Thermostatic equipment control system based on electronic expansion valve and electronic equipment

Abstract

The invention discloses a thermostatic equipment control system based on an electronic expansion valve and electronic equipment, and aims to solve the problems that in the prior art, an inverter compressor is high in cost, and other schemes cannot accurately control heating power. The constant temperature equipment comprises a circulation pipeline formed by sequentially connecting an evaporator, a fixed frequency compressor and a condenser in series and two electronic expansion valves, one electronic expansion valve serves as a refrigeration electronic expansion valve and is located on a pipeline between an outlet of the condenser and an inlet of the evaporator, and the other electronic expansion valve serves as a hot gas bypass electronic expansion valve and is located on a pipeline between an outlet of the condenser and an inlet of the evaporator. The condenser is integrally connected with the refrigeration electronic expansion valve in parallel; the control system comprises a first PID (Proportion Integration Differentiation) controller, a second PID controller and a third PID controller; the opening degree of the hot gas bypass electronic expansion valve and the opening degree of the refrigeration electronic expansion valve are determined based on the PIDValue 1, the PIDValue 2 and the PIDValue 3 output by the control system, and control over the constant temperature system is achieved.

Description

Technical Field

[0001] The present application relates to the field of refrigeration technology, and in particular to the control of a constant temperature device. Background Art

[0002] There are two main solutions for fluorine circuit control of constant temperature equipment in the market:

[0003] Solution 1: Use solenoid valves, capillaries (or thermal expansion valves) and fixed-frequency compressors to achieve stable temperature control. The main function of the compressor is to compress and transport the refrigerant. The solenoid valve controls the circulation path of the refrigerant in the fluorine circuit to achieve the temperature control effect. The capillary tube (or thermal expansion valve) as a throttling device can prevent the compressor from inhaling liquid refrigerant, thereby avoiding wet compression and liquid hammer, thereby improving the refrigeration effect and service life of the system.

[0004] The disadvantage of this control scheme is that the solenoid valve makes a lot of noise during use, which is not very friendly to indoor use scenarios such as laboratories. In addition, the solenoid valve needs to be opened and closed frequently, which is also a great challenge to the service life of the solenoid valve. At the same time, the use of capillaries also has certain limitations. Once installed, its flow rate cannot change with the difference in system use. Another throttling device, the thermal expansion valve, also has disadvantages such as response delay, low adjustment accuracy, and limited adjustment range.

[0005] Solution 2: Use an electronic expansion valve and a variable frequency compressor to work together to achieve the purpose of temperature control. In addition to realizing the functions of compressing and transporting refrigerant like a fixed frequency compressor, the variable frequency compressor can also adjust the temperature by changing its own operating frequency. The electronic expansion valve is used as a throttling device to adjust the superheat of the refrigerant in the fluorine system, so that the fluorine system can reach a good operating state, improve the refrigeration performance of the equipment, and extend the service life of the equipment.

[0006] The cost of variable frequency compressors is higher than that of fixed frequency compressors. In addition, they need to be used with a matching frequency converter, which further increases the manufacturing cost. In addition, many customers have requirements for the spatial dimensions of constant temperature equipment. Variable frequency compressors and frequency converters will occupy more space inside the equipment, which will greatly increase the difficulty of designing and manufacturing constant temperature equipment.

[0007] In addition, the patent document "A high-precision refrigerator controlled by dual electronic expansion valves" (publication number CN207180108U) discloses a high-precision refrigerator controlled by dual electronic expansion valves, including a compressor, a condenser and an evaporator for forming a refrigeration and heat release circuit, a throttling electronic expansion valve is installed on the pipeline between the condenser and the evaporator, and a bypass electronic expansion valve connected in parallel with the throttling electronic expansion valve and the condenser is also provided on one side of the throttling electronic expansion valve and the condenser. The throttling electronic expansion valve and the bypass electronic expansion valve are both connected to the control of a PID controller, and a pipe for heat exchange with the evaporator is provided on one side of the evaporator. The pipe is connected to a liquid tank, and a liquid pump is installed on the pipe. This patent document uses high-pressure switches and low-pressure switches in the pipeline construction, which increases the welding process and is not conducive to maintaining the stability of the equipment. In addition, this patent document controls the electronic expansion valve only based on the temperature difference between the inlet and outlet of the evaporator, and the temperature difference between the set temperature and the actual liquid temperature. The disadvantage is that the heating power cannot be accurately controlled. When the equipment requires a small amount of heating effect, the throttling electronic expansion valve will be closed, and only adjusting the bypass electronic expansion valve will cause low-pressure protection of the pipeline, and long-term operation will cause the compressor to shut down for protection. Summary of the invention

[0008] The present application provides a thermostatic equipment control system and electronic equipment based on an electronic expansion valve, aiming to solve the problems in the prior art such as high noise and short life of the solenoid valves, flow rate cannot be changed when using throttling devices such as capillaries, increased cost and large space occupied when using variable frequency compressors, and the use of high-voltage switches and low-voltage switches in other solutions, which increase the welding process, are not conducive to maintaining the stability of the equipment, and cannot accurately control the heating power.

[0009] In a first aspect, a thermostatic device control system based on an electronic expansion valve, the thermostatic device comprising a circulation pipeline formed by an evaporator, a fixed-frequency compressor, and a condenser connected in series in sequence, and two electronic expansion valves, wherein one electronic expansion valve is used as a refrigeration electronic expansion valve and is located on a pipeline between a condenser outlet and an evaporator inlet, and the other electronic expansion valve is used as a hot gas bypass electronic expansion valve and is integrally connected in parallel with the condenser and the refrigeration electronic expansion valve; the control system comprises: a first PID controller, a second PID controller, and a third PID controller;

[0010] The first PID controller has an input of the difference between the actual outlet temperature of the evaporator and the target outlet temperature, and outputs a first PID value denoted as PID_Value1;

[0011] The second PID controller has an input of the difference between the measured evaporation pressure and the preset evaporation pressure lower limit, and outputs a second PID value recorded as PID_Value2;

[0012] The third PID controller has the following inputs: the measured temperature of the liquid outlet - the preset superheat target value - the saturation temperature corresponding to the measured evaporation pressure, and outputs the third PID value, which is recorded as PID_Value3;

[0013] Among them, PID_Value1 and PID_Value2 are used to determine the opening of the hot gas bypass electronic expansion valve; PID_Value1 and PID_Value3 are used to determine the first opening of the refrigeration electronic expansion valve.

[0014] In the above scheme, further optionally, it also includes: a fourth PID controller, whose input is the difference between the compressor outlet temperature and the preset compressor outlet temperature upper limit, and outputs a fourth PID value recorded as PID_Value4;

[0015] PID_Value1, PID_Value3 and PID_Value4 are used to determine the second opening degree of the refrigeration electronic expansion valve.

[0016] In the above solution, optionally, a pressure transmitter is provided between the evaporator and the fixed-frequency compressor.

[0017] In the above scheme, optionally, a first temperature sensor for detecting the compressor outlet temperature is provided between the compressor and the condenser; and a second temperature sensor for detecting the actual outlet temperature of the constant temperature device is provided at the outlet of the evaporator.

[0018] In a second aspect, a thermostatic device control method based on an electronic expansion valve is provided. The method is based on the thermostatic device control system based on the electronic expansion valve as described above, and specifically comprises:

[0019] Obtain the measured liquid outlet temperature, the target liquid outlet temperature, the measured evaporation pressure, the saturation temperature corresponding to the measured evaporation pressure, and the preset evaporation pressure lower limit of the thermostatic device;

[0020] According to the measured liquid outlet temperature and the target liquid outlet temperature, a first PID value PID_Value1 is calculated by a first PID controller;

[0021] According to the measured evaporation pressure and the preset evaporation pressure lower limit, a second PID value PID_Value2 is calculated by a second PID controller;

[0022] Determine the opening value A of the hot gas bypass electronic expansion valve based on PID_Value1 and PID_Value2 h , calculated as follows:

[0023] A h =PID_Value1+PID_Value2;

[0024] The third PID value PID_Value3 is calculated by the third PID controller according to the saturation temperature corresponding to the measured liquid outlet temperature minus the preset superheat target value and the measured evaporation pressure;

[0025] Subtract the PID value corresponding to the maximum opening of the electronic expansion valve from PID_Value1 to obtain value A hr ;

[0026] Determine the first opening value A of the refrigeration electronic expansion valve according to the PID value, PID_Value1 and PID_Value3 corresponding to the maximum opening of the electronic expansion valve c , the determination method is:

[0027] A c =A hr *PID_Value3.

[0028] In the above scheme, further optionally, it also includes: obtaining the compressor outlet temperature and presetting the compressor outlet temperature upper limit;

[0029] According to the compressor outlet temperature and the preset compressor outlet temperature upper limit, a fourth PID value PID_Value4 is calculated by a fourth PID controller;

[0030] According to A hr , PID_Value3 and PID_Value4 determine the second opening value A of the refrigeration electronic expansion valve c ', calculated as follows:

[0031] A c '=A hr *PID_Value3+PID_Value4.

[0032] According to a third aspect, an electronic device includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method described above.

[0033] Compared with the prior art, this application has at least the following beneficial effects:

[0034] Based on further analysis and research of the existing technical problems, this application recognizes that the solenoid valve in the prior art has high noise and short life, the throttling devices such as capillaries have their limitations in use, and the variable frequency compressor has high cost and large space occupation. This application uses two electronic expansion valves and a fixed frequency compressor as the main refrigeration actuators for temperature control, one of which is used as a refrigeration electronic expansion valve, and the other is used as a hot gas bypass electronic expansion valve. Through the mutual adjustment of the opening of the two electronic expansion valves, the function of temperature control can be achieved, and the refrigeration performance of the equipment can be improved and the service life of the equipment can be extended. In addition, the fixed frequency compressor used in the present invention also reduces the design and manufacturing costs of the equipment, and the equipment operates well during long-term operation.

[0035] Compared with the patent document "A high-precision refrigerator controlled by dual electronic expansion valves" (publication number CN207180108U) in which pipeline pressure is controlled by high-pressure switches and low-pressure switches, the present application detects the pressure in the pipeline through a pressure transmitter, and uses the pipeline pressure as a variable parameter in the control logic to control the opening of the two electronic expansion valves, thereby improving the sensitivity of pipeline pressure detection.

[0036] Compared with the high-pressure switch, low-pressure switch, evaporator outlet temperature probe, evaporator inlet temperature probe, and oil outlet temperature probe set in the above-mentioned patent document, the present application only sets two temperature sensors at the liquid outlet of the evaporator and the exhaust port of the compressor, and sets a pressure transmitter between the fluorine filling port and the evaporator, which saves manufacturing time. In addition, the temperature sensor only needs to be set on the surface of the pipeline without being welded on the pipeline. Therefore, only two welding points are needed for welding the pressure transmitter. Compared with the four welding points required for welding the high-pressure switch and the low-pressure switch, the welding process is reduced, the stability of the equipment is improved, and the manufacturing time is saved.

[0037] Compared with the above patent documents, the control of the electronic expansion valve is only based on the temperature difference between the evaporator inlet and outlet and the temperature difference between the set temperature and the actual liquid temperature. The control logic is simple but the heating power cannot be accurately controlled. When the device needs a small amount of heating effect, the throttling electronic expansion valve will be closed, and only the adjustment of the bypass electronic expansion valve will cause low-pressure protection of the pipeline, causing the compressor to shut down. This application realizes the control of the opening of the two electronic expansion valves through multiple parameters such as the measured liquid outlet temperature, the target liquid outlet temperature, the measured evaporation pressure, the saturation temperature corresponding to the measured evaporation pressure (calculated from the measured evaporation pressure), the preset evaporation pressure lower limit, the compressor outlet temperature, and the preset compressor outlet temperature upper limit. Its advantages are as follows:

[0038] (1) Improve system efficiency. By considering the measured outlet temperature and target temperature, evaporation pressure and its corresponding saturation temperature at the same time, the system can more accurately adjust the refrigerant flow rate to ensure that the evaporator operates under optimal conditions, thereby improving the energy efficiency ratio (COP) of the entire refrigeration system and reducing the overall energy consumption of the constant temperature system. The preset evaporation pressure lower limit can prevent frost or ice problems caused by too low evaporation pressure, protect the evaporator and maintain system stability.

[0039] (2) Enhance system stability. Introducing the compressor outlet temperature and preset upper limit as control parameters helps prevent the compressor from overheating, protects the compressor from damage, and extends its service life. The control logic that integrates multiple parameters can better respond to changes in external environment and load conditions, reduce system fluctuations, improve stability, reduce failures caused by overheating, overcooling, etc., and reduce maintenance costs.

[0040] (3) Optimizing response speed: The multi-parameter control logic of the present application can more quickly identify and respond to changes in system status, such as quickly restoring the optimal working state of the evaporator by adjusting the expansion valve opening in real time, thereby shortening the system adjustment time and improving the response speed.

[0041] (4) Improve control accuracy: Compared with the control method of a single or a few parameters, the multi-parameter control of the present application can more comprehensively reflect the system status, reduce control errors, improve control accuracy, and enable the system to more effectively transfer heat from the evaporator to the condenser, thereby improving refrigeration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A pipeline structure diagram of a constant temperature device provided in one embodiment of the present application;

[0043] Figure 2 A connection diagram of a thermostatic device control system based on an electronic expansion valve provided in one embodiment of the present application;

[0044] Figure 3 A connection diagram of a thermostatic device control system based on an electronic expansion valve provided in another embodiment of the present application;

[0045] Figure 4 FIG. 4 is a diagram showing the internal structure of a computer device in one embodiment.

[0046] In the figure: 1. fan; 2. condenser; 3. first temperature sensor; 4. fixed frequency compressor; 5. fluorine filling port; 6. pressure transmitter; 7. evaporator; 8. second temperature sensor; 9. hot gas bypass electronic expansion valve; 10. refrigeration electronic expansion valve; 11. drying filter. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0048] In the description of this application: unless otherwise specified, the meaning of "plurality" is two or more. The terms "first", "second", "third", etc. in this application are intended to distinguish the objects referred to, and do not have special meanings in terms of technical connotations (for example, they should not be understood as emphasizing the importance or order, etc.). Expressions such as "including", "comprising", "having", etc. also mean "not limited to" (certain units, components, materials, steps, etc.).

[0049] In one embodiment, a thermostatic device control system based on an electronic expansion valve is provided. The thermostatic device includes a circulation pipeline formed by an evaporator, a fixed-frequency compressor, and a condenser connected in series in sequence, and two electronic expansion valves. One of the electronic expansion valves is used as a refrigeration electronic expansion valve and is located on the pipeline between the condenser outlet and the evaporator inlet. The other electronic expansion valve is used as a hot gas bypass electronic expansion valve and is connected in parallel with the condenser and the refrigeration electronic expansion valve. The thermostatic device is as follows: Figure 1 The control system includes: a first PID controller, a second PID controller and a third PID controller. The connection relationship of the control system is specifically referred to Figure 2 .

[0050] The first PID controller has an input of the difference between the actual outlet temperature of the evaporator and the target outlet temperature, and outputs a first PID value recorded as PID_Value1. The output range of PID_Value1 is 0 to 100%.

[0051] The second PID controller has an input of the difference between the actual evaporation pressure and the preset evaporation pressure lower limit, and outputs a second PID value recorded as PID_Value2. The output range of PID_Value2 is 0-40%.

[0052] The third PID controller has the following inputs: the measured liquid outlet temperature - the preset superheat target value - the saturation temperature corresponding to the measured evaporation pressure. The output of the third PID value is recorded as PID_Value3. The output range of PID_Value3 is 0.1 to 1.

[0053] Among them, PID_Value1 and PID_Value2 are used to determine the opening of the hot gas bypass electronic expansion valve; PID_Value1 and PID_Value3 are used to determine the first opening of the refrigeration electronic expansion valve.

[0054] In this embodiment, the present application uses two electronic expansion valves and a fixed-frequency compressor as the main refrigeration actuators for temperature control, wherein one electronic expansion valve is used as a refrigeration electronic expansion valve, and the other electronic expansion valve is used as a hot gas bypass electronic expansion valve. By adjusting the openings of the two electronic expansion valves, the temperature control function is achieved, and the refrigeration performance of the equipment can be improved and the service life of the equipment can be extended. In addition, the fixed-frequency compressor used in the present application also reduces the design and manufacturing costs of the equipment.

[0055] In this embodiment, the main function of the compressor is to compress and transport the refrigerant, and the electronic expansion valve is used as a throttling device to adjust the superheat of the refrigerant in the fluorine circuit system, so that the fluorine circuit system can reach a good operating state, improve the refrigeration performance of the equipment, and extend the service life of the equipment.

[0056] The purpose of the hot gas bypass electronic expansion valve is to adjust the high-temperature and high-pressure gas generated by the compressor to the low-pressure side before the evaporator, ensuring that the high-temperature and high-pressure gas condenses at an appropriate speed. Its main function is to control the flow and pressure of the high-pressure and high-temperature gas in the hot gas bypass by adjusting the amount of bypass refrigerant, so that the refrigerant can condense in the evaporator and effectively release heat to achieve the heating effect. At the same time, it avoids overheating and overloading of the compressor and improves the stability and efficiency of the system.

[0057] The function of the refrigeration electronic expansion valve is to adjust the refrigerant flow entering the evaporator, ensuring that the refrigerant in the evaporator evaporates at an appropriate speed and temperature, thereby effectively absorbing heat and achieving a refrigeration effect. Its main function is to control the flow and pressure of the refrigerant so that the refrigerant can fully evaporate and absorb heat in the evaporator, thereby achieving a refrigeration effect. At the same time, it can also prevent liquid refrigerant from entering the compressor, protecting the compressor from damage caused by wet compression and liquid hammer.

[0058] In one embodiment, in addition to the above-mentioned first PID controller, second PID controller and third PID controller, it also includes: a fourth PID controller, whose input is the difference between the compressor outlet temperature and the preset compressor outlet temperature upper limit, that is, the input is: compressor outlet temperature - preset compressor outlet temperature upper limit, and the output fourth PID value is recorded as PID_Value4, and the output range of PID_Value4 is 0-40%. Among them, PID_Value1, PID_Value3 and PID_Value4 are used to determine the second opening of the refrigeration electronic expansion valve.

[0059] In one embodiment, a pressure transmitter is provided between the evaporator and the fixed-frequency compressor.

[0060] In one embodiment, a first temperature sensor for detecting the outlet temperature of the compressor is provided between the compressor and the condenser; and a second temperature sensor for detecting the actual outlet temperature of the liquid from the thermostatic device is provided at the outlet of the evaporator.

[0061] In this embodiment, a pressure transmitter is used to detect the pressure in the pipeline, and the pipeline pressure is used as a variable parameter in the control logic to control the opening of the two electronic expansion valves, thereby replacing the pipeline pressure control using high-pressure switches and low-pressure switches in the prior art. While improving the sensitivity of pipeline pressure detection, it reduces the pipeline welding process and improves the stability of the equipment.

[0062] The present application only sets two temperature sensors at the liquid outlet of the evaporator and the exhaust port of the fixed-frequency compressor, which saves manufacturing time compared to the prior art. In addition, the temperature sensor only needs to be set on the surface of the pipeline without being welded on the pipeline, so there will be no increase in the welding points of the pipeline.

[0063] In one embodiment, continue to refer to Figure 2 , also provides a thermostatic device control method based on an electronic expansion valve, the method is based on the thermostatic device control system based on an electronic expansion valve described in one of the embodiments of the present application, the method specifically includes:

[0064] Obtain the measured liquid outlet temperature, the target liquid outlet temperature, the measured evaporation pressure, the saturation temperature corresponding to the measured evaporation pressure (calculated from the measured evaporation pressure), and the preset evaporation pressure lower limit of the thermostatic device;

[0065] According to the measured liquid outlet temperature and the target liquid outlet temperature, a first PID value PID_Value1 is calculated by a first PID controller;

[0066] According to the measured evaporation pressure and the preset evaporation pressure lower limit, a second PID value PID_Value2 is calculated by a second PID controller;

[0067] Determine the opening value A of the hot gas bypass electronic expansion valve based on PID_Value1 and PID_Value2 h , calculated as follows:

[0068] A h =PID_Value1+PID_Value2;

[0069] The third PID value PID_Value3 is calculated by the third PID controller according to the saturation temperature corresponding to the measured liquid outlet temperature minus the preset superheat target value and the measured evaporation pressure;

[0070] Subtract the PID value corresponding to the maximum opening of the electronic expansion valve from PID_Value1 to obtain value Ahr ;

[0071] Determine the first opening value A of the refrigeration electronic expansion valve according to the PID value, PID_Value1 and PID_Value3 corresponding to the maximum opening of the electronic expansion valve c , the determination method is:

[0072] A c =A hr *PID_Value3.

[0073] In this embodiment, when the superheat target value increases, the refrigeration efficiency will decrease; when the superheat target value decreases, incomplete evaporation of the refrigerant or even liquid hammer may occur.

[0074] In this embodiment, the saturation temperature corresponding to the measured evaporation pressure is obtained by converting the measured evaporation pressure. When converting the saturation temperature, a corresponding physical comparison table is used according to the refrigerant.

[0075] In one embodiment, reference Figure 3 In addition to the steps of the method provided in the above embodiment, the thermostatic device control method based on the electronic expansion valve further includes:

[0076] Obtain the compressor outlet temperature and preset the compressor outlet temperature upper limit;

[0077] According to the compressor outlet temperature and the preset compressor outlet temperature upper limit, a fourth PID value PID_Value4 is calculated by a fourth PID controller;

[0078] According to A hr , PID_Value3 and PID_Value4 determine the second opening value A of the refrigeration electronic expansion valve c ', calculated as follows:

[0079] A c '=A hr *PID_Value3+PID_Value4.

[0080] In this embodiment, when there is a fourth PID controller, that is, when the compressor outlet temperature and the preset compressor outlet temperature upper limit are introduced as a new feedback mechanism into the calculation of the opening value of the refrigeration electronic expansion valve, the limitation on the minimum opening of the refrigeration electronic expansion valve according to the opening of the hot gas bypass electronic expansion valve in the above embodiment is cancelled.

[0081] In one embodiment, an electronic device is provided, whose internal structure diagram can be as follows: Figure 4As shown. The electronic device includes a processor, a memory and a network interface connected through a system bus. The processor of the electronic device is used to provide computing and control capabilities, and the network interface is used to communicate with an external terminal through a network connection. The electronic device loads and runs a computer program to implement the above-mentioned thermostatic device control method based on an electronic expansion valve.

[0082] Those skilled in the art will understand that Figure 4 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0083] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A thermostatic equipment control system based on an electronic expansion valve, characterized in that: The constant temperature device comprises a circulation pipeline formed by an evaporator, a fixed frequency compressor, and a condenser connected in series in sequence, and two electronic expansion valves, wherein one electronic expansion valve is used as a refrigeration electronic expansion valve and is located on the pipeline between the condenser outlet and the evaporator inlet, and the other electronic expansion valve is used as a hot gas bypass electronic expansion valve and is connected in parallel with the condenser and the refrigeration electronic expansion valve as a whole; the control system comprises: a first PID controller, a second PID controller, and a third PID controller; The first PID controller has an input of the difference between the actual outlet temperature of the evaporator and the target outlet temperature, and outputs a first PID value denoted as PID_Value1; The second PID controller has an input of the difference between the measured evaporation pressure and the preset evaporation pressure lower limit, and outputs a second PID value recorded as PID_Value2; The third PID controller has the following inputs: the measured temperature of the liquid outlet - the preset superheat target value - the saturation temperature corresponding to the measured evaporation pressure, and outputs the third PID value, which is recorded as PID_Value3; Among them, PID_Value1 and PID_Value2 are used to determine the opening of the hot gas bypass electronic expansion valve; PID_Value1 and PID_Value3 are used to determine the first opening of the refrigeration electronic expansion valve.

2. The thermostatic equipment control system based on the electronic expansion valve according to claim 1 is characterized in that: Also includes: A fourth PID controller, whose input is the difference between the compressor outlet temperature and a preset compressor outlet temperature upper limit, and whose output is a fourth PID value recorded as PID_Value4; PID_Value1, PID_Value3 and PID_Value4 are used to determine the second opening degree of the refrigeration electronic expansion valve.

3. The thermostatic equipment control system based on the electronic expansion valve according to claim 1 is characterized in that: A pressure transmitter is arranged between the evaporator and the fixed-frequency compressor.

4. The thermostatic equipment control system based on the electronic expansion valve according to claim 1, characterized in that: A first temperature sensor for detecting the compressor outlet temperature is provided between the compressor and the condenser; The outlet of the evaporator is provided with a second temperature sensor for detecting the actual measured temperature of the liquid outlet of the constant temperature device.

5. A method for controlling a thermostatic device based on an electronic expansion valve, the method being based on the thermostatic device control system based on an electronic expansion valve as claimed in claim 1, and specifically comprising: Obtain the measured liquid outlet temperature, the target liquid outlet temperature, the measured evaporation pressure, the saturation temperature corresponding to the measured evaporation pressure, and the preset evaporation pressure lower limit of the thermostatic device; According to the measured liquid outlet temperature and the target liquid outlet temperature, a first PID value PID_Value1 is calculated by a first PID controller; According to the measured evaporation pressure and the preset evaporation pressure lower limit, a second PID value PID_Value2 is calculated by a second PID controller; Determine the opening value A of the hot gas bypass electronic expansion valve based on PID_Value1 and PID_Value2 h , calculated as follows: A h =PID_Value1+PID_Value2; The third PID value PID_Value3 is calculated by the third PID controller according to the saturation temperature corresponding to the measured liquid outlet temperature minus the preset superheat target value and the measured evaporation pressure; Subtract the PID value corresponding to the maximum opening of the electronic expansion valve from PID_Value1 to obtain value A hr ; Determine the first opening value A of the refrigeration electronic expansion valve according to the PID value, PID_Value1 and PID_Value3 corresponding to the maximum opening of the electronic expansion valve c , the determination method is: A c =A hr *PID_Value3。 6. The method for controlling a thermostatic device based on an electronic expansion valve according to claim 5, characterized in that: Also includes: Obtain the compressor outlet temperature and preset the compressor outlet temperature upper limit; According to the compressor outlet temperature and the preset compressor outlet temperature upper limit, a fourth PID value PID_Value4 is calculated by a fourth PID controller; According to A hr , PID_Value3 and PID_Value4 determine the second opening value A of the refrigeration electronic expansion valve c ', calculated as follows: A c ’=A hr *PID_Value3+PID_Value4。 7. An electronic device comprising a memory, a processor and a computer program stored in the memory, characterized in that: The processor executes the computer program to implement the steps of the method of claim 5.

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