Refrigerating system suitable for fixed-frequency compressor and control method of refrigerating system

Abstract

According to the refrigerating system suitable for the fixed-frequency compressor and the control method thereof, a control device obtains the evaporator outlet temperature, the evaporator inlet temperature and bypass valve adjusting reference data, and the opening degree of a main path throttling valve is adjusted according to the evaporator inlet temperature so that the evaporator inlet temperature can be kept stable; and when the outlet temperature of the evaporator is smaller than the inlet temperature of the evaporator, the opening degree of the bypass valve is adjusted based on the bypass valve adjusting reference data and a set target reference value, so that the difference value between the bypass valve adjusting reference data and the target reference value is within a set deviation range. The main throttle valve and the bypass valve are cooperatively controlled by acquiring related parameters, and the opening degree of the bypass valve is adjusted by combining the adjustment reference data of the bypass valve and the set target reference value on the basis of maintaining the stability of the inlet temperature of the evaporator. And one part of the total air volume of the compressor is bypassed for neutralizing the liquid refrigerant which is not evaporated by the evaporator, so that the temperature control precision of the system and the reliability of the compressor are improved.

Description

Technical Field

[0001] This application relates to the field of refrigeration equipment technology, and in particular to a refrigeration system and control method applicable to a fixed-frequency compressor. Background Technology

[0002] Vapor compression refrigeration cycles are widely used in air conditioning, refrigeration, and cold storage. These cycles utilize a compressor to provide power and change the properties of the refrigerant. Since the compressor is the driving force for the refrigeration cycle, it is often selected and designed for full load operation. However, refrigeration systems frequently operate under partial load. To achieve reliability and energy efficiency, the industry often uses variable frequency compressors to adjust the compressor speed and achieve variable load output. However, this method has limitations due to cost. Most manufacturers, considering cost, choose fixed frequency compressors and adjust the load output through start-stop control, which leads to temperature fluctuations and low temperature control accuracy. Summary of the Invention

[0003] Therefore, it is necessary to provide a refrigeration system and its control method that can improve temperature control accuracy for fixed-frequency compressors, in order to address the above problems.

[0004] The first aspect of this application provides a refrigeration system suitable for a fixed-frequency compressor, including a refrigerant circuit, a refrigerant flow path, a bypass pipeline, and a control device; the refrigerant circuit is provided with a compressor, a condenser, a main circuit expansion valve, and an evaporator, which are sequentially connected and closed; the refrigerant flow path is thermally coupled to the refrigerant circuit through the evaporator; one end of the bypass pipeline is connected to the discharge end of the compressor, and the other end is connected to the evaporator, and a bypass valve is provided on the bypass pipeline;

[0005] The control device connects the main throttle valve and the bypass valve to acquire the evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment reference data. The control device adjusts the opening of the main throttle valve according to the evaporator inlet temperature to maintain a stable evaporator inlet temperature. When the evaporator outlet temperature is lower than the evaporator inlet temperature, the control device also adjusts the opening of the bypass valve based on the bypass valve adjustment reference data and a set target reference value to ensure that the difference between the bypass valve adjustment reference data and the target reference value is within a set deviation range.

[0006] In one embodiment, the bypass line is connected to the outlet of the evaporator, where the high-temperature, high-pressure refrigerant is throttled and depressurized, then mixed with the refrigerant at the outlet of the evaporator before being sent to the compressor; the bypass valve adjustment reference data includes the compressor superheat, and the target reference value includes a target superheat value; the control device maintains the opening of the bypass valve at zero when the evaporator outlet temperature is greater than or equal to the evaporator inlet temperature, and adjusts the opening of the bypass valve according to the compressor superheat when the evaporator outlet temperature is less than the evaporator inlet temperature, so that the difference between the compressor superheat and the set target superheat value is less than or equal to a preset accuracy deviation value.

[0007] In one embodiment, the compressor superheat includes compressor return gas superheat.

[0008] In one embodiment, the bypass line is connected to the inlet of the evaporator, where the high-temperature, high-pressure refrigerant is throttled and depressurized, then mixed with the refrigerant throttled and depressurized by the main line throttle valve before entering the evaporator. The bypass valve adjustment reference data includes the evaporator outlet refrigerant temperature, and the target reference value includes the target refrigerant temperature. When the evaporator outlet temperature is greater than or equal to the evaporator inlet temperature, the control device maintains the bypass valve opening at zero, and when the evaporator outlet temperature is less than the evaporator inlet temperature, it adjusts the bypass valve opening according to the outlet refrigerant temperature so that the difference between the outlet refrigerant temperature and the set target refrigerant temperature is less than or equal to the set accuracy deviation value.

[0009] In one embodiment, after the control device controls the main throttle valve to operate at a preset initial opening for a set period of time, it adjusts the opening of the main throttle valve according to the evaporator inlet temperature so that the difference between the evaporator inlet temperature and the target inlet temperature is less than or equal to a preset temperature deviation value; the target inlet temperature is determined based on the target refrigerant temperature and the evaporator heat exchange temperature difference.

[0010] In one embodiment, the control device also acquires the actual discharge pressure of the compressor; the control device adjusts the cooling parameters of the condenser according to the target condensing pressure and the actual discharge pressure of the compressor; the target condensing pressure is calculated based on the target condensing temperature and the refrigerant properties, and the target condensing temperature is calculated based on the ambient temperature and the preset condenser heat exchange temperature difference.

[0011] In one embodiment, the condenser is an air-cooled condenser, and the cooling parameters include the fan speed of the condenser; the control device performs PID adjustment on the fan speed of the condenser according to the actual discharge pressure of the compressor, so that the difference between the actual discharge pressure of the compressor and the target condensing pressure is less than or equal to a preset pressure deviation value.

[0012] In one embodiment, the condenser is a water-cooled condenser, and the cooling parameters include the opening degree of the condenser's cooling water valve; the control device performs PID adjustment on the opening degree of the condenser's cooling water valve according to the actual discharge pressure of the compressor, so that the difference between the actual discharge pressure of the compressor and the target condensing pressure is less than or equal to a preset pressure deviation value.

[0013] In one embodiment, the control module includes a main controller and a temperature sensor and a pressure sensor connected to the main controller; the main controller adjusts the opening degree of the bypass valve and the main throttle valve, and adjusts the cooling parameters of the condenser based on the temperature data detected by the temperature sensor and the pressure data detected by the pressure sensor.

[0014] A second aspect of this application provides a control method for a refrigeration system with a fixed-frequency compressor as described above, comprising:

[0015] Obtain reference data for evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment;

[0016] The opening of the main throttle valve is adjusted according to the evaporator inlet temperature to maintain a stable evaporator inlet temperature.

[0017] When the evaporator outlet temperature is lower than the evaporator inlet temperature, the opening of the bypass valve is adjusted based on the bypass valve adjustment reference data and the set target reference value, so that the difference between the bypass valve adjustment reference data and the target reference value is within the set deviation range.

[0018] The aforementioned refrigeration system and control method applicable to fixed-frequency compressors involve a control device acquiring evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment reference data. The control device adjusts the opening of the main circuit throttle valve based on the evaporator inlet temperature to maintain a stable evaporator inlet temperature. Furthermore, when the evaporator outlet temperature is lower than the evaporator inlet temperature, the control device adjusts the opening of the bypass valve based on the bypass valve adjustment reference data and a set target reference value, ensuring the difference between the bypass valve adjustment reference data and the target reference value is within a set deviation range. By acquiring relevant parameters and coordinating the control of the main circuit throttle valve and the bypass valve, while maintaining a stable evaporator inlet temperature, the control device adjusts the opening of the bypass valve based on the bypass valve adjustment reference data and the set target reference value. This allows a portion of the compressor's total gas volume to be bypassed to neutralize any unevaporated liquid refrigerant in the evaporator, thereby adapting to changes in external load and improving system temperature control accuracy and compressor reliability. Attached Figure Description

[0019] Figure 1 This is a structural block diagram of a refrigeration system applicable to a fixed-frequency compressor in one embodiment;

[0020] Figure 2 This is a schematic diagram of the structural principle of a refrigeration system applicable to a fixed-frequency compressor in one embodiment;

[0021] Figure 3 This is a schematic diagram of the control flow of a refrigeration system applicable to a fixed-frequency compressor in one embodiment;

[0022] Figure 4 This is a schematic diagram of a refrigeration system applicable to a fixed-frequency compressor in another embodiment;

[0023] Figure 5 This is a schematic diagram of the control flow of a refrigeration system applicable to a fixed-frequency compressor in another embodiment. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0026] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., transmit electrical signals or data to each other. When used herein, the singular forms "a," "an," and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "comprising / including" or "having," etc., specify the presence of the stated features, integrals, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, integrals, steps, operations, components, parts, or combinations thereof.

[0027] In one embodiment, such as Figure 1As shown, a refrigeration system suitable for a fixed-frequency compressor is provided, including a refrigerant circuit, a refrigerant flow path, a bypass pipeline, and a control device. The refrigerant circuit includes a compressor, a condenser, a main circuit expansion valve EXV-1, and an evaporator, which are sequentially connected and closed. The refrigerant flow path is thermally coupled to the refrigerant circuit through the evaporator. One end of the bypass pipeline is connected to the compressor discharge end, and the other end is connected to the evaporator. A bypass valve EXV-2 is installed on the bypass pipeline. Both the main circuit expansion valve EXV-1 and the bypass valve EXV-2 can be electronic expansion valves. The refrigerant circuit and bypass pipeline are used to transport the refrigerant. The condenser can be an air-cooled or water-cooled condenser, and the evaporator can be a water-cooled evaporator. The refrigerant flow path is a cooling water circuit, delivering water to the evaporator for heat exchange with the refrigerant circuit.

[0028] A control device (not shown in the figure) connects the main throttle valve EXV-1 and the bypass valve EXV-2 to acquire the evaporator outlet temperature TS2, the evaporator inlet temperature TS1, and the bypass valve adjustment reference data. The control device adjusts the opening of the main throttle valve EXV-1 based on the evaporator inlet temperature TS1 to maintain a stable evaporator inlet temperature. Furthermore, when the evaporator outlet temperature TS2 is lower than the evaporator inlet temperature TS1, the control device adjusts the opening of the bypass valve EXV-2 based on the bypass valve adjustment reference data and a set target reference value, ensuring that the difference between the bypass valve adjustment reference data and the target reference value is within a set deviation range. Maintaining a stable evaporator inlet temperature can mean either keeping the evaporator inlet temperature constant at the target inlet temperature Te, or ensuring that the difference between the evaporator inlet temperature and the target inlet temperature Te is within an allowable deviation range.

[0029] The bypass line can connect to either the inlet or outlet of the evaporator. Depending on the connection between the bypass line and the evaporator, the specific types of bypass valve adjustment reference data and target reference values ​​will also differ. By acquiring relevant parameters and coordinating the control of the main throttle valve EXV-1 and the bypass valve EXV-2, while maintaining a stable evaporator inlet temperature, the opening of the bypass valve EXV-2 is adjusted based on the bypass valve adjustment reference data and the set target reference value. This allows a portion of the compressor's total gas volume to be bypassed to neutralize the liquid refrigerant that has evaporated in the evaporator, thereby adapting to changes in external load, achieving variable cooling capacity control, and solving problems such as repeated compressor start-stop, low temperature control accuracy, and low compressor reliability.

[0030] In addition, the control device can also acquire the actual discharge pressure of the compressor and adjust the cooling parameters of the condenser based on the actual discharge pressure. Specifically, the control device may include a main controller and temperature and pressure sensors connected to it. The main controller adjusts the opening of the bypass valve EXV-2 and the main throttle valve EXV-1, and adjusts the cooling parameters of the condenser based on the temperature data detected by the temperature sensor and the pressure data detected by the pressure sensor. The main controller can be a processor such as a CPU, MCU, or FPGA.

[0031] It should be noted that the refrigeration system provided in this application is also applicable to variable frequency compressors; the frequency can be adjusted or not when using a variable frequency compressor. Conventional refrigeration technology using variable frequency compressors generally involves coordinated adjustment of the compressor frequency and the opening of the expansion valve. The advantage of the refrigeration system provided in this application is that the cooling capacity control process differs from the traditional approach, as it does not rely on compressor frequency adjustment and has universal applicability.

[0032] In one embodiment, after the control device controls the main throttle valve EXV-1 to operate at a preset initial opening for a set time, the opening of the main throttle valve EXV-1 is adjusted according to the evaporator inlet temperature TS1, so that the difference between the evaporator inlet temperature TS1 and the target inlet temperature Te is less than or equal to a preset temperature deviation value. The specific values ​​of the initial opening, set time, and preset temperature deviation value are not unique and can be set according to actual needs. In this embodiment, the initial opening is 20%, the set time is 1 minute, and the preset temperature deviation value (i.e., dead zone temperature) can be set to 0.5℃. The target inlet temperature Te is determined based on the target refrigerant temperature Ts and the evaporator heat exchange temperature difference ΔTe, specifically: Target inlet temperature Te = Target refrigerant temperature Ts - Evaporator heat exchange temperature difference ΔTe. The target refrigerant temperature Ts is set by the user.

[0033] Furthermore, such as Figure 2As shown, the bypass line connects to the evaporator outlet, throttling and depressurizing the high-temperature, high-pressure refrigerant before mixing it with the refrigerant at the evaporator outlet and sending it to the compressor. The bypass valve adjustment reference data includes the compressor superheat, and the target reference value includes the superheat target value. When the evaporator outlet temperature TS2 is greater than or equal to the evaporator inlet temperature TS1, the control device maintains the opening of the bypass valve EXV-2 at zero. When the evaporator outlet temperature TS2 is less than the evaporator inlet temperature TS1, the control device adjusts the opening of the bypass valve EXV-2 according to the compressor superheat, so that the difference between the compressor superheat and the set superheat target value is less than or equal to the preset accuracy deviation value. The compressor superheat can include compressor return gas superheat or compressor exhaust superheat; in this embodiment, the compressor superheat includes compressor return gas superheat. The specific values ​​of the superheat target value and the preset accuracy deviation value are not unique and can be set according to actual needs. For example, the superheat target value can be 10℃, and the preset accuracy deviation value (i.e., dead zone temperature) can be 5℃.

[0034] In addition, the control device also acquires the actual discharge pressure PS2 of the compressor; based on the target condensing pressure Pc and the actual discharge pressure PS2 of the compressor, the control device adjusts the cooling parameters of the condenser; the target condensing pressure Pc is calculated based on the target condensing temperature Tc and the refrigerant properties, and the target condensing temperature Tc is calculated based on the ambient temperature Ta and the preset condenser heat exchange temperature difference ΔTc. The cooling parameters will vary depending on the type of condenser. For example, if the condenser is air-cooled or water-cooled, the cooling parameters may be the fan speed or the cooling water valve opening.

[0035] When the condenser is an air-cooled condenser, the cooling parameters include the condenser fan speed. The control device uses PID control to adjust the condenser fan speed based on the actual discharge pressure PS2 of the compressor, so that the difference between the actual discharge pressure PS2 and the target condensing pressure Pc is less than or equal to a preset pressure deviation value. When the condenser is a water-cooled condenser, the cooling parameters include the condenser cooling water valve opening. The control device uses PID control to adjust the condenser cooling water valve opening based on the actual discharge pressure PS2 of the compressor, so that the difference between the actual discharge pressure and the target condensing pressure Pc is less than or equal to a preset pressure deviation value. The preset pressure deviation value (i.e., dead zone pressure) is not unique; in this embodiment, the preset pressure deviation value is 50 kPa. For ease of understanding, the following explanation uses an air-cooled condenser as an example.

[0036] Specifically, see Figure 2The compressor draws in low-temperature, low-pressure refrigerant. After compression, the high-temperature, high-pressure refrigerant discharged is divided into two paths. One path enters the condenser to release heat. After the high-temperature, high-pressure refrigerant releases heat in the condenser, it condenses into high-pressure liquid refrigerant. The high-pressure liquid refrigerant flows through the main path throttling valve EXV-1 to reduce pressure and generate a gas-liquid two-phase refrigerant. It then enters the evaporator to exchange heat with the refrigerant in the flow path. The other path passes through the bypass valve EXV-2 to reduce pressure and mixes with the refrigerant at the evaporator outlet in the gas-liquid separator. After mixing, it is drawn into the compressor for compression and pressure increase. This cycle repeats, achieving the transfer of heat to the air side.

[0037] The control device includes temperature sensors installed at the evaporator inlet, evaporator outlet, and compressor return port to detect the evaporator inlet temperature TS1, evaporator outlet temperature TS2, and compressor return temperature TS3, respectively. The control device also includes pressure sensors installed at the compressor return port and exhaust port to detect the compressor return pressure PS1 and actual exhaust pressure PS2, respectively.

[0038] like Figure 3 As shown, the control flow of a refrigeration system applicable to a fixed-frequency compressor in one embodiment of this application is as follows:

[0039] 1.1 Control Principle of Main Circuit Throttling Valve EXV-1

[0040] The user presets a target refrigerant temperature Ts, and the target inlet temperature Te = target refrigerant temperature Ts - evaporator heat exchange temperature difference ΔTe. The target inlet temperature Te, or its equivalent pressure, is used as the control target for the main throttle valve EXV-1. The main throttle valve EXV-1 operates at an initial opening (e.g., 20%) and maintains this position for 1 minute. Then, PID control is applied with the evaporator inlet temperature TS1 as the target. When the actual evaporator inlet temperature TS1 is higher than the target inlet temperature Te, the opening of the main throttle valve EXV-1 decreases; when the actual evaporator inlet temperature TS1 is lower than the target inlet temperature Te, the opening of the main throttle valve EXV-1 increases. The dead zone temperature is 0.5℃.

[0041] 1.2 Fan Control Principle

[0042] The condenser detects the ambient temperature Ta and calculates the target condensing temperature Tc = Ta + ΔTc based on the preset condenser heat exchange temperature difference ΔTc. Then, it converts the corresponding saturation pressure (target condensing pressure Pc) according to the refrigerant properties. A pressure sensor is installed on the compressor discharge pipe to detect the actual discharge pressure PS2 in real time. The fan speed is controlled by PID based on the actual discharge pressure PS2. When the actual discharge pressure PS2 is greater than the target condensing pressure Pc, the fan speed increases; when the actual discharge pressure PS2 is less than the target condensing pressure Pc, the fan speed decreases. The dead zone pressure is 50 kPa.

[0043] 1.3 Control Principle of Bypass Valve EXV-2

[0044] Temperature sensors are installed at the inlet and outlet of the evaporator to monitor the evaporator inlet temperature TS1 and the evaporator outlet temperature TS2 in real time. When the rated cooling capacity of the system is basically equal to the heat load, the evaporator outlet temperature TS2 is greater than or equal to the evaporator inlet temperature TS1, and the current logic operation is maintained, with the bypass valve EXV-2 opening at 0.

[0045] When the heat load suddenly decreases and the cooling capacity exceeds the heat load, the evaporator outlet temperature TS2 will be lower than the evaporator inlet temperature TS1 (there is a certain pressure drop between the evaporator outlet and inlet; when the heat load is insufficient, the evaporator outlet temperature will be lower than the inlet temperature). Therefore, variable cooling capacity control is required. The bypass valve EXV-2 is controlled by the compressor return gas superheat. The compressor return gas superheat = compressor return gas temperature TS3 - (saturation temperature converted from compressor return gas pressure PS1) is used as the control object. The target superheat value is set to 10℃, with an accuracy deviation of 5℃. Using PID control, when the compressor return gas superheat increases, the opening of the bypass valve EXV-2 increases; when the compressor return gas superheat decreases, the opening of the bypass valve EXV-2 decreases. Simultaneously, the main throttle valve EXV-1 continuously controls according to the evaporator inlet temperature TS1, working in conjunction with the bypass valve EXV-2 to ensure a stable evaporator outlet temperature.

[0046] In this embodiment, the temperature sensor for evaporator outlet temperature TS2 is located near the evaporator outlet, and the temperature sensor for compressor return gas temperature TS3 is located near the compressor return gas port. When the bypass pipe outlet of bypass valve EXV-2 is connected to the outlet of the load evaporator, the refrigerant mixing point is specifically located between the TS2 and TS3 detection points. Since the compressor return gas superheat is calculated based on the compressor return gas temperature TS3, and the temperature sensor for compressor return gas temperature TS3 is located close to the refrigerant mixing point, it can promptly provide feedback on the cooling capacity adjustment after the refrigerant mixing point. Therefore, selecting the compressor return gas superheat to control the opening of bypass valve EXV-2 can reduce the system cooling capacity adjustment delay, thereby effectively addressing the problem of sudden load changes. In other embodiments, if bypass valve EXV-2 is controlled by compressor discharge superheat, the temperature sensor for TS3 is located at the compressor discharge port, which will not be elaborated here.

[0047] In another embodiment, such as Figure 4As shown, the bypass line connects to the evaporator inlet, where the high-temperature, high-pressure refrigerant is throttled and depressurized, then mixed with the refrigerant throttled and depressurized by the main line throttle valve EXV-1 before entering the evaporator. The bypass valve adjustment reference data includes the evaporator outlet refrigerant temperature Two, and the target reference value includes the target refrigerant temperature Ts. When the evaporator outlet temperature TS2 is greater than or equal to the evaporator inlet temperature TS1, the control device maintains the opening of the bypass valve EXV-2 at zero. When the evaporator outlet temperature TS2 is less than the evaporator inlet temperature TS1, the control device adjusts the opening of the bypass valve EXV-2 according to the outlet refrigerant temperature Two, so that the difference between the outlet refrigerant temperature Two and the set target refrigerant temperature Ts is less than or equal to the set accuracy deviation value. The specific value of the set accuracy deviation value is not unique and can be set according to actual needs; for example, the set accuracy deviation value (i.e., dead zone temperature) can be 0.5℃.

[0048] Specifically, see Figure 4 The compressor draws in low-temperature, low-pressure gas, which is then compressed and split into two paths. One path enters the condenser for condensation, and after passing through the main throttling valve EXV-1, it is throttled and depressurized before entering the evaporator. The other path passes through the bypass valve EXV-2 and mixes with the throttled refrigerant before entering the evaporator. The hot gas mixes with the low-temperature steam to increase the dryness of the evaporator inlet, thereby achieving the purpose of controlling the cooling capacity.

[0049] The control device includes temperature sensors installed at the refrigerant inlet, refrigerant outlet, and secondary refrigerant outlet of the evaporator, respectively detecting the refrigerant temperature TS1 at the evaporator inlet, TS2 at the evaporator outlet, and Two at the outlet secondary refrigerant temperature (specifically, the secondary refrigerant is water, and Two is the outlet water temperature). The control device also includes a pressure sensor installed at the exhaust port to detect the actual exhaust pressure PS2 of the compressor.

[0050] like Figure 5 As shown, the control flow of a refrigeration system applicable to a fixed-frequency compressor in another embodiment of this application is as follows:

[0051] 1.1 Control Principle of Main Circuit Throttling Valve EXV-1

[0052] The user presets a target refrigerant temperature Ts, and the target inlet temperature Te = target refrigerant temperature Ts - evaporator heat exchange temperature difference ΔTe. The target inlet temperature Te, or its equivalent pressure, is used as the control target for the main throttle valve EXV-1. The main throttle valve EXV-1 operates at an initial opening (e.g., 20%) and maintains this position for 1 minute. Then, PID control is applied with the evaporator inlet temperature TS1 as the target. When the actual evaporator inlet temperature TS1 is higher than the target inlet temperature Te, the opening of the main throttle valve EXV-1 decreases; when the actual evaporator inlet temperature TS1 is lower than the target inlet temperature Te, the opening of the main throttle valve EXV-1 increases. The dead zone temperature is 0.5℃.

[0053] 1.2 Fan Control Principle

[0054] The condenser detects the ambient temperature Ta and calculates the target condensing temperature Tc = Ta + ΔTc based on the preset condenser heat exchange temperature difference ΔTc. Then, it converts the corresponding saturation pressure (target condensing pressure Pc) according to the refrigerant properties. A pressure sensor is installed on the compressor discharge pipe to detect the actual discharge pressure PS2 in real time. The fan speed is controlled by PID based on the discharge pressure. When the actual discharge pressure PS2 is greater than the target condensing pressure Pc, the fan speed increases; when the actual discharge pressure PS2 is less than the target condensing pressure Pc, the fan speed decreases. The dead zone pressure is 50 kPa.

[0055] 1.3 Control Principle of Bypass Valve EXV-2

[0056] Temperature sensors are installed at the inlet and outlet of the evaporator to monitor the evaporator inlet temperature TS1 and the evaporator outlet temperature TS2 in real time. When the rated cooling capacity of the system is basically equal to the heat load, the evaporator outlet temperature TS2 is greater than or equal to the evaporator inlet temperature TS1, and the current logic operation is maintained, with the bypass valve EXV-2 opening at 0.

[0057] When the heat load suddenly decreases and the cooling capacity exceeds the heat load, the evaporator outlet temperature TS2 will be lower than the evaporator inlet temperature TS1, requiring variable cooling capacity control. The bypass valve EXV-2 is controlled based on the outlet refrigerant temperature Two, with a water temperature dead zone of 0.5℃. A temperature sensor is installed at the refrigerant outlet of the evaporator to detect the outlet refrigerant temperature Two. When the outlet refrigerant temperature Two is lower than the target refrigerant temperature Ts, the opening of the bypass valve EXV-2 increases; when the outlet refrigerant temperature Two is higher than the target refrigerant temperature Ts, the opening of the bypass valve EXV-2 decreases. Simultaneously, the main throttle valve EXV-1 continuously controls according to the evaporator inlet temperature TS1, working in conjunction with the bypass valve EXV-2 to ensure a stable evaporator outlet temperature.

[0058] In this embodiment, the temperature sensor for the evaporator inlet temperature TS1 is located near the refrigerant inlet of the evaporator, and the temperature sensor for the outlet refrigerant temperature Two is located near the refrigerant outlet of the evaporator. When the bypass pipe containing the bypass valve EXV-2 is connected to the inlet of the load evaporator, the refrigerant mixing point is specifically located between the main throttle valve EXV-1 and the TS1 detection point. Since the outlet refrigerant temperature Two reflects the physical information of the refrigerant in the refrigerant circuit after heat exchange with the refrigerant in the refrigerant circuit through the load evaporator, and is also close to the refrigerant mixing point, it can provide timely and effective feedback on the cooling capacity adjustment after the refrigerant mixing point. Therefore, controlling the opening of the bypass valve EXV-2 based on the outlet refrigerant temperature Two can reduce the system cooling capacity adjustment delay, thereby effectively dealing with the problem of sudden load changes.

[0059] In one embodiment, a control method for a refrigeration system using a fixed-frequency compressor, as described above, is also provided, comprising: acquiring evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment reference data; adjusting the opening of the main throttle valve according to the evaporator inlet temperature to maintain a stable evaporator inlet temperature; and adjusting the opening of the bypass valve based on the bypass valve adjustment reference data and a set target reference value when the evaporator outlet temperature is lower than the evaporator inlet temperature, so that the difference between the bypass valve adjustment reference data and the target reference value is within a set deviation range. A temperature sensor and a pressure sensor can be connected to the main controller. The main controller acquires the evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment reference data to control the opening of the main throttle valve and the bypass valve.

[0060] In one embodiment, a bypass line connects to the evaporator outlet, where the high-temperature, high-pressure refrigerant is throttled and depressurized before being mixed with the refrigerant at the evaporator outlet and then fed into the compressor. The bypass valve adjustment reference data includes the compressor superheat, and the target reference value includes a target superheat value. When the evaporator outlet temperature is greater than or equal to the evaporator inlet temperature, the main controller maintains the bypass valve opening at zero. When the evaporator outlet temperature is less than the evaporator inlet temperature, the controller adjusts the bypass valve opening based on the compressor superheat to ensure that the difference between the compressor superheat and the set target superheat value is less than or equal to a preset accuracy deviation value.

[0061] In one embodiment, a bypass line connects to the evaporator inlet, where the delivered high-temperature, high-pressure refrigerant is throttled and depressurized, then mixed with the refrigerant throttled and depressurized by the main line throttle valve before entering the evaporator. The bypass valve adjustment reference data includes the evaporator outlet refrigerant temperature, and the target reference value includes the target refrigerant temperature. The main controller maintains the bypass valve opening at zero when the evaporator outlet temperature is greater than or equal to the evaporator inlet temperature, and adjusts the bypass valve opening based on the outlet refrigerant temperature when the evaporator outlet temperature is less than or equal to the set accuracy deviation value.

[0062] In one embodiment, the method further includes: controlling the main throttle valve to operate at a preset initial opening for a set time, and then adjusting the opening of the main throttle valve according to the evaporator inlet temperature so that the difference between the evaporator inlet temperature and the target inlet temperature is less than or equal to a preset temperature deviation value; the target inlet temperature is determined based on the target refrigerant temperature and the evaporator heat exchange temperature difference.

[0063] In one embodiment, the method further includes: obtaining the actual discharge pressure of the compressor; adjusting the cooling parameters of the condenser according to the target condensing pressure and the actual discharge pressure of the compressor; the target condensing pressure is calculated based on the target condensing temperature and the refrigerant properties, and the target condensing temperature is calculated based on the ambient temperature and the preset condenser heat exchange temperature difference.

[0064] It is understood that specific embodiments of the control method applicable to the refrigeration system of the fixed-frequency compressor have been explained in detail in the refrigeration system applicable to the fixed-frequency compressor, and will not be repeated here.

[0065] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0066] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A refrigeration system suitable for a fixed-frequency compressor, characterized in that, It includes a refrigerant circuit, a refrigerant flow path, a bypass pipeline, and a control device; the refrigerant circuit is equipped with a compressor, a condenser, a main circuit expansion valve, and an evaporator, which are connected and closed in sequence; the refrigerant flow path is thermally coupled to the refrigerant circuit through the evaporator; one end of the bypass pipeline is connected to the discharge end of the compressor, and the other end is connected to the evaporator, and a bypass valve is provided on the bypass pipeline; The control device connects the main throttle valve and the bypass valve to acquire the evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment reference data. The control device adjusts the opening of the main throttle valve according to the evaporator inlet temperature to maintain a stable evaporator inlet temperature. When the evaporator outlet temperature is lower than the evaporator inlet temperature, the control device also adjusts the opening of the bypass valve based on the bypass valve adjustment reference data and a set target reference value to ensure that the difference between the bypass valve adjustment reference data and the target reference value is within a set deviation range.

2. The system according to claim 1, characterized in that, The bypass line connects to the outlet of the evaporator, where the high-temperature, high-pressure refrigerant is throttled and depressurized, then mixed with the refrigerant at the evaporator outlet before being fed into the compressor. The bypass valve adjustment reference data includes the compressor superheat, and the target reference value includes a target superheat value. When the evaporator outlet temperature is greater than or equal to the evaporator inlet temperature, the control device maintains the opening of the bypass valve at zero, and when the evaporator outlet temperature is less than the evaporator inlet temperature, it adjusts the opening of the bypass valve according to the compressor superheat, so that the difference between the compressor superheat and the set target superheat value is less than or equal to a preset accuracy deviation value.

3. The system according to claim 2, characterized in that, The compressor superheat includes the compressor return gas superheat.

4. The system according to claim 1, characterized in that, The bypass pipeline connects to the inlet of the evaporator, where the high-temperature, high-pressure refrigerant is throttled and depressurized, then mixed with the refrigerant throttled and depressurized by the main throttle valve before entering the evaporator. The bypass valve adjustment reference data includes the evaporator outlet refrigerant temperature, and the target reference value includes the target refrigerant temperature. When the evaporator outlet temperature is greater than or equal to the evaporator inlet temperature, the control device maintains the bypass valve opening at zero, and when the evaporator outlet temperature is less than the evaporator inlet temperature, it adjusts the bypass valve opening according to the outlet refrigerant temperature so that the difference between the outlet refrigerant temperature and the set target refrigerant temperature is less than or equal to the set accuracy deviation value.

5. The system according to claim 1, characterized in that, After the control device controls the main throttle valve to operate at a preset initial opening for a set period of time, it adjusts the opening of the main throttle valve according to the evaporator inlet temperature so that the difference between the evaporator inlet temperature and the target inlet temperature is less than or equal to a preset temperature deviation value; the target inlet temperature is determined based on the target refrigerant temperature and the evaporator heat exchange temperature difference.

6. The system according to any one of claims 1 to 5, characterized in that, The control device also acquires the actual discharge pressure of the compressor; the control device adjusts the cooling parameters of the condenser according to the target condensing pressure and the actual discharge pressure of the compressor; the target condensing pressure is calculated based on the target condensing temperature and the refrigerant properties, and the target condensing temperature is calculated based on the ambient temperature and the preset condenser heat exchange temperature difference.

7. The system according to claim 6, characterized in that, The condenser is an air-cooled condenser, and the cooling parameters include the fan speed of the condenser. The control device performs PID adjustment on the fan speed of the condenser according to the actual discharge pressure of the compressor, so that the difference between the actual discharge pressure of the compressor and the target condensing pressure is less than or equal to a preset pressure deviation value.

8. The system according to claim 6, characterized in that, The condenser is a water-cooled condenser, and the cooling parameters include the opening degree of the condenser's cooling water valve. The control device performs PID adjustment on the opening degree of the condenser's cooling water valve according to the actual discharge pressure of the compressor, so that the difference between the actual discharge pressure of the compressor and the target condensing pressure is less than or equal to a preset pressure deviation value.

9. The system according to claim 6, characterized in that, The control module includes a main controller and a temperature sensor and a pressure sensor connected to the main controller; the main controller adjusts the opening degree of the bypass valve and the main throttle valve, and adjusts the cooling parameters of the condenser based on the temperature data detected by the temperature sensor and the pressure data detected by the pressure sensor.

10. A control method for a refrigeration system using a fixed-frequency compressor as described in any one of claims 1 to 9, characterized in that, include: Obtain reference data for evaporator outlet temperature, evaporator inlet temperature, and bypass valve adjustment; The opening of the main throttle valve is adjusted according to the evaporator inlet temperature to maintain a stable evaporator inlet temperature. When the evaporator outlet temperature is lower than the evaporator inlet temperature, the opening of the bypass valve is adjusted based on the bypass valve adjustment reference data and the set target reference value, so that the difference between the bypass valve adjustment reference data and the target reference value is within the set deviation range.

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