Lithium iron phosphate battery SOC estimation method based on static stress and DEIS

Abstract

The invention relates to the technical field of battery SOC estimation, and discloses a lithium iron phosphate battery SOC estimation method based on static stress and DEIS, and the method comprises the following steps: collecting the total stress F and full-frequency dynamic impedance spectroscopy EIS of a lithium iron phosphate battery during working, carrying out the SOC equal-interval charging of the lithium iron phosphate battery under different charging currents I, and calculating the SOC of the lithium iron phosphate battery; after charging of each section is completed, standing is conducted for 2 hours, after standing is completed, next equal-interval charging is conducted till the SOC reaches 100%, and the dynamic stress FD generated by charging of each SOC section is calculated; according to the method, static stress and dynamic stress are defined, the static stress is accurately separated to estimate the SOC, compared with an existing method, the method overcomes the defects that the requirement for model precision is high, and estimation in a voltage platform area is not accurate, a solution more sensitive to charging and discharging history and current is provided, a t-FS-SOC estimator is established, and the SOC estimation accuracy is improved. And estimating the SOC according to the obtained static stress FS.

Description

Technical Field

[0001] The present invention relates to the technical field of battery SOC estimation, and in particular to a method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS. Background Art

[0002] Lithium iron phosphate battery (LiFePO4) is known for its excellent safety and long life. Compared with other lithium-ion batteries, lithium iron phosphate battery has better thermal stability and can withstand high temperatures without thermal runaway. At the same time, its cycle life is very long, which can exceed thousands of charge and discharge cycles. In addition, lithium iron phosphate battery has low material cost, does not contain rare metals, and has environmental advantages. However, with the growth of market demand and the development of technology, the requirements for lithium batteries are becoming higher and higher, not only in terms of their energy density and charge and discharge rate, but also in terms of their safety and life management capabilities. Among these requirements, SOC reflects the available power in lithium-ion batteries and measures the endurance of lithium-ion batteries. The SOC estimation of lithium batteries is particularly important and has become one of the key factors affecting the performance and safety of electric vehicles.

[0003] Traditional SOC estimation methods for lithium-ion batteries include ampere-hour measurement and model-based methods. The ampere-hour measurement method relies on the accuracy of the initial SOC, but the initial SOC is difficult to obtain accurately under the flat open circuit voltage (OCV) characteristics of lithium iron phosphate batteries. Model-based methods, such as equivalent circuit models (ECMs), data-driven models, or electrochemical models, although they can improve the estimation accuracy, their computational complexity and difficult parameter identification make them challenging in practical applications. In addition, the flatness and hysteresis effects of the OCV-SOC curve further limit the accuracy of voltage-based estimation methods. Therefore, previous studies have found that the stress generated during battery charging and discharging can establish a significant relationship with SOC, but because the stress changes obtained during charging and discharging are nonlinear, it has become a difficult problem to establish a direct correspondence between stress and SOC, and the nonlinear problem of stress changes needs to be solved. In addition, electrochemical impedance spectroscopy is used to realize SOC estimation of lithium iron phosphate batteries. Although electrochemical impedance spectroscopy (EIS) can provide detailed information on the electrochemical process inside the battery, the traditional EIS method still has some limitations. Traditional EIS mainly relies on low-frequency and high-frequency data to estimate SOC, but the EIS parameters in the mid-frequency region are often affected by multiple factors, and it is difficult to obtain clear regular changes, resulting in inaccurate SOC estimation results. Therefore, a SOC estimation method for lithium iron phosphate batteries based on static stress and DEIS is proposed to solve the above problems. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a SOC estimation method for a lithium iron phosphate battery based on static stress and DEIS, which has the advantages of accurate estimation of the SOC of a lithium iron phosphate battery, and solves the problem that it is difficult to obtain clear regular changes in EIS parameters in the mid-frequency region, resulting in inaccurate SOC estimation results.

[0005] In order to achieve the above-mentioned accurate purpose of the SOC of the lithium iron phosphate battery, the present invention provides the following technical solution: a method for estimating the SOC of a lithium iron phosphate battery based on static stress and DEIS, comprising the following steps: S1: Collect the total stress F and full-frequency dynamic impedance spectrum DEIS of the lithium iron phosphate battery during operation; S2: The lithium iron phosphate battery is charged at equal intervals of SOC at different charging currents I. After each interval is charged, it is left to stand for 2 hours. After the standing time is completed, the next equal interval is charged again until the SOC reaches 100%. The dynamic stress F generated by charging in each SOC interval is calculated. D , and obtain the dynamic stress change rate ΔF for each SOC interval D , in each SOC range, the charging current I and the dynamic stress change rate ΔF D The relationship between the dynamic stress change rate and the current is fitted to obtain the fitting expression ΔF D (I); S3: Use different charging currents I to charge the lithium iron phosphate battery at equal intervals of SOC under different charging processes. After each interval is charged, let it stand, and then charge it at the next equal interval until the SOC reaches 100%. Fit the dynamic stress change rate ΔF under different charging processes D，t , current I, front dynamic stress F D,t-1 The relationship between the two equations is used to obtain the fitting expression F for each SOC interval. D,t-1 (ΔF D , I); S4: Through the total stress F and dynamic stress F D The static stress F is calculated S , establish F by table lookup method S -SOC estimator, due to static stress F S The nonlinearity of the static stress F S The slope and impedance spectrum EIS are used as discrimination conditions to accurately estimate SOC.

[0006] Preferably, the step S2 is specifically: S2.1: The lithium iron phosphate battery is charged at intervals of 10% SOC at different charging currents I, and the total stress F1 after charging and the total stress F2 after standing are obtained at different SOC intervals and different charging currents I. The dynamic stress F generated by each 10% SOC charging is calculated.D , the expression is: ; Among them, F1 is the total stress after charging, and F2 is the total stress after standing; S2.2: Dynamic stress F generated by charging in each SOC interval D The dynamic stress change rate ΔF of each SOC interval is calculated D , the expression is: ; in, It is the dynamic stress after the SOC interval is charged. is the dynamic stress at the start SOC moment of the SOC interval, is the charging time in the SOC interval; S2.3: Use the dynamic stress change rate ΔF generated by different charging currents I in each SOC interval calculated in step S2.2 D Fitting is performed to obtain the dynamic stress change rate ΔF D The relationship between ΔF and charging current I D (I), the specific expression is; ; Where I is the charging current, α1, α2, and α3 are all fitting expressions ΔF D Fitting parameters in (I).

[0007] Preferably, the step S3 is specifically: S3.1: Set different charging processes. The same SOC interval is charged using different charging processes at different charging currents I. Different charging processes will generate different pre-dynamic stress F D，t-1 ; S3.2: Repeat step S3.1 for each SOC interval to obtain the dynamic stress F at different front ends. D，t-1 Dynamic stress change rate ΔF generated by using different charging currents I D,t , the dynamic stress change rate ΔF in each SOC interval is obtained by fitting method D,t , charging current I, front dynamic stress F D,t-1 The fitting expression F of the three D,t-1 (ΔF D , I), the expression is: ; where F D,t-1 is the initial dynamic stress at time t, I is the charging current, ΔF D,t is the dynamic stress change rate at time t, are all fitting parameters in the fitting expression.

[0008] Preferably, the specific steps in step S4 are: S4.1: In each SOC interval, the current charging current I and the fitting relationship ΔF D (I) Calculate the dynamic stress change rate ΔF at the current moment D,t , and according to the fitting relationship F D,t-1 (ΔF D , I) calculate the current moment's forward dynamic stress F D,t-1 , the previous dynamic stress F at each moment D,t-1 The dynamic stress F at the previous moment D , the dynamic stress F at each moment can be calculated D ; S4.2: Through total stress F, dynamic stress F D The static stress F is calculated S , the expression is: ; S4.3: Based on the real-time total stress F data measured experimentally, the dynamic stress F is calculated and D , the static stress F per second can be calculated S Data, based on the real SOC data of the battery every second, establish time t, static stress F S , and the actual SOC correspond to the table method, and get a tF S -SOC estimator; S4.4: Increase static stress F S The slope K S As a supplementary discriminant condition, fitting tF S -tF in SOC estimator S and find the first-order derivative of static stress , thus obtaining the static stress slope K S , the expression is: ; ; ; Among them, F S is the static stress, is the first-order derivative of static stress, K S is the static stress slope, is the fitting parameter in the fitting relationship between static stress and time.

[0009] S4.5: Real-time monitoring of the dynamic impedance spectrum DEIS of the lithium iron phosphate battery during charging, and extraction of the charge transfer resistance in the impedance spectrum , double layer capacitor , Equivalent Series Capacitance Three key parameters, expressed as: ; ; ;

[0010] in, are the real values ​​of the low-frequency and high-frequency ends of the semicircular curve in the mid-frequency region of the impedance spectrum, is the circumference of a circle, is the frequency corresponding to the maximum value of the imaginary part of the semicircular curve in the mid-frequency region of the impedance spectrum, is the scanning frequency in the mid-frequency region of the impedance spectrum.

[0011] Compared with the prior art, the present invention provides a method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS, which has the following beneficial effects: 1. This method for estimating SOC of lithium iron phosphate batteries based on static stress and DEIS defines static stress and dynamic stress to accurately separate static stress to estimate SOC. Compared with existing methods, this method overcomes the defects of high model accuracy requirements and inaccurate estimation in the voltage platform area, and provides a solution that is more sensitive to charge and discharge history and current, and establishes t-F S -SOC estimator, estimates SOC based on the obtained static stress FS.

[0012] 2. The SOC estimation method of lithium iron phosphate battery based on static stress and DEIS, combined with the static stress slope K S As a solution to the static stress F S A supplementary discrimination method corresponding to multiple SOC values ​​is proposed based on the dynamic impedance spectrum parameter changes of lithium iron phosphate batteries, and the equivalent series capacitance of EIS parameters in the mid-frequency region is proposed. As a further discrimination method for SOC estimation, the static stress F S Under the nonlinear state, the static stress slope K S and equivalent series capacitance As a SOC estimation and judgment method, it can achieve accurate estimation of the SOC of lithium iron phosphate batteries, making up for the deficiency of nonlinear stress change in previous methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of the overall process of a method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS proposed by the present invention; Figure 2 A schematic diagram of a SOC estimation method for a lithium iron phosphate battery based on static stress and DEIS proposed by the present invention, showing a charging curve of 10% SOC at different current intervals; Figure 3 The present invention proposes a method for estimating the SOC of lithium iron phosphate batteries based on static stress and DEIS. The equivalent series capacitance obtained under 100mHz frequency sweep in the medium frequency region at different SOCs is shown in FIG. Change trend chart; Figure 4 This is a schematic diagram of a method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS proposed by the present invention, in which one static stress Fs corresponds to multiple SOC values. DETAILED DESCRIPTION

[0014] 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.

[0015] See also Figure 1-4 , a method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS, comprising the following steps: S1: Collect the total stress F and full-frequency dynamic impedance spectrum DEIS of the lithium iron phosphate battery during operation; S2: The lithium iron phosphate battery is charged at equal intervals of SOC at different charging currents I. After each interval is charged, it is left to stand for 2 hours. After the standing time is completed, the next equal interval is charged again until the SOC reaches 100%. The dynamic stress F generated by charging in each SOC interval is calculated. D , and obtain the dynamic stress change rate ΔF for each SOC interval D , in each SOC range, the charging current I and the dynamic stress change rate ΔF D The relationship between the dynamic stress change rate and the current is fitted to obtain the fitting expression ΔF D (I); S3: Use different charging currents I to charge the lithium iron phosphate battery at equal intervals of SOC under different charging processes. After each interval is charged, let it stand, and then charge it at the next equal interval until the SOC reaches 100%. Fit the dynamic stress change rate ΔF under different charging processes D，t , current I, front dynamic stress F D,t-1 The relationship between the two equations is used to obtain the fitting expression F for each SOC interval. D,t-1 (ΔF D, I); S4: Through the total stress F and dynamic stress F D The static stress F is calculated S , establish F by table lookup method S -SOC estimator, due to static stress F S The nonlinearity of the static stress F S The slope and impedance spectrum EIS are used as discrimination conditions to accurately estimate SOC.

[0016] Get ΔF in each 10% SOC interval D (I) relationship, that is, knowing the charging current I in different SOC ranges, the dynamic stress change rate ΔF can be calculated D， As shown in Table 1.

[0017] Table 1

[0018] Step S2 is specifically as follows: S2.1: The lithium iron phosphate battery is charged at intervals of 10% SOC at different charging currents I, and the total stress F1 after charging and the total stress F2 after standing are obtained at different SOC intervals and different charging currents I. The dynamic stress F generated by each 10% SOC charging is calculated. D , the expression is: ;

[0019] Among them, F1 is the total stress after charging, and F2 is the total stress after standing; S2.2: Dynamic stress F generated by charging in each SOC interval D The dynamic stress change rate ΔF of each SOC interval is calculated D , the expression is: ; in, It is the dynamic stress after the SOC interval is charged. is the dynamic stress at the start SOC moment of the SOC interval, is the charging time in the SOC interval; S2.3: Use the dynamic stress change rate ΔF generated by different charging currents I in each SOC interval calculated in step S2.2 D Fitting is performed to obtain the dynamic stress change rate ΔF D The relationship between ΔF and charging current I D (I), the specific expression is; ; Where I is the charging current, α1, α2, and α3 are all fitting expressions ΔF D Fitting parameters in (I).

[0020] Step S3 is specifically as follows: S3.1: Set different charging processes. The same SOC interval is charged using different charging processes at different charging currents I. Different charging processes will generate different pre-dynamic stress F D，t-1 ; Set four different charging processes, taking the 30%-40% SOC range as an example, please refer to Table 2.

[0021] Table 2

[0022] Each static state is to obtain the total stress before and after static state according to the real-time data of stress sensor, so as to calculate the dynamic stress F D .

[0023] In process 1, since the battery is directly charged from 30% to 40% SOC, and it is left to stand for 2 hours after being charged from 0% to 30% SOC, in overcharge 1, the dynamic stress F D，30%SOC is 0.

[0024] In process 2, since the battery is charged from 0% to 40% SOC, the front dynamic stress of the 30%-40% SOC part is the accumulation of the dynamic stress of the previous 0%-30% SOC. Therefore, the front dynamic stress F of the 30%-40% SOC in process 2 is D，30%SOC It is not 0. The process of charging the battery from 0% to 30% SOC and leaving it at rest is to calculate the dynamic stress accumulation from 0% to 30% SOC, and use this dynamic stress accumulation as the previous dynamic stress F for the subsequent 30% to 40% SOC. D，30%SOC .

[0025] Process 3 is the same as process 2. The dynamic stress before 30%-40% SOC is the accumulation of the dynamic stress before 10%-30% SOC. Therefore, the dynamic stress before 30%-40% SOC in process 2 is F D，30%SOC It is not 0 either. The difference from process 2 is that the battery is charged from 10% to 40% SOC, that is, the previous dynamic stress is only the dynamic stress accumulation of 10%-30% SOC. The process of charging the battery from 10% to 30% SOC and leaving it to stand is to calculate the dynamic stress accumulation of 10%-30% SOC, and use this dynamic stress accumulation as the previous dynamic stress F of the subsequent 30%-40% SOC D，30%SOC .

[0026] The principle of process 4 is the same as process 3. The dynamic stress of the 30%-40% SOC part is the accumulation of the dynamic stress of the previous 20%-30% SOC. Therefore, the dynamic stress of the 30%-40% SOC in process 2 is F D，30%SOC It is not 0 either. The difference from process 2 is that the battery is charged from 20% to 40% SOC, that is, the previous dynamic stress is only the dynamic stress accumulation of 20%-30% SOC. The process of charging the battery from 20% to 30% SOC and leaving it to stand is to calculate the dynamic stress accumulation of 20%-30% SOC, and use this dynamic stress accumulation as the previous dynamic stress F of the subsequent 30%-40% SOC D，30%SOC .

[0027] Obviously, the difference between the four processes is that the magnitude of the pre-dynamic stress is different. This is to obtain the dynamic stress change rate ΔF of different magnitudes of pre-dynamic stress D impact.

[0028] S3.2: Repeat step S3.1 for each SOC interval to obtain the dynamic stress F at different front ends. D，t-1 Dynamic stress change rate ΔF generated by using different charging currents I D,t , the dynamic stress change rate ΔF in each SOC interval is obtained by fitting method D,t , charging current I, front dynamic stress F D,t-1 The fitting expression F of the three D,t-1 (ΔF D , I), the expression is: ; where F D,t-1 is the initial dynamic stress at time t, I is the charging current, ΔF D,t is the dynamic stress change rate at time t, are all fitting parameters in the fitting expression.

[0029] The specific steps in step S4 are: S4.1: In each SOC interval, the current charging current I and the fitting relationship ΔF D (I) Calculate the dynamic stress change rate ΔF at the current moment D,t , and according to the fitting relationship F D,t-1 (ΔF D , I) calculate the current moment's forward dynamic stress F D,t-1 , the previous dynamic stress F at each moment D,t-1 The dynamic stress F at the previous moment D , the dynamic stress F at each moment can be calculated D， Please refer to Table 3.

[0030] Table 3

[0031] S4.2: Through total stress F, dynamic stress F D The static stress F is calculated S , the expression is: ; S4.3: Based on the real-time total stress F data measured experimentally, the dynamic stress F is calculated and D , the static stress F per second can be calculated S Data, based on the real SOC data of the battery every second, establish time t, static stress F S , the actual SOC three corresponding to the table method, get a Estimator; S4.4: Due to the static stress F S Nonlinearity, some static stress F S The value will correspond to multiple SOC values, increasing the static stress F S The slope K S As a supplementary discriminant condition, fitting Estimator tF S and find the first-order derivative of static stress , thus obtaining the static stress slope K S , the expression is: ; ; ; Among them, F S is the static stress, is the first-order derivative of static stress, K S is the static stress slope, is the fitting parameter in the fitting relationship between static stress and time.

[0032] exist Figure 4 For example, when the static stress F S When the value corresponds to the two SOC values ​​of c and g, if the static stress slope K S is "zero", then SOC is the value at point c. If the static stress slope K S If the value is positive, then SOC is the g-point value. Similarly, the static stress F can be determined. S The value corresponds to the two SOC values ​​a and e. When the static stress F S When the value corresponds to the three SOC values ​​of b, d, and f, if the static stress slope K S If the static stress slope K is negative, then SOC is the value at point d.S If is "positive", the SOC is at point b or point f.

[0033] By judging the static stress slope K S The "positive, negative, and zero" conditions can further estimate SOC; S4.5: When a static stress F S The value will correspond to multiple SOC values, and the static stress slope K S When the "positive, negative, and zero" conditions are the same, further discrimination is required to achieve accurate SOC estimation. The dynamic impedance spectrum DEIS of the lithium iron phosphate battery during charging is monitored in real time, and the charge transfer resistance in the impedance spectrum is extracted. , double layer capacitor , Equivalent Series Capacitance Three key parameters, expressed as: ; ; ; in, are the real values ​​of the low-frequency and high-frequency ends of the semicircular curve in the mid-frequency region of the impedance spectrum, is the circumference of a circle, is the frequency corresponding to the maximum value of the imaginary part of the semicircular curve in the mid-frequency region of the impedance spectrum, is the scanning frequency in the mid-frequency region of the impedance spectrum.

[0034] Equivalent series capacitance in the mid-frequency region of the impedance spectrum of lithium iron phosphate batteries It is found that it shows a monotonically decreasing relationship with the increase of SOC, so it can be used as a judgment condition for further estimating SOC to achieve accurate estimation of SOC.

[0035] Set a threshold , this threshold is the static stress F S The impedance spectrum at any point in the decreasing value area at 100mHz in the mid-frequency region Value, this The value can be obtained by a preliminary experiment. In the preliminary experiment, the static stress F S When the value starts to decrease, the impedance online measurement device is used to detect and calculate the equivalent series capacitance of a point in real time. value, use this as the threshold ,because As SOC increases, it decreases monotonically, so at F S The equivalent series capacitance of the impedance spectrum at 100mHz in the mid-frequency region before the value decreases. The value must be greater than the threshold , F SThe equivalent series capacitance of the impedance spectrum in the increasing region after the decreasing value at the mid-frequency region of 100mHz The value must be less than the threshold .

[0036] exist Figure 4 When the static stress F S When the value corresponds to the three SOC values ​​of b, d, and f, if the static stress slope K S If the static stress slope K is negative, then SOC is the value at point d. S If the value is positive, then SOC is at point b or point f. S The equivalent series capacitance of the impedance spectrum at 100mHz in the mid-frequency region ,like Greater than threshold , then SOC is the value at point b, if Less than threshold , then SOC is the value at point f. This completely solves the problem of static stress F S The problem of not being able to accurately estimate SOC when the value corresponds to multiple SOC values.

[0037] When used, by defining static stress and dynamic stress, the static stress can be accurately separated to estimate SOC. Compared with the existing methods, this method overcomes the defects of high model accuracy and inaccurate estimation in the voltage platform area, and provides a solution that is more sensitive to charge and discharge history and current, and establishes t-F S -SOC estimator, estimates SOC based on the obtained static stress FS.

[0038] In summary, this SOC estimation method for lithium iron phosphate batteries based on static stress and DEIS is presented.

[0039] And, combined with the static stress slope K S As a solution to the static stress F S A supplementary discrimination method corresponding to multiple SOC values ​​is proposed based on the dynamic impedance spectrum parameter changes of lithium iron phosphate batteries, and the equivalent series capacitance of EIS parameters in the mid-frequency region is proposed. As a further discrimination method for SOC estimation, the static stress F S Under the nonlinear state, the static stress slope K S and equivalent series capacitance As a SOC estimation and judgment method, it can achieve accurate estimation of the SOC of lithium iron phosphate batteries, making up for the deficiency of nonlinear stress change in previous methods.

[0040] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0041] 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 method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS, characterized in that: The following steps are involved: S1: Collect the total stress F and full-frequency dynamic impedance spectrum DEIS of the lithium iron phosphate battery during operation; S2: The lithium iron phosphate battery is charged at equal intervals of SOC at different charging currents I. After each interval is charged, it is left to stand for 2 hours. After the standing time is completed, the next equal interval is charged again until the SOC reaches 100%. The dynamic stress F generated by charging in each SOC interval is calculated. D , and obtain the dynamic stress change rate ΔF for each SOC interval D , in each SOC range, the charging current I and the dynamic stress change rate ΔF D The relationship between the dynamic stress change rate and the current is fitted to obtain the fitting expression ΔF D (I); S3: Use different charging currents I to charge the lithium iron phosphate battery at equal intervals of SOC under different charging processes. After each interval is charged, let it stand, and then charge it at the next equal interval until the SOC reaches 100%. Fit the dynamic stress change rate ΔF under different charging processes D，t , current I, front dynamic stress F D,t-1 The relationship between the two equations is used to obtain the fitting expression F for each SOC interval. D,t-1 (ΔF D , I); S4: Through the total stress F and dynamic stress F D The static stress F is calculated S , establish F by table lookup method S -SOC estimator, due to static stress F S The nonlinearity of the static stress F S The slope and impedance spectrum EIS are used as discrimination conditions to accurately estimate SOC.

2. A method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS according to claim 1, characterized in that: The step S2 is specifically as follows: S2.1: The lithium iron phosphate battery is charged at intervals of 10% SOC at different charging currents I, and the total stress F1 after charging and the total stress F2 after standing are obtained at different SOC intervals and different charging currents I. The dynamic stress F generated by each 10% SOC charging is calculated. D , the expression is: ； Among them, F1 is the total stress after charging, and F2 is the total stress after standing; S2.2: Dynamic stress F generated by charging in each SOC interval D The dynamic stress change rate ΔF of each SOC interval is calculated D , the expression is: ； in, It is the dynamic stress after the SOC interval is charged. is the dynamic stress at the start SOC moment of the SOC interval, is the charging time in the SOC interval; S2.3: Use the dynamic stress change rate ΔF generated by different charging currents I in each SOC interval calculated in step S2.2 D Fitting is performed to obtain the dynamic stress change rate ΔF D The relationship between ΔF and charging current I D (I), the specific expression is; ； Where I is the charging current, α1, α2, and α3 are all fitting expressions ΔF D Fitting parameters in (I).

3. The method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS according to claim 1, characterized in that: The step S3 is specifically as follows: S3.1: Set different charging processes. The same SOC interval is charged using different charging processes at different charging currents I. Different charging processes will generate different pre-dynamic stress F D，t-1 ; S3.2: Repeat step S3.1 for each SOC interval to obtain the dynamic stress F at different front ends. D，t-1 Dynamic stress change rate ΔF generated by using different charging currents I D,t , the dynamic stress change rate ΔF in each SOC interval is obtained by fitting method D,t , charging current I, front dynamic stress F D,t-1 The fitting expression F of the three D,t-1 (ΔF D , I), the expression is: ； where F D,t-1 is the initial dynamic stress at time t, I is the charging current, ΔF D,t is the dynamic stress change rate at time t, are all fitting parameters in the fitting expression.

4. The method for estimating SOC of a lithium iron phosphate battery based on static stress and DEIS according to claim 1, characterized in that: The specific steps in step S4 are: S4.1: In each SOC interval, the current charging current I and the fitting relationship ΔF D (I) Calculate the dynamic stress change rate ΔF at the current moment D,t , and according to the fitting relationship F D,t-1 (ΔF D , I) calculate the current moment's forward dynamic stress F D,t-1 , the previous dynamic stress F at each moment D,t-1 The dynamic stress F at the previous moment D , the dynamic stress F at each moment can be calculated D ; S4.2: Through total stress F, dynamic stress F D The static stress F is calculated S , the expression is: ； S4.3: Based on the real-time total stress F data measured experimentally, the dynamic stress F is calculated and D , the static stress F per second can be calculated S Data, based on the real SOC data of the battery every second, establish time t, static stress F S , and the actual SOC correspond to the table method, and get a tF S -SOC estimator; S4.4: Increase static stress F S The slope K S As a supplementary discriminant condition, fitting tF S -tF in SOC estimator S and find the first-order derivative of static stress , thus obtaining the static stress slope K S , the expression is: ； ； ； Among them, F S is the static stress, is the first-order derivative of static stress, K S is the static stress slope, is the fitting parameter in the fitting relationship between static stress and time; S4.5: Real-time monitoring of the dynamic impedance spectrum DEIS of the lithium iron phosphate battery during charging, and extraction of the charge transfer resistance in the impedance spectrum , double layer capacitor , Equivalent Series Capacitance Three key parameters, expressed as: ； ； ； in, are the real values ​​of the low-frequency and high-frequency ends of the semicircular curve in the mid-frequency region of the impedance spectrum, is the circumference of a circle, is the frequency corresponding to the maximum value of the imaginary part of the semicircular curve in the mid-frequency region of the impedance spectrum, is the scanning frequency in the mid-frequency region of the impedance spectrum.

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