CN115902677A - Method for acquiring direct current internal resistance parameter of lithium ion battery - Google Patents

Abstract

The invention belongs to the technical field of battery internal resistance data measurement, and particularly relates to a method for acquiring direct current internal resistance parameters of a lithium ion battery, which comprises the following steps: setting the ranges of direct current internal resistance test influence factors SOC, temperature and multiplying power; step two, setting test value taking points in the range; acquiring charge and discharge data of the battery to be detected; on the basis of the charge and discharge data, a temperature constant device is adopted, and charge and discharge tests at different temperatures are carried out on the basis of the same multiplying power; and step five, extracting data and calculating corresponding direct current internal resistance. According to the invention, through the continuous charge and discharge test of fixed temperature and multiplying power in each test, only SOC adjustment in the initial state is needed, adjustment of each SOC point is not needed, and only continuous SOC access points are needed in the later data processing, so that the time for accurately obtaining the internal resistance parameters is effectively saved.

Description

A method for obtaining direct current internal resistance parameters of a lithium-ion battery

Technical Field

The invention belongs to the technical field of battery internal resistance data measurement, and in particular relates to a method for acquiring direct current internal resistance parameters of a lithium-ion battery.

Background Art

Internal resistance is one of the key parameters of lithium-ion batteries. It is crucial for accurately estimating and predicting the battery status (such as SOC, SOH, SOP and SOF) in the field of new energy vehicles and energy storage. The internal resistance of lithium-ion batteries is generally divided into AC internal resistance and DC internal resistance. AC internal resistance is generally tested by an AC impedance meter and is used to evaluate the internal resistance of single cells. Due to the voltage and capacity of lithium-ion battery modules and battery packs after grouping, DC internal resistance is generally evaluated and used. Therefore, the DC internal resistance of the battery cells before grouping will also be measured and used to facilitate the research and evaluation of single cells at the single cell level.

The main methods for measuring the DC internal resistance of a single battery are:

1) Rate pulse method and AC impedance test method. Typical rate pulse methods include the HPPC test method in the US FreedomCar Battery Test Manual, the test method of Japan DEVSD713 2003, the internal resistance test method specified in GB/T 31467, and other derivative methods. The core idea is to apply currents of different rates under different SOC states and temperatures, and use the ratio of the voltage difference to the current before and after a certain period of time as the DC internal resistance of the battery.

2) Parameter identification based on equivalent circuit model, mainly involving pulse multi-sinusoidal signal measurement and real-time estimation based on Kalman filtering under mixed working conditions. The core idea of the two methods is to identify the open circuit voltage, resistance and capacitance in the circuit by acquiring current and voltage signals based on the equivalent circuit model.

However, the above technologies still have the following defects:

As an electrochemical energy storage device, the internal resistance of lithium-ion batteries is affected by the battery's state of charge SOC, temperature, time scale, and expansion state. According to traditional orthogonal testing, the adjustment time of SOC and temperature is relatively long. For example, in the HPPC test, the SOC is adjusted and tested at a certain temperature and a certain rate, and a charge and discharge pulse test is performed at each SOC point. After each charge/discharge pulse test, the pulse current is proportionally reduced (for example, one tenth of the pulse current) to perform equal capacity discharge/charge to adjust the SOC to the previous operating condition, and then the next set of pulse tests are performed at the same SOC point. After the charge and discharge pulse test at each SOC point is completed, the pulse current is also proportionally reduced to perform constant capacity discharge, and the SOC is adjusted to the next SOC point for a new set of pulse tests. There are both capacity differences and SOC inaccuracies caused by different temperatures, and there is also the problem of adjusting the SOC point back and forth.

The online parameter identification of the equivalent circuit can identify the open-circuit voltage, DC internal resistance, charge transfer resistance and interface capacitance under the corresponding working conditions. For example, after considering SOC, temperature and rate, there is a complex identification algorithm, and after coupling multiple factors, there are single parameter differences but the final result deviates from the actual phenomenon. In the actual vehicle operation process, the SOC, rate and temperature conditions cannot cover the full range of parameters, resulting in the inability to accurately identify the internal resistance under special and extreme conditions.

Summary of the invention

In view of the shortcomings of the existing lithium-ion battery DC internal resistance test process, low accuracy, narrow boundary range and poor actual vehicle usability, the purpose of the present invention is to propose a new method for obtaining the DC internal resistance parameters of a lithium-ion battery.

To achieve the above object, the present invention provides the following technical solutions:

A method for obtaining a direct current internal resistance parameter of a lithium-ion battery comprises the following steps:

Step 1: Set the range of SOC, temperature and rate of the DC internal resistance test influencing factors;

Step 2: Set the test value points within the above range;

Step 3, obtaining the charge and discharge data of the battery to be tested;

Step 4: Based on the above charge and discharge data, a temperature constant device is used to perform different

Charge and discharge test at the same temperature;

Step 5: Extract data and calculate the corresponding DC internal resistance.

As a preferred technical solution, the following formula is used for calculation in step 5:

Among them, R is the internal resistance related to SOC, temperature and rate; OCV is the open circuit voltage of the battery; Voltage is the battery voltage during the test; I is the current during the test.

As a preferred technical solution, the OCV value is obtained by linear difference or quadratic difference.

As a preferred technical solution, the value points in step 2 are averagely distributed.

As a preferred technical solution, the SOC range is [0,1], and the SOC value is taken at an interval of ≤10%; the temperature value is taken at an interval of ≥5.

As a preferred technical solution, the temperature constant device in step 4 is an isothermal calorimeter. Compared with the prior art, the constant temperature and constant rate charge and discharge test based on the isothermal calorimeter proposed in the present invention does not need to repeatedly adjust the battery SOC and can quickly complete the test.

As a preferred technical solution, the sampling time interval of step 4 is set to 1s.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention performs continuous charge and discharge tests at fixed temperature and rate each time, and only needs to adjust the SOC in the initial state, and no adjustment is required for each SOC point. In the subsequent data processing, only continuous SOC points need to be taken, which effectively saves the time for accurately obtaining the internal resistance parameters.

The temperature and rate points of this invention are determined based on the nonlinear characteristics of the battery internal resistance, and the nonlinear accuracy can be guaranteed with the minimum required number.

The difference selection requirement of the present invention can avoid local distortion caused by nonlinear problems.

In the present invention, the number of sampling points is set to 1s, based on the actual working conditions during the use of the actual vehicle, and there is no need to consider the influence of the time scale on the internal resistance parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the steps of the method provided by the present invention.

DETAILED DESCRIPTION

The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

The implementation process of the present invention is as follows:

1. Given the range (minimum and maximum) of the factors affecting the DC internal resistance test of lithium-ion batteries, SOC, temperature, and rate: [SOC _max , SOC _min ], [T _min , T _max ], [I _min , I _max ].

2. SOC is taken at intervals of ≤10%. For example, if the SOC range is [0,1], the values are [0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1]. Temperature is taken at points ≥5. For example, if the temperature range is [-30,50], the values can be [-30,-10,10,30,50]. For example, if the multiplier range is [0.1,2], the values can be [0.1,0.5,1,1.5,2].

3. Test and obtain the open circuit voltage of the battery at different SOC and temperature, as shown below

0 0.1 0.2 0.3 0.45 0.5 0.6 0.7 0.8 0.9 1 -30 OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV -10 OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV 10 OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV 30 OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV 50 OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV OCV

4. Perform charge and discharge tests at different temperatures at the same rate in the isothermal calorimeter, with the sampling interval set to 1s. For example, first determine a rate, perform charge and discharge tests at a single temperature, set the sampling interval to 1s, and obtain the actual voltage.

5. Extract the actual voltage at the temperature corresponding to the SOC in each test. We can get the following results. In the actual process, if the SOC is not 100%, there is no need to extract data.

0 0.1 0.2 0.3 0.45 0.5 0.6 0.7 0.8 0.9 1 -30 Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage -10 Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage 10 Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage 30 Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage 50 Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage Voltage

6. Identification and extraction of resistance

The charging segment data can be used to identify the internal resistance of the charging segment, and the discharge segment data can be used to identify the short-circuit data of the discharge segment.

According to the following formula:

Among them, R is the internal resistance related to SOC, temperature and rate; OCV is the open circuit voltage of the battery; Voltage is the battery voltage during the test; I is the current during the test.

OCV is performed by linear interpolation or quadratic interpolation, avoiding the use of cubic spline interpolation to avoid distortion in areas with large changes in the slope of the low SOC.

0.1C

0 0.1 0.2 0.3 0.45 0.5 0.6 0.7 0.8 0.9 1 -30 R R R R R R R R R R R -10 R R R R R R R R R R R 10 R R R R R R R R R R R 30 R R R R R R R R R R R 50 R R R R R R R R R R R

0.5C

0 0.1 0.2 0.3 0.45 0.5 0.6 0.7 0.8 0.9 1 -30 R R R R R R R R R R R -10 R R R R R R R R R R R 10 R R R R R R R R R R R 30 R R R R R R R R R R R 50 R R R R R R R R R R R

1C

2C

0 0.1 0.2 0.3 0.45 0.5 0.6 0.7 0.8 0.9 1 -30 R R R R R R R R R R R -10 R R R R R R R R R R R 10 R R R R R R R R R R R 30 R R R R R R R R R R R 50 R R R R R R R R R R R

From the above steps, it can be seen that the present invention only needs to adjust the SOC in the initial state through continuous charge and discharge tests with fixed temperature and rate each time, and there is no need to adjust each SOC point. The temperature and rate points of this invention are determined based on the nonlinear characteristics of the battery internal resistance, and the nonlinear accuracy can be guaranteed with the minimum required number. The difference selection requirements of the present invention can avoid local distortion caused by nonlinear problems. The number of sampling points in the present invention is set to 1s, based on the actual working conditions during the use of the actual vehicle, and there is no need to consider the influence of the time scale on the internal resistance parameters.

Obviously, the specific implementation scheme described above is only a further detailed description of the purpose, technical scheme and beneficial effects of the present invention. It should be understood that the above is only a specific example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A method for acquiring direct current internal resistance parameters of a lithium ion battery is characterized by comprising the following steps:

setting the ranges of direct current internal resistance test influence factors SOC, temperature and multiplying power;

step two, setting test value taking points in the range;

acquiring charge and discharge data of the battery to be detected;

on the basis of the charge and discharge data, a temperature constant device is adopted to carry out charge and discharge tests at different temperatures based on the same multiplying power;

and step five, extracting data and calculating corresponding direct current internal resistance.

2. The method for acquiring the direct current internal resistance parameter of the lithium ion battery according to claim 1, wherein the calculation is performed by adopting the following formula in the fifth step:

wherein R is internal resistance related to soc, temperature and multiplying power; OCV is the battery open circuit voltage; voltage is the battery Voltage in the testing process; i is the test process current.

3. The method for obtaining the direct current internal resistance parameter of the lithium ion battery according to claim 1, wherein the OCV value is obtained by a linear difference value or a quadratic difference value.

4. The method for acquiring the direct current internal resistance parameter of the lithium ion battery according to claim 1, wherein the average distribution value is adopted for the value points in the second step.

5. The method for acquiring the direct-current internal resistance parameter of the lithium ion battery according to claim 4, wherein the SOC ranges from [0,1], and the SOC takes values at intervals of less than or equal to 10%; the temperature is taken at intervals of 5 or more.

6. The method for acquiring the direct current internal resistance parameter of the lithium ion battery according to claim 1, wherein the temperature-stabilizing device in the fourth step is an isothermal calorimeter.

7. The method for acquiring the direct current internal resistance parameter of the lithium ion battery according to claim 1 or 6, wherein the sampling time interval of the four steps is set to 1s.

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