Battery imbalance degree evaluation method based on battery OCV database

Abstract

The present invention relates to a method for evaluating the battery imbalance degree based on a battery OCV database, which includes: S1. According to different average voltage values, collect the voltages V of D battery cells within a preset number and a preset single-cell voltage range during the discharge of the battery system H and V K , and the corresponding average voltage values V 均1 and V 均2 of the battery system at this time; S2. Classify the battery cells into four categories according to the performance characteristics of the collected battery cell voltages V H and V K , and determine the R-type battery cells as the analysis object; S3. Calculate the inverse ratio of the SOC of the R-type battery cells to the SOC of the standard battery cells according to the voltage values of the R-type battery cells and the optimized OCV database; S4. Output two alarm faults according to the inverse ratio of the SOC power difference of the R-type battery cells obtained in step S323 to the SOC power difference of the standard battery cells. Based on the method of the present invention, the vehicle can predict the battery maintenance time according to the output value, and the battery manufacturer can use it for the evaluation of the battery cell quality after summarizing the data. This direct feedback information enables the quality of the battery to be accurately measured, and the maintenance management becomes more specific and accurate.

Description

Technical Field

[0001] The present invention relates to the field of battery usage state evaluation, and specifically relates to a method for evaluating battery imbalance degree based on a battery OCV database. Background Art

[0002] New energy vehicles have developed rapidly. Especially last year, the sales volume of pure electric vehicles reached more than three million. The battery manufacturers supporting the vehicle manufacturers have also seen a sharp increase in shipments and have achieved rapid development. A large number of battery systems are constantly charging and discharging, posing unprecedented challenges to battery system management. Battery quality evaluation is particularly important.

[0003] Currently, most battery packs use battery parameters such as SOH, SOC, voltage, current, temperature, and power to reach preset critical conditions to comprehensively formulate control strategies to ensure the safe charging and discharging operation of the vehicle battery pack. The charging and discharging cut-off conditions of the battery are formulated by the control strategy according to the characteristics of the battery itself. Whether it is a ternary, lithium iron phosphate, sodium ion battery or other batteries with electrochemical properties, they basically have similar electrochemical characteristics. At the end of the battery charge and near full charge, the voltage and charge slope curves change significantly. The battery cells in the same battery pack will show corresponding voltage differences according to their different capacities at these two stages. Specifically, at the end or near the end of the battery pack charge, the voltage parameter can almost accurately reflect the capacity difference of the battery. Within the same temperature range, battery manufacturers mainly formulate battery protection strategies based on this key parameter of voltage. It should be noted that for the series-connected battery pack analyzed as a whole, if one of the battery cells has a fault, under normal circumstances, the voltage value of the battery cell will show several situations. When the faulty battery cell has a high overall capacity, the voltage may be higher or lower compared to the average voltage. When the charge is close to the low point, the voltage of the faulty battery cell may be higher or lower compared to the average voltage. According to the two possible high and low voltage values corresponding to high and low charges, the faulty battery cell will get 4 possible combinations, and the weights of the impacts of these possibilities on the battery are also different. Selecting an appropriate critical value will accurately help to judge the performance state of the battery.

[0004] In terms of battery usage, generally, maintenance personnel have little data for reference. Battery replacement and maintenance rely on experience, and it is even more impossible to predict the battery attenuation trend and make preparations for maintenance. The vehicle range assessment has a large deviation. Only based on simple data such as SOH, it cannot be applied to specific problems such as differential pressure protection. Battery manufacturers only know the general reasons for battery replacement and roughly count the battery failure rate. They cannot distinguish what exactly causes battery imbalance, whether it is self-discharge, energy attenuation, or other reasons, resulting in slow technological improvement. Each time there is a battery charge and discharge failure, the available range, and the comprehensive failure status, these complex information cannot be comprehensively utilized and cannot be regularly output to maintenance personnel. It is an urgent problem to provide reliable analysis data for vehicle range assessment and battery manufacturers. In short, there is an urgent need for a relatively perfect solution to solve the above problems. Summary of the Invention

[0005] To solve the above-mentioned deficiencies of the prior art, the present invention provides a method for evaluating battery imbalance based on a battery OCV database, specifically involving a method and device for distinguishing and measuring the actual available state of a battery system by analyzing the voltage difference values of individual battery cells in a battery pack to obtain the weight value of the cell performance and quality status.

[0006] Specifically, the present invention provides a method for evaluating battery imbalance based on a battery OCV database, which includes the following steps:

[0007] S1. Collect D cell voltages V of the battery system during discharge within a preset number and a preset individual voltage range according to different average voltage values H and V K as well as the corresponding average voltage values V 均1 and V 均2 of the battery system at this time. The specific method is as follows:

[0008] When -10mV ≤ V e ≤ V 均1 ≤ V e +10mV and the current value satisfies -10A ≤ I ≤ 10A, collect the average voltage V 均1 of the battery system at this time, D voltage values of the lowest individual cell and the highest individual cell each, and mark this voltage as V H . Save multiple individual cell voltage values V H together with the numbers of the individual cells;

[0009] When -10mV ≤ V f ≤ V 均2 ≤ V f +10mV and the current value satisfies -10A ≤ I ≤ 10A, collect D voltage values of the lowest individual cell and the highest individual cell each, and mark this voltage as VK Save the voltage values V of multiple single-cell batteries K along with the numbers of the single-cell batteries; among them, V e and V f are both voltage reference values;

[0010] S2. Classify the battery cells into four categories according to the performance characteristics of the collected battery cell voltage values V H and V K . Assume that the four types of battery cells are R-type battery cells, U-type battery cells, V-type battery cells, and W-type battery cells, and determine the R-type battery cells as the analysis object. The specific steps are as follows:

[0011] S21. Among all the V H values collected in step S1, if a certain V H value satisfies |V 均1 -V h |≥20 mV, then save this V H value; otherwise, eliminate this V H value;

[0012] S22. Among all the V K values collected in step S1, if a certain V K value satisfies |V 均2 -V k |≥20 mV, then save this V k value; otherwise, eliminate this V K value;

[0013] S23. Determine the analysis object: Establish a battery classification table, analyze the characteristics of different faulty battery cells, compare all the saved V H and V k values, and conclude that the U-type, V-type, and W-type battery cells have little impact on faults, while the R-type battery cells have a large impact. Determine the R-type battery cells as the analysis object and retain the voltage values of the valuable R-type battery cells;

[0014] S3. Calculate the inverse ratio of the SOC of the R-type battery cells to the SOC of the standard battery cells according to the voltage values of the R-type battery cells and the optimized OCV database. The specific steps are as follows:

[0015] S31. Establish an optimized OCV database: Preset the SOC and voltage values in the ordinary OCV database to 5*M% and V 5*M respectively, and make the voltage values and SOC correspond one by one and appear in pairs. Calculate N + 1 groups of voltage values and SOC values according to the following formula, and save the N + 1 groups of voltage values and SOC values to obtain the optimized OCV database;

[0016] N = 5*M

[0017]

[0018] Among them, i takes positive integers from 1 to 4, the value of M is a natural number from 0 to 20, and N is a natural number from 0 to 100;

[0019] S32. During the discharge process of the battery system, according to the voltage value collected in step S1 and corresponding to the optimized OCV database in step S31, calculate the inverse ratio of the SOC of R-type battery cells to the SOC of standard battery cells, which specifically includes the following sub-steps:

[0020] S321. Calculate the SOC charge difference ΔQ of the standard battery cell voltage from V 均1 to V 均2 during the discharge of the battery system according to the following formula 标 :

[0021] ΔQ 标 = Q 均1 - Q 均2

[0022] Among them, Q 均1 and Q 均2 are the SOC values corresponding to the voltage values of V 均1 and V 均2 of the standard battery cell in the optimized OCV database respectively;

[0023] S322. Calculate the SOC charge difference ΔQ of the R-type battery cell according to the following formula R :

[0024] ΔQ R = Q H - Q K

[0025] Among them, Q H and Q K are the SOC values corresponding to the voltage values of V H and V K of the R-type battery cell in the optimized OCV database respectively;

[0026] S323. Calculate the inverse ratio of the SOC charge difference of the R-type battery cell to the SOC charge difference of the standard battery cell according to the following formula:

[0027]

[0028] S4. According to the inverse ratio of the SOC charge difference of the R-type battery cell to the SOC charge difference of the standard battery cell obtained in step S323, output two alarm faults, which are the first type of alarm fault and the second type of alarm fault respectively, and the first type of alarm fault and the second type of alarm fault each output three fault levels.

[0029] Preferably, in step S1, a suitable reference voltage value is selected as the calculation reference value, and it is preset that V e and V f are 3.891V and 3.464V respectively.

[0030] Preferably, in step S4, for the first type of alarm fault, the inverse ratio B large of the SOC power difference of the R type of battery cells with the most severe attenuation to the SOC power difference of the standard battery cells is selected as the measurement criterion:

[0031] If B large < 80%, then a level 3 fault of the battery system is output;

[0032] If 80% ≤ B large < 90%, then a level 2 fault of the battery system is output;

[0033] If 90% ≤ B large < 95%, then a level 1 fault of the battery system is output.

[0034] Preferably, in step S4, for the second type of alarm fault, the sum θ of the actual attenuation capacities of the m battery cells with the largest attenuation selected from the R type of battery cells is calculated according to the following formula, where m is less than or equal to 3,

[0035] θ = (1 - B1) + (1 - B2) + (1 - B3)

[0036] The overall attenuation situation of the battery is judged according to the value of θ. The larger the value, the more severe the battery attenuation. If θ < 80%, then a level 1 fault of the battery system is output; if 80% ≤ θ < 90%, then a level 2 fault of the battery system is output; if 90% ≤ θ < 95%, then a level 3 fault of the battery system is output.

[0037] Preferably, the method for determining the four types of battery cells in step S2 is specifically as follows: It is preset that the R type of battery cells are the battery cells with capacity attenuation, the V type of battery cells are the battery cells with capacity higher than the standard capacity, the U type of battery cells are the battery cells with voltage higher than the standard voltage, and the W type of battery cells are the battery cells with voltage lower than the standard voltage. The battery cells are classified according to the following formula:

[0038] When V H > V 均1 and V K < V 均2 at this time, this battery cell is an R type of battery cell;

[0039] When V H > V 均1 and V K > V 均2 at this time, this battery cell is a U type of battery cell;

[0040] When V H < V 均1 and V K > V 均2 at this time, this battery cell is a V type of battery cell;

[0041] When V H <V 均1 and V K <V 均2 at this time, this battery cell is a type W battery cell.

[0042] Preferably, for the first type of alarm fault, select the one with the largest attenuation B from the R-type battery cells 大 , and use B 大 as a reference value when the vehicle performs strategy fault level protection on the battery system. According to the size of this reference value, judge the fault status level of the overall battery cells and set the battery maintenance warning value according to this reference value.

[0043] Preferably, for the second type of alarm fault, the battery manufacturer can judge the overall attenuation degree of the battery according to the size of θ, and measure the overall state and service life of the battery.

[0044] Preferably, after the fault detection is completed, analyze according to the specific fault. If a three-level fault of the battery system is output, repair and balance or replace the battery. If a two-level fault of the battery system is output, pay key attention to or balance the battery. If a first-level fault of the battery system is output, record and count the fault.

[0045] Compared with the prior art, the technical effects of the present invention are as follows:

[0046] (1) The present invention selects the voltage difference for classification and analysis, which just conforms to the battery characteristics. At the end or near the end of the battery pack's power, within the same temperature range, the voltage parameter can almost accurately reflect the capacity difference of the battery. Compared with other methods, the SOC result is more accurate. Therefore, the analysis of faults is more accurate, the faults can be detected in time, and the battery can be intervened to different degrees according to the severity of the faults, avoiding the occurrence of greater faults and extending the service life of the battery at the same time.

[0047] (2) The overall method of the present invention is simple and accurate in calculation, strong in feasibility, and can be mastered by general technical workers. Therefore, it is suitable for large-scale popularization and use. And this scheme has a wide range of applications, is not limited to battery models, and can be applied to multiple fields, such as energy storage and automotive power batteries and other fields.

[0048] (3) After the present invention outputs a fault, when a technical worker repairs the battery pack, he can refer to the performance quality status weight values and their corresponding numbers of various battery cells. The values of different classifications represent different battery faults, and the size represents their severity. Take corresponding operations such as charging or replacing the battery cells as needed to maximize the safety of the battery.

[0049] (4) The intermediate weight value calculated by the present invention can also be referred to when the vehicle performs strategy protection on the battery system, and the fault state of the specific battery cell can be judged according to the size of this value. Description of the Drawings

[0050] Figure 1 is the overall process schematic diagram of the present invention;

[0051] Figure 2 is the schematic diagram of the voltage and SOC value curves of the present invention;

[0052] Figure 3 is the classification schematic diagram of the R-type battery cells, U-type battery cells, V-type battery cells and W-type battery cells of the present invention;

[0053] Figure 4 is the schematic diagram of the existing OCV form of the present invention. Detailed Embodiment

[0054] Hereinafter, the embodiments of the present invention will be described with reference to the drawings.

[0055] The present invention provides a method for evaluating the battery imbalance degree based on a battery OCV database, as Figure 1 shown, which includes the following steps:

[0056] S1. At normal temperature, according to different average voltage values, D battery cell voltages V H , V K and the corresponding average voltage value V 均1 , V 均2 of the battery system during discharge are collected. The specific method is as follows:

[0057] When -10 mV ≤ V e ≤ V 均1 ≤ V e + 10 mV and the current value -10 A ≤ I ≤ 10 A are satisfied, the average voltage V 均1 of the battery system at this time, the voltage values of the lowest single battery cell and the highest single battery cell, each D, are collected, and this voltage is marked as V H . The voltage values V H of multiple single battery cells together with the numbers of the single battery cells are saved;

[0058] When -10 mV ≤ V f ≤ V 均2 ≤ V f + 10 mV and the current value -10 A ≤ I ≤ 10 A are satisfied, the voltage values of the lowest single battery cell and the highest single battery cell, each D, are collected, and this voltage is marked as V k . The voltage values V KSave together with the serial number of the single battery cell.

[0059] In this embodiment, a suitable reference voltage value is selected as the calculation reference value according to S1, and V is preset. e ,V f They are 3.891V and 3.464V respectively;

[0060] S2. Classify the battery cells into four categories according to the performance characteristics of the collected battery cell voltage values V H and V k . Let the four types of battery cells be R-type battery cells, U-type battery cells, V-type battery cells and W-type battery cells respectively. The specific steps are as follows:

[0061] S21. Among all the V H values collected in step S1, if |V 均1 -V h |≥20mV, then save the V H value, otherwise eliminate it;

[0062] S22. Among all the V k values collected in step S1, if |V 均2 -V k |≥20mV, then save the V k value, otherwise eliminate it;

[0063] S23. Determine the analysis object: establish a battery classification table, obtain the characteristics of different faulty battery cells through analysis, analyze and compare and classify all the saved V H and V k values, and conclude that the U-type, V-type and W-type battery cells have little impact on faults, and the R-type battery cells have a large impact. Determine the R-type battery cells as the analysis object and retain the valuable voltage values of the R-type battery cells;

[0064] S3. According to the voltage value of the R-type battery cell and the optimized OCV table, obtain the actual capacity value of the R-type battery cell, and calculate the inverse ratio of the SOC of the R-type battery cell to the SOC of the standard battery cell. The specific steps are as follows:

[0065] S31. Optimize the OCV database. According to the existing battery cell OCV form information, Figure 4 shows the existing battery cell OCV form information, and then optimize it through the following calculation model. The specific steps are as follows:

[0066] Preset the SOC and voltage values of each row in the ordinary OCV table as 5*M% and V 5*M respectively. The value of M is a natural number from 0 to 20, that is, 0%, 5%,... 100% correspond to V0, V5... V 100, 101 voltage values of the optimized OCV table are set in sequence and correspond one-to-one with the SOC and appear in pairs, that is, the preset V N corresponds one-to-one with N%, where N is a natural number from 0 to 100, and M takes values from 0 to 19 in sequence. The expression of the calculation model is:

[0067] N = 5 * M

[0068]

[0069] Among them, i takes positive integers from 1 to 4, the value of M is a natural number from 0 to 20, and N is a natural number from 0 to 100; Figure 2 shows the schematic diagram of the voltage and SOC value curve of the present invention.

[0070] S32. During the discharge process of the battery system, according to the voltage value collected in step S1 and corresponding to the optimized database in step S31, the following calculations are carried out:

[0071] S321. Calculate the SOC power difference ΔQ of the battery system discharging from V 均1 to V 均2 as 标 ,

[0072] ΔQ 标 = Q 均1 - Q 均2

[0073] Among them, Q 均1 and Q 均2 are the SOC values of the battery system corresponding to the V 均1 and V 均2 voltage values of the standard cell respectively;

[0074] S322. Calculate the SOC power difference ΔQ R corresponding to the R-type cell. The calculation formula is as follows:

[0075] ΔQ R = Q H - Q K

[0076] Among them, Q H and Q K are the SOC values of the R-type cell corresponding to the V H and V K voltage values of the R-type cell respectively;

[0077] S323. Calculate the inverse proportion of the SOC of the R-type cell to the SOC of the standard cell. Calculate the inverse proportion of the SOC of the R-type cell to the SOC of the standard cell according to the following formula:

[0078]

[0079] S4. Output two alarm faults according to the inverse ratio of the SOC of the R-type battery cells to the SOC of the standard battery cells. The two alarm faults are the first-class alarm fault and the second-class alarm fault respectively. The first-class alarm fault is based on the comparison of the single-cell SOC values in the R-type battery cells, and the minimum value is taken as the measurement standard. The second-class alarm fault is calculated by adding up the capacity attenuation values of all R-type battery cells. The first-class alarm fault and the second-class alarm fault will output three fault levels.

[0080] Preferably, in step S4, for the first-class alarm fault, the SOC value of the battery cell with the most severe attenuation can be selected according to the actual application. The specific method for classifying common alarm faults is as follows:

[0081] If 100 * B large % < 80%, the battery system is set as a third-level fault;

[0082] If 80% ≤ 100 * B large % < 90%, the battery system is set as a second-level fault;

[0083] If 90% ≤ 100 * B 大 % < 95%, the battery system is set as a first-level fault.

[0084] According to the first-class alarm fault, select the B with the largest attenuation from the R-type battery cells 大 , and use B 大 as the final reference value when the vehicle performs strategy fault level protection for the battery system. According to the size of this value, judge the fault status level of the overall battery cells. Maintenance personnel can refer to this value to set the battery maintenance warning value.

[0085] Preferably, in step S4, for the second-class alarm fault, calculate the sum θ of the actual attenuation capacities of the m battery cells with the largest attenuation selected from the R-type battery cells according to the following formula, where m is less than or equal to 3.

[0086] θ = (1 - B1) + (1 - B2) + (1 - B3)

[0087] Judge the overall attenuation of the battery according to the size of the θ value. The larger the value, the more severe the battery attenuation. If θ < 80%, output the first-level fault of the battery system; if 80% ≤ θ < 90%, output the second-level fault of the battery system; if 90% ≤ θ < 95%, output the third-level fault of the battery system.

[0088] According to the second-class alarm fault, the battery manufacturer can judge the overall attenuation degree of the battery according to the specific value size and measure the overall state of the battery.

[0089] The specific method for determining the R-type battery cell as the analysis object in step S3 is as follows: presetting the R-type battery cell as D1, which is a capacity-attenuated battery cell; setting the V-type battery cell as D2, which is a battery cell with a capacity higher than the standard capacity; setting the U-type battery cell as D3 (judging from a single voltage value, the capacity will be mistakenly considered to be 105%), and the battery cell voltage is higher than the standard voltage; setting the W-type battery cell as D4 (judging from a single voltage value, the capacity will be mistakenly considered to be 95%), and the battery cell voltage is lower than the standard voltage.

[0090] Continuing, in the same experimental battery system connected in series, the above 4 types of cells will follow the corresponding voltage characteristics described in the table when discharged in series. The cell voltage value corresponds to 21 values, namely V0 to V100, and the SOC can be divided into 21 values ​​0% to 100%. The voltage and SOC correspond one to one. Figure 3 The analysis is as follows:

[0091] For R-type cells, when the experimental battery system is charged to SOC of 75%, the voltage of the R-type cell is V100, which has reached the maximum protection voltage of the battery, that is, the charging limit voltage has been reached for the R-type battery. When the same battery system is discharged to SOC of 25%, the voltage of the R-type cell is V0, which has reached the minimum protection voltage of the battery. At this time, the voltage value of the R-type cell itself is V 100 The corresponding capacity to V0 is:

[0092] ΔQ R =Q H -Q K , 100% = 100% - 0%,

[0093] At this time, the average voltage of the battery system is V75 to V25, and the corresponding capacity is:

[0094] ΔQ 标 =Q 均1 -Q 均2 , 50% = 75% - 25%,

[0095] calculate The capacity of R-type battery is B=50%

[0096] It can be seen that the SOC calculated by the voltage difference of the faulty cell and the SOC calculated by the system voltage are inversely proportional. Therefore, when V H ﹥V 均1 And V K ﹤V 均2 When the battery cell is an R-type battery cell, the capacity of the R-type battery cell decays, which seriously limits the charge and discharge power usage of the battery system.

[0097] For U-type battery cells, when the experimental battery system is charged to 100% SOC, the voltage of the U-type battery cell at this time is V95, which does not reach the maximum protection voltage of the battery. That is, for the U-type battery, it is still 5% short of reaching the charging limit voltage. Similarly, when the battery system is discharged to 5% SOC, the voltage of the U-type battery cell at this time is V0, which has reached the minimum protection voltage of the battery. That is, for the U-type battery, it has reached the discharge limit voltage. From the above, it can be seen that the voltage value of the U-type battery cell has a tendency to increase simultaneously compared with the standard battery cell. Therefore, when V H ﹥V 均1 and V K ﹥V 均2 , this battery cell is a U-type battery cell. Another example: According to Figure 3 , when the experimental battery system is discharged to 90% SOC, the average voltage of the system battery cells is V90 = 4.036V. At this time, the voltage of the corresponding U-type battery cell is V 85 = 3.956V, SOC is 85%. Continuing, when the experimental battery system is discharged to 25% SOC, the average voltage is V25 = 3.499V. At this time, the voltage of the corresponding U-type battery cell is V 20 = 3.464V, SOC is 20%. Most of these battery cells have a relatively higher voltage compared to other battery cells when the battery cells are grouped. This problem can be solved by discharging the U-type battery cells separately. During use, only a slight impact on the discharge capacity will occur.

[0098] For V-type battery cells, when the experimental battery system is charged to 100% SOC, the voltage of the V-type battery cell at this time is V75, that is, it only reaches the voltage V75 corresponding to 75% SOC of the battery system. For the V-type battery, it is far from reaching the charging limit voltage. Similarly, when the battery system is discharged to 0% SOC, the voltage of the V-type battery cell is V 25 , that is, it only reaches the voltage V25 corresponding to 25% SOC of the battery system. For the V-type battery, it is far from reaching the discharge limit voltage. Therefore, when V H ﹤V 均1 and V K ﹥V 均2 , this battery cell is a V-type battery cell. Another example: According to Figure 3 , when the experimental battery system is discharged to 70% SOC, the average voltage is V70 = 3.752V. At this time, the voltage of the corresponding V-type battery cell is V 60 = 3.659V, SOC is 60%. Continuing, when the experimental battery system is discharged to 30% SOC, the average voltage is V30 = 3.534V. At this time, the voltage of the corresponding V-type battery cell is V 40 = 3.579V, SOC is 40%. The voltage range of the V-type battery cells is completely within the safe applicable range.

[0099] Therefore, the Class V battery cells basically only cause the problem of large voltage differences, which only occurs when the performance of a very small number of battery cells is higher than that of other battery cells.

[0100] For Class W battery cells, when the experimental battery system is charged to an SOC of 95%, the voltage of the Class W battery cells, V100, has reached the maximum protection voltage of the battery, that is, the charging limit voltage for the Class W battery cells. Similarly, when the battery system is discharged to an SOC of 0%, the voltage of the Class W battery cells, V5, has not reached the minimum protection voltage of the battery. From the above, it can be seen that the voltage values of the Class W battery cells tend to decrease simultaneously compared with the standard battery cells. Therefore, when V H ﹤V 均1 and V K ﹤V 均2 at this time, this battery cell is a Class W battery cell. Another example: According to Figure 3 , when the experimental battery system is discharged to an SOC of 80%, the average voltage of the battery cells in the system is V80 = 3.891V. At this time, the voltage of the corresponding Class W battery cells is V 85 = 3.956V, and the SOC is 85%. Continuing, when the experimental battery system is discharged to an SOC of 30%, the average voltage is V30 = 3.534V. At this time, the voltage of the corresponding Class W battery cells is V 35 = 3.559V, and the SOC is 35%. Most of these battery cells have a lower voltage than other battery cells when the battery system is grouped, which causes this problem. This problem can be solved by charging the Class W battery cells separately, and only a slight impact on the discharge capacity will occur during use.

[0101] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for evaluating the battery imbalance degree based on a battery OCV database, characterized in that: It includes the following steps: S1. Collect the voltages V of D battery cells within a preset quantity and a preset single-cell voltage range during the discharge of the battery system according to different average voltage values H and V K as well as the corresponding average voltage value V of the battery system at this time 均1 and V 均2 , and the specific method is as described below: When V e -10 mV ≤ V 均1 ≤ V e ≤ +10 mV and the current value satisfies -10 A ≤ I ≤ 10 A, collect the average voltage V 均1 of the battery system at this time, D voltage values of the lowest single cell and the highest single cell each, and mark this voltage as V H , and save the voltage values V H of multiple single cells together with the numbers of the single cells; When V f -10 mV ≤ V 均2 ≤ V f ≤ +10 mV and the current value satisfies -10 A ≤ I ≤ 10 A, collect D voltage values of the lowest single cell and the highest single cell respectively, and mark this voltage as V K , save multiple single cell voltage values V K together with the numbers of the single cells; Among them, V e and V f are both voltage reference values; S2. According to the collected cell voltage values V H and V K classify the cells into four categories according to their performance characteristics. Let the four types of cells be R-type cells, U-type cells, V-type cells, and W-type cells, and determine the R-type cells as the analysis object. The specific steps are as follows: S21. Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. H Among all the V H values collected in step S1, if a certain V 均1 value satisfies |V h - V H | ≥ 20 mV, then save this V H value; otherwise, eliminate this V S22. Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. K Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. K Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. 均2 Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. k Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. k Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. K Among all the V values collected in step S1, if a certain V value satisfies |V - V| ≥ 20 mV, then save this V value; otherwise, eliminate this V value. S23. Determine the analysis object: Establish a battery classification table, analyze the characteristics of different faulty battery cells, and compare all the saved V H and V k values through analysis. It is concluded that the faults of U-type, V-type, and W-type battery cells have little impact, while the R-type battery cells have a great impact. Determine the R-type battery cells as the analysis object and retain the voltage values of the valuable R-type battery cells; S3. According to the voltage value of the R-type battery cells and the optimized OCV database, calculate the inverse ratio of the SOC of the R-type battery cells to the SOC of the standard battery cells, which specifically includes the following steps: S31. Establish an optimized OCV database: Preset the SOC and voltage values in the ordinary OCV database to 5*M% and V respectively 5*M , and make the voltage values and SOC correspond one by one and appear in pairs. Calculate N + 1 groups of voltage values and SOC values according to the following formula, and save the N + 1 groups of voltage values and SOC values to obtain an optimized OCV database; N = 5 * M where i takes positive integers from 1 to 4, the value of M is a natural number from 0 to 20, and N is a natural number from 0 to 100; S32. During the discharge process of the battery system, according to the voltage value collected in step S1 and corresponding to the optimized OCV database in step S31, calculate the inverse ratio of the SOC of the R-type battery cells to the SOC of the standard battery cells, which specifically includes the following sub-steps: S321. Calculate the difference in SOC charge ΔQ of the standard cell voltage from V 均1 to V 均2 during the discharge of the battery system according to the following formula 标 : ΔQ 标 = Q 均1 - Q 均2 Among them, Q 均1 and Q 均2 respectively correspond to the SOC values when the V 均1 and V 均2 voltage values of the standard battery cells are in the optimized OCV database; S322. Calculate the SOC power difference ΔQ of the R-type battery cells according to the following formula R :[[]]END]] ΔQ R = Q H - Q K Among them, Q H and Q K are the SOC values corresponding to the V H and V K voltage values of the R-type battery cells in the optimized OCV database, respectively; S323. Calculate the inverse ratio of the difference in the SOC of the R-type battery cells to the difference in the SOC of the standard battery cells according to the following formula: S4. According to the inverse ratio of the difference in the SOC of the R-type battery cells to the difference in the SOC of the standard battery cells obtained in step S323, output two types of alarm faults, which are the first type of alarm fault and the second type of alarm fault respectively, and the first type of alarm fault and the second type of alarm fault each output three fault levels.

2. The battery imbalance degree evaluation method based on the battery OCV database according to claim 1, characterized in that: Step S1 selects a suitable reference voltage value as the calculation reference value, and presets V e and V f to be 3.891V and 3.464V respectively.

3. The battery imbalance degree evaluation method based on the battery OCV database according to claim 1, wherein: In step S4, for the first type of alarm fault, select the inverse ratio B large of the difference in the SOC of the R-type battery cell with the most severe attenuation to the difference in the SOC of the standard battery cell as the measurement standard: If B large < 80%, output a three-level fault of the battery system; If 80% ≤ B 大 < 90%, then output a secondary fault of the battery system; If 90% ≤ B 大 < 95%, then output a primary fault of the battery system.

4. The battery imbalance degree evaluation method based on the battery OCV database according to claim 1, characterized in that: In step S4, for the second type of alarm fault, calculate the sum θ of the actual attenuation capacities of the m battery cells with the largest attenuation selected from the R-type battery cells according to the following formula, where m is less than or equal to 3, θ = (1 - B1) + (1 - B2) + (1 - B3) Judge the overall attenuation of the battery according to the value of θ. The larger the value, the more severe the battery attenuation. If θ < 80%, output a first-level fault of the battery system; if 80% ≤ θ < 90%, output a second-level fault of the battery system; if 90% ≤ θ < 95%, output a three-level fault of the battery system.

5. The battery imbalance degree evaluation method based on the battery OCV database according to claim 1, characterized in that: The method for determining the four types of battery cells in step S2 is specifically as follows: Preset the R-type battery cells as the battery cells with capacity attenuation, preset the V-type battery cells as the battery cells with capacity higher than the standard capacity, preset the U-type battery cells as the battery cells with voltage higher than the standard voltage, and preset the W-type battery cells as the battery cells with voltage lower than the standard voltage. Classify the battery cells according to the following formula: When V H > V 均1 and V K < V 均2 at this time, this battery cell is an R-type battery cell; When V H > V 均1 and V K > V 均2 at this time, this battery cell is a type U battery cell; When V H <V 均1 and V K >V 均2 at this time, this battery cell is a V-type battery cell; When V H <V 均1 and V K <V 均2 , this battery cell is a type W battery cell.

6. The battery imbalance degree evaluation method based on the battery OCV database according to claim 3, characterized in that: For the first type of alarm fault, select the largest attenuation B large from the R-type battery cells, and use B large as the reference value when the vehicle performs strategy fault level protection on the battery system. Judge the fault state level of the overall battery cells according to the size of this reference value and set the battery maintenance warning value according to this reference value.

7. The battery imbalance degree evaluation method based on the battery OCV database according to claim 4, wherein: For the second type of alarm fault, the battery manufacturer can judge the overall attenuation degree of the battery according to the size of θ, and measure the overall state and service life of the battery.

8. The battery imbalance degree evaluation method based on the battery OCV database according to claim 4, characterized in that: After the fault detection is completed, analyze according to the specific fault. If a three-level fault of the battery system is output, repair and balance or replace the battery. If a second-level fault of the battery system is output, pay key attention to or balance the battery. If a first-level fault of the battery system is output, record and count the fault.

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