Estimation method for discharge capacity of battery, program product, and battery management system

Abstract

The invention relates to a method for estimating the discharge capacity of a battery. The method comprises the following steps: acquiring a differential voltage curve of the battery in a charging process; determining an entry point and a departure point behind the entry point according to a comparison of the differential voltage curve and a differential voltage threshold, the differential voltage curve being greater than the differential voltage threshold between the entry point and the departure point, determining an intermediate feature point of the battery based on the entry point and the departure point; obtaining a first charging capacity corresponding to the intermediate feature point; recording a second charging capacity charged from the middle feature point to the end of charging; and calculating the discharge capacity of the battery according to the first charge capacity and the second charge capacity. A corresponding computer program product and a corresponding battery management system are also proposed. The discharge capacity of the battery can be easily and accurately estimated.

Description

Technical Field

[0001] This invention relates to the technical field of batteries, and in particular to a method for estimating the discharge capacity of a battery. The invention also relates to a corresponding computer program product and a corresponding battery management system. Background Technology

[0002] With the rapid development of battery technology, lithium-ion batteries are widely used in electric vehicles. To accurately assess the remaining driving range of an electric vehicle, the battery's discharge capacity is a key parameter, indicating the total amount of electricity the battery can actually release from its current state.

[0003] Currently, the estimation of battery discharge capacity is usually based on the mapping relationship between the battery's open-circuit voltage and charge level. This mapping relationship needs to be calibrated through a complete full charge-discharge cycle, which is time-consuming, inconvenient, and prone to estimation errors. Summary of the Invention

[0004] Therefore, the object of this invention is to provide an improved method for estimating the discharge capacity of a battery, which can easily and accurately estimate the battery's discharge capacity. Another object of this invention is to provide a corresponding computer program product and a corresponding battery management system.

[0005] According to a first aspect of the present invention, a method for estimating the discharge capacity of a battery is provided, wherein the estimation method includes at least the following steps: S1: Obtain the differential voltage curve of the battery during the charging process; S2: Determine the entry point and the exit point located after the entry point based on the comparison of the differential voltage curve and the differential voltage threshold, wherein the differential voltage curve is greater than the differential voltage threshold between the entry point and the exit point, and determine the intermediate feature point of the battery based on the entry point and the exit point; S3: Obtain the first charging capacity corresponding to the intermediate feature point; S4: Record the second charging capacity from the intermediate feature point to the end of charging; S5: Calculate the discharge capacity of the battery from the first charging capacity and the second charging capacity.

[0006] Within the framework of this invention, "intermediate feature point" should be understood as a feature point caused by the phase transition of the graphite negative electrode during battery charging. This feature point manifests as an inflection point in the plateau region on the charging curve or as a peak point on the differential voltage curve. During battery cycling, the structure of the graphite material in the negative electrode and its inherent phase transition sequence are very stable, ensuring that the number of lithium ions embedded in the graphite crystal structure remains essentially stable. Consequently, the charging capacity corresponding to the intermediate feature point also remains essentially constant. Therefore, the intermediate feature point can be considered as a capacity anchor point during cycling.

[0007] Compared to existing technologies, in the method for estimating the discharge capacity of a battery according to the present invention, the entry and exit points are determined based on the differential voltage curve of the battery during charging and a preset differential voltage threshold. An intermediate feature point can be determined based on the entry and exit points. This determined intermediate feature point effectively avoids peak point drift caused by noise, thereby more accurately locating the intermediate feature point. Furthermore, the first charging capacity corresponding to the intermediate feature point and the second charging capacity from the intermediate feature point to the end of charging are obtained. The discharge capacity of the battery is calculated from the first charging capacity and the second charging capacity. Therefore, the discharge capacity of the battery can be easily and accurately estimated without performing time-consuming and laborious full-charge-discharge cycles.

[0008] For example, the entry point corresponds to a first time point when the differential voltage curve rises to the differential voltage threshold, the exit point corresponds to a second time point when the differential voltage curve falls to the differential voltage threshold, and the intermediate feature point corresponds to the average time point of the first time point and the second time point.

[0009] For example, in step S4, starting from the average time point corresponding to the intermediate feature point, the charging current of the battery is integrated over time until the charging is completed, so as to record the second charging capacity.

[0010] For example, the entry point and the exit point are located in a preset state of charge interval, which corresponds to the plateau region of the charging curve.

[0011] For example, in step S3, the first charging capacity is determined based on the rated intermediate capacity of the intermediate feature point.

[0012] For example, the rated intermediate capacity is provided by the battery supplier and stored in the battery management system for the battery; and / or, the first charging capacity is calculated based on the rated intermediate capacity and a correction factor, the correction factor being determined based on at least one of the following influencing factors: average charging current, initial state of charge, charging temperature, battery aging degree, and battery rated capacity.

[0013] For example, if charging ends when the battery's charging voltage reaches the charging cutoff voltage, then the discharge capacity is the battery's maximum usable total capacity; and / or, in step S1, the differential voltage curve is determined based on the differential value of the battery's charging voltage and the accumulated charging capacity; and / or, the differential voltage threshold is predetermined by experimental data and / or empirical data and stored in the battery management system for the battery.

[0014] For example, the battery is a lithium iron phosphate battery.

[0015] According to a second aspect of the present invention, a computer program product is provided, comprising a computer program, wherein when the computer program is executed by one or more processors, the processors are capable of performing the estimation method according to the present invention.

[0016] According to a third aspect of the present invention, a battery management system is provided, wherein the battery management system includes a memory and a processor, the processor being configured to implement the estimation method according to the present invention using a computer program product according to the present invention. Attached Figure Description

[0017] The invention will now be described in more detail with reference to the accompanying drawings, which will provide a better understanding of its principles, features, and advantages. The drawings include: Figure 1 A schematic diagram of a battery charging curve according to an exemplary embodiment of the present invention is shown; Figure 2 A schematic diagram of the differential voltage curve for a method of estimating the discharge capacity of a battery according to an exemplary embodiment of the present invention is shown. Figure 3 A schematic flowchart of a method for estimating the discharge capacity of a battery according to an exemplary embodiment of the present invention is shown. Detailed Implementation

[0018] To make the technical problems to be solved, the technical solutions, and the beneficial technical effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and several exemplary embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0019] This specification provides the operational steps for the methods described in the embodiments or flowcharts, but based on conventional or non-inventive labor, more or fewer operational steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only possible execution order.

[0020] Figure 1 A schematic diagram of the charging curve of a battery according to an exemplary embodiment of the present invention is shown.

[0021] Here, the battery is particularly a lithium iron phosphate battery, which has a positive electrode made of lithium iron phosphate and a negative electrode made of graphite. During operation, lithium ions are inserted and extracted between the positive and negative electrode materials, accompanied by the external flow of electrons.

[0022] like Figure 1 As shown, the charging curve is a curve showing the change of battery voltage with charge level. Its vertical axis is the charging voltage Vol, in volts (V), and the horizontal axis is the state of charge (SOC), in percentage (%). This charging curve has a low SOC region, a plateau region, and a high SOC region.

[0023] In the low SOC region (e.g., 0% to 20% SOC), the charging voltage increases rapidly with increasing SOC, exhibiting a steep curve slope. During this process, lithium ions are deintercalated from the positive electrode and rapidly migrate to the graphite negative electrode.

[0024] In the plateau region (e.g., 20% to 90% SOC), the charging voltage remains almost constant within a narrow range, such as 3.3V to 3.4V. There is a relatively sloping inflection point in the plateau region where the voltage exhibits a relatively significant jump within a small range of SOC variation. This inflection point is the intermediate characteristic point (MFP), which is a phase transition characteristic point determined by crystal structure and thermodynamics, and the corresponding capacity does not change significantly with battery aging.

[0025] In the high SOC region (e.g., 90% to 100% SOC), the charging voltage rises rapidly again until it reaches the charging cutoff voltage. During this process, the phase transition reaction is nearing completion, and the cathode material is essentially converted into a lithium-poor phase.

[0026] Figure 2 A schematic diagram of the differential voltage curve for a method of estimating the discharge capacity of a battery according to an exemplary embodiment of the present invention is shown. Figure 3 A schematic flowchart of a method for estimating the discharge capacity of a battery according to an exemplary embodiment of the present invention is shown.

[0027] like Figure 2 As shown, the differential voltage curve is a functional relationship curve of the derivative of voltage with respect to the amount of electricity passed as a function of the cumulative amount of electricity passed or the charge level. Its vertical axis is the differential voltage dV / dQ, in mV / Ah, and the horizontal axis is the charge level SOC, in percentage (%). However, it is also possible that the horizontal axis is the cumulative amount of electricity passed, in ampere-hours (Ah).

[0028] like Figure 1 and Figure 2 As shown, a comparison of the charging curve and the differential voltage curve reveals that in the low SOC region, the differential voltage dV / dQ has a large value and decreases significantly with charging; in the high SOC region, the differential voltage dV / dQ also has a large value and increases significantly with charging; while in the plateau region, as the SOC level increases, the differential voltage dV / dQ initially has a significantly lower value, exhibiting a distinct peak region around the inflection point of the charging curve, i.e., the intermediate characteristic point MFP. This peak region has rising and falling edges, with the peak point between the rising and falling edges corresponding to the intermediate characteristic point MFP, after which the value stabilizes at a lower level. However, due to individual battery performance differences or the influence of measurement noise, the intermediate characteristic point MFP may drift, which adversely affects the accuracy of capacity estimation.

[0029] like Figure 3 As shown, the method for estimating the discharge capacity of a battery according to the present invention includes at least the following steps: S1: Obtain the differential voltage curve of the battery during the charging process; S2: Determine the entry point P1 and the exit point P2 located after the entry point P1 based on the comparison of the differential voltage curve and the differential voltage threshold T. The differential voltage curve is greater than the differential voltage threshold T between the entry point P1 and the exit point P2. Determine the intermediate feature point MFP of the battery based on the entry point P1 and the exit point P2. S3: Obtain the first charging capacity corresponding to the intermediate feature point MFP; S4: Record the second charging capacity from the intermediate feature point MFP to the end of charging; S5: Calculate the discharge capacity of the battery from the first charging capacity and the second charging capacity.

[0030] In this case, the intermediate feature point (MFP) of the battery is determined based on the entry point P1 and the exit point P2, without having to determine the intermediate feature point MFP by directly identifying the peak point. This avoids the peak point drift problem caused by individual battery performance differences or noise, thus locating the intermediate feature point MFP more accurately.

[0031] For example, in the plateau region of the charging curve, the battery is charged with a constant current, thereby making it easy to integrate and calculate the amount of charge deposited in the plateau region.

[0032] For example, in step S1, the differential voltage curve is determined based on the differential value of the battery's charging voltage and the cumulative charging capacity. Specifically, the battery voltage and charging current are collected, the cumulative charging capacity is obtained by integrating the charging current, and the differential voltage dV / dQ can be calculated from the voltage difference ΔV and the capacity difference ΔQ.

[0033] For example, such as Figure 2 As shown, the entry point P1 corresponds to the first time point t1 when the differential voltage curve rises to the differential voltage threshold T, and the exit point P2 corresponds to the second time point t2 when the differential voltage curve falls to the differential voltage threshold T. The intermediate feature point MFP corresponds to the average time point t0 of the first and second time points. This avoids peak point drift and accurately determines the intermediate feature point MFP. Furthermore, it easily determines the average time point t0 when the battery reaches the intermediate feature point MFP, which is beneficial for subsequent battery capacity calculations.

[0034] For example, such as Figure 2 As shown, the entry point P1 and the exit point P2 are located within a preset state of charge (SOC) interval, which corresponds to the plateau region of the charging curve. This prevents the identification of erroneous intermediate feature points in the low SOC and high SOC regions and significantly improves the accuracy of discharge capacity estimation.

[0035] For example, in step S2, the differential voltage threshold T is predetermined by experimental data and / or empirical data and stored in the battery management system for the battery. Here, the differential voltage threshold T is significantly higher than the differential voltage value outside the peak region in the plateau region. In particular, the differential voltage threshold T is calibrated using experimental data of the battery under standard conditions.

[0036] For example, in step S3, the first charging capacity is determined based on the rated intermediate capacity at the intermediate characteristic point. This rated intermediate capacity characterizes the amount of electricity or lithium ions transferred from 0% SOC to the intermediate characteristic point, which is stable during battery use and does not change with aging. In particular, the rated intermediate capacity should be measured under standard conditions, which refers to a brand-new battery or a battery that has undergone a small number of standard cycle activations being charged from 0% SOC to 100% SOC with a small charging current and allowed sufficient resting time to eliminate polarization and ensure voltage stability.

[0037] For example, the rated intermediate capacity at the intermediate feature point (MFP) can be directly provided by the battery supplier and stored in the battery management system used for the battery. When implementing the estimation method, the rated intermediate capacity at the intermediate feature point (MFP) is directly invoked by the battery management system.

[0038] For example, the first charging capacity is calculated based on the rated intermediate capacity and a correction factor, which is determined based on at least one of the following influencing factors: average charging current, initial state of charge, charging temperature, battery aging degree, and battery rated capacity. This compensates for the influence of each influencing factor on the intermediate characteristic point (MFP) and further improves the accuracy of capacity estimation during actual charging. Each influencing factor is assigned a corresponding individual correction factor; for example, a current correction factor is set for the average charging current, and a state of charge correction factor is set for the initial state of charge, etc. The final correction factor for the first charging capacity can be calculated jointly from the individual correction factors of each influencing factor. Of course, other influencing factors that are considered meaningful by those skilled in the art can also be considered.

[0039] For example, in step S4, starting from the average time point t0 corresponding to the intermediate feature point MFP, the charging current of the battery is integrated over time until charging is completed, to record the second charging capacity. The second charging capacity is a variable capacity that starts from the intermediate feature point MFP and depends on the specific charging process. This variable capacity can be easily and accurately obtained using ampere-hour integration.

[0040] For example, if charging ends when the battery's charging voltage reaches the charging cutoff voltage, then 100% SOC has been reached, and the discharge capacity at this point is the battery's maximum usable total capacity. It's easy to understand that as the battery ages, the second charging capacity gradually decreases, causing the battery's maximum usable total capacity to decrease accordingly. If charging ends before reaching the charging cutoff voltage, for example, if the user manually ends charging, then the discharge capacity is less than the battery's maximum usable total capacity.

[0041] Furthermore, if the battery is used in an electric vehicle, the remaining driving range of the electric vehicle can be obtained based on the estimated discharge capacity.

[0042] According to the present invention, a computer program product is provided, comprising a computer program that, when executed by one or more processors, enables the processors to perform the method for estimating the discharge capacity of a battery according to the present invention.

[0043] According to the present invention, a battery management system is also proposed, comprising a memory and a processor configured to implement, using a computer program product according to the present invention, a method for estimating the discharge capacity of a battery according to the present invention. Here, the memory stores, in particular, the rated intermediate capacity and / or differential voltage threshold at intermediate characteristic points of the battery.

[0044] The foregoing description of the embodiments is limited to the framework of the examples given. Of course, the various features of the embodiments can be freely combined with each other without departing from the framework of the invention, as long as it is technically meaningful.

[0045] Other advantages and alternative embodiments of the present invention will be apparent to those skilled in the art. Therefore, the present invention is not, in its broader sense, limited to the specific details, representative structures, and exemplary embodiments shown and described. Rather, those skilled in the art can make various modifications and substitutions without departing from the basic spirit and scope of the invention.

Claims

1. A method for estimating the discharge capacity of a battery, characterized in that, The estimation method includes at least the following steps: S1: Obtain the differential voltage curve of the battery during the charging process; S2: Determine the entry point and the exit point located after the entry point based on the comparison of the differential voltage curve and the differential voltage threshold, wherein the differential voltage curve is greater than the differential voltage threshold between the entry point and the exit point, and determine the intermediate feature point of the battery based on the entry point and the exit point; S3: Obtain the first charging capacity corresponding to the intermediate feature point; S4: Record the second charging capacity from the intermediate feature point to the end of charging; S5: Calculate the discharge capacity of the battery from the first charging capacity and the second charging capacity.

2. The estimation method according to claim 1, characterized in that, The entry point corresponds to the first time point when the differential voltage curve rises to the differential voltage threshold, the exit point corresponds to the second time point when the differential voltage curve falls to the differential voltage threshold, and the intermediate feature point corresponds to the average time point of the first time point and the second time point.

3. The estimation method according to claim 2, characterized in that, In step S4, starting from the average time point corresponding to the intermediate feature point, the charging current of the battery is integrated over time until the charging is completed, so as to record the second charging capacity.

4. The estimation method according to any one of claims 1 to 3, characterized in that, The entry point and the exit point are located within a preset state of charge interval, which corresponds to the plateau region of the charging curve.

5. The estimation method according to any one of claims 1 to 4, characterized in that, In step S3, the first charging capacity is determined based on the rated intermediate capacity of the intermediate feature point.

6. The estimation method according to claim 5, characterized in that, The rated intermediate capacity is provided by the battery supplier and stored in the battery management system used for the battery; and / or The first charging capacity is calculated based on the rated intermediate capacity and a correction factor, which is determined based on at least one of the following influencing factors: average charging current, initial state of charge, charging temperature, battery aging degree, and battery rated capacity.

7. The estimation method according to any one of the preceding claims, characterized in that, If charging ends when the charging voltage of the battery reaches the charging cutoff voltage, then the discharge capacity is the maximum usable total capacity of the battery. and / or In step S1, the differential voltage curve is determined based on the differential values ​​of the battery's charging voltage and cumulative charging capacity. and / or The differential voltage threshold is predetermined by experimental and / or empirical data and stored in the battery management system used for the battery.

8. The early warning method according to any one of the preceding claims, characterized in that, The battery is a lithium iron phosphate battery.

9. A computer program product comprising a computer program, characterized in that, When the computer program is executed by one or more processors, the processors are capable of performing the estimation method according to any one of claims 1 to 8.

10. A battery management system, characterized in that, The battery management system includes a memory and a processor, the processor being configured to implement the estimation method according to any one of claims 1 to 8 using the computer program product according to claim 9.

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