Fusing protection effectiveness analysis method for low-voltage test and high-voltage simulation battery system

Abstract

The invention discloses a fusing protection effectiveness analysis method for a low-voltage test and high-voltage simulation battery system. The method comprises the following steps: testing an external short-circuit response characteristic of a single battery; testing external short-circuit response characteristics of the low-voltage battery pack; modeling an external short-circuit equivalent circuit of the battery; identifying equivalent circuit model parameters; simulating short-circuit current outside the high-voltage system; external short circuit fusing effective current transformation; judging fusing protection time; and analyzing the external short-circuit protection effectiveness of the battery system. According to the invention, the fusing protection of the battery system is divided into the low-voltage unit and the high-voltage unit, and testing and simulation are carried out respectively, so that the problem that the high-voltage system fusing protection verification test is difficult to implement due to cost and risks is solved, and the safety and reliability of the battery system can be improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for analyzing the effectiveness of fuse protection of a low-voltage test plus high-voltage simulation battery system. Background Art

[0002] Currently, batteries have been widely used in energy storage systems, electric vehicles, new energy rail transit and other fields. The voltage level of battery systems has reached more than 1,000 volts. However, battery safety issues have become increasingly prominent as the scope of application increases, especially for high-voltage and large-capacity battery energy storage systems. Due to the large number of battery cells in the system, there are a large number of series nodes. When any two nodes are connected to the same potential at the same time, the batteries between the nodes will be short-circuited, and a large short-circuit current will be generated in an instant, releasing huge energy, which can easily cause safety accidents such as thermal runaway of the battery. Since the energy release during the battery short-circuit process is rapid and difficult to block, the most effective means of protection is to arrange a fuse in the potential short-circuit circuit to ensure that the circuit is promptly melted and cut off to protect the battery when an external short-circuit occurs in the battery.

[0003] However, since the battery short-circuit current has nonlinear variation characteristics and there are many nodes in the system, the current response process when a short circuit occurs in the battery cells between different nodes is not the same. In addition, the battery system has huge energy, and there are huge risks and costs in verifying the effectiveness of the fuse protection of the high-voltage battery system as a whole, which is difficult to test in practice. Therefore, the present invention proposes a battery system fuse protection effectiveness analysis method of low-voltage testing + high-voltage simulation, which analyzes the protection time and effectiveness of the fuse protection design in the high-voltage battery system to improve the safety and reliability of the external short-circuit protection of the battery system. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for analyzing the effectiveness of fuse protection of a low-voltage test plus high-voltage simulation battery system, the method comprising: Step 1: Single cell external short circuit response characteristic test; Step 2: Low-voltage battery pack external short-circuit response characteristic test; Step 3: Modeling of battery external short-circuit equivalent circuit; Step 4: Equivalent circuit model parameter identification; Step 5: High voltage system external short-circuit current simulation; Step 6: External short circuit fuse effective current transformation; Step 7: Determine the fuse protection time; Step 8: Analysis of effectiveness of short-circuit protection outside the battery system.

[0005] Furthermore, the step 1 specifically includes: using a single battery as a test object to perform an external short circuit test; and obtaining a current response change curve of the battery single battery under an external short circuit state.

[0006] Furthermore, in step 1, the short circuit time is greater than or equal to 10ms, and the external short circuit test using a single battery as a test object specifically includes: S101: Select multiple short-circuit test SOC points according to the SOC range used in the battery system design; S102: Under a specific SOC, an external short circuit test is performed on the single battery under different external resistances. After each test, the single battery is readjusted to a specified SOC and allowed to stand for a long time. S103: Adjust the single battery to the next SOC point to be tested, and repeat S102.

[0007] Furthermore, the step 2 specifically includes: using a low-voltage battery pack as a test object to perform an external short-circuit test; obtaining a characteristic curve of the battery short-circuit current changing with the voltage level; the low-voltage battery pack is composed of n battery cells connected in series, n≥2, and the short-circuit test time and test SOC are consistent with the external short-circuit response characteristic test of the single battery.

[0008] Furthermore, the external short circuit test using the low-voltage battery pack as the test object specifically includes: S201: Under a specific SOC, perform an external short circuit test on the low-voltage battery pack under different external resistance values. After each test, readjust the low-voltage battery pack to the specified SOC and let it stand for a long time; S202: Adjust the number of batteries connected in series in the low-voltage battery pack, n≥2, and repeat S202; S203: Adjust the low-voltage battery pack to the next SOC point to be tested, and repeat S201 and S202.

[0009] Furthermore, the step 3 specifically includes: Use equivalent circuit model to simulate the battery external short circuit process; N batteries are connected in series and short-circuited through an external circuit, N ≥ 1, and the external circuit simulation includes RL reflecting the external resistance and LL reflecting the line inductance.

[0010] Furthermore, the step 4 specifically includes, when the number of batteries connected in series is known, measuring and obtaining the open circuit voltage OCV of the battery, obtaining the internal resistance R0 of the battery, the initial values ​​of the parameters of the RC link and the RL link by the AC impedance method, and obtaining the external resistance R by measuring the bridge device. L , line inductance L LInitial value; use optimization algorithm to accurately fit the parameters; the optimization goal in the fitting process is to minimize the root mean square between the test current value and the simulation current value. The specific calculation method is shown in formula (1): ; in, J To optimize the goal, I r is the test current value, I s is the simulated current value, j is the data point, N is the number of data points.

[0011] Furthermore, the step 5 specifically includes, according to the number of battery systems connected in series and parallel, based on the battery equivalent circuit, connecting the systems in series and parallel to form a system short-circuit simulation model, and performing a short-circuit simulation under given SOC and external line conditions to obtain an external short-circuit current response curve of the high-voltage battery system.

[0012] Furthermore, the step 6 specifically includes transforming the short-circuit current outside the high-voltage battery system according to formula (2) to obtain the effective fuse current: ; in t Indicates time, I t for t The battery external short-circuit current value at the moment, I mt is the effective current for fusing; since the fusing mechanism of the fuse is that the Joule heat generated by the flowing current causes the fuse to melt and fusing, the fusing time is inversely proportional to the square integral of the flowing current.

[0013] Furthermore, the step 7 specifically includes: comparing the obtained effective current of the fuse with the fuse I - t The inverse time curve is compared, and the fuse breaking time of the battery system external short circuit is determined based on the intersection of the two curves. t f ; The step 8 specifically includes: t f Expected time for fuse t e For comparison, if t f < t e , the fuse protection is effective, otherwise, the fuse protection is invalid.

[0014] Beneficial effects of the present invention: The present invention is designed for external short-circuit fuse protection of the battery system, and its goal is to analyze whether the effectiveness of the fuse protection time of the battery system meets the design requirements. By splitting the fuse protection of the battery system into low-voltage units and high-voltage units, and conducting tests and simulations respectively, the problem that the verification test of the fuse protection of the high-voltage system is difficult to implement due to cost and risk is solved. The low-voltage battery unit has small energy, low cost, controllable risk, and high test feasibility. The actual current response of the battery external short circuit can be obtained through testing; the equivalent circuit model can reflect the change process of the battery short-circuit current with the number of series connections, SOC state and other factors after parameter identification and optimization, and maximize the reflection of the true nonlinear change process of the battery external short-circuit current; the effectiveness analysis of the system external short-circuit protection conducted on this basis takes into account the authenticity of the data and the safety of the test, and can realize the external short-circuit protection risk analysis of the battery system, especially the high-voltage battery system, under low-risk and low-cost conditions. It is an effective way to achieve qualitative to quantitative risk analysis, which is of great significance to improving the safety and reliability of the battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of battery cell short-circuit current changing with external resistance (specific SOC); Figure 2 Schematic diagram of short-circuit current of low-voltage battery pack changing with the number of series connections (specific SOC and external resistance); Figure 3 Schematic diagram of battery external circuit simulation model; Figure 4 Schematic diagram of external short-circuit simulation current of battery system; Figure 5 Schematic diagram of effective fuse current for external short circuit of battery system; Figure 6 Schematic diagram of the fuse protection time judgment process; Figure 7 A schematic diagram of a process of analyzing the effectiveness of fuse protection of a low-voltage test plus high-voltage simulation battery system according to the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings: The present invention is carried out according to the following steps: Step 1: Test the external short-circuit response characteristics of a single cell. Use a single cell as the test object to perform an external short-circuit test to obtain the current response curve of the battery cell under the external short-circuit state. To ensure that the test data can reflect the external short-circuit response characteristics of the battery, the short-circuit time generally needs to be more than 10ms. The specific test process is as follows: Step 101: Select multiple short-circuit test SOC points based on the SOC range used in the battery system design.

[0017] Step 102: Under a certain SOC, perform external short circuit tests on the single battery with different external resistance values. Figure 1 The short-circuit current of a battery changes with external resistance at a specific SOC. After each test, the single cell needs to be readjusted to the specified SOC and left to rest for a long time.

[0018] Step 103: Adjust the single cell to the next SOC point to be tested, and repeat Step 102.

[0019] Step 2: Low-voltage battery pack external short-circuit response characteristic test. Use a low-voltage battery pack as the test object to perform an external short-circuit test to obtain a characteristic curve of the battery short-circuit current changing with voltage level. Figure 2 The short-circuit current of a low-voltage battery pack changes with the number of battery cells in series under specific SOC and external resistance conditions. The low-voltage battery pack is composed of n (n≥2) battery cells in series. The short-circuit test time and test SOC can be consistent with the external short-circuit response characteristic test of the single battery. The specific test process is as follows: Step 201: Under a certain SOC, the low-voltage battery pack is subjected to an external short-circuit test under different external resistances. After each test, the low-voltage battery pack needs to be readjusted to the specified SOC and allowed to stand for a long time.

[0020] Step 202: Adjust the number n of batteries connected in series in the low-voltage battery pack, and repeat Step 202.

[0021] Step 203: Adjust the low voltage battery pack to the next SOC point to be tested, and repeat Step 201 and Step 202.

[0022] Step 3: Modeling of the battery external short circuit equivalent circuit. Use an equivalent circuit model to simulate the battery external short circuit process, including but not limited to the RC equivalent circuit model. It should be noted that in addition to the battery open circuit voltage OCV, the battery internal resistance R0 and the RC parallel link in the equivalent circuit, the battery inductance should also be considered due to the short response time of the battery external short circuit, so the RL parallel link is added. Figure 3 The schematic diagram of the battery external short-circuit simulation model is shown. After n batteries are connected in series, they are short-circuited through an external circuit (when n=1, it is a single battery). The external circuit simulation needs to include R that reflects the external resistance. L and line inductance L L .

[0023] Step 4: Identify parameters of the equivalent circuit model. The number of batteries in series n is known, and the battery open circuit voltage OCV can be obtained by measurement. Other parameters include R0, RC link, RL link, and R L and L LIt is impossible to obtain accurate values ​​by direct measurement, and it is necessary to obtain them based on the short-circuit response changes of the battery cells and low-voltage battery packs. The initial values ​​of the R0, RC link, and RL link parameters can be obtained through methods such as AC impedance. L and L L The initial value can be obtained by measuring with a device such as a bridge, and then an optimization algorithm (including but not limited to a particle swarm algorithm or a genetic algorithm, etc.) is used to accurately fit the parameters. The optimization goal in the fitting process is to minimize the root mean square (RMSE) between the test current value and the simulation current value. The specific calculation method is shown in formula (1): ; in, J To optimize the goal, I r is the test current value, I s is the simulated current value, j is the data point, N is the number of data points.

[0024] Step 5: High-voltage system external short-circuit current simulation. According to the number of battery systems in series and parallel, based on the battery equivalent circuit, the series and parallel connections constitute a system short-circuit simulation model, and perform short-circuit simulation under given SOC and external line conditions, such as Figure 4 As shown, the external short-circuit current response curve of the high-voltage battery system can be obtained.

[0025] Step 6: External short circuit fuse effective current conversion. According to formula (2), the external short circuit current of the high-voltage battery system is converted to obtain the fuse effective current. t Indicates time, I t for t The external short-circuit current value of the battery at the moment. Since the fuse's melting mechanism is that the Joule heat generated by the flowing current causes the fuse to melt and melt, the melting time is inversely proportional to the square integral of the flowing current. I mt To be the effective current of the fuse, Figure 5 The changing curve of effective current of a battery system is shown.

[0026] ; Step 7: Determine the fuse protection time. Figure 6 As shown, the effective current of the fuse is I - t The inverse time curve is compared, and the fuse breaking time of the battery system external short circuit is determined based on the intersection of the two curves. t f .

[0027] Step 8: Analysis of the effectiveness of short-circuit protection of the battery system. t f Expected time for fuse t e For comparison, if t f < t e , the fuse protection is effective, otherwise, the fuse protection is invalid.

[0028] Obviously, the examples of the present invention (including short-circuit external resistance, number of low-voltage battery packs in series, system short-circuit current, fuse It curve, etc.) are only examples for clearly explaining the present invention, and are not limitations of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

[0029] The above embodiments describe the technical solutions of the present invention in detail. Obviously, the present invention is not limited to the described embodiments. Based on the embodiments of the present invention, people familiar with the technical field can also make various changes accordingly, but any changes that are equivalent or similar to the present invention belong to the scope of protection of the present invention.

[0030] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A method for analyzing the effectiveness of fuse protection of a low-voltage test plus high-voltage simulation battery system, characterized in that: The method comprises: Step 1: Single cell external short circuit response characteristic test; Step 2: Low-voltage battery pack external short-circuit response characteristic test; Step 3: Modeling of battery external short-circuit equivalent circuit; Step 4: Equivalent circuit model parameter identification; Step 5: High voltage system external short-circuit current simulation; Step 6: External short circuit fuse effective current transformation; Step 7: Determine the fuse protection time; Step 8: Analysis of effectiveness of short-circuit protection outside the battery system.

2. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 1, characterized in that: The step 1 specifically includes: Use single battery as test object to conduct external short circuit test; Obtain the current response change curve of the battery cell under the external short circuit state.

3. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 2, characterized in that: In the step 1, the short circuit time is greater than or equal to 10ms, and the external short circuit test using a single battery as a test object specifically includes: S101: Select multiple short-circuit test SOC points according to the SOC range used in the battery system design; S102: Under a specific SOC, an external short circuit test is performed on the single battery under different external resistances. After each test, the single battery is readjusted to a specified SOC and allowed to stand for a long time. S103: Adjust the single battery to the next SOC point to be tested, and repeat S102.

4. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 3, characterized in that: The step 2 specifically includes: Use low voltage battery pack as test object to conduct external short circuit test; Obtain the characteristic curve of battery short-circuit current changing with voltage level; The low-voltage battery pack is composed of n battery cells connected in series, where n≥2, and the short-circuit test time and the test SOC are consistent with the single-cell battery external short-circuit response characteristic test.

5. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 4, characterized in that: The external short circuit test using a low voltage battery pack as a test object specifically includes: S201: Under a specific SOC, perform an external short circuit test on the low-voltage battery pack under different external resistance values. After each test, readjust the low-voltage battery pack to the specified SOC and let it stand for a long time; S202: Adjust the number of batteries connected in series in the low-voltage battery pack, n≥2, and repeat S202; S203: Adjust the low-voltage battery pack to the next SOC point to be tested, and repeat S201 and S202.

6. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 5, characterized in that: The step 3 specifically includes: Use equivalent circuit model to simulate the battery external short circuit process; N batteries are connected in series and short-circuited through an external circuit, N ≥ 1, and the external circuit simulation includes RL reflecting the external resistance and LL reflecting the line inductance.

7. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 6, characterized in that: The step 4 specifically includes, when the number of batteries in series is known, measuring and obtaining the open circuit voltage OCV of the battery, obtaining the internal resistance R0 of the battery, the initial values ​​of the parameters of the RC link and the RL link by the AC impedance method, and obtaining the external resistance R by measuring the bridge device. L , line inductance L L Initial value; use optimization algorithm to accurately fit the parameters; the optimization goal in the fitting process is to minimize the root mean square between the test current value and the simulation current value. The specific calculation method is shown in formula (1): ; in, J To optimize the goal, I r is the test current value, I s is the simulated current value, j is the data point, N is the number of data points.

8. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 7, characterized in that: The step 5 specifically includes, according to the number of battery systems connected in series and parallel, based on the battery equivalent circuit, connecting in series and parallel to form a system short-circuit simulation model, and performing short-circuit simulation under given SOC and external line conditions to obtain an external short-circuit current response curve of the high-voltage battery system.

9. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 8, characterized in that: The step 6 specifically includes transforming the short-circuit current outside the high-voltage battery system according to formula (2) to obtain the effective fuse current: ; in t Indicates time, I t for t The battery external short-circuit current value at the moment, I mt is the effective current for fusing; since the fusing mechanism of the fuse is that the Joule heat generated by the flowing current causes the fuse to melt and fusing, the fusing time is inversely proportional to the square integral of the flowing current.

10. A method for analyzing the effectiveness of fuse protection of a low voltage test plus high voltage simulation battery system as claimed in claim 9, characterized in that: The step 7 specifically includes: comparing the obtained effective fuse current with the fuse I - t The inverse time curve is compared, and the fuse breaking time of the battery system external short circuit is determined based on the intersection of the two curves. t f ; The step 8 specifically includes: t f Expected time for fuse t e For comparison, if t f < t e , the fuse protection is effective, otherwise, the fuse protection is invalid.

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