A method and system for suppressing the imbalance of a transcritical carbon dioxide heat pump

Abstract

The present invention discloses a method and system for suppressing the imbalance of a transcritical carbon dioxide heat pump. The method for suppressing the imbalance of the transcritical carbon dioxide heat pump includes the following steps: obtaining the superheat degree and liquid carry-over degree of a transcritical carbon dioxide heat pump air-conditioning system; and based on the obtained superheat degree and liquid carry-over degree, using an electronic expansion valve PID controller to achieve imbalance suppression control. In the technical solution provided by the present invention, the control logics of the compressor and the electronic expansion valve of the transcritical carbon dioxide air-conditioning heat pump are provided, which can solve the technical problem in the prior art that control imbalance is likely to occur when using a PID controller for control after liquid carry-over at the suction or overheating at the outlet of the evaporator.

Description

Technical Field

[0001] The present invention belongs to the technical field of transcritical carbon dioxide heat pumps, and particularly relates to a method and system for suppressing the imbalance of a transcritical carbon dioxide heat pump. Background Art

[0002] The application and popularization of new energy electric vehicles have alleviated the problems of environmental pollution and shortage of fossil energy; due to the lack of recoverable engine waste heat, an independent heat pump system has become an indispensable part of new energy electric vehicles. At present, R134a heat pump air-conditioning systems are mainly used in new energy electric vehicles; however, the heating performance of R134a in winter is low. In order to ensure the thermal comfort of passengers, new energy electric vehicles usually need to use PTC auxiliary electric heating to provide additional heat for the compartment; in addition, the GWP value of R134a is as high as 1430, which is very unfriendly to the environment and faces the current situation of being phased out comprehensively. In summary, the transcritical carbon dioxide heat pump air-conditioning system has good development prospects.

[0003] Research has found that in the heat pump working condition of a transcritical carbon dioxide heat pump air-conditioning system, since the fluids on both sides of the regenerator are in the low-pressure side of the system, the temperatures of the two fluids are almost the same, and the refrigerant at the outlet of the evaporator enters the compressor directly without being heated after passing through the accumulator. When the system operates normally, the refrigerant at the outlet of the evaporator is in a saturated state, and the impact is not significant; once the liquid level in the accumulator is higher than the liquid separation critical value, the refrigerant at the outlet of the accumulator is two-phase. When the compressor speed remains unchanged, the system flow rate increases sharply, and the discharge temperature also drops sharply due to liquid carry-over during suction, and the system control characteristics change, and the original control logic faces the risk of imbalance. When the system is undercharged, the target discharge pressure value remains unchanged. The system may have difficulty reaching the target discharge pressure due to severe undercharging, and the valve opening continues to decrease, resulting in a decrease in the low-pressure pressure, and the system performance deteriorates. The system also faces the risk of control imbalance. During the start-up stage of the system, due to different initial parameters, even if the charging amount does not reach the upper limit of this working condition, the system is very likely to enter a serious overcharged state during PID regulation, seriously affecting the safety of the system.

[0004] In summary, in a complex and diverse working environment, it is one of the great challenges faced by the transcritical CO2 heat pump system at present to still be able to adopt a certain control method to make the system operate in a safe and stable state after the compressor has been operating in a liquid carry-over state during suction or there is a certain degree of superheat at the outlet of the evaporator. Summary of the Invention

[0005] The object of the present invention is to provide a control method and system for suppressing the imbalance of a transcritical carbon dioxide heat pump, so as to solve one or more of the above-mentioned technical problems. In the technical solution provided by the present invention, the control logics of the compressor and the electronic expansion valve of the transcritical carbon dioxide air-conditioning heat pump are provided, which can solve the technical problem that the use of a PID controller in the prior art is prone to control imbalance after liquid carry-over in the suction or overheating at the evaporator outlet.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A control method for suppressing the imbalance of a transcritical carbon dioxide heat pump provided by the present invention includes the following steps:

[0008] Obtain the superheat degree and the liquid carry-over degree of the transcritical carbon dioxide heat pump air-conditioning system;

[0009] Based on the obtained superheat degree and liquid carry-over degree, use an electronic expansion valve PID controller to achieve imbalance suppression control;

[0010] Among them, the calculation formula for the liquid carry-over degree is,

[0011]

[0012] In the formula, θ is the liquid carry-over degree; S suc is the suction entropy value; P dis is the compressor discharge pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor discharge temperature; η is the compressor isentropic efficiency; T(H, P) and H(T, P) are refrigerant property functions.

[0013] A further improvement of the present invention is that the step of obtaining the superheat degree and the liquid carry-over degree of the transcritical carbon dioxide heat pump air-conditioning system includes:

[0014] Obtain the operating parameters of the transcritical carbon dioxide heat pump air-conditioning system; among them, the operating parameters include the compressor discharge temperature, discharge pressure, suction temperature, suction pressure, evaporator outlet temperature, and pressure;

[0015] Based on the obtained operating parameters, calculate the liquid carry-over degree through the formula.

[0016] A further improvement of the present invention is that the step of using an electronic expansion valve PID controller to achieve imbalance suppression control based on the obtained superheat degree and liquid carry-over degree includes:

[0017] When the superheat degree is greater than the first preset threshold, control the input of the electronic expansion valve PID controller to be the superheat degree, and the output to be the opening degree of the electronic expansion valve;

[0018] When the liquid carry - over degree is greater than the second preset threshold, control the input of the electronic expansion valve PID controller to be the liquid carry - over degree, and the output to be the opening degree of the electronic expansion valve;

[0019] Under other conditions, control the input of the electronic expansion valve PID controller to be the target exhaust pressure, and the output to be the opening degree of the electronic expansion valve.

[0020] A further improvement of the present invention lies in that the value range of the first preset threshold is greater than or equal to 2 and less than or equal to 5; the value range of the second preset threshold is greater than or equal to 5 and less than or equal to 10.

[0021] A further improvement of the present invention lies in that the steps for obtaining the target exhaust pressure include:

[0022] Obtain the ambient working conditions and calculate to obtain the optimal exhaust pressure, the adjusted optimal exhaust pressure, the temperature before the valve and the evaporator outlet pressure;

[0023] Given the target exhaust pressure according to whether the ambient working conditions change and the magnitude relationship between the optimal exhaust pressure and the adjusted optimal exhaust pressure.

[0024] A cross - critical carbon dioxide heat pump imbalance suppression control system provided by the present invention includes:

[0025] An acquisition module for acquiring the superheat degree and the liquid carry - over degree of a cross - critical carbon dioxide heat pump air - conditioning system;

[0026] A control module for realizing imbalance suppression control by using an electronic expansion valve PID controller based on the obtained superheat degree and liquid carry - over degree;

[0027] Among them, the calculation formula of the liquid carry - over degree is,

[0028]

[0029] In the formula, θ is the liquid carry - over degree; S suc is the suction entropy value; P dis is the compressor exhaust pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor exhaust temperature; η is the compressor isentropic efficiency; T(H, P) and H(T, P) are refrigerant property functions.

[0030] A further improvement of the present invention lies in that in the acquisition module, the steps for acquiring the superheat degree and the liquid carry - over degree of a cross - critical carbon dioxide heat pump air - conditioning system include:

[0031] Obtain the operating parameters of a transcritical carbon dioxide heat pump air-conditioning system; wherein, the operating parameters include the compressor discharge temperature, discharge pressure, suction temperature, suction pressure, evaporator outlet temperature, and pressure;

[0032] Based on the obtained operating parameters, calculate the liquid carry-over through a formula.

[0033] A further improvement of the present invention lies in that, in the control module, based on the obtained superheat degree and liquid carry-over, the steps of implementing offset suppression control using an electronic expansion valve PID controller include:

[0034] When the superheat degree is greater than the first preset threshold, control the input of the electronic expansion valve PID controller to be the superheat degree, and the output to be the opening of the electronic expansion valve;

[0035] When the liquid carry-over is greater than the second preset threshold, control the input of the electronic expansion valve PID controller to be the liquid carry-over, and the output to be the opening of the electronic expansion valve;

[0036] Under other conditions, control the input of the electronic expansion valve PID controller to be the target discharge pressure, and the output to be the opening of the electronic expansion valve.

[0037] A further improvement of the present invention lies in that the value range of the first preset threshold is greater than or equal to 2 and less than or equal to 5; the value range of the second preset threshold is greater than or equal to 5 and less than or equal to 10.

[0038] A further improvement of the present invention lies in that the steps for obtaining the target discharge pressure include:

[0039] Obtain the ambient conditions and calculate the optimal discharge pressure, the adjusted optimal discharge pressure, the temperature before the valve, and the evaporator outlet pressure;

[0040] Give the target discharge pressure according to whether the ambient conditions change and the magnitude relationship between the optimal discharge pressure and the adjusted optimal discharge pressure.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] In the technical solution provided by the present invention, a control logic for the compressor and the electronic expansion valve of a transcritical carbon dioxide air-conditioning heat pump is provided, which can solve the technical problem that the use of a PID controller in the prior art is prone to control imbalance after liquid carry-over at the suction or overheating at the evaporator outlet. Specifically, based on the research on the system behavior state after liquid carry-over at the compressor suction in the heat pump mode of a transcritical carbon dioxide heat pump air-conditioning system, the present invention collects the suction temperature, discharge temperature, suction pressure, discharge pressure, evaporator outlet temperature, and evaporator outlet pressure of the real-time compressor of the system, and calculates the liquid carry-over degree and superheat degree; through these two values, the appropriate control logic under the real-time system state is judged, so as to avoid the occurrence of control imbalance. To sum up, the technical solution provided by the present invention combines the research on the refrigerant charge of a transcritical carbon dioxide heat pump air-conditioning system, focuses on the control and regulation of the heat pump system and the undercharge and overcharge states, and uses the relevant control logic to adjust the system control, ensuring safety and control stability while enabling the system to have a higher energy efficiency ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the description of the embodiments or the prior art; obviously, the drawings in the following description are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0044] Figure 1 is a flow schematic block diagram of a transcritical carbon dioxide heat pump imbalance suppression control method provided by an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of a transcritical carbon dioxide air-conditioning heat pump system in an embodiment of the present invention;

[0046] Figure 3 is a logic schematic block diagram of a transcritical carbon dioxide heat pump imbalance suppression control method provided by an embodiment of the present invention;

[0047] Figure 4 is a flow schematic block diagram for obtaining the target discharge pressure in an embodiment of the present invention;

[0048] Figure 5 is a schematic block diagram of a transcritical carbon dioxide heat pump imbalance suppression control system provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solution in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0050] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above accompanying drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data used can be interchanged under appropriate circumstances 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 "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0051] The following further describes the present invention in detail with reference to the accompanying drawings:

[0052] Please refer to Figure 1 , a method for suppressing the imbalance of a transcritical carbon dioxide heat pump provided by an embodiment of the present invention includes the following steps:

[0053] Step 1, obtaining the superheat degree and liquid carry-over degree of a transcritical carbon dioxide heat pump air-conditioning system;

[0054] Step 2, based on the obtained superheat degree and liquid carry-over degree, using an electronic expansion valve PID controller to achieve imbalance suppression control.

[0055] The technical solution provided by the embodiment of the present invention can solve the technical problem in the prior art that control imbalance is likely to occur when using a PID controller for control after liquid carry-over in suction or overheating at the evaporator outlet.

[0056] Step 1 of the embodiment of the present invention specifically includes: collecting and obtaining the real-time operation parameters of a transcritical carbon dioxide heat pump air-conditioning system, and calculating the superheat degree σ and the liquid carry-over degree θ; wherein, the system parameters include the compressor discharge temperature, discharge pressure, suction temperature, suction pressure, evaporator outlet temperature, and pressure;

[0057] The calculation formula for the liquid carry-over degree is:

[0058]

[0059] Where: θ is the liquid carry-over; S suc is the suction entropy value; P dis is the compressor discharge pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor discharge temperature; η is the compressor isentropic efficiency, calculated by a fitting formula.

[0060] Step 2 of the embodiment of the present invention specifically includes, by way of example: PID control mode 2, when the superheat σ > 2°C, it is determined that the system is undercharged, and the input of the PID controller of the electronic expansion valve is the superheat σ, and the output is the opening of the electronic expansion valve; wherein, the value range of the superheat threshold is 2 to 5; PID control mode 3, when the liquid carry-over θ > 5°C, the input of the PID controller of the electronic expansion valve is the liquid carry-over θ, and the output is the opening of the electronic expansion valve; wherein, the value range of the liquid carry-over threshold is 5 to 10; PID control mode 1, under other conditions, the input of the PID controller of the electronic expansion valve is the target discharge pressure P target , and the output is the opening of the electronic expansion valve. Further specifically, the present invention determines whether the current system is in an undercharged or suction liquid-carrying state based on the superheat σ at the evaporator outlet and the liquid carry-over θ to determine the system control logic; the control logic is divided into three types, including: PID control mode 1 is the conventional control logic in which the compressor controls the supply air temperature and the electronic expansion valve controls the discharge pressure; PID control mode 2 is the undercharged control logic in which the compressor controls the supply air temperature and the electronic expansion valve controls the superheat σ at the evaporator outlet; PID control mode 3 is the out-of-balance suppression control logic in which the compressor controls the supply air temperature and the electronic expansion valve controls the liquid carry-over θ.

[0061] Exemplarily and optionally in the embodiment of the present invention, when using PID control mode 2 or 3, if the system has been adjusted to be stable, a new optimal discharge pressure P adjust is given to the system and the control logic is switched back to PID control mode 1 to achieve stable control of the system. Among them, after the system enters PID control mode 2 or 3 due to undercharging or suction liquid-carrying, it is judged whether it is adjusted to be stable. The basis for adjustment to be stable is that the superheat σ and the liquid carry-over θ do not change by more than 0.5°C within 60 s, where 60 s and 0.5°C are recommended values and can be appropriately adjusted according to the operating characteristics of the system. In addition, when performing control mode conversion, it is necessary to judge whether the running time t of the current control mode > 150 s. Only when t > 150 s can the mode conversion be performed. Here, 150 s is a recommended value and can be appropriately adjusted according to the operating characteristics of the system.

[0062] Exemplarily and optionally in the embodiment of the present invention, the optimal discharge pressure P optimal is calculated by inputting the environmental working conditions into the control system, and the optimal discharge pressure P adjust after adjustment calculation, the temperature before the valve and the evaporator outlet pressure are adjusted. According to whether the working conditions change, Poptimal With P adjust The given target discharge pressure P has a size relationship target . Among them, the operating condition change is based on the temperature before the valve and the pressure at the evaporator outlet changing by Δξ < 0.5 °C and Δφ < 0.5 bar within 60 s. Here, 60 s, 0.5 °C, and 0.5 bar are recommended values and can be adjusted appropriately according to the system operation characteristics; if the operating condition changes and |P optimal - P adjust | > 0.3 MPa, then the target discharge pressure P target = P adjust , and in other cases P target = P optimal .

[0063] Please refer to Figure 2 , in the transcritical carbon dioxide heat pump air - conditioning system in the embodiments of the present invention, it includes: the outlet of the compressor 1 is connected to port A of the four - way reversing valve 2, port B of the four - way reversing valve 2 is connected to the inlet of the defrosting heat exchanger 3, the outlet of the defrosting heat exchanger 3 is connected to the main heat exchanger 4, the outlet of the main heat exchanger 4 is connected to the electronic expansion valve 5, the outlet of the electronic expansion valve 5 is connected to the first passage of the regenerator 6, the outlet of the first passage of the regenerator 6 is connected to the outdoor heat exchanger 7, the outlet of the outdoor heat exchanger 7 is connected to port C of the four - way reversing valve 2, port D of the four - way reversing valve 2 is connected to the accumulator 8, the accumulator 8 is connected to the second passage of the regenerator 6, and the outlet of the second passage of the regenerator 6 is connected to the inlet of the compressor 1. Indoor air supply is blown in through the indoor fan 9. The first PID controller 10 controls the compressor speed by collecting the supply air temperature in real time; the second PID controller 11 controls the opening of the electronic expansion valve 5 by collecting the exhaust pressure value in real time. In the present invention, the transcritical carbon dioxide reverse defrosting system can be controlled to operate in the heating mode or the cooling mode through the four - way reversing valve.

[0064] In the heating mode of the above - mentioned transcritical carbon dioxide air - conditioning heat pump system provided by the embodiments of the present invention, the high - temperature and high - pressure steam flow (refrigerant) at the outlet of the compressor 1 flows through the A - B channel of the four - way reversing valve 2 and then flows into the defrosting heat exchanger 3, and then enters the main heat exchanger 4. After releasing heat in the two heat exchangers, the high - temperature and high - pressure steam is throttled to a low - temperature and low - pressure state through the electronic expansion valve 5, enters the outdoor heat exchanger 7 to absorb ambient heat, and then the low - temperature and low - pressure steam passes through the C - D channel of the four - way reversing valve and then returns to the compressor 1 through the accumulator 8. In addition, in the cooling mode, the high - temperature and high - pressure steam flow at the outlet of the compressor 1 flows through the A - C channel of the four - way reversing valve 2, enters the outdoor heat exchanger 7 to release heat, then passes through the second channel of the regenerator 6, exchanges heat with the low - pressure - side refrigerant, and after further cooling, flows into the electronic expansion valve 5 to be throttled to a low pressure, enters the main heat exchanger 4 and the defrosting heat exchanger 3 to absorb heat, and then returns to the compressor 1 through the B - D channel of the four - way reversing valve and the accumulator 8 in sequence.

[0065] In the control method provided by the embodiment of the present invention, the liquid carry - over degree of the compressor suction and the superheat degree at the outlet of the outdoor heat exchanger 7 are calculated based on the state parameters of the real - time acquisition system. Different control strategies are adopted for control within different ranges of liquid carry - over degree and superheat degree, which can be referred to Figure 3 As shown, one of the advantages of this method is its strong applicability and can be used in most transcritical carbon dioxide heat pump systems.

[0066] In the embodiment of the present invention, during control, it is necessary to collect the current state parameters of the system in real time to determine whether there is a risk of control imbalance. Specifically, six signal values of the suction temperature, suction pressure, discharge temperature, discharge pressure of the compressor 1, and the outlet pressure and temperature of the evaporator (outdoor heat exchanger 7 in heat pump mode) are collected by the PT sensor. The liquid carry - over degree is calculated according to the proposed formula and the superheat degree at the outlet of the outdoor heat exchanger 7 is calculated.

[0067] More specifically, the control method proposed in the embodiment of the present invention includes three control logics in total. The first is that when the system charge is appropriate, the compressor controls the supply air temperature and the electronic expansion valve controls the discharge pressure of the compressor; the second is when the system charge is insufficient, the compressor controls the supply air temperature and the electronic expansion valve controls the superheat degree σ at the outlet of the refrigerant outdoor heat exchanger 7; the third is when there is liquid carry - over at the compressor suction, the compressor controls the supply air temperature and the electronic expansion valve controls the liquid carry - over degree θ. The control logic suitable for the current system state is judged and switched according to the superheat degree σ and the liquid carry - over degree θ calculated from the above - collected signals; after liquid carry - over at the compressor suction or when the superheat degree at the outlet of the outdoor heat exchanger 7 is too large, it enters unconventional control. Whether the control is stable is judged by the difference between the maximum value and the minimum value of the superheat degree σ and the liquid carry - over degree θ within 60 s. After the control is stable, the target value of the discharge pressure of the PID control mode 1 is given and the control mode is switched to the PID control mode 1.

[0068] During the operation of the system, P optimal Due to factors such as inappropriate charge, etc., it may be not equal to P adjust When the operating conditions of the system do not change, P adjust can be directly adopted, and the system will not enter an out - of - balance state. However, if the operating conditions change and P adjust continues to be used, it may lead to a decline in system performance. Here, the difference between the maximum value and the minimum value of the valve - front temperature and the outlet pressure of the outdoor heat exchanger 7 within 60 s is introduced to judge the change of the current working condition. If the difference exceeds the set threshold, and P optimal and P adjust differ greatly, then P optimal is used as the target discharge pressure to continue operating the system. If the difference is not large, P adjustControl is carried out for the target exhaust pressure, which effectively improves the variable operating condition adaptability of the system. To avoid frequent switching of the control mode caused by system parameter fluctuations due to reasons such as the system not being stable and operating condition parameters during the control process, the control time of each control mode is collected, and it is ensured that the system can be switched only after running for 150 s in the current control mode, so as to ensure the stability of the control.

[0069] Please refer to Figure 3 , a method for suppressing the imbalance of a transcritical carbon dioxide heat pump specifically provided by an embodiment of the present invention includes the following steps:

[0070] Step 1: Collect the real-time state parameters of the system and perform data processing to provide a basis for the selection of subsequent control logics; among them, parameters such as the suction pressure, suction temperature, exhaust pressure, exhaust temperature, the outlet pressure of the outdoor heat exchanger 7, and the outlet temperature of the outdoor heat exchanger 7 in the system are collected to calculate the liquid carry-over degree at the compressor suction and the refrigerant superheat degree at the outlet of the outdoor heat exchanger 7. The calculation formula for the liquid carry-over degree is:

[0071]

[0072] In the formula: θ is the liquid carry-over degree; S suc is the suction entropy value; P dis is the compressor exhaust pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor exhaust temperature; η is the compressor isentropic efficiency, which is calculated by a fitting formula. Step 1 of the embodiment of the present invention is the signal collection and preprocessing stage of the entire control system. Among them, each parameter is determined through a large number of experiments and simulation studies and has high reliability. The liquid carry-over degree θ is also a value that can better reflect the liquid carry-over degree at the compressor suction proposed through continuous improvement and practice. This step provides a basis for subsequent control.

[0073] Step 2: Select the control logic according to the calculation results in Step 1. The specific steps are as follows:

[0074] Step 2.1: Determine whether the superheat degree at the outlet of the outdoor heat exchanger 7 satisfies σ < 2 °C. If so, enter Judgment 2.2; if not, adopt the PID control mode 2. The input of the electronic expansion valve PID controller is the superheat degree σ at the outlet of the outdoor heat exchanger 7, and the output is the opening degree of the electronic expansion valve. Next, enter Step 2.3;

[0075] Step 2.2: Calculate the suction liquid-carrying degree θ and determine whether θ > 5°C is satisfied. If so, adopt PID control mode 3. The input of the electronic expansion valve PID controller is the suction liquid-carrying degree θ, and the output is the opening of the electronic expansion valve. Then proceed to step 2.4 in the next step. If not, enter PID control mode 1. The input of the electronic expansion valve PID controller is the target discharge pressure P target , and the output is the opening of the electronic expansion valve. Then proceed to step 2.5 in the next step;

[0076] Step 2.3: By collecting the value of the superheat degree σ at the outlet of the outdoor heat exchanger 7 within 60 s, if the maximum value - minimum value < 0.5°C, it is considered that the adjustment is stable at this time and is in a position close to the optimal discharge pressure. Since there is still 2°C of superheat, set the adjusted discharge pressure P adjust = P dis - ΔP1, and the recommended value of ΔP1 is 0.5 MPa, which can be appropriately adjusted according to the operating characteristics of the system. If the maximum value - minimum value ≥ 0.5°C, continue to collect signals and loop for judgment;

[0077] Step 2.4: By collecting the value of the suction liquid-carrying degree θ of the compressor within 60 s, if the maximum value - minimum value < 0.5°C, it is considered that the adjustment is stable at this time and is in a position close to the optimal discharge pressure. Since there is still 5°C of liquid-carrying degree, set the adjusted discharge pressure P adjust = P dis + ΔP2, and the recommended value of ΔP2 is 0.3 MPa, which can be appropriately adjusted according to the operating characteristics of the system. If the maximum value - minimum value ≥ 0.5°C, continue to collect signals and loop for judgment;

[0078] Step 2.5: Receive the target discharge pressure P target signal in step 3 of synchronous operation and use it as the target signal to input into the PID controller of the electronic expansion valve for control.

[0079] Step 2 of the embodiment of the present invention involves the switching and selection of control methods. It should be noted that the present invention realizes the effect of suppressing control imbalance by changing the controlled quantity of PID control. When using the conventional PID control mode 1, the compressor controls the air supply temperature of the carriage, and the opening of the electronic expansion valve controls the discharge pressure of the system. When liquid is carried at the suction of the compressor, the system flow rate increases sharply and the discharge temperature drops sharply. At this time, the air supply temperature cannot meet the requirements, so the compressor speed increases. However, the increase in speed will cause the discharge pressure to increase, the opening of the electronic expansion valve to increase, resulting in an excessive system flow rate, poor heat exchange on the high-pressure side, and the refrigerant that should originally accumulate on the high-pressure side continuously enters the low-pressure side, leading to a more serious situation of liquid carrying at the suction of the compressor and ultimately resulting in the control imbalance of the system.

[0080] In the technical solution of the embodiment of the present invention, the calculation of the liquid carry - over degree θ of the compressor suction is defined, and when the liquid carry - over degree is relatively large, a control method of controlling the liquid carry - over degree of the suction by the opening of the electronic expansion valve is adopted. Its main principle is that as the opening of the electronic expansion valve decreases, the system high - pressure continuously increases, and the low - pressure refrigerant can continuously flow back to the high - pressure side, gradually slowing down the liquid carry - over phenomenon at the suction until the liquid carry - over phenomenon at the compressor suction is relatively slight. At this time, the control mode is switched so that the opening of the electronic expansion valve continues to control the exhaust pressure, and the exhaust pressure target value at this time is given according to the then exhaust pressure after the liquid carry - over is slight and the system is stable, which can ensure that the system is in a state where there is basically no liquid carry - over at the suction, and at this time, the system also has the highest energy efficiency ratio. At the same time, it should be noted that during the control process, the switching of various PID control modes is involved, and during the switching process, the mode may frequently mutate due to various factors such as system instability. To solve this problem, in the present invention, when switching between various PID control modes, it is necessary to ensure that the system runs in the current mode for a time t > 150s, where 150s is a recommended value and can be appropriately adjusted according to the system operation characteristics.

[0081] In the logic of the present invention, when the liquid carry - over at the compressor suction is less and has not reached the point of complete system imbalance, its liquid carry - over degree θ is also at a relatively high level. At this time, the energy efficiency ratio of the system will also be greatly reduced, and this problem can be effectively solved by applying the control logic of the present invention. For such phenomena caused by over - charging / liquid carry - over at the suction, it can be well solved. When the system is in an under - charged state, due to insufficient refrigerant, it may be difficult to reach the original exhaust pressure, and there may be imbalance phenomena such as too high compressor speed and exhaust pressure. The present invention also optimizes this situation. The superheat at the evaporator outlet represents the under - charged degree of the system to a certain extent. When the system is significantly under - charged, instead of controlling the exhaust pressure, controlling the superheat to a certain value can effectively protect the transcritical carbon dioxide heat pump system and prevent it from being damaged due to under - charge imbalance. At the same time, when the system is under - charged, its COP will decrease sharply, and through the control method of the present invention, the system can also be controlled to operate at a higher energy efficiency ratio, improving the system efficiency.

[0082] Please refer to Figure 4 In the embodiment of the present invention, the steps of collecting data, calculating and comparing, and then giving the target exhaust pressure P in PID control mode 1 target The specific values may specifically include:

[0083] Step 3.1, collect the optimal exhaust pressure P under the current operating conditions optima , the adjusted exhaust pressure P synchronously calculated in step 2 adjust , the temperature in front of the current system valve, and the pressure at the outlet of the outdoor heat exchanger. Where P optima is calculated according to the current system operating conditions;

[0084] Step 3.2: Judge according to the maximum - minimum value Δξ of the valve - front temperature within 60 s and the maximum - minimum value Δφ of the evaporator outlet pressure within 60 s collected. If Δφ < 0.5 bar and Δξ < 0.5 °C, it is considered that the system is stable. Here, 60 s, 0.5 °C, and 0.5 bar are recommended values and can be adjusted appropriately according to the system operation characteristics. If the system is stable, proceed to Step 3.3 for judgment; if the system is judged to be unstable, maintain P target = P adjust ;

[0085] Step 3.3: Calculate whether |P optimal - P adjust |> 0.3 MPa is satisfied; if so, it indicates that the working condition has changed and the optimal discharge pressure has changed greatly, and P target = P optimal needs to be updated; if not, then maintain P target = P adjust .

[0086] Due to the variability of the system operation conditions, it is required that the imbalance suppression control logic can still adjust the system to operate efficiently and safely when the working conditions change. The above - mentioned Step 3 can effectively solve this problem. When the system working condition remains unchanged, the system still controls according to the original control logic. After the working condition changes, compare the exhaust pressure value of the original control logic with the theoretical optimal exhaust pressure value under the new working condition. If the deviation is large, then adopt the calculated value under the new working condition; otherwise, maintain the original target discharge pressure unchanged. This ensures the update of the system exhaust pressure under variable working conditions and avoids situations such as the decrease of the system COP and unsafe operation caused by no action of the control system after the change of the working condition.

[0087] In the technical solution of the embodiment of the present invention, a method for real-time judging the operation state of the system according to the superheat degree σ and the liquid carry-over degree θ is proposed; among them, the charging state parameters of the system are proposed to be judged, that is, the suction pressure of the compressor, the suction temperature, the discharge pressure and the discharge temperature, the evaporator outlet pressure, and the evaporator outlet temperature to accurately judge the undercharging and overcharging states of the system; when the system is not in the proper charging state under the optimal discharge pressure, it can be further adjusted according to the present invention to improve the system performance. For the control logic proposed by the present invention after liquid carry-over in suction compared with the original control logic, the control imbalance phenomenon can be well suppressed and the system can operate safely and stably; when judging the system mode switch, a judgment mechanism for protecting the current logic operation time is added to prevent the problem of frequent switching of the control mode caused by fluctuations in system parameters due to various reasons during operation; after the environmental working condition changes, the system can update the target discharge pressure value according to the comparison between the current target discharge pressure and the optimal discharge pressure after the working condition changes. To sum up, the embodiment of the present invention discloses a method for suppressing imbalance control of a transcritical carbon dioxide heat pump, which realizes the judgment of the undercharging, proper charging, and liquid carry-over states in suction of the system by collecting the real-time state parameters of the carbon dioxide heat pump system, and selects the appropriate PID control logic according to the current state to prevent system control imbalance and improve the energy efficiency ratio of the system.

[0088] The following is the device embodiment of the present invention, which can be used to execute the method embodiment of the present invention. For the details not disclosed in the device embodiment, please refer to the method embodiment of the present invention.

[0089] Please refer to Figure 5 , in another embodiment of the present invention, a transcritical carbon dioxide heat pump imbalance suppression control system is provided, including:

[0090] An acquisition module, configured to acquire the superheat degree and the liquid carry-over degree of the transcritical carbon dioxide heat pump air-conditioning system;

[0091] A control module, configured to implement imbalance suppression control by using an electronic expansion valve PID controller based on the obtained superheat degree and liquid carry-over degree;

[0092] Among them, the calculation formula of the liquid carry-over degree is,

[0093] In the formula, θ is the liquid carry-over degree; S suc is the suction entropy value; P dis is the compressor discharge pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor discharge temperature; η is the compressor isentropic efficiency.

[0094] A control system for suppressing imbalance in a transcritical carbon dioxide heat pump disclosed in an embodiment of the present invention calculates superheat and liquid carry-over based on the compressor suction pressure, suction temperature, discharge pressure, discharge temperature, evaporator outlet pressure, and outlet temperature collected in real time from the system, and suppresses the control imbalance of the transcritical carbon dioxide heat pump system by using different control methods according to the calculation results; the present invention solves the problem of control imbalance in the transcritical carbon dioxide heat pump system, promotes the application and popularization of the transcritical carbon dioxide heat pump, and makes significant contributions to environmental protection, alleviating the fossil energy crisis, and achieving carbon neutrality and carbon peak.

[0095] In another embodiment of the present invention, a computer device is provided. The computer device includes a processor and a memory. The memory is used to store a computer program. The computer program includes program instructions. The processor is used to execute the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of the transcritical carbon dioxide heat pump imbalance suppression control method.

[0096] In another embodiment of the present invention, the present invention further provides a storage medium, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in a computer device and is used to store programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and, of course, the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, and the operating system of the terminal is stored in this storage space. Moreover, one or more instructions suitable for being loaded and executed by the processor are stored in this storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. One or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the method for suppressing the imbalance of a transcritical carbon dioxide heat pump in the above embodiments.

[0097] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0098] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the specified functions in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0099] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the functions in Figure 1 one flow or multiple flows and / or blocksFigure 1 The functions specified in one or more boxes.

[0100] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide for implementing the steps of the functions specified in one Figure 1 process or multiple processes and / or boxes Figure 1 or more boxes.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for suppressing the imbalance of a transcritical carbon dioxide heat pump, characterized in that, Including the following steps: Obtain the superheat degree and liquid carry-over of the transcritical carbon dioxide heat pump air-conditioning system; Based on the obtained superheat degree and liquid carry-over, adopt an electronic expansion valve PID controller to achieve offset suppression control; Wherein, the calculation formula of the liquid carry-over is where θ is the liquid-carrying degree; S suc is the suction entropy value; P dis is the compressor discharge pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor discharge temperature; η is the compressor isentropic efficiency; T(H, P) and H(T, P) are refrigerant property functions; The step of adopting an electronic expansion valve PID controller to achieve offset suppression control based on the obtained superheat degree and liquid carry-over includes: when the superheat degree is greater than the first preset threshold, control the input of the electronic expansion valve PID controller to be the superheat degree, and the output to be the opening of the electronic expansion valve; when the liquid carry-over is greater than the second preset threshold, control the input of the electronic expansion valve PID controller to be the liquid carry-over, and the output to be the opening of the electronic expansion valve; under other conditions, control the input of the electronic expansion valve PID controller to be the target exhaust pressure, and the output to be the opening of the electronic expansion valve.

2. The method for suppressing the imbalance of a transcritical carbon dioxide heat pump according to claim 1, characterized in that, The step of obtaining the superheat degree and liquid carry-over of the transcritical carbon dioxide heat pump air-conditioning system includes: Obtain the operating parameters of the transcritical carbon dioxide heat pump air-conditioning system; wherein, the operating parameters include compressor exhaust temperature, exhaust pressure, suction temperature, suction pressure, evaporator outlet temperature, and pressure; Based on the obtained operating parameters, calculate the liquid carry-over through a formula.

3. The method for suppressing the imbalance of a transcritical carbon dioxide heat pump according to claim 1, characterized in that, The value range of the first preset threshold is greater than or equal to 2 and less than or equal to 5; the value range of the second preset threshold is greater than or equal to 5 and less than or equal to 10.

4. The method for suppressing the imbalance of a transcritical carbon dioxide heat pump according to claim 1, characterized in that, The step of obtaining the target exhaust pressure includes: Obtain the ambient working condition and calculate the optimal exhaust pressure, the adjusted optimal exhaust pressure, the valve front temperature, and the evaporator outlet pressure; Given the target exhaust pressure according to whether the ambient working condition changes and the size relationship between the optimal exhaust pressure and the adjusted optimal exhaust pressure.

5. A system for suppressing the imbalance of a transcritical carbon dioxide heat pump, characterized in that, Including: An acquisition module for obtaining the superheat degree and liquid carry-over of the transcritical carbon dioxide heat pump air-conditioning system; A control module for adopting an electronic expansion valve PID controller to achieve offset suppression control based on the obtained superheat degree and liquid carry-over; Wherein, the calculation formula of the liquid carry-over is where θ is the liquid-carrying rate; S suc is the suction entropy value; P dis is the compressor discharge pressure; T suc is the compressor suction temperature; P suc is the compressor suction pressure; T dis is the compressor discharge temperature; η is the compressor isentropic efficiency; T(H, P) and H(T, P) are refrigerant property functions; In the control module, the step of adopting an electronic expansion valve PID controller to achieve offset suppression control based on the obtained superheat degree and liquid carry-over includes: when the superheat degree is greater than the first preset threshold, control the input of the electronic expansion valve PID controller to be the superheat degree, and the output to be the opening of the electronic expansion valve; when the liquid carry-over is greater than the second preset threshold, control the input of the electronic expansion valve PID controller to be the liquid carry-over, and the output to be the opening of the electronic expansion valve; under other conditions, control the input of the electronic expansion valve PID controller to be the target exhaust pressure, and the output to be the opening of the electronic expansion valve.

6. The system for suppressing the imbalance of a transcritical carbon dioxide heat pump according to claim 5, characterized in that, In the acquisition module, the step of obtaining the superheat degree and liquid carry-over of the transcritical carbon dioxide heat pump air-conditioning system includes: Obtain the operating parameters of the transcritical carbon dioxide heat pump air-conditioning system; wherein, the operating parameters include compressor exhaust temperature, exhaust pressure, suction temperature, suction pressure, evaporator outlet temperature, and pressure; Based on the obtained operating parameters, calculate the liquid carry-over through a formula.

7. The system for suppressing the imbalance of a transcritical carbon dioxide heat pump according to claim 5, characterized in that, The value range of the first preset threshold is greater than or equal to 2 and less than or equal to 5; the value range of the second preset threshold is greater than or equal to 5 and less than or equal to 10.

8. The system for suppressing the imbalance of a transcritical carbon dioxide heat pump according to claim 5, characterized in that, The step of obtaining the target exhaust pressure includes: Obtain the environmental operating conditions and calculate to obtain the optimal discharge pressure, adjust the calculated optimal discharge pressure, the temperature before the valve, and the evaporator outlet pressure; Given the target exhaust pressure according to whether the environmental operating conditions change and the magnitude relationship between the optimal discharge pressure and the adjusted calculated optimal discharge pressure.

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