A battery pack leakage current calculation method

Abstract

The application discloses a battery pack leakage current calculation method and belongs to the technical field of battery packs. i ; the equivalent dielectric constant epsilon between conductors is calculated j ; the parasitic capacitance C s between conductors is calculated; the leakage current I s between conductors is calculated; and the total leakage current I of the battery pack is calculated. The total leakage current value of the battery pack is calculated by calculating the capacitance values and the leakage current values of the various parasitic capacitances in the calculation model. The application can control the size of the battery pack leakage current, prevent safety accidents caused by the leakage current, improve the safety and reliability of the designed battery pack, and reduce the detection and sample costs.

Description

Technical Field

[0001] This invention belongs to the field of battery pack technology, specifically a method for calculating battery pack leakage current. Background Technology

[0002] Battery packs are widely used in electric vehicles, energy storage systems, and other applications. Leakage current refers to the phenomenon where current leaks through unexpected paths during normal operation or storage of a battery pack due to factors such as aging or damage to insulation materials or design defects. Leakage current not only reduces the lifespan of the battery pack but can also seriously damage electrical components and create safety hazards. Therefore, accurately calculating battery pack leakage current and implementing corresponding measures are crucial for the safe operation and performance optimization of battery packs.

[0003] The battery pack mainly consists of battery housing, battery modules, module end plates, electrical plastic brackets, output terminals, output terminal protection covers, protection covers, busbars, low-voltage acquisition boards, low-voltage communication harnesses, high-voltage power copper busbars, liquid cooling plate assemblies, liquid cooling pipeline assemblies, BCC, FPC flexible circuit boards, explosion-proof vent valves, manual maintenance switches, high-voltage connectors, low-voltage connectors, sealing gaskets, thermally conductive structural adhesive, support plates, module fixing bolts, module support foam, single-strand blind rivets, and other components.

[0004] Currently, commercial vehicles have electrical performance testing requirements for battery pack leakage current. Theoretical calculation and design for prevention are of paramount importance for battery pack safety. However, at present, there are only theoretical formulas for calculation, and no method for calculating leakage current of different battery packs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for calculating the leakage current of a battery pack. This method can calculate the actual leakage current of the battery pack, improve the safety and reliability of the designed battery pack, and reduce testing and prototype costs.

[0006] To achieve the above objectives, the present invention provides a method for calculating battery pack leakage current, comprising the following steps:

[0007] Construct an equivalent calculation model for battery pack leakage current;

[0008] Calculate the equivalent dielectric constant between conductors: For any two conductors in the model, calculate the equivalent dielectric constant ε between them. i ;

[0009] ε i =(ε1*d1+ε2*d2……+ε n *dn) / (d1+d2……+d n )

[0010] Where ε1, ..., ε nThe dielectric constants of the different insulating materials between the conductors are d1, ..., d2. n Indicates the thickness of the corresponding insulating material;

[0011] Calculate the parasitic capacitance between conductors: Based on the calculated equivalent dielectric constant, calculate the parasitic capacitance C between the conductors. j ;

[0012] C j =ε i A / d

[0013] Where A is the effective area between the two conductors, and d is the distance between the two conductors;

[0014] Calculate the leakage current between conductors: based on the calculated equivalent dielectric constant ε i and parasitic capacitance C j Calculate the leakage current I between the two conductors. s ;

[0015] I s =2πfC j U

[0016] Where f is the frequency of the applied AC test signal, and U is the applied AC test voltage;

[0017] Calculate the total leakage current of the battery pack: Calculate the leakage current I between all conductors in the model. s Summing these values, we obtain the total leakage current I of the battery pack:

[0018] I = I1 + I2 + ... + I k

[0019] Where I1, ..., I k These represent the leakage current values ​​between different conductors.

[0020] As a further aspect of the present invention: the equivalent calculation model for battery pack leakage current includes the equivalent capacitance C1 between cells, the equivalent capacitance C2 between a cell and the bottom wall of the battery pack housing, the equivalent capacitance C3 between a cell and the top wall of the battery pack housing, the equivalent capacitance C4 between the copper busbar and the top wall of the battery pack housing, the equivalent capacitance C5 between a cell and the side wall of the battery pack housing, the equivalent capacitance C6a between a cell and the steel strip, and the equivalent capacitance C6b between a cell and the end plate.

[0021] As a further aspect of the present invention: the equivalent capacitance C1 is equivalent to the parasitic capacitance between the battery pack cells, and its calculation formula is as follows:

[0022] 1 / C1 = 1 / c1 + 1 / c2 + ... + 1 / cn

[0023] Where c1, ..., cn represent the capacitance of different battery cells.

[0024] As a further aspect of the present invention: the capacitors C1 to C6b are parasitic Y-type capacitors.

[0025] As a further aspect of the present invention: when the applied AC current is constant, the values ​​of AC frequency f and AC voltage U are determined. The magnitude of leakage current I is related to three variables: dielectric constant ε, effective area A, and effective distance d. The larger the dielectric constant ε and effective area A are, the larger the leakage current is; the larger the effective distance d is, the smaller the leakage current is.

[0026] Compared with existing technologies, this invention constructs an equivalent calculation model for battery pack leakage current to calculate the leakage current value of the battery pack. This allows for optimization of the battery pack's design structure and gaps, control of the leakage current magnitude, and prevention of safety accidents caused by leakage current. The presence or excessive leakage current can accelerate battery pack aging and performance degradation. This invention can address this issue from the design stage, helping to extend the battery pack's lifespan and reduce battery replacement costs. It provides more accurate leakage current parameters for battery management, enabling better control of battery pack charging and discharging, equalization management, etc., thereby improving the overall performance and reliability of the battery pack. Through this calculation method, the leakage current of the battery pack can be theoretically calculated, avoiding the cost of prototype manufacturing. It allows for repeated optimization of the structural scheme without the need for additional testing equipment and battery prototypes, and the computational workload is small, reducing testing and prototype costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the equivalent calculation model of the battery pack of the present invention.

[0028] Figure 2 This is a schematic diagram of the overall structure of the battery pack according to an embodiment of the present invention.

[0029] Figure 3 This is the equivalent diagram of the equivalent capacitance C1 in the embodiment of the present invention.

[0030] Figure 4 This is the equivalent diagram of the equivalent capacitance C2 in the embodiment of the present invention.

[0031] Figure 5 This is the equivalent diagram of the equivalent capacitance C3 in the embodiment of the present invention.

[0032] Figure 6 (a) and (b) are equivalent diagrams of the equivalent capacitances C4 and C5 in the embodiments of the present invention, respectively.

[0033] Figure 7 (a) and (b) are equivalent diagrams of the equivalent capacitances C6a and C6b in the embodiments of the present invention, respectively. Detailed Implementation

[0034] The invention will now be further described with reference to the accompanying drawings.

[0035] A method for calculating battery pack leakage current includes the following steps:

[0036] Constructing an equivalent calculation model for battery pack leakage current: Within the battery pack's internal structure, under AC voltage, high-potential components and the casing form a capacitive effect, creating an equivalent current loop through the casing to ground. The equivalent calculation model is as follows: Figure 1 As shown, the equivalent capacitances include C1 between battery cells, C2 between a battery cell and the bottom wall of the battery pack housing, C3 between a battery cell and the top wall of the battery pack housing, C4 between the copper busbar and the top wall of the battery pack housing, C5 between a battery cell and the side wall of the battery pack housing, and other equivalent capacitances C6. Here, the equivalent capacitance C6 includes C6a between a battery cell and the steel strip and C6b between a battery cell and the end plate.

[0037] The equivalent capacitance C1 is equivalent to the parasitic capacitance generated between the battery cells in the battery pack, and its calculation formula is as follows:

[0038] 1 / C1 = 1 / c1 + 1 / c2 + ... + 1 / cn

[0039] Where c1, ..., cn represent the capacitance of different battery cells.

[0040] Capacitors C1 to C6b are parasitic Y-type capacitors.

[0041] Calculate the equivalent dielectric constant between conductors: For any two conductors in the model, calculate the equivalent dielectric constant ε between them. i ;

[0042] ε i =(ε1*d1+ε2*d2……+ε n *dn) / (d1+d2……+d n )

[0043] Where ε1, ..., ε n The dielectric constants of different insulating materials between conductors, d1……d n Indicates the thickness of the corresponding insulating material;

[0044] Calculate the parasitic capacitance between conductors: Based on the calculated equivalent dielectric constant, calculate the parasitic capacitance C between the conductors. j ;

[0045] C j =ε i A / d

[0046] Where A is the effective area between the two conductors, and d is the distance between the two conductors;

[0047] Calculate the leakage current between conductors: based on the calculated equivalent dielectric constant ε i and parasitic capacitance C j Calculate the leakage current I between the two conductors. s ;

[0048] I s =2πfC j U

[0049] Where f is the frequency of the applied AC test signal, and U is the applied AC test voltage;

[0050] Calculate the total leakage current of the battery pack: Calculate the leakage current I between all conductors in the model. s Summing these values, we obtain the total leakage current I of the battery pack:

[0051] I = I1 + I2 + ... + I k

[0052] Where I1, ..., I k These represent the leakage current values ​​between different conductors.

[0053] Based on the characteristic of capacitors to "block DC and pass AC," when alternating current passes through a capacitor, a current is generated. Excessive current flowing through the human body can cause harm. The national standard GB 18384-2020 specifies a requirement for the energy stored in the Y-axis capacitor of a battery system to be <0.2J. Based on the parasitic capacitance formula and the leakage current formula between conductors, we can obtain:

[0054] I s =2πfε i AU / d

[0055] It can be seen that the leakage current I is related to the AC voltage U, AC frequency f, effective area A, effective distance d, and dielectric constant ε. When the AC current applied in the test is constant, the values ​​of AC frequency f and AC voltage U can be determined. The magnitude of the leakage current I is related to three variables: dielectric constant ε, effective area A, and effective distance d. From the perspective of design and development, the larger the dielectric constant ε and effective area A are, the larger the leakage current is, and the larger the effective distance d is, the smaller the leakage current is.

[0056] Example:

[0057] A method for calculating battery pack leakage current is applicable to any battery pack. Taking the application of the Z324S07 battery pack as an example, this invention will be introduced. The overall structural diagram of the Z324S07 battery pack is shown below. Figure 2 As shown, insulating materials have corresponding dielectric constants based on their different material properties. The dielectric constant ε between the corresponding conductors is calculated under room temperature conditions. i :

[0058] ε i = (ε1*d1+ε2*d2+……+ε n *d n ) / (d1+d2+……+d n )

[0059] Where ε1, ..., ε n The dielectric constants of different insulating materials between conductors, d1……d n This indicates the thickness of the corresponding insulation material. Then, the parasitic Y-direction capacitance is calculated, i.e., the corresponding equivalent capacitances C1 to C6 are calculated. The equivalent diagram for the inter-cell equivalent capacitance C1 is shown below. Figure 3 As shown, the equivalent capacitance C2 between the cell and the bottom wall of the battery pack casing is illustrated in the diagram. Figure 4 As shown, the equivalent capacitance C3 between the cell and the top wall of the battery pack casing is illustrated in the diagram. Figure 5 As shown, the equivalent capacitance C4 between the copper busbar and the top wall of the battery pack housing, and the equivalent capacitance C5 between the battery cell and the side wall of the battery pack housing are respectively shown in the diagrams below. Figure 6 As shown in (a) and (b), the equivalent capacitance C6a between the cell and the steel strip, and the equivalent capacitance C6b between the cell and the end plate are respectively shown in the equivalent diagrams. Figure 7 As shown in (a) and (b).

[0060] The basic parameters of the battery pack cells are shown in the table below:

[0061]

[0062] That is, the basic parameters of the battery pack cells are known quantities.

[0063] The theoretical calculation of dielectric constant is shown in the table below:

[0064]

[0065]

[0066] The parasitic capacitance and leakage current of the battery pack were calculated using the different dielectric constant values ​​obtained from the table above. The calculation results for parasitic capacitance and leakage current are shown in the table below.

[0067]

[0068]

[0069] This invention calculates the leakage current of the battery pack by calculating the capacitance and leakage current of each parasitic capacitor in the calculation model. This allows for optimization of the battery pack's design structure and spacing, control of the leakage current, prevention of safety accidents caused by leakage current, improvement of the safety and reliability of the designed battery pack, and reduction of testing and prototype costs.

Claims

1. A method for calculating the leakage current of a battery pack, characterized in that, Includes the following steps: Construct an equivalent calculation model for battery pack leakage current; Calculate the equivalent dielectric constant between conductors: For any two conductors in the model, calculate the equivalent dielectric constant ε between them. i ; e i =(ε1*d1+ε2*d2+……+ε n *dn) / (d1+d2+……+d n ) Where ε1, ..., ε n The dielectric constants of the different insulating materials between the conductors are d1, ..., d2. n Indicates the thickness of the corresponding insulating material; Calculate the parasitic capacitance between conductors: Based on the calculated equivalent dielectric constant, calculate the parasitic capacitance C between the conductors. j ; C j =e i A / d Where A is the effective area between the two conductors, and d is the distance between the two conductors; Calculate the leakage current between conductors: based on the calculated equivalent dielectric constant ε i and parasitic capacitance C j Calculate the leakage current I between the two conductors. s ; I s =2πfC j U Where f is the frequency of the applied AC test signal, and U is the applied AC test voltage; Calculate the total leakage current of the battery pack: Calculate the leakage current I between all conductors in the model. s Summing these values, we obtain the total leakage current I of the battery pack: I=I1+I2+……+I k Where I1, ..., I k These represent the leakage current values ​​between different conductors.

2. The method for calculating battery pack leakage current according to claim 1, characterized in that, The equivalent calculation model for battery pack leakage current includes the equivalent capacitance C1 between cells, the equivalent capacitance C2 between a cell and the bottom wall of the battery pack housing, the equivalent capacitance C3 between a cell and the top wall of the battery pack housing, the equivalent capacitance C4 between the copper busbar and the top wall of the battery pack housing, the equivalent capacitance C5 between a cell and the side wall of the battery pack housing, the equivalent capacitance C6a between a cell and the steel strip, and the equivalent capacitance C6b between a cell and the end plate.

3. The battery pack leakage current calculation method according to claim 2, characterized in that, The equivalent capacitance C1 is equivalent to the parasitic capacitance generated between the battery cells in the battery pack, and its calculation formula is as follows: 1 / C1 = 1 / c1 + 1 / c2 + ... + 1 / cn Where c1, ..., cn represent the capacitance of different battery cells.

4. The method for calculating battery pack leakage current according to claim 2, characterized in that, The capacitors C1 to C6b are parasitic Y-type capacitors.

5. The method for calculating battery pack leakage current according to claim 1, characterized in that, When the applied AC current is constant, the values ​​of the AC frequency f and AC voltage U are determined, and the leakage current I is also determined. s The magnitude of leakage current is related to three variables: dielectric constant ε, effective area A, and effective distance d. The larger the dielectric constant ε and effective area A are, the larger the leakage current is, and the larger the effective distance d is, the smaller the leakage current is.

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