A CO2 system integrating fire protection and thermal management and its control method

Abstract

The application discloses a fire-fighting and thermal management integrated CO2 system and a control method thereof, and belongs to the field of vehicle thermal management, and comprises a direct cooling circulation module and a direct cooling module, and the inlet and outlet of the direct cooling module are connected with the direct cooling circulation module; the direct cooling module comprises a direct cooling plate and a battery pack, and the battery pack is arranged on the direct cooling plate; the direct cooling plate comprises a composite PCM material and an isothermal cold plate, the composite PCM material is embedded in the isothermal cold plate, the surface of the composite PCM material is flush with the surface of the isothermal cold plate, and the working medium of the direct cooling circulation module is carbon dioxide; the direct cooling circulation module comprises a compressor, an air-cooled heat exchanger, an evaporator branch throttle valve, a battery cold plate branch throttle valve, a four-way reversing valve, a first evaporator, a second evaporator, a gas-liquid separator and a regenerator. The application can solve the problem of thermal runaway of the battery in the battery thermal management system.

Description

Technical Field

[0001] The present invention belongs to the field of vehicle thermal management, and in particular relates to a CO2 system integrating fire protection and thermal management and a control method thereof. Background Art

[0002] Lithium-ion batteries are a core component of electric vehicles. Lithium-ion battery systems offer advantages such as high specific energy and power, low self-discharge, and a long lifespan, holding enormous potential for application in electric and hybrid vehicles. However, the drawbacks of lithium-ion batteries include high cost, limited lifespan, and safety concerns, primarily due to temperature-induced degradation. The optimal operating temperature range for electric vehicles is 15°C to 35°C, and the maximum temperature difference between modules and cells within a battery pack should be less than 5°C. Exceeding this temperature limit can lead to thermal failure. To ensure the safety and extend the service life of lithium-ion batteries in electric vehicles, a thermal management system is essential. An electric vehicle battery thermal management system ensures that the battery operates within the appropriate temperature range. This system can reduce internal temperature variations, improve temperature uniformity, extend battery life, ensure safety, maintain an optimal operating environment, and enhance battery efficiency.

[0003] However, excessively high or low battery temperatures, or large temperature differences, can lead to reduced efficiency and thermal runaway. Thermal runaway can cause fires and spontaneous combustion in electric vehicles, endangering the property and lives of passengers and significantly limiting the pace of electric vehicle development towards higher energy densities. Therefore, addressing fire safety issues under direct battery cooling conditions is crucial to prevent the spread of thermal runaway and the resulting serious damage. Summary of the Invention

[0004] The purpose of the present invention is to provide a CO2 system integrating fire protection and thermal management and a control method thereof, so as to solve the problem of thermal runaway of batteries in a battery thermal management system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, a fire protection and thermal management integrated CO2 system comprises: a direct cooling circulation module and a direct cooling module, wherein an inlet and outlet of the direct cooling module are connected to the direct cooling circulation module;

[0007] The direct cooling module includes: a direct cooling plate and a battery pack, wherein the battery pack is arranged on the direct cooling plate;

[0008] The direct cooling plate includes: composite PCM material and a temperature-averaging cold plate. The composite PCM material is embedded in the temperature-averaging cold plate. The surface of the composite PCM material is flush with the surface of the temperature-averaging cold plate. The working fluid of the direct cooling circulation module is carbon dioxide.

[0009] The direct cooling cycle module comprises a compressor, an air-cooled heat exchanger, an evaporator branch throttle valve, a battery cold plate branch throttle valve, a four-way reversing valve, a first evaporator, a second evaporator, a gas-liquid separator and a regenerator;

[0010] The compressor is connected to the regenerator and the four-way reversing valve, the air-cooled heat exchanger is connected to the regenerator and the four-way reversing valve, the gas-liquid separator is connected to the regenerator and the four-way reversing valve, the first evaporator and the direct cooling module are connected to the regenerator and the second evaporator in parallel, the second evaporator is connected to the four-way reversing valve, the evaporator branch throttle valve is arranged at the outlet of the first evaporator, and the battery cold plate branch throttle valve is arranged at the outlet of the direct cooling module.

[0011] In some embodiments, the uniform temperature cold plate comprises a cold plate body, a refrigerant inlet, a refrigerant outlet, a refrigerant distribution header and a micro-channel cooling pipe;

[0012] The refrigerant distribution header and the micro-channel cooling pipe are arranged inside the cold plate body, the refrigerant distribution header is connected to the micro-channel cooling pipe, and the refrigerant inlet and the refrigerant outlet are arranged at the edges of the cold plate body, respectively.

[0013] In some embodiments, the melting point of the composite PCM material is less than 60℃, and the strength of the composite PCM material when it presents a complete solid state is not less than 8MPa.

[0014] In some embodiments, the refrigerant inlet is communicated with the outlet pipeline of the battery cold plate branch throttle valve, and the refrigerant outlet is communicated with the outlet pipeline of the first evaporator.

[0015] In some embodiments, the battery pack comprises batteries and heat-conducting pads, the heat-conducting pads are arranged between adjacent batteries, and the number of batteries is consistent with the number of composite PCM materials.

[0016] In some embodiments, the composite PCM material is in a circular truncated cone structure, the top surface diameter of which is less than the bottom surface diameter, and the top surface diameter is less than one third of the diameter of the battery, a circular truncated cone type groove is arranged on the uniform temperature cold plate, and the composite PCM material is arranged in the circular truncated cone type groove.

[0017] In some embodiments, a pressure sensor is arranged at the outlet of the compressor, and temperature sensors are arranged at the outlets and inlets of the first evaporator and the second evaporator.

[0018] In a second aspect, a control method of a CO2 system integrating fire fighting and thermal management, based on the CO2 system, comprises the following steps:

[0019] In the battery direct cooling process, the speed of the compressor is increased when the actual temperature of the passenger cabin is higher than the preset temperature, and the speed of the compressor is decreased when the actual temperature of the passenger cabin is lower than the preset temperature; the battery cooling plate branch throttle valve is used to control the superheat degree of the outlet branch of the second evaporator to be 2-5℃; the evaporator branch throttle valve is used to control the discharge pressure of the compressor to be the optimal discharge pressure under the current working condition;

[0020] In the battery direct heating process, the speed of the compressor is decreased when the actual temperature of the passenger cabin is higher than the preset temperature, and the speed of the compressor is increased when the actual temperature of the passenger cabin is lower than the preset temperature; the battery cooling plate branch throttle valve is used to control the temperature of the refrigerant at the inlet of the battery pack to be less than 50℃; the evaporator branch throttle valve is used to control the discharge pressure of the compressor to be the optimal discharge pressure under the current working condition;

[0021] In the battery fast charging process, the evaporator branch throttle valve is closed, and the speed of the compressor is fixed, and the opening of the battery cooling plate branch throttle valve is adjusted so that the battery reaches the preset temperature.

[0022] In some embodiments, the strength of the composite PCM material should satisfy, let the lower limit of the battery pack safety temperature be T safe_min , let the upper limit of the battery pack safety temperature be T safe_max , the recommended lower limit of the battery pack safety temperature T safe_min is 50℃, and the recommended upper limit of the battery pack safety temperature T safe_max is 60℃. The preset safety time is t safe , the preset melting time is t PCM , the recommended safety time t safe is 600s, and the recommended melting time t PCM is 180s:

[0023] 1) When the battery pack temperature T<T safe_min , the strength of the composite PCM material is not less than 8MPa.

[0024] 2) When the battery pack temperature T safe_min <T<T safe_max , let the melting percentage x% of the composite PCM material change with time t as x%=f(t), when t>t safe , the strength of (1-x%) of the composite PCM material should be not more than 3MPa

[0025] 3) When the battery pack temperature T>T safe_max , the composite PCM material should be completely melted into liquid within t PCM .

[0026] In some embodiments, a truncated cone-shaped groove is provided on the temperature-averaging cold plate. A distance c is set between the refrigerant flow channel of the temperature-averaging cold plate and the bottom of the truncated cone-shaped groove. The parameter c is selected according to the following requirements: when the solid composite PCM material filled in the truncated cone-shaped groove is not melted, the bottom distance ensures normal operation of the system; after the solid composite PCM material melts into liquid, the cold plate material of the temperature-averaging cold plate with a thickness of c cannot withstand the refrigerant pressure in the refrigerant flow channel. Under the action of the refrigerant pressure, the cold plate material with a thickness of c can be broken through by the refrigerant, allowing the refrigerant to be ejected into the battery pack.

[0027] Alternatively, set the bottom distance to 0.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention provides a CO2 system that integrates fire protection and thermal management. The inlet and outlet of a direct cooling module are connected to a direct cooling circulation module. The direct cooling module comprises a direct cooling plate and a battery pack, with the battery pack mounted on the direct cooling plate. The direct cooling plate comprises a composite PCM material and a temperature-isolating cold plate, with the composite PCM material embedded within the temperature-isolating cold plate, the surface of the composite PCM material being flush with the surface of the temperature-isolating cold plate. The working fluid of the direct cooling circulation module is carbon dioxide. This system ensures the normal operation of the direct cooling plate under normal direct cooling and direct heating conditions. In the event of localized overheating of a battery, the composite PCM material at that point is melted, allowing refrigerant in the microchannel cooling tube to penetrate the temperature-isolating cold plate and enter the battery pack, cooling the battery at that point and preventing the occurrence and spread of thermal runaway, which could lead to serious consequences. This invention not only ensures the temperature requirements of the battery during normal operation, but also meets fire safety requirements in the event of thermal runaway, preventing the spread of thermal runaway and the resulting serious hazards such as fire, thereby promoting the further development of direct cooling in electric vehicles.

[0030] Furthermore, the melting point of the composite PCM material of the present invention is less than 60° C., and the strength of the composite PCM material is not less than 8 MPa when in a completely solid state, which can ensure normal operation of the system in normal direct cooling mode and normal direct heating mode without causing refrigerant leakage.

[0031] Furthermore, the composite PCM material has a truncated cone structure, the top diameter of which is larger than the bottom diameter, and the top diameter is less than one-third of the diameter of the battery. A truncated cone-shaped groove is provided on the temperature-equalizing cold plate, and the composite PCM material is provided in the truncated cone-shaped groove to ensure that the temperature-equalizing cold plate and the composite PCM material will not separate when the battery temperature is lower than 60°C and the refrigerant pressure is less than 8MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A schematic structural diagram of a CO2 system integrating fire protection and thermal management provided in Example 1;

[0033] Figure 2 A schematic structural diagram of a direct cooling module of a CO2 system integrating fire protection and thermal management provided in Example 1;

[0034] Figure 3 A schematic diagram of a heat balancing cold plate structure with a composite PCM material embedded on the surface in a CO2 system integrating fire protection and thermal management provided in Example 1;

[0035] In the figure, 1. Battery pack; 2. Composite PCM material; 3. Uniform temperature cold plate; 4. Cold plate body; 5. Refrigerant inlet; 6. Refrigerant outlet; 7. Refrigerant distribution header; 8. Microchannel cooling tube; 9. Battery; 10. Thermal pad; 11. Compressor; 12. Air-cooled heat exchanger; 13. Evaporator branch throttle valve; 14. Battery cold plate branch throttle valve; 15. Four-way reversing valve; 16. First evaporator; 17. Second evaporator; 18. Gas-liquid separator; 19. Regenerator; 101. Direct cooling module; 102. Direct cooling circulation module; 103. Direct cooling plate. DETAILED DESCRIPTION

[0036] Hereinafter, only certain exemplary embodiments are briefly described, and the described embodiments may be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operate in a specific orientation, and therefore should not be understood as limiting the present invention.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0039] In the present invention, unless otherwise expressly specified or limited, terms such as "installed," "connected," "connected," and "fixed" should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0040] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0041] Example 1

[0042] like Figures 1 to 3 As shown, this embodiment provides a fire protection and thermal management integrated CO2 system, comprising: a direct cooling module 101 with composite materials attached and a direct cooling circulation module 102;

[0043] The direct cooling module 101 includes a battery pack 1 and a direct cooling plate 103 with composite materials attached thereto, and the battery pack 1 is arranged on the direct cooling plate 103;

[0044] The direct cooling plate 103 includes a composite PCM material 2 and a temperature-averaging cold plate 3 into which the composite PCM material can be embedded. The composite PCM material 2 is a truncated cone structure and can be completely embedded in the temperature-averaging cold plate 3. After embedding, the upper surfaces of the composite PCM material 2 and the temperature-averaging cold plate 3 are flush.

[0045] The temperature-averaging cold plate 3 includes a cold plate body 4, a refrigerant inlet 5, a refrigerant outlet 6, a refrigerant distribution header 7, and microchannel cooling tubes 8. The refrigerant inlet 5 can be connected to the outlet pipe of the battery cold plate branch throttle valve 14, and the refrigerant outlet 6 can be connected to the outlet pipe of the first evaporator 16.

[0046] The battery pack 1 includes batteries 9 and thermal pads 10. The thermal pads 10 are placed between adjacent batteries 9 to uniformly distribute the battery temperatures.

[0047] The direct cooling cycle module 102 includes a compressor 11, an air-cooled heat exchanger 12, an evaporator branch throttle valve 13, a battery cold plate branch throttle valve 14, a four-way reversing valve 15, a first evaporator 16, a second evaporator 17, a gas-liquid separator 18, and a regenerator 19. The direct cooling cycle module 102 is connected to the inlet and outlet of the direct cooling module 101; the compressor 11 is connected to the regenerator 19 and the four-way reversing valve 15, the air-cooled heat exchanger 12 is connected to the regenerator 19 and the four-way reversing valve 15, the gas-liquid separator 18 is connected to the regenerator 19 and the four-way reversing valve 15, the first evaporator 16 and the direct cooling module 101 are connected in parallel and connected to the regenerator 19 and the second evaporator 17, the second evaporator 17 is connected to the four-way reversing valve 15, the evaporator branch throttle valve 13 is arranged at the outlet of the first evaporator 16, and the battery cold plate branch throttle valve 14 is arranged at the outlet of the direct cooling module 101;

[0048] The direct cooling cycle module 102 uses carbon dioxide (CO2) as a working fluid and adopts a transcritical carbon dioxide cycle;

[0049] The selection of composite PCM material 2 should meet the following conditions: (1) The melting point of composite PCM material 2 is less than 60°C, ensuring that the CO2 system operates normally in normal direct cooling mode and normal direct heating mode without causing refrigerant leakage; (2) Composite PCM material 2 is safe and non-toxic and will not cause harm to the human body; (3) Composite PCM material 2 meets the corrosion requirements and will not cause chemical corrosion to the battery and battery cold plate under normal working conditions.

[0050] In this embodiment, since existing organic PCM materials all have the problem of poor thermal conductivity, a high thermal conductivity material should be mixed into the composite PCM material 2 to ensure the thermal conductivity of the direct cooling plate 103 and prevent the adverse effect of thermal conductivity on the temperature uniformity of the battery 9.

[0051] The shape of the composite PCM material 2 should meet the following conditions: (1) The composite PCM material 2 is set to a truncated cone structure, with the contact surface with the battery 9 as the top surface and the contact surface with the uniform temperature cold plate 3 as the bottom surface. The top surface diameter is set to a, the bottom surface diameter is set to b, and the height of the truncated cone structure is set to h; (2) The top surface diameter a is smaller than the diameter L of the battery 9. Since the composite PCM material 2 generally does not have good thermal conductivity, considering the thermal management and thermal fire protection effects, the top surface diameter satisfies a.<L / 3;(3)底面直径b> The top diameter a, the larger bottom diameter can ensure that when the battery is directly heated, the height of the melted part of the PCM material accounts for a smaller proportion of the total PCM material height, avoiding the accidental fire caused by the direct heating process, and also ensuring that the fire fighting process can be completed when the battery has thermal runaway; (4) The comprehensive determination of the dimensions of a, b, and h depends on the material strength, melting point, thermal conductivity, etc. The selected dimensions should meet the requirements of the battery 9 bottom surface temperature of 60℃ (T safe_max ) when the composite PCM material 2 can be PCM) is completely melted into liquid. When not melted, the composite PCM material 2 has a strength sufficient to achieve normal performance when the pressure is lower than 8 MPa, and will not cause deformation or degeneration caused by pressure.

[0052] The composite PCM material 2 in the direct cooling plate 103 should be placed at the bottom of each battery 9. The amount of composite PCM material is equal to the number of battery cells. When the direct cooling plate 103 is heating the battery, the inlet temperature of the cold plate should be ensured to be lower than 50°C.

[0053] The material strength of the composite PCM material 2 should comply with the following limitations:

[0054] Among them, the strength of composite PCM material 2 is F , the melting point of composite PCM material 2 is T, and the heat capacity of composite PCM material 2 is , the maximum refrigerant pressure in the pipeline is , the maximum temperature of the refrigerant in the pipeline is ;

[0055] It should be noted that the temperature parameters of the battery 9 set below are equivalent to the temperature parameters of the battery pack 1;

[0056] Assume that the lower limit of the safe temperature of battery 9 is T safe_min , let the upper limit of battery 9 safety temperature be T safe_max , recommended battery 9 safe temperature lower limit T safe_min The recommended safe temperature limit for battery 9 is 50℃. safe_max The value is 60℃. The preset safety time is t safe , the preset melting time is t PCM , recommended safety time t safe The value is 600s, and the recommended melting time t PCM The value is 180s. The melting process intensity of the composite PCM material 2 should meet the following conditions:

[0057] 1) At battery 9 temperature T <T safe_min When the allowable ultimate strength of the material is , the strength of composite PCM material 2 is not less than , The recommended value is 8MPa.

[0058] 2) At battery 9 temperature T safe_min <T<T safe_max When t>t safe When (1-x%), the strength of the composite PCM material 2 should not be greater than 3MPa;

[0059] 3) When the battery 9 temperature T>T safe_max When t PCM Completely melted into liquid.

[0060] The temperature-averaging cold plate 3 is provided with a truncated cone-shaped groove under each battery 9 for embedding the composite PCM material 2. After the composite PCM material 2 is embedded, the top of the composite PCM material 2 is flush with the upper end of the temperature-averaging cold plate 3. The composite PCM material 2 and the temperature-averaging cold plate 3 are bonded together with an adhesive to ensure that the composite PCM material 2 and the temperature-averaging cold plate 3 will not separate when the temperature of the battery 9 is below 60°C and the refrigerant pressure is less than 8 MPa.

[0061] In this embodiment, the distance between the refrigerant flow channel and the bottom of the truncated cone-shaped groove is set to c. This parameter c is selected according to the following requirements: (1) After the solid composite PCM material is filled into the truncated cone-shaped groove embedded with the composite PCM material, the normal operation of the system can be guaranteed under normal operating conditions, that is, when the composite PCM material is not melted. (2) After the composite PCM material melts into liquid, the cold plate material with a thickness of c cannot withstand the refrigerant pressure in the current pipeline. Under the action of the refrigerant pressure, the cold plate material with a thickness of c can break through the cold plate material with a thickness of c, allowing the refrigerant to be sprayed into the battery pack. If necessary, the value of c can be set to 0 to ensure that the refrigerant can be directly sprayed into the battery pack after the battery overheats and the composite PCM material melts.

[0062] The CO2 system provided in this embodiment ensures the normal operation of the direct cooling plate under normal direct cooling and heating conditions. When a battery cell experiences local overheating at a single point, the composite PCM material at that point melts, allowing the refrigerant in the microchannel cooling tube to penetrate the temperature-averaging cold plate and enter the battery pack, cooling the battery cell at that point, thereby preventing the occurrence and spread of thermal runaway and the serious consequences it could cause.

[0063] Example 2

[0064] In this embodiment, a pressure sensor is set at the outlet of the compressor 11, and the exhaust pressure of the compressor 11 is recorded as P1 A temperature sensor is set at the outlet of the first evaporator 16, and the outlet air temperature of the first evaporator 16 is recorded as T1 , the speed of compressor 11 is recorded as N , temperature sensors are set at the inlet and outlet of the second evaporator 17, and the inlet temperature of the second evaporator 17 is recorded as T2 , the outlet temperature of the second evaporator 17 is recorded as T3 .

[0065] This embodiment provides a control method for a CO2 system integrating fire protection and thermal management, specifically including:

[0066] (1) During normal battery direct cooling, adjust the four-way reversing valve 15 to put it in cooling mode. The system uses PID to control the parameters, using the compressor speed N The air outlet temperature is controlled to meet the passenger compartment's cooling needs. When the actual passenger compartment temperature is higher than the set temperature, the compressor 11 speed is increased to increase the cooling capacity. Otherwise, the cooling capacity is reduced until the actual passenger compartment temperature equals the set temperature. The battery cold plate branch throttle valve 14 opening is used to control the superheat of the second evaporator 17 branch. The superheat of the second evaporator 17 branch is defined as:

[0067]

[0068] Without considering the evaporator pressure drop, the evaporator inlet temperature can be considered T2 = is the saturation temperature at that pressure. Controlling the superheat of the evaporator branch ensures that the refrigerant at the battery cold plate branch outlet is in a two-phase state, preventing false fires caused by overheated refrigerant. The recommended SH value is 2°C to 5°C. The evaporator branch expansion valve controls the compressor discharge pressure P1. Optimal discharge pressures exist for different transcritical CO2 system operating conditions. Adjusting the opening of the evaporator branch expansion valve allows the system to operate at the optimal discharge pressure, improving overall system performance.

[0069] (2) During the direct heating process of the battery, adjust the four-way reversing valve to put it in heating mode. The system uses PID to control the parameters and uses the compressor speed N Control the outlet air temperature, which is used to meet the heating needs of the passenger compartment. When the actual temperature of the passenger compartment is higher than the set temperature, the compressor speed is reduced to reduce the heating capacity, and vice versa. The evaporator branch expansion valve is used to adjust the compressor exhaust pressure. P1 Control is performed to ensure that optimal discharge pressure exists for different transcritical CO2 system operating conditions. By adjusting the opening of the evaporator branch expansion valve, the system operates at the optimal discharge pressure, improving overall system performance. The battery cold plate branch throttle valve 14 controls the refrigerant temperature at the battery pack 1 inlet, keeping it below 50°C.

[0070] (3) During the battery fast charging process, the four-way reversing valve is adjusted to be in cooling mode, and the evaporator branch throttle valve 13 is completely closed. The first evaporator 16 and the second evaporator 17 do not participate in the circulation. The system uses PID parameters for control to establish a control relationship between the battery cold plate branch throttle valve 14 and the battery temperature. In the fast charging mode, the battery temperature is set to 20°C. The compressor speed is fixed, and the battery temperature is adjusted to the predetermined value by adjusting the opening of the battery cold plate branch throttle valve 14.

[0071] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the embodiments disclosed above are merely illustrative in all respects and are not exclusive. All modifications within the scope of the present invention or equivalent to the scope of the present invention are intended to be encompassed by the present invention.

Claims

1. A CO2 system integrating fire protection and thermal management, characterized in that: include: A direct cooling circulation module (102) and a direct cooling module (101), wherein the inlet and outlet of the direct cooling module (101) are connected to the direct cooling circulation module (102); The direct cooling module (101) comprises: a direct cooling plate (103) and a battery pack (1), wherein the battery pack (1) is arranged on the direct cooling plate (103); The direct cooling plate (103) comprises: a composite PCM material (2) and a temperature-averaging cold plate (3); the composite PCM material (2) is embedded in the temperature-averaging cold plate (3); the surface of the composite PCM material (2) is flush with the surface of the temperature-averaging cold plate (3); and the working fluid of the direct cooling circulation module (102) is carbon dioxide; The direct cooling cycle module (102) includes: a compressor (11), an air-cooled heat exchanger (12), an evaporator branch throttle valve (13), a battery cold plate branch throttle valve (14), a four-way reversing valve (15), a first evaporator (16), a second evaporator (17), a gas-liquid separator (18), and a regenerator (19); The compressor (11) is connected to the regenerator (19) and the four-way reversing valve (15), the air-cooled heat exchanger (12) is connected to the regenerator (19) and the four-way reversing valve (15), the gas-liquid separator (18) is connected to the regenerator (19) and the four-way reversing valve (15), the first evaporator (16) and the direct cooling module (101) are connected in parallel and connected to the regenerator (19) and the second evaporator (17), the second evaporator (17) is connected to the four-way reversing valve (15), the evaporator branch throttle valve (13) is arranged at the outlet of the first evaporator (16), and the battery cold plate branch throttle valve (14) is arranged at the outlet of the direct cooling module (101); The temperature-averaging cold plate (3) comprises: a cold plate body (4), a refrigerant inlet (5), a refrigerant outlet (6), a refrigerant distribution header (7) and a microchannel cooling pipe (8); a truncated cone-shaped groove is provided on the temperature-averaging cold plate (3); The refrigerant distribution header (7) and the microchannel cooling tube (8) are arranged inside the cold plate body (4), the refrigerant distribution header (7) is connected to the microchannel cooling tube (8), and the refrigerant inlet (5) and the refrigerant outlet (6) are respectively arranged at the edge of the cold plate body (4); The distance between the microchannel cooling tube (8) and the bottom of the truncated cone groove satisfies the following conditions: After the solid composite PCM material (2) is filled into the truncated cone-shaped groove, the normal operation of the CO2 system can be ensured when the composite PCM material (2) is not melted; After the composite PCM material (2) melts into liquid, the cold plate material of the temperature-isolating cold plate (3) with a thickness of the distance cannot withstand the refrigerant pressure in the microchannel cooling tube (8), and the cold plate material of the temperature-isolating cold plate (3) with a thickness of the distance is broken under the refrigerant pressure, so that the refrigerant is sprayed into the battery pack (1).

2. A fire protection and thermal management integrated CO2 system according to claim 1, characterized in that: The refrigerant inlet (5) is connected to the outlet pipeline of the battery cold plate branch throttle valve (14), and the refrigerant outlet (6) is connected to the outlet pipeline of the first evaporator (16).

3. The CO2 system integrating fire protection and thermal management according to claim 1, characterized in that: The battery pack (1) comprises batteries (9) and thermal pads (10), wherein the thermal pads (10) are arranged between adjacent batteries (9), and the number of batteries (9) is consistent with the number of composite PCM materials (2).

4. A fire protection and thermal management integrated CO2 system according to claim 3, characterized in that: The composite PCM material (2) is a truncated cone structure, the contact surface between the truncated cone structure and the battery (9) is the top surface, the contact surface between the truncated cone structure and the temperature-equalizing cold plate (3) is the bottom surface, the diameter of the top surface is smaller than the diameter of the bottom surface, the composite PCM material (2) is arranged in the truncated cone groove, and the diameter of the top surface is smaller than one-third of the diameter of the battery (9).

5. The CO2 system integrating fire protection and thermal management according to claim 1, characterized in that: A pressure sensor is provided at the outlet of the compressor (11), and temperature sensors are provided at the outlet and inlet of the first evaporator (16) and the second evaporator (17).

6. A control method for a CO2 system integrating fire protection and thermal management, characterized in that: The CO2 system according to any one of claims 1 to 5 comprises the following steps: During the direct cooling process of the battery, when the actual temperature of the passenger cabin is higher than the preset temperature, the speed of the compressor (11) is increased, and when the actual temperature of the passenger cabin is lower than the preset temperature, the speed of the compressor (11) is reduced; the battery cold plate branch throttle valve (14) is used to control the superheat of the outlet branch of the second evaporator (17) to 2°C~5°C; the evaporator branch throttle valve (13) is used to control the exhaust pressure of the compressor (11) to the optimal exhaust pressure under the current working conditions; During the direct heating process of the battery, when the actual temperature of the passenger compartment is higher than the preset temperature, the speed of the compressor (11) is reduced, and when the actual temperature of the passenger compartment is lower than the preset temperature, the speed of the compressor (11) is increased; a battery cold plate branch throttle valve (14) is used to control the temperature of the refrigerant at the inlet of the battery pack (1) to be less than 50° C.; an evaporator branch throttle valve (13) is used to control the exhaust pressure of the compressor (11) to be the optimal exhaust pressure under the current working condition; During the battery fast charging process, the evaporator branch throttle valve (13) is closed, the rotation speed of the compressor (11) is fixed, and the opening of the battery cold plate branch throttle valve (14) is adjusted so that the battery reaches a preset temperature.

7. The control method of a CO2 system integrating fire protection and thermal management according to claim 6, characterized in that: The material strength of the composite PCM material (2) satisfies the following conditions: Among them, the strength of composite PCM material is , the melting point of the composite PCM material is T, and the heat capacity of the composite PCM material is , the maximum refrigerant pressure in the pipeline is , the maximum temperature of the refrigerant in the pipeline is ; The melting process strength of the composite PCM material (2) satisfies the following conditions: When the temperature of the battery pack (1) is lower than the lower limit of its own safety temperature, the allowable ultimate strength of the material is , the strength of the composite PCM material is greater than or equal to ; When the temperature of the battery pack (1) is greater than the lower limit of its own safety temperature and less than the upper limit of its own safety temperature, the function of the melting percentage of the composite PCM material (2) changing with time is x%=f(t), wherein x% is the melting percentage and t is the time. When the time is greater than the preset safety time of the composite PCM material (2), the strength of the (1-x%) composite PCM material (2) is less than or equal to 3 MPa. When the temperature of the battery pack (1) is greater than its own safety temperature upper limit, the composite PCM material (2) completely melts into a liquid state within a preset melting time.

8. The control method of a CO2 system integrating fire protection and thermal management according to claim 6, characterized in that: A truncated cone-shaped groove is provided on the temperature-averaging cold plate (3), and a distance between the refrigerant flow channel of the temperature-averaging cold plate (3) and the bottom of the truncated cone-shaped groove is set to c. The parameter c is selected according to the following requirements: when the solid composite PCM material filled in the truncated cone-shaped groove is not melted, the bottom distance ensures the normal operation of the system; after the solid composite PCM material is melted into liquid, the cold plate material of the temperature-averaging cold plate (3) with a thickness of c cannot withstand the refrigerant pressure in the refrigerant flow channel, and the refrigerant can break through the cold plate material with a thickness of c under the action of pressure, so that the refrigerant is sprayed into the battery pack; Alternatively, set the bottom distance to 0.

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