A compressor oil return system and control method thereof

Abstract

The present invention relates to a compressor oil return system, which is characterized by comprising a main liquid circulation system, a cold oil system, an oil return system, an oil supply system, a first auxiliary oil return system and a second auxiliary oil return system, wherein the main liquid circulation system comprises a compressor, a condenser, a throttling electronic expansion valve and an evaporator; the cold oil system comprises a condenser, a cooling electronic expansion valve, a plate heat exchanger and an evaporator; the oil return system comprises a condenser, an oil return solenoid valve, a plate heat exchanger and an oil storage tank; the oil supply system comprises an oil storage tank and a compressor; the first auxiliary oil return system comprises an evaporator, a liquid extraction pump and a compressor; and the second auxiliary oil return system comprises an oil storage tank, an air extraction solenoid valve, a liquid extraction pump and a compressor. The present invention also discloses a control method for a compressor oil return system. The present invention improves the reliability of the oil return system, reduces the vibration and operating noise of the unit, avoids the abnormal bearing lubrication failure caused by the inability to establish a pressure difference when the machine is turned on and off, and improves the operating stability and operating life of the system unit.

Description

Technical Field

[0001] The invention relates to the technical field of compressor oil return systems, in particular to a compressor oil return system and a control method thereof. Background Art

[0002] The refrigeration oil of commercial screw chillers circulates synchronously with the refrigerant system. The reliability of the oil return system directly affects the noise, vibration and service life of the unit. At present, the oil tank of the water-cooled screw unit in the industry is built under the exhaust port of the compressor and the oil return is assisted by the injection oil return method. The oil return system has the following problems:

[0003] 1) The unit oil tank is built under the exhaust end of the compressor. The oil tank temperature is affected by the exhaust temperature, resulting in poor lubrication effect of the unit;

[0004] 2) The unit uses injection to assist oil return. Abnormalities such as injection blockage, filter blockage, and welding concentricity may cause injection oil return failure;

[0005] 3) When the unit is shut down or started at low ambient temperature, it is impossible to quickly establish an effective oil supply pressure difference, resulting in bearing lubrication failure and affecting the service life of the unit;

[0006] 4) The unit oil supply temperature is uncontrollable, and the lubricating oil temperature cannot be guaranteed to be within the optimal range, which affects the viscosity of the lubricating oil and easily causes the oil to oxidize and deteriorate;

[0007] 5) In a low temperature environment, the unit needs to be heated with oil when it is started. Direct startup is very likely to cause oil leakage, and a large amount of refrigerant oil will enter the evaporator, causing the unit to inhale liquid.

[0008] In summary, the current water-cooled screw unit compressor oil return system and control method have certain defects, and the unit is prone to oil leakage under harsh operating conditions after sales, with risks such as lubrication failure and increased vibration and noise of the unit. Summary of the invention

[0009] In order to solve the defects of auxiliary oil return failure, poor lubrication effect and oil leakage during low-temperature startup, the primary purpose of the present invention is to provide a compressor oil return system that improves the reliability of the oil return system, reduces unit vibration and noise, and improves the operating stability and service life of the unit.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical scheme: a compressor oil return system, including a main liquid circuit circulation system, a cooling oil system, an oil return system, an oil supply system, a first auxiliary oil return system and a second auxiliary oil return system; the main liquid circuit circulation system includes a compressor, a condenser, a throttling electronic expansion valve and an evaporator, the upper end exhaust port of the compressor is connected with the upper end of the condenser through a pipeline, the bottom liquid collecting bag of the condenser is connected with one end of the throttling electronic expansion valve through a pipeline, the other end of the throttling electronic expansion valve is connected with the liquid collection bag at the bottom of the evaporator through a pipeline, and the top outlet of the evaporator is connected with the suction port of the compressor through a pipeline; the cooling oil system includes a condenser, a cooling electronic expansion valve, a plate heat exchanger and an evaporator, the small liquid collecting bag of the condenser is connected with one end of the cooling electronic expansion valve through a pipeline, the other end of the cooling electronic expansion valve is connected with one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger is connected to the middle of the shell of the evaporator through a pipeline The oil return system includes a condenser, an oil return solenoid valve, a plate heat exchanger and an oil storage tank, one end of the condenser is connected to one end of the oil return solenoid valve through a pipeline, the other end of the oil return solenoid valve is connected to one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger is connected to the oil storage tank through a pipeline; the oil supply system includes an oil storage tank and a compressor, the oil storage tank is connected to the compressor through a pipeline, and the refrigerant oil is supplied to the compressor from the oil storage tank through a pressure difference; the first auxiliary oil return system includes an evaporator, a liquid pump and a compressor, the lower and middle part of the shell of the evaporator is connected to one end of the liquid pump through a pipeline, and the other end of the liquid pump is connected to the suction end of the compressor through a pipeline; the second auxiliary oil return system includes an oil storage tank, an air solenoid valve, a liquid pump and a compressor, the oil storage tank is connected to one end of the air solenoid valve through a pipeline, the other end of the air solenoid valve is connected to one end of the liquid pump through a pipeline, and the other end of the liquid pump is connected to the suction end of the compressor through a pipeline.

[0011] In the main liquid circulation system, the low-temperature and low-pressure gaseous refrigerant is compressed by the compressor and discharged from the upper exhaust port, enters the condenser, and forms a high-temperature and high-pressure liquid refrigerant after heat exchange with cooling water. It flows out from the bottom liquid collecting bag in the condenser, is throttled and reduced in pressure by the throttling electronic expansion valve, and then enters the liquid accumulation bag at the bottom of the evaporator. The refrigerant evaporates in the evaporator and exchanges heat with the chilled water. After evaporation, the gaseous refrigerant enters the suction port of the compressor from the top outlet of the evaporator.

[0012] In the cold oil system, high-temperature and high-pressure liquid refrigerant is taken from the small liquid collection bag in the condenser, throttled and reduced in pressure by the cooling electronic expansion valve and enters the plate heat exchanger to cool the refrigeration oil. The gaseous refrigerant after heat exchange enters the middle part of the low-pressure evaporator shell, and enters the compressor through the evaporator outlet to participate in the circulation.

[0013] In the oil return system, the high-temperature and high-pressure gas discharged from the compressor is impact-separated in the built-in oil separator in the condenser, and the separated high-temperature and high-pressure refrigeration oil flows out from the upper outlet of the condenser shell, enters the plate heat exchanger for cooling, and then flows into the oil storage tank.

[0014] In the first auxiliary oil return system, an auxiliary oil return pipe is led from the lower part of the evaporator shell, and the rotation of the liquid extraction pump impeller provides power to extract the refrigerant oil inside the evaporator and enter the suction end of the compressor; in the second auxiliary oil return system, the high-pressure gas in the oil storage tank is separated by the gas-liquid separation net inside the oil storage tank and then enters the liquid extraction pump from the top to provide power for the liquid extraction pump, and the gas finally flows into the suction end of the compressor.

[0015] A magnet for absorbing impurities is arranged at the bottom of the oil storage tank, an oil return filter for filtering impurities in the return oil is arranged inside the oil storage tank, and a gas-liquid separation net for oil-gas separation is arranged inside the oil storage tank.

[0016] Another object of the present invention is to provide a method for controlling a compressor oil return system, the method comprising the following steps in sequence:

[0017] (1) Before the system is turned on, the default opening of the throttling electronic expansion valve and the air intake solenoid valve is 0. When the system receives the start-up command, the oil return solenoid valve opens. When the actual system pressure difference is less than the pressure difference setting value, the throttling electronic expansion valve and the air intake solenoid valve remain at 0. At this time, the condenser and the oil storage tank quickly increase the pressure to lubricate the compressor bearings in time. When the system pressure difference is greater than or equal to the pressure difference setting value, the throttling electronic expansion valve enters the pressure difference free adjustment mode and the system starts normally;

[0018] (2) During normal shutdown, the system first unloads to 50% load. At this time, the oil return solenoid valve and the air intake solenoid valve are closed, the system is shut down synchronously, and the oil storage tank is in a high-pressure state, continuously providing the system with refrigeration oil for lubrication;

[0019] (3) In case of emergency, failure or power failure, the oil return solenoid valve and the air intake solenoid valve are immediately closed. At this time, the oil storage tank is still kept at a high pressure state to continue to supply oil to the compressor bearings. When the system is powered on and receives the start-up command, the above step (1) is executed.

[0020] It can be seen from the above technical scheme that the beneficial effects of the present invention are: first, the present invention ensures that the lubricating viscosity of the refrigeration oil is in an optimal state, improves the reliability of the oil return system, reduces the vibration and operating noise of the unit, avoids the bearing lubrication failure abnormality caused by the inability to establish a pressure difference when turning on and off the machine, and improves the operating stability and service life of the system unit; second, the present invention stores the refrigeration oil in an external oil storage tank to avoid the influence of the exhaust temperature on the oil tank temperature. At the same time, the refrigeration oil does not need to be preheated when the system unit is started, avoiding oil leakage and liquid suction, thereby improving user satisfaction; third, the auxiliary oil return of the present invention adopts a pump body extraction type, and the high-pressure gas is used as a power source stably and reliably, which can avoid the oil return failure abnormality caused by system dirt and blockage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the system principle diagram of the present invention;

[0022] Figure 2 This is the fuel supply control logic diagram of the present invention. DETAILED DESCRIPTION

[0023] like Figure 1As shown, a compressor oil return system comprises a main liquid circuit circulation system, a cold oil system, an oil return system, an oil supply system, a first auxiliary oil return system and a second auxiliary oil return system; the main liquid circuit circulation system comprises a compressor 1, a condenser, a throttling electronic expansion valve 12 and an evaporator, the upper end exhaust port of the compressor 1 is connected with the upper end of the condenser through a pipeline, the bottom liquid collecting bag of the condenser is connected with one end of the throttling electronic expansion valve 12 through a pipeline, the other end of the throttling electronic expansion valve 12 is connected with the liquid accumulation bag at the bottom of the evaporator through a pipeline, and the top outlet of the evaporator is connected with the air intake port of the compressor 1 through a pipeline; the cold oil system comprises a condenser, a cooling electronic expansion valve, a plate heat exchanger 5 and an evaporator, the small liquid collecting bag of the condenser is connected with one end of the cooling electronic expansion valve through a pipeline, the other end of the cooling electronic expansion valve is connected with one end of the plate heat exchanger 5 through a pipeline, and the other end of the plate heat exchanger 5 is connected with the middle part of the shell of the evaporator through a pipeline; the oil return system comprises a condenser, a return oil electric valve, a condenser, a throttling electronic expansion valve and an evaporator, the upper end exhaust port of the compressor 1 is connected with the upper end of the condenser through a pipeline, the bottom liquid collecting bag of the condenser is connected with one end of the throttling electronic expansion valve 12 through a pipeline, the other end of the throttling electronic expansion valve is connected with the liquid accumulation bag at the bottom of the evaporator through a pipeline, and the top outlet of the evaporator is connected with the air intake port of the compressor 1 through a pipeline The oil return system comprises an evaporator, a plate heat exchanger, and an oil storage tank. The condenser comprises an evaporator, a plate heat exchanger, and an oil storage tank. The condenser comprises an evaporator, a plate heat exchanger, and an oil storage tank. The evaporator comprises an evaporator, a plate heat exchanger, and an oil storage tank. The evaporator comprises an evaporator, a plate heat exchanger, and an oil storage tank. The evaporator comprises an evaporator, a plate heat exchanger, and an oil storage tank. The evaporator comprises an evaporator, a plate heat exchanger, and an oil storage tank. Liquid pump 9 and compressor 1, the lower middle part of the shell of the evaporator is connected to one end of the liquid pump 9 through a pipeline, and the other end of the liquid pump 9 is connected to the suction end of the compressor 1 through a pipeline; the second auxiliary oil return system includes an oil storage tank 6, an air intake solenoid valve 8, a liquid pump 9 and a compressor 1, the oil storage tank 6 is connected to one end of the air intake solenoid valve 8 through a pipeline, the other end of the air intake solenoid valve 8 is connected to one end of the liquid pump 9 through a pipeline, and the other end of the liquid pump 9 is connected to the suction end of the compressor 1 through a pipeline.

[0024] In the main liquid circulation system, the low-temperature and low-pressure gaseous refrigerant is compressed by the compressor 1 and discharged from the upper exhaust port, enters the condenser, and forms a high-temperature and high-pressure liquid refrigerant after heat exchange with the cooling water. It flows out from the bottom liquid collecting bag in the condenser, is throttled and reduced in pressure by the throttling electronic expansion valve 12, and then enters the liquid accumulation bag at the bottom of the evaporator. The refrigerant evaporates in the evaporator and exchanges heat with the chilled water. After evaporation, the gaseous refrigerant enters the air intake of the compressor 1 from the top outlet of the evaporator.

[0025] In the cold oil system, high-temperature and high-pressure liquid refrigerant is taken from the small liquid collection bag in the condenser, throttled and reduced in pressure by the cooling electronic expansion valve and enters the plate heat exchanger 5 to cool the refrigeration oil. The gaseous refrigerant after heat exchange enters the middle part of the low-pressure evaporator shell, and enters the compressor 1 through the evaporator outlet to participate in the circulation.

[0026] In the oil return system, the high-temperature and high-pressure gas discharged from the compressor 1 is impact-separated in the built-in oil separator in the condenser, and the separated high-temperature and high-pressure refrigeration oil flows out from the upper outlet of the condenser shell, enters the plate heat exchanger 5 for cooling, and then flows into the oil storage tank 6.

[0027] In the first auxiliary oil return system, an auxiliary oil return pipe is led from the lower part of the evaporator shell, and the refrigerant oil inside the evaporator is extracted by the rotation of the impeller of the liquid extraction pump 9 to provide power, and the refrigerant oil inside the evaporator is extracted and enters the suction end of the compressor 1; in the second auxiliary oil return system, the high-pressure gas in the oil storage tank 6 is separated by the gas-liquid separation net inside the oil storage tank 6 and then enters the liquid extraction pump 9 from the top to provide power for the liquid extraction pump 9, and the gas finally flows into the suction end of the compressor 1.

[0028] A magnet 10 for absorbing impurities is disposed at the bottom of the oil storage tank 6 , an oil return filter 11 for filtering impurities in the return oil is disposed inside the oil storage tank 6 , and a gas-liquid separation net 7 for oil-gas separation is disposed inside the oil storage tank 6 .

[0029] like Figure 2 As shown, the control method of the present invention includes the following steps in order:

[0030] (1) Before the system is turned on, the default opening of the throttling electronic expansion valve 12 and the air extraction solenoid valve 8 is 0. When the system receives the start-up command, the oil return solenoid valve 4 opens. When the actual system pressure difference is less than the pressure difference setting value, the throttling electronic expansion valve 12 and the air extraction solenoid valve 8 remain at 0. At this time, the condenser and the oil storage tank 6 quickly increase the pressure to lubricate the compressor 1 bearing in time. When the system pressure difference is greater than or equal to the pressure difference setting value, the throttling electronic expansion valve 12 enters the pressure difference free adjustment mode, and the system starts normally.

[0031] (2) During normal shutdown, the system first unloads to 50% load. At this time, the oil return solenoid valve 4 and the air intake solenoid valve 8 are closed, the system is shut down synchronously, and the inside of the oil storage tank 6 is in a high pressure state, continuously providing the system with refrigeration oil for lubrication;

[0032] (3) In case of emergency, failure or power failure, the oil return solenoid valve 4 and the air intake solenoid valve 8 are immediately closed. At this time, the oil storage tank 6 is still kept at a high pressure state to continue to supply oil to the bearing of the compressor 1. When the system is powered on and receives the start-up command, the above step (1) is executed.

[0033] The following combination Figure 1 , 2 The present invention is further described.

[0034] The present invention adopts an oil storage tank 6 to separate the refrigeration oil from the exhaust gas, eliminate oil heating, and start the machine directly at low temperature to avoid liquid in the air. A cold oil plate exchange structure is added at the oil inlet. The oil supply temperature is accurately controlled by taking liquid from the condenser and cooling the electronic expansion valve throttling method to ensure the lubrication effect.

[0035] The present invention adopts a pump body extraction auxiliary oil return, and uses the high-pressure gas in the oil storage tank 6 as a power source to drive the impeller of the liquid pump 9 to rotate, thereby providing power for the evaporator oil return flow path; this structure uses high-pressure gas as the power source to prevent dirty blockage, and the extracted liquid and the high-pressure gas of the power source run in independent cavities, which is stable and reliable.

[0036] The present invention adds fast oil supply and continuous oil supply control logic. When the unit is turned on or off, the air intake solenoid valve 8, the oil return solenoid valve 4, and the electronic expansion valve control the flow path on and off, so that the cavity of the oil storage tank 6 maintains a high pressure state, providing continuous refrigeration oil lubrication for the bearings of the compressor 1. In the present invention, the unit refers to Figure 1 The entire system shown.

[0037] The unit uses pressure difference for oil supply and return. The mixture of refrigeration oil and high-pressure gas is exchanged from the built-in oil separation condenser through the oil return solenoid valve 4 and the cold oil plate back to the oil storage tank 6. The return oil filter 11 can filter impurities in the return oil system. When the condenser pressure detection value P1-P2 ≥ 100Pa (100Pa setting value is the pressure loss from the condenser to the oil storage tank 6), the system prompts to replace the return oil filter 11. The magnet 10 is evenly distributed at the bottom of the oil storage tank 6 to absorb impurities such as iron filings to avoid dirty blockage of the oil supply pipeline; the top of the oil storage tank 6 is a gas-liquid separation net for separating lubricating oil from refrigerant gas. After gas-liquid separation, the top of the oil storage tank 6 is high-pressure gas, and the bottom is liquid refrigeration oil. The temperature package detects the refrigeration oil temperature t, and uses the cold oil plate to cooperate with the electronic expansion valve to keep the temperature of the oil storage tank 6 at the best state. When the detected temperature t is between the set temperature T±2, the cooling electronic expansion valve maintains the opening degree. When the detected temperature t is greater than the set temperature T+2, the cooling electronic expansion valve opens wide. When the detected temperature t is less than the set temperature T-2, the cooling electronic expansion valve opens less, so as to achieve the purpose of accurately controlling the oil temperature. Compared with the built-in oil tank structure of the compressor 1, adding an external oil storage tank 6 can separate the oil supply system from the exhaust of the compressor 1, avoiding the problem of oil soaking in the unit caused by the low temperature environment of the unit. At the same time, the oil heating system can be cancelled, and the unit can be started without waiting. The compressor 1 has a built-in oil tank structure. When starting in winter, the exhaust temperature is greatly affected by the oil tank temperature, and a large amount of refrigeration oil cannot be separated in time, resulting in oil soaking in the unit. Some units are equipped with oil heating. The heating time in winter takes about 5 hours, which affects the start-up time of the unit.

[0038] After the mixture of refrigerant and oil in the oil storage tank 6 is separated by gas-liquid, the top is high-pressure gas, and the high-pressure gas enters the liquid extraction pump 9 through the gas extraction solenoid valve 8. The high-pressure gas serves as a power source to drive the impeller of the liquid extraction pump 9 to rotate, so that the pressure energy is converted into mechanical energy, and then returns to the suction port of the compressor 1 through the connecting pipeline. The impeller on the other side rotates synchronously through the coaxial axis, so as to extract the mixed liquid of the refrigeration oil and refrigerant on the liquid level surface of the evaporator to the suction port of the compressor 1. When the unit is operating normally, the gas extraction solenoid valve 8 is opened once every 1 hour, and the opening time is one hour. While achieving the auxiliary oil return effect, it reduces the loss of cooling capacity. Compared with the induced oil return system, which is prone to failure, the high-pressure gas of the auxiliary oil return system serves as a power source to avoid the auxiliary oil return failure caused by system impurities. The extracted liquid and the high-pressure gas of the power source run in independent cavities, which is stable and reliable, and the oil return effect is better.

[0039] When the unit is started, the throttling electronic expansion valve 12 is closed to 0, the air intake solenoid valve 8 is closed, and the exhaust of the unit is only connected to the condenser and the oil storage tank 6. At this time, the pressure of the condenser and the oil storage tank 6 increases rapidly, and the pressure difference can be quickly established. The refrigerant oil inside the oil storage tank 6 can be quickly delivered to the compressor 1 bearing for lubrication. When the system pressure difference Δp exceeds the pressure difference setting value P, the throttling electronic expansion valve 12 enters the pressure difference adjustment mode, and the unit starts normally. When the unit is shut down, the yin and yang rotors continue to rotate due to inertia. When the unit is shut down normally and the load drops to 50%, the unit is shut down, the oil return solenoid valve 4 and the air intake solenoid valve 8 are closed, and the inside of the oil storage tank 6 is in a high-pressure state. After the unit is shut down, the compressor 1 bearing can be continuously supplied with oil; when the unit is shut down due to emergency or fault or suddenly loses power, the oil return solenoid valve 4 and the air intake solenoid valve 8 are closed. At this time, the oil storage tank 6 acts as a high-pressure source to continuously supply oil to the bearing, and when the unit fault is cleared and the startup command is received, it is executed according to the normal startup logic; this solves the problem of bearing lubrication failure of the unit under different on and off states.

[0040] To sum up, the present invention ensures that the lubricating viscosity of the refrigeration oil is in an optimal state, improves the reliability of the oil return system, reduces the vibration and operating noise of the unit, avoids the bearing lubrication failure abnormality caused by the inability to establish a pressure difference when turning on and off the machine, and improves the operating stability and service life of the system unit; the present invention stores the refrigeration oil in an external oil storage tank 6 to avoid the influence of the exhaust temperature on the oil temperature. At the same time, the system unit does not need to preheat the refrigeration oil when starting the machine, avoiding oil leakage and liquid suction, thereby improving user satisfaction; the auxiliary oil return of the present invention adopts a pump body extraction type, and the high-pressure gas is used as a power source stably and reliably, which can avoid the oil return failure abnormality caused by system dirt and blockage.

Claims

1. A compressor oil return system, characterized in that: It includes a main liquid circulation system, a cooling oil system, an oil return system, an oil supply system, a first auxiliary oil return system and a second auxiliary oil return system; The main liquid circuit circulation system includes a compressor, a condenser, a throttling electronic expansion valve and an evaporator. The upper exhaust port of the compressor is connected to the upper end of the condenser through a pipeline, the bottom liquid collecting bag of the condenser is connected to one end of the throttling electronic expansion valve through a pipeline, the other end of the throttling electronic expansion valve is connected to the liquid collecting bag at the bottom of the evaporator through a pipeline, and the top outlet of the evaporator is connected to the suction port of the compressor through a pipeline; the cold oil system includes a condenser, a cooling electronic expansion valve, a plate heat exchanger and an evaporator. The small liquid collecting bag of the condenser is connected to one end of the cooling electronic expansion valve through a pipeline, the other end of the cooling electronic expansion valve is connected to one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger is connected to the middle of the shell of the evaporator through a pipeline; the return oil system includes a condenser, an oil return solenoid valve, a plate heat exchanger and an oil storage tank. The end is connected with one end of the return oil solenoid valve through a pipeline, the other end of the return oil solenoid valve is connected with one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger is connected with the oil storage tank through a pipeline; the oil supply system includes an oil storage tank and a compressor, the oil storage tank is connected with the compressor through a pipeline, and the refrigerant oil is supplied to the compressor from the oil storage tank through a pressure difference; the first auxiliary oil return system includes an evaporator, a liquid pump and a compressor, the lower middle part of the shell of the evaporator is connected with one end of the liquid pump through a pipeline, and the other end of the liquid pump is connected to the suction end of the compressor through a pipeline; the second auxiliary oil return system includes an oil storage tank, an air solenoid valve, a liquid pump and a compressor, the oil storage tank is connected with one end of the air solenoid valve through a pipeline, the other end of the air solenoid valve is connected with one end of the liquid pump through a pipeline, and the other end of the liquid pump is connected to the suction end of the compressor through a pipeline.

2. The compressor oil return system according to claim 1, characterized in that: In the main liquid circulation system, the low-temperature and low-pressure gaseous refrigerant is compressed by the compressor and discharged from the upper exhaust port, enters the condenser, and forms a high-temperature and high-pressure liquid refrigerant after heat exchange with cooling water. It flows out from the bottom liquid collecting bag in the condenser, is throttled and reduced in pressure by the throttling electronic expansion valve, and then enters the liquid accumulation bag at the bottom of the evaporator. The refrigerant evaporates in the evaporator and exchanges heat with the chilled water. After evaporation, the gaseous refrigerant enters the suction port of the compressor from the top outlet of the evaporator.

3. The compressor oil return system according to claim 1, characterized in that: In the cold oil system, high-temperature and high-pressure liquid refrigerant is taken from the small liquid collection bag in the condenser, throttled and reduced in pressure by the cooling electronic expansion valve and enters the plate heat exchanger to cool the refrigeration oil. The gaseous refrigerant after heat exchange enters the middle part of the low-pressure evaporator shell, and enters the compressor through the evaporator outlet to participate in the circulation.

4. The compressor oil return system according to claim 1, characterized in that: In the oil return system, the high-temperature and high-pressure gas discharged from the compressor is impact-separated in the built-in oil separator in the condenser, and the separated high-temperature and high-pressure refrigeration oil flows out from the upper outlet of the condenser shell, enters the plate heat exchanger for cooling, and then flows into the oil storage tank.

5. The compressor oil return system according to claim 1, characterized in that: In the first auxiliary oil return system, an auxiliary oil return pipe is led from the lower part of the evaporator shell, and the rotation of the liquid extraction pump impeller provides power to extract the refrigerant oil inside the evaporator and enter the suction end of the compressor; in the second auxiliary oil return system, the high-pressure gas in the oil storage tank is separated by the gas-liquid separation net inside the oil storage tank and then enters the liquid extraction pump from the top to provide power for the liquid extraction pump, and the gas finally flows into the suction end of the compressor.

6. The compressor oil return system according to claim 1, characterized in that: A magnet for absorbing impurities is arranged at the bottom of the oil storage tank, an oil return filter for filtering impurities in the return oil is arranged inside the oil storage tank, and a gas-liquid separation net for oil-gas separation is arranged inside the oil storage tank.

7. The control method of the compressor oil return system according to any one of claims 1 to 6, characterized in that: The method comprises the following steps in order: (1) Before the system is turned on, the default opening of the throttling electronic expansion valve and the air intake solenoid valve is 0. When the system receives the start-up command, the oil return solenoid valve opens. When the actual system pressure difference is less than the pressure difference setting value, the throttling electronic expansion valve and the air intake solenoid valve remain at 0 opening. At this time, the condenser and the oil storage tank quickly increase the pressure to lubricate the compressor bearings in time. When the system pressure difference is greater than or equal to the pressure difference setting value, the throttling electronic expansion valve enters the pressure difference free adjustment mode, and the system starts normally; (2) During normal shutdown, the system first unloads to 50% load, at which time the oil return solenoid valve and the air intake solenoid valve are closed, the system shuts down synchronously, and the oil storage tank is in a high-pressure state, continuously providing the system with refrigeration oil for lubrication; (3) In case of emergency, failure or power failure, the oil return solenoid valve and the air intake solenoid valve are immediately closed. At this time, the oil storage tank is still kept at a high pressure state to continue to supply oil to the compressor bearings. When the system is powered on and receives the start-up command, the above step (1) is executed.

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