulation process: Repeat the data acquisition process, the first judgment process, the strategy screening process, and the balancing process until the voltage difference between the corresponding voltages of every two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between the corresponding SOCs of every two adjacent single cells is within the SOC difference threshold range.

[0018] A further improvement of the present invention is that in the data acquisition process, through the established second-order equivalent circuit model of the lithium battery, combined with the current value of the lithium battery and the voltage values corresponding to each single cell, calculate the SOC corresponding to each single cell; wherein, obtain the state equation and output equation of the second-order RC model according to the second-order equivalent circuit model;

[0019] The state equation of the second-order RC model is:

[0020] = +

[0021] The output equation of the second-order RC model is as follows:

[0022]

[0023] Wherein, and are the ohmic internal resistance, the electrochemical and concentration polarization resistances respectively, and are the electrochemical and concentration polarization capacitances respectively; and are the terminal voltages of and at the k-th moment respectively, and are the terminal voltages of and at the (k + 1)-th moment respectively, is the voltage value corresponding to the single battery at the k-th moment, is the open-circuit voltage of the battery; is the current value of the lithium battery; T is the sampling interval; k is the discrete time; is the current value at the k-th moment;

[0024] Based on the state equation and output equation of the second-order RC model, the conversion equation is obtained as follows:

[0025]

[0026] Wherein, is the process noise, and the process noise adopts Gaussian white noise with a mean of zero and a variance of Q; is the observation noise, and the observation noise adopts Gaussian white noise with a mean of zero and a variance of R; is the state transition matrix, is the control input matrix, is the observation matrix, is the feedforward matrix; and are the system state vector and the system input respectively, and are specifically expressed as follows:

[0027] = =

[0028] = =-

[0029] = =

[0030] Among them, , ; represents the maximum battery capacity;

[0031] The extended Kalman filter algorithm is used to solve the conversion equation, and the SOC corresponding to each single battery is calculated.

[0032] A further improvement of the present invention lies in that the specific steps of the strategy screening process are as follows:

[0033] If the passive equalization instruction is received as the first judgment result, a passive equalization strategy mainly based on passive equalization and supplemented by active equalization is adopted;

[0034] If the active equalization instruction is received as the first judgment result, an active equalization strategy mainly based on active equalization and supplemented by passive equalization is adopted.

[0035] A further improvement of the present invention lies in that when the passive equalization strategy is adopted, the duty ratio μ1 of active equalization is 10% - 20%; the duty ratio μ2 of passive equalization is 1 - μ1.

[0036] A further improvement of the present invention lies in that when the active equalization strategy is adopted, the voltage values corresponding to each single battery are respectively judged against the second voltage threshold range. If the voltage values corresponding to each single battery are all within the second voltage threshold range, the second voltage judgment condition is satisfied;

[0037] At the same time, the SOCs corresponding to each single battery are respectively judged against the second SOC threshold range. If the SOCs corresponding to each single battery are all within the second SOC threshold range, the second SOC judgment condition is satisfied;

[0038] If the second voltage judgment condition or / and the second SOC judgment condition are satisfied, it is judged whether the voltage difference between two adjacent single batteries is greater than the first voltage difference threshold; if so, the duty ratio μ1 of active equalization is ; the duty ratio μ2 of passive equalization is 1 - μ1; if not, the duty ratio μ1 of active equalization is ; the duty ratio μ2 of passive equalization is 1 - μ1;

[0039] If neither the second voltage judgment condition nor the second SOC judgment condition is satisfied, it is judged whether the voltage difference between two adjacent single batteries is greater than the second voltage difference threshold; if so, the duty ratio μ1 of active equalization is ​; the duty cycle μ2 of the passive equalization is 1 - μ1; otherwise, the duty cycle μ1 of the active equalization is ; the duty cycle μ2 of the passive equalization is 1 - μ1;

[0040] In the formula, is the voltage difference between two adjacent single cells.

[0041] A further improvement of the present invention lies in that the specific steps of the equalization process are as follows:

[0042] When adopting the active equalization strategy, based on the active equalization strategy, the SOC corresponding to each single cell, and the voltage difference corresponding to every two adjacent single cells, the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the active equalization strategy are obtained;

[0043] Based on the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the active equalization strategy, an active equalization process and a passive equalization process are performed on the lithium battery;

[0044] When adopting the passive equalization strategy, based on the passive equalization strategy, the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the passive equalization strategy are obtained;

[0045] Based on the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the passive equalization strategy, an active equalization process and a passive equalization process are performed on the lithium battery;

[0046] The active equalization process is: transferring energy from the high-energy single cells in the lithium battery to the low-energy single cells;

[0047] The passive equalization process is: consuming the energy of the high-energy single cells in the lithium battery by using a dissipative resistor;

[0048] Among them, the high-energy single cells refer to those with higher voltage or SOC between two adjacent single cells; the low-energy single cells refer to those with lower voltage or SOC between two adjacent single cells.

[0049] In the second aspect, the present invention provides a multi-threshold active and passive equalization control system for a lithium battery, including:

[0050] A data acquisition module for performing a data acquisition process; the data acquisition process: collecting the current value of the lithium battery and the voltage values corresponding to each single cell in the lithium battery, and at the same time obtaining the SOC corresponding to each single cell based on the current value of the lithium battery and the voltage values corresponding to each single cell;

[0051] The first judgment module is used to execute the first judgment process; the first judgment process: judge the voltage values corresponding to each single battery respectively against the first voltage threshold range, and at the same time judge the SOC corresponding to each single battery respectively against the first SOC threshold range to obtain the first judgment result;

[0052] The specific steps of the first judgment process are as follows:

[0053] Judge the voltage values corresponding to each single battery respectively against the first voltage threshold range. If all the voltage values corresponding to each single battery are within the first voltage threshold range, the first voltage judgment condition is satisfied;

[0054] Judge the SOC corresponding to each single battery respectively against the first SOC threshold range. If all the SOC corresponding to each single battery are within the first SOC threshold range, the first SOC judgment condition is satisfied;

[0055] If the first voltage judgment condition or / and the first SOC judgment condition is satisfied, output a passive equalization instruction as the first judgment result;

[0056] Otherwise, output an active equalization instruction as the first judgment result;

[0057] The strategy screening module is used to execute the strategy screening process; the strategy screening process: screen the active equalization strategy or the passive equalization strategy based on the first judgment result;

[0058] The battery equalization module is used to execute the equalization process; the equalization process: perform equalization on each single battery by using the active equalization strategy or the passive equalization strategy;

[0059] The loop module is used to execute the loop process; the loop process: repeatedly execute the data acquisition process, the first judgment process, the strategy screening process and the equalization process until the voltage difference between every two adjacent single batteries is within the voltage difference threshold range, or / and the SOC difference between every two adjacent single batteries is within the SOC difference threshold range.

[0060] A further improvement of the present invention is that the battery equalization module includes a first switching tube and a second switching tube; the conduction pulses corresponding to the first switching tube and the second switching tube are a pair of complementary pulses; wherein, when the first switching tube is conducting, the lithium battery multi-threshold active and passive equalization control system performs the active equalization process; when the second switching tube is conducting, the lithium battery multi-threshold active and passive equalization control system performs the passive equalization process.

[0061] A further improvement of the present invention is that it further includes:

[0062] The battery protection module is used to compare the current operating data of the single battery obtained by monitoring with the operating data under normal conditions, and protect the single battery according to the comparison result; the protection process includes an undervoltage protection process and a current limiting protection process.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] The present invention provides a multi-threshold active and passive equalization control method for lithium batteries. By collecting the current, voltage and SOC data of lithium batteries in real time and combining with a multi-threshold judgment mechanism, this method can more accurately reflect the dynamic changes of the battery pack, trigger the equalization operation in time, and effectively avoid the over-equalization or under-equalization problems that may be caused by the single-threshold strategy; at the same time, the intelligent selection of the active equalization and passive equalization strategies further improves the equalization efficiency and effect, ensures that the voltage difference and SOC difference between the single batteries in the battery pack are kept within a reasonable range, thereby extending the service life of the battery pack, improving the overall performance, and reducing the safety hazards. Using this method can provide a strong guarantee for the stable operation of the energy storage system.

[0065] Preferably, in the present invention, by establishing a second-order equivalent circuit model of the lithium battery and combining with the extended Kalman filter algorithm, the SOC of each single battery can be calculated more accurately; this method improves the accuracy of SOC estimation, provides more reliable data support for subsequent equalization control, and thus enhances the accuracy and effectiveness of equalization control.

[0066] Preferably, in the present invention, by setting the first voltage threshold range and the first SOC threshold range and making judgments based on these thresholds, the dynamic changes during the use of the battery pack can be flexibly adapted; this method ensures the timeliness and accuracy of the equalization operation, avoids the problems of over-equalization or under-equalization, and improves the performance and safety of the battery pack.

[0067] Preferably, in the present invention, the active equalization strategy or the passive equalization strategy is intelligently selected according to the first judgment result, or the two strategies are used in combination; this flexible strategy selection mechanism helps to improve the efficiency and effect of equalization control, ensures the consistency of the voltage and SOC between the single batteries in the battery pack, and thus extends the service life of the battery pack.

[0068] Preferably, in the present invention, when the passive equalization strategy is adopted, by setting the duty cycles of the active equalization and the passive equalization, the equalization process can be more finely controlled; the setting of this duty cycle helps to balance the equalization efficiency and energy consumption and improve the overall performance of the battery pack.

[0069] Preferably, in the present invention, when adopting the active equalization strategy, by presetting the second voltage threshold range and the second SOC threshold range, and combining the voltage difference between two adjacent single cells for judgment, the triggering timing and equalization intensity of the equalization operation can be controlled more precisely; this further improves the accuracy and effectiveness of the equalization control, helps to extend the service life of the battery pack and improve the overall performance.

[0070] Preferably, in the present invention, the specific steps of the equalization process include the implementation methods of active equalization and passive equalization; by defining high-energy and low-energy single cells, as well as the specific equalization operation process, the feasibility and effectiveness of the equalization control are ensured; this method helps to achieve the rapid equalization of the voltage and SOC between single cells in the battery pack, improving the performance and safety of the battery pack.

[0071] The present invention provides a lithium battery multi-threshold active and passive equalization control system. By integrating functional modules such as data acquisition, multi-threshold judgment, strategy screening, equalization execution, and loop control, the system realizes the dynamic monitoring and intelligent equalization of the performance of the battery pack. Using this system can accurately reflect the actual state changes of the battery pack, timely adopt appropriate equalization strategies, and effectively avoid the limitations of single-threshold equalization strategies, such as over-equalization, under-equalization and other problems; at the same time, the combined use of active and passive equalization strategies further improves the equalization efficiency and effect, ensures the consistency of the voltage and SOC between single cells in the battery pack, thereby extending the service life of the battery pack, improving the overall performance, reducing potential safety hazards, and providing a strong guarantee for the stable operation of the energy storage system.

[0072] Preferably, in the present invention, through the complementary pulse control of the first switch tube and the second switch tube, the switching between active equalization and passive equalization is realized, simplifying the logic of the equalization control; moreover, the clear division of labor of the switch tubes makes the equalization process more stable and reliable, avoiding the equalization failure caused by chaotic control logic.

[0073] Preferably, in the present invention, a battery protection module is introduced. The battery protection module can real-time monitor the operation data of single cells, compare it with the data under normal conditions, timely detect abnormal situations and take protection measures; through processes such as under-voltage protection and current-limiting protection, effectively avoid the damage of the battery due to over-discharge, over-current and other reasons, reducing the risk of battery failure. Description of the Drawings

[0074] Figure 1 It is a flowchart of a lithium battery multi-threshold active and passive equalization control method provided by the present invention;

[0075] Figure 2 It is a schematic diagram of a lithium battery multi-threshold active and passive equalization control method provided by an embodiment of the present invention;

[0076] Figure 3 This is the circuit schematic diagram of the battery equalization module of the lithium battery multi-threshold active and passive equalization control system provided by the embodiments of the present invention, where (a) is the active equalization circuit schematic diagram; (b) is the passive equalization circuit schematic diagram;

[0077] Figure 4 This is the circuit schematic diagram of the ADC acquisition circuit provided by the embodiments of the present invention;

[0078] Figure 5 This is the circuit schematic diagram of the current measurement circuit provided by the embodiments of the present invention;

[0079] Figure 6 This is the OCV-SOC characteristic curve graph of the lithium battery provided by the embodiments of the present invention;

[0080] Figure 7 This is the curve graph of the OCV change rate within the unit SOC provided by the embodiments of the present invention;

[0081] Figure 8 This is the curve graph of the voltage change rate provided by the embodiments of the present invention;

[0082] Figure 9 This is the second-order equivalent circuit model diagram of the lithium battery provided by the embodiments of the present invention;

[0083] Figure 10 This is the flowchart of a lithium battery multi-threshold active and passive equalization control method provided by the embodiments of the present invention;

[0084] Figure 11 This is the equalization effect diagram of the lithium battery containing 12 single cells provided by the embodiments of the present invention;

[0085] Figure 12 This is the structural schematic diagram of a lithium battery multi-threshold active and passive equalization control system provided by the present invention. Detailed implementation manners

[0086] To further understand the content of the present invention, the following describes the present invention in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention rather than limiting it.

[0087] As Figure 1 shown, this embodiment provides a lithium battery multi-threshold active and passive equalization control method, including:

[0088] Data acquisition process: Collect the current value of the lithium battery and the voltage values corresponding to each single cell in the lithium battery, and at the same time obtain the SOC corresponding to each single cell based on the current value of the lithium battery and the voltage values corresponding to each single cell;

[0089] First judgment process: Compare the voltage values corresponding to each single battery with the first voltage threshold range respectively, and at the same time compare the SOC corresponding to each single battery with the first SOC threshold range respectively to obtain the first judgment result;

[0090] The specific steps of the first judgment process are as follows:

[0091] Compare the voltage values corresponding to each single battery with the first voltage threshold range respectively. If all the voltage values corresponding to each single battery are within the first voltage threshold range, the first voltage judgment condition is satisfied;

[0092] Compare the SOC corresponding to each single battery with the first SOC threshold range respectively. If all the SOC corresponding to each single battery are within the first SOC threshold range, the first SOC judgment condition is satisfied;

[0093] If the first voltage judgment condition or / and the first SOC judgment condition is satisfied, output the passive equalization instruction as the first judgment result;

[0094] Otherwise, output the active equalization instruction as the first judgment result;

[0095] Strategy screening process: Screen the active equalization strategy or the passive equalization strategy based on the first judgment result;

[0096] Equalization process: Use the active equalization strategy or the passive equalization strategy to equalize each single battery;

[0097] Circulation process: Repeat the data acquisition process, the first judgment process, the strategy screening process and the equalization process until the voltage difference between every two adjacent single batteries is within the voltage difference threshold range, or / and the SOC difference between every two adjacent single batteries is within the SOC difference threshold range.

[0098] It can be seen that this method can more accurately reflect the dynamic changes of the battery pack by real-time collecting the current, voltage and SOC data of the lithium battery, and combining with the multi-threshold judgment mechanism, timely trigger the equalization operation, effectively avoiding the over-equalization or under-equalization problems that may be caused by the single-threshold strategy; at the same time, the intelligent screening of the active equalization and passive equalization strategies further improves the equalization efficiency and effect, ensuring that the voltage difference and SOC difference between each single battery in the battery pack are kept within a reasonable range, thereby prolonging the service life of the battery pack, improving the overall performance and reducing the safety hazards. Using this method can provide a strong guarantee for the stable operation of the energy storage system.

[0099] The following further explains the equalization method provided in this embodiment with reference to the drawings:

[0100] Now make the following explanations for the following terms:

[0101] SOC (State of Charge), that is, the state of charge, also known as the remaining battery capacity, is used to reflect the remaining capacity of the battery. Numerically, it is defined as the ratio of the remaining capacity to the battery capacity, usually expressed as a percentage.

[0102] Second-order RC model: It is used to describe a circuit model composed of a resistor (R) and a capacitor (C). The resistor and capacitor in the model respectively correspond to different physical characteristics inside the battery, such as charge transfer resistance, diffusion resistance, and the corresponding capacitive effects.

[0103] Duty Cycle refers to the proportion of the high level (or effective level) in a pulse cycle, and it can also be interpreted as the proportion of the time when the circuit is turned on to the total cycle time. The duty cycle calculation formula is: Duty Cycle = Pulse Width / Pulse Period.

[0104] OCV (Open Circuit Voltage), that is, the open circuit voltage, refers to the terminal voltage of the battery in the open circuit state, that is, the potential difference between the positive and negative electrodes of the battery when there is no current passing through.

[0105] HPPC (Hybrid Pulse Power Characterization), that is, hybrid pulse power characterization, is a pulse signal used to test the battery performance. This signal consists of a series of square wave pulses and can simulate the load and charging pulses that the battery may encounter in actual use.

[0106] ADC (Analog-to-Digital Converter), that is, analog-to-digital converter, is an electronic device that converts analog signals (such as continuously changing physical quantities like sound, light, temperature, etc.) into digital signals (such as binary codes composed of 0 and 1).

[0107] DMA (Direct Memory Access) refers to direct memory access. It is a data exchange method that allows certain hardware devices to independently read and write system memory directly without going through the central processing unit.

[0108] Combined Figure 2 and Figure 10 As shown, this embodiment provides a multi-threshold active and passive equalization control method for lithium batteries, including:

[0109] Data acquisition process: Collect the current value of the lithium battery and the voltage values corresponding to each single battery in the lithium battery. At the same time, based on the current value of the lithium battery and the voltage values corresponding to each single battery, obtain the SOC corresponding to each single battery.

[0110] The first judgment process: Compare the voltage values corresponding to each single battery with the range of 3.9V to 4.05V respectively; at the same time, compare the SOC corresponding to each single battery with the range of 20% to 80% respectively to obtain the first judgment result.

[0111] Strategy screening process: Based on the first judgment result, screen an active equalization strategy that mainly uses active equalization and supplemented by passive equalization, or a passive equalization strategy that mainly uses passive equalization and supplemented by active equalization.

[0112] When adopting the passive equalization strategy, the duty cycle μ1 of active equalization is 10% to 20%; the duty cycle μ2 of passive equalization is 1 - μ1.

[0113] When adopting the active equalization strategy, compare the voltage values corresponding to each single battery with the range of 4.05V to 4.2V respectively. If all the voltage values corresponding to each single battery are within the range of 4.05V to 4.2V, then the second voltage judgment condition is satisfied;

[0114] At the same time, compare the SOC corresponding to each single battery with the range of 80% to 100% respectively. If all the SOC corresponding to each single battery are within the range of 80% to 100%, then the second SOC judgment condition is satisfied;

[0115] If the second voltage judgment condition or / and the second SOC judgment condition are satisfied, then judge whether the voltage difference between adjacent single batteries is greater than the first voltage difference threshold; if so, the duty cycle μ1 of active equalization is ; the duty cycle μ2 of passive equalization is 1 - μ1; if not, the duty cycle μ1 of active equalization is ; the duty cycle μ2 of passive equalization is 1 - μ1;

[0116] If both the second voltage judgment condition and the second SOC judgment condition are not satisfied, then judge whether the voltage difference between adjacent single batteries is greater than the second voltage difference threshold; if so, the duty cycle μ1 of active equalization is ; the duty cycle μ2 of passive equalization is 1 - μ1; if not, the duty cycle μ1 of active equalization is ; the duty cycle μ2 of passive equalization is 1 - μ1;

[0117] Wherein, is the voltage difference between adjacent single batteries.

[0118] Equalization process: Equalize each single battery according to the above passive equalization strategy or active equalization strategy.

[0119] Circulation process: Repeat the data acquisition process, the first judgment process, the strategy screening process, and the equalization process until the absolute value of the voltage difference corresponding to every two adjacent single cells is less than 0.01 V, and / or the absolute value of the SOC difference corresponding to every two adjacent single cells is less than 0.1%, then end the circulation process.

[0120] In this embodiment, when the active equalization strategy is adopted, based on the active equalization strategy, the SOC corresponding to each single cell, and the voltage difference corresponding to every two adjacent single cells, obtain the duty ratio of active equalization and the duty ratio of passive equalization corresponding to the active equalization strategy;

[0121] Based on the duty ratio of active equalization and the duty ratio of passive equalization corresponding to the active equalization strategy, perform the active equalization process and the passive equalization process on the lithium battery;

[0122] When the passive equalization strategy is adopted, based on the passive equalization strategy, obtain the duty ratio of active equalization and the duty ratio of passive equalization corresponding to the passive equalization strategy;

[0123] Based on the duty ratio of active equalization and the duty ratio of passive equalization corresponding to the passive equalization strategy, perform the active equalization process and the passive equalization process on the lithium battery;

[0124] The active equalization process is: Transfer the energy of the high-energy single cell in the lithium battery to the low-energy single cell;

[0125] The passive equalization process is: Use a dissipative resistor to consume the energy of the high-energy single cell in the lithium battery;

[0126] Among them, the high-energy single cell refers to the one with a higher voltage or SOC between two adjacent single cells; the low-energy single cell refers to the one with a lower voltage or SOC between two adjacent single cells.

[0127] As Figure 12 shown, in order to implement the above multi-threshold active and passive equalization control method for lithium batteries, design a multi-threshold active and passive equalization control system for lithium batteries, including:

[0128] The data acquisition module is used to execute the data acquisition process; the data acquisition process: collect the current value of the lithium battery and the voltage value corresponding to each single battery in the lithium battery, and at the same time obtain the SOC corresponding to each single battery based on the current value of the lithium battery and the voltage value corresponding to each single battery; the first judgment module is used to execute the first judgment process; the first judgment process: judge the voltage value corresponding to each single battery with the first voltage threshold range respectively, and at the same time judge the SOC corresponding to each single battery with the first SOC threshold range respectively, and obtain the first judgment result; the specific steps of the first judgment process are as follows: judge the voltage value corresponding to each single battery with the first voltage threshold range respectively, if the voltage values corresponding to each single battery are all within the first voltage threshold range, the first voltage judgment condition is satisfied; judge the SOC corresponding to each single battery with the first SOC threshold range respectively, if the SOCs corresponding to each single battery are all within the first SOC threshold range, the first SOC judgment condition is satisfied; if the first voltage judgment condition or / and the first SOC judgment condition is satisfied, output the passive equalization instruction as the first judgment result; otherwise, output the active equalization instruction as the first judgment result; the strategy screening module is used to execute the strategy screening process; the strategy screening process: screen the active equalization strategy or the passive equalization strategy based on the first judgment result; the battery equalization module is used to execute the equalization process; the equalization process: use the active equalization strategy or the passive equalization strategy to equalize each single battery; the loop module is used to execute the loop process; the loop process: repeat the data acquisition process, the first judgment process, the strategy screening process and the equalization process until the voltage difference corresponding to every two adjacent single batteries is within the voltage difference threshold range, or / and the SOC difference corresponding to every two adjacent single batteries is within the SOC difference threshold range.

[0129] This equalization system further includes a battery protection module, which is used to compare the currently monitored operating data of the single battery with the operating data under normal conditions, and protect the single battery according to the comparison result; the protection process includes an undervoltage protection process and a current limiting protection process.

[0130] Based on the lithium battery multi-threshold active and passive equalization control method and system provided in this embodiment, the specific implementation process is as follows:

[0131] Step 1, as Figure 9 shown, establish a second-order equivalent circuit model for the lithium battery, use the least squares method with a forgetting factor to estimate the model parameters, and then collect the SOC corresponding to each single battery.

[0132] Among them, according to the circuit model, the state equation and output equation of the second-order RC model are obtained, as shown in formulas (1) and (2):

[0133] = + (1)

[0134] (2)

[0135] In the formula, and are the ohmic internal resistance, the electrochemistry and concentration polarization resistances respectively; and are the electrochemistry and concentration polarization capacitances respectively; and are respectively k at the moment and the terminal voltages; and are respectively the terminal voltages at the (k + 1)-th moment and ; is k the battery terminal voltage at the moment, is the battery open-circuit voltage; is the battery charge and discharge current, that is, the current value of the lithium battery; T is the sampling interval; k is the discrete time; is the current value at the k-th moment.

[0136] The memory length of the recursive least squares method is infinite. As the number of recursions increases, there is a lot of old data accumulated, and it is difficult for new data to play a corrective role. The algorithm loses the ability to track and correct, thus affecting the parameter estimation effect. In a time-varying system, the above situation is particularly serious. In this embodiment, a forgetting factor λ is introduced, so as to reduce the occupancy of old data in P(k). Even if the amount of data is large, P(k + 1) does not tend to zero, avoiding the "data saturation" problem. At the same time, the tracking and correction capabilities of the algorithm are enhanced, and a more accurate identification result is obtained; among them, P(k) represents the covariance matrix at the k-th recursion.

[0137] The final calculation formula of the recursive least squares method with a forgetting factor is as follows:

[0138] (5)

[0139] (6)

[0140] (7)

[0141] In the formula, is an identity matrix of the same type; is k the vector of undetermined coefficients at the moment; and are respectively k the gain and covariance matrix at the moment; Indicates k The output value of the time-difference equation

[0142] For parameter identification of the established second-order RC equivalent circuit model of the battery, the battery model needs to be converted into a mathematical form applicable to the least squares method. As Figure 9 shown in the second-order equivalent circuit model, we can obtain:

[0143] (8)

[0144] Let , , and discretize Equation (3), introducing the parameter :

[0145]

[0146]

[0147] The above equation can be directly substituted into the recursive least squares identification method with a forgetting factor. Taking as the direct identification parameter, and then obtaining all the parameters of the battery model from the identification results of these parameters.

[0148] Step 2: Use the extended Kalman filter method to estimate the SOC. In a single HPPC pulse discharge condition, after the discharge is completed and after a long rest, the voltage at this time is used as the battery OCV. Therefore, record the SOC value and its corresponding OCV value after each pulse discharge. The relationship between the two can be represented by a sixth-degree polynomial, and the fitting curve is as Figure 6 shown.

[0149] The basic idea of the extended Kalman filter is: use the Taylor formula to perform a first-order Taylor expansion of the nonlinear system at the state estimate value to linearize the system, and then use the Kalman filter algorithm to estimate the system state.

[0150] Establish the state equation of the lithium battery system according to the second-order RC model structure:

[0151] (10)

[0152] (11)

[0153] According to Equation (10) and Equation (11), convert the state equation and observation equation of the battery model into:

[0154] (12)

[0155] In the formula: is the process noise, and the process noise is Gaussian white noise with a mean of zero and a variance of Q; is the observation noise, which is Gaussian white noise with a mean of zero and a variance of R; T is the sampling interval, which is 1 s here; where, is the state transition matrix, is the control input matrix, is the observation matrix, is the feedforward matrix; , , , , , are the system state vector and the system input respectively, and the specific expressions are as follows:

[0156] = =

[0157] = =-

[0158] = =

[0159] The steps of the extended Kalman filter algorithm are as follows:

[0160] (1) Initialize the state x0 + and the covariance matrix P0 +

[0161] (13)

[0162] (2) State prediction

[0163] (14)

[0164] (3) Covariance prediction

[0165] (15)

[0166] (4) Calculate the Kalman gain

[0167] (16)

[0168] (5) Use the measured voltage yk and the estimated voltage y k to calculate the voltage error

[0169] (17) ​

[0170] (6) Update status

[0171] (18)

[0172] In the formula, and are the prior estimate and posterior estimate of the system respectively; is the Kalman filter gain; and are the prior estimate and posterior estimate of the error covariance matrix of the system respectively; represents the maximum battery capacity.

[0173] By repeating and iterating the steps of the above extended Kalman filter algorithm, the SOC of each single battery is finally output.

[0174] In this embodiment, the change in terminal voltage and the state of charge are used as multiple thresholds, and reasonable segmentation and appropriate threshold types are adopted for control. Compared with the traditional multiple threshold method, this method improves the accuracy while reducing the frequent access of switching devices in the equalization circuit control, thereby reducing device losses and improving the equalization rate.

[0175] As Figure 6 shown, Figure 6 is the OCV-SOC characteristic curve of the lithium battery. When the battery SOC is between 0% and 20% or 80% and 100%, the change rate of the terminal voltage changes rapidly. In this case, using only the SOC as the equalization variable will result in a very small interval between SOCs but a large voltage difference; when the SOC is between 20% and 80%, the change rate of the terminal voltage changes very slowly; if only the change rate of the terminal voltage is used as the equalization variable, the difference in the change rate of the terminal voltage is very small, but the SOC error is very large. Therefore, a single equalization variable (single threshold) cannot fully describe the inconsistency of the battery pack. To achieve a higher-precision equalization effect, it is necessary to segment and adjust the criterion in a timely manner according to the situation. Figure 6 The charge and discharge process of the battery is divided into 3 segments, and the start and stop of equalization are jointly determined by the two criterion thresholds of the change rate of the terminal voltage and the SOC in each segment. Based on their different weights, there is a primary and secondary relationship.

[0176] In this embodiment, the selection of the threshold will affect the equalization effect. If the threshold is too large, the equalization effect is not good; if the threshold is too small, the equalization action is too fast, with a high frequency, and it is easy to start equalization. The entire equalization process takes a long time and has high requirements for hardware. Therefore, it is crucial to select the threshold reasonably.

[0177] As Figure 7As shown, the minimum OCV change rate is determined by looking up the curve of the OCV change rate within the unit SOC. At the same time, the current value of the battery between 20% and 80% is monitored in real time to prevent the criterion misalignment problem caused by unilateral current and voltage overshoot.

[0178] As Figure 8 shown, the corresponding voltage change rate range is found. In addition, it should be noted that there is a voltage fluctuation phenomenon when the battery cell is charging and discharging, that is, a small voltage drop occurs when the switch tube is turned on, and a reverse voltage rise occurs when it is turned off; this may cause the voltage to reach the set equalization voltage difference threshold in advance or reverse exceed this threshold, resulting in the equalization stopping or reversing, and then the battery pack repeatedly equalizes. Therefore, a 2% error needs to be considered when determining the threshold.

[0179] As Figure 10 shown, the open-circuit voltage and terminal voltage difference are compared and analyzed, aiming to establish the connection between SOC and terminal voltage.

[0180] According to the multi-threshold criterion, the entire equalization process is segmented. First, determine the charge and discharge state of the battery pack, and it is necessary to clearly locate the boundary value to determine the state of the battery pack; then switch the equalization circuit as needed and strictly perform equalization according to the multi-threshold conditions, and observe the voltage change situation in real time; the entire control strategy process is as Figure 11 shown.

[0181] The series batteries are divided into intervals, and the division is carried out according to the real-time SOC estimation, ignoring the estimation error. When determining the equalization threshold, multiple thresholds are determined in the previous calculation.

[0182] Step 3, the design of the active and passive equalization circuit, that is, the design of the multi-threshold active and passive equalization control system for lithium batteries. STM32F103 is selected as the main controller, and the battery voltage and current sampling and the equalization circuit of the battery pack are completed in combination with the ETA3000 active equalization chip. The hardware circuit mainly includes function modules such as the main control module, voltage and current acquisition module, equalization module, temperature acquisition and communication, and the circuit principle is as Figure 2 shown.

[0183] First, design the voltage sampling circuit;

[0184] The potential at both ends of the single battery cell is collected through the built-in ADC of STM32F103RCT6, and the real-time voltage of the single battery cell is obtained by calculating the potential difference at both ends; in this embodiment, since the overall voltage of multiple series single battery cells is relatively high, in order to protect the IO port of the single-chip microcomputer from being damaged, the voltage is collected by means of resistor voltage division, as Figure 4 shown, a 10K resistor and a 1K resistor are used for voltage division, and the collected voltage value is multiplied by 11 to obtain the potential of the battery.

[0185] In this embodiment, in order to obtain the output current of the single cell, a 0.05 Ω current detection resistor is connected in series at the output end of the single cell, as Figure 5 shown, the output current expression of the single cell is expressed as:

[0186] (19)

[0187] In the formula, i is the output current of the single cell; u is the output voltage; R6 is the current detection resistor.

[0188] In this embodiment, in order to obtain the voltage of the single cell in real time, a voltage acquisition circuit is designed. First, the ADC peripheral is initialized, and channels 1-12 of the ADC are selected for voltage acquisition. In order to make the ADC sampling value range of STM32F103 be [0, 3.3V], it is necessary to ensure that the externally acquired voltage is within the range of [0, 3.3V]; DMA is used to transfer data and process ADC data. After the configuration is completed, the ADC conversion is started through software instructions. After the ADC conversion is completed, the conversion result is read from the ADC_CR register, and the read data is processed by the median filtering method. Samples are continuously taken N times (N is an odd number), denoted as , and the N sampling values are arranged in ascending order, and the middle value is taken as the effective value of this time.

[0189] Secondly, the lithium battery multi-threshold active and passive equalization control system provided in this embodiment also designs a temperature acquisition circuit, which is specifically as follows:

[0190] In order to realize the real-time monitoring of the temperature of the equalization circuit and avoid overheating of the battery, a temperature acquisition circuit is designed. The DHT11 sensor is selected for temperature acquisition. First, the data line of the DHT11 module is connected to the IO port PB11 of the STM32F103C8T6 minimum system board, and the IO port connected to the DHT11 is configured as an open-drain mode; by setting the clock of GPIOB, creating a GPIO_initTypeDef structure, selecting pin 11, the output rate is 50MHz, and the input / output mode of the IO port is open-drain output; the host configures the bus IO port as an output mode, pulls down the bus for 18 ms as the start signal, and then pulls up the bus and delays for [20 μs , 40 μs . The host configures the bus IO port as an input mode and waits for the DHT11 to respond and receive data. The DHT11 will send 40-bit data through the bus, with the high bits first. After the host receives the data, it parses and processes it according to the data format of the DHT11 to obtain the temperature and humidity values.

[0191] Thirdly, an equalization circuit is designed, that is, a battery equalization module;

[0192] Among them, the SOC-OCV relationship of the battery can be expressed by Equation (20):

[0193] (20)

[0195] In this embodiment, the battery equalization module is the key part of this system. To achieve real-time voltage equalization, reduce the circuit volume, and improve the equalization efficiency, the ETA3000 chip is selected and its external circuit is designed, specifically as Figure 3 shown.

[0196] As Figure 3 shown in (a), the active equalization process is as follows: If the voltage U1 or SOC of battery E1 is higher than that of E2, then turn on M1 and M1 1 with a duty cycle 2 , and use ETA3000 to transfer the energy of E1 to E2; as Figure 3 shown in (b), the passive equalization process is as follows: At a duty cycle , turn off M1 1 and M1 2 , and at the same time turn on M2 1 , and use the resistor R28 to consume the energy of battery E1. Here, it should be noted that in a lithium battery, all the single cells are of the same model and specification, so the battery voltage is positively correlated with the SOC; that is to say, among two adjacent single cells, the one with a higher voltage also has a higher SOC; similarly, among two adjacent single cells, the one with a lower voltage also has a lower SOC.

[0197] It should be noted that this application uses the switching tube M1 i and the switching tube M2 i to control the active and passive equalization states. The conduction pulses corresponding to the switching tube M1 i and the switching tube M2 i are a pair of complementary pulses. Among them, when the switching tube M1 i is conducting, it is active equalization, and when the switching tube M2 i is conducting, it is passive equalization; the voltage and SOC of the single cell are selected and set in intervals:

[0198] When the battery voltage is between 3.0 - 3.9V and the SOC is between 0 - 20%, the change in SOC caused by the change in the single cell voltage is relatively large. An equalization control method with active equalization as the main and passive equalization as the auxiliary is adopted. In this interval range, when ΔU > 0.1V, the duty cycle i of the switching tube M1 is , and the duty cycle i of the switching tube M2 is ; When ΔU < 0.1V, turn on switch M1 i duty cycle is , and the duty cycle of switch M2 i duty cycle is ;

[0199] When the battery voltage is between 3.9 - 4.05V and the SOC is between 20% - 80%, the change in SOC caused by the change in the voltage of a single battery is relatively small. A balanced control method mainly based on passive balancing and supplemented by active balancing is adopted. In this range, when the duty cycle of switch M1 i duty cycle is 10% - 20%, and the duty cycle of switch M2 i duty cycle is 1 - ;

[0200] When the battery voltage is between 4.05 - 4.2V and the SOC is between 80% - 100%, the change in SOC caused by the change in the voltage of a single battery is relatively large. An active balancing - based and passive balancing - supplemented balanced control method is adopted. In this range, when ΔU > 0.1V, the duty cycle of switch M1 i duty cycle is , and the duty cycle of switch M2 i duty cycle is ; When ΔU < 0.1V, turn on switch M1 i duty cycle is , and the duty cycle of switch M2 i duty cycle is ; Among them, ; In the formula, is the voltage difference between two adjacent single batteries.

[0201] In this embodiment, the system also introduces a battery protection module. During the actual monitoring process, the operation data is mainly monitored by the single - chip microcomputer ADC. The monitored operation data is compared with the operation data under normal conditions. If the voltage of a single battery is less than 3.5V, it is considered that the single battery is in an under - voltage state, and an alarm of low power needs to be issued and charging should be carried out in time; when the discharge current of a single battery is greater than 4.4A, the single battery gets severely heated. When the discharge current of a single battery is too large, a current - limiting circuit is designed to disconnect the circuit. In this embodiment, the multi - threshold active - passive balanced control method for lithium batteries remotely transmits the operation data and comparison results monitored by the single - chip microcomputer ADC to the client through a wireless module to achieve multi - threshold active - passive balanced control.

[0202] The multi-threshold active and passive equalization control method for lithium batteries provided in this embodiment is applied and implemented as follows:

[0203] As Figure 11 shown, two groups of batteries are used as the experimental objects, with each group containing 12 batteries, to verify the above equalization control method and control system. It can be seen that the number of components used in the entire equalization and monitoring process is small, which can significantly reduce the circuit volume. At the same time, the equalization time is shortened by 25.6%. When the equalization ends, the maximum voltage difference within the group is reduced by 31.25%, the average voltage of the battery pack is increased by 0.074 V, the equalization loss is reduced, and the equalization efficiency is significantly improved.

[0204] In summary, the present invention provides a multi-threshold active and passive equalization control method and system for lithium batteries. Compared with the existing equalization measures, it has the following advantages:

[0205] The present invention proposes a multi-threshold active and passive equalization control method based on the combination of multi-parameters of lithium battery voltage, voltage change amount, and state of charge, designs an active and passive equalization strategy and circuit based on real-time monitoring of voltage and current parameters, dynamic control of switching tubes and duty cycles, real-time monitors and manages the state of each battery unit. The multi-threshold ensures that the battery units in the battery pack can be equalized in time, effectively avoids the overall performance decline caused by the lag of battery pack equalization, reduces the overcharge or over-discharge phenomenon caused by the imbalance of single cells, thereby slowing down the battery aging speed, extending the service life of lithium batteries, and reducing the maintenance cost in long-term operation.

[0206] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A multi-threshold active and passive equalization control method for lithium batteries, characterized in that Including: Data acquisition process: Collect the current value of the lithium battery and the voltage values corresponding to each single cell in the lithium battery. At the same time, obtain the SOC corresponding to each single cell based on the current value of the lithium battery and the voltage values corresponding to each single cell. First judgment process: Judge the voltage values corresponding to each single cell respectively against the first voltage threshold range, and at the same time judge the SOC corresponding to each single cell respectively against the first SOC threshold range to obtain the first judgment result. The specific steps of the first judgment process are as follows: Judge the voltage values corresponding to each single cell respectively against the first voltage threshold range. If all the voltage values corresponding to each single cell are within the first voltage threshold range, the first voltage judgment condition is satisfied. Judge the SOC corresponding to each single cell respectively against the first SOC threshold range. If all the SOC corresponding to each single cell are within the first SOC threshold range, the first SOC judgment condition is satisfied. If the first voltage judgment condition or / and the first SOC judgment condition is satisfied, output a passive equalization instruction as the first judgment result. Otherwise, output an active equalization instruction as the first judgment result. Strategy screening process: Screen an active equalization strategy or a passive equalization strategy with dynamic duty cycle control based on the first judgment result. Equalization process: Use an active equalization strategy or a passive equalization strategy with dynamic duty cycle control to equalize each single cell. Circulation process: Repeat the data acquisition process, the first judgment process, the strategy screening process, and the equalization process until the voltage difference between every two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between every two adjacent single cells is within the SOC difference threshold range. The specific steps of the strategy screening process are as follows: If a passive equalization instruction is received as the first judgment result, use a passive equalization strategy with passive equalization as the main and active equalization as the supplement. If an active equalization instruction is received as the first judgment result, use an active equalization strategy with active equalization as the main and passive equalization as the supplement. When using the active equalization strategy, judge the voltage values corresponding to each single cell respectively against the second voltage threshold range. If all the voltage values corresponding to each single cell are within the second voltage threshold range, the second voltage judgment condition is satisfied. At the same time, judge the SOC corresponding to each single cell respectively against the second SOC threshold range. If all the SOC corresponding to each single cell are within the second SOC threshold range, the second SOC judgment condition is satisfied. If the second voltage judgment condition or / and the second SOC judgment condition are satisfied, it is judged whether the voltage difference between two adjacent single cells is greater than the first voltage difference threshold; if so, the duty cycle μ1 of the active equalization is ; the duty cycle μ2 of the passive equalization is 1 - μ1; if not, the duty cycle μ1 of the active equalization is ; the duty cycle μ2 of the passive equalization is 1 - μ1; If both the second voltage judgment condition and the second SOC judgment condition are not satisfied, then it is judged whether the voltage difference between two adjacent single cells is greater than the second voltage difference threshold; if so, the duty ratio μ1 of the active equalization is ; the duty ratio μ2 of the passive equalization is 1 - μ1; if not, the duty ratio μ1 of the active equalization is ; the duty ratio μ2 of the passive equalization is 1 - μ1; In the formula, is the pressure difference between two adjacent single cells.

2. The method for controlling multi-threshold active and passive equalization of a lithium battery according to claim 1, wherein, During the data acquisition process, through the established second-order equivalent circuit model of the lithium battery, combined with the current value of the lithium battery and the voltage values corresponding to each single cell, calculate the SOC corresponding to each single cell; among them, obtain the state equation and output equation of the second-order RC model according to the second-order equivalent circuit model. The state equation of the second-order RC model is: = + The output equation of the second-order RC model is: Wherein, and are the ohmic internal resistance, the electrochemical polarization resistance, and the concentration polarization resistance respectively, and are the electrochemical polarization capacitance and the concentration polarization capacitance respectively; and are the terminal voltages of and at the k-th moment respectively, and are the terminal voltages of and at the (k + 1)-th moment respectively, is the voltage value corresponding to the single battery at the k-th moment, is the open-circuit voltage of the battery; is the current value of the lithium battery; T is the sampling interval; k is the discrete time; is the current value at the k-th moment; Based on the state equation and output equation of the second-order RC model, the following conversion equation is obtained: wherein, is the process noise, and the process noise is Gaussian white noise with a mean of zero and a variance of Q; is the observation noise, and the observation noise is Gaussian white noise with a mean of zero and a variance of R; is the state transition matrix, is the control input matrix, is the observation matrix, is the feedforward matrix; and are the system state vector and the system input respectively, and are specifically expressed as follows: = = = =- =[ ] = Among them, , ; represents the maximum battery capacity; Use the extended Kalman filter algorithm to solve the conversion equation and calculate the SOC corresponding to each single cell.

3. A multi-threshold master-slave equalization control method for a lithium battery according to claim 1, characterized in that When the passive equalization strategy is adopted, the duty cycle μ1 of the active equalization is 10% - 20%; the duty cycle μ2 of the passive equalization is 1 - μ1.

4. A multi-threshold active and passive equalization control method for a lithium battery according to claim 1, characterized in that, The specific steps of the equalization process are as follows: When the active equalization strategy is adopted, based on the active equalization strategy, the SOCs corresponding to each single cell, and the voltage differences corresponding to every two adjacent single cells, the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the active equalization strategy are obtained; Based on the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the active equalization strategy, the active equalization process and the passive equalization process are performed on the lithium battery; When the passive equalization strategy is adopted, based on the passive equalization strategy, the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the passive equalization strategy are obtained; Based on the duty cycle of the active equalization and the duty cycle of the passive equalization corresponding to the passive equalization strategy, the active equalization process and the passive equalization process are performed on the lithium battery; The active equalization process is: transferring energy from the single cells with high energy in the lithium battery to the single cells with low energy; The passive equalization process is: using a dissipative resistor to consume the energy of the single cells with high energy in the lithium battery; Among them, the single cell with high energy refers to the one with a higher voltage or SOC between two adjacent single cells; the single cell with low energy refers to the one with a lower voltage or SOC between two adjacent single cells.

5. A multi-threshold master-slave balancing control system for lithium batteries, which is used to implement the steps of the multi-threshold master-slave balancing control method for lithium batteries according to any one of claims 1-4, characterized in that, It includes: A data acquisition module for performing the data acquisition process; The data acquisition process: collecting the current value of the lithium battery and the voltage values corresponding to each single cell in the lithium battery, and simultaneously obtaining the SOC corresponding to each single cell based on the current value of the lithium battery and the voltage values corresponding to each single cell; A first judgment module for performing the first judgment process; The first judgment process: judging the voltage values corresponding to each single cell respectively against the first voltage threshold range, and at the same time judging the SOCs corresponding to each single cell respectively against the first SOC threshold range to obtain the first judgment result; The specific steps of the first judgment process are as follows: Judging the voltage values corresponding to each single cell respectively against the first voltage threshold range. If all the voltage values corresponding to each single cell are within the first voltage threshold range, the first voltage judgment condition is satisfied; Judging the SOCs corresponding to each single cell respectively against the first SOC threshold range. If all the SOCs corresponding to each single cell are within the first SOC threshold range, the first SOC judgment condition is satisfied; If the first voltage judgment condition or / and the first SOC judgment condition is satisfied, a passive equalization instruction is output as the first judgment result; Otherwise, an active equalization instruction is output as the first judgment result; A strategy screening module for performing the strategy screening process; The strategy screening process: screening the active equalization strategy or the passive equalization strategy based on the first judgment result; A battery equalization module for performing the equalization process; Equalization Process: Equalizing each single cell by adopting the active equalization strategy or the passive equalization strategy; A loop module for performing a loop process; the loop process: repeatedly execute the data acquisition process, the first judgment process, the strategy screening process, and the balancing process until the voltage difference between every two adjacent single cells is within the voltage difference threshold range, and / or the SOC difference between every two adjacent single cells is within the SOC difference threshold range.

6. The multi-threshold master-slave passive equalization control system for a lithium battery according to claim 5, characterized in that, The battery balancing module includes a first switch tube and a second switch tube; the conduction pulses corresponding to the first switch tube and the second switch tube are a pair of complementary pulses; wherein, when the first switch tube conducts, the lithium battery multi-threshold active and passive balancing control system performs an active balancing process; when the second switch tube conducts, the lithium battery multi-threshold active and passive balancing control system performs a passive balancing process.

7. A multi-threshold active and passive equalization control system for a lithium battery according to claim 5, characterized in that It further includes: A battery protection module for comparing the currently monitored operating data of the single cell with the operating data under normal conditions, and performing a protection process on the single cell according to the comparison result; The protection process includes an undervoltage protection process and a current limiting protection process.

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