A series lithium ion battery active equalization control method

Abstract

The present application relates to the technical field of battery management, in particular to a kind of active equalization control method of series lithium ion battery, comprising the following steps: obtaining single cell voltage, temperature, state of charge, group end current and charge-discharge state, and determining protection state;Calculate voltage difference and state of charge difference, determine working stage and SOC interval;The collection parameter is normalized as fuzzy variable, generates equalization current control quantity by fuzzy rule inference and defuzzification;Determine energy output monomer, energy receiving monomer and alternate equalization sequence, when equalization permission condition meets, control DC-DC bidirectional converter, SW1, SW2 and inductive active equalization branch shift energy, when condition is not satisfied, flow is reduced or suspended.The present application forms continuous control relationship between equalization current, equalization object and switch drive by the cooperative judgment of SOC interval, fuzzy inference, deviation direction and protection state.

Description

Technical Field

[0001] This invention relates to the field of battery management technology, and in particular to an active balancing control method for series lithium-ion batteries. Background Technology

[0002] Battery management technology typically revolves around battery packs, individual cells, battery management controllers, sampling harnesses, equalization circuits, and charge / discharge circuits, involving the acquisition, transmission, estimation, comparison, storage, and control of parameters such as voltage, current, temperature, and state of charge. The relevant data is obtained by sampling chips, temperature sensors, and current detectors, and transmitted to the controller via isolated communication or bus.

[0003] The traditional active balancing control method for series lithium-ion batteries refers to reading the estimated values ​​of individual cell voltage, end current, temperature, and state of charge during charging, discharging, or resting, based on the state differences of each cell in the series battery pack. The balancing judgment is formed based on the voltage difference, state of charge difference, temperature limit, operating state, and preset threshold. Then, the MOS switch, relay, and inductor, capacitor, or transformer-type energy transfer circuit are driven to perform energy transfer control between designated cells according to the set timing sequence.

[0004] In traditional active balancing control of series battery packs, the controller reads the estimated values ​​of individual cell voltage, pack end current, temperature, and state of charge. Based on the voltage difference, state of charge difference, temperature limit, operating state, and preset threshold, it makes a balancing judgment. The judgment criteria have limited expression of the correlation between different state of charge stages and charging and discharging conditions. The correspondence between the balancing current and the degree of deviation of individual cells is insufficient. The basis for determining the energy transfer direction is scattered. When multiple cells participate in energy transfer, the sequential constraints are not clear enough, resulting in discontinuous selection of balancing objects and connection of switch drive control. Summary of the Invention

[0005] The purpose of this invention is to provide an active balancing control method for series lithium-ion batteries. The method uses the voltage, temperature, state of charge, end current, and charge / discharge state of each individual cell in the series lithium-ion battery pack as the basis for balancing judgment. This method forms a continuous control link between the balancing current control quantity, energy transfer object, alternating balancing sequence, and balancing permission conditions. This reduces the problem of insufficient connection between balancing object selection, balancing current determination, and active switching execution when relying solely on a single difference or fixed threshold for balancing judgment.

[0006] To achieve the above objectives, the present invention provides an active balancing control method for series lithium-ion batteries, comprising the following steps: acquiring the voltage, temperature, state of charge (SOC), terminal current, and charge / discharge state of each individual cell in a series lithium-ion battery pack; determining overvoltage and undervoltage states based on the voltage and a preset voltage protection threshold; determining overcurrent states based on the terminal current and a preset discharge current protection threshold; and determining short-circuit states based on a short-circuit protection detection signal; calculating the voltage difference of each individual cell relative to the average voltage based on the voltage; calculating the SOC difference of each individual cell relative to the average SOC based on the SOC; and determining the balancing stage based on the charge / discharge state; determining the SOC range based on the SOC; and adjusting the voltage, temperature, SOC, terminal current, charge / discharge state, and charge / discharge state of each individual cell in the series lithium-ion battery pack. After normalization, the voltage difference and the state of charge difference are converted into fuzzy variables. Fuzzy rules corresponding to the SOC interval and the working stage are called for reasoning and defuzzification to generate a balancing current control quantity. Based on the deviation direction of the voltage difference and the state of charge difference from their corresponding mean values, the energy output unit and the energy receiving unit are determined, and the alternating balancing sequence is determined in combination with the temperature and the group terminal current. When the temperature, the group terminal current, the overvoltage state, the undervoltage state, the discharge overcurrent state, and the short circuit state all meet the balancing permission conditions, the DC-DC bidirectional converter, SW1, SW2, and the inductive active balancing branch are controlled to transfer energy between the energy output unit and the energy receiving unit according to the balancing current control quantity. When any balancing permission condition is not met, the balancing current control quantity is reduced or balancing is suspended.

[0007] Furthermore, the process of acquiring the voltage, temperature, state of charge, end-of-cell current, and charge / discharge state of each individual cell in a series-connected lithium-ion battery pack is as follows: the voltage of each individual cell is acquired by the voltage acquisition interface according to the series sequence of the individual cells, and the sampling sequence number of the individual cell is bound to the acquired voltage; the temperature corresponding to the sampling sequence number is acquired by the temperature detector, and the end-of-cell current is acquired by the current detector; the state of charge is obtained by the battery management controller based on the cumulative result of the end-of-cell current and the voltage correction result, and the charge / discharge state is obtained by identifying the signal from the direction of the charge / discharge circuit; the voltage, temperature, state of charge, end-of-cell current, and charge / discharge state are combined into an individual cell state data group according to the same sampling period.

[0008] Furthermore, the individual unit state data group undergoes validity processing. When the voltage, temperature, state of charge, terminal current, and charge / discharge state in the individual unit state data group all have the same sampling period marker, and the voltage, temperature, and state of charge are all bound to the same sampling sequence number, the individual unit state data group is used as the input for subsequent calculation of voltage difference and state of charge difference. When any acquired value in the individual unit state data group is missing, the sampling period marker is inconsistent, or the sampling sequence number is not fully bound, the corresponding voltage acquisition interface, temperature detector, or current detector is re-triggered to perform acquisition, and the conversion of individual unit state data groups that do not meet the validity processing conditions into fuzzy variables is prohibited.

[0009] Further, after the individual unit status data group meets the validity processing conditions, a protection state is determined. The protection states include overvoltage state, undervoltage state, discharge overcurrent state, and short circuit state. An overvoltage state is determined when any voltage in the individual unit status data group is higher than an overvoltage threshold, an undervoltage state is determined when any voltage in the individual unit status data group is lower than an undervoltage threshold, and the overvoltage state and undervoltage state are cancelled when all voltages in the individual unit status data group are between the undervoltage threshold and the overvoltage threshold. A discharge overcurrent state is determined when the group terminal current in the individual unit status data group is higher than a preset discharge current protection threshold, and the discharge overcurrent state is cancelled when the group terminal current in the individual unit status data group is not higher than the preset discharge current protection threshold. A short circuit state is determined when the short circuit protection detection signal is at an active level, and the short circuit state is cancelled when the short circuit protection detection signal is at an inactive level.

[0010] Further, the process of calculating the voltage difference and state of charge difference and determining the working stage of the equalization judgment is as follows: After the single cell state data group meets the validity processing conditions and the protection state has been determined, the voltage and state of charge of each single cell in the single cell state data group are read according to the sampling sequence number; the average voltage of all single cells in the series lithium-ion battery pack is used as the voltage mean, and the difference between the voltage of each single cell and the voltage mean is calculated to obtain the voltage difference; the average state of charge of all single cells in the series lithium-ion battery pack is used as the state of charge mean, and the difference between the state of charge of each single cell and the state of charge mean is calculated to obtain the state of charge difference; when the charging and discharging state is one of charging, discharging or resting, the corresponding state is determined as the working stage of the equalization judgment.

[0011] Further, the process of determining and normalizing the SOC interval based on the state of charge is as follows: After the operating stage is determined, the mean state of charge is compared sequentially with the threshold values ​​for the low and high state of charge intervals. When the mean state of charge is not higher than the threshold value for the low state of charge interval, a low SOC interval is determined; when the mean state of charge is higher than the threshold value for the low state of charge interval but lower than the threshold value for the high state of charge interval, a medium SOC interval is determined; and when the mean state of charge is not lower than the threshold value for the high state of charge interval, a high SOC interval is determined. Based on the SOC interval and the operating stage, the corresponding normalization boundary is retrieved, and the voltage, temperature, state of charge, terminal current, charge / discharge state, voltage difference, and state of charge difference are converted into normalized state quantities. When any normalized state quantity exceeds the corresponding normalization boundary, the normalized state quantity exceeding the corresponding normalization boundary is restricted within the normalization boundary, and a boundary limiting mark is generated.

[0012] Further, the process of invoking fuzzy rules for reasoning and defuzzification is as follows: the normalized state variables are converted into voltage fuzzy variables, temperature fuzzy variables, state of charge fuzzy variables, terminal current fuzzy variables, charge / discharge state fuzzy variables, voltage difference fuzzy variables, and state of charge difference fuzzy variables; a set of fuzzy rules is selected based on the SOC interval and the working stage; the rule trigger strength is calculated according to the membership relationship of each fuzzy variable; and candidate equalization current levels are formed by the rule trigger strength; the candidate equalization current levels are weighted and synthesized to obtain a comprehensive reasoning result; and the comprehensive reasoning result is defuzzified to generate an equalization current control quantity; when the boundary limiting mark exists, the equalization current control quantity is limited according to the normalized boundary corresponding to the boundary limiting mark.

[0013] Further, the process of determining the energy output cells, energy receiving cells, and alternating equalization order is as follows: Read the voltage difference and state of charge (SOC) difference; include cells with both positive voltage differences and positive SOC differences in the candidate output cell set, and include cells with both negative voltage differences and negative SOC differences in the candidate receiving cell set; when the deviation direction of the voltage difference is inconsistent with the deviation direction of the SOC difference, determine the cell's affiliation according to the priority rules corresponding to the SOC interval and operating stage; sort the candidate output cell set and the candidate receiving cell set according to the absolute value of the deviation, and eliminate cells that do not meet the equalization permission conditions based on temperature and terminal current; pair the cells in the candidate output cell set and the candidate receiving cell set in sequence according to the sorting results to obtain the energy output cells, energy receiving cells, and alternating equalization order.

[0014] Furthermore, the process of controlling the energy transfer of the DC-DC bidirectional converter, SW1, SW2, and inductive active balancing branch according to the equalization current control quantity is as follows: when the equalization permission condition is met, the currently paired energy output unit and energy receiving unit are selected according to the alternating equalization sequence; the operating current command of the DC-DC bidirectional converter is determined according to the equalization current control quantity, and the conduction sequence of SW1 and SW2 is determined according to the energy transfer direction; during the charging phase of the inductive active balancing branch, the energy output unit stores energy in the inductor, and during the discharging phase of the inductive active balancing branch, the inductor releases energy to the energy receiving unit; after the current pairing completes the preset transfer time or reaches the corresponding deviation convergence condition, the process switches to the next pairing in the alternating equalization sequence.

[0015] Furthermore, the process of determining the balancing permission conditions and adjusting the balancing current control quantity is as follows: when the temperature does not exceed the temperature limit, the terminal current does not exceed the current limit, the overvoltage state is not triggered, the undervoltage state is not triggered, the discharge overcurrent state is not triggered, and the short circuit state is not triggered, the balancing permission conditions are determined to be met, and energy transfer is performed according to the balancing current control quantity; when the temperature or terminal current exceeds the corresponding limit and the protection state is not triggered, the balancing current control quantity is reduced according to the over-limit type, and the balancing permission conditions are re-determined; when the overvoltage state, undervoltage state, discharge overcurrent state, or short circuit state is triggered, balancing is suspended and SW1, SW2, and the DC-DC bidirectional converter are turned off.

[0016] Compared with the prior art, the advantages and positive effects of the present invention are as follows: In this invention, voltage, temperature, state of charge (SOC), terminal current, and charge / discharge status are collected from the same source. The average voltage and SOC are used to form a voltage difference and a SOC difference, and the balance judgment is based on whether a single cell deviates from the benchmark. The collected parameters and operating stages are normalized into fuzzy variables, and the balance current control quantity is obtained by calling fuzzy rules according to the SOC interval, so that the balance current corresponds to the SOC stage and operating condition. After the energy output cell, energy receiving cell, and alternating balance sequence are determined, temperature, terminal current, and protection status are used as balance permission conditions. When the conditions are not met, the current is reduced or suspended to reduce the conflict between switching drive and safety boundary. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1This is the main flowchart of the active balancing control of series lithium-ion batteries in this invention; Figure 2 This is a schematic diagram illustrating the formation and validity processing of the individual state data group of the present invention; Figure 3 This is a schematic diagram of the SOC interval and fuzzy inference processing of the present invention; Figure 4 This is a schematic diagram illustrating the equalization object identification and alternating equalization sequence of the present invention; Figure 5 This is a schematic diagram of the active equalization energy transfer and permission control of the present invention. Detailed Implementation

[0019] The following describes the embodiments of the present invention in conjunction with the protection scope text, the technical solutions described in the application documents, the original disclosure materials, and the accompanying drawings. In subsequent embodiments, the series-connected lithium-ion battery pack is an energy storage object formed by multiple individual cells connected in series. The voltage, temperature, state of charge, terminal current, and charge / discharge state of the individual cells serve as the basic inputs for equalization judgment; overvoltage state, undervoltage state, discharge overcurrent state, and short-circuit state serve as protection states for equalization permission conditions; voltage difference, state of charge difference, SOC range, operating stage, fuzzy variable, equalization current control quantity, energy output cell, energy receiving cell, and alternating equalization sequence serve as intermediate processing results or control outputs. The DC-DC bidirectional converter, SW1, SW2, and inductive active equalization branch involved in subsequent embodiments are all used to perform energy transfer control. If component names with numerical labels appear in the accompanying drawings, the component names have the same meaning as the corresponding components in the protection scope text, the accompanying drawing description, and the original disclosure materials. The numerical labels are only used to identify components and do not constitute a limitation on quantity, parameters, order, or range; no new component numerical labels have been assigned in this embodiment.

[0020] Please see Figures 1 to 5 This embodiment provides an active balancing control method for series lithium-ion batteries. This method is used to actively balance the state differences of each individual cell in a series lithium-ion battery pack. During execution, the individual cell state parameters obtained in the same sampling period are used as the data source, the SOC range and operating stage are used as fuzzy rule calling conditions, the deviation direction of voltage difference and state of charge difference is used to determine the energy transfer object, and the execution process of the DC-DC bidirectional converter, SW1, SW2 and inductive active balancing branch are constrained by balancing permission conditions.

[0021] S1: Obtain the voltage, temperature, state of charge, terminal current, and charge / discharge status of each individual cell in the series-connected lithium-ion battery pack, and determine the protection status.

[0022] S101, the voltage acquisition interface acquires the voltage of each individual cell sequentially according to the series connection order of the individual cells in the series lithium-ion battery pack. After the voltage acquisition is completed, the voltage acquisition interface binds the sampling sequence number of the individual cell with the corresponding acquired voltage, so that the correspondence between the individual cell and the voltage data can be maintained when calculating the average voltage, voltage difference, and identifying energy output cells and energy receiving cells.

[0023] S102, a temperature detector collects the temperature corresponding to the sampling sequence number. The temperature collected by the temperature detector is consistent with the sampling sequence number of the individual battery cell, so that the temperature can be associated with the corresponding individual battery cell when determining the alternating equalization sequence and judging the equalization permission conditions. A current detector collects the group terminal current of the series lithium-ion battery pack, and the group terminal current is used as the input for state of charge estimation, discharge overcurrent state determination, and equalization permission condition judgment.

[0024] S103, the battery management controller obtains the state of charge (SOC) based on the accumulated current at the battery bank and the voltage correction result. The accumulated current at the battery bank reflects the change in charge during charging and discharging, while the voltage correction result is used to correct the SOC, establishing a correlation between the SOC and the voltage acquisition results within the same sampling period. The battery management controller also obtains the charging and discharging status by identifying signals from the charging and discharging circuit direction. The charging and discharging status is used to determine the current operating stage for the equalization judgment.

[0025] S104: Within the same sampling period, voltage, temperature, state of charge, terminal current, and charge / discharge status are grouped into individual cell state data sets. Each individual cell state data set uses its sampling sequence number as the corresponding identifier and the sampling period marker as the synchronization identifier, enabling subsequent voltage difference calculations, state of charge difference calculations, SOC interval determination, normalization processing, and fuzzy variable transformations to utilize data from the same time period.

[0026] S105, determine overvoltage and undervoltage states based on the voltage and preset voltage protection thresholds. The preset voltage protection thresholds include overvoltage and undervoltage thresholds. When any voltage in the individual status data group is higher than the overvoltage threshold, an overvoltage state is determined; when any voltage in the individual status data group is lower than the undervoltage threshold, an undervoltage state is determined; when all voltages in the individual status data group are between the undervoltage and overvoltage thresholds, the overvoltage and undervoltage states are canceled.

[0027] S106: Determine the discharge overcurrent state based on the group terminal current and the preset discharge current protection threshold. When the group terminal current in the individual unit status data group is higher than the preset discharge current protection threshold, the discharge overcurrent state is determined; when the group terminal current in the individual unit status data group is not higher than the preset discharge current protection threshold, the discharge overcurrent state is cancelled. Determine the short-circuit state based on the short-circuit protection detection signal. When the short-circuit protection detection signal is at an active level, the short-circuit state is determined; when the short-circuit protection detection signal is at an inactive level, the short-circuit state is cancelled.

[0028] S2 performs validity processing on the individual state data group.

[0029] S201: When the voltage, temperature, state of charge, terminal current, and charge / discharge state in a single-cell state data set all have the same sampling period marker, and the voltage, temperature, and state of charge are all bound to the same sampling sequence number, the single-cell state data set is used as the input for subsequent calculations of voltage difference and state of charge difference. This validity processing ensures that the voltage, temperature, and state of charge of the same single cell can be synchronously called in subsequent normalization and fuzzy inference, avoiding data from different sampling periods from being mixed into the same equalization judgment.

[0030] S202: When any acquired value is missing, the sampling period marker is inconsistent, or the sampling sequence number is not properly bound in a single-unit status data group, the corresponding voltage acquisition interface, temperature detector, or current detector is re-triggered to perform acquisition, and the conversion of single-unit status data groups that do not meet the validity processing conditions into fuzzy variables is prohibited. The re-acquired object corresponds to the missing or inconsistent data type, and the binding check of the sampling period marker and sampling sequence number is performed again after the re-acquisition is completed.

[0031] S3 calculates the voltage difference and state-of-charge difference, and determines the working stage of the equilibrium judgment.

[0032] S301: After the individual cell status data group meets the validity processing conditions and the protection status has been determined, read the voltage and state of charge of each individual cell in the individual cell status data group according to the sampling sequence number. The reading process maintains the series sequence of the individual cells, so that the subsequent average voltage, average state of charge, candidate output cell set, and candidate receiving cell set are all formed based on the same individual cell sequence.

[0033] S302, using the average voltage of all individual cells in the series-connected lithium-ion battery pack as the voltage mean, calculates the difference between the voltage of each individual cell and the voltage mean, obtaining the voltage difference. The voltage difference is used to characterize the direction and degree of deviation of the voltage of each individual cell from the overall voltage level of the series-connected lithium-ion battery pack.

[0034] S303 uses the average state of charge (SOC) of all individual cells in the series-connected lithium-ion battery pack as the mean SOC. It then calculates the difference between the SOC of each individual cell and the mean SOC, obtaining the SOC difference. The SOC difference characterizes the direction and degree of deviation of the SOC of each individual cell from the overall SOC level of the series-connected lithium-ion battery pack.

[0035] S304: When the charging / discharging state is one of charging, discharging, or resting, the corresponding state is determined as the working stage for the equalization judgment. The working stage is used to subsequently retrieve the normalized boundary and fuzzy rule set, so that the same voltage difference or state of charge difference can enter different control judgment paths in different working stages.

[0036] S4 determines the SOC range based on the state of charge and normalizes the voltage, temperature, state of charge, terminal current, charge / discharge state, voltage difference, and state of charge difference.

[0037] S401, after the working phase is determined, the average state of charge (SOC) is compared sequentially with the low SOC interval threshold and the high SOC interval threshold. When the average SOC is not higher than the low SOC interval threshold, the low SOC interval is determined; when the average SOC is higher than the low SOC interval threshold but lower than the high SOC interval threshold, the medium SOC interval is determined; when the average SOC is not lower than the high SOC interval threshold, the high SOC interval is determined. The SOC interval reflects the position of the series-connected lithium-ion battery pack throughout its entire SOC cycle.

[0038] S402 retrieves the corresponding normalized boundaries based on the SOC interval and operating stage, converting voltage, temperature, state of charge, terminal current, charge / discharge state, voltage difference, and state of charge difference into normalized state variables. The normalized state variables retain the relative change direction of the original input parameters and their meaning in the judgment, and transfer data of different dimensions into a unified processing interval that can participate in fuzzy variable transformation.

[0039] S403: When any normalized state variable exceeds the corresponding normalization boundary, the normalized state variable exceeding the corresponding normalization boundary is restricted within the normalization boundary, and a boundary limiting marker is generated. The boundary limiting marker is used to identify the restricted input state in the subsequent fuzzy inference and equalization current control quantity generation process, so that the output result obtained by defuzzification is constrained by the corresponding normalization boundary.

[0040] S5 calls fuzzy rules for reasoning and defuzzification to generate balanced current control quantities.

[0041] S501 converts the normalized state variables into voltage fuzzy variables, temperature fuzzy variables, state of charge fuzzy variables, terminal current fuzzy variables, charge / discharge state fuzzy variables, voltage difference fuzzy variables, and state of charge difference fuzzy variables. Each fuzzy variable is formed by the corresponding normalized state variable and participates in rule reasoning within the same SOC interval and operating stage.

[0042] S502, selects a fuzzy rule set based on the SOC range and operating stage. The fuzzy rule set receives voltage fuzzy variables, temperature fuzzy variables, state of charge fuzzy variables, group terminal current fuzzy variables, charging and discharging state fuzzy variables, voltage difference fuzzy variables, and state of charge difference fuzzy variables. The rule triggering strength is calculated according to the membership relationship of each fuzzy variable, and the candidate equalization current level is formed by the rule triggering strength.

[0043] S503 performs weighted synthesis of candidate equalization current levels to obtain a comprehensive inference result, and then defuzzifies the comprehensive inference result to generate an equalization current control quantity. The equalization current control quantity serves as the input to the subsequent control command for the DC-DC bidirectional converter's operating current, and also participates in the reduction processing when the equalization permission conditions are not met.

[0044] S504, when a boundary limiting marker exists, limits the equalization current control quantity according to the normalized boundary corresponding to the boundary limiting marker. Through this limitation, the restriction of the input state by the normalized boundary can be transmitted to the output control quantity, so that the subsequent energy transfer process is constrained by the same input boundary.

[0045] S6 determines the energy output unit, energy receiving unit, and alternating balancing sequence.

[0046] S601 reads the voltage difference and state-of-charge difference, and includes single-cell batteries with both positive voltage difference and positive state-of-charge difference in the candidate output cell set, and single-cell batteries with both negative voltage difference and negative state-of-charge difference in the candidate receiving cell set. The candidate output cell set is used to characterize single-cell batteries with both voltage and state-of-charge higher than the corresponding average value, and the candidate receiving cell set is used to characterize single-cell batteries with both voltage and state-of-charge lower than the corresponding average value.

[0047] S602, when the deviation direction of the voltage difference is inconsistent with the deviation direction of the state of charge difference, the allocation of the individual cell is determined according to the priority determination rule corresponding to the SOC range and operating stage. This priority determination rule uses the SOC range and operating stage as the selection basis, so that when the voltage difference and the state of charge difference have inconsistent deviation directions, there is a clear determination order and allocation result.

[0048] S603 sorts the candidate output cell set and candidate receiver cell set according to their absolute deviations, and eliminates individual cells that do not meet the equalization permission conditions based on temperature and group terminal current. The sorting results are used to determine the order in which they participate in energy transfer, and the elimination results are used to prevent individual cells that do not meet the temperature or group terminal current constraints from entering the current equalization pairing.

[0049] S604, according to the sorting result, the individual cells in the candidate output cell set and the individual cells in the candidate receiving cell set are paired sequentially to obtain the energy output cell, the energy receiving cell, and the alternating equalization sequence. The alternating equalization sequence records the execution order between multiple pairings, so that the subsequent energy transfer process can switch sequentially between multiple pairings.

[0050] S7 controls the transfer of energy by the DC-DC bidirectional converter, SW1, SW2 and the inductive active balancing branch according to the equalization current control quantity.

[0051] S701: When the balancing permission conditions are met, the currently paired energy output cell and energy receiving cell are selected according to the alternating balancing sequence. The current pairing is the target of this energy transfer, and the balancing current control quantity serves as the basis for the current control of this energy transfer.

[0052] S702 determines the operating current command of the DC-DC bidirectional converter based on the equalization current control quantity, and determines the conduction sequence of SW1 and SW2 according to the energy transfer direction. The DC-DC bidirectional converter participates in energy transfer according to the operating current command. SW1 and SW2 form switching states corresponding to the energy transfer direction according to the conduction sequence, so that the inductive active equalization branch establishes charging and discharging paths between selected cells.

[0053] In the charging phase of the inductive active balancing branch, S703 enables the energy output unit to store energy in the inductor; in the discharging phase, it enables the inductor to release energy to the energy receiving unit. The charging and discharging phases together constitute a single energy transfer process, forming a defined energy path and control path between the energy output unit, the energy receiving unit, the DC-DC bidirectional converter, SW1, SW2, and the inductive active balancing branch.

[0054] S704: After the current pairing completes the preset transfer time or reaches the corresponding deviation convergence condition, switch to the next pairing in the alternating equilibrium sequence. The preset transfer time and deviation convergence condition serve as the trigger conditions for the end of the current pairing. The next pairing is determined according to the alternating equilibrium sequence until the pairing to be participated in completes the corresponding energy transfer, or the equilibrium permission condition changes.

[0055] S8 determines the balancing permission conditions and adjusts the balancing current control quantity.

[0056] S801 determines that the balancing permission conditions are met when the temperature does not exceed the temperature limit, the terminal current does not exceed the current limit, the overvoltage condition is not triggered, the undervoltage condition is not triggered, the discharge overcurrent condition is not triggered, and the short circuit condition is not triggered. Energy transfer is then executed according to the balancing current control quantity. This determination incorporates temperature, terminal current, and protection status into the execution boundary, ensuring that the energy transfer process proceeds while meeting protection constraints.

[0057] S802: When the temperature or terminal current exceeds the corresponding limit and the protection status is not triggered, the equalization current control quantity is reduced according to the over-limit type, and the equalization permission conditions are re-determined. The reduced equalization current control quantity re-enters the operating current command generation process of the DC-DC bidirectional converter, thus establishing a feedback relationship between current control and temperature and terminal current constraints.

[0058] S803, when triggered by overvoltage, undervoltage, overcurrent discharge, or short-circuit conditions, pauses balancing and shuts down SW1, SW2, and the DC-DC bidirectional converter. After balancing is paused, the inductive active balancing branch no longer performs the currently paired energy transfer. After the protection status is canceled and the balancing permission conditions are met again, subsequent control is executed according to the redefined individual unit status data group, balancing current control quantity, and alternating balancing sequence.

[0059] Through the continuous execution of S1 to S8, this embodiment forms a complete control chain from state acquisition, data validity processing, protection state determination, difference calculation, SOC interval determination, fuzzy inference, equalization object identification, alternating equalization sorting, to active switch execution and permission condition feedback. Voltage, temperature, state of charge, group terminal current, and charging / discharging state are all invoked in subsequent processing. Voltage difference and state of charge difference are used to determine the deviation direction and candidate unit set. SOC interval and operating stage are used to constrain fuzzy rule invocation. Equalization current control quantity is used to control the DC-DC bidirectional converter and the execution process of SW1 and SW2. Temperature, group terminal current, and protection state are used for equalization permission condition determination and equalization current control quantity adjustment.

[0060] The specific processes, field states, processing order, judgment conditions, parameter sources, component coordination, and control relationships described in the above embodiments are used to explain the possible implementations of the present invention and should not be limited to the specific embodiments listed. Without departing from the technical solutions described in this invention and the scope of the original disclosure, any equivalent substitutions, modifications, combinations, order adjustments, equivalent transformations of field names, equivalent inheritance of the executing entity, or equivalent changes in the carrier form that can be conceived by those skilled in the art should fall within the scope of protection of this patent; however, they should not be extended to unclaimed topics, nor should the substantive correspondence of the technical objects be changed through changes in reference numerals. Equivalent changes should not replace, delete, or weaken the method features, control relationships, data relationships, temporal relationships, parameter relationships, or physical action relationships necessary to achieve the technical effect.

Claims

1. A method for active balancing control of a series lithium-ion battery, characterized in that, Includes the following steps: The system acquires the voltage, temperature, state of charge, terminal current, and charge / discharge state of each individual cell in a series lithium-ion battery pack. It determines overvoltage and undervoltage states based on the voltage and a preset voltage protection threshold, determines overcurrent states based on the terminal current and a preset discharge current protection threshold, and determines short-circuit states based on short-circuit protection detection signals. The voltage difference of each individual cell relative to the average voltage is calculated based on the voltage, the state of charge difference of each individual cell relative to the average state of charge is calculated based on the state of charge, and the working stage is determined based on the charging and discharging state. The SOC range is determined based on the state of charge. The voltage, temperature, state of charge, terminal current, charging and discharging state, voltage difference, and state of charge difference are normalized and converted into fuzzy variables. The fuzzy rules corresponding to the SOC range and the working stage are called for reasoning and defuzzification processing to generate the equalization current control quantity. Based on the deviation direction of the voltage difference and the state of charge difference from the corresponding mean, the energy output unit and the energy receiving unit are determined, and the alternating balancing sequence is determined in combination with the temperature and the group terminal current; When the temperature, terminal current, overvoltage state, undervoltage state, discharge overcurrent state, and short circuit state all meet the equalization permission conditions, the DC-DC bidirectional converter, SW1, SW2, and inductive active equalization branch are controlled to transfer energy between the energy output unit and the energy receiving unit according to the equalization current control amount. When any equalization permission condition is not met, the equalization current control amount is reduced or equalization is suspended.

2. The active balancing control method for series lithium-ion batteries according to claim 1, characterized in that, The steps for obtaining the voltage, temperature, state of charge, terminal current, and charge / discharge state of each individual cell in a series-connected lithium-ion battery pack include: The voltage of each individual battery cell is acquired by the voltage acquisition interface in the series sequence of the individual cells, and the sampling number of the individual battery cell is bound to the acquired voltage. The temperature corresponding to the sampling number is collected by a temperature detector, and the group terminal current is collected by a current detector; The battery management controller obtains the state of charge based on the cumulative current at the battery terminal and the voltage correction result, and obtains the charging and discharging status by identifying signals from the direction of the charging and discharging circuit. Voltage, temperature, state of charge, terminal current, and charge / discharge status are grouped into individual unit state data sets according to the same sampling period.

3. The active balancing control method for series lithium-ion batteries according to claim 2, characterized in that, It also includes validation processing of the individual state data group, the validation processing including: When the voltage, temperature, state of charge, terminal current and charge / discharge state in the individual unit state data group all have the same sampling period mark, and the voltage, temperature and state of charge are all bound to the same sampling sequence number, the individual unit state data group is used as the input for subsequent calculation of voltage difference and state of charge difference. When any acquired value is missing, the sampling period marking is inconsistent, or the sampling sequence number is not bound, the corresponding voltage acquisition interface, temperature detector, or current detector is re-triggered to perform acquisition, and the conversion of individual state data groups that do not meet the validity processing conditions into fuzzy variables is prohibited.

4. The active balancing control method for series lithium-ion batteries according to claim 3, characterized in that, It also includes determining the protection status after the individual status data group meets the validity processing conditions. The protection status includes overvoltage status, undervoltage status, discharge overcurrent status and short circuit status. An overvoltage state is determined when any voltage in the individual unit status data group is higher than the overvoltage threshold; an undervoltage state is determined when any voltage in the individual unit status data group is lower than the undervoltage threshold; and the overvoltage and undervoltage states are canceled when all voltages in the individual unit status data group are between the undervoltage and overvoltage thresholds. When the group terminal current in the individual unit status data group is higher than the preset discharge current protection threshold, the discharge overcurrent state is determined; when the group terminal current in the individual unit status data group is not higher than the preset discharge current protection threshold, the discharge overcurrent state is cancelled. A short circuit is determined when the short circuit protection detection signal is at an active level, and the short circuit is canceled when the short circuit protection detection signal is at an inactive level.

5. The active balancing control method for series lithium-ion batteries according to claim 4, characterized in that, The process of calculating the voltage difference and state-of-charge difference and determining the operating stage for the equilibrium judgment includes: After the individual cell status data group meets the validity processing conditions and the protection status has been determined, read the voltage and state of charge of each individual cell in the individual cell status data group according to the sampling sequence number. The average voltage of all individual cells in the series-connected lithium-ion battery pack is used as the average voltage. The difference between the voltage of each individual cell and the average voltage is calculated to obtain the voltage difference. The average state of charge (SOC) of all individual cells in the series-connected lithium-ion battery pack is used as the mean SOC. The difference between the SOC of each individual cell and the mean SOC is calculated to obtain the SOC difference. When the charging / discharging state is one of charging, discharging, or resting, the corresponding state is determined as the working stage of the equalization judgment.

6. The active balancing control method for series lithium-ion batteries according to claim 5, characterized in that, The process of determining the SOC range based on the state of charge and then normalizing it includes: After the working stage is determined, the mean state of charge is compared with the low state of charge interval threshold and the high state of charge interval threshold in turn. When the mean state of charge is not higher than the low state of charge interval threshold, the low SOC interval is determined. When the mean state of charge is higher than the low state of charge interval threshold but lower than the high state of charge interval threshold, the medium SOC interval is determined. When the mean state of charge is not lower than the high state of charge interval threshold, the high SOC interval is determined. Based on the SOC range and operating stage, the corresponding normalized boundaries are retrieved, and the voltage, temperature, state of charge, terminal current, charge / discharge state, voltage difference, and state of charge difference are converted into normalized state quantities respectively. When any normalized state variable exceeds the corresponding normalization boundary, the normalized state variable exceeding the corresponding normalization boundary is restricted to within the normalization boundary, and a boundary limiting marker is generated.

7. The active balancing control method for series lithium-ion batteries according to claim 6, characterized in that, The process of invoking fuzzy rules for reasoning and defuzzification includes: The normalized state variables are converted into voltage fuzzy variables, temperature fuzzy variables, state of charge fuzzy variables, terminal current fuzzy variables, charge and discharge state fuzzy variables, voltage difference fuzzy variables, and state of charge difference fuzzy variables. A set of fuzzy rules is selected based on the SOC range and the working stage. The rule triggering intensity is calculated according to the membership relationship of each fuzzy variable, and the candidate equalization current level is formed by the rule triggering intensity. The candidate equalization current levels are weighted and synthesized to obtain a comprehensive reasoning result, and the comprehensive reasoning result is defuzzified to generate an equalization current control quantity. When the boundary limiting mark exists, the equalization current control amount is limited according to the normalized boundary corresponding to the boundary limiting mark.

8. The active balancing control method for series lithium-ion batteries according to claim 7, characterized in that, The process of determining the energy output cell, energy receiving cell, and alternating equalization sequence includes: Read the voltage difference and state of charge difference, and include the individual cells with positive voltage difference and positive state of charge difference in the candidate output cell set, and include the individual cells with negative voltage difference and negative state of charge difference in the candidate receiving cell set. When the deviation direction of the voltage difference is inconsistent with the deviation direction of the state of charge difference, the ownership of the individual cell is determined according to the priority judgment rules corresponding to the SOC range and the working stage. The candidate output cell set and the candidate receiving cell set are sorted according to the absolute value of deviation, and cell cells that do not meet the equalization permission conditions are eliminated in combination with temperature and group terminal current. According to the sorting results, the individual cells in the candidate output cell set and the individual cells in the candidate receiving cell set are paired in sequence to obtain the energy output cell, energy receiving cell, and alternating equalization sequence.

9. The active balancing control method for series lithium-ion batteries according to claim 8, characterized in that, The process of controlling the energy transfer of the DC-DC bidirectional converter, SW1, SW2, and inductive active balancing branch according to the equalization current control includes: When the equalization permission conditions are met, the currently paired energy output unit and energy receiving unit are selected according to the alternating equalization order; The operating current command of the DC-DC bidirectional converter is determined based on the equalization current control quantity, and the conduction sequence of SW1 and SW2 is determined based on the energy transfer direction. During the charging phase of the inductive active balancing branch, the energy output cell stores energy in the inductor, and during the discharging phase of the inductive active balancing branch, the inductor releases energy to the energy receiving cell. After the current pairing completes the preset transition time or reaches the corresponding deviation convergence condition, it switches to the next pairing in the alternating equilibrium sequence.

10. The active balancing control method for series lithium-ion batteries according to claim 9, characterized in that, The process of determining the balancing permission conditions and adjusting the balancing current control quantity includes: When the temperature does not exceed the temperature limit, the terminal current does not exceed the current limit, the overvoltage state is not triggered, the undervoltage state is not triggered, the discharge overcurrent state is not triggered, and the short circuit state is not triggered, the equalization permission condition is determined to be met, and energy transfer is performed according to the equalization current control quantity. When the temperature or group terminal current exceeds the corresponding limit and the protection status is not triggered, the equalization current control quantity is reduced according to the over-limit type and the equalization permission condition is re-determined. When an overvoltage condition, undervoltage condition, discharge overcurrent condition, or short circuit condition is triggered, equalization is paused and SW1, SW2, and the DC-DC bidirectional converter are turned off.

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