An immersion type energy storage thermal management method and battery box for extreme temperature variation working conditions

Abstract

The application discloses an immersed energy storage thermal management method and a battery box for extreme temperature change working conditions, and belongs to the technical field of energy storage battery thermal management. In view of the problems of the prior art, such as the incapability of adapting to extreme temperature change working conditions, the large temperature difference of the battery cell, the temperature control lag, the low charging and discharging efficiency, and the incapability of the battery box to adapt to the dynamic expansion and shrinkage of the immersed liquid and the easy leakage failure, the application calibrates the specific heat capacity characteristics of the immersed liquid in a wide temperature range, combines the dynamic heat generation law of the battery cell to construct a coupled heat balance model, adopts a double feedback mechanism to calculate the temperature control compensation heat, and realizes adaptive switching of three modes of heat dissipation, heat preservation and heating. The battery box is additionally provided with an adaptive expansion buffer device, so that the volume expansion and shrinkage of the immersed liquid can be dynamically adapted, and the pressure in the box can be stabilized. The application effectively improves the temperature control precision in extreme working conditions, guarantees the sealing safety of equipment, and prolongs the service life of the energy storage system.

Description

Technical Field

[0001] This invention relates to thermal management technology for energy storage batteries, and is particularly suitable for outdoor immersion energy storage systems in remote rural power grid areas with large day-night temperature differences and drastic high-low temperature alternation. Specifically, it is a thermal management method and battery box for immersion energy storage under extreme temperature change conditions. Background Technology

[0002] With the large-scale implementation of photovoltaic-supported energy storage and outdoor distributed energy storage technologies, a large number of energy storage devices are deployed in mountainous and rural power grid areas. In such scenarios, the ambient temperature fluctuates drastically, with diurnal temperature differences exceeding 20°C under extreme weather conditions. The energy storage cells are constantly exposed to extreme temperature variations caused by alternating hot and cold environments. Existing traditional immersion energy storage thermal management solutions have two major technological shortcomings:

[0003] Traditional immersion temperature control only uses a fixed circulating pump flow rate and a single static temperature threshold to start and stop the cooling / heating device, without considering the nonlinear changes in the specific heat capacity and density of the immersion fluid with temperature. Under conditions of large temperature variations between day and night, the heat capacity of the immersion fluid fluctuates drastically with temperature, resulting in a severe mismatch between the real-time heat generation of the battery cells and the system's heat dissipation / heating capacity. The internal temperature difference of the battery cells can reach more than 5°C. Long-term operation with large temperature differences will exacerbate the degradation of cell consistency and significantly reduce the charging and discharging efficiency of the energy storage system. At the same time, existing heat balance calculations only use static steady-state formulas, which cannot adapt to the dynamic operating conditions of rapid day-night temperature changes in outdoor energy storage, resulting in lagging temperature control and poor accuracy.

[0004] Within extreme temperature ranges, the thermal expansion and contraction volume change rate of the insulating immersion fluid can reach up to 5%. Traditional battery boxes are equipped with fixed-volume expansion tanks that only reserve buffer space based on the static maximum volume, which cannot match the actual expansion amount of the immersion fluid density as the temperature changes dynamically. The internal pressure of the box fluctuates violently with repeated temperature changes, which can easily cause aging of the sealing strips and leakage of pipe joints, thereby causing the insulation performance of the immersion fluid to fail and posing a safety hazard of thermal runaway of the battery cells.

[0005] In summary, the industry urgently needs to develop a precise thermal management algorithm that can couple the thermophysical parameters of the immersion liquid and adapt to extreme temperature dynamic conditions, as well as an immersion energy storage battery box with an adaptive volume buffer and pressure self-stabilizing structure. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing submerged energy storage thermal management technologies, such as inability to adapt to extreme outdoor temperature variations, low temperature control accuracy, and poor enclosure sealing reliability. Firstly, it provides a dynamic adaptive thermal management method that couples the temperature and specific heat capacity characteristics of the immersion liquid, accurately matching the real-time heat generation of the battery cells with the system's temperature control compensation capability, thereby reducing cell temperature differences and lowering energy consumption. Secondly, it provides a sealed battery enclosure with an adaptive expansion buffer device to absorb the expansion and contraction of the immersion liquid due to temperature changes, stabilize the internal pressure, eliminate the risk of leakage and insulation failure, and improve the operational safety and service life of the energy storage system under extreme conditions.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for thermal management of submerged energy storage under extreme temperature variations includes the following steps:

[0009] S1: Real-time acquisition of ambient temperature, immersion liquid temperature, cell charging and discharging power, charging and discharging current and terminal voltage during the operation of the energy storage system; pre-obtain the specific heat capacity-temperature characteristic curve of the immersion liquid in the extreme temperature change range through experimental calibration; establish a theoretical calculation benchmark for cell heat generation, and complete the experimental fitting calibration of cell internal resistance and cell electrochemical reaction entropy change;

[0010] S2: Based on the real-time collected charging and discharging current, combined with the dynamic change relationship of the cell's internal resistance with temperature and the entropy change of the electrochemical reaction, calculate the cumulative net heat generation of the cell per unit time.

[0011] S3: Based on the heat balance of the battery box, a coupled control heat balance model integrating the dynamic specific heat capacity characteristics of the immersion liquid is constructed. The model associates the cumulative net heat generated by the battery cell per unit time, the heat dissipation of the environment, the heat stored in the immersion liquid, and the compensation heat. The real-time specific heat capacity is obtained according to the real-time temperature of the immersion liquid, and the compensation heat is dynamically corrected according to the deviation between the real-time specific heat capacity and the target specific heat capacity to offset the impact of changes in the thermal properties of the immersion liquid on the heat balance.

[0012] S4: Based on the heat capacity fluctuation caused by the change in the specific heat capacity of the immersion liquid and the deviation between the actual temperature and the target control temperature, a dual feedback mechanism is used to calculate the compensation heat required by the cooling or heating device.

[0013] S5: Based on the calculated heat compensation and the deviation threshold between the measured temperature of the immersion liquid and the target temperature, the control system switches between heat dissipation mode, heat preservation mode and heating mode.

[0014] Furthermore, in step S1, the specific heat capacity-temperature characteristic curve of the immersion liquid covers the entire extreme operating temperature range from -30 degrees Celsius to 60 degrees Celsius; and fitting or interpolation processing is performed to ensure that the calculation error of the specific heat capacity of the immersion liquid corresponding to any temperature point does not exceed one percent; when collecting the charging and discharging power of the battery cell, positive and negative values ​​are distinguished, with the charging power recorded as a positive value and the discharging power recorded as a negative value.

[0015] Furthermore, in step S2, the cumulative net heat generation per unit time of the battery cell is composed of the superposition of ohmic heat generation and electrochemical reaction heat; wherein, the ohmic heat generation is the product of the square of the charging and discharging current and the internal resistance of the battery cell that changes dynamically with temperature, and the internal resistance of the battery cell is obtained through experimental calibration; the electrochemical reaction heat is the product of the measured temperature of the immersion liquid, the charging and discharging current and the entropy change of the electrochemical reaction of the battery cell divided by the Faraday constant, and the entropy change of the electrochemical reaction of the battery cell is obtained through experimental calibration.

[0016] Furthermore, the heat balance relationship of the coupled control heat balance model in step S3 is as follows: the sum of the cumulative net heat generated by the battery cell per unit time and the heat stored in the immersion liquid is equal to the sum of the system's convective heat dissipation and the heat compensated by the temperature control device; wherein, the heat stored in the immersion liquid is the product of the total mass of the immersion liquid, the specific heat capacity of the immersion liquid at the current temperature, and the difference between the measured temperature of the immersion liquid and the ambient temperature; the system's convective heat dissipation is the product of the system's comprehensive heat transfer coefficient, the effective heat transfer area between the battery cell and the immersion liquid, and the difference between the measured temperature of the immersion liquid and the target control temperature.

[0017] Furthermore, in step S4, the compensated heat is calculated by superimposing the heat capacity fluctuation compensation term and the conventional temperature deviation adjustment term;

[0018] The heat capacity fluctuation compensation term is determined based on the specific heat capacity deviation influence coefficient, the total mass of the immersion liquid, the difference between the specific heat capacity of the immersion liquid at the current measured temperature and the specific heat capacity of the immersion liquid at the target control temperature, and the difference between the measured temperature of the immersion liquid and the ambient temperature.

[0019] The conventional temperature deviation adjustment item is determined based on the temperature deviation feedback coefficient, the total mass of the immersion liquid, the specific heat capacity of the immersion liquid at the current measured temperature, and the difference between the target control temperature and the measured temperature of the immersion liquid.

[0020] The value range of the specific heat capacity deviation influence coefficient is 0.2 to 0.8, and the value range of the temperature deviation feedback coefficient is 0.1 to 0.5; the specific heat capacity of the immersion liquid corresponding to the target control temperature is calculated by interpolation of the pre-stored specific heat capacity-temperature characteristic curve;

[0021] When the calculated compensation heat result is greater than zero, the system is considered to have excess heat; when it is less than zero, the system is considered to have insufficient heat.

[0022] Furthermore, in step S5, the specific control strategies for the three working modes—heat dissipation mode, heat preservation mode, and heating mode—are as follows:

[0023] (1) Forced heat dissipation mode: The triggering condition is that the actual temperature of the immersion liquid is more than 3 degrees Celsius higher than the target control temperature, and the calculated result of the compensation heat is greater than zero; after triggering, the forced convection circulation device of the immersion liquid is started, and the circulation flow rate is adaptively adjusted according to the following logic: take the reference flow rate at 25 degrees Celsius, first calculate the ratio of the specific heat capacity of the immersion liquid at the current temperature to the specific heat capacity of the standard immersion liquid at 25 degrees Celsius, subtract 1 from the ratio and then multiply it by 0.2, add the obtained value to 1 to obtain the total adjustment coefficient, multiply the total adjustment coefficient by the reference flow rate at 25 degrees Celsius to obtain the actual circulation flow rate;

[0024] (2) Constant temperature insulation mode: The triggering condition is that the absolute value of the difference between the measured temperature of the immersion liquid and the target control temperature is less than or equal to 3 degrees Celsius, and the calculated result of the heat compensation is close to zero; after triggering, the forced convection circulation device is completely shut down, and the internal temperature of the battery box is passively maintained by the natural convection of the immersion liquid and its own heat storage performance.

[0025] (3) Low temperature heating mode: The triggering condition is that the actual temperature of the immersion liquid is more than 3 degrees Celsius lower than the target control temperature, and the calculated result of the compensation heat is less than zero; after triggering, the heating device of the box is started, and the total heat of the product of the heating power of the heating device and the heating time is equal to the compensation heat.

[0026] An immersion energy storage battery box for extreme temperature fluctuation conditions includes a sealed enclosure, battery cell modules, a liquid cooling unit, and an adaptive expansion buffer device.

[0027] The sealed enclosure is filled with insulating immersion liquid, and the battery cell module is completely immersed in the insulating immersion liquid. The sealed enclosure is provided with a liquid inlet and a liquid outlet, and is connected to the liquid cooling unit through pipelines to form a closed liquid circulation loop.

[0028] The adaptive expansion buffer device includes an expansion tank, a telescopic airbag, a pressure sensor, and a one-way pressure relief valve. The expansion tank is connected to the immersion liquid cavity of the sealed box through a connecting pipe. The telescopic airbag is installed inside the expansion tank to isolate the gas and liquid space inside the expansion tank.

[0029] The pressure sensor is installed on the connecting pipeline to collect the liquid pressure in the pipeline in real time; the one-way pressure relief valve is installed on the expansion tank, and when the pressure inside the pipeline exceeds a preset threshold, the one-way pressure relief valve opens to release pressure.

[0030] Furthermore, the retractable airbag is made of corrosion-resistant rubber.

[0031] Furthermore, the volume of the buffer cavity formed by the air bladder inside the expansion tank is set to be no less than 1.2 times the maximum expansion volume of the insulating immersion liquid under extreme high temperature conditions.

[0032] Furthermore, the calculation method for the maximum expansion volume of the insulating immersion liquid under extreme high temperature conditions is as follows: First, calculate the ratio of the density of the immersion liquid at 25 degrees Celsius to the density of the immersion liquid at 60 degrees Celsius, subtract 1 from this ratio, and then multiply the resulting value by the standard immersion liquid volume at 25 degrees Celsius.

[0033] The present invention has the following beneficial effects:

[0034] 1. This invention abandons the traditional temperature control mode with fixed parameters and static thresholds. It couples the nonlinear change characteristics of the specific heat capacity of the immersion liquid in the extreme temperature range of -30℃ to 60℃, and combines the dynamic laws of cell temperature-related internal resistance heat generation and electrochemical entropy change heat generation to construct a thermal balance model. It can match the cell heat generation and the system temperature control compensation capability in real time, solve the problems of temperature control lag and heat generation and dissipation mismatch under outdoor large temperature difference conditions, significantly reduce the cell operating temperature difference, effectively delay the cell consistency decay, and significantly improve the charging and discharging operation efficiency of the energy storage system.

[0035] 2. This invention employs a dual feedback mechanism, superimposed with thermal capacity fluctuations and temperature deviations, to calculate and compensate for heat loss. This allows for adaptive correction of temperature control requirements under extreme temperature variations. It also features intelligent switching between three operating modes. In the ambient temperature range, the temperature control equipment can be shut off, relying on the natural convection of the immersion liquid and the passive pressure stabilization of the thermal storage performance for temperature control. This reduces the frequency and duration of start-up and shutdown of cooling and heating devices, effectively lowering the overall energy consumption of the energy storage system while ensuring temperature control accuracy.

[0036] 3. The battery box of this invention is equipped with an adaptive expansion buffer device with a telescopic airbag. It can adaptively adjust the buffer volume according to the dynamic expansion and contraction of the immersion liquid across the entire temperature range, match the maximum expansion volume of the immersion liquid under extreme working conditions, stabilize the pipeline pressure in the box in real time, solve the problem of repeated pressure fluctuations caused by traditional fixed volume expansion tanks, avoid aging of sealing strips and pipeline leakage, eliminate safety hazards such as failure of immersion liquid insulation performance and thermal runaway of battery cells, and improve the reliability of equipment during long-term outdoor operation. Attached Figure Description

[0037] Figure 1 This is a flowchart of an immersion energy storage thermal management method for extreme temperature variations proposed in this invention.

[0038] Figure 2 This is a schematic diagram of the structure of an immersion energy storage battery box for extreme temperature variations proposed in this invention.

[0039] In the picture:

[0040] 1. Sealed housing; 2. Liquid inlet; 3. Liquid outlet; 4. Liquid cooling unit; 5. Pressure sensor; 6. Expansion tank; 7. Telescopic airbag; 8. One-way pressure relief valve. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1:

[0043] Please see the appendix Figure 1 A method for thermal management of submerged energy storage under extreme temperature variations includes the following steps:

[0044] S1: Real-time acquisition of ambient temperature, immersion liquid temperature, cell charging and discharging power, charging and discharging current and terminal voltage during the operation of the energy storage system; pre-obtain the specific heat capacity-temperature characteristic curve of the immersion liquid in the extreme temperature change range through experimental calibration; establish a theoretical calculation benchmark for cell heat generation, and complete the experimental fitting calibration of cell internal resistance and cell electrochemical reaction entropy change;

[0045] S2: Based on the real-time collected charging and discharging current, combined with the dynamic change of the cell's internal resistance with temperature and the entropy change of the electrochemical reaction, calculate the cumulative net heat generation of the cell per unit time.

[0046] S3: Based on the heat balance of the battery box, a coupled control heat balance model is constructed that integrates the dynamic specific heat capacity characteristics of the immersion liquid. The model correlates the net heat generated by the battery cell per unit time, the heat dissipation of the environment, the heat stored in the immersion liquid, and the compensation heat. Specifically, the real-time specific heat capacity is obtained according to the real-time temperature of the immersion liquid, and the compensation heat is dynamically corrected according to the deviation between the real-time specific heat capacity and the target specific heat capacity to offset the impact of changes in the thermal properties of the immersion liquid on the heat balance.

[0047] S4: Based on the heat capacity fluctuation caused by the change in the specific heat capacity of the immersion liquid and the deviation between the actual temperature and the target control temperature, a dual feedback mechanism is used to calculate the compensation heat required by the cooling or heating device.

[0048] S5: Based on the calculated heat compensation and the deviation threshold between the measured temperature of the immersion liquid and the target temperature, the control system switches between heat dissipation mode, heat preservation mode and heating mode.

[0049] In step S1, the specific heat capacity-temperature characteristic curve of the immersion liquid covers the entire extreme operating temperature range from -30 degrees Celsius to 60 degrees Celsius; and fitting or interpolation processing is performed to ensure that the calculation error of the specific heat capacity of the immersion liquid corresponding to any temperature point does not exceed one percent; when collecting the charging and discharging power of the battery cell, positive and negative values ​​are distinguished, with the charging power recorded as a positive value and the discharging power recorded as a negative value.

[0050] In step S2, the cumulative net heat generated per unit time by the battery cell is composed of the superposition of ohmic heat generation and electrochemical reaction heat. The ohmic heat generation is the product of the square of the charging and discharging current and the internal resistance of the battery cell that changes dynamically with temperature. The internal resistance of the battery cell is obtained through experimental calibration. The electrochemical reaction heat is the product of the measured temperature of the immersion liquid, the charging and discharging current, and the entropy change of the electrochemical reaction of the battery cell, divided by the Faraday constant. The entropy change of the electrochemical reaction of the battery cell is obtained through experimental calibration.

[0051] The heat balance relationship of the coupled control heat balance model in step S3 is as follows: the sum of the cumulative net heat generated by the battery cell per unit time and the heat stored in the immersion liquid is equal to the sum of the system convective heat dissipation and the heat compensated by the temperature control device; wherein, the heat stored in the immersion liquid is the product of the total mass of the immersion liquid, the specific heat capacity of the immersion liquid at the current temperature, and the difference between the measured temperature of the immersion liquid and the ambient temperature; the system convective heat dissipation is the product of the system comprehensive heat transfer coefficient, the effective heat transfer area between the battery cell and the immersion liquid, and the difference between the measured temperature of the immersion liquid and the target control temperature.

[0052] In step S4, the compensation heat is calculated by superimposing the heat capacity fluctuation compensation term and the conventional temperature deviation adjustment term;

[0053] Among them, the heat capacity fluctuation compensation item is determined based on the specific heat capacity deviation influence coefficient, the total mass of the immersion liquid, the difference between the specific heat capacity of the immersion liquid at the current measured temperature and the specific heat capacity of the immersion liquid at the target control temperature, and the difference between the measured temperature of the immersion liquid and the ambient temperature.

[0054] The standard temperature deviation adjustment item is determined based on the temperature deviation feedback coefficient, the total mass of the immersion liquid, the specific heat capacity of the immersion liquid at the current measured temperature, and the difference between the target control temperature and the measured temperature of the immersion liquid.

[0055] The value range of the specific heat capacity deviation influence coefficient is 0.2 to 0.8, and the value range of the temperature deviation feedback coefficient is 0.1 to 0.5; the specific heat capacity of the immersion liquid corresponding to the target control temperature is calculated by interpolation of the pre-stored specific heat capacity-temperature characteristic curve;

[0056] If the calculated heat compensation result is greater than zero, the system is considered to have excess heat; if it is less than zero, the system is considered to have insufficient heat.

[0057] In step S5, the specific control strategies for the three working modes—heat dissipation mode, heat preservation mode, and heating mode—are as follows:

[0058] (1) Forced heat dissipation mode: The triggering condition is that the actual temperature of the immersion liquid is more than 3 degrees Celsius higher than the target control temperature, and the calculated result of the compensation heat is greater than zero; after triggering, the forced convection circulation device of the immersion liquid is started, and the circulation flow rate is adaptively adjusted according to the following logic: take the reference flow rate at 25 degrees Celsius, first calculate the ratio of the specific heat capacity of the immersion liquid at the current temperature to the specific heat capacity of the standard immersion liquid at 25 degrees Celsius, subtract 1 from the ratio and then multiply it by 0.2, add the obtained value to 1 to obtain the total adjustment coefficient, multiply the total adjustment coefficient by the reference flow rate at 25 degrees Celsius to obtain the actual circulation flow rate;

[0059] (2) Constant temperature insulation mode: The triggering condition is that the absolute value of the difference between the measured temperature of the immersion liquid and the target control temperature is less than or equal to 3 degrees Celsius, and the calculated result of the heat compensation is close to zero; after triggering, the forced convection circulation device is completely shut down, and the internal temperature of the battery box is passively maintained by the natural convection of the immersion liquid and its own heat storage performance.

[0060] (3) Low temperature heating mode: The triggering condition is that the actual temperature of the immersion liquid is more than 3 degrees Celsius lower than the target control temperature, and the calculated result of the compensation heat is less than zero; after triggering, the heating device of the box is started, and the total heat of the product of the heating power of the heating device and the heating time is equal to the compensation heat.

[0061] Example 2:

[0062] Please see the appendix Figure 2 An immersion energy storage battery box for extreme temperature change conditions includes a sealed box 1, a cell module, a liquid cooling unit 4, and an adaptive expansion buffer device.

[0063] The sealed enclosure 1 is a fully sealed pressure-resistant shell, completely filled with insulating immersion liquid, and the entire battery cell module is immersed in the immersion liquid; the side wall of the sealed enclosure 1 has liquid inlet 2 and liquid outlet 3 respectively, which are connected to the external liquid cooling unit 4 through metal pipelines to form a closed-loop heat exchange circuit; the liquid cooling unit 4 has a built-in circulating micro pump, heat exchange cooler, and low temperature heat tracing device to provide forced convection circulation and temperature compensation for the immersion liquid.

[0064] The expansion buffer device consists of an expansion tank 6, a telescopic airbag 7 made of corrosion-resistant rubber, a pressure sensor 5, a one-way pressure relief valve 8, and a connecting pipeline. The expansion tank 6 is connected to the immersion liquid chamber inside the sealed box 1 through an independent pipeline. The telescopic airbag 7 is installed inside the expansion tank 6 to isolate the gas and liquid space inside the expansion tank 6.

[0065] Calculate the maximum expansion at extreme high temperatures based on the density-temperature characteristics of the immersion liquid:

[0066]

[0067] In the formula: The volume of immersion liquid under standard operating conditions at 25℃; The density of the immersion solution at 25℃; The density of the immersion liquid at an extreme high temperature of 60℃;

[0068] The expansion tank 6 has an internal telescopic airbag 7 buffer chamber with a volume that meets the requirements. A 20% safety margin is reserved to fully cover the total volume change of the immersion liquid under a daily temperature difference of 20℃.

[0069] During the daytime heating phase, the volume of the immersion liquid expands, and the pipeline directs the excess liquid into the expansion tank 6, compressing the internal telescopic airbag 7 to contract and absorb the increased volume. During the nighttime cooling phase, the volume of the immersion liquid contracts, and the telescopic airbag 7 returns to its original position using its own elasticity, replenishing the immersion liquid into the sealed chamber 1. Throughout the process, the internal pressure of the sealed chamber 1 remains stable, with pressure fluctuations ≤5%.

[0070] Pressure sensor 5 is installed on the connecting pipeline to collect the liquid pressure in the pipeline in real time; one-way pressure relief valve 8 is installed on expansion tank 6. When the pressure inside the pipeline exceeds the preset threshold, one-way pressure relief valve 8 opens to release pressure, so as to prevent deformation of the sealing box 1 and pipeline leakage.

[0071] Application example:

[0072] A method for thermal management of submerged energy storage under extreme temperature variations includes the following steps:

[0073] Step 1: Parameter Acquisition and Characteristic Curve Pre-calibration

[0074] (1) Real-time operating condition parameter acquisition: The ambient temperature T0, the immersion liquid temperature T1 in the battery box, the cell charging and discharging power P (charging is positive and discharging is negative), the charging and discharging current I, and the cell terminal voltage U are continuously collected during the operation of the energy storage system to realize dynamic monitoring of all operating condition parameters.

[0075] (2) Pre-storage of the thermophysical property curve of the immersion liquid: The specific heat capacity-temperature characteristic curve C of the target immersion liquid is obtained in advance through high and low temperature experiments. p (T), the curve covers the entire extreme operating temperature range of -30℃ to 60℃. To adapt to engineering applications, experimental data fitting algorithms or table lookup linear interpolation algorithms are used to process the curve data, strictly ensuring that the error of the specific heat capacity calculation value corresponding to any temperature point is ≤1%, ensuring the accuracy of the thermal property parameter calculation.

[0076] (3) Cell energy parameter calibration: Based on the basic energy relationship of cell charging and discharging, the cell charging and discharging time t and the cell electrochemical energy change ΔE are preset. This set of parameters is used to establish the theoretical calculation benchmark for cell heat generation during the offline calibration stage; the cell internal resistance is calculated through the theoretical energy formula. Experimental fitting and calibration of the entropy change ΔS of the electrochemical reaction in the battery cell; direct access to pre-calibrated data during online operation. The parameters ΔS and t and ΔE are not used in real-time calculations.

[0077] Step 2: Real-time net heat generation calculation of battery cells

[0078] First, the basic theoretical energy formula for heat generation in battery cells is given:

[0079]

[0080] In the formula: P is the cell charging and discharging power, t is the charging and discharging duration, and ΔE is the change in the cell's electrochemical energy. This formula is used for offline analysis of the cell's heat generation mechanism and parameter calibration, and is not used for online real-time heat generation calculation.

[0081] Based on the actual heat generation mechanism of energy storage cells, a simplified and accurate calculation formula for engineering is obtained:

[0082]

[0083] The parameters in the formula are defined as follows: I is the cell charging and discharging current; The internal resistance of the battery cell, which changes dynamically with temperature, is obtained through experimental calibration; ΔS is the entropy change of the electrochemical reaction in the battery cell, obtained through experimental measurement; and F is the Faraday constant. This formula allows for the real-time output of the cumulative net heat generation Q per unit time of the battery cell, providing core heat source data for subsequent thermal balance control.

[0084] Step 3: Construct a coupled and controlled thermal equilibrium model

[0085] Based on the principle of heat balance within the enclosure and incorporating the dynamic specific heat capacity characteristics of the immersion liquid, a coupled control heat balance model adapted to extreme temperature variations is constructed. The correlation between cell heat generation, environmental heat exchange, immersion liquid heat storage, and compensation heat is established. The model formulas are as follows:

[0086]

[0087] Parameter definitions: Q is the cumulative net heat generated by the battery cell per unit time; m1 is the total mass of the immersion liquid in the battery box; C p (T1) represents the real-time isobaric specific heat capacity at the current measured temperature of the immersion liquid; T1 is the measured temperature of the immersion liquid; T0 is the real-time ambient temperature; k is the overall system heat transfer coefficient; A is the effective heat transfer area between the battery cell and the immersion liquid; T a To control the temperature of the immersion liquid; The heat absorbed or provided to compensate for the cooling / heating device.

[0088] By leveraging the dynamic change in the specific heat capacity of the immersion liquid with temperature, dynamic adjustment of heat exchange requirements is achieved. When the system is in the heating phase, the immersion liquid temperature rises, and C... p (T1) increases, improving heat compensation. To enhance the system's heat dissipation capacity; when the system is in the cooling phase, the immersion liquid temperature decreases, C p (T1) decreases, adaptively reduces the compensation heat, accurately compensates for the heat loss of the box, and solves the problem of inaccurate control of fixed heat exchange parameters under extreme temperature changes.

[0089] Step 4: Calculate the compensation heat

[0090] To address the dual interferences of temperature fluctuations in the immersion liquid's heat capacity and system temperature deviations, a dual-feedback quantitative calculation formula is established to accurately solve for the compensating heat under extreme operating conditions. The formula is as follows:

[0091]

[0092] In the formula: β is the specific heat capacity deviation influence coefficient, ranging from 0.2 to 0.8, used to characterize the heat capacity compensation weight for the specific heat capacity deviating from the target value; γ is the temperature deviation feedback coefficient, ranging from 0.1 to 0.5, used for conventional temperature deviation proportional adjustment; C p (T a The specific heat capacity of the immersion liquid at the target control temperature is obtained by interpolation of a pre-stored characteristic curve.

[0093] The formula consists of two independent control logics: the first is a heat capacity fluctuation compensation term, which is used to offset the fluctuation of heat storage and exchange capacity caused by the change of specific heat capacity of the immersion liquid with temperature; the second is a conventional temperature proportional adjustment term, which is used to accurately correct the deviation between the actual temperature and the target temperature.

[0094] Step 5: Adaptive dynamic temperature control

[0095] Compensation heat based on the output of step 4 Based on the calculation results and the deviation threshold between the measured temperature of the immersion liquid and the target temperature, three working modes are defined: heat dissipation, heat preservation, and heating. This enables adaptive and precise control under all extreme temperature change conditions. The mode switching threshold is ±3℃. The specific control strategy is as follows:

[0096] (1) Forced cooling mode: The trigger condition is T1 > T a +3℃, and >0 (System heat excess). Upon triggering, a micro-pump or other forced convection device is activated, and the immersion liquid circulation flow rate is dynamically and linearly adjusted according to the real-time specific heat capacity. The adjustment formula is:

[0097]

[0098] In the formula: The reference flow rate is at 25℃. To achieve the standard constant pressure specific heat capacity of the immersion liquid at 25℃, the flow rate is adaptively increased under high temperature and high specific heat capacity conditions, thereby enhancing heat dissipation efficiency.

[0099] (2) Constant temperature insulation mode: The trigger condition is |T1-T a |≤3℃, and Approaching 0 (system thermal balance, no excess or deficiency). Upon triggering, the forced convection device is completely shut off. Relying on the natural convection and specific heat capacity stability of the immersion liquid, the temperature balance inside the battery box is maintained passively, minimizing heat fluctuations in the box under extreme temperature changes and reducing system energy consumption.

[0100] (3) Low temperature heating mode: The trigger condition is T1 < T a -3℃, and <0 (Insufficient system heat). Upon triggering, the enclosure heating device will start, strictly matching the power and duration relationship:

[0101]

[0102] In the formula: P h Δt represents the heating power of the heat tracing device; Δt represents the heating duration of the heat tracing device. Through precise heating heat compensation, the defects of immersion liquid specific heat capacity decay and heat exchange capacity failure under extreme low temperature conditions are compensated for, ensuring the temperature stability of the energy storage system in low temperature environments.

[0103] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for thermal management of submerged energy storage under extreme temperature variations, characterized in that: Includes the following steps: S1: Real-time acquisition of ambient temperature, immersion liquid temperature, cell charging and discharging power, charging and discharging current and terminal voltage during the operation of the energy storage system; pre-obtain the specific heat capacity-temperature characteristic curve of the immersion liquid in the extreme temperature change range through experimental calibration; establish a theoretical calculation benchmark for cell heat generation, and complete the experimental fitting calibration of cell internal resistance and cell electrochemical reaction entropy change; S2: Based on the real-time collected charging and discharging current, combined with the dynamic change relationship of the cell's internal resistance with temperature and the entropy change of the electrochemical reaction, calculate the cumulative net heat generation of the cell per unit time. S3: Based on the heat balance of the battery box, a coupled control heat balance model integrating the dynamic specific heat capacity characteristics of the immersion liquid is constructed. The model associates the cumulative net heat generated by the battery cell per unit time, the heat dissipation of the environment, the heat stored in the immersion liquid, and the compensation heat. The real-time specific heat capacity is obtained according to the real-time temperature of the immersion liquid, and the compensation heat is dynamically corrected according to the deviation between the real-time specific heat capacity and the target specific heat capacity to offset the impact of changes in the thermal properties of the immersion liquid on the heat balance. S4: Based on the heat capacity fluctuation caused by the change in the specific heat capacity of the immersion liquid and the deviation between the actual temperature and the target control temperature, a dual feedback mechanism is used to calculate the compensation heat required by the cooling or heating device. S5: Based on the calculated heat compensation and the deviation threshold between the measured temperature of the immersion liquid and the target temperature, the control system switches between heat dissipation mode, heat preservation mode and heating mode.

2. The method for immersion energy storage thermal management under extreme temperature variations according to claim 1, characterized in that: In step S1, the specific heat capacity-temperature characteristic curve of the immersion liquid covers the entire extreme operating temperature range from -30 degrees Celsius to 60 degrees Celsius; and fitting or interpolation processing is performed to ensure that the calculation error of the specific heat capacity of the immersion liquid corresponding to any temperature point does not exceed one percent; when collecting the charging and discharging power of the battery cell, positive and negative values ​​are distinguished, with the charging power recorded as a positive value and the discharging power recorded as a negative value.

3. The method for immersion energy storage thermal management under extreme temperature variations according to claim 1, characterized in that: In step S2, the cumulative net heat generated per unit time by the battery cell is composed of the superposition of ohmic heat generation and electrochemical reaction heat; wherein, the ohmic heat generation is the product of the square of the charging and discharging current and the internal resistance of the battery cell that changes dynamically with temperature, and the internal resistance of the battery cell is obtained through experimental calibration; the electrochemical reaction heat is the product of the measured temperature of the immersion liquid, the charging and discharging current and the entropy change of the electrochemical reaction of the battery cell divided by the Faraday constant, and the entropy change of the electrochemical reaction of the battery cell is obtained through experimental calibration.

4. The method for immersion energy storage thermal management under extreme temperature variations according to claim 1, characterized in that: The heat balance relationship of the coupled control heat balance model described in step S3 is as follows: the sum of the cumulative net heat generated by the battery cell per unit time and the heat stored in the immersion liquid is equal to the sum of the system's convective heat dissipation and the heat compensated by the temperature control device; wherein, the heat stored in the immersion liquid is the product of the total mass of the immersion liquid, the specific heat capacity of the immersion liquid at the current temperature, and the difference between the measured temperature of the immersion liquid and the ambient temperature; the system's convective heat dissipation is the product of the system's comprehensive heat transfer coefficient, the effective heat transfer area between the battery cell and the immersion liquid, and the difference between the measured temperature of the immersion liquid and the target control temperature.

5. The method for immersion energy storage thermal management under extreme temperature variations according to claim 1, characterized in that: In step S4, the compensated heat is composed of the superposition of the heat capacity fluctuation compensation term and the conventional temperature deviation adjustment term; The heat capacity fluctuation compensation term is determined based on the specific heat capacity deviation influence coefficient, the total mass of the immersion liquid, the difference between the specific heat capacity of the immersion liquid at the current measured temperature and the specific heat capacity of the immersion liquid at the target control temperature, and the difference between the measured temperature of the immersion liquid and the ambient temperature. The conventional temperature deviation adjustment item is determined based on the temperature deviation feedback coefficient, the total mass of the immersion liquid, the specific heat capacity of the immersion liquid at the current measured temperature, and the difference between the target control temperature and the measured temperature of the immersion liquid. The value range of the specific heat capacity deviation influence coefficient is 0.2 to 0.8, and the value range of the temperature deviation feedback coefficient is 0.1 to 0.5; the specific heat capacity of the immersion liquid corresponding to the target control temperature is calculated by interpolation of the pre-stored specific heat capacity-temperature characteristic curve; When the calculated compensation heat result is greater than zero, the system is considered to have excess heat; when it is less than zero, the system is considered to have insufficient heat.

6. The method for immersion energy storage thermal management under extreme temperature variations according to claim 1, characterized in that: In step S5, the specific control strategies for the three working modes—heat dissipation mode, heat preservation mode, and heating mode—are as follows: (1) Forced heat dissipation mode: The triggering condition is that the actual temperature of the immersion liquid is more than 3 degrees Celsius higher than the target control temperature, and the calculated result of the compensation heat is greater than zero; after triggering, the forced convection circulation device of the immersion liquid is started, and the circulation flow rate is adaptively adjusted according to the following logic: take the reference flow rate at 25 degrees Celsius, first calculate the ratio of the specific heat capacity of the immersion liquid at the current temperature to the specific heat capacity of the standard immersion liquid at 25 degrees Celsius, subtract 1 from the ratio and then multiply it by 0.2, add the obtained value to 1 to obtain the total adjustment coefficient, multiply the total adjustment coefficient by the reference flow rate at 25 degrees Celsius to obtain the actual circulation flow rate; (2) Constant temperature insulation mode: The triggering condition is that the absolute value of the difference between the measured temperature of the immersion liquid and the target control temperature is less than or equal to 3 degrees Celsius, and the calculated result of the heat compensation is close to zero; after triggering, the forced convection circulation device is completely shut down, and the internal temperature of the battery box is passively maintained by the natural convection of the immersion liquid and its own heat storage performance. (3) Low temperature heating mode: The triggering condition is that the actual temperature of the immersion liquid is more than 3 degrees Celsius lower than the target control temperature, and the calculated result of the compensation heat is less than zero; after triggering, the heating device of the box is started, and the total heat of the product of the heating power of the heating device and the heating time is equal to the compensation heat.

7. A submersible energy storage battery box for extreme temperature fluctuation conditions, characterized in that: This includes a sealed enclosure, battery cell modules, a liquid cooling unit, and an adaptive expansion buffer device; The sealed enclosure is filled with insulating immersion liquid, and the battery cell module is completely immersed in the insulating immersion liquid. The sealed enclosure is provided with a liquid inlet and a liquid outlet, and is connected to the liquid cooling unit through pipelines to form a closed liquid circulation loop. The adaptive expansion buffer device includes an expansion tank, a telescopic airbag, a pressure sensor, and a one-way pressure relief valve. The expansion tank is connected to the immersion liquid cavity of the sealed box through a connecting pipe. The telescopic airbag is installed inside the expansion tank to isolate the gas and liquid space inside the expansion tank. The pressure sensor is installed on the connecting pipeline to collect the liquid pressure in the pipeline in real time; the one-way pressure relief valve is installed on the expansion tank, and when the pressure inside the pipeline exceeds a preset threshold, the one-way pressure relief valve opens to release pressure.

8. The immersion energy storage battery box for extreme temperature fluctuation conditions according to claim 7, characterized in that: The retractable airbag is made of corrosion-resistant rubber.

9. A submersible energy storage battery box for extreme temperature fluctuation conditions according to claim 7, characterized in that: The volume of the buffer chamber formed by the air bladder inside the expansion tank is set to be no less than 1.2 times the maximum expansion volume of the insulating immersion liquid under extreme high temperature conditions.

10. A submersible energy storage battery box for extreme temperature fluctuation conditions according to claim 9, characterized in that: The maximum expansion volume of the insulating immersion liquid under extreme high temperature conditions is calculated by the following formula: First, calculate the ratio of the density of the immersion liquid at 25 degrees Celsius to the density of the immersion liquid at 60 degrees Celsius, subtract 1 from this ratio, and then multiply the resulting value by the standard immersion liquid volume at 25 degrees Celsius.

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