Method and system for estimating soc of lithium iron phosphate battery and method for estimating soh

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By identifying feature values and determining correction conditions during the slow charging process of lithium iron phosphate batteries, and using the ampere-hour integration method and a preset table to determine the SOC correction value, the problem of low SOC and SOH estimation accuracy of lithium iron phosphate batteries is solved, achieving accurate SOC and SOH estimation, and optimizing vehicle control and user experience.

CN115524614BActive Publication Date: 2026-07-24DEEPAL AUTOMOBILE TECH CO LTD

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Patent Information

Authority / Receiving Office: CN · China
Patent Type: Patents(China)
Current Assignee / Owner: DEEPAL AUTOMOBILE TECH CO LTD
Filing Date: 2022-09-27
Publication Date: 2026-07-24

AI Technical Summary

Technical Problem

The SOC and SOH estimation accuracy of lithium iron phosphate batteries is relatively low, especially in Kalman filtering and ampere-hour integration methods, which are affected by the accuracy of on-board current sensors and the long plateau period of voltage curves, resulting in insufficient estimation accuracy.

Method used

During the slow charging process of lithium iron phosphate batteries, the SOC value is estimated by using the ampere-hour integration method through feature value identification and correction condition judgment. The first and second SOC correction values are determined by the preset SOC correction value table, and the SOH value is combined for accurate correction, thus forming an SOC estimation system and an SOH estimation method.

Benefits of technology

It improves the SOC estimation accuracy of lithium iron phosphate batteries, optimizes the vehicle mileage calculation and BMS control, improves the user driving experience, and improves the SOH estimation accuracy, avoiding the problem of not updating for a long time.

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Abstract

The application discloses a lithium iron phosphate battery SOC estimation method and system and an SOH estimation method. The SOC estimation method comprises the following steps: obtaining an SOH value of a current battery; collecting a voltage of the current battery in a slow charging process of the lithium iron phosphate battery, estimating an SOC value of the current battery by using an ampere-hour integral method, and storing the SOC value; performing eigenvalue identification condition judgment; if the eigenvalue identification condition is met, determining a first SOC correction value SOC cav1 and a second SOC correction value SOC cav2 , and then performing SOC correction condition judgment; if SOC correction condition I is met, making the SOC value of the current battery be the first SOC correction value SOC cav1 , and if SOC correction condition II is met, making the SOC value of the current battery be the second SOC correction value SOC cav2 . The application can improve the SOC and SOH estimation accuracy.

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Description

Technical Field

[0001] This invention belongs to the field of new energy vehicle battery management systems, specifically relating to a method, system, and method for estimating the SOC of lithium iron phosphate batteries and SOH. Background Technology

[0002] Pure electric vehicles need to acquire basic battery information in real time during operation, such as current, voltage, and temperature. Through secondary calculations of this basic information, information such as battery charge status and health status can be obtained, in order to calculate the remaining driving range and maximum discharge power of the vehicle, ensuring safe driving for the owner. Therefore, improving the accuracy of battery charge status and health status is crucial.

[0003] The State of Charge (SOC) of a battery is defined as the ratio of its remaining capacity after a period of use or inactivity to its capacity when fully charged. SOC affects the calculation of a vehicle's remaining range and is the basis for calculating maximum discharge power. Improving the accuracy of SOC estimation and controlling SOC can enhance battery safety and slow down battery degradation.

[0004] Battery State of Health (SOH) is another important indicator for evaluating battery performance. SOH is related to factors such as battery internal resistance, current capacity, self-discharge rate, and temperature. SOH directly affects the battery's and vehicle's lifespan and safety. When the overall SOH of the battery pack is below 70%, the electric vehicle industry believes that the battery pack should be scrapped, as continued use increases the risk of thermal runaway.

[0005] For lithium iron phosphate batteries, due to the long plateau period of their voltage curve, under the same temperature and charge / discharge conditions, the difference in OCV change between 25% and 60% SOC and 70% and 90% SOC is no more than 20mV. Furthermore, the influence of onboard voltage sensors affects the convergence speed of iterative algorithms such as Kalman filtering, reducing their estimation accuracy and limiting the accuracy of initial value correction in the ampere-hour integration method. Therefore, the current SOC estimation accuracy for lithium iron phosphate batteries is relatively low. Since the commonly used method for capacity estimation is the ratio of the charged battery capacity to the difference between the final SOC and the initial SOC, the low SOC estimation accuracy of lithium iron phosphate batteries, coupled with the influence of the accuracy of onboard current sensors, results in similarly low SOH estimation accuracy. Summary of the Invention

[0006] The purpose of this invention is to provide a method, system, and method for estimating the SOC and SOH of lithium iron phosphate batteries, so as to improve the accuracy of SOC and SOH estimation.

[0007] The SOC estimation method for lithium iron phosphate batteries described in this invention includes: Get the current SOH value of the battery.

[0008] During the slow charging process of lithium iron phosphate batteries, the current battery voltage is collected, the current state of charge (SOC) value of the battery is estimated using the ampere-hour integration method, and the data is stored.

[0009] The feature value recognition condition is determined. If the feature value recognition condition is met, the first SOC correction value (SOC) is determined based on the SOH value. cav1 Second SOC correction value SOC cav2 Then, the SOC correction condition is checked; if SOC correction condition I is met, the current battery SOC value is set to the first SOC correction value. cav1 If SOC correction condition II is met, then the current SOC value of the battery is set to the second SOC correction value. cav2 .

[0010] Preferably, the steps for determining the feature value recognition conditions include: Step P11: Determine whether the difference between the current SOC value of the battery and SOC0 is greater than or equal to 9%. If yes, proceed to step P12; otherwise, continue to step P11. Here, SOC0 represents the initial SOC value of the stored lithium iron phosphate battery when it starts slow charging.

[0011] Step P12: Assign the 10 most recently stored SOC values with a tolerance of 1% to SOC1, SOC2, SOC3, ..., SOC in ascending order. 10 This will correspond to 10 voltages based on 10 SOC values with a tolerance of 1% from the latest stored values (i.e., when the battery's SOC value is equal to SOC1, SOC2, SOC3, ..., SOC...). 10 The battery voltage at the time of use is assigned to U1, U2, U3, ..., U... 10 Then proceed to step P13.

[0012] Step P13, using the formula: S i-2 =(U i -U i-2 ) / (SOC i -SOC i-2 ), calculate the voltage change rate S i-2 Then, step P14 is executed; where i takes all integers from 3 to 10 in sequence, resulting in a total of 8 voltage change rates, namely S1, S2, S3, S4, S5, S6, S7, and S8.

[0013] Step P14, using the formula: V j-3=S j-2 -S j-3 Calculate the voltage change rate increment V j-3 Then execute step P15; where j takes all integers from 4 to 10 in sequence, resulting in a total of 7 voltage change rate increments, namely V1, V2, V3, V4, V5, V6, and V7.

[0014] Step P15: Determine whether condition 1a or condition 1b is satisfied. If yes, it means the feature value recognition condition is met; otherwise, return to step P11. Condition 1a is: V1, V2, and V3 are all greater than 0, V4 ≥ 0, V5 and V6 are all less than 0, and S5 ≥ S TBD Condition 1b is: V1, V2, V3, and V4 are all greater than or equal to 0, and two consecutive values of V1, V2, V3, and V4 are greater than 0, and V5, V6, and V7 are all less than 0, and S5 ≥ S TBD Among them, S TBD This indicates the preset voltage change rate threshold.

[0015] By judging the above feature value identification conditions, the SOC points that may need to be corrected can be accurately identified.

[0016] Preferably, the method for determining the SOC correction condition is as follows: If U7 < U TBD And the current SOC value of the battery is related to the SOC cav1 The absolute value of the difference is less than SOC TBD This indicates that SOC correction condition I is satisfied. If U7 > U TBD And the current SOC value of the battery is related to the SOC cav2 The absolute value of the difference is less than SOC TBD This indicates that SOC correction condition II is satisfied. Where, U TBD This indicates the preset voltage threshold, SOC. TBD This indicates the preset SOC threshold.

[0017] By judging the above SOC correction conditions, it can be accurately determined whether correction is needed, and specifically whether to correct to the first SOC correction value or the second SOC correction value.

[0018] Preferably, the first SOC correction value (SOC) is determined based on the SOH value. cav1 Second SOC correction value SOC cav2 The method is as follows: Based on the SOH value, query the preset SOC correction value table to obtain the corresponding first SOC correction value (SOC). cav1 Second SOC correction value SOC cav2The preset SOC correction value table is a table showing the correspondence between the SOH values obtained through calibration on the test bench and the first and second SOC correction values. Finding the SOC correction value by looking up the table is easy.

[0019] Preferably, the preset SOC correction value table is obtained by calibration in the following manner: First, select n lithium iron phosphate batteries of the same type but with different SOH values, and then proceed to the second step.

[0020] The second step is to mount the first lithium iron phosphate battery on a test bench at room temperature and slowly charge it from 0% to 100%. The battery voltage is collected during the slow charging process, and the SOC value of the battery is estimated using the ampere-hour integration method. The corresponding curve of the SOC value and voltage of the first lithium iron phosphate battery is obtained, and then the third step is performed.

[0021] The third step is to identify the correlation curve between SOC value and voltage, and extract 101 SOC values with a tolerance of 1% in ascending order: SOC'1 (equal to 0), SOC'2 (equal to 1%), SOC'3 (equal to 2%), ..., SOC' 101 (equal to 100%) and 101 voltages U'1, U'2, U'3, ..., U' corresponding to 101 SOC values with a tolerance of 1%. 101 Then proceed to step four.

[0022] Step 4: Using the formula: S' k-2 =(U' k -U' k-2 ) / (SOC' k -SOC' k-2 ), calculate the voltage change rate S' k-2 Then, proceed to step five; where k takes all integers from 3 to 101, resulting in a total of 99 voltage change rates, namely S'1, S'2, S'3, ..., S' 99 .

[0023] Step 5: Using the formula: V' m-3 =S' m-2 -S' m-3 Calculate the voltage change rate increment V' m-3 Then proceed to step six; where m takes all integers from 4 to 101, resulting in a total of 98 voltage change rate increments, namely V'1, V'2, V'3, ..., V' 98 .

[0024] Step 6: Identify the SOC correction value and find the value that satisfies: V' h V' h+1 V'h+2 Both are greater than 0, and V' h+3 ≥0, and V' h+4 V' h+5 Both are less than 0, and S' h+4 ≥S TBD , and U' h+6 <U TBD A numerical value h; find the value that satisfies: V' t V' t+1 V' t+2 V' t+3 All are greater than or equal to 0, and V' t V' t+1 V' t+2 V' t+3 Two out of the four data points are consecutively greater than 0, and V' t+4 V' t+5 V' t+6 Both are less than 0, and S' t+4 ≥S TBD , and U' t+6 >U TBD A numerical value t; SOC' h+6 (i.e., the (h+6th)th SOC value) is used as the first SOC correction value corresponding to the SOH value of the lithium iron phosphate battery, and SOC' is adjusted accordingly. t+6 (i.e., the (t+6th) SOC value) is used as the second SOC correction value corresponding to the SOH value of the lithium iron phosphate battery, and then the seventh step is executed; where h and t are integers, and 1≤h≤92, 1≤t≤92.

[0025] Step 7: Determine whether n first SOC correction values and n second SOC correction values corresponding to the SOH values of n lithium iron phosphate batteries have been obtained. If so, proceed to step 9; otherwise, proceed to step 8.

[0026] Step 8: At room temperature, place the next lithium iron phosphate battery on the test bench and slowly charge it from 0% to 100%. Collect the battery voltage during the slow charging process, estimate the SOC value of the battery using the ampere-hour integration method, and obtain the corresponding curve of the SOC value and voltage of the lithium iron phosphate battery. Then return to step 3.

[0027] Step 9: Assign a one-to-one correspondence between the SOH values of the n lithium iron phosphate batteries and the n first SOC correction values and n second SOC correction values corresponding to the SOH values of the n lithium iron phosphate batteries, to form the preset SOC correction value table.

[0028] By calibrating the SOC correction value using the above method on a test bench, more accurate first and second SOC correction values can be obtained.

[0029] Preferably, the preset voltage change rate threshold S TBD The value range is 0.002~0.005; the preset SOC threshold is... TBD The value range is 18%~22%; the preset voltage threshold U TBD The range of values for U is: OCV1 +0.01V~ U OCV2 +0.03V; where U OCV1 U represents the open-circuit voltage when the battery's SOC is 50%. OCV2 This represents the open-circuit voltage when the battery's SOC is 60%. These numerical ranges are obtained through extensive experimental research and represent a range with good estimation accuracy.

[0030] Preferably, the charging current range for slow charging of lithium iron phosphate batteries is 0.1C~0.3C, and the ambient temperature is 23℃~30℃.

[0031] Preferably, when SOC correction condition I is met, the first SOC correction value SOC is adjusted. cav1 Assign to SOC b Set the SOC correction flag to 1 and restart the calculation of the battery's charging capacity (i.e., cumulative charging capacity); when SOC correction condition II is met, set the second SOC correction value to 1. cav2 Assign to SOC b Set the SOC correction flag to position 1 and recalculate the battery's charging capacity; when the battery is fully charged, set the battery full charge flag to position 1; when the vehicle is powered off, reset the SOC... b The value is stored as the initial SOC for charging, and the battery's charging capacity, SOC correction flag, and battery full charge flag are also stored. These are used to estimate the SOH when the vehicle is powered on again and the SOH estimation conditions are met.

[0032] The SOC estimation system for lithium iron phosphate batteries of the present invention includes a controller, which is programmed to execute the above-described SOC estimation method.

[0033] The SOH estimation method for lithium iron phosphate batteries described in this invention is as follows: When the vehicle is powered on, if the SOC correction flag is 1 and the battery full charge flag is 1, then first use the formula: Q=Q cd Calculate the current total battery capacity Q using (100% - initial SOC), then use the formula: SOH0 = Q / Q rc Estimate the SOH value (SOH0) of the lithium iron phosphate battery. Wherein, Q cd Q represents the battery's charge capacity. rc Indicates the battery's rated capacity; SOC correction flag, battery full charge flag, initial charging SOC, and battery charging capacity Q.cd It is obtained by performing the SOC estimation method described above.

[0034] The present invention has the following effects: (1) During the slow charging process of lithium iron phosphate battery, the characteristic value recognition condition is judged by online SOC and voltage data processing. If the characteristic value recognition condition is met, the first SOC correction value SOC is determined. cav1 Second SOC correction value SOC cav2 Then, the SOC correction condition is checked; if SOC correction condition I is met, the current battery SOC value is set to the first SOC correction value. cav1 If SOC correction condition II is met, then the current SOC value of the battery is set to the second SOC correction value. cav2 It enables SOC correction during slow charging, improves SOC estimation accuracy, facilitates the calculation of vehicle mileage, facilitates the optimization of vehicle BMS control, and improves the user's driving experience.

[0035] (2) Upon meeting either SOC correction condition I or SOC correction condition II, the acquisition and storage of relevant parameters for SOH estimation are triggered. The next time the vehicle is powered on, if the SOH estimation trigger condition is met, SOH estimation is performed, increasing the frequency of SOH estimation triggers and avoiding the problem of SOH not being updated for extended periods. The initial charging SOC used for estimation is the first SOC correction value. cav1 Or the second SOC correction value SOC cav2 This improves the accuracy of SOH estimation. Attached Figure Description

[0036] Figure 1 This is a flowchart of the SOC estimation method for lithium iron phosphate batteries in this embodiment.

[0037] Figure 2 This is a flowchart of the calibration process for the preset SOC correction value table in this embodiment. Detailed Implementation

[0038] like Figure 1 As shown, the SOC estimation method for lithium iron phosphate batteries in this embodiment is applied to the controller. The controller acquires the current SOH value of the battery and, during the slow charging process of the lithium iron phosphate battery (charging current of 0.1C and ambient temperature of 23℃~30℃), collects the current battery voltage, estimates the current SOC value of the battery using the ampere-hour integration method, calculates the battery's charging capacity, stores the collected voltage and estimated SOC value, and then executes the following steps: Step P21: Set the SOC correction flag to 0, so that the SOC... b =0, then proceed to step P22.

[0039] Step P22: Determine whether a vehicle power-off signal has been received. If yes, proceed to step P213; otherwise, proceed to step P23.

[0040] Step P23: Determine whether the difference between the current SOC value of the battery and SOC0 is greater than or equal to 9%. If yes, proceed to step P24; otherwise, return to step P22. Here, SOC0 represents the initial SOC value of the stored lithium iron phosphate battery when it starts slow charging.

[0041] Step P24: Assign the 10 most recently stored SOC values with a tolerance of 1% to SOC1, SOC2, SOC3, SOC4, SOC5, SOC6, SOC7, SOC8, SOC9, and SOC1 respectively, in ascending order. 10 This will correspond to 10 voltages based on 10 SOC values with a tolerance of 1% from the latest stored values (i.e., when the battery's SOC value is equal to SOC1, SOC2, SOC3, ..., SOC...). 10 The battery voltage at that time is assigned to U1, U2, U3, U4, U5, U6, U7, U8, U9, U1 respectively. 10 Then proceed to step P25.

[0042] Step P25, using the formula: S i-2 =(U i -U i-2 ) / (SOC i -SOC i-2 ), calculate the voltage change rate S i-2 Then execute step P26; where i takes all integers from 3 to 10 in sequence, resulting in a total of 8 voltage change rates, namely S1, S2, S3, S4, S5, S6, S7, and S8.

[0043] Step P26, using the formula: V j-3 =S j-2 -S j-3 Calculate the voltage change rate increment V j-3 Then execute step P27; where j takes all integers from 4 to 10 in sequence, resulting in a total of 7 voltage change rate increments, namely V1, V2, V3, V4, V5, V6, and V7.

[0044] Step P27: Determine whether condition 1a or condition 1b is satisfied. If yes (indicating that the feature value recognition condition is met), proceed to step P28; otherwise, return to step P22. Condition 1a is: V1, V2, and V3 are all greater than 0, V4 ≥ 0, V5 and V6 are all less than 0, and S5 ≥ S... TBDCondition 1b is: V1, V2, V3, and V4 are all greater than or equal to 0, and two consecutive values of V1, V2, V3, and V4 are greater than 0, and V5, V6, and V7 are all less than 0, and S5 ≥ S TBD Among them, S TBD This represents a preset voltage change rate threshold; in this embodiment, S... TBD =0.0035.

[0045] Step P28: Determine the first SOC correction value (SOC) based on the SOH value. cav1 Second SOC correction value SOC cav2 Then proceed to step P29. This involves determining the first SOC correction value (SOC) based on the SOH value. cav1 Second SOC correction value SOC cav2 The method is as follows: Query the preset SOC correction value table based on the SOH value to obtain the corresponding first SOC correction value (SOC). cav1 Second SOC correction value SOC cav2 The preset SOC correction value table is a table showing the correspondence between the SOH values obtained through calibration on the test bench and the first and second SOC correction values.

[0046] like Figure 2 As shown, the calibration steps for the preset SOC correction value table include: Step 1: Select n lithium iron phosphate batteries of the same type but with different SOH values, then proceed to step 2. The SOH values of the n lithium iron phosphate batteries are selected based on actual application requirements, and the number of n batteries is also selected based on actual application requirements.

[0047] The second step is to mount the first lithium iron phosphate battery on a test bench at room temperature and slowly charge it from 0% to 100%. The battery voltage is collected during the slow charging process, and the SOC value of the battery is estimated using the ampere-hour integration method. The corresponding curve of the SOC value and voltage of the first lithium iron phosphate battery is obtained, and then the third step is performed.

[0048] The third step is to identify the correlation curve between SOC value and voltage, and extract 101 SOC values with a tolerance of 1% in ascending order: SOC'1 (equal to 0), SOC'2 (equal to 1%), SOC'3 (equal to 2%), ..., SOC' 101 (equal to 100%) and 101 voltages U'1, U'2, U'3, ..., U' corresponding to 101 SOC values with a tolerance of 1%. 101 Then proceed to step four.

[0049] Step 4: Using the formula: S' k-2 =(U' k -U' k-2) / (SOC' k -SOC' k-2 ), calculate the voltage change rate S' k-2 Then, proceed to step five; where k takes all integers from 3 to 101, resulting in a total of 99 voltage change rates, namely S'1, S'2, S'3, ..., S' 99 .

[0050] Step 5: Using the formula: V' m-3 =S' m-2 -S' m-3 Calculate the voltage change rate increment V' m-3 Then proceed to step six; where m takes all integers from 4 to 101, resulting in a total of 98 voltage change rate increments, namely V'1, V'2, V'3, ..., V' 98 .

[0051] Step 6: Identify the SOC correction value and find the value that satisfies: V' h V' h+1 V' h+2 Both are greater than 0, and V' h+3 ≥0, and V' h+4 V' h+5 Both are less than 0, and S' h+4 ≥S TBD (0.0035), and U' h+6 <U TBD A numerical value h; find the value that satisfies: V' t V' t+1 V' t+2 V' t+3 All are greater than or equal to 0, and V' t V' t+1 V' t+2 V' t+3 Two out of the four data points are consecutively greater than 0, and V' t+4 V' t+5 V' t+6 Both are less than 0, and S' t+4 ≥S TBD , and U' t+6 >U TBD A numerical value t; SOC' h+6 (i.e., the (h+6th)th SOC value) is used as the first SOC correction value corresponding to the SOH value of the lithium iron phosphate battery, and SOC' is adjusted accordingly. t+6 (i.e., the (t+6th)th SOC value) is used as the second SOC correction value corresponding to the SOH value of the lithium iron phosphate battery, and then the seventh step is executed; where h and t are integers, and 1≤h≤92, 1≤t≤92, U TBDThis indicates the preset voltage threshold, SOC. TBD This represents the preset SOC threshold; in this embodiment, U TBD =3.34V (i.e., the open-circuit voltage when the battery's SOC is 55% + 0.02V), SOC TBD =20%.

[0052] Step 7: Determine whether n first SOC correction values and n second SOC correction values corresponding to the SOH values of n lithium iron phosphate batteries have been obtained. If so, proceed to step 9; otherwise, proceed to step 8.

[0053] Step 8: At room temperature, place the next lithium iron phosphate battery on the test bench and slowly charge it from 0% to 100%. Collect the battery voltage during the slow charging process, estimate the SOC value of the battery using the ampere-hour integration method, and obtain the corresponding curve of the SOC value and voltage of the lithium iron phosphate battery. Then return to step 3.

[0054] Step 9: Match the SOH values of the n lithium iron phosphate batteries with the n first SOC correction values and n second SOC correction values corresponding to the SOH values of the n lithium iron phosphate batteries to form a preset SOC correction value table.

[0055] Step P29: Determine if U7 < U TBD (3.34V), and the current SOC value of the battery is consistent with the SOC value. cav1 The absolute value of the difference is less than SOC TBD (20%), if so (indicating that SOC correction condition I is met), proceed to step P210; otherwise, proceed to step P211.

[0056] Step P210: Set the current battery SOC value to the first SOC correction value. cav1 (That is, the current SOC value of the battery is corrected to the first SOC correction value) cav1 ), and adjust the first SOC value SOC cav1 Assign to SOC b Set the SOC correction flag to 1, and start recalculating the battery's charge capacity (i.e., cumulative charge capacity), then return to step P22.

[0057] Step P211: Determine if U7 > U TBD And the current SOC value of the battery is related to the SOC cav2 The absolute value of the difference is less than SOC TBD If yes, then (indicating that SOC correction condition II is met) proceed to step P212; otherwise, return to step P22.

[0058] Step P212: Set the current battery SOC value to the second SOC correction value. cav2 (That is, the current SOC value of the battery is corrected to the second SOC correction value) cav2 ), and adjust the second SOC value SOC cav2 Assign to SOC b Set the SOC correction flag to 1, and start recalculating the battery's charge capacity (i.e., cumulative charge capacity), then return to step P22.

[0059] Step P213: Determine if the battery is fully charged. If yes, proceed to step P214; otherwise, proceed to step P215.

[0060] Step P214: Set the battery full charge flag to 1, and then proceed to step P216.

[0061] Step P215: Set the battery full charge flag to 0, and then proceed to step P216.

[0062] Step P216, SOC b The value is stored as the starting SOC for charging, and the battery's charging capacity, SOC correction flag, and battery full charge flag are also stored, then the process ends.

[0063] The SOC estimation system for lithium iron phosphate batteries in this embodiment includes a controller programmed to execute the SOC estimation method for lithium iron phosphate batteries described above.

[0064] The SOH estimation method for the lithium iron phosphate battery in this embodiment is as follows: When the vehicle is powered on, if the SOC correction flag is 1 and the battery full charge flag is 1, then the formula Q = Q is first used. cd Calculate the current total battery capacity Q using (100% - initial SOC), then use the formula: SOH0 = Q / Q rc Estimate the SOH value (SOH0) of the lithium iron phosphate battery. Wherein, Q cd Q represents the battery's charge capacity. rc This indicates the battery's rated capacity. It includes a SOC correction flag, a full charge flag, a starting charge SOC, and the battery's charge capacity Q. cd It was obtained by performing the SOC estimation method for lithium iron phosphate batteries described above.

Claims

1. A method for estimating the state of charge (SOC) of a lithium iron phosphate battery, characterized in that, include: Get the current SOH value of the battery; During the slow charging process of lithium iron phosphate batteries, the current battery voltage is collected, the current SOC value of the battery is estimated using the ampere-hour integration method, and the data is stored. The feature value recognition condition is determined. If the feature value recognition condition is met, the first SOC correction value (SOC) is determined based on the SOH value. cav1 Second SOC correction value SOC cav2 Then, the SOC correction condition is checked; if SOC correction condition I is met, the current battery SOC value is set to the first SOC correction value. cav1 If SOC correction condition II is met, then the current SOC value of the battery is set to the second SOC correction value. cav2 ; The steps for feature value recognition condition judgment include: Step P11: Determine whether the difference between the current SOC value of the battery and SOC0 is greater than or equal to 9%. If yes, proceed to step P12; otherwise, continue to step P11. Here, SOC0 represents the initial SOC value of the stored lithium iron phosphate battery when it starts slow charging. Step P12: Assign the 10 most recently stored SOC values with a tolerance of 1% to SOC1, SOC2, SOC3, ..., SOC in ascending order. 10 The 10 voltages corresponding to the 10 SOC values with a tolerance of 1% from the latest stored values are assigned to U1, U2, U3, ..., U... 10 Then proceed to step P13; Step P13, using the formula: S i-2 =(U i -U i-2 ) / (SOC i -SOC i-2 ), calculate the voltage change rate S i-2 Then execute step P14; where i takes all integers from 3 to 10 in sequence; Step P14, using the formula: V j-3 =S j-2 -S j-3 Calculate the voltage change rate increment V j-3 Then execute step P15; where j takes all integers from 4 to 10 in sequence; Step P15: Determine whether condition 1a or condition 1b is satisfied. If yes, it means the feature value recognition condition is met; otherwise, return to step P11. Condition 1a is: V1, V2, and V3 are all greater than 0, V4 ≥ 0, V5 and V6 are all less than 0, and S5 ≥ S TBD Condition 1b is: V1, V2, V3, and V4 are all greater than or equal to 0, and there are two consecutive values in V1, V2, V3, and V4 that are greater than 0, and V5, V6, and V7 are all less than 0, and S5 ≥ S TBD Among them, S TBD This indicates the preset voltage change rate threshold.

2. The SOC estimation method for lithium iron phosphate batteries according to claim 1, characterized in that: The method for determining SOC correction conditions is as follows: If U7 < U TBD And the current SOC value of the battery is related to the SOC cav1 The absolute value of the difference is less than SOC TBD This indicates that SOC correction condition I is satisfied; If U7 > U TBD And the current SOC value of the battery is related to the SOC cav2 The absolute value of the difference is less than SOC TBD This indicates that SOC correction condition II is satisfied; Among them, U TBD This indicates the preset voltage threshold, SOC. TBD This indicates the preset SOC threshold.

3. The SOC estimation method for lithium iron phosphate batteries according to claim 2, characterized in that: The first SOC correction value (SOC) is determined based on the SOH value. cav1 Second SOC correction value SOC cav2 The method is as follows: Based on the SOH value, query the preset SOC correction value table to obtain the corresponding first SOC correction value (SOC). cav1 Second SOC correction value SOC cav2 The preset SOC correction value table is a table showing the correspondence between the SOH value obtained through calibration on the test bench and the first SOC correction value and the second SOC correction value.

4. The SOC estimation method for lithium iron phosphate batteries according to claim 3, characterized in that: The preset SOC correction value table is obtained by calibration in the following manner: Step 1: Select n lithium iron phosphate batteries of the same type but with different SOH values, and then proceed to step 2; The second step is to mount the first lithium iron phosphate battery on the test bench at room temperature and slowly charge it from 0% to 100%. The voltage of the battery is collected during the slow charging process. The SOC value of the battery is estimated using the ampere-hour integration method. The corresponding curve of the SOC value and voltage of the first lithium iron phosphate battery is obtained. Then, the third step is performed. The third step is to identify the correlation curve between SOC value and voltage, and extract 101 SOC values with a tolerance of 1% in ascending order: SOC'1, SOC'2, SOC'3, ..., SOC' 101 And 101 voltages U'1, U'2, U'3, ..., U' corresponding to 101 SOC values with a tolerance of 1%. 101 Then proceed to step four; Step 4: Using the formula: S' k-2 =(U' k -U' k-2 ) / (SOC' k -SOC' k-2 ), calculate the voltage change rate S' k-2 Then proceed to step five; where k takes all integers from 3 to 101 in sequence; Step 5: Using the formula: V' m-3 =S' m-2 -S' m-3 Calculate the voltage change rate increment V' m-3 Then execute step six; where m takes all integers from 4 to 101 in sequence; Step 6: Identify the SOC correction value and find the value that satisfies: V' h V' h+1 V' h+2 Both are greater than 0, and V' h+3 ≥0, and V' h+4 V' h+5 Both are less than 0, and S' h+4 ≥S TBD , and U' h+6 <U TBD A numerical value h; find the value that satisfies: V' t V' t+1 V' t+2 V' t+3 All are greater than or equal to 0, and V' t V' t+1 V' t+2 V' t+3 There are two consecutive data points that are greater than 0, and V' t+4 V' t+5 V' t+6 Both are less than 0, and S' t+4 ≥S TBD , and U' t+6 >U TBD A numerical value t; SOC' h+6 As the first SOC correction value corresponding to the SOH value of the lithium iron phosphate battery, SOC' t+6 As the second SOC correction value corresponding to the SOH value of the lithium iron phosphate battery, then the seventh step is executed; where h and t are integers, and 1≤h≤92, 1≤t≤92; Step 7: Determine whether n first SOC correction values and n second SOC correction values corresponding to the SOH values of n lithium iron phosphate batteries have been obtained. If so, proceed to step 9; otherwise, proceed to step 8. Step 8: At room temperature, place the next lithium iron phosphate battery on the test bench and slowly charge it from 0% to 100%. Collect the battery voltage during the slow charging process, estimate the SOC value of the battery using the ampere-hour integration method, and obtain the corresponding curve of the SOC value and voltage of the lithium iron phosphate battery. Then return to step 3. Step 9: Assign a one-to-one correspondence between the SOH values of the n lithium iron phosphate batteries and the n first SOC correction values and n second SOC correction values corresponding to the SOH values of the n lithium iron phosphate batteries, to form the preset SOC correction value table.

5. The SOC estimation method for lithium iron phosphate batteries according to any one of claims 2 to 4, characterized in that: The preset voltage change rate threshold S TBD The value range is 0.002~0.005; the preset SOC threshold is... TBD The value range is 18%~22%; the preset voltage threshold U TBD The range of values for U is: OCV1 +0.01V~ U OCV2 +0.03V; where U OCV1 U represents the open-circuit voltage when the battery's SOC is 50%. OCV2 This indicates the open-circuit voltage when the battery's SOC value is 60%.

6. The SOC estimation method for lithium iron phosphate batteries according to any one of claims 1 to 3, characterized in that: The charging current range for slow charging of lithium iron phosphate batteries is 0.1C~0.3C, and the ambient temperature is 23℃~30℃.

7. The SOC estimation method for lithium iron phosphate batteries according to claim 6, characterized in that: When SOC correction condition I is met, the first SOC correction value SOC is adjusted. cav1 Assign to SOC b Set the SOC correction flag to 1 and restart the calculation of the battery's charging capacity; when SOC correction condition II is met, set the second SOC correction value to SOC. cav2 Assign to SOC b Set the SOC correction flag to 1 and recalculate the battery's charging capacity; when the battery is fully charged, set the battery full charge flag to 1. When the vehicle is powered off, the SOC b The value is stored as the starting SOC for charging, and the battery's charging capacity, SOC correction flag, and battery full charge flag are also stored.

8. A SOC estimation system for lithium iron phosphate batteries, comprising a controller, characterized in that: The controller is programmed to perform the SOC estimation method as described in any one of claims 1 to 7.

9. A method for estimating the state of matter (SOH) of a lithium iron phosphate battery, characterized in that: When the vehicle is powered on, if the SOC correction flag is 1 and the battery full charge flag is 1, then first use the formula: Q=Q cd Calculate the current total battery capacity Q using (100% - initial SOC), then use the formula: SOH0 = Q / Q rc Estimate the SOH value (SOH0) of the lithium iron phosphate battery; where Q cd Q represents the battery's charge capacity. rc Indicates the battery's rated capacity; SOC correction flag, battery full charge flag, initial charging SOC, and battery charging capacity Q. cd It is obtained by performing the SOC estimation method as described in claim 7.