Battery pack leakage current calculation method

Abstract

The invention discloses a battery pack leakage current calculation method, and belongs to the technical field of battery packs. Comprising the steps of constructing a battery pack leakage current equivalent calculation model; calculating an effective dielectric constant epsilon i between conductors; calculating stray capacitance Cj between the conductors; calculating leakage current Is between the conductors; the total leakage current value of the battery pack is calculated by calculating the capacitance value and the leakage current value of each stray capacitor in the calculation model, the magnitude of the leakage current of the battery pack can be well controlled, safety accidents caused by the leakage current are prevented, the safety and reliability of the designed battery pack are improved, and the reliability of the battery pack is improved. And the detection and sample piece cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery pack, and particularly relates to a battery pack leakage current calculation method. BACKGROUND

[0002] The battery pack is widely used in electric vehicles, energy storage systems and the like, and the leakage current refers to a phenomenon that, due to aging, damage or design defects of insulating materials, current leaks through an unintended path during normal operation or storage of the battery pack, which not only reduces the service life of the battery pack, but also seriously causes damage to electrical components and safety hazards. Therefore, accurate calculation of the leakage current of the battery pack and good relative measures are crucial for safe operation and performance optimization of the battery pack.

[0003] The battery pack is mainly composed of a battery box, a battery module, a module end plate, an electrical plastic support, an output pole seat, an output pole protection cover, a protection cover, a bus bar, a low-voltage acquisition board, a low-voltage communication wire harness, a high-voltage power copper bar, a liquid cooling plate assembly, a liquid cooling pipe assembly, a BCC, an FPC flexible circuit board, an explosion-proof breather valve, a manual maintenance switch, a high-voltage connector, a low-voltage connector, a sealing gasket, a heat-conducting structural adhesive, a support plate, a module fixing bolt, a module support foam, a single-core cored rivet and the like.

[0004] The current commercial vehicle has a leakage current regulation requirement for the electrical performance test of the battery pack, and how to theoretically calculate and design the prevention of the battery pack is of great importance to the safety of the battery pack. However, at present, only the theoretical formula is calculated, and there is no method for calculating the leakage current of different battery packs. SUMMARY

[0005] The purpose of the present application is to provide a battery pack leakage current calculation method, which can calculate the actual leakage current of the battery pack, improve the safety and reliability of the designed battery pack, and reduce the detection and sample cost.

[0006] To achieve the above purpose, the present application provides a battery pack leakage current calculation method, which comprises the following steps:

[0007] An equivalent calculation model of the leakage current of the battery pack is constructed.

[0008] The equivalent dielectric constant between conductors is calculated: for any two conductors in the model, the equivalent dielectric constant ε i between them is calculated.

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

[0010] Wherein, ε1, …, ε nrepresenting the dielectric constant of different insulating materials between conductors, d1, …, d n representing 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 the parasitic capacitance C j , calculate the leakage current I s between the two conductors;

[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: sum the leakage currents I s between all conductors in the model to obtain the total leakage current I of the battery pack:

[0018] I = I1 + I2 + … + I k

[0019] where I1, …, I k represent the leakage current values between different conductors, respectively.

[0020] As a further scheme of the present application: the equivalent calculation model of the battery pack leakage current includes the equivalent capacitance C1 between the battery cells and the battery cells, the equivalent capacitance C2 between the battery cells and the bottom wall of the battery pack box, the equivalent capacitance C3 between the battery cells and the top wall of the battery pack box, the equivalent capacitance C4 between the copper bar and the top wall of the battery pack box, the equivalent capacitance C5 between the battery cells and the side wall of the battery pack box, the equivalent capacitance C6a between the battery cells and the steel belt, and the equivalent capacitance C6b between the battery cells and the end plate.

[0021] As a further scheme of the present application: the equivalent capacitance C1 is equivalent to the parasitic capacitance between the battery cells and the battery cells, and its calculation formula is:

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

[0023] Wherein, c1, …, cn respectively represent the capacitances of different battery cells.

[0024] As a further scheme of the present application: the capacitances C1-C6b belong to parasitic Y-direction capacitances.

[0025] As a further scheme of the present application: when the test applied alternating current is certain, the values of the alternating frequency f and the alternating voltage U are determined, the size of the leakage current I is related to three variables of the dielectric constant ε, the effective area A and the effective distance d, the larger the dielectric constant ε and the effective area A are, the larger the leakage current is, and the larger the effective distance d is, the smaller the leakage current is.

[0026] Compared with the prior art, the present application can optimize the design structure and gap of the battery pack, control the size of the battery pack leakage current, prevent safety accidents caused by the leakage current, and prolong the service life of the battery pack, thereby reducing the cost of replacing the battery. BRIEF DESCRIPTION OF DRAWINGS

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

[0028] Figure 2 is a structural schematic diagram of the battery pack of the embodiment of the present application

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

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

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

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

[0033] Figure 7 (a) and (b) are equivalent diagrams of the equivalent capacitances C6a and C6b in the embodiment of the present application, respectively. DETAILED DESCRIPTION

[0034] The application will be further described below with reference to the accompanying drawings.

[0035] A battery pack leakage current calculation method, comprising the following steps:

[0036] An equivalent calculation model of the battery pack leakage current is constructed: under the action of alternating voltage, the high potential components and the shell form a capacitive effect, and an equivalent current loop is formed through the shell connection, and the equivalent calculation model is as shown in Figure 1 The equivalent calculation model includes equivalent capacitances C1 between the battery cells, equivalent capacitances C2 between the battery cells and the bottom wall of the battery pack box, equivalent capacitances C3 between the battery cells and the top wall of the battery pack box, equivalent capacitances C4 between the copper bar and the top wall of the battery pack box, equivalent capacitances C5 between the battery cells and the side wall of the battery pack box, and other equivalent capacitances C6. The equivalent capacitances C6 include equivalent capacitances C6a between the battery cells and the steel belt, and equivalent capacitances C6b between the battery cells and the end plate.

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

[0038] 1 / C1=1 / c1+1 / c2+…+1 / cn

[0039] Wherein, c1, …, cn represent the capacitances of different battery cells.

[0040] The capacitances C1-C6b belong to parasitic Y-direction capacitances.

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

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

[0043] Wherein, ε1, …, ε n represent the dielectric constants of different insulating materials between the conductors, and d1……d n represent the thicknesses of the corresponding insulating materials.

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

[0045] C j =ε i A / d

[0046] Wherein, 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 the parasitic capacitance C j , calculate the leakage current I s between the two conductors;

[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: sum the leakage currents I s between all conductors in the model to get the total leakage current I of the battery pack:

[0051] I = I1 + I2 + … + I k

[0052] where I1, …, I k represent the leakage current values between different conductors, respectively.

[0053] According to the characteristics of capacitive "direct current through alternating current", when alternating current passes through the capacitor, a current will be generated, and excessive current flowing through the human body will cause harm to humans. The national standard GB 18384-2020 has a clear requirement for the energy storage size of Y-direction capacitors in battery systems, which must be <0.2J. According to the parasitic capacitance formula and the leakage current formula between conductors, we can get:

[0054] I s = 2πfε i AU / d

[0055] From this, it can be seen that the leakage current I is related to the alternating voltage U, the alternating frequency f, the effective area A, the effective distance d, and the dielectric constant ε. When the applied alternating current is fixed, the values of alternating frequency f and alternating voltage U can be determined, and the size of 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, the larger the leakage current, and the larger the effective distance d, the smaller the leakage current.

[0056] Embodiment:

[0057] A battery pack leakage current calculation method is applicable to any battery pack. Take the application of Z324S07 battery pack as an example to introduce the present application. The overall structure of Z324S07 battery pack is shown in Figure 2 , wherein according to the characteristics of different materials, the insulating substances have corresponding dielectric constants. Under room temperature conditions, the dielectric constant ε i between the corresponding conductors is calculated:

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

[0059] wherein ε1, …, ε n represent the dielectric constant of different insulating materials between conductors, d1 … d n represent the thickness of the corresponding insulating material. Then the parasitic Y-direction capacitance is calculated, i.e. the corresponding equivalent capacitances C1-C6 are calculated, wherein the equivalent diagram of the equivalent capacitance C1 between the battery cell and the battery cell is as shown in Figure 3 , the equivalent diagram of the equivalent capacitance C2 between the battery cell and the bottom wall of the battery pack box is as shown in Figure 4 , the equivalent diagram of the equivalent capacitance C3 between the battery cell and the top wall of the battery pack box is as shown in Figure 5 , the equivalent diagram of the equivalent capacitance C4 between the copper bar and the top wall of the battery pack box, the equivalent diagram of the equivalent capacitance C5 between the battery cell and the side wall of the battery pack box are as shown in Figure 6 (a) and (b) respectively, the equivalent diagram of the equivalent capacitance C6a between the battery cell and the steel belt, the equivalent diagram of the equivalent capacitance C6b between the battery cell and the end plate are as shown in Figure 7 (a) and (b) respectively.

[0060] The basic parameters of the battery cell of the battery pack are as shown in the following table:

[0061]

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

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

[0064]

[0065]

[0066] The parasitic capacitance and leakage current of the battery pack are calculated by the different dielectric constant values calculated in the above table. The calculation results of the parasitic capacitance and leakage current are as shown in the following table,

[0067]

[0068]

[0069] The application calculates the leakage current value of the battery pack by calculating the capacitance value and the leakage current value of each parasitic capacitance in the calculation model, can optimize the design structure and gap of the battery pack, control the leakage current value of the battery pack, prevent safety accidents caused by the leakage current, improve the safety and reliability of the designed battery pack, and reduce the detection and sample cost.

Claims

1. A battery pack leakage current calculation method, characterized by, The method comprises the following steps: constructing an equivalent calculation model of battery pack leakage current; Calculate the equivalent dielectric constant between conductors: For any two conductors in the model, calculate the equivalent dielectric constant ε i between them e i = (e1 * d1 + e2 * d2 +... + en * dn) / (d1 + d2 +... + dn) n * dn) / (d1 + d2 +... + dn) n ) where ε1,..., εn represent the dielectric constants of the different insulating materials between the conductors, d1,..., dn represent the thicknesses of the corresponding insulating materials; and n where ε1,..., εn represent the dielectric constants of the different insulating materials between the conductors, d1,..., dn represent the thicknesses of the corresponding insulating materials; and n where ε1,..., Calculate the parasitic capacitance between conductors: based on the calculated equivalent dielectric constant, calculate the parasitic capacitance C between the conductors j ; C j = ε i A / d wherein A is the effective area between two conductors, and d is the distance between two conductors; Calculate the leakage current between the conductors: based on the calculated equivalent dielectric constant ε i and the parasitic capacitance C j , calculate the leakage current I s between the two conductors; I s = 2πfC j U wherein 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: sum the leakage currents I between all conductors in the model s summed to get the total leakage current I of the battery pack: I = I1+ I2+... + I k wherein I1,..., In represent the leakage current values between different conductors. k wherein I1,..., In represent the leakage current values between different conductors.

2. The battery pack leakage current calculation method of claim 1, wherein, The equivalent calculation model of the battery pack leakage current comprises equivalent capacitances C1 between battery cells, equivalent capacitances C2 between battery cells and the bottom wall of the battery pack box, equivalent capacitances C3 between battery cells and the top wall of the battery pack box, equivalent capacitances C4 between the copper bar and the top wall of the battery pack box, equivalent capacitances C5 between battery cells and the side wall of the battery pack box, equivalent capacitances C6a between battery cells and the steel belt, and equivalent capacitances C6b between battery cells and the end plate.

3. The battery pack leakage current calculation method of claim 2, wherein, The equivalent capacitance C1 is equivalent to the parasitic capacitance generated between the battery cells and the battery cells, and the calculation formula is: 1 / C1 = 1 / c1 + 1 / c2 + … + 1 / cn wherein c1, …, cn represent the capacitances of different battery cells.

4. The battery pack leakage current calculation method of claim 2, wherein, The capacitances C1-C6b belong to parasitic Y-direction capacitances.

5. The battery pack leakage current calculation method of claim 1, wherein, When the test applied AC voltage is certain, the value of AC frequency f and AC voltage U is determined, the leakage current I s The size of the 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, the larger the leakage current. The larger the effective distance d, the smaller the leakage current.

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