CN111693876A - Battery pack evaluation method and system - Google Patents

Abstract

The present application relates to a battery pack evaluation method and system. The battery pack evaluation method involves obtaining characteristic data of the battery pack to be tested. Determine the consistency evaluation index of the key characteristic parameters of the battery pack to be tested. Combined with the threshold of the consistency evaluation index of the key characteristic parameters of the battery pack to be tested, the unweighted score of the consistency evaluation index of the battery pack to be tested is calculated. Determine the weight of the consistency evaluation index of the battery pack to be tested. Calculate the consistency-weighted total score for the battery pack under test. The battery pack evaluation method effectively and quantitatively evaluates the consistency of the battery pack with the evolution of the battery during use, combined with the durability, consistency and safety of the battery. In the process of battery pack evaluation, there is no need to disassemble the battery pack, and the characteristic parameters involved are relatively comprehensive. Finally, the consistency weighted total score of the battery pack to be tested is calculated, and the conclusion is more quantitative and objective, the amount of calculation required is small, and the evaluation accuracy is high.

Description

Battery pack evaluation method and system

technical field

The present application relates to the technical field of battery detection, and in particular, to a battery pack evaluation method and system.

Background technique

Lithium-ion batteries have the advantages of high energy density, long service life and low self-discharge rate. At present, the application fields of lithium-ion batteries are constantly expanding, especially in the field of electric vehicles and hybrid vehicles. However, the range and safety of EVs still have consumers concerned. For electric vehicles, due to the limited voltage and capacity of a single battery, it is necessary to build a battery pack consisting of hundreds of single cells in parallel or in series to meet the power and energy required by electric vehicles. However, due to the inconsistency of the manufacturing process and the inconsistency of the use environment, the inconsistency among the battery cells always exists and cannot be eliminated. The inconsistency between the cells of the battery pack will speed up the decay rate of the battery pack life and reduce the performance and safety of the battery pack.

In the traditional scheme, the rapid evaluation method of symmetrical electrodes or the comprehensive evaluation method of battery pack inconsistency based on information entropy are used. During the evaluation process, the selection of parameters for evaluating the inconsistency between battery cells is inaccurate, and the evaluation accuracy is low.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a battery pack evaluation method and system to solve the problems of inaccurate selection of inconsistency evaluation parameters between battery cells and low evaluation accuracy during the evaluation process of the traditional technical solution.

A battery pack evaluation method, comprising:

Obtain characteristic data of the battery pack to be tested;

Determine the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data;

Calculate the unweighted score of the consistency evaluation index of the battery pack to be tested according to the consistency evaluation index of the key characteristic parameter of the battery pack to be tested and the threshold of the consistency evaluation index of the key characteristic parameter of the battery pack to be tested;

determining the weight of the consistency evaluation index of the battery pack to be tested;

According to the unweighted score of the consistency evaluation index of the battery pack to be tested and the weight of the consistency evaluation index of the battery pack to be tested, the consistency weighted total score of the battery pack to be tested is calculated. The higher the consistency-weighted total score, the better the consistency of the battery pack under test.

A battery pack evaluation system, comprising:

a characteristic data acquisition device, used for acquiring characteristic data of the battery pack to be tested;

A battery pack consistency evaluation index determination device, connected to the characteristic data acquisition device, used to determine the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data, and to determine the key characteristics of the battery pack to be tested. Thresholds for the consistency evaluation metrics of the feature parameters; and

The battery pack consistency evaluation index score calculation device is connected to the battery pack consistency evaluation index determination device, and is used to calculate the unweighted score of the battery pack consistency evaluation index to be tested, and determine the consistency of the battery pack to be tested. The weight of the evaluation index, and the consistency weighted total score of the battery pack to be tested is calculated.

The present application provides a battery pack evaluation method and system. The characteristic data of the battery pack to be tested is obtained in the battery pack evaluation method. Determine the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data. According to the consistency evaluation index and its threshold of the key characteristic parameters of the battery pack to be tested, the unweighted score of the consistency evaluation index of the battery pack to be tested is calculated. Determine the weight of the consistency evaluation index of the battery pack to be tested. According to the unweighted score of the consistency evaluation index of the battery pack to be tested and the weight of the consistency evaluation index of the battery pack to be tested, the consistency weighted total score of the battery pack to be tested is calculated. The higher the consistency-weighted total score of the battery pack under test, the better the consistency of the battery pack under test. The battery pack evaluation method provided in this application can effectively quantitatively evaluate the consistency of the battery pack with the evolution of the battery during use, combined with the durability, consistency and safety of the battery. In the process of evaluating the battery pack, it is not necessary to disassemble the battery pack, and the characteristic parameters involved are relatively comprehensive. Finally, the consistency weighted total score of the battery pack to be tested is calculated, and the conclusion is more quantitative and objective, the amount of calculation required is small, and the evaluation accuracy is high.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the traditional technology, the following briefly introduces the accompanying drawings that are used in the description of the embodiments or the traditional technology. Obviously, the drawings in the following description are only the For some embodiments of the application, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

1 is a flowchart of steps of a battery pack evaluation method provided in an embodiment of the present application;

2 is a flowchart of steps for obtaining external characteristic data of the battery pack to be tested provided in an embodiment of the present application;

3 is a schematic diagram of an experiment for obtaining external characteristic data of the battery pack to be tested provided in an embodiment of the application;

FIG. 4 is a diagram of a design idea of a battery pack evaluation method provided in an embodiment of the application;

FIG. 5 is a diagram of a specific embodiment of the battery pack evaluation method provided in an example of the application;

FIG. 6 is a schematic diagram of the calculation of capacitance and power in the battery pack evaluation method provided in an embodiment of the present application;

FIG. 7 is an enlarged view of the area A in FIG. 6 provided in an embodiment of the present application;

FIG. 8 is an enlarged view of region B in FIG. 6 provided in an embodiment of the application;

FIG. 9 is a structural model for obtaining the consistency of a battery pack by using an AHP model provided in an embodiment of the present application.

Description of reference numbers:

Battery pack to be tested 10

Thermostat 20

Battery charging and discharging equipment 30

Data Collection Setup 40

Controller 50

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the related drawings. The preferred embodiments of the present application are shown in the accompanying drawings. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of this application is provided.

It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for the purpose of illustration only and do not represent the only embodiment.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the present application are for the purpose of describing particular embodiments only, and are not intended to limit the present application.

There are multiple battery packs used to provide power and energy in electric and hybrid vehicles. Different battery packs may include hundreds of cells in parallel or in series. The inventor's research found that the inconsistency of the battery pack mainly includes the inconsistency of the voltage of the battery cells in the battery pack, the inconsistency of the internal resistance, the inconsistency of the temperature, the inconsistency of the capacity and the inconsistency of the state of charge of the battery. Among them, the state of charge (State of Charge, abbreviated SOC). The reasons for the inconsistency of battery cells mainly include two aspects, and the two aspects are coupled with each other. The first aspect is the difference in the initial performance of the cells before the battery cells are grouped, that is, in the production process. In the second aspect, after the battery cells are grouped, that is, during use, the internal performance of the battery is inconsistent due to inconsistent use conditions.

Although a lithium-ion battery is an energy storage and conversion device, it is not unlimited. That is, the cycle life of lithium-ion batteries is limited. This is because the performance of lithium-ion batteries gradually degrades as the battery is used. The attenuation of the capacity of each battery cell in the battery pack may lead to the attenuation of the capacity of the battery pack. This phenomenon is ultimately caused by the inconsistency of the battery cells. However, the current system for evaluating the consistency method of Li-ion batteries is not perfect. Therefore, the present application provides a battery pack evaluation method and system.

This application proposes a consistency-based battery pack evaluation method for the problem that the inconsistency among different battery cells in the battery pack will accelerate the decay rate of the battery pack life and reduce the performance and safety of the battery pack. Referring to FIG. 1, the present application provides a battery pack evaluation method, including:

S100, acquiring characteristic data of the battery pack to be tested. In this step, the characteristic data of the battery pack during multiple charging and discharging processes can be obtained by means of a battery management system (BMS) on the vehicle, cloud big data, or experiments. The characteristic data may include external characteristic data and internal characteristic data.

S200. Determine, according to the characteristic data, a consistency evaluation index of the key characteristic parameters of the battery pack to be tested. In this step, a consistency evaluation method may be adopted, and the consistency evaluation index of the key characteristic parameters of the battery pack to be tested is determined in the characteristic data. The consistency evaluation method includes standard deviation, range, variance, root mean square error, Shannon entropy, coefficient of variation and Gini coefficient. In one embodiment, parameter values of indicators such as voltage consistency, temperature consistency, internal resistance consistency, capacity consistency, and power consistency can be calculated.

S300, according to the consistency evaluation index of the key characteristic parameter of the battery pack to be tested and the threshold of the consistency evaluation index of the key characteristic parameter of the battery pack to be tested, calculate the unweighted score of the consistency evaluation index of the battery pack to be tested .

In this step, before calculating the unweighted score of the consistency evaluation index of the battery pack to be tested, it may further include separately determining the thresholds of the consistency evaluation index of the key characteristic parameters of the battery pack to be tested. Specifically, it includes determining the threshold of the consistency evaluation index of the key external characteristic parameters of the battery pack to be tested and the threshold of the consistency evaluation index of the key internal characteristic data of the battery pack to be tested.

In this step, the method of determining the threshold value of the highest score and the lowest score may be used to determine the threshold value of each indicator. The interpolation method is further used to calculate the unweighted score of each index according to the threshold. In some embodiments, the interpolation method includes linear interpolation, functional interpolation, piecewise linear interpolation, piecewise functional interpolation, and the like.

S400: Determine the weight of the consistency evaluation index of the battery pack to be tested. In this step, the weight analysis method may be used to determine the weight of each indicator. In some embodiments, the weight analysis method includes AHP, Fuzzy AHP, and the like.

S500, according to the unweighted score of the consistency evaluation index of the battery group to be tested and the weight of the consistency evaluation index of the battery group to be tested, calculate the consistency weighted total score of the battery group to be tested. The higher the consistency-weighted total score of the battery pack to be tested, the better the consistency of the battery pack to be tested.

Specifically in this step, according to the unweighted score of the consistency evaluation index of the key external characteristic parameters of the battery pack to be tested, the unweighted score of the consistency evaluation index of the key internal characteristic data of the battery pack to be tested, the unweighted score of the consistency evaluation index of the key internal characteristic data of the battery pack to be tested The weight of the consistency evaluation index of the key external characteristic parameters of the test battery pack and the weight of the consistency evaluation index of the key internal characteristic data of the battery pack to be tested are calculated, and the consistency weighted total score of the battery pack to be tested is calculated. The higher the consistency-weighted total score of the battery pack to be tested, the better the consistency of the battery pack to be tested.

In this embodiment, the battery pack evaluation method includes obtaining characteristic data of the battery pack to be tested. Determine the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data. According to the consistency evaluation index and its threshold of the key characteristic parameters of the battery pack to be tested, the unweighted score of the consistency evaluation index of the battery pack to be tested is calculated. Determine the weight of the consistency evaluation index of the battery pack to be tested. According to the unweighted score of the consistency evaluation index of the battery pack to be tested and the weight of the consistency evaluation index of the battery pack to be tested, the consistency weighted total score of the battery pack to be tested is calculated. The higher the consistency-weighted total score of the battery pack under test, the better the consistency of the battery pack under test. The battery pack evaluation method provided in this embodiment can effectively quantitatively evaluate the consistency of the battery pack by combining the battery's durability, consistency and safety with the evolution of the battery during use. In the process of evaluating the battery pack, it is not necessary to disassemble the battery pack, and the characteristic parameters involved are relatively comprehensive. Finally, the consistency weighted total score of the battery pack to be tested is calculated, and the conclusion is more quantitative and objective, the amount of calculation required is small, and the evaluation accuracy is high.

Please refer to FIGS. 4 to 5 , and FIG. 4 is a diagram of a design idea of a battery pack evaluation method provided in an embodiment of the present application. Steps S10 to S70 in FIG. 4 are further refinement steps of the above steps S100 to S500. FIG. 5 is a diagram of a specific embodiment of the battery pack evaluation method provided in an example of the application. Steps S11 to S16 in FIG. 5 are further refinement steps of the above steps S100 to S500. Wherein, the consistency evaluation index of the key characteristic parameters of the battery pack to be tested includes the voltage consistency, the temperature consistency, the internal resistance consistency, the capacity consistency, and the power consistency.

In one embodiment, the characteristic data of the battery pack to be tested includes: external characteristic data and internal characteristic data. The external characteristic data includes time, voltage, current, temperature, battery state of charge (SOC), or other parameters capable of monitoring the external state of the battery pack to be tested. The internal characteristic data includes internal resistance, capacity, power, impedance or other parameters of the internal state of the battery pack to be tested. Of course, the external characteristic data and the internal characteristic data may also include other data other than the time, voltage, current, temperature, internal resistance, capacity, and electricity listed above.

In this embodiment, the external characteristic data may be data collected during multiple charging and discharging processes, or may be data directly obtained by a vehicle-mounted battery management system. Calculate the internal characteristic data of the battery pack to be tested during multiple charging and discharging processes according to the external characteristic data.

In one embodiment, the step of acquiring characteristic data of the battery pack to be tested includes:

S101 , providing a battery pack to be tested, where the battery pack to be tested includes a plurality of battery cells. The battery pack to be tested may include hundreds of battery cells connected in parallel or in series.

S102 , charge and discharge the battery pack to be tested, and obtain characteristic data of the battery pack to be tested during multiple charging and discharging processes.

S103: Calculate the internal characteristic data according to the external characteristic data.

In this embodiment, an embodiment of obtaining characteristic data of the battery pack to be tested through an experiment is provided. For specific implementation steps, please refer to FIG. 2 and FIG. 3 . The steps of obtaining the external characteristic data of the battery pack to be tested include:

S110, providing the battery pack 10 to be tested, and placing the battery pack 10 to be tested in a temperature box 20, where the temperature in the temperature box 20 is set to a standard temperature, and the specific standard temperature is 25°C. Stand still for the first time. The first time may be set at 2 hours to 12 hours. In one embodiment, the first time may be 3 hours. A temperature sensor is provided in the battery pack 10 to be tested.

S120 , providing a charging and discharging device 30 , discharging the battery pack 10 to be tested with a constant current at a first rate to a discharge cut-off voltage, and leaving it for a second time. The first rate constant current may be a constant current of 1/4C to 1/2C. In one embodiment, the first rate constant current may be set to a constant current of 1/3C. The second time may be 30 minutes to 60 minutes. In one embodiment, the second time may be 30 minutes.

S130: Charge the battery pack to be tested for a first charging time with the first rate constant current. The first charging time may be 2 hours to 3 hours. In one embodiment, the first charging time may be 2 hours.

S140, charge with a second rate of constant current to a charge cut-off voltage, and let stand for a third time. The second rate constant current may be a constant current of 1/10C to 1/4C. In one embodiment, the second rate constant current is set to 1/4C. The third time may be 30 minutes to 60 minutes. In one embodiment, the third time may be 30 minutes. Wherein, the first magnification is greater than the second magnification. After the battery pack to be tested is charged after the first charging time, the SOC of the battery pack to be tested is 70%-80%. SOC is the state of charge of the battery pack to be tested.

S150, the constant current discharge to the discharge cut-off voltage, the second time of standing, the first charging time of the constant current charging, the constant current charging to the charging cut-off voltage, and the third time of standing are an experimental cycle. The above S120-S140 is an experiment cycle. The experimental cycle is repeated multiple times to obtain external characteristic data of the battery pack to be tested during multiple charging and discharging processes.

In one embodiment, a certain ternary system lithium-ion power battery pack is used as the research object. The charge-discharge cut-off voltages of the battery pack to be tested are set to 4.15V and 3.1V, respectively. The battery pack to be tested includes 96 battery cells (in series) and is equipped with 18 temperature sensors. The specific steps of the experiment are as follows:

FIG. 3 shows an experimental device for measuring the characteristic parameters of the battery pack 10 to be tested. The experimental conditions can be set by the controller 50 (the controller 50 can be a computer). The control signal is transmitted to the battery charging and discharging device 30 (or called a battery test system, abbreviated BTS) through a network cable. In a specific embodiment, the battery charging and discharging device 30 may adopt an Arbin battery testing system. The battery charging and discharging device 30 collects and monitors the entire experimental process. In the experiment, experimental data such as the current of the battery cell, the voltage of the battery cell, and the temperature of the battery cell are obtained through the data acquisition instrument 40 and finally stored in the controller 50 . The battery cell voltage acquisition accuracy is about 1mV, the current acquisition accuracy is about 0.1%, and the temperature acquisition accuracy is about 0.1°C. The sampling frequency of the experiment was set to 1 Hz, and the experiment was carried out in the incubator 20, and the temperature was controlled at 25°C.

In one embodiment, the specific experimental steps are as follows: (1) The battery pack is allowed to stand at 25° C. for 3 hours to achieve thermal stability of the battery system. (2) 1/3C constant current discharge to discharge cut-off voltage. (3) Set aside for 30 minutes (4) 1/3C constant current charging for 2 hours. (5) The current is switched to 1/4C, and the constant current charging is continued to the charging cut-off voltage; (6) It is left on hold for 30 minutes; (7) Steps (2) to (6) are cycled 5 times. Finally, the external characteristic data of time, voltage, current and temperature are acquired by the controller 50 .

In one embodiment, after the step of obtaining the external characteristic data of the battery pack to be tested, it includes:

Calculate the internal resistance of the battery pack to be tested according to the following formula (1):

表示第i_C个电池单体的内阻，所述待测试电池组中共有n_C个电池单体，单位是mΩ。

表示充电过程中电流切换前的最后时刻第i_C个电池单体的电压。

表示充电过程中电流切换后的起始时刻第i_C个电池单体的电压。I_A表示充电过程中电流切换前的最后时刻的电流。I_B表示充电过程中电流切换后的起始时刻的电流。In the formula,

Indicates the internal resistance of the ith _{Cth battery cell, there are n C battery} cells in the battery pack to be tested, and the unit is mΩ.

Indicates the voltage of the ith and _Cth battery cells at the last moment before the current switching during the charging process.

Indicates the voltage of the i _Cth battery cell at the starting time after the current switching during the charging process. I _A represents the current at the last moment before the current switching in the charging process. _IB represents the current at the initial moment after current switching during the charging process.

Calculate the capacity of the battery pack to be tested and the power of the battery pack to be tested according to the following formulas (2) to (8):

表示第i_C个电池单体的剩余充电时间。

是第i_C个电池单体的t₂时刻的电压经过A点平移到B点，在充电结束电压最高的单体的充电电压曲线上所对应的时间。

表示第i_C个电池单体的剩余放电时间。

表示第i_C个电池单体的t₁时刻的电压经过C点平移到D点，在放电结束电压最低的单体的充电电压曲线上所对应的时间。I表示充电电流，在恒流充电工况下，I是个定值。在恒功率充电工况下，I是个变量。

表示第i_C个电池单体的剩余放电电量。

表示第i_C个电池单体的剩余充电电量。Q_sys表示所述待测试电池组的系统容量。

表示第i_C个电池单体的容量。

表示第i_C个电池单体的电量。In the above formula, t ₁ is the starting time of charging the battery pack to be tested. t ₂ is the end time of charging of the battery pack to be tested.

Indicates the remaining charging time of the i _C -th battery cell.

is the time when the voltage of the ith and _C th battery cells at time t ₂ is shifted from point A to point B, on the charging voltage curve of the cell with the highest end-of-charge voltage.

Indicates the remaining discharge time of the i _C -th battery cell.

It represents the time corresponding to the voltage at time t ₁ of the ith and _C th battery cells shifted from point C to point D on the charging voltage curve of the cell with the lowest end-of-discharge voltage. I represents the charging current, and under constant current charging conditions, I is a fixed value. Under constant power charging conditions, I is a variable.

Indicates the remaining discharge capacity of the i _C -th battery cell.

Indicates the remaining charging capacity of the i _C -th battery cell. Q _sys represents the system capacity of the battery pack to be tested.

Indicates the capacity of the i _Cth battery cell.

Indicates the power of the i _C -th battery cell.

In this embodiment, a specific calculation formula for calculating the internal characteristic data according to the external characteristic data is given. Of course, it can be understood that other methods may also be used to calculate the internal characteristic data, which is not limited to a calculation method in this embodiment.

Please refer to FIG. 6 , which is a schematic diagram of the calculation of capacitance and power in the battery pack evaluation method provided in an embodiment of the present application. Please refer to FIG. 7 , which is an enlarged view of the area A in FIG. 6 provided in an embodiment of the present application. Please refer to FIG. 8 , which is an enlarged view of region B in FIG. 6 provided in an embodiment of the present application.

In one embodiment, the step of determining the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data includes:

According to the external characteristic data and the internal characteristic data, respectively calculate the consistency evaluation index of the key external characteristic parameters of the battery pack to be tested and the consistency evaluation index of the key internal characteristic data of the battery pack to be tested;

The consistency evaluation indexes of the key external characteristic parameters of the battery pack to be tested include: voltage consistency and temperature consistency;

The consistency evaluation indexes of the key internal characteristic data of the battery pack to be tested include: consistency of internal resistance, consistency of capacity and consistency of electric quantity.

In this embodiment, the consistency evaluation index of the key characteristic parameters of the battery pack to be tested can be obtained by relying on the consistency evaluation method. The consistency rating method may include one or more of standard deviation, range, variance, root mean square error, Shannon entropy, coefficient of variation, and Gini coefficient. The consistency evaluation indexes of the key characteristic parameters of the battery pack to be tested calculated in this embodiment include voltage consistency, temperature consistency, internal resistance consistency, capacity consistency and power consistency, which are the corresponding parameters of these five indexes. The consistency evaluation methods employed in one embodiment include standard deviation, range, root mean square error, and coefficient of variation.

In one embodiment, the evaluation index of the voltage consistency is evaluated by a _voltage consistency parameter δV: the larger the δV, the worse the _voltage consistency. The voltage consistency parameter δ _V is obtained by the following formulas (9) to (14):

表示第i_C个单体在充电阶段第j时刻(共有k个时刻)的电压。V_m-j表示在充电阶段第j时刻的各电池单体电压平均值，其全部数值构成充电过程的平均电压曲线。

表示平均电压曲线的平均值。V_max-j表示各电池单体在充电阶段第j时刻的最大电压值，其全部数值构成充电过程的最高电压曲线。V_min-j表示各电池单体在充电阶段第j时刻的最小电压值，其全部数值构成充电过程的最低电压曲线。σ_V表示在充电阶段的最高电压曲线数据与最低电压曲线数据的均方根误差。δ_V表示各单体充电电压的变异系数，即为所述电压一致性参数。In the formula, n _c represents a total of n _c battery cells in the battery pack to be tested.

Indicates the voltage of the ith and _Cth cells at the jth moment in the charging phase (k moments in total). V _mj represents the average voltage of each battery cell at the jth time in the charging stage, and all the values constitute the average voltage curve of the charging process.

Indicates the mean value of the mean voltage curve. V _max-j represents the maximum voltage value of each battery cell at the jth moment in the charging phase, and all of its values constitute the highest voltage curve during the charging process. V _min-j represents the minimum voltage value of each battery cell at the jth moment in the charging phase, and all the values constitute the minimum voltage curve of the charging process. σ _V represents the root mean square error between the highest voltage curve data and the lowest voltage curve data during the charging phase. δ _V represents the variation coefficient of the charging voltage of each cell, which is the voltage consistency parameter.

The evaluation index of the temperature consistency is evaluated by the temperature consistency parameter σ _T : the larger the σ _T , the worse the temperature consistency. The temperature uniformity parameter σ _T is obtained by the following equations (15) to (19):

表示第i_T个温度传感器，所述待测试电池组共有n_T个温度传感器。在充电阶段第j时刻的温度，充电阶段共有k个时刻。T_m-j表示在充电阶段第j时刻的各温度传感器温度平均值，其全部数值构成充电过程的平均温度曲线。

表示平均温度曲线的平均值。T_max-j表示各温度传感器在充电阶段第j时刻的最大温度值，其全部数值构成充电过程的最高温度曲线。T_min-j表示各温度传感器在充电阶段第j时刻的最小温度值，其全部数值构成充电过程的最低温度曲线。σ_T表示在充电阶段的最高温度曲线数据与最低温度曲线数据的均方根误差，即为所述温度一致性参数。In the formula, n _T represents that the battery pack to be tested has a total of n _T temperature sensors.

represents the ith temperature sensor, and the battery pack to be tested has n _T temperature sensors in total _. At the temperature at the jth moment in the charging phase, there are k moments in the charging phase. T _mj represents the average temperature of each temperature sensor at the jth time in the charging stage, and all the values constitute the average temperature curve of the charging process.

Indicates the mean of the mean temperature profile. T _max-j represents the maximum temperature value of each temperature sensor at the jth time in the charging stage, and all the values constitute the maximum temperature curve of the charging process. T _min-j represents the minimum temperature value of each temperature sensor at the jth moment in the charging phase, and all the values constitute the minimum temperature curve of the charging process. σ _T represents the root mean square error between the highest temperature curve data and the lowest temperature curve data in the charging stage, which is the temperature consistency parameter.

The evaluation index of the internal resistance consistency is evaluated by the internal resistance consistency parameter _δR : the larger the _δR , the worse the internal resistance consistency. The internal resistance consistency parameter δ _R is obtained by the following formulas (20) to (22):

表示各单体的内阻平均值。σ_R表示各单体内阻的标准差。δ_R表示各单体内阻的变异系数，即为所述内阻一致性评价参数。In the formula, n _c represents that the battery pack to be tested has a total of n _c battery cells.

Indicates the average value of the internal resistance of each monomer. σ _R represents the standard deviation of the internal resistance of each monomer. δ _R represents the coefficient of variation of the internal resistance of each monomer, that is, the internal resistance consistency evaluation parameter.

来评价：σ_Q和

越大，所述容量一致性越差。所述容量一致性参数σ_Q和

通过以下公式(23)至公式(26)得出：The evaluation index of the capacity consistency is determined by the capacity consistency parameter σ _Q and

to evaluate: σ _Q and

The larger, the worse the capacity consistency. The capacity consistency parameter σ _Q and

It is obtained from the following equations (23) to (26):

表示各单体容量的平均值。σ_Q表示各单体容量的标准差。δ_Q表示各单体容量的标准差变异系数，是评价容量一致性的参数之一。Q_max表示各单体容量的最大值，Q_min表示各单体容量的最小值。

表示各单体容量的极差变异系数，即为容量一致性评价参数。In the formula, n _c represents that the battery pack to be tested has a total of n _c battery cells.

The average value of the capacity of each monomer is shown. σ _Q represents the standard deviation of the capacity of each cell. δ _Q represents the standard deviation coefficient of variation of the capacity of each monomer, and is one of the parameters for evaluating the consistency of capacity. Q _max represents the maximum value of the capacity of each cell, and Q _min represents the minimum value of the capacity of each cell.

Represents the range variation coefficient of the capacity of each monomer, which is the capacity consistency evaluation parameter.

来评价：δ_E和

越大，所述电量一致性越差。所述电量一致性参数δ_E和

通过以下公式(27)至公式(30)得出：The evaluation index of the electric quantity consistency is determined by the electric quantity consistency parameter δ _E and

to evaluate: δ _E and

The larger the value, the worse the power consistency. The power consistency parameter δ _E and

It is obtained from the following equations (27) to (30):

表示各单体电量的平均值。σ_E表示各单体容量的标准差。δ_E表示各单体电量的标准差变异系数，是评价电量一致性的参数之一。E_max表示各单体电量的最大值，E_min表示各单体电量的最小值。

表示各单体电量的极差变异系数，即为所述电量一致性评价参数。In the formula, n _c represents that the battery pack to be tested has a total of n _c battery cells.

Indicates the average value of the power of each cell. σ _E represents the standard deviation of the capacity of each cell. δ _E represents the coefficient of variation of the standard deviation of the power of each cell, and is one of the parameters for evaluating the consistency of the power. E _max represents the maximum value of the power of each cell, and E _min represents the minimum value of the power of each cell.

Represents the range variation coefficient of the electric quantity of each monomer, which is the electric quantity consistency evaluation parameter.

In this embodiment, the calculation method for calculating each index parameter given in the above formula (9)-formula (30) is only an embodiment, and this application is not the only calculation method to obtain the above indicators parameter.

In one embodiment, the step of calculating the unweighted score of the consistency evaluation index of the battery pack to be tested includes:

的满分阈值、所述电量一致性参数δ_E和

的满分阈值均为0；Set the full score threshold of the voltage consistency parameter δ _V , the full score threshold of the temperature consistency parameter σ _T , the full score threshold of the internal resistance consistency parameter δ _R , the capacity consistency parameter σ _Q and

The full score threshold of , the power consistency parameter δ _E and

The full score threshold is 0;

的满分阈值都设置为t_Q＝5％，所述电量一致性参数δ_E和

的满分阈值都设置为t_E＝5％；The full score threshold of the voltage consistency parameter δ _V is set to t _V =2.5%, the full score threshold of the temperature consistency parameter σ _T is set to t _T =10°C, and the full score threshold of the internal resistance consistency parameter δ _R Set to t _R =50%, the capacity consistency parameter δ _Q and

The full-score thresholds are set to t _Q = 5%, the power consistency parameters δ _E and

The full score thresholds are set to t _E = 5%;

The method of piecewise linear interpolation is used to obtain the unweighted score of the consistency evaluation index of the battery pack to be tested; the unweighted score of the voltage consistency is recorded as G _V , and the unweighted score of the temperature consistency is recorded as _GT , the unweighted score of the internal resistance consistency is recorded as _GR , the unweighted score of the capacity consistency is recorded as G _Q , and the _unweighted score of the electric quantity consistency is recorded as GE ;

分别为所述容量一致性参数，δ_E和

分别为所述电量一致性参数；

表示容量的过程变量；k_Q表示容量的系数；

表示电量的过程变量；k_E表示电量的系数。δ _V is the voltage consistency parameter, σ _T is the temperature consistency parameter, δ _R is the internal resistance consistency parameter, σ _Q and

are the capacity consistency parameters, δ _E and

are the power consistency parameters, respectively;

Process variable representing capacity; k _Q representing the coefficient of capacity;

Process variable that represents the amount of electricity; k _E is the coefficient of the amount of electricity.

In this embodiment, the setting of the above-mentioned full score threshold may be adjusted according to actual or engineering needs. In this embodiment, only the above formulas (31) to (39) are used as examples to implement operations. The above formulas (31) to (39) have no mutually restrictive conditions, and each segment interpolation in the formulas is not fixed and can be set separately. In addition, the above formula for obtaining the unweighted score of the consistency evaluation index of the battery pack to be tested is not necessarily a piecewise linear interpolation, but may also be other interpolation methods such as parabolic interpolation. The principle of using piecewise linear interpolation to construct an interpolation calculation formula can be referred to as shown in Table 1 below.

Table 1. Interpolation calculation principle of piecewise linear interpolation construction

In one embodiment, the AHP is used to determine the weight of the consistency evaluation index of the battery pack to be tested.

AHP is a combination of qualitative and quantitative, systematic and hierarchical analysis method. Because of its practicability and effectiveness in dealing with complex decision-making problems, its applications have spread throughout the fields of economy and management, energy distribution, military command, agriculture, transportation and so on. The steps to determine the weights in the Analytic Hierarchy Process (AHP) are as follows:

First, construct a judgment (pairwise comparison) matrix. When determining the weights between factors at various levels, if it is only a qualitative result, it is often not easily accepted by others. Therefore, the researchers proposed the consistent matrix method, that is, not to compare all factors together, but to compare each other. Relative scales are used in the comparison to minimize the difficulty of comparing factors with different properties and to improve accuracy. a _i , a _j (i,j=1,2,3,...,n) represent the factors that determine the goal; a _ij represents the relative importance of a _i to a _j (Table 2 lists the 9 importance levels and their assignments); all a _ij form a judgment matrix P, as shown in formula (40):

The judgment matrix has the following properties:

Table 2 Proportional scale table

Second, the hierarchical ordering. According to the judgment matrix, the eigenvector w corresponding to its maximum eigenroot _λmax is obtained, as shown in formula (42):

Pw=λ _max w (42)

After the feature vector w is normalized, the vector v is obtained, which is the sorting weight of the relative importance of the same level factor to a factor in the previous level factor, that is, the weight distribution. If the system consists of the target layer and the first layer factors, then the vector v is the weight of the relative importance of the first layer factors to the target layer.

Third, consistency check. Whether the weight distribution obtained by the judgment matrix is reasonable, the consistency test of the judgment matrix is also required, as shown in formula (43)-formula (44):

In the formula, XI is the general consistency index of the judgment matrix; n is the order of the judgment matrix P; XR is the random consistency ratio of the judgment matrix; RI is the average random consistency index of the judgment matrix P (1-10th order judgment The RI standard value of matrix P is shown in Table 3).

Table 3 Average random consistency index RI standard value

When the judgment matrix P satisfies the condition CR<0.1, it is considered that P passes the consistency test, otherwise it fails, and the elements in P need to be readjusted.

Please refer to FIG. 9. FIG. 9 is a structural model for obtaining the consistency of a battery pack by using an AHP model provided in an embodiment of the present application. In one embodiment, the step of determining the weight of the consistency evaluation index of the battery pack to be tested includes:

Determine a target layer and an evaluation factor layer, the target layer includes battery pack consistency evaluation, and the evaluation factor layer includes the voltage consistency factor a ₁ , the temperature consistency factor a ₂ , and the internal resistance consistency factor a3, the capacity consistency factor _a4 , and the power consistency factor _{a5 ;}

According to the target layer and the evaluation factor layer, construct a judgment matrix, where a _ij in the judgment matrix represents the relative importance value of a _i to a _j ; i and j are respectively 1, 2, 3, 4 or 5; The judgment matrix P is shown in the following formula (45):

It is calculated that the maximum eigenroot _λmax of the judgment matrix P is 5.43, and the eigenvector W=(0.2286, 0.1242, 0.1774, 0.0999, 0.3699) corresponding to the maximum eigenroot _λmax ;

The consistency check is performed on the feature vector W, and n=5, λ _max =5.43, and RI=1.12 are substituted into the above formula (43)-formula (44).

According to formula (43)-formula (44), it is calculated that CR=0.0954<0.1, so the judgment matrix P has satisfactory consistency. According to formula (43)-formula (44), it is calculated that CR≥0.1, then the elements in the judgment matrix P need to be readjusted, so that the judgment matrix P passes the consistency check. The weight of the voltage consistency is denoted as W _V =22.86%, the weight of the temperature consistency is denoted as W _T =12.42%, the weight of the internal resistance consistency is denoted as W _R =17.74%, and the capacity is consistent The weight of the consistency is recorded as W _Q =9.99%, and the weight of the electric quantity consistency is recorded as W _E =36.99%.

In this embodiment, a calculation method for determining the weight of the consistency evaluation index of the battery pack to be tested in combination with the AHP is provided. Of course, the weight of the consistency evaluation index of the battery pack to be tested can also be obtained by other methods. In this embodiment, the relationship between the weights of the above-mentioned consistency evaluation indicators of the battery pack to be tested satisfies:

W _V +W _T +W _R +W _Q +W _E =100% (46)

That is, the sum of the weights of the consistency evaluation indexes of the battery pack to be tested is 1 (100%).

In one embodiment, the consistency weighted total score of the battery pack to be tested is recorded as G _S , and the consistency weighted total score of the battery pack to be tested is calculated by the following formula (47):

G _S =W _V ×G _V +W _T ×G _T +W _R ×G _R +W _Q ×G _Q +W _E ×G _E (47)

G _V is the unweighted score of the voltage consistency, _GT is the unweighted score of the temperature consistency, _GR is the unweighted score of the internal resistance consistency, G _Q is the unweighted score of the capacity consistency Weighted score, G _E is the unweighted score of the electric quantity consistency;

W _V is the weight of the voltage consistency, _WT is the weight of the temperature consistency, WR is the weight of the internal resistance consistency, _{W Q} is the weight of the capacity consistency, _WE is the weight of the consistency Weight of power consistency.

In this embodiment, the total consistency weighted score of the battery pack to be tested is equal to the unweighted score of each of the consistency evaluation indicators of the battery pack to be tested multiplied by the weight of the corresponding consistency evaluation index of the battery pack to be tested Reconcile.

In a specific embodiment, the consistency weighted total score of the battery pack to be tested can be obtained through calculation in combination with the calculation method given in the above embodiment. The higher the consistency-weighted total score of the battery pack to be tested, the better the consistency of the battery pack to be tested.

First, the external characteristic data of the battery pack during multiple charging and discharging processes, such as time, voltage, current and temperature, are obtained through the battery management system (BMS) on the car, cloud big data or experiments.

Further, the internal characteristic data of the battery, such as internal resistance, capacity, and electricity, are calculated.

Further, the consistency of key internal and external characteristic parameters of the battery, such as voltage consistency, temperature consistency, internal resistance consistency, capacity consistency, and power consistency, are calculated separately.

Further, the threshold of each index is determined, and then the unweighted score of each index is calculated according to the threshold.

Further, the weight of each index is determined, and then the weighted score of each index is calculated based on the weight, and the total score of the consistency of the battery pack is calculated.

Through this consistency-based battery pack evaluation method, the evolution of durability, consistency, and safety with the use of batteries can be effectively and quantitatively evaluated, requiring a small amount of calculation and no need to disassemble the battery pack.

The following Table 4 is the scoring system obtained by adopting the battery pack evaluation method of the present application. Table 5 shows the scoring results obtained by using the battery pack evaluation method of the present application.

Table 4 Scoring System

Table 5 Scoring Results

The data presented in Tables 4 to 5 above were tested on three battery packs, respectively. Battery pack A is a severely aged battery pack, battery pack B is a new battery pack, and battery pack C is a used battery. The three battery packs were charged and discharged to obtain external characteristic data of time, voltage, current and temperature. Substituting the external characteristic data into the above Table 4 and Table 5, it can be calculated that as shown in Table 5, the total score of battery pack consistency of battery pack A is 60.72 points, and the total score of battery pack consistency of battery pack B is 60.72 points. 92.06 points, the total score of battery pack consistency is 76.67 points. Through the consistency-based battery pack evaluation method in this application, the evolution of the durability, consistency, and safety of the battery can be effectively and quantitatively evaluated, requiring a small amount of calculation and no need to disassemble the battery pack.

The present application provides a battery pack evaluation system, including: a characteristic data acquisition device, a battery pack consistency evaluation index determination device, and a battery pack consistency evaluation index score calculation device.

The characteristic data acquisition device acts on the battery to be tested. The characteristic data acquisition device is used for acquiring characteristic data of the battery pack to be tested during multiple charging and discharging processes. Or, the characteristic data of the battery pack to be tested can be obtained during the operation of the battery pack to be tested.

The battery pack consistency evaluation index determination device is connected to the characteristic data acquisition device. The battery pack consistency evaluation index determination device is used for determining the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data. The battery pack consistency evaluation index determination device is further configured to determine the threshold value of the consistency evaluation index of the key characteristic parameters of the battery pack to be tested.

The battery pack consistency evaluation index score calculation device is connected to the battery pack consistency evaluation index determination device. The battery pack consistency evaluation index score computing device is used to calculate the unweighted score of the battery pack consistency evaluation index to be tested. The battery pack consistency evaluation index score computing device determines the weight of the battery pack consistency evaluation index to be tested. The battery pack consistency evaluation index score computing device calculates the consistency weighted total score of the battery pack to be tested.

The battery pack evaluation system in this embodiment can implement the steps of the battery pack evaluation method involved in any of the above embodiments. The battery pack evaluation system can effectively and quantitatively evaluate the consistency of the battery pack according to the evolution of the battery during use, combined with the durability, consistency and safety of the battery. In the process of evaluating the battery pack, it is not necessary to disassemble the battery pack, and the characteristic parameters involved are relatively comprehensive. Finally, the consistency weighted total score of the battery pack to be tested is calculated, and the conclusion is more quantitative and objective, the amount of calculation required is small, and the evaluation accuracy is high.

The present application also provides a battery pack evaluation system, including a characteristic data acquisition device and an arithmetic controller.

The characteristic data acquisition device acts on the battery to be tested. The characteristic data acquisition device is used for acquiring characteristic data of the battery pack to be tested during multiple charging and discharging processes. Or, the characteristic data of the battery pack to be tested can be obtained during the operation of the battery pack to be tested.

An arithmetic controller is connected to the characteristic data acquisition device. The arithmetic controller is configured to determine the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data. The arithmetic controller determines the threshold value of the consistency evaluation index of the key characteristic parameters of the battery pack to be tested. The arithmetic controller calculates the unweighted score of the consistency evaluation index of the battery pack to be tested. The arithmetic controller determines the weight of the consistency evaluation index of the battery pack to be tested. The arithmetic controller calculates the consistency weighted total score of the battery pack to be tested.

The battery pack evaluation system in this embodiment can implement the steps of the battery pack evaluation method involved in any of the above embodiments. The battery pack evaluation system can effectively and quantitatively evaluate the consistency of the battery pack according to the evolution of the battery during use, combined with the durability, consistency and safety of the battery. In the process of evaluating the battery pack, it is not necessary to disassemble the battery pack, and the characteristic parameters involved are relatively comprehensive. Finally, the consistency weighted total score of the battery pack to be tested is calculated, and the conclusion is more quantitative and objective, the amount of calculation required is small, and the evaluation accuracy is high.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present application, and the descriptions thereof are relatively specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be noted that, for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims (11)

1. A battery pack evaluation method, characterized by comprising:

acquiring characteristic data of a battery pack to be tested;

determining a consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data;

calculating the unweighted score of the consistency evaluation index of the battery pack to be tested according to the consistency evaluation index of the key characteristic parameters of the battery pack to be tested and the threshold value of the consistency evaluation index of the key characteristic parameters of the battery pack to be tested;

determining the weight of the consistency evaluation index of the battery pack to be tested;

and calculating the consistency weighted total score of the battery pack to be tested according to the unweighted score of the consistency evaluation index of the battery pack to be tested and the weight of the consistency evaluation index of the battery pack to be tested, wherein the higher the score of the consistency weighted total score of the battery pack to be tested is, the better the consistency of the battery pack to be tested is.

2. The battery pack evaluation method according to claim 1, wherein the characteristic data of the battery pack to be tested includes: external characteristic data and internal characteristic data;

the external characteristic data comprises time, voltage, current and temperature;

the internal characteristic data includes internal resistance, capacity, and electric quantity;

the step of acquiring the characteristic data of the battery pack to be tested comprises the following steps:

providing a battery pack to be tested, wherein the battery pack to be tested comprises a plurality of battery monomers;

charging and discharging the battery pack to be tested, and acquiring external characteristic data of the battery pack to be tested in multiple charging and discharging processes;

calculating the internal characteristic data from the external characteristic data.

3. The battery pack evaluation method according to claim 2, wherein the step of obtaining external characteristic data of the battery pack to be tested includes:

providing the battery pack to be tested, placing the battery pack to be tested in an incubator, setting the temperature in the incubator to be a standard temperature, and standing for the first time;

discharging the battery pack to be tested to a discharge cut-off voltage at a first multiplying power constant current, and standing for a second time;

charging the battery pack to be tested for a first charging time at the first multiplying power constant current;

charging the battery to a charging cut-off voltage at a constant current at a second multiplying factor, and standing for a third time;

the step of discharging the battery pack to be tested in the constant current mode until the discharge cut-off voltage is reached, the step of standing the battery pack for the second time, the step of charging the battery pack in the constant current mode for the first charging time, the step of charging the battery pack in the constant current mode until the charge cut-off voltage is reached, and the step of standing the battery pack for the third time are an experiment period, and the experiment period is repeated for multiple times so that external characteristic data of the battery.

4. The battery pack evaluation method according to claim 3, wherein the step of obtaining external characteristic data of the battery pack to be tested is followed by:

calculating the internal resistance of the battery pack to be tested according to the following formula (1):

in the formula (I), the compound is shown in the specification,

denotes the ith_CThe internal resistance of each battery cell is n in the battery pack to be tested_CEach single battery is in m omega;

indicating the ith last moment before current switching in the charging process_CThe voltage of each cell;

indicating the starting time ith after current switching in the charging process_CThe voltage of each cell; i is_AThe current representing the last moment before the current switching in the charging process; i is_BThe current represents the initial moment after the current is switched in the charging process;

calculating the capacity of the battery pack to be tested and the electric quantity of the battery pack to be tested according to the following formulas (2) to (8):

in the above formula, t₁Is the starting time for charging the battery pack to be tested; t is t₂Is the end time of charging of the battery pack to be tested;

denotes the ith_CThe remaining charge time of each cell;

is the ith_CT of individual battery cell₂The voltage at the moment is translated to a point B through a point A, and the corresponding time is set on the charging voltage curve of the single body with the highest charging ending voltage;

denotes the ith_CThe remaining discharge time of each cell;

denotes the ith_CT of individual battery cell₁The voltage at the moment is translated to a point D through a point C, and the corresponding time is set on the charging voltage curve of the monomer with the lowest discharging ending voltage; i represents charging current, and is a constant value under the constant current charging working condition; under the constant-power charging condition, I is a variable;

denotes the ith_CThe residual discharge capacity of each battery cell;

denotes the ith_CThe residual charge capacity of each battery cell; q_sysRepresenting the system capacity of the battery pack to be tested;

denotes the ith_CThe capacity of each cell;

denotes the ith_CThe electric quantity of each battery cell.

5. The battery pack evaluation method according to claim 4, wherein the step of determining a consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data comprises:

respectively calculating a consistency evaluation index of the key external characteristic parameters of the battery pack to be tested and a consistency evaluation index of the key internal characteristic data of the battery pack to be tested according to the external characteristic data and the internal characteristic data;

the consistency evaluation index of the key external characteristic parameters of the battery pack to be tested comprises the following steps: voltage consistency, temperature consistency;

the consistency evaluation index of the key internal characteristic data of the battery pack to be tested comprises the following steps: consistent internal resistance, capacity and electric quantity.

6. The battery pack evaluation method according to claim 5, wherein the evaluation index of the voltage uniformity is determined by a voltage uniformity parameter_VTo evaluate:_Vthe larger the voltage uniformity is; the voltage uniformity parameter_VThe following equations (9) to (14) yield:

in the formula, n_cRepresenting that the battery to be tested has n_cA plurality of battery cells;

denotes the ith_CThe voltage of the single body at the j-th moment (k moments in total) in the charging stage; v_m-jThe average value of the voltage of each battery monomer at the j moment of the charging stage is shown, and all the values form an average voltage curve of the charging process;

represents the average of the average voltage curve; v_max-jThe maximum voltage value of each battery monomer at the j-th moment in the charging stage is represented, and all values of the maximum voltage values form a maximum voltage curve in the charging process; v_min-jThe minimum voltage value of each battery monomer at the j-th moment in the charging stage is represented, and all values of the minimum voltage values form a minimum voltage curve in the charging process; sigma_VData representing the highest voltage curve and the lowest voltage curve in the charging phaseRoot mean square error of the voltage curve data;_Vrepresenting the variation coefficient of the charging voltage of each monomer, namely the voltage consistency parameter;

the evaluation index of the temperature consistency passes through a temperature consistency parameter o_TTo evaluate: o ° o_TThe larger the temperature, the worse the temperature consistency; the temperature uniformity parameter σ_TThe following equations (15) to (19) yield:

in the formula, n_TRepresenting that the battery to be tested has n_TA temperature sensor;

denotes the ith_TA temperature sensor, the battery pack to be tested has n_TA temperature sensor; at the temperature of the j-th moment in the charging stage, the number of the k moments in the charging stage is total; t is_m-jThe average value of the temperature of each temperature sensor at the j th moment of the charging stage is shown, and all values of the average value form an average temperature curve of the charging process;

mean value representing mean temperature curve；T_max-jThe maximum temperature value of each temperature sensor at the jth moment in the charging stage is represented, and all numerical values of the maximum temperature values form a maximum temperature curve in the charging process; t is_min-jThe minimum temperature value of each temperature sensor at the j-th moment in the charging stage is represented, and all numerical values of the minimum temperature values form a minimum temperature curve in the charging process; sigma_TThe root mean square error of the highest temperature curve data and the lowest temperature curve data in the charging stage is represented, and the root mean square error is the temperature consistency parameter;

the evaluation index of the internal resistance consistency passes through the internal resistance consistency parameter_RTo evaluate:_Rthe larger the internal resistance is, the worse the internal resistance uniformity is; the internal resistance consistency parameter_RThe following equations (20) to (22) yield:

in the formula, n_cRepresenting that the battery to be tested has n_cA plurality of battery cells;

represents the average value of the internal resistances of the monomers; sigma_RThe standard deviation of the internal resistance of each monomer is shown;_Rexpressing the variation coefficient of the internal resistance of each monomer, namely the internal resistance consistency evaluation parameter;

the evaluation index of the capacity consistency passes through a capacity consistency parameter sigma_QAnd

to evaluate: sigma_QAnd

the larger the capacity consistency is, the worse the capacity consistency is; the capacity consistency parameter σ_QAnd

the following equations (23) to (26) yield:

in the formula, n_cRepresenting that the battery to be tested has n_cA plurality of battery cells;

represents the average value of the capacities of the respective monomers; sigma_QRepresents the standard deviation of the capacity of each monomer;_Qthe standard deviation coefficient of variation, which represents the capacity of each monomer, is one of the parameters for evaluating the consistency of the capacity; q_maxRepresents the maximum value of the capacity of each monomer, Q_minRepresents the minimum value of the capacity of each monomer;

the range variation coefficient of each monomer capacity is represented, namely the capacity consistency evaluation parameter is obtained;

the evaluation index of the electric quantity consistency passes through the electric quantity consistency parameter_EAnd

to evaluate:_Eand

the larger the electric quantity, the worse the electric quantity consistency; the electric quantity consistency parameter_EAnd

the following equations (27) to (30) yield:

in the formula, n_cRepresenting that the battery to be tested has n_cA plurality of battery cells;

represents the average value of the electric quantity of each monomer; sigma_ERepresents the standard deviation of the capacity of each monomer;_Ethe standard deviation coefficient of variation of each monomer electric quantity is one of parameters for evaluating the consistency of the electric quantity; e_maxRepresents the maximum value of each individual charge, E_minRepresents the minimum value of each monomer electric quantity;

and expressing the range variation coefficient of each monomer electric quantity, namely the electric quantity consistency evaluation parameter.

7. The battery pack evaluation method of claim 6, wherein the step of calculating an unweighted score for the battery pack consistency evaluation index to be tested comprises:

setting the voltage uniformity parameter_VThe temperature uniformity parameter sigma_TThe full score threshold value and the internal resistance consistency parameter_RThe full-scale threshold value of (a), the capacity consistency parameter σ_QAnd

the full score threshold value and the electric quantity consistency parameter_EAnd

the full score threshold of (a) is 0;

the voltage uniformity parameter_VIs set to T_V2.5%, the temperature consistency parameter σ_TIs set to T_T10 ℃, said internal resistance consistency parameter_RIs set to T_R50%, the capacity consistency parameter_QAnd

are all set to T_Q5%, the electrical quantity consistency parameter_EAnd

are all set to T_E＝5％；

Obtaining the unweighted score of the consistency evaluation index of the battery pack to be tested by adopting a piecewise linear interpolation method; the unweighted score of the voltage uniformity is denoted as g_VThe unweighted score of the temperature uniformity is denoted as g_TAnd the unweighted score of the internal resistance consistency is recorded as g_RThe unweighted score of the capacity consistency is denoted as g_QAnd the unweighted score of the consistency of the electric quantity is recorded as g_E；

_VFor the voltage uniformity parameter, σ_TFor the purpose of said temperature consistency parameter,_Ris the internal resistance consistency parameter, σ_QAnd

respectively, are the capacity consistency parameters and,_Eand

respectively are the electric quantity consistency parameters;

a process variable representing capacity; k_QA coefficient representing a capacity;

a process variable representing an electrical quantity; k_EA coefficient representing the amount of electricity.

8. The battery pack evaluation method of claim 7, wherein the step of determining the weight of the battery pack consistency evaluation index to be tested comprises:

determining a target layer and an evaluation factor layer, wherein the target layer comprises a battery pack consistency evaluation, and the evaluation factor layer comprises the voltage consistency factor a₁The temperature uniformity factor a₂The internal resistance uniformity factor a₃The capacity uniformity factor a₄And the electric quantity consistency factor a₅；

Constructing a judgment matrix according to the target layer and the evaluation factor layer, wherein a in the judgment matrix_ijDenotes a_iTo a_jRelative importance value of; i and j are respectively 1,2,3, 4 or 5; a is₁For the evaluation of the voltage uniformity, a₂For the evaluation of the temperature uniformity, a₃As an internal resistance uniformity evaluation parameter, a₄For the capacity consistency evaluation parameter, a₅For the electric quantity consistency evaluation parameter, the judgment matrix P is shown as the following formula (40):

the judgment matrix P has the following properties:

calculating to obtain the maximum characteristic root lambda of the judgment matrix P_maxAnd the maximum characteristic root λ_maxCorresponding feature vector W ═ W (W)_V,W_T,W_R,W_Q,W_E)，W_VIs a weight of the voltage uniformity, W_TIs a weight of the temperature uniformity, W_RIs a weight of the internal resistance consistency, W_QWeight for the capacity consistency, W_EThe weight of the electric quantity consistency;

the feature vector W is subjected to a consistency check according to the following equation (43) -44:

CI represents a general consistency index of the judgment matrix; n represents the order of the judgment matrix P; CR represents a random consistency ratio of the decision matrix; RI represents the average random consistency index of the judgment matrix P, and RI has a standard value;

and calculating the value of CR according to a formula (43) -a formula (44), wherein when the judgment matrix P meets a condition CR <0.1, the judgment matrix P passes consistency check, otherwise, the judgment matrix P does not pass and the elements in the judgment matrix P need to be readjusted.

9. The battery pack evaluation method of claim 8, wherein the battery pack to be tested has a consistency weighted sum score of G_SThe consistency weighted total score of the battery pack to be tested is calculated by the following formula (47):

G_S＝W_V×G_V+W_T×G_T+W_R×G_R+W_Q×G_Q+W_E×G_E(47)

G_Vis an unweighted score of the voltage uniformity, G_TIs an unweighted score, G, of the temperature uniformity_RIs an unweighted score of the internal resistance consistency, G_QIs an unweighted score, G, of the capacity consistency_EAn unweighted score for the consistency of the electrical quantities;

W_Vis a weight of the voltage uniformity, W_TIs a weight of the temperature uniformity, W_RIs a weight of the internal resistance consistency, W_QWeight for the capacity consistency, W_EAnd the weight of the consistency of the electric quantity.

10. A battery pack evaluation system, comprising:

the characteristic data acquisition device is used for acquiring the characteristic data of the battery pack to be tested;

the battery pack consistency evaluation index determining device is connected with the characteristic data acquiring device and is used for determining the consistency evaluation index of the key characteristic parameters of the battery pack to be tested according to the characteristic data and determining the threshold value of the consistency evaluation index of the key characteristic parameters of the battery pack to be tested; and

and the battery pack consistency evaluation index score calculation device is connected with the battery pack consistency evaluation index determination device and is used for calculating the unweighted score of the consistency evaluation index of the battery pack to be tested, determining the weight of the consistency evaluation index of the battery pack to be tested and calculating the consistency weighted total score of the battery pack to be tested.

11. A battery pack evaluation system, comprising:

the characteristic data acquisition device is used for acquiring the characteristic data of the battery pack to be tested; and

the operation controller is connected with the characteristic data acquisition device and used for determining consistency evaluation indexes of the key characteristic parameters of the battery pack to be tested according to the characteristic data; determining a threshold value of a consistency evaluation index of the key characteristic parameters of the battery pack to be tested; calculating the unweighted score of the consistency evaluation index of the battery pack to be tested; determining the weight of the consistency evaluation index of the battery pack to be tested; and calculating a consistency weighted total score of the battery pack to be tested.

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