Standard setting method for monitoring and evaluating consistency between battery cells in battery pack

Abstract

The invention relates to the technical field of battery cell evaluation, and discloses a standard setting method for monitoring and evaluating consistency between battery cells in a battery pack, which comprises the following steps of: 1, setting judgment standards under different SOC (State of Charge) and different temperatures; 2, receiving BMS data and charging and discharging data; the current temperature and SOC of the battery pack are judged; 3, identifying a corresponding judgment standard according to the temperature and the SOC; step 4, performing judgment according to an identified judgment standard, and calibrating a result; and when the terminal voltage standard exceeds the standard, the number of the abnormal cells and the capacity needing to be balanced are output at the same time. According to the method, the corresponding standard can be set under any SOC, the applicability and effectiveness of the standard are ensured, meanwhile, the standard is independently controlled at the highest temperature, it is ensured that the difference of different battery packs is captured, the evaluation flexibility and accuracy are improved, the misjudgment risk is reduced, and the evaluation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power battery cell evaluation, and in particular to a standard setting method for monitoring and evaluating consistency between cells in a battery pack. Background Art

[0002] In the current battery pack production process, charge and discharge testing is a key step in evaluating battery performance and consistency. Existing monitoring systems primarily rely on metrics such as capacity, charge level, temperature, direct current internal resistance (DCIR), and terminal voltage differential to determine quality. However, these parameters have limited ability to characterize the internal consistency of a battery pack. While the terminal voltage differential can reflect differences between cells to a certain extent, its judgment criteria are significantly affected by temperature, requiring adjustment of the threshold based on temperature. This leads to inconsistent evaluation criteria and can easily lead to misjudgments. Furthermore, existing systems can only capture terminal voltage differential data under static operating conditions, and are unable to perform real-time monitoring and automated analysis of key consistency indicators such as dynamic voltage differential changes at different states of charge (SOCs) and temperatures, as well as temperature differences during each charge and discharge phase. These issues make battery pack consistency assessments lacking in comprehensiveness and accuracy, making it difficult to accurately identify potential defects.

[0003] Currently, battery consistency assessment still relies on human calculations, which is inefficient, increases labor costs, and can introduce the risk of misjudgment due to human error. More critically, existing technology cannot automatically calculate the specific capacity required for cell balancing after an anomaly is detected. This results in a lack of data support for subsequent balancing adjustments, impacting the overall performance and reliability of the battery pack. Summary of the Invention

[0004] The present invention aims to provide a standard setting method for monitoring and evaluating the consistency between battery cells in a battery pack, so as to solve the problems of inconsistent evaluation standards, lack of comprehensiveness and reliability of evaluation results, and easy misjudgment in existing methods of evaluating consistency between battery cells.

[0005] To achieve the above objectives, the present invention adopts the following technical solution, which is a method for setting a standard for monitoring and evaluating consistency between cells in a battery pack, comprising the following steps: Step 1: Set the judgment criteria at different SOC and different temperatures; Step 2: Receive BMS data and charge and discharge data; and determine the current battery pack temperature and SOC; Step 3: Identify the corresponding judgment criteria based on temperature and SOC; Step 4: Make a judgment according to the identification criteria and calibrate the result; when the terminal voltage standard exceeds the standard, the number of abnormal cells and the capacity that needs to be balanced are output at the same time.

[0006] The principles and advantages of this solution are: In existing technologies, because early battery management systems were derived from internal combustion engine control logic, their design approach was deeply influenced by the traditional "calibrated operating point" approach. This led to the habit of setting fixed thresholds at specific SOC nodes. This approach also met the needs of lead-acid batteries, without much consideration of inapplicability. However, for lithium batteries, despite the increasing nonlinearity of batteries, most technologies still use the original control framework. This is because reconfiguring the system requires subverting the existing verification system, which means that tens of thousands of test cases need to be redesigned, exponentially increasing the cost of the entire product development process, and reinforcing the logic of the existing evaluation method.

[0007] Secondly, existing technologies generally believe that aging primarily affects capacity decay, while ignoring its role in reshaping internal resistance distribution and thermal characteristics. This cognitive bias often leads to standard thresholds being adjusted only linearly. However, extensive experimental data analysis reveals that actual battery aging exhibits strong nonlinear characteristics, yet existing standards systems are unable to dynamically respond to these changes, leading to frequent false alarms, misreporting, and random reporting in the middle and later stages of a battery's lifespan.

[0008] This solution replaces fixed anchor points with dynamic benchmarks and fixed SOC points with actual temperature peaks, avoiding blind spots in management and control caused by individual battery differences. By introducing real-time temperature field reconstruction and aging factor feedback, the same set of standards can cover the application requirements of different scenarios, from power batteries to energy storage batteries, improving the applicability and uniformity of the standards. Furthermore, through deep coupling analysis of voltage and temperature data, it can distinguish between real faults and measurement noise, improve test accuracy, and reduce false alarm rates. This breaks the self-reinforcing technical lock-in state of traditional technologies, making the evaluation system more flexible and versatile, improving overall test efficiency, and reducing the risk of false alarms. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of the flow of the standard setting method for monitoring and evaluating consistency between cells in a battery pack according to the present invention; Figure 2 Schematic diagram of the process of establishing and determining voltage difference standards at different SOCs in the standard setting method for consistency monitoring and evaluation between battery cells in a battery pack of the present invention; Figure 3 Schematic diagram of the process of establishing and determining temperature difference standards at different SOCs in the standard setting method for consistency monitoring and evaluation between battery cells in a battery pack according to the present invention; Figure 4 This is a schematic diagram of the process for establishing and determining the discharge end voltage distribution standard in the standard setting method for monitoring and evaluating consistency between cells in a battery pack according to the present invention; Figure 5 This is a schematic diagram of the process for establishing and determining the temperature distribution standard when the entire pack has the highest temperature in the standard setting method for monitoring and evaluating consistency between cells in a battery pack of the present invention. DETAILED DESCRIPTION

[0010] The following is further described in detail through specific implementation methods: Example 1 The standard setting method for monitoring and evaluating the consistency between cells in a battery pack in this embodiment sets the pressure difference and temperature difference standards at different SOCs and temperatures, automatically determines the pressure difference and temperature difference at different SOCs and temperatures, and presents them in the form of graphs, making the results more intuitive and achieving accurate automatic determination of the terminal pressure difference, improving determination flexibility and reducing the risk of misjudgment. In this embodiment, as shown in the attached figure, Figure 1 As shown, the following steps are included: S1, set the judgment criteria at different SOC and different temperatures.

[0011] In this embodiment, the judgment criteria include four types, namely, the voltage difference standard under different SOCs, the temperature difference standard under different SOCs, the discharge end voltage distribution standard, and the temperature distribution standard at the highest temperature of the whole pack.

[0012] (1) Pressure difference standards under different SOCs.

[0013] The establishment process is as follows: Figure 2 As shown, the current battery pack SOC (state of charge), differential pressure, and maximum temperature data are obtained from the BMS. The differential pressure = maximum cell voltage - minimum cell voltage. The acquired data must cover at least a complete charge and discharge cycle, such as >100 sets of data, to ensure comprehensiveness and validity.

[0014] A line graph of pressure difference versus SOC is calculated based on the data. In this embodiment, each temperature range is processed separately, such as dividing the temperature into 0-15°C, 15-30°C, and 30-45°C. A line graph of pressure difference versus SOC is obtained using piecewise linear regression or multi-segment fitting of the relationship between SOC and pressure difference.

[0015] According to the line graph, the standard threshold is set to establish the correlation mode of SOC, pressure difference and temperature. Normal threshold = fitted value + 3δ; warning threshold = fitted value + 2δ; where δ is the standard deviation of historical data.

[0016] (2) Temperature difference standards under different SOCs.

[0017] This standard needs to take into account the impact of temperature on cell consistency. The establishment process is as follows: Figure 3As shown, historical data of SOC, pressure difference and temperature are collected. The temperature difference and SOC curves are fitted according to the SOC, pressure difference and maximum temperature data to obtain a broken line graph of temperature difference versus SOC. The pressure difference indirectly reflects the difference in internal resistance of the battery cell. The greater the internal resistance, the greater the heat generated, and thus the higher the temperature rise. The temperature characteristic is strongly correlated with SOC. When the SOC is higher, the chemical reaction releases heat more violently. The dynamic grading thresholds of SOC and temperature difference are determined based on the broken line graph. In this embodiment, they can be graded into three levels: normal, warning and fault. The normal threshold is set to the estimated value + 2 standard deviations; the alarm threshold is set to the estimated value + 3 standard deviations.

[0018] In addition, the threshold is updated every 100 cycles to improve the accuracy and effectiveness of the threshold.

[0019] (3) Discharge end voltage distribution standard.

[0020] The establishment process is as follows: Figure 4 As shown, all cell voltage values ​​at SOC=0 and the maximum temperature of the battery pack at SOC=0 are obtained from the BMS, that is, the voltage / temperature matrix at SOC=0% is obtained. The average voltage at SOC=0 is calculated. , voltage extreme difference And standard deviation σ, and construct the voltage distribution SPC control chart. According to the SPC control chart, the upper limit and lower limit are obtained, and the upper limit can be expressed as ; The lower limit is expressed as ; Where, It is a statistical coefficient and can be obtained by looking up the table according to the number of battery cells.

[0021] This embodiment also includes updating temperature history data and dynamically adjusting the upper and lower limits based on the temperature history data, such as allowing a smaller pressure difference at high temperatures, thereby improving the accuracy and reliability of the standard.

[0022] (4) Temperature distribution standard when the whole package reaches the highest temperature.

[0023] The establishment process is as follows: Figure 5 As shown, during the battery charging and discharging process, all temperature change data is acquired at a sampling frequency. In this embodiment, a sampling frequency of ≥1 Hz is used to collect values ​​at all temperature sampling points, such as the cell surface, module center, and cooling plate inlet and outlet. The charge and discharge current and voltage are used to correlate the temperature rise with power, and the corresponding data timestamps are used to analyze the temperature change rate. In this embodiment, the temperature sensors are evenly distributed to avoid local blind spots.

[0024] When the battery pack temperature reaches its highest value, such as the peak temperature at the end of charging, the overall temperature average is calculated. , that is, the mean and temperature range of all sampling points (the difference between the highest and lowest temperature points) and the standard deviation , used to evaluate the uniformity of temperature distribution, and construct the SPC control chart of each temperature point when the temperature is the highest based on the calculated values. The upper control limit and lower control limit are obtained based on the SPC control chart. The upper control limit can be expressed as ; The lower control limit can be expressed as .

[0025] In this embodiment, the threshold value is also corrected according to the ambient temperature. For example, the upper control limit is increased by 5% in high temperature weather.

[0026] It also includes dynamically adjusting the upper and lower control limits according to the degree of battery aging.

[0027] S2, receives BMS data and charge and discharge data; and determines the current battery pack temperature and SOC.

[0028] In this embodiment, BMS data and charge / discharge data from the charging and discharging device are received via CAN communication. BMS data includes voltage, temperature, and SOC data. When receiving the real-time data stream from the BMS, the current data from the charging and discharging device must also be time-aligned to ensure an error of less than 10ms. This prevents SOC estimation errors caused by data collection delays, ensuring that the multi-source data is synchronized and valid.

[0029] The system continuously records the last 30 seconds of temperature data and determines the temperature. When the temperature drops at three consecutive sampling points, the previous point is determined to be the actual temperature peak to avoid interference from instantaneous fluctuations. The system also categorizes the SOC state. In this embodiment, the SOC is divided into five key intervals: 0-10%, 10-30%, 30-70%, 70-90%, and 90-100%. Different benchmark parameters are applied to each interval to achieve dynamic peak capture, improving capture efficiency while ensuring accuracy and effectiveness.

[0030] S3, identifying corresponding judgment criteria based on temperature and SOC.

[0031] In this embodiment, the measured temperature is first converted to a standard temperature threshold to achieve standard normalization for different battery models. A dynamic standard is then found based on SOC, temperature, and position. Specifically, a base standard curve is determined using the current SOC, and then an interpolation method is used to derive a temperature compensation standard. This allows battery packs with different thermal designs to share the same standard logic, reducing adaptation costs. Finally, the position compensation is added to obtain the final standard.

[0032] S4, judge according to the identification criteria and calibrate the results; when the terminal voltage standard exceeds the standard, the number of abnormal battery cells and the capacity that needs to be balanced are output at the same time.

[0033] In this embodiment, after the determination, the corresponding chart is output and the result is calibrated according to the standard. The determination process of the four determination standards is as follows.

[0034] (1) Pressure difference standards under different SOCs.

[0035] As attached Figure 2 As shown, according to the current SOC, pressure difference and temperature values ​​obtained, the threshold mode corresponding to the temperature range is selected, the allowable pressure difference under the current SOC is queried, and the current pressure difference is compared to see whether it exceeds the allowable pressure difference. The judgment result is then output and displayed visually. (2) Temperature difference standards under different SOCs.

[0036] As attached Figure 3 As shown, the SOC, temperature difference, and maximum temperature are obtained from the BMS in real time. The temperature difference threshold at the current SOC is selected based on the set standard. The temperature difference is compared with the selected temperature difference threshold. If the temperature difference is less than the temperature difference threshold, the system is in a normal state. If the temperature difference is greater than the temperature difference threshold, the system further determines whether the pressure difference exceeds the standard. If both the pressure difference and the threshold are exceeded, a warning is issued and the system is shut down. If the pressure difference is within the standard, cooling is initiated.

[0037] In this embodiment, the measured temperature is also corrected based on the position difference of the battery cells. According to the position difference of the battery cells, such as the difference between the center position and the edge position, position weight coefficients are set respectively to correct and compensate the temperature at different positions.

[0038] By setting the pressure difference and temperature difference standards under different SOC and temperature, the pressure difference and temperature difference under different SOC and temperature can be automatically judged and presented in the form of graphs, making the results more intuitive and clear, and the judgment efficiency higher.

[0039] (3) Discharge end voltage distribution standard.

[0040] As attached Figure 4As shown, during the judgment, the allowable pressure difference and standard value at the current temperature are obtained by combining the temperature and pressure difference standards with the statistical control limits, namely the upper and lower limits. The number of cells exceeding the standard is determined according to the set conditions and marked as abnormal cells. In this embodiment, condition 1 is that the voltage exceeds the control limit. When the voltage is higher than the upper limit, it may be overcharged or abnormal internal resistance; when the voltage is lower than the lower limit, it may be over-discharged or capacity decay. Condition 2 is that the pressure difference between adjacent cells exceeds the standard. Abnormal cells are marked according to the judgment conditions.

[0041] For abnormal cells, the capacity to be compensated is calculated and output together with the result. In this embodiment, the charge and discharge capacity and cell voltage change data are obtained, the abnormal cell voltage is compared with the upper and lower limits, and the balanced capacity value is output based on the comparison result.

[0042] When the voltage of the abnormal cell is greater than the upper limit, it means that energy needs to be released. At this time, the charge and discharge data of the normal cell with the lowest voltage is used as the benchmark, and the capacity released when the benchmark cell is discharged from the current voltage to the average voltage of the battery pack is calculated as the balanced capacity, which is expressed as Q 放 = (voltage - average value) / (dV / dQ).

[0043] When the abnormal cell voltage is lower than the lower limit, it means that energy needs to be replenished. At this time, the capacity of this cell discharged from the average voltage to the current voltage is calculated as the balanced capacity, which is expressed as Q 充 = (average value - voltage) / (dV / dQ). Here, dV / dQ represents the slope of the end-of-discharge voltage as it changes with capacity, also known as the voltage-capacity slope. This can be calibrated experimentally, for example, approximately 0.2V / Ah for lithium iron phosphate batteries. At high temperatures, dV / dQ may increase and requires dynamic adjustment to correct for temperature and improve numerical accuracy. For example, if a cell has a voltage of 2.68V (average value 2.75V), and dV / dQ = 0.2V / Ah, the required replenishment capacity is calculated to be (2.75-2.68) / 0.2 = 0.35Ah. This quantifies the balancing requirement based on voltage deviation and the dV / dQ slope, enabling targeted energy replenishment or release and ensuring battery pack consistency.

[0044] This embodiment also includes selecting a corresponding balancing method based on the type of abnormality. For cells with excessively high voltage, this balancing method involves discharging via resistors or transferring energy to low-voltage cells. For cells with excessively low voltage, charging is prioritized or energy is transferred from high-voltage cells. Furthermore, when multiple cells are abnormal, the lowest-voltage cell is prioritized to prevent overdischarge and potential performance degradation.

[0045] By setting the pressure difference standard at different temperatures at the end, the end pressure difference can be accurately and automatically judged. The consistency can also be judged directly by setting the standard deviation. Both standards can be enabled for judgment to increase flexibility.

[0046] At the same time, when the terminal voltage exceeds the standard, the system will automatically check the temperature history data of the module where the battery cell is located. If there is an abnormal temperature gradient at the same time, it will be marked as "internal resistance degradation" rather than a simple balancing demand, guiding more accurate maintenance.

[0047] (4) Temperature distribution standard when the whole package reaches the highest temperature.

[0048] As attached Figure 5 As shown, during the judgment, a multi-dimensional judgment is performed based on the set conditions in combination with the temperature difference and standard deviation. In this embodiment, condition 1 is a single-point temperature exceeding the control limit. That is, when the temperature of any sampling point is greater than the upper control limit or less than the lower control limit, an alarm is triggered. Condition 2 is a temperature difference exceeding the control limit. That is, when the difference between the highest and lowest temperatures is greater than the allowable threshold, it is marked as abnormal. Condition 3 is a standard deviation exceeding the control limit. That is, when the standard deviation is greater than twice the historical baseline value, it is determined to be a temperature distribution abnormality.

[0049] A graded response is implemented based on the criteria, accurately capturing abnormal situations. In this embodiment, a warning is triggered when only condition 1 is met. A critical alarm is triggered when both conditions 2 and 3 are met. An emergency alarm is triggered when condition 1 is met and the temperature at a single point continues to rise above the safety limit.

[0050] By setting temperature difference standards at different maximum temperatures, anomalies can be accurately identified. Consistency can also be determined directly by setting the standard deviation, or two standards can be used to enable judgment. This increases judgment flexibility, reduces judgment errors, and improves overall production efficiency.

[0051] In this embodiment, precise management of battery pack variations is achieved through three-dimensional adaptive calibration of temperature, voltage, and SOC. When the system reaches its maximum temperature, the temperature difference standard is automatically triggered, rather than a fixed SOC point. This addresses the drift in the SOC-temperature relationship caused by individual battery pack variations in traditional methods. Temperature gradient compensation is then used to eliminate sensor position errors and ensure accurate temperature differential assessment between the edge and center cells.

[0052] In this embodiment, by directly reading the real-time SOC data of the BMS, the corresponding pressure difference or temperature difference standard is dynamically loaded at any SOC point, and a dual judgment method is set for the discharge end and high temperature range to achieve accurate abnormal statistics and threshold management, thereby improving judgment accuracy.

[0053] Furthermore, through dynamic dV / dQ slope conversion, the voltage difference is converted into an executable equalization capacity instruction. When an anomaly occurs, the required equalization capacity can be intuitively understood, improving processing efficiency, avoiding overcharge or over-discharge, ensuring stability and safety, and also reducing losses and waste. Even in high-temperature conditions, stricter voltage difference standards can be automatically activated to ensure standard reliability.

[0054] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A standard setting method for monitoring and evaluating consistency between cells in a battery pack, characterized in that: The following steps are involved: Step 1: Set the judgment criteria at different SOC and different temperatures; Step 2, receiving BMS data and charge and discharge data; And determine the current battery pack temperature and SOC; Step 3: Identify the corresponding judgment criteria based on temperature and SOC; Step 4: Make a judgment according to the identification criteria and calibrate the result; when the terminal voltage standard exceeds the standard, the number of abnormal cells and the capacity that needs to be balanced are output at the same time.

2. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 1, characterized in that: The judgment criteria include four types, namely, the voltage difference standard under different SOCs, the temperature difference standard under different SOCs, the voltage distribution standard at the end of discharge, and the temperature distribution standard at the highest temperature of the entire package.

3. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 2, characterized in that: In step 1, the establishment of the pressure difference standard under different SOCs includes: obtaining SOC, pressure difference and maximum temperature value data; calculating a line graph of pressure difference versus SOC based on the data; setting a standard threshold based on the line graph, and establishing a correlation pattern among SOC, pressure difference and temperature.

4. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 2, characterized in that: In step 1, the establishment of the temperature difference standard under different SOCs includes: calculating a line graph of temperature difference versus SOC based on SOC, pressure difference and maximum temperature value data; and determining dynamic grading thresholds of SOC and temperature difference based on the line graph.

5. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 2, characterized in that: In step 1, the establishment of the discharge end voltage distribution standard includes: obtaining the voltage values ​​of all battery cells when SOC=0 and the maximum temperature value when SOC=0; calculating the voltage average value, voltage range and standard deviation when SOC=0, and constructing a voltage distribution SPC control chart; obtaining the upper limit and lower limit values ​​according to the SPC control chart.

6. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 2, characterized in that: In step 1, the establishment of the temperature distribution standard when the entire pack reaches the highest temperature includes: obtaining all temperature change data during charging and discharging according to the sampling frequency; when the battery pack temperature reaches the highest value, calculating the overall temperature average, temperature range and standard deviation; and constructing an SPC control chart for each temperature point when the temperature is the highest; obtaining the upper control limit and the lower control limit according to the SPC control chart; and correcting the threshold according to the ambient temperature.

7. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 5, characterized in that: In step 4, the process for determining the discharge end voltage distribution standard is as follows: Obtain the allowable pressure difference and standard value at the current temperature; determine the number of cells that exceed the standard and mark them as abnormal cells; Obtain charge and discharge capacity and cell voltage change data, compare abnormal cell voltage with upper and lower limits, and output balanced capacity value based on the comparison result.

8. The method for setting standards for monitoring and evaluating consistency between cells in a battery pack according to claim 7, wherein: When the voltage of the abnormal cell is greater than the upper limit, the charge and discharge data of the normal cell with the lowest voltage is used as a benchmark to calculate the capacity released when the benchmark cell is discharged from the current voltage to the average voltage of the battery pack. This is used as the balanced capacity and is expressed as Q 放 = (voltage - average value) / (dV / dQ); When the abnormal cell voltage is less than the lower limit, calculate the capacity of the cell when it is discharged from the average voltage to the current voltage as the balanced capacity, expressed as Q 充 = (average value - voltage) / (dV / dQ); where dV / dQ represents the slope of the discharge end voltage as the capacity changes.

9. The method for setting standards for monitoring and evaluating consistency between cells in a battery pack according to claim 4, wherein: It also includes gradient correction of the measured temperature according to the difference in battery cell positions.

10. The standard setting method for monitoring and evaluating consistency between cells in a battery pack according to claim 6, characterized in that: It also includes dynamically adjusting the upper and lower control limits according to the degree of battery aging.

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