Thermal management system of all-vanadium redox flow battery energy storage system and control method

Abstract

The invention discloses a thermal management system of an all-vanadium redox flow battery energy storage system and a control method, and relates to the technical field of energy storage. Through the original system configuration, the technological process and the control method, the problems of high energy consumption, poor adaptability and single function of current flow battery thermal management are effectively solved, one set of thermal management system can realize double circulation of natural cooling and compression cooling, and one set of thermal management system can realize refrigeration and heating, so that the energy consumption of the flow battery is reduced, and the service life of the flow battery is prolonged. The flow battery system is ensured to operate in a proper temperature interval, the operation efficiency of the system is improved, and the stable, safe and efficient operation of the system is ensured; the system has the advantages of being low in investment, operation and maintenance cost, high in heat exchange efficiency, convenient and flexible to operate and adjust, high in equipment integration degree, safe, reliable, long in service life, small in maintenance workload and the like, and is very suitable for unattended large and medium-sized flow battery energy storage power stations.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and in particular relates to a thermal management system and a control method of an all-vanadium liquid flow battery energy storage system. Background Art

[0002] Liquid flow battery is a new type of electrochemical energy storage technology. It is an excellent green large-scale energy storage system because of its high safety, independent capacity, environmental protection, long life, high energy efficiency, simple maintenance, short construction period, flexible configuration and other advantages. Although liquid flow battery has the above advantages, there will be a certain degree of loss of electric energy during the charge and discharge conversion process of the battery. The energy storage system will have about 20-30% energy loss during the charge and discharge process, which is mainly dissipated in the form of heat energy. The temperature change caused by the heat dissipation effect greatly affects the performance of liquid flow battery.

[0003] The thermal management of liquid flow batteries is to maintain the temperature of liquid flow batteries and electrolytes within a suitable range through reasonable design and control to ensure the performance and life of the battery. The operating temperature range of all-vanadium liquid flow batteries is generally 5 to 40°C. The conventional thermal management cooling method adopts direct cooling. During the operation of all-vanadium liquid flow batteries, the heat generated is mainly stored and enriched in the electrolyte. The object of thermal management is liquid, flowing, and the temperature of the electrolyte is almost uniform. The cooling system includes a refrigerator, a heat exchanger and related pipelines. The refrigerator provides cold water, which is transported to the heat exchanger through related pipelines. The heat exchanger exchanges heat with the electrolyte in the storage tank, takes away the heat generated by the battery charging and discharging, and ensures that the electrolyte is maintained within a certain temperature range to ensure the normal operation of the system.

[0004] All-vanadium liquid flow batteries are very suitable for large-scale energy storage applications at the megawatt and 100-megawatt levels due to their high safety and reliability, high cost-effectiveness over their entire life cycle, and minimal impact on the environment. When working, all-vanadium liquid flow batteries produce electrochemical reactions between the electrolyte and the positive and negative electrodes of the battery, which dissipate a large amount of heat. The optimal operating temperature of all-vanadium liquid flow batteries is around 20 to 35°C. In order to improve the battery charging and discharging performance, it is necessary to adopt thermal management measures to reduce the battery temperature and prevent excessive heat accumulation from causing battery performance degradation or even thermal runaway. If the temperature of the electrolyte accumulates and rises, chemical reactions will also occur between the electrolyte itself and between the electrolyte and the positive and negative electrodes, which will lead to electrolyte decomposition and capacity loss, which will seriously affect the working efficiency of the battery. Therefore, it is crucial to adopt a thermal management cooling and heat dissipation method that is suitable for different environmental conditions.

[0005] The energy storage thermal management of all-vanadium liquid flow batteries that have been published so far includes air-cooled heat exchangers, water-cooled heat exchangers or immersion heat exchangers. Most of these technologies consume a lot of energy, which has an adverse effect on system efficiency, and cannot achieve accurate local heating and cooling of all-vanadium liquid flow batteries. The refrigeration technology is basically a single cycle of direct cooling, with high energy consumption, a general COP of 2.5, and no special design for environmental adaptability. When used on large-scale energy storage battery modules, it is easy to cause uneven heat dissipation of the battery, affecting the normal operation of the battery, resulting in low overall efficiency of the all-vanadium liquid flow battery energy storage system and affecting the battery life. Therefore, a thermal management system and control method for an all-vanadium liquid flow battery energy storage system are proposed. Summary of the invention

[0006] The purpose of the present invention is to design an intelligent all-vanadium liquid flow battery energy storage thermal management system that is suitable for large-scale energy storage and has ultra-low energy consumption. It uses a low-temperature environment to achieve natural cooling, reduces the high energy consumption caused by mechanical compression cooling, and while completing the thermal management temperature control function, minimizes energy loss to the greatest extent, improves charging and discharging efficiency, and achieves the requirements of safe and reliable control of the system. It solves the problems of the existing direct cooling method, the direct cooling performance coefficient (COP) is low, the direct cooling method cannot effectively utilize low-temperature environmental conditions, and the environmental adaptability is poor. By setting up natural cooling, the adaptability to low-temperature environments is improved and energy consumption is reduced; in extremely high temperature conditions, once the mechanical compression refrigeration output is insufficient, the fluorine pump system can be started in an emergency to enhance the refrigeration effect and the thermal management method can only cool but has no heating function.

[0007] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0008] The present invention is a thermal management system for an all-vanadium liquid flow battery energy storage system, wherein the thermal management system configuration includes a variable frequency compressor, a fluorine side temperature sensor, an oil separator, a fan, a cooling coil, a check valve A, a liquid reservoir, a drying filter, a fluorine pump, an electric valve, a check valve B, an electronic expansion valve, a stop valve A, an evaporator, a stop valve B, a PTC heater and an electrolyte storage tank;

[0009] The variable frequency compressor is arranged in parallel with the oil separator, a PTC heater is arranged in series at the connection between the variable frequency compressor and the oil separator, the oil separator is arranged in series with the fan, a one-way valve A is arranged in series at the connection between the oil separator and the cooling coil, the one-way valve A is arranged in series with the PTC heater, a stop valve B is arranged in series at the connection between the one-way valve A and the PTC heater, the fan is arranged in parallel with the cooling coil, the cooling coil is arranged in series with the liquid reservoir, the liquid reservoir is arranged in series with the drying filter, the drying filter, the fluorine pump, the electric valve, the stop valve A, the evaporator 14 and the stop valve B are arranged in series, the one-way valve B and the electronic expansion valve are arranged in parallel with the fluorine pump and the electric valve, and the electrolyte storage tank is arranged in parallel with the evaporator;

[0010] The process flow of the thermal management system is as follows: the control system enters the cooling mode or the heating mode according to the ambient temperature; the cooling mode is divided into the compression cooling mode and the fluorine pump natural cooling mode;

[0011] The compression refrigeration mode uses four steps of isentropic compression, condensation liquefaction, adiabatic throttling and evaporation heat absorption to exchange heat; the compression system inhales low-temperature and low-pressure Freon vapor through the variable frequency compressor 1, and after compression, forms high-temperature and high-pressure gaseous Freon that enters the condenser, and the fan forces the outdoor atmosphere to exchange heat with the condenser. After the refrigerant is cooled to normal-temperature and high-pressure liquid Freon, it is throttled by the electronic expansion valve to become low-temperature and low-pressure gas-liquid mixed Freon, and enters the evaporator. The electrolyte in the evaporator is evaporated and absorbs heat to become low-temperature and low-pressure gaseous Freon, which is sucked in again by the variable frequency compressor; this reciprocating cycle continuously produces the cooling capacity required by the load; the refrigerant exchanges heat with the low-temperature and low-pressure gas-liquid mixed Freon through the evaporator;

[0012] The fluorine pump natural cooling mode is achieved by shutting down the variable frequency compressor 1 and using the fluorine pump 9 alone to process the environmental cold source to achieve natural cooling.

[0013] In one embodiment, the control method of the thermal management system is: using CAN / RS485 communication, the BMS sends a mode request and an electrolyte target temperature, using a temperature compensation algorithm, the control range is target temperature - temperature bandwidth ≤ electrolyte temperature ≤ target temperature + temperature bandwidth, the initial target temperature is set to "xx" (this temperature is automatically calculated as dew point temperature + 3°C), and the thermal management system acts according to the instruction;

[0014] The temperature control strategy of the battery system is as follows: after the battery starts to charge, the current storage capacity of the battery is determined, and the temperature of the electrolyte after the battery is fully discharged (i.e., SOC = 0) is obtained based on the battery storage capacity, the initial temperature of the electrolyte, and the temperature rise curve obtained by the system test;

[0015] The control method of the thermal management system includes the following modes:

[0016] 1) Standby mode: When the electrolyte temperature t1 is higher than the lower limit and lower than the upper limit (5℃<t1<35℃), the thermal management system does not operate;

[0017] 2) Compression cooling mode: When the electrolyte temperature approaches the upper limit (t1 ≥ 35°C), the thermal management system receives the compression cooling mode request sent by the BMS, and the variable frequency compressor and fan start working at the same time;

[0018] 3) Natural cooling cycle mode: When the external ambient temperature is low (t0<20℃) and the electrolyte operating temperature is close to the upper limit (t1≥35℃), the thermal management system receives the natural cooling mode request sent by the BMS, the variable frequency compressor stops, and only the fluorine pump and fan are turned on;

[0019] 4) Shutdown and insulation mode: When the system is shut down for a long time and the electrolyte temperature drops to near the lower limit temperature (t1 < 5°C), the PTC heater system is started to ensure that the electrolyte temperature is within a reasonable range;

[0020] 5) Automatic mode: The thermal management system receives the automatic mode request sent by the BMS, and the unit automatically adjusts the cooling, heating, and self-circulation modes of the unit according to the difference between the water temperature and the target water temperature.

[0021] The present invention has the following beneficial effects:

[0022] The present invention effectively solves the current problems of high energy consumption, poor adaptability and single function of thermal management of liquid flow batteries through original system configuration and control method. A thermal management system can realize dual circulation of natural cooling and compression cooling, and a thermal management system can realize both cooling and heating, ensuring that the liquid flow battery system operates in an appropriate temperature range, improving the system operation efficiency, and ensuring stable, safe and efficient operation of the system.

[0023] The present invention has the advantages of low investment and operation and maintenance cost, high heat exchange efficiency, convenient and flexible operation and adjustment, high equipment integration, safety and reliability, long life, and low maintenance workload. It is very suitable for unmanned large and medium-sized liquid flow battery energy storage power stations.

[0024] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0026] Figure 1 A system block diagram of a thermal management system for an all-vanadium liquid flow battery energy storage system;

[0027] Figure 2 The control flow chart of a thermal management system of an all-vanadium liquid flow battery energy storage system.

[0028] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0029] Inverter compressor 1, fluorine side temperature sensor 2, oil separator 3, fan 4, cooling coil 5, one-way valve A6, liquid reservoir 7, drying filter 8, fluorine pump 9, electric valve 10, one-way valve B11, electronic expansion valve 12, stop valve A13, evaporator 14, stop valve B15, PTC heater 16, electrolyte storage tank 17. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be understood that the terms "upper", "middle", "outer", "inner" and the like indicating directions or positional relationships are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0032] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] Embodiment 1

[0034] See also Figure 1-Figure 2 As shown, the present invention is a thermal management system for an all-vanadium liquid flow battery energy storage system, the thermal management system comprising a variable frequency compressor 1, a fluorine side temperature sensor 2, an oil separator 3, a fan 4, a cooling coil 5, a one-way valve A6, a liquid reservoir 7, a drying filter 8, a fluorine pump 9, an electric valve 10, a one-way valve B11, an electronic expansion valve 12, a stop valve A13, an evaporator 14, a stop valve B15, a PTC heater 16 and an electrolyte storage tank 17;

[0035] The variable frequency compressor 1 is arranged in parallel with the oil separator 3, a PTC heater 16 is arranged in series at the connection between the variable frequency compressor 1 and the oil separator 3, the oil separator 3 and the fan 4 are arranged in series, a check valve A6 is arranged in series at the connection between the oil separator 3 and the cooling coil 5, the check valve A6 and the PTC heater 16 are arranged in series, a stop valve B15 is arranged in series at the connection between the check valve A6 and the PTC heater 16, the fan 4 is arranged in parallel with the cooling coil 5, the cooling coil 5 and the liquid reservoir 7 are arranged in series, the liquid reservoir 7 and the drying filter 8 are arranged in series, the drying filter 8, the fluorine pump 9, the electric valve 10, the stop valve A13, the evaporator 14 and the stop valve B15 are arranged in series, the check valve B11 and the electronic expansion valve 12 are arranged in parallel with the fluorine pump 9 and the electric valve 10, and the electrolyte storage tank 17 is arranged in parallel with the evaporator 14;

[0036] The process flow of the thermal management system is as follows: the control system enters the cooling mode or the heating mode according to the ambient temperature; the cooling mode is divided into the compression cooling mode and the fluorine pump natural cooling mode;

[0037] The compression refrigeration mode uses four steps of isentropic compression, condensation liquefaction, adiabatic throttling and evaporation heat absorption to exchange heat; the compression system inhales low-temperature and low-pressure Freon vapor through the variable frequency compressor 1, and after compression, it forms high-temperature and high-pressure gaseous Freon and enters the condenser. The fan 4 forces the outdoor atmosphere to exchange heat with the condenser. After the refrigerant is cooled to normal temperature and high-pressure liquid Freon, it is throttled to low-temperature and low-pressure gas-liquid mixed Freon through the electronic expansion valve 12 and enters the evaporator 14. The electrolyte in the evaporator is evaporated and absorbs heat to become low-temperature and low-pressure gaseous Freon, which is sucked in again by the variable frequency compressor 1; this reciprocating cycle continuously produces the cooling capacity required by the load; the refrigerant exchanges heat with the low-temperature and low-pressure gas-liquid mixed Freon through the evaporator 14;

[0038] The fluorine pump natural cooling mode is achieved by shutting down the variable frequency compressor 1 and using the fluorine pump 9 alone to handle the natural cooling from the environmental cold source.

[0039] In the embodiment, the control method of the thermal management system is: using CAN / RS485 communication, the BMS sends a mode request and an electrolyte target temperature, using a temperature compensation algorithm, the control range is target temperature - temperature bandwidth ≤ electrolyte temperature ≤ target temperature + temperature bandwidth, the initial target temperature is set to "xx" (this temperature is automatically calculated as dew point temperature + 3°C), and the thermal management system acts according to the instruction;

[0040] The temperature control strategy of the battery system is as follows: after the battery starts to charge, the current storage capacity of the battery is determined, and the temperature of the electrolyte after the battery is fully discharged (i.e., SOC = 0) is obtained based on the battery storage capacity, the initial temperature of the electrolyte, and the temperature rise curve obtained by the system test;

[0041] like Figure 2As shown, the control method of the thermal management system includes the following modes:

[0042] 1) Standby mode: When the electrolyte temperature t1 is higher than the lower limit and lower than the upper limit (5℃<t1<35℃), the thermal management system does not operate;

[0043] 2) Compression cooling mode: When the electrolyte temperature approaches the upper limit (t1 ≥ 35°C), the thermal management system receives the compression cooling mode request sent by the BMS, and the variable frequency compressor 1 and the fan 4 start working at the same time;

[0044] 3) Natural cooling cycle mode: When the external environment temperature is low (t0<20℃) and the electrolyte operating temperature is close to the upper limit (t1≥35℃), the thermal management system receives the natural cooling mode request sent by the BMS, the variable frequency compressor 1 stops, and only the fluorine pump 9 and the fan 4 are turned on;

[0045] 4) Shutdown and insulation mode: When the system is shut down for a long time and the electrolyte temperature drops to near the lower limit temperature (t1 < 5°C), the PTC heater 16 system is started to ensure that the electrolyte temperature is within a reasonable range;

[0046] 5) Automatic mode: The thermal management system receives the automatic mode request sent by the BMS, and the unit automatically adjusts the cooling, heating, and self-circulation modes of the unit according to the difference between the water temperature and the target water temperature.

[0047] It should be further explained that the technology proposed in the present invention is suitable for the application scenario of large-scale new energy supporting energy storage, especially for the northern region rich in wind power and photovoltaic new energy, with low annual average temperature and long winter climate characteristics, and proposes a "natural cooling + compression cooling" intelligent dual-cycle thermal management technology with a natural cooling module, which also has a heating function, can effectively reduce the energy consumed by thermal management and improve the efficiency of the energy storage system. Its working principle is that when the ambient temperature is low in winter or transition season, the refrigerant pump (fluorine pump) of the refrigeration system is used to circulate heat for the refrigerant (refrigerant) outdoors, making full use of the outdoor natural cold source. At this time, the fluorine pump works alone, the refrigeration compressor is turned off, and the refrigeration energy consumption is extremely low. When the ambient temperature is -30℃, COP>25; when the temperature is high in summer, the compressor is used to compress and circulate the refrigerant for heat exchange, and when the ambient temperature is 35℃, the COP can reach 3.8; in the transition season, the low condensing temperature compressor and the fluorine pump are maintained to work together for refrigeration; the thermal management system design of the present invention technology can be used without turning on the compressor for refrigeration within a certain period of time throughout the year, which greatly reduces the refrigeration energy consumption.

[0048] The present invention effectively utilizes the lower ambient temperature in winter by designing a "natural cooling + compression cooling" dual circulation system, and effectively realizes ultra-energy thermal management through natural cooling of the flow battery.

[0049] The present invention adds a device with a PTC heating function, which can achieve the insulation of the electrolyte in the case of long-term shutdown or severe winter cold, thereby ensuring the safe wintering of the electrolyte.

[0050] The present invention realizes functions such as intelligent optimization and updating of control and operation and maintenance strategies by real-time control of electrolyte operation parameters, and can monitor the operation status and working mode of the battery system in real time with high sensitivity and low energy consumption.

[0051] The equipment configuration of the present invention is highly integrated, and realizes both the dual functions of refrigeration and heating, and also realizes the dual circulation of direct cooling and natural cooling, thus simplifying the system. The thermal management does not need to configure complex electric heaters and pipelines separately, and the cost is low and the implementation is convenient.

[0052] Embodiment 2

[0053] A 200MW / 400MWh energy storage power station of Huadian Jiangsu includes a 10MW / 20MWh all-vanadium liquid flow battery energy storage system, using a 417kW energy storage module, and each energy storage module has a cooling demand of 70-100kW. This method was used to design, and after debugging, the thermal management system operated normally, charging and discharging were normal, and the system heat dissipation was normal.

[0054] Test steps:

[0055] 1) The operation signal of the thermal management system is transmitted to the BMS via RS485 communication;

[0056] 2) The thermal management system enters the refrigeration mode, starts the compressor, and controls the return temperature of the vanadium electrolyte;

[0057] 3) The compressor and condensing fan are internally interlocked and started;

[0058] 4) The compressor and electrolyte circulation pump are interlocked and started to provide a circulation pump operation signal;

[0059] 5) When the electrolyte temperature is lower than the target temperature-temperature bandwidth, stop the compressor;

[0060] 6) When the liquid temperature is greater than the target temperature + temperature bandwidth, the compressor is started and the 3-minute delay protection is met;

[0061] 7) The system detects various protections. The compressor has high and low pressure and over-temperature protection. When one of them fails, a separate alarm will be issued. After the fault is eliminated, the compressor will start cooling.

[0062] The test results show that:

[0063] When the test environment temperature is 35°C and SOC=70%, the actual heat exchange is 45kW, the cooling capacity is 70kW, and the COP reaches 4.3; when the test environment temperature is 40°C and SOC=100%, the actual heat exchange is 45.77kW, the cooling capacity is 70kW, and the COP reaches 3.6, which meets the design requirements and system requirements. According to the test, the thermal management system of the present invention can adjust the operating conditions according to different ambient temperatures, and the cooling effect is higher than the design value, meeting the design requirements.

[0064] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0065] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A thermal management system for an all-vanadium liquid flow battery energy storage system, characterized in that: The thermal management system includes a variable frequency compressor 1, a fluorine side temperature sensor 2, an oil separator 3, a fan 4, a cooling coil 5, a one-way valve A6, a liquid reservoir 7, a drying filter 8, a fluorine pump 9, an electric valve 10, a one-way valve B11, an electronic expansion valve 12, a stop valve A13, an evaporator 14, a stop valve B15, a PTC heater 16 and an electrolyte storage tank 17; The variable frequency compressor 1 is arranged in parallel with the oil separator 3, a PTC heater 16 is arranged in series at the connection between the variable frequency compressor 1 and the oil separator 3, the oil separator 3 is arranged in series with the fan 4, a one-way valve A6 is arranged in series at the connection between the oil separator 3 and the cooling coil 5, the one-way valve A6 is arranged in series with the PTC heater 16, a stop valve B15 is arranged in series at the connection between the one-way valve A6 and the PTC heater 16, the fan 4 is arranged in parallel with the cooling coil 5, the cooling coil 5 is arranged in series with the liquid reservoir 7, the liquid reservoir 7 is arranged in series with the drying filter 8, the drying filter 8, the fluorine pump 9, the electric valve 10, the stop valve A13, the evaporator 14 and the stop valve B15 are arranged in series, the one-way valve B11 and the electronic expansion valve 12 are arranged in parallel with the fluorine pump 9 and the electric valve 10, and the electrolyte storage tank 17 is arranged in parallel with the evaporator 14; The process flow of the thermal management system is as follows: the control system enters the cooling mode or the heating mode according to the ambient temperature; the cooling mode is divided into the compression cooling mode and the fluorine pump natural cooling mode; The compression refrigeration mode uses four steps of isentropic compression, condensation and liquefaction, adiabatic throttling and evaporation heat absorption to perform heat exchange; The compression system sucks in low-temperature and low-pressure Freon vapor through the variable frequency compressor 1, and after compression, it forms high-temperature and high-pressure gaseous Freon that enters the condenser. The fan 4 forces the outdoor atmosphere to exchange heat with the condenser. After the refrigerant is cooled to normal-temperature and high-pressure liquid Freon, it is throttled by the electronic expansion valve 12 to become low-temperature and low-pressure gas-liquid mixed Freon and enters the evaporator 14. The electrolyte in the evaporator is evaporated and absorbs heat to become low-temperature and low-pressure gaseous Freon, which is sucked in again by the variable frequency compressor 1. This reciprocating cycle continuously produces the cooling capacity required by the load. The refrigerant exchanges heat with the low-temperature and low-pressure gas-liquid mixed Freon through the evaporator 14. The fluorine pump natural cooling mode is achieved by shutting down the variable frequency compressor 1 and using the fluorine pump 9 alone to process the environmental cold source to achieve natural cooling.

2. The control method of a thermal management system of an all-vanadium liquid flow battery energy storage system according to claim 1, characterized in that: The control method of the thermal management system is as follows: using CAN / RS485 communication, the BMS sends a mode request and an electrolyte target temperature, using a temperature compensation algorithm, the control range is target temperature - temperature bandwidth ≤ electrolyte temperature ≤ target temperature + temperature bandwidth, the initial target temperature is set to "xx" (this temperature is automatically calculated as dew point temperature + 3°C), and the thermal management system acts according to the instruction; The temperature control strategy of the battery system is as follows: after the battery starts to charge, the current storage capacity of the battery is determined, and the temperature of the electrolyte after the battery is fully discharged (i.e., SOC = 0) is obtained based on the battery storage capacity, the initial temperature of the electrolyte, and the temperature rise curve obtained by the system test; The control method of the thermal management system includes the following modes: 1) Standby mode: When the electrolyte temperature t1 is higher than the lower limit and lower than the upper limit (5℃<t1<35℃), the thermal management system does not operate; 2) Compression cooling mode: When the electrolyte temperature approaches the upper limit (t1 ≥ 35°C), the thermal management system receives the compression cooling mode request sent by the BMS, and the variable frequency compressor 1 and the fan 4 start working at the same time; 3) Natural cooling cycle mode: When the external environment temperature is low (t0<20℃) and the electrolyte operating temperature is close to the upper limit (t1≥35℃), the thermal management system receives the natural cooling mode request sent by the BMS, the variable frequency compressor 1 stops, and only the fluorine pump 9 and the fan 4 are turned on; 4) Shutdown and insulation mode: When the system is shut down for a long time and the electrolyte temperature drops to near the lower limit temperature (t1 < 5°C), the PTC heater 16 system is started to ensure that the electrolyte temperature is within a reasonable range; 5) Automatic mode: The thermal management system receives the automatic mode request sent by the BMS, and the unit automatically adjusts the cooling, heating, and self-circulation modes of the unit according to the difference between the water temperature and the target water temperature.

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