A method and system for evaluating the consistency of battery cells in a power battery pack

Abstract

The present invention discloses a method and system for evaluating the consistency of power battery pack monomers, including dividing power batteries into a voltage jump region and a voltage slow change region according to the charge and discharge curves of the power batteries; calculating the consistency coefficient of the power batteries in the voltage slow change region according to the first set parameter of the battery ξ缓变 ; calculating the consistency coefficient of the power batteries in the voltage jump region according to the second set parameter of the battery ξ跃变； According to the consistency coefficient of the power battery ξ缓变 and the consistency coefficient of the power battery ξ跃变 and the set weight, the consistency coefficient of the power battery pack monomers in the full SOC range is obtained, which is used to evaluate the consistency of the power battery pack monomers. The system and method of the present invention design a comprehensive evaluation method suitable for the consistency of different types of power battery monomers, making the monomer consistency evaluation method more reasonable, more accurate, and having strong versatility and adaptability. At the same time, it can provide a certain reference value for the BMS balancing and power control strategies

Description

Technical Field

[0001] The present invention belongs to the technical field of power battery consistency evaluation, and particularly relates to a method and system for evaluating the consistency of power battery pack monomers. Background Art

[0002] Power batteries are the energy units of electric vehicles and also important key components of electric vehicles. Currently, the voltage levels of electrical loads in electric vehicles such as drive motors and air conditioners are more than 300 volts, while the voltage level of a single power battery cell is only about 3V. Therefore, it is necessary to connect multiple battery cells in series to form a power battery pack to match the electrical loads of electric vehicles. The grouped battery pack is similar to a "wooden bucket", and each single cell is similar to the "wooden boards" that make up the wooden bucket. Poor consistency of battery cells will lead to deterioration of the overall performance of the power battery pack.

[0003] At the same time, power battery usage (such as balancing, power, etc.) strategies also need to be formulated with reference to the consistency state of the monomers. Therefore, it is very necessary to evaluate the consistency state of the power battery pack monomers.

[0004] Patent CN108363011A proposes a method for evaluating the consistency of battery pack monomers. First, the battery pack is fully charged, and the battery pack is discharged at a constant current at rates of 1.5C, 1C, and 2C. When the battery SOC is 90%, 50%, and 20% respectively, the voltage difference between the highest voltage of the single cell and the lowest voltage of the single cell is measured. At 90%, 50%, and 20% SOC, the battery pack is discharged at a constant current at rates of 1.5C, 1C, and 2C for 30s respectively, and the voltage difference between the highest voltage of the single cell and the lowest voltage of the single cell is measured. Then the battery pack is discharged completely, and the battery pack is charged at a constant current at rates of 1.5C, 1C, and 2C. When the charge reaches 20%, 50%, and 90% SOC, the voltage difference between the highest voltage of the single cell and the lowest voltage of the single cell is measured, and the battery pack is charged at a constant current at rates of 1.5C, 1C, and 2C for 30s respectively, and the voltage difference between the highest voltage of the single cell and the lowest voltage of the single cell is measured. Finally, the consistency of the single cells is judged based on the voltage differences of the single cells at the above test points.

[0005] Although the above technical solution uses the voltage difference between the highest voltage of the single cell and the lowest voltage of the single cell as a reference to evaluate the consistency of the single cells, it also has the following disadvantages:

[0006] Constant current continuous and 30s pulsed charge and discharge at rates of 1.5C, 1C, and 2C do not conform to the actual on-vehicle working conditions of power batteries and are not convenient for real-time evaluation of the consistency of power battery monomers; the factors for evaluating the consistency of monomers are single, only the battery voltage, and relying only on the voltage difference between the highest voltage of the single cell and the lowest voltage of the single cell is likely to cause deviation in evaluation.

[0007] Patent CN104656023 A proposes a method for evaluating the consistency of battery pack monomers. First, the battery management system collects and records the temperature, current, remaining battery capacity of the battery system, and the voltage values of each monomer at each segmented moment within the total time; calculates the monomer voltage difference based on the voltage values of each monomer, and counts the total number of monomer voltage differences within the same temperature, remaining battery capacity, and current range, as well as the proportion of the number of each monomer voltage difference to the total number; evaluates the monomer consistency according to the proportion. When the proportion of the number of monomer voltage differences exceeding a predetermined threshold in the same current range is higher, it indicates that the monomer consistency is worse.

[0008] Although the above technical solution evaluates the monomer consistency under real-time on-vehicle working conditions of power batteries, there are also problems. The factors for evaluating monomer consistency are single, only the battery voltage, and relying only on the voltage difference between the highest monomer voltage and the lowest monomer voltage is likely to cause deviation in evaluation. Summary of the Invention

[0009] To solve the problem of deviation in the evaluation of the consistency of single batteries, the present invention proposes a more reasonable method and system for evaluating the consistency of power battery pack monomers.

[0010] The method for evaluating the consistency of power battery pack monomers for achieving one of the purposes of the present invention includes the following steps:

[0011] S1. Divide the power battery into a voltage jump region and a voltage slow change region according to the charge and discharge curve of the power battery;

[0012] The charge and discharge curve of the power battery is used to represent the relationship between the dynamic voltage of the power battery and the SOC of the power battery;

[0013] The voltage jump region is the SOC interval of the power battery corresponding to when the ratio ΔV / ΔSOC of the dynamic voltage change value to the SOC change value of the power battery is greater than the first set ratio;

[0014] The voltage slow change region is the SOC interval of the power battery corresponding to when the ratio ΔV / ΔSOC of the dynamic voltage change value to the SOC change value of the power battery is less than the second set ratio;

[0015] In the present invention, there is no limitation on the above first set ratio and second set ratio, and they can be set according to the charge and discharge curve of the power battery by itself;

[0016] S2. For the voltage slow change region, calculate the consistency coefficient ξ of the power battery in the voltage slow change region according to the first set parameter of the battery 缓变 ; for the voltage jump region, calculate the consistency coefficient ξ of the power battery in the voltage jump region according to the second set parameter of the battery 跃变 ;

[0017] S3. Obtain the consistency coefficient ξ of the power battery cells in the full SOC range based on the consistency coefficient ξ of the power battery cells in the voltage slow change region 缓变 and the consistency coefficient ξ of the power battery cells in the voltage jump region 跃变 to obtain the consistency coefficient ξ of the power battery pack cells in the full SOC range, where the consistency coefficient ξ of the power battery pack cells in the full SOC range is used to evaluate the consistency of the power battery pack cells.

[0018] The calculation method of the consistency coefficient ξ of the power battery pack cells in the full SOC range includes:

[0019]

[0020] In the formula:

[0021] a represents the number of voltage jump regions;

[0022] ξ 跃变,i represents the consistency coefficient of the power battery cells in the i-th voltage jump region;

[0023] α i represents the percentage weight of the i-th voltage jump region; it is allocated according to the type of power battery;

[0024] b represents the number of voltage slow change regions;

[0025] ξ 缓变,j represents the consistency coefficient of the power battery cells in the j-th voltage slow change region;

[0026] β j represents the percentage weight of the j-th voltage slow change region; it is allocated according to the type of power battery.

[0027] The smaller the consistency coefficient ξ of the power battery pack cells, the better the consistency of the power battery pack cells.

[0028] Further, in step S2, the method for calculating the consistency coefficient ξ of the power battery cells in the voltage slow change region 缓变 includes:

[0029] S201. Select M power batteries according to the SOC of the power battery;

[0030] S202. Sort the single cells included in each selected power battery according to the value of the first set parameter to obtain M sequences S1 to S M ;

[0031] S203. Sequentially process the sequences S1 to S MCalculate the values of the first set parameters of the single cells corresponding to the multiple set positions of each sequence in [battery pack], and obtain the single cell consistency coefficient of each power battery; obtain the consistency coefficient ξ of the power batteries in the voltage slow change region according to the single cell consistency coefficient of each power battery and the set weight 缓变 ;

[0032] Further, in the step S202, sort the single cells included in each selected power battery according to the values of the first set parameter to obtain M sequences S1 to S M When [condition], it further includes screening the single cells included in each power battery, and the screening method includes:

[0033] Step 1: Obtain the value of the first set parameter of each single cell of each power battery; obtain the value of the first set parameter of the power battery;

[0034] Step 2: Calculate the absolute value of the difference between the value of the first set parameter of each single cell and the value of the first set parameter of the power battery where the single cell is located;

[0035] Step 3: When the absolute value of the difference is greater than the first deviation value, remove the element corresponding to the single cell from the sequence where it is located.

[0036] In the step S203, obtain the consistency coefficient ξ of the power batteries in the voltage slow change region according to the single cell consistency coefficient of each power battery and the set weight 缓变 The method includes:

[0037]

[0038] In the formula:

[0039] ξ 缓变 Represents the consistency coefficient of the power batteries in a selected voltage slow change region A;

[0040] ξ i,缓变 Represents the single cell consistency coefficient of the i-th power battery in the voltage slow change region A;

[0041] ω i Represents the set weight of the i-th power battery in the voltage slow change region A.

[0042] Calculate the consistency coefficient ξ of the power batteries in the voltage jump region 跃变 The method includes:

[0043] S2001: Select N power batteries according to the SOC of the power battery;

[0044] S2002. Calculate the value of the third set parameter of each single cell based on the value of the second set parameter of the single cells included in each power battery, the charge and discharge current, and the resistance of the single cell;

[0045] S2003. Sort the single cells included in each selected power battery in descending order according to the value of the third set parameter to obtain N sequences S1’~S N ’;

[0046] S2004. Calculate the numerical value of the third set parameter of the single cells at multiple set positions in each sequence in the sequences S1’~S N ’ in turn to obtain the single cell consistency coefficient of each power battery; Obtain the consistency coefficient ξ of the power batteries in the voltage jump region according to the single cell consistency coefficient of each power battery and the set weight 跃变 .

[0047] Further, in the step S2003, after sorting the single cells included in each selected power battery in descending order according to the value of the third set parameter to obtain N sequences S1’~S N ’, it further includes screening the single cells included in each power battery, and the screening method includes:

[0048] Calculate the mean value of the third set parameter of the single cells corresponding to multiple set positions in each sequence to obtain the mean value of each sequence;

[0049] Compare the difference between the value of the third set parameter of each single cell in each sequence and the mean value of its sequence; When the absolute value of the difference is greater than the second deviation value, the element corresponding to the single cell is removed from the sequence where it is located.

[0050] Further, in the step S2004, the method for obtaining the consistency coefficient ξ of the power batteries in the voltage jump region according to the single cell consistency coefficient of each power battery and the set weight 跃变 includes:

[0051]

[0052] Where:

[0053] ξ 跃变 represents the consistency coefficient of the power batteries in a selected voltage jump region B;

[0054] N represents the number of selected power batteries in the voltage jump region B;

[0055] ξ i,跃变 represents the single cell consistency coefficient of the i-th power battery in the voltage jump region B;

[0056] ω i ' represents the set weight of the i-th power battery in the voltage slow change region B.

[0057] Further, when calculating the consistency coefficient ξ of the power batteries in the voltage slow change region 缓变 In step S203, the method for calculating the values of the first set parameters of the single cells corresponding to multiple set positions in each sequence of the sequences S1 to S M to obtain the single cell consistency coefficient of each power battery includes:

[0058]

[0059] In the formula:

[0060] σ a : represents the single cell consistency coefficient of the a-th power battery, a ∈ [1, M];

[0061] m: represents selecting m set positions from the sequence to which the a-th power battery belongs;

[0062] X i : represents the value of the first set parameter of the single cell corresponding to the i-th element of the sequence S a to which the a-th power battery belongs;

[0063] represents the mean value of the first set parameters of the single cells corresponding to all elements of the sequence S a to which the a-th power battery belongs;

[0064] Further, when calculating the consistency coefficient ξ of the power batteries in the voltage slow change region 缓变 When calculating the single cell consistency coefficient σ i of the power battery (i ∈ [1, M]), it further includes dividing the single cell consistency coefficient σ i of the power battery by a set reference value for normalization processing.

[0065] When calculating the consistency coefficient ξ of the power batteries in the voltage jump region 跃变 In step S2004, the method for calculating the values of the third set parameters of the single cells at multiple set positions in each sequence of the sequences S1' to S N ' to obtain the single cell consistency coefficient of each power battery includes:

[0066]

[0067] In the formula:

[0068] σ b : represents the single cell consistency coefficient of the b-th power battery, b ∈ [1, N];

[0069] n: It represents selecting n set positions from the sequence to which the b-th power battery belongs;

[0070] X i : It represents the value of the third set parameter of the single cell corresponding to the i-th element of the sequence S a to which the a-th power battery belongs;

[0071] It represents the average value of the first set parameters of the single cells corresponding to all elements of the sequence S a to which the a-th power battery belongs.

[0072] Further, when calculating the consistency coefficient ξ 跃变 of the power batteries in the voltage jump region, when calculating the single-cell consistency coefficient σ i of the power batteries (i ∈ [1, N]), it further includes dividing the single-cell consistency coefficient σ i of the power batteries by a set reference value for normalization processing.

[0073] Further, in the step S203, the method for selecting multiple set positions of each sequence in the sequences S1 to S M includes: selecting the middle K / 2 or (K + 1) / 2 elements of the sequence S i , where K is the number of elements of the sequence S i , and i ∈ [1, M];

[0074] Further, in the step S2004, the method for setting multiple set positions of each sequence in the sequences S1' to S N ' includes: selecting the middle K' / 2 or (K' + 1) / 2 elements of the sequence S i ', where K' is the number of elements of the sequence S i ', and i ∈ [1, N].

[0075] Further, the first set parameter is the SOC of the single cell; the second set parameter is the dynamic voltage of the single cell;

[0076] Even further, the third set parameter is the open-circuit voltage of the single cell;

[0077] In the step S2002, the method for calculating the value of the third set parameter of the single cell according to the value of the second set parameter of the single cells included in each power battery, the charge and discharge current, and the resistance of the single cell includes:

[0078] V OCV = V R + I * R

[0079] Wherein:

[0080] V OCV is the open-circuit voltage of the single cell;

[0081] I is the charge and discharge current, with a negative current sign during charging and a positive current sign during discharging;

[0082] R is the internal resistance of the single cell.

[0083] A power battery pack single cell consistency evaluation system for achieving the second object of the present invention includes a voltage partitioning module, a first power battery consistency coefficient calculation module, a second power battery consistency coefficient calculation module, and a power battery pack single cell consistency coefficient calculation module for the full SOC range;

[0084] The voltage partitioning module is used to divide the power battery into a voltage jump region and a voltage slow change region according to the charge and discharge curve of the power battery;

[0085] The first power battery consistency coefficient calculation module is used to calculate the consistency coefficient ξ of the power battery in the voltage slow change region according to the first set parameter of the power battery 缓变 ;

[0086] The second power battery consistency coefficient calculation module is used to calculate the consistency coefficient ξ of the power battery in the voltage jump region according to the second set parameter of the power battery 跃变 ;

[0087] The power battery pack single cell consistency coefficient calculation module for the full SOC range is used to obtain the power battery pack single cell consistency coefficient ξ for the full SOC range according to the consistency coefficient ξ of the power battery in the voltage slow change region 缓变 and the consistency coefficient ξ of the power battery in the voltage jump region 跃变 and the set weight, and the power battery pack single cell consistency coefficient ξ for the full SOC range is used to evaluate the consistency of the power battery pack single cells.

[0088] Furthermore, the first power battery consistency coefficient calculation module further includes a first data cleaning module, which is used to screen the values of the first set parameter of the single cells included in the power battery pack according to the value of the first set parameter of the power battery pack, so as to obtain single cells that meet the national standard and industry accuracy requirements for calculating the consistency coefficient ξ of the power battery in the voltage slow change region 缓变 .

[0089] Furthermore, the second power battery consistency coefficient calculation module further includes a second data cleaning module, which is used to clean the single cells included in the power battery pack for calculating the consistency coefficient ξ 跃变 of the power battery, so as to obtain single cells that meet the conditions, and the cleaning method includes:

[0090] 1. Obtain the value of the third set parameter of each single cell based on the second set parameter value of each single cell included in the power battery; the calculation method includes:

[0091] V OCV = V R + I * R

[0092] In the formula:

[0093] V R is the second set parameter value of the single cell;

[0094] V OCV is the third set parameter value of the single cell;

[0095] I is the charge and discharge current, with the current symbol being negative during charging and positive during discharging;

[0096] R is the internal resistance of the single cell.

[0097] 2. Sort the single cells included in each power battery according to the value of the third set parameter to obtain sequences S1’~S N ’, where N is the number of selected power batteries, and the elements in each sequence are the values of the third set parameters of the single cells included in each power battery;

[0098] 3. Select multiple elements at the set positions in each sequence in turn, calculate the average value of the multiple elements in each sequence to obtain the average value of each sequence, and compare the value of each element in the sequence with the average value of the sequence where it is located one by one. When the absolute value of the difference is greater than the judgment threshold, remove the element from the sequence where it is located.

[0099] Beneficial effects:

[0100] The system and method of the present invention design a comprehensive evaluation method for adapting to the consistency of different types of power battery single cells, making the evaluation method of single cell consistency more reasonable, more accurate, and having strong versatility and adaptability. At the same time, it can provide certain reference value for the BMS balancing and power control strategies. Description of the drawings

[0101] Figure 1 is the flow schematic diagram of the method of the present invention;

[0102] Figure 2 is the schematic diagram of the charge and discharge curve of the power battery in the embodiment of the present invention. Detailed implementation manners

[0103] The following specific embodiments are used to explain the technical solutions of the claims of the present invention so that those skilled in the art can understand this claim book. The protection scope of the present invention is not limited to the following specific implementation structures. Those made by those skilled in the art that include the technical solutions of the claim book of the present invention and are different from the following specific embodiments are also within the protection scope of the present invention.

[0104] In the description of the present invention, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0105] The following combines Figure 1 and Figure 2 to describe the method for evaluating the consistency of battery cells in a power battery pack.

[0106] S1. Divide the power battery into a voltage jump region and a voltage slow change region according to the charge and discharge curve of the power battery;

[0107] As Figure 2 shown, the charge and discharge curve of the power battery can be divided into three regions, namely, the voltage jump region with high SOC, the voltage slow change region with medium SOC, and the voltage jump region with low SOC. It can be clearly seen that when the power battery is in the voltage jump region with high SOC and the voltage jump region with low SOC, the voltage changes greatly, and the pressure difference differentiation degree between single cells is also large, so the single cell consistency can be judged and evaluated from the voltage angle. While the battery change in the voltage slow change region with medium SOC is small, and the pressure difference differentiation degree between single cells is also small, so it is not very suitable to judge and evaluate the single cell consistency by voltage, and the single cell consistency can be judged and evaluated from the battery SOC angle. In this embodiment, the voltage slow change region of the power battery is set as the SOC interval of 30% - 70% SOC. In this interval, the single cell consistency in this region is evaluated by the battery SOC. When the power battery SOC is in the interval of 0 - 29% or 71% - 100%, it is set as the voltage jump region, and the single cell consistency in the region is evaluated by the battery voltage.

[0108] S2.1. For the voltage slow change region, calculate the consistency coefficient ξ of the power battery in the voltage slow change region according to the first set parameter of the battery 缓变 ;

[0109] As Figure 2 seen, when the power battery is at 30% - 70% SOC, that is, in the voltage slow change region, the consistency coefficient ξ of the power battery in the voltage slow change region can be calculated according to the SOC of the battery 缓变 , so the first set parameter in this embodiment is the SOC of the single cell;

[0110] S201. Select M power batteries according to the SOC of the power battery;

[0111] In this embodiment, power batteries corresponding to the two endpoints of the SOC range of 30% to 70%, namely 30% and 70% SOC, are selected, that is, M is equal to 2. The present invention does not limit the selection method and the number of selected ones, and can be selected according to the actual situation or requirements;

[0112] S202. Sort the single cells included in the two selected power batteries according to the SOC values of the single cells to obtain two sequences S1 to S2. S1 to S2 respectively correspond to the sorting based on SOC of the single cells included in the selected power battery with 30% SOC and the selected power battery with 70% SOC;

[0113] Screen the single cells included in each power battery, and remove the single cells that do not meet the conditions from the sequence. The removal method is as follows: calculate the absolute value of the difference between the SOC value of each single cell in the power battery and the SOC value of the power battery pack; when the absolute value is greater than the first deviation value, then remove the single cell from the corresponding sequence S.

[0114] In this embodiment, the judgment basis for the non - compliant conditions is that the difference between the SOC of each single cell and the SOC of the power battery where it is located should be within a certain range. The single cells whose differences are not within a certain range are non - compliant single cells.

[0115] According to the requirement in the national standard GB / T 38661 - 2020 "Technical Conditions for Battery Management Systems for Electric Vehicles" that the estimation accuracy of the SOC of power batteries is not less than 95%, combined with the average SOC estimation error level in the BMS industry being 5%, 5% estimation deviation is used as the above - mentioned first deviation value in this embodiment. Based on this, taking the endpoint when the power battery SOC is 30% as an example, the corresponding range is [25%, 35%]. The SOC of the single cells with lower SOC after sorting should not be less than 25%. If the SOC value of a certain single cell is less than 25%, then the single cell does not meet the conditions and needs to be removed. The SOC of the single cells with higher SOC after sorting should not be greater than 35%. If the SOC value of a certain single cell is greater than 35%, then it does not meet the conditions and needs to be removed.

[0116] Similarly, when the power battery SOC is 70%, the corresponding range is [65%, 75%]. The SOC of the single cells with lower SOC after sorting should not be less than 65%, and the SOC of the single cells with higher SOC after sorting should not be greater than 75%. Remove the single cells whose SOC is not within this range, and sort the remaining single cells in ascending order of SOC;

[0117] S203. Calculate the SOC values of the single cells corresponding to multiple set positions in each of the sequences S1 to S2 in sequence, and obtain the single cell consistency coefficients of the two power batteries; obtain the consistency coefficient ξ of the power batteries in the voltage slow change region according to the single cell consistency coefficient of each power battery and the set weight. 缓变 ;

[0118] In this embodiment, the multiple set positions are the SOCs of the single cells that are centered in the sequences S1 to S2 and the number is 1 / 2 of the number of sequence elements, and averaging processing is performed to obtain an average value; the following is an example:

[0119] Suppose that after removing the single cells that do not meet the conditions from the power battery pack corresponding to 30% SOC, there are 8 remaining single cells, and the SOC sequence S1 composed is 26%, 27%, 28%, 29%, 30%, 31%, 32%, 34%. Then the SOCs of the single cells that are centered and the number is 1 / 2 of the number of sequence elements are: 28%, 29%, 30%, 31%, and the average value obtained by averaging processing is 29.5%.

[0120] For the power battery at 30% SOC, after removing the single cells that do not meet the conditions, the remaining quantity is represented by N 30 ; the average value is represented by For the power battery at 70% SOC, after removing the false values, the remaining quantity is represented by N 70 ; the average value is represented by

[0121] Finally, calculate the consistency coefficient ξ of the power batteries in the voltage slow change region according to the SOC of the battery 缓变 ;

[0122] In this embodiment, the method for calculating the consistency coefficient ξ of the power batteries in the SOC range of 30% to 70% of the power batteries is as follows: 缓变 :

[0123] Step 1. Evaluate the consistency of the single cells at the endpoints of 30% SOC and 70% SOC respectively. In this embodiment, the variance formula is used for evaluation. The variance σ of the single cell SOC values of the power battery at 30% SOC 30 :

[0124]

[0125] Preferably, when performing the single cell consistency evaluation, the variance value is divided by the reference value of 5% for normalization processing to obtain the single cell consistency coefficient α at 30% SOC 30 = σ 30 / 5%,

[0126] The single cell consistency coefficient α at 70% SOC can be obtained in the same way70 = σ 70 / 5%, where σ 70 The calculation method is as follows:

[0127]

[0128] Step 2: Calculate the consistency coefficient ξ of the power battery within the range of 30% - 70% of the power battery 缓变 , in this embodiment, for σ 30 and σ 70 , each is assigned a weight of 0.5, and the average value of the single - cell consistency coefficients σ 30 and σ 70 at 30% SOC and 70% SOC is taken, that is, the consistency coefficient ξ of the power battery within the range of 30% - 70% 缓变 =(α 30 +α 70 ) / 2.

[0129] S2.2: For the voltage jump region, calculate the consistency coefficient ξ of the power battery in the voltage jump region according to the second set parameter of the battery 跃变 ;

[0130] As Figure 2 shown, when the SOC of the power battery is in the range of 0 - 29% and 71% - 100%, the current during the charge and discharge of the power battery changes continuously, and the difference in internal resistance of the battery is caused by the temperature difference between single cells. Therefore, in this embodiment, the dynamic voltage is used as the second set parameter to evaluate the consistency of single - cell batteries according to the dynamic voltage of the battery.

[0131] Next, taking the SOC of the power battery in the range of 0 - 29% as an example, the method of calculating the consistency coefficient ξ of the power battery in the voltage jump region is described. The calculation method for the range of 71% - 100% of the SOC of the power battery is the same and will not be elaborated here; 跃变

[0132] S2001: Select N power batteries according to the SOC of the power battery;

[0133] In this embodiment, the dynamic voltages V R of all single cells of 2 power batteries corresponding to the two end points of the range of 0 - 29%, that is, 0 and 29% SOC, are selected. The selection method and the number of selected ones are not limited to this, and the present invention does not limit this;

[0134] S2002: Calculate the value of the third set parameter of the single cell according to the value of the dynamic voltage, charge - discharge current and resistance of the single cell included in each power battery;

[0135] ​In this embodiment, the third set parameter is the open-circuit voltage; the open-circuit voltage V of each single battery is calculated through the following formula OCV ;

[0136] V OCV =V R +I*R

[0137] In the formula:

[0138] V R is the dynamic voltage of the single battery;

[0139] I is the charge and discharge current, the current symbol is negative during charging, and the current symbol is positive during discharging;

[0140] R is the internal resistance of the single cell.

[0141] S2003. Sort the single batteries included in each selected power battery according to the value of the third set parameter to obtain two sequences S1' to S2';

[0142] Preferably, it further includes data screening for the open-circuit voltage values, and the method is as follows:

[0143] In this embodiment, the open-circuit voltages V at the positions in the middle and with a quantity of 1 / 2 of the number of sequence elements in the sequences S1' to S N ' are sequentially taken for averaging to obtain an average value; if the difference between the open-circuit voltage value of a certain single cell and the average value exceeds the judgment threshold, it can be determined that the open-circuit voltage value is a false value and needs to be removed from the sequence. In this embodiment, the judgment threshold is set to 500 mV. The following is an example: OCV Suppose there are 12 single batteries in the power battery pack, and the values of the elements in the sorted sequence of the open-circuit voltages V of the 12 single batteries are: 2500 mV, 2520 mV, 3030 mV, 3035 mV, 3040 mV, 3055 mV, 3070 mV, 3075 mV, 3090 mV, 3095 mV, 3575 mV, 3585 mV. The average value is 3055.83 mV. After removing the false values 2500 mV, 2520 mV, 3575 mV, and 3585 mV, the sequence 3030 mV, 3035 mV, 3040 mV, 3055 mV, 3070 mV, 3075 mV, 3090 mV, 3095 mV is obtained.

[0144] OCV

[0145] S2004. Calculate the numerical values of the open-circuit voltages of the single batteries at multiple set positions in each sequence of the sequences S1' to S2' in sequence to obtain the single-cell consistency coefficient of each power battery; according to the single-cell consistency coefficient of each power battery and the set weight, obtain the consistency coefficient ξ of the power batteries in the voltage jump region​​跃变 ;

[0146] After sorting the remaining single cells in ascending order of their open circuit voltage values, the open circuit voltages of half of the remaining cells in the middle are averaged to obtain an average value, and the variance of the single cell open circuit voltage is calculated;

[0147] In the above sequence 3030mV, 3035mV, 3040mV, 3055mV, 3070mV, 3075mV, 3090mV, 3095mV, the open circuit voltage V at the middle position and with a quantity of 1 / 2 of the number of sequence elements OCV The values are 3040mV, 3055mV, 3070mV, 3075mV; the average value is 3060mV.

[0148] It should be noted that when the number of remaining sequence elements is odd, 1 / 2 of the number of sequence elements can be the number of sequence elements plus 1 or minus 1, and the middle position can also be offset one or two positions to the left or right. The present invention does not strictly limit this.

[0149] Next, calculate the variance σ0 of the open circuit voltage value of the single cell of the power battery corresponding to 0% SOC, and the method is as follows:

[0150]

[0151] In the formula:

[0152] N0 is the number of elements in the sequence after removing the false values;

[0153] X i represents the open circuit voltage value of the selected i-th single cell;

[0154] represents the mean value of the open circuit voltages of the single cells at the middle position and with a quantity of half of the remaining quantity after cleaning and sorting the false values of the open circuit voltage.

[0155] Similarly, the calculation method for the variance of the open circuit voltage value of the single cell of the power battery at 29% SOC can be obtained as follows:

[0156]

[0157] N 29 is the number of remaining single cells after cleaning the false values of the open circuit voltage when the power battery is at 29% SOC;

[0158] X i represents the open circuit voltage value of the selected i-th single cell;

[0159] It is the average of the open - circuit voltages of the monomers whose positions are centered after cleaning and sorting the pseudo - values and the number is half of the remaining number.

[0160] Finally, evaluate the consistency of the single cells of the power battery in the SOC range of 0% - 29%. The consistency coefficient ξ of the single cells in this range 跃变1 =(σ0 / 500 + σ 29 / 500) / 2.

[0161] Similarly, the consistency coefficient ξ of the single cells of the power battery in the SOC range of 71% - 100% 跃变2 =(σ 71 / 500 + σ 100 / 500) / 2.

[0162] S3. According to the consistency coefficient ξ 缓变 of the power battery in the voltage slow - change region and the consistency coefficient ξ 跃变 of the power battery in the voltage jump region and the set weights, obtain the consistency coefficient ξ of the single cells of the power battery pack in the full SOC range. The consistency coefficient ξ of the single cells of the power battery pack in the full SOC range is used to evaluate the consistency of the single cells of the power battery pack.

[0163] The consistency of the single cells of the power battery pack in the full SOC range is comprehensive of the consistency of the single cells in the three ranges of 0 - 29% SOC, 30 - 70% SOC, and 71 - 100% SOC and is weighted according to the interval weight ratio, that is:

[0164] The consistency coefficient ξ of the single cells of the power battery pack = β1 * ξ 跃变1 + β2 * ξ 缓变 + β3 * ξ 跃变2 ;

[0165] In the formula:

[0166] β1, β2, and β3 respectively correspond to the percentage weights of the three ranges of 0 - 29% SOC, 30 - 70% SOC, and 71 - 100% SOC, and β1 + β2 + β3 = 100;

[0167] In this embodiment, β1, β2, and β3 can be allocated according to the type of power battery. For example, for ternary - system lithium - ion batteries, β1 = 35, β2 = 30, β3 = 35; for lithium iron phosphate - system lithium - ion batteries, β1 = 50, β2 = 20, β3 = 30; for lithium manganese oxide - system lithium - ion batteries, β1 = 40, β2 = 25, β3 = 35.

[0168] The smaller the consistency coefficient ξ of the single cells of the power battery pack, the better the consistency of the single cells of the power battery pack.

[0169] Specifically, ξ less than 50 indicates good monomer consistency and does not affect the overall performance of the power battery pack; ξ greater than or equal to 50 and less than or equal to 90 indicates average monomer consistency, which has affected the overall performance of the power battery pack and requires the activation of the BMS balancing function for maintenance; ξ greater than 90 indicates poor monomer consistency, which cannot be solved by balancing and requires replacement.

[0170] It should be understood that the magnitudes of the sequence numbers of the steps in the above embodiments do not imply the order of execution, and the order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0171] The content not described in detail in this specification belongs to the prior art well known to those skilled in the art.

Claims

1. A method for evaluating the consistency of battery cells in a power battery pack, characterized in that, It includes the following steps: S1. Divide the power battery into a voltage jump region and a voltage slow change region according to the charge and discharge curve of the power battery; S2. For the voltage slow change region, calculate the consistency coefficient ξ of the power battery in the voltage slow change region according to the first set parameter of the power battery 缓变 ; for the voltage jump region, calculate the consistency coefficient ξ of the power battery in the voltage jump region according to the second set parameter of the power battery 跃变 ; S3. According to the consistency coefficient ξ of the power batteries in the voltage slow change region 缓变 and the consistency coefficient ξ of the power batteries in the voltage jump region 跃变 and the set weight, obtain the consistency coefficient ξ of the power battery pack monomers in the full SOC range, and the consistency coefficient ξ of the power battery pack monomers in the full SOC range is used to evaluate the consistency of the power battery pack monomers; The first set parameter is the SOC of the single battery; the second set parameter is the dynamic voltage of the single battery.

2. The method for evaluating the consistency of battery cell units of the power battery pack according to claim 1, wherein In the step S2, for the voltage slow change region, calculate the consistency coefficient ξ of the power battery in the voltage slow change region 缓变 The method includes: S201. Select M power batteries according to the SOC of the power battery; S202. Sort the individual cells included in each selected power battery according to the value of the first set parameter to obtain M sequences S1 to S M ; S203. Calculate the values of the first set parameters of the single battery cells corresponding to multiple set positions of each sequence in the sequences S1 to S M to obtain the single cell consistency coefficient of each power battery; obtain the consistency coefficient ξ of the power batteries in the voltage slow change region according to the single cell consistency coefficient of each power battery and the set weight 缓变 .

3. The method for evaluating the consistency of battery cell units of a power battery pack according to claim 2, wherein In the step S203, the selection method of multiple set positions of each sequence in the sequences S1 to S M includes: selecting the middle K / 2 or (K + 1) / 2 single cells of the sequence S i , where K is the number of elements in the sequence S i , and i ∈ [1, M].

4. The method for evaluating the consistency of battery cells in a power battery pack according to claim 1, wherein, In the step S2, for the voltage jump region, calculate the consistency coefficient ξ of the power battery in the voltage jump region 跃变 The method includes: S2001. Select N power batteries according to the SOC of the power battery; S2002. Calculate the value of the third set parameter of the single battery according to the value of the second set parameter of the single battery included in each power battery; S2003. Sort the single cells included in each selected power battery according to the value of the third set parameter to obtain N sequences S1’~S N ’; S2004. Calculate the values of the third set parameters of the single cells at multiple set positions of each sequence in the sequences S1’~S N ’ to obtain the single cell consistency coefficient of each power battery; obtain the consistency coefficient ξ of the power batteries in the voltage jump region according to the single cell consistency coefficient of each power battery and the set weight 跃变 .

5. The method for evaluating the consistency of battery cells in a power battery pack according to claim 4, characterized in that, In the step S2004, the setting method for multiple set positions of each sequence in the sequences S1’~S N ’ includes: selecting the middle K’ / 2 or (K’+1) / 2 single cells of the sequence S i ’, where K’ is the number of elements in the sequence S i ’, and i ∈ [1, N].

6. A consistency evaluation system for battery cell units of a power battery pack using the method described in claim 1, characterized in that It includes a voltage partition module, a first power battery consistency coefficient calculation module, a second power battery consistency coefficient calculation module, and a power battery pack single cell consistency coefficient calculation module for the full SOC range; The voltage partition module is used to divide the power battery into a voltage jump region and a voltage slow change region according to the charge and discharge curve of the power battery; The first power battery consistency coefficient calculation module is used to calculate the consistency coefficient ξ of the power batteries in the voltage slow change region according to the first set parameters of the power batteries 缓变 ; The second power battery consistency coefficient calculation module is used to calculate the consistency coefficient ξ of the power batteries in the voltage jump region according to the second set parameters of the power batteries 跃变 ; The calculation module for the consistency coefficient of the power battery pack monomers in the full SOC range is used to obtain the consistency coefficient ξ of the power battery pack monomers in the full SOC range according to the consistency coefficient ξ of the power batteries in the voltage slow change region 缓变 and the consistency coefficient ξ of the power batteries in the voltage jump region 跃变 and the set weight, and the consistency coefficient ξ of the power battery pack monomers in the full SOC range is used to evaluate the consistency of the power battery pack monomers.

7. The battery cell consistency evaluation system for a power battery pack according to claim 6, wherein The second power battery consistency coefficient calculation module further includes a second data cleaning module, which is used to clean the single cells included in the power battery for calculating the consistency coefficient ξ 跃变 of the power battery to obtain single cells meeting the conditions. The cleaning method includes: Obtain the value of the third set parameter of each single battery according to the value of the second set parameter of each single battery included in the power battery; Sort the single cells included in each power battery according to the value of the third setting parameter to obtain sequences S1’~S N ’, where N is the number of selected power batteries; Select multiple elements at the set positions in each sequence, and calculate the mean value of the third set parameter corresponding to each element to obtain the mean value of each sequence; Calculate the absolute value of the difference between the value of the third set parameter corresponding to each element in each sequence and the mean value of the sequence one by one. If the absolute value exceeds the judgment threshold, remove the element from the sequence where it is located; The single batteries corresponding to the remaining elements in the sequence are the single batteries meeting the conditions.

8. The battery cell consistency evaluation system for a power battery pack according to claim 7, wherein In the second data cleaning module, the method for obtaining the value of the third set parameter of each single battery according to the value of the second set parameter of each single battery included in the power battery includes: V OCV = V R + I * R In the formula: V R is the second set parameter value of the single cell; V OCV is the third set parameter value of the single cell I is the charge and discharge current, the current symbol is negative during charging, and the current symbol is positive during discharging; R is the internal resistance of the single battery; The third set parameter is the open circuit voltage of the single battery.

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