Power battery consistency evaluation method based on multi-stage current fitting and slope analysis

Abstract

The invention provides a power battery consistency evaluation method based on multi-stage current fitting and slope analysis, and relates to the technical field of power batteries, and the method comprises the steps: obtaining the voltage and current data of a battery cell in real time through a BMS battery management system, carrying out the multi-stage data fitting, and obtaining a charging and discharging curve of each time period; forming a slope data set by calculating the slope of the charging and discharging curve; and performing consistency analysis on the slope of the battery cell according to the Pauta criterion, and judging whether the battery cell meets the consistency requirement or not. The method can accurately identify the performance difference of the battery cell, optimize the performance of the battery pack, prolong the service life, improve the safety of the system, and provide support for the innovation of the battery material and the manufacturing technology.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a power battery consistency evaluation method based on multi-stage current fitting and slope analysis. Background Art

[0002] With the widespread use of electric vehicles and portable electronic devices, the performance and safety of power batteries have become key technical issues. In existing battery management systems, the consistency evaluation of battery cells mainly relies on real-time monitoring of battery cell voltage and current; however, these monitoring methods have certain limitations.

[0003] Traditional battery management systems mainly rely on simple monitoring of voltage and current, and lack in-depth analysis of the consistency of battery cell performance; this makes it difficult to promptly detect and handle slight differences in battery cell performance, increasing the safety risks of the battery system. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides a power battery consistency evaluation method based on multi-stage current fitting and slope analysis, which solves the problem of how to evaluate the consistency of battery cells through current fitting and slope analysis.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions: A power battery consistency evaluation method based on multi-stage current fitting and slope analysis, comprising:

[0008] S1. Data collection step: The voltage and current signals of each battery cell are obtained in real time through the BMS battery management system to form a charge and discharge current data set for multiple time periods; the current signal comes from two systems: one is a parallel system to improve the current capacity, and the other is a series system to improve the voltage capacity; the initial charge and discharge current set A1 of the battery cell in the parallel system is A1=[A 11 |A 21 |A 31 |…|A i1 ], the current data set Aj of the subsequent time period is represented by A j =[A 1j |A 2j |A 3j |…|A ij ];

[0009] S2. Data fitting step, fitting the charge and discharge current data of each time period by the least square method, generating a multi-stage charge and discharge curve, and fitting the curve by the formula y=f(x);

[0010] S3. Slope calculation step: based on the fitted charge and discharge curve, the partial derivative of the curve of each battery cell in each time period is calculated to obtain the slope of each battery cell in each time period. The slope calculation formula is: Get the slope data set K j , where K j =[k 1i k 2i …k ij ];

[0011] S4. Consistency analysis steps, according to the formula Perform consistency evaluation on the slope data set Kj of the battery cell to determine whether the battery cell meets the consistency requirements.

[0012] Preferably, during the data collection process, the voltage and current signals of each battery cell are obtained in real time through the BMS, and the BMS system monitors the status of each battery cell through built-in sensors and measuring devices; the BMS continuously monitors the voltage changes of each battery cell, records the voltage at different time points, and simultaneously collects the current signal of each battery cell; in the BMS, the connection method of the battery cells is divided into a parallel system for improving the current capacity and a series system for improving the voltage capacity; for the parallel system, multiple battery cells are connected together to increase the overall current capacity, and the BMS system monitors the voltage and current of each parallel battery cell.

[0013] Preferably, in a parallel system, the total current capacity is increased by connecting multiple battery cells in parallel. When multiple battery cells are connected in parallel, the voltage remains the same, but the total current is the sum of the currents of each battery cell; the BMS monitors the current of the parallel battery cells by installing a current sensor at each battery cell connection, and the current sensor measures the current output of each battery cell in real time; the BMS continuously receives these current signals and performs real-time analysis; the BMS adjusts the current distribution of each battery cell based on the current data of each battery cell; if it is detected that the current of a battery cell is too high, the BMS reduces the current of the battery cell by adjusting the current distribution to prevent it from overheating or damage due to overcurrent, and the means for adjusting the current includes controlling the impedance of the shunt resistor adjustment circuit in the battery.

[0014] Preferably, in a series system, the total voltage is increased by connecting the battery cells in sequence, and the voltage of each battery cell is added to form the total voltage of the BMS, while the total current remains unchanged; the BMS accurately monitors the voltage of the series battery cells by installing a voltage sensor on each battery cell to monitor the voltage, and the voltage sensor measures the voltage of each battery cell in real time; the BMS continuously receives these voltage data and performs real-time analysis; through these data, the BMS determines the charging and discharging status of each battery cell; when the BMS detects that the voltage of some battery cells is higher than that of other battery cells, the BMS transfers excess energy from the high-energy battery cells to the lower-voltage battery cells; according to the passive balancing technology, the excess energy is shunted by resistors, and the energy in the higher-voltage battery cells is converted into heat.

[0015] Preferably, the BMS battery management system measures voltage and current in real time by installing sensors on each battery cell or battery cell group; the voltage sensor accurately detects the voltage level of each battery cell, and the output of the voltage sensor is an analog signal representing the real-time voltage of the battery cell. The BMS can use an analog-to-digital converter ADC to convert the analog signal of the voltage sensor into a digital signal. Through the conversion, the voltage signal is digitized, allowing the BMS to accurately monitor and analyze the voltage of each battery cell; the current sensor measures the current flowing through the battery cell; the current sensor detects the electromagnetic effect or voltage drop generated by the flow of current, and converts the detected current signal into a corresponding electrical signal; The analog-to-analog converter ADC converts the data into a digital signal; after digitization, the digital signal is transmitted to the main controller of the BMS, where the data is further processed. The processing steps include filtering to remove noise from the signal; by comparing and adjusting with existing standards; the BMS continuously monitors the voltage and current status of the battery cell to ensure that the battery remains within the preset safe operating range. If any abnormality is detected, such as excessive voltage, too low voltage, or excessive current, the BMS takes corresponding protective measures, including reducing the charge and discharge current, cutting off the circuit or starting the cooling system to prevent the battery pack from being damaged due to overcharging, over-discharging or overheating.

[0016] Preferably, the charge and discharge curve function f(x) of each battery cell is determined, wherein x represents time, and f(x) represents the voltage or current of the battery cell at time x; the state of the battery cell is continuously monitored by a sensor, and the voltage and current data of each battery cell at different time points are recorded; a mathematical function f(x)=ax+b is determined, and the voltage or current change of each battery cell during the entire charge and discharge process is fitted. After the charge and discharge curve function f(x) of each battery cell is determined, the slope of the curve in each time period is calculated; the slope is calculated by taking the partial derivative of the curve function f(x); the slope calculation formula is: Where dx represents a small change in time, and f(x) represents the value of the curve at time x. This formula describes the slope of the curve of function f(x) at time x. When calculating, select a set of small x values ​​and approximate the slope using the numerical difference method. For each battery cell, calculate the slope at different time points to obtain the slope data set kj of the battery cell in the entire time period, where j represents a different battery cell number, and the slope data reflects the changes in the charge and discharge characteristics of the battery cell in different time periods. Summarize the slope data sets of all battery cells, and evaluate the consistency and performance differences of the battery cells by comparing the slope data of different battery cells. If the slope changes of some battery cells are significantly different from those of other battery cells, it indicates that these battery cells are abnormal and require further inspection and management.

[0017] Preferably, the slope data set kj of each cell in different time periods, where K j =[k 1i k 2i … k ij ],pass Get the average value of the statistical characteristics of the slope of the charge and discharge curve of the group of batteries, through Get the standard deviation of the statistical characteristics of the slope of the charge and discharge curve of this group of batteries, according to Judge the charge and discharge curves of all cells; if the curves of all cells meet the formula If the requirements are met, the consistency is considered good, otherwise it will be marked for attention to facilitate later battery cell management.

[0018] (III) Beneficial effects

[0019] The present invention provides a power battery consistency evaluation method based on multi-stage current fitting and slope analysis, which has the following beneficial effects:

[0020] 1. The present invention can more accurately identify small differences in battery cell performance, thereby achieving more refined battery cell management; it helps to optimize the overall performance of the battery pack, extend battery life, and reduce early failures caused by battery cell inconsistency.

[0021] 2. The present invention provides a new battery cell performance evaluation tool, which can serve as the basis for battery research and promote the innovation of battery materials and manufacturing technologies. By extending the service life of batteries and reducing the number of discarded batteries, the present invention helps to reduce the impact on the environment and is in line with the trend of green energy and sustainable development.

[0022] 3. By identifying and marking cells with inconsistent performance, the present invention allows for targeted maintenance and replacement rather than blindly replacing the entire battery pack, reducing maintenance costs and long-term operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a step framework diagram of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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.

[0025] During the data acquisition process, the voltage and current signals of each battery cell are obtained in real time through the BMS. The BMS system monitors the status of each battery cell through built-in sensors and measuring devices; the BMS continuously monitors the voltage changes of each battery cell, records the voltage values ​​at different time points, and collects the current signal of each battery cell at the same time; in the BMS, the connection methods of the battery cells are divided into parallel systems for improving current capacity and series systems for improving voltage capacity; for parallel systems, multiple battery cells are connected together to increase the overall current capacity, and the BMS system monitors the voltage and current of each parallel battery cell; in series systems, multiple battery cells are connected in series to increase the total voltage of the system; for example, assuming there is a battery pack consisting of five battery cells, after parallel connection, the voltage of each battery cell is 3.7V and the total current is 20A; in different time periods, the data sets recorded through the BMS system monitoring include: at time t1, the current data is A1=4{A, 4A, 4A, 4A, 4A}; at time t2, the current data is A2={3.8A, 4.1A, 4A, 4A, 4.1A}.

[0026] In a parallel battery system, the total current capacity is increased by connecting multiple cells in parallel so that the voltage of all cells remains consistent, and the total current is the superposition of the currents of each cell. The battery management system BMS ensures the safety and efficiency of the system by monitoring the current of the parallel cells. The BMS installs current sensors at the connection of each cell, which are responsible for measuring and recording the current signal of each cell in real time. The current signal is then received by the BMS for real-time data analysis. By analyzing the instantaneous value, average value, maximum value, minimum value and the change trend of the current, the BMS understands the current state of each cell, thereby accurately controlling the current distribution of the entire parallel system. During the monitoring process, if the BMS detects that the current of a cell is abnormally high, the BMS will immediately take measures to prevent the cell from overheating or damage due to overcurrent. The BMS achieves this goal by adjusting the current distribution. Specific means include controlling the shunt resistor in the battery or adjusting the impedance of the circuit through an electronic controller to reduce the current load of the cell with excessive current.

[0027] In a series system, the total voltage is increased by connecting the cells in sequence, and the voltage of each cell is added to form the total voltage of the BMS, while the total current remains unchanged; the BMS accurately monitors the voltage of the series cells by installing a voltage sensor on each cell to monitor the voltage, and the voltage sensor measures the voltage of each cell in real time; the BMS continuously receives these voltage data and performs real-time analysis; through these data, the BMS determines the charge and discharge status of each cell; when the BMS detects that the voltage of some cells is higher than that of other cells, the BMS transfers the excess energy from the high-energy cells to the cells with lower voltage; this process is achieved through passive balancing technology, which involves shunting the excess energy through resistors, converting the energy in the higher-voltage cells into heat, thereby reducing their voltage.

[0028] The BMS battery management system measures voltage and current in real time by installing sensors on each battery cell or battery cell group; the voltage sensor accurately detects the voltage level of each battery cell, and the output of the voltage sensor is an analog signal representing the real-time voltage of the battery cell. The BMS can use the analog-to-digital converter ADC to convert the analog signal of the voltage sensor into a digital signal. Through the conversion, the voltage signal is digitized, allowing the BMS to accurately monitor and analyze the voltage of each battery cell; the current sensor measures the current flowing through the battery cell; the current sensor detects the electromagnetic effect or voltage drop caused by the flow of current, and converts the detected current signal into a corresponding electrical signal; the current signal is also analog, and is converted into a digital-to-analog converter ADC After digitization, the digital signal is transmitted to the main controller of the BMS, where the data is further processed. The processing steps include filtering to remove noise from the signal. Next, calibration is performed to ensure that the measured voltage and current values ​​are accurate and reliable by comparing and adjusting with known standards. The BMS continuously monitors the voltage and current status of the battery cell to ensure that the battery remains within the preset safe operating range. If any abnormality is detected, such as excessive voltage, too low voltage, or excessive current, the BMS takes corresponding protective measures, including reducing the charge and discharge current, cutting off the circuit, or starting the cooling system to prevent the battery pack from being damaged due to overcharging, over-discharging or overheating.

[0029] Determine the charge and discharge curve function f(x) of each battery cell, where x represents time, and f(x) represents the voltage or current of the battery cell at time x; continuously monitor the state of the battery cell through a sensor, and record the voltage and current data of each battery cell at different time points; determine a mathematical function f(x)=ax+b, fit the voltage or current change of each battery cell during the entire charge and discharge process, and after determining the charge and discharge curve function f(x) of each battery cell, calculate the slope of the curve in each time period; the slope is calculated by taking the partial derivative of the curve function f(x); the slope calculation formula is: Where dx represents a small change in time, and f(x) represents the value of the curve at time x. This formula describes the slope of the function f(x) at time x. When calculating, a set of small x values ​​is selected and the slope is approximated by the numerical difference method. For each battery cell, the slope at different time points is calculated to obtain the slope data set k of the battery cell in the entire time period. j , where j represents different battery cell numbers, and the slope data reflects the changes in the charge and discharge characteristics of the battery cell in different time periods; the slope data sets of all battery cells are summarized, and the consistency and performance differences of the battery cells are evaluated by comparing the slope data of different battery cells; if the slope changes of some battery cells are significantly different from those of other battery cells, it indicates that these battery cells are abnormal and need further inspection and management; for example, for the current data A1 at time t1, the charge and discharge curve obtained by least squares fitting is y1=f1(x)=a1x+b1, where a1 and b1 are fitting parameters; similarly, the curve obtained by fitting the current data A2 at time t2 is y2=f2(x)=a2x+b2; assuming that the expression of the fitting curve y=f(x) is y=3x+5, then the slope k=f'(x)=3, in this way, the slope data set K of each battery cell in different time periods is calculated j , where K j Contains the slope value of each cell in each time period.

[0030] Preferably, the slope data set k of each cell in different time periods is j , where K j =[k 1i k 2i … k ij ],pass Get the average value of the statistical characteristics of the slope of the charge and discharge curve of the group of batteries, through Get the standard deviation of the statistical characteristics of the slope of the charge and discharge curve of this group of batteries, according to Judge the charge and discharge curves of all cells; if the curves of all cells meet the formula If the requirements are met, the consistency is considered good, otherwise it will be marked for attention to facilitate later battery cell management.

[0031] Assume that in actual operation, there is a battery pack, and the data recorded in its data acquisition step are as follows: at time t1, the current data is A1=4{A, 4A, 4A, 4A, 4A}; at time t2, the current data is A2={3.8A, 4.1A, 4A, 4A, 4.1A}; the curves obtained by least squares fitting are: y1=f1(x)=0.1x+3.9, y2=f2(x)=0.15x+3.95; in the slope calculation step, the calculated slopes are: k1=0.1, k2=0.15; the slope data set is K1={0.1,0.15}, the average value K=0.125, and the standard deviation δK=0.025; judging by the Laida criterion being less than or equal to 1, the slopes of this group of cells meet the consistency requirements, so it is considered that the consistency of the battery pack is good.

[0032] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A power battery consistency evaluation method based on multi-stage current fitting and slope analysis, characterized in that: include: S1. Data collection step: The voltage and current signals of each battery cell are obtained in real time through the BMS battery management system to form a charge and discharge current data set for multiple time periods; the current signal comes from two systems: one is a parallel system to improve the current capacity, and the other is a series system to improve the voltage capacity; the initial charge and discharge current set A1 of the battery cell in the parallel system is A1=[A 11 |A 21 |A 31 |…|A i1 ], the current data set Aj of the subsequent time period is represented by A j =[A 1j |A 2j |A 3j |…|A ij ]; S2. Data fitting step, fitting the charge and discharge current data of each time period by the least square method, generating a multi-stage charge and discharge curve, and fitting the curve by the formula y=f(x); S3. Slope calculation step: based on the fitted charge and discharge curve, the partial derivative of the curve of each battery cell in each time period is calculated to obtain the slope of each battery cell in each time period. The slope calculation formula is: Get the slope data set K j , where K j =[k 1i k 2i …k ij ]; S4. Consistency analysis steps, according to the formula Perform consistency evaluation on the slope data set Kj of the battery cell to determine whether the battery cell meets the consistency requirements.

2. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 1 is characterized in that: In S1, the data acquisition step obtains the voltage and current signals of each battery cell in real time through the BMS battery management system, including a parallel system for improving current capability and a series system for improving voltage capability.

3. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 1 is characterized in that: The parallel system increases the total current capacity by connecting multiple battery cells in parallel; in the parallel system, the voltage of each battery cell remains the same, and the total current is the sum of the currents of each battery cell; the parallel system monitors the current of each battery cell and adjusts the current to evenly distribute the current in all battery cells, thereby preventing some battery cells from being damaged by overcurrent; the series system increases the total voltage by connecting the battery cells in sequence. In the series system, the total current remains unchanged, and the total voltage is the sum of the voltages of each battery cell; the series system monitors the voltage of each battery cell and transfers excess energy to the battery cell with lower voltage to balance the voltage in all battery cells, thereby preventing some battery cells from being damaged by overcharging or over-discharging.

4. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 3 is characterized in that: The BMS battery management system measures voltage and current by installing sensors on each battery cell or battery cell group, and converts the analog signal of the sensor into a digital signal through a digital-to-analog converter, so that the BMS can accurately read the real-time data of each battery cell; the voltage sensor uses an analog-to-digital converter to convert the voltage level of the battery cell into digital form, and the current sensor detects the current flowing through the battery cell and converts these current signals into electrical signals; the converted digital signal is transmitted to the main controller of the BMS, where the data is further processed, including filtering to remove noise, calibration to ensure the accuracy of measurement, and calculation of the instantaneous value or average value of the current; the BMS continuously monitors the status of the battery cell to maintain the voltage and current within the preset safe operating range to avoid overcharging, over-discharging or overheating.

5. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 1 is characterized in that: For a certain moment, the data A of all cells j =[A 1j |A 2j |A 3j |…|A ij ], then the corresponding statistical characteristic average value is calculated based on this set of charge and discharge data and the experimental standard deviation δ A ;in According to the Raida guidelines Judge the group of battery cells. If the charging and discharging currents of all battery cells conform to the formula, it is considered that their consistency is good. If the current value of a certain battery cell in the group does not conform, mark it and pay attention to it to facilitate subsequent battery cell management.

6. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 1 is characterized in that: In the step S3, the charge and discharge curve function f(x) of each battery cell is determined, where x represents time, and f(x) represents the voltage and current of the battery cell at time x; the slope of each battery cell curve in each time period is calculated, and the partial derivative of the charge and discharge curve function f(x) is obtained. The calculation formula of the slope is: Where dx represents a small change in time, and f(x) represents the value of the curve at time x. This formula represents the instantaneous rate of change of the function f(x) at time x, that is, the slope of the curve. By calculating the slope of the curve at each time point, we can obtain the slope data set kj of each cell in different time periods, where j represents different cell numbers.

7. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 6 is characterized in that: The slope data set k of each battery cell in different time periods j , where K j =[k 1i k 2i …k ij ],pass Get the average value of the statistical characteristics of the slope of the charge and discharge curve of the group of batteries, through Get the standard deviation of the statistical characteristics of the slope of the charge and discharge curve of this group of batteries, according to Judge the charge and discharge curves of all cells; if the curves of all cells meet the formula If the requirements are met, the consistency is considered good, otherwise it will be marked for attention to facilitate later battery cell management.

8. The power battery consistency evaluation method based on multi-stage current fitting and slope analysis according to claim 1 is characterized in that: In S4, the consistency analysis step calculates the average slope and standard deviation of each battery cell based on the slope data set of each battery cell in each time period, and determines the consistency of the battery cell according to a preset threshold value.

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