Thermal management method and management system of energy storage unit

Abstract

The invention relates to the technical field of energy storage batteries, in particular to a heat management method and system of an energy storage unit, the heat management method is used for executing a cooling mode, a heating mode and a defrosting mode, and the defrosting mode comprises a reverse circulation defrosting mode and an auxiliary heating defrosting mode; heat required by the reverse circulation defrosting mode comes from heat converted from electric energy consumed by a compressor and heat absorbed by a refrigerant from a battery cell; by pre-judging the frosting degree of the heat exchanger, the temperature when the battery cell starts to cool and the temperature when the battery cell stops cooling in the reverse circulation defrosting mode and the cooling mode are correspondingly adjusted; and whether the auxiliary heating defrosting mode needs to be started or not is judged by calculating the temperature of the battery core when the reverse circulation defrosting mode is finished. Through the thermal management method and system, the problem that the safety of the battery cell is uncontrollable during defrosting can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage battery management, and in particular to a thermal management method and management system for an energy storage unit. Background Art

[0002] An energy storage unit is a device or system that stores energy, allowing it to be used when needed. Energy storage units are often used to improve energy efficiency, reduce energy waste, and enhance grid stability. They can include devices or technologies such as batteries, supercapacitors, flywheels, and hydraulic systems, with batteries being the most common form of energy storage. They can be used in a variety of scenarios, including grid peak shaving, renewable energy integration, electric vehicle charging, and home energy storage.

[0003] In the prior art, a Chinese invention patent document with publication number CN118943568A and publication date November 12, 2024 is proposed. The technical solution disclosed in the patent document is as follows: an energy storage unit and its thermal management system, a heat supply module and a thermal management method, including a heat supply module, a heat transfer component, a first pipe and a second pipe for connecting the heat transfer component with the heat supply module, the heat transfer component having a fluid channel, and the fluid channel having such a shape that when the fluid flows through the fluid channel, the pressure difference between the two ports is less than a preset value, the heat supply module includes a gas compressor, a gas-liquid separator, a heat exchanger group, a regenerator, a fluid storage tank, and a pressure sensor, the thermal management system includes a cooling circulation path, a heating circulation path and a defrost circulation path, and a controller for controlling the opening or closing of each path.

[0004] When defrosting, the above technical solution absorbs heat from the battery cells of the battery pack through the refrigerant, and the temperature of the battery cells drops rapidly. The temperature of the local battery cells may approach or fall below the safety lower limit, resulting in a significant increase in the internal impedance of the lithium-ion battery, a decrease in the battery cell capacity, and even the risk of lithium dendrites. The safety of the battery pack cannot be controlled. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a thermal management method and management system for an energy storage unit, which can effectively solve the problem of uncontrollable battery cell safety during defrosting.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] A thermal management method for an energy storage unit is provided, for executing a cooling mode, a heating mode, and a defrost mode. The defrost modes include a reverse cycle defrost mode and an auxiliary heat defrost mode. The heat required for the reverse cycle defrost mode comes from the heat converted from the electrical energy consumed by the compressor and the heat absorbed by the refrigerant from the battery cells. By predicting the degree of frost on the heat exchanger, the temperature of the battery cells at the start and stop of cooling in the reverse cycle defrost mode and the cooling mode are adjusted accordingly. By calculating the battery cell temperature at the end of the reverse cycle defrost mode, it is determined whether the auxiliary heat defrost mode needs to be activated. The calculation method for the battery cell temperature at the end of the reverse cycle defrost mode is as follows:

[0008]

[0009] Where, T B,end is the calculated cell temperature at the end of the reverse cycle defrost mode, T B,current is the cell temperature before defrosting, m ft (t) is the total mass of the current frost layer when it is judged to be the best defrosting time, L f is the latent heat of melting of the frost layer, P C is the rated power of the compressor, t exp is the expected defrost time, c B is the specific heat capacity of the battery cell; m B is the total mass of the battery cells in the energy storage unit.

[0010] The following steps are involved:

[0011] Step S1. Determine whether heating, cooling, or neither is currently required; if heating is required, proceed to step S2; if cooling is required, proceed to step S3; if neither is required, proceed to standby;

[0012] Step S2. Execute the heating mode based on the thermal management threshold. During the heating process, continuously monitor the frost status of the heat exchanger. If no frost is present, continue heating until the set heating exit condition is met. If frost is detected on the heat exchanger and the optimal defrost timing has been reached, execute the defrost mode. After defrosting is complete, re-enter step S2.

[0013] Step S3: Execute a cooling mode according to the thermal management threshold.

[0014] The best defrost timing is determined by calculating the accumulated amount of frost on the heat exchanger and the blockage ratio in space in real time.

[0015] The method for determining the optimal defrosting time specifically includes the following steps:

[0016] According to the frost rate, the frost thickness is calculated iteratively:

[0017] d f(t+△t)=△d f (t)+d f (t),

[0018]

[0019] Calculate the ratio of the frost layer thickness to the fin gap thickness at the current moment:

[0020]

[0021] When the thickness ratio reaches a preset critical value, it is determined that the current moment is the best time to defrost;

[0022] Where, d f (t+△t) is the thickness of the frost layer at the current moment, △d f (t) is the thickness of the newly added frost layer, d f (t) is the thickness of the frost layer at the previous moment; m f is the frosting rate, △t is the calculation period, ρ f is the average density of the frost layer, A eff is the effective frost deposition area of ​​the heat exchanger fin; d gap is the thickness of the gap between the heat exchanger fins.

[0023] Frosting rate m f The calculation method is:

[0024]

[0025] Q eva =m ref (h ref,out -h ref,in ),

[0026] Where w a is the humidity content of the incoming air, w asat,sur is the saturated moisture content of the heat exchanger fin surface, h a is the inlet air enthalpy, h asat,sur is the enthalpy of saturated wet air on the fin surface, Q eva is the heat exchanger heat transfer rate, R is the frost layer growth rate under shutdown conditions, m ref is the refrigerant flow rate, h ref,out is the refrigerant enthalpy at the heat exchanger outlet, h ref,in is the refrigerant enthalpy at the heat exchanger inlet.

[0027] The following steps are involved in executing the defrost mode:

[0028] Step S 21 .Calculate the total mass of the current frost layer at the optimal defrost time;

[0029] Step S 22.Calculate the battery cell temperature at the end of reverse cycle defrost mode;

[0030] Step S 23 .Judgment step S 22 Is the cell temperature calculated in step S higher than the cell protection temperature? If not, proceed to step S 24 If so, turn on the reverse cycle defrost mode and determine whether the real-time temperature of the battery cell is less than the battery cell protection temperature. If so, proceed to step S 24 If not, continue to perform the reverse cycle defrost mode for defrosting until the surface temperature of the heat exchanger is greater than the preset value;

[0031] Step S 24 .Turn on the reverse cycle defrost mode and the auxiliary heating defrost mode, and determine whether the real-time temperature of the battery cell is lower than the battery cell protection temperature. If so, exit the reverse cycle defrost mode until the surface temperature of the heat exchanger is higher than the preset value; if not, continue to execute the reverse cycle defrost mode and the auxiliary heating defrost mode for defrosting until the surface temperature of the heat exchanger is higher than the preset value.

[0032] Predicting the degree of frost on the heat exchanger specifically refers to: judging the degree of frost on the heat exchanger as light frost, moderate frost, or heavy frost based on the ambient temperature and relative humidity.

[0033] Corresponding adjustments are made to the temperature when the battery cells start cooling down in the reverse cycle defrost mode and the cooling mode, and the temperature when cooling stops. Specifically, when there is light frost, the temperature when the battery cells start cooling down in the cycle defrost mode and the cooling mode is Tc1+3°C, and the temperature when the battery cells stop cooling down is Tc2+3°C; when there is moderate frost, the temperature when the battery cells start cooling down in the cycle defrost mode and the cooling mode is Tc1+5°C, and the temperature when the battery cells stop cooling down is Tc2+5°C; when there is heavy frost, the temperature when the battery cells start cooling down in the cycle defrost mode and the cooling mode is Tc1+10°C, and the temperature when the battery cells stop cooling down is Tc2+10°C; wherein, Tc1 and Tc2 are the preset basic values ​​when the battery cells start and stop cooling, respectively.

[0034] The method for calculating the battery cell temperature at the end of the reverse cycle defrost mode specifically includes the following steps:

[0035] Step S 11 .Calculate the heat E converted from compressor electrical energy at the optimal defrost time C And the total mass of the current frost layer m ft (t):

[0036] E C =P C t exp ;

[0037] Step S 12 .Calculate the heat E that the battery cell can provideB :

[0038] E B =m ft (t)·L f -E C

[0039] Step S 13 .Calculate the battery cell temperature at the end of reverse cycle defrost mode:

[0040]

[0041] It also includes the generation of time-frost thickness curves for fault diagnosis.

[0042] A thermal management system for an energy storage unit includes a sensor, a controller, and a four-way valve. The first port of the four-way valve is sequentially connected to a heat exchanger, a liquid storage tank, a first fluid path of a regenerator, a plurality of battery thermal management circuits arranged in parallel, a second fluid path of the regenerator, and the second port of the four-way valve; the third port of the four-way valve is sequentially connected to a gas-liquid separator, a compressor, and a fourth port of the four-way valve; the controller is connected to the four-way valve and executes a cooling mode, a heating mode, and a defrost mode by controlling the reversing of the four-way valve; the controller is also used to control the start and stop timing of the reverse cycle defrost mode and the cooling mode based on the battery cell temperature detected by the sensor and the potential degree of frost on the heat exchanger.

[0043] Also includes auxiliary heat defrost device.

[0044] Each battery thermal management circuit includes an expansion valve, a liquid distributor and several battery direct cooling plates connected in sequence.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention utilizes the high thermal capacity of the battery cell to store heat, and during reverse cycle defrosting, it quickly absorbs heat from the battery cell to increase the defrosting rate; at the same time, the prior art generally adopts a fixed cooling mode, that is, it cannot be dynamically adjusted for different ambient temperatures and battery cell states. The present invention breaks this conventional idea and can dynamically adjust the temperature of the battery cell when it starts cooling and the temperature when it stops cooling in different temperature ranges. Through the combination of the above schemes, not only can the thermal capacity of the battery cell itself be used to store additional heat, which is beneficial to reduce the number of heating requests in low temperature environments, reduce the possibility of frosting and reduce energy consumption, but also avoid the risk of the battery cell temperature being too low. Through this method, the dependence of the energy storage unit on the additional bypass circuit can be effectively reduced, while the overall energy efficiency during defrosting is optimized, and the safety of the battery cell during defrosting is more controllable.

[0047] Furthermore, by real-time monitoring of the degree of frost formation on the heat exchanger, the present invention dynamically assesses the feasibility of reverse-cycle defrosting and the battery cell temperature safety margin. When conditions permit, the efficient reverse-cycle defrost mode is prioritized, combining it with the battery cell's heat storage to increase the heat exchange rate, speeding up defrosting and reducing energy consumption. If the battery cell's heat storage is insufficient or the battery cell temperature is predicted to fall below the safety threshold, the system switches to auxiliary heat defrost mode, ensuring rapid and reliable defrosting even in extremely low temperatures, maintaining stable system operation.

[0048] Among them, when evaluating the feasibility of reverse cycle defrosting and the safety margin of the battery cell temperature, the present invention can calculate the battery cell temperature at the end of the reverse cycle defrosting mode before the defrosting starts. The calculation method is simple and has a high accuracy rate.

[0049] Through the above method, the present invention can complete defrosting in a shorter time, ensuring that frosted components can quickly return to working order, thereby reducing battery temperature fluctuations and improving system response speed. Compared with conventional hot gas bypass defrosting, the defrosting method adopted by the present invention reduces both defrosting duration and energy consumption.

[0050] 2. By designing the temperature at which the battery starts cooling and the temperature at which it stops cooling in the reverse cycle defrost mode and the cooling mode, the opening and closing timing of the reverse cycle defrost mode and the cooling mode can be better controlled to ensure the safety of the battery.

[0051] 3. Traditional methods (such as the time-temperature method) have difficulty accurately determining the optimal defrost timing, which can easily lead to premature or delayed defrosting and reduce heat pump efficiency. The present invention can accurately determine the optimal defrost timing by calculating the accumulated frost layer and the spatial blockage ratio of the heat exchanger in real time.

[0052] 4. This invention uses iterative calculations of frost thickness, achieving high real-time performance and dynamically tracking the frost growth process. This calculation method allows for adjustable time steps, tailored to the severity of the environment, striking a balance between system flexibility and computing resource consumption. This calculation enables accurate and real-time determination of the optimal defrost time, avoiding premature or late defrosting.

[0053] 5. By obtaining the time-frost thickness curve, fault diagnosis can be facilitated, and coupling analysis with environmental parameters, unit parameters, etc. can be performed when analyzing faults.

[0054] 6. The present invention improves the calculation method for the frost rate. Specifically, it takes into account both operating conditions and the frost rate in the idle state, thus avoiding the omission of frost accumulation during the idle state, which can lead to defrosting delays. Furthermore, in the operating state, the air humidity and enthalpy values ​​can be easily measured quickly using temperature and humidity sensors or calculated using built-in data tables or fitting formulas. This eliminates the need for complex sensors or equipment, making it easy to implement in engineering.

[0055] 7. The thermal management system of this invention utilizes a four-way valve to switch to reverse cycle mode, eliminating the need for additional components such as bypass valves and heating throttles. Combined with the battery cell heat storage mode, this reduces reliance on external heat sources (such as electric heating), thereby reducing the overall system complexity. By optimizing the system architecture, efficient defrosting is achieved without an additional bypass loop, reducing hardware costs, simplifying system control, and reducing potential equipment failure points. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

[0057] Figure 1 Schematic diagram of the thermal management method of the present invention;

[0058] Figure 2 Schematic diagram of the defrosting mode of the present invention;

[0059] Figure 3 Schematic diagram of the operating principle of the thermal management system of the present invention in cooling mode;

[0060] Figure 4 Schematic diagram of the operating principle of the thermal management system of the present invention in heating mode;

[0061] Markings in the figure:

[0062] 1. Four-way valve, 2. Heat exchanger, 3. Liquid storage tank, 4. Regenerator, 5. Gas-liquid separator, 6. Compressor, 7. Expansion valve, 8. Liquid distributor, 9. Battery direct cooling plate. DETAILED DESCRIPTION

[0063] Example 1

[0064] As a basic embodiment of the present invention, the present invention includes a thermal management method for an energy storage unit, which is used to execute a cooling mode, a heating mode, and a defrost mode. The heat required for the defrost mode comes from the heat converted from the electrical energy consumed by the compressor and the heat absorbed by the refrigerant from the battery cell. This thermal management method adjusts the temperature of the battery cell when it starts cooling and the temperature when it stops cooling in the reverse cycle defrost mode and the cooling mode by predicting the degree of frost on the heat exchanger. Among them, the temperature when the battery cell starts cooling specifically refers to: the battery cell reaches a certain degree, and the reverse cycle defrost mode and the cooling mode are started. The temperature when the battery cell stops cooling specifically refers to: the battery cell reaches a certain degree, and the reverse cycle defrost mode and the cooling mode are exited.

[0065] This thermal management method also predicts whether it is necessary to start the auxiliary heat defrost mode by calculating the battery cell temperature at the end of the reverse cycle defrost mode. The calculation method of the battery cell temperature at the end of the reverse cycle defrost mode is:

[0066]

[0067] Where, T B,end is the calculated cell temperature at the end of the reverse cycle defrost mode, T B,current is the cell temperature before defrosting, m ft (t) is the total mass of the current frost layer when it is judged to be the best defrosting time, L f is the latent heat of melting of the frost layer, P C is the rated power of the compressor, t exp is the expected defrost time, c B is the specific heat capacity of the battery cell; m B is the total mass of the battery cells in the energy storage unit.

[0068] Example 2

[0069] As a preferred embodiment of the present invention, the present invention includes a thermal management method for an energy storage unit, which is used to execute a cooling mode, a heating mode, and a defrost mode. The heat required for the defrost mode comes from the heat converted from the electrical energy consumed by the compressor and the heat absorbed by the refrigerant from the battery cell. This thermal management method adjusts the temperature at which the battery cell starts cooling and stops cooling in the reverse cycle defrost mode and the cooling mode by predicting the degree of frost on the heat exchanger. The degree of frost on the heat exchanger can be judged as light frost, moderate frost, or heavy frost based on the ambient temperature and relative humidity.

[0070] This thermal management method also predicts whether to activate the auxiliary heat defrost mode by calculating the battery cell temperature at the end of the reverse cycle defrost mode. Specifically, it determines whether the calculated battery cell temperature at the end of the reverse cycle defrost mode is higher than the battery cell protection temperature. If so, only the defrost mode is activated. If not, both the defrost mode and the auxiliary heat defrost mode are activated.

[0071] The calculation method of the battery cell temperature at the end of the reverse cycle defrost mode is:

[0072]

[0073] Where, T B,end is the calculated cell temperature at the end of the reverse cycle defrost mode, T B,current is the cell temperature before defrosting, m ft (t) is the total mass of the current frost layer when it is judged to be the best defrosting time, L f is the latent heat of melting of the frost layer, P C is the rated power of the compressor, t exp is the expected defrost time, c B is the specific heat capacity of the battery cell; m B is the total mass of the battery cells in the energy storage unit.

[0074] Example 3

[0075] As another preferred embodiment of the present invention, the present invention includes a thermal management method for an energy storage unit, configured to operate in cooling, heating, and defrost modes. The heat required for the defrost mode is derived from heat converted from electrical energy consumed by the compressor and heat absorbed by the refrigerant from the battery cells. This thermal management method predicts the degree of frost on the heat exchanger and adjusts the temperature at which the battery cells begin and stop cooling in both reverse cycle defrost and cooling modes.

[0076] This thermal management method also predicts whether it is necessary to start the auxiliary heat defrost mode by calculating the battery cell temperature at the end of the reverse cycle defrost mode. The calculation method of the battery cell temperature at the end of the reverse cycle defrost mode is:

[0077]

[0078] Where, T B,end is the calculated cell temperature at the end of the reverse cycle defrost mode, T B,current is the cell temperature before defrosting, m ft (t) is the total mass of the current frost layer when it is judged to be the best defrosting time, L f is the latent heat of melting of the frost layer, P C is the rated power of the compressor, t exp is the expected defrost time, c B is the specific heat capacity of the battery cell; m B is the total mass of the battery cells in the energy storage unit.

[0079] The best defrosting time is determined by calculating the accumulated amount of frost on the heat exchanger and the blockage ratio in space in real time.

[0080] Furthermore, the frost rate m f The calculation method is:

[0081]

[0082] Q eva =m ref (h ref,out -h ref,in ),

[0083] Where w a is the humidity content of the incoming air, w asat,sur is the saturated moisture content of the fin surface, h a is the inlet air enthalpy, h asat,sur is the enthalpy of saturated wet air on the fin surface, Q eva is the evaporator heat exchange rate, R is the frost growth rate under shutdown conditions, m ref is the refrigerant flow rate, h ref,out is the refrigerant enthalpy at the evaporator outlet, h ref,in is the refrigerant enthalpy at the evaporator inlet.

[0084] Example 4

[0085] As another preferred embodiment of the present invention, the present invention includes a thermal management system for an energy storage unit, including a sensor, a controller, and a four-way valve 1. The first port of the four-way valve 1 is connected in sequence to the heat exchanger 2, the liquid storage tank 3, the first fluid path of the regenerator 4, several groups of battery thermal management circuits arranged in parallel, the second fluid path of the regenerator 4, and the second port of the four-way valve 1. The third port of the four-way valve 1 is connected in sequence to the gas-liquid separator 5, the compressor 6, and the fourth port of the four-way valve 1. The controller is connected to the four-way valve 1 and executes the cooling mode, heating mode, and defrost mode by controlling the reversing of the four-way valve 1. The controller is also used to adjust the temperature of the battery cell when it starts cooling and the temperature when it stops cooling in the reverse cycle defrost mode and the cooling mode according to the battery cell temperature detected by the sensor and the potential degree of frost on the heat exchanger 2, that is, it can control the start and stop timing of the reverse cycle defrost mode and the cooling mode.

[0086] Example 5

[0087] As another preferred embodiment of the present invention, the present invention includes a thermal management system for an energy storage unit, including a sensor, a controller, an auxiliary heat defrost device, and a four-way valve 1. The first port of the four-way valve 1 is connected in sequence to the heat exchanger 2, the liquid storage tank 3, the first fluid path of the regenerator 4, several groups of battery thermal management circuits arranged in parallel, the second fluid path of the regenerator 4, and the second port of the four-way valve 1. The third port of the four-way valve 1 is connected in sequence to the gas-liquid separator 5, the compressor 6, and the fourth port of the four-way valve 1. Each group of battery thermal management circuits includes an expansion valve 7, a liquid separator 8, and several battery direct cooling plates 9 connected in sequence. The auxiliary heat defrost device can be an electric heating device or a hot gas generating device for heating the heat exchanger 2.

[0088] The controller is connected to four-way valve 1 and controls the switching of four-way valve 1 to execute cooling mode, heating mode, and defrost mode. The controller is also used to control the start and stop timing of the reverse cycle defrost mode and cooling mode based on the battery cell temperature detected by the sensor and the potential degree of frost on heat exchanger 2.

[0089] A thermal management method for an energy storage unit can be implemented based on the above thermal management system to execute cooling mode, heating mode and defrosting mode. The defrosting mode includes a reverse cycle defrosting mode and an auxiliary heat defrosting mode. Figure 1 , the thermal management method comprises the following steps:

[0090] Step S1: Determine whether heating, cooling, or neither is currently required based on the BMS thermal management request. If heating is required, proceed to step S2; if cooling is required, proceed to step S3; if neither heating nor cooling is required, proceed to standby.

[0091] Step S2. Execute the heating mode according to the thermal management threshold. Figure 4 Compressor 6 compresses the low-pressure refrigerant gas into a high-temperature, high-pressure gas. The refrigerant then reverses flow through four-way valve 1, flows through the second fluid path of regenerator 4, and enters multiple battery direct cooling plates 9, transferring heat to the battery pack. The refrigerant then passes through liquid separator 8, expansion valve 7, and the first fluid path of regenerator 4, then through liquid storage tank 3 and heat exchanger 2, and finally through gas-liquid separator 5 to separate the gas and liquid before entering compressor 6.

[0092] During the above heating process, heat is absorbed from the environment through the heat exchanger 2, and the temperature of the heat exchanger 2 is lower than the ambient temperature. When the ambient temperature is low, such as below 0°C, and the ambient humidity is high, frost is easily formed on the fin surface of the heat exchanger 2, resulting in a significant reduction in heat exchange capacity. The battery pack cannot be heated, and the power consumption of the compressor 6 is increased, and even the life of the compressor 6 and the fan is reduced.

[0093] Therefore, during the heating process, the frost state of heat exchanger 2 is continuously monitored. If no abnormality is found, heating is continued until the set heating exit condition is met, at which point heating is terminated. If frost is found on heat exchanger 2 and the optimal defrosting time has arrived, the defrost mode is executed. After defrosting is complete, the process re-enters step S2.

[0094] The method for determining the optimal defrosting time is as follows: the optimal defrosting time is determined by calculating the accumulated amount of frost layer and the blockage ratio of the space in real time on the heat exchanger 2. Specifically, the method includes the following steps:

[0095] Utilizing the system's existing temperature, humidity, and pressure sensors, the system measures the surface temperature of the heat exchanger's fins, the outdoor air temperature and humidity, and the refrigerant temperature and pressure in real time. Using the principle of energy conservation, the system calculates the amount of frost added at each moment in real time and accumulates the total thickness of the frost layer. When the accumulated frost layer thickness reaches a set threshold, the defrost process is triggered. This method accurately determines the optimal defrost time in real time, avoiding premature or late defrosting. More specifically, it includes the following steps:

[0096] Real-time heat pump operating parameters are collected, including evaporator inlet air temperature Ta, evaporator inlet air relative humidity RH, evaporator fin surface temperature Tsurface, evaporator inlet refrigerant temperature Tref,in, evaporator outlet refrigerant temperature Tref,out, evaporator outlet refrigerant pressure Pref,out, and refrigerant flow rate mref. The refrigerant flow rate can be measured directly with a flow meter or calculated using the ten-coefficient method.

[0097] Calculate the evaporator heat transfer capacity:

[0098] Q eva =m ref (h ref,out -h ref,in ),

[0099] Where h ref,out is the refrigerant enthalpy at the evaporator outlet (J / kg), h ref,in is the refrigerant enthalpy at the evaporator inlet (J / kg).

[0100] Calculate the frost mass rate on the air side: Based on the humidity difference between the air and the fin surface, calculate the frost mass per unit time in the working state or the shutdown state:

[0101]

[0102] Q eva =m ref (h ref,out -h ref,in ),

[0103] Where m fis the frosting rate (kg / s), w a is the humidity content of the incoming air, w asat,sur is the saturated moisture content of the fin surface of heat exchanger 2, h a is the inlet air enthalpy value (J / kg), h asat,sur is the enthalpy of saturated wet air on the fin surface (J / kg), Q eva is the heat exchanger 2 heat transfer rate, R is the frost layer growth rate under shutdown conditions, m ref is the refrigerant flow rate.

[0104] Frost layer mass iteration: In each time step, the total mass of the accumulated frost layer is updated:

[0105] m ft (t+△t)=m ft (t)+m f △t,

[0106] Where m ft (t+△t) is the total frost layer mass after update (kg), m ft (t) is the total frost mass at the previous moment (kg), and Δt is the calculation period in seconds (s).

[0107] Frost layer thickness iteration: In each time step, the frost layer continues to accumulate, and the thickness of the new frost layer is:

[0108]

[0109] Where, △d f (t) is the thickness of the newly added frost layer; ρ f The average density of the frost layer is about 100-200 kg / m 3 ; A eff is the effective frost deposition area of ​​heat exchanger 2 fins (m 2 ).

[0110] The total frost layer thickness is:

[0111] d f (t+△t)=△d f (t)+d f (t),

[0112] Where, d f (t+△t) is the updated frost layer thickness, d f (t) is the thickness of the frost layer at the previous moment.

[0113] Calculation of frost layer volume ratio: Calculate the ratio of the frost layer thickness to the thickness of the gap between the fins of the heat exchanger 2. When this ratio reaches a critical value (such as 0.5), it is the best time to defrost and it is necessary to start defrosting:

[0114]

[0115] Where, d gap is the thickness of the gap between the fins of heat exchanger 2, that is, the thickness when the frost layer is completely blocked.

[0116] Furthermore, a time-frost thickness curve for fault diagnosis can be generated.

[0117] Further, refer to the instructions attached Figure 2 , executing the defrost mode specifically includes the following steps:

[0118] Step S 21 .Calculate the total mass of the current frost layer at the optimal defrost time. That is, iteratively calculate the frost layer mass and frost layer thickness according to the above method until the optimal defrost time is reached, and determine the current frost layer mass as the total mass of the current frost layer at the optimal defrost time m ft (t).

[0119] Step S 22 .Calculate the battery core temperature at the end of the reverse cycle defrost mode. Specifically include the following steps:

[0120] Step S 11 The heat required for the reverse cycle defrosting mode comes from the heat converted from the electric energy consumed by the compressor 6 and the heat absorbed by the refrigerant from the battery core. Calculate the heat E converted from the electric energy of the compressor 6 at the optimal defrosting time. C :

[0121] E C =P C t exp .

[0122] Step S 12 The remaining heat needs to be provided by the battery cells. Since the sensible heat accounts for a very low proportion, only the latent heat of the frost layer is considered when calculating the remaining heat, ignoring its sensible heat. Calculate the heat E that the battery cells can provide B :

[0123] E B =m ft (t)·L f -E C

[0124] Step S 13 .Calculate the battery cell temperature at the end of reverse cycle defrost mode:

[0125]

[0126] Where, T B,end is the calculated cell temperature at the end of the reverse cycle defrost mode, T B,current is the cell temperature before defrosting, m ft(t) is the total mass of the current frost layer when it is judged to be the best defrosting time, L f is the latent heat of melting of the frost layer, P C is the rated power of compressor 6, t exp is the desired defrosting time, preferably 300s to 600s, c B is the specific heat capacity of the battery cell; m B is the total mass of the battery cells in the energy storage unit.

[0127] Step S 23 .Judgment step S 22 Is the cell temperature calculated in step S higher than the cell protection temperature? If not, proceed to step S 24 If so, turn on the reverse cycle defrost mode and determine whether the real-time temperature of the battery cell is less than the battery cell protection temperature. If so, proceed to step S 24 If not, continue to execute the reverse cycle defrost mode for defrosting until the surface temperature of heat exchanger 2 is greater than the preset value.

[0128] Step S 24 . Turn on the reverse cycle defrost mode and the auxiliary heating defrost mode, and determine whether the real-time temperature of the battery cell is lower than the battery cell protection temperature. If so, exit the reverse cycle defrost mode until the surface temperature of the heat exchanger 2 is higher than the preset value; if not, continue to execute the reverse cycle defrost mode and the auxiliary heating defrost mode for defrosting until the surface temperature of the heat exchanger 2 is higher than the preset value.

[0129] Reverse-cycle defrosting specifically involves redirecting the refrigerant flow through four-way valve 1, directing the high-temperature refrigerant gas discharged from compressor 6 directly into the frosted heat exchanger 2, where it releases heat through condensation to melt the frost. During this process, the battery pack temporarily stops heating due to the reverse flow of refrigerant, entering cooling mode. Once the frost melts, four-way valve 1 returns to its original direction, and the system switches back to heating mode.

[0130] The thermal capacity of lithium-ion battery cells in energy storage systems is relatively high. For a 5MWh system, for example, the thermal capacity is approximately 28,100 kJ / K, equivalent to 6.7 tons of water. The core of this invention is to utilize the cells as thermal storage capacity and, through a rational thermal management control mode, ensure rapid heat absorption from the cells during reverse cycle defrosting while preventing the cells from overheating.

[0131] The auxiliary heat defrost mode may be hot gas bypass defrost, electric heating defrost, etc.

[0132] Step S3. Execute cooling mode according to the thermal management threshold. Figure 3, the compressor 6 compresses the low-pressure refrigerant gas to a high-temperature and high-pressure gas, which is then transported to the heat exchanger 2 after passing through the four-way valve 1. The heat exchanger 2 dissipates heat, and the refrigerant is condensed from a high-temperature and high-pressure gas to a high-pressure liquid, releasing heat to the environment. The high-pressure liquid refrigerant flows through the liquid storage tank 3 for storage to regulate the system pressure and flow. After passing through the first fluid path of the regenerator 4, the refrigerant is partially supercooled to improve the heat exchange efficiency. The refrigerant flows through the expansion valve 7 for throttling, and the pressure drops sharply, turning into a low-temperature and low-pressure two-phase flow. The liquid separator 8 evenly distributes the refrigerant to multiple battery direct cooling plates 9, which absorb the heat of the battery by evaporation to achieve battery cooling. After absorbing heat, the low-pressure refrigerant passes through the second fluid path of the regenerator 4 and the four-way valve 1, and then flows back to the gas-liquid separator 5 to ensure that only the gaseous refrigerant returns to the compressor 6 to complete a complete cycle.

[0133] Furthermore, in the above-mentioned thermal management, the degree of frost can be judged according to the outdoor environment, so as to adjust the temperature of the battery cell when it starts cooling and the temperature when it stops cooling in the reverse cycle defrost mode and the cooling mode, appropriately increase the battery cell temperature in advance, and use the battery cell's own heat capacity to store additional heat, thereby reducing the number of heating requests, reducing the possibility of frost and reducing energy consumption.

[0134] Severe frost is more likely to form under relatively high ambient temperature and humidity conditions. When the ambient temperature is lower, such as below -15°C, although the relative humidity may still be high, the absolute moisture content is low, frosting is not severe, and the frost layer at this time is often low in density, which has little impact on heat exchange. Therefore, based on the ambient temperature and relative humidity, the degree of frost on heat exchanger 2 is judged as light frosting, moderate frosting, or heavy frosting, as shown in the following table:

[0135]

[0136] Under different temperature and humidity environments, the heat storage capacity of the battery cells is adjusted by changing the temperature at which the battery cells start cooling and the temperature at which they stop cooling. Specifically: When there is light frost, the temperature at which the battery cells start cooling in the cyclic defrost mode and cooling mode is Tc1+3°C, and the temperature at which the battery cells stop cooling is Tc2+3°C; when there is moderate frost, the temperature at which the battery cells start cooling in the cyclic defrost mode and cooling mode is Tc1+5°C, and the temperature at which the battery cells stop cooling is Tc2+5°C; when there is heavy frost, the temperature at which the battery cells start cooling in the cyclic defrost mode and cooling mode is Tc1+10°C, and the temperature at which the battery cells stop cooling is Tc2+10°C; where Tc1 and Tc2 are the preset base values ​​for when the battery cells start and stop cooling, respectively. Tc1 can be 26°C, and Tc2 can be 23°C.

[0137] This thermal management approach dynamically adjusts the alternating heating and defrosting cycles. If the request is for cooling, the system directly executes cooling mode, cooling the battery via the refrigeration circuit. If the request is for thermal storage mode, the cooling threshold is adjusted accordingly. Otherwise, the system enters standby mode.

[0138] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical solutions and technical concepts of the present invention without creative mental work, which all fall within the scope of protection of the present invention.

Claims

1. A thermal management method for an energy storage unit, for executing a cooling mode, a heating mode, and a defrosting mode, characterized in that: The defrost mode includes a reverse cycle defrost mode and an auxiliary heat defrost mode; the heat required for the reverse cycle defrost mode comes from the heat converted from the electrical energy consumed by the compressor and the heat absorbed by the refrigerant from the battery cell; by predicting the degree of frost on the heat exchanger, the temperature of the battery cell when cooling starts and when cooling stops in the reverse cycle defrost mode and cooling mode is adjusted accordingly; by calculating the battery cell temperature at the end of the reverse cycle defrost mode, it is determined whether the auxiliary heat defrost mode needs to be turned on; wherein, the calculation method of the battery cell temperature at the end of the reverse cycle defrost mode is: Where, T B,end is the calculated cell temperature at the end of the reverse cycle defrost mode, T B,current is the cell temperature before defrosting, m ft (t) is the total mass of the current frost layer when it is judged to be the best defrosting time, L f is the latent heat of melting of the frost layer, P C is the rated power of the compressor, t exp is the expected defrost time, c B is the specific heat capacity of the battery cell; m B is the total mass of the battery cells in the energy storage unit.

2. The thermal management method of an energy storage unit according to claim 1, characterized in that: The following steps are involved: Step S1. Determine whether heating, cooling, or neither is currently required; if heating is required, proceed to step S2; if cooling is required, proceed to step S3; if neither is required, proceed to standby; Step S2. Execute the heating mode according to the thermal management threshold; during the heating process, continuously monitor the frosting state of the heat exchanger. If no frost is formed, continue heating until the set heating exit condition is met and then terminate the heating; If frost is found on the heat exchanger and the best defrosting time is reached, the defrost mode is executed. After the defrost is completed, the process goes back to step S2; Step S3: Execute a cooling mode according to the thermal management threshold.

3. A thermal management method for an energy storage unit according to claim 1 or 2, characterized in that: The best defrost timing is determined by calculating the accumulated amount of frost on the heat exchanger and the blockage ratio in space in real time.

4. The thermal management method of an energy storage unit according to claim 3, characterized in that: The method for determining the optimal defrosting time specifically includes the following steps: According to the frost rate, the frost thickness is calculated iteratively: d f (t+Δt)=Δd f (t)+d f (t), Calculate the ratio of the frost layer thickness to the fin gap thickness at the current moment: When the thickness ratio reaches a preset critical value, it is determined that the current moment is the best time to defrost; Where, d f (t+Δt) is the thickness of the frost layer at the current moment, Δd f (t) is the thickness of the newly added frost layer, d f (t) is the thickness of the frost layer at the previous moment; m f is the frosting rate, Δt is the calculation period, ρ f is the average density of the frost layer, A eff is the effective frost deposition area of ​​the heat exchanger fin; d gap is the thickness of the gap between the heat exchanger fins.

5. The thermal management method of an energy storage unit according to claim 4, characterized in that: Frosting rate m f The calculation method is: Q eva =m ref (h ref,out -h ref,in ), Where w a is the humidity content of the incoming air, w asat,sur is the saturated moisture content of the heat exchanger fin surface, h a is the inlet air enthalpy, h asat,sur is the enthalpy of saturated wet air on the fin surface, Q eva is the heat exchanger heat transfer rate, R is the frost layer growth rate under shutdown conditions, m ref is the refrigerant flow rate, h ref,out is the refrigerant enthalpy at the heat exchanger outlet, h ref,in is the refrigerant enthalpy at the heat exchanger inlet.

6. The thermal management method of an energy storage unit according to claim 2, characterized in that: The following steps are involved in executing the defrost mode: Step S 21 .Calculate the total mass of the current frost layer at the optimal defrost time; Step S 22 .Calculate the battery cell temperature at the end of reverse cycle defrost mode; Step S 23 .Judgment step S 22 Is the cell temperature calculated in step S higher than the cell protection temperature? If not, proceed to step S 24 If so, turn on the reverse cycle defrost mode and determine whether the real-time temperature of the battery cell is less than the battery cell protection temperature. If so, proceed to step S 24 If not, continue to perform the reverse cycle defrost mode for defrosting until the surface temperature of the heat exchanger is greater than the preset value; Step S 24 .Turn on the reverse cycle defrost mode and the auxiliary heating defrost mode, and determine whether the real-time temperature of the battery cell is lower than the battery cell protection temperature. If so, exit the reverse cycle defrost mode until the surface temperature of the heat exchanger is higher than the preset value; if not, continue to execute the reverse cycle defrost mode and the auxiliary heating defrost mode for defrosting until the surface temperature of the heat exchanger is higher than the preset value.

7. The thermal management method of an energy storage unit according to claim 1, characterized in that: Predicting the degree of frost on the heat exchanger specifically refers to: judging the degree of frost on the heat exchanger as light frost, moderate frost, or heavy frost based on the ambient temperature and relative humidity.

8. The thermal management method of an energy storage unit according to claim 7, characterized in that: Corresponding adjustments are made to the temperature when the battery cells start cooling down in the reverse cycle defrost mode and the cooling mode, and the temperature when cooling stops. Specifically, when there is light frost, the temperature when the battery cells start cooling down in the cycle defrost mode and the cooling mode is Tc1+3°C, and the temperature when the battery cells stop cooling down is Tc2+3°C; when there is moderate frost, the temperature when the battery cells start cooling down in the cycle defrost mode and the cooling mode is Tc1+5°C, and the temperature when the battery cells stop cooling down is Tc2+5°C; when there is heavy frost, the temperature when the battery cells start cooling down in the cycle defrost mode and the cooling mode is Tc1+10°C, and the temperature when the battery cells stop cooling down is Tc2+10°C; wherein, Tc1 and Tc2 are the preset basic values ​​when the battery cells start and stop cooling, respectively.

9. The thermal management method of an energy storage unit according to claim 1, characterized in that: The method for calculating the battery cell temperature at the end of the reverse cycle defrost mode specifically includes the following steps: Step S 11 .Calculate the heat E converted from compressor electrical energy at the optimal defrost time C And the total mass of the current frost layer m ft (t): E C =P C t exp ; Step S 12 .Calculate the heat E that the battery cell can provide B : E B =m ft (t)·L f -E C Step S 13 .Calculate the battery cell temperature at the end of reverse cycle defrost mode:

10. The thermal management method of an energy storage unit according to claim 4, characterized in that: It also includes the generation of time-frost thickness curves for fault diagnosis.

11. A thermal management system for an energy storage unit, characterized in that: The invention comprises a sensor, a controller and a four-way valve (1); the first port of the four-way valve (1) is connected in sequence to a heat exchanger (2), a liquid storage tank (3), a first fluid path of a regenerator (4), a plurality of battery thermal management circuits arranged in parallel, a second fluid path of the regenerator (4) and the second port of the four-way valve (1); the third port of the four-way valve (1) is connected in sequence to a gas-liquid separator (5), a compressor (6) and a fourth port of the four-way valve (1); the controller is connected to the four-way valve (1) and executes a cooling mode, a heating mode and a defrosting mode by controlling the reversing of the four-way valve (1); the controller is also used to control the start and stop timing of the reverse cycle defrosting mode and the cooling mode according to the battery core temperature detected by the sensor and the potential frosting degree of the heat exchanger (2).

12. The thermal management system of an energy storage unit according to claim 11, characterized in that: Also includes auxiliary heat defrost device.

13. The thermal management system of an energy storage unit according to claim 12, characterized in that: Each battery thermal management circuit comprises an expansion valve (7), a liquid distributor (8) and a plurality of battery direct cooling plates (9) which are connected in sequence.

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