Carbon dioxide refrigeration heat pump system and composite control method

Abstract

The application discloses a carbon dioxide refrigeration heat pump system and a composite control method of the carbon dioxide refrigeration heat pump system. The carbon dioxide refrigeration heat pump system comprises a first compressor, a second compressor, a third compressor, a water cooler, a first regenerator, a first throttling valve, a flash tank, a second throttling valve, an evaporator, a liquid storage barrel, a flash bypass valve and a second regenerator which are connected and matched with each other. The carbon dioxide refrigeration heat pump system and the composite control method have the advantages that the design is scientific, the working condition of the carbon dioxide refrigeration heat pump system can be accurately controlled, the control precision is improved, the working condition energy efficiency is obviously improved, the operation efficiency of the working condition is ensured, and the application has great practical significance. The composite control method of the carbon dioxide refrigeration heat pump system specially designed by the application is a dimension reduction decoupling control method for coping with the operation of a complex system with variable working conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refrigeration heat pump, in particular to a carbon dioxide refrigeration heat pump system and a compound control method. BACKGROUND

[0002] At present, the refrigeration heat pump system using traditional artificial synthetic refrigerants such as freon will produce a great greenhouse effect. Carbon dioxide working medium has a greenhouse effect potential of only 1, which is an excellent alternative working medium for realizing carbon neutral refrigeration and heat pump system. However, the carbon dioxide refrigeration heat pump system still needs to pass through a complex system structure to improve its energy efficiency and then reduce the greenhouse effect in the operation process.

[0003] However, the control of the existing complex system structure is difficult, the control precision is not high, and the operating condition in the actual operation often deviates from the optimal operating condition.

[0004] Therefore, it is urgent to develop a technology which can effectively realize accurate control of the operating condition of the carbon dioxide refrigeration heat pump system, improve the control precision and significantly improve the energy efficiency of the operating condition. SUMMARY

[0005] The purpose of the present application is to provide a carbon dioxide refrigeration heat pump system and a compound control method to overcome the technical defects of the prior art.

[0006] To this end, the present application provides a carbon dioxide refrigeration heat pump system, characterized in that it comprises a first compressor, a second compressor, a third compressor, a water cooler, a first regenerator, a first throttling valve, a flash tank, a second throttling valve, an evaporator, a liquid storage barrel, a flash bypass valve and a second regenerator.

[0007] The working medium outlets of the first compressor, the second compressor and the third compressor are connected to the working medium inlet of the water cooler after converging and intersecting;

[0008] The working medium outlet of the water cooler is connected to the high-pressure side inlet a of the first regenerator;

[0009] The high-pressure side outlet b of the first regenerator is connected to the inlet of the first throttling valve;

[0010] The outlet of the first throttling valve is connected to the working medium inlet a of the flash tank;

[0011] The first working medium outlet b of the flash tank is connected to the low-pressure side inlet c of the first regenerator;

[0012] The second working medium outlet d of the flash tank is connected to the high-pressure side inlet b of the second regenerator;

[0013] The third working medium outlet c of the flash tank is connected to one end of the flash bypass valve.

[0014] The other end of the flash bypass valve is connected with the third working medium inlet d above the liquid storage barrel;

[0015] The low-pressure side outlet d of the first regenerator is connected with the working medium inlets of the second compressor and the third compressor respectively;

[0016] The high-pressure side outlet a of the second regenerator is connected with the inlet of the second throttling valve;

[0017] The outlet of the second throttling valve is connected with the second working medium inlet b of the liquid storage barrel;

[0018] The second working medium outlet e on the lower side of the liquid storage barrel is connected with the working medium inlet of the evaporator;

[0019] The working medium outlet of the evaporator is connected with the first working medium inlet a on the upper side of the liquid storage barrel;

[0020] The first working medium outlet c on the upper side of the liquid storage barrel is connected with the low-pressure side inlet d of the second regenerator;

[0021] The low-pressure side outlet c of the second regenerator is connected with the working medium inlet of the first compressor.

[0022] In addition, the application also provides a composite control method of the carbon dioxide refrigeration heat pump system, comprising the following steps:

[0023] Step S1, input the cold and heat demand parameters and environmental parameters of the carbon dioxide refrigeration heat pump system, and judge the current working mode of the system;

[0024] Step S2, set the system operation parameter control target, determine the associated control object according to the system operation parameter control target, then adjust and control the control object through the setting of the variable working condition operation composite control logic, so as to realize the actual value of the system operation parameter control target approaching the target value set in advance.

[0025] From the above technical solutions provided by the application, compared with the prior art, the application provides a carbon dioxide refrigeration heat pump system and a composite control method, which are designed scientifically, can effectively realize accurate control of the working condition of the carbon dioxide refrigeration heat pump system, improve the control precision, significantly improve the working condition energy efficiency, guarantee the operation efficiency of the working condition, and have great practical significance.

[0026] For the complex carbon dioxide refrigeration heat pump system, the composite control method of the carbon dioxide refrigeration heat pump system specially designed by the present invention is a dimension reduction decoupling control method for coping with the operation of a complex system under variable working conditions. The present invention proposes a new control logic. By decomposing the multi-dimensional control objectives through dimension reduction, obtaining the main influencing parameters of the control objectives based on sensitivity analysis, and collaborating with multiple control components to approximate the control objectives, the controllability of the complex system can be significantly enhanced, the complexity of the control system development can be reduced, and the comprehensive performance evaluation is carried out based on the dynamic response and tracking effect of the components, forming a full-process control system of control logic, control method, specific implementation, performance evaluation and feedback. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. is a schematic structural diagram of a carbon dioxide refrigeration heat pump system provided by the present invention;

[0028] Figure 2 FIG. is a working flow chart of a composite control method of a carbon dioxide refrigeration heat pump system provided by the present invention;

[0029] In the figure, 1 - first compressor; 2 - second compressor; 3 - third compressor; 4 - water cooler; 5 - first internal heat exchanger;

[0030] 6 - first throttle valve; 7 - flash tank; 8 - second throttle valve; 9 - evaporator; 10 - liquid storage barrel;

[0031] 11 - flash bypass valve; 12 - second internal heat exchanger; 13 - controller;

[0032] 16 is the frequency control parameter of the first compressor 1, 17 is the frequency control parameter of the second compressor 2, 18 is the frequency control parameter of the third compressor 3, 19 is the operating frequency of the cooling fan supporting the water cooler 4;

[0033] 20 is the system evaporation pressure and temperature parameter, 21 is the system intermediate pressure and temperature parameter 21, 22 is the system high-pressure pressure parameter, 23 is the system water cooler outlet temperature parameter 23;

[0034] 24 is the opening control parameter of the first throttle valve 6, 25 is the opening control parameter of the second throttle valve 8, 26 is the opening control parameter of the flash bypass valve 11.

[0035] 27 - externally input cold and heat demand parameters. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of the present application.

[0037] In the description of the present patent, it should be noted that unless otherwise explicitly specified and limited, the terms "mount", "connect", "connection", "set" should be understood in a broad sense, for example, can be fixedly connected, set, or detachably connected, set, or integrally connected, set. For those of ordinary skill in the art, the specific meanings of the above terms in the present patent can be understood according to the specific circumstances.

[0038] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly specified and limited.

[0039] Referring to Figure 1 , the present application provides a carbon dioxide refrigeration heat pump system, comprising: a first compressor 1, a second compressor 2, a third compressor 3, a water cooler 4, a first regenerator 5, a first throttling valve 6, a flash tank 7, a second throttling valve 8, an evaporator 9, a liquid storage barrel 10, a flash bypass valve 11 and a second regenerator 12;

[0040] The working medium outlets of the first compressor 1, the second compressor 2 and the third compressor 3 are connected with the working medium inlet of the water cooler 4 after converging intersection;

[0041] The working medium outlet of the water cooler 4 is connected with the high-pressure side inlet a of the first regenerator 5;

[0042] The high-pressure side outlet b of the first regenerator 5 is connected with the inlet of the first throttling valve 6;

[0043] The outlet of the first throttling valve 6 is connected with the working medium inlet a of the flash tank 7;

[0044] The first working medium outlet b of the flash tank 7 is connected with the low-pressure side inlet c of the first regenerator 5;

[0045] The second working medium outlet d of the flash tank 7 is connected with the high-pressure side inlet b of the second regenerator 12;

[0046] The third working medium outlet c of the flash tank 7 is connected with one end of the flash bypass valve 11.

[0047] The other end of the flash bypass valve 11 is connected with the third working medium inlet d above the liquid storage tank 10.

[0048] The low-pressure side outlet d of the first regenerator 5 is connected with the working medium inlets of the second compressor 2 and the third compressor 3 respectively.

[0049] The high-pressure side outlet a of the second regenerator 12 is connected with the inlet of the second throttling valve 8.

[0050] The outlet of the second throttling valve 8 is connected with the second working medium inlet b of the liquid storage tank 10.

[0051] The second working medium outlet e on the lower side of the liquid storage tank 10 is connected with the working medium inlet of the evaporator 9.

[0052] The working medium outlet of the evaporator 9 is connected with the first working medium inlet a on the upper side of the liquid storage tank 10.

[0053] The first working medium outlet c (i.e. the outlet of the gaseous carbon dioxide) on the upper side of the liquid storage tank 10 is connected with the low-pressure side inlet d of the second regenerator 12.

[0054] The low-pressure side outlet c of the second regenerator 12 is connected with the working medium inlet of the first compressor 1.

[0055] In the present application, specifically, the first compressor 1 is a low-pressure stage compressor, which is used to realize the pressure and temperature rising process of the low-pressure side carbon dioxide working medium, and form the high-temperature and high-pressure carbon dioxide working medium.

[0056] The second compressor 2 and the third compressor 3 are intermediate pressure compressors, which are used to realize the pressure and temperature rising process of the intermediate pressure side carbon dioxide working medium.

[0057] For example, the exhaust pressure below 0-3 MPa is a low-pressure compressor; the exhaust pressure of 2-10 MPa is a medium (intermediate pressure) compressor.

[0058] It should be noted that the first compressor 1, the second compressor 2 and the third compressor 3 can be frequency-adjusted, in order to ensure the stable operation of the system and avoid the frequent start and stop of the compressors as much as possible, the intermediate pressure compressors of the present application include two: the second compressor 2 and the third compressor 3, which can be frequency-controlled according to the specific working condition requirements.

[0059] In the present application, specifically, the upper part of the inner cavity of the flash tank 7 is the saturated gaseous carbon dioxide area, and the lower part of the inner cavity of the flash tank 7 is the saturated liquid carbon dioxide area. The flash tank 7 itself has three working medium outlets.

[0060] In the present application, the inner cavity of the liquid storage barrel 10 has low-temperature and low-pressure carbon dioxide liquid on the lower side, and has low-temperature and low-pressure carbon dioxide gas on the upper side.

[0061] In order to more clearly understand the technical solutions of the present application, the working principle of the carbon dioxide refrigeration heat pump system of the present application is described below, that is, the present application includes the following working modes:

[0062] In the first step, the carbon dioxide working medium at the outlet of the first compressor 1, the second compressor 2 and the third compressor 3 is then introduced into the water cooler 4, and the process realizes the cooling of the carbon dioxide working medium to have refrigeration capacity. At the same time, water or the like is selected as the cooling medium to realize the heating of the carbon dioxide to the water to have heat supply capacity.

[0063] In the second step, the carbon dioxide working medium flowing out of the outlet of the water cooler 4 is then introduced into the high-pressure side inlet of the first regenerator 5 to further reduce the temperature of the carbon dioxide working medium and improve the refrigerating capacity per unit volume of the carbon dioxide working medium;

[0064] In the third step, the high-pressure side outlet of the first regenerator 5 is further connected to the first throttling valve 6, and through the isenthalpic throttling process in the first throttling valve, the pressure and temperature of the carbon dioxide can be significantly reduced to form carbon dioxide working medium with intermediate pressure and intermediate temperature;

[0065] In the fourth step, the carbon dioxide after the first throttling valve 6 enters the flash tank 7, and the gas-liquid separation of the carbon dioxide working medium is realized by the flash tank 7;

[0066] In the fifth step, after the gas-liquid separation of the carbon dioxide working medium is realized in the flash tank 7, the following preset working circuit is run to form continuous refrigeration capacity:

[0067] Working circuit one: through the first working medium outlet b of the flash tank 7, the saturated gas above the flash tank 7 with intermediate temperature and intermediate pressure enters the low-pressure side inlet c of the first regenerator 5 to cool the carbon dioxide on the high-pressure side and is heated itself, and the carbon dioxide passing through the low-pressure side outlet d of the first regenerator 5 enters the intermediate-pressure parallel compressor (i.e., the second compressor 2 and the third compressor 3), and through the compression of the second compressor 2 and the third compressor 3, the carbon dioxide with intermediate pressure is raised to high-pressure;

[0068] Working circuit two: through the second working medium outlet of the flash tank 7, the saturated liquid-phase carbon dioxide below the flash tank 7 flows into the high-pressure side inlet b of the second regenerator 12, and through the cooling of the second regenerator 12, the carbon dioxide has higher refrigerating capacity per unit volume;

[0069] Then, the cooled part of the carbon dioxide flows into the second throttle valve 8 through the high-pressure side outlet a of the second regenerator 12, realizes throttling and cooling, and becomes low-temperature and low-pressure carbon dioxide working medium;

[0070] Then, the low-temperature and low-pressure carbon dioxide working medium flowing through the second throttle valve 8 is introduced into the liquid storage tank 10, and gas-liquid separation is carried out in the liquid storage tank 10. Since the low-temperature and low-pressure carbon dioxide liquid is stored in the lower side of the inner cavity of the liquid storage tank 10, and the low-temperature and low-pressure carbon dioxide gas is stored in the upper side of the inner cavity of the liquid storage tank 10, the low-temperature and low-pressure carbon dioxide liquid in the lower side of the inner cavity of the liquid storage tank 10 absorbs heat to realize refrigeration capacity when introduced into the evaporator 9, and the carbon dioxide heated by the evaporator 9 becomes gas-liquid two-phase or gaseous working medium and returns to the upper side of the liquid storage tank 10;

[0071] Then, the low-temperature and low-pressure gaseous carbon dioxide is introduced into the low-pressure side inlet d of the second regenerator 12 through the first working medium outlet c (i.e. the outlet of gaseous carbon dioxide) in the upper side of the liquid storage tank 10, is used to cool the carbon dioxide working medium in the high-pressure side of the second regenerator 12, and is heated itself. The carbon dioxide working medium after being heated has superheat degree, which ensures that no liquid hammer phenomenon occurs when entering the first compressor 1 and the first compressor 1 is damaged.

[0072] Then, the carbon dioxide flowing out of the low-pressure side outlet c of the second regenerator 12 is introduced into the first compressor 1, and the gaseous carbon dioxide in the liquid storage tank 10 is continuously extracted by the suction operation of the first compressor 1 to form continuous refrigeration capacity.

[0073] Working circuit three: The saturated gaseous carbon dioxide is introduced into the flash bypass valve 11 through the third working medium outlet (i.e. gaseous working medium outlet) c of the flash tank 7, and then is introduced into the liquid storage tank 10 through the flash bypass valve 11, so as to realize the control of the internal pressure of the flash tank 7 and the unloading in emergency (convenient for maintenance).

[0074] In order to more clearly understand the technical solutions of the present application, the functions of the main components in the present application and the working principle of mutual cooperation are described below.

[0075] In the present application, the first compressor 1 is used to compress the low-pressure carbon dioxide to high pressure, and the temperature of the carbon dioxide also rises.

[0076] The second compressor 2 is used to compress the carbon dioxide working medium with an intermediate pressure value to high pressure.

[0077] The third compressor 3 is used to compress the carbon dioxide working medium with an intermediate pressure value to high pressure.

[0078] The outlets of the first compressor 1, the second compressor 2 and the third compressor 3 are in communication, and are jointly merged and connected to the left inlet of the water cooler 4, and are cooled, and the temperature of the carbon dioxide is reduced.

[0079] The right outlet of the water cooler 4 is further connected to the high-pressure side inlet a of the first internal heat exchanger 5, and after the high-pressure side carbon dioxide passes through the first internal heat exchanger 5, the temperature thereof is reduced, and the high-pressure side outlet b of the first internal heat exchanger 5 is flowed out and communicated to the first throttling valve 6, and under the pressure reduction and expansion effect of the first throttling valve 6 with the opening degree adjustment function, the temperature and pressure of the carbon dioxide are reduced, and the first throttling valve 6 is further connected to the high-pressure side inlet a of the flash tank 7.

[0080] The flash tank 7 is a space for storing gaseous and liquid carbon dioxide, and the internal space is gaseous and liquid carbon dioxide with a certain pressure and in a phase equilibrium state. The gaseous phase outlet of the flash tank 7 has two, which are the first working medium outlet b and the second working medium outlet c (i.e. the gaseous phase outlet c), wherein the first working medium outlet b is further connected to the low-pressure side inlet c of the first internal heat exchanger 5, and through heat exchange with the high-pressure side carbon dioxide, the temperature of the low-pressure side carbon dioxide is increased and the temperature of the high-pressure side carbon dioxide is reduced, and the low-pressure side carbon dioxide is further connected to the second compressor 2 and the third compressor 3 through the low-pressure side outlet d of the first internal heat exchanger 5. The gaseous phase outlet c of the flash tank 7 is further connected to the flash bypass valve 11, and the flash bypass valve 11 is arranged to directly control the pressure of the flash tank 7, so as to avoid the pressure of the flash tank 7 exceeding the design upper limit pressure. The carbon dioxide passing through the flash bypass valve 11 is further connected to the gaseous phase inlet d in the liquid storage barrel 10.

[0081] The storage tank 10 is a space capable of storing gaseous and liquid carbon dioxide. Below the flash tank 7 is the liquid phase outlet d, which further connects to the high-pressure side inlet b of the second internal regenerator 12. In the second internal regenerator 12, the high-pressure side carbon dioxide is cooled, further reducing its temperature. The high-pressure side carbon dioxide flows out from the outlet a of the second internal regenerator and connects to the second throttle valve 8. Under the pressure-reducing expansion action of the second throttle valve 8, which has an opening adjustment function, both the temperature and pressure of the carbon dioxide decrease, and it further connects to the gas phase inlet b in the storage tank 10 through the second throttle valve 8. The storage tank 10 has two gas phase inlets a and b (i.e., the first working fluid inlet a and the second working fluid inlet b) at the top, and one gas phase outlet c (i.e., the first working fluid outlet c). On the right side is a gas phase inlet (i.e., the third working fluid inlet d), and below is a liquid phase outlet e (i.e., the second working fluid outlet e). The lower liquid phase outlet e is connected to one side inlet of the evaporator 9, where the liquid carbon dioxide undergoes evaporation, becoming gaseous. Its temperature remains constant during the phase change, but it experiences superheat after becoming gaseous. This gaseous carbon dioxide is connected to the gas phase inlet a of the storage tank 10 via the outlet of the evaporator 9. The upper gas phase outlet c of the storage tank 10 further connects the gaseous carbon dioxide to the low-pressure side inlet d of the second internal regenerator 12. The temperature of the low-pressure side carbon dioxide is increased, flowing out from the low-pressure side outlet d of the second internal regenerator 12 and further connected to the inlet of the first compressor 1.

[0082] Based on the carbon dioxide refrigeration heat pump system provided by the present invention, see [link to related document]. Figure 2 As shown, the present invention also provides a combined control method for a carbon dioxide refrigeration heat pump system, which includes the following steps S1 to S3:

[0083] Step S1: Input the cooling and heating demand parameters and environmental parameters of the carbon dioxide refrigeration and heat pump system, and determine the current working mode of the system;

[0084] In step S1, it should be noted that step S1 is the prior condition for the implementation of the composite control method, providing the boundary input of the composite control method and providing the basis for mode selection for the execution of the composite control method.

[0085] In step S1, specifically, the cooling and heating demand parameters include: the cooling temperature T of the carbon dioxide refrigeration heat pump system. e The heating temperature T of the carbon dioxide refrigeration heat pump system h The cooling load Q of the carbon dioxide refrigeration heat pump system e The heating load Q of the carbon dioxide refrigeration heat pump system h ;

[0086] Environmental parameters, including: the dry-bulb temperature T of the environment in which the carbon dioxide refrigeration heat pump system operates.amb and wet bulb temperature T aw and relative humidity h r .

[0087] It should be noted that the refrigeration temperature T e of the carbon dioxide refrigeration heat pump system is the temperature of the cooling medium required to be provided by the carbon dioxide refrigeration heat pump system; the heat supply temperature T h of the carbon dioxide refrigeration heat pump system is the heat supply medium temperature required to be provided by the carbon dioxide refrigeration heat pump system; the refrigeration load Q e of the carbon dioxide refrigeration heat pump system is the cold load possessed by the cooling medium required to be provided by the carbon dioxide refrigeration heat pump system; and the heat supply load Q h of the carbon dioxide refrigeration heat pump system is the heat load possessed by the heat supply medium required to be provided by the carbon dioxide refrigeration heat pump system. Generally, these parameters are requirements provided by the demand side (i.e. system user).

[0088] It should be noted that the power order of magnitude of the carbon dioxide refrigeration heat pump system mainly depends on the internal working medium mass flow rate M f , which is solved by the cold and heat demand parameters, and the larger value corresponding to the realization of refrigeration and heat pump demand is taken, i.e. the internal working medium mass flow rate M f of the carbon dioxide refrigeration heat pump system = Max[f(Q e , T e ), f(Q h , T h )].

[0089] The above parameters determine the working condition in which the carbon dioxide refrigeration heat pump system needs to operate, and directly affect the operation mode of the system.

[0090] Specifically, step S1 specifically includes the following sub-steps:

[0091] Step S11, based on the cold and heat demand parameters and the environmental parameters of the carbon dioxide refrigeration heat pump system, determines the outlet temperature T gc of the water cooler of the carbon dioxide refrigeration heat pump system, the refrigeration temperature T evap required for the operation of the carbon dioxide refrigeration heat pump system, and the heat supply temperature T hot required for the operation of the carbon dioxide refrigeration heat pump system.

[0092] In the present application, the heat transfer temperature difference dT1 between the environmental temperature and the carbon dioxide working medium in the water cooler 4 is considered, and a certain temperature drop value is selected as the difference (i.e. dT1) between the outlet temperature T gc of the water cooler and the environmental dry bulb temperature T amb according to the design of the heat exchanger, at this time T gc = T amb +dT1.

[0093] T amb is the dry-bulb temperature of the environment in which the carbon dioxide refrigeration heat pump system is operating, T gc is the outlet temperature of the water cooler of the carbon dioxide refrigeration heat pump system.

[0094] In the present application, the direct evaporation phase change process of carbon dioxide is considered to be an isothermal process, and the heat exchange temperature difference dT2 between the evaporator 9 and the heat exchanger is considered, and a certain temperature drop value is selected as the required refrigeration temperature T evap , which is the difference between the required refrigeration temperature T evap and the cooling demand temperature T e , at this time T evap =T e -dT2.

[0095] T e is the refrigeration temperature of the carbon dioxide refrigeration heat pump system (i.e. the cooling demand temperature), T evap is the required refrigeration temperature of the carbon dioxide refrigeration heat pump system.

[0096] In the present application, the heat exchange temperature difference dT3 between the carbon dioxide cooling heat release process and the heat medium is considered, and a certain temperature drop value is selected as the difference between the highest temperature of carbon dioxide and the heat demand temperature T h , at this time T hot =T h +dT3.

[0097] T hot is the required heating temperature of the carbon dioxide refrigeration heat pump system, T h is the heating temperature of the carbon dioxide refrigeration heat pump system (i.e. the heat demand temperature).

[0098] Step S12, according to the outlet temperature T gc of the water cooler of the carbon dioxide refrigeration heat pump system, the required refrigeration temperature of the carbon dioxide refrigeration heat pump system, and the required heating temperature of the carbon dioxide refrigeration heat pump system, determine the current working mode of the carbon dioxide refrigeration heat pump system.

[0099] It should be noted that the required refrigeration temperature of the carbon dioxide refrigeration heat pump system, such as refrigeration capacity and evaporation temperature, is used to serve different cooling demands. The required heating temperature of the carbon dioxide refrigeration heat pump system, such as heating capacity and cooling temperature, is used to serve different heating demands.

[0100] It should be noted that, for the present invention, the operating mode of the carbon dioxide refrigeration and heat pump system refers to the mode in which the refrigeration and heat pump system operates when responding to changes in cooling and heating demand parameters and environmental parameters. The proposal of this operating mode provides a basis for the selection of specific control methods for the refrigeration and heat pump system.

[0101] In step S12, specifically, when the outlet temperature T of the water cooler in the carbon dioxide refrigeration heat pump system... gc When the temperature value is less than A (e.g., 26℃), it operates in mode one, which is the subcritical low-temperature operating region mode M. sub ;

[0102] It should be noted that temperature value A is the boundary temperature between operating mode one and operating mode two. The condition that temperature value A satisfies is: when the outlet temperature T of water cooler 4... gc When the temperature is below this value A, the high-pressure of the carbon dioxide refrigeration heat pump system (i.e., the system operating high-pressure pressure HP, which is also the compressor outlet pressure, equal to the total pressure of the working fluid flowing out of the outlets of the first compressor 1, the second compressor 2, and the third compressor 3 after they converge) can be lower than the critical pressure of carbon dioxide. At this time, the cooling process of carbon dioxide in the water cooler 4 of the system is basically located in the subcritical phase transition region. This temperature value A is obtained based on experimental experience. Dividing the operating mode into operating mode one and operating mode two based on this temperature value A can ensure the stable operation of the system.

[0103] When the outlet temperature of the water cooler in the carbon dioxide refrigeration heat pump system is T gc Satisfy the following condition: Temperature value A (e.g., 26℃) ≤ T gc When the critical temperature of the carbon dioxide working medium (specifically 31.1℃) is reached, it operates in mode two, which is the transitional linear interpolation operating region mode M. tran ;

[0104] When the outlet temperature of the water cooler in the carbon dioxide refrigeration heat pump system is T gc When the temperature of the working fluid (specifically 31.1℃) is greater than or equal to the critical temperature of carbon dioxide, the operating mode is mode three, which is the supercritical optimal control operating region mode M. sup .

[0105] It should be noted that the operating mode 1 (subcritical low temperature operating region mode M) sub Working mode 2 (transitional linear interpolation operating region mode M) tran And working mode three (supercritical optimal control operating region mode M) sup These three operating modes, as defined in this invention, are defined separately based on the classification of the water cooler outlet temperature. Different operating modes correspond to different ambient temperatures, and the selection of the operating mode also determines the control method adopted subsequently, which is a prerequisite for the subsequent invention.

[0106] For the present application, the above temperature division is based on two considerations. One is to consider the critical parameters of carbon dioxide itself, among which the critical temperature is 31.1℃. If the outlet temperature of the water cooler of the carbon dioxide refrigeration and heat pump system is near the critical temperature of carbon dioxide, the properties of carbon dioxide will fluctuate in a large range, which puts high requirements on the control response and accuracy of the refrigeration and heat pump system. The second is based on actual test data. The above temperature division can realize high-efficiency dynamic control in all working conditions.

[0107] It should be noted that carbon dioxide is a common gas that can exhibit different physical states under different temperatures and pressures. When the temperature reaches 31.1 degrees Celsius and the pressure reaches 7.38 megapascals, carbon dioxide enters a special state, i.e., the critical state. In this state, the physical properties of carbon dioxide change significantly, making it neither completely a gas nor completely a liquid, but a special state between gas and liquid. The temperature and pressure in this state are called critical temperature and critical pressure, respectively.

[0108] In step S1, specifically, the environmental parameters of the carbon dioxide refrigeration and heat pump system include the dry-bulb temperature T amb ;

[0109] When the dry-bulb temperature T amb < the temperature value A (e.g., 26℃), the current working mode of the carbon dioxide refrigeration and heat pump system that can be operated includes any one of the three operating modes: working mode one, working mode two, and working mode three.

[0110] When the temperature value A (e.g., 26℃) ≤ the dry-bulb temperature T amb < the critical temperature of the carbon dioxide working medium (specifically 31.1℃), the current working mode of the carbon dioxide refrigeration and heat pump system that can be operated includes any one of the two operating modes: working mode two and working mode three.

[0111] When the dry-bulb temperature T amb ≥ the critical temperature of the carbon dioxide working medium (specifically 31.1℃), the current working mode of the carbon dioxide refrigeration and heat pump system that can be operated includes working mode three.

[0112] Step S2, set the system operating parameter control target, and determine the associated control object according to the system operating parameter control target, then adjust and control the control object through the setting of the variable working condition operation composite control logic, realize the actual value of the system operating parameter control target to approach (i.e., close, narrow the gap) the target value set in advance;

[0113] It should be noted that in the present application, for step S2, through which the multi-dimensional control target decoupling and key component coordination are realized. This step is a specific means for implementing the composite control method, based on the mode selection criteria of step S1, the control target parameters of the refrigeration heat pump system have the characteristics of large number and different types, the sensitive and related influence parameters are extracted, the multiple control targets are decoupled, the association of different control components (i.e. control objects) and control targets is realized, and then the high-precision and high-tracking control of the complex system is realized.

[0114] In step S2, the system operation parameter control target is specifically realized, including at least one of the control target of the outlet temperature T gc of the water cooler 4, the control target of the system operation high pressure HP and the control target of the system operation intermediate pressure IP.

[0115] It should be noted that in the present application, the outlet temperature T gc of the water cooler 4, i.e. the temperature of carbon dioxide at the outlet position after the carbon dioxide is cooled by the water cooler, which can be used as an important parameter for judging the system working mode, and is also an important controlled parameter, the value of which mainly affects the state of carbon dioxide after the first throttle valve 6, and then can affect the system efficiency;

[0116] The system operation high pressure HP, i.e. the outlet pressure of the compressor (i.e. the total pressure of the working medium flowing out of the working medium outlets of the first compressor 1, the second compressor 2 and the third compressor 3 after the convergence), which is an important controlled parameter during system operation, and its value mainly affects the compressor power consumption, and then significantly affects the system efficiency;

[0117] The system operation intermediate pressure IP, i.e. the phase equilibrium pressure of the flash tank 7, which is an important controlled parameter during system operation, and its value mainly affects the compressor power consumption, and then significantly affects the system efficiency.

[0118] In the present application, the outlet temperature T gc of the water cooler 4, the system operation high pressure HP and the system operation intermediate pressure IP can be measured by setting temperature and pressure sensors at the corresponding positions.

[0119] In step S2, the associated control objects specifically include open loop control objects and closed loop control objects.

[0120] The open loop control objects specifically include the flash tank 7 (i.e. the flash evaporator).

[0121] The closed-loop control object specifically comprises: a first compressor 1, a second compressor 2, a third compressor 3, a heat dissipation fan matched with a water cooler 4, a first throttling valve 6 and a second throttling valve 8 (i.e., an electronic expansion valve), and a flash bypass valve 11 (i.e., a bypass regulating valve).

[0122] In step S2, specifically, the associated control object is determined according to the system operation parameter control target, and the following operations are specifically implemented:

[0123] According to the system operation parameter control target, the operation parameter sensitivity analysis is performed, the control object with the highest influence sensitivity to the system operation parameter control target is extracted, and the control object is the associated control object.

[0124] It should be noted that, in the present application, the control variable method is adopted, the running parameter variation range is-20% to 20%, and the sensitivity degree affecting the system energy efficiency is investigated. When the evaporation temperature variation range is-20% to 20%, the system energy efficiency variation range is-7.4-8.18%. When the outlet temperature variation range of the water cooler 4 is-20% to 20%, the system energy efficiency variation range is-53.4% to 11.7%. When the suction superheat degree, the flash gas injection superheat degree and other parameters vary in the range of-20% to 20%, the system energy efficiency varies in the range of-0.43% to 0.41% and-0.097% to 0.075%. In the present application, the running parameter with the highest sensitivity is selected for key control.

[0125] It should be noted that, in the present application, the overall control target of the refrigeration heat pump system is to improve the energy efficiency of the refrigeration heat pump system and reduce the system power consumption on the premise of realizing the refrigeration and heating demand based on different environmental parameters. The factors affecting the system energy efficiency mainly depend on: the system multiple operation parameters, i.e., each important operation parameter directly determines the system energy efficiency. Therefore, the present application proposes to obtain the multiple-dimensional core operation parameter control target with the highest influence on the system energy efficiency based on the overall control target and the sensitivity analysis. In the present application, it is proposed that the multiple-dimensional control target is decoupled, and the system operation parameter control targets of the water cooler outlet temperature T gc , the system operation high pressure HP and the system operation intermediate pressure IP are set.

[0126] In step S2, the application associates the decoupled control target with the control object, and sets two types of control objects, namely open-loop control object and closed-loop control object. The open-loop control object is a controlled object that is not actively intervened during the dynamic operation of the system, and is mainly indirectly affected by the operation performance of other parts of the system, but the operation of the object itself also affects the stable operation of the system. The closed-loop control object is an object that needs to be actively intervened during the dynamic operation of the system, and achieves the predetermined control requirement through certain means. In the application, five specific control objects are proposed, namely the closed-loop control objects: the first compressor 1, the second compressor 2, the third compressor 3, the cooling fan matched with the water cooler 4, the first throttling valve 6 and the second throttling valve 8 (i.e. electronic expansion valve), and the flash evaporation bypass valve 11 (i.e. bypass regulating valve), and the open-loop control object: the flash tank 7 (i.e. flash evaporator).

[0127] In step S2, the application realizes the approximation of the actual value and the target value of the system operation parameter control target by setting the variable working condition operation composite control logic. Specifically, the variable working condition operation composite control logic includes the following three groups of automatic control logic, which can find the optimal parameters of the dimension reduction control target under the variable working condition operation. Based on this, for the control target, the control target is realized by reasonably combining the above-mentioned closed-loop and open-loop control objects, and the control target is in the optimal operation state. In the subsequent system introduction, the specific refrigeration heat pump system will be combined with the step to expand the composite control method in detail.

[0128] In the application, an efficient control logic for the decoupled control target is proposed, which controls the system high pressure HP, intermediate pressure IP and water cooler outlet temperature T gc with high precision, establishes parameter sensitivity analysis, allocates specific control objects for different control targets, and realizes optimal control parameters through the coordinated control of the control objects.

[0129] In step S2, specifically, in order to realize the control target of the system operation high pressure HP, the variable working condition operation composite control logic includes the first group of automatic control logic;

[0130] The first group of automatic control logic specifically includes the following operations:

[0131] First, input the upper and lower limits HP up and HP low of the current system high pressure HP;

[0132] Then, judge the set relationship between the measured value of the current system high pressure HP and the input upper and lower limits [HP up , HP low ], and adjust the opening O of the first throttling valve 6 (i.e. high pressure throttling valve) according to the judgment resulthp ;

[0133] Specifically, for the first set of automatic control logic, if HP∈[HP low , HP up ], the opening O hp of the first throttle valve 6 (i.e., the high-pressure throttle valve) is adjusted according to the current operating mode of the system obtained in step S1.

[0134] If the current operating mode of the system is the first working mode (i.e., the subcritical low-temperature operating mode M sub ), the saturation pressure HP opt under the supercooling degree is further calculated, and the saturation pressure HP opt under the supercooling degree is used as the target value of the control target, and the measured current system high-pressure pressure HP is combined to perform PID control (proportional integral derivative control) adjustment of the opening O hp of the first throttle valve 6 (i.e., the high-pressure throttle valve), so that the actual value of the control target of the system operating high-pressure pressure HP approaches (i.e., approaches, reduces the gap) the target value of the control target.

[0135] Further, the calculation method of the saturation pressure HP opt under the supercooling degree is as follows:

[0136] HP opt = f(T gc , HP, T sc ).

[0137] In the above formula, T gc is the outlet temperature of the water cooler, which is measured by the temperature sensor arranged at the outlet of the water cooler.

[0138] HP is the outlet pressure of the compressor of the refrigeration heat pump system (i.e., the total pressure of the working medium flowing out of the working medium outlets of the first compressor 1, the second compressor 2 and the third compressor 3 after the convergence), which is measured by the pressure sensor installed at the convergence position of the working medium output pipelines of the first compressor 1, the second compressor 2 and the third compressor 3.

[0139] T sc is the supercooling temperature, which is a pre-set value.

[0140] It should be noted that for the present application, the saturation pressure HP opt under the supercooling degree is calculated by inputting the current state temperature, pressure and supercooling degree into the fitting formula above, and HP opt = f(T gc , HP, T sc ) is proposed in the present application.

[0141] If the current operation mode of the system is the second operation mode (i.e., the transition linear interpolation operation mode M tran ), the saturation pressure HP opt,low under the supercooling degree is further calculated opt,up , and the measured water cooler outlet temperature T gc is used as a division, and a linear interpolation method is used to calculate the target value of the controlled pressure (i.e., the target value of the control target), which can be as follows: the target value of the controlled pressure should be between HP opt,low and HP opt,up , the pressure values under the water cooler outlet temperature of 26℃ and 31.1℃ are calculated respectively, and according to the relative relationship between the current water cooler outlet temperature and [26, 31.1], the target value of the controlled pressure corresponding to the actual water cooler outlet temperature in the transition linear interpolation operation mode is calculated. Combined with the measured current system high pressure HP, the PID control (proportional integral derivative control) adjustment of the opening O hp of the first throttle valve 6 (i.e., the high pressure throttle valve) is performed, so that the actual value of the control target of the system operation high pressure HP approaches (i.e., approaches, reduces the gap) the target value of the control target;

[0142] Further, the calculation method of the saturation pressure HP opt,low under the supercooling degree is as follows:

[0143] HP opt,low = f(T gc , HP, T sc );

[0144] In the above formula, T gc is the water cooler outlet temperature, which is measured by the temperature sensor arranged at the water cooler outlet;

[0145] HP is the compressor outlet pressure (i.e., the total pressure of the working medium flowing out of the working medium outlet of the first compressor 1, the second compressor 2 and the third compressor 3 after the convergence), which is measured by the pressure sensor installed at the convergence position of the working medium output pipeline of the first compressor 1, the second compressor 2 and the third compressor 3;

[0146] T sc is the supercooling temperature, which is a pre-set value.

[0147] It should be noted that for the present application, the saturation pressure HP opt,low under the supercooling degree is calculated by calling the current state temperature, pressure and supercooling degree and inputting the fitting formula above, and HP opt,low = f(T gc , HP, T scIn this invention, a subcooling setting of 1°C to 3°C is proposed.

[0148] Furthermore, the supercritical optimal pressure HP opt,up The calculation method is as follows:

[0149] HP opt,up =f(T) gc ,Te);

[0150] In the formula above, T e It is the evaporation temperature, T gc It is the outlet temperature of the water cooler;

[0151] It should be noted that for the refrigeration heat pump system proposed in this invention, the supercritical optimal pressure HP opt,up The calculation depends on four parameters: evaporation temperature T. e Water cooler outlet temperature T gc Compressor suction superheat T sh Flash vaporization and superheat T sh,f Based on sensitivity analysis, the parameters with higher influence can be selected, and the fitting formula for the supercritical optimal pressure result can be finally determined as HP. opt,up =f(T) gc ,Te).

[0152] In specific implementation, for the first group of automatic control logic, if HP∈[0, HP low In order to achieve rapid response and control of the system's optimal operating pressure, the opening degree of the first throttle valve 6 (i.e., the high-pressure throttle valve) is adjusted at this time. hp The pressure is 0. At this point, the high-pressure side pressure HP will gradually increase until it reaches the lower limit of the high-pressure value.

[0153] In specific implementation, for the first group of automatic control logic, if HP∈[HP] up If the value is +∞, then in order to achieve safe operation control of the system, the opening degree of the first throttle valve 6 (i.e., the high-pressure throttle valve) is adjusted to O. hp The value is 1. At this point, the system's high-pressure will gradually decrease until it reaches the upper limit of the high-pressure value.

[0154] In step S2, specifically, in order to achieve the control target of the intermediate pressure IP during system operation, the variable operating condition composite control logic includes a second set of automatic control logic.

[0155] The second set of automatic control logic specifically includes the following operations:

[0156] First, input the expected value of the current system intermediate pressure IP. exp Hysteresis value IP of intermediate pressure ret ;

[0157] It should be noted that the return difference value refers to the difference between the set value (expected value, target value) and the actual value.

[0158] Then, the set relationship between the current system intermediate pressure IP measured value and the input expected value and the return difference value [IP exp -IP ret , IP exp +IP ret ] is judged, and according to the judgment result, the opening O bv of the flash bypass valve 11 (i.e. the bypass regulating valve), the operating frequency F hp,a of the second compressor 2, and the operating frequency F hp,b of the third compressor 3 are adjusted.

[0159] Specifically, for the second set of automatic control logic, if IP∈[IP exp +IP ret , +∞], the second compressor 2 is started, and the PID control adjustment of the opening O bv of the flash bypass valve 11 (i.e. the bypass regulating valve) is performed in combination with the measured current system intermediate pressure IP, so that the actual value of the control target of the system operating intermediate pressure IP approaches (i.e. approaches, reduces the gap) the target value of the control target; the target value of the control target is the expected value IP exp of the current system intermediate pressure IP.

[0160] It should be noted that if IP∈[IP exp +IP ret , +∞], the intermediate pressure value in the refrigeration heat pump system is too high, exceeding the sum of the expected intermediate pressure IP exp and the return difference pressure IP ret , at this time, the cooperative control method of the compressor and the bypass valve is proposed. That is, the second compressor 2 is started and the starting frequency is set to operate, the current system intermediate pressure IP actual value is dynamically monitored, the intermediate pressure IP development trend is observed, and the PID control adjustment of the opening O bv of the flash bypass valve 11 is performed in combination with the measured current system intermediate pressure IP. The initial opening of the flash bypass valve 11 is in a closed state, as the intermediate pressure rises and approaches the safety threshold, and when the second compressor 2 is started and the intermediate pressure still shows a rapid growth trend, the flash bypass valve 11 is opened, which can realize the rapid pressure relief of the intermediate pressure IP and ensure the safety of system operation.

[0161] Specifically, for the second set of automatic control logic, if IP∈[IP exp , IP exp +IP retIf the system fails to shut down, the flash bypass valve 11 (i.e., the bypass regulating valve) will be closed, the second compressor 2 will be shut down, and the third compressor 3 will be started. The operating frequency F of the third compressor 3 will be determined based on the measured current system intermediate pressure IP. hp,b The PID control adjusts the system so that the actual value of the intermediate system pressure IP approaches (i.e., gets closer to, or reduces the gap with) the target value of the control objective; the target value of this control objective is the expected value IP of the current intermediate system pressure IP. exp .

[0162] It should be noted that if IP∈[IP exp IP exp +IP ret At this point, the intermediate pressure IP of the refrigeration and heat pump system is at the ideal intermediate pressure IP. exp Above, and at this point the ideal intermediate pressure IP has not been reached. exp With hysteresis pressure IP ret In summary, this invention proposes a coordinated control of the high-pressure compressor, namely, closing the flash bypass valve 11, shutting down the second compressor 2, starting the third compressor 3, and adjusting the frequency F of the third compressor 3 based on the current measured intermediate system pressure IP. hp,b PID control adjustment. Through the frequency conversion adjustment of the third compressor 3, the intermediate pressure IP of the refrigeration / heat pump system can be more precisely controlled relative to the ideal intermediate pressure IP. exp Rapid approach improves system energy efficiency.

[0163] In specific implementation, for the second set of automatic control logic, if IP∈[0, IP exp If the flash bypass valve 11 (i.e., bypass regulating valve) is closed, the second compressor 2 is closed, and the third compressor 3 is maintained at the minimum operating frequency (i.e., the rated minimum operating frequency).

[0164] It should be noted that, for this invention, if IP∈[0, IP exp At this point, the intermediate pressure IP of the refrigeration and heat pump system is lower than the ideal intermediate pressure IP. exp At this point, the present invention proposes a compressor coordinated control that combines time judgment. That is, the flash bypass valve 11 is closed, the second compressor 2 is shut down, and the third compressor 3 is maintained at the lowest operating frequency.

[0165] In practical implementation, attention should be paid to the measured results of the intermediate pressure IP of the refrigeration and heat pump system, and further determination of the current status of the system is required over a delay time T. del And compare the delay time with the set delay time T. del,s The set relationship between them;

[0166] It should be noted that the current state of the system is delayed by time T. delThe time length that the value of the representative system measured intermediate pressure IP is higher than the expected value IPexp of the system intermediate pressure IP, due to the dynamic running process of the system, there is a certain delay in the control of the intermediate pressure IP, which leads to the existence of the system intermediate pressure IP being higher than the intermediate pressure expected value IPexp for a certain time, but at the same time, the intermediate pressure IP is related to the safe running of the system, and cannot be higher than the intermediate pressure expected value IPexp for a long time, otherwise the overpressure risk will be caused. Therefore, the present application proposes a delay time T del If the time that the actual system intermediate pressure IP value is higher than the intermediate pressure expected value IPexp is greater than the delay time T del The set value (i.e. set the delay time T del,s ), the flash bypass control strategy needs to be further adopted.

[0167] If T del ∈[0, T del,s ], it indicates that the running time of the state has not reached the set delay time, and the current running state of the second compressor 2, the third compressor 3 and the flash bypass valve 11 is maintained;

[0168] If T del ∈[T del,s , +∞], the third compressor 3 is closed, and the flash bypass valve 11 (i.e. bypass regulating valve) is opened, and the PID control adjustment of the opening O bv of the flash bypass valve 11 is carried out in combination with the current measured system intermediate pressure IP, so that the actual value of the control target of the system running intermediate pressure IP approaches (i.e. close, reduce the gap) the target value of the control target; the target value of the control target, that is, the expected value IP exp of the current system intermediate pressure IP.

[0169] It should be noted that further with the increase of the time delay, if T del ∈[T del,s , +∞], it indicates that the intermediate pressure IP of the refrigeration heat pump system is lower than the ideal intermediate pressure IP exp and the time of running in this state is long, then the third compressor 3 is closed, the flash bypass regulating valve 11 is opened, and the PID control of the opening O bv of the flash bypass valve 11 is carried out in combination with the current measured system intermediate pressure IP.

[0170] In step S2, specifically, in order to realize the control target of the water cooler outlet temperature T gc , the variable working condition running composite control logic includes a third group of automatic control logic;

[0171] The third group of automatic control logic specifically includes the following operations:

[0172] First, input the expected value T of the outlet temperature of the current system's water cooler gc,exp and the return difference value T of the outlet temperature of the water cooler gc,ret ;

[0173] Then, judge the set relationship between the measured value of the outlet temperature T of the current system's water cooler gc and the input expected value and return difference value [T gc,exp -T gc,ret , T gc,exp +T gc,ret , and adjust the operating frequency F of the cooling fan配套 to the water cooler according to the judgment result gc .

[0174] Specifically, for the third set of automatic control logic, if T gc =T gc,exp , then maintain the operating frequency of the cooling fan配套 to the current water cooler 4;

[0175] It should be noted that at this time, the outlet temperature T of the water cooler of the refrigeration heat pump system gc is the same as the ideal temperature T gc,exp , and there is no need to adjust the cooling fan of the water cooler.

[0176] For the third set of automatic control logic, if T gc ∈[T gc,exp -T gc,ret , T gc,exp , then maintain the minimum operating frequency of the cooling fan配套 to the current water cooler 4;

[0177] It should be noted that at this time, the outlet temperature T of the water cooler of the refrigeration heat pump system gc is slightly lower than the ideal temperature T gc,exp . Considering the safe operation of the system, set to maintain the minimum operating frequency of its cooling fan.

[0178] For the third set of automatic control logic, if T gc ∈[0, T gc,exp -T gc,ret , then close the cooling fan配套 to the water cooler 4, that is, adjust its operating frequency to zero;

[0179] It should be noted that at this time, the outlet temperature T of the water cooler of the refrigeration heat pump system gc is much lower than the ideal temperature T gc,exp , and the cooling fan can be closed.

[0180] For the third set of automatic control logic, if T gc ∈[T gc,exp +T gc,ret, +∞], the operating frequency of the cooling fan supporting the water cooler 4 is adjusted to the maximum rated frequency.

[0181] It should be noted that at this time, the measured value T of the outlet temperature of the system water cooler gc is higher than the set ideal outlet temperature T of the water cooler gc,exp plus the hysteresis temperature T gc,ret sum, indicating that the outlet temperature T of the water cooler gc is too high, then the frequency of the cooling fan of the water cooler is adjusted to the maximum rated frequency.

[0182] For the third set of automatic control logic, if T gc ∈[T gc,exp , T gc,exp +T gc,ret , then based on the measured outlet temperature T of the water cooler gc and the target temperature, the operating frequency of the cooling fan supporting the water cooler is obtained and adjusted by using the method of linear interpolation. The method of linear interpolation can be: by calculating the position of the current measured outlet temperature T of the water cooler gc in the range of [T gc,exp , T gc,exp +T gc,ret set, the result obtained by multiplying this ratio by the difference between the maximum rated frequency and the minimum operating frequency (i.e., the product) is the controlled frequency of the cooling fan supporting the water cooler.

[0183] It should be noted that at this time, it shows that the outlet temperature of the water cooler is slightly higher than the set ideal outlet temperature T of the water cooler gc,exp , and has not reached the upper limit. Therefore, for this working condition, based on the measured outlet temperature T of the water cooler gc and the target temperature T gc,exp , the method of linear interpolation is used to obtain and adjust the frequency of the cooling fan of the water cooler.

[0184] In the present invention, specifically, after step S2, the following steps are further included:

[0185] Step S3, obtain the performance evaluation index of the energy efficiency improvement of the system and the performance evaluation index of the dynamic tracking ability of the system, and then adjust the associated control object, so as to optimize the index values of the performance evaluation index of the energy efficiency improvement of the system and the performance evaluation index of the dynamic tracking ability of the system (optimize the index value, that is, increase the index value).

[0186] It should be noted that for step S3, the performance evaluation indexes of the composite method in terms of energy efficiency improvement and dynamic tracking are specified. The performance evaluation index of the energy efficiency improvement of the system refers to the refrigeration energy efficiency η of the system after adopting the composite control method provided by the present invention c2 , the heating energy efficiency η h2The relative improvement value of refrigeration energy efficiency η c1 , heating energy efficiency η h1 .

[0187] In step S3, the calculation method of the energy efficiency improvement performance evaluation index of the system is as follows:

[0188]

[0189] Wherein, imp represents the relative improvement evaluation index, and η represents the system energy efficiency.

[0190] imp c is the relative improvement value between the refrigeration energy efficiency of the carbon dioxide refrigeration heat pump system adopting the composite control method provided by the present application and the refrigeration energy efficiency of the carbon dioxide refrigeration heat pump system without adopting the composite control method provided by the present application.

[0191] imp h is the relative improvement value between the heating energy efficiency of the carbon dioxide refrigeration heat pump system adopting the composite control method provided by the present application and the heating energy efficiency of the carbon dioxide refrigeration heat pump system without adopting the composite control method provided by the present application.

[0192] η c2 is the refrigeration energy efficiency of the carbon dioxide refrigeration heat pump system after adopting the composite control method provided by the present application; η h2 is the heating energy efficiency of the carbon dioxide refrigeration heat pump system after adopting the composite control method provided by the present application.

[0193] η c1 is the refrigeration energy efficiency of the carbon dioxide refrigeration heat pump system without adopting the composite control method provided by the present application; η h1 is the heating energy efficiency of the carbon dioxide refrigeration heat pump system without adopting the composite control method provided by the present application.

[0194] It should be noted that the refrigeration energy efficiency and the heating energy efficiency of the refrigeration heat pump system are the ratio of refrigeration capacity and heating capacity to input power, which are obtained according to the corresponding national standard documents, and refer to GB / T29033-2012 “Calculation method of thermodynamic perfection of water-water heat pump unit”.

[0195] For step S3, the dynamic tracking performance evaluation strategy is to compare the measured results and target results of the control target under dynamic time scale, and then evaluate the tracking performance of the control target.

[0196] In step S3, the dynamic tracking ability performance evaluation index of the system specifically includes: the outlet temperature T gca dynamic tracking capability evaluation index of the water cooler 4, a dynamic tracking capability evaluation index of the system operating high-pressure pressure HP, and a dynamic tracking capability evaluation index of the system operating intermediate pressure IP;

[0197] wherein, T gc T The calculation method is as follows:

[0198]

[0199] In the above formula, T gc represents the measured carbon dioxide temperature at the outlet of the water cooler 4, which is measured by a temperature sensor at the corresponding position, and T gc,set represents the pre-set carbon dioxide temperature value at the outlet of the water cooler, which is given by the user.

[0200] wherein, fol HP represents the dynamic tracking capability evaluation index of the system operating high-pressure pressure HP, and the calculation method is as follows:

[0201]

[0202] In the above formula, HP represents the measured system operating high-pressure pressure (i.e. the compressor outlet pressure), that is, the measured carbon dioxide pressure after the outlet of the first compressor 1, the second compressor 2 and the third compressor 3 are merged, which is measured by a pressure sensor at the corresponding position;

[0203] HP set represents the pre-set carbon dioxide pressure value after the outlet of the first compressor 1, the second compressor 2 and the third compressor 3 are merged, which is given by the user.

[0204] wherein, fol IP represents the dynamic tracking capability evaluation index of the system operating intermediate pressure IP, and the calculation method is as follows:

[0205]

[0206] wherein, fol represents the dynamic tracking capability evaluation index, and the table set below represents the set optimal value.

[0207] In the above formula, IP represents the measured system operating intermediate pressure IP (i.e. the phase equilibrium pressure of the flash tank 7), that is, the measured carbon dioxide pressure at the inlet of the second compressor 2 and the third compressor 3, which is measured by a pressure sensor at the corresponding position;

[0208] IP set represents the pre-set carbon dioxide pressure value at the inlet of the second compressor 2 and the third compressor 3, which is given by the user. ​

[0209] Based on the evaluation result, real-time feedback is fed back to the controller (i.e. the PID controller) through the data transmission system, and the controller continuously adjusts the first compressor 1, the second compressor 2, the third compressor 3, the cooling fan matched with the water cooler 4, the first throttling valve 6 and the second throttling valve 8 (i.e. the electronic expansion valve), the flash bypass valve 11 (i.e. the bypass regulating valve), and the flash tank 7 (i.e. the flash evaporator) according to the feedback value, so as to realize the optimization of the above-mentioned energy efficiency and dynamic tracking control performance.

[0210] It should be noted that by running step S3, the component response (i.e. the control object response) based on the composite control method and the control target approximation can be realized, the energy efficiency improvement performance evaluation strategy of the composite method is proposed, and the dynamic tracking performance evaluation strategy. The energy efficiency improvement performance evaluation strategy is that after adopting the composite control method, the system refrigeration and heating energy efficiency is improved. The dynamic tracking performance evaluation strategy is that the measured results and target results of the control target are compared in the dynamic time scale, and then the tracking performance of the control target is evaluated. Based on the evaluation result, real-time feedback is fed back to the controller (i.e. the PID controller), and the corresponding devices in the control system are continuously adjusted, so as to realize the optimization of the above-mentioned energy efficiency and dynamic tracking control performance.

[0211] In the present application, the composite control method is applied to the carbon dioxide refrigeration heat pump system described above.

[0212] In the present application, the carbon dioxide refrigeration heat pump system comprises a controller 13 (i.e. a PID controller);

[0213] The controller 13 is connected with the control end of the first compressor 1, the second compressor 2, the third compressor 3, the cooling fan matched with the water cooler 4, the first throttling valve 6 and the second throttling valve 8 (i.e. the electronic expansion valve), the flash bypass valve 11 (i.e. the bypass regulating valve), and the flash tank 7 (i.e. the flash evaporator), respectively, and combines the externally input parameters 27 (including the cold and hot demand parameters and the environmental parameters) to control the working state of the connected devices. That is, the controller is specifically used to run the composite control method.

[0214] Specifically, for the carbon dioxide refrigeration heat pump system, bidirectional transmission of operating parameters and control parameters can be realized.

[0215] The operating parameters include the system evaporation pressure and temperature parameters 20, the system intermediate pressure and temperature parameters 21, the system high pressure parameters 22, and the system water cooler outlet temperature parameters 23.

[0216] The control parameters include: a frequency control parameter 16 of the first compressor 1, a frequency control parameter 17 of the second compressor 2, a frequency control parameter 18 of the third compressor 3, an operating frequency 19 of a heat dissipation fan matched with the water cooler 4, an opening control parameter 24 of the first throttling valve 6, an opening control parameter 25 of the second throttling valve 8, and an opening control parameter 26 of the flash bypass valve 11.

[0217] It should be noted that the system evaporation pressure parameter is the carbon dioxide pressure in the pipeline after the liquid phase outlet e below the liquid storage tank 10, which is measured by the pressure sensor at this position. The system evaporation temperature parameter is the carbon dioxide temperature in the pipeline after the liquid phase outlet e below the liquid storage tank 10, which is measured by the temperature sensor at this position.

[0218] The system intermediate pressure parameter is the carbon dioxide pressure in the pipeline at the inlet of the second compressor 2 and the third compressor 3, which is measured by the pressure sensor at this position. The system intermediate temperature parameter is the carbon dioxide temperature in the pipeline at the inlet of the second compressor 2 and the third compressor 3, which is measured by the temperature sensor at this position.

[0219] The system high-pressure pressure parameter 22 is the carbon dioxide pressure in the pipeline after the outlet of the first compressor 1, the second compressor 2 and the third compressor 3 are combined, which is measured by the pressure sensor at this position.

[0220] The water cooler outlet temperature parameter 23 is the carbon dioxide temperature in the pipeline at the outlet of the water cooler 4, which is measured by the temperature sensor at this position.

[0221] It should be noted that for the present application, the above-mentioned composite control method is implemented by the controller 13, and each device in the carbon dioxide refrigeration heat pump system is controlled. The actual component operating parameters are read to judge the state of the refrigeration heat pump system, and the control command of the refrigeration heat pump system is input into the refrigeration heat pump system to realize the bidirectional communication between the refrigeration heat pump system and the composite control method.

[0222] The above-mentioned is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principle of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be regarded as the protection scope of the present application.

Claims

1. A carbon dioxide refrigeration heat pump system, characterized in that, include: First compressor (1), second compressor (2), third compressor (3), water cooler (4), first regenerator (5), first throttle valve (6), flash tank (7), second throttle valve (8), evaporator (9), liquid storage tank (10), flash bypass valve (11) and second regenerator (12); The working fluid outlets of the first compressor (1), the second compressor (2) and the third compressor (3) are connected to the working fluid inlet of the water cooler (4) after they converge and intersect. The working fluid outlet of the water cooler (4) is connected to the high-pressure side inlet a of the first regenerator (5); The high-pressure side outlet b of the first regenerator (5) is connected to the inlet of the first throttle valve (6); The outlet of the first throttle valve (6) is connected to the working fluid inlet a of the flash tank (7); The first working fluid outlet b of the flash tank (7) is connected to the low-pressure side inlet c of the first regenerator (5); The second working fluid outlet d of the flash tank (7) is connected to the high-pressure side inlet b of the second regenerator (12); The third working fluid outlet c of the flash tank (7) is connected to one end of the flash bypass valve (11), and the third working fluid outlet c of the flash tank (7) is a gaseous working fluid outlet. The other end of the flash bypass valve (11) is connected to the third working fluid inlet d above the storage tank (10); The low-pressure outlet d of the first regenerator (5) is connected to the working fluid inlet of the second compressor (2) and the third compressor (3), respectively; The high-pressure side outlet a of the second regenerator (12) is connected to the inlet of the second throttle valve (8); The outlet of the second throttle valve (8) is connected to the second working fluid inlet b of the liquid storage tank (10); The second working fluid outlet e on the lower side of the liquid storage tank (10) is connected to the working fluid inlet of the evaporator (9); The working fluid outlet of the evaporator (9) is connected to the first working fluid inlet a on the upper side of the liquid storage tank (10); The first working fluid outlet c on the upper side of the liquid storage tank (10) is connected to the low-pressure side inlet d of the second regenerator (12); The low-pressure side outlet c of the second regenerator (12) is connected to the working fluid inlet of the first compressor (1); The lower side of the inner cavity of the liquid storage tank (10) contains low-temperature, low-pressure carbon dioxide liquid, and the upper side of the inner cavity of the liquid storage tank (10) contains low-temperature, low-pressure carbon dioxide gas.

2. The carbon dioxide refrigeration heat pump system as described in claim 1, characterized in that, The following working modes are included: In the first step, the carbon dioxide working fluid from the outlets of the first compressor (1), the second compressor (2), and the third compressor (3) is then fed into the water cooler (4). The second step is that the carbon dioxide working fluid flowing out of the working fluid outlet of the water cooler (4) is then introduced into the high-pressure side inlet of the first regenerator (5) to further reduce the temperature of the carbon dioxide working fluid and increase its cooling capacity per unit volume. In the third step, the high-pressure side outlet of the first regenerator (5) is further connected to the first throttling valve (6). Through the isenthalpic throttling process in the first throttling valve, the pressure and temperature of carbon dioxide are reduced to form a carbon dioxide working medium with intermediate pressure and intermediate temperature. In the fourth step, the carbon dioxide after passing through the first throttle valve (6) enters the flash tank (7), and the gas and liquid separation of the carbon dioxide working fluid is achieved by the flash tank (7); The fifth step is to achieve gas-liquid separation of carbon dioxide working fluid in the flash tank (7), and then form a continuous refrigeration capacity by running the preset working circuit. The preset working circuits include working circuit one, working circuit two, and working circuit three; In the first working loop: through the first working fluid outlet b of the flash tank (7), the saturated gas above the flash tank (7) with intermediate temperature and intermediate pressure enters the low-pressure side inlet c of the first regenerator (5), which cools the carbon dioxide on the high-pressure side and heats itself. The carbon dioxide passing through the low-pressure side outlet d of the first regenerator (5) enters the second compressor (2) and the third compressor (3). Through the compression of the second compressor (2) and the third compressor (3), this part of the intermediate pressure carbon dioxide is raised to the high pressure. The details of working loop two are as follows: First, through the second working fluid outlet d of the flash tank (7), the saturated liquid carbon dioxide below the flash tank (7) flows into the high-pressure side inlet b of the second regenerator (12), and the carbon dioxide has a higher cooling capacity per unit volume through the cooling of the second regenerator (12). Then, the cooled portion of carbon dioxide flows into the second throttling valve (8) through the high-pressure side outlet a of the second regenerator (12), achieving throttling and cooling, making it a low-temperature and low-pressure carbon dioxide working fluid; Then, the low-temperature and low-pressure carbon dioxide working fluid flowing through the second throttle valve (8) is introduced into the storage tank (10). Gas-liquid separation is performed inside the storage tank (10). Since the lower side of the inner cavity of the storage tank (10) contains low-temperature and low-pressure carbon dioxide liquid and the upper side of the inner cavity of the storage tank (10) contains low-temperature and low-pressure carbon dioxide gas, the low-temperature and low-pressure carbon dioxide liquid on the lower side of the inner cavity of the storage tank (10) is introduced into the evaporator (9) to absorb heat and achieve refrigeration capacity. After being heated by the evaporator (9), the carbon dioxide becomes a two-phase gas-liquid or gaseous working fluid and flows back to the top of the storage tank (10). Then, the low-temperature and low-pressure gaseous carbon dioxide is introduced into the low-pressure side inlet d of the second regenerator (12) through the first working fluid outlet c above the storage tank (10) to cool the carbon dioxide working fluid on the high-pressure side of the second regenerator (12), while being heated itself. The heated carbon dioxide working fluid has superheat, ensuring that no liquid slugging occurs when it enters the first compressor (1) and damages the first compressor (1). Then, the carbon dioxide flowing out of the low-pressure side outlet c of the second regenerator (12) enters the first compressor (1). Through the suction operation of the first compressor (1), the gaseous carbon dioxide in the liquid storage tank (10) is continuously extracted to form a continuous cooling capacity. Among them, the third working loop: through the third working medium outlet c of the flash tank (7), saturated gaseous carbon dioxide is introduced into the flash bypass valve (11), and further introduced into the storage tank (10) through the flash bypass valve (11).

3. A composite control method for a carbon dioxide refrigeration heat pump system as described in claim 1 or 2, characterized in that, Includes the following steps: Step S1: Input the cooling and heating demand parameters and environmental parameters of the carbon dioxide refrigeration and heat pump system, and determine the current working mode of the system; Step S2: Set the system operating parameter control target, determine the associated control object based on the system operating parameter control target, and then adjust and control the control object by setting the variable operating condition composite control logic to make the actual value of the system operating parameter control target approach the preset target value.

4. The composite control method for a carbon dioxide refrigeration heat pump system as described in claim 3, characterized in that, Step S1 specifically includes the following sub-steps: Step S11: Based on the cooling and heating demand parameters and environmental parameters of the carbon dioxide refrigeration heat pump system, determine the water cooler outlet temperature T of the carbon dioxide refrigeration heat pump system. gc The required cooling temperature and the required heating temperature for the operation of a carbon dioxide refrigeration heat pump system. Step S12, based on the outlet temperature T of the water cooler in the carbon dioxide refrigeration heat pump system gc Determine the current operating mode of the carbon dioxide refrigeration and heat pump system by determining the required cooling temperature and heating temperature for its operation. Among them, the cooling and heating demand parameters include: the cooling temperature T of the carbon dioxide refrigeration heat pump system. e The heating temperature T of the carbon dioxide refrigeration heat pump system h The cooling load Q of the carbon dioxide refrigeration heat pump system e The heating load Q of the carbon dioxide refrigeration heat pump system h ; Environmental parameters, including: the dry-bulb temperature T of the environment in which the carbon dioxide refrigeration heat pump system operates. amb and wet-bulb temperature T aw and relative humidity h r .

5. The composite control method for a carbon dioxide refrigeration heat pump system as described in claim 3, characterized in that, In step S12, when the outlet temperature T of the water cooler in the carbon dioxide refrigeration heat pump system... gc When the temperature is A, it is operating mode one, which is the subcritical low-temperature operating region mode M. sub ; When the outlet temperature of the water cooler in a carbon dioxide refrigeration heat pump system satisfies: Temperature value A ≤ T gc When the working fluid reaches its critical temperature (less than carbon dioxide), the operating mode is mode two, i.e., the transitional linear interpolation operating region mode M. tran ; When the outlet temperature of the water cooler in the carbon dioxide refrigeration heat pump system is T gc When the temperature of the working fluid is greater than or equal to the critical temperature of carbon dioxide, it is operating mode three, which is the supercritical optimal control operating region mode M. sup ; And / or, Environmental parameters for a carbon dioxide refrigeration and heat pump system include the dry-bulb temperature T of the environment in which the system operates. amb ; When the dry bulb temperature T amb At temperature value A, the current operating modes that the carbon dioxide refrigeration heat pump system can operate in include: any one of the three operating modes: operating mode one, operating mode two, and operating mode three. When temperature value A ≤ dry bulb temperature T amb At the critical temperature of carbon dioxide working fluid, the current operating modes that the carbon dioxide refrigeration heat pump system can operate in include either operating mode two or operating mode three. When the dry bulb temperature T amb When the temperature of the carbon dioxide working fluid is greater than or equal to the critical temperature, the current operating modes that the carbon dioxide refrigeration heat pump system can operate in include: Operating Mode 3; The condition that the above temperature value A satisfies is: when the outlet temperature T of the water cooler (4) is... gc When the temperature is below this value A, the system operating high pressure HP of the carbon dioxide refrigeration heat pump system is lower than the critical pressure of carbon dioxide.

6. The composite control method for a carbon dioxide refrigeration heat pump system as described in claim 3, characterized in that, In step S2, the system operating parameter control targets include the water cooler outlet temperature T. gc At least one of the following: the control objective, the control objective of the system operating high pressure HP, and the control objective of the system operating intermediate pressure IP; The associated control objects include: open-loop control objects and closed-loop control objects; The open-loop control objects specifically include: flash tank (7); The closed-loop control objects specifically include: the first compressor (1), the second compressor (2), the third compressor (3), the cooling fan of the water cooler (4), the first throttle valve (6) and the second throttle valve (8), and the flash bypass valve (11).

7. The composite control method for a carbon dioxide refrigeration heat pump system as described in claim 3, characterized in that, In step S2, in order to achieve the control objective of the system operating high pressure HP, the variable operating condition composite control logic includes the first group of automatic control logic. The first set of automatic control logic specifically includes the following operations: First, enter the upper limit of the current system high pressure (HP). up and lower limit HP low ; Then, determine the measured value of the current system high pressure HP and the input upper and lower limits [HP]. up HP low The set relationship is determined, and the opening degree of the first throttle valve (6) is adjusted according to the judgment result. hp ; And / or, In order to achieve the control objective of intermediate pressure IP during system operation, the variable operating condition composite control logic includes a second set of automatic control logic. The second set of automatic control logic specifically includes the following operations: First, input the expected value of the current system intermediate pressure IP. exp Hysteresis value IP of intermediate pressure ret ; Then, compare the measured value of the current system intermediate pressure IP with the input expected value and the hysteresis value [IP]. exp -IP ret IP exp +IP ret The set relationship is determined, and the opening degree of the flash bypass valve (11) is adjusted according to the judgment result. bv The operating frequency F of the second compressor (2) hp,a The operating frequency F of the third compressor (3) hp,b ; And / or, To achieve the water cooler outlet temperature T gc The control objective is to implement the composite control logic for variable operating conditions, which includes a third set of automatic control logic. The third set of automatic control logic specifically includes the following operations: First, input the desired value T of the current system water cooler outlet temperature. gc,exp Hysteresis T of water cooler outlet temperature gc,ret ; Then, judge the outlet temperature T of the current system water cooler gc The measured value and the input expected value and the dead band value [T gc,exp - T gc,ret , T gc,exp + T gc,ret , and adjust the operating frequency F of the cooling fan supporting the water cooler according to the judgment result gc .

8. The composite control method for a carbon dioxide refrigeration heat pump system as described in claim 7, characterized in that, For the first set of automatic control logic, if HP∈[HP] low HP up If the current operating mode of the system is determined in step S1, the opening degree of the first throttle valve (6) is adjusted accordingly. hp ; If the system is currently operating in the first working mode, then the saturation pressure HP under subcooling is further calculated. opt And using this as the target value for control, combined with the measured current system high pressure HP, the opening degree of the first throttle valve (6) is determined. hp The PID control adjustment makes the actual value of the control target HP of the system operation approach the target value of the control target; Saturation pressure HP under supercooling opt The calculation method is as follows: HP opt =f(T gc ,HP,T sc ); If the system is currently operating in the second mode, the saturation pressure HP under subcooling is further calculated. opt,low With supercritical optimal pressure HP opt,up And based on the measured water cooler outlet temperature T gc，o To achieve segmentation, the target value of the control objective is calculated using linear interpolation. Combined with the measured current system high pressure HP, the opening degree of the first throttle valve (6) is determined. hp The PID control adjustment makes the actual value of the control target HP of the system operation approach the target value of the control target; Saturation pressure HP under supercooling opt,low The calculation method is as follows: HP opt,low =f(T gc ,HP,T sc ); Supercritical optimal pressure HP opt,up The calculation method is as follows: HP opt,up =f(T gc ,T e ); In the formula above, T e It is the evaporation temperature, T gc It is the outlet temperature of the water cooler, T. sc This refers to the supercooling temperature. For the first set of automatic control logic, if HP∈[0, HP low Then adjust the opening degree O of the first throttle valve (6). hp =0; For the first set of automatic control logic, if HP∈[HP] up If +∞], then adjust the opening degree O of the first throttle valve (6). hp =1; For the second set of automatic control logic, if IP∈[IP] exp +IP ret If +∞], then start the second compressor (2), and adjust the opening of the flash bypass valve (11) to O based on the measured current system intermediate pressure IP. bv The PID control adjusts the system so that the actual value of the intermediate pressure IP approaches the target value of the control objective; the target value of this control objective is the expected value IP of the current intermediate pressure IP of the system. exp ; For the second set of automatic control logic, if IP∈[IP] exp IP exp +IP ret If the flash bypass valve (11) is closed, the second compressor (2) is shut down, and the third compressor (3) is started. The operating frequency F of the third compressor (3) is determined based on the measured current system intermediate pressure IP. hp,b The PID control adjusts the system so that the actual value of the intermediate pressure IP approaches the target value of the control objective; the target value of this control objective is the expected value IP of the current intermediate pressure IP of the system. exp ; For the second set of automatic control logic, if IP∈[0, IP exp If the flash bypass valve (11) is closed, the second compressor (2) is shut down, and the third compressor (3) is kept at the lowest operating frequency. For the third set of automatic control logic, if T gc =T gc,exp Then the operating frequency of the cooling fan that is currently matched with the water cooler will be maintained; For the third set of automatic control logic, if T gc ∈[T gc,exp -T gc,ret T gc,exp If the minimum operating frequency of the cooling fan that is currently matched with the water cooler (4) is maintained, then the minimum operating frequency of the cooling fan will be maintained. For the third set of automatic control logic, if T gc ∈[0,T gc,exp -T gc,ret If the fan is turned off, the cooling fan of the water cooler (4) will be turned off, that is, its operating frequency will be adjusted to zero. For the third set of automatic control logic, if T gc ∈ [T gc,exp + T gc,ret , +∞], then adjust the operating frequency of the cooling fan supporting the water cooler to the maximum rated frequency; For the third set of automatic control logic, if T gc ∈[T gc,exp , T gc,exp +T gc,ret , then based on the measured outlet temperature T gc of the water cooler and the target temperature, the operating frequency of the cooling fan supporting the water cooler is obtained and adjusted by using the method of linear interpolation.

9. The composite control method for a carbon dioxide refrigeration heat pump system as described in claim 3, characterized in that, Following step S2, the following steps are also included: Step S3: Obtain the system's energy efficiency improvement performance evaluation index and the system's dynamic tracking capability performance evaluation index, and then adjust the related control objects to optimize the index values ​​of the system's energy efficiency improvement performance evaluation index and the system's dynamic tracking capability performance evaluation index. In step S3, the system's energy efficiency improvement performance evaluation index is calculated as follows: Among them, imp c , is the relative improvement in cooling energy efficiency between a carbon dioxide refrigeration heat pump system using the composite control method and a carbon dioxide refrigeration heat pump system not using the composite control method. imp h , is the relative improvement value between the heating energy efficiency of the carbon dioxide refrigeration heat pump system using the composite control method and the heating energy efficiency of the carbon dioxide refrigeration heat pump system without the composite control method. η c2 η is the cooling energy efficiency of the carbon dioxide refrigeration heat pump system after adopting the aforementioned composite control method; h2 , is the heating efficiency of the carbon dioxide refrigeration heat pump system after adopting the aforementioned composite control method; η c1 η is the cooling energy efficiency of the carbon dioxide refrigeration heat pump system without employing the aforementioned composite control method; h1 The heating efficiency of the carbon dioxide refrigeration heat pump system without the aforementioned composite control method is as follows: In step S3, the performance evaluation indicators for the system's dynamic tracking capability specifically include: water cooler outlet temperature T. gc The evaluation indicators for dynamic tracking capability, the evaluation indicators for dynamic tracking capability of high pressure HP during system operation, and the evaluation indicators for dynamic tracking capability of intermediate pressure IP during system operation. Among them, the outlet temperature T of the water cooler gc Dynamic tracking capability evaluation index fol T The calculation method is as follows: In the formula above, T gc T represents the measured carbon dioxide temperature at the outlet of the water cooler (4); gcset This represents the preset carbon dioxide temperature value at the outlet of the water cooler. Evaluation index of the system's dynamic tracking capability of high pressure (HP) HP The calculation method is as follows: In the formula above, HP represents the measured carbon dioxide pressure after the outlets of the first compressor (1), the second compressor (2), and the third compressor (3) are combined; HP set This represents the carbon dioxide pressure value after the outlets of the first compressor (1), the second compressor (2), and the third compressor (3) are combined (pre-set); Evaluation index of dynamic tracking capability of intermediate pressure IP during system operation (fol) IP The calculation method is as follows: Where fol represents the dynamic tracking capability evaluation index, and set represents setting the optimal value; In the formula above, IP represents the measured carbon dioxide pressure at the inlet of the second compressor (2) and the third compressor (3); IP set This represents the pre-set carbon dioxide inlet pressure values ​​of the second compressor (2) and the third compressor (3).

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