Liquid-cooled gas cooler and method for controlling flow of coolant liquid

Abstract

The application belongs to the technical field of heating, ventilation, refrigeration and heat pump, and discloses a liquid-cooled gas cooler and a cooling liquid flow control method thereof. l The cooling liquid heat exchange channel inlet of the first plate heat exchanger in the N plate heat exchangers is connected with the cooling liquid inlet, the cooling liquid heat exchange channel inlets of the second to Nth plate heat exchangers are respectively connected with the cooling liquid inlet through stop valves, the cooling liquid heat exchange channel outlets of the Nth plate heat exchangers are respectively connected with the cooling liquid outlet through three-way valves, the cooling liquid heat exchange channel inlet of the Nth+1 plate heat exchanger is connected with the cooling liquid outlet, the cooling liquid heat exchange channel outlet of the Nth plate heat exchanger is connected with the cooling liquid outlet, and the refrigerant inlet is sequentially connected with the refrigerant outlet through the refrigerant heat exchange channels of the Nth to first plate heat exchangers. l The technical scheme can improve the overall system performance.

Description

Technical Field

[0001] This invention belongs to the field of heating, ventilation, refrigeration and heat pump technology, and relates to a transcritical carbon dioxide secondary loop thermal management system, and particularly to a liquid-cooled gas cooler and its coolant flow control method. Background Technology

[0002] The application and popularization of new energy electric vehicles have alleviated the problems of environmental pollution and fossil energy shortage; among them, due to the lack of recyclable engine waste heat, independent heat pump systems have become an indispensable part of new energy electric vehicles.

[0003] Currently, electric vehicles primarily use R134a heat pump air conditioning systems. However, R134a has poor heating performance in winter, so to ensure passenger comfort, electric vehicles typically use PTC auxiliary electric heating to provide additional heat to the cabin. Furthermore, R134a has a high GWP (Global Power Wishlist) of 1430, making it very environmentally unfriendly and facing complete phase-out. Carbon dioxide, as a natural refrigerant, has become one of the most ideal alternative refrigerants due to its non-toxic, non-polluting, and inexpensive characteristics. In addition, compared to PTC auxiliary electric heating, carbon dioxide heat pumps offer superior heating performance, saving a significant amount of battery power in winter and indirectly extending the driving range of electric vehicles.

[0004] In existing technologies, most automotive air conditioning systems are direct expansion systems; in these systems, the refrigerant directly enters the passenger compartment for heat exchange. If a leak occurs, passengers may be directly exposed to the refrigerant. For transcritical carbon dioxide systems, high operating pressures can lead to excessively high carbon dioxide concentrations in the cabin. Against this backdrop, an increasing number of researchers are beginning to study indirect systems, hoping to develop a more efficient thermal management system for new energy vehicles.

[0005] The transcritical carbon dioxide secondary loop thermal management system is an indirect system as described above. During operation, the carbon dioxide refrigerant exchanges heat with the coolant, and then the coolant exchanges heat with the air to achieve the purpose of thermal management of the vehicle compartment or components. Unlike the direct system, the heat exchange between carbon dioxide and coolant takes place in a liquid-cooled gas cooler. The liquid-cooled gas cooler is generally a plate heat exchanger, which is a high-efficiency heat exchanger composed of a certain number of metal plates stacked together. Thin rectangular channels are formed between the various plates, and the refrigerant and coolant flow through the channels and exchange heat through the plates. It is an ideal heat exchanger for liquid-liquid heat exchange. Further explanation reveals that the transcritical carbon dioxide secondary loop system has numerous optimizable parameters. Among them, the optimization design of the coolant flow rate is an additional parameter in the secondary loop, distinct from that of the direct system, and the coolant flow rate has a significant impact on the performance of the secondary loop system, possessing an optimal value similar to the optimal discharge pressure. Specifically, due to the large temperature glide in the gas cooler, the system requires a small coolant flow rate to provide a large temperature difference between the inlet and outlet of the heat exchanger under heating conditions, while under cooling conditions, the temperature difference between the inlet and outlet is smaller, and a large coolant flow rate is beneficial for heat exchange. The significant differences between the two operating conditions make it impossible to achieve suitable pressure drop and good heat exchange under different operating conditions in the same simple liquid-cooled gas cooler (LCGC).

[0006] In summary, for transcritical carbon dioxide secondary loop thermal management systems, in order to provide excellent heat exchange under reasonable pressure drop in various operating conditions and ensure the system operates at optimal performance, a new and effective liquid-cooled gas cooler for transcritical carbon dioxide secondary loop thermal management systems of new energy vehicles is urgently needed. Summary of the Invention

[0007] The purpose of this invention is to provide a liquid-cooled gas cooler and a method for controlling its coolant flow rate, thereby solving one or more of the aforementioned technical problems. The technical solution provided by this invention addresses the significant difference in suitable coolant flow rate under heating and cooling conditions in a transcritical carbon dioxide secondary loop thermal management system. By employing different heat exchanger arrangements under different conditions, it solves the problem of simultaneously achieving suitable pressure drop and good heat exchange in a single LCGC, thus improving overall system performance. Furthermore, this invention provides an efficient control method for adjusting the coolant flow rate, simplifying the parameter adjustment process.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a liquid-cooled gas cooler, comprising: N plate heat exchangers, each plate heat exchanger having the same number of plates; wherein,

[0010] The liquid-cooled gas cooler is provided with a coolant inlet, a coolant outlet, a refrigerant inlet, and a refrigerant outlet;

[0011] The inlet of the cooling liquid heat exchange channel of the first plate heat exchanger among the N plate heat exchangers is connected to the cooling liquid inlet, and the inlets of the cooling liquid heat exchange channels of the second to Nth plate heat exchangers are respectively connected to the cooling liquid inlet via shut-off valves.

[0012] The Nth of the N plate heat exchangers l The coolant heat exchange channel outlets of each plate heat exchanger are respectively connected to the coolant outlet and the Nth... l The inlets of the cooling liquid heat exchange channels of the +1 plate heat exchanger are connected, and the outlets of the cooling liquid heat exchange channels of the Nth plate heat exchanger are connected to the cooling liquid outlets, where 1 ≤ N. l <N;

[0013] The refrigerant inlet is connected to the refrigerant outlet via the refrigerant heat exchange channel from the Nth plate heat exchanger to the first plate heat exchanger.

[0014] A further improvement of the present invention is that,

[0015] In heating mode, all three-way valves are connected to the coolant outlet and all shut-off valves are opened, allowing the refrigerant to flow through each plate heat exchanger in parallel.

[0016] A further improvement of the present invention is that,

[0017] In cooling mode, all three-way valves are connected to the inlet of the coolant heat exchange channel of each plate heat exchanger and all shut-off valves are closed. The refrigerant flows through each plate heat exchanger in series.

[0018] A further improvement of the present invention is that the design steps for the number N of plate heat exchangers include:

[0019] Get the total number of preset plates N 板 The initial value N of the number of plate heat exchangers 初始 The number of plate heat exchangers N is obtained by iterative calculation; where,

[0020] During iterative calculations, for each iteration N 初始 All values ​​need to be determined before N is calculated. 板 Can it be N 初始 Divisible by N; if not divisible by N, then for N... 初始 Increment by 1 until the result is divisible by N; for each N divisible by N... 板 N 初始Based on the inlet parameters of the heat exchanger, the heat exchange capacity, pressure drop, and heat exchange pressure drop efficiency value of the LCGC are calculated. The heat exchange pressure drop efficiency value calculated in each new iteration is compared with the maximum value in previous iterations, and the larger value obtained from the comparison is used to replace the maximum value. After the iteration termination condition is reached, the number of heat exchangers corresponding to the maximum heat exchange pressure drop efficiency value is the number of plate heat exchangers N.

[0021] A further improvement of the present invention is that the iteration termination condition is that the number of plate heat exchangers is not less than N. 板 / 3.

[0022] A further improvement of the present invention is that, for each divisible by N... 板 N 初始 In the steps of calculating the heat exchange capacity, pressure drop, and heat exchange pressure drop efficiency value of LCGC based on the heat exchanger inlet parameters,

[0023] The inlet parameters of LCGC remain unchanged during each iteration calculation. The inlet parameters include refrigerant inlet temperature, inlet pressure, inlet enthalpy, refrigerant flow rate, coolant flow rate, and coolant inlet temperature.

[0024] The formula for calculating the heat exchange of LCGC is as follows:

[0025] Q x =m r *(h r,out -h r,in ) = m c *C p,c (T c,out -T c,in );

[0026]

[0027] In the formula, m r It is the refrigerant flow rate; h r,in and h r,out These are the inlet and outlet enthalpies of the refrigerant, respectively; A j,i S is the heat transfer coefficient in each heat exchange unit. j,i It is the heat exchange area of ​​the heat exchanger, T r,j,i and T c,j,i These are the temperatures of the refrigerant and coolant in the heat exchanger, respectively.

[0028] A further improvement of the present invention is that, for each divisible by N... 板 N 初始 In the steps of calculating the heat exchange capacity, pressure drop, and heat exchange pressure drop efficiency value of LCGC based on the heat exchanger inlet parameters,

[0029] The expression for calculating the voltage drop ΔP of LCGC is as follows:

[0030]

[0031] In the formula, σ is the flow length of the refrigerant; ρ is the density of the refrigerant; ξ is the dynamic viscosity of the refrigerant; Pn and ρ n ξ n m n These are the rated pressure drop, rated density, rated dynamic viscosity, and rated flow rate, respectively; id is set to 0, and iv and im are exponential parameters related to viscosity and mass flow rate, respectively.

[0032] A further improvement of the present invention is that, for each divisible by N... 板 N 初始 In the steps of calculating the heat exchange capacity, pressure drop, and heat exchange pressure drop efficiency value of LCGC based on the heat exchanger inlet parameters,

[0033] The formula for calculating the heat exchange pressure drop efficiency value R of LCGC is as follows:

[0034]

[0035] In the formula, w1, w2, d1, and d2 are constants; w is the heat exchange rate Q. x The weighting coefficients for the pressure drop ΔP; d is an exponential constant.

[0036] The present invention provides a method for controlling the coolant flow rate of a liquid-cooled gas cooler, comprising:

[0037] An RBF neural network PID controller is used for coolant flow control. The input value of the RBF neural network PID controller is the target coolant flow rate, and the output value is the water pump motor power of the LCGC coolant circuit. The relationship between the water pump motor power and the coolant flow rate Q is expressed as follows:

[0038]

[0039] In the formula, T is the power of the water pump motor, and η b H represents the pump shaft efficiency, and H represents the pump head.

[0040] A further improvement of the present invention is that the RBF neural network PID controller is an RBF neural network nested within a traditional PID controller; wherein,

[0041] The RBF neural network consists of three layers: an input layer, a hidden layer, and an output layer. The neurons in the hidden layer are composed of activation functions, and the activation functions are Gaussian functions.

[0042] The process of adjusting PID parameters in the RBF neural network uses gradient descent to iteratively optimize the weights of the hidden layer, the radial basis vector, and the width of the Gaussian function.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The liquid-cooled gas cooler provided by this invention adopts a combination structure of plate heat exchanger, three-way valve and shut-off valve. By adjusting the three-way valve and shut-off valve, the series and parallel connection can be switched. The heat exchanger adopts different arrangement methods under different operating conditions, which solves the problem that it is impossible to achieve a suitable pressure drop and good heat exchange in a single LCGC at the same time, so as to improve the overall system performance.

[0045] In this invention, the series and parallel connection modes can be switched by adjusting the three-way valve and the shut-off valve. In heating mode, a low-flow parallel arrangement is prioritized to provide a large temperature difference between the heat exchanger inlet and outlet, meeting winter heating needs. In cooling mode, a high-flow series arrangement is prioritized to reduce pressure drop and improve heat exchange efficiency. Further, this invention allows for low-flow coolant operation in heating mode and high-flow operation in cooling mode. This solves the problem of insufficient pressure drop and good heat exchange in liquid-cooled gas coolers caused by the difference in suitable coolant flow rates under heating and cooling conditions in the transcritical carbon dioxide secondary loop thermal management system, thus improving overall system performance.

[0046] In this invention, based on the comparison of heat exchange and pressure drop of LCGC under different arrangements of the same plates, the LCGC arrangement with the highest comprehensive energy efficiency ratio of heat exchange and pressure drop is found through iterative optimization.

[0047] In this invention, after determining the LCGC (Liquid Coolant Controller) layout in the system, the optimal coolant flow rate will change as the system operating state and environmental conditions change. Flow control is implemented for different coolant flow rate requirements, enabling the system to quickly and efficiently switch to the required coolant flow rate. Specifically, considering the unique thermodynamic properties of CO2 refrigerant, different coolant flow rate control strategies, i.e., different heat exchange architectures, are required for the LCGC under different system operating modes. When changes in vehicle operating state or environmental conditions cause changes in the optimal coolant flow rate, the control accuracy and stability of the system are improved by nesting an RBF (Radio-Resistant Filter) neural network into a simple PID controller, simplifying the parameter tuning process and enabling rapid adjustment of the coolant flow rate. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below; obviously, the drawings described below are some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0049] Figure 1This is a schematic diagram of the structure of a liquid-cooled gas cooler provided in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the series arrangement of liquid-cooled gas coolers in an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of the parallel arrangement of liquid-cooled gas coolers in an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram illustrating the design logic of the number of plate heat exchangers in a liquid-cooled gas cooler according to an embodiment of the present invention.

[0053] Figure 5 This is a schematic diagram of a transcritical carbon dioxide secondary loop thermal management system provided in an embodiment of the present invention;

[0054] Figure 6 This is a schematic block diagram of the PID control logic for coolant flow control in an embodiment of the present invention;

[0055] In the diagram, 1. Compressor; 2. Gas cooler; 3. Regenerator; 4. Shut-off valve; 5. Expansion valve; 6. Evaporator; 7. Receiver tank; 8. Cold circuit water pump; 9. Cold circuit water tank; 10. First four-way valve; 11. Indoor heat exchanger; 12. Flow meter; 13. Hot circuit water pump; 14. Second four-way valve; 15. Hot circuit water tank; 16. Outdoor heat exchanger; 17. RBF neural network PID controller. Detailed Implementation

[0056] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0057] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0058] The present invention will now be described in further detail with reference to the accompanying drawings:

[0059] Please see Figures 1 to 3 The present invention provides a liquid-cooled gas cooler comprising: N plate heat exchangers, each plate heat exchanger having the same number of plates; wherein,

[0060] The liquid-cooled gas cooler is provided with a coolant inlet, a coolant outlet, a refrigerant inlet, and a refrigerant outlet;

[0061] The inlet of the cooling liquid heat exchange channel of the first plate heat exchanger among the N plate heat exchangers is connected to the cooling liquid inlet, and the inlets of the cooling liquid heat exchange channels of the second to Nth plate heat exchangers are respectively connected to the cooling liquid inlet via shut-off valves.

[0062] The Nth of the N plate heat exchangers l The coolant heat exchange channel outlets of each plate heat exchanger are respectively connected to the coolant outlet and the Nth... l The inlets of the cooling liquid heat exchange channels of the +1 plate heat exchanger are connected, and the outlets of the cooling liquid heat exchange channels of the Nth plate heat exchanger are connected to the cooling liquid outlets, where 1 ≤ N. l <N;

[0063] The refrigerant inlet is connected to the refrigerant outlet via the refrigerant heat exchange channels of the Nth to the first plate heat exchangers in sequence.

[0064] In the technical solution provided by the embodiments of the present invention, the series and parallel switching can be realized by adjusting the three-way valve and the shut-off valve, so that the system can operate with a small flow rate of coolant in heating mode and a large flow rate in cooling mode. This can solve the problem that the difference in the appropriate coolant flow rate in the transcritical carbon dioxide secondary loop thermal management system under heating and cooling conditions makes it impossible to achieve a suitable pressure drop and good heat exchange in the liquid-cooled gas cooler, thereby improving the overall system performance.

[0065] Specifically, such as Figure 2 As shown, all three-way valves are opened to the right and all shut-off valves are closed, and the refrigerant flows through each plate heat exchanger in series.

[0066] Specifically, such as Figure 3 As shown, all three-way valves are opened upwards and all shut-off valves are activated, allowing the refrigerant to flow sequentially through each plate heat exchanger in parallel.

[0067] Explanation of the principle of the technical solution of the present invention: The liquid-cooled gas cooler disclosed in the present invention can preferentially adopt a parallel arrangement with small flow rate in heating mode to provide a large temperature difference at the inlet and outlet of the heat exchanger to meet the heating demand in winter; in cooling mode, it can preferentially adopt a series arrangement with large flow rate to reduce pressure drop to a certain extent and improve heat exchange effect.

[0068] Please see Figure 4 In a further preferred embodiment of the present invention, the number of plate heat exchangers in the liquid-cooled gas cooler is optimized, and the specific steps are as follows:

[0069] Step 1: Determine the total number of plates y in the LCGC according to different application scenarios, i.e., the preset total number of plates; use the number x of the plate heat exchangers to be determined in the LCGC as the initial value for iteration, generally set to 1 initially; specifically, for a particular new energy vehicle transcritical carbon dioxide secondary loop thermal management system, in the early design stage, it is necessary to determine the external geometric dimensions of the LCGC used, etc., based on the system heat exchange requirements and the spatial arrangement of the vehicle's thermal management components, and calculate the plate requirements to meet the heat exchange under various operating conditions based on heat exchange simulation, so as to determine the appropriate number of plates for the plate heat exchanger; among them, for the LCGC, a larger size and a larger number of plates will be beneficial for sufficient heat exchange if the pressure drop is permissible, but due to the limited space and weight restrictions of the air conditioning system on new energy vehicles, it is necessary to select the external size and volume according to the actual situation.

[0070] Step 2: For each iteration of x value, it is necessary to determine whether y is divisible by x before calculation. If it is not divisible, x is incremented by 1 until it is divisible, in order to ensure that the number of heat exchanger plates is consistent.

[0071] Step 3: For each number of heat exchangers x that is divisible by y, calculate the heat transfer capacity, pressure drop, and heat exchange pressure drop efficiency value of the LCGC based on the heat exchanger inlet parameters; where,

[0072] The inlet parameters of LCGC remain unchanged during each iteration calculation. The inlet parameters include refrigerant inlet temperature, inlet pressure, inlet enthalpy, refrigerant flow rate, coolant flow rate, and coolant inlet temperature.

[0073] 1) The formula for calculating the heat exchange of LCGC is:

[0074] Q x =m r *(h r,out -h r,in ) = m c *C p,c (T c,out -T c,in );

[0075]

[0076] In the formula, m r It is the refrigerant flow rate; h r,in and h r,out These are the inlet and outlet enthalpies of the refrigerant, respectively; A j,i S is the heat transfer coefficient in each heat exchange unit. j,i It is the heat exchange area of ​​the heat exchanger, T r,j,i and T c,j,i These are the temperatures of the refrigerant and coolant in the heat exchanger, respectively.

[0077] 2) When calculating the pressure drop ΔP of the LCGC, the user needs to determine the maximum refrigerant flow rate (m) based on the system settings. l To avoid calculation errors caused by abnormal refrigerant flow, the pressure drop is calculated in segments based on the refrigerant flow range; among which,

[0078] When the refrigerant flow rate m>m l When the pressure drop ΔP is at that time, the expression for calculating it is:

[0079]

[0080] When the refrigerant flow rate is within the normal threshold and the regularization condition is met, the expression for calculating the pressure drop ΔP is:

[0081]

[0082] When the refrigerant flow rate m < -m l When the pressure drop ΔP is at that time, the expression for calculating it is:

[0083]

[0084] To simplify calculations, the three formulas can be integrated into one.

[0085]

[0086] In the formula, σ is the flow length of the refrigerant, ρ is the density of the refrigerant, ξ is the dynamic viscosity of the refrigerant, and Pn, ρ n ξ n m nThese are the rated pressure drop, rated density, rated dynamic viscosity, and rated flow rate, respectively. They are all related to the inlet conditions and the parameters of the plate heat exchanger, and exist as constants in the calculation. For refrigerant, id is generally taken as 0, and iv and im are exponential parameters related to viscosity and mass flow rate, respectively.

[0087] 3) When the number of plate heat exchangers increases, the heat transfer capacity Q increases due to the increased heat transfer coefficient. x The pressure drop ΔP will also increase due to the increased flow resistance. To achieve the optimization goal of large heat exchange and small pressure drop, a balance needs to be struck between the two to find a suitable plate arrangement. The heat exchange pressure drop efficiency value R is an indicative parameter calculated by substituting the heat exchange and pressure drop into the cost formula. The larger the value, the higher the optimization degree of LCGC. Its calculation expression is as follows:

[0088]

[0089] In the formula, w1, w2, d1, and d2 are constants, and w is the weighting coefficient for heat exchange and pressure drop, representing the degree of importance attached to heat exchange and pressure drop. Q can be controlled by adjusting the value of w. x The trade-off relationship between ΔP and d is an exponential constant. Through iteration, the optimal value among all plate replacement numbers can be obtained, maximizing the R value of LCGC.

[0090] The R value calculated in each new iteration is compared with the maximum value of previous iterations, and the larger value is used to replace the maximum value. The iteration terminates when the number of plate heat exchangers x is not less than y / 3. This is because any plate heat exchanger requires at least 3 plates. A value of x larger than the iteration termination condition will not match reality and will lose the meaning of the iteration. If x is less than y / 3, the process is repeated from step 3 until the iteration termination point is reached, that is, the arrangement of LCGC is determined and the final number is obtained.

[0091] In the technical solution provided by this invention, different water flow control strategies, i.e., different heat exchange architectures, are adopted under different system operating modes. Parallel arrangement is preferred in heating mode, while series arrangement is preferred in cooling mode. The LCGC arrangement with the highest comprehensive energy efficiency ratio (R value) for heat exchange and pressure drop is found through iterative optimization. After determining the LCGC arrangement in the system, the optimal coolant flow rate will change when the system operating state and environmental conditions change. Flow control is performed for different coolant flow rate requirements, enabling the system to quickly and efficiently switch to the required coolant flow rate.

[0092] Please see Figure 5This invention provides a transcritical carbon dioxide secondary loop thermal management system, comprising: a compressor 1, a gas cooler 2, a regenerator 3, a shut-off valve 4, an expansion valve 5, an evaporator 6, a liquid storage tank 7, a cold loop water pump 8, a cold loop water tank 9, a first four-way valve 10, an indoor heat exchanger 11, a flow meter 12, a hot loop water pump 13, a second four-way valve 14, a hot loop water tank 15, and an outdoor heat exchanger 16; wherein,

[0093] Gas cooler 2 is the liquid-cooled gas cooler disclosed in the above embodiments of the present invention; the gas cooler 2 provides a function similar to the condenser in a conventional refrigerant system, for heat exchange between refrigerant and coolant;

[0094] The regenerator 3 is used for reheating the refrigerant, and the refrigerant at the outlet of the gas cooler and the refrigerant at the outlet of the evaporator achieve internal heat exchange, thereby improving the refrigeration performance.

[0095] The evaporator 6 is used for heat exchange between the refrigerant and the coolant, and the coolant is cooled in the evaporator;

[0096] The indoor heat exchanger 11 includes a main heat exchanger and an auxiliary heat exchanger, used to exchange heat between the coolant and the air and to supply air to the carriage.

[0097] The outdoor heat exchanger 16 is used for heat exchange between the coolant and the outdoor air.

[0098] The shut-off valve 4 is used to bypass the regenerator in heating mode to avoid the regenerator's impact on heating performance.

[0099] The aforementioned transcritical carbon dioxide secondary loop thermal management system can switch between heating and cooling modes via a combination of the first four-way valve 10 and the second four-way valve 14; wherein,

[0100] In heating mode, the high-temperature, high-pressure steam output from compressor 1 flows into gas cooler 2, releases heat to the coolant, and then enters regenerator 3. At this time, shut-off valve 4 is open, and regenerator 3 no longer provides a heat recovery effect. The high-temperature, high-pressure steam from regenerator 3 is throttled to a low-temperature, low-pressure state by expansion valve 5 (exemplarily, an electronic expansion valve), enters evaporator 6, absorbs heat from the coolant, and then returns to the suction port of compressor 1 via shut-off valve 4 after passing through storage tank 7. The coolant in the heat circuit absorbs heat from gas cooler 2, flows through flow meter 12 into heat circuit water tank 15, and then enters indoor heat exchanger 11 through the bc channel of the first four-way valve 10 to heat the air. After passing through the cb channel of the second four-way valve 14, it is pumped by heat circuit water pump 13 to the inlet of gas cooler 2. After the coolant in the cold circuit releases heat in the evaporator 6, it enters the outdoor heat exchanger 16 through the da channel of the second four-way valve 14 to absorb ambient heat. Then it enters the cold circuit water tank 9 through the ad channel of the first four-way valve 10, flows through the cold circuit water pump 8, and returns to the inlet of the evaporator 6.

[0101] In cooling mode, the high-temperature, high-pressure steam output from compressor 1 flows into gas cooler 2, releases heat to the coolant, and then enters regenerator 3. At this time, shut-off valve 4 is closed, and regenerator 3 provides a heat recovery effect. The steam released in regenerator 3 is throttled to a low-temperature, low-pressure state through expansion valve 5, enters evaporator 6 to absorb heat from the coolant, passes through liquid storage tank 7, enters regenerator 3 to be heated, and then returns to the suction port of compressor 1. The coolant in the hot circuit absorbs heat from gas cooler 2, flows through flow meter 12 into hot circuit water tank 15, and then enters outdoor heat exchanger 16 through the ba channel of first four-way valve 10 to release heat to the environment. After passing through the ad channel of second four-way valve 14, it is pumped by hot circuit water pump 13 to the inlet of gas cooler 2. After the coolant in the cold circuit releases heat in the evaporator 6, it enters the indoor heat exchanger 11 through the DC channel of the second four-way valve 14 to cool the air, and then enters the cold circuit water tank 9 through the CD channel of the first four-way valve 10. After flowing through the cold circuit water pump 8, it returns to the inlet of the evaporator 6.

[0102] In this embodiment of the invention, a parallel arrangement with low flow rates is preferred in heating mode, while a series arrangement with high flow rates is preferred in cooling mode. This solves the problem that the difference in suitable coolant flow rates under heating and cooling conditions in the transcritical carbon dioxide secondary loop thermal management system cannot achieve appropriate pressure drop and good heat exchange in a single LCGC with simple flow control, thus improving the overall system performance. Specifically, current research on transcritical carbon dioxide secondary loop thermal management systems is still relatively limited. In the few studies on coolant flow rates, the system still uses two different LCGCs to meet the heat exchange requirements of heating and cooling respectively. This invention provides an integrated solution for LCGC structure design. Furthermore, since coolant flow rate has a significant impact on the performance of the transcritical carbon dioxide thermal management system, the system operation requires fast and effective flow control. By embedding an RBF neural network into a simple PID controller to dynamically adjust the coolant flow rate, the problem of time-consuming, labor-intensive, and inefficient traditional PID parameter tuning process is solved, simplifying the control process.

[0103] Please see Figure 6 In this embodiment of the invention, an RBF neural network PID controller is used for coolant flow control. The input value of the RBF neural network PID controller is the target coolant flow rate, and the output value is the power of the water pump motor in the LCGC coolant circuit. The conversion relationship between water pump speed and coolant flow rate is described as follows:

[0104]

[0105] In the formula, T is the motor power of the water pump, and η b H represents the shaft efficiency of the water pump, and H represents the head of the water pump.

[0106] Further illustratively, this embodiment of the invention demonstrates that the RBF neural network PID controller nests an RBF neural network within a traditional PID controller, simplifying the PID parameter tuning process; wherein,

[0107] RBF neural networks consist of three layers: an input layer, a hidden layer, and an output layer, where i = [i1, i2, ..., i...]. n ] T These are the input values ​​of the RBF neural network. The neurons in the hidden layer are composed of activation functions; in this system, the most commonly used Gaussian function is employed as the activation function.

[0108]

[0109] In the formula, a j Let v = [v1, v2, ..., vj] be the output value of the j-th neuron in the hidden layer. n Let h be the radial basis vector of the Gaussian function, where h = [h1, h2, ..., h]. n ] T Let be the width of the Gaussian function of the j-th neuron. Between the hidden layer and the output layer, the weight function c = [c1, c2, ..., c3] is used. n ] T The connection is made so that the neural network outputs y. m =c1a1+c2a2+…+c m a m ;

[0110] The process of adjusting PID parameters in an RBF neural network typically uses gradient descent to iteratively optimize the weights of the hidden layer, the radial basis vector, and the width of the Gaussian function; the iterative equation is as follows:

[0111] s j (t)=s j-1 (t)+Δs(t)+ε(s j (t-1)-s j (t-2));

[0112] In the formula, s = v, c, h, and ε are the momentum factors of the neuron;

[0113] Specifically, regarding the adjustment of PID parameters,

[0114]

[0115] In the formula, b(t) is the successive output result of the PID, and γ is the learning rate of the PID parameters. According to the above iterative formula, the parameters of the PID can be quickly adjusted to achieve efficient control of the coolant flow rate.

[0116] In the technical solution provided by this invention, considering the unique thermodynamic properties of CO2 refrigerant, LCGC needs to adopt different coolant flow control strategies, i.e., different heat exchange architectures, under different system operating modes. Simultaneously, when changes in vehicle operating status or environmental conditions cause changes in the optimal coolant flow rate, by nesting an RBF neural network into a simple PID controller, the system's control accuracy and stability are improved, the parameter tuning process is simplified, and rapid adjustment of the coolant flow rate is achieved.

[0117] In summary, this invention discloses an optimized LCGC design structure and coolant flow control method for a transcritical carbon dioxide secondary loop thermal management system. The LCGC optimization scheme primarily compares the heat exchange and pressure drop of LCGCs with different plate arrangements. Through iterative optimization, it finds the LCGC with the highest overall energy efficiency ratio in terms of heat exchange and pressure drop. In heating mode, a parallel arrangement with low flow rate is preferred, while in cooling mode, a series arrangement with high flow rate is preferred. Furthermore, the suitable coolant flow rate differs significantly between heating and cooling conditions in the transcritical carbon dioxide secondary loop thermal management system. By embedding an RBF neural network into a simple PID controller, the problem of time-consuming, labor-intensive, and inefficient traditional PID parameter tuning is solved. This promotes the application and widespread use of carbon dioxide refrigerant, facilitates the development of secondary loop thermal management systems, and makes a significant contribution to environmental protection and alleviating the fossil fuel crisis.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A liquid-cooled gas cooler, characterized in that, include: There are N plate heat exchangers, each with the same number of plates; among them... The liquid-cooled gas cooler is provided with a coolant inlet, a coolant outlet, a refrigerant inlet, and a refrigerant outlet; The inlet of the cooling liquid heat exchange channel of the first plate heat exchanger among the N plate heat exchangers is connected to the cooling liquid inlet, and the inlets of the cooling liquid heat exchange channels of the second to Nth plate heat exchangers are respectively connected to the cooling liquid inlet via shut-off valves. The Nth of the N plate heat exchangers l The coolant heat exchange channel outlets of each plate heat exchanger are respectively connected to the coolant outlet and the Nth... l The inlets of the cooling liquid heat exchange channels of the +1 plate heat exchanger are connected, and the outlets of the cooling liquid heat exchange channels of the Nth plate heat exchanger are connected to the cooling liquid outlets, where 1 ≤ N. l <N; The refrigerant inlet is connected to the refrigerant outlet via the refrigerant heat exchange channels of the Nth to the first plate heat exchangers in sequence. in, In heating mode, all three-way valves are connected to the coolant outlet and all shut-off valves are opened, and the refrigerant flows through each plate heat exchanger in parallel. In cooling mode, all three-way valves are connected to the inlet of the coolant heat exchange channel of each plate heat exchanger and all shut-off valves are closed. The refrigerant flows through each plate heat exchanger in series. The design steps for the number N of plate heat exchangers include: Get the total number of preset plates N 板 The initial value N of the number of plate heat exchangers 初始 The number of plate heat exchangers N is obtained by iterative calculation; where, During iterative calculations, for each iteration N 初始 All values ​​need to be determined before N is calculated. 板 Can it be N 初始 Divisible by N; if not divisible by N, then for N... 初始 Increment by 1 until the result is divisible by N; for each N divisible by N... 板 N 初始 Based on the inlet parameters of the heat exchanger, the heat exchange capacity, pressure drop, and heat exchange pressure drop efficiency value of the liquid-cooled gas cooler LCGC are calculated; the heat exchange pressure drop efficiency value calculated in each new iteration is compared with the maximum value in previous iterations, and the larger value obtained from the comparison is used to replace the maximum value; after the iteration termination condition is reached, the number of heat exchangers corresponding to the maximum heat exchange pressure drop efficiency value is the number of plate heat exchangers N. The iteration termination condition is that the number of plate heat exchangers is not less than N. 板 / 3; For each divisible by N, 板 N 初始 In the steps of calculating the heat exchange capacity, pressure drop, and heat exchange pressure drop efficiency value of LCGC based on the heat exchanger inlet parameters, The inlet parameters of LCGC remain unchanged during each iteration calculation. The inlet parameters include refrigerant inlet temperature, inlet pressure, inlet enthalpy, refrigerant flow rate, coolant flow rate, and coolant inlet temperature. The formula for calculating the heat exchange of LCGC is as follows: Q x =m r *(h r,out -h r,in )=m c *C p,c (T c,out -T c,in ); In the formula, m r It is the refrigerant flow rate; h r,in and h r,out These are the enthalpy values ​​of the refrigerant inlet and outlet, respectively. The expression for calculating the voltage drop ΔP of LCGC is as follows: The formula for calculating the heat exchange pressure drop efficiency value R of LCGC is as follows: In the formula, w1, w2, d1, and d2 are constants; w is the heat exchange rate Q. x The weighting coefficients for the pressure drop ΔP; d is an exponential constant; A j,i S is the heat transfer coefficient in each heat exchange unit. j,i It is the heat exchange area of ​​the heat exchanger, T r,j,i and T c,j,i These are the temperatures of the refrigerant and coolant in the heat exchanger, respectively; ρ is the refrigerant density; ξ is the dynamic viscosity of the refrigerant; Pn, ρ n ξ n m n These are the rated pressure drop, rated density, rated dynamic viscosity, and rated flow rate, respectively; id is set to 0, and iv and im are exponential parameters related to viscosity and mass flow rate, respectively.

2. A method for controlling the coolant flow rate of a liquid-cooled gas cooler as described in claim 1, characterized in that, include: An RBF neural network PID controller is used for coolant flow control. The input value of the RBF neural network PID controller is the target coolant flow rate, and the output value is the water pump motor power of the LCGC coolant circuit. The relationship between the water pump motor power and the coolant flow rate Q is expressed as follows: In the formula, T is the power of the water pump motor, and η b H represents the pump shaft efficiency, and H represents the pump head.

3. The coolant flow control method according to claim 2, characterized in that, The RBF neural network PID controller is an RBF neural network nested within a traditional PID controller; wherein... The RBF neural network consists of three layers: an input layer, a hidden layer, and an output layer. The neurons in the hidden layer are composed of activation functions, and the activation functions are Gaussian functions. The process of adjusting PID parameters in the RBF neural network uses gradient descent to iteratively optimize the weights of the hidden layer, the radial basis vector, and the width of the Gaussian function.

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