Method for improving accuracy of battery SOC in charging process
By introducing battery cell voltage to calibrate the lithium battery SOC, combining the calibration curve of internal resistance and temperature and the indexing meter design, the problem of inaccurate SOC calculation in the prior art is solved, and higher SOC accuracy and reliability are achieved.
Patent Information
- Application Number
- CN202411870665.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-18
- Publication Date
- 2025-04-11
AI Technical Summary
In the prior art, when calculating the SOC of lithium batteries, there are errors due to factors such as temperature and battery characteristics, resulting in inaccurate SOC calculations.
By introducing the battery cell voltage as a correspondence relationship with the SOC, the SOC of the battery is calibrated based on the battery cell voltage, a calibration curve between internal resistance and temperature is established, and the calibration curve is designed by the indexing meter to improve the accuracy of the SOC.
By calibrating the battery SOC, the accuracy of the SOC can be significantly improved, the errors caused by the simple ampere calculation method can be avoided, and the accuracy and reliability of SOC calculation can be ensured.
Smart Images
Figure CN119805233A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of battery calibration, and in particular to a method for improving the SOC accuracy of a battery during a charging process. Background Art
[0002] In recent years, with the rapid development of new energy, lithium batteries, as an important energy storage product, have been widely used in various scenarios. Currently, various key technical issues of lithium batteries have become the core issues in the development of the new energy field.
[0003] In order to ensure the reliability and durability of new energy batteries, monitoring the state of charge (SOC) of lithium batteries is the key to protecting the life of lithium batteries. Currently, the commonly used SOC calculation methods are the ampere-hour integration method and the open circuit voltage method.
[0004] In actual application, the battery SOC is calculated by the ampere-hour method. However, due to the influence of factors such as temperature and battery characteristics, the conventional ampere-hour calculation method may cause errors.
[0005] To address this problem, by introducing the battery cell voltage as a corresponding relationship with the SOC, the battery SOC is calibrated based on the battery cell voltage, which can improve the accuracy of the SOC. Summary of the invention
[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for improving the accuracy of battery SOC during charging. When calculating the battery SOC by the ampere-hour method, the battery cell voltage is introduced to calibrate the SOC to improve the accuracy of the battery SOC.
[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for improving the accuracy of battery SOC during charging, comprising the following steps:
[0008] S1, after starting, analyze the battery characteristics, measure the internal resistance of the battery cells at room temperature, establish a calibration curve between internal resistance and temperature, calculate the average value of each battery cell voltage detected by the sensor, and use the formula V = V cell -(A*res) to calibrate the internal resistance of the battery, where V cell Represents the sampled battery cell voltage, res represents the internal resistance value at this temperature, A represents the charging current at this time, and V represents the actual battery cell voltage value after eliminating the influence of internal resistance;
[0009] S2, establish a scale table based on historical charging data: at room temperature, charge and discharge the battery cells with a small current, record the relationship between SOC and battery cell voltage, compare the historical charging and discharging records, and comprehensively obtain a scale table between battery cell voltage and battery SOC;
[0010] S3, calculating the actual SOC of the battery during the charging and discharging process, based on the scale, querying the SOC at this time through the scale, calculating the difference between the actual SOC, and querying the calibration curve to obtain the calibration coefficient;
[0011] S4, confirming the calibration coefficient according to the difference, and calibrating the battery SOC to be close to the design value;
[0012] S5, in the last division stage, the voltage of the sampled battery cell is judged and the voltage of the battery cell is eliminated to eliminate the influence of the internal resistance on the voltage of the battery cell;
[0013] S6, during the discharge process, the battery cell voltage is used to determine whether the battery is fully charged or has dropped to 10%. If so, the charging is terminated and the SOC is calibrated to be consistent with the battery cell voltage at 10%. Otherwise, the SOC calculation is stopped and this step is repeated.
[0014] Furthermore, in the step S2, a battery cell voltage is recorded at every 5% of the SOC scale, and a calibration curve is designed according to the difference between the actual SOC and the battery cell voltage corresponding to the SOC scale table.
[0015] Furthermore, in step S3, during the charging process, the battery SOC is calculated by the ampere-hour method, and the calibration coefficient is introduced into the calculation process: Ah = t*A*x + Ah remain , where t represents time, A represents current, x represents calibration coefficient, Ah remain Indicates the current time.
[0016] Furthermore, the step S5 performs a strong calibration on the SOC before the battery is fully charged. When the SOC of the battery rises to 99%, it is determined whether the current battery cell voltage is the voltage of the fully charged battery. During this period, the SOC is stopped from rising until the battery cell voltage rises to the fully charged battery cell voltage. It is determined that the battery is fully charged, the SOC changes to 100%, and charging is stopped.
[0017] Furthermore, the step S5 performs a strong calibration on the SOC during the discharge process. When the SOC of the battery drops to 10%, the decrease of the SOC is stopped during this period until the battery cell voltage drops to the battery cell voltage corresponding to 10%. It is judged that the battery SOC is low at this time and attention should be paid to the power. The SOC changes to 10%, and the decrease of the SOC is restarted.
[0018] Beneficial effects of the present invention:
[0019] The present invention calibrates the SOC of the battery based on the battery cell voltage, takes into account the influence of temperature on the internal resistance and the situation of insufficient calibration, and designs a calibration curve based on the battery cell voltage by relying on a graduation table. The battery SOC is calibrated by the calibration curve, avoiding the error caused by the simple ampere-hour calculation method; the patent structure of the present invention is simple, easy to implement, and can well meet the needs of practical engineering applications;
[0020] The method of the present invention improves the accuracy of the battery SOC by using a table lookup method and improving the accuracy of the battery cell voltage. On the one hand, the SOC value can be made more accurate during the charging and discharging process. On the other hand, it can avoid the battery SOC from being falsely charged and play an alarm role when it drops to 10%. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figure 1 This is a flow chart of battery charge and discharge calibration of the present invention;
[0022] Figure 2 is the internal resistance correction coefficient of the battery cell at different temperatures of the present invention;
[0023] Figure 3 It is the SOC calibration coefficient of the present invention based on the graduation table. DETAILED DESCRIPTION
[0024] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings.
[0025] This implementation case takes a certain type of battery as an example, mainly involving the internal resistance of the battery cell, the environment and other factors, and discloses a method for improving the accuracy of the battery SOC during the charging process, which improves the accuracy of the power battery capacity SOC by calibrating the scale and limiting the capacity SOC, such as Figure 1 As shown, the specific implementation steps are as follows.
[0026] Step 1: Considering the influence of internal resistance on the battery cell voltage of the sampled battery, the internal resistance value of the battery cell at room temperature is measured by charging and discharging at room temperature. The internal resistance of the battery cell at room temperature is 720.
[0027] Through the charge and discharge experiment, the influence curve of temperature on the internal resistance value is determined as follows Figure 2 As shown, a calibration curve between internal resistance and temperature is established. By eliminating the influence of internal resistance at different temperatures, the sampling voltage is made close to the actual value according to the battery cell voltage detected by the sensor, and the average value is calculated according to the voltage of each battery cell. cell -(A*res) to calibrate the internal resistance of the battery, where V cell represents the sampled battery cell voltage, res represents the internal resistance value at this temperature, A represents the charging current at this time, and V represents the actual battery cell voltage value after eliminating the influence of internal resistance.
[0028] When the battery cell voltage is detected by the sensor, the battery's internal resistance value will be affected by temperature and change with the temperature. The change in the sensor's internal resistance value will cause the detected battery cell voltage to be different from the actual value: the higher the temperature, the greater the internal resistance value. In order to eliminate the influence of temperature on the battery cell voltage, a calibration curve between temperature and internal resistance is established. During the charging and discharging process, as the temperature rises, the internal resistance is gradually calibrated so that the detected battery cell voltage tends to the actual value. The calibration curve is designed according to the difference in SOC values. The larger the gap, the larger the corresponding calibration coefficient, and the greater the correction force on the SOC.
[0029] Battery SOC is the ratio of available power in the battery to the nominal capacity. The battery SOC is generally calculated using the ampere-hour method. Affected by the current sensor, temperature, battery characteristics, etc., the conventional ampere-hour method will have errors. The corresponding relationship between the battery SOC and the battery cell voltage is relatively stable. A scale between the battery cell voltage and the battery SOC is used to calibrate the battery SOC.
[0030] Step 2: Establish a graduation table based on historical charging data: The effect of internal resistance on battery cell voltage is positively correlated with current. The greater the current, the greater the effect of internal resistance on the detected battery cell voltage. Therefore, a graduation table between battery SOC and battery cell voltage can be established through small current charge and discharge experiments and historical charge and discharge data of the battery.
[0031] Record a battery cell voltage at every 5% of SOC. According to the difference between the actual SOC and the corresponding SOC of the battery cell voltage, design a calibration curve as follows: Figure 3 shown.
[0032] At room temperature, the battery cells are charged and discharged with a small current, and the relationship between SOC and battery cell voltage is recorded. By comparing the historical charge and discharge records, a comprehensive table between battery cell voltage and battery SOC is obtained.
[0033] Step three, during the charge and discharge process, based on the scale table, query the SOC at this time through the scale table, calculate the difference between the actual SOC, and query the calibration curve to obtain the calibration coefficient.
[0034] During the charging process, sample the average value of the battery cell voltage at this time, query the corresponding SOC according to the graduation table, compare the difference between the calculated value and the query value by the ampere-hour calculation method, determine the calibration coefficient according to the difference, adjust the SOC value in the process of calculating the battery SOC by the ampere-hour method, and bring the calibration coefficient into the calculation process: Ah = t*A*x+Ah remain , where t represents time, A represents current, x represents calibration coefficient, Ah remain Indicates the current time.
[0035] During the charging process, in order to avoid insufficient calibration and false power, the battery cell voltage is used to determine whether the battery is fully charged. The SOC is calibrated to be consistent with the battery cell voltage before full charging.
[0036] Step 4: In every 5% interval of the battery charge and discharge SOC, the SOC is calibrated in each cycle of the program, and the calibrated SOC value is close to the actual value.
[0037] Step 5: In the last division stage, the voltage of the sampled battery cells is determined and the influence of the internal resistance on the voltage of the battery cells is eliminated.
[0038] In order to improve the accuracy of battery SOC and avoid the situation where the gap between the battery cluster SOC and the actual value is too large, resulting in insufficient calibration, a full judgment condition is added during the charging process. A strong calibration of the SOC is performed before the battery is fully charged. When the battery SOC rises to 99%, it is judged whether the current battery cell voltage has reached the battery cell voltage of the fully charged battery. During this period, the SOC is stopped from rising until the battery cell voltage rises to the fully charged battery cell voltage. The battery is judged to be fully charged, the SOC changes to 100%, and charging is stopped.
[0039] During the discharge process, a strong calibration judgment of battery discharge is also added. In order to avoid sudden situations caused by the battery judging that the battery is fully discharged and stopping discharge directly, the sudden death method is not used during the discharge process. The judgment condition is left with a margin and the judgment is made at 10%. During this period, the SOC is stopped from decreasing until the battery cell voltage drops to the battery cell voltage corresponding to 10%. It is judged that the battery SOC is low at this time and attention should be paid to the power. The SOC changes to 10%, and the SOC decrease is restarted.
[0040] Step 6: During the discharge process, the battery cell voltage is used to determine whether the battery is fully charged or has dropped to 10%. If so, the charging is terminated and the SOC is calibrated to be consistent with the battery cell voltage at 10%. Otherwise, the SOC calculation is stopped and this step is repeated.
[0041] This step uses the battery cell voltage as the judgment condition for whether the battery is fully charged during the battery charging and discharging process. Considering that simply using the sampled battery cell voltage as the judgment condition may be inaccurate when the temperature is high. In order to avoid this situation, two voltages, the sampled battery cell voltage and the battery cell voltage without the influence of internal resistance, are used as judgment conditions. On this basis, the battery cell voltage is continuously sampled and the battery cell voltage without the influence of internal resistance is calculated and judged in a cycle until the judgment is completed.
[0042] When the calculation gap of the ampere-hour method is too large or the difference between the battery SOC and the actual value is too large, there may be insufficient SOC calibration. In this case, the SOC is calibrated once in the last division of the calibration, when the battery is fully charged and before the SOC drops to 10%. At this stage, the calculation of the ampere-hour method is temporarily stopped to wait for the change of the battery cell voltage. When the battery cell voltage reaches the corresponding value of the division table, it is considered that the battery is fully charged or discharged to 10%, and the judgment cycle is exited, and charging is stopped or the discharge SOC is continued to be calculated.
[0043] When using the battery cell voltage as a criterion to determine whether the battery is fully charged, the average battery cell voltage alone may be affected by individual differences and may be inaccurate. Use the highest cell voltage and the highest cell voltage sampled after temperature calibration as criterion conditions to determine whether the battery is fully charged and 10% as determined by the scale.
[0044] The above embodiments are only illustrative of the principles and effects of the present invention, as well as some embodiments of its application. For those skilled in the art, several modifications and improvements may be made without departing from the creative concept of the present invention, and all of these belong to the protection scope of the present invention.
Claims
1. A method for improving the accuracy of battery SOC during charging, characterized in that: The steps are as follows S1, analyze battery characteristics, measure the internal resistance of battery cells at room temperature, establish a calibration curve between internal resistance and temperature, calculate the average value of the battery cell voltage detected by the sensor, and use the formula V = V cell -(A*res) calibrates the internal resistance of the battery, where V cell Represents the sampled battery cell voltage, res represents the internal resistance value at this temperature, A represents the charging current at this time, and V represents the actual battery cell voltage value after eliminating the influence of internal resistance; S2, at room temperature, the battery cells are charged and discharged with a small current, the relationship between SOC and battery cell voltage is recorded, and the relationship between battery cell voltage and battery SOC is obtained by comparing the historical charge and discharge records; S3, during the charging and discharging process, the actual SOC of the battery is calculated based on the scale, the SOC at this time is queried through the scale, the difference between the calculated SOC and the actual SOC is calculated, and the calibration coefficient is obtained by querying the calibration curve; S4, calibrating the battery SOC according to the calibration coefficient; S5, determining and sampling the battery cell voltage in the last division stage; S6, determine whether the battery is fully charged or has dropped to 10%, if so, end charging, otherwise stop SOC calculation, and then repeat this step.
2. A method for improving the accuracy of battery SOC during charging according to claim 1, characterized in that: In the step S2, a battery cell voltage is recorded at every 5% of SOC.
3. A method for improving the accuracy of battery SOC during charging according to claim 1 or 2, characterized in that: In step S3, during the charging process, the battery SOC is calculated by the ampere-hour method, and the calibration coefficient is introduced into the calculation process: Ah = t*A*x + Ah remain , where t represents time, A represents current, x represents calibration coefficient, Ah remain Indicates the current time.
4. A method for improving the accuracy of battery SOC during charging according to claim 3, characterized in that: The step S5 performs a strong calibration on the SOC before the battery is fully charged. When the SOC of the battery rises to 99%, it is determined whether the current battery cell voltage is the voltage of the battery being fully charged, and the SOC rise is stopped until it is determined that the battery is fully charged, and charging is stopped.
5. A method for improving the accuracy of battery SOC during charging according to claim 3, characterized in that: The step S5 performs a strong calibration on the SOC during the discharge process. When the SOC of the battery drops to 10%, the decrease of the SOC is stopped until it is determined that the battery SOC is low and attention needs to be paid to the power.