A quantitative diagnostic method for internal short circuits in batteries under float charging conditions

Abstract

This invention proposes a quantitative diagnostic method for internal short circuits in batteries under float charging conditions. The method includes the following steps: S1: Calibrate a float charging voltage curve Map of two normal lithium iron phosphate batteries connected in series under different SOC differences; S2: Randomly collect voltage data of the two lithium iron phosphate batteries under series float charging, observe the battery voltage curves. If the voltage curve does not show a downward trend, it indicates that the battery does not have an internal short circuit fault; if the voltage curve shows a downward trend, it indicates that the battery has an internal short circuit fault; S3: When an internal short circuit occurs, based on the voltage curve Map calibrated in S1, find the intersection point between the faulty battery voltage curve in S2 and the Map, and record the time and voltage of the intersection point; S4: Record the SOC difference ΔSOC corresponding to two intersection points in the Map, and the time difference ΔT between the two intersection points, and calculate the leakage current I based on ΔSOC and ΔT. leak S5: Calculate the average voltage U between the two intersection points in S4, and calculate the short-circuit resistance R = U / I according to Ohm's law. leak .

Description

Technical Field

[0001] This invention belongs to the field of battery fault diagnosis, specifically relating to a quantitative diagnostic method for internal short circuits in batteries under float charging conditions. Background Technology

[0002] Lithium iron phosphate (LFP) batteries boast advantages such as high output voltage, long lifespan, good safety, and excellent high-temperature performance, making them widely used as backup power sources and energy storage in systems like 5G base stations and substation DC power supplies. However, LFP batteries still present some safety concerns. Regardless of the type of battery, various issues can arise during production and use. Dust and raw material burrs during production, along with misuse during use such as overcharging, over-discharging, and impacts, can lead to micro-short circuits. Over time, these micro-short circuits worsen, continuously draining the battery, increasing heat generation, and potentially causing serious safety problems like thermal runaway. Therefore, early diagnosis and warning of internal short circuit faults in batteries are crucial.

[0003] Most existing patents for diagnosing internal short circuits in batteries diagnose internal short circuits under constant current charging and discharging or dynamic operating conditions. However, there is currently no effective method for diagnosing internal short circuit faults under constant voltage conditions. Summary of the Invention

[0004] This invention is made to solve the above-mentioned problems, and aims to provide a method for identifying and quantitatively diagnosing individual cells that have internal short-circuit faults under constant voltage conditions.

[0005] This invention provides a method for quantitative diagnosis of internal short circuits in batteries under float charging conditions, characterized by the following steps:

[0006] Step S1: calibrate the float charge voltage curve map of two normal lithium iron phosphate batteries connected in series under different SOC differences, i.e., the summary map of float charge voltage curves connected in series under different SOC differences.

[0007] Step S2: Determine the voltage curve of the lithium iron phosphate battery to be diagnosed, and determine whether an internal short circuit has occurred based on the voltage curve of the lithium iron phosphate battery to be diagnosed.

[0008] Step S3: When an internal short circuit occurs in the lithium iron phosphate battery to be diagnosed, based on the float charge voltage curve Map, find the intersection point between the voltage curve of the lithium iron phosphate battery with the internal short circuit and the float charge voltage curve Map, and record the time and voltage of the intersection point.

[0009] Step S4: Record the SOC difference ΔSOC at the two intersection points of the voltage curve and float charge voltage curve Map of the lithium iron phosphate battery experiencing an internal short circuit, as well as the time difference ΔT between the two intersection points. Calculate the leakage current I based on ΔSOC and ΔT. leak ;

[0010] Step S5: Calculate the average voltage U between the two intersection points, and calculate the short-circuit resistance R = U / I according to Ohm's law. leak .

[0011] The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions provided by this invention may also have the following feature: the method is applicable to constant voltage conditions.

[0012] The method for quantitative diagnosis of internal short circuits in a battery under float charging conditions provided by this invention may also have the following feature: step S1 includes the following sub-steps:

[0013] Step S1-1: Number the two normal lithium iron phosphate batteries as Battery 1 and Battery 2, and charge Battery 1 and Battery 2 to the cutoff voltage using constant current and constant voltage.

[0014] Step S1-2: Before each float charge, discharge the No. 2 battery to different SOC levels.

[0015] Steps S1-3: Connect the No. 2 battery with different SOCs of charge to the No. 1 battery in series;

[0016] Steps S1-4: Discharge the voltage of the series-connected batteries to below the float charge voltage, then charge them to the float charge voltage and perform float charging.

[0017] Steps S1-5: During each float charge, record the float charge voltage data of the series-connected battery under different SOC differences to form the float charge voltage curve of the series-connected battery under different SOC differences.

[0018] Steps S1-6: Summarize the float charge voltage curves of the series-connected batteries under different SOC differences to form the float charge voltage curve Map.

[0019] In the quantitative diagnosis method for internal short circuit of battery under float charging condition provided by the present invention, it may also have the following feature: wherein, in steps S1-4, the float charging voltage is higher than the plateau voltage of lithium iron phosphate battery.

[0020] The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions provided by this invention may also have the following feature: wherein step S2 includes the following sub-steps:

[0021] Step S2-1: Collect voltage data of the lithium iron phosphate battery to be diagnosed and the normal lithium iron phosphate battery under series floating charge to form a battery voltage curve;

[0022] Step S2-2: Determine whether the lithium iron phosphate battery to be diagnosed has an internal short circuit based on the trend of the battery voltage curve. The determination rule is: if the voltage curve does not show a downward trend, it is determined that the lithium iron phosphate battery to be diagnosed does not have an internal short circuit fault; if the voltage curve shows a downward trend, it is determined that the lithium iron phosphate battery to be diagnosed has an internal short circuit fault.

[0023] The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions provided by this invention may also have the following feature: wherein, in step S4, the leakage current I leak The calculation formula is:

[0024] The method for quantitative diagnosis of internal short circuits in a battery under float charging conditions provided by this invention may also have the following feature: wherein the formula for calculating the average voltage U in step S5 is as follows: Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for quantitative diagnosis of internal short circuits in batteries under float charging conditions according to an embodiment of the present invention.

[0026] Figure 2 This is a Map diagram of the float charge voltage curves of two normal lithium iron phosphate batteries connected in series under different SOC differences, according to an embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram of a lithium iron phosphate battery connected in series according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the lithium iron phosphate battery voltage curve and operation calculation in this embodiment. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate the method for quantitative diagnosis of internal short circuits in batteries under float charging conditions.

[0030] In this embodiment, two 86Ah lithium iron phosphate batteries manufactured by CATL (Contemporary Amperex Technology Co., Limited) were randomly selected for verification.

[0031] Figure 1 This is a flowchart of a method for quantitative diagnosis of internal short circuits in batteries under float charging conditions, according to an embodiment of the present invention.

[0032] like Figure 1As shown, the battery internal short circuit quantitative diagnosis method S100 under float charging conditions according to an embodiment of the present invention includes the following steps:

[0033] Step S1: Calibrate the float charge voltage curves (Map) of two normal lithium iron phosphate batteries connected in series under different SOC differences in this embodiment. Specifically, this includes the following steps:

[0034] Step S1-1: Number the two normal lithium iron phosphate batteries as Battery 1 and Battery 2. Charge Battery 1 and Battery 2 with constant current and constant voltage until the cutoff voltage is 3.65V. In order to make the initial state of charge of the batteries consistent, constant current and constant voltage charging is used. The cutoff current of constant current and constant voltage charging is set to 0.05C.

[0035] Steps S1-2: Before each float charge experiment, discharge 0% SOC, 0.125% SOC, 0.25% SOC, 0.5% SOC, and 1% SOC of battery No. 2 respectively. This can be done by discharging battery No. 2 with a current of 20A for 0s, 19s, 39s, 77s, and 155s respectively, or by using other currents. The time required to discharge different amounts of charge can be calculated using ampere-hour integration.

[0036] Steps S1-3: Connect battery 1 and battery 2 in series.

[0037] Steps S1-4 involve discharging the voltage of the series-connected batteries to below the float charge voltage, then charging them back to the float charge voltage for float charging. In this embodiment, the battery's operating voltage is 2.5V-3.65V, and the float charge voltage is set to 3.45V.

[0038] Steps S1-5: During each float charge, record the float charge voltage data of the series-connected batteries under different SOC differences to form the float charge voltage curve of the series-connected batteries under different SOC differences.

[0039] Steps S1-6: Summarize the float charge voltage curves of series-connected batteries under different SOC differences to form a float charge voltage curve map.

[0040] Figure 2 This is a map of the float charge voltage curves of two normal lithium iron phosphate batteries connected in series under different SOC differences, according to an embodiment of the present invention.

[0041] Battery 1 is connected in series with batteries 2 of different SOCs and then float-charged, such as... Figure 2As shown, when there is no or very small difference in SOC, the voltage curves of the two batteries during float charging almost overlap, and the voltage difference between the two batteries is close to 0, indicating good consistency. The voltage difference during float charging is 66mV at a 0.125% SOC difference; 129mV at a 0.25% SOC difference; 203mV at a 0.5% SOC difference; and 216mV at a 1% SOC difference. It can be seen that the larger the SOC difference, the larger the voltage difference during float charging. Furthermore, during float charging within the range of 0% to 0.5% SOC, the voltage difference and SOC difference are nearly linear. However, during float charging with a 1% SOC difference, since battery #2 is close to its plateau voltage, the voltage difference and SOC difference do not show a nearly linear relationship. Therefore, the voltage curve for the 1% SOC segment is not used in this example for calculating the short-circuit resistance.

[0042] Step S2 involves determining the voltage curves of batteries Cell01 and Cell02 in this embodiment, and then judging whether an internal short circuit has occurred based on the battery voltage curves. Specifically, this includes the following steps:

[0043] Step S2-1: Collect the voltage data of battery Cell01 and battery Cell01 floating charge in series in this embodiment to form a battery voltage curve.

[0044] Figure 3 This is a schematic diagram of a lithium iron phosphate battery connected in series according to an embodiment of the present invention.

[0045] like Figure 3 As shown, in order to simulate the internal short circuit of the battery, the battery Cell01 and battery Cell02 in this embodiment of the invention are connected in series to form a battery pack, and a resistor with a resistance of 10Ω is connected in parallel outside the battery Cell01.

[0046] Step S2-2: Determine whether the lithium iron phosphate battery in this embodiment has an internal short circuit based on the trend of the battery voltage curve. The determination rule is: if the battery voltage curve does not show a downward trend, it is determined that there is no internal short circuit fault; if the battery voltage curve shows a downward trend, it is determined that there is an internal short circuit fault.

[0047] The specific method for judging internal short circuit faults is as follows: combine the formed battery voltage curve with the float charge voltage curve Map diagram from step S1, and then observe whether the battery voltage curve shows a downward trend.

[0048] Figure 4 This is a schematic diagram of the lithium iron phosphate battery voltage curve and operation calculation in this embodiment.

[0049] like Figure 4As shown, the voltage curve of battery Cell01 in this embodiment shows a significant downward trend, indicating that battery Cell01 has an internal short circuit fault. Step S3 is then executed.

[0050] Step S3: Determine the intersection point of the battery Cell01 voltage curve and the float charge voltage curve Map, and record the time and voltage of the intersection point.

[0051] like Figure 4 As shown, in this embodiment, the battery Cell01 voltage curve begins to decrease at 4202s with a voltage of 3.45V; the intersection time with the voltage curve showing a difference of 0.125% SOC is 5202s with a voltage of 3.416V; the intersection time with the voltage curve showing a difference of 0.25% SOC is 6306s with a voltage of 3.385V; and the intersection time with the voltage curve showing a difference of 0.5% SOC is 8132s with a voltage of 3.349V.

[0052] Step S4: Record the SOC difference ΔSOC corresponding to two intersection points of the battery Cell01 voltage curve and the float charge voltage curve, and the time difference ΔT between the two intersection points. Calculate the leakage current Ileak based on ΔSOC and ΔT.

[0053] like Figure 4 As shown, the intersection time of the battery Cell01 voltage curve and the float charge voltage curve with ΔSOC = 0.125% is 5202s. The time from the start of the short circuit to the consumption of 0.125% SOC by the short circuit is ΔT = 5202s - 4202s = 1000s. In this embodiment, the battery capacity Q is 86Ah, so the leakage current Ileak is:

[0054]

[0055] Similarly, the time to reach the intersection of the voltage curve corresponding to ΔSOC = 0.25% is ΔT = 2104s, and the time to reach the intersection of the voltage curve corresponding to ΔSOC = 0.5% is ΔT = 3929s, with leakage currents of 0.368A and 0.394A respectively.

[0056] Step S5: Calculate the average voltage U between two intersection points of the battery Cell01 voltage curve and the float charge voltage curve, and calculate the short-circuit resistance R = U / Ileak according to Ohm's law.

[0057] like Figure 4 As shown, the average voltage is the voltage averaged over time. The time it takes for the battery Cell01 voltage curve to intersect with the float charge voltage curve at ΔSOC = 0.125% is 1000s, meaning it takes 1000s for the voltage to drop from 3.45V to 3.416V. The average voltage U is 3.433V, and the short-circuit resistance R is:

[0058] R = U / I leak =3.433V / 0.387A = 8.87Ω

[0059] Similarly, the short-circuit resistance calculated using the float charge voltage curve corresponding to ΔSOC = 0.25% is 9.16V, and the short-circuit resistance calculated using the float charge voltage curve corresponding to ΔSOC = 0.5% is 8.69V.

[0060] Therefore, the above steps can accurately determine whether a lithium iron phosphate battery has an internal short circuit, and can also quantitatively determine the leakage degree of a battery with an internal short circuit, with high calculation accuracy.

[0061] The role and effect of the embodiments

[0062] The quantitative diagnostic method for internal short circuits in batteries under float charging conditions provided by embodiments of the present invention can effectively detect internal short circuit faults under float charging conditions by examining the trend of the battery voltage curve to determine whether an internal short circuit has occurred, thus overcoming the shortcomings of existing technologies in fault diagnosis under float charging conditions. Since no battery model is required, only the float charging voltage curves of two batteries are needed, making the method simple and easy to operate. This invention can not only detect faulty cells but also quantitatively diagnose the severity of internal short circuits, thereby enabling timely handling of faulty batteries to prevent thermal runaway.

Claims

1. A method for quantitative diagnosis of internal short circuits in batteries under float charging conditions, characterized in that, Includes the following steps: Step S1: Calibrate the float charge voltage curve Map of two normal lithium iron phosphate batteries connected in series under different SOC differences; Step S2: Determine the voltage curve of the lithium iron phosphate battery to be diagnosed, and determine whether an internal short circuit has occurred based on the voltage curve of the lithium iron phosphate battery to be diagnosed. Step S3: When the lithium iron phosphate battery to be diagnosed experiences an internal short circuit, based on the float charge voltage curve Map, find the intersection point between the voltage curve of the lithium iron phosphate battery experiencing an internal short circuit and the float charge voltage curve Map, and record the time and voltage of the intersection point. Step S4: Record the SOC difference ΔSOC corresponding to the two intersection points of the voltage curve of the lithium iron phosphate battery experiencing an internal short circuit and the float charge voltage curve Map, as well as the time difference ΔT between the two intersection points. Calculate the leakage current I based on ΔSOC and ΔT. leak ; Step S5: Calculate the average voltage U between the two intersection points, and calculate the short-circuit resistance R = U / I according to Ohm's law. leak .

2. The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions according to claim 1, characterized in that: The method is applicable to constant pressure operating conditions.

3. The method for quantitative diagnosis of internal short circuits in a battery under float charging conditions as described in claim 1. Its features are: Step S1 includes the following sub-steps: Step S1-1: Number the two normal lithium iron phosphate batteries as Battery 1 and Battery 2, and charge Battery 1 and Battery 2 to the cutoff voltage using constant current and constant voltage. Step S1-2: Before each float charge, discharge the No. 2 battery to different SOC levels. Steps S1-3: Connect the No. 2 battery with different SOCs of charge to the No. 1 battery in series; Steps S1-4: Discharge the voltage of the series-connected batteries to below the float charge voltage, then charge them to the float charge voltage and perform float charging. Steps S1-5: During each float charge, record the float charge voltage data of the series-connected battery under different SOC differences to form the float charge voltage curve of the series-connected battery under different SOC differences. Steps S1-6: Summarize the float charge voltage curves of the series-connected batteries under different SOC differences to form the float charge voltage curve Map.

4. The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions according to claim 3, characterized in that: in, The float charge voltage mentioned in steps S1-4 is higher than the plateau voltage of the lithium iron phosphate battery.

5. The method for quantitative diagnosis of internal short circuits in a battery under float charging conditions according to claim 1. Its features are: Step S2 includes the following sub-steps: Step S2-1: Collect voltage data of the lithium iron phosphate battery to be diagnosed and the normal lithium iron phosphate battery under series floating charge to form a battery voltage curve; Step S2-2: Determine whether the lithium iron phosphate battery to be diagnosed has an internal short circuit based on the trend of the battery voltage curve. The determination rule is: if the voltage curve does not show a downward trend, it is determined that the lithium iron phosphate battery to be diagnosed does not have an internal short circuit fault; if the voltage curve shows a downward trend, it is determined that the lithium iron phosphate battery to be diagnosed has an internal short circuit fault.

6. The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions according to claim 1, characterized in that: in, The leakage current I mentioned in step S4 leak The calculation formula is:

7. The method for quantitative diagnosis of internal short circuit in a battery under float charging conditions according to claim 1, characterized in that: in, The formula for calculating the average voltage U in step S5 is as follows:

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