Battery capacity calculation method, ocv curve correction method, device, medium and product

Abstract

This application provides a battery capacity calculation method, an OCV curve correction method, equipment, medium, and product, belonging to the field of battery technology. The method includes: determining the intermediate inflection point of a lithium iron phosphate battery; obtaining the absolute value of capacity change in a first interval during the current charge / discharge period of the lithium iron phosphate battery, where the first interval is the stage between the intermediate inflection point and full charge; based on the absolute value of capacity change in the first interval, determining whether it is necessary to correct the initial absolute value of capacity change in a second interval during the initial charge / discharge period of the lithium iron phosphate battery, and based on the determination result, determining the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery, where the second interval is the stage between the intermediate inflection point and full discharge; and determining the sum of the absolute values ​​of capacity change in the first and second intervals during the current charge / discharge period of the lithium iron phosphate battery as the capacity of the lithium iron phosphate battery. This application can accurately quantify the health status of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery capacity calculation method, an OCV curve correction method, equipment, medium, and product. Background Technology

[0002] Energy conservation and emission reduction are key to the sustainable development of the automotive industry, and electric vehicles, due to their energy-saving and environmentally friendly advantages, have become an important component of this sustainable development. For electric vehicles, battery technology is a crucial factor in their development.

[0003] State of Health (SOH) correction accurately quantifies battery health by dynamically updating parameters related to capacity decay and internal resistance changes. For example, due to the material characteristics of lithium iron phosphate batteries, their voltage-capacity curves exhibit a shortening plateau and a shift in voltage transition points as SOH decreases. After correction, the Battery Management System (BMS) can adjust charging and discharging strategies based on the corrected curve, such as lowering the cutoff voltage to avoid deep discharge or optimizing equalization strategies to reduce capacity loss. Furthermore, SOH correction improves the accuracy of State of Charge (SOC) estimation, avoiding range display deviations caused by model aging and ensuring safe battery operation. However, current inaccurate battery capacity estimations prevent more precise quantification of battery health. Summary of the Invention

[0004] This application aims to at least address one of the technical problems existing in the background art. Therefore, one objective of this application is to provide a battery capacity calculation method, an OCV curve correction method, an apparatus, a medium, and a product to improve the accuracy of quantifying battery health status.

[0005] An embodiment of the first aspect of this application provides a battery capacity calculation method applied to lithium iron phosphate batteries. The method includes: determining the intermediate inflection point of the lithium iron phosphate battery, wherein the intermediate inflection point is the critical point connecting the low voltage platform when switching between the low voltage platform and the high voltage platform during the charging / discharging period of the lithium iron phosphate battery; obtaining the absolute value of the capacity change in a first interval during the current charging / discharging period of the lithium iron phosphate battery, wherein the first interval is the stage between the intermediate inflection point and full charge of the lithium iron phosphate battery; based on the absolute value of the capacity change in the first interval, determining whether it is necessary to correct the absolute value of the initial capacity change in a second interval during the initial charging / discharging period of the lithium iron phosphate battery, and determining, based on the determination result, that the absolute value of the capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery is the absolute value of the initial capacity change in the second interval or the value after correction of the absolute value of the initial capacity change in the second interval, wherein the second interval is the stage between the intermediate inflection point and full discharge of the lithium iron phosphate battery; and determining that the sum of the absolute values ​​of the capacity change in the first interval and the absolute values ​​of the capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery is the capacity of the lithium iron phosphate battery.

[0006] In the technical solution of this application embodiment, the full capacity change range of the lithium iron phosphate battery during charging / discharging is divided into a first range and a second range by utilizing the intermediate inflection point. As the lithium iron phosphate battery ages to a certain extent, it experiences loss of active lithium, resulting in a significant capacity change loss in the high SOC first range, while the capacity change in the low SOC second range shows almost no loss. When the capacity change loss in the first range reaches a certain level, it indicates a significant degree of aging of the lithium iron phosphate battery, at which point a capacity change loss will occur in the low SOC second range. Based on this, this application embodiment obtains the absolute value of the capacity change in the first range to determine whether the initial absolute value of the capacity change in the second range needs to be corrected, thereby determining the absolute value of the capacity change in the second range during the current charging / discharging period of the lithium iron phosphate battery, and thus obtaining the full capacity change during the charging / discharging period of the lithium iron phosphate battery, i.e., the capacity of the lithium iron phosphate battery. This method of estimating the capacity of lithium iron phosphate batteries only requires detecting the absolute value of the capacity change in the first interval during the current charge / discharge period. The absolute value of the capacity change in the second interval can be obtained by directly using the initial absolute value of the capacity change in the second interval or by correcting it. This allows the lithium iron phosphate battery to be fully charged without being fully discharged, which is suitable for situations where lithium iron phosphate batteries are more likely to be fully charged than fully discharged in actual applications. Therefore, the method of this application embodiment can increase the frequency of updating the capacity of lithium iron phosphate batteries, thereby accurately quantifying the health status of the battery.

[0007] In some embodiments, obtaining the absolute value of the capacity change in a first interval during the current charge / discharge period of the lithium iron phosphate battery includes: obtaining a first moment when the lithium iron phosphate battery is at the midpoint of the current charge / discharge period and a second moment when it is fully charged; obtaining the real-time current of the lithium iron phosphate battery between the first moment and the second moment; and obtaining the integral of the real-time current over time between the first moment and the second moment based on the ampere-hour integration method, with the integral result serving as the absolute value of the capacity change in the first interval. Using the ampere-hour integration method to detect the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery enables real-time dynamic monitoring of the actual capacity change of the lithium iron phosphate battery in the first interval, thereby improving the accuracy of the calculation of the lithium iron phosphate capacity.

[0008] In some embodiments, the method for determining the absolute value of capacity change in a second interval during the current charge / discharge period of a lithium iron phosphate battery includes: obtaining the OCV curve of the lithium iron phosphate battery at the time of manufacture, wherein the OCV curve is used to characterize the change in static voltage of the lithium iron phosphate battery with capacity; based on the OCV curve, obtaining the absolute value of capacity change in a first interval as a first initial absolute value of capacity change, and obtaining the absolute value of capacity change in a second interval as a second initial absolute value of capacity change; obtaining the degree of deviation of the absolute value of capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery relative to the first initial absolute value of capacity change; and determining the second initial absolute value of capacity change as the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery in response to the deviation degree not reaching a preset deviation degree. When the degree of deviation of capacity change in the first interval at high SOC relative to the first initial value of capacity change is small, it indicates that the lithium iron phosphate battery is less aged. In this case, the capacity of the second interval can be directly obtained by looking up the OCV curve at the time of manufacture, simplifying the steps.

[0009] In some embodiments, the method for determining the absolute value of capacity change in a second interval during the current charge / discharge period of the lithium iron phosphate battery further includes: correcting a second initial absolute value of capacity change in response to a deviation reaching a preset deviation level, to obtain the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery. When the deviation of the absolute value of capacity change in the first interval from the first initial capacity change insulation value reaches a preset deviation level, it indicates that the lithium iron phosphate battery is severely aged. At this time, the absolute value of capacity change in the second interval may also have changed due to aging. Therefore, it is necessary to correct the second initial absolute value of capacity change to improve the accuracy of correcting the remaining total capacity of the lithium iron phosphate battery.

[0010] In some embodiments, correcting the second initial absolute value of capacity change to obtain the absolute value of capacity change in a second interval during the current charge / discharge period of the lithium iron phosphate battery includes: obtaining the difference between the absolute value of capacity change in a first interval during the current charge / discharge period of the lithium iron phosphate battery and the first initial absolute value of capacity change as a first change value; obtaining a correction coefficient; obtaining a second change value based on the first change value and the correction coefficient, the second change value being the difference between the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery and the second initial absolute value of capacity change; and determining the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery based on the second change value and the second initial absolute value of capacity change. When the battery is severely aged, the first change value and the second change value have a fixed proportional relationship. After obtaining the first change value, using the correction coefficient as this proportional relationship, the second change value of the absolute value of capacity change in the second interval relative to the second initial absolute value of capacity change can be obtained based on the first change value. When the second initial absolute value of capacity change is known, the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery can be determined.

[0011] In some embodiments, obtaining the correction coefficient includes: obtaining historical charge / discharge information of the lithium iron phosphate battery; obtaining a complete charge / discharge curve of the lithium iron phosphate battery based on the historical charge / discharge information, wherein the complete charge / discharge curve is used to characterize the voltage change with capacity during the period from full discharge to full charge / full charge to full discharge of the lithium iron phosphate battery; obtaining the absolute value of capacity change in a first interval as a first historical absolute value of capacity change based on the complete charge / discharge curve, obtaining the absolute value of capacity change in a second interval as a second historical absolute value of capacity change; obtaining the difference between the absolute value of capacity change in the first historical interval and the absolute value of capacity change in the first initial interval as a third change value; obtaining the difference between the absolute value of capacity change in the second historical interval and the absolute value of capacity change in the second initial interval as a fourth change value; and obtaining the ratio of the fourth change value to the third change value as a correction coefficient. By tracing historical charge / discharge information and finding a complete charge / discharge curve, a fixed proportional relationship is obtained from the previous complete charge / discharge curve as a correction coefficient, making the obtained correction coefficient closer to the actual ratio of the first change value and the second change value, thereby improving the accuracy of the calculated capacity of the lithium iron phosphate battery.

[0012] In some embodiments, determining the intermediate inflection point of a lithium iron phosphate battery includes: acquiring the OCV curve of the lithium iron phosphate battery at the time of manufacture, whereby the OCV curve characterizes the change in the static voltage of the lithium iron phosphate battery with capacity; and determining the intermediate inflection point based on the OCV curve. By finding the intermediate inflection point in the OCV curve at the time of manufacture, the voltage corresponding to the intermediate inflection point can be obtained. During the current charging / discharging process, only the battery voltage needs to be monitored to detect the corresponding intermediate inflection point, simplifying the method of obtaining the intermediate inflection point.

[0013] In some embodiments, determining the intermediate inflection point of a lithium iron phosphate battery includes: performing charge / discharge tests on the lithium iron phosphate battery at different charge / discharge rates to obtain a reference charge / discharge curve, which characterizes the voltage change of the lithium iron phosphate battery with capacity; and determining the intermediate inflection point based on the reference charge / discharge curve. Pre-testing the lithium iron phosphate battery at different rates to obtain the intermediate inflection point improves the accuracy of the obtained intermediate inflection point.

[0014] An embodiment of the second aspect of this application provides a method for correcting the OCV curve of a lithium iron phosphate battery, comprising: obtaining the capacity of the lithium iron phosphate battery using the battery capacity calculation method described in the above embodiments; obtaining the current state of charge (SOH) of the lithium iron phosphate battery based on its capacity and rated capacity; and correcting the OCV curve based on the current SOH of the lithium iron phosphate battery. The correction method described in the above embodiments can dynamically update the SOH of the lithium iron phosphate battery, improving the accuracy of SOH correction. Thus, when dynamically correcting the OCV curve based on the corrected current SOH, the accuracy of OCV curve correction can be improved, which is beneficial for accurately determining the remaining capacity of the battery and mitigating problems such as overcharging, over-discharging, and accelerated aging of the lithium iron phosphate battery due to misjudgment of the remaining capacity.

[0015] An embodiment of the third aspect of this application provides a computing device comprising: at least one processor; and at least one memory communicatively connected to the at least one processor, the at least one memory storing instructions which, when executed individually or jointly by the at least one processor, cause the computing device to perform the battery capacity calculation method or the battery OCV curve correction method described in the above embodiments.

[0016] An embodiment of the fourth aspect of this application provides a computer-readable storage medium storing instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform the battery capacity calculation method or the battery OCV curve correction method described in the above embodiments.

[0017] An embodiment of the fifth aspect of this application provides a computer program product including instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform the battery capacity calculation method or the battery OCV curve correction method described in the above embodiments.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0019] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0020] Figure 1 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0021] Figure 2 This is a flowchart of a battery capacity calculation method according to some embodiments of this application;

[0022] Figure 3 Capacity-voltage curves of lithium iron phosphate batteries during the charging process of some embodiments of this application;

[0023] Figure 4 A schematic diagram of the aging mechanism of lithium iron phosphate-graphite batteries;

[0024] Figure 5 This is a flowchart of a battery OCV curve correction method according to some embodiments of this application;

[0025] Figure 6 This is one of the schematic diagrams of the original OCV curve and the corrected OCV curve of the lithium iron phosphate battery according to some embodiments of this application;

[0026] Figure 7 This is the second schematic diagram of the original OCV curve and the corrected OCV curve of the lithium iron phosphate battery in some embodiments of this application;

[0027] Figure 8 This is the third schematic diagram of the original OCV curve and the corrected OCV curve of the lithium iron phosphate battery of some embodiments of this application;

[0028] Figure 9 This is the fourth schematic diagram of the original OCV curve and the corrected OCV curve of the lithium iron phosphate battery in some embodiments of this application;

[0029] Figure 10 This is the fifth of several schematic diagrams showing the original OCV curves and corrected OCV curves of lithium iron phosphate batteries according to some embodiments of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1000 vehicles;

[0032] Battery 100, controller 200, motor 300;

[0033] The intermediate inflection point is O, the first inflection point is P, and the second inflection point is Q. Detailed Implementation

[0034] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0036] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0037] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0038] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0039] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0040] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the system or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0041] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0042] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used as energy storage modules in hydropower, thermal power, wind power, and solar power plants, but also widely applied in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0043] Correcting the State of Health (SOH) curve of the capacity-voltage profile is crucial during battery use. The capacity-voltage profile describes the change in battery terminal voltage as a function of stored charge; its shape is significantly affected by temperature, charge / discharge rate, and cycle life. As batteries age, increased loss of active lithium and increased internal resistance alter the capacity-voltage profile. Failure to correct the capacity-voltage profile based on the current SOH may lead to misjudgment of the battery's remaining capacity in the battery management system (BMS), resulting in overcharging and over-discharging, and accelerating battery aging.

[0044] For example, due to the material characteristics of lithium iron phosphate batteries, their voltage-capacity curves exhibit a shortening plateau and a shift in voltage transition points as the State of Charge (SOH) decreases. After correction, the Battery Management System (BMS) can adjust charging and discharging strategies based on the corrected curve, such as lowering the cutoff voltage to avoid deep discharge or optimizing balancing strategies to reduce capacity loss. Furthermore, SOH correction can improve the accuracy of SOC (State of Charge) estimation, avoid range display deviations caused by model aging, and ensure safe battery operation.

[0045] When obtaining the current State of Health (SOH) of a lithium iron phosphate (LFP) battery, it is necessary to first calculate the battery's current capacity, i.e., to obtain the full capacity change during the current charging or discharging process. However, currently, accurate capacity correction for LFP batteries requires fully charging and discharging them, but LFP batteries rarely have the opportunity to be fully discharged, spending most of their time in the high SOC range. Therefore, the current method cannot update the capacity of LFP batteries frequently, and thus cannot accurately quantify the battery's health status.

[0046] Based on the above considerations, a battery capacity calculation method is designed and applied to lithium iron phosphate batteries. The method includes: determining the intermediate inflection point of the lithium iron phosphate battery, which is the critical point connecting the low voltage platform during the switching between the low voltage platform and the high voltage platform during the charging / discharging period of the lithium iron phosphate battery; obtaining the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery, where the first interval is the stage between the intermediate inflection point and full charge; based on the absolute value of the capacity change in the first interval, determining whether it is necessary to correct the absolute value of the initial capacity change in the second interval during the initial charging / discharging period of the lithium iron phosphate battery, and determining, based on the judgment result, that the absolute value of the capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery is the absolute value of the initial capacity change in the second interval or the value after correction of the absolute value of the initial capacity change in the second interval, where the second interval is the stage between the intermediate inflection point and full discharge of the lithium iron phosphate battery; and determining that the sum of the absolute values ​​of the capacity change in the first interval and the absolute values ​​of the capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery is the capacity of the lithium iron phosphate battery.

[0047] In this embodiment, the full capacity change range of the lithium iron phosphate battery during charging / discharging is divided into a first range and a second range using an intermediate inflection point. As the lithium iron phosphate battery ages to a certain extent, it experiences active lithium loss, resulting in a significant capacity loss in the high SOC first range, while the capacity change in the low SOC second range shows almost no loss. When the capacity change in the first range reaches a certain level, it indicates a significant degree of aging of the lithium iron phosphate battery, at which point a capacity loss will occur in the low SOC second range. Based on this, this embodiment obtains the absolute value of the capacity change in the first range to determine whether the initial absolute value of the capacity change in the second range needs to be corrected, thereby determining the absolute value of the capacity change in the second range during the current charging / discharging period of the lithium iron phosphate battery, and thus obtaining the full capacity change during charging / discharging, i.e., the capacity of the lithium iron phosphate battery. This method of estimating the capacity of lithium iron phosphate batteries only requires detecting the absolute value of the capacity change in the first interval during the current charge / discharge period. The absolute value of the capacity change in the second interval can be obtained by directly using the initial absolute value of the capacity change in the second interval or by correcting it. This allows the lithium iron phosphate battery to be fully charged without being fully discharged, which is suitable for situations where lithium iron phosphate batteries are more likely to be fully charged than fully discharged in actual applications. Therefore, the method of this application embodiment can increase the frequency of updating the capacity of lithium iron phosphate batteries, thereby accurately quantifying the health status of the battery.

[0048] The lithium iron phosphate batteries disclosed in this application can be used, but are not limited to, in electrical systems for vehicles, ships, or aircraft. Power modules comprising such electrical systems can be constructed using lithium iron phosphate batteries disclosed in this application.

[0049] This application provides an electrical system that uses lithium iron phosphate batteries as a power source. The electrical system can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0050] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical system according to an embodiment of this application.

[0051] Please refer to Figure 1 , Figure 1This is a schematic diagram of the structure of a vehicle provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0052] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0053] This application provides a battery capacity calculation method 400, applied to lithium iron phosphate batteries, for reference. Figure 2 The methods include:

[0054] Step 410: Determine the intermediate inflection point of the lithium iron phosphate battery. The intermediate inflection point is the critical point at which the lithium iron phosphate battery connects to the low voltage platform when switching between the low voltage platform and the high voltage platform during charging / discharging.

[0055] Step 420: Obtain the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery. The first interval is the stage between the lithium iron phosphate battery being at the middle inflection point and being fully charged.

[0056] Step 430: Based on the absolute value of the capacity change in the first interval, determine whether it is necessary to correct the absolute value of the initial capacity change in the second interval during the initial charge / discharge period of the lithium iron phosphate battery, and based on the judgment result, determine that the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery is the absolute value of the initial capacity change in the second interval or the value after correcting the absolute value of the initial capacity change in the second interval. The second interval is the stage between the intermediate inflection point and full discharge of the lithium iron phosphate battery.

[0057] Step 440: Determine the capacity of the lithium iron phosphate battery as the sum of the absolute values ​​of the capacity changes in the first interval and the second interval during the current charge / discharge period.

[0058] The positive electrode of a lithium iron phosphate battery is lithium iron phosphate, and the negative electrode can be graphite.

[0059] A voltage plateau refers to the stage during which the battery voltage remains within a relatively stable range for an extended period, without significant fluctuations due to capacity changes, during charging / discharging. Lithium iron phosphate batteries exhibit two relatively stable voltage plateaus and a high voltage plateau during charging / discharging. The voltage of the low voltage plateau is lower than that of the high voltage plateau. The area between the low and high voltage plateaus is the voltage transition region, an intermediate process where the voltage fluctuates rapidly with capacity changes. The inflection point is the boundary between the voltage transition region and the low voltage plateau, i.e., the critical point where the low and high voltage plates connect. In this embodiment, charging / discharging refers to either charging or discharging.

[0060] During the charging / discharging process of lithium iron phosphate batteries, in addition to the intermediate inflection point, there are two other inflection points, namely the first inflection point and the second inflection point. The intermediate inflection point is located between the first and second inflection points. The first inflection point is located at the beginning of the low voltage platform, and the second inflection point is located at the end of the high voltage platform.

[0061] For example, such as Figure 3 As shown, Figure 3 As an example, the capacity-voltage curve during the charging process of a lithium iron phosphate battery is illustrated. Figure 3 During the initial charging process, as the capacity of the lithium iron phosphate battery increases, the voltage rises relatively rapidly. When the battery capacity reaches approximately 20% SOC, it reaches the first inflection point P, entering a low-voltage plateau. Around 60% SOC, the low-voltage plateau ends, reaching the intermediate inflection point O and entering the voltage transition region. In this transition region, the battery voltage exhibits a relatively rapid growth trend until it enters a high-voltage plateau. Around 80% SOC, the high-voltage plateau ends, reaching the second inflection point Q.

[0062] The discharge trend of lithium iron phosphate (LFP) batteries is opposite to that of charging, but it also exhibits a first inflection point, a second inflection point, an intermediate inflection point, a low-voltage plateau, and a high-voltage plateau. At the beginning of discharge, as the LFP battery capacity decreases, the voltage drops rapidly. After a period of time, it reaches the second inflection point, where the voltage transitions from a rapid decline to a stable high-voltage plateau. Around 60% SOC, the LFP battery enters a voltage transition region, where the voltage exhibits a relatively rapid decline. After the voltage transition region ends, the voltage returns to a stable state, entering a low-voltage plateau. The boundary between the voltage transition region and the low-voltage plateau is the intermediate inflection point. After the low-voltage plateau ends, the LFP battery voltage transitions from stable to a rapid decline; the critical point of this transition is the first inflection point.

[0063] It is understandable that a high-voltage plateau corresponds to a higher SOC range for lithium iron phosphate batteries, while a low-voltage plateau corresponds to a lower SOC range. Therefore, by determining the intermediate inflection point, the full capacity variation range of lithium iron phosphate batteries during charging / discharging is divided into a high SOC range and a low SOC range.

[0064] In step 420, "full charge" refers to charging the lithium iron phosphate battery to its set maximum usable capacity limit. In some embodiments, the BMS is configured with a cutoff condition to control charging to full charge, such as a charging cutoff voltage. When the BMS detects that the voltage of the lithium iron phosphate battery has reached the charging cutoff voltage, it considers that the lithium iron phosphate battery has been charged to its maximum usable capacity limit, and then cuts off the charging circuit to the lithium iron phosphate battery.

[0065] The current charge / discharge period of a lithium iron phosphate battery refers to the ongoing charging or discharging period during actual use. The BMS records the voltage, current, and time during each charge / discharge process of the lithium iron phosphate battery.

[0066] like Figure 3 As shown, the high-voltage plateau lies between the intermediate inflection point O and full charge; therefore, the first interval corresponds to the high SOC interval. During the current charging period of the lithium iron phosphate battery, the absolute value of the capacity change in the first interval is the capacity increase from the intermediate inflection point O to full charge. During the current discharging period of the lithium iron phosphate battery, the absolute value of the capacity change in the first interval is the capacity decrease from full charge to the intermediate inflection point.

[0067] The absolute value of the capacity change in the first interval was obtained through actual testing.

[0068] In step 430, full discharge means discharging the lithium iron phosphate battery to its set minimum usable capacity. In some embodiments, the BMS is configured with a cutoff condition to control charging to full discharge, such as a discharge cutoff voltage. When the BMS detects that the voltage of the lithium iron phosphate battery has reached the discharge cutoff voltage, it considers that the lithium iron phosphate battery has been discharged to its minimum usable capacity and thus stops discharging the lithium iron phosphate battery.

[0069] like Figure 3 As shown, the low-voltage plateau lies between the intermediate inflection point O and full discharge; therefore, the second interval corresponds to the low SOC interval. During the current charging period of the lithium iron phosphate battery, the absolute value of the capacity change in the second interval is the capacity increase from full discharge to the intermediate inflection point O. During the current discharging period of the lithium iron phosphate battery, the absolute value of the capacity change in the second interval is the capacity decrease from the intermediate inflection point to full discharge.

[0070] In step 430, each lithium iron phosphate battery has an OCV curve at the time of manufacture. The OCV curve is used to characterize the change in the static voltage of the lithium iron phosphate battery with capacity. The charge / discharge curve corresponding to the initial charge / discharge of the lithium iron phosphate battery can be the OCV curve at the time of manufacture. The absolute values ​​of the capacity change in the first interval and the second interval are obtained from the OCV curve at the time of manufacture, which are the absolute values ​​of the initial capacity change in the first interval and the second interval, respectively.

[0071] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the aging mechanism of lithium iron phosphate-graphite batteries. Figure 4 The left side shows the capacity-voltage curve of a lithium iron phosphate-graphite battery before aging, while the right side shows the capacity-voltage curve after aging. The voltage of a lithium iron phosphate-graphite battery is equal to the positive electrode voltage minus the negative electrode voltage. Therefore, the capacity-voltage curve of a lithium iron phosphate-graphite battery is obtained by subtracting the capacity-voltage intersection of the capacity-voltage curves of lithium iron phosphate (the positive electrode) and graphite (the negative electrode). Figure 4 In the diagram, the single-dotted line represents the capacity-voltage curve of lithium iron phosphate, the solid line represents the capacity-voltage curve of graphite before aging, the single-dotted dashed line represents the capacity-voltage curve of graphite after aging, and the double-dotted line represents the capacity-voltage curve of a lithium iron phosphate-graphite battery. (Reference) Figure 4 On the right, when lithium iron phosphate-graphite batteries age, they lose active lithium, and the capacity-voltage curve of graphite shifts to the right to the dotted line. This results in a shortening of the high SOC range in the final capacity-voltage curve of the lithium iron phosphate-graphite battery, that is, a shortening of the high voltage plateau. Consequently, the capacity change loss in the first range is relatively large, while there is no effect on the low SOC range, that is, the second range.

[0072] It is evident that as lithium iron phosphate (LFP) batteries age to a certain extent, they experience active lithium loss, resulting in significant capacity loss in the high SOC range, while the capacity loss in the low SOC range is negligible. In other words, as the aging of LFP batteries increases, the deviation of the absolute value of the capacity change in the first range during the current charge / discharge period from the initial absolute value of the capacity change in the first range of the OCV curve increases. However, when the aging of the LFP battery is not significant, the absolute value of the capacity change in the second range during the current charge / discharge period changes very little from the initial absolute value of the capacity change in the second range, and can be considered unchanged. Therefore, it is only necessary to detect the absolute value of the capacity change in the first range (high SOC) during the current charge / discharge period, without needing to detect the absolute value of the capacity change in the second range (low SOC). When the absolute value of the capacity change in the first interval during the current charge / discharge period of a lithium iron phosphate battery is too large relative to the absolute value of the initial capacity change in the first interval, it can be considered that the lithium iron phosphate battery is too aged. In this case, it is considered that the absolute value of the capacity change in the second interval at low SOC has deviated from the second initial absolute value of the capacity change. Therefore, it is necessary to correct the second initial absolute value of the capacity change to determine the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

[0073] In step 440, the first interval and the second interval are actually divisions between the stages of full charge and full discharge of the battery. Therefore, during the current charging period of the lithium iron phosphate battery, the absolute values ​​of the capacity change in the first interval and the absolute values ​​of the capacity change in the second interval represent the total capacity change from full charge to full discharge, and this total capacity change represents the capacity of the lithium iron phosphate battery. During the current discharging period of the lithium iron phosphate battery, the absolute values ​​of the capacity change in the first interval and the absolute values ​​of the capacity change in the second interval represent the total capacity change from full charge to full discharge, and this total capacity change represents the capacity of the lithium iron phosphate battery.

[0074] The actual capacity of a lithium iron phosphate battery at its current aging level is obtained by summing the absolute values ​​of capacity changes in the first and second intervals during the current charge / discharge period. Dividing the actual capacity at the current aging level by the rated capacity yields the current state of equilibrium (SOH) of the lithium iron phosphate battery. Rated capacity refers to the maximum amount of electricity a lithium iron phosphate battery can discharge under standard conditions (specific temperature, discharge rate, and cutoff voltage). It is a benchmark value for measuring the energy storage capacity of a lithium iron phosphate battery, and the unit is usually ampere-hour (Ah) or watt-hour (Wh, Wh = Ah × voltage).

[0075] In the above technical solution, the full capacity change range of the lithium iron phosphate battery during charging / discharging is divided into a first interval and a second interval by utilizing the intermediate inflection point. By obtaining the absolute value of the capacity change in the first interval, it is determined whether the initial absolute value of the capacity change in the second interval needs to be corrected, thus determining the absolute value of the capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery. This allows for the full capacity change during charging / discharging, i.e., the capacity of the lithium iron phosphate battery. This method of estimating the capacity of the lithium iron phosphate battery ensures that it only needs to be fully charged and not fully discharged. It is suitable for situations where lithium iron phosphate batteries are more likely to be fully charged in practical applications than fully discharged. Therefore, the method in this embodiment can increase the frequency of updating the capacity of the lithium iron phosphate battery, thereby accurately quantifying the battery's health status.

[0076] According to some embodiments of this application, step 420 includes:

[0077] Acquire the first moment when the lithium iron phosphate battery is at the midpoint of the current charge / discharge cycle and the second moment when it is fully charged;

[0078] Obtain the real-time current of the lithium iron phosphate battery between the first and second time points;

[0079] The real-time current integral over time between the first and second moments is obtained using the ampere-hour integration method, and the integral result is used as the absolute value of the capacity change in the first interval.

[0080] The Battery Management System (BMS) continuously collects voltage, current, and time data during each charge / discharge cycle of the lithium iron phosphate (LFP) battery, plotting these data as voltage-time and current-time curves. The BMS analyzes these voltage-time curves using a pre-defined algorithm, revealing the voltage change over time during charging / discharging. The determination of the intermediate inflection point is related to the voltage change of the LFP battery; therefore, the BMS can identify the step inflection points between high and low voltage plateaus in the voltage-time curve, thus identifying the intermediate inflection point and obtaining the first moment corresponding to it. When the BMS detects that the LFP battery voltage reaches the discharge cutoff voltage, it considers the battery fully charged, thus obtaining the second moment corresponding to full charge.

[0081] Based on the detected first and second moments, the BMS can integrate the real-time current between the first and second moments with respect to time in its recorded current-time curve to obtain the absolute value of the capacity change in the first interval.

[0082] In the above technical solution, the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery is detected by the ampere-hour integration method. This enables real-time dynamic monitoring of the actual capacity change of the lithium iron phosphate battery in the first interval, thereby improving the accuracy of the calculation of the lithium iron phosphate capacity.

[0083] According to some embodiments of this application, step 430 includes:

[0084] Obtain the OCV curve of the lithium iron phosphate battery at the time of manufacture. The OCV curve is used to characterize the change of the static voltage of the lithium iron phosphate battery with capacity.

[0085] Based on the OCV curve, the absolute value of capacity change in the first interval is obtained as the first initial absolute value of capacity change, and the absolute value of capacity change in the second interval is obtained as the second initial absolute value of capacity change.

[0086] Obtain the degree of deviation of the absolute value of capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery from the absolute value of the first initial capacity change;

[0087] In response to the deviation level not reaching the preset deviation level, the absolute value of the second initial capacity change is determined to be the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

[0088] The OCV curve of a lithium iron phosphate (LFP) battery at the time of manufacture includes both the discharge OCV curve during discharging and the charging OCV curve during charging. At the time of manufacture, LFP batteries undergo offline calibration testing, simultaneously acquiring both the charging and discharging OCV curves, which together form the battery's capacity-voltage characteristic benchmark. From the factory-manufactured OCV curve, the high-voltage plateau, low-voltage plateau, and intermediate inflection point are identified, determining the first and second intervals. The first initial absolute value of capacity change can be the capacity corresponding to a full charge on the OCV curve minus the capacity corresponding to the intermediate inflection point. The second initial absolute value of capacity change can be the capacity corresponding to the intermediate inflection point on the OCV curve. It is worth noting that for the charging and discharging processes of LFP batteries, the corresponding first and second initial absolute values ​​of capacity change can be obtained from the charging and discharging OCV curves, respectively.

[0089] The preset deviation level can be used to characterize the minimum deviation of the absolute value of capacity change in the second interval relative to the second initial absolute value of capacity change as the lithium iron phosphate battery ages. The preset deviation level can be an empirical value. The algorithm for the preset deviation level is consistent with the deviation level of the absolute value of capacity change in the first interval relative to the first initial absolute value of capacity change during the current charge / discharge period of the lithium iron phosphate battery.

[0090] In some embodiments, the degree of deviation of the absolute value of capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery relative to the absolute value of the first initial capacity change can be represented by the ratio of the absolute value of capacity change in the first interval during the current charge / discharge period to the absolute value of the first initial capacity change. For example, the degree of deviation during charging is obtained by dividing the absolute value of capacity change in the first interval during the current charging period of the lithium iron phosphate battery by the absolute value of the first initial capacity change in the charging OCV curve, and the degree of deviation during discharging is obtained by dividing the absolute value of capacity change in the first interval during the current discharging period of the lithium iron phosphate battery by the absolute value of the first initial capacity change in the discharging OCV curve.

[0091] In other embodiments, the sum of the absolute value of the capacity change in the first interval during the current charge / discharge period and the second initial capacity change value can be obtained first to preliminarily determine the current capacity of the lithium iron phosphate battery. This capacity value is denoted as the reference capacity value. Dividing the reference capacity value by the rated capacity of the lithium iron phosphate battery yields the reference SOH, which represents the degree of deviation of the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery relative to the absolute value of the first initial capacity change. The preset deviation degree is the preset SOH. For example, the preset SOH is 90%. That is, if the reference SOH is less than 90%, the deviation degree has not reached the preset deviation degree; if the reference SOH is greater than or equal to 90%, the deviation degree has reached the preset deviation degree. It can be understood that in the process of obtaining the reference SOH, the second initial capacity change value and the rated capacity are quantitative, and only the absolute value of the capacity change in the first interval during the current charge / discharge period is variable. Therefore, the reference SOH can characterize the degree of deviation of the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery relative to the absolute value of the first initial capacity change.

[0092] In the above technical solution, when the deviation of the capacity in the first high SOC range from the first initial capacity change value is small, it indicates that the lithium iron phosphate is less aged. At this time, the capacity in the second range can be obtained directly from the OCV curve at the time of battery delivery, simplifying the process.

[0093] According to some embodiments of this application, step 430 further includes:

[0094] In response to the deviation reaching a preset deviation level, the absolute value of the second initial capacity change is corrected to obtain the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

[0095] When the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery deviates from the first initial absolute value of the capacity change to a preset deviation level, it indicates that the lithium iron phosphate battery is severely aged at this time. The absolute value of the capacity change in the second interval at low SOC also deviates significantly, thus requiring correction of the second initial absolute value of the capacity change to obtain the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

[0096] In some embodiments, the absolute value of the second initial capacity change can be corrected based on experience. For example, the correlation between the absolute value of the second initial capacity change in previous charge / discharge cycles and the actual absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery can be summarized based on experience, and then the absolute value of the second initial capacity change can be corrected based on the obtained correlation.

[0097] In the above technical solution, when the absolute value of the capacity change in the first interval deviates from the first initial capacity change insulation value to a preset deviation level, it indicates that the lithium iron phosphate battery is severely aged. At this time, the absolute value of the capacity change in the second interval may also change due to the aging. Therefore, it is necessary to correct the absolute value of the second initial capacity change to improve the accuracy of correcting the remaining total capacity of the lithium iron phosphate battery.

[0098] In other embodiments, in response to the deviation reaching a preset deviation level, the lithium iron phosphate battery can also be fully discharged to actually detect the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

[0099] According to some embodiments of this application, the absolute value of the second initial capacity change is corrected to obtain the absolute value of the capacity change in a second interval during the current charge / discharge period of the lithium iron phosphate battery, including:

[0100] The difference between the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery and the absolute value of the first initial capacity change is obtained as the first change value;

[0101] Obtain the correction factor;

[0102] Based on the first change value and the correction coefficient, the second change value is obtained. The second change value is the difference between the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery and the absolute value of the second initial capacity change.

[0103] Based on the second change value and the second initial absolute value of capacity change, the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery is determined.

[0104] The lithium iron phosphate battery has corresponding first change values ​​during both the current charging and discharging periods. Specifically, the first change value during the current charging period is the difference between the absolute value of the capacity change in a first interval during the current charging period and the absolute value of the first initial capacity change obtained based on the charging OCV curve. Similarly, the first change value during the current discharging period is the difference between the absolute value of the capacity change in a first interval during the current discharging period and the absolute value of the first initial capacity change obtained based on the discharging OCV curve. Likewise, the lithium iron phosphate battery has corresponding second change values ​​during both the current charging and discharging periods. The second change value during the current charging period is the difference between the absolute value of the capacity change in a second interval during the current charging period and the absolute value of the second initial capacity change obtained based on the charging OCV curve. The second change value during the current discharging period is the difference between the absolute value of the capacity change in a second interval during the current discharging period and the absolute value of the second initial capacity change obtained based on the discharging OCV curve.

[0105] Both the first and second changes are absolute values.

[0106] During the research, the applicant discovered that when the absolute value of the capacity change in the second interval deviates significantly from the absolute value of the second initial capacity change, the difference between the absolute value of the capacity change in the first interval and the absolute value of the first initial capacity change for each charge / discharge cycle exhibits a fixed proportional relationship with the difference between the absolute value of the capacity change in the second interval and the absolute value of the second initial capacity change. In other words, the first change value and the second change value are in a fixed proportional relationship. Therefore, this fixed proportional relationship can be used as a correction coefficient. That is, the first change value divided by the second change value equals the correction coefficient. Based on this relationship, the second change value can be obtained using the known first change value and the correction coefficient. Since the absolute value of the second initial capacity change is also known, the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery can be deduced from the calculated second change value.

[0107] In some embodiments, the above-mentioned fixed ratio relationship can be determined by empirical values. For batteries of the same model and specifications, the above-mentioned fixed ratio relationship is usually consistent. Therefore, the fixed ratio relationship can be obtained as a correction coefficient by testing a large number of batteries of the same model and specifications.

[0108] In the above technical solution, when the battery is severely aged, the first change value and the second change value are in a fixed proportional relationship. After obtaining the first change value, a correction coefficient is used as the proportional relationship. Based on the first change value, the second change value of the absolute value of capacity change in the second interval relative to the absolute value of the second initial capacity change can be obtained. When the absolute value of the second initial capacity change is known, the absolute value of capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery can be determined.

[0109] According to some embodiments of this application, the correction coefficient is obtained, including:

[0110] Obtain historical charge / discharge information for lithium iron phosphate batteries;

[0111] Based on historical charge / discharge information, complete charge / discharge curves of lithium iron phosphate batteries are obtained. These complete charge / discharge curves are used to characterize the voltage change with capacity during the period from full discharge to full charge and from full charge to full discharge of lithium iron phosphate batteries.

[0112] Based on the complete charge / discharge curve, the absolute value of capacity change in the first interval is obtained as the first historical absolute value of capacity change, and the absolute value of capacity change in the second interval is obtained as the second historical absolute value of capacity change.

[0113] The difference between the absolute value of the first historical capacity change and the absolute value of the first initial capacity change is used as the third change value;

[0114] The difference between the absolute value of the second historical capacity change and the absolute value of the second initial capacity change is used as the fourth change value;

[0115] Obtain the ratio of the fourth change value to the third change value, and use it as a correction factor.

[0116] Historical charge / discharge information refers to the information recorded during previous charge / discharge cycles of the lithium iron phosphate battery. The BMS can record the historical charge / discharge information of the lithium iron phosphate battery.

[0117] A complete charge / discharge curve is obtained by fully charging and fully discharging the lithium iron phosphate battery. Although the number of times lithium iron phosphate batteries are fully discharged in practical applications is relatively small, in the embodiments of this application, it is only necessary to find one complete charge / discharge curve that can characterize the above fixed ratio relationship in the historical charge / discharge information, and it will not increase the frequency of fully discharging the lithium iron phosphate battery.

[0118] A complete charge / discharge curve represents a single complete charge / discharge process. The difference between the absolute value of the first historical capacity change and the absolute value of the first initial capacity change in the first interval, and the difference between the absolute value of the second historical capacity change and the absolute value of the second initial capacity change in the second interval, exhibit a fixed proportional relationship as described in the above embodiments. Therefore, by tracing the complete charge / discharge curves in the historical charge / discharge information of the lithium iron phosphate battery, the ratio of the fourth change value to the third change value can be obtained as the aforementioned fixed proportional relationship, thereby obtaining the correction coefficient.

[0119] The third and fourth changes are both absolute values.

[0120] For example, during the charging process, the third change value is the difference between the absolute value of the first historical capacity change in the first interval of the complete charging curve and the absolute value of the first initial capacity change obtained based on the charging OCV curve; the fourth change value is the difference between the absolute value of the second historical capacity change in the second interval of the complete charging curve and the absolute value of the second initial capacity change obtained based on the charging OCV curve. During the discharging process, the third change value is the difference between the absolute value of the first historical capacity change in the first interval of the complete discharging curve and the absolute value of the first initial capacity change obtained based on the discharging OCV curve; the fourth change value is the difference between the absolute value of the second historical capacity change in the second interval of the complete discharging curve and the absolute value of the second initial capacity change obtained based on the discharging OCV curve.

[0121] In the above technical solution, by tracing historical charge / discharge information and finding complete charge / discharge curves, a fixed ratio relationship is obtained from the previous complete charge / discharge curves as a correction coefficient, so that the obtained correction coefficient is closer to the actual ratio of the first change value and the second change value, thereby improving the accuracy of the calculated capacity of the lithium iron phosphate battery.

[0122] According to some embodiments of this application, step 110 may include:

[0123] Obtain the OCV curve of the lithium iron phosphate battery at the time of manufacture. The OCV curve is used to characterize the change of the static voltage of the lithium iron phosphate battery with capacity.

[0124] The intermediate inflection point is determined based on the OCV curve.

[0125] When lithium iron phosphate (LFP) batteries age, the voltages of the high-voltage and low-voltage platforms remain unchanged; only the switching time between them may vary. In other words, the timing of the intermediate inflection point may change. Therefore, by identifying the intermediate inflection point during charging and discharging in the LFP battery's original charge / discharge OCV curve and determining the voltage at this point, subsequent monitoring of the LFP battery's voltage during actual charging / discharging can pinpoint the exact time of the inflection point. This allows for the detection of the absolute value of capacity changes in the first interval.

[0126] In the above technical solution, by finding the intermediate inflection point in the OCV curve when the battery leaves the factory, the voltage corresponding to the intermediate inflection point can be obtained. During the current charging / discharging, only the battery voltage needs to be monitored to detect the corresponding intermediate inflection point, which simplifies the method of obtaining the intermediate inflection point.

[0127] According to some embodiments of this application, step 110 may also include:

[0128] Charge / discharge tests were conducted on lithium iron phosphate batteries at different charge / discharge rates to obtain reference charge / discharge curves, which were used to characterize the voltage change of lithium iron phosphate batteries with capacity.

[0129] The intermediate inflection point is determined based on the reference charge / discharge curve.

[0130] The lithium iron phosphate battery can be pre-tested at different rates to obtain reference charge / discharge curves. Then, based on the reference charge / discharge curves, the intermediate inflection point can be determined, and the voltage at the intermediate inflection point corresponding to charging and discharging can be determined. Subsequently, during the actual charging / discharging process of the lithium iron phosphate battery, it is only necessary to monitor the voltage of the lithium iron phosphate battery to determine the time when the intermediate inflection point occurs, and thus the absolute value of the capacity change in the first interval can be detected.

[0131] In the above technical solution, the lithium iron phosphate battery is pre-tested at different rates to obtain the intermediate inflection point, thereby improving the accuracy of the obtained intermediate inflection point.

[0132] This application provides a method 500 for correcting the OCV curve of a battery, referring to... Figure 5 The methods include:

[0133] Step 510: Obtain the capacity of the lithium iron phosphate battery using the battery capacity calculation method 400 in the above embodiment;

[0134] Step 520: Obtain the current SOH of the lithium iron phosphate battery based on its capacity and rated capacity.

[0135] Step 530: Correct the OCV curve based on the current SOH of the lithium iron phosphate battery.

[0136] Step 510 can be referred to the relevant description in the above embodiments, and will not be repeated here.

[0137] In step 520, the current SOH is obtained based on the ratio of the current capacity to the rated capacity of the lithium iron phosphate battery obtained in step 510.

[0138] In step 530, the OCV curve obtained when the SOH of the lithium iron phosphate battery is 100% can be corrected based on the current SOH of the lithium iron phosphate battery.

[0139] For example, the OCV curve obtained when the SOH of the lithium iron phosphate battery is 100% is recorded as the original OCV curve, which can be the OCV curve of the lithium iron phosphate battery at the time of manufacture.

[0140] In some embodiments, step 530 may record the characteristic voltage Vi and the initial capacity Qi corresponding to the characteristic voltage Vi in the original OCV curve. Then, the corrected capacity Qi' is obtained by correcting the initial capacity Qi based on the current SOH using the following formula:

[0141] (1)

[0142] The position of the characteristic voltage Vi remains unchanged, and the corrected OCV curve is regenerated based on the characteristic voltage Vi and the corrected capacity Qi'.

[0143] In other embodiments, the OCV curve may also be corrected based on the current SOH of the lithium iron phosphate battery using other methods familiar to those skilled in the art.

[0144] The correction method described in the above embodiments can dynamically update the State of Harmonic Drive (SOH) of lithium iron phosphate batteries, thereby improving the accuracy of SOH correction. In this way, when dynamically correcting the OCV curve based on the corrected current SOH, the accuracy of OCV curve correction can be improved, which is beneficial for accurately determining the remaining capacity of the battery and improving the problems of overcharging, over-discharging, and accelerated aging of lithium iron phosphate batteries caused by misjudging the remaining capacity of the battery.

[0145] Based on steps 510 to 530 above, the applicant corrected the original OCV curve of the lithium iron phosphate battery (LFP) under operating conditions of 35℃, 45℃, 55℃, 65℃, and 75℃, respectively, to obtain the corrected OCV curve, as shown below. Figures 6 to 10 As shown.

[0146] Figures 6 to 10The original and corrected OCV curves of the lithium iron phosphate battery are shown for operating conditions of 35℃, 45℃, 55℃, 65℃, and 75℃, respectively. Figure 6 The original OCV curves and the corrected OCV curves for 50 cycles and 600 cycles are shown respectively. Figure 7 The original OCV curves and the corrected OCV curves for 50 cycles and 750 cycles are shown respectively. Figure 8 The original OCV curves and the corrected OCV curves for 50 cycles and 600 cycles are shown respectively. Figure 9 The original OCV curves and the corrected OCV curves for 25 cycles and 575 cycles are shown respectively. Figure 10 The original OCV curves and the corrected OCV curves for 25 cycles and 775 cycles are shown respectively.

[0147] Depend on Figures 6 to 10 It can be seen that as the number of cycles increases, the degree of battery aging increases, the high-voltage plateau shortens, while the low-voltage plateau remains almost unchanged; that is, the first interval shortens while the second interval remains almost unchanged. Therefore, in the embodiments of this application, under different cycle numbers and different temperature conditions, the correction of the original OCV curve through the above steps 510 to 530 can reconstruct the current corrected OCV curve with relatively high accuracy. The method provided in the embodiments of this application has a certain degree of universality.

[0148] This application provides a computing device, which includes: at least one processor; and at least one memory communicatively connected to the at least one processor. The at least one memory stores instructions that, when executed by the at least one processor individually or jointly, cause the computing device to perform the battery capacity calculation method 400 or the OCV curve correction method 500 for lithium iron phosphate batteries described in the above embodiments.

[0149] Various embodiments of the systems and technologies described above in this application can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip systems, payload-130 programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include implementations in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a dedicated or general-purpose programmable processor, capable of receiving data and instructions from a storage system, at least one input device, and at least one output device, and transmitting data and instructions to the storage system, the at least one input device, and the at least one output device.

[0150] This application provides a computer-readable storage medium storing instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform the battery capacity calculation method 400 or the OCV curve correction method 500 for lithium iron phosphate batteries described in the above embodiments.

[0151] Computer-readable media can be tangible media that may contain or store programs for use by or in conjunction with an instruction execution system, apparatus, or device. Machine-readable media can be machine-readable signal media or machine-readable storage media. Machine-readable media can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0152] This application provides a computer program product, including instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform the battery capacity calculation method 400 or the OCV curve correction method 500 for lithium iron phosphate batteries described in the above embodiments.

[0153] The technical solution of this application will be further described below with reference to a specific embodiment.

[0154] The method for correcting the OCV curve of lithium iron phosphate batteries includes the following steps 610 to 660.

[0155] Step 610: Determine the midpoint of the lithium iron phosphate battery.

[0156] Step 620: Obtain the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery. In step 620, the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery is obtained using the ampere-hour integration method.

[0157] Step 630: Based on the absolute value of capacity change in the first interval, determine the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery. In Step 630, based on the OCV curve of the lithium iron phosphate battery at the time of manufacture, obtain the absolute value of capacity change in the first interval as the first initial absolute value of capacity change, and obtain the absolute value of capacity change in the second interval as the second initial absolute value of capacity change. Then, obtain the deviation degree of the absolute value of capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery relative to the first initial absolute value of capacity change. In response to the deviation degree not reaching the preset deviation degree, determine the second initial absolute value of capacity change as the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery. In response to the deviation degree reaching the preset deviation degree, correct the second initial absolute value of capacity change to obtain the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

[0158] The process of correcting the absolute value of the second initial capacity change to obtain the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery includes the following steps:

[0159] The difference between the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery and the absolute value of the first initial capacity change is obtained as the first change value;

[0160] Obtain the correction factor;

[0161] Based on the first change value and the correction coefficient, the second change value is obtained. The second change value is the difference between the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery and the absolute value of the second initial capacity change.

[0162] Based on the second change value and the second initial absolute value of capacity change, the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery is determined.

[0163] To obtain the correction factor, the following steps are included:

[0164] Obtain historical charge / discharge information for lithium iron phosphate batteries;

[0165] Based on historical charge / discharge information, complete charge / discharge curves of lithium iron phosphate batteries are obtained. These complete charge / discharge curves are used to characterize the voltage change with capacity during the period from full discharge to full charge and from full charge to full discharge of lithium iron phosphate batteries.

[0166] Based on the complete charge / discharge curve, the absolute value of capacity change in the first interval is obtained as the first historical absolute value of capacity change, and the absolute value of capacity change in the second interval is obtained as the second historical absolute value of capacity change.

[0167] The difference between the absolute value of the first historical capacity change and the absolute value of the first initial capacity change is used as the third change value;

[0168] The difference between the absolute value of the second historical capacity change and the absolute value of the second initial capacity change is used as the fourth change value;

[0169] Obtain the ratio of the fourth change value to the third change value, and use it as a correction factor.

[0170] Step 640: Determine the capacity of the lithium iron phosphate battery as the sum of the absolute values ​​of the capacity change in the first interval and the absolute values ​​of the capacity change in the second interval during the current charge / discharge period.

[0171] Step 650: Obtain the current SOH of the lithium iron phosphate battery based on its capacity and rated capacity.

[0172] Step 660: Correct the OCV curve based on the current SOH of the lithium iron phosphate battery.

[0173] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery capacity calculation method, applied to lithium iron phosphate batteries, characterized in that, include: The intermediate inflection point of the lithium iron phosphate battery is determined. The intermediate inflection point is the critical point at which the lithium iron phosphate battery connects to the low voltage platform when switching between the low voltage platform and the high voltage platform during charging / discharging. Obtain the absolute value of the capacity change of the lithium iron phosphate battery during the current charging / discharging period of the first interval, where the first interval is the stage between the intermediate inflection point and full charge of the lithium iron phosphate battery; Based on the degree of deviation between the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery and the initial absolute value of the capacity change in the first interval during the initial charging / discharging period of the lithium iron phosphate battery, it is determined whether the initial absolute value of the capacity change in the second interval during the initial charging / discharging period of the lithium iron phosphate battery needs to be corrected. Based on the determination result, it is determined that the absolute value of the capacity change in the second interval during the current charging / discharging period of the lithium iron phosphate battery is the initial absolute value of the capacity change in the second interval or the value after correction of the initial absolute value of the capacity change in the second interval. The second interval is the stage between the intermediate inflection point and full discharge of the lithium iron phosphate battery. The capacity of the lithium iron phosphate battery is determined by the sum of the absolute values ​​of the capacity changes in the first interval and the second interval during the current charge / discharge period.

2. The method according to claim 1, characterized in that, The step of obtaining the absolute value of the capacity change in the first interval during the current charge / discharge period of the lithium iron phosphate battery includes: The first moment when the lithium iron phosphate battery is at the intermediate inflection point during the current charge / discharge period and the second moment when it is fully charged are obtained. Obtain the real-time current of the lithium iron phosphate battery between the first time point and the second time point; The real-time current integral over time between the first and second time points is obtained using the ampere-hour integration method, and the integral result is used as the absolute value of the capacity change in the first interval.

3. The method according to claim 1, characterized in that, The method for determining the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery includes: Obtain the OCV curve of the lithium iron phosphate battery at the time of manufacture. The OCV curve is used to characterize the change of the static voltage of the lithium iron phosphate battery with capacity. Based on the OCV curve, the absolute value of the capacity change in the first interval is obtained as the first initial absolute value of the capacity change, and the absolute value of the capacity change in the second interval is obtained as the second initial absolute value of the capacity change. The degree of deviation between the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery and the first initial absolute value of the capacity change is obtained; In response to the deviation level not reaching the preset deviation level, the absolute value of the second initial capacity change is determined to be the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

4. The method according to claim 3, characterized in that, The method for determining the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery further includes: In response to the deviation reaching the preset deviation level, the absolute value of the second initial capacity change is corrected to obtain the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery.

5. The method according to claim 4, characterized in that, The step of correcting the absolute value of the second initial capacity change to obtain the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery includes: The difference between the absolute value of the capacity change in the first interval during the current charging / discharging period of the lithium iron phosphate battery and the absolute value of the first initial capacity change is obtained as the first change value; Obtain the correction factor; Based on the first change value and the correction coefficient, a second change value is obtained. The second change value is the difference between the absolute value of the capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery and the absolute value of the second initial capacity change. Based on the second change value and the second initial absolute value of capacity change, the absolute value of capacity change in the second interval during the current charge / discharge period of the lithium iron phosphate battery is determined.

6. The method according to claim 5, characterized in that, The process of obtaining the correction coefficient includes: Obtain the historical charge / discharge information of the lithium iron phosphate battery; Based on the historical charge / discharge information, the complete charge / discharge curve of the lithium iron phosphate battery is obtained. The complete charge / discharge curve is used to characterize the change in voltage with capacity during the period from full discharge to full charge / full charge to full discharge of the lithium iron phosphate battery. Based on the complete charge / discharge curve, the absolute value of the capacity change in the first interval is obtained as the first historical absolute value of capacity change, and the absolute value of the capacity change in the second interval is obtained as the second historical absolute value of capacity change. The difference between the absolute value of the first historical capacity change and the absolute value of the first initial capacity change is used as the third change value; The difference between the absolute value of the second historical capacity change and the absolute value of the second initial capacity change is used as the fourth change value; The ratio of the fourth change value to the third change value is obtained and used as the correction coefficient.

7. The method according to any one of claims 1-6, characterized in that, Determining the intermediate inflection point of the lithium iron phosphate battery includes: Obtain the OCV curve of the lithium iron phosphate battery at the time of manufacture. The OCV curve is used to characterize the change of the static voltage of the lithium iron phosphate battery with capacity. The intermediate inflection point is determined based on the OCV curve.

8. The method according to any one of claims 1-6, characterized in that, Determining the intermediate inflection point of the lithium iron phosphate battery includes: The lithium iron phosphate battery was charged / discharged at different charge / discharge rates to obtain a reference charge / discharge curve, which was used to characterize the change in voltage of the lithium iron phosphate battery with capacity. The intermediate inflection point is determined based on the reference charge / discharge curve.

9. A method for correcting the OCV curve of a battery, characterized in that, include: The capacity of a lithium iron phosphate battery is obtained using the battery capacity calculation method described in any one of claims 1-8. The current SOH of the lithium iron phosphate battery is obtained based on its capacity and its rated capacity. The OCV curve is corrected based on the current SOH of the lithium iron phosphate battery.

10. A computing device, characterized in that, include: At least one processor; as well as At least one memory communicatively connected to the at least one processor, the at least one memory storing instructions that, when executed individually or jointly by the at least one processor, cause the computing device to perform the method of any one of claims 1 to 8 or the method of claim 9.

11. A computer-readable storage medium, characterized in that, The device stores instructions that, when executed individually or jointly by one or more processors of the computing device, cause the computing device to perform the method of any one of claims 1 to 8 or the method of claim 9.

12. A computer program product, characterized in that, Includes instructions that, when executed individually or jointly by one or more processors of a computing device, cause the computing device to perform the method of any one of claims 1 to 8 or the method of claim 9.

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