Fire-fighting and thermal management integrated CO2 system and control method thereof

Abstract

The invention discloses a fire-fighting and thermal management integrated CO2 system and a control method thereof, and belongs to the field of vehicle thermal management, the fire-fighting and thermal management integrated CO2 system comprises a direct cooling circulation module and a direct cooling module, and an inlet and an 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 a uniform-temperature cooling plate, the composite PCM material is embedded into the uniform-temperature cooling plate, the surface of the composite PCM material is flush with the surface of the uniform-temperature cooling plate, and a working medium of the direct cooling circulation module is carbon dioxide; the direct cooling circulation module comprises a compressor, an air cooling heat exchanger, an evaporator branch throttling valve, a battery cold plate branch throttling valve, a four-way reversing valve, a first evaporator, a second evaporator, a gas-liquid separator and a heat regenerator. The problem of thermal runaway of the battery in the battery thermal management system can be solved.

Description

Technical Field

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

[0002] Lithium-ion batteries are the core component of electric vehicles. Lithium-ion battery systems have the advantages of high specific energy, high specific power, low self-discharge rate, and long life cycle, and have great application potential in electric vehicles and hybrid vehicles. The disadvantages of lithium-ion batteries are high price, limited life, and high safety. The most important factor is degradation caused by temperature. The optimal operating temperature range of electric vehicles is 15°C to 35°C. The maximum temperature difference between each module and the battery in the battery pack should be less than 5°C. Exceeding this temperature will cause thermal failure of the battery. In order to ensure the safety of lithium-ion power batteries in electric vehicles and extend their service life, a thermal management system is essential. The thermal management system of electric vehicle batteries is a technology that ensures that the battery works in a suitable temperature range. The battery thermal management system can reduce the temperature difference inside the battery, improve the temperature uniformity of the battery, extend the service life of the battery, ensure the safety of the battery, put the battery in an optimal working environment, and improve the battery efficiency.

[0003] However, if the battery temperature is too high, too low, or the temperature difference is too large, the battery efficiency will decrease and cause thermal runaway. Thermal runaway can cause electric vehicles to catch fire and spontaneously ignite, endangering the property and life safety of passengers, and greatly limiting the speed of electric vehicles to develop towards higher energy density. Therefore, it is necessary to solve the fire safety problem under direct battery cooling conditions to prevent the spread of thermal runaway and prevent fires from causing serious harm. Summary of the invention

[0004] The object 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: 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; The direct cooling module comprises: a direct cooling plate and a battery pack, wherein the battery pack is arranged on the direct cooling plate; The direct cooling plate includes: a 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. The direct cooling cycle module includes: 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 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 in parallel and connected to the regenerator and the second evaporator, 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.

[0006] In some embodiments, the temperature-averaging cold plate includes: a cold plate body, a refrigerant inlet, a refrigerant outlet, a refrigerant distribution header, and a microchannel cooling tube; The refrigerant distribution header and the microchannel cooling tube are arranged inside the cold plate body, the refrigerant distribution header is connected to the microchannel cooling tube, and the refrigerant inlet and the refrigerant outlet are respectively arranged at the edge of the cold plate body.

[0007] In some embodiments, the melting point of the composite PCM material is less than 60° C., and the strength of the composite PCM material when in a completely solid state is not less than 8 MPa.

[0008] In some embodiments, the refrigerant inlet is connected to an outlet pipeline of a battery cold plate branch throttle valve, and the refrigerant outlet is connected to an outlet pipeline of the first evaporator.

[0009] In some embodiments, the battery pack includes: batteries and thermal pads, the thermal pads are arranged between adjacent batteries, and the number of batteries is consistent with the number of composite PCM materials.

[0010] In some embodiments, the composite PCM material is a truncated cone structure, the top diameter of which is smaller than the bottom diameter, and the top diameter is smaller than one-third of the diameter of the battery. A truncated cone groove is provided on the temperature equalizing cold plate, and the composite PCM material is provided in the truncated cone groove.

[0011] In some embodiments, a pressure sensor is disposed at the outlet of the compressor, and temperature sensors are disposed at the outlet and inlet of the first evaporator and the second evaporator.

[0012] In a second aspect, a control method of a CO2 system integrating fire protection and thermal management is provided, based on the CO2 system, and comprises the following steps: During the direct cooling of the battery, when the actual temperature of the passenger compartment is higher than the preset temperature, the speed of the compressor is increased, and when the actual temperature of the passenger compartment is lower than the preset temperature, the speed of the compressor is reduced; the battery cold plate branch throttle valve is used to control the superheat of the outlet branch of the second evaporator to 2°C~5°C; the evaporator branch throttle valve is used to control the compressor exhaust pressure to the optimal exhaust pressure under the current working conditions; During the direct heating of the battery, when the actual temperature of the passenger compartment is higher than the preset temperature, the speed of the compressor is reduced, and when the actual temperature of the passenger compartment is lower than the preset temperature, the speed of the compressor is increased; the battery cold 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°C; the evaporator branch throttle valve is used to control the compressor exhaust pressure to the optimal exhaust pressure under the current working conditions; During the fast charging process of the battery, the evaporator branch throttle valve is closed, the compressor speed is fixed, and the opening of the battery cold plate branch throttle valve is adjusted so that the battery reaches the preset temperature.

[0013] In some embodiments, the strength of the composite PCM material should meet the following requirements: safe_min , let the upper limit of battery pack safety temperature be T safe_max , recommended battery pack safety temperature lower limit T safe_min The recommended upper limit of battery pack safety temperature is 50°C. 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: 1) At the battery pack temperature T <T safe_min The strength of the composite PCM material shall not be less than 8MPa.

[0014] 2) At the battery pack temperature T safe_min <T<T safe_max When t>t safe When (1-x%), the composite PCM material strength should not be greater than 3MPa 3) When the battery pack temperature T>T safe_max When the composite PCM material is PCM Completely melted into liquid.

[0015] In some embodiments, a truncated cone groove is provided on the temperature-averaging cold plate, and the distance between the refrigerant flow channel of the temperature-averaging cold plate and the bottom of the truncated cone groove is set to c, and the parameter c is selected according to the following requirements: when the solid composite PCM material filled in the truncated cone 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 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.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a CO2 system integrating fire protection and thermal management, wherein the inlet and outlet of the direct cooling module are connected to the direct cooling circulation module; the direct cooling module comprises: a direct cooling plate and a battery pack, wherein the battery pack is arranged on the direct cooling plate; the direct cooling plate comprises: a composite PCM material and a temperature equalizing cold plate, wherein the composite PCM material is embedded in the temperature equalizing cold plate, wherein the surface of the composite PCM material is flush with the surface of the temperature equalizing cold plate, and the working fluid of the direct cooling circulation module is carbon dioxide. The system can ensure that the direct cooling plate can operate normally under normal direct cooling and direct heating conditions. When a single-point local overheating occurs in the battery, the composite PCM material at the corresponding point can be melted, and the refrigerant in the microchannel cooling tube breaks through the temperature equalizing cold plate and enters the battery pack to cool the battery at a single point, so as to prevent the serious consequences caused by the generation and spread of thermal runaway. The present invention can not only ensure the temperature requirements of the battery during normal operation, but also meet the fire safety requirements in the case of thermal runaway of the battery, prevent the spread of thermal runaway, prevent the generation of fire and other serious hazards, and promote the further development of direct cooling of electric vehicles.

[0017] 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 the normal operation of the system in normal direct cooling mode and normal direct heating mode without causing refrigerant leakage.

[0018] Furthermore, the composite PCM material is a truncated cone structure, the top diameter of which is larger than the bottom diameter, and the top diameter is smaller than one-third of the diameter of the battery. A truncated cone groove is provided on the temperature-averaging cold plate, and the composite PCM material is provided in the truncated cone groove to ensure that the temperature-averaging cold plate and the composite PCM material will not separate when the battery temperature is lower than 60°C and the refrigerant pressure is lower than 8MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of a CO2 system integrating fire protection and thermal management provided in Example 1; Figure 2 A schematic diagram of the structure of a direct cooling module of a CO2 system integrating fire protection and thermal management provided in Example 1; Figure 3 A schematic diagram of a temperature-averaging 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; 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

[0020] In the following, only certain exemplary embodiments are briefly described, and the described embodiments can 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.

[0021] In the description of the present invention, it is to 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”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, 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.

[0022] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0023] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0025] Embodiment 1 like Figure 1~Figure 3 As shown, the present embodiment provides a fire protection and thermal management integrated CO2 system, comprising: a direct cooling module 101 with composite material attached and a direct cooling circulation module 102; The direct cooling module 101 includes a battery pack 1 and a direct cooling plate 103 attached with a composite material, and the battery pack 1 is arranged on the direct cooling plate 103; 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. 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 a microchannel cooling tube 8. The refrigerant inlet 5 can be connected to the outlet pipeline of the battery cold plate branch throttle valve 14, and the refrigerant outlet 6 can be connected to the outlet pipeline of the first evaporator 16.

[0026] The battery pack 1 includes batteries 9 and thermal pads 10, wherein the thermal pads 10 are placed between adjacent batteries 9 to make the battery temperature uniform; 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 entrance and exit 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; The direct cooling cycle module 102 uses carbon dioxide (CO2) as a working fluid and adopts a transcritical carbon dioxide cycle; 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.

[0027] In this embodiment, since existing organic PCM materials all have the problem of poor thermal conductivity, high thermal conductivity materials should be blended in the composite PCM material 2 to ensure the thermal conductivity of the direct cooling plate 103 and prevent adverse effects on the temperature uniformity of the battery 9 due to thermal conductivity problems.

[0028] The shape of the composite PCM material 2 should meet the following conditions: (1) The composite PCM material 2 is set as a frustum structure, the contact surface with the battery 9 is the top surface, and the contact surface with the temperature equalizing cold plate 3 is the bottom surface. Let the top surface diameter be a, the bottom surface diameter be b, and the height of the frustum structure be 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) The bottom surface diameter b > the top surface diameter a. A larger bottom surface 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 height of the PCM material, avoiding false fire protection during the direct heating process, and at the same time can ensure that the fire protection process can be completed when the battery undergoes thermal runaway; (4) The sizes of a, b, and h are determined comprehensively depending on material strength, melting point, thermal conductivity, etc. The selected sizes should meet the condition that when the bottom surface temperature of the battery 9 is 60°C (T safe_max ), the composite PCM material 2 can be completely melted into a liquid within 180 s (t PCM ), and when not melted, the strength of the composite PCM material 2 meets the requirement that it can achieve normal performance when the pressure is lower than 8 MPa, without causing deformation or denaturation due to pressure.

[0029] The composite PCM material 2 in the direct cooling plate 103 should be placed at the bottom of each battery 9, and the number of composite PCM materials is equal to the number of battery monomers. When the direct cooling plate 103 heats the battery, ensure that the cold plate inlet temperature is lower than 50°C.

[0030] The material strength of the composite PCM material 2 should comply with the following limitations:

[0031] Among them, the strength of the composite PCM material 2 is F , the melting point of the composite PCM material 2 is T, the heat capacity of the composite PCM material 2 is , the maximum pressure of the refrigerant in the pipeline is , the highest temperature of the refrigerant in the pipeline is ; It should be noted that the temperature parameters of the battery 9 set below are all equivalent to the temperature parameters of the battery pack 1; Let the lower limit of the safe temperature of the battery 9 be T safe_min , let the upper limit of the safe temperature of the battery 9 be T safe_max , it is recommended that the lower limit of the safe temperature of the battery 9, T safe_min , takes a value of 50°C, and it is recommended that the upper limit of the safe temperature of the battery 9, T safe_maxThe 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: 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.

[0032] 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; 3) When the battery 9 temperature T>T safe_max When the composite PCM material 2 is PCM Completely melted into liquid.

[0033] The temperature-averaging cold plate 3 is provided with a truncated cone-shaped groove capable of embedding the composite PCM material 2 under each battery 9. 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 by 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 lower than 60°C and the refrigerant pressure is less than 8MPa.

[0034] In this embodiment, the distance between the refrigerant flow channel and the bottom of the truncated cone groove is set to c. The parameter c is selected according to the following requirements: (1) After the solid composite PCM material is filled in the truncated cone groove embedded with the composite PCM material, the normal operation of the system can be guaranteed under normal operation, 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 pressure, the refrigerant can break through the cold plate material with a thickness of c, so that the refrigerant is sprayed into the battery pack. If necessary, the c value can be set to 0 to ensure that the refrigerant can be directly sprayed into the battery pack after the battery is overheated and the composite PCM material melts.

[0035] The CO2 system provided in this embodiment can ensure that the direct cooling plate can operate normally under normal direct cooling and direct heating conditions. When a single point of local overheating occurs in the battery, the composite PCM material at the corresponding point can be melted, and the refrigerant in the microchannel cooling tube breaks through the temperature-averaging cold plate and enters the battery pack to cool the battery at a single point, thereby preventing the generation and spread of thermal runaway and causing serious consequences.

[0036] Embodiment 2 In this embodiment, a pressure sensor is provided at the outlet of the compressor 11, and the exhaust pressure of the compressor 11 is recorded as P1 A temperature sensor is provided 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 provided 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 .

[0037] This embodiment provides a control method for a CO2 system integrating fire protection and thermal management, which specifically includes: (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 parameters and uses the compressor speed N Control the outlet air temperature, which is used to meet the cooling demand of the passenger compartment. When the actual temperature of the passenger compartment is higher than the set temperature, increase the speed of the compressor 11 to increase the cooling capacity, otherwise reduce the cooling capacity until the actual temperature of the passenger compartment is equal to the set temperature. Use the opening of the battery cold plate branch throttle valve 14 to control the superheat of the second evaporator 17 branch. The superheat of the second evaporator 17 branch is defined as:

[0038] Without considering the evaporator pressure drop, the evaporator inlet temperature can be considered T2 is the saturation temperature at this pressure. Controlling the superheat of the evaporator branch can be used to ensure that the refrigerant at the outlet of the battery cold plate branch is in two states, avoiding false firefighting due to overheating of the refrigerant. The SH value is recommended to be set to 2℃~5℃. The evaporator branch expansion valve is used to control the compressor exhaust pressure P1. There is an optimal exhaust pressure for different transcritical CO2 system operating conditions. By adjusting the opening of the evaporator branch expansion valve, the system can operate at the optimal exhaust pressure, thereby improving the overall system performance.

[0039] (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 NControl 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, reduce the compressor speed and reduce the heating capacity, otherwise increase the heating capacity. Use the evaporator branch expansion valve to adjust the compressor exhaust pressure P1 Control is performed, and there is an optimal discharge pressure for different transcritical CO2 system operating conditions. The opening of the evaporator branch expansion valve is adjusted to make the system operate at the optimal discharge pressure, thereby improving the overall system performance. The battery cold plate branch throttle valve 14 is used to control the refrigerant temperature at the inlet of the battery pack 1, so that the refrigerant temperature at the inlet of the battery branch is lower than 50°C.

[0040] (3) During the fast charging process of the battery, the four-way reversing valve is adjusted to be in the 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 reaches the predetermined value by adjusting the opening of the battery cold plate branch throttle valve 14.

[0041] 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 above disclosed embodiments are only illustrative in all respects, not exclusive, and all changes within the scope of the present invention or equivalent to the scope of the present invention are included in 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 an 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) comprises: 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).

2. A fire protection and thermal management integrated CO2 system according to claim 1, characterized in that: The temperature-averaging cold plate (3) comprises: a cold plate body (4), a cold medium inlet (5), a cold medium outlet (6), a cold medium distribution header (7) and a microchannel cooling tube (8); 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).

3. A CO2 system integrating fire protection and thermal management 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).

4. A fire protection and thermal management integrated CO2 system according to claim 2, characterized in that: The battery pack (1) comprises: batteries (9) and thermal pads (10); the thermal pads (10) are arranged between adjacent batteries (9); the number of batteries (9) is the same as the number of composite PCM materials (2).

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

6. A fire protection and thermal management integrated CO2 system according to claim 4, characterized in that: The distance between the microchannel cooling tube (8) and the bottom of the truncated cone-shaped 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-averaging 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-averaging 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).

7. A fire protection and thermal management integrated CO2 system 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).

8. 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 7 comprises the following steps: During the direct cooling of the battery, when the actual temperature of the passenger compartment is higher than a preset temperature, the speed of the compressor (11) is increased, and when the actual temperature of the passenger compartment is lower than the preset temperature, the speed of the compressor (11) is reduced; a 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 to 5°C; an 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 direct heating of the battery, when the actual temperature of the passenger compartment is higher than a 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.

9. The control method of a CO2 system integrating fire protection and thermal management according to claim 8, characterized in that: The material strength of the composite PCM material (2) satisfies the following condition: 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 its own safety temperature lower limit and less than its own safety temperature upper limit, the function of the melting percentage of the composite PCM material (2) changing with time is assumed to be 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.

10. The control method of a CO2 system integrating fire protection and thermal management according to claim 8, characterized in that: A truncated cone-shaped groove is provided on the temperature-averaging cold plate (3), and the 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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