Carbon dioxide transcritical injection refrigeration system and control method

Abstract

The application relates to the field of refrigeration technology and discloses a carbon dioxide transcritical injection refrigeration system and a control method, which uses a combination of gravity liquid supply and direct expansion liquid supply to solve the situation that the electronic expansion valve stops supplying liquid when the injection pressure boosting capacity is insufficient, simplifies the control quantity of valves in the system operation process, meets the transient load change demand and the precise control of the gas cooler outlet pressure; the system comprises an ejector, the ejector is connected with a compressor, a gas-liquid separator and an evaporator, the compressor is connected with the gas-liquid separator, the medium-pressure CO2 gas is sucked in, and the medium-pressure CO2 gas is compressed to be supercritical; the compressor is further connected with an oil separator and a gas cooler in sequence; the gas cooler is further connected with the ejector, and an electric ball valve one is installed on the connecting pipeline between the gas cooler and the ejector to control the optimal pressure of the gas cooler outlet; the gas-liquid separator is further connected with the evaporator, and an electric ball valve two and an electronic expansion valve are installed on the connecting pipeline between the gas-liquid separator and the evaporator.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of refrigeration technology, in particular to a carbon dioxide transcritical injection refrigeration system and a control method. BACKGROUND

[0002] Under typical operating conditions, the carbon dioxide refrigeration system is prone to enter a transcritical state, with the high-pressure side in a supercritical region and the low-pressure side in a subcritical region, and a significant pressure difference of 5-8 MPa between the two sides, which makes the energy loss of the throttling process of the traditional carbon dioxide transcritical refrigeration system large, and the system coefficient of performance (COP) lower than that of a system using a conventional refrigerant, affecting the economic efficiency and market competitiveness of the technology. To break through the energy efficiency bottleneck, replacing the high-pressure throttling valve with an ejector has become a mainstream technical solution. The ejector can recover the kinetic energy of the expansion process, inject the low-pressure gas at the evaporator outlet, increase the suction pressure of the compressor, and convert the expansion work into useful work. A large amount of research data shows that this technology can increase the system COP by 10%-30%, bringing new opportunities for the development of carbon dioxide transcritical refrigeration technology.

[0003] However, this technology still has many limitations. In terms of system design, taking the dry direct expansion liquid supply method as an example, the opening of the electronic expansion valve is usually controlled based on the superheat of the evaporator. However, in a carbon dioxide transcritical injection refrigeration system, when the ejector's pressure boosting capacity is insufficient, the pressure difference before and after the electronic expansion valve continues to decrease, eventually causing the electronic expansion valve to stop supplying liquid, resulting in the failure of the refrigeration system. To ensure system reliability, the current method is to increase the number of valves and pipelines to switch to a conventional compression cycle when the ejector fails, which undoubtedly increases the complexity of system control and the cost of unit manufacturing. In terms of ejector design and control, there are two main forms: 1. Adjustable ejector, which dynamically matches system load changes by adjusting the throat area of the nozzle, but has the problems of complex structure, high control difficulty, and durability. 2. Multi-nozzle ejector, which matches system load changes by connecting multiple fixed-size ejectors in parallel, but has low adjustment accuracy. SUMMARY

[0004] The present application aims to solve the problems raised in the background art and proposes a carbon dioxide transcritical injection refrigeration system and a control method.

[0005] The technical solution adopted by the present application to solve its technical problems is:

[0006] The application discloses a carbon dioxide transcritical injection refrigeration system, which comprises an ejector, wherein the ejector is connected with a compressor, a gas-liquid separator and an evaporator, and the compressor is connected with the gas-liquid separator to suck in medium-pressure CO2 gas and compress the medium-pressure CO2 gas to be supercritical; the compressor is further connected with an oil separator and a gas cooler in sequence; the gas cooler is further connected with the ejector, and an electric ball valve one is arranged on a connecting pipeline between the gas cooler and the ejector to form the medium-pressure gas into the gas-liquid separator; the gas-liquid separator is further connected with the evaporator, and an electric ball valve two and an electronic expansion valve are arranged on a connecting pipeline between the gas-liquid separator and the evaporator.

[0007] According to the above scheme, the electric ball valve two is opened when the ejector exceeds the working range, and the liquid CO2 directly flows into the evaporator under the action of gravity; the electronic expansion valve is opened under the normal working condition of the ejector, and the liquid CO2 is throttled to enter the evaporator.

[0008] According to the above scheme, a check valve one is further arranged on the connecting pipeline between the gas-liquid separator and the evaporator, and the check valve one is used to allow the low-pressure fluid at the outlet of the evaporator to flow into the gas-liquid separator when the ejector cannot inject the low-pressure fluid of the evaporator; a check valve two is arranged on the connecting pipeline between the ejector and the evaporator, and the check valve two is used to prevent the medium-pressure fluid of the gas-liquid separator from flowing back to the evaporator; and the connecting pipeline between the gas-liquid separator and the evaporator is communicated with the connecting pipeline between the ejector and the evaporator.

[0009] According to the above scheme, the oil separator is connected with an oil collector, and an electromagnetic valve one and a ball valve are arranged on a connecting pipeline between the oil separator and the oil collector; the oil collector is further connected with the compressor, and an electromagnetic valve two and a pressure reducing valve are arranged on a connecting pipeline between the oil collector and the compressor.

[0010] According to the above scheme, the number of the ejectors is matched with the capacity of the compressor, different flow rates are designed for each group of ejectors, the total flow rate of the ejectors covers the flow rate variation range of the compressor, an electric ball valve one is arranged in front of each group of ejectors, the circulation amount of the refrigerant is controlled by adjusting the opening degree of the electric ball valve one, and then the optimal pressure at the outlet of the gas cooler is controlled; and the opening and closing and the opening degree of the electric ball valve one are controlled according to the difference between the actual outlet pressure of the gas cooler and the corresponding optimal pressure under the outlet temperature of the gas cooler.

[0011] According to the above scheme, the compressor has five groups and is in parallel connection, the working flow rate is in the range of 0-6000 m 3 / h, three groups of ejectors are arranged, the flow rates of the three groups of ejectors are respectively 1000 m 3 / h, 2000 m 3 / h and 3500 m 3 / h, and eight combination modes are formed to control the circulation amount of the refrigerant of the system.

[0012] Further, the difference ΔP between the actual outlet pressure of the gas cooler and the optimal outlet pressure of the gas cooler is within ±2 bar; when ΔP>5 bar, the electric ball valve before the ejector with the smallest flow in the ejectors not opened is opened; when 2 bar<ΔP≤5 bar, the electric ball valve before the ejector with the smallest flow in the ejectors not opened is gradually opened in steps of 5%; when ΔP<-5 bar, the electric ball valve before the ejector with the smallest flow in the ejectors opened is closed; when-5 bar≤ΔP<-2 bar, the electric ball valve before the ejector with the smallest flow in the ejectors opened is gradually closed in steps of 5%; and when-2 bar<ΔP<-2 bar, the control of the electric ball valve is ended.

[0013] Further, when the ejectors are in the applicable range, the evaporation pressure of the evaporator is controlled by the compressor frequency and the opening degree of the electronic expansion valve.

[0014] Further, when the ejectors are out of the applicable range, the evaporation pressure of the evaporator is controlled by the compressor frequency and the opening degree of the electric ball valve.

[0015] Another aspect of the present application provides a transcritical carbon dioxide ejector refrigeration method, comprising an ejector applicable range control mode and an ejector out-of-applicable range control mode.

[0016] In the ejector applicable range control mode:

[0017] The electric ball valve two is closed, the electronic expansion valve is opened, the compressor sucks the medium-pressure CO2 gas from the gas-liquid separator, compresses to supercritical, passes through an oil separator and a gas cooler, and then the high-pressure CO2 enters the ejector to inject the low-pressure CO2 at the outlet of the evaporator; the medium-pressure CO2 formed after mixing enters the gas-liquid separator, the gaseous part is sucked by the compressor, and the liquid part enters the evaporator through the electronic expansion valve;

[0018] In the ejector out-of-applicable range control mode:

[0019] The electric ball valve two is opened, the electronic expansion valve is closed, the compressor sucks the medium-pressure CO2 gas from the gas-liquid separator, compresses to supercritical, passes through an oil separator and a gas cooler, and then the high-pressure CO2 directly throttles to medium pressure in the ejector to enter the gas-liquid separator; the liquid CO2 in the gas-liquid separator enters the evaporator through the electric ball valve two under the action of gravity, and the gas in the evaporator returns to the gas-liquid separator under the suction of the compressor.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] This invention uses a combination of gravity-fed and direct-expansion fluid supply to address the issue of the electronic expansion valve stopping fluid supply when the injector's pressurization capacity is insufficient. By detecting the pressure and temperature of the primary flow at the secondary inlet of the injector, it determines whether the current operating condition is within the injector's applicable range. If it is not within the injector's applicable range, the electronic expansion valve is closed, and the electric ball valve is opened for gravity-fed fluid supply. When the operating condition is detected to be within the injector's operating range, the second electric ball valve is closed, and the electronic expansion valve is opened for direct-expansion fluid supply. This design reduces the number of valves and pipelines required in traditional designs, simplifies the number of valves controlled during system operation, reduces system size and cost, and provides fast response, meeting the requirements of transient load changes. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention;

[0023] Figure 2 This is a schematic diagram showing the connection position of the oil collector;

[0024] Figure 3 This is a control flowchart of the present invention;

[0025] The components include: 1. Ejector; 2. Compressor; 3. Gas-liquid separator; 4. Evaporator; 5. Oil separator; 6. Air cooler; 7. Electric ball valve one; 8. Electric ball valve two; 9. Electronic expansion valve; 10. Check valve one; 11. Check valve two; 12. Oil collector; 13. Solenoid valve one; 14. Ball valve; 15. Solenoid valve two; 16. Pressure reducing valve. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The present invention will be further described with reference to the accompanying drawings and embodiments:

[0027] This invention proposes a transcritical carbon dioxide jet refrigeration system, as shown in the attached figure. Figure 1As shown, the system includes an ejector 1, which is connected to a compressor 2, a gas-liquid separator 3, and an evaporator 4. The compressor 2 is connected to the gas-liquid separator 3 to draw in medium-pressure CO2 gas and compress it to supercritical pressure. The compressor 2 is also connected in sequence to an oil separator 5 and an air cooler 6. The air cooler 6 is also connected to the ejector 1, and an electric ball valve 7 is installed on the connecting pipeline between the air cooler 6 and the ejector 1 to allow medium-pressure gas to enter the gas-liquid separator 3. The gas-liquid separator 3 is also connected to the evaporator 4, and an electric ball valve 8 and an electronic expansion valve 9 are installed on the connecting pipeline between the gas-liquid separator 3 and the evaporator 4. The electric ball valve 8 opens when the ejector 1 exceeds its operating range, allowing liquid CO2 to flow directly into the evaporator 4 under gravity. The electronic expansion valve 9 opens under normal operating conditions of the ejector 1 to control the throttling of liquid CO2 into the evaporator 4.

[0028] A check valve 10 is installed on the connecting pipeline between the gas-liquid separator 3 and the evaporator 4. When the ejector 1 cannot eject the low-pressure fluid from the evaporator 4, the low-pressure fluid from the outlet of the evaporator 4 is allowed to flow into the gas-liquid separator 3. A check valve 21 is installed on the connecting pipeline between the ejector 1 and the evaporator 4 to prevent the medium-pressure fluid of the gas-liquid separator 3 from flowing back to the evaporator 4, ensuring a unique flow direction. The connecting pipeline between the gas-liquid separator 3 and the evaporator 4 is connected to the connecting pipeline between the ejector 1 and the evaporator 4. Under this condition, the pressure of the gas-liquid separator 3 is medium pressure, so the low-pressure CO2 at the outlet of the evaporator 4 will only flow through the check valve 10 and not through the check valve 21. Furthermore, due to the presence of the check valve 211, the medium-pressure gaseous refrigerant of the gas-liquid separator 3 will not flow back to the evaporator 4.

[0029] Additionally, refer to the appendix Figure 2 As shown, the oil separator 5 is connected to the oil collector 12, and a solenoid valve 13 and a ball valve 14 are installed on the connecting pipeline between the oil separator 5 and the oil collector 12. The oil collector 12 is also connected to the compressor 2, and a solenoid valve 25 and a pressure reducing valve 16 are installed on the connecting pipeline between the oil collector 12 and the compressor 2. The oil separator 5 separates the lubricating oil in the exhaust of the compressor 2 to prevent the lubricating oil from entering the air cooler 6 and the evaporator 4, which would affect the heat exchange efficiency. The oil collector 12 collects the separated lubricating oil and, controlled by the solenoid valve 25 and the pressure reducing valve 16, sends the oil back to the compressor 2 to achieve lubricating oil circulation.

[0030] When ejector 1 is in the applicable range, electric ball valve 2 8 is closed and electronic expansion valve 9 is opened. Compressor 2 draws in medium-pressure CO2 gas from gas-liquid separator 3, compresses it to supercritical, and enters air cooler 6 through oil separator 5. High-pressure CO2 (primary flow) from air cooler 6 enters ejector 1, which in turn ejects low-pressure CO2 (secondary flow) from the outlet of evaporator 4. After mixing, they form medium-pressure gas, which enters gas-liquid separator 3. The gas in gas-liquid separator 3 is drawn out by compressor 2, and the liquid medium-pressure CO2 is throttled by electronic expansion valve 9 and enters evaporator 4 for heat exchange.

[0031] When ejector 1 jumps out of the applicable range, electric ball valve 2 opens and electronic expansion valve 9 closes. Compressor 2 draws in medium-pressure CO2 gas from gas-liquid separator 3, compresses it to supercritical, and enters air cooler 6 through oil separator 5. High-pressure CO2 (primary flow) from air cooler 6 enters ejector 1. In this state, ejector 1 cannot eject CO2 from the outlet of evaporator 4. The high-pressure CO2 from air cooler 6 is directly throttled to medium pressure in ejector 1 and enters gas-liquid separator 3. The gas in gas-liquid separator 3 is drawn out by compressor 2. Liquid medium-pressure CO2, under the action of gravity, enters evaporator 4 through electric ball valve 2. The gas in evaporator 4 returns to gas-liquid separator 3 under the suction of compressor 2 and is drawn back by compressor 2.

[0032] Furthermore, the number of ejectors 1 is matched to the capacity of compressor 2. Each group of ejectors 1 is designed with a different flow rate to ensure that the total flow rate of ejectors 1 covers the flow rate variation range of compressor 2. An electric ball valve 7 is installed before each ejector 1. The refrigerant circulation rate is controlled by adjusting the opening of the electric ball valve 7, thereby controlling the optimal pressure at the outlet of the air cooler 6. For example, by connecting five groups of compressors 2 in parallel, the operating flow rate is 0-6000 m³ / h. 3 Within a range of / h, three sets of injectors 1 are installed, each with a flow rate of 1000m³ / h. 3 / h, 2000m 3 / h, 3500m 3 / h, thus there are eight combinations to control the refrigerant circulation rate, as shown in the table below:

[0033]

[0034] During implementation, refer to the appendix. Figure 3As shown, the difference ΔP between the actual outlet pressure of air cooler 6 and the optimal outlet pressure of air cooler 6 is within ±2 bar; when ΔP>5 bar, the electric ball valve 7 before the injector 1 with the smallest flow rate among the unopened injectors 1 (checking for 10 seconds each time) opens; when 2 bar<ΔP≤5 bar, the electric ball valve 7 before the injector 1 with the smallest flow rate among the unopened injectors 1 gradually opens in 5% increments; when ΔP<-5 bar, the electric ball valve 7 before the injector 1 with the smallest flow rate among the opened injectors 1 closes; when -5 bar≤ΔP<-2 bar, the electric ball valve 7 before the injector 1 with the smallest flow rate among the opened injectors 1 closes gradually in 5% increments; when -2 bar<ΔP<-2 bar, the control of electric ball valve 7 ends.

[0035] In this way, the actual outlet pressure of the system air cooler 6 can be stabilized within the range of ±5 bar of the optimal pressure. Controlling multiple sets of injectors 1 in this way can match the changes in system load in real time. The logic is simple and reliable. At the same time, it also ensures that the difference between the actual outlet pressure of the air cooler 6 and the optimal pressure of the air cooler 6 fluctuates within ±2 bar, further improving the efficiency of the system. Moreover, through the dual optimization mechanism of "minimum flow rate priority + last operation valve fine adjustment", the pressure is quickly and stably regulated, solving the problems of response lag and insufficient accuracy of traditional methods.

[0036] Furthermore, when the ejector 1 is within the applicable range, the evaporation pressure of the evaporator 4 is controlled by the frequency of the compressor 2 and the opening degree of the electronic expansion valve 9; when the ejector 1 is outside the applicable range, the evaporation pressure of the evaporator 4 is controlled by the frequency of the compressor 2 and the opening degree of the electric ball valve 14.

[0037] In addition, another aspect of the present invention proposes a carbon dioxide transcritical injection refrigeration control method, including an injector 1 applicable range control mode and an injector 1 exiting the applicable range control mode.

[0038] In the zone control mode applicable to injector 1:

[0039] Electric ball valve 28 is closed, and electronic expansion valve 9 is opened; compressor 2 draws in medium-pressure CO2 gas from gas-liquid separator 3 and compresses it to supercritical. After passing through oil separator 5 and air cooler 6, high-pressure CO2 enters ejector 1 to eject low-pressure CO2 from the outlet of evaporator 4; the medium-pressure CO2 formed after mixing enters gas-liquid separator 3, the gaseous part is drawn in by compressor 2, and the liquid part is throttled by electronic expansion valve 9 and enters evaporator 4 for heat exchange.

[0040] When the ejector 1 exits the applicable range control mode: electric ball valve 28 opens and electronic expansion valve 9 closes; compressor 2 draws in medium-pressure CO2 gas from gas-liquid separator 3 and compresses it to supercritical pressure. After passing through oil separator 5 and air cooler 6, high-pressure CO2 is directly throttled to medium pressure in ejector 1 and enters gas-liquid separator 3; liquid CO2 in gas-liquid separator 3 enters evaporator 4 under the action of gravity through electric ball valve 28, and gas in evaporator 4 returns to gas-liquid separator 3 under the suction of compressor 2.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A transcritical carbon dioxide jet refrigeration system, comprising an ejector (1), characterized in that: The ejector (1) is connected to a compressor (2), a gas-liquid separator (3) and an evaporator (4); The compressor (2) is connected to the gas-liquid separator (3) to draw in medium-pressure CO2 gas and compress it to supercritical; The compressor (2) is also connected in sequence to an oil separator (5) and an air cooler (6); The air cooler (6) is also connected to the ejector (1), and an electric ball valve (7) is installed on the connecting pipeline between the air cooler (6) and the ejector (1) to control the optimal pressure at the outlet of the air cooler (6); The gas-liquid separator (3) is also connected to the evaporator (4), and an electric ball valve (8) and an electronic expansion valve (9) are installed on the connecting pipeline between the gas-liquid separator (3) and the evaporator (4). Electric ball valve 2 (8) opens when the injector (1) is out of working range, and liquid CO2 flows directly into the evaporator (4) under the action of gravity. Electronic expansion valve (9) opens under normal working conditions of injector (1) to control the throttling of liquid CO2 into the evaporator (4). A check valve (10) is also installed on the connecting pipeline between the gas-liquid separator (3) and the evaporator (4) to allow the low-pressure fluid at the outlet of the evaporator (4) to flow into the gas-liquid separator (3) when the ejector (1) cannot eject the low-pressure fluid of the evaporator (4). A check valve 2 (11) is installed on the connecting pipeline between the ejector (1) and the evaporator (4) to prevent the medium-pressure fluid of the gas-liquid separator (3) from flowing back to the evaporator (4). Furthermore, the connecting pipeline between the gas-liquid separator (3) and the evaporator (4) is connected to the connecting pipeline between the ejector (1) and the evaporator (4); The control method for a transcritical carbon dioxide jet refrigeration system. This includes the applicable zone control mode for injector (1) and the exit zone control mode for injector (1); In the applicable zone control mode of injector (1): Electric ball valve 2 (8) is closed, and electronic expansion valve (9) is opened; compressor (2) draws in medium-pressure CO2 gas from gas-liquid separator (3) and compresses it to supercritical. After passing through oil separator (5) and air cooler (6), high-pressure CO2 enters ejector (1) to eject low-pressure CO2 from the outlet of evaporator (4); medium-pressure CO2 formed after mixing enters gas-liquid separator (3), the gaseous part is drawn in by compressor (2), and the liquid part is throttled by electronic expansion valve (9) and enters evaporator (4) for heat exchange; When the injector (1) exits the applicable range control mode: Electric ball valve 2 (8) opens, and electronic expansion valve (9) closes; compressor (2) draws in medium-pressure CO2 gas from gas-liquid separator (3) and compresses it to supercritical. After passing through oil separator (5) and air cooler (6), high-pressure CO2 is directly throttled to medium pressure in ejector (1) and enters gas-liquid separator (3); liquid CO2 in gas-liquid separator (3) enters evaporator (4) under the action of gravity through electric ball valve 2 (8), and gas in evaporator (4) returns to gas-liquid separator (3) under the suction of compressor (2).

2. The transcritical carbon dioxide jet refrigeration system according to claim 1, characterized in that: The oil separator (5) is connected to an oil collector (12), and a solenoid valve (13) and a ball valve (14) are installed on the connecting pipeline between the oil separator (5) and the oil collector (12). The oil collector (12) is also connected to the compressor (2), and a solenoid valve (15) and a pressure reducing valve (16) are installed on the connecting pipeline between the oil collector (12) and the compressor (2).

3. The transcritical carbon dioxide jet refrigeration system according to claim 2, characterized in that: The number of injectors (1) is matched according to the capacity of the compressor (2). Each group of injectors (1) is designed with a different flow rate, and the total flow rate of the injectors (1) is designed to cover the flow rate variation range of the compressor (2). An electric ball valve (7) is installed in front of each group of injectors (1). The amount of refrigerant circulation is controlled by adjusting the opening degree of the electric ball valve (7), thereby controlling the optimal pressure at the outlet of the air cooler (6). The opening and closing of the electric ball valve (7) are controlled according to the difference between the actual outlet pressure of the air cooler (6) and the corresponding optimal pressure at the outlet temperature of the air cooler (6).

4. A transcritical carbon dioxide jet refrigeration system according to claim 3, characterized in that: The compressor (2) has five sets connected in parallel, with a working flow rate in the range of 0-6000 m³ / h, and is equipped with three sets of ejectors (1), with flow rates of 1000 m³ / h, 2000 m³ / h, and 3500 m³ / h for each set of ejectors, so as to form eight combinations to control the circulation of the refrigerant in the system.

5. A transcritical carbon dioxide jet refrigeration system according to claim 4, characterized in that: The difference ΔP between the actual outlet pressure of the air cooler (6) and the optimal outlet pressure of the air cooler (6) is within ±2 bar; when ΔP>5 bar, the electric ball valve 1 (7) before the injector (1) with the smallest flow rate among the unopened injectors (1) is opened; when 2 bar<ΔP≤5 bar, the electric ball valve 1 (7) before the injector (1) with the smallest flow rate among the unopened injectors (1) is opened gradually in 5% increments; when ΔP<-5 bar, the electric ball valve 1 (7) before the injector (1) with the smallest flow rate among the opened injectors (1) is closed; when -5 bar≤ΔP<-2 bar, the electric ball valve 1 (7) before the injector (1) with the smallest flow rate among the opened injectors (1) is closed gradually in 5% increments; when -2 bar<ΔP<-2 bar, the control of the electric ball valve 1 (7) ends.

6. A transcritical carbon dioxide jet refrigeration system according to claim 5, characterized in that: When the injector (1) is in the applicable range, the evaporation pressure of the evaporator (4) is controlled by the frequency of the compressor (2) and the opening degree of the electronic expansion valve (9).

7. A transcritical carbon dioxide jet refrigeration system according to claim 6, characterized in that: When the injector (1) jumps out of the applicable range, the evaporation pressure of the evaporator (4) is controlled by the frequency of the compressor (2) and the opening degree of the electric ball valve (8).

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