A power control method for a battery pack based on a heating film

Abstract

A power control method for a battery pack based on a heating film belongs to the technical field of new energy battery packs, and includes the following steps: establishing a geometric model of a battery pack, and meshing the geometric model to obtain a mesh model of the battery pack; importing the mesh model into the fluid analysis simulation software Ansys Fluent, and setting basic parameters for completing simulation calculations in the ANSYS Fluent software; establishing a cell ECM model and a capacity attenuation model based on the HPPC charging and discharging parameters of the selected cell; writing a heat source condition expression for the heating film, and writing a condition expression for water cooling on; deriving the corresponding cell temperature in the ANSYS Fluent software, as well as the parameters and corresponding curves of the voltage changing with time; and using the cell aC discharge at room temperature as a control group under standard working conditions. Advantages: Maximizing the battery capacity by simulating the battery working conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy battery packs, and in particular relates to a power control method of a battery pack based on a heating film. Background Art

[0002] With the rapid development of the domestic new energy industry, it is becoming increasingly important to design and develop battery packs quickly and efficiently. At the same time, how to verify the reliability of battery packs in low-temperature environments has also become crucial. When encountering actual projects, engineers are required to quickly determine the feasibility of thermal management of battery packs. If the thermal effect is measured after production is completed, it is not only time-consuming but also costly. Therefore, it is cost-effective to determine the heating situation and reasonably optimize the cost before actual production.

[0003] For a battery pack, heat will be generated as long as it is charged and discharged normally. However, if the battery is in a low temperature environment, such as a lithium iron phosphate battery, it will be extremely difficult to discharge and the capacity will decay severely. At this time, an auxiliary heat source must be provided to heat the battery so that it can reach a temperature that can discharge normally. The heat source can be cut off when the battery can maintain normal working state by its own heat generation. The current mainstream solution is to use a heating film for heating or a liquid cooling system for heating. Among them, the liquid cooling system is large and complex and is not suitable for small battery packs. Therefore, small battery packs give priority to heating films, but how to efficiently turn on and off the heating function still needs to be judged. If the heating is turned on for a long time, the effective output energy will be wasted. If the heating time is not enough, the battery temperature will be too low and the capacity will decay severely. In view of this problem, the applicant has made a beneficial design and developed a battery pack heating management method. The technical solution to be introduced below was produced in this context. Summary of the invention

[0004] The object of the present invention is to provide a power control method for a battery pack based on a heating film, which can maximize the battery capacity by simulating the battery operating conditions.

[0005] The object of the present invention is achieved by providing a power control method for a battery pack based on a heating film, comprising the following steps:

[0006] S1) establishing a geometric model of the battery pack and meshing the geometric model to obtain a mesh model of the battery pack;

[0007] S2) importing the grid model into the fluid analysis simulation software Ansys Fluent, and setting basic parameters for completing the simulation calculation in the ANSYS Fluent software;

[0008] S3) Based on the HPPC charge and discharge parameters of the selected battery cells, establish the ECM model and capacity attenuation model of the battery cells. According to the battery cell specification sheet, determine the initial capacity of the battery cells at the test condition temperature, set the number of cycles to 0, and then set the following basic parameters, including the physical properties of materials, the physical properties of the water coolant, the water flow rate, the simulation conditions, the charge and discharge rates, and the charge and discharge cut-off voltages;

[0009] S4) Write the heat source condition expression of the heating film as

[0010] IF({cell - tem}<T1(288[K]),P(7185185[w / m 3]),0[W / m 3]), where T1 represents the heating film off temperature, P represents the heating power per unit volume, convert the constant power of the heating film to obtain the heat power per unit volume as an intermediate parameter, and control the on or off of the heating function through the temperature threshold;

[0011] At the same time, write the condition expression for the opening of the water cooling as

[0012] IF({cell - tem}>T2(308[K]),V(0.05[m / s]),0[m / s]), where T2 represents the water cooling on temperature, V represents the water cooling flow rate, and set the condition for the opening or closing of the water cooling as the battery cell temperature range;

[0013] S5) Record the change of temperature with time and the change of battery cell voltage with time in the ANSYS Fluent software, and establish an excel log file to export the corresponding battery cell temperature, as well as the parameters and corresponding curves of the voltage change with time;

[0014] S6) Take the aC discharge of the battery cells at room temperature as the control group under the standard condition. At this time, do not turn on the heating film. Based on the theoretical time of the aC discharge of the battery cells being 60 / amin and a total of 3600 / as, set the simulation time in the ANSYS Fluent software to 3600 / as, each step to bs, with a total of 3600 / ab intervals, and view the temperature change curve and voltage change curve from the calculation results of the ANSYS Fluent software;

[0015] S7) According to the.out file exported from the ANSYS Fluent software, organize in excel to obtain the temperature data and voltage data of each battery cell changing with the discharge time. Set the starting voltage of each period as V0, the cut-off voltage as V1, and the current as I. Obtain the approximate battery discharge capacity Q1 of each step in each period through the following formula

[0016] Q1 = (V0 + V1) / 2 * I * 5 / 3600, in Wh. The actual battery discharge capacity Q2 is obtained by accumulating the discharge capacity Q1 of all steps;

[0017] S8) Repeat step S6), set the initial temperature of the low-temperature discharge of an experimental group to T, turn on the heating film function and do not turn off the water cooling, and obtain voltage data and temperature data in the same way. Set the heating film power to a constant power W, and the heating time to be the time range from T to the specified temperature T1. By searching the temperature file to obtain the heating time t seconds, the power consumed by the heating film Q3 is Q2 = W*t / 3600. At this time, the actual battery discharge power is Q5 obtained by the same method as step S7), and the actual battery discharge effective power Q4 = another actual battery discharge power Q5-heating film consumption power Q3;

[0018] S9) According to step S6), set the low-temperature discharge temperature T of another experimental group, but do not turn on the heating film function, and do not turn off the water cooling. Same as step S8), obtain another actual battery discharge effective power Q6;

[0019] S10) Comparing and analyzing Q2 in step S7), Q4 in step S8) and Q6 in step S9), it is concluded that if the heating film function is not turned on, the low-temperature capacity decay is large, thereby determining that heating with the heating film meets the working conditions;

[0020] S11) When it is determined that the heating film is suitable for the working conditions, repeat step S8), set different temperature ranges, and repeat the experiment by controlling the opening and closing time of the heating film to maximize the effective discharge of the battery cell. At the same time, observe the temperature cloud map in the ANSYS Fluent software to ensure the temperature consistency of the battery cell.

[0021] In a specific embodiment of the present invention, in the step S4), when setting the conditions for turning on or off the water cooling, it is ensured that the temperature difference between the battery cells is less than 5°C.

[0022] In another specific embodiment of the present invention, in the step S10), if Q2>Q4>Q6, it is concluded that if the heating film function is not turned on, the low-temperature capacity attenuation is large, and it is determined that the heating film heating meets the working conditions; if Q2>Q6>Q4, it means that the effect of the heating film is not great, and it is determined that the heating film solution is not suitable.

[0023] Due to the adoption of the above structure, the present invention improves the operation effect of the entire battery pack by judging within which battery cell temperature band the heating function and the heat dissipation function are turned on; the fluid analysis simulation software ANSYS Fluent is used to simulate the discharge and auxiliary heating conditions to obtain the discharged electricity and temperature rise, and finally actual testing is performed, thereby reducing the manpower and time costs required for actual testing; there is no need to change the overall structure of the battery pack, and the cost is further controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the present invention;

[0025] Figure 2 Schematic diagram of the geometric model of the battery pack of the present invention. DETAILED DESCRIPTION

[0026] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but the description of the embodiments is not a limitation of the technical solution. Any changes in form rather than substance based on the concept of the present invention should be regarded as the protection scope of the present invention.

[0027] In the following description, all concepts related to directionality (or orientation) such as up, down, left, right, front and back are referring to the position state of the figure being described, and are intended to facilitate public understanding. Therefore, they should not be understood as special limitations on the technical solution provided by the present invention.

[0028] See Figure 1 The present invention relates to a power control method of a battery pack based on a heating film, comprising the following steps.

[0029] Step S1) Establish a geometric model of the battery pack and mesh the geometric model to obtain a mesh model of the battery pack. Figure 2 As shown, the battery pack includes a cell group 1 composed of a plurality of battery cells 11 stacked in sequence, adjacent battery cells 11 are bonded by thermally conductive silicone 2, a water cooling plate 3 is arranged at the bottom of the cell group 1, and the heating film 4 is arranged on at least one outer surface of the cell group 1 perpendicular to the stacking direction of the battery cells 11.

[0030] Step S2) importing the grid model into the fluid analysis simulation software Ansys Fluent, and setting basic parameters for completing the simulation calculation in the ANSYS Fluent software, such as selection based on the pressure solver, transient solution, energy equation and turbulence model.

[0031] Step S3) Based on the HPPC charge and discharge parameters of the selected battery cells, establish an ECM model and a capacity attenuation model of the battery cells. According to the battery cell specification sheet, determine the initial capacity of the battery cells at the test condition temperature, set the number of cycles to 0, and then set the following basic parameters, including the physical properties of materials, the physical properties of the water-cooling liquid, the water flow rate, the simulation conditions, the charge and discharge rates, and the charge and discharge cut-off voltages.

[0032] Step S4) Compile the heat source condition expression of the heating film:

[0033] IF({cell-tem}<T1(288[K]),P(7185185[w / m 3]),0[W / m 3]), where T1 represents the heating film off temperature and P represents the heating power per unit volume. Further, convert the constant power of the heating film to obtain the corresponding heating power per unit volume as an intermediate parameter, and control the on or off of the heating function through a temperature threshold.

[0034] Meanwhile, compile the condition expression for water-cooling activation:

[0035] IF({cell-tem}>T2(308[K]),V(0.05[m / s]),0[m / s]), where T2 represents the water-cooling activation temperature and V represents the water-cooling flow rate. Set the condition for water-cooling activation or deactivation as the battery cell temperature range. Meanwhile, ensure that the temperature difference between battery cells is less than 5°C through the battery cell layout, water-cooling row layout, and thermal conductive silicone coefficient. If the temperature difference is large, there will be a pressure difference between battery cells, which is not conducive to the overall management of the battery pack, and even individual battery cells will be protected in advance and the discharge will end.

[0036] Step S5) Record the change of temperature over time and the change of battery cell voltage over time in ANSYS Fluent software, and establish an excel log file to export the corresponding battery cell temperature, the parameters of voltage change over time, and the corresponding curves.

[0037] Step S6) Take the aC discharge of the battery cells at room temperature as the control group under the standard condition. In this embodiment, the set room temperature is 25°C. The 1C discharge of a 20ah battery cell represents a current of 20A, and the 2C discharge represents 40A. At this time, the heating film does not need to be activated. Based on the theoretical time of aC discharge of the battery cells being 60 / amin, a total of 3600 / as, set the simulation time in ANSYS Fluent software to 3600 / as, with each step being bs and a total of 3600 / ab intervals. Check the temperature change curve and voltage change curve from the calculation results of ANSYS Fluent software.

[0038] Step S7) According to the .out file exported from ANSYS Fluent software, the temperature data and voltage data of each battery cell based on the discharge time are sorted in Excel, and the starting voltage of each period is set to V0, the ending voltage is set to V1, and the current is set to I. The approximate battery discharge power Q1 of each step in each period is obtained by the following formula. The smaller the time interval, the more accurate it is.

[0039] Q1 = (V0 + V1) / 2 * I * 5 / 3600, in Wh. The actual battery discharge capacity Q2 is obtained by accumulating the discharge capacity Q1 of all steps;

[0040] Step S8) Repeat step S6), set the initial temperature of the low-temperature discharge of an experimental group to T. In this embodiment, T is set to -10°C, turn on the heating film function and do not turn off the water cooling, and obtain the voltage data and temperature data in the same way. Set the heating film power to a constant power W, and the heating time to be the time range from T to the specified temperature T1. By searching the temperature file, the heating time t seconds is obtained, and the power Q3 consumed by the heating film is:

[0041] Q3=W*t / 3600. At this time, another actual battery discharge quantity Q5 is obtained by the same method as step S7), then the actual battery discharge effective quantity Q4=another actual battery discharge quantity Q5-the quantity Q3 consumed by the heating film;

[0042] Step S9) According to step S6), set the low-temperature discharge temperature of another experimental group to -10°C, but do not turn on the heating film function, and do not turn off the water cooling. Same as step S8), obtain another actual battery discharge effective power Q6;

[0043] Step S10) compares and analyzes the three results (Q2, Q4, Q6) in step S7), step S8) and step S9):

[0044] In the first case, if Q2>Q4>Q6, it is concluded that if the heating film function is not turned on, the low-temperature capacity attenuation is large, thus determining that the use of heating film heating meets the working conditions.

[0045] In the second case, if Q2>Q6>Q4, it can be found that the heating film has little effect. Instead, it increases the cost due to excessive energy consumption. Therefore, it is determined that the heating film solution is not suitable.

[0046] Step S11) After the first situation mentioned in step S10) is established, repeat step S8) to set different temperature ranges, and repeat the experiment by controlling the opening and closing time of the heating film to maximize the effective discharge of the battery cell. During the process, the temperature cloud map in ANSYS Fluent needs to be observed to ensure the consistency of the battery cell temperature. Of course, different heating film powers can be replaced. The shape and power of the film will result in different prices, and products with higher cost performance are preferred.

[0047] The present invention uses fluid analysis simulation software ANSYS Fluent to establish a battery cell ECM model and a capacity attenuation model, simulate the working conditions of the battery, set the battery cell temperature threshold, and automatically turn on or off when the temperature is reached. The actual heating time is obtained by checking the battery cell temperature change curve, and then the energy consumed by heating is subtracted. According to the final discharged capacity, it is determined within which temperature range to turn on the heating function, so as to maximize the overall battery pack capacity.

Claims

1. A power control method for a battery pack based on a heating film, characterized in that: It includes the following steps: S1) Establish a geometric model of the battery pack, perform mesh division on the geometric model to obtain a mesh model of the battery pack; S2) Import the mesh model into the fluid analysis simulation software Ansys Fluent, and set the basic parameters for completing the simulation calculation in the ANSYS Fluent software; S3) Based on the hppc charge and discharge parameters of the selected battery cells, establish an ECM model and a capacity attenuation model of the battery cells. According to the battery cell specification sheet, determine the initial capacity of the battery cells at the test condition temperature, set the number of cycles to 0, and then set the following basic parameters, including the physical properties of the materials, the physical properties of the water-cooling liquid, the water flow rate, the simulation conditions, the charge and discharge rates, and the charge and discharge cut-off voltages; S4) Write the heat source condition expression of the heating film as IF({cell-tem}<T1(288[K]),P(7185185[w / m3]),0[W / m 3]), where T1 represents the heating film off temperature, P represents the heating power per unit volume, convert the constant power of the heating film to obtain the heat power per unit volume as an intermediate parameter, and control the on or off of the heating function through a temperature threshold; At the same time, write the water-cooling on condition expression as IF({cell-tem}>T2(308[K]),V(0.05[m / s]),0[m / s]), where T2 represents the water-cooling on temperature, V represents the water-cooling flow rate, and set the water-cooling on or off condition as the battery cell temperature range; S5) Record the change of temperature with time and the change of battery cell voltage with time in the ANSYS Fluent software, establish an excel log file, and export the corresponding battery cell temperature, as well as the parameters and corresponding curves of the voltage change with time; S6) Take the aC discharge of the battery cells at room temperature as the control group under the standard condition. At this time, the heating film does not need to be turned on. Based on the theoretical time of the aC discharge of the battery cells being 60 / amin and a total of 3600 / as, set the simulation time in the ANSYS Fluent software to 3600 / as, each step is bs, and there are a total of 3600 / ab intervals. Check the temperature change curve and voltage change curve from the calculation results of the ANSYS Fluent software; S7) According to the.out file exported from the ANSYS Fluent software, organize in excel to obtain the temperature data and voltage data of each battery cell changing with the discharge time. Set the starting voltage of each period as V0, the cut-off voltage as V1, and the current as I. Calculate the approximate battery discharge capacity Q1 in each step and each period through the following formula Q1=(V0+V1) / 2*I*5 / 3600, The unit is Wh. By accumulating the discharge capacities Q1 of all steps, obtain an actual battery discharge capacity Q2; S8) Repeat step S6), set the initial temperature of the low-temperature discharge of an experimental group to T, turn on the heating film function and do not turn off the water cooling, and obtain the voltage data and temperature data in the same way. Set the heating film power to a constant power W, and the heating time to be the time range from T to the specified temperature T1. By searching the temperature file, the heating time t seconds is obtained, and the power consumed by the heating film Q3 is Q2=W*t / 3600, At this time, another actual battery discharge quantity Q5 is obtained by the same method as step S7), then the actual battery discharge effective quantity Q4 = another actual battery discharge quantity Q5 - the quantity Q3 consumed by the heating film; S9) According to step S6), set the low-temperature discharge temperature T of another experimental group, but do not turn on the heating film function, and do not turn off the water cooling. Same as step S8), obtain another actual battery discharge effective power Q6; S10) Comparing and analyzing Q2 in step S7), Q4 in step S8) and Q6 in step S9), it is concluded that if the heating film function is not turned on, the low-temperature capacity decay is large, thereby determining that heating with the heating film meets the working conditions; S11) When it is determined that the heating film is suitable for the working conditions, repeat step S8), set different temperature ranges, and repeat the experiment by controlling the opening and closing time of the heating film to maximize the effective discharge of the battery cell. At the same time, observe the temperature cloud map in the ANSYS Fluent software to ensure the temperature consistency of the battery cell.

2. According to claim 1, a power control method for a battery pack based on a heating film is characterized in that: In the step S4), when setting the conditions for turning water cooling on or off, ensure that the temperature difference between the battery cells is less than 5°C.

3. The power control method of a battery pack based on a heating film according to claim 1, characterized in that: In the step S10), if Q2>Q4>Q6, it is concluded that if the heating film function is not turned on, the low-temperature capacity attenuation is large, and it is determined that the heating film heating meets the working conditions; if Q2>Q6>Q4, it means that the effect of the heating film is not great, and it is determined that the heating film solution is not suitable.

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