Lithium battery multi-threshold active and passive equalization control method and system

Abstract

The invention belongs to the field of battery health state monitoring, and discloses a lithium battery multi-threshold active and passive equalization control method and system.According to the method, by collecting current, voltage and SOC data of a lithium battery in real time and combining a multi-threshold judgment mechanism, the dynamic change of a battery pack can be reflected more accurately, equalization operation is triggered in time, and the equalization efficiency is improved. The problem of over-equalization or under-equalization possibly caused by a single-threshold strategy is effectively avoided; meanwhile, the intelligent screening of the active equalization strategy and the passive equalization strategy further improves the equalization efficiency and effect, and ensures that the voltage difference and the SOC difference between the single batteries in the battery pack are kept in a reasonable range, thereby prolonging the service life of the battery pack, improving the overall performance, and reducing the potential safety hazard. The method can provide powerful guarantee for stable operation of the energy storage system.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery health status monitoring, and in particular relates to a lithium battery multi-threshold active and passive balancing control method and system. Background Art

[0002] In energy storage systems, multiple single cells are usually connected in series or in parallel to form a battery pack to provide the required electrical energy. Due to differences in the manufacturing process, changes in the use environment, and the aging of the battery itself, the individual cells in the battery pack often have different degrees of performance differences, such as inconsistencies in parameters such as charge capacity, voltage, and internal resistance; due to the existence of the above differences, the overall performance of the battery pack will be reduced, which will in turn affect the service life of the battery pack and may even cause safety hazards.

[0003] In response to the above problems, researchers in this field have proposed battery balancing technology. The existing balancing technology can better solve the problem of performance differences of multiple battery cells in a battery pack; however, the existing balancing technology has certain limitations, which are specifically manifested in: the existing balancing means usually use a single threshold as the criterion for the balancing strategy, which 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 the battery cells, the working environment and the number of times used, its performance will change. The single-threshold balancing strategy often determines whether balancing 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 balancing operation in time, resulting in a decrease in the performance of the battery pack; and it is also easy to cause over-balancing or under-balancing problems: the single-threshold balancing strategy often needs to consider multiple factors when setting the threshold, such as the initial differences of the battery cells, the working environment, etc.; 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-balancing operations in some cases, wasting energy and accelerating battery aging; while in other cases, it may cause under-balancing and fail to effectively improve the performance of the battery pack.

[0004] It can be seen that the existing battery balancing measures, due to the use of a single threshold balancing strategy, cannot adapt to the dynamic changes of the battery pack, resulting in poor balancing effect and low balancing efficiency. Summary of the invention

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

[0006] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present invention provides a lithium battery multi-threshold active and passive balancing control method, comprising: Data collection process: collect the current value of the lithium battery and the voltage value of each single cell in the lithium battery, and obtain the SOC of each single cell based on the current value of the lithium battery and the voltage value of each single cell; The first judgment process: the voltage value corresponding to each single battery is judged with the first voltage threshold range respectively, and the SOC corresponding to each single battery is judged with the first SOC threshold range respectively, to obtain a first judgment result; The specific steps of the first judgment process are as follows: The voltage values ​​corresponding to the individual cells are respectively compared with the first voltage threshold range. If the voltage values ​​corresponding to the individual cells are all within the first voltage threshold range, the first voltage judgment condition is met. The SOC corresponding to each single battery is judged against the first SOC threshold range respectively. If the SOC corresponding to each single battery is all within the first SOC threshold range, the first SOC judgment condition is met; If the first voltage judgment condition and / or the first SOC judgment condition are met, a passive balancing instruction is output as a first judgment result; Otherwise, outputting an active balancing instruction as the first judgment result; Strategy screening process: screening active balancing strategy or passive balancing strategy based on the first judgment result; Balancing process: Use active balancing strategy or passive balancing strategy to balance each single battery; Cyclic process: Repeat the data collection process, the first judgment process, the strategy screening process and the balancing process until the voltage difference between each two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between each two adjacent single cells is within the SOC difference threshold range.

[0007] A further improvement of the present invention is that, during the data collection process, the SOC corresponding to each single cell is calculated by combining the current value of the lithium battery and the voltage value corresponding to each single cell through the established second-order equivalent circuit model of the lithium battery; wherein the state equation and output equation of the second-order RC model are obtained according to the second-order equivalent circuit model; The state equation of the second-order RC model is: = +

[0008] The output equation of the second-order RC model is:

[0009] In the formula, and are ohmic internal resistance, electrochemical resistance and concentration polarization resistance respectively, and are electrochemical and concentration polarization capacitance, respectively; and are k moments respectively and The terminal voltage, and are k+1 moments respectively and The terminal voltage, is the voltage value of the single cell at time k, 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 time k; Based on the state equation and output equation of the second-order RC model, the conversion equation is as follows:

[0010] In the formula, is the process noise, which uses Gaussian white noise with a mean of zero and a variance of Q; is the observation noise, which uses Gaussian white noise with a mean of zero and a variance of R; is the state transfer matrix, is the control input matrix, is the observation matrix, is the feedforward matrix; and are the system state vector and system input respectively, which are expressed as follows: = =

[0011] = =-

[0012] =[ ] =

[0013] in, , ; Indicates the maximum capacity of the battery; The extended Kalman filter algorithm is used to solve the conversion equation and calculate the SOC corresponding to each single battery.

[0014] A further improvement of the present invention is that the specific steps of the strategy screening process are as follows: If a passive balancing instruction is received as the first judgment result, a passive balancing strategy with passive balancing as the main and active balancing as the auxiliary is adopted; If an active balancing instruction is received as the first judgment result, an active balancing strategy with active balancing as the main and passive balancing as the auxiliary is adopted.

[0015] A further improvement of the present invention is that, when a passive balancing strategy is adopted, the duty cycle μ1 of active balancing is 10%-20%; and the duty cycle μ2 of passive balancing is 1-μ1.

[0016] A further improvement of the present invention is that, when the active balancing strategy is adopted, the voltage value corresponding to each single cell is judged against the second voltage threshold range respectively, and if the voltage values ​​corresponding to each single cell are all within the second voltage threshold range, the second voltage judgment condition is met; At the same time, the SOC corresponding to each single battery is judged against the second SOC threshold range respectively. If the SOC corresponding to each single battery is all within the second SOC threshold range, the second SOC judgment condition is met; If the second voltage judgment condition and / or the second SOC judgment condition are met, it is determined whether the voltage difference between two adjacent single cells is greater than the first voltage difference threshold; if so, the duty cycle μ1 of active balancing is ; The duty cycle μ2 of passive balancing is 1-μ1; if not, the duty cycle μ1 of active balancing is ;The duty cycle μ2 of passive balancing is 1-μ1; If the second voltage judgment condition and the second SOC judgment condition are not met, it is determined whether the voltage difference between two adjacent single cells is greater than the second voltage difference threshold; if so, the duty cycle μ1 of active balancing is ; The duty cycle μ2 of passive balancing is 1-μ1; if not, the duty cycle μ1 of active balancing is ;The duty cycle μ2 of passive balancing is 1-μ1; In the formula, is the voltage difference between two adjacent cells.

[0017] A further improvement of the present invention is that the specific steps of the equalization process are as follows: When the active balancing strategy is adopted, based on the active balancing strategy and the SOC corresponding to each single cell and the voltage difference between each two adjacent single cells, the corresponding active balancing duty cycle and passive balancing duty cycle under the active balancing strategy are obtained; Based on the corresponding active balancing duty cycle and passive balancing duty cycle under the active balancing strategy, the lithium battery is subjected to active balancing process and passive balancing process; When a passive balancing strategy is adopted, the corresponding active balancing duty ratio and passive balancing duty ratio under the passive balancing strategy are obtained based on the passive balancing strategy; Based on the corresponding active balancing duty cycle and passive balancing duty cycle under the passive balancing strategy, the lithium battery is subjected to active balancing process and passive balancing process; The active balancing process is: transferring energy from high-energy cells to low-energy cells in the lithium battery; The passive balancing process is: using energy-consuming resistors to consume the energy of the high-energy single cells in the lithium battery; Among them, a single cell with high energy means the one with higher voltage or SOC between two adjacent single cells; a single cell with low energy means the one with lower voltage or SOC between two adjacent single cells.

[0018] In a second aspect, the present invention provides a lithium battery multi-threshold active and passive balancing control system, comprising: The data acquisition module is used to execute the data acquisition process; the data acquisition process: the current value of the lithium battery and the voltage value corresponding to each single cell in the lithium battery are collected, and the SOC corresponding to each single cell is obtained based on the current value of the lithium battery and the voltage value corresponding to each single cell; The first judgment module is used to perform a first judgment process; the first judgment process: the voltage value corresponding to each single battery is judged with the first voltage threshold range, and the SOC corresponding to each single battery is judged with the first SOC threshold range to obtain a first judgment result; The specific steps of the first judgment process are as follows: The voltage values ​​corresponding to the individual cells are respectively compared with the first voltage threshold range. If the voltage values ​​corresponding to the individual cells are all within the first voltage threshold range, the first voltage judgment condition is met. The SOC corresponding to each single battery is judged against the first SOC threshold range respectively. If the SOC corresponding to each single battery is all within the first SOC threshold range, the first SOC judgment condition is met; If the first voltage judgment condition and / or the first SOC judgment condition are met, a passive balancing instruction is output as a first judgment result; Otherwise, outputting an active balancing instruction as the first judgment result; A strategy screening module, used to execute a strategy screening process; the strategy screening process: screening an active balancing strategy or a passive balancing strategy based on the first judgment result; The battery balancing module is used to perform the balancing process; the balancing process: the active balancing strategy or the passive balancing strategy is used to balance each single battery; A loop module is used to execute 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 each two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between each two adjacent single cells is within the SOC difference threshold range.

[0019] A further improvement of the present invention is 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 is turned on, the lithium battery multi-threshold active and passive balancing control system performs an active balancing process; when the second switch tube is turned on, the lithium battery multi-threshold active and passive balancing control system performs a passive balancing process.

[0020] A further improvement of the present invention is that it also includes: 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 perform a protection process on the single battery according to the comparison result; wherein the protection process includes an undervoltage protection process and a current limiting protection process.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a multi-threshold active and passive balancing control method for lithium batteries. This method can more accurately reflect the dynamic changes of the battery pack by real-time collection of the current, voltage and SOC data of the lithium battery, and timely trigger the balancing operation, effectively avoiding the over-balancing or under-balancing problems that may be caused by the single threshold strategy; at the same time, the intelligent screening of active balancing and passive balancing strategies further improves the balancing efficiency and effect, ensuring that the voltage difference and SOC difference between each single cell in the battery pack remain within a reasonable range, thereby extending the service life of the battery pack, improving the overall performance, and reducing safety hazards. The use of this method can provide a strong guarantee for the stable operation of the energy storage system.

[0022] Preferably, in the present invention, by establishing a second-order equivalent circuit model of the lithium battery and combining it with an extended Kalman filter algorithm, the SOC of each single cell can be calculated more accurately; this method improves the accuracy of SOC estimation and provides more reliable data support for subsequent balancing control, thereby enhancing the accuracy and effectiveness of balancing control.

[0023] Preferably, in the present invention, by setting a first voltage threshold range and a first SOC threshold range, and making judgments based on these thresholds, it is possible to flexibly adapt to dynamic changes of the battery pack during use; this method ensures the timeliness and accuracy of the balancing operation, avoids the problems of over-balancing or under-balancing, and improves the performance and safety of the battery pack.

[0024] Preferably, in the present invention, an active balancing strategy or a passive balancing 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 balancing control, ensure the consistency of voltage and SOC between each single cell in the battery pack, thereby extending the service life of the battery pack.

[0025] Preferably, in the present invention, when a passive balancing strategy is adopted, the balancing process can be more finely controlled by setting the duty cycle of active balancing and passive balancing; such duty cycle setting helps to balance balancing efficiency and energy consumption, and improve the overall performance of the battery pack.

[0026] Preferably, in the present invention, when an active balancing strategy is adopted, the triggering timing and balancing strength of the balancing operation can be more accurately controlled by using the preset second voltage threshold range and the second SOC threshold range and combining the voltage difference between two adjacent single cells. This further improves the accuracy and effectiveness of the balancing control, which helps to extend the service life of the battery pack and improve the overall performance.

[0027] Preferably, in the present invention, the specific steps of the balancing process include implementation methods of active balancing and passive balancing; by clarifying the definition of high-energy and low-energy single cells, as well as the specific balancing operation process, the feasibility and effectiveness of balancing control are ensured; this method helps to achieve rapid balancing of voltage and SOC between single cells in a battery pack, thereby improving the performance and safety of the battery pack.

[0028] The present invention provides a multi-threshold active and passive balancing control system for lithium batteries. The system realizes dynamic monitoring and intelligent balancing of battery pack performance by integrating functional modules such as data acquisition, multi-threshold judgment, strategy screening, balancing execution and cycle control. The system can accurately reflect the actual state changes of the battery pack, take appropriate balancing strategies in time, and effectively avoid the limitations of the single threshold balancing strategy, such as over-balancing, under-balancing and other problems; at the same time, the combined use of active and passive balancing strategies further improves the balancing efficiency and effect, ensures the consistency of voltage and SOC between each single cell in the battery pack, thereby extending the service life of the battery pack, improving the overall performance, reducing safety hazards, and providing a strong guarantee for the stable operation of the energy storage system.

[0029] Preferably, in the present invention, the switching between active balancing and passive balancing is achieved through the complementary pulse control of the first switch tube and the second switch tube, which simplifies the logic of balancing control; and the clear division of labor of the switch tubes makes the balancing process more stable and reliable, avoiding balancing failure caused by chaotic control logic.

[0030] Preferably, in the present invention, a battery protection module is introduced, which can monitor the operating data of the single battery in real time and compare it with the data under normal conditions, so as to promptly detect abnormal conditions and take protective measures; through processes such as undervoltage protection and current limiting protection, the battery is effectively prevented from being damaged due to over-discharge, over-current, etc., and the risk of battery failure is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A flow chart of a multi-threshold active and passive balancing control method for a lithium battery provided by the present invention; Figure 2 A schematic diagram of a multi-threshold active and passive balancing control method for a lithium battery provided by an embodiment of the present invention; Figure 3 The circuit schematic diagram of the battery balancing module of the lithium battery multi-threshold active and passive balancing control system provided by the embodiment of the present invention, wherein (a) is the active balancing circuit schematic diagram; (b) is the passive balancing circuit schematic diagram; Figure 4 Schematic diagram of the ADC acquisition circuit provided by an embodiment of the present invention; Figure 5 A schematic diagram of a current measurement circuit provided by an embodiment of the present invention; Figure 6 The OCV-SOC characteristic curve of the lithium battery provided by the embodiment of the present invention; Figure 7 A curve diagram of the OCV change rate within a unit SOC provided by an embodiment of the present invention; Figure 8 A curve diagram of voltage change rate provided by an embodiment of the present invention; Fig. 9 A second-order equivalent circuit model diagram of a lithium battery provided in an embodiment of the present invention; Fig.10 A flowchart of a multi-threshold active and passive balancing control method for a lithium battery provided by an embodiment of the present invention; Fig.11 A diagram showing the balancing effect of a lithium battery having 12 cells provided by an embodiment of the present invention; Fig.12 A schematic structural diagram of a lithium battery multi-threshold active and passive balancing control system provided by the present invention. DETAILED DESCRIPTION

[0032] In order to further understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0033] like Figure 1 As shown, this embodiment provides a lithium battery multi-threshold active and passive balancing control method, including: Data collection process: collect the current value of the lithium battery and the voltage value of each single cell in the lithium battery, and obtain the SOC of each single cell based on the current value of the lithium battery and the voltage value of each single cell; The first judgment process: the voltage value corresponding to each single battery is judged with the first voltage threshold range respectively, and the SOC corresponding to each single battery is judged with the first SOC threshold range respectively, to obtain a first judgment result; The specific steps of the first judgment process are as follows: The voltage values ​​corresponding to the individual cells are respectively compared with the first voltage threshold range. If the voltage values ​​corresponding to the individual cells are all within the first voltage threshold range, the first voltage judgment condition is met. The SOC corresponding to each single battery is judged against the first SOC threshold range respectively. If the SOC corresponding to each single battery is all within the first SOC threshold range, the first SOC judgment condition is met; If the first voltage judgment condition and / or the first SOC judgment condition are met, a passive balancing instruction is output as a first judgment result; Otherwise, outputting an active balancing instruction as the first judgment result; Strategy screening process: screening active balancing strategy or passive balancing strategy based on the first judgment result; Balancing process: Use active balancing strategy or passive balancing strategy to balance each single battery; Cyclic process: Repeat the data collection process, the first judgment process, the strategy screening process and the balancing process until the voltage difference between each two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between each two adjacent single cells is within the SOC difference threshold range.

[0034] It can be seen that this method can more accurately reflect the dynamic changes of the battery pack by collecting the current, voltage and SOC data of the lithium battery in real time and combining the multi-threshold judgment mechanism, trigger the balancing operation in time, and effectively avoid the over-balancing or under-balancing problems that may be caused by the single threshold strategy; at the same time, the intelligent screening of active balancing and passive balancing strategies further improves the balancing efficiency and effect, ensuring that the voltage difference and SOC difference between each single cell in the battery pack remain within a reasonable range, thereby extending the service life of the battery pack, improving the overall performance, and reducing safety hazards. The use of this method can provide a strong guarantee for the stable operation of the energy storage system.

[0035] The balancing method provided by this embodiment is further explained below with reference to the accompanying drawings: The following nouns are explained as follows: SOC (State of Charge), also known as the remaining power, is used to reflect the remaining capacity of the battery. Its value is defined as the ratio of the remaining capacity to the battery capacity, usually expressed as a percentage.

[0036] Second-order RC model: used to describe a circuit model composed of resistance (R) and capacitance (C). The resistance and capacitance in the model correspond to different physical properties inside the battery, such as charge transfer resistance, diffusion resistance and corresponding capacitance effect.

[0037] Duty cycle refers to the proportion of high level (or effective level) in a pulse cycle, which is also interpreted as the proportion of the time when the circuit is connected to the total cycle time; the duty cycle calculation formula is: Duty cycle = pulse width / pulse cycle.

[0038] OCV (Open Circuit Voltage) refers to the terminal voltage of the battery in the open circuit state, that is, the difference in electrode potential between the positive and negative electrodes of the battery when no current passes through.

[0039] HPPC (Hybrid Pulse Power Characterization) is a pulse signal used to test battery performance. The signal consists of a series of square wave pulses that can simulate the load and charging pulses that the battery may encounter in actual use.

[0040] ADC (Analog-to-Digital Converter) is an electronic device that converts analog signals (continuously changing physical quantities such as sound, light, temperature, etc.) into digital signals (such as binary codes composed of 0 and 1).

[0041] DMA (Direct Memory Access) refers to direct memory access, which is a data exchange method that allows certain hardware devices to read and write system memory independently without going through the central processor.

[0042] Combination Figure 2 and Fig.10 As shown, this embodiment provides a lithium battery multi-threshold active and passive balancing control method, including: Data collection process: collect the current value of the lithium battery and the voltage value corresponding to each single cell in the lithium battery, and obtain the SOC corresponding to each single cell based on the current value of the lithium battery and the voltage value corresponding to each single cell.

[0043] The first judgment process: the voltage value corresponding to each single battery is judged with 3.9V~4.05V respectively; at the same time, the SOC corresponding to each single battery is judged with 20%~80% respectively to obtain the first judgment result.

[0044] Strategy screening process: based on the first judgment result, an active balancing strategy with active balancing as the main strategy and passive balancing as the auxiliary strategy or a passive balancing strategy with passive balancing as the main strategy and active balancing as the auxiliary strategy is screened.

[0045] When the passive balancing strategy is adopted, the duty cycle μ1 of active balancing is 10%~20%; the duty cycle μ2 of passive balancing is 1-μ1.

[0046] When the active balancing strategy is adopted, the voltage value corresponding to each single cell is judged against 4.05V~4.2V respectively. If the voltage values ​​corresponding to each single cell are all within the range of 4.05V~4.2V, the second voltage judgment condition is met; At the same time, the SOC corresponding to each single battery is judged to be between 80% and 100%. If the SOC corresponding to each single battery is all between 80% and 100%, the second SOC judgment condition is met; If the second voltage judgment condition and / or the second SOC judgment condition are met, it is determined whether the voltage difference between two adjacent single cells is greater than the first voltage difference threshold; if so, the duty cycle μ1 of active balancing is ; The duty cycle μ2 of passive balancing is 1-μ1; if not, the duty cycle μ1 of active balancing is ;The duty cycle μ2 of passive balancing is 1-μ1; If the second voltage judgment condition and the second SOC judgment condition are not met, it is determined whether the voltage difference between two adjacent single cells is greater than the second voltage difference threshold; if so, the duty cycle μ1 of active balancing is ; The duty cycle μ2 of passive balancing is 1-μ1; if not, the duty cycle μ1 of active balancing is ;The duty cycle μ2 of passive balancing is 1-μ1; In the formula, is the voltage difference between two adjacent cells.

[0047] Balancing process: Balance each single cell according to the above passive balancing strategy or active balancing strategy.

[0048] Cyclic process: Repeat the data collection process, the first judgment process, the strategy screening process and the balancing process until the absolute value of the voltage difference between each two adjacent single cells is less than 0.01V, or / and the absolute value of the SOC difference between each two adjacent single cells is less than 0.1%, and then the cyclic process ends.

[0049] In this embodiment, when the active balancing strategy is adopted, based on the active balancing strategy and the SOC corresponding to each single cell and the voltage difference between each two adjacent single cells, the corresponding active balancing duty cycle and passive balancing duty cycle under the active balancing strategy are obtained; Based on the corresponding active balancing duty cycle and passive balancing duty cycle under the active balancing strategy, the lithium battery is subjected to active balancing process and passive balancing process; When a passive balancing strategy is adopted, the corresponding active balancing duty ratio and passive balancing duty ratio under the passive balancing strategy are obtained based on the passive balancing strategy; Based on the corresponding active balancing duty cycle and passive balancing duty cycle under the passive balancing strategy, the lithium battery is subjected to active balancing process and passive balancing process; The active balancing process is: transferring energy from high-energy cells to low-energy cells in the lithium battery; The passive balancing process is: using energy-consuming resistors to consume the energy of the high-energy single cells in the lithium battery; Among them, a single cell with high energy means the one with higher voltage or SOC between two adjacent single cells; a single cell with low energy means the one with lower voltage or SOC between two adjacent single cells.

[0050] like Fig.12 As shown, in order to realize the above-mentioned lithium battery multi-threshold active and passive balancing control method, a lithium battery multi-threshold active and passive balancing control system is designed, including: A data acquisition module is used to execute a data acquisition process; a data acquisition process: collecting the current value of the lithium battery and the voltage value corresponding to each single cell in the lithium battery, and obtaining the SOC corresponding to each single cell based on the current value of the lithium battery and the voltage value corresponding to each single cell; a first judgment module is used to execute a first judgment process; a first judgment process: judging the voltage value corresponding to each single cell with a first voltage threshold range, and judging the SOC corresponding to each single cell with a first SOC threshold range, to obtain a first judgment result; the specific steps of the first judgment process are as follows: judging the voltage value corresponding to each single cell with a first voltage threshold range, if the voltage value corresponding to each single cell is all within the first voltage threshold range, then the first voltage judgment condition is met; judging the SOC corresponding to each single cell with a first SOC threshold range, if the voltage value corresponding to each single cell is all within the first voltage threshold range, then the first voltage judgment condition is met; judging the SOC corresponding to each single cell with a first SOC threshold range, if the voltage value corresponding to each single cell is all within the first voltage threshold range, then the SOC corresponding to each single cell is If all the SOCs of the batteries are within the first SOC threshold range, the first SOC judgment condition is met; if the first voltage judgment condition or / and the first SOC judgment condition are met, a passive balancing instruction is output as the first judgment result; otherwise, an active balancing instruction is output as the first judgment result; a strategy screening module is used to execute a strategy screening process; strategy screening process: active balancing strategy or passive balancing strategy is screened based on the first judgment result; a battery balancing module is used to execute a balancing process; balancing process: each single battery is balanced using an active balancing strategy or a passive balancing strategy; a loop module is used to execute a loop process; a loop process: data acquisition process, first judgment process, strategy screening process and balancing process are repeatedly executed until the voltage difference between each two adjacent single batteries is within the voltage difference threshold range, or / and the SOC difference between each two adjacent single batteries is within the SOC difference threshold range.

[0051] The balancing system also includes a battery protection module, which is used to compare the current operating data of the single cell obtained by monitoring with the operating data under normal conditions, and perform a protection process on the single cell according to the comparison result; wherein the protection process includes an undervoltage protection process and a current limiting protection process.

[0052] Based on the lithium battery multi-threshold active and passive balancing control method and system provided in this embodiment, the specific implementation process is as follows: Step 1, such as Fig. 9 As shown, a second-order equivalent circuit model of the lithium battery is established, and the least square method with a forgetting factor is used to estimate the model parameters, and then the SOC corresponding to each single battery is collected; Among them, the state equation and output equation of the second-order RC model are obtained according to the circuit model, as shown in equations (1) and (2): = + (1) (2) In the formula, and They are ohmic internal resistance, electrochemical resistance and concentration polarization resistance respectively; and are electrochemical and concentration polarization capacitance, respectively; and They are k time and The terminal voltage of and are k+1 moments respectively and The terminal voltage, for k The battery terminal voltage at the moment, is the open circuit voltage of the battery; is the battery charging and discharging 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 time k.

[0053] The memory length of the recursive least squares method is infinite. As the number of recursions increases, more old data is accumulated, and new data is difficult to play a correction role. The algorithm loses its tracking and correction capabilities, which in turn affects the parameter estimation effect. In time-varying systems, the above situation is particularly serious. In this embodiment, the forgetting factor λ is introduced to reduce the amount 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, while enhancing the algorithm's tracking and correction capabilities, and obtaining more accurate identification results; where P(k) represents the covariance matrix at the kth recursion.

[0054] The final calculation formula of the recursive least squares method with forgetting factor is as follows: (5) (6) (7) In the formula, is the same type of identity matrix; for k The vector of unknown coefficients at time; and They are k Gain and covariance matrices at time instant; express k The output value of the time difference equation.

[0055] To identify the parameters of the established second-order RC equivalent circuit model of the battery, it is necessary to convert the battery model into a mathematical form that can be applied with the least squares method. Fig. 9The second-order equivalent circuit model shown can be obtained: (8) make , , and discretize equation (3) to introduce the parameter :

[0056]

[0057] The above formula can be directly substituted into the recursive least squares identification method with forgetting factor. As direct identification parameters, all parameters of the battery model are obtained from the identification results of these parameters.

[0058] Step 2: Use the extended Kalman filter method to estimate the SOC. In a single HPPC pulse discharge condition, after a long period of rest after the discharge is completed, the voltage at this time is taken as the battery OCV. Therefore, the SOC value after each pulse discharge and its corresponding OCV value are recorded. The relationship between the two can be expressed by a sixth-order polynomial. The fitting curve is as follows: Figure 6 shown.

[0059] The basic idea of ​​the extended Kalman filter is to use the Taylor formula to perform a first-order Taylor expansion on the nonlinear system at the state estimate, linearize the system, and then use the Kalman filter algorithm to estimate the system state.

[0060] The state equation of the lithium battery system is established based on the second-order RC model structure: (10) (11) According to equations (10) and (11), the battery model state equation and observation equation are transformed into: (12) Where: is the process noise, which is a Gaussian white noise with a mean of zero and a variance of Q; is the observation noise, which is a Gaussian white noise with a mean of zero and a variance of R; T is the sampling interval, which is 1s here; where, is the state transfer matrix, is the control input matrix, is the observation matrix, is the feedforward matrix; , , , , , are the system state vector and system input respectively, which are expressed as follows: = =

[0061] = =-

[0062] =[ ] =

[0063] The steps to expand the Kalman filter algorithm are as follows: (1) Initialization state x0 + And the covariance matrix P0 + (13) (2) State prediction (14) (3) Covariance prediction (15) (4) Calculate Kalman gain (16) (5) Using the measured voltage yk and the estimated voltage y k Calculating Voltage Error (17) (6) Update status (18) In the formula, and are the prior and a posteriori estimates of the system respectively; is the Kalman filter gain; and are the prior and a posteriori estimates of the error covariance matrix of the system respectively; Indicates the maximum battery capacity.

[0064] The steps of the above extended Kalman filter algorithm are repeated and iterated, and finally the SOC of each single battery is output.

[0065] This embodiment uses the terminal voltage change and the state of charge as multiple thresholds, and uses reasonable segmentation and appropriate threshold types for control. Compared with the traditional multi-threshold method, this method improves accuracy while reducing the frequent access of switching devices in the balancing circuit control, thereby reducing device loss and improving the balancing rate.

[0066] like Figure 6 As shown, Figure 6 The OCV-SOC characteristic curve of lithium battery. When the battery SOC is between 0% and 20% or 80% and 100%, the terminal voltage change rate changes rapidly. In this case, using only SOC as the balancing variable will result in a small interval between SOCs, but a large voltage difference; when the SOC is between 20% and 80%, the terminal voltage change rate changes very slowly; if only the terminal voltage change rate is used as the balancing variable, the difference in the terminal voltage change rate is small, but the SOC error is large. Therefore, a single balancing variable (single threshold) cannot fully describe the inconsistency of the battery pack. In order to achieve a more accurate balancing effect, it is necessary to timely segment and adjust the criteria according to the situation. Figure 6 The battery charging and discharging process is divided into three sections. The opening and closing of the balancing is determined by two criterion thresholds, namely the terminal voltage change rate and the SOC. Based on their different weights, they are divided into primary and secondary.

[0067] In this embodiment, the selection of the threshold value will affect the balancing effect. If the threshold value is too large, the balancing effect is poor; if the threshold value is too small, the balancing action is too fast, the frequency is high, and the balancing is easy to start. The entire balancing process takes a long time and has high hardware requirements. Therefore, it is very important to select a reasonable threshold value.

[0068] like Figure 7 As shown, by finding the curve of the OCV change rate within the unit SOC, the minimum OCV change rate is determined. At the same time, the current value of the battery between 20% and 80% is monitored in real time to prevent the judgment from being inaccurate due to unilateral current and voltage overshoot.

[0069] like Figure 8 As shown, find the corresponding voltage change rate range. In addition, it is necessary to note that there is voltage fluctuation in the battery cell during 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 exceed this threshold in the reverse direction, thereby causing the equalization to stop or reverse, and then the battery pack is repeatedly equalized. Therefore, a 2% error needs to be considered when determining the threshold.

[0070] like Fig.10 As shown, a comparative analysis of the open circuit voltage and the terminal voltage difference is performed in order to establish a connection between SOC and the terminal voltage.

[0071] According to the multi-threshold criteria, the entire balancing process is segmented. First, the charge and discharge status of the battery pack is determined. The limit value needs to be clearly located to determine the status of the battery pack; then the balancing circuit is switched as needed, and the balancing is performed strictly according to the multi-threshold conditions, and the voltage changes are observed in real time; the entire control strategy process is as follows Fig.11 shown.

[0072] The series-connected batteries are divided into intervals and divided according to the real-time SOC estimation, ignoring the estimation error. When determining the equalization threshold, multiple thresholds are determined in the previous calculation.

[0073] Step 3, active and passive balancing circuit design, that is, the design of lithium battery multi-threshold active and passive balancing control system. STM32F103 is selected as the main controller, combined with ETA3000 active balancing chip to complete the design of battery voltage and current sampling and battery pack balancing circuit. The hardware circuit mainly includes main control module, voltage and current acquisition module, balancing module, temperature acquisition and communication and other functional modules. The circuit principle is as follows Figure 2 shown.

[0074] First, design the voltage sampling circuit; The potential at both ends of the single cell is collected by the built-in ADC of STM32F103RCT6, and the potential difference between the two ends is calculated to obtain the real-time voltage of the single cell. In this embodiment, since the overall voltage of multiple single cells connected in series is relatively high, in order to protect the IO port of the single chip from being damaged, the voltage is collected by means of resistor voltage division, such as Figure 4 As 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 battery potential.

[0075] In this embodiment, in order to obtain the output current of the single cell, a 0.05Ω current sensing resistor is connected in series to the output end of the single cell. Figure 5 As shown, the output current expression of the single battery is expressed as: (19) In the formula, i is the output current of the single battery; u is the output voltage; R6 is the current sensing resistor.

[0076] In this embodiment, in order to obtain the single cell voltage 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 range of STM32F103 [0, 3.3V], it is necessary to ensure that the externally collected voltage is within the interval of [0, 3.3V]; DMA is used to transfer data and ADC data processing. 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, and the continuous sampling is N times (N is an odd number), which is recorded as , arrange the N sampling values ​​in order of size and take the middle value as the effective value this time.

[0077] Secondly, the lithium battery multi-threshold active and passive balancing control system provided in this embodiment also designs a temperature acquisition circuit, which is as follows: In order to realize real-time monitoring of the temperature of the balancing circuit and avoid battery overheating, 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 open-drain mode; by setting the clock of GPIOB, creating the GPIO_initTypeDef structure, selecting pin 11, the output rate is 50MHz, and the IO port input and output mode is open-drain output; the host configures the bus IO port to output mode, pulls the bus low for 18ms as a start signal, and then pulls the bus high and delays [20 μs , 40 μs ]. The host configures the bus IO port to input mode, waits for DHT11 to respond and receive data. DHT11 will send 40-bit data through the bus, with the high bit out first. After receiving the data, the host parses and processes it according to the data format of DHT11 to obtain the temperature and humidity values.

[0078] Thirdly, design the balancing circuit, i.e. the battery balancing module; Among them, the SOC-OCV relationship of the battery can be expressed by formula (20): (20) In this embodiment, the battery balancing module is the key part of the system. In order to achieve real-time voltage balancing, reduce circuit size, and improve balancing efficiency, the ETA3000 chip is selected and its external circuit is designed. Figure 3 shown.

[0080] like Figure 3 As shown in (a), the active balancing process is as follows: If the voltage U1 or SOC corresponding to the E1 battery is higher than that of the E2 battery, the duty cycle Turn on M11 and M1 2 , use ETA3000 to transfer energy from E1 to E2; Figure 3 (b) shows that the passive balancing process is as follows: Close M1 1 and M1 2 , while opening M2 1 , using resistor R28 to consume the energy of battery E1. Here, it should be noted that in a lithium battery, single cells of the same type and specification are used, so the battery voltage is positively correlated with the SOC; that is, the higher the voltage between two adjacent single cells, the higher its SOC; similarly, the lower the voltage between two adjacent single cells, the lower its SOC.

[0081] It should be noted that this application uses the switch tube M1 i And switch tube M2 i To control the active and passive balance state, switch tube M1 i And switch tube M2 i The corresponding conduction pulse is a pair of complementary pulses, in which the switch tube M1 i When it is turned on, it is active balancing, and the switch tube M2 i When it is turned on, it is passive balancing; the voltage and SOC of the single battery are selected and set in intervals: When the battery voltage is between 3.0-3.9V and the SOC is between 0-20%, the SOC change caused by the change of the single battery voltage is relatively large. The active balance is mainly used and the passive balance is supplemented. In this range, when ΔU>0.1V, the switch tube M1 is i Duty cycle for , switch tube M2 i Duty cycle for ; When ΔU<0.1V, switch tube M1 i Duty cycle for , switch tube M2 i Duty cycle for ; When the battery voltage is between 3.9-4.05V and the SOC is between 20%-80%, the SOC change caused by the single battery voltage change is small. The passive balancing is mainly used and the active balancing is supplemented. In this range, the switch tube M1 is set to i Duty cycle 10%-20%, switch tube M2 i Duty cycle 1- ; When the battery voltage is between 4.05-4.2V and the SOC is between 80%-100%, the SOC change caused by the change of the single battery voltage is relatively large. The active balance is mainly used and the passive balance is supplemented. In this range, when ΔU>0.1V, the switch tube M1 is turned on. i Duty cycle for , switch tube M2 i Duty cycle for ; When ΔU<0.1V, switch tube M1 i Duty cycle for , switch tube M2 i Duty cycle for ;in, ; In the formula, is the voltage difference between two adjacent cells.

[0082] In this embodiment, the system also introduces a battery protection module. In the actual monitoring process, the operating data is mainly monitored through the single-chip microcomputer ADC, and the monitored operating data is compared with the operating data under normal conditions. If the voltage of the single cell battery is less than 3.5V, it is considered that the single cell battery is in an undervoltage state, and a low power alarm needs to be issued and charged in time; when the discharge current of the single cell battery is greater than 4.4A, the single cell battery heats up seriously. When the discharge current of the single cell battery is too large, a current limiting circuit is designed to disconnect the circuit. In this embodiment, the lithium battery multi-threshold active and passive balancing control method remotely transmits the operating data and comparison results monitored by the single-chip microcomputer ADC to the client through a wireless module to realize multi-threshold active and passive balancing control.

[0083] The lithium battery multi-threshold active and passive balancing control method provided in this embodiment is applied and implemented as follows: like Fig.11 As shown in the figure, two groups of batteries are used as experimental objects, each group contains 12 batteries, and the above-mentioned balancing control method and control system are verified. It can be seen that the number of components used in the entire balancing and monitoring process is relatively small, which can significantly reduce the circuit volume, and the balancing time is shortened by 25.6%. At the end of balancing, the maximum difference in battery voltage in the group is reduced by 31.25%, and the average voltage of the battery group is increased by 0.074 V, the balancing loss is reduced, and the balancing efficiency is significantly improved.

[0084] In summary, the present invention provides a lithium battery multi-threshold active and passive balancing control method and system, which has the following advantages over existing balancing measures: The present invention proposes a multi-threshold active and passive balancing control method based on a multi-parameter combination of lithium battery voltage, voltage change, and charge state, designs an active and passive balancing strategy and circuit based on real-time monitoring of voltage and current parameters and dynamic control of switch tubes and duty cycles, monitors and manages the status of each battery cell in real time, and multiple thresholds ensure that the battery cells in the battery pack can be balanced in time, effectively avoiding the overall performance degradation caused by battery pack balance lag, reducing overcharging or over-discharging caused by unbalanced single cells, thereby slowing down the battery aging rate, extending the service life of the lithium battery, and reducing the maintenance cost in long-term operation.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A multi-threshold active and passive balancing control method for lithium batteries, characterized in that: include: Data collection process: collect the current value of the lithium battery and the voltage value of each single cell in the lithium battery, and obtain the SOC of each single cell based on the current value of the lithium battery and the voltage value of each single cell; The first judgment process: the voltage value corresponding to each single battery is judged with the first voltage threshold range respectively, and the SOC corresponding to each single battery is judged with the first SOC threshold range respectively, to obtain a first judgment result; The specific steps of the first judgment process are as follows: The voltage values ​​corresponding to the individual cells are respectively compared with the first voltage threshold range. If the voltage values ​​corresponding to the individual cells are all within the first voltage threshold range, the first voltage judgment condition is met. The SOC corresponding to each single battery is judged against the first SOC threshold range respectively. If the SOC corresponding to each single battery is all within the first SOC threshold range, the first SOC judgment condition is met; If the first voltage judgment condition and / or the first SOC judgment condition are met, a passive balancing instruction is output as a first judgment result; Otherwise, outputting an active balancing instruction as the first judgment result; Strategy screening process: screening active balancing strategy or passive balancing strategy based on the first judgment result; Balancing process: Use active balancing strategy or passive balancing strategy to balance each single battery; Cyclic process: Repeat the data collection process, the first judgment process, the strategy screening process and the balancing process until the voltage difference between each two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between each two adjacent single cells is within the SOC difference threshold range.

2. A lithium battery multi-threshold active and passive balancing control method according to claim 1, characterized in that: During the data collection process, the SOC corresponding to each single cell is calculated by combining the established second-order equivalent circuit model of the lithium battery with the current value of the lithium battery and the voltage value corresponding to each single cell. The state equation and output equation of the second-order RC model are obtained 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: In the formula, and are ohmic internal resistance, electrochemical resistance and concentration polarization resistance respectively, and are electrochemical and concentration polarization capacitance, respectively; and are k moments respectively and The terminal voltage, and are k+1 moments respectively and The terminal voltage, is the voltage value of the single cell at time k, 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 time k; Based on the state equation and output equation of the second-order RC model, the conversion equation is as follows: In the formula, is the process noise, which uses Gaussian white noise with a mean of zero and a variance of Q; is the observation noise, which uses Gaussian white noise with a mean of zero and a variance of R; is the state transfer matrix, is the control input matrix, is the observation matrix, is the feedforward matrix; and are the system state vector and system input respectively, which are expressed as follows: = = = =- =[ ] = in, , ; Indicates the maximum capacity of the battery; The extended Kalman filter algorithm is used to solve the conversion equation and calculate the SOC corresponding to each single battery.

3. A lithium battery multi-threshold active and passive balancing control method according to claim 1, characterized in that: The specific steps of the strategy screening process are as follows: If a passive balancing instruction is received as the first judgment result, a passive balancing strategy with passive balancing as the main and active balancing as the auxiliary is adopted; If an active balancing instruction is received as the first judgment result, an active balancing strategy with active balancing as the main and passive balancing as the auxiliary is adopted.

4. A lithium battery multi-threshold active and passive balancing control method according to claim 3, characterized in that: When the passive balancing strategy is adopted, the duty cycle μ1 of active balancing is 10%~20%; the duty cycle μ2 of passive balancing is 1-μ1.

5. A lithium battery multi-threshold active and passive balancing control method according to claim 3, characterized in that: When the active balancing strategy is adopted, the voltage value corresponding to each single cell is judged against the second voltage threshold range respectively. If the voltage values ​​corresponding to each single cell are all within the second voltage threshold range, the second voltage judgment condition is met; At the same time, the SOC corresponding to each single battery is judged against the second SOC threshold range respectively. If the SOC corresponding to each single battery is all within the second SOC threshold range, the second SOC judgment condition is met; If the second voltage judgment condition and / or the second SOC judgment condition are met, it is determined whether the voltage difference between two adjacent single cells is greater than the first voltage difference threshold; if so, the duty cycle μ1 of active balancing is ; The duty cycle μ2 of passive balancing is 1-μ1; if not, the duty cycle μ1 of active balancing is ;The duty cycle μ2 of passive balancing is 1-μ1; If the second voltage judgment condition and the second SOC judgment condition are not met, it is determined whether the voltage difference between two adjacent single cells is greater than the second voltage difference threshold; if so, the duty cycle μ1 of active balancing is ; The duty cycle μ2 of passive balancing is 1-μ1; if not, the duty cycle μ1 of active balancing is ;The duty cycle μ2 of passive balancing is 1-μ1; In the formula, is the voltage difference between two adjacent cells.

6. A lithium battery multi-threshold active and passive balancing control method according to claim 1, characterized in that: The specific steps of the balancing process are as follows: When the active balancing strategy is adopted, based on the active balancing strategy and the SOC corresponding to each single cell and the voltage difference between each two adjacent single cells, the corresponding active balancing duty cycle and passive balancing duty cycle under the active balancing strategy are obtained; Based on the corresponding active balancing duty cycle and passive balancing duty cycle under the active balancing strategy, the lithium battery is subjected to active balancing process and passive balancing process; When a passive balancing strategy is adopted, the corresponding active balancing duty ratio and passive balancing duty ratio under the passive balancing strategy are obtained based on the passive balancing strategy; Based on the corresponding active balancing duty cycle and passive balancing duty cycle under the passive balancing strategy, the lithium battery is subjected to active balancing process and passive balancing process; The active balancing process is: transferring energy from high-energy cells to low-energy cells in the lithium battery; The passive balancing process is: using energy-consuming resistors to consume the energy of the high-energy single cells in the lithium battery; Among them, a single cell with high energy means the one with higher voltage or SOC between two adjacent single cells; a single cell with low energy means the one with lower voltage or SOC between two adjacent single cells.

7. A lithium battery multi-threshold active and passive balancing control system, characterized in that: include: A data acquisition module, used for executing a data acquisition process; Data collection process: collect the current value of the lithium battery and the voltage value of each single cell in the lithium battery, and obtain the SOC of each single cell based on the current value of the lithium battery and the voltage value of each single cell; A first judgment module, used to execute a first judgment process; The first judgment process: the voltage value corresponding to each single battery is judged with the first voltage threshold range respectively, and the SOC corresponding to each single battery is judged with the first SOC threshold range respectively, to obtain a first judgment result; The specific steps of the first judgment process are as follows: The voltage values ​​corresponding to the individual cells are respectively compared with the first voltage threshold range. If the voltage values ​​corresponding to the individual cells are all within the first voltage threshold range, the first voltage judgment condition is met. The SOC corresponding to each single battery is judged against the first SOC threshold range respectively. If the SOC corresponding to each single battery is all within the first SOC threshold range, the first SOC judgment condition is met; If the first voltage judgment condition and / or the first SOC judgment condition are met, a passive balancing instruction is output as a first judgment result; Otherwise, outputting an active balancing instruction as the first judgment result; A policy screening module, used to perform a policy screening process; Strategy screening process: screening active balancing strategy or passive balancing strategy based on the first judgment result; A battery balancing module, used to perform the balancing process; balanced Process: Use active balancing strategy or passive balancing strategy to balance each single battery; A loop module is used to execute 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 each two adjacent single cells is within the voltage difference threshold range, or / and the SOC difference between each two adjacent single cells is within the SOC difference threshold range.

8. A lithium battery multi-threshold active and passive balancing control system according to claim 7, 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 is turned on, the lithium battery multi-threshold active and passive balancing control system performs an active balancing process; when the second switch tube is turned on, the lithium battery multi-threshold active and passive balancing control system performs a passive balancing process.

9. A lithium battery multi-threshold active and passive balancing control system according to claim 7, characterized in that: Also includes: 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 perform a protection process on the single battery according to the comparison result; The protection process includes undervoltage protection process and current limiting protection process.

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