Immersed liquid cooling energy storage temperature control system and control method

Abstract

The invention 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 that the temperature difference of a battery pack is calculated based on the heat energy transfer relation between the battery pack and immersed cooling liquid; determining a temperature control strategy based on the battery pack temperature difference and a preset safety threshold; controlling battery pack temperature change based on battery pack parameters of a single lithium battery in the battery pack and the temperature control strategy to obtain battery pack temperature; and realizing control of the immersed liquid cooling energy storage temperature control system based on the flow rate of the cooling liquid and the temperature of the battery pack. According to the invention, the temperature control system is combined with the actual running state and temperature of the battery pack, so that the temperature constraint of the battery pack and the accurate estimation of energy consumption are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage systems, and in particular relates to an immersion liquid-cooled energy storage temperature control system and a control method. Background Art

[0002] Lithium-ion battery energy storage systems use lithium-ion batteries as carriers for energy release and storage. Lithium-ion batteries are affected by their intrinsic physical and chemical properties. During operation, as the temperature changes dynamically, the battery performance changes significantly. When the battery is inconsistent, it will greatly reduce the system conversion efficiency and battery life, and increase the full life cycle cost and operating energy consumption of the energy storage system. Therefore, after being integrated into a large-scale energy storage system, the consistency control of temperature between batteries and the improvement of energy consumption have become a major bottleneck problem in the development process of the energy storage system.

[0003] In response to the above problems, the air cooling system currently commonly used in China is a typical technical configuration of precision industrial air conditioning combined with fans. However, as the air cooling device continues to operate during the battery charging and discharging process, the power consumption of the lithium-ion battery energy storage system also increases significantly.

[0004] The prior art discloses an immersion liquid-cooled energy storage temperature control system and a control method thereof. The system is connected to a shell through a first delivery branch flow path and a second delivery branch flow path through a combined outflow pipeline. A first oil pump and an electric heater are provided on the combined outflow pipeline. The multi-way valve is connected to the shell to give full play to the effect of the coolant, reduce the system flow resistance, increase the oil pump flow, improve the heat exchange efficiency, and reduce the system energy consumption.

[0005] However, in the actual operation of the battery pack, the above method will cause a certain delay in the cooling process of the cooling liquid during the injection process due to the immersion of the battery pack, which will cause the temperature change to lag and make the battery pack temperature characteristics nonlinear. Therefore, by reducing the system flow resistance and increasing the oil pump flow, it is only applicable to the case where the battery pack temperature is too high and the overall system triggers an alarm, without considering the constraints and energy consumption of the battery pack temperature control. Therefore, the present invention proposes an immersion liquid-cooled energy storage temperature control system and control method. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes an immersion liquid-cooled energy storage temperature control system and a control method to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above object, the present invention provides a control method for an immersion liquid-cooled 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 immersion coolant;

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

[0010] The battery pack temperature is obtained by 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;

[0011] The immersion liquid-cooled energy storage temperature control system is controlled based on the coolant flow rate and the battery pack temperature.

[0012] Optionally, the battery pack temperature difference includes: battery pack heat generation and battery pack heat dissipation;

[0013] The calculation expression of the heat dissipation of the battery pack 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 coolant temperature.

[0016] Optionally, the temperature control strategy includes:

[0017] 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 coolant in the cooling system is immersed into the energy storage system through the injection hole;

[0018] 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 coolant in the cooling system is not sprayed;

[0019] 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 coolant in the energy storage system is discharged from the discharge pipe;

[0020] 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, the coolant in the cooling system is not sprayed and the existing coolant is not discharged.

[0021] Optionally, the battery pack parameters include real-time battery temperature, ambient temperature, battery charge, battery status and battery health rate.

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

[0023] Calculate the energy consumed by the cooling system based on the temperature of the first lithium battery and the temperature of the last lithium battery near the injection hole;

[0024] Calculating the total amount of coolant sprayed based on the energy consumed by the cooling system and the coolant flow rate;

[0025] A battery pack temperature change is controlled based on the coolant injection total amount.

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

[0027]

[0028] In the formula, C represents the total amount of coolant sprayed, P represents the energy consumption of the cooling system, u represents the coolant flow rate, T b,1 represents the temperature of the first lithium battery near the injection hole, T b.n Represents the nth lithium battery temperature, and K is the energy consumption proportional coefficient.

[0029] The present invention also provides an immersion liquid-cooled energy storage temperature control system, which is used to implement a control method for the immersion liquid-cooled energy storage temperature control system. The system includes:

[0030] A detection module is used to obtain battery pack parameters based on the built-in sensor of the lithium battery;

[0031] 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;

[0032] The control module is used to complete the startup of the cooling system based on the temperature control strategy and determine the energy consumption and startup time of the cooling system.

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

[0034] The control method of the immersion liquid-cooled energy storage temperature control system of the present invention accurately calculates the heat transfer relationship between the battery pack and the coolant, accurately obtains the temperature difference of the battery pack, and then formulates a reasonable temperature control strategy based on the preset safety threshold. This method can dynamically adjust the temperature control strategy according to the real-time parameters of a single lithium battery in the battery pack, such as the real-time battery temperature, ambient temperature, battery state of charge, battery health, etc., to achieve precise control of the battery pack temperature. In addition, by combining the coolant flow rate with the battery pack temperature, the control effect of the temperature control system is further optimized, ensuring that the energy storage system operates within an efficient and safe temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0036] Figure 1 It is a flow chart of a control method of an immersion liquid-cooled energy storage temperature control system according to an embodiment of the present invention;

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

[0038] Figure 3 This is a flow chart of the control of the immersion liquid cooling energy storage temperature control system according to an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of an immersion liquid-cooled energy storage temperature control system implemented in the present invention. DETAILED DESCRIPTION

[0040] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

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

[0042] Embodiment 1

[0043] like Figure 1 As shown, this embodiment provides a control method for an immersion liquid-cooled energy storage temperature control system, comprising the following steps: calculating the battery pack temperature difference based on the heat energy transfer relationship between the battery pack and the immersion coolant; determining the 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 and the temperature control strategy of a single lithium battery in the battery pack 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: According to the cooling system structure design, and based on the law of conservation of energy, a heat transfer relationship is established between the battery pack and the immersed coolant, the temperature difference of the battery pack is calculated, and a temperature control strategy for the energy storage system is provided 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 with known lithium battery parameters. i , battery reaction heat Q j , Battery polarization heat Q k And the battery side reaction heat Q t get;

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

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

[0049] According to Newton's law of cooling, the total heat dissipated by the battery can be obtained as: Q s =hA(T b -T f ), where 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 coolant temperature;

[0050] From the above, we can see 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, and the temperature difference of the battery pack is greater than the preset safety threshold, the coolant in the cooling system is immersed into the energy storage system through the injection hole;

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

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

[0055] When the heat generated by the battery pack is ≤ the heat dissipated by the battery pack, the temperature difference of the battery pack is ≤ the preset safety threshold, the coolant in the cooling system is not sprayed and the existing coolant is not discharged.

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

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

[0058] The iterative dynamic programming algorithm in S2 sets the temperature T of the first lithium battery near the injection hole b,1 And the nth lithium battery temperature T b.n The energy consumed by the cooling system P is used as the control output, and the coolant flow rate u is used as the control quantity.

[0059] Because for the battery pack, the temperature of the corresponding coolant will rise after each battery is cooled, and each time a battery is cooled, the temperature of the coolant gathered 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 coolant temperature will become higher and higher, thereby affecting the temperature of the battery, causing the battery temperature to become higher and higher.

[0060] The temperature difference between the first battery and the last battery can represent the temperature distribution in the battery pack. Therefore, the energy consumption P of the cooling system is calculated based on 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 proportional coefficient; Where C is equal to the total amount of coolant injected.

[0062] S3: Taking the coolant flow rate as the control variable, the temperature of the energy storage system is controlled by designing a controller;

[0063] The specific process of designing the controller in S3 is as follows Figure 2 As shown, the control of the coolant injection switch in the cooling system, the control of the coolant injection flow rate u and the control of the coolant injection time t are completed through the controller.

[0064] in

[0065] Three specific control models are described as follows:

[0066] Coolant injection switch control model:

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

[0068] When T d >T t When the heat generated by the battery pack is greater than the heat dissipation, f s =1, indicating that the coolant injection is turned on; when T d ≤T t And the heat generated by the battery pack is greater than the heat dissipation, or T d ≤T t When the heat generated by the battery pack is less than or equal to the heat dissipation, f s =0, which means turning off the coolant injection.

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

[0070] Coolant injection flow rate control model:

[0071] A proportional-integral-derivative (PID) controller is used to accurately control the injection flow rate of the coolant. Assume that the target flow rate is u t , the actual flow rate is u a .

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

[0073] Among them, K p , K i , K d They are proportional, integral and differential coefficients respectively. By adjusting these three coefficients, the coolant flow rate can be adjusted quickly and accurately, reducing the overshoot and steady-state error of the system.

[0074] Coolant 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. Assume that the battery pack temperature during cooling is T b , after cooling, the temperature is T a , the target temperature is T t .

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

[0077] S4: After the coolant immerses the top surface of the battery pack, the real-time temperature of the battery pack is obtained to achieve the effect of the temperature control strategy. The coolant enters the condenser after being compressed by the compressor, transfers the heat to the outside air and then condenses. After condensation, it is depressurized by the throttle valve and enters the evaporator to absorb heat, realizing the cycle cooling process, such as Figure 3 shown.

[0078] Therefore, the present invention calculates the temperature difference of the battery pack, provides a temperature control strategy for the energy storage system based on a preset safety threshold, links the coolant flow rate in the cooling pipe with the battery pack temperature, and predicts the total amount of coolant sprayed and the immersion spray time according to the temperature of the battery pack, thereby completing the precise control of the temperature of the energy storage system, combining the temperature control system with the actual operating status and temperature of the battery pack, and realizing the constraint of the battery pack temperature and the accurate estimation of energy consumption.

[0079] Embodiment 2

[0080] like Figure 4 As shown, this embodiment also provides an immersion liquid-cooled energy storage temperature control system, the system includes a detection module, and the detection module obtains battery temperature, ambient temperature, battery charge, battery status, and battery health rate based on the built-in sensor of the lithium battery.

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

[0082] The system also includes a control module, which completes the startup of the cooling system based on the control strategy and determines the energy consumption P of the cooling system and its startup time t based on the detection result of the detection module.

[0083] The present invention calculates the temperature difference of the battery pack according to the cooling system structure design, provides a temperature control strategy, obtains the battery pack parameters, controls the temperature change of the battery pack, takes the coolant flow rate as the control quantity, and completes the control of the temperature of the energy storage system by designing a controller. The present invention calculates the temperature difference of the battery pack and provides a temperature control strategy for the energy storage system based on a preset safety threshold. The coolant flow rate in the cooling pipe is linked to the battery pack temperature, and the total amount of coolant sprayed and the time of immersion spraying are predicted based on the temperature of the battery pack, so as to complete the precise control of the temperature of the energy storage system, combine the temperature control system with the actual operating state and temperature of the battery pack, and realize the constraint of the battery pack temperature and the accurate estimation of energy consumption.

[0084] The immersion liquid-cooled energy storage temperature control system and control method provided by the present invention calculate the temperature difference of the battery pack, provide a temperature control strategy for the energy storage system based on a preset safety threshold, link the coolant flow rate in the cooling pipe with the battery pack temperature, and predict the total amount of coolant sprayed and the immersion spraying time according to the temperature of the battery pack, thereby completing the precise control of the temperature of the energy storage system, combining the temperature control system with the actual operating state and temperature of the battery pack, and realizing the constraint of the battery pack temperature and the accurate estimation of energy consumption.

[0085] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A control method for an immersion liquid-cooled energy storage temperature control system, characterized in that: The following steps are involved: Calculating the battery pack temperature difference based on the heat energy 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; The battery pack temperature is obtained by 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; The immersion liquid-cooled energy storage temperature control system is controlled based on the coolant flow rate and the battery pack temperature.

2. The control method of the immersion liquid cooling energy storage temperature control system according to claim 1, characterized in that: The battery pack temperature difference includes: the amount of heat generated by the battery pack and the amount of heat dissipated by the battery pack; The calculation expression of the heat dissipation of the battery pack is: Q s =hA(T b -T f ) 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 coolant temperature.

3. The control method of the immersion liquid cooling energy storage temperature control system according to claim 2 is characterized in that: Temperature control strategies include: 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 coolant in the cooling system is immersed into the energy storage system through the injection hole; 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 coolant in the cooling system is not sprayed; 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 coolant in the energy storage system is discharged from the discharge pipe; 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, the coolant in the cooling system is not sprayed and the existing coolant is not discharged.

4. The control method of the immersion liquid cooling energy storage temperature control system according to claim 3 is characterized in that: The battery pack parameters include battery real-time temperature, ambient temperature, battery charge, battery status and battery health rate.

5. The control method of the immersion liquid cooling energy storage temperature control system according to claim 4, characterized in that: The process of controlling the temperature change of the battery pack based on the battery pack parameters of a single lithium battery in the battery pack and the temperature control strategy includes: Calculate the energy consumed by the cooling system based on the temperature of the first lithium battery and the temperature of the last lithium battery near the injection hole; Calculating the total amount of coolant sprayed based on the energy consumed by the cooling system and the coolant flow rate; A battery pack temperature change is controlled based on the coolant injection total amount.

6. The control method of the immersion liquid cooling energy storage temperature control system according to claim 5, characterized in that: The calculation expression of the total amount of coolant injection is: In the formula, C represents the total amount of coolant sprayed, P represents the energy consumption of the cooling system, u represents the coolant flow rate, T b,1 represents the temperature of the first lithium battery near the injection hole, T b.n Represents the nth lithium battery temperature, and K is the energy consumption proportional coefficient.

7. An immersion liquid cooling energy storage temperature control system, characterized in that: A control method for implementing the immersion liquid-cooled energy storage temperature control system according to any one of claims 1 to 6, the system comprising: A detection module is used to obtain battery pack parameters based on the built-in sensor of the lithium battery; 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; The control module is used to complete the startup of the cooling system based on the temperature control strategy and determine the energy consumption and startup time of the cooling system.

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