Lithium battery consistency evaluation method

Abstract

According to the lithium battery consistency evaluation method provided by the invention, the charging and discharging tail end voltage variation coefficient and the charging and discharging SOC range are taken as indexes for evaluating the consistency of the battery, dynamic assignment is carried out on the weight of each index during calculation of the consistency comprehensive score, and weighted summation is carried out on the score of each index, so that the consistency of the battery is evaluated. Quantitative evaluation of the battery consistency is realized, and the technical problems of single dimension and low evaluation accuracy of the traditional method for evaluating the battery consistency are solved. Only the terminal voltage of the battery needs to be collected in the evaluation process, and online evaluation of the health state of the battery can be achieved.

Description

Technical Field

[0001] This application relates to the field of battery performance evaluation technology, specifically to a method for evaluating the consistency of lithium batteries. Background Technology

[0002] With the development of new energy technologies and the proposal of dual-carbon goals, new energy has been widely used in many fields, especially in the field of energy storage. Lithium batteries have been widely used in electric vehicles, electronic devices, energy storage power stations and other fields due to their advantages such as high energy storage capacity, long cycle life and low self-discharge rate.

[0003] The performance of lithium batteries varies to varying degrees during use, especially when used in series-parallel battery clusters. Under different operating conditions, inconsistencies in the performance of individual cells within the cluster are inevitable. As operating time increases, the inconsistencies between individual cells may widen, leading to a decline in the overall performance of the battery cluster and consequently, a reduction in its usable capacity and cycle life. Furthermore, decreased inconsistency may cause individual cells to overcharge or over-discharge, potentially resulting in thermal runaway, explosion, and fire, posing a significant threat to the safety of battery-powered devices.

[0004] Existing methods for evaluating the consistency of lithium battery performance typically employ traditional methods such as the range method and the standard deviation method. These methods have a single dimension for consistency evaluation, and the accuracy of the evaluation results is not ideal, making it difficult to effectively prevent the aforementioned safety threats. Summary of the Invention

[0005] This application provides a lithium battery consistency evaluation method for the purpose of accurately assessing battery performance consistency.

[0006] To achieve this objective, the following technical solution is adopted in this application:

[0007] A method for evaluating the consistency of lithium batteries is provided, comprising the following steps:

[0008] S1, Calculate the voltage variation coefficient of the battery pack. and SOC range ;

[0009] S2, assign scores to each indicator used to evaluate the consistency of battery performance, and assign corresponding weights to each indicator;

[0010] S3, calculate the weighted sum of the scores for each indicator to obtain a consistency composite score. This serves as an evaluation result of the battery performance consistency of the battery pack.

[0011] Preferably, step S1 specifically includes the following steps:

[0012] S11, Collect the terminal voltage of the battery pack within a preset time window to form a terminal voltage sequence;

[0013] S12, calculate the average value of each voltage value in the terminal voltage sequence. Standard deviation and range ;

[0014] S13, according to and Calculate the voltage variation coefficient ;according to The SOC range was calculated. .

[0015] Preferably, ; ; ;

[0016] Represents the first in the terminal voltage sequence Terminal voltage;

[0017] This indicates the number of terminal voltages in the terminal voltage sequence;

[0018] Represents the first in the terminal voltage sequence The value of the terminal voltage;

[0019] The time represents the average value, standard deviation, and range of the charging terminal voltage of the battery pack; The time represents the average value, standard deviation, and range of the discharge terminal voltage of the battery pack.

[0020] Preferably, voltage variation coefficient The calculation expression is:

[0021]

[0022] SOC range The calculation expression is:

[0023]

[0024] Indicates the proportional threshold;

[0025] or ; It represents the difference in charging voltage when the battery's remaining state of charge (SOC) is between 95% and 100% during the battery pack charging process. It represents the difference in discharge voltage when the remaining battery charge (SOC) is between 5% and 0% during the battery pack discharge process; hour, ; hour, .

[0026] Preferably, ; .

[0027] Preferably, in step S2, the indicator includes the coefficient of variation of the charging terminal voltage of the battery pack. Coefficient of variation of discharge terminal voltage SOC range calculated based on the charging end voltage SOC range calculated based on discharge terminal voltage Any one or more of the following.

[0028] Preferably, in step S2, the method for assigning scores to each of the indicators used to evaluate the consistency of battery performance is expressed by the following expression:

[0029]

[0030] , , , To calculate the specific index The first, second, third, and fourth parameters of the assigned score; Corresponding lower limit indicator value The assigned score; Corresponding upper limit indicator value The assigned score; Indicates the specific indicator number A number; For specific indicators The assigned score for each; among which ;

[0031] The formula represents and and between The numerical value and its corresponding value and and between The scores are assigned in a linear correspondence.

[0032] When the specific indicator is the SOC range calculated from the discharge terminal voltage. hour,

[0033] , , ;

[0034] When the specific indicator is the coefficient of variation of the discharge terminal voltage hour,

[0035] , , ;

[0036] When the specific indicator is the SOC range calculated from the charging end voltage. hour,

[0037] , , ;

[0038] When the specific indicator is the coefficient of variation of the charging terminal voltage of the battery pack hour,

[0039] , , .

[0040] Preferably, in step S2, the method for assigning corresponding weights to each of the indicators includes the following steps:

[0041] S21, Construct the fuzzy judgment matrix :

[0042] S22, regarding the fuzzy judgment matrix Defuzzification is performed to obtain the definite judgment matrix. ;

[0043] S23, Determine the judgment matrix Perform a consistency check.

[0044] If the test is successful, then the judgment matrix is ​​determined. Calculate the weight corresponding to each of the aforementioned indicators;

[0045] If the test fails, return to step S21 and reconstruct the fuzzy judgment matrix. .

[0046] Preferably,

[0047]

[0048] Determine the judgment matrix The first in Line 1 Element value of column element The calculation method is expressed as follows: , , These represent the lower limit, middle value, and upper limit of the triangular fuzzy number in the fuzzy judgment matrix, respectively. The fuzzy judgment matrix is ​​a positive definite inverse matrix.

[0049] Preferably, the determination matrix is... The method for performing consistency verification includes the following steps:

[0050] S231, Calculate the largest eigenvalue The calculation method is as follows:

[0051] The power method is used to iteratively find the largest eigenvalue of matrix A. The specific steps are as follows: Choose any initial vector. ≠0;

[0052] Repeated updates = · The normalized vector is used until convergence; Indicates the first A third or fourth parameter, Indicates the first A third or fourth parameter;

[0053] The final Rayleigh quotient is Approximate value;

[0054] S232, Calculate the consistency index , The determination matrix represents the determination matrix. The order of;

[0055] S233, Calculate the consistency ratio , Indicates the random consistency index;

[0056] S234, judgment Is it less than the preset ratio threshold?

[0057] If so, then determine the determination matrix. The consistency check was successful;

[0058] If not, then determine the determination matrix. The consistency check failed.

[0059] Preferably, the determination judgment matrix is... After the consistency check passes, the determination judgment matrix is ​​used as described above. The method for calculating the weight corresponding to each of the above indicators includes the following steps:

[0060] A1, Calculate the determination matrix. geometric mean ;

[0061] A2, Calculate the normalized weight values. ;

[0062] , , , , These represent the coefficients of variation of the charging terminal voltage, respectively. The coefficient of variation of the discharge terminal voltage The SOC range calculated based on the charging end voltage. The SOC range calculated based on the discharge terminal voltage. Calculated weights.

[0063] The lithium battery consistency evaluation method provided in this application uses the coefficient of variation of charge and discharge terminal voltage and the state of charge / discharge (SOC) range as indicators to evaluate battery consistency. By dynamically assigning weights to each indicator when calculating the overall consistency score and then weighted summing the scores of each indicator, a quantitative evaluation of battery consistency is achieved. This overcomes the technical problem of traditional methods having limited accuracy due to their single-dimensional approach. The evaluation process only requires collecting the battery terminal voltage, enabling online assessment of the battery's health status. Attached Figure Description

[0064] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0065] Figure 1 This is a diagram illustrating the implementation steps of the lithium battery consistency evaluation method provided in the embodiments of this application. Detailed Implementation

[0066] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. These drawings are for illustrative purposes only, representing schematic diagrams rather than actual physical objects, and should not be construed as limiting this patent. Those skilled in the art can obtain other drawings based on these drawings without any creative effort. The lithium battery consistency evaluation method provided in the embodiments of this application, such as... Figure 1 As shown, the steps include:

[0067] S1, Calculate the voltage variation coefficient of the battery pack. and SOC range ;

[0068] S2, assign scores to each indicator used to evaluate the consistency of battery performance, and assign corresponding weights to each indicator;

[0069] S3, calculate the weighted sum of the scores for each indicator to obtain a consistency composite score. This serves as an evaluation result of the battery performance consistency of the battery pack.

[0070] Step S1 specifically includes the following steps:

[0071] S11, the terminal voltage of the battery pack is collected within a preset time window to form a terminal voltage sequence; for example, the charging terminal voltage data of the battery pack collected within this time window is sequenced. Expressed as:

[0072]

[0073] The discharge end voltage data of the battery pack collected within the time window is used to... Expressed as:

[0074]

[0075] , The unit for each voltage in the table is mV;

[0076] In this embodiment, the charging end of the battery pack refers to the battery's remaining SOC being between 95% and 100% during the charging process; the discharging end of the battery pack refers to the battery's remaining SOC being between 5% and 0% during the discharging process.

[0077] S12, calculate the average value of each voltage value in the terminal voltage sequence. Standard deviation and range ; The time represents the average, standard deviation, and range of the charging terminal voltage of the battery pack. The time represents the calculated average, standard deviation, and range of the discharge terminal voltage of the battery pack;

[0078] In this embodiment, ; ; ;

[0079] Represents the first in the terminal voltage sequence Terminal voltage;

[0080] This indicates the number of terminal voltages in the terminal voltage sequence;

[0081] Represents the first in the terminal voltage sequence The value of the terminal voltage.

[0082] For example, for , ,but

[0083]

[0084]

[0085] And for ,but

[0086]

[0087]

[0088] S13, according to and Calculate the voltage variation coefficient ;according to Calculate the SOC range .

[0089] In this embodiment, the voltage variation coefficient The calculation expression is:

[0090]

[0091] SOC range The calculation expression is:

[0092]

[0093] Indicates the proportional threshold; preferably, ; .

[0094] Here 100% refers to

[0095] 100% refers to the voltage variation coefficient. = Percentage of mean / standard deviation;

[0096] 5% refers to: This represents the difference between 100% and 95% of the charging voltage when the battery's remaining SOC is between 95% and 100% during the charging process.

[0097] or ; It represents the difference in charging voltage when the battery's remaining state of charge (SOC) is between 95% and 100% during the battery pack charging process. It represents the difference in discharge voltage when the remaining battery charge (SOC) is between 5% and 0% during the battery pack's discharge process.

[0098] , The coefficient of variation of the charging end voltage and the coefficient of variation of the discharging end voltage of the battery pack, respectively; , These represent the SOC range calculated from the battery pack's charging terminal voltage and the SOC range calculated from the discharging terminal voltage, respectively.

[0099] Or with , For example, hour, ,but

[0100]

[0101]

[0102] hour, ,but,

[0103]

[0104]

[0105] In this embodiment, the metric used to evaluate battery performance consistency includes the coefficient of variation of the battery pack's terminal charging voltage. Coefficient of variation of discharge terminal voltage SOC range calculated based on the charging end voltage SOC range calculated based on discharge terminal voltage Any one or more of the following.

[0106] In step S2, the method for assigning scores to the various indicators used to evaluate the consistency of battery performance is expressed by the following expression:

[0107]

[0108] , , , To calculate the first The first, second, third, and fourth parameters for assigning scores to each indicator; Corresponding lower limit indicator value The assigned score; Corresponding upper limit indicator value The assigned score; Indicates the specific indicator number A number; For specific indicators The assigned score for each; among which .

[0109] The formula represents and and between The numerical value and its corresponding value and and between The assigned scores form a linear correspondence.

[0110] When the specific indicator is the SOC range calculated from the discharge terminal voltage. hour,

[0111] , , ;

[0112] When the specific indicator is the coefficient of variation of the discharge terminal voltage hour,

[0113] , , ;

[0114] When the specific indicator is the SOC range calculated from the charging end voltage. hour,

[0115] , , ;

[0116] When the specific indicator is the coefficient of variation of the charging terminal voltage of the battery pack hour,

[0117] , , .

[0118] Assuming, ,but

[0119]

[0120] Assumption ,but:

[0121]

[0122] Assumption ,but:

[0123]

[0124] Assumption ,but:

[0125]

[0126] Specifically, Indicates the lower limit indicator value The corresponding score, the lower limit indicator value Indicates the upper limit indicator value The corresponding score, the upper limit indicator value Determined through empirical evaluation.

[0127] In step S2 of this embodiment, the method for assigning corresponding weights to each indicator includes the following steps:

[0128] S21, Construct the fuzzy judgment matrix In this embodiment, preferably,

[0129] The element values ​​of each element in the array are as follows: The process of determining is briefly described as follows: ...

[0130] In Indicates the first Compared to the first indicator The importance of each indicator ( Similarly, it means The first in Line 1 Based on expert knowledge and experience, the importance of the four indicators can be ranked as follows:

[0131] Ranked by importance, the fuzzy triangular values ​​are... These represent the levels of importance: equally important, slightly important, relatively important, and more important, respectively. For example... This indicates that the first indicator is more important than the fourth indicator.

[0132] Where the fuzzy judgment matrix It has reciprocity, that is ;but At the same time, the main diagonal is (1,1,1), which must meet the principle of "no difference between itself".

[0133] S22, regarding the fuzzy judgment matrix Defuzzification is performed to obtain the definite judgment matrix. ;

[0134] In this embodiment, preferably,

[0135] Determine the judgment matrix The first in Line 1 Element value of column element The calculation method is expressed as follows: , , These represent the lower limit, middle value, and upper limit of the triangular fuzzy number in the fuzzy judgment matrix, respectively.

[0136] For example, based on the fuzzy judgment matrix expressed above. The element values ​​and the fuzzy judgment matrix in the matrix have the property of positive reciprocity, which shows that... and It is a positive reciprocity, that is for ,but for Then substitute The calculation formula is obtained. .

[0137] S23, Determine the judgment matrix Perform a consistency check.

[0138] If the test is successful, then the judgment matrix is ​​determined. Calculate the weight corresponding to each of the aforementioned indicators;

[0139] If the test fails, return to step S21 and reconstruct the fuzzy judgment matrix. .

[0140] In this embodiment, the determination judgment matrix is... The specific steps involved in performing consistency checks are as follows:

[0141] S231, Calculate the largest eigenvalue The calculation method is as follows: The maximum eigenvalue of matrix A is found iteratively using the power method. The specific steps are as follows:

[0142] (1) Choose any initial vector ≠0;

[0143] (2) Repeated updates = A· The normalized vector is used until convergence; Indicates the first A third or fourth parameter;

[0144] (3) The final Rayleigh quotient is Approximate value.

[0145] S232, Calculate the consistency index , The determination matrix represents the determination matrix. The order in, assuming , ,but ;

[0146] S233, Calculate the consistency ratio , This represents the random consistency index, obtained by looking up the average CI value table derived from statistical analysis of a large number of randomly generated positive and negative reciprocal matrices. The table lookup shows: when... hour, ≈0.90 (standard value). When , hour, ;

[0147] S234, judgment Is it less than a preset ratio threshold (e.g., set to)? ),

[0148] If so, then the determination matrix is ​​correct. The consistency check was successful;

[0149] If not, then determine the judgment matrix. The consistency check failed.

[0150] In this embodiment, the determination judgment matrix is... After the consistency check passes, the judgment matrix is ​​determined. The method for calculating the weight corresponding to each indicator includes the following steps:

[0151] A1, Calculate and determine the judgment matrix. geometric mean ;For example, , middle, , , , ,therefore, 2.2134;

[0152] A2, Calculate the normalized weight values. ;but , , , , Following the same method, the calculation was obtained. [0.4551, 0.2812, 0.1648, 0.0988].

[0153] , , , , These represent the coefficients of variation of the charging terminal voltage, respectively. The coefficient of variation of the discharge terminal voltage The SOC range calculated based on the charging end voltage. The SOC range calculated based on the discharge terminal voltage. Calculated weights.

[0154] Ultimately, as Figure 1 As shown, in step S3, the scores of each indicator are weighted and summed to obtain the overall consistency score. This serves as an assessment result of the battery pack's battery performance consistency.

[0155] .

[0156] For example, .

[0157] When the consistency score If the overall score is less than the preset threshold, the battery pack is deemed to have a safety hazard or its usable capacity or expected lifespan is not ideal, and an abnormal alarm is triggered.

[0158] In summary, the lithium battery consistency assessment method provided in this application uses the coefficient of variation of charge and discharge terminal voltages and the state of charge / discharge (SOC) range as indicators to evaluate battery consistency. By dynamically assigning weights to each indicator when calculating the overall consistency score and then weighted summing the scores of each indicator, a quantitative assessment of battery consistency is achieved. This overcomes the technical problem of traditional methods, which suffer from low accuracy due to their single-dimensional approach to battery consistency assessment. The assessment process only requires collecting the battery terminal voltage, enabling online assessment of the battery's health status.

[0159] It should be stated that the above-described specific embodiments are merely preferred embodiments and technical principles applied in this application. Those skilled in the art should understand that various modifications, equivalent substitutions, and variations can be made to this application. However, such variations, as long as they do not depart from the spirit of this application, should be within the scope of protection of this application. Furthermore, some terminology used in this application's specification and claims is not limiting but merely for ease of description.

Claims

1. A method for evaluating the consistency of lithium batteries, characterized in that the steps include... include: S1, Calculate the voltage variation coefficient of the battery pack. and SOC range ; S2, assign scores to each indicator used to evaluate the consistency of battery performance, and assign corresponding weights to each indicator; S3, calculate the weighted sum of the scores for each indicator to obtain a consistency composite score. This serves as an evaluation result of the battery performance consistency of the battery pack.

2. The lithium battery consistency evaluation method according to claim 1, characterized in that, Step S1 specifically includes the following steps: S11, Collect the terminal voltage of the battery pack within a preset time window to form a terminal voltage sequence; S12, calculate the average value of each voltage value in the terminal voltage sequence. Standard deviation and range ; S13, according to and Calculate the voltage variation coefficient ;according to The SOC range was calculated. .

3. The lithium battery consistency evaluation method according to claim 2, characterized in that, ； ； ； Represents the first in the terminal voltage sequence Terminal voltage; This indicates the number of terminal voltages in the terminal voltage sequence; Represents the first in the terminal voltage sequence The value of the terminal voltage; The time represents the average value, standard deviation, and range of the charging terminal voltage of the battery pack; The time represents the average value, standard deviation, and range of the discharge terminal voltage of the battery pack.

4. The lithium battery consistency evaluation method according to claim 3, characterized in that, Voltage variation coefficient The calculation expression is: ； SOC range The calculation expression is: ； Indicates the proportional threshold; or ; It represents the difference in charging voltage when the battery's remaining state of charge (SOC) is between 95% and 100% during the battery pack charging process. It represents the difference in discharge voltage when the remaining battery charge (SOC) is between 5% and 0% during the battery pack discharge process; hour, ; hour, .

5. The lithium battery consistency evaluation method according to claim 4, characterized in that, ； 。 6. The lithium battery consistency evaluation method according to any one of claims 1-5, characterized in that, In step S2, the indicator includes the coefficient of variation of the charging terminal voltage of the battery pack. Coefficient of variation of discharge terminal voltage SOC range calculated based on the charging end voltage SOC range calculated based on discharge terminal voltage Any one or more of the following.

7. The lithium battery consistency evaluation method according to claim 6, characterized in that, In step S2, the method for assigning scores to each of the indicators used to evaluate the consistency of battery performance is expressed by the following expression: ； , , , To calculate the specific index The first, second, third, and fourth parameters of the assigned score; Corresponding lower limit indicator value The assigned score; Corresponding upper limit indicator value The assigned score; Indicates the specific indicator number A number; For specific indicators The assigned score for each; among which ; The formula represents and and between The numerical value and its corresponding value and and between The scores are assigned in a linear correspondence. When the specific indicator is the SOC range calculated from the discharge terminal voltage. hour, ， 、 ； When the specific indicator is the coefficient of variation of the discharge terminal voltage hour, ， 、 ； When the specific indicator is the SOC range calculated from the charging end voltage. hour, ， 、 ； When the specific indicator is the coefficient of variation of the charging terminal voltage of the battery pack hour, ， 、 。 8. The lithium battery consistency evaluation method according to any one of claims 1-5, characterized in that, Step S2, the method for assigning corresponding weights to each of the indicators includes the following steps: S21, Construct the fuzzy judgment matrix : S22, regarding the fuzzy judgment matrix Defuzzification is performed to obtain the definite judgment matrix. ; S23, Determine the judgment matrix Perform a consistency check. If the test is successful, then the judgment matrix is ​​determined. Calculate the weight corresponding to each of the aforementioned indicators; If the test fails, return to step S21 and reconstruct the fuzzy judgment matrix. .

9. The lithium battery consistency evaluation method according to claim 8, characterized in that, ； ； Determine the judgment matrix The first in Line number Element value of column element The calculation method is expressed as follows: , , These represent the lower limit, middle value, and upper limit of the triangular fuzzy number in the fuzzy judgment matrix, respectively. The fuzzy judgment matrix is ​​a positive definite inverse matrix.

10. The lithium battery consistency evaluation method according to claim 8, characterized in that, For the determination matrix The method for performing consistency verification includes the following steps: S231, Calculate the largest eigenvalue The calculation method is as follows: The power method is used to iteratively find the largest eigenvalue of matrix A. The specific steps are as follows: Choose any initial vector. ≠0; Repeated updates = · The normalized vector is used until convergence; Indicates the first A third or fourth parameter, Indicates the first A third or fourth parameter; The final Rayleigh quotient is Approximate value; S232, Calculate the consistency index , The determination matrix represents the determination matrix. The order of; S233, Calculate the consistency ratio , Indicates the random consistency index; S234, judgment Is it less than the preset ratio threshold? If so, then determine the determination matrix. The consistency check was successful; If not, then determine the determination matrix. The consistency check failed.

11. The lithium battery consistency evaluation method according to claim 9, characterized in that, For the determination matrix After the consistency check passes, the determination judgment matrix is ​​used as described above. The method for calculating the weight corresponding to each of the above indicators includes the following steps: A1, Calculate the determination matrix. geometric mean ; A2, Calculate the normalized weight values. ; , , , , These represent the coefficients of variation of the charging terminal voltage, respectively. The coefficient of variation of the discharge terminal voltage The SOC range calculated based on the charging end voltage. The SOC range calculated based on the discharge terminal voltage. Calculated weights.

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