Air conditioning system and control method thereof

Abstract

The embodiment of the invention provides an air conditioning system and a control method thereof, and relates to the technical field of air conditioners. According to the air conditioning system, the oil return pipeline and the oil balancing pipeline are arranged in the outdoor units, so that when the refrigerating machine oil in the compressor of one outdoor unit is too much and the refrigerating machine oil in the compressor of the other outdoor unit is too little, the oil balancing electromagnetic valve of the outdoor unit with more refrigerating machine oil can be opened, and the oil return expansion valve of the outdoor unit with more refrigerating machine oil can be closed; the compressor is shut down or operates at low frequency, so that refrigerating machine oil separated by the oil separator can enter a compressor of another outdoor unit with less refrigerating machine oil through the oil return pipeline, the oil balancing pipeline and the second branch pipeline. Therefore, the refrigerating machine oil is conveyed from the outdoor unit with more refrigerating machine oil to the outdoor unit with less refrigerating machine oil, so that the refrigerating machine oil is uniformly distributed.

Description

Technical Field

[0001] The present application relates to the technical field of air conditioning, and in particular to an air conditioning system and a control method thereof. Background Art

[0002] A certain amount of refrigeration oil is often added to the pipelines of the air-conditioning system. The refrigeration oil can play a role in lubrication and cooling during the operation of the compressor. If the refrigeration oil level in the compressor is too low, bearing burnout is likely to occur. In order to increase the overall capacity of the air-conditioning system, multiple outdoor units arranged in parallel are used in the relevant technology. However, when the overall pipelines of the air-conditioning system are complicated, it is easy for the refrigeration oil to be unevenly distributed in the compressors of multiple outdoor units. For example, there is too much refrigeration oil in the compressor of one outdoor unit, while there is insufficient refrigeration oil in the compressor of another outdoor unit. Therefore, it is easy to cause compressor failure. Summary of the invention

[0003] The problem to be solved by the present application is how to alleviate the problem of uneven distribution of refrigeration oil in multiple outdoor units.

[0004] To solve the above problems, in a first aspect, the present application provides an air-conditioning system, comprising an indoor unit and at least two outdoor units, each outdoor unit comprising a compressor, an outdoor heat exchanger, a four-way valve, an oil separator, a first branch pipeline, a second branch pipeline, an oil return pipeline and an oil equalizing pipeline, the exhaust end of the compressor is connected to the four-way valve through an exhaust side pipeline, the suction end of the compressor is connected to the four-way valve through an suction side pipeline, one end of the first branch pipeline of each outdoor unit is connected to the corresponding four-way valve, and the other end is connected to the indoor unit after merging, one end of the second branch pipeline of each outdoor unit is connected to the corresponding four-way valve, and the other end is connected to the indoor unit after merging, the outdoor heat exchanger is arranged on the first branch pipeline, the oil separator has an air inlet end, an air outlet end and an oil outlet end, and the oil separator is connected to the exhaust side pipeline through the air inlet end and the air outlet end;

[0005] One end of the oil return pipeline is connected to the oil outlet end of the oil separator, and the other end is connected to the air suction side pipeline. An oil return expansion valve is provided on the oil return pipeline;

[0006] One end of the oil balancing pipeline is connected to the oil return pipeline between the oil separator and the oil return expansion valve, and the other end is connected to the second branch pipeline. An oil balancing solenoid valve is arranged on the oil balancing pipeline.

[0007] In the embodiment of the present application, by setting the return oil pipeline and the oil equalization pipeline in the outdoor unit, when there is too much refrigeration oil in the compressor of one outdoor unit and too little refrigeration oil in the compressor of another outdoor unit, the oil equalization solenoid valve of the outdoor unit with more refrigeration oil can be opened, the return oil expansion valve can be closed, and the compressor can be shut down or run at a low frequency, so that under the refrigeration condition, the refrigeration oil separated by the oil separator will enter the second branch pipeline of the other outdoor unit through the return oil pipeline, the oil equalization pipeline, and the second branch pipeline under the suction action of the other outdoor unit with less refrigeration oil, and finally enter the compressor of the other outdoor unit. In this way, the refrigeration oil is transported from the outdoor unit with more refrigeration oil to the outdoor unit with less refrigeration oil, so as to achieve uniform distribution of the refrigeration oil.

[0008] In an optional embodiment, a gas-liquid separator is provided on the air intake side pipeline, and the connection position of the oil return pipeline to the air intake side pipeline is located upstream of the gas-liquid separator. By providing a gas-liquid separator, the liquid refrigerant entering the compressor can be reduced, reducing the damage to the compressor due to liquid absorption.

[0009] In an optional embodiment, the outdoor unit further includes an exhaust temperature sensor for detecting the exhaust temperature of the compressor. By providing the exhaust temperature sensor, the exhaust temperature of the compressor can be monitored to promptly detect abnormalities in the operation of the compressor. The exhaust temperature can also be used as a reference for controlling the opening of the oil return expansion valve.

[0010] In an optional embodiment, the exhaust temperature sensor is arranged on the exhaust side pipeline between the compressor and the oil separator.

[0011] In an optional implementation, the outdoor unit further includes an oil temperature sensor for detecting the oil temperature in the oil return pipeline.

[0012] In an optional embodiment, the oil temperature sensor is arranged on the oil return pipeline of the oil return expansion valve away from the oil separator. By arranging the oil temperature sensor, the oil temperature can be monitored in real time, so that the abnormality of the oil temperature can be discovered in time. And the temperature information fed back by the oil temperature sensor can be used as a reference for controlling the opening of the oil return expansion valve.

[0013] In an optional embodiment, the outdoor unit further includes a one-way valve, which is arranged in the exhaust side pipeline and is located between the gas outlet end of the oil separator and the four-way valve, and the one-way valve allows the refrigerant to be transmitted from the oil separator to the four-way valve. By setting the one-way valve, backflow in the exhaust side pipeline can be avoided.

[0014] In an optional embodiment, an external machine expansion valve is arranged on the first branch pipeline, and the external machine expansion valve is arranged on a side of the outdoor heat exchanger away from the four-way valve. The external machine expansion valve is used to reduce the pressure of the high-pressure liquid refrigerant passing through.

[0015] In an optional embodiment, the indoor unit includes an indoor heat exchanger and an indoor expansion valve, the two ends of the indoor heat exchanger are connected to the first branch pipeline and the second branch pipeline respectively through pipelines, and the indoor expansion valve is arranged on the pipeline between the indoor heat exchanger and the first branch pipeline. The indoor expansion valve is used to reduce the pressure of the high-pressure liquid refrigerant passing through.

[0016] In an optional embodiment, multiple indoor units are included, and the air-conditioning system also includes a first main line and a second main line. The first branch lines of each outdoor unit merge into the first main line, the second branch lines of each outdoor unit merge into the second main line, and each indoor unit is connected in parallel to the first main line and the second main line.

[0017] In a second aspect, the present application provides a control method for an air conditioning system, which is applied to the air conditioning system provided in the first aspect, comprising:

[0018] Determine a first target outdoor unit and a second target outdoor unit among the outdoor units in operation, the first target outdoor unit being an outdoor unit with too much refrigeration oil, and the second target outdoor unit being an outdoor unit with too little refrigeration oil;

[0019] The oil return expansion valve of the first target outdoor unit is closed, the oil equalization solenoid valve of the first target outdoor unit is opened, and the frequency of the compressor of the first target outdoor unit is controlled to be lower than the frequency of the compressor of the second target outdoor unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of an air conditioning system in an embodiment of the present application.

[0021] Explanation of the reference numerals: 010 - air conditioning system; 100 - outdoor unit; 110 - compressor; 111 - exhaust side pipeline; 112 - suction side pipeline; 113 - exhaust temperature sensor; 114 - oil separator; 115 - check valve; 116 - gas-liquid separator; 120 - four-way valve; 130 - first branch pipeline; 131 - outdoor heat exchanger; 132 - outdoor unit expansion valve; 140 - second branch pipeline; 150 - return oil pipeline; 151 - return oil expansion valve; 152 - oil temperature sensor; 160 - oil equalizing pipeline; 161 - oil equalizing solenoid valve; 200 - indoor unit; 210 - indoor heat exchanger; 220 - indoor unit expansion valve; 300 - first main pipeline; 400 - second main pipeline. DETAILED DESCRIPTION

[0022] In large air-conditioning systems, the pipeline path is very long, and a considerable part of the refrigeration oil is retained in the pipeline and the indoor unit, resulting in a possible shortage of refrigeration oil in the outdoor unit. If the refrigeration oil level in the compressor is too low, the compressor is prone to burn. Therefore, it is often necessary to regularly control the recovery of refrigeration oil. For example, increase the circulation speed of the refrigerant (reach a refrigerant flow rate that allows the oil to move with the refrigerant) to recover the refrigeration oil in the pipeline. However, in an air-conditioning system with multiple outdoor units, it is difficult to ensure that the compressor of each outdoor unit has a suitable amount of refrigeration oil. It is easy to have uneven distribution of refrigeration oil in the compressors of multiple outdoor units, such as excessive refrigeration oil in the compressor of one outdoor unit, and insufficient refrigeration oil in the compressor of another outdoor unit. Therefore, it is easy to cause the compressor with too little refrigeration oil to fail.

[0023] To this end, the embodiment of the present application provides an air conditioning system and a control method thereof. By setting an oil return pipeline, an oil equalization pipeline and reasonable control, the refrigeration oil discharged from the compressor with too much refrigeration oil can enter other outdoor units with less refrigeration oil.

[0024] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0025] Figure 1 FIG. 1 is a schematic diagram of an air conditioning system 010 in an embodiment of the present application. Figure 1 As shown, an embodiment of the present application provides an air conditioning system 010, including multiple indoor units 200 and at least two outdoor units 100. In this embodiment, each outdoor unit 100 includes a compressor 110, an outdoor heat exchanger 131, a four-way valve 120, an oil separator 114, a first branch pipeline 130, a second branch pipeline 140, an oil return pipeline 150 and an oil equalization pipeline 160. The exhaust end of the compressor 110 is connected to the four-way valve 120 through the exhaust side pipeline 111, and the suction end of the compressor 110 is connected to the four-way valve 120 through the suction side pipeline 112. One end of the first branch pipeline 130 of each outdoor unit 100 is connected to the corresponding four-way valve 120, and the other end is connected to the indoor unit 200 after merging. One end of the second branch pipeline 140 of each outdoor unit 100 is connected to the corresponding four-way valve 120, and the other end is connected to the indoor unit 200 after merging. The outdoor heat exchanger 131 is arranged on the first branch pipeline 130.

[0026] The oil separator 114 has an air inlet end, an air outlet end and an oil outlet end, and the oil separator 114 is connected to the exhaust side pipeline 111 through the air inlet end and the air outlet end. One end of the return oil pipeline 150 is connected to the oil outlet end of the oil separator 114, and the other end is connected to the suction side pipeline 112. The return oil pipeline 150 is provided with an oil return expansion valve 151.

[0027] One end of the oil balancing pipeline 160 is connected to the oil return pipeline 150 between the oil separator 114 and the oil return expansion valve 151 , and the other end is connected to the second branch pipeline 140 . An oil balancing solenoid valve 161 is provided on the oil balancing pipeline 160 .

[0028] In this embodiment, the four-way valve 120 can be switched in a controlled manner so that the exhaust side pipeline 111 is selectively connected to the first branch pipeline 130 or the second branch pipeline 140; correspondingly, the suction side pipeline 112 is selectively connected to the second branch pipeline 140 or the first branch pipeline 130. Therefore, by controlling the four-way reversing valve, the operating condition of the air conditioning system 010 can be controlled, that is, in the heating mode or the cooling mode. In the cooling mode (such as Figure 1 As shown), the exhaust end of the compressor 110 is connected to the first branch pipeline 130 through the exhaust side pipeline 111, and the suction end of the compressor 110 is connected to the second branch pipeline 140 through the suction side pipeline 112; in the heating mode, the exhaust end of the compressor 110 is connected to the second branch pipeline 140 through the exhaust side pipeline 111, and the suction end of the compressor 110 is connected to the first branch pipeline 130 through the suction side pipeline 112.

[0029] In this embodiment, the air-conditioning system 010 also includes a first main line 300 and a second main line 400, the first branch lines 130 of each outdoor unit 100 converge into the first main line 300, the second branch lines 140 of each outdoor unit 100 converge into the second main line 400, and each indoor unit 200 is connected in parallel with the first main line 300 and the second main line 400.

[0030] In this embodiment, an external expansion valve 132 is disposed on the first branch pipeline 130, and the external expansion valve 132 is disposed on a side of the outdoor heat exchanger 131 away from the four-way valve 120. The external expansion valve 132 is used to reduce the pressure of the high-pressure liquid refrigerant passing through.

[0031] In this embodiment, the indoor unit 200 includes an indoor heat exchanger 210 and an indoor unit expansion valve 220. The two ends of the indoor heat exchanger 210 are respectively connected to the first branch pipeline 130 and the second branch pipeline 140 through pipelines, so that the indoor unit 200 and the outdoor unit 100 form a circulation loop through the first main pipeline 300 and the second main pipeline 400. The indoor unit expansion valve 220 is arranged on the pipeline between the indoor heat exchanger 210 and the first branch pipeline 130. Specifically in this embodiment, one end of the indoor heat exchanger 210 is connected to the first main pipeline 300 through a pipeline, and then communicates with the first branch pipeline 130 through the first main pipeline 300; the other end of the indoor heat exchanger 210 is connected to the second main pipeline 400 through a pipeline, and then communicates with the second branch pipeline 140 through the second main pipeline 400. The indoor unit expansion valve 220 is arranged on the pipeline between the outdoor heat exchanger 131 and the first main pipeline 300, and is used to reduce the pressure of the high-pressure liquid refrigerant passing through.

[0032] In this embodiment, a gas-liquid separator 116 is provided on the air suction side pipeline 112, and the connection position of the oil return pipeline 150 to the air suction side pipeline 112 is located upstream of the gas-liquid separator 116. By providing the gas-liquid separator 116, the liquid refrigerant entering the compressor 110 can be reduced, and the damage of the compressor 110 due to liquid absorption can be reduced.

[0033] In this embodiment, the oil separator 114 is used to separate the gaseous refrigerant transmitted in the exhaust side pipeline 111 from the refrigeration oil. The separated refrigeration oil is stored at the bottom of the oil separator 114 and can be returned to the suction side pipeline 112 through the oil return pipeline 150, and finally returned to the compressor 110. Therefore, the refrigeration oil in the compressor 110 is continuously discharged and continuously recovered, and can be in dynamic balance under normal circumstances. The oil return rate can be adjusted by adjusting the opening of the oil return expansion valve 151. Generally, if the refrigeration oil level in the compressor 110 is high, the oil discharge speed is fast, and the oil accumulation speed in the oil separator 114 is fast, the oil return expansion valve 151 can maintain a relatively large opening to ensure the oil return speed; on the contrary, if the refrigeration oil level in the compressor 110 is low, the oil discharge speed of the compressor 110 is relatively slow, and the oil return expansion valve 151 can maintain a relatively low opening to prevent the oil level in the oil separator 114 from being too low, and the gaseous refrigerant enters the oil return pipeline 150 from the oil outlet end of the oil separator 114. Under this control logic, the opening of the oil return expansion valve 151 can characterize the height of the refrigeration oil level in the compressor 110 to a certain extent, that is, the larger the opening, the higher the refrigeration oil level in the compressor 110, and vice versa.

[0034] Furthermore, the outdoor unit 100 further includes an exhaust temperature sensor 113 and an oil temperature sensor 152. The exhaust temperature sensor 113 is used to detect the exhaust temperature of the compressor 110, and the oil temperature sensor 152 is used to detect the oil temperature in the oil return line 150.

[0035] Further, the exhaust temperature sensor 113 is arranged on the exhaust side pipeline 111 between the compressor 110 and the oil separator 114. In other optional embodiments, the exhaust temperature sensor 113 can also be arranged at the oil separator 114. By arranging the exhaust temperature sensor 113, the exhaust temperature of the compressor 110 can be monitored, and the abnormality of the operation of the compressor 110 can be discovered in time. In addition, the exhaust temperature can also be used as a reference for controlling the opening of the oil return expansion valve 151.

[0036] Furthermore, the oil temperature sensor 152 is disposed on the oil return pipeline 150 on the side of the oil return expansion valve 151 away from the oil separator 114. By disposing the oil temperature sensor 152, the oil temperature can be monitored in real time, so that the abnormality of the oil temperature can be discovered in time. And the temperature information fed back by the oil temperature sensor 152 can be used as a reference for controlling the opening of the oil return expansion valve 151.

[0037] In this embodiment, the liquid level of the refrigeration oil in the oil separator 114 can be comprehensively judged by the temperature feedback from the exhaust temperature sensor 113 and the oil temperature sensor 152. For example, the temperature information feedback from the exhaust temperature sensor 113 can characterize the refrigerant temperature in the oil separator 114 to a certain extent, and the refrigerant temperature in the oil separator 114 is similar to the temperature of the refrigeration oil in the oil separator 114. When the refrigeration oil in the oil separator 114 maintains a relatively high liquid level, only the refrigeration oil passes through the return oil pipeline 150, and the temperature change of the liquid refrigeration oil is small when passing through the return oil expansion valve 151, so the temperature difference between the feedback from the oil temperature sensor 152 and the exhaust temperature sensor 113 is small. However, if the liquid level in the oil separator 114 is too low or there is no liquid surface, the gaseous refrigerant will enter the return oil pipeline 150 through the oil outlet. After the gaseous refrigerant passes through the oil return expansion valve 151, the pressure is reduced, the volume is expanded, and the temperature is significantly reduced. At this time, the temperature difference between the feedback of the oil temperature sensor 152 and the exhaust temperature sensor 113 is relatively large. When the liquid level in the oil separator 114 is too low, the opening of the oil return expansion valve 151 can be appropriately closed, because at this time the compressor 110 discharges oil slowly, and the refrigeration oil in the oil separator 114 accumulates slowly. Closing the oil return expansion valve 151 is conducive to raising the oil level in the oil separator 114. Therefore, the temperature difference between the two temperature sensors can be used to control the opening of the oil return expansion valve 151.

[0038] In an optional embodiment, the outdoor unit 100 further includes a one-way valve 115, which is disposed in the exhaust side pipeline 111 and is located between the gas outlet end of the oil separator 114 and the four-way valve 120. The one-way valve 115 allows the refrigerant to be transmitted from the oil separator 114 to the four-way valve 120. By providing the one-way valve 115, backflow in the exhaust side pipeline 111 can be avoided.

[0039] In the embodiment of the present application, by setting the oil return pipeline 150 and the oil equalization pipeline 160 in the outdoor unit 100, when the refrigeration oil in the compressor 110 of one outdoor unit 100 is too much and the refrigeration oil in the compressor 110 of the other outdoor unit 100 is too little, the oil equalization solenoid valve 161 of the outdoor unit 100 with more refrigeration oil can be opened, the oil return expansion valve 151 can be closed, and the compressor 110 can be shut down or run at a low frequency, so that the refrigeration oil separated by the oil separator 114 can enter the second branch pipeline 140 of the other outdoor unit 100 through the oil return pipeline 150, the oil equalization pipeline 160, and the second branch pipeline 140 under the suction action of the other outdoor unit 100 with less refrigeration oil, and finally enter the compressor 110 of the other outdoor unit 100. In this way, the refrigeration oil is transported from the outdoor unit 100 with more refrigeration oil to the outdoor unit 100 with less refrigeration oil, so as to achieve uniform distribution of the refrigeration oil.

[0040] The control method of the air conditioning system provided in this embodiment can be applied to the air conditioning system 010 provided in the first aspect, including:

[0041] Step S100: determining a first target outdoor unit and a second target outdoor unit in the operating outdoor units, wherein the first target outdoor unit is an outdoor unit with too much refrigeration oil, and the second target outdoor unit is an outdoor unit with too little refrigeration oil.

[0042] If the liquid level of the refrigeration oil is too high, it means that there is too much refrigeration oil, and if the liquid level of the refrigeration oil is too low, it means that there is too little refrigeration oil. Specifically, the height of the refrigeration oil level in the compressor 110 can be estimated by the opening of the return oil expansion valve 151. In the above introduction to the air-conditioning system 010, it is mentioned that the return oil expansion valve 151 will control the opening size according to the oil discharge rate of the compressor 110. Fast oil discharge means that the oil return speed is also fast, so as to keep the amount of refrigeration oil in the compressor 110 in dynamic balance as much as possible. Then the faster the compressor 110 discharges the refrigeration oil, the larger the opening of the return oil expansion valve 151. The discharge rate of the refrigeration oil is proportional to the frequency of the compressor 110 and the liquid level of the refrigeration oil. After the frequency of the compressor 110 and the opening of the return oil expansion valve 151 are determined, the liquid level of the refrigeration oil can be estimated.

[0043] Of course, in other optional embodiments, the liquid level of the refrigeration oil can be obtained in other ways, such as directly measuring it using a sensor.

[0044] Step S200, closing the oil return expansion valve of the first target outdoor unit, opening the oil equalizing solenoid valve of the first target outdoor unit, and controlling the frequency of the compressor of the first target outdoor unit to be lower than the frequency of the compressor of the second target outdoor unit.

[0045] The step of controlling the frequency of the compressor 110 of the first target outdoor unit 100 to be lower than the frequency of the compressor 110 of the second target outdoor unit 100 includes stopping the operation of the compressor 110 of the first target outdoor unit 100; or, reducing the operating frequency of the compressor 110 of the first target outdoor unit 100 and / or increasing the operating frequency of the compressor 110 of the second target outdoor unit 100.

[0046] Taking the refrigeration condition as an example, after it is determined that the refrigeration oil of the first target outdoor unit 100 needs to be supplemented to the second target outdoor unit 100, the oil return expansion valve 151 of the first target outdoor unit 100 is closed, and the compressor 110 of the first target outdoor unit 100 is suspended from returning oil through the oil return pipeline 150. Then, the oil equalization solenoid valve 161 of the first target outdoor unit 100 is opened, and the compressor 110 of the first target outdoor unit 100 is closed or the frequency of the compressor 110 is reduced, thereby increasing the pressure in the suction side pipeline 112 of the first target outdoor unit 100.

[0047] During this period, the second target outdoor unit 100 keeps running, so that the second branch pipe 140 of the second target outdoor unit 100 has a suction effect on the second branch pipe 140 of the first target outdoor unit 100. Under the suction effect, the refrigeration oil in the first target outdoor unit 100 enters the second branch pipe 140 of the second target outdoor unit 100 through the oil return pipe 150, the oil balancing pipe 160, and the second branch pipe 140, and finally enters the compressor 110 of the second target outdoor unit 100. In this way, the refrigeration oil is transported from the outdoor unit 100 with more refrigeration oil to the outdoor unit 100 with less refrigeration oil, so as to achieve uniform distribution of the refrigeration oil.

[0048] Taking the heating condition as an example, after it is determined that the refrigerating machine oil of the first target outdoor unit 100 needs to be supplemented to the second target outdoor unit 100, the oil return expansion valve 151 of the first target outdoor unit 100 is closed, and the compressor 110 of the first target outdoor unit 100 is suspended from returning oil through the oil return pipeline 150. Then the oil equalization solenoid valve 161 of the first target outdoor unit 100 is opened, and the frequency of the compressor 110 of the first target outdoor unit 100 is reduced and / or the frequency of the compressor 110 of the second target outdoor unit 100 is increased. In this way, the refrigerating machine oil in the oil separator 114 of the first target outdoor unit 100 will enter the second branch pipeline 140, and enter the indoor unit 200 together with the high-pressure gaseous refrigerant in the second branch pipeline 140. Then the refrigerant is transported from the indoor unit 200 to the outdoor unit 100, and the second target outdoor unit 100 with a higher frequency will naturally obtain more refrigerant and refrigerating machine oil, so as to achieve uniform allocation of the refrigerant.

[0049] Optionally, if it is monitored that there is too much refrigeration oil in both outdoor units 100, the operation can continue; if there is too little refrigeration oil in both outdoor units 100, the frequency of each compressor 110 can be increased, and the refrigeration oil accumulated in the pipeline can be recovered to the compressor 110 by increasing the refrigerant flow rate.

[0050] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application shall be subject to the scope defined by the claims.

Claims

1. An air conditioning system, characterized in that: The invention comprises an indoor unit (200) and at least two outdoor units (100), each of the outdoor units (100) comprising a compressor (110), an outdoor heat exchanger (131), a four-way valve (120), an oil separator (114), a first branch pipeline (130), a second branch pipeline (140), an oil return pipeline (150) and an oil equalizing pipeline (160), an exhaust end of the compressor (110) being connected to the four-way valve (120) via an exhaust side pipeline (111), an intake end of the compressor (110) being connected to the four-way valve (120) via an intake side pipeline (112), and each of the outdoor units (100) ) is connected to the corresponding four-way valve (120) at one end, and the other end is connected to the indoor unit (200) after merging; the second branch pipeline (140) of each outdoor unit (100) is connected to the corresponding four-way valve (120) at one end, and the other end is connected to the indoor unit (200) after merging; the outdoor heat exchanger (131) is arranged on the first branch pipeline (130); the oil separator (114) has an air inlet end, an air outlet end and an oil outlet end; the oil separator (114) is connected to the exhaust side pipeline (111) through the air inlet end and the air outlet end; One end of the oil return pipeline (150) is connected to the oil outlet end of the oil separator (114), and the other end is connected to the air intake side pipeline (112); an oil return expansion valve (151) is provided on the oil return pipeline (150); one end of the oil equalizing pipeline (160) is connected to the oil return pipeline (150) between the oil separator (114) and the oil return expansion valve (151), and the other end is connected to the second branch pipeline (140); an oil equalizing solenoid valve (161) is provided on the oil equalizing pipeline (160).

2. The air conditioning system according to claim 1, characterized in that: A gas-liquid separator (116) is provided on the air intake side pipeline (112), and the oil return pipeline (150) is located upstream of the gas-liquid separator (116) at a connection position with the air intake side pipeline (112).

3. The air conditioning system according to claim 1, characterized in that: The outdoor unit (100) further includes an exhaust temperature sensor (113) for detecting the exhaust temperature of the compressor (110).

4. The air conditioning system according to claim 3, characterized in that: The exhaust temperature sensor (113) is arranged on the exhaust side pipeline (111) between the compressor (110) and the oil separator (114).

5. The air conditioning system according to claim 1, characterized in that: The outdoor unit (100) further comprises an oil temperature sensor (152) for detecting the oil temperature in the oil return pipeline (150).

6. The air conditioning system according to claim 5, characterized in that: The oil temperature sensor (152) is arranged on the oil return pipeline (150) at a side of the oil return expansion valve (151) away from the oil separator (114).

7. The air conditioning system according to claim 1, characterized in that: The outdoor unit (100) also includes a one-way valve (115), which is arranged in the exhaust side pipeline (111) and is located between the outlet end of the oil separator (114) and the four-way valve (120). The one-way valve (115) allows the refrigerant to be transmitted from the oil separator (114) to the four-way valve (120).

8. The air conditioning system according to claim 1, characterized in that: An external expansion valve (132) is provided on the first branch pipeline (130), and the external expansion valve (132) is arranged on a side of the outdoor heat exchanger (131) away from the four-way valve (120).

9. The air conditioning system according to claim 1, characterized in that: The indoor unit (200) comprises an indoor heat exchanger (210) and an indoor expansion valve (220); two ends of the indoor heat exchanger (210) are respectively connected to the first branch pipeline (130) and the second branch pipeline (140) through pipelines; and the indoor expansion valve (220) is arranged on the pipeline between the indoor heat exchanger (210) and the first branch pipeline (130).

10. The air conditioning system according to claim 1, characterized in that: The air conditioning system (010) comprises a plurality of indoor units (200), and the air conditioning system (010) further comprises a first main line (300) and a second main line (400), wherein the first branch lines (130) of each outdoor unit (100) merge into the first main line (300), and the second branch lines (140) of each outdoor unit (100) merge into the second main line (400), and each indoor unit (200) is connected in parallel to the first main line (300) and the second main line (400).

11. A control method for an air conditioning system, applied to the air conditioning system (010) according to any one of claims 1 to 10, characterized in that: include: Determining a first target outdoor unit (100) and a second target outdoor unit (100) among the outdoor units (100) in operation, wherein the first target outdoor unit (100) is the outdoor unit (100) with excessive refrigeration oil, and the second target outdoor unit (100) is the outdoor unit (100) with insufficient refrigeration oil; The oil return expansion valve (151) of the first target outdoor unit (100) is closed, the oil equalizing solenoid valve (161) of the first target outdoor unit (100) is opened, and the frequency of the compressor (110) of the first target outdoor unit (100) is controlled to be lower than the frequency of the compressor (110) of the second target outdoor unit (100).

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