A method for low-temperature thermal management and balanced control of battery packs

Abstract

This invention relates to the field of lithium-ion battery temperature control technology, specifically disclosing a method for low-temperature thermal management and balanced coordinated control of a battery pack. The method includes: establishing a battery pack electrothermal coupling simulation model; performing discharge calibration on the battery pack cells under different temperature conditions; dynamically selecting a heating strategy for the battery pack based on ambient temperature and heat exchange capacity; initiating heating based on user habits and navigation information; and performing balanced compensation on the battery pack based on discharge deviation during the charging phase. This invention obtains the mapping relationship between temperature difference and discharge difference by establishing a simulation model and cell discharge calibration; dynamically selects a heating strategy for the battery pack based on ambient temperature and heat exchange capacity; calculates the energy gain from temperature difference and the energy gain from heating based on user habits and navigation information to determine heating initiation; and initiates balanced compensation based on discharge deviation of different cells during the charging phase. This improves the usable capacity, energy efficiency, and cell consistency of the battery pack under low-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery temperature control technology, specifically to a method for low-temperature thermal management and balanced coordinated control of battery packs. Background Technology

[0002] In low-temperature environments, the internal activity of lithium-ion batteries decreases and internal resistance increases, leading to a significant reduction in discharge capacity. Simultaneously, cells in different locations within the battery pack exhibit distinct temperature gradients due to differences in heat dissipation conditions (faster heat dissipation at the edges, slower at the center) and varying heat generation rates within the cells themselves. Cells with lower temperatures have limited discharge capacity, while cells with higher temperatures can still release more energy. Since the system's discharge energy depends on the lowest-energy cell's bottleneck effect, this inconsistency reduces the overall usable capacity of the battery pack.

[0003] Existing technologies concerning heating control, thermal energy gain assessment, and charging equalization compensation methods for lithium-ion battery packs under low-temperature conditions are mainly distributed in the following three categories of published literature and product solutions: (1) Static power distribution design technology for heating film: such as the heating film power design method disclosed in patent application CN202310214009.1, which determines the heat dissipation difference at different locations in the battery pack through simulation (faster heat dissipation at the edges and slower heat dissipation at the center), and designs the power density of the heating film to increase from the center to both ends, thereby compensating for the heat dissipation loss at the edges. This scheme determines the power distribution of the heating film at one time during the battery pack design stage, which belongs to "static design".

[0004] (2) Low-temperature heating decision-making technology based on energy gain: such as the battery heating method for low-temperature driving disclosed in patent application CN202210145263.6, which determines whether to start driving heating by calculating the difference between the energy consumed by heating and the discharge capacity recovered by the battery after heating. This scheme only considers the total capacity recovery gain and does not consider the additional usable power release caused by the reduction of temperature difference between cells.

[0005] (3) Technology of using equalization elements to power heating devices: such as the patent "Battery Low Temperature Heating System and Method of Coupled Non-dissipative Equalization System" published by Shandong University, which uses equalization energy storage elements (such as supercapacitors) to store energy and then power the heating device to achieve low temperature self-heating.

[0006] (4) Existing product solutions: Currently, the low-temperature heating strategies of mainstream electric vehicles (such as Tesla, BYD, NIO, etc.) are mostly as follows: after detecting that the lowest cell temperature is lower than the threshold (such as 0°C), the PTC or heating film is activated at full power until the temperature reaches the standard and then turned off. This solution does not distinguish the cell temperature difference, does not conduct a benefit assessment, and has high energy consumption.

[0007] Existing technologies include methods such as simulating cell temperature distribution, designing static power distribution for heating films, and making heating start-up decisions based on energy gain. However, these technologies have the following shortcomings: 1. The temperature difference between cells cannot be directly mapped to the difference in discharge capacity between cells, and there is a lack of engineering means to quantify the energy loss due to temperature difference. 2. The power distribution of heating films is mostly statically designed and cannot adapt to changes in operating conditions (such as dynamic changes in heat generation caused by changes in current, SOC, and charge / discharge rate). 3. Comparing heating energy consumption and recovery capacity alone is a rather rough calculation method, and it does not take into account the electricity gains from reducing the temperature difference or the gains under different driving conditions. 4. It lacks a closed-loop energy flow design that utilizes the highest temperature battery cell in the system to directly power the heating film, and couples the discharge deviation caused by the temperature difference in the low-temperature discharge stage with the equalization compensation in the charging stage for control.

[0008] Based on this technical background, this invention studies a method and preparation method for low-temperature thermal management and balanced synergistic control of battery packs. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for low-temperature thermal management and balanced coordinated control of battery packs. By establishing a battery pack electrothermal coupling simulation model and obtaining the mapping relationship between temperature difference and discharge quantity difference through cell discharge calibration, the method dynamically selects a heating strategy for the battery pack based on ambient temperature and heat exchange capacity. Furthermore, it calculates the energy gain from temperature difference and the energy gain from heating based on user habits and navigation information to determine heating initiation. Simultaneously, during the charging phase, it initiates balanced compensation based on the discharge quantity deviation of different cells, thereby improving the usable capacity, energy efficiency, and cell consistency of the battery pack under low-temperature conditions.

[0010] To achieve the above objectives, the present invention provides a method for low-temperature thermal management and balanced coordinated control of a battery pack, comprising: Establish a simulation model of the electrothermal coupling of the battery pack; The cells of the battery pack are discharged and calibrated under different temperature conditions; The heating strategy for the battery pack is dynamically selected based on the ambient temperature and heat exchange capacity. The battery pack is heated and started based on a revenue decision made according to user habits and navigation information. During the charging phase, the battery pack is balanced and compensated based on the discharge deviation.

[0011] The beneficial effects of this invention include: (1) The battery pack low temperature thermal management and equalization coordinated control method proposed in this invention establishes a battery pack electrothermal coupling simulation model and obtains the mapping relationship between temperature difference and discharge amount difference through cell discharge calibration. It dynamically selects the heating strategy for the battery pack according to the ambient temperature and heat exchange capacity, and calculates the temperature difference energy gain and heating energy gain based on user habits and navigation information to decide the heating start. At the same time, equalization compensation is started according to the discharge amount deviation of different cells during the charging stage, thereby improving the battery pack's usable capacity, energy efficiency and cell consistency under low temperature conditions.

[0012] (2) The battery pack low temperature thermal management and equalization coordinated control method proposed in this invention establishes for the first time an engineering mapping from cell temperature distribution to discharge difference, providing a precise basis for profit decision-making; and takes "reducing cell temperature difference to release more power" as an independent profit item, filling the gap in the existing technology.

[0013] (3) The battery pack low-temperature thermal management and equalization coordinated control method proposed in this invention dynamically adjusts the heating rate and heating mode: a small number of heating films are arranged and the thermal conductivity is asymmetrically designed. The heating rate of the heating film is dynamically adjusted by discharging the battery pack or high-temperature area to heat the low-temperature area. At the same time, the SOC deviation is monitored to ensure the safe application of the system. The entire battery pack and the high-temperature central area cells are connected in series as heating power supplies to form two independent heating circuits, which are controlled by BMS. The BMS couples different working conditions at different times and uses two different heating strategies to coordinate the benefit and environmental changes to ensure the maximum benefit.

[0014] (4) The battery pack low temperature thermal management and equalization coordinated control method proposed in this invention has greater freedom of temperature equalization and lower energy consumption: if there are multiple low temperature edge zones in the battery pack under low temperature conditions, a heating film is arranged in each zone, an external parallel heating power supply is connected, and independent power regulation is performed.

[0015] (5) The battery pack low temperature thermal management and equalization coordinated control method proposed in this invention has cross-stage coordinated equalization: actively compensates for the power deviation caused by low temperature discharge during the charging stage, improves long-term consistency, and extends battery life; and has adaptive learning capability: updates the mapping model through historical data to continuously optimize the control strategy.

[0016] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0017] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.

[0018] Figure 1This is a flowchart illustrating the battery pack low-temperature thermal management and balanced coordinated control method proposed in this invention.

[0019] Figure 2 This is a flowchart illustrating a specific implementation of the battery pack low-temperature thermal management and balanced coordinated control method proposed in this invention.

[0020] Figure 3 This is a schematic diagram illustrating the heating strategy execution of the battery pack low-temperature thermal management and balanced coordinated control method proposed in this invention.

[0021] Figure 4 This is a schematic diagram of the non-outermost cell structure in the low-temperature region of the battery pack's low-temperature thermal management and balanced collaborative control method proposed in this invention.

[0022] Figure 5 This is a schematic diagram of the outermost cell structure in the low-temperature zone of the battery pack's low-temperature thermal management and balanced collaborative control method proposed in this invention. Detailed Implementation

[0023] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0024] This invention provides a method for low-temperature thermal management and balanced coordinated control of a battery pack, such as... Figure 1 As shown, it includes: Establish a simulation model of the electrothermal coupling of the battery pack; Discharge calibration of battery pack cells under different temperature conditions; The heating strategy for the battery pack is dynamically selected based on the ambient temperature and heat exchange capacity. The battery pack is heated to start based on revenue decisions made according to user habits and navigation information. During the charging phase, the battery pack is balanced and compensated based on the discharge deviation.

[0025] In this invention, a battery pack electrothermal coupling simulation model is established, and the mapping relationship between temperature difference and discharge quantity difference is obtained through cell discharge calibration. The heating strategy for the battery pack is dynamically selected based on the ambient temperature and heat exchange capacity. The energy gain from temperature difference and the energy gain from heating are calculated based on user habits and navigation information to determine the start of heating. At the same time, during the charging stage, equalization compensation is initiated based on the discharge quantity deviation of different cells, thereby improving the usable capacity, energy efficiency and cell consistency of the battery pack under low temperature conditions.

[0026] In this invention, each thermal management module is integrated and controlled through a battery management system (BMS) or a vehicle control unit (VCU).

[0027] According to the present invention, establishing a battery pack electrothermal coupling simulation model includes: CFD simulation and operating condition calibration were performed on the battery pack, and the ambient temperature was set to low temperature operating condition. The heat generation rate model of the battery cells in the input battery pack at different temperatures and different SOCs, as well as the heat transfer boundary conditions at each location; The temperature distribution of each cell in the battery pack is simulated under different SOC discharge, different low temperature discharge, and different driving conditions. The location of high temperature and low temperature regions, the number of cells, and the temperature difference are calculated. The location and number of high temperature discharge heating power supply and low temperature heated unit are determined, and the maximum temperature difference is calculated.

[0028] This invention establishes for the first time an engineering mapping from cell temperature distribution to discharge capacity differences, providing a precise basis for profit decisions; and treats "reducing cell temperature difference to release more electricity" as an independent profit item, filling a gap in existing technology.

[0029] According to the present invention, the ambient temperature is -40℃ to 25℃; The formula for calculating the maximum temperature difference is ΔT = T. max - T min Where ΔT is the maximum temperature difference, T max T represents the highest temperature of the cells inside the battery pack. min This is the lowest temperature of the cells inside the battery pack.

[0030] According to the present invention, the discharge calibration of the battery pack cells under different temperature conditions includes: Based on the vehicle's energy consumption and operating conditions, the discharge process of individual battery cells is broken down, and the discharge tests of individual battery cells at different temperatures are conducted in a laboratory environment. The relationship function between discharge energy and temperature was obtained by fitting the data. Write the relational functions into the BMS control strategy; Estimate the discharge energy retention rate at different SOC and temperatures based on the end battery pack temperature and temperature distribution under different discharge conditions; The BMS calculates the increased discharge energy gain under the current temperature difference conditions, which is the energy loss caused by the temperature difference.

[0031] According to the present invention, different temperatures include -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 15°C, and 20°C; The expression for the relational function is E(T) = Eref f(T), where E is the discharge energy, T is the temperature, and E ref Where f(T) is the capacity at room temperature, and f(T) is the energy decay coefficient at low temperature. The expression for the energy gain from discharge is ΔE = E ref (f(T)max )-f(T min )).

[0032] According to the present invention, dynamically selecting a heating strategy for the battery pack based on ambient temperature and heat exchange capacity includes: Strategy 1: By discharging the battery pack, heat the cells in the low-temperature area, increase the temperature of the cells in the low-temperature area, and thus improve the overall energy retention rate of the pack. Determine whether there is a benefit in reducing the SOC of the entire pack by heating and increasing the energy in the low-temperature area. Strategy 2: Adopt a different zone heating-discharge control strategy, that is, use the discharge of the high temperature zone cell to heat the low temperature zone cell through the heating film to ensure that the state of charge of the low temperature zone cell is not lost, and ensure the energy redundancy generated by the temperature of the high temperature zone cell. Determine whether the reduction of the state of charge of the high temperature zone cell by heating and the increase of the energy in the low temperature zone are beneficial. At the same time, the benefits of strategy 1 and strategy 2 are determined by BMS, and the optimal strategy is selected for execution.

[0033] In this invention, the heating rate and heating method are dynamically adjusted: a small number of heating films are arranged, and an asymmetric thermal conductivity structure is designed. The heating rate of the heating films is dynamically adjusted by discharging the battery pack or high-temperature area to heat the low-temperature area. At the same time, the SOC deviation is monitored to ensure the safe application of the system. The entire battery pack and the high-temperature central cell are connected in series to serve as heating power supplies, forming two independent heating circuits, which are controlled by the BMS. The BMS couples different operating conditions at different times and uses two different heating strategies to coordinate the benefits and environmental changes to ensure maximum benefits.

[0034] In this invention, if the entire battery pack is discharged to heat the heating film, although the temperature of the cells in the low-temperature zone will rise and the discharge energy will increase, it will cause the SOC of all cells to drop, thereby reducing the discharge energy of the battery pack and affecting the low-temperature discharge energy gain. Therefore, this invention innovatively proposes two execution strategies, which the BMS needs to determine which strategy to use based on the environment. Strategy 1 involves discharging the battery pack to heat the cells in the low-temperature region, thereby increasing the cell temperature in the low-temperature region and improving the overall energy retention rate of the pack. It is necessary to determine whether the reduction in SOC due to overall heating and the increase in energy in the low-temperature region are beneficial. Strategy 2 employs a different heating-discharging control strategy for different regions. That is, the cells in the high-temperature region are discharged to heat the cells in the low-temperature region through a heating film. This can ensure that the SOC of the cells in the low-temperature region is not lost, while making full use of the energy redundancy generated by the higher temperature of the cells in the high-temperature region. It is necessary to determine whether the reduction in SOC due to heating the cells in the high-temperature region and the increase in energy in the low-temperature region are beneficial. At the same time, the BMS determines the benefits of strategy 1 and strategy 2 and selects the optimal strategy to execute. This invention can reduce the number of heating films, lower the overall cost of the battery pack, and improve the overall energy utilization rate. Specifically, the heating film is only placed in the lower-temperature edge areas, typically the areas with strong heat exchange capacity at the front / rear of the battery pack in the driving direction. If the battery pack has multiple low-temperature edge areas under low-temperature conditions, a heating film is placed in each area, with an external parallel heating power supply and independent power regulation. The entire battery pack and the cells in the higher-temperature central area are connected in series as heating power supplies, which are then connected to both ends of the heating film to form two independent heating circuits, controlled by the BMS. The series connection of multiple individual cells can provide higher heating voltage and ensure more heating energy, while keeping the SOC change of the cells in the high-temperature area relatively small, avoiding excessive drop in the discharge SOC of a single cell, which would result in less remaining energy than before heating. The heating strategy is executed as follows: Figure 3 As shown.

[0035] According to the present invention, dynamically selecting a heating strategy for the battery pack based on ambient temperature and heat exchange capacity further includes: By reducing the number of heating films, the overall cost of the battery pack is reduced and the energy utilization rate of the entire pack is improved. That is, heating films are only placed in the edge areas of the battery pack where the temperature is low. If there are multiple low-temperature edge areas in the battery pack under low-temperature conditions, heating films are placed in each zone, and an external parallel heating power supply is connected and independently regulated. The entire battery pack and the cells in the high-temperature central area are connected in series to serve as heating power supplies. They are connected to both ends of the heating film to form two independent heating circuits, which are controlled by the BMS. The series connection of multiple individual cells is used to provide higher heating voltage to ensure more heating energy, while keeping the SOC change of the cells in the high-temperature area small, avoiding excessive drop in the discharge SOC of a single cell, which would result in less remaining energy than that of the unheated cells. PTC, liquid thermal system or MOx type photoelectric conversion thin film material is used, with MOx type photoelectric conversion thin film material preferred to improve heating efficiency, heat conversion efficiency and temperature uniformity. The thickness of the thin film material is 100-500μm. A layer of insulating material is coated on the heating film surface of the outermost battery cell, while the low-temperature battery cells that are not on the outermost layer are not coated. This reduces the rapid heat dissipation of the outermost battery cell in the low-temperature zone of the battery pack, improves heating efficiency, and reduces energy loss. The thickness of the insulating material coating is 100-2000μm, and it is selected from any one of aerogel, ceramic fiber, mica, or flame-retardant foam. The structure of the non-outermost battery cell in the low-temperature zone is as follows: Figure 4 As shown, the outermost cell structure in the low-temperature region is as follows: Figure 5 As shown.

[0036] In this invention, the temperature balance has greater freedom and the energy consumption is lower: if the battery pack has multiple low-temperature edge zones under low-temperature conditions, a heating film is arranged in each zone, and an external parallel heating power supply is connected and independently regulated.

[0037] According to the present invention, the heating start-up of the battery pack based on user habits and navigation information includes: The system obtains the user's historical driving habits from the vehicle's infotainment system or mobile phone. If the user turns on navigation, it obtains the estimated driving distance and road condition information for this trip from the in-vehicle navigation system, calculates the estimated driving time, and uses the BMS to calculate and control the heat dissipation power. Through laboratory calibration, a temperature difference-discharge mapping relationship is established. Based on this relationship, the usable energy E1 of the battery pack without heating, the usable energy E2 of the battery pack after heating using strategy 1, and the usable energy E3 of the battery pack after heating using strategy 2 are calculated. If E2 > E1 or E3 > E1, heating is activated; otherwise, it is deactivated. If E2 > E3, strategy 1 is used for whole-pack heating; otherwise, strategy 2 is used for heating the high-temperature area of ​​the battery. During driving, the heating strategy is adjusted in real time according to the above two strategy logics based on changes in ambient temperature and battery pack temperature. If the discharge energy of the SOC corresponding to the high-temperature region Tmax is greater than the discharge energy of the SOC corresponding to Tmin, i.e. ΔE=E ref (f(T) max,soc -ΔSOC)-f(T min,soc If the SOC deviation is greater than 0, discharge continues; otherwise, discharge of the high-temperature cells is stopped to avoid a phenomenon where the profit increases first and then decreases. If the SOC deviation is greater than the set upper limit threshold, i.e., ΔSOC = SOC max -SOC min >The upper limit threshold also stops cell discharge in the high-temperature zone.

[0038] According to the present invention, the user's historical driving habits include average single-trip mileage, frequently used routes, average vehicle speed, and vehicle usage time; The heat generation power calculated and controlled by the BMS includes: The BMS calculates and controls the heating power in real time based on route navigation and ambient temperature to ensure driving efficiency. The formula for calculating the controlled heating power is: P=Cp m (T 目标 -T min ) / t; The upper limit threshold is 5-10%; E1=E ref f(T min,soc1 ); E2=E ref f(T 目标，soc2 ); E3=Min(E ref f(T max,soc2 ),E ref f(T 目标,soc1 )); Among them, Eref f(T max,soc2 E represents the energy of the battery cell in the high-temperature region. ref f(T 目标,soc1 SOC2 represents the energy of the heated battery cell; SOC2 = SOC1 - Cp m (T) 目标 -T min ) N2 / (N1 3600 C V);T 目标 Set the target temperature to T. max - (2~4℃); t is the driving time; Cp is the specific heat capacity; m is the cell mass; N1 is the number of cells heated in the high-temperature zone; N2 is the number of cells heated in the low-temperature zone; C is the cell capacity; V is the nominal voltage of the cell.

[0039] According to the present invention, the equalization compensation of the battery pack based on the discharge deviation during the charging phase includes: After completing the low-temperature driving or low-temperature discharge process, the BMS calculates the actual discharge energy of each cell or each parallel unit and converts it into the remaining SOC; When the battery pack is connected to the charging pile and starts charging, the ΔSOC deviation of each cell is read through the BMS; When the battery pack is charging, the equalization function is activated to ensure that the SOC of all cells is consistent when the charging is finished. If the SOC of the whole pack is still deviated after the charging is finished, the automatic equalization is activated until the SOC is consistent, forming a cross-stage collaborative closed loop of low temperature discharge → charging equalization. The data after this low-temperature discharge-charge equalization is stored in the historical database to update the temperature difference-discharge mapping model in the module and achieve adaptive calibration. By introducing SOH as a third dimension into the mapping model, we can ensure that the benefit decision remains optimal throughout the entire battery life cycle.

[0040] This invention features cross-stage collaborative balancing: actively compensating for power deviations caused by low-temperature discharge during the charging stage, improving long-term consistency and extending battery life; and adaptive learning capability: updating the mapping model through historical data to continuously optimize the control strategy.

[0041] The present invention will be described in more detail below through embodiments.

[0042] Examples 1-7 and Comparative Example 1 of the present invention take a pure electric passenger vehicle as an example. The system information is as follows: ternary lithium battery cell, nominal capacity 150Ah, 1P132S, room temperature energy of about 72.3kWh, equipped with a mid-sized pure electric sedan, with a room temperature CLTC standard range of 600km.

[0043] Example 1

[0044] This embodiment provides a method for low-temperature thermal management and balanced coordinated control of a battery pack, such as... Figure 2 As shown, it includes: The mapping relationship between temperature difference and discharge difference is obtained through simulation calibration. A small number of heating films are arranged according to the temperature distribution. The method of discharging the battery pack or high-temperature area to heat the low-temperature area is adopted. The energy gain from temperature difference and the energy gain from heating are calculated based on user habits and navigation information to decide the heating start. During the process, the heating rate of the heating film is dynamically adjusted, and the SOC deviation is monitored to ensure the safe application of the system. In the charging stage, equalization compensation is initiated according to the discharge deviation of different cells, thereby improving the usable capacity, energy efficiency and cell consistency of the battery pack under low temperature conditions. Specifically, it includes: Under long-distance operating conditions in a low-temperature environment of -15℃ (Beijing, Hebei, Inner Mongolia, etc.), the vehicle was driven from 100% SOC to 0% SOC. The temperature difference of the entire package was small, with Tmax -2℃, Tmin -6℃, a temperature difference of 4℃, and a temperature difference of 2℃ after averaging. Heating Strategy 1: The heating cells are 32 cells in the core high-temperature area of ​​the PACK, and the heated cells are 28 cells in the periphery area of ​​the PACK. Heating Strategy 2: All cells in the PACK are discharged, and the cells to be heated are treated the same as in Strategy 1; The discharge energy of the unheated solution is 65.04 kWh; the discharge energy of heating strategy 1 is 66.37 kWh, with a 2% increase in energy capacity and an 11 km increase in driving range, and the inter-cell ΔSOC is 0.25%, which can be recovered through charging equalization; the discharge energy of heating strategy 2 is 66.54 kWh, with a 2.3% increase in energy capacity and an 12 km increase in driving range; both heating strategies are beneficial, but heating strategy 2 is more beneficial. The system executes strategy 2, and the battery pack thermal management parameters and equalization coordination control are shown in Table 1.

[0045] Example 2

[0046] This embodiment provides a battery pack low-temperature thermal management and equalization coordinated control method, which specifically includes: Under long-distance operating conditions in a low-temperature environment of -15℃ (Beijing, Hebei, Inner Mongolia, etc.), the vehicle was driven from 100% SOC to 0% SOC. The temperature difference of the entire package was moderate, with Tmax -2℃ and Tmin -10℃, a temperature difference of 8℃. After averaging, the temperature difference was 2℃. In this embodiment, the two heating strategies are the same as in Embodiment 1; Heating Strategy 2: All cells in the PACK are discharged, and the cells to be heated are the same as in Strategy 1; The discharge energy of the no-heating scheme is 64.32kWh; The discharge energy of heating strategy 1 is 65.63kWh, the energy is increased by 2%, the driving range is increased by 11km, and the ΔSOC between cells is 0.74%, which can be recovered through charging equalization; The discharge energy of heating strategy 2 is 66.46kWh, the energy is increased by 3.3%, and the driving range is increased by 17km; Both heating strategies are beneficial, but heating strategy 2 is more beneficial. The system executes strategy 2, and the battery pack thermal management parameters and equalization collaborative control are shown in Table 1.

[0047] Example 3

[0048] This embodiment provides a battery pack low-temperature thermal management and equalization coordinated control method, which specifically includes: Long-distance operation in a low-temperature environment of -15℃ (Beijing, Hebei, Inner Mongolia and other places), driving from 100% SOC to 0% SOC, the temperature difference of the whole package is large, with Tmax -2℃, Tmin -12℃, a temperature difference of 10℃, and a temperature difference of 2℃ after averaging. In this embodiment, the two heating strategies are the same as in Embodiment 1; the discharge energy of the non-heating scheme is 61.43 kWh; the discharge energy of heating strategy 1 is 66.58 kWh, with an 8.4% increase in energy capacity and a 43 km increase in driving range, and the inter-cell ΔSOC is 0.98%, which can be recovered through charging equalization; the discharge energy of heating strategy 2 is 66.42 kWh, with an 8.1% increase in energy capacity and a 41 km increase in driving range; both heating strategies are beneficial, but heating strategy 1 is more beneficial. The system executes strategy 1, and the battery pack thermal management parameters and equalization coordination control are shown in Table 1.

[0049] Example 4

[0050] This embodiment provides a battery pack low-temperature thermal management and equalization coordinated control method, which specifically includes: Long-distance operation in extremely cold environments (such as Northeast China, Xinjiang, and Tibet) with a full charge of 100% SOC, driving from 0% SOC results in a large temperature difference throughout the vehicle, with Tmax at -2℃ and Tmin at -20℃, a temperature difference of 18℃, and a temperature difference of 2℃ after averaging. In this embodiment, the two heating strategies are the same as in Embodiment 1; the discharge energy of the non-heating scheme is 57.82 kWh; the discharge energy of heating strategy 1 is 66.6 kWh, with a 15.2% increase in energy capacity and a 73 km increase in driving range, and the inter-cell ΔSOC is 1.96%, which can be recovered through charging equalization; the discharge energy of heating strategy 2 is 66.26 kWh, with a 14.6% increase in energy capacity and a 70 km increase in driving range; both heating strategies are beneficial, but heating strategy 1 is more beneficial. The system executes strategy 1, and the battery pack thermal management parameters and strategy benefits are shown in Table 1.

[0051] Example 5

[0052] This embodiment provides a battery pack low-temperature thermal management and equalization coordinated control method, which specifically includes: Long-distance operation in extremely cold environments (such as Northeast China, Xinjiang, and Tibet) with the vehicle not fully charged, driving from 80% SOC to 0% SOC, with a large temperature difference throughout the vehicle, including Tmax -2℃ and Tmin -20℃, a temperature difference of 18℃, and a temperature difference of 2℃ after averaging. In this embodiment, the two heating strategies are the same as in Embodiment 1; the discharge energy of the non-heating scheme is 46.25 kWh; the discharge energy of heating strategy 1 is 53.02 kWh, with a 14.6% increase in energy capacity and a 56 km increase in driving range, and the inter-cell ΔSOC is 1.96%, which can be recovered through charging equalization; the discharge energy of heating strategy 2 is 52.94 kWh, with a 14.5% increase in energy capacity and a 56 km increase in driving range; both heating strategies are beneficial, but heating strategy 1 is more beneficial. The system executes strategy 1, and the battery pack thermal management parameters and strategy benefits are shown in Table 1.

[0053] Example 6

[0054] This embodiment provides a battery pack low-temperature thermal management and equalization coordinated control method, which specifically includes: Long-distance operation in extremely cold environments (such as Northeast China, Xinjiang, and Tibet) with the vehicle not fully charged, driving from 60% SOC to 0% SOC, with a large temperature difference throughout the vehicle, including Tmax -2℃ and Tmin -20℃, a temperature difference of 18℃, and a temperature difference of 2℃ after averaging. In this embodiment, the two heating strategies are the same as in Embodiment 1; the discharge energy of the non-heating scheme is 34.69 kWh; the discharge energy of heating strategy 1 is 39.43 kWh, with a 13.7% increase in energy capacity and a 39 km increase in driving range, and the inter-cell ΔSOC is 1.96%, which can be recovered through charging equalization; the discharge energy of heating strategy 2 is 39.63 kWh, with a 14.2% increase in energy capacity and a 41 km increase in driving range; both heating strategies are beneficial, but heating strategy 2 is more beneficial. The system executes strategy 2, and the battery pack thermal management parameters and strategy benefits are shown in Table 1.

[0055] Example 7

[0056] The difference between this embodiment and Embodiment 6 is that the outermost heating film surface of the cell in the low-temperature zone is not covered with a heat-insulating coating, resulting in 20% energy loss of the heating element to the environment; the discharge energy of the non-heating scheme is still 34.69 kWh; the discharge energy of heating strategy 1 is 39.1 kWh, the energy is increased by 12.7%, the driving range is increased by 37 km, and the ΔSOC between cells is 2.5%; the discharge energy of heating strategy 2 is 39.55 kWh, the energy is increased by 14%, and the driving range is increased by 40 km; both heating strategies are beneficial, but heating strategy 2 is more beneficial, so the system executes strategy 2; this embodiment is degraded to varying degrees in terms of discharge energy and driving range improvement compared to Embodiment 6, and the battery pack thermal management parameters and strategy benefits are shown in Table 1.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 4 is that all the cells in this example are used as external heating units to heat all the cells, raising the temperature of the entire battery pack from -20°C to -4°C. The discharge energy of the unheated scheme is 57.82 kWh, while the discharge energy of the heated pack is 65.08 kWh, representing a 12.6% increase in energy and a 60 km increase in range. In Example 4, the discharge energy is 66.6 kWh, representing a 15.2% increase in energy and a 73 km increase in range, which is 13 km more than Comparative Example 1. This example has the advantages of lower energy consumption, longer range, and lower cost. The battery pack thermal management parameters and strategy benefits are shown in Table 1.

[0059] Table 1. Comparison of thermal management parameters and strategies for battery packs in Examples 1-7 and the comparative example.

[0060] Note: All battery cells in the battery pack are used as external heating units to heat all cells and raise the temperature of the entire battery pack.

[0061] The embodiments of the present invention establish a battery pack electrothermal coupling simulation model and obtain the mapping relationship between temperature difference and discharge amount difference through cell discharge calibration. The heating strategy for the battery pack is dynamically selected according to the ambient temperature and heat exchange capacity. The energy gain from temperature difference and the energy gain from heating are calculated based on user habits and navigation information to decide on the start of heating. At the same time, during the charging stage, equalization compensation is initiated according to the discharge amount deviation of different cells, thereby improving the usable capacity, energy efficiency and cell consistency of the battery pack under low temperature conditions.

[0062] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for low-temperature thermal management and balanced coordinated control of a battery pack, characterized in that, include: Establish a simulation model of the electrothermal coupling of the battery pack; The cells of the battery pack are discharged and calibrated under different temperature conditions; The heating strategy for the battery pack is dynamically selected based on the ambient temperature and heat exchange capacity. The battery pack is heated and started based on a revenue decision made according to user habits and navigation information. During the charging phase, the battery pack is balanced and compensated based on the discharge deviation.

2. The control method according to claim 1, characterized in that, The establishment of the battery pack electrothermal coupling simulation model includes: CFD simulation and operating condition calibration were performed on the battery pack, and the ambient temperature was set to low temperature operating condition. Input the heat generation rate model of the battery pack cells at different temperatures and different SOCs, as well as the heat transfer boundary conditions at each location; The temperature distribution of each cell in the battery pack is simulated under different SOC discharge, different low temperature discharge, and different driving conditions. The location of high temperature and low temperature regions, the number of cells, and the temperature difference are calculated. The location and number of high temperature discharge heating power supply and low temperature heated unit are determined, and the maximum temperature difference is calculated.

3. The control method according to claim 2, characterized in that, The ambient temperature is -40℃ to 25℃; The formula for calculating the maximum temperature difference is ΔT = T max - T min Where ΔT is the maximum temperature difference, T max T represents the highest temperature of the cells inside the battery pack. min This is the lowest temperature of the cells inside the battery pack.

4. The control method according to claim 3, characterized in that, Discharge calibration of the battery pack cells under different temperature conditions includes: Based on the vehicle's energy consumption and operating conditions, the discharge process of individual battery cells is broken down, and the discharge tests of individual battery cells at different temperatures are conducted in a laboratory environment. The relationship function between discharge energy and temperature was obtained by fitting the data. Write the aforementioned relational function into the BMS control strategy; Estimate the discharge energy retention rate at different SOC and temperatures based on the end battery pack temperature and temperature distribution under different discharge conditions; The BMS calculates the increased discharge energy gain under the current temperature difference conditions, which is the energy loss caused by the temperature difference.

5. The control method according to claim 4, characterized in that, The different temperatures include -40℃, -30℃, -20℃, -10℃, 0℃, 10℃, 15℃, and 20℃; The expression for the relational function is E(T) = Eref f(T), where E is the discharge energy, T is the temperature, and E ref Where f(T) is the capacity at room temperature, and f(T) is the energy decay coefficient at low temperature. The expression for the discharge energy gain is ΔE=E ref (f(T) max )-f(T min )).

6. The control method according to claim 5, characterized in that, The heating strategy for the battery pack is dynamically selected based on the ambient temperature and heat exchange capacity, including: Strategy 1: By discharging the battery pack, heat the cells in the low-temperature area, increase the temperature of the cells in the low-temperature area, and thus improve the overall energy retention rate of the pack. Determine whether there is a benefit in reducing the SOC of the entire pack by heating and increasing the energy in the low-temperature area. Strategy 2: Adopt a different zone heating-discharge control strategy, that is, use the discharge of the high temperature zone cell to heat the low temperature zone cell through the heating film to ensure that the state of charge of the low temperature zone cell is not lost, and ensure the energy redundancy generated by the temperature of the high temperature zone cell. Determine whether the reduction of the state of charge of the high temperature zone cell by heating and the increase of the energy in the low temperature zone are beneficial. Simultaneously, the benefits of strategy 1 and strategy 2 are determined through BMS, and the optimal strategy is selected for execution.

7. The control method according to claim 6, characterized in that, The dynamic selection of a heating strategy for the battery pack based on ambient temperature and heat exchange capacity also includes: By reducing the number of heating films, the overall cost of the battery pack is reduced and the energy utilization rate of the entire pack is improved. That is, heating films are only placed in the edge areas of the battery pack where the temperature is low. If there are multiple low-temperature edge areas in the battery pack under low-temperature conditions, heating films are placed in each zone, and an external parallel heating power supply is connected and independently regulated. The entire battery pack and the cells in the high-temperature central area are connected in series to serve as heating power supplies. They are connected to both ends of the heating film to form two independent heating circuits, which are controlled by the BMS. The series connection of multiple individual cells is used to provide higher heating voltage to ensure more heating energy, while keeping the SOC change of the cells in the high-temperature area small, avoiding excessive drop in the discharge SOC of a single cell, which would result in less remaining energy than that of the unheated cells. PTC, liquid thermal system or MOx type photoelectric conversion thin film material is used, preferably MOx type photoelectric conversion thin film material to improve heating efficiency, heat conversion efficiency and temperature uniformity, and the thickness of the thin film material is 100-500μm; A layer of heat-insulating material is coated on the heating film surface of the outermost battery cell, while the low-temperature battery cells that are not the outermost layer are not coated. This reduces the heat dissipation of the outermost battery cell in the low-temperature zone of the battery pack, improves heating efficiency, and reduces energy loss. The thickness of the heat-insulating material coating is 100-2000μm and is selected from any one of aerogel, ceramic fiber, mica, or flame-retardant foam.

8. The control method according to claim 6, characterized in that, The battery pack is heated and started based on user habits and navigation information to make a revenue decision. The system obtains the user's historical driving habits from the vehicle's infotainment system or mobile phone. If the user turns on navigation, it obtains the estimated driving distance and road condition information for this trip from the in-vehicle navigation system, calculates the estimated driving time, and uses the BMS to calculate and control the heat dissipation power. Through laboratory calibration, a temperature difference-discharge mapping relationship is established. Based on this relationship, the usable energy E1 of the battery pack without heating, the usable energy E2 of the battery pack after heating using strategy 1, and the usable energy E3 of the battery pack after heating using strategy 2 are calculated. If E2 > E1 or E3 > E1, heating is activated; otherwise, it is not activated. If E2 > E3, strategy 1 is used for whole-pack heating; otherwise, strategy 2 is used for heating the high-temperature area of ​​the battery. During driving, the heating strategy is adjusted in real time according to the above two strategy logics based on changes in ambient temperature and battery pack temperature. If the discharge energy of the SOC corresponding to the high-temperature region Tmax is greater than the discharge energy of the SOC corresponding to Tmin, i.e. ΔE=E ref (f(T) max,soc -ΔSOC)-f(T min,soc If the SOC deviation is greater than 0, discharge continues; otherwise, discharge of the high-temperature cells is stopped to avoid a phenomenon where the profit increases first and then decreases. If the SOC deviation is greater than the set upper limit threshold, i.e., ΔSOC = SOC max -SOC min >The upper limit threshold also stops cell discharge in the high-temperature zone.

9. The control method according to claim 8, characterized in that, The user's historical driving habits include average single-trip mileage, frequently used routes, average vehicle speed, and vehicle usage time; The heat generation power calculated and controlled by the BMS includes: The BMS calculates and controls the heating power in real time based on route navigation and ambient temperature to ensure driving efficiency. The formula for calculating the controlled heating power is as follows: P=Cp m (T 目标 -T min ) / t; The upper limit threshold is 5-10%; E1=E ref f(T min,soc1 ); E2=E ref f(T 目标，soc2 ); E3=Min(E ref f(T max,soc2 ),IT ref f(T 目标,soc1 )): Among them, Eref f(T max,soc2 E represents the energy of the battery cell in the high-temperature region. ref f(T 目标,soc1 SOC2 represents the energy of the heated battery cell; SOC2 = SOC1 - Cp m (T) 目标 -T min ) N2 / (N1 3600 C V);T 目标 Set the target temperature to T. max - (2~4℃); t is the driving time; Cp is the specific heat capacity; m is the cell mass; N1 is the number of cells heated in the high-temperature zone; N2 is the number of cells heated in the low-temperature zone; C is the cell capacity; V is the nominal voltage of the cell.

10. The control method according to claim 8, characterized in that, The equalization compensation of the battery pack based on the discharge deviation during the charging phase includes: After completing the low-temperature driving or low-temperature discharge process, the BMS calculates the actual discharge energy of each cell or each parallel unit and converts it into the remaining SOC; When the battery pack is connected to the charging pile and starts charging, the ΔSOC deviation of each cell is read through the BMS; When the battery pack is charging, the equalization function is activated to ensure that the SOC of all cells is consistent when the charging is finished. If the SOC of the whole pack is still deviated after the charging is finished, the automatic equalization is activated until the SOC is consistent, forming a cross-stage collaborative closed loop of low temperature discharge → charging equalization. The data obtained after low-temperature discharge-charge equalization described above is stored in the historical database to update the temperature difference-discharge mapping model in the module and achieve adaptive calibration. By introducing SOH as a third dimension into the mapping model, we can ensure that the benefit decision remains optimal throughout the entire battery life cycle.

Images