Liquid-cooled gas cooler and cooling liquid flow control method thereof

Abstract

The invention belongs to the technical fields of heating, ventilation, refrigeration and heat pumps, and relates to a liquid-cooled gas cooler and a cooling liquid flow control method thereof. In the liquid-cooled gas cooler, a cooling liquid heat exchange channel inlet of a first plate-type heat exchanger among N plate-type heat exchangers is communicated with a cooling liquid inlet, and respective cooling liquid heat exchange channel inlets of a second to an Nth plate-type heat exchanger are each communicated with the cooling liquid inlet via a stop valve; a cooling liquid heat exchange channel outlet of an Nthl plate-type heat exchanger is separately communicated with a cooling liquid heat exchange channel inlet of an Nthl+1 plate-type heat exchanger and a cooling liquid outlet via a three-way valve, and a cooling liquid heat exchange channel outlet of the Nth plate-type heat exchanger is communicated with the cooling liquid outlet; and a refrigerant inlet is communicated with a refrigerant outlet via refrigerant heat exchange channels from the Nth to the first plate-type heat exchanger in sequence. The technical solution of the present invention improves overall system performance.

Description

Liquid-cooled gas cooler and cooling liquid flow control method thereof Technical Field

[0001] The present invention belongs to the technical field of heating, ventilation, refrigeration and heat pumps, and relates to a transcritical carbon dioxide secondary circuit thermal management system, in particular to a liquid-cooled gas cooler and a coolant flow control method thereof. Background Art

[0002] The application and popularization of new energy electric vehicles have alleviated the problems of environmental pollution and fossil energy shortages. 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's winter heating performance is poor, so to ensure passenger thermal comfort, electric vehicles often employ PTC-assisted electric heating to provide additional heat in the cabin. Furthermore, R134a has a high global warming potential (GWP) of 1430, making it environmentally unfriendly and facing widespread phase-out. Carbon dioxide, a purely natural refrigerant, is non-toxic, pollution-free, and inexpensive, making it a promising alternative for the next generation. Furthermore, compared to PTC-assisted electric heating, carbon dioxide heat pumps offer superior heating performance, significantly saving battery power in winter and indirectly extending the range of electric vehicles.

[0004] Most existing automotive air conditioners use direct expansion systems, where refrigerant enters the passenger compartment directly for heat exchange. A leak could expose passengers to the refrigerant. Transcritical CO2 systems, however, face the risk of high operating pressures leading to excessively high CO2 concentrations in the cabin. Consequently, a growing number of researchers are investigating indirect systems, hoping to develop more efficient thermal management systems for new energy vehicles.

[0005] The transcritical carbon dioxide secondary loop thermal management system is an indirect system mentioned 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 cabin or components. Unlike the direct system, the heat exchange between carbon dioxide and coolant is carried out 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 stacked metal plates. Thin rectangular channels are formed between the various plates. The refrigerant and coolant flow through the channels respectively and exchange heat through the plates. It is an ideal heat exchanger for liquid-liquid heat exchange. To further explain, there are many optimizable parameters in the transcritical carbon dioxide secondary loop system, among which the optimization design of the coolant flow rate is different from that of the direct system in the secondary loop, and the coolant flow rate has a greater impact on the performance of the secondary loop system. Like the optimal discharge pressure, there is an optimal value. Among them, due to the large temperature slip 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. Under cooling conditions, the inlet and outlet temperature difference is smaller, and a large coolant flow rate is conducive to heat exchange. The difference between the two working conditions is large, resulting in the inability to achieve appropriate pressure drop and good heat exchange under different working conditions in the same simple liquid cooled gas cooler (LCGC).

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

[0007] Summary of the Invention

[0008] The present invention aims to provide a liquid-cooled gas cooler and a coolant flow control method therefor to address one or more of the aforementioned technical issues. The technical solution provided by the present invention addresses the significant differences in the appropriate coolant flow rates for a transcritical carbon dioxide secondary circuit thermal management system under heating and cooling conditions. Different heat exchanger arrangements are employed under different operating conditions to address the resulting inability to achieve both a suitable pressure drop and good heat exchange within a single LCGC, thereby improving overall system performance. Furthermore, the present invention provides an efficient control method for regulating the coolant flow rate, simplifying the parameter adjustment process.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] 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,

[0011] The liquid-cooled gas cooler is provided with a coolant inlet, a coolant outlet, a refrigerant inlet and a refrigerant outlet;

[0012] The coolant heat exchange channel inlet of the first plate heat exchanger among the N plate heat exchangers is connected to the coolant inlet, and the coolant heat exchange channel inlets of the second plate heat exchanger to the Nth plate heat exchanger are respectively connected to the coolant inlet via a stop valve;

[0013] The Nth of the N plate heat exchangers l The coolant heat exchange channel outlets of the plate heat exchangers are connected to the coolant outlet, the Nth l The coolant heat exchange channel inlet of +1 plate heat exchanger is connected, and the coolant heat exchange channel outlet of the Nth plate heat exchanger is connected to the coolant outlet, 1≤N l <N;

[0014] The refrigerant inlet is connected to the refrigerant outlet through a refrigerant heat exchange channel from the Nth plate heat exchanger to the first plate heat exchanger among the N plate heat exchangers.

[0015] A further improvement of the present invention is that

[0016] In heating mode, all three-way valves are connected to the coolant outlet and all stop valves are opened, and the refrigerant flows through each plate heat exchanger in parallel.

[0017] A further improvement of the present invention is that

[0018] In cooling mode, all three-way valves are connected to the coolant heat exchange channel inlet of each plate heat exchanger and all stop valves are closed. The refrigerant flows through each plate heat exchanger in series.

[0019] A further improvement of the present invention is that the steps for designing the number N of plate heat exchangers include:

[0020] Get the total number of preset patterns N 板 and the initial value N of the number of plate heat exchangers 初始 , and iteratively calculate to obtain the number N of plate heat exchangers; wherein,

[0021] When performing iterative calculations, N for each iteration 初始 Values ​​need to be determined before calculation. 板 Can it be N 初始 Divisible, if not divisible, then N 初始 Perform +1 processing until it is divisible; for each divisible N 板 N 初始, based on the heat exchanger inlet parameters, calculate the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC; compare the heat transfer pressure drop energy efficiency value calculated in each new iteration with the maximum value in the previous iteration, and replace the maximum value with the larger value obtained by comparison; after the iteration termination condition is reached, the number of heat exchangers corresponding to the maximum heat transfer pressure drop energy efficiency value is the number N of plate heat exchangers.

[0022] 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.

[0023] A further improvement of the present invention is that for each 板 N 初始 , in the step of calculating the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC based on the heat exchanger inlet parameters,

[0024] The inlet parameters of LCGC remain unchanged during each iterative calculation. The inlet parameters include refrigerant inlet temperature, inlet pressure, inlet enthalpy, refrigerant flow rate, coolant flow rate, and coolant inlet temperature.

[0025] The heat transfer calculation expression of LCGC is: Q x =m r *(h r,out -h r,in )=m c *C p,c (T c,out -T c,in );

[0026] Where m r is the refrigerant flow rate; h r,in and h r,out are the refrigerant inlet and outlet enthalpies respectively; A j,i is the heat transfer coefficient of each heat exchange unit, S j,i is the heat transfer area of ​​the heat exchanger, T r,j,i and T c,j,i are the temperatures of the refrigerant and coolant in the heat exchanger, respectively.

[0027] A further improvement of the present invention is that for each 板 N 初始 , in the step of calculating the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC based on the heat exchanger inlet parameters,

[0028] The calculation expression of LCGC pressure drop ΔP is:

[0029] Where, σ is the flow length of the refrigerant; ρ is the refrigerant density; ξ is the dynamic viscosity of the refrigerant; Pn, ρ n ,ξ n 、m n are rated pressure drop, rated density, rated dynamic viscosity and rated flow rate respectively; id is taken as 0, iv and im are index parameters related to viscosity and mass flow rate respectively.

[0030] A further improvement of the present invention is that for each 板 N 初始 , in the step of calculating the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC based on the heat exchanger inlet parameters,

[0031] The calculation expression of the heat exchange pressure drop energy efficiency value R of LCGC is:

[0032] Where w1, w2, d1, d2 are constants; w is the heat transfer Q x and the weight coefficient of pressure drop ΔP; d is an exponential constant.

[0033] The present invention provides a method for controlling the flow rate of coolant in a liquid-cooled gas cooler, comprising:

[0034] The RBF neural network PID controller is used to control the coolant flow rate. The input value of the RBF neural network PID controller is the target coolant flow rate, and the output 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:

[0035] Where, T is the pump motor power, η b is the pump shaft efficiency, and H is the pump head.

[0036] A further improvement of the present invention is that the RBF neural network PID controller is a RBF neural network embedded in a traditional PID controller; wherein,

[0037] The RBF neural network consists of a three-layer structure: input layer, hidden layer and output layer; wherein the neurons in the hidden layer are composed of activation functions, and the activation function adopts a Gaussian function;

[0038] The process of adjusting PID parameters by RBF neural network uses gradient descent method to iteratively optimize the weights of hidden layer, radial basis vectors and Gaussian function width.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The liquid-cooled gas cooler provided by the present invention adopts a combined structure of a plate heat exchanger, a three-way valve, and a stop valve. By adjusting the three-way valve and the stop valve, switching between series and parallel connections can be achieved. The heat exchanger adopts different arrangements under different operating conditions, which solves the problem of being unable to simultaneously achieve a suitable pressure drop and good heat exchange in a single LCGC, thereby improving the overall system performance.

[0041] In the present invention, by adjusting the three-way valve and the stop valve, switching between series and parallel connections can be achieved. In the heating mode, a small flow parallel arrangement can be preferentially adopted to provide a large temperature difference at the inlet and outlet of the heat exchanger to meet the heating needs in winter; in the cooling mode, a large flow series arrangement can be preferentially adopted to reduce the pressure drop to a certain extent and improve the heat exchange effect. Further explanation, the present invention can achieve low coolant flow operation in the heating mode and high flow operation in the cooling mode. It can solve the problem that the difference in the appropriate coolant flow rate under the heating and cooling conditions of the transcritical carbon dioxide secondary loop thermal management system leads to the inability to achieve a suitable pressure drop and good heat exchange in the liquid-cooled gas cooler, thereby improving the overall system performance.

[0042] In the present invention, based on the comparison of LCGC heat transfer and pressure drop under different arrangements of the same plate, the LCGC arrangement with the highest comprehensive energy efficiency ratio of heat transfer and pressure drop is found through iterative optimization.

[0043] In this invention, after determining the LCGC arrangement in the system, the optimal coolant flow rate will change as the system operating state and environmental conditions change. Flow control is implemented to adapt to varying coolant flow requirements, enabling the system to quickly and efficiently switch to the desired coolant flow rate. Specifically, considering the unique thermal properties of CO2 refrigerant, the LCGC requires different coolant flow control strategies, i.e., different heat exchange architectures, in different system operating modes. When changes in vehicle operating state or environmental conditions cause the optimal coolant flow rate to vary, the RBF neural network is embedded in a simple PID controller to improve system control accuracy and stability, simplify the parameter adjustment process, and achieve rapid coolant flow adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a schematic structural diagram of a liquid-cooled gas cooler provided in an embodiment of the present invention;

[0045] FIG2 is a schematic diagram of a series arrangement of liquid-cooled gas coolers in an embodiment of the present invention;

[0046] FIG3 is a schematic diagram of a parallel arrangement of liquid-cooled gas coolers in an embodiment of the present invention;

[0047] FIG4 is a schematic diagram showing the logic for designing the number of plate heat exchangers in a liquid-cooled gas cooler according to an embodiment of the present invention;

[0048] FIG5 is a schematic diagram of a transcritical carbon dioxide secondary circuit thermal management system provided by an embodiment of the present invention;

[0049] FIG6 is a schematic block diagram of the PID control logic for coolant flow control according to an embodiment of the present invention;

[0050] In the figure, 1. Compressor; 2. Gas cooler; 3. Regenerator; 4. Stop valve; 5. Expansion valve; 6. Evaporator; 7. Liquid storage 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 DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first," "second," and the like in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the numbers used in this manner are interchangeable where appropriate so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatus.

[0053] The present invention is described in further detail below with reference to the accompanying drawings:

[0054] Referring to FIG. 1 to FIG. 3 , an embodiment of 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,

[0055] The liquid-cooled gas cooler is provided with a coolant inlet, a coolant outlet, a refrigerant inlet and a refrigerant outlet;

[0056] The coolant heat exchange channel inlet of the first plate heat exchanger among the N plate heat exchangers is connected to the coolant inlet, and the coolant heat exchange channel inlets of the second to Nth plate heat exchangers are respectively connected to the coolant inlet via stop valves;

[0057] The Nth of the N plate heat exchangers l The coolant heat exchange channel outlets of the plate heat exchangers are connected to the coolant outlet, the Nth l The coolant heat exchange channel inlet of +1 plate heat exchanger is connected, and the coolant heat exchange channel outlet of the Nth plate heat exchanger is connected to the coolant outlet, 1≤N l <N;

[0058] The refrigerant inlet is connected to the refrigerant outlet through the refrigerant heat exchange channels from the Nth to the first plate heat exchangers among the N plate heat exchangers.

[0059] In the technical solution provided in the embodiment of the present invention, by adjusting the three-way valve and the stop valve, switching between series and parallel can be achieved, so that the system can operate with a small coolant flow in the heating mode and a large flow in the cooling mode. It can solve the problem that the appropriate coolant flow rate difference between the heating and cooling working conditions of the transcritical carbon dioxide secondary loop thermal management system leads to the inability to achieve a suitable pressure drop and good heat exchange in the liquid-cooled gas cooler, thereby improving the overall system performance.

[0060] Specifically, as shown in FIG2 , all three-way valves are opened to the right and all stop valves are closed, and the refrigerant flows through each plate heat exchanger in series.

[0061] Specifically, as shown in FIG3 , all three-way valves are opened upward and all stop valves are opened, and the refrigerant flows through each plate heat exchanger in parallel.

[0062] The principle explanation of the technical solution of the embodiment of the present invention: The liquid-cooled gas cooler disclosed in the present invention can preferentially adopt a small-flow parallel arrangement in the heating mode, provide a large temperature difference at the inlet and outlet of the heat exchanger, and meet the heating needs in winter; in the cooling mode, preferentially adopt a large-flow series arrangement, reduce the pressure drop to a certain extent, and improve the heat exchange effect.

[0063] Referring to FIG4 , a further preferred technical solution of the embodiment of the present invention further includes an optimized design of the number of plate heat exchangers in the liquid-cooled gas cooler, and the specific steps are as follows:

[0064] Step 1: Determine the total number of plates y of the LCGC, that is, the preset total number of plates, according to different application scenarios; use the number x of plate heat exchangers to be determined in the LCGC as the initial value of the iteration, which is generally 1; specifically, for a specific new energy vehicle transcritical carbon dioxide secondary loop thermal management system, it is necessary to clarify the external geometric dimensions of the LCGC used in the initial design based on the system heat exchange requirements and the spatial layout of the thermal management components in the vehicle, and calculate the appropriate number of plates of the plate heat exchanger based on the heat exchange simulation to meet the heat exchange requirements under various working conditions; for LCGC, a large size and a large number of plates will be conducive to sufficient heat exchange if the pressure drop is allowed. However, due to the limited space available for the air-conditioning system on new energy vehicles and weight restrictions, the external dimensions and volume need to be selected based on actual conditions.

[0065] Step 2: For each iterative value of x, it is necessary to determine whether y is divisible by x before calculation. If not, add 1 to x until it is divisible to ensure the same number of plates in each heat exchanger.

[0066] Step 3: For each number x of heat exchangers that can divide y, calculate the heat transfer, pressure drop, and heat transfer pressure drop energy efficiency value of LCGC based on the heat exchanger inlet parameters; where,

[0067] The inlet parameters of LCGC remain unchanged during each iterative calculation. The inlet parameters include refrigerant inlet temperature, inlet pressure, inlet enthalpy, refrigerant flow rate, coolant flow rate, and coolant inlet temperature.

[0068] 1) The heat transfer calculation expression of LCGC is, Q x =m r *(h r,out -h r,in )=m c *C p,c (T c,out -T c,in );

[0069] Where m r is the refrigerant flow rate; h r,in and h r,out are the refrigerant inlet and outlet enthalpies respectively; A j,i is the heat transfer coefficient of each heat exchange unit, S j,i is the heat transfer area of ​​the heat exchanger, T r,j,i and T c,j,i are the temperatures of the refrigerant and coolant in the heat exchanger, respectively.

[0070] 2) When calculating the pressure drop ΔP of LCGC, the user needs to set the upper limit of the refrigerant flow rate m according to the system l, to avoid calculation errors caused by abnormal refrigerant flow, and then calculate the pressure drop in sections according to the refrigerant flow interval; among them,

[0071] When the refrigerant flow rate m>m l When , the calculation expression of pressure drop ΔP is:

[0072] When the refrigerant flow rate is at the normal threshold and meets the regularization conditions, the calculation expression of the pressure drop ΔP is,

[0073] When the refrigerant flow rate m<-m l When , the calculation expression of pressure drop ΔP is:

[0074] To simplify the calculation, the three formulas can be integrated into:

[0075] Where σ is the flow length of the refrigerant, ρ is the refrigerant density, ξ is the dynamic viscosity of the refrigerant, Pn, ρ n ,ξ n , m n They are rated pressure drop, rated density, rated dynamic viscosity and rated flow, which are all related to the inlet conditions and parameters of the plate heat exchanger and exist in the form of constants during calculation. For refrigerant id, 0 is generally taken, iv, and im are exponential parameters related to viscosity and mass flow, respectively.

[0076] 3) When the number of plate heat exchangers increases, the heat transfer coefficient increases, and the heat transfer Q x The heat transfer pressure drop energy efficiency value R is an indicative parameter calculated by substituting the heat transfer and pressure drop into the cost formula. The larger the value, the higher the degree of optimization of LCGC. Its calculation expression is:

[0077] Where w1, w2, d1, d2 are constants, w is the weight coefficient of heat transfer and pressure drop, which represents the importance of heat transfer and pressure drop. Q can be controlled by adjusting the size of w. x The trade-off between ΔP and d is an exponential constant. Through iteration, the optimal value of the number of plate changes can be obtained to maximize the R value of LCGC.

[0078] The R value calculated from each new iteration is compared with the maximum value of the previous iteration, and the larger value obtained from the comparison replaces the maximum value. The termination condition of the iteration is that 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. An x value greater than the iteration termination condition will not conform to the actual situation and lose the meaning of the iteration. If x is less than y / 3, the operation 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.

[0079] In the technical solution provided by the embodiments of the present invention, the LCGC employs different water flow control strategies, i.e., different heat exchange architectures, in different system operating modes. A parallel arrangement is preferred for heating mode, while a series arrangement is preferred for cooling. An iterative optimization process is used to identify the LCGC arrangement with the highest combined energy efficiency ratio (R) for heat exchange and pressure drop. Once the LCGC arrangement is determined, the optimal coolant flow rate will change as the system operating state and environmental conditions change. Flow control is implemented to adapt to varying coolant flow requirements, enabling the system to quickly and efficiently switch to the desired coolant flow rate.

[0080] Referring to FIG5 , an embodiment of the present invention provides a transcritical carbon dioxide secondary circuit thermal management system, comprising: a compressor 1, a gas cooler 2, a regenerator 3, a stop valve 4, an expansion valve 5, an evaporator 6, a liquid storage tank 7, a cold circuit water pump 8, a cold circuit water tank 9, a first four-way valve 10, an indoor heat exchanger 11, a flow meter 12, a hot circuit water pump 13, a second four-way valve 14, a hot circuit water tank 15, and an outdoor heat exchanger 16; wherein,

[0081] The gas cooler 2 is the liquid-cooled gas cooler disclosed in the embodiment of the present invention; the gas cooler 2 provides a function similar to that of a condenser in a conventional refrigerant system, for heat exchange between the refrigerant and the coolant;

[0082] The regenerator 3 is used to reheat the refrigerant. 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.

[0083] The evaporator 6 is used for heat exchange between the refrigerant and the coolant, and the coolant is cooled in the evaporator;

[0084] The indoor heat exchanger 11 includes a main heat exchanger and an auxiliary heat exchanger for realizing heat exchange between the coolant and the air and supplying air to the vehicle compartment;

[0085] The outdoor heat exchanger 16 is used for heat exchange between the coolant and the outdoor air;

[0086] The stop valve 4 is used to bypass the regenerator in the heating mode to avoid the influence of the regenerator on the heating performance.

[0087] The above-mentioned transcritical carbon dioxide secondary circuit thermal management system can switch between heating mode and cooling mode through the combined switching of the first four-way valve 10 and the second four-way valve 14; wherein,

[0088] In heating mode, the high-temperature, high-pressure steam output from compressor 1 flows into gas cooler 2, releasing heat to the coolant before entering regenerator 3. At this point, shutoff valve 4 is open, and regenerator 3 no longer provides heat recovery. The high-temperature, high-pressure steam exiting regenerator 3 is throttled to a low-temperature, low-pressure state by expansion valve 5 (illustratively, an electronic expansion valve). It then enters evaporator 6, absorbs heat from the coolant, passes through liquid storage tank 7, and returns to the intake port of compressor 1 through shutoff valve 4. After absorbing heat from gas cooler 2, the coolant in the hot circuit flows through flowmeter 12 and enters hot circuit water tank 15. It then flows through channel bc of first four-way valve 10 into indoor heat exchanger 11 to heat the air. It then passes through channel cb of second four-way valve 14 and is pumped by hot circuit water pump 13 to the water inlet of gas cooler 2. After releasing heat in the evaporator 6, the coolant in the cold circuit enters the outdoor heat exchanger 16 through the da channel of the second four-way valve 14 to absorb ambient heat. It then 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 water inlet of the evaporator 6.

[0089] In cooling mode, the high-temperature, high-pressure vapor output from compressor 1 flows into gas cooler 2, releasing heat to the coolant before entering regenerator 3. At this point, shutoff valve 4 is closed, allowing regenerator 3 to regenerate heat. After releasing heat in regenerator 3, the vapor is throttled to a low-temperature, low-pressure state by expansion valve 5. It then enters evaporator 6, absorbs heat from the coolant, passes through reservoir 7, and enters regenerator 3 to be heated before returning to the intake port of compressor 1. The coolant in the hot circuit absorbs heat from gas cooler 2, flows through flowmeter 12, enters hot circuit water tank 15, and then passes through channel ba of first four-way valve 10 to enter outdoor heat exchanger 16, releasing heat to the environment. It then passes through channel ad of second four-way valve 14 and is pumped by hot circuit water pump 13 to the water inlet of gas cooler 2. After releasing heat in the evaporator 6, the coolant in the cold circuit 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, flows through the cold circuit water pump 8 and returns to the water inlet of the evaporator 6.

[0090] In an embodiment of the present invention, a small flow parallel arrangement is preferably adopted in the heating mode, and a large flow series arrangement is preferably adopted in the cooling mode. This solves the problem that the difference in suitable coolant flow in the transcritical carbon dioxide secondary loop thermal management system under heating and cooling conditions causes simple flow control to be unable to achieve appropriate pressure drop and good heat exchange in a single LCGC, thereby improving the overall system performance. Specifically, the current research on transcritical carbon dioxide secondary loop thermal management systems is still relatively limited. In the few studies on coolant flow, the system still uses two different LCGCs to meet the heat exchange requirements of heating and cooling respectively. The present invention provides an integrated solution for LCGC structural design. At the same time, since the coolant flow has a great influence on the performance of the transcritical carbon dioxide thermal management system, the system operation process requires fast and effective flow control. By embedding the RBF neural network into a simple PID controller to dynamically adjust the coolant flow, the problem of the currently widely used traditional PID parameter adjustment process being time-consuming, labor-intensive, and inefficient is solved, simplifying the control process.

[0091] Please refer to Figure 6. In the embodiment of the present invention, an RBF neural network PID controller is used to control the coolant flow rate. The input value of the RBF neural network PID controller is the target coolant flow rate, and the output is the water pump motor power of the LCGC coolant circuit. The conversion relationship between the water pump speed and the coolant flow rate is described as follows:

[0092] Where, T is the motor power of the water pump, η b is the shaft efficiency of the water pump, and H is the head of the water pump.

[0093] The embodiment of the present invention further explains that the RBF neural network PID controller embeds the RBF neural network in the traditional PID controller, which can simplify the PID parameter adjustment process; wherein,

[0094] RBF neural network consists of three layers: input layer, hidden layer and output layer, i=[i1,i2,…,i n ] T Is the input value 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 used as the activation function.

[0095] Where a j is the output value of the jth neuron in the hidden layer, v=[v1,v2,…,v n ] is the radial basis vector of the Gaussian function, h=[h1,h2,…,h n ] T is the Gaussian function width of the jth neuron. Between the hidden layer and the output layer, there is a weight function c=[c1,c,…,cn ] T Connection, the neural network output value is y m =c1a1+c2a2+…+c m a m ;

[0096] The process of adjusting PID parameters by RBF neural network generally uses gradient descent method to iteratively optimize the weights of hidden layer, radial basis vectors and Gaussian function width; the iterative equation is:

[0097] Where s = v, c, h, ε is the momentum factor of the neuron;

[0098] Specifically, for the adjustment of PID parameters,

[0099] Where b(t) is the successive output of PID, and γ is the PID parameter learning rate. According to the above iterative formula, the PID parameters can be quickly adjusted to achieve efficient control of the coolant flow rate.

[0100] The technical solution provided by the embodiments of this invention takes into account the unique thermal properties of CO2 refrigerant. Different coolant flow control strategies, or heat exchange architectures, are required for the LCGC in different system operating modes. Furthermore, when changes in vehicle operating status or environmental conditions cause variations in the optimal coolant flow rate, the RBF neural network is embedded within a simple PID controller to improve system control accuracy and stability, simplify the parameter adjustment process, and achieve rapid coolant flow adjustment.

[0101] In summary, the embodiments of the present invention disclose an optimized design structure of LCGC and a coolant flow control method for a transcritical carbon dioxide secondary loop thermal management system; wherein, the LCGC optimization scheme mainly compares the LCGC heat exchange and pressure drop under different arrangements of the same plate, and finds the LCGC with the highest comprehensive energy efficiency ratio of heat exchange and pressure drop through iterative optimization. In the heating mode, a small flow parallel arrangement is preferably adopted, and in the cooling mode, a large flow series arrangement is preferably adopted; in addition, the suitable coolant flow rate of the transcritical carbon dioxide secondary loop thermal management system under heating and cooling conditions is greatly different. By embedding the RBF neural network into a simple PID controller, the problems of the widely used traditional PID parameter adjustment process being time-consuming, labor-intensive and inefficient are solved, which promotes the application and popularization of carbon dioxide refrigerants, promotes the development of secondary loop thermal management systems, and makes significant contributions to environmental protection, alleviating the fossil energy crisis, and achieving carbon neutrality and carbon peak.

[0102] 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, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A liquid-cooled gas cooler, characterized in that: include: N plate heat exchangers, each plate heat exchanger has the same number of plates; wherein, The liquid-cooled gas cooler is provided with a coolant inlet, a coolant outlet, a refrigerant inlet and a refrigerant outlet; The coolant heat exchange channel inlet of the first plate heat exchanger among the N plate heat exchangers is connected to the coolant inlet, and the coolant heat exchange channel inlets of the second to Nth plate heat exchangers are respectively connected to the coolant inlet via stop valves; The Nth of the N plate heat exchangers l The coolant heat exchange channel outlets of the plate heat exchangers are respectively connected to the coolant outlet, the Nth l The coolant heat exchange channel inlet of +1 plate heat exchanger is connected, and the coolant heat exchange channel outlet of the Nth plate heat exchanger is connected to the coolant outlet, 1≤N l <N; The refrigerant inlet is connected to the refrigerant outlet through the refrigerant heat exchange passages from the Nth to the first plate heat exchangers among the N plate heat exchangers in sequence.

2. A liquid-cooled gas cooler according to claim 1, characterized in that: In the heating mode, all three-way valves are connected to the coolant outlet and all stop valves are opened, and the refrigerant flows through each plate heat exchanger in parallel.

3. A liquid-cooled gas cooler according to claim 1, characterized in that: In the cooling mode, all three-way valves are connected to the coolant heat exchange channel inlet of each plate heat exchanger and all stop valves are closed, and the refrigerant flows through each plate heat exchanger in series.

4. The liquid-cooled gas cooler according to claim 1, characterized in that: The design steps for the number of plate heat exchangers N include: Get the total number of preset plates N 板 and the initial value of the number of plate heat exchangers N 初始 , and iterate to calculate and obtain the plate The number of heat exchangers is N; where: When performing iterative calculations, for each iteration N 初始 Values ​​need to be determined before calculation. 板 Can it be N 初始 If it is not divisible, then N 初始 Perform +1 processing until it is divisible; for each number that is divisible by N 板 N 初始 , according to the heat exchanger inlet parameters, calculate the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC; compare the heat transfer pressure drop energy efficiency value calculated by each new iteration with the maximum value in the previous iteration, and replace the maximum value with the larger value obtained by comparison; after the iteration termination condition is reached, the number of heat exchangers corresponding to the maximum heat transfer pressure drop energy efficiency value is the number N of plate heat exchangers.

5. A liquid-cooled gas cooler according to claim 4, characterized in that: The iteration termination condition is that the number of plate heat exchangers is not less than N 板 / 3.

6. A liquid-cooled gas cooler according to claim 4, characterized in that: For every N that is divisible 板 N 初始 , in the step of calculating the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC according to the heat exchanger inlet parameters, The inlet parameters of LCGC remain unchanged in each iterative calculation, including refrigerant inlet temperature, inlet pressure, inlet enthalpy, refrigerant flow rate, coolant flow rate and coolant inlet temperature; The heat transfer calculation expression of LCGC is: 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 is the refrigerant flow rate; h r,in and h r,out are the refrigerant inlet and outlet enthalpies respectively; A j,i is the heat transfer coefficient in each heat exchange unit, S j,i is the heat transfer area of ​​the heat exchanger, T r,j,i and T c,j,i are the temperatures of the refrigerant and coolant in the heat exchanger, respectively.

7. A liquid-cooled gas cooler according to claim 6, characterized in that: For every N that is divisible 板 N 初始 , in the step of calculating the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC according to the heat exchanger inlet parameters, The calculation expression of LCGC pressure drop ΔP is: Where σ is the flow length of the refrigerant; ρ is the refrigerant density; ξ is the dynamic viscosity of the refrigerant; Pn, ρ n , n 、m n They are rated pressure drop, rated density, rated dynamic viscosity and rated flow rate respectively; id is taken as 0, iv and im are exponential parameters related to viscosity and mass flow rate respectively.

8. A liquid-cooled gas cooler according to claim 7, characterized in that: For every N that is divisible 板 N 初始 , in the step of calculating the heat transfer, pressure drop and heat transfer pressure drop energy efficiency value of LCGC according to the heat exchanger inlet parameters, The calculation expression of the heat exchange pressure drop energy efficiency value R of LCGC is: Where w1, w2, d1, d2 are constants; w is the heat transfer Q x and the weight coefficient of pressure drop ΔP; d is an exponential constant.

9. A method for controlling the coolant flow rate of a liquid-cooled gas cooler according to claim 1, characterized in that: include: The RBF neural network PID controller is used to control the coolant flow rate. The input value of the RBF neural network PID controller is the target coolant flow rate, and the output 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, η b is the pump shaft efficiency, and H is the pump head.

10. The coolant flow control method according to claim 9, characterized in that: The RBF neural network PID controller is to embed the RBF neural network in the traditional PID controller; wherein, The RBF neural network comprises a three-layer structure of input layer, hidden layer and output layer; wherein the neurons of the hidden layer are composed of an activation function, and the activation function adopts a Gaussian function; The process of adjusting PID parameters by RBF neural network uses gradient descent method to iteratively optimize the weights of hidden layer, radial basis vectors and Gaussian function width.

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