CN116222023A - A compressor oil return system and its control method - Google Patents

Abstract

The invention relates to a compressor oil return system, which is characterized in that: the system comprises a main liquid path 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 path 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 electromagnetic 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 taking pump and a compressor; the second auxiliary oil return system comprises an oil storage tank, an air taking electromagnetic valve, an air taking pump and a compressor. The invention also discloses a control method of the compressor oil return system. The invention improves the reliability of the oil return system, reduces the vibration and operation noise of the unit, avoids abnormal lubrication failure of the bearing caused by incapability of establishing pressure difference of the startup and shutdown, and improves the operation stability and the operation life of the unit of the system.

Description

A compressor oil return system and its control method

technical field

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 technique

The refrigeration oil of commercial screw chillers circulates synchronously with the refrigerant system, and the reliability of the oil return system directly affects the noise, vibration and operating life of the unit. The oil return system has the following problems:

1) The oil tank of the unit is built under the exhaust end of the compressor, and the temperature of the oil tank is affected by the exhaust temperature, resulting in poor lubrication of the unit;

2) The unit adopts ejector-assisted oil return, and abnormalities such as ejector dirty plugging, filter dirty plugging, and welding concentricity lead to ejector oil return failure;

3) The effective oil supply pressure difference cannot be quickly established when the unit is shut down or started at low ambient temperature, which leads to bearing lubrication failure and affects the service life of the unit;

4) The oil supply temperature of the unit is uncontrollable, and the temperature of the lubricating oil 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;

5) In a low temperature environment, oil heating is required to start the unit. Direct start-up is prone to oil leakage, and a large amount of refrigerated oil enters the evaporator, causing the unit to inhale liquid.

To sum up, the current water-cooled screw unit compressor oil return system and control method have certain defects, and after-sales units are prone to oil leakage under severe working conditions, and there are risks such as lubrication failure and increased vibration and noise of the unit.

Contents of the invention

In order to solve defects such as auxiliary oil return failure, poor lubrication effect, and low-temperature start-up oil leakage, the primary purpose of the present invention is to provide a system that improves the reliability of the oil return system, reduces the vibration and noise of the unit, and improves the operating stability and service life of the unit. Compressor oil return system.

In order to achieve the above object, the present invention adopts the following technical solutions: a compressor oil return system, including 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 circulation system includes a compressor, a condenser, a throttling electronic expansion valve and an evaporator, the upper exhaust port of the compressor communicates with the upper end of the condenser through a pipeline, and the bottom of the condenser The liquid collecting bag communicates with one end of the throttling electronic expansion valve through the pipeline, and the other end of the throttling electronic expansion valve communicates with the liquid accumulation bag at the bottom of the evaporator through the pipeline, and the top outlet of the evaporator connects with the suction of the compressor through the pipeline. The air port is connected; the cold oil system includes a condenser, a cooling electronic expansion valve, a plate heat exchanger and an evaporator, and the small liquid collection bag of the condenser communicates with one end of the cooling electronic expansion valve through a pipeline to cool the electronic expansion valve The other end of the valve communicates with one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger communicates with the middle of the evaporator shell through a pipeline; the oil return system includes a condenser, an oil return solenoid valve, a plate type Heat exchanger and oil storage tank, one end of the condenser communicates with one end of the oil return solenoid valve through a pipeline, the other end of the oil return solenoid valve communicates with one end of the plate heat exchanger through a pipeline, and the plate heat exchanger The other end communicates with the oil storage tank through a pipeline; the oil supply system includes an oil storage tank and a compressor, the oil storage tank communicates with the compressor through a pipeline, and the refrigerated oil is supplied from the oil storage tank to the compressor through a pressure difference. machine; the first auxiliary oil return system includes an evaporator, a liquid extraction pump and a compressor, the middle and lower part of the shell of the evaporator is connected to one end of the liquid extraction pump through a pipeline, and the other end of the liquid extraction pump is connected through a pipeline It is connected with the suction end of the compressor; the second auxiliary oil return system includes an oil storage tank, an air intake solenoid valve, a liquid intake pump and a compressor, and the oil storage tank communicates with one end of the air intake solenoid valve through a pipeline, The other end of the air-taking electromagnetic valve communicates with one end of the liquid-taking pump through a pipeline, and the other end of the liquid-taking pump communicates with the suction end of the compressor through a pipeline.

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 after exchanging heat with cooling water, it forms a high-temperature and high-pressure liquid refrigerant, which is discharged from the condensing The liquid collecting bag at the bottom of the evaporator flows out, goes through the throttling electronic expansion valve to reduce the pressure, and then enters the liquid collecting bag at the bottom of the evaporator. The refrigerant evaporates in the evaporator and exchanges heat with the chilled water. The top outlet of the evaporator enters the suction port of the compressor.

In the cold oil system, the high temperature and high pressure liquid refrigerant is taken from the small liquid collection bag in the condenser, throttled and reduced by the cooling electronic expansion valve, and enters the plate heat exchanger to cool down the refrigerant oil. The gaseous refrigerant enters the middle part of the low-pressure evaporator shell, enters the compressor along with the outlet of the evaporator, and participates in the cycle.

In the oil return system, the high-temperature and high-pressure gas discharged from the compressor is impacted and separated from the built-in oil in the condenser, and the separated high-temperature and high-pressure refrigerated oil flows out from the upper outlet of the condenser shell and enters the plate heat exchanger Cool down, and then flow into the oil storage tank.

In the first auxiliary oil return system, an auxiliary oil return pipe is led from the middle and lower part of the evaporator shell, relying on the rotation of the impeller of the liquid extraction pump to provide power, extract the refrigerated 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 vapor-liquid separation network 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 of the compressor. end.

The bottom of the oil storage tank is provided with a magnet for absorbing impurities, an oil return filter for filtering oil return impurities is provided in the oil storage tank, and a gas-liquid separation net for oil and gas separation is provided in the oil storage tank.

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

(1) Before the system is turned on, the throttle electronic expansion valve and air intake solenoid valve have a default opening of 0. When the system receives a start-up command, the oil return solenoid valve opens. When the actual value of the system differential pressure is less than the differential pressure set value , the throttling electronic expansion valve and the air intake solenoid valve keep the opening degree unchanged at 0. At this time, the pressure of the condenser and the oil storage tank increases rapidly, and the compressor bearing is lubricated 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 is first unloaded to 50% load, at this time the oil return solenoid valve and air intake solenoid valve are closed, the system shuts down synchronously, and the inside of the oil storage tank is in a state of high pressure, continuously providing refrigeration oil for lubrication to the system;

(3) In case of emergency, failure or power failure, the oil return solenoid valve and gas intake solenoid valve are closed immediately. At this time, the inside of the oil storage tank is still guaranteed to be in a high pressure state, and continue to supply oil to the compressor bearings. When the system is powered on, it receives a start-up command , follow step (1) above.

It can be seen from the above technical solution that the beneficial effects of the present invention are as follows: First, the present invention ensures that the lubricating viscosity of the refrigeration oil is in the best state, improves the reliability of the oil return system, reduces the vibration and operating noise of the unit, and avoids the failure of the switch to establish a pressure difference. The bearing lubrication failure is abnormal, which improves the operation stability and service life of the system unit; second, the invention stores the refrigerated oil in the external oil storage tank to avoid the influence of the exhaust gas temperature on the oil tank temperature, and at the same time, the system unit does not need to be refrigerated when starting up The oil is preheated to avoid the phenomenon of oil leakage and suction liquid, and improve user satisfaction; third, the auxiliary oil return of the present invention adopts the pump body extraction type, and the high-pressure gas is used as a stable and reliable power source, which can avoid the system dirty blockage. The oil return failure is abnormal.

Description of drawings

Fig. 1 is a system schematic diagram of the present invention;

Fig. 2 is a logic diagram of fuel supply control in the present invention.

Detailed ways

As shown in Figure 1, a compressor oil return system 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 liquid circuit circulation system includes a compressor 1, a condenser 2, a throttling electronic expansion valve 12 and an evaporator 13. The exhaust port at the upper end of the compressor 1 communicates with the upper end of the condenser 2 through a pipeline, and the bottom of the condenser 2 The liquid collecting bag communicates with one end of the throttling electronic expansion valve 12 through a pipeline, and the other end of the throttling electronic expansion valve 12 communicates with the liquid accumulation bag at the bottom of the evaporator 13 through a pipeline, and the top outlet of the evaporator 13 communicates with the The suction port of the compressor 1 is connected; the cold oil system includes a condenser 2, a cooling electronic expansion valve 3, a plate heat exchanger 5 and an evaporator 13. One end of the electronic expansion valve 3 is communicated, the other end of the cooling electronic expansion valve 3 is communicated with one end of the plate heat exchanger 5 through a pipeline, and the other end of the plate heat exchanger 5 is communicated with the middle part of the shell of the evaporator 13 through a pipeline; The oil return system includes a condenser 2, an oil return solenoid valve 4, a plate heat exchanger 5 and an oil storage tank 6, one end of the condenser 2 communicates with one end of the oil return solenoid valve 4 through a pipeline, and the oil return electromagnetic valve The other end of the valve 4 communicates with one end of the plate heat exchanger 5 through a pipeline, and the other end of the plate heat exchanger 5 communicates with the oil storage tank 6 through a pipeline; the oil supply system includes the oil storage tank 6 and the compressor 1 , the oil storage tank 6 communicates with the compressor 1 through a pipeline, and the refrigerated oil is supplied from the oil storage tank 6 to the compressor 1 through a pressure difference; the first auxiliary oil return system includes an evaporator 13, a liquid extraction pump 9 and the compressor 1, the lower part of the housing of the evaporator 13 is connected to one end of the liquid extraction pump 9 through a pipeline, and the other end of the liquid extraction pump 9 is connected to the suction end of the compressor 1 through a pipeline; the second The auxiliary oil return system includes an oil storage tank 6, an air intake solenoid valve 8, a liquid extraction pump 9 and a compressor 1. The oil storage tank 6 communicates with one end of the air intake electromagnetic valve 8 through a pipeline, and the air intake solenoid valve 8 The other end communicates with one end of the liquid extraction pump 9 through a pipeline, and the other end of the liquid extraction pump 9 communicates with the suction end of the compressor 1 through a pipeline.

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, and then enters the condenser 2. After exchanging heat with cooling water, it forms a high-temperature and high-pressure liquid refrigerant, and Flow out from the liquid collection bag at the bottom of the condenser 2, go through the throttling electronic expansion valve 12 for throttling and pressure reduction, and then enter the liquid accumulation bag at the bottom of the evaporator 13, where the refrigerant evaporates in the evaporator 13 and exchanges heat with the chilled water After evaporation, the gaseous refrigerant enters the suction port of the compressor 1 from the top outlet of the evaporator 13 .

In the cold oil system, high temperature and high pressure liquid refrigerant is taken from the small liquid collection bag in the condenser 2, throttled and depressurized by the cooling electronic expansion valve 3, and enters the plate heat exchanger 5 to cool down the temperature of the refrigerated oil. The gaseous refrigerant after heat exchange enters the middle part of the shell of the low-pressure evaporator 13, enters the compressor 1 along with the gas outlet of the evaporator 13, and participates in the cycle.

In the oil return system, the high-temperature and high-pressure gas discharged from the compressor 1 is impacted and separated from the built-in oil in the condenser 2, and the separated high-temperature and high-pressure refrigerated oil flows out from the upper outlet of the condenser 2 shell and enters the plate type The heat exchanger 5 cools down, and then flows into the oil storage tank 6 .

In the first auxiliary oil return system, an auxiliary oil return pipe is led from the lower part of the shell of the evaporator 13, relying on the rotation of the impeller of the liquid extraction pump 9 to provide power, to extract the refrigerated oil inside the evaporator 13, and enter the compressor 1 for suction end; in the second auxiliary oil return system, the high-pressure gas in the oil storage tank 6 enters the liquid extraction pump 9 from the top after being separated by the vapor-liquid separation network inside the oil storage tank 6 to provide power for the liquid extraction pump 9, The gas finally flows into the suction end of compressor 1.

The bottom of the oil storage tank 6 is provided with a magnet 10 for absorbing impurities, the oil storage tank 6 is provided with an oil return filter 11 for filtering oil return impurities, and the oil storage tank 6 is provided with a gas-liquid separation for oil-gas separation net7.

As shown in Figure 2, the control method of the present invention comprises the steps of following sequence:

(1) Before the system is turned on, the throttle electronic expansion valve 12 and the air intake solenoid valve 8 default to 0 openings. When the system receives the start-up command, the oil return solenoid valve 4 opens. When the value is fixed, the throttling electronic expansion valve 12 and the air intake solenoid valve 8 keep the opening degree unchanged at 0. At this time, the pressure of the condenser 2 and the oil storage tank 6 increases rapidly to lubricate the bearing of the compressor 1 in time. When the system pressure When the difference is greater than or equal to the set value of the pressure difference, the throttling electronic expansion valve 12 enters the pressure difference free adjustment mode, and the system starts normally;

(2) During normal shutdown, the system is first unloaded to 50% of the load. At this time, the oil return solenoid valve 4 and the air intake solenoid valve 8 are closed, and the system is shut down synchronously. lubricating;

(3) In the event of an 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 inside of the oil storage tank 6 is still guaranteed to be in a high pressure state, and the oil supply for the bearing of the compressor 1 is continued. When the system is on When the computer receives the power-on command, execute according to the above step (1).

The present invention will be further described below in conjunction with FIGS. 1 and 2 .

The present invention adopts the oil storage tank 6 to separate the refrigerated oil from the exhaust gas, cancel the oil heating, start the machine directly at low temperature, avoid suction with liquid, and add a cold oil plate at the oil inlet to replace the structure, and take liquid and cool it through the condenser 2 The electronic expansion valve has 3 throttling methods to precisely control the oil supply temperature to ensure the lubrication effect.

The present invention adopts pump body extracting auxiliary oil return, uses oil storage tank 6 high-pressure gas as the power source, drives the liquid extraction pump 9 impellers to rotate, and provides power for the evaporator 13 to measure the oil return flow path; the power source of this structure can use high-pressure gas to Eliminate dirt and blockage, the liquid to be extracted and the high-pressure gas of the power source run in independent chambers, which is stable and reliable.

The present invention adds rapid oil supply and continuous oil supply control logic. When the unit is turned on and off, the air intake solenoid valve 8, the oil return solenoid valve 4, and the electronic expansion valve are used to control the on-off of the flow path, so that the cavity of the oil storage tank 6 maintains high pressure. state, providing continuous refrigeration oil lubrication for compressor 1 bearings. In the present invention, the unit refers to the whole system as shown in FIG. 1 .

The unit adopts differential pressure for oil supply and return. The mixture of refrigerated oil and high-pressure gas is exchanged from the built-in oil condenser 2 to the oil storage tank 6 through the oil return solenoid valve 4 and the cold oil plate. The oil return filter 11 can filter the oil return system Impurities, when the pressure detection value of condenser 2 P1-P2≥100Pa (the set value of 100Pa is the pressure loss from condenser 2 to oil storage tank 6), the system prompts to replace the oil return filter 11, and the magnet 10 is at the bottom of the oil storage tank 6 Evenly distributed, used to absorb impurities such as iron filings to avoid dirty oil supply pipelines; the top of the oil storage tank 6 is a vapor-liquid separation net, which is used to separate the lubricating oil from the refrigerant gas. After the vapor-liquid separation, the top of the oil storage tank 6 It is high-pressure gas, and the bottom is liquid refrigerated oil. Use a temperature-sensing package to detect the temperature t of the refrigerated oil, and use the cold oil plate to cooperate with the electronic expansion valve to keep the temperature of the oil storage tank 6 in the best state. When the detected temperature t is at the set temperature T± 2, the cooling electronic expansion valve 3 maintains the opening degree, when the detected temperature t is greater than the set temperature T+2, the cooling electronic expansion valve 3 is opened larger, and when the detected temperature t is lower than the set temperature T-2, the cooling electronic expansion valve 3 The opening degree is reduced to achieve the purpose of precisely 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 start-up of the unit in a low-temperature environment This leads to the oil bubble problem of the unit, and at the same time, the oil heating system can be canceled, and the unit can be started without waiting. Compressor 1 has a built-in oil tank structure. When starting up in winter, the exhaust gas temperature is greatly affected by the temperature of the oil tank, and a large amount of refrigerated oil cannot be separated in time, causing the unit to soak in oil. Some units are equipped with oil heating. The heating time in winter takes about 5 hours, which affects Unit start time.

After the mixture of refrigerant and oil in the oil storage tank 6 undergoes vapor-liquid separation, the top is high-pressure gas. The high-pressure gas enters the liquid extraction pump 9 through the gas extraction solenoid valve 8. The high-pressure gas drives the impeller of the liquid extraction pump 9 to rotate as a power source. The pressure energy is converted into mechanical energy, and then returned to the suction port of compressor 1 through the connecting pipeline, and the impeller on the other side rotates coaxially and synchronously, so as to extract the mixed liquid of refrigerated oil and refrigerant on the liquid level surface of the evaporator 13 to the compressor The suction port of machine 1, when the unit is in normal operation, the air intake solenoid valve 8 is opened every 1 hour, and the opening time is one hour at a time, which can achieve the effect of auxiliary oil return and reduce the loss of cooling capacity, which is easier than ejection and oil return. The failure is abnormal. The high-pressure gas of the auxiliary oil return system is used as the power source to avoid the failure of the auxiliary oil return caused by system impurities. The extracted liquid and the high-pressure gas of the power source run in an independent chamber, which is stable and reliable, and the oil return effect is good.

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 2 and the oil storage tank 6. At this time, the pressure of the condenser 2 and the oil storage tank 6 increases rapidly. The pressure difference can be quickly established, and the refrigerated oil inside the oil storage tank 6 can be quickly sent to the compressor 1 for bearing 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 Normal start. When the unit is shut down, the male and female 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 at this time, 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, it can continue to supply oil to the bearing of compressor 1; when the unit is shut down in an emergency, failure or sudden power failure, the oil return solenoid valve 4 and the air intake solenoid valve 8 are closed, and the oil storage tank 6 acts as a high pressure source to continuously supply oil to the bearing Oil supply, fault clearing of the standby unit When receiving the start-up command, it will be executed according to the normal start-up logic; in order to solve the problem of bearing lubrication failure of the unit under different on-off states.

In summary, the present invention ensures that the lubricating viscosity of the refrigeration oil is in the best state, improves the reliability of the oil return system, reduces unit vibration and operating noise, avoids abnormal bearing lubrication failure caused by the inability to establish a pressure difference when switching on and off, and improves the stability of the system unit. performance and operating life; the present invention stores the refrigerated oil in the external oil storage tank 6 to avoid the influence of the exhaust temperature on the oil temperature, and at the same time, the system unit does not need to preheat the refrigerated oil when starting up, avoiding oil leakage and suction liquid Phenomenon, improve user satisfaction; the auxiliary oil return of the present invention adopts the pump body extraction type, and high-pressure gas is used as a stable and reliable power source, which can avoid abnormal oil return failure caused by dirty blockage of the system.

Claims (7)

1. An oil return system of a compressor, which is characterized in that: the system comprises a main liquid path 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 path circulation system comprises a compressor, a condenser, a throttling electronic expansion valve and an evaporator, wherein an exhaust port at the upper end of the compressor is communicated with the upper end of the condenser through a pipeline, a liquid collecting bag at the bottom of the condenser is communicated with one end of the throttling electronic expansion valve through a pipeline, the other end of the throttling electronic expansion valve is communicated with a liquid collecting bag at the bottom of the evaporator through a pipeline, and an outlet at the top of the evaporator is communicated with an air suction port of the compressor through a pipeline; the oil cooling system comprises a condenser, a cooling electronic expansion valve, a plate heat exchanger and an evaporator, wherein a small liquid collecting bag of the condenser is communicated with one end of the cooling electronic expansion valve through a pipeline, the other end of the cooling electronic expansion valve is communicated with one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger is communicated with the middle part of a shell of the evaporator through a pipeline; the oil return system comprises a condenser, an oil return electromagnetic valve, a plate heat exchanger and an oil storage tank, wherein one end of the condenser is communicated with one end of the oil return electromagnetic valve through a pipeline, the other end of the oil return electromagnetic valve is communicated with one end of the plate heat exchanger through a pipeline, and the other end of the plate heat exchanger is communicated with the oil storage tank through a pipeline; the oil supply system comprises an oil storage tank and a compressor, wherein the oil storage tank is communicated with the compressor through a pipeline, and refrigerating oil is supplied to the compressor from the oil storage tank through a pressure difference; the first auxiliary oil return system comprises an evaporator, a liquid taking pump and a compressor, wherein the middle lower part of a shell of the evaporator is connected with one end of the liquid taking pump through a pipeline, and the other end of the liquid taking pump is connected with the air suction end of the compressor through a pipeline; the second auxiliary oil return system comprises an oil storage tank, an air taking electromagnetic valve, an air taking pump and a compressor, wherein the oil storage tank is communicated with one end of the air taking electromagnetic valve through a pipeline, the other end of the air taking electromagnetic valve is communicated with one end of the air taking pump through a pipeline, and the other end of the air taking pump is communicated with the air suction end of the compressor through a pipeline.

2. The compressor oil return system of claim 1, wherein: in the main liquid path circulation system, low-temperature low-pressure gaseous refrigerant is compressed by a compressor and then is discharged from an upper end exhaust port, enters a condenser, forms high-temperature high-pressure liquid refrigerant after heat exchange with cooling water, flows out of a bottom liquid collecting bag in the condenser, is throttled and depressurized by a throttle electronic expansion valve, then enters a liquid accumulating bag at the bottom of the evaporator, is evaporated in the evaporator and exchanges heat with chilled water, and the evaporated gaseous refrigerant enters an air suction port of the compressor from an outlet at the top of the evaporator.

3. The compressor oil return system of claim 1, wherein: in the oil cooling system, a high-temperature high-pressure liquid refrigerant is taken from a small liquid collecting bag in a condenser, throttled and depressurized by a cooling electronic expansion valve and enters a plate heat exchanger to cool refrigerating oil, and the gaseous refrigerant after heat exchange enters the middle part of a low-pressure evaporator shell and enters a compressor along with an air outlet of the evaporator to participate in circulation.

4. The compressor oil return system of claim 1, wherein: in the oil return system, high-temperature and high-pressure gas discharged by a compressor is impacted and separated in built-in oil in a condenser, and separated high-temperature and high-pressure frozen oil flows out from an upper outlet in a shell of the condenser, enters a plate heat exchanger for cooling, and then flows into an oil storage tank.

5. The compressor oil return system of claim 1, wherein: in the first auxiliary oil return system, an auxiliary oil return pipe is led from the middle lower part of the evaporator shell, power is provided by rotation of a liquid taking pump impeller, refrigerating oil in the evaporator is extracted, and the refrigerating oil enters a suction end of a compressor; in the second auxiliary oil return system, high-pressure gas in the oil storage tank enters the liquid taking pump from the top end after being separated by a gas-liquid separation net in the oil storage tank, power is provided for the liquid taking pump, and the gas finally flows into the air suction end of the compressor.

6. The compressor oil return system of claim 1, wherein: the bottom of oil storage tank sets up the magnet that is used for adsorbing impurity, sets up the oil return filter that is used for filtering the oil return impurity in the oil storage tank, sets up the gas-liquid separation net that is used for oil-gas separation in 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 sequence:

(1) Before the system is not started, the default opening degree of the throttling electronic expansion valve and the air taking electromagnetic valve is 0, when the system receives a starting command, the oil return electromagnetic valve is started, when the actual pressure difference value of the system is smaller than the set pressure difference value, the opening degree of the throttling electronic expansion valve and the air taking electromagnetic valve is kept unchanged by 0, at the moment, the condenser and the oil storage tank rapidly raise the pressure to lubricate a compressor bearing in time, and when the pressure difference value of the system is larger than or equal to the set pressure difference value, the throttling electronic expansion valve enters a pressure difference free regulation mode, and the system is started normally;

(2) When the system is normally shut down, the system is firstly unloaded to 50% of load, at the moment, the oil return electromagnetic valve and the gas taking electromagnetic valve are closed, the system is synchronously shut down, the inside of the oil storage tank is in a high-pressure state, and refrigerating oil is continuously supplied to the system for lubrication;

(3) And (3) when the emergency, the fault and the power failure occur, the oil return electromagnetic valve and the gas taking electromagnetic valve are immediately closed, the inside of the oil storage tank is still guaranteed to be in a high-pressure state, the oil is continuously supplied to the compressor bearings, and when the system is powered on and receives a starting command, the step (1) is executed.

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