Cascade refrigeration system and control method thereof

Abstract

The invention discloses a cascade refrigerating system and a control method thereof.The cascade refrigerating system comprises a first-stage refrigerating system and a second-stage refrigerating system, the first-stage refrigerating system comprises a first-stage compressor, a dual-system plate heat exchanger, a first-stage throttling mechanism and an evaporative condenser, and the first-stage compressor, the dual-system plate heat exchanger, the first-stage throttling mechanism and the evaporative condenser are connected through pipelines and form a loop; the second-stage refrigerating system comprises a second-stage compressor, a dual-system plate heat exchanger, an evaporative condenser, a temperature adjusting module and an evaporator which are connected through a pipeline and form a loop; the first-stage refrigerating system and the second-stage refrigerating system share the evaporative condenser and the dual-system plate heat exchanger; an inlet of the evaporator is connected with an outlet of the evaporative condenser and an outlet of the oil separator through the temperature adjusting module. An outlet of the evaporator is connected with an air return port of the second-stage compressor, an outlet of the oil separator and an outlet of the evaporative condenser through the temperature adjusting module. According to the invention, the reliability of the cascade refrigeration system and the temperature uniformity of the evaporator are improved.

Description

Technical Field

[0001] The present invention relates to a cascade refrigeration system and a control method thereof, belonging to the technical field of semiconductor preparation. Background Art

[0002] With the rapid development of the domestic semiconductor industry, cryogenic refrigeration systems are increasingly widely used in electronic component test equipment, mainly to simulate various complex environments encountered by electronic components during actual operation, so as to test the performance and reliability of electronic components under various working conditions.

[0003] Currently, the commonly used cryogenic refrigeration system is a two-stage cascade refrigeration system. In order to meet the temperature control requirements, heating needs to be set on the evaporator side, and the temperature control is stabilized by the confrontation between heating and refrigeration. In order to make the system operate reliably and stably, the settings need to be adjusted to make the refrigeration system free of liquid hammer risk. At the same time, in order to meet the uniformity of the evaporator temperature, higher requirements need to be put forward for the evaporator design, and the debugging process is complex. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: how to improve the reliability of the cascade refrigeration system and the temperature uniformity of the evaporator.

[0005] In order to solve the above technical problem, the technical solution of the present invention is to provide a cascade refrigeration system, which is characterized in that it includes a primary refrigeration system and a secondary refrigeration system. The primary refrigeration system includes a primary compressor, a dual-system plate heat exchanger, a primary throttling mechanism, and an evaporation condenser connected by pipelines to form a loop. The secondary refrigeration system includes a secondary compressor, a dual-system plate heat exchanger, an evaporation condenser, a temperature adjustment module, and an evaporator connected by pipelines to form a loop. The primary refrigeration system and the secondary refrigeration system share the evaporation condenser and the dual-system plate heat exchanger. The inlet of the evaporator is connected to the outlet of the evaporation condenser and the outlet of the oil separator through the temperature adjustment module. The outlet of the evaporator is connected to the suction port of the secondary compressor, the outlet of the oil separator, and the outlet of the evaporation condenser through the temperature adjustment module.

[0006] Preferably, the primary refrigeration system and the secondary refrigeration system are coupled through the evaporation condenser, so that the primary refrigeration system and the secondary refrigeration system perform heat exchange through the evaporation condenser.

[0007] Preferably, it further includes a first temperature acquisition unit and a first pressure acquisition unit. An outlet stop valve and a return port stop valve are respectively provided at the inlet and outlet of the evaporator. The temperature adjustment module includes a secondary refrigeration electronic expansion valve, a secondary heating electronic expansion valve, and a gas-liquid separator. The inlet of the secondary refrigeration electronic expansion valve and the inlet of the secondary heating electronic expansion valve are respectively connected to the outlet of the evaporative condenser and the outlet of the oil separator. The outlets of the secondary refrigeration electronic expansion valve and the secondary heating electronic expansion valve are both connected to the evaporator through the outlet stop valve. The inlet of the oil separator is connected to the exhaust port of the secondary compressor, and the outlet of the oil separator is also connected to the inlet of the dual-system plate heat exchanger. The first temperature acquisition unit is arranged at the outlet of the secondary refrigeration electronic expansion valve and the inlet of the outlet stop valve. The first pressure acquisition unit is arranged at the inlet of the secondary compressor and the outlet of the gas-liquid separator. The gas-liquid separator is connected to the outlet of the return port stop valve.

[0008] Preferably, it further includes a second temperature acquisition unit and a third temperature acquisition unit. The second temperature acquisition unit is arranged at the outlet of the return port stop valve. The third temperature acquisition unit is arranged at the suction port of the secondary compressor. The temperature adjustment module further includes a secondary suction cooling electronic expansion valve and a secondary suction heating electronic expansion valve. The inlets of the secondary suction cooling electronic expansion valve and the secondary suction heating electronic expansion valve are respectively connected to the outlet of the evaporative condenser and the outlet of the oil separator. The outlet of the oil separator is also connected to the inlet of the secondary suction heating electronic expansion valve.

[0009] Preferably, the dual-system plate heat exchanger has three flow paths, and each flow path has an inlet and an outlet. The evaporative condenser has two flow paths, and each flow path has an inlet and an outlet.

[0010] In the primary refrigeration system, the exhaust port of the primary compressor is connected to the inlet of the primary throttling mechanism through the first flow path of the dual-system plate heat exchanger. The outlet of the primary throttling mechanism is connected to the inlet of the first flow path of the evaporative condenser. The outlet of the first flow path of the evaporative condenser is connected to the suction port of the primary compressor. The pipeline of the primary refrigeration system is filled with a primary refrigerant.

[0011] In the secondary refrigeration system, the exhaust port of the secondary compressor is connected to the inlet of the oil separator. The outlet of the oil separator is connected to the inlet of the second flow path of the dual-system plate heat exchanger. The third flow path of the dual-system plate heat exchanger is connected to the inlet and outlet of the cooling water. The outlet of the second flow path of the dual-system plate heat exchanger is connected to the inlet of the second flow path of the evaporative condenser. The outlet of the second flow path of the evaporative condenser is connected to the inlet of the evaporator through the secondary refrigeration electronic expansion valve. The outlet of the evaporator is connected to the suction port of the secondary compressor through the gas-liquid separator. The secondary refrigeration system is filled with a secondary refrigerant.

[0012] Preferably, the primary refrigeration system further includes a primary dryer filter, which is disposed on the pipeline between the dual-system plate heat exchanger and the primary throttling mechanism to absorb moisture in the primary refrigeration system and block impurities in the primary refrigeration system.

[0013] Preferably, it further includes a fourth temperature acquisition unit, a fifth temperature acquisition unit, a sixth temperature acquisition unit, a second pressure acquisition unit, a third pressure acquisition unit, and a fourth pressure acquisition unit; the fourth temperature acquisition unit and the second pressure acquisition unit are both disposed at the exhaust port of the secondary compressor; the fifth temperature acquisition unit and the third pressure acquisition unit are both disposed at the suction port of the primary compressor; the sixth temperature acquisition unit and the fourth pressure acquisition unit are both disposed at the exhaust port of the primary compressor.

[0014] A control method for a cascade refrigeration system, characterized in that the cascade refrigeration system controls the temperature regulating module to adjust the temperature of the refrigerant entering the evaporator according to the set temperature; specifically including the following steps:

[0015] S110. Obtain the first temperature T1 collected by the first temperature acquisition unit and the first pressure P1 collected by the first pressure acquisition unit;

[0016] Judge whether the set temperature T of the cascade refrigeration system SP and the preset value T of the control zone 预设1 meet the first condition; the first condition includes T sp ≥T 预设1 ;

[0017] If so, the secondary heating electronic expansion valve is adjusted according to the temperature T1 obtained by the first temperature acquisition unit and the set temperature T sp : when T SP > T1, the opening increases, and when T sp < T1, the opening decreases; at the same time, the secondary refrigeration electronic expansion valve is adjusted according to the saturation temperature T p1 converted from the pressure P1 collected by the first pressure acquisition unit and T sp : when T sp > T p1 , the opening increases, and when T sp < T p1 , the opening decreases;

[0018] If not, the secondary heating electronic expansion valve is closed, and the secondary refrigeration electronic expansion valve is adjusted according to the saturation temperature T p1 converted from the pressure P1 collected by the first pressure acquisition unit and T sp : when T sp > T p1 , the opening increases, and when T sp < T p1 , the opening decreases;

[0019] S120. Obtain the third temperature T1 collected by the first temperature acquisition unit and the second temperature T2 collected by the second temperature acquisition unit;

[0020] Judge whether the first temperature T1 and the second temperature T2 meet the second condition; the second condition includes T2 - T1 ≥ T 预 Set 2;

[0021] If so, upwardly correct the current set temperature value;

[0022] If not, maintain the current temperature set value;

[0023] S130. Obtain the first pressure P1 collected by the first pressure acquisition unit and the third temperature T3 collected by the third temperature acquisition unit;

[0024] Judge whether the first pressure P1 and the third temperature T3 meet the third condition; the third condition includes T3 - T p1 ≥ T 预设3 ; where T p1 is determined by the first pressure and the secondary refrigerant; T 预设3 is greater than or equal to the minimum suction superheat requirement of the secondary compressor;

[0025] If so, the secondary suction temperature rising electronic expansion valve performs PID regulation and the opening is closed;

[0026] If not, the secondary suction temperature rising electronic expansion valve performs PID regulation and the opening is opened;

[0027] S140. Obtain the fourth temperature T4 collected by the fourth temperature acquisition unit;

[0028] Judge whether the fourth temperature T4 meets the fourth condition; the fourth condition includes T4 ≥ T 预设4 ; where T 预设4 is less than or equal to the exhaust temperature warning value of the secondary compressor;

[0029] If so, the secondary suction temperature decreasing electronic expansion valve performs PID regulation and the opening is opened;

[0030] If not, the secondary suction temperature decreasing electronic expansion valve performs PID regulation and the opening is reduced;

[0031] S150. Obtain the first pressure P1 collected by the first pressure acquisition unit;

[0032] Judge whether the first pressure P1 meets the fifth condition; the fifth condition includes P1 < P 预设1 , where P 预设1 is greater than or equal to the lower limit of the allowable suction pressure of the secondary compressor;

[0033] If so, the secondary return air temperature-rising electronic expansion valve maintains the preset opening degree A;

[0034] If not, the secondary return air temperature-rising electronic expansion valve is adjusted according to S130, and the fifth condition control priority is higher than the third condition.

[0035] Preferably, when the difference between the outlet temperature and the inlet temperature of the evaporator is too large during the operation of the cascade refrigeration system, the temperature adjustment module is controlled to reduce the temperature difference between the inlet and outlet of the evaporator.

[0036] Preferably, the temperature adjustment module adjusts the temperature of the refrigerant entering the evaporator according to the set temperature, and at the same time corrects the set temperature according to the superheat degree of the refrigerant at the outlet of the evaporator, so that the temperature difference between the inlet and outlet of the evaporator is as small as possible, thereby improving the temperature uniformity of the evaporator, and further making the temperatures of the chips placed on the evaporator consistent.

[0037] The present invention provides a cascade refrigeration system and its control method to solve the problems existing in the prior art and improve the reliability of the cascade refrigeration system and the temperature uniformity of the evaporator. The temperature adjustment module adjusts the temperature of the refrigerant entering the evaporator according to the set temperature, and at the same time corrects the set temperature according to the superheat degree of the refrigerant at the outlet of the evaporator, so that the temperature difference between the inlet and outlet of the evaporator is as small as possible, thereby improving the temperature uniformity of the evaporator, and further making the temperatures of the chips placed on the evaporator consistent; through the return air temperature-rising electronic expansion valve and the return air temperature-lowering electronic expansion valve, the return air temperature of the secondary compressor is controlled within the allowable range, eliminating the risks brought to the system by ensuring the uniformity of the evaporator, and at the same time improving the reliability of the system operation. Description of the Drawings

[0038] Figure 1 It is a schematic structural diagram of a cascade refrigeration system.

[0039] Among them, 1: primary compressor, 2: dual-system plate heat exchanger, 3: primary throttling mechanism, 4: evaporation condenser, 5: primary dry filter, 6: secondary compressor, 7: oil separator, 8: temperature adjustment module, 9: secondary refrigeration electronic expansion valve, 10: secondary return air temperature-lowering electronic expansion valve, 11: secondary heating electronic expansion valve, 12: secondary return air temperature-rising electronic expansion valve, 13: gas-liquid separator, 14: secondary dry filter, 15: first temperature acquisition unit, 16: second temperature acquisition unit, 17: third temperature acquisition unit, 18: fourth temperature acquisition unit, 19: fifth temperature acquisition unit, 20: sixth temperature acquisition unit, 21: first pressure acquisition unit, 22: second pressure acquisition unit, 23: third pressure acquisition unit, 24: fourth pressure acquisition unit, 25: outlet stop valve, 26: return port stop valve, 27: evaporator. Detailed Embodiments

[0040] To make the present invention more obvious and understandable, preferred embodiments will be described in detail below in conjunction with the accompanying drawings.

[0041] The present invention provides a cascade refrigeration system, as Figure 1 shown, which includes a primary refrigeration system and a secondary refrigeration system. The primary refrigeration system includes a primary compressor 1, a dual-system plate heat exchanger 2, a primary throttling mechanism 3, and an evaporative condenser 4 that are connected by pipes to form a loop; the secondary refrigeration system includes a secondary compressor 6, a dual-system plate heat exchanger 2, an evaporative condenser 4, a temperature regulation module 8, and an evaporator 27 that are connected by pipes to form a loop; the primary refrigeration system and the secondary refrigeration system share the evaporative condenser 4 and the dual-system plate heat exchanger 2; the primary refrigeration system and the secondary refrigeration system are coupled through the evaporative condenser 4, so that the primary refrigeration system and the secondary refrigeration system can exchange heat through the evaporative condenser 4;

[0042] The inlet of the evaporator 27 is connected to the outlet of the evaporative condenser 4 and the outlet of the oil separator 7 through the temperature regulation module 8; the outlet of the evaporator 27 is connected to the suction port of the secondary compressor 6, the outlet of the oil separator 7, and the outlet of the evaporative condenser 4 through the temperature regulation module 8. The temperature regulation module 8 is used to regulate the temperature of the refrigerant entering the evaporator 27 and improve the operating safety of the system.

[0043] Among them, the dual-system plate heat exchanger 2 has three flow paths (the first flow path, the second flow path, and the third flow path), and each flow path has an inlet and an outlet. The evaporative condenser 4 has two flow paths (the first flow path and the second flow path), and each flow path has an inlet and an outlet; in the primary refrigeration system, the discharge port of the primary compressor 1 is connected to the inlet of the primary throttling mechanism 3 through the first flow path of the dual-system plate heat exchanger 2, the outlet of the primary throttling mechanism 3 is connected to the inlet of the first flow path of the evaporative condenser 4, and the outlet of the first flow path of the evaporative condenser 4 is connected to the suction port of the primary compressor 1; the pipes of the primary refrigeration system are filled with a primary refrigerant.

[0044] In an alternative embodiment, the primary refrigeration system further includes a primary dryer filter 5, which is disposed between the dual-system plate heat exchanger 2 and the primary throttling mechanism 3 to absorb moisture in the primary refrigeration system and block impurities in the primary refrigeration system, preventing ice blockage and dirt blockage of the pipelines in the primary refrigeration system.

[0045] In the secondary refrigeration system, the exhaust port of the secondary compressor 6 is connected to the inlet of the oil separator, the outlet of the oil separator 7 is connected to the inlet of the second flow path of the dual-system plate heat exchanger 2, the third flow path of the dual-system plate heat exchanger 2 is connected to the cooling water inlet and outlet, the outlet of the second flow path of the dual-system plate heat exchanger 2 is connected to the inlet of the second flow path of the evaporative condenser 4, the outlet of the second flow path of the evaporative condenser 4 is connected to the inlet of the evaporator 27 through the secondary refrigeration electronic expansion valve 9, and the outlet of the evaporator 27 is connected to the suction port of the secondary compressor 6 through the gas-liquid separator 13; the secondary refrigerant is filled in the secondary refrigeration system. An outlet stop valve 25 and a return port stop valve 26 are respectively arranged at the inlet and outlet of the evaporator 27.

[0046] The cascade refrigeration system of the present invention further includes a first temperature acquisition unit 15 and a first pressure acquisition unit 21;

[0047] The temperature regulation module 8 includes a secondary refrigeration electronic expansion valve 9 and a secondary heating electronic expansion valve 11; a gas-liquid separator 13;

[0048] The inlet of the secondary refrigeration electronic expansion valve 9 and the inlet of the secondary heating electronic expansion valve 11 are respectively connected to the outlet of the evaporative condenser 4 and the outlet of the oil separator 7. The outlets of the secondary refrigeration electronic expansion valve 9 and the secondary heating electronic expansion valve 11 are both connected to the evaporator 27 through the outlet stop valve 25. The inlet of the oil separator 7 is connected to the exhaust port of the secondary compressor 6. In addition to connecting to the inlet of the secondary heating electronic expansion valve 11, the outlet of the oil separator 7 is also connected to the dual-system plate heat exchanger 2 and the inlet of the secondary return air heating electronic expansion valve 12. The first temperature acquisition unit 15 is arranged at the outlet of the secondary refrigeration electronic expansion valve 9 and the inlet of the outlet stop valve 25; the first pressure acquisition unit 21 is arranged at the inlet of the secondary compressor 6 and the outlet of the gas-liquid separator 13; the gas-liquid separator 13 is connected to the outlet of the return port stop valve 26;

[0049] The cascade refrigeration system of the present invention further includes: a second temperature acquisition unit 16, a third temperature acquisition unit 17;

[0050] The temperature regulation module 8 further includes: a secondary return air cooling electronic expansion valve 10 and a secondary return air heating electronic expansion valve 12;

[0051] The inlet of the secondary return air cooling electronic expansion valve 10 and the inlet of the secondary return air heating electronic expansion valve 12 are respectively connected to the outlet of the evaporative condenser 4 and the outlet of the oil separator 7;

[0052] The second temperature acquisition unit 16 is arranged at the outlet of the return port stop valve 26; the third temperature acquisition unit 17 is arranged at the suction port of the secondary compressor 6;

[0053] The cascade refrigeration system of the present invention further includes: a fourth temperature acquisition unit 18, a fifth temperature acquisition unit 19, a sixth temperature acquisition unit 20, a second pressure acquisition unit 22, a third pressure acquisition unit 23, and a fourth pressure acquisition unit 24;

[0054] Both the fourth temperature acquisition unit 18 and the second pressure acquisition unit 22 are disposed at the exhaust port of the secondary compressor 6.

[0055] Both the fifth temperature acquisition unit 19 and the third pressure acquisition unit 23 are disposed at the suction port of the primary compressor 1.

[0056] Both the sixth temperature acquisition unit 20 and the fourth pressure acquisition unit 24 are disposed at the exhaust port of the primary compressor 1.

[0057] The present invention also provides a control method for a cascade refrigeration system to improve the temperature uniformity of the evaporator. The cascade refrigeration system controls the temperature adjustment module 8 to adjust the temperature of the refrigerant entering the evaporator 27 according to the set temperature. When the cascade refrigeration system is operating, when the difference between the outlet temperature and the inlet temperature of the evaporator 27 is too large, the temperature adjustment module 8 is controlled to reduce the temperature difference between the inlet and outlet of the evaporator 27. Specifically, it includes:

[0058] S110. Obtain the first temperature T1 collected by the first temperature acquisition unit 15 and the first pressure P1 collected by the first pressure acquisition unit 21;

[0059] Judge whether the set temperature T of the cascade refrigeration system SP and the preset value T of the control zone 预设1 meet the first condition; the first condition includes T sp ≥T 预设1 ;

[0060] If so, the secondary heating electronic expansion valve 11 is adjusted according to the temperature T1 obtained by the first temperature acquisition unit 15 and the set temperature T sp : when T SP > T1, the opening increases; when T sp < T1, the opening decreases; at the same time, the secondary refrigeration electronic expansion valve 9 is adjusted according to the saturation temperature T p1 converted from the pressure P1 collected by the first pressure acquisition unit 21 and T sp : when T sp > T p1 , the opening increases; when T sp < T p1 , the opening decreases.

[0061] If not, the secondary heating electronic expansion valve 11 is closed, and the secondary refrigeration electronic expansion valve 9 is based on the saturation temperature T p1and T sp Adjust: T sp > T p1 When, the opening increases, T sp < T p1 When, the opening decreases.

[0062] S120. Obtain the third temperature T1 collected by the first temperature acquisition unit 15 and the second temperature T2 collected by the second temperature acquisition unit 16;

[0063] Judge whether the first temperature T1 and the second temperature T2 meet the second condition; the second condition includes T2 - T1 ≥ T 预 Set 2;

[0064] If so, upwardly correct the current set temperature value;

[0065] If not, maintain the current temperature set value.

[0066] S130. Obtain the first pressure P1 collected by the first pressure acquisition unit 21 and the third temperature T3 collected by the third temperature acquisition unit 17;

[0067] Judge whether the first pressure P1 and the third temperature T3 meet the third condition; the third condition includes T3 - T p1 ≥ T 预设3 ; where, T p1 Is determined by the first pressure and the secondary refrigerant; T 预设3 Is greater than or equal to the minimum suction superheat requirement of the secondary compressor 6;

[0068] If so, the secondary suction temperature rising electronic expansion valve 12 performs PID adjustment and the opening is closed;

[0069] If not, the secondary suction temperature rising electronic expansion valve 12 performs PID adjustment and the opening is opened;

[0070] S140. Obtain the fourth temperature T4 collected by the fourth temperature acquisition unit 18;

[0071] Judge whether the fourth temperature T4 meets the fourth condition; the fourth condition includes T4 ≥ T 预设4 ; where, T 预设4 Is less than or equal to the exhaust temperature warning value of the secondary compressor 6;

[0072] If so, the secondary suction temperature decreasing electronic expansion valve 10 performs PID adjustment and the opening is opened;

[0073] If not, the secondary suction temperature decreasing electronic expansion valve 10 performs PID adjustment and the opening is decreased;

[0074] S150. Obtain the first pressure P1 collected by the first pressure acquisition unit 21;

[0075] Determine whether the first pressure P1 satisfies the fifth condition; the fifth condition includes P1 < P 预设1 , where P 预设1 is greater than or equal to the lower limit of the allowable return air pressure of the second-stage compressor 6;

[0076] If so, the second-stage return air temperature-rising electronic expansion valve 10 maintains the preset opening A;

[0077] If not, the second-stage return air temperature-rising electronic expansion valve 10 is adjusted according to the steps of S130, that is, the control priority of the fifth condition is higher than that of the third condition.

Claims

1. A cascade refrigeration system, characterized in that: The invention comprises a primary refrigeration system and a secondary refrigeration system. The primary refrigeration system comprises a primary compressor (1), a dual-system plate heat exchanger (2), a primary throttling mechanism (3), and an evaporative condenser (4) which are connected through pipelines to form a loop. The secondary refrigeration system comprises a secondary compressor (6), a dual-system plate heat exchanger (2), an evaporative condenser (4), a temperature regulating module (8), and an evaporator (27) which are connected through pipelines to form a loop. The primary refrigeration system and the secondary refrigeration system share the evaporative condenser (4) and the dual-system plate heat exchanger (2). The inlet of the evaporator (27) is connected to the outlet of the evaporative condenser (4) and the outlet of the oil separator (7) through the temperature regulating module (8). The outlet of the evaporator (27) is connected to the return air port of the secondary compressor (6), the outlet of the oil separator (7), and the outlet of the evaporative condenser (4) through the temperature regulating module (8).

2. A cascade refrigeration system according to claim 1, characterized in that: The primary refrigeration system and the secondary refrigeration system are coupled via the evaporative condenser (4), so that the primary refrigeration system and the secondary refrigeration system perform heat exchange via the evaporative condenser (4).

3. A cascade refrigeration system according to claim 1, characterized in that: The invention also comprises a first temperature acquisition unit (15) and a first pressure acquisition unit (21); an outlet stop valve (25) and a return stop valve (26) are respectively provided at the inlet and outlet of the evaporator (27); the temperature adjustment module (8) comprises a secondary refrigeration electronic expansion valve (9), a secondary heating electronic expansion valve (11), and a gas-liquid separator (13); the inlet of the secondary refrigeration electronic expansion valve (9) and the inlet of the secondary heating electronic expansion valve (11) are respectively connected to the outlet of the evaporator condenser (4) and the outlet of the oil separator (7); the secondary refrigeration electronic expansion valve (9) and ... oil separator (7); the secondary refrigeration electronic expansion valve (9) and the secondary heating electronic expansion valve (11) are respectively connected to the outlet of the evaporator condenser (4) and the oil separator (7); the secondary refrigeration electronic expansion valve (9) and the secondary heating electronic expansion valve (11) are respectively connected to the outlet of the evaporator condenser (4) and the oil separator (7); the secondary refrigeration electronic expansion valve (9) and the secondary heating electronic expansion valve (11) are respectively connected to the outlet of the evaporator condenser (4) and the oil separator (7); the secondary refrigeration The outlet of the thermoelectronic expansion valve (11) is connected to the evaporator (27) via the outlet stop valve (25); the inlet of the oil separator (7) is connected to the exhaust port of the secondary compressor (6); the outlet of the oil separator (7) is also connected to the inlet of the dual-system plate heat exchanger (2); the first temperature acquisition unit (15) is arranged at the outlet of the secondary refrigeration electronic expansion valve (9) and the inlet of the outlet stop valve (25); the first pressure acquisition unit (21) is arranged at the inlet of the secondary compressor (6) and the outlet of the gas-liquid separator (13); the gas-liquid separator (13) is connected to the outlet of the return stop valve (26).

4. A cascade refrigeration system according to claim 3, characterized in that: It also includes a second temperature acquisition unit (16) and a third temperature acquisition unit (17), wherein the second temperature acquisition unit (16) is arranged at the outlet of the return stop valve (26); the third temperature acquisition unit (17) is arranged at the return air port of the secondary compressor (6); the temperature adjustment module (8) also includes a secondary return air cooling electronic expansion valve (10) and a secondary return air heating electronic expansion valve (12), wherein the inlet of the secondary return air cooling electronic expansion valve (10) and the inlet of the secondary return air heating electronic expansion valve (12) are respectively connected to the outlet of the evaporative condenser (4) and the outlet of the oil separator (7); the outlet of the oil separator (7) is also connected to the inlet of the secondary return air heating electronic expansion valve (12).

5. A cascade refrigeration system according to claim 3, characterized in that: The dual-system plate heat exchanger (2) has three flow paths, each of which has an inlet and outlet; the evaporative condenser (4) has two flow paths, each of which has an inlet and outlet; In the primary refrigeration system, the exhaust port of the primary compressor (1) is connected to the inlet of the primary throttling mechanism (3) through the first flow path of the dual-system plate heat exchanger (2), the outlet of the primary throttling mechanism (3) is connected to the first flow path inlet of the evaporative condenser (4), and the first flow path outlet of the evaporative condenser (4) is connected to the return air port of the primary compressor (1); the pipeline of the primary refrigeration system is filled with primary refrigerant; In the secondary refrigeration system, the exhaust port of the secondary compressor (6) is connected to the inlet of the oil separator (7), the outlet of the oil separator (7) is connected to the inlet of the second flow path of the dual-system plate heat exchanger (2), the third flow path of the dual-system plate heat exchanger (2) is connected to the inlet and outlet of cooling water, the second flow path outlet of the dual-system plate heat exchanger (2) is connected to the second flow path inlet of the evaporative condenser (4), the second flow path outlet of the evaporative condenser (4) is connected to the inlet of the evaporator (27) through the secondary refrigeration electronic expansion valve (9), and the outlet of the evaporator (27) is connected to the return air port of the secondary compressor (6) through the gas-liquid separator (13); the secondary refrigeration system is filled with secondary refrigerant.

6. A cascade refrigeration system according to claim 5, characterized in that: The primary refrigeration system further comprises a primary drying filter (5), which is arranged on the pipeline between the dual-system plate heat exchanger (2) and the primary throttling mechanism (3) to absorb moisture in the primary refrigeration system and block impurities in the primary refrigeration system.

7. A cascade refrigeration system according to claim 4, characterized in that: It also comprises a fourth temperature collection unit (18), a fifth temperature collection unit (19), a sixth temperature collection unit (20), a second pressure collection unit (22), a third pressure collection unit (23), and a fourth pressure collection unit (24); the fourth temperature collection unit (18) and the second pressure collection unit (22) are both arranged at the exhaust port of the secondary compressor (6); the fifth temperature collection unit (19) and the third pressure collection unit (23) are both arranged at the return air port of the primary compressor (1); and the sixth temperature collection unit (20) and the fourth pressure collection unit (24) are both arranged at the exhaust port of the primary compressor (1).

8. A control method for a cascade refrigeration system according to claim 7, characterized in that: The cascade refrigeration system controls the temperature regulating module (8) to regulate the temperature of the refrigerant entering the evaporator (27) according to the set temperature; specifically, it comprises the following steps: S110, acquiring a first temperature T1 collected by a first temperature collection unit (15) and a first pressure P1 collected by a first pressure collection unit (21); Determine the set temperature T of the cascade refrigeration system SP and control partition preset value T 预设1 Whether the first condition is met; the first condition includes T sp ≥T 预设1 ; If so, the secondary heating electronic expansion valve (11) is set according to the temperature T1 obtained by the first temperature acquisition unit (15) and the set temperature T sp Adjustment: T SP >T1, the opening increases, T sp When <T1, the opening degree decreases; at the same time, the secondary refrigeration electronic expansion valve (9) converts the saturation temperature T according to the pressure P1 collected by the first pressure collection unit (21). p1 and T sp Adjustment: T sp >T p1 When the opening increases, T sp <T p1 When , the opening decreases; If not, the secondary heating electronic expansion valve (11) is closed, and the secondary cooling electronic expansion valve (9) is set according to the saturation temperature T converted from the pressure P1 collected by the first pressure collection unit (21). p1 and T sp Adjustment: T sp >T p1 When the opening increases, T sp <T p1 When , the opening decreases; S120, acquiring a third temperature T1 collected by the first temperature collection unit (15) and a second temperature T2 collected by the second temperature collection unit (16); Determine whether the first temperature T1 and the second temperature T2 meet the second condition; the second condition includes T2-T1≥T 预 Assume 2; If yes, the current set temperature value is revised upward; If not, maintain the current temperature setting value; S130, acquiring a first pressure P1 collected by a first pressure collection unit (21) and a third temperature T3 collected by a third temperature collection unit (17); Determine whether the first pressure P1 and the third temperature T3 meet the third condition; the third condition includes T3-T p1 ≥T 预设3 ; Among them, T p1 Determined by the primary pressure and the secondary refrigerant; T 预设3 Greater than or equal to the minimum return air superheat requirement of the secondary compressor (6); If so, the secondary return air heating electronic expansion valve (12) is PID regulated and the opening is reduced; If not, the secondary return air heating electronic expansion valve (12) is PID regulated and opened wider; S140, obtaining a fourth temperature T4 collected by a fourth temperature collection unit (18); Determine whether the fourth temperature T4 satisfies the fourth condition; the fourth condition includes T4 ≥ T 预设4 ; Among them, T 预设4 Less than or equal to the exhaust temperature warning value of the secondary compressor (6); If yes, the secondary return air cooling electronic expansion valve (10) is PID regulated and opened wider; If not, the secondary return air cooling electronic expansion valve (10) performs PID adjustment and the opening degree is reduced; S150, obtaining a first pressure P1 collected by a first pressure collection unit (21); Determine whether the first pressure P1 satisfies the fifth condition; the fifth condition includes P1 <P 预设1 , where P 预设1 Greater than or equal to the lower limit of the return air pressure allowed by the secondary compressor (6); If yes, the secondary return air heating electronic expansion valve (10) maintains a preset opening degree A; If not, the secondary return air heating electronic expansion valve (10) is adjusted according to S130, and the fifth condition has a higher control priority than the third condition.

9. A control method for a cascade refrigeration system according to claim 8, characterized in that: When the cascade refrigeration system is in operation, when the difference between the outlet temperature of the evaporator (27) and the inlet temperature of the evaporator (27) is too large, the temperature adjustment module (8) is controlled to reduce the inlet and outlet temperature difference of the evaporator (27).

10. The control method of a cascade refrigeration system according to claim 9, characterized in that: The temperature regulating module (8) regulates the temperature of the refrigerant entering the evaporator (27) according to the set temperature, and at the same time corrects the set temperature according to the superheat of the refrigerant at the outlet of the evaporator (27), so that the temperature difference between the inlet and outlet of the evaporator (27) is as small as possible, thereby improving the temperature uniformity of the evaporator (27) and further making the temperature of the chip placed on the evaporator (27) consistent.

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