An immersion liquid cooling energy storage temperature control system and control method

Abstract

The application discloses an immersed liquid cooling energy storage temperature control system and a control method, and belongs to the field of energy storage systems. The method comprises the following steps: calculating a battery pack temperature difference based on the heat energy transmission relationship between the battery pack and the immersed cooling liquid; determining a temperature control strategy based on the battery pack temperature difference and a preset safety threshold; controlling the battery pack temperature change based on the battery pack parameters of a single lithium battery in the battery pack and the temperature control strategy to obtain a battery pack temperature; and realizing the control of the immersed liquid cooling energy storage temperature control system based on the cooling liquid flow rate and the battery pack temperature. The application combines the temperature control system with the actual operation state and temperature of the battery pack, realizes the constraint of the battery pack temperature and the accurate estimation of the energy consumption.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage systems, and particularly relates to an immersed liquid cooling energy storage temperature control system and a control method. BACKGROUND

[0002] The lithium ion battery energy storage system uses lithium ion batteries as energy release and storage carriers. Due to the intrinsic physicochemical properties of the lithium ion batteries, the battery performance changes obviously with the dynamic change of the temperature in the running process. When the batteries are inconsistent, the system conversion efficiency and the battery life are greatly reduced, and the full life cycle cost and the operation energy consumption of the energy storage system are increased. Therefore, after being integrated into a large energy storage system, the temperature consistency control and the energy consumption improvement between the batteries have become a major bottleneck problem in the development process of the energy storage system.

[0003] In view of the above problems, the commonly used air cooling device system in China at present is a typical technical configuration in which a precision industrial air conditioner is matched with a fan. However, with the continuous operation of the air cooling device in the battery charging and discharging process, the power consumption of the lithium ion battery energy storage system is also obviously increased.

[0004] The immersed liquid cooling energy storage temperature control system and the control method disclosed by the prior art are connected in communication with the shell through a first conveying branch flow path and a second conveying branch flow path through a merging outflow pipe, the first oil pump and the electric heater are arranged on the merging outflow pipe, and the multi-way valve is connected with the shell, so that the cooling liquid can fully play a role, the system flow resistance is reduced, the oil pump flow is increased, the heat exchange efficiency is improved, and the system energy consumption is reduced.

[0005] However, in the actual running process of the battery pack, due to the immersion, the cooling liquid will be delayed in the process of jet cooling, so that the temperature change lags behind, and the temperature characteristics of the battery pack present nonlinearity. Therefore, the reduction of the system flow resistance and the increase of the oil pump flow are only applicable to the case that the battery pack temperature is too high and the overall system triggers an alarm, and the constraint and energy consumption problem of the battery pack temperature control is not considered. Therefore, the present application provides an immersed liquid cooling energy storage temperature control system and a control method. SUMMARY

[0006] To solve the above technical problems, the present application provides an immersed liquid cooling energy storage temperature control system and a control method to solve the problems existing in the prior art.

[0007] To achieve the above purpose, the present application provides a control method of an immersed liquid cooling energy storage temperature control system, comprising the following steps:

[0008] calculating the battery pack temperature difference based on the heat energy transfer relationship between the battery pack and the immersed cooling liquid;

[0009] determining a temperature control strategy based on the battery pack temperature difference and a preset safety threshold value;

[0010] controlling the battery pack temperature change based on the battery pack parameters of the single lithium battery in the battery pack and the temperature control strategy to obtain the battery pack temperature;

[0011] controlling the immersion liquid cooling energy storage temperature control system based on the cooling liquid flow rate and the battery pack temperature.

[0012] Optionally, the battery pack temperature difference comprises: battery pack heat generation and battery pack heat dissipation.

[0013] The calculation expression of the battery pack heat dissipation is:

[0014] Q s = hA (T b -T f )

[0015] In the formula, Q s is the total heat dissipation of the battery, h is the convective heat transfer coefficient between the cooling fluid and the solid contact surface, A is the convective heat transfer area, T f is the cooling liquid temperature.

[0016] Optionally, the temperature control strategy comprises:

[0017] When the battery pack heat generation is greater than the battery pack heat dissipation, the battery pack temperature difference is greater than the preset safety threshold value, and the cooling liquid in the cooling system is immersed into the energy storage system from the injection hole;

[0018] When the battery pack heat generation is greater than the battery pack heat dissipation, the battery pack temperature difference is less than or equal to the preset safety threshold value, and the cooling liquid in the cooling system is not injected;

[0019] When the battery pack heat generation is less than or equal to the battery pack heat dissipation, the battery pack temperature difference is greater than the preset safety threshold value, and the existing cooling liquid in the energy storage system is discharged from the discharge pipeline;

[0020] When the battery pack heat generation is less than or equal to the battery pack heat dissipation, the battery pack temperature difference is less than or equal to the preset safety threshold value, and the cooling liquid in the cooling system is not injected and the existing cooling liquid is not discharged.

[0021] Optionally, the battery pack parameters comprise: battery real-time temperature, ambient temperature, battery charge, battery state and battery health rate.

[0022] Optionally, the process of controlling the battery pack temperature change based on the battery pack parameters of the single lithium battery in the battery pack and the temperature control strategy comprises:

[0023] calculating the cooling system energy consumption based on the first lithium battery temperature and the last lithium battery temperature close to the injection hole;

[0024] calculating a total amount of cooling liquid injection based on the consumed energy of the cooling system and the flow rate of the cooling liquid;

[0025] controlling the temperature change of the battery pack based on the total amount of cooling liquid injection.

[0026] Optionally, the calculation expression of the total amount of cooling liquid injection is:

[0027]

[0028] In the formula, C represents the total amount of cooling liquid injection, P represents the consumed energy of the cooling system, u represents the flow rate of the cooling liquid, T b,1 represents the temperature of the first lithium battery close to the injection hole, b.n represents the temperature of the nth lithium battery, and K is the energy consumption proportionality coefficient.

[0029] The application also provides an immersion liquid cooling energy storage temperature control system for implementing the control method of the immersion liquid cooling energy storage temperature control system.

[0030] The detection module is configured to acquire battery pack parameters based on a lithium battery built-in sensor.

[0031] The temperature control module is configured to calculate a battery pack temperature difference based on the battery pack parameters, and determine a temperature control strategy based on the battery pack temperature difference and a preset safety threshold.

[0032] The control module is configured to complete the start of the cooling system based on the temperature control strategy, and determine the consumed energy and the start time of the cooling system.

[0033] Compared with the prior art, the application has the following advantages and technical effects:

[0034] The immersion liquid cooling energy storage temperature control system control method of the application accurately calculates the heat energy transfer relationship between the battery pack and the cooling liquid, accurately obtains the temperature difference of the battery pack, and then formulates a reasonable temperature control strategy according to the preset safety threshold. The method can dynamically adjust the temperature control strategy according to the real-time parameters of the single lithium battery in the battery pack, such as the real-time temperature of the battery, the environmental temperature, the state of charge of the battery, the health status of the battery, and the like, and realize the accurate control of the temperature of the battery pack. In addition, the cooling liquid flow rate and the temperature of the battery pack are combined to further optimize the control effect of the temperature control system, and ensure that the energy storage system operates in an efficient and safe temperature range. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which form a part of the present application, are included to provide a further understanding of the application and are incorporated herein in their entirety. The application is illustrated by and described with reference to the accompanying drawings, which, by way of illustration, are described in the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 This is a schematic flowchart of the control method for the immersion liquid-cooled energy storage temperature control system according to an embodiment of the present invention;

[0037] Figure 2 Design a controller flowchart for an embodiment of the present invention;

[0038] Figure 3 This is a flowchart illustrating the control process of the immersion liquid-cooled energy storage temperature control system according to an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the immersion liquid-cooled energy storage temperature control system of the present invention. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0041] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0042] Example 1

[0043] like Figure 1 As shown, this embodiment provides a control method for an immersion liquid-cooled energy storage temperature control system, including the following steps: calculating the temperature difference of the battery pack based on the heat transfer relationship between the battery pack and the immersion coolant; determining a temperature control strategy based on the battery pack temperature difference and a preset safety threshold; controlling the battery pack temperature change based on the battery pack parameters of individual lithium batteries in the battery pack and the temperature control strategy to obtain the battery pack temperature; and realizing the control of the immersion liquid-cooled energy storage temperature control system based on the coolant flow rate and the battery pack temperature.

[0044] S1: Based on the cooling system structure design and the law of conservation of energy, establish a heat transfer relationship between the battery pack and the immersed coolant, calculate the temperature difference of the battery pack, and provide a temperature control strategy for the energy storage system based on a preset safety threshold.

[0045] The battery pack temperature difference in S1 includes the heat generated by the battery pack and the heat dissipated by the battery pack.

[0046] The heat generated by the battery pack is based on the internal thermal resistance Q of the battery, which is a known parameter of the lithium battery. i , Battery reaction heat Q j Battery polarization heat Q k and the heat of battery side reactions Q t get;

[0047] Because the internal resistance of the battery can be divided into two parts, i.e. ohmic resistance and polarization resistance, when the current passes through the battery, due to the existence of various internal resistances, internal resistance heat, i.e. Q i =I 2 R, it can be known from the above that the total heat generated by the battery Q p =Q i +Q j +Q k +Q t ; according to the battery heat generation rate model, the obtained open circuit voltage E oc , working voltage U, battery temperature T b and total current I of the battery are introduced, and the total heat generated by the battery is obtained. , i.e. the total heat generated by the battery.

[0048] The heat dissipation of the battery pack is obtained based on the product of the difference between the battery temperature and the cooling liquid temperature, the convection heat transfer coefficient and the convection heat transfer area.

[0049] According to Newton's cooling law, the total heat dissipated by the battery is Q s =hA(T b -T f ), wherein Q s is the total heat dissipated by the battery, h is the convection heat transfer coefficient between the cooling fluid and the solid contact surface, A is the convection heat transfer area, T f is the cooling liquid temperature.

[0050] It can be known from the above that,

[0051] The temperature control strategy in S1 includes at least one of the following strategies:

[0052] When the heat generated by the battery pack is greater than the heat dissipated by the battery pack, the temperature difference of the battery pack is greater than the preset safety threshold, and the cooling liquid in the cooling system is immersed into the energy storage system from the injection hole;

[0053] When the heat generated by the battery pack is greater than the heat dissipated by the battery pack, the temperature difference of the battery pack is less than or equal to the preset safety threshold, and the cooling liquid in the cooling system is not injected;

[0054] When the heat generated by the battery pack is less than or equal to the heat dissipated by the battery pack, the temperature difference of the battery pack is greater than the preset safety threshold, and the existing cooling liquid in the energy storage system is discharged from the discharge pipeline;

[0055] When the heat generated by the battery pack is less than or equal to the heat dissipated by the battery pack, the temperature difference of the battery pack is less than or equal to the preset safety threshold, and the cooling liquid in the cooling system is not injected and the existing cooling liquid is not discharged.

[0056] S2: Obtain the battery parameters of the single lithium battery in the battery pack and the generated temperature control strategy, and control the battery pack temperature change based on the iterative dynamic programming algorithm; the battery parameters include real-time battery temperature, ambient temperature, battery charge, battery state, and battery health rate;

[0057] The process of controlling the battery pack temperature change based on the battery parameters of the single lithium battery in the battery pack and the temperature control strategy includes: calculating the cooling system energy consumption based on the first lithium battery temperature and the last lithium battery temperature close to the injection hole; calculating the total cooling liquid injection amount based on the cooling system energy consumption and the cooling liquid flow rate; and controlling the battery pack temperature change based on the total cooling liquid injection amount.

[0058] In S2, the iterative dynamic programming algorithm takes the first lithium battery temperature T b,1 and the last lithium battery temperature T b.n and the cooling system energy consumption P as control outputs, and takes the cooling liquid flow rate u as a control variable.

[0059] Because for the battery pack, the temperature of the corresponding cooling liquid will rise after each battery is cooled, and the temperature of the cooling liquid collected in the energy storage system after cooling will gradually increase with the number of lithium batteries in the battery pack, if the flow rate is small, the temperature of the cooling liquid will be higher and higher, which will affect the temperature of the battery, and thus the temperature of the battery will also be higher and higher.

[0060] The temperature difference between the first battery and the last battery can represent the temperature distribution in the battery pack, so the cooling system energy consumption P is calculated according to the temperature difference and the number of lithium batteries;

[0061] Therefore, P = |T b,1 -T b.n | × nK, where K is the energy consumption proportionality coefficient; Where C is equal to the total cooling liquid injection amount.

[0062] S3: Taking the cooling liquid flow rate as the control variable, the controller is designed to complete the control of the temperature of the energy storage system;

[0063] The controller design process in S3 is shown in detail in Figure 2 The controller completes the control of the cooling liquid injection switch in the cooling system, the control of the cooling liquid injection flow rate u, and the control of the cooling liquid injection time t.

[0064] Where

[0065] The three specific control models are described as follows,

[0066] Cooling liquid injection switch control model:

[0067] Define a logical function f s (T d ,T t ), where T d is the battery pack temperature difference, T t is the preset safety threshold.

[0068] When T d >T t and the battery pack heat generation is greater than the heat dissipation, f s =1, indicating that the cooling liquid injection is turned on; when T d ≤T t and the battery pack heat generation is greater than the heat dissipation, or T d ≤T t and the battery pack heat generation is less than or equal to the heat dissipation, f s =0, indicating that the cooling liquid injection is turned off.

[0069] This logical judgment model can accurately control the opening and closing of the cooling liquid injection according to the real-time temperature difference and threshold, avoiding unnecessary cooling liquid waste and energy loss.

[0070] Cooling liquid injection flow rate control model:

[0071] A proportional-integral-derivative (PID) controller is used to accurately control the injection flow rate of the cooling liquid. Let the target flow rate be u t , and the actual flow rate be u a .

[0072] The output u c of the PID controller is used to adjust the speed of the cooling liquid pump, thereby changing the flow rate. Its expression is:

[0073] where K p , K i , and K d are the proportional, integral, and derivative coefficients, respectively. By adjusting these three coefficients, rapid and accurate adjustment of the cooling liquid flow rate can be achieved, reducing system overshoot and steady-state error.

[0074] Cooling liquid injection time control model:

[0075] During the cooling process, the temperature change of the battery pack is monitored in real time, and the injection time is dynamically adjusted according to the cooling effect. Let the battery pack temperature during cooling be T b , the temperature after cooling be T a , and the target temperature be T t .

[0076] Define a cooling effect evaluation index E Adjust the injection time according to the value of E. If E<E t (Et If E < E0, then the injection time is extended; if E > E0, then the current injection time is maintained or appropriately shortened. This adjustment model based on cooling effect feedback can ensure that the coolant exerts the maximum cooling effect within the optimal time, improving the cooling efficiency and energy utilization of the system. t

[0077] S4: After the battery pack is immersed in the cooling liquid, the real-time temperature of the battery pack is obtained, the temperature control strategy effect is achieved, the cooling liquid is compressed by the compressor and enters the condenser, the heat is transferred to the outside air to be condensed, and then the condensed cooling liquid enters the evaporator through the pressure reducing valve to absorb heat, realizing the process of circulating cooling, as shown in Figure 3 .

[0078] Therefore, the present application provides a temperature control strategy for the energy storage system by calculating the temperature difference of the battery pack based on a preset safety threshold, links the flow rate of the cooling liquid in the cooling pipeline to the temperature of the battery pack, and predicts the total amount of the cooling liquid injection and the immersion injection time of the cooling liquid according to the temperature of the battery pack, thereby achieving accurate control of the temperature of the energy storage system. The temperature control system is combined with the actual operating state and temperature of the battery pack to realize the constraint of the battery pack temperature and the accurate prediction of the energy consumption.

[0079] Embodiment Two

[0080] As shown in Figure 4 , the present embodiment also provides an immersion liquid cooling energy storage temperature control system, which comprises a detection module that obtains the battery temperature, the ambient temperature, the battery charge, the battery state, and the battery health rate based on the built-in sensor of the lithium battery.

[0081] The system also comprises a temperature control module that calculates the temperature difference of the battery pack based on the temperature obtained by the detection module, determines the difference between the temperature difference of the battery pack and the safety threshold, and generates a control strategy based on the difference.

[0082] The system also comprises a control module that completes the start of the cooling system based on the control strategy, and determines the consumed energy P and the start time t of the cooling system based on the detection results of the detection module.

[0083] ​The application calculates the temperature difference of the battery pack, provides a temperature control strategy, obtains the parameters of the battery pack, controls the temperature change of the battery pack, takes the flow rate of the cooling liquid as a control quantity, and controls the temperature of the energy storage system through the designed controller.

[0084] The immersion liquid cooling energy storage temperature control system and the control method provided by the application calculate the temperature difference of the battery pack, provide a temperature control strategy of the energy storage system based on a preset safety threshold, associate the flow rate of the cooling liquid in the cooling pipeline with the temperature of the battery pack, predict the total amount of the injection of the cooling liquid and the immersion injection time thereof according to the temperature of the battery pack, accurately control the temperature of the energy storage system, combine the temperature control system with the actual operation state and the temperature of the battery pack, constrain the temperature of the battery pack, and accurately estimate the energy consumption.

[0085] The above is only a preferred specific embodiment of the application, but the protection scope of the application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A control method of an immersion liquid cooling energy storage temperature control system, characterized in that, The method comprises the following steps: calculating a battery pack temperature difference based on a heat transfer relationship between the battery pack and the immersion cooling liquid; determining a temperature control strategy based on the battery pack temperature difference and a preset safety threshold; controlling a battery pack temperature change based on battery pack parameters of individual lithium batteries in the battery pack and the temperature control strategy to obtain a battery pack temperature; implementing immersion liquid cooling energy storage temperature control system control based on a cooling liquid flow rate and the battery pack temperature; the battery pack temperature difference comprises a battery pack heat generation amount and a battery pack heat dissipation amount; a calculation expression of the battery pack heat generation amount is: ； a calculation expression of the battery pack heat dissipation amount is: ； Battery pack temperature delta ; wherein, Qg is the heat generated by the battery pack, Qp is the heat generated by the battery polarization, Qs is the heat generated by the battery side reactions, It is the total current of the battery, It is the internal resistance of the battery, It is the battery temperature, It is the open circuit voltage, Qs is the total heat dissipation of the battery, It is the convective heat transfer coefficient between the cooling liquid and the solid contact surface, It is the convective heat transfer area, It is the cooling liquid temperature; the process of controlling the battery pack temperature change based on the battery pack parameters of individual lithium batteries in the battery pack and the temperature control strategy comprises: calculating cooling system energy consumption based on a first lithium battery temperature close to a jet hole and a last lithium battery temperature; calculating a total amount of cooling liquid jetting based on the cooling system energy consumption and a cooling liquid flow rate; and controlling the battery pack temperature change based on the total amount of cooling liquid jetting; a calculation expression of the total amount of cooling liquid jetting is: ； In the formula, C represents the total amount of coolant injection, P represents the energy consumption of the cooling system, u represents the coolant flow rate, represents the temperature of the first lithium battery close to the injection hole, represents the temperature of the n-th lithium battery, and K is the energy consumption proportionality coefficient.

2. The control method of the immersion liquid cooling energy storage temperature control system according to claim 1, wherein, the temperature control strategy comprises: when the battery pack heat generation amount is greater than the battery pack heat dissipation amount, the battery pack temperature difference is greater than the preset safety threshold, and the cooling liquid in the cooling system is immersed into the energy storage system from the jet hole; when the battery pack heat generation amount is greater than the battery pack heat dissipation amount, the battery pack temperature difference is less than or equal to the preset safety threshold, and the cooling liquid in the cooling system is not jetted; when the battery pack heat generation amount is less than or equal to the battery pack heat dissipation amount, the battery pack temperature difference is greater than the preset safety threshold, and the existing cooling liquid in the energy storage system is discharged through a discharge pipeline; when the battery pack heat generation amount is less than or equal to the battery pack heat dissipation amount, the battery pack temperature difference is less than or equal to the preset safety threshold, and the cooling liquid in the cooling system is not jetted and the existing cooling liquid is not discharged.

3. The control method of the immersion liquid cooling energy storage temperature control system according to claim 2, characterized in that, The battery pack parameters comprise a battery real-time temperature, an ambient temperature, a battery charge, a battery state, and a battery health rate.

4. An immersion liquid-cooled energy storage temperature control system, characterized by, A control method for implementing the immersion liquid cooling energy storage temperature control system according to any one of claims 1-3, wherein the system comprises: a detection module configured to acquire battery pack parameters based on lithium battery built-in sensors; a temperature control module configured to calculate a battery pack temperature difference based on the battery pack parameters, and determine a temperature control strategy based on the battery pack temperature difference and a preset safety threshold; a control module configured to complete starting of a cooling system based on the temperature control strategy, and determine cooling system energy consumption and a starting time.

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