A method for quantitatively diagnosing internal short circuit of battery under float charging based on intermittent equalization

Abstract

This invention provides a quantitative diagnostic method for internal short circuits in batteries under float charging based on intermittent equalization, comprising the following steps: Step S1, charging the lithium iron phosphate battery pack to float charging state; Step S2, maintaining the float charging state for a period of time, randomly collecting float charging voltage data of the lithium iron phosphate battery pack, and observing the voltage curves of each cell in the lithium iron phosphate battery pack to determine whether the cell has an internal short circuit fault; Step S3, after determining that the corresponding cell has an internal short circuit fault, starting or stopping the equalization system by judging whether the voltage difference exceeds a threshold; Step S4, recording the voltage, equalization resistor value, equalization time and non-equalization time during intermittent equalization; Step S5, calculating the equalization current at each moment based on the recorded voltage and equalization resistor value, calculating the average equalization current during the equalization on period, and calculating the average leakage current; Step S6, calculating the average voltage between the equalization shutdown and the next equalization on, and calculating the internal short circuit resistance value.

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 based on intermittent equalization. Background Technology

[0002] Lithium iron phosphate (LFP) batteries boast advantages such as long cycle life, high 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. No battery type is perfect during production and use. Dust and raw material burrs during manufacturing, along with misuse during use (including overcharging, over-discharging, and impacts), can cause micro-short circuits. Over time, these micro-short circuits can escalate into severe internal short circuits, continuously draining the battery, increasing heat generation, and potentially leading to thermal runaway and other serious safety issues. Therefore, early warning systems for internal short circuits are crucial.

[0003] Most existing methods for diagnosing internal short circuits in batteries are designed for constant current charging and discharging or dynamic discharge conditions. However, there is currently no effective method for diagnosing internal short circuits under float charging conditions. Summary of the Invention

[0004] This invention is made to solve the above-mentioned problems, and aims to provide a quantitative diagnosis method for internal short circuits in batteries under float charging based on intermittent equalization.

[0005] This invention provides a quantitative diagnosis method for internal short circuits in batteries under float charging based on intermittent equalization, which is used to perform quantitative diagnosis of internal short circuits in lithium iron phosphate battery packs under float charging conditions. It has the following features and includes the following steps: Step S1, charging the lithium iron phosphate battery pack to float charging state;

[0006] Step S2: After maintaining the float charging state for a period of time, randomly collect the float charging voltage data of the lithium iron phosphate battery pack and observe whether the voltage curve of each cell in the lithium iron phosphate battery pack shows a downward trend. When the voltage curve of each cell does not show a downward trend, it is determined that the cells do not have internal short circuit faults. When the voltage curve of a certain cell shows a downward trend, it is determined that the corresponding cell has an internal short circuit fault.

[0007] In step S3, after determining that the corresponding cell has an internal short circuit fault in step S2, it is determined whether the voltage difference exceeds the threshold, and a first threshold and a second threshold are set. When the first threshold is exceeded, the equalization system is started to perform intermittent equalization. When the voltage difference is lower than the second threshold, the equalization system is turned off.

[0008] Step S4: Record the voltage, equalization resistor value, equalization time, and unbalanced time during intermittent equalization.

[0009] Step S5: Calculate the balancing current at each moment based on the voltage and balancing resistor value recorded in step S4, and then calculate the average balancing current I during the balancing activation period. eq Based on the duty cycle of the equalization process, the average leakage current I is calculated equivalently from the time the equalization process is turned off until the next equalization process is turned on. leak ;

[0010] Step S6: Calculate the average voltage U between the time the equalization is turned off and the time the equalization is turned on again. mean According to Ohm's law, the internal short-circuit resistance RISC = U is calculated. mean / I leak The severity of the internal short circuit is determined based on the internal short circuit resistance value.

[0011] The quantitative diagnosis method for internal short circuits in batteries based on intermittent equalization under float charging provided by this invention may also have the following feature: wherein step S1 includes the following sub-steps:

[0012] Step S1-1: First, charge the lithium iron phosphate battery pack at a constant current to the float charge voltage;

[0013] Step S1-2: After charging to the float charging voltage, switch to constant voltage charging to maintain the float charging voltage.

[0014] The quantitative diagnosis method for internal short circuits in batteries based on intermittent equalization float charging provided by this invention may also have the following feature: the float charging voltage is higher than the plateau voltage of the lithium iron phosphate battery pack.

[0015] The quantitative diagnosis method for internal short circuits in batteries under float charging based on intermittent equalization provided by the present invention may also have the following features: in step S3, the voltage difference is the voltage difference between the highest voltage cell and the lowest voltage cell, the equalization method of the equalization system is passive equalization, and the first threshold and the second threshold are set according to the specific usage environment.

[0016] The quantitative diagnosis method for internal short circuits in batteries based on intermittent equalization under float charging provided by this invention may also have the following feature: wherein step S5 includes the following sub-steps:

[0017] Step S5-1: Within one equalization cycle, the equalization on time is t1, the equalization off time is t2, and the equalization current I... i For voltage U i With equalization resistor R eq The ratio of: I i =U i / R eqThe average equalization current I was calculated. eq for:

[0018]

[0019] Step S5-2: Based on the fact that the sum of the voltage drops of normal cells in the lithium iron phosphate battery pack when the balancing system is turned on equals the voltage rise of a short-circuited cell, the equivalent average leakage current I is calculated using the duty cycle of the balancing current. leak The calculation formula is as follows:

[0020]

[0021] In formula (2), n-1 is the number of normal cells in the lithium iron phosphate battery pack.

[0022] The quantitative diagnosis method for battery internal short circuits under float charging based on intermittent equalization provided by this invention may also have the following feature: wherein, in step S6, the average voltage U between the equalization shutdown and the next equalization startup... mean The calculation formula is as follows:

[0023]

[0024] The role and effect of invention

[0025] The present invention discloses a method for detecting internal short-circuit faults under float charging based on intermittent equalization. The calculation method is simple, requires no battery model, and only needs to collect float charge voltage data of the lithium iron phosphate battery pack to identify individual cells experiencing internal short-circuit faults under float charging conditions. Furthermore, by recording relevant information during equalization by the equalization system, the internal short-circuit resistance can be calculated for quantitative diagnosis, thereby determining the severity of the internal short circuit and enabling timely handling of faulty cells to prevent thermal runaway. Therefore, the present invention can effectively detect internal short-circuit faults in cells under float charging conditions, i.e., constant voltage conditions, overcoming the shortcomings of existing fault diagnosis technologies under float charging conditions. Attached Figure Description

[0026] Figure 1 This is a flowchart of an internal short-circuit fault detection method based on intermittent equalization under float charging, according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a lithium iron phosphate battery pack in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the operation calculation in an embodiment of the present invention. Detailed Implementation

[0029] To make the technical means and effects of the present invention easy to understand, the present invention will be specifically described below in conjunction with embodiments and accompanying drawings.

[0030] <Example>

[0031] Figure 1 This is a flowchart of an internal short-circuit fault detection method based on intermittent equalization floating charge in an embodiment of the present invention.

[0032] like Figure 1 As shown in this embodiment, a quantitative diagnosis method for internal short circuits in batteries under intermittent equalization float charging is used to perform quantitative diagnosis of internal short circuits in lithium iron phosphate battery packs under float charging conditions (float charging conditions refer to charging individual battery cells or battery packs to a certain higher voltage with a certain current, and then maintaining the current voltage in a constant voltage state, providing only a small amount of current to compensate for the losses caused by local effects on the battery pack or the self-discharge of the battery). The method includes the following steps:

[0033] Step S1: Charge the lithium iron phosphate battery pack to float charge state.

[0034] Step S1 includes the following sub-steps:

[0035] Step S1-1: First, charge the lithium iron phosphate battery pack at a constant current to the float charge voltage;

[0036] Step S1-2: After charging to the float charging voltage, switch to constant voltage charging to maintain the float charging voltage.

[0037] Figure 2 This is a schematic diagram of a lithium iron phosphate battery pack in an embodiment of the present invention.

[0038] like Figure 2 As shown, a lithium iron phosphate battery pack consists of n cells connected in series.

[0039] Figure 3 This is a schematic diagram of the operation calculation in an embodiment of the present invention.

[0040] like Figure 3 As shown, the lithium iron phosphate battery pack in this embodiment has a total of 6 cells, which reach the float charging state at time T1. The float charging voltage is generally set to a higher SOC voltage, which is higher than the plateau voltage of the lithium iron phosphate battery. In this embodiment, the float charging voltage is set to 3.45V.

[0041] Step S2: After maintaining the float charge state for a period of time, randomly collect the float charge voltage data of the lithium iron phosphate battery pack and observe whether the voltage curve of each cell in the lithium iron phosphate battery pack shows a downward trend. When the voltage curve of each cell does not show a downward trend, it is determined that the cells do not have internal short circuit faults. When the voltage curve of a certain cell shows a downward trend, it is determined that the corresponding cell has an internal short circuit fault. Figure 3As shown, in this embodiment, an internal short circuit fault occurred in a certain cell at time T2.

[0042] In step S3, after determining that the corresponding cell has an internal short circuit fault in step S2, it is determined whether the voltage difference exceeds the threshold, and a first threshold and a second threshold are set. When the first threshold is exceeded, the equalization system is started to perform intermittent equalization, and when the voltage difference is lower than the second threshold, the equalization system is turned off.

[0043] In step S3, the voltage difference is the voltage difference between the highest voltage cell and the lowest voltage cell. The equalization method of the equalization system is passive equalization with a sufficiently strong equalization capability. The first threshold and the second threshold are set according to the specific usage environment. In this embodiment, the first threshold is 10mV and the second threshold is 3mV.

[0044] like Figure 3 As shown in this embodiment, during the time period from T2 to T3, the internal short circuit continuously consumes battery power, causing the voltage to drop. At time T3, the voltage difference reaches the first threshold of 10mV, and the balancing system is activated. The power of the normal cells gradually decreases due to the consumption of the balancing resistor, and the voltage gradually decreases. Since float charging maintains a constant voltage for the total battery pack voltage, the voltage of the normal cells decreases, so the voltage of the short-circuited cells gradually increases. At time T4, the voltage difference is less than the second threshold of 3mV, and the balancing system is deactivated.

[0045] Step S4: Record the voltage, equalization resistor value, equalization time, and non-equalization time during intermittent equalization.

[0046] Step S5: Calculate the balancing current at each moment based on the voltage and balancing resistor value recorded in step S4, and then calculate the average balancing current I during the balancing activation period. eq Based on the duty cycle of the equalization process, the average leakage current I is calculated equivalently from the time the equalization process is turned off until the next equalization process is turned on. leak .

[0047] Step S5 includes the following sub-steps:

[0048] Step S5-1, as follows Figure 3 As shown, in this embodiment, within one balancing cycle, the balancing on time is t1, and the balancing off time is t2. During the time period t1, the balancing current I of each normal cell at each moment is... i For voltage U i With equalization resistor R eq The ratio of: I i =U i / R eq The average equalization current I was calculated. eq for:

[0049]

[0050] Step S5-2: Based on the fact that the sum of the voltage drops of the five normal cells in the lithium iron phosphate battery pack when the balancing system is turned on equals the voltage rise of the short-circuit cell, the equivalent average leakage current I is calculated using the duty cycle of the balancing current. leak The calculation formula is as follows:

[0051]

[0052] In this embodiment, the equivalent leakage current of the second and third equalization cycles can also be calculated, and then the average of the equivalent leakage current of the three equalization cycles is taken to obtain the final average leakage current.

[0053] Step S6: Calculate the average voltage U between the time the equalization is turned off and the time the equalization is turned on again. mean According to Ohm's law, the internal short-circuit resistance RISC = U is calculated. mean / I leak The severity of the internal short circuit is determined based on the internal short circuit resistance value.

[0054] In step S6, the average voltage U between the time the equalization is turned off and the time the equalization is turned on again is... mean The calculation formula is as follows:

[0055]

[0056] The role and effect of the embodiments

[0057] The method for detecting internal short-circuit faults under float charging based on intermittent equalization described in this embodiment is simple to calculate, requires no battery model, and only needs to collect the float charge voltage data of the lithium iron phosphate battery pack to identify individual cells experiencing internal short-circuit faults under float charging conditions. Furthermore, by recording relevant information during equalization by the equalization system, the internal short-circuit resistance can be calculated for quantitative diagnosis, thereby determining the severity of the internal short circuit and enabling timely handling of faulty cells to prevent thermal runaway. Therefore, this embodiment can effectively detect internal short-circuit faults in cells under float charging conditions, i.e., constant voltage conditions, overcoming the shortcomings of existing fault diagnosis technologies under float charging conditions.

[0058] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A quantitative diagnostic method for internal short circuits in batteries under float charging based on intermittent equalization, used for quantitative diagnostics of internal short circuits in lithium iron phosphate battery packs under float charging conditions, characterized in that... Includes the following steps: Step S1: Charge the lithium iron phosphate battery pack to a float charge state; Step S2: After maintaining the float charging state for a period of time, randomly collect the float charging voltage data of the lithium iron phosphate battery pack and observe whether the voltage curve of each cell in the lithium iron phosphate battery pack shows a downward trend. When the voltage curve of each cell does not show a downward trend, it is determined that the cells do not have internal short circuit faults. When the voltage curve of a certain cell shows a downward trend, it is determined that the corresponding cell has an internal short circuit fault. In step S3, after determining that the corresponding cell has an internal short circuit fault in step S2, it is determined whether the voltage difference exceeds the threshold, and a first threshold and a second threshold are set. When the voltage difference exceeds the first threshold, the equalization system is started to perform intermittent equalization. When the voltage difference is lower than the second threshold, the equalization system is turned off. Step S4: Record the voltage, equalization resistor value, equalization time, and unbalanced time during the intermittent equalization. Step S5, according to the voltage recorded in step S4 and the balancing resistance value, the balancing current at each time is calculated, and then the average balancing current I of the balancing opening time period is calculated eq ; according to the duty cycle of the balancing, the average leakage current I from the balancing closing to the next balancing opening is calculated leak ; Step S6: Calculate the average voltage U between the time the equalization is turned off and the time the equalization is turned on again. mean According to Ohm's law, the internal short-circuit resistance RISC = U is calculated. mean / I leak The severity of the internal short circuit is determined based on the internal short circuit resistance value.

2. The method for quantitative diagnosis of internal short circuits in batteries under float charging based on intermittent equalization as described in claim 1, characterized in that: in, Step S1 includes the following sub-steps: Step S1-1: First, charge the lithium iron phosphate battery pack to the float charge voltage using a constant current. Step S1-2: After charging to the float charging voltage, switch to constant voltage charging to maintain the float charging voltage.

3. The method for quantitative diagnosis of internal short circuits in batteries under float charging based on intermittent equalization as described in claim 2, characterized in that: in, The value of the float charge voltage is higher than the plateau voltage value of the lithium iron phosphate battery pack.

4. The method for quantitative diagnosis of internal short circuits in batteries under float charging based on intermittent equalization as described in claim 1, characterized in that: in, In step S3, the voltage difference is the voltage difference between the highest voltage cell and the lowest voltage cell, the equalization method of the equalization system is passive equalization, and the first threshold and the second threshold are set according to the specific usage environment.

5. The method for quantitative diagnosis of internal short circuits in batteries under float charging based on intermittent equalization according to claim 1, characterized in that: in, Step S5 includes the following sub-steps: Step S5-1: Within one equalization cycle, the equalization on time is t1, the equalization off time is t2, and the equalization current I... i For voltage U i With equalization resistor R eq The ratio of: I i =U i / R eq The average equalization current I was calculated. eq for: （1）； Step S5-2: Based on the fact that the sum of the voltage drops of normal cells in the lithium iron phosphate battery pack when the balancing system is turned on equals the voltage rise of a short-circuited cell, the equivalent average leakage current I is calculated using the duty cycle of the balancing current. leak The calculation formula is as follows: （2）， In formula (2), n-1 is the number of normal cells in the lithium iron phosphate battery pack.

6. The method for quantitative diagnosis of internal short circuits in batteries under float charging based on intermittent equalization according to claim 1, characterized in that: in, In step S6, the average voltage U between the time the equalization is turned off and the next time the equalization is turned on is... mean The calculation formula is as follows: （3）。

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