An immersion liquid-cooled battery energy storage system and its working method

Abstract

An immersion liquid-cooled battery energy storage system and its working method. The energy storage system includes a secondary-side coolant circulation system, a primary-side cold source system, a heat exchanger, and a control system. The secondary-side coolant circulation system includes a battery cabinet filled with coolant, battery packs located in the battery cabinet and immersed in the coolant, a coolant refrigeration circulation pipeline, and a coolant heating circulation pipeline. The coolant refrigeration circulation pipeline is used to make the coolant flow through the heat exchanger to exchange heat with the primary-side cold source system to cool the coolant when the return liquid temperature is higher than the first preset temperature value. The coolant heating circulation pipeline is used to make the coolant flow through the heater to be heated when the return liquid temperature is lower than the second preset temperature value. The two circulation pipelines are switched between modes through a first three-way valve. The present invention also includes a working method for an immersion liquid-cooled battery energy storage system. The present invention can efficiently ensure the operating temperature of the storage battery in different seasons, and greatly improve the refrigeration efficiency and energy-saving efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage batteries, in particular to an immersion liquid-cooled battery energy storage system and its working method. Background Art

[0002] With the rapid development of fields such as electric vehicles, renewable energy storage, and portable devices, the importance of battery thermal management has become increasingly prominent. During the charging and discharging process of the battery, heat is generated. The high-temperature environment and poor battery temperature uniformity have a negative impact on the battery's efficiency, resulting in performance problems such as battery capacity loss, power decline, and shortened cycle life. Currently, the main ways to solve the problem of high battery heat generation are air-cooling and cold plate liquid-cooling technologies, which have the disadvantages of low heat dissipation efficiency, high energy consumption, relatively complex structures, large contact thermal resistance, and poor temperature uniformity.

[0003] CN 116163985A discloses an energy storage thermal management system and its control method. It circulates the refrigerant through the refrigeration cycle module, and takes away heat through the phase change of the refrigerant, thereby cooling the coolant. The coolant is circulated through the coolant circulation module to cool or heat the energy storage device, and the two are coupled through an intermediate heat exchanger. However, this technology has the following defects: (1) The heater and the intermediate heat exchanger are connected in series. After passing through the heat exchanger, the coolant has to pass through the heater before returning to the energy storage device, which cannot achieve the two working conditions of refrigeration and heating of the coolant according to the return temperature of the coolant; (2) The centrifugal compressor is used on the cold source side to cool the coolant. In the transitional season, the high-quality natural cold source outdoors cannot be utilized, and when the outdoor temperature is low in winter, the compressor is prone to low-pressure protection, which cannot meet the temperature control requirements of the battery; (3) When the external mains power is cut off, the centrifugal compressor stops working, which is likely to cause the temperature of the battery to rise sharply. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above deficiencies of the prior art and provide an immersion liquid-cooled battery energy storage system and its working method with strong functionality, high refrigeration efficiency and energy-saving efficiency, and uniform battery temperature distribution.

[0005] The technical solution of the present invention is as follows:

[0006] An immersion liquid-cooled battery energy storage system of the present invention includes:

[0007] Secondary side coolant circulation system, including a battery cabinet filled with coolant, a battery pack located in the battery cabinet and immersed in the coolant, a coolant refrigeration circulation pipeline and a coolant heating circulation pipeline; the coolant refrigeration circulation pipeline is used to make the coolant flow through a heat exchanger to exchange heat with the primary side cold source system to cool the coolant when it is detected that the return liquid temperature is higher than the first preset temperature value; the coolant heating circulation pipeline is used to make the coolant flow through a heater to heat the coolant when it is detected that the return liquid temperature is lower than the second preset temperature value; the coolant refrigeration circulation pipeline and the coolant heating circulation pipeline are switched in mode through a first three-way valve;

[0008] Primary side cold source system, including a gravity heat pipe circulation system, a mechanical refrigeration system and a phase change energy storage system, which operate independently or jointly among the three systems; the gravity heat pipe circulation unit is used to exchange heat between the outdoor natural cold source and the coolant flowing through the heat exchanger to cool the coolant when it is detected that the outdoor temperature is lower than the third preset temperature value; the phase change energy storage system is used to exchange heat between the phase change material and the coolant flowing through the heat exchanger to cool the coolant when it is detected that the outdoor temperature is higher than the third preset temperature value; the mechanical refrigeration system is used to start when it is detected that the outdoor temperature is higher than the third preset temperature value and the return liquid temperature is higher than the first preset temperature value when the phase change energy storage system is started, so as to reduce the working medium temperature of the phase change energy storage system; the gravity heat pipe circulation system and the phase change energy storage system are switched in mode through a second three-way valve and a third three-way valve;

[0009] The heat exchanger is used to couple the primary side cold source system and the secondary side coolant circulation system for heat transfer;

[0010] Control system, including a first temperature sensor for detecting the return liquid temperature, a second temperature sensor for detecting the supply liquid temperature, an outdoor temperature sensor for detecting the outdoor temperature, and a control module connected to each sensor, and the control module is used to control each mode switching and the start and stop of each system.

[0011] Furthermore, the liquid outlet side of the battery cabinet is sequentially connected to a return liquid pipeline, a circulation pump, the secondary side of the heat exchanger, a supply liquid pipeline and the liquid inlet side of the battery cabinet to form the coolant refrigeration circulation pipeline; the liquid outlet side of the battery cabinet is sequentially connected to a return liquid pipeline, a circulation pump, a heater, a supply liquid pipeline and the liquid inlet side of the battery cabinet to form the coolant heating circulation pipeline.

[0012] Furthermore, one inlet end of the first three-way valve is connected to the heater, the other inlet end is connected to the secondary side outlet of the heat exchanger, and the outlet end is connected to the supply liquid pipeline; the heater and the secondary side of the heat exchanger are arranged in parallel; a liquid filling / draining port is provided on the battery cabinet.

[0013] Further, the gravity heat pipe circulation system includes an air-cooled condenser, a gas pipe, and a liquid pipe; the air-cooled condenser is used to cause the gaseous refrigerant in the heat exchanger to rise through the gas pipe and enter the air-cooled condenser to be cooled into a liquid state, and then flow back to the heat exchanger through the liquid pipe to evaporate; the phase change energy storage system includes a phase change energy storage heat exchanger and a refrigeration pipeline; the phase change energy storage heat exchanger is connected to the primary side of the heat exchanger through the refrigeration pipeline, and the gaseous refrigerant in the heat exchanger is sent to the phase change energy storage heat exchanger through the refrigeration pipeline on one side to be cooled into a liquid state, and then sent to the heat exchanger through the refrigeration pipeline on the other side.

[0014] Further, the mechanical refrigeration system includes a condenser, a compressor, and an expansion valve; the compressor is used to transport the cold generated by the condenser into the phase change energy storage heat exchanger for storage, and the expansion valve is arranged between the outlet of the condenser and the inlet of the phase change energy storage heat exchanger, and the storage of cold is realized under the on-off action of the expansion valve.

[0015] Further, one inlet end of the second three-way valve is connected to the outlet side of the phase change energy storage heat exchanger, the other inlet end is connected to the outlet side of the air-cooled condenser, and the outlet end is connected to the primary side inlet of the heat exchanger; one outlet end of the third three-way valve is connected to the inlet side of the phase change energy storage heat exchanger, the other outlet end is connected to the inlet side of the air-cooled condenser, and the inlet end is connected to the primary side outlet of the heat exchanger.

[0016] Further, the first temperature sensor is arranged on the liquid return pipeline; the second temperature sensor is arranged on the liquid supply pipeline; the control module is electrically connected to the first three-way valve, the second three-way valve, the third three-way valve, the circulation pump, the heater, and each electrical component of the primary side cold source system, and is used to control the flow rate of the circulation pump and the start and stop of the heater according to the liquid return temperature detected by the first temperature sensor; and to control the switching and start and stop of the gravity heat pipe circulation system, the mechanical refrigeration system, and the phase change energy storage system according to the outdoor temperature detected by the outdoor ambient temperature.

[0017] Further, the coolant of the battery cabinet includes mineral oil, which contains a flame retardant and a nanostructured high thermal conductivity medium.

[0018] Further, the first preset temperature value is 35 °C, the second preset temperature value is 10 °C, and the third preset temperature value is 25 °C.

[0019] A control method for an immersion liquid-cooled battery energy storage system of the present invention includes the following steps

[0020] Refrigeration condition: When the first temperature sensor detects that the return liquid temperature is higher than 35°C, first increase the rotation speed of the circulation pump to increase the flow rate of the coolant, so as to achieve rapid heat exchange between the battery cells and the coolant. The coolant transfers heat to the heat exchanger through the circulation pump, and exchanges heat with the primary side cold source system through the heat exchanger, so that the coolant is cooled. The cooled coolant enters the battery cabinet again to exchange heat with the battery cells, reducing the temperature of the battery cells; when increasing the rotation speed of the circulation pump still cannot reduce the return liquid temperature of the coolant, a liquid supplement operation is performed;

[0021] Heating condition: When the first temperature sensor detects that the return liquid temperature is lower than 10°C, first reduce the rotation speed of the circulation pump or even turn off the operation of the circulation pump. When the return liquid temperature is still lower than 10°C, change the direction of the first three-way valve, and the coolant enters the heater to be heated. The heated coolant enters the battery cabinet again to exchange heat with the battery pack to meet the working temperature of the battery cells;

[0022] The primary side cold source system in the refrigeration condition includes the following refrigeration modes:

[0023] Gravity heat pipe cooling refrigeration mode: When the outdoor temperature sensor detects that the outdoor air temperature is lower than 25°C, change the directions of the second three-way valve and the third three-way valve, and the air-cooled condenser is turned on. The heat transferred from the secondary side to the heat exchanger causes the refrigerant in the heat exchanger to change from liquid to gas due to heat absorption. The gaseous refrigerant rises and enters the air-cooled condenser to be cooled and become liquid refrigerant. The absorbed heat is quickly transferred to the outside and flows back to the heat exchanger to evaporate under the action of gravity, forming a cooling cycle;

[0024] Phase change energy storage cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is higher than 25°C, change the directions of the second three-way valve and the third three-way valve, and the phase change energy storage mode is turned on. The heat transferred from the secondary side to the heat exchanger causes the refrigerant in the heat exchanger to change from liquid to gas due to heat absorption, and is cooled to liquid through the phase change energy storage heat exchanger and flows back to the heat exchanger to exchange heat with the primary side, forming a cooling cycle.

[0025] Mechanical refrigeration cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is higher than 25°C, and when starting the phase change energy storage cooling mode and detecting that the return liquid temperature of the battery pack is higher than 35°C, start the mechanical refrigeration cooling mode to reduce the temperature of the working medium in the phase change energy storage heat exchanger.

[0026] The beneficial effects of the present invention:

[0027] (1) Through the immersion liquid cooling technology, the battery pack is completely immersed in the coolant. The coolant fully contacts the battery cells and covers the entire surface of the battery pack, enabling the coolant to evenly absorb and conduct heat, reducing the temperature difference between the upper and lower parts of the battery cells, thereby improving the thermal balance of the entire device. Moreover, the structure is simple, which is conducive to the installation and maintenance of the system and is applicable to various application scenarios of the battery energy storage system. In addition, a flame retardant is added to the coolant used. When a battery fails, it can be used for fire extinguishing to ensure the safety of the storage battery and prevent large-scale explosion incidents.

[0028] (2) By setting the first three-way valve to achieve the switching between the heat exchanger and the heater, it is possible to realize two working conditions of cooling and heating of the coolant according to the temperature of the coolant, and efficiently ensure the operating temperature of the storage battery in different seasons.

[0029] (3) Through the gravity heat pipe technology and the mechanical refrigeration technology, the outdoor natural cold source can be utilized to reduce the system operation energy consumption, contribute to improving the performance and reliability of the battery energy storage system, and promote the development of renewable energy storage technology.

[0030] (4) Through the phase change energy storage cooling technology, the long-time and efficient application of the natural cold source is realized. When the outdoor temperature is relatively low at night, the mechanical refrigeration technology is started to charge the phase change material with cold, and the cold is released during the day. The peak-valley electricity price difference can be utilized to reduce the system operation cost. At the same time, the low temperature at night can reduce the condensation temperature of the mechanical refrigeration system, that is, improve the refrigeration efficiency, and the system energy-saving efficiency is improved. Different from the existing technology of directly wrapping the storage battery with the phase change energy storage material, the utilization of the phase change material has a cold charging and cold releasing process, and this process operates automatically driven by temperature. If the temperature of the storage battery is higher than the temperature of the phase change material, the phase change material automatically releases cold, but the cold release amount gradually decreases with the progress of the cold release process. At this time, the storage battery continuously generates heat, and it is extremely easy to form a high temperature of the storage battery. In addition, the phase change materials used for storage batteries are mostly paraffin-based or inorganic salt-based. Paraffin-based materials are flammable, and once the storage battery catches fire at a high temperature, the paraffin-based materials will become a combustion aid; inorganic salt-based phase change materials are corrosive to metals and are likely to cause corrosion, short circuit and other hazards to the metal components of the storage battery.

[0031] (5) By setting the second three-way valve and the third three-way valve, it is possible to realize the switching between the gravity heat pipe cooling refrigeration mode, the mechanical refrigeration mode and the phase change energy storage cooling mode according to the outdoor temperature, with strong flexibility and high reliability. Description of the Drawings

[0032] Figure 1 is the overall working schematic diagram of the embodiment of the present invention;

[0033] Figure 2 is the working schematic diagram of the embodiment of the present invention under the secondary side heating mode;

[0034] Figure 3This is the working principle diagram of the gravity heat pipe cooling and refrigeration mode in the embodiment of the present invention;

[0035] Figure 4 This is the working principle diagram of the phase change energy storage cooling mode and the mechanical refrigeration cooling mode in the embodiment of the present invention.

[0036] Explanation of the attached drawing reference numerals:

[0037] 1. Secondary side coolant circulation system; 2. Primary side cold source system; 3. Heat exchanger; First temperature sensor 4, Second temperature sensor 5;

[0038] 11. Coolant; 12. Battery pack; 13. Circulation pump; 14. Heater; 15. First three-way valve; 16. Liquid filling / drainage port; 17. Liquid supply pipeline; 18. Liquid return pipeline; 21. Gravity heat pipe circulation system; 22. Phase change energy storage system; 23. Mechanical refrigeration system; 24. Second three-way valve; 25. Third three-way valve;

[0039] 211. Air-cooled condenser; 212. Gas pipe; 213. Liquid pipe; 221. Phase change energy storage heat exchanger; 222. Refrigeration pipeline; 231. Condenser; 232. Compressor; 233. Expansion valve. Detailed implementation manners

[0040] The present invention will be further described in detail below with reference to the accompanying drawings of the specification and specific embodiments.

[0041] As Figures 1 to 4 shown, an immersion liquid-cooled battery energy storage system includes a secondary side coolant circulation system 1, a primary side cold source system 2, a heat exchanger 3 and a control system. Among them, the secondary side coolant circulation system 1 and the primary side cold source system 2 are coupled through the heat exchanger 3 to achieve heat transfer.

[0042] In this embodiment, the secondary side coolant circulation system 1 includes a battery cabinet filled with coolant 11, a battery pack 12 located in the battery cabinet and immersed in the coolant, a circulation pump 13, a heater 14, a first three-way valve 15, a liquid supply pipe 17, and a liquid return pipe 18. The coolant 11 is connected to the secondary side inlet of the heat exchanger 3 through the liquid return pipe 18 and the circulation pump 13, and the secondary side outlet of the heat exchanger 3 is connected to the battery cabinet through the liquid supply pipe 17. The heater 14 is connected in parallel between the secondary side inlet and the secondary side outlet of the heat exchanger 3. One inlet end of the first three-way valve 15 is connected to the heater 14, the other inlet end is connected to the secondary side outlet of the heat exchanger 3, and the outlet end is connected to the liquid supply pipe 17. Under the action of the first three-way valve 15, a coolant refrigeration circulation pipeline is formed between the liquid outlet side of the battery cabinet, the liquid return pipe 18, the circulation pump 13, the secondary side of the heat exchanger 3, the liquid supply pipe 17, and the liquid inlet side of the battery cabinet; a coolant heating circulation pipeline is formed between the liquid outlet side of the battery cabinet, the liquid return pipe 18, the circulation pump 13, the heater 14, the liquid supply pipe 17, and the liquid inlet side of the battery cabinet.

[0043] In addition, ball valves for opening and closing are provided on both the liquid return pipe 18 and the liquid supply pipe 17, and a liquid filling / draining port 16 is provided on the battery cabinet, and coolant is replenished into the battery cabinet through a liquid replenisher. The coolant in the battery cabinet is mainly mineral oil, which contains a flame retardant, a nanostructured high thermal conductivity medium, etc., and can be used as a fire extinguishing agent when the storage battery catches fire at high temperature, and the high thermal conductivity medium increases the heat exchange performance of the mineral oil.

[0044] In this embodiment, the primary side cold source system 2 includes a gravity heat pipe circulation system 21, a phase change energy storage cooling system 22, a mechanical refrigeration system 23, a second three-way valve 24, and a third three-way valve 25. The three systems can operate independently or jointly, and the operating mode is automatically switched according to outdoor environmental parameters.

[0045] Specifically, the gravity heat pipe circulation system 21 includes an air-cooled condenser 211, a gas pipe 212, and a liquid pipe 213.

[0046] The air-cooled condenser 211 is used to cool the gaseous refrigerant in the primary side of the heat exchanger, which rises through the gas pipe 212 into the air-cooled condenser 211 and is cooled into a liquid state, and then flows back to the heat exchanger 3 through the liquid pipe 213 for evaporation.

[0047] The phase change energy storage cooling system 22 includes a phase change energy storage heat exchanger 221 and a refrigeration pipeline 222; the phase change energy storage heat exchanger 221 is connected to the primary side of the heat exchanger 3 through the refrigeration pipeline 222. Due to the heat transferred from the secondary side to the heat exchanger, the refrigerant in the heat exchanger is heated and changes from a liquid state to a gaseous state, and is sent to the phase change energy storage heat exchanger 221 through one side of the refrigeration pipeline for cooling into a liquid state, and then sent to the heat exchanger 3 through the refrigeration pipeline on the other side, forming a cooling cycle.

[0048] The mechanical refrigeration system 23 includes a condenser 231, a compressor 232, and an expansion valve 233. The compressor 232 is used to transport the cold generated by the condenser 231 into the phase change energy storage heat exchanger 27 for storage. The expansion valve 233 is arranged between the outlet of the condenser 231 and the inlet of the phase change energy storage heat exchanger 221. Under the on-off action of the expansion valve, the storage of cold is realized. In this embodiment, the mechanical refrigeration system operates in combination with the phase change energy storage system. The condenser of the mechanical refrigeration system is connected to the phase change energy storage heat exchanger, which can further cool the refrigerant in the refrigeration pipeline and increase the refrigeration capacity of the system. In the emergency condition when the mechanical refrigeration system stops operating, the cold in the phase change energy storage heat exchanger can be used to cool the coolant to ensure the safety of the battery.

[0049] In this embodiment, one inlet end of the second three-way valve 24 is connected to the outlet side of the phase change energy storage heat exchanger 221, the other inlet end is connected to the outlet side of the air-cooled condenser 211, and the outlet end is connected to the primary side inlet of the heat exchanger 3. One outlet end of the third three-way valve 25 is connected to the inlet side of the phase change energy storage heat exchanger 221, the other outlet end is connected to the inlet side of the air-cooled condenser 211, and the inlet end is connected to the primary side outlet of the heat exchanger 3.

[0050] When the battery cells of the battery pack 12 are in direct contact with the coolant 11 for heat exchange, the coolant 11 enters the heat exchanger 3 through the return pipe 18 via the circulation pump 13. The heat exchanger 3 transfers the heat absorbed by the coolant 11 to the primary side cold source system 2. The primary side cold source system 2 transfers the absorbed heat to the outdoor side through the gravity heat pipe circulation system 21 or the phase change energy storage system 22. Among them, an outdoor temperature sensor for detecting the outdoor temperature is provided on the outdoor side. According to the measured value of the outdoor temperature sensor, the directions of the second three-way valve 24 and the third three-way valve 25 are selectively controlled. That is, in one switching mode, a gravity heat pipe cooling circulation pipeline is formed between the gravity heat pipe circulation system 21 and the primary side of the heat exchanger 3; in another switching mode, a phase change energy storage cooling circulation pipeline is formed between the phase change energy storage system 22 and the primary side of the heat exchanger 3 to refrigerate the coolant flowing through the heat exchanger. The mechanical refrigeration system 23 generates cold and stores it in the phase change energy storage heat exchanger 221 to facilitate reducing the temperature of the working medium in the phase change energy storage heat exchanger 221 in the mechanical refrigeration mode.

[0051] In this embodiment, the control system includes a first temperature sensor 4 provided on the liquid return pipe 18, a second temperature sensor 5 provided on the liquid supply pipe 17, an outdoor temperature sensor provided on the outdoor side, and a control module connected to each sensor; and the control module is also electrically connected to the first three-way valve, the second three-way valve, the third three-way valve, the circulation pump, the heater, and each electrical component of the primary side cold source system. The first temperature sensor 4 is used to detect the liquid return temperature, and the second temperature sensor 5 is used to detect the liquid supply temperature. The control module is used to control the flow rate of the circulation pump and the start and stop of the heater according to the first temperature sensor 4; and control the switching and start and stop of the gravity heat pipe circulation system, the mechanical refrigeration system, and the phase change energy storage cooling system according to the outdoor ambient temperature. For example: when the first temperature sensor detects that the liquid return temperature of the secondary side coolant is greater than 35°C, the flow rate of the circulation pump is preferentially increased. When the temperature is still greater than 35°C after the flow rate is increased, the liquid filling port is opened to fill the primary side. When it is detected that the outdoor ambient air temperature is lower than 25°C, the gravity heat pipe circulation system of the primary side cold source system is started. When the outdoor ambient temperature is greater than 25°C, the mechanical refrigeration system of the primary side cold source system is started; when the primary side cold source system fails, the phase change energy storage cooling system is started.

[0052] In this embodiment, according to the measured value of the first temperature sensor 4, the operation of the circulation pump, the start and stop of liquid filling / draining, and the direction of the first three-way valve 15 are controlled, so that the secondary side coolant circulation system 1 operates independently in the following two working conditions.

[0053] Refrigeration working condition: When the first temperature sensor 4 monitors that the liquid return temperature is higher than 35°C, the rotation speed of the circulation pump is preferentially increased to increase the flow rate of the coolant, so as to achieve rapid heat exchange between the battery cells and the coolant 11. The coolant transfers heat to the heat exchanger 3 through the circulation pump 13, and exchanges heat with the primary side cold source system 2 through the heat exchanger 3, so that the coolant 11 is cooled. The cooled coolant enters the battery cabinet again through the liquid supply pipe 17 to exchange heat with the battery cells, reducing the temperature of the battery cells and reducing the battery temperature difference. When increasing the rotation speed of the circulation pump still cannot reduce the liquid return temperature of the coolant, the liquid filling / draining port 16 is opened.

[0054] Heating working condition: When the first temperature sensor 8 detects that the liquid return temperature is lower than 10°C, the rotation speed of the circulation pump is preferentially reduced or even the operation of the circulation pump is stopped. When the liquid return temperature is still lower than 10°C, the direction of the first three-way valve 10 is changed, and the coolant 11 enters the heater 14 through the liquid return pipe 18 via the circulation pump 13, so that the coolant 11 is heated. The heated coolant 11 enters the battery cabinet again through the liquid supply pipe 17 to exchange heat with the battery pack 12, meeting the working operating temperature of the battery cells, reducing the battery temperature difference at the same time, and improving the battery working efficiency. When the coolant is too much or too little, the liquid filling / draining port 16 can be opened.

[0055] In this embodiment, the outdoor temperature sensor on the secondary side of the primary-side cold source system 2 can monitor the outdoor air temperature in real time. According to the measured value of the outdoor temperature sensor, the directions of the second three-way valve 24 and the third three-way valve 25 are controlled so that the primary-side cold source system 2 operates independently in the following three modes.

[0056] Gravity heat pipe cooling refrigeration mode: When the outdoor temperature sensor detects that the outdoor air temperature is lower than 25°C, the directions of the second three-way valve 24 and the third three-way valve 25 are changed, and the air-cooled condenser 211 is turned on. The heat transferred from the secondary side to the heat exchanger causes the refrigerant in the heat exchanger 3 to be heated and change from the liquid phase to the gas phase. It rises through the gas pipe 212 and enters the air-cooled condenser 211 to be cooled and become liquid refrigerant. The absorbed heat is quickly transferred to the outside. At this time, through the action of gravity, it flows back to the heat exchanger 3 through the liquid pipe 213 to evaporate, forming a cooling cycle.

[0057] Phase change energy storage cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is higher than 25°C, the directions of the second three-way valve 24 and the third three-way valve 25 are changed, and the phase change energy storage mode is turned on. The heat transferred from the secondary side to the heat exchanger causes the refrigerant in the heat exchanger to be heated and change from the liquid phase to the gas phase. It is cooled by the phase change energy storage heat exchanger 221 and becomes liquid, and then flows back to the heat exchanger to exchange heat with the primary side, forming a cooling cycle.

[0058] Mechanical refrigeration cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is higher than 25°C, and when the phase change energy storage cooling mode is started and the battery pack return liquid temperature is detected to be higher than 35°C, the mechanical refrigeration cooling mode is started to reduce the temperature of the working medium in the phase change energy storage heat exchanger, thereby reducing the temperature of the battery coolant.

[0059] In this embodiment, the phase change energy storage heat exchanger is added with phase change materials, and the phase change process of the phase change materials is used to realize charging cold at night and discharging cold during the day. When the battery system is on standby at night, the compressor 232 is started to store the cold in the phase change energy storage heat exchanger 221. When the outdoor temperature is higher than 25°C during the day, the phase change energy storage heat exchanger 221 starts to discharge cold for battery cooling to make up for the insufficient cold of the heat pipe.

[0060] The beneficial effects that can be achieved by the above embodiments are as follows:

[0061] (1) Through the immersion liquid cooling technology, the battery pack is completely immersed in the coolant, and the coolant fully contacts the battery cells and covers the entire surface of the battery pack, so that the coolant can evenly absorb and conduct heat, reduce the temperature difference between the upper and lower parts of the battery cells, thereby improving the thermal balance of the entire device; and the structure is simple, which is beneficial to the installation and maintenance of the system and is applicable to various application scenarios of the battery energy storage system; in addition, the coolant used is added with a flame retardant, which can be used for fire extinguishing when the battery fails, ensuring the safety of the battery and avoiding large-scale explosion events.

[0062] (2) By setting the first three-way valve to achieve the switching between the heat exchanger and the heater, it is possible to realize two working conditions of refrigeration and heating of the coolant according to the temperature of the coolant, and efficiently ensure the operating temperature of the storage battery of the battery pack in different seasons.

[0063] (3) Through the gravity heat pipe technology and mechanical refrigeration technology, the outdoor natural cold source can be utilized to reduce the system operation energy consumption, contribute to improving the performance and reliability of the battery energy storage system, and promote the development of renewable energy energy storage technology;

[0064] (4) Through the phase change cold storage technology, the long-delay and high-efficiency application of the natural cold source can be realized. When the outdoor temperature is relatively low at night, the mechanical refrigeration technology is started to charge the phase change material with cold, and the cold is released during the day. The valley-to-peak electricity price difference can be utilized to reduce the system operation cost. At the same time, the low temperature at night can reduce the condensation temperature of the mechanical refrigeration system, that is, improve the refrigeration efficiency and enhance the system energy-saving efficiency. Different from the existing technology of directly wrapping the storage battery with the phase change energy storage material, the utilization of the phase change material has a cold charging and cold releasing process, and this process runs automatically driven by temperature. If the temperature of the storage battery is higher than the temperature of the phase change material, the phase change material automatically releases cold, but the cold release amount gradually decreases with the progress of the cold release process. At this time, the storage battery continuously generates heat, which is extremely likely to form a high temperature of the storage battery. In addition, the phase change materials used for storage batteries are mostly paraffin-based or inorganic salt-based. Paraffin-based materials are flammable, and once the storage battery catches fire at high temperature, the paraffin-based materials will become combustion aids; inorganic salt-based phase change materials are corrosive to metals and are likely to cause corrosion, short circuit and other hazards to the metal components of the storage battery.

[0065] (5) By setting the second three-way valve and the third three-way valve, it is possible to realize the switching between the gravity heat pipe cooling refrigeration mode, the mechanical refrigeration mode and the phase change cold storage cooling mode according to the outdoor temperature, with strong flexibility and high reliability.

[0066] The above shows and describes the basic principles, main features and advantages of the present invention.

[0067] Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and modifications all fall within the scope of the present invention claimed.

Claims

1. A control method for an immersion liquid-cooled battery energy storage system, characterized in that, it includes the following steps, Cooling condition: When the first temperature sensor detects that the return liquid temperature of the coolant is higher than 35°C, first increase the rotation speed of the circulation pump to increase the flow rate of the coolant, realize the rapid heat exchange between the battery cells and the coolant, and the coolant transfers heat to the heat exchanger through the circulation pump, and exchanges heat with the primary side cold source system through the heat exchanger, so that the coolant is cooled, and the cooled coolant enters the battery cabinet again to exchange heat with the battery cells to reduce the temperature of the battery cells; when increasing the rotation speed of the circulation pump still cannot reduce the return liquid temperature of the coolant, then perform a liquid replenishment operation; Heating condition: When the first temperature sensor detects that the return liquid temperature of the coolant is lower than 10°C, first reduce the rotation speed of the circulation pump or even turn off the operation of the circulation pump. When the return liquid temperature is still lower than 10°C, change the direction of the first three-way valve, and the coolant enters the heater to be heated. The heated coolant enters the battery cabinet again to exchange heat with the battery pack to meet the working temperature of the battery cells; The primary side cold source system in the cooling condition includes the following cooling modes: Gravity heat pipe cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is lower than 25°C, change the directions of the second three-way valve and the third three-way valve, and the air-cooled condenser is turned on. The heat transferred from the secondary side to the heat exchanger causes the refrigerant in the heat exchanger to change from liquid phase to gas phase due to heat absorption. The gaseous refrigerant rises and enters the air-cooled condenser to be cooled into liquid refrigerant. The absorbed heat is quickly transferred to the outside and flows back to the heat exchanger to evaporate under the action of gravity, forming a cooling cycle; Phase change energy storage cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is higher than 25°C, change the directions of the second three-way valve and the third three-way valve, and the phase change energy storage mode is turned on. The heat transferred from the secondary side to the heat exchanger causes the refrigerant in the heat exchanger to change from liquid phase to gas phase due to heat absorption, and is cooled into liquid through the phase change energy storage heat exchanger and flows back to the heat exchanger to exchange heat with the primary side, forming a cooling cycle; Mechanical refrigeration cooling mode: When the outdoor temperature sensor detects that the outdoor air temperature is higher than 25°C, and when starting the phase change energy storage cooling mode and detecting that the return liquid temperature of the battery pack is higher than 35°C, start the mechanical refrigeration cooling mode to reduce the temperature of the working medium in the phase change energy storage heat exchanger.

2. An immersion liquid-cooled battery energy storage system adopted by the control method for the immersion liquid-cooled battery energy storage system according to claim 1, characterized in that, it includes: Secondary side coolant circulation system, including a battery cabinet filled with coolant, a battery pack located in the battery cabinet and immersed in the coolant, a coolant refrigeration circulation pipeline and a coolant heating circulation pipeline; the coolant refrigeration circulation pipeline is used to make the coolant flow through the heat exchanger to exchange heat with the primary side cold source system to cool the coolant when it is detected that the return liquid temperature is higher than the first preset temperature value; The coolant heating circulation pipeline is used to make the coolant flow through the heater to heat the coolant when it is detected that the return liquid temperature is lower than the second preset temperature value; the coolant refrigeration circulation pipeline and the coolant heating circulation pipeline are switched between modes through the first three-way valve. The primary-side cold source system includes a gravity heat pipe circulation system, a mechanical refrigeration system, and a phase change energy storage cooling system, which can operate independently or jointly; the gravity heat pipe circulation system is used to utilize the outdoor natural cold source to exchange heat with the coolant flowing through the heat exchanger to cool the coolant when it is detected that the outdoor temperature is lower than the third preset temperature value; the phase change energy storage cooling system is used to utilize the phase change material to exchange heat with the coolant flowing through the heat exchanger to cool the coolant when it is detected that the outdoor temperature is higher than the third preset temperature value; the mechanical refrigeration system is started when it is detected that the outdoor temperature is higher than the third preset temperature value and it is detected that the return liquid temperature is higher than the first preset temperature value when starting the phase change energy storage cooling system, to reduce the working medium temperature of the phase change energy storage cooling system; the gravity heat pipe circulation system and the phase change energy storage cooling system perform mode switching through a second three-way valve and a third three-way valve; the heat exchanger is used to couple the primary-side cold source system with the secondary-side coolant circulation system for heat transfer; The control system includes a first temperature sensor for detecting the return liquid temperature, a second temperature sensor for detecting the supply liquid temperature, an outdoor temperature sensor for detecting the outdoor temperature, and a control module connected to each sensor, and the control module is used to control each mode switching and the start and stop of each system.

3. The immersion liquid cooling battery energy storage system according to claim 2, wherein, The liquid outlet side of the battery cabinet is sequentially connected to a return liquid pipeline, a circulation pump, the secondary side of the heat exchanger, a supply liquid pipeline, and the liquid inlet side of the battery cabinet to form the coolant refrigeration circulation pipeline; the liquid outlet side of the battery cabinet is sequentially connected to a return liquid pipeline, a circulation pump, a heater, a supply liquid pipeline, and the liquid inlet side of the battery cabinet to form the coolant heating circulation pipeline.

4. The immersion liquid cooling battery energy storage system according to claim 3, wherein, One inlet end of the first three-way valve is connected to the heater, the other inlet end is connected to the outlet of the secondary side of the heat exchanger, and the outlet end is connected to the supply liquid pipeline; the heater is arranged in parallel with the secondary side of the heat exchanger; a liquid filling / draining port is provided on the battery cabinet.

5. The immersion liquid cooling battery energy storage system according to claim 2, wherein, The gravity heat pipe circulation system includes an air-cooled condenser, a gas pipe, and a liquid pipe; the air-cooled condenser is used to make the gaseous refrigerant in the heat exchanger rise through the gas pipe and enter the air-cooled condenser to be cooled into a liquid state, and then flow back to the heat exchanger through the liquid pipe to evaporate; the phase change energy storage cooling system includes a phase change energy storage heat exchanger and a refrigeration pipeline; the phase change energy storage heat exchanger is connected to the primary side of the heat exchanger through the refrigeration pipeline, and the gaseous refrigerant in the heat exchanger is sent to the phase change energy storage heat exchanger through one side of the refrigeration pipeline to be cooled into a liquid state, and then sent to the heat exchanger through the refrigeration pipeline on the other side.

6. The immersion liquid cooling battery energy storage system according to claim 5, wherein, The mechanical refrigeration system includes a condenser, a compressor, and an expansion valve; the compressor is used to transport the cold generated by the condenser into the phase change cold storage heat exchanger for storage, and the expansion valve is arranged between the outlet of the condenser and the inlet of the phase change cold storage heat exchanger, and cold storage is achieved under the on-off action of the expansion valve.

7. The immersion liquid cooling battery energy storage system according to claim 5, characterized in that one inlet end of the second three-way valve is connected to the outlet side of the phase change cold storage heat exchanger, the other inlet end is connected to the outlet side of the air-cooled condenser, and the outlet end is connected to the primary side inlet of the heat exchanger; one outlet end of the third three-way valve is connected to the inlet side of the phase change cold storage heat exchanger, the other outlet end is connected to the inlet side of the air-cooled condenser, and the inlet end is connected to the primary side outlet of the heat exchanger.

8. The immersion liquid cooling battery energy storage system according to claim 3, characterized in that the first temperature sensor is arranged on the liquid return pipeline; the second temperature sensor is arranged on the liquid supply pipeline; the control module is electrically connected to the first three-way valve, the second three-way valve, the third three-way valve, the circulation pump, the heater, and each electrical component of the primary side cold source system, and is used to control the flow rate of the circulation pump and the start and stop of the heater according to the liquid return temperature detected by the first temperature sensor; and control the switching and start and stop of the gravity heat pipe circulation system, the mechanical refrigeration system, and the phase change cold storage system according to the outdoor temperature detected by the outdoor ambient temperature.

9. The immersion liquid cooling battery energy storage system according to claim 2, characterized in that the coolant of the battery cabinet includes mineral oil, which contains a flame retardant and a nanostructured high thermal conductivity medium.

10. The immersion liquid cooling battery energy storage system according to claim 2, characterized in that the first preset temperature value is 35 °C, the second preset temperature value is 10 °C, and the third preset temperature value is 25 °C.

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