Outdoor unit and multi-connected air conditioning system with same

Abstract

The utility model provides an outdoor unit and a multi-split air-conditioning system with the outdoor unit, the outdoor unit is used on a multi-split air-conditioning system, the outdoor unit comprises a compressor and an oil-liquid separator, and an exhaust port of the compressor is connected with an air inlet of the oil-liquid separator; the outdoor unit further comprises an enthalpy increasing branch, and the enthalpy increasing branch is connected with a refrigerant outlet of the oil-liquid separator and a medium-pressure cavity of the compressor. The oil return branch is respectively connected with an oil outlet of the oil-liquid separator and an air suction port of the compressor; the oil return branch and the enthalpy increasing branch are connected with the compressor through the heat exchange structure; and when the outdoor unit executes enthalpy increasing control, the heat exchange structure is used for transferring at least part of heat in the high-temperature oil in the oil return branch to the refrigerant in the enthalpy increasing branch. The outdoor unit is simple in structure, and can effectively solve the technical problem that in the prior art, part of lost heat of lubricating oil in an oil return pipeline of a multi-split system cannot be fully utilized in the backflow process.

Description

Technical Field

[0001] The utility model relates to the technical field of air conditioners, and particularly relates to an outdoor unit and a multi-connected air conditioner system having the same. Background Art

[0002] At present, to ensure the efficient operation and extended service life of the compressor, the oil return structure in multi-connected units with heat pump or heat recovery functions in commercial multi-connected units usually adopts the scheme of "one or more oil return capillary tubes + oil return solenoid valve". This scheme realizes the refined control of the compressor oil circuit management through the coordinated operation of the main and auxiliary oil return paths.

[0003] Specifically, the main oil return system relies on a single oil return capillary tube that is continuously open to ensure that the lubricating oil precipitated in the oil separator can be smoothly pumped back to the compressor under normal working conditions, providing uninterrupted lubrication guarantee for the compressor. The oil separator, as a key component, is responsible for efficiently separating the lubricating oil from the high-temperature and high-pressure gaseous refrigerant discharged from the compressor, preventing the mixing of the lubricating oil and the refrigerant, and ensuring the efficient and stable operation of the system.

[0004] The auxiliary oil return system intervenes under specific conditions, that is, when the external ambient temperature drops to 15°C or lower, the opening and closing of the auxiliary oil return branch are intelligently controlled through the combination of the oil return capillary tube and the solenoid valve. This design aims to address the challenges that may be encountered during low-temperature heating, such as the increase in the viscosity of the lubricating oil due to low temperature and the possible migration of the refrigerant, which will cause the dilution of the lubricating oil by the refrigerant, thereby affecting the lubrication effect and accelerating the wear of the compressor in the long run. Through the precise control of the solenoid valve, the above problems are effectively prevented, ensuring reliable lubrication and operation of the system in a low-temperature environment.

[0005] However, although the current oil return pipeline design is compact and efficient, there is inevitably a problem of heat dissipation. The temperature of the lubricating oil separated in the oil separator is relatively high. Even if the oil return path is short, part of the heat of the lubricating oil in the pipeline will be dissipated during the return process. This heat dissipation not only means energy loss, and the unused heat energy is lost from the system, but also may affect the overall energy efficiency performance of the system. Summary of the Utility Model

[0006] The purpose of the utility model is to overcome the above technical deficiencies and provide an outdoor unit and a multi-connected air conditioner system having the same, so as to solve the technical problem that part of the heat dissipated by the lubricating oil in the oil return pipeline of the multi-connected unit system in the prior art during the return process is not fully utilized.

[0007] To achieve the above technical objectives, according to one aspect of the present utility model: there is provided an outdoor unit for a multi-connected air conditioner system. The outdoor unit includes: a compressor and an oil separator, and the exhaust port of the compressor is connected to the intake port of the oil separator; the outdoor unit further includes: an enthalpy-increasing branch, which is respectively connected to the refrigerant outlet of the oil separator and the medium-pressure chamber of the compressor; an oil return branch, which is respectively connected to the oil outlet of the oil separator and the suction port of the compressor; a heat exchange structure, and both the oil return branch and the enthalpy-increasing branch are connected to the compressor through the heat exchange structure; wherein, when the outdoor unit performs enthalpy-increasing control, the heat exchange structure transfers at least part of the heat in the high-temperature oil in the oil return branch to the refrigerant in the enthalpy-increasing branch.

[0008] Further, the outdoor unit further includes: a subcooler, which has a first pipeline and a second pipeline, and one end of the first pipeline and one end of the second pipeline are both connected to the refrigerant outlet of the oil separator; the other end of the first pipeline is connected to the indoor unit; a subcooling branch, which is parallel to the enthalpy-increasing branch, and the ends of the subcooling branch and the enthalpy-increasing branch away from the compressor are both connected to the end of the second pipeline away from the refrigerant outlet of the oil separator; a first expansion valve, which is located between the refrigerant outlet of the oil separator and the second pipeline, and the refrigerant outlet of the oil separator is connected to the end of the second pipeline away from the enthalpy-increasing branch through the first expansion valve; the first expansion valve is used to adjust the refrigerant flow rate flowing into the second pipeline.

[0009] Further, the outdoor unit further includes: an outdoor heat exchanger, one end of the outdoor heat exchanger is connected to the refrigerant outlet of the oil separator; the other end of the outdoor heat exchanger is connected to the end of the first expansion valve away from the second pipeline; the first expansion valve is connected to the refrigerant outlet of the oil separator through the outdoor heat exchanger; a control valve, which is respectively connected to the subcooling branch and the enthalpy-increasing branch, and the control valve is used to control the on-off of the subcooling branch or the on-off of the enthalpy-increasing branch; wherein, when the control valve controls the subcooling branch to be in the first cut-off state, the control valve controls the enthalpy-increasing branch to be in the second conduction state; when the control valve controls the subcooling branch to be in the first conduction state, the control valve controls the enthalpy-increasing branch to be in the second cut-off state.

[0010] Further, the outdoor unit further includes: a first flow pipeline and a second expansion valve, one end of the first flow pipeline is connected to the end of the outdoor heat exchanger away from the oil separator, and the other end of the first flow pipeline is respectively connected to the end of the first pipeline close to the oil separator and the end of the second pipeline close to the oil separator; the second expansion valve is arranged on the first flow pipeline; when the multi-connected air conditioner system is in the heating mode, the second expansion valve is used to adjust the refrigerant flow rate flowing into the outdoor heat exchanger.

[0011] Further, the outdoor unit further includes: a four-way valve, a first port A of the four-way valve is connected to a refrigerant outlet of an oil separator, a second port B of the four-way valve is connected to an end of the outdoor heat exchanger away from the subcooler, a third port C of the four-way valve is connected to the indoor unit, and a fourth port D of the four-way valve is connected to a subcooling branch.

[0012] Further, the outdoor unit further includes: a low-pressure sensor disposed at a suction port of the compressor for detecting an evaporation pressure; and / or a gas-liquid separator, an inlet of the gas-liquid separator is connected to an end of the subcooling branch away from the subcooler; and an outlet of the gas-liquid separator is connected to the suction port of the compressor.

[0013] Further, the outdoor unit further includes: a first temperature sensor and a second temperature sensor, the first temperature sensor is disposed at an input end of the second pipeline for detecting a temperature of the refrigerant before entering the subcooler; the second temperature sensor is disposed at an output end of the second pipeline for detecting a temperature of the refrigerant after leaving the subcooler.

[0014] Further, the outdoor unit further includes: a third temperature sensor disposed at an exhaust port of the compressor for detecting an exhaust temperature of the compressor; and / or a high-pressure sensor disposed at a refrigerant outlet of the oil separator and close to the refrigerant outlet of the oil separator for detecting a condensation pressure.

[0015] Further, an oil return regulating valve is provided on the oil return branch, and the oil return regulating valve is located between the oil separator and the heat exchange structure.

[0016] According to another aspect of the present invention, a multi-connected air conditioning system is provided, and the multi-connected air conditioning system includes: an outdoor unit, the outdoor unit is the above-mentioned outdoor unit; and a plurality of indoor units, and the plurality of indoor units are all connected to the outdoor unit.

[0017] Beneficial effects:

[0018] Applying the technical solution of the present utility model, the outdoor unit provided by the present utility model is provided with a compressor, an oil separator, an enthalpy-increasing branch, an oil return branch and a heat exchange structure through simple settings. Moreover, both the oil return branch and the enthalpy-increasing branch are connected to the compressor through the heat exchange structure. Thus, the high-temperature oil coming out of the oil outlet of the oil separator sequentially enters the suction pipe of the compressor through the oil return branch, the heat exchange structure and the suction port of the compressor. When the outdoor unit performs enthalpy-increasing control, the refrigerant entering the enthalpy-increasing branch can exchange heat with the high-temperature oil in the oil return branch through the heat exchange structure, enabling at least part of the heat in the high-temperature oil in the oil return branch to be transferred to the refrigerant in the enthalpy-increasing branch, increasing the temperature of the refrigerant in the enthalpy-increasing branch, and allowing the heated refrigerant to enter the intermediate-pressure chamber of the compressor, so as to further increase the injection enthalpy temperature of the intermediate-pressure chamber of the compressor, thereby increasing the enthalpy value of the refrigerant in the intermediate-pressure chamber of the compressor, enabling the compressor to release more heat during the condensation process, improving the heating efficiency of the multi-split air-conditioning system. Especially at low ambient temperatures, this effect is more significant, effectively enhancing the heating capacity of the multi-split air-conditioning system in cold seasons. At the same time, by increasing the injection enthalpy temperature in the intermediate-pressure chamber of the compressor, the output heat can be increased without increasing the compressor load, indirectly reducing the compression ratio of the compressor and reducing the energy consumption during the compression process, which is beneficial to reducing the operating cost and extending the service life of the compressor. And at extremely low temperatures, increasing the injection enthalpy temperature also helps to reduce the drop in the condensation pressure of the outdoor unit, enabling the multi-split air-conditioning system to still operate efficiently at low ambient temperatures, avoiding the problem of the sharp decline in the heating capacity of the traditional system in low-temperature environments and broadening the applicable range of the multi-split air-conditioning system. In addition, by recycling part of the heat of the high-temperature oil in the oil return branch, the energy efficiency ratio can be effectively improved, reducing the dependence of the outdoor unit on external heat sources and the energy consumption of the outdoor unit, making the multi-split air-conditioning system operate more stably and maintaining good performance even when the external environment changes drastically. The structure of this outdoor unit is simple, effectively solving the technical problem that part of the heat dissipated during the reflux of the lubricating oil in the oil return pipeline of the existing multi-connected unit system fails to be fully utilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. shows a connection schematic diagram of an embodiment of the outdoor unit according to the present utility model.

[0020] Wherein, the above-mentioned drawings include the following reference numerals:

[0021] 1. Compressor; 2. Oil separator; 3. Enthalpy-increasing branch; 4. Oil return branch; 5. Heat exchange structure; 6. Subcooler; 61. First pipeline; 62. Second pipeline; 7. Subcooling branch; 8. First expansion valve; 9. Outdoor heat exchanger; 10. Control valve; 11. First flow pipeline; 12. Second expansion valve; 13. Four-way valve; 14. Low-pressure sensor; 15. Gas-liquid separator; 16. First temperature sensor; 17. Second temperature sensor; 18. Third temperature sensor; 19. High-pressure sensor; 20. Oil return regulating valve; 21. Liquid storage tank; 100. Indoor unit. Detailed implementation manners

[0022] In order to enable those skilled in the art of the present technology to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0023] Please refer to Figure 1 , according to the embodiment of the present utility model, the present utility model provides an outdoor unit for a multi-connected air conditioner system. The outdoor unit includes: a compressor 1 and an oil separator 2, and the exhaust port of the compressor 1 is connected to the intake port of the oil separator 2; the outdoor unit further includes: an enthalpy-increasing branch 3, an oil return branch 4 and a heat exchange structure 5. The enthalpy-increasing branch 3 is respectively connected to the refrigerant outlet of the oil separator 2 and the medium-pressure chamber of the compressor 1; the oil return branch 4 is respectively connected to the oil outlet of the oil separator 2 and the suction port of the compressor 1; both the oil return branch 4 and the enthalpy-increasing branch 3 are connected to the compressor 1 through the heat exchange structure 5; wherein, when the outdoor unit performs enthalpy-increasing control, the heat exchange structure 5 transfers at least part of the heat in the high-temperature oil in the oil return branch 4 to the refrigerant in the enthalpy-increasing branch 3.

[0024] It can be seen that for the outdoor unit provided by the present utility model, by simply arranging a compressor 1, an oil separator 2, an enthalpy-increasing branch 3, an oil return branch 4 and a heat exchange structure 5, and both the oil return branch 4 and the enthalpy-increasing branch 3 are connected to the compressor 1 through the heat exchange structure 5. Then, the high-temperature oil coming out of the oil outlet of the oil separator 2 sequentially enters the suction pipe of the compressor 1 through the oil return branch 4, the heat exchange structure 5 and the suction port of the compressor 1. When the outdoor unit performs enthalpy-increasing control, the refrigerant entering the enthalpy-increasing branch 3 can exchange heat with the high-temperature oil in the oil return branch 4 through the heat exchange structure 5, so that at least part of the heat in the high-temperature oil in the oil return branch 4 is transferred to the refrigerant in the enthalpy-increasing branch 3, raising the temperature of the refrigerant in the enthalpy-increasing branch 3, and the heated refrigerant enters the middle-pressure chamber of the compressor 1, further increasing the injection enthalpy temperature of the middle-pressure chamber of the compressor 1, thereby increasing the enthalpy value of the refrigerant in the middle-pressure chamber of the compressor 1, enabling the compressor to release more heat during the condensation process, improving the heating efficiency of the multi-split air-conditioning system. Especially at low ambient temperatures, this effect is more significant, effectively enhancing the heating capacity of the multi-split air-conditioning system in cold seasons. At the same time, by raising the injection enthalpy temperature in the middle-pressure chamber of the compressor 1, the output heat can be increased without increasing the load of the compressor 1, indirectly reducing the compression ratio of the compressor 1 and reducing the energy consumption during the compression process, which is beneficial to reducing the operating cost and extending the service life of the compressor. And at extremely low temperatures, raising the injection enthalpy temperature also helps to reduce the drop in the condensation pressure of the outdoor unit, enabling the multi-split air-conditioning system to still operate efficiently at low ambient temperatures, avoiding the problem of the sharp decline in the heating capacity of the traditional system in low-temperature environments and broadening the applicable range of the multi-split air-conditioning system. In addition, by recycling part of the heat of the high-temperature oil in the oil return branch 4, the energy efficiency ratio can be effectively improved, reducing the dependence of the outdoor unit on external heat sources and the energy consumption of the outdoor unit, making the multi-split air-conditioning system operate more stably, and maintaining good performance even when the external environment changes drastically. The structure of this outdoor unit is simple and can effectively solve the technical problem that part of the heat dissipated during the reflux of the lubricating oil in the oil return pipeline of the existing multi-connected unit system fails to be fully utilized.

[0025] Preferably, the heat exchange structure 5 is a heat exchanger.

[0026] In this embodiment, the outdoor unit further includes: a subcooler 6, a subcooling branch 7, and a first expansion valve 8. The subcooler 6 has a first pipeline 61 and a second pipeline 62. One end of the first pipeline 61 and one end of the second pipeline 62 are both connected to the refrigerant outlet of the oil separator 2; the other end of the first pipeline 61 is connected to the indoor unit 100; the subcooling branch 7 is connected in parallel with the enthalpy-increasing branch 3. One end of the subcooling branch 7 and the enthalpy-increasing branch 3 away from the compressor 1 are both connected to one end of the second pipeline 62 away from the refrigerant outlet of the oil separator 2; the first expansion valve 8 is located between the refrigerant outlet of the oil separator 2 and the second pipeline 62, and the refrigerant outlet of the oil separator 2 is connected to one end of the second pipeline 62 away from the enthalpy-increasing branch 3 through the first expansion valve 8; the first expansion valve 8 is used to adjust the refrigerant flow rate flowing into the second pipeline 62. With such a structural arrangement, the subcooler 6 can cool the refrigerant entering the indoor unit 100, thereby increasing the evaporation efficiency of the refrigerant in the evaporator of the indoor unit, reducing the risk of liquid refrigerant directly entering the compressor, and avoiding the "liquid hammer" phenomenon. At the same time, the subcooling branch 7 is provided, and the subcooling branch 7 is connected in parallel with the enthalpy-increasing branch 3, which can reduce the proportion of liquid refrigerant that may exist in the evaporator of the indoor unit 100 and further reduce the risk of the "liquid hammer" phenomenon. In addition, the first expansion valve 8 is arranged between the refrigerant outlet of the oil separator 2 and the second pipeline 62, which can accurately adjust the refrigerant flow rate flowing into the second pipeline 62, enabling the outdoor unit to timely adjust the refrigerant amount according to the changes in indoor and outdoor environmental conditions, ensuring the best refrigeration or heating effect, and optimizing the energy use efficiency at the same time.

[0027] Specifically, when the outdoor unit performs enthalpy-increasing control or subcooling control, when the refrigerant flows from the refrigerant outlet of the oil separator 2 to the subcooler 6, it will split into two paths. Part of the refrigerant will flow into the first pipeline 61, and the other part of the refrigerant will flow into the second pipeline 62. The flow rate of the refrigerant flowing into the second pipeline 62 is adjusted by the first expansion valve 8. At the same time, in the subcooler 6, the temperature of the refrigerant in the first pipeline 61 will be transferred to the temperature in the second pipeline 62, so as to reduce the temperature of the refrigerant in the first pipeline 61, and further ensure that the refrigerant in the first pipeline 61 obtains sufficient subcooling degree, thereby reducing the temperature of the refrigerant flowing into the indoor unit 100.

[0028] Specifically, the outdoor unit further includes: an outdoor heat exchanger 9 and a control valve 10. One end of the outdoor heat exchanger 9 is connected to the refrigerant outlet of the oil separator 2; the other end of the outdoor heat exchanger 9 is connected to one end of the first expansion valve 8 away from the second pipeline 62; the first expansion valve 8 is connected to the refrigerant outlet of the oil separator 2 through the outdoor heat exchanger 9; the control valve 10 is respectively connected to the subcooling branch 7 and the enthalpy-increasing branch 3, and the control valve 10 is used to control the on / off of the subcooling branch 7 or the on / off of the enthalpy-increasing branch 3; wherein, when the control valve 10 controls the subcooling branch 7 to be in the first cut-off state, the control valve 10 controls the enthalpy-increasing branch 3 to be in the second conducting state; when the control valve 10 controls the subcooling branch 7 to be in the first conducting state, the control valve 10 controls the enthalpy-increasing branch 3 to be in the second cut-off state. With such a structural arrangement, by providing the outdoor heat exchanger 9, the gaseous refrigerant coming out of the refrigerant outlet of the oil separator 2 can be cooled and converted into a liquid refrigerant. At the same time, by providing the control valve 10 and enabling the control valve 10 to alternately control the subcooling branch 7 and the enthalpy-increasing branch 3, the outdoor unit can be flexibly switched according to the actual operating requirements, achieving an efficient conversion of the operating mode of the multi-connected air-conditioning system.

[0029] Specifically, the outdoor unit further includes: a first flow pipeline 11 and a second expansion valve 12. One end of the first flow pipeline 11 is connected to the end of the outdoor heat exchanger 9 away from the oil separator 2, and the other end of the first flow pipeline 11 is respectively connected to one end of the first pipeline 61 close to the oil separator 2 and one end of the second pipeline 62 close to the oil separator 2; the second expansion valve 12 is arranged on the first flow pipeline 11; when the multi-connected unit system is in the heating mode, the second expansion valve 12 is used to adjust the refrigerant flow rate flowing into the outdoor heat exchanger 9. With such a structural arrangement, one end of the first flow pipeline 11 is connected to the end of the outdoor heat exchanger 9 away from the oil separator 2, the other end of the first flow pipeline 11 is respectively connected to one end of the first pipeline 61 close to the oil separator 2 and one end of the second pipeline 62 close to the oil separator 2, and the second expansion valve 12 is arranged on the first flow pipeline 11, which can adjust the refrigerant flow rate flowing into the outdoor heat exchanger 9 when the multi-connected unit system is heating, thereby playing a role in throttling and reducing the pressure of the refrigerant flowing into the outdoor heat exchanger 9.

[0030] Specifically, the outdoor unit further includes: a four-way valve 13. The first port A of the four-way valve 13 is connected to the refrigerant outlet of the oil separator 2, the second port B of the four-way valve 13 is connected to the end of the outdoor heat exchanger 9 away from the subcooler 6, the third port C of the four-way valve 13 is connected to the indoor unit 100, and the fourth port D of the four-way valve 13 is connected to the subcooling branch 7. With such a structural arrangement, by providing the four-way valve 13, the switching between the refrigeration mode and the heating mode can be realized, and the refrigerant flow direction can be changed, thereby realizing the refrigeration or heating of the indoor unit.

[0031] Specifically, the outdoor unit further includes: a low-pressure sensor 14, which is arranged at the suction port of the compressor 1 and is used to detect the evaporation pressure. With such a structural arrangement, by setting the low-pressure sensor 14, the evaporation pressure can be monitored in real time to ensure the efficient, stable, and safe operation of the outdoor unit.

[0032] Specifically, the outdoor unit further includes: a gas-liquid separator 15, the inlet of the gas-liquid separator 15 is connected to the end of the subcooling branch 7 away from the subcooler 6; thus, the outlet of the gas-liquid separator 15 is connected to the suction port of the compressor 1. With such a structural arrangement, by setting the gas-liquid separator 15, it is possible to prevent liquid refrigerant from directly entering the compressor 1, effectively reducing the risk of "liquid slugging" and protecting the safe operation of the compressor 1.

[0033] Specifically, the outdoor unit further includes: a first temperature sensor 16 and a second temperature sensor 17. The first temperature sensor 16 is arranged at the input end of the second pipeline 62 to detect the temperature of the refrigerant before entering the subcooler 6; the second temperature sensor 17 is arranged at the output end of the second pipeline 62 to detect the temperature of the refrigerant after leaving the subcooler 6. With such a structural arrangement, by setting the first temperature sensor 16 at the input end of the second pipeline 62 and the second temperature sensor 17 at the output end of the second pipeline 62, the temperature of the refrigerant before entering the second pipeline 62 of the subcooler 6 and the temperature of the refrigerant after leaving the second pipeline 62 of the subcooler 6 can be detected in real time. Furthermore, the actual superheat degree of the subcooler 6 can be obtained in real time, and thus the opening degree of the first expansion valve 8 can be accurately adjusted through the actual superheat degree of the subcooler 6.

[0034] Specifically, the outdoor unit further includes: a third temperature sensor 18, which is arranged at the exhaust port of the compressor 1 to detect the exhaust temperature of the compressor 1. With such a structural arrangement, by setting the third temperature sensor 18 at the exhaust port of the compressor 1, the exhaust temperature of the compressor 1 can be detected in real time, so as to be able to promptly detect abnormal high-temperature situations, prevent the compressor from overheating, and be able to timely adjust the working state of the outdoor unit according to the detected exhaust temperature of the compressor 1, thereby improving the stability of the multi-split air-conditioning system.

[0035] Specifically, the outdoor unit further includes: a high-pressure sensor 19, which is arranged at the refrigerant outlet of the oil separator 2 and is close to the refrigerant outlet of the oil separator 2, and the high-pressure sensor 19 is used to detect the condensation pressure. With such a structural arrangement, setting the high-pressure sensor 19 at the refrigerant outlet of the oil separator 2 can monitor the condensation pressure in real time, thereby ensuring the efficient, stable, and safe operation of the outdoor unit.

[0036] In this embodiment, an oil return regulating valve 20 is provided on the oil return branch 4, and the oil return regulating valve 20 is located between the oil separator 2 and the heat exchange structure 5. With such a structural arrangement, by providing the oil return regulating valve 20 on the oil return branch 4, the outdoor unit can dynamically adjust the oil return amount according to the actual operating conditions, instead of simply designing the specification of the oil return capillary according to the worst conditions. Under non-severe operating conditions, the bypass amount can be reduced through the oil return regulating valve 20, avoiding the problem that a large amount of refrigerant bypasses through the oil return branch, resulting in an abnormal increase in the low-pressure of the system, thereby ensuring an appropriate flow rate and evaporation amount of the refrigerant in the indoor unit 100. At the same time, through the precise control of the oil return regulating valve 20, excessive bypass of the refrigerant under non-extreme conditions can be avoided, reducing energy waste caused by bypass and improving the overall energy efficiency ratio of the outdoor unit. This not only improves the refrigeration or heating efficiency but also reduces the unnecessary load on the compressor 1 and extends the service life of the equipment. In addition, the oil return regulating valve 20 can dynamically adjust the oil return flow according to the actual operating frequency of the compressor 1 and the system load, helping to maintain the pressure stability on the low-pressure side of the compressor 1 and being able to adapt to the lubrication requirements of the compressor 1 when changing from low frequency to high frequency, ensuring that the compressor 1 can obtain an appropriate lubricating oil supply at various frequencies.

[0037] Specifically, to provide a storage space for the excess liquid refrigerant, the outdoor unit further includes a liquid storage tank 21. The liquid storage tank 21 is located between the subcooler 6 and the first flow pipeline 11. One end of the liquid storage tank 21 is connected to the end of the first flow pipeline 11 away from the outdoor heat exchanger 9. The other end of the liquid storage tank 21 is respectively connected to one end of the first pipeline 61 close to the oil separator 2 and one end of the second pipeline 62 close to the oil separator 2. The first flow pipeline 11 is connected to one end of the first pipeline 61 close to the oil separator 2 and one end of the second pipeline 62 close to the oil separator 2 through the liquid storage tank 21 respectively.

[0038] Specifically, the outdoor unit further includes a control module. The control module is respectively connected to the first expansion valve 8, the control valve 10, the second expansion valve 12, the four-way valve 13, the low-pressure sensor 14, the first temperature sensor 16, the second temperature sensor 17, the third temperature sensor 18, the high-pressure sensor 19 and the oil return regulating valve 20 through signals. The control module is used to control the opening degrees of the first expansion valve 8, the second expansion valve 12 and the oil return regulating valve 20, control the switching states of the control valve 10 and the four-way valve 13, and receive the data detected by the low-pressure sensor 14, the first temperature sensor 16, the second temperature sensor 17, the third temperature sensor 18 and the high-pressure sensor 19.

[0039] Specifically, a one-way valve is provided at the inlet of the middle-pressure chamber of the compressor 1 (i.e., the injection enthalpy port of the compressor 1) to prevent the reverse discharge of the refrigerant.

[0040] The present utility model further provides a multi-connected air conditioning system, which includes: an outdoor unit and multiple indoor units 100. The outdoor unit is the outdoor unit of the above-mentioned embodiment; the multiple indoor units 100 are all connected to the outdoor unit. With such a structural arrangement, the heating efficiency of the multi-connected air conditioning system is improved, especially at low ambient temperatures, and this effect is more significant, effectively enhancing the heating capacity of the multi-connected air conditioning system in cold seasons. And it also makes the multi-connected air conditioning system operate more stably, and can maintain good performance even when the external environment changes violently.

[0041] When the multi-connected air conditioning system is in the cooling mode and performs enthalpy-increasing control, the control valve 10 cuts off the subcooling branch 7 (i.e., the subcooling branch 7 is in the first cut-off state) and conducts the enthalpy-increasing branch 3 (i.e., the enthalpy-increasing branch 3 is in the second conducting state). The high-temperature and high-pressure refrigerant coming out from the discharge port of the compressor 1 enters the oil separator 2 through the air inlet of the oil separator 2 to separate the lubricating oil. The separated high-temperature lubricating oil comes out from the oil outlet of the oil separator 2 and sequentially passes through the oil return branch 4, the heat exchange structure 5 and the suction port of the compressor 1 and enters the suction pipe of the compressor 1. And the separated gaseous refrigerant flows out from the refrigerant outlet of the oil separator 2 and sequentially passes through the first port A of the four-way valve 13 and the second port B of the four-way valve 13 and flows into the outdoor heat exchanger 9. The gaseous refrigerant is converted into a liquid refrigerant through the outdoor heat exchanger 9, and then the liquid refrigerant flows out from the outdoor heat exchanger 9 and sequentially passes through the first flow pipeline 11, the second expansion valve 12 (at this time, the second expansion valve 12 is in the fully open state) and the liquid storage tank 21 and enters the first pipeline 61 and the second pipeline 62 of the subcooler 6 respectively. The flow rate of the refrigerant entering the second pipeline 62 is controlled according to the opening degree of the first expansion valve 8. When the refrigerant enters the first pipeline 61 and the second pipeline 62 of the subcooler 6 respectively, the refrigerant in the first pipeline 61 of the subcooler 6 is cooled, and the cooled refrigerant flows into the indoor unit 100. At the same time, the refrigerant in the second pipeline 62 is heated, and the heated refrigerant flows into the enthalpy-increasing branch 3, and then the refrigerant in the enthalpy-increasing branch 3 will enter the middle-pressure cavity of the compressor 1 through the heat exchange structure 5. When the refrigerant in the enthalpy-increasing branch 3 enters the heat exchange structure 5, it will exchange heat with the high-temperature oil in the oil return branch 4 (at this time, the high-temperature oil in the oil return branch 4 also enters the heat exchange structure 5) through the heat exchange structure 5, so that at least part of the heat in the high-temperature oil in the oil return branch 4 is transferred to the refrigerant in the enthalpy-increasing branch 3, increasing the temperature of the refrigerant in the enthalpy-increasing branch 3, and making the heated refrigerant enter the middle-pressure cavity of the compressor 1.

[0042] When the multi-connected air-conditioning system is in the cooling mode and performs subcooling control, the control valve 10 conducts the subcooling branch 7 (i.e., the subcooling branch 7 is in the first conducting state) and cuts off the enthalpy-increasing branch 3 (i.e., the enthalpy-increasing branch 3 is in the second cutting-off state). The high-temperature and high-pressure refrigerant discharged from the outlet of the compressor 1 enters the oil separator 2 through the inlet of the oil separator 2 to separate the lubricating oil. The separated high-temperature lubricating oil exits from the oil outlet of the oil separator 2 and sequentially enters the suction pipe of the compressor 1 through the oil return branch 4, the heat exchange structure 5, and the suction port of the compressor 1. And the separated gaseous refrigerant flows out from the refrigerant outlet of the oil separator 2 and sequentially flows into the outdoor heat exchanger 9 through the first port A and the second port B of the four-way valve 13. The gaseous refrigerant is converted into a liquid refrigerant through the outdoor heat exchanger 9. Then the liquid refrigerant flows out from the outdoor heat exchanger 9 and sequentially enters the first pipeline 61 and the second pipeline 62 of the subcooler 6 through the first flow pipeline 11, the second expansion valve 12 (at this time, the second expansion valve 12 is in the fully open state), and the liquid storage tank 21. The flow rate of the refrigerant entering the second pipeline 62 is controlled according to the opening degree of the first expansion valve 8. When the refrigerant enters the first pipeline 61 and the second pipeline 62 of the subcooler 6 respectively, the refrigerant in the first pipeline 61 of the subcooler 6 is cooled, and the cooled refrigerant flows into the indoor unit 100. At the same time, the refrigerant in the second pipeline 62 flows into the subcooling branch 7, and then the refrigerant in the subcooling branch 7 will sequentially enter the suction pipe of the compressor 1 through the gas-liquid separator 15 and the suction port of the compressor 1. When the multi-connected air-conditioning system performs subcooling control, there is no heat exchange process, and the oil return branch 4 only functions as an oil return bypass.

[0043] When the multi-connected air-conditioning system is in the cooling mode and performs static control, the opening degree of the first expansion valve 8 is 0 (i.e., the first expansion valve 8 is in the closed state). The high-temperature and high-pressure refrigerant discharged from the outlet of the compressor 1 enters the oil separator 2 through the inlet of the oil separator 2 to separate the lubricating oil. The separated high-temperature lubricating oil exits from the oil outlet of the oil separator 2 and sequentially enters the suction pipe of the compressor 1 through the oil return branch 4, the heat exchange structure 5, and the suction port of the compressor 1. And the separated gaseous refrigerant flows out from the refrigerant outlet of the oil separator 2 and sequentially flows into the outdoor heat exchanger 9 through the first port A and the second port B of the four-way valve 13. The gaseous refrigerant is converted into a liquid refrigerant through the outdoor heat exchanger 9. Then the liquid refrigerant flows out from the outdoor heat exchanger 9 and sequentially enters the first pipeline 61 of the subcooler 6 through the first flow pipeline 11, the second expansion valve 12 (at this time, the second expansion valve 12 is in the fully open state), and the liquid storage tank 21, and then flows out from the first pipeline 61 and into the indoor unit 100.

[0044] When the multi-connected air-conditioning system is in the heating mode and performs enthalpy-increasing control, the control valve 10 cuts off the sub-cooling branch 7 (i.e., the sub-cooling branch 7 is in the first cut-off state) and conducts the enthalpy-increasing branch 3 (i.e., the enthalpy-increasing branch 3 is in the second conducting state). The high-temperature and high-pressure refrigerant discharged from the outlet of the compressor 1 enters the oil separator 2 through the air inlet of the oil separator 2 to separate the lubricating oil. The separated high-temperature lubricating oil exits from the oil outlet of the oil separator 2 and sequentially enters the suction pipe of the compressor 1 through the oil return branch 4, the heat exchange structure 5, and the suction port of the compressor 1. And the separated gaseous refrigerant flows out from the refrigerant outlet of the oil separator 2, and sequentially flows into the indoor unit 100 through the first port A of the four-way valve 13 and the third port C of the four-way valve 13 for heat exchange, and the gaseous refrigerant is converted into a liquid refrigerant by the indoor unit 100. Then the liquid refrigerant flows out from the indoor unit 100 and enters the first pipeline 61 of the sub-cooler 6. After the liquid refrigerant flows out from the first pipeline 61, it is divided into two paths. One part of the liquid refrigerant enters the second pipeline 62, and the other part of the liquid refrigerant sequentially passes through the liquid storage tank 21 and the second expansion valve 12 (at this time, the second expansion valve 12 adjusts the opening according to the actual situation) and enters the outdoor heat exchanger 9 for cooling, and then flows out from the outdoor heat exchanger 9 and sequentially passes through the second port B of the four-way valve 13, the fourth port D of the four-way valve 13, the sub-cooling branch 7, the gas-liquid separator 15, and the suction port of the compressor 1 and enters the suction pipe of the compressor 1. At the same time, the refrigerant in the second pipeline 62 will flow into the enthalpy-increasing branch 3, and then the refrigerant in the enthalpy-increasing branch 3 will enter the middle-pressure cavity of the compressor 1 through the heat exchange structure 5. When the refrigerant in the enthalpy-increasing branch 3 enters the heat exchange structure 5, it will exchange heat with the high-temperature oil in the oil return branch 4 (at this time, the high-temperature oil in the oil return branch 4 also enters the heat exchange structure 5) through the heat exchange structure 5, so that at least part of the heat in the high-temperature oil in the oil return branch 4 is transferred to the refrigerant in the enthalpy-increasing branch 3, increasing the temperature of the refrigerant in the enthalpy-increasing branch 3, and the heated refrigerant enters the middle-pressure cavity of the compressor 1.

[0045] When the multi-connected air-conditioning system is in the heating mode and performs subcooling control, the control valve 10 conducts the subcooling branch 7 (i.e., the subcooling branch 7 is in the first conducting state) and cuts off the enthalpy-increasing branch 3 (i.e., the enthalpy-increasing branch 3 is in the second cutting-off state). The high-temperature and high-pressure refrigerant discharged from the outlet of the compressor 1 enters the oil separator 2 through the inlet of the oil separator 2 to separate the lubricating oil. The separated high-temperature lubricating oil flows out from the oil outlet of the oil separator 2 and sequentially enters the suction pipe of the compressor 1 through the oil return branch 4, the heat exchange structure 5, and the suction port of the compressor 1. And the separated gaseous refrigerant flows out from the refrigerant outlet of the oil separator 2, and sequentially passes through the first port A of the four-way valve 13 and the third port C of the four-way valve 13 and flows into the indoor unit 100 for heat exchange, and the gaseous refrigerant is converted into a liquid refrigerant through the indoor unit 100. Then the liquid refrigerant flows out from the indoor unit 100 and enters the first pipeline 61 of the subcooler 6. After flowing out from the first pipeline 61, the liquid refrigerant is divided into two paths. Part of the liquid refrigerant enters the second pipeline 62, and the other part of the liquid refrigerant sequentially passes through the liquid storage tank 21 and the second expansion valve 12 (at this time, the second expansion valve 12 adjusts the opening according to the actual situation) and enters the outdoor heat exchanger 9 for cooling, and then flows out from the outdoor heat exchanger 9 and sequentially passes through the second port B of the four-way valve 13, the fourth port D of the four-way valve 13, the subcooling branch 7, the gas-liquid separator 15, and the suction port of the compressor 1 and enters the suction pipe of the compressor 1. At the same time, the refrigerant in the second pipeline 62 flows into the subcooling branch 7, and then the refrigerant in the subcooling branch 7 will sequentially pass through the gas-liquid separator 15 and the suction port of the compressor 1 and enter the suction pipe of the compressor 1. When the multi-connected air-conditioning system performs subcooling control, there is no heat exchange process, and the oil return branch 4 only functions as an oil return bypass.

[0046] The present utility model further provides a control method, which is used to control the outdoor unit in the above embodiment. The control method includes: obtaining the operating mode of the multi-connected air-conditioning system, and when the multi-connected air-conditioning system is in the cooling mode or the heating mode, determining whether the outdoor unit performs enthalpy-increasing control; when the outdoor unit performs enthalpy-increasing control, controlling at least part of the refrigerant flowing out from the refrigerant outlet of the oil separator 2 to flow onto the enthalpy-increasing branch 3; when the refrigerant in the enthalpy-increasing branch 3 passes through the heat exchange structure 5, the heat exchange structure 5 transfers at least part of the heat in the high-temperature oil in the oil return branch 4 to the refrigerant in the enthalpy-increasing branch 3, so that the heat-exchanged refrigerant flows into the middle-pressure cavity of the compressor 1.

[0047] With such a structural arrangement, when the outdoor unit performs enthalpy-increasing control, the refrigerant entering the enthalpy-increasing branch 3 can exchange heat with the high-temperature oil in the oil return branch 4 through the heat exchange structure 5, so that at least part of the heat in the high-temperature oil in the oil return branch 4 is transferred to the refrigerant in the enthalpy-increasing branch 3, increasing the temperature of the refrigerant in the enthalpy-increasing branch 3, and causing the heated refrigerant to enter the intermediate-pressure chamber of the compressor 1, so as to further increase the enthalpy-increasing temperature of the intermediate-pressure chamber of the compressor 1, thereby increasing the enthalpy value of the refrigerant in the intermediate-pressure chamber of the compressor 1, enabling the compressor to release more heat during the condensation process, improving the heating efficiency of the multi-split air-conditioning system. Especially at low ambient temperatures, this effect is more significant, effectively enhancing the heating capacity of the multi-split air-conditioning system in cold seasons. At the same time, by increasing the enthalpy-increasing temperature in the intermediate-pressure chamber of the compressor 1, the output heat can be increased without increasing the load of the compressor 1, indirectly reducing the compression ratio of the compressor 1 and reducing the energy consumption during the compression process, which is beneficial to reducing the operating cost and extending the service life of the compressor. And at extremely low temperatures, increasing the enthalpy-increasing temperature also helps to reduce the drop in the condensation pressure of the outdoor unit, enabling the multi-split air-conditioning system to still operate efficiently at low ambient temperatures, avoiding the problem of the sharp decline in the heating capacity of the traditional system at low temperatures, and broadening the applicable range of the multi-split air-conditioning system. In addition, by recycling part of the heat of the high-temperature oil in the oil return branch 4, the energy efficiency ratio can be effectively improved, reducing the dependence of the outdoor unit on external heat sources and reducing the energy consumption of the outdoor unit, making the multi-split air-conditioning system operate more stably, and maintaining good performance even when the external environment changes drastically.

[0048] Specifically, when the multi-split air-conditioning system is in the cooling mode, the method for judging whether the outdoor unit performs enthalpy-increasing control includes: when the multi-split air-conditioning system is in the cooling mode, obtaining the actual operating frequency F of the compressor 1 in the current outdoor unit, the saturated condensation temperature C corresponding to the condensation pressure, and the exhaust temperature T; comparing the obtained actual operating frequency F with the allowable enthalpy-increasing operating frequency F 0 comparing the obtained saturated condensation temperature C corresponding to the condensation pressure with the first preset saturated condensation temperature C 1 comparing the obtained exhaust temperature T with the allowable enthalpy-increasing exhaust temperature T 0 comparing, and based on the comparison result of the obtained actual operating frequency F and the allowable enthalpy-increasing operating frequency F 0 the comparison result of the obtained saturated condensation temperature C corresponding to the condensation pressure and the first preset saturated condensation temperature C 1 and the comparison result of the obtained exhaust temperature T and the allowable enthalpy-increasing exhaust temperature T 0 judging whether the outdoor unit performs enthalpy-increasing control; when F≥F 0 , and C≤C 1 , and T≥T 0When the outdoor unit performs enthalpy-increasing control; otherwise, the outdoor unit performs subcooling control or static control. By adopting such a control method, the outdoor unit can automatically adjust the control strategy according to the real-time operating conditions without manual intervention, improving the adaptability and flexibility of the outdoor unit, ensuring efficient operation under various external environments and different working conditions. And it avoids unnecessary energy waste, improving the energy efficiency ratio of the outdoor unit as a whole. In addition, dynamic monitoring and timely adjustment reduce the possibility of abnormal operation of the outdoor unit, helping to detect and avoid potential faults in advance, reducing the maintenance cost and the downtime of the outdoor unit.

[0049] Preferably, the allowable enthalpy-increasing operation frequency F 0 is set to 40HZ, and the first preset saturated condensation temperature C 1 is set to 50°C, and the allowable enthalpy-increasing exhaust temperature T 0 is set to 55°C.

[0050] Among them, the above-mentioned allowable enthalpy-increasing operation frequency F 0 can be understood as the highest safe pressure limit value that the high-pressure side of the system is allowed to reach when implementing enthalpy-increasing control in the air-conditioning system. The above-mentioned allowable enthalpy-increasing exhaust temperature T 0 can be understood as a highest allowable exhaust temperature value set in the air-conditioning system design or operation specifications. When the system performs enthalpy-increasing control, the exhaust temperature should not exceed this set value. The above-mentioned first preset saturated condensation temperature C 1 can be understood as the saturated condensation temperature corresponding to the allowable enthalpy-increasing high pressure, which is a value set according to the design requirements. The allowable enthalpy-increasing high pressure refers to the maximum safe pressure value of the high-pressure side of the condenser allowed by the system design or operation specifications when implementing enthalpy-increasing control.

[0051] Specifically, the method for determining whether the outdoor unit performs subcooling control or static control includes: obtaining the saturated condensation temperature C corresponding to the condensation pressure of the current compressor 1, obtaining the saturated evaporation temperature V corresponding to the evaporation pressure of the current compressor 1, and obtaining the exhaust temperature T of the current compressor 1; comparing the saturated condensation temperature C corresponding to the condensation pressure of the current compressor 1 with the second preset saturated condensation temperature C 2 for comparison, comparing the saturated evaporation temperature V corresponding to the evaporation pressure of the current compressor 1 with the preset saturated evaporation temperature V 0 for comparison, and comparing the exhaust temperature T of the current compressor 1 with the exhaust high-temperature limit temperature T 1 for comparison, so as to, according to the comparison result between the saturated condensation temperature C corresponding to the condensation pressure of the current compressor 1 and the second preset saturated condensation temperature C 2 and the comparison result between the saturated evaporation temperature V corresponding to the evaporation pressure of the current compressor 1 and the preset saturated evaporation temperature V 0The comparison result, and the comparison result between the exhaust temperature T of the current compressor 1 and the exhaust high-temperature limit temperature T 1 The method for judging whether the outdoor unit performs subcooling control or static control; when within the first preset duration, continuously C≥C 2 And / or, when within the second preset duration, continuously V≤V 0 And / or, when within the third preset duration, continuously T≥T 1 The outdoor unit performs subcooling control; otherwise, it performs static control. By adopting such a control method, through the comparison result between the saturation condensation temperature C corresponding to the condensation pressure of the current compressor 1 and the second preset saturation condensation temperature C 2 The comparison result, the saturation evaporation temperature V corresponding to the evaporation pressure of the current compressor 1 and the preset saturation evaporation temperature V 0 The comparison result, and the comparison result between the exhaust temperature T of the current compressor 1 and the exhaust high-temperature limit temperature T 1 The comparison result, judging whether the outdoor unit performs subcooling control or static control can keep the outdoor unit in the best state, avoid subcooling or overheating, thereby maximizing the energy efficiency ratio and reducing energy consumption. In addition, by real-time monitoring and controlling the condensation temperature, evaporation temperature and exhaust temperature, it can effectively prevent the compressor from overheating or equipment damage caused by abnormal refrigerant state, and extend the service life of the compressor and the entire system.

[0052] Among them, the above-mentioned preset saturation evaporation temperature V 0 Can be understood as the saturation evaporation temperature corresponding to the lowest operating pressure threshold set by the compressor (i.e., the limit low pressure of the compressor 1), and this preset saturation evaporation temperature V 0 Is set when designing this outdoor unit. The above-mentioned second preset saturation condensation temperature C 2 Can be understood as the upper limit value of the saturation condensation temperature C corresponding to the condensation pressure of the compressor 1 (i.e., the upper limit value of the saturation condensation temperature set for the condensation pressure of the compressor 1). The above-mentioned exhaust high-temperature limit temperature T 1 Refers to the highest safe operating limit value of the exhaust temperature of the compressor 1.

[0053] Preferably, C 2 = 1 +5°C.

[0054] Preferably, the first preset duration is 2 minutes, the second preset duration is 1 minute, the third preset duration is 1 minute, and the exhaust high-temperature limit temperature T 1 Is set to 95°C.

[0055] Furthermore, the actual process of the method for judging whether the outdoor unit performs subcooling control or static control is as follows:

[0056] Obtain the saturated condensation temperature C corresponding to the condensation pressure of the compressor 1 in real time, the saturated evaporation temperature V corresponding to the evaporation pressure of the compressor 1, and the exhaust temperature T of the compressor 1. When within 2 consecutive minutes (within the first preset duration), C ≥ C 2 ; and / or, when within 1 consecutive minute (within the second preset duration) V ≤ V 0 ; and / or, when within 1 consecutive minute (within the third preset duration) T ≥ T 1 , the outdoor unit performs subcooling control, otherwise the outdoor unit performs static control.

[0057] Specifically, when the multi-split air-conditioning system is in the heating mode, the method for determining whether the outdoor unit performs enthalpy-increasing control includes: when the multi-split air-conditioning system is in the cooling mode, obtain the actual operating frequency F of the compressor 1 in the current outdoor unit, the saturated condensation temperature C corresponding to the condensation pressure, and the exhaust temperature T, as well as the outer ring temperature H of the outdoor unit; compare the obtained actual operating frequency F with the allowable enthalpy injection operating frequency F 0 , compare the obtained saturated condensation temperature C corresponding to the condensation pressure with the first preset saturated condensation temperature C 1 , compare the obtained exhaust temperature T with the allowable enthalpy injection exhaust temperature T 0 , and compare the obtained outer ring temperature H of the outdoor unit with the allowable temperature H 0 to determine whether the outdoor unit performs enthalpy-increasing control according to the comparison result of the obtained actual operating frequency F and the allowable enthalpy injection operating frequency F 0 , the comparison result of the obtained saturated condensation temperature C corresponding to the condensation pressure and the first preset saturated condensation temperature C 1 , the comparison result of the obtained exhaust temperature T and the allowable enthalpy injection exhaust temperature T 0 , and the comparison result of the obtained outer ring temperature H of the outdoor unit and the allowable temperature H 0 ; when F ≥ F 0 , and C ≤ C 1 , and T ≥ T 0 , and H ≤ H 0 , the outdoor unit performs enthalpy-increasing control; otherwise, the outdoor unit performs subcooling control. By adopting such a method, the outdoor unit can automatically adjust the control strategy according to the real-time operating conditions, without manual intervention, improving the self-adaptability and flexibility of the outdoor unit, ensuring efficient operation under various external environments and different working conditions. And it avoids unnecessary energy waste, overall improving the energy efficiency ratio of the outdoor unit. In addition, dynamic monitoring and timely adjustment reduce the possibility of abnormal operation of the outdoor unit, help to detect and avoid potential faults in advance, reducing the maintenance cost and the downtime of the outdoor unit. In addition, adjust the execution status of the outdoor unit according to the outer ring temperature H of the outdoor unit to maintain indoor comfort while optimizing energy consumption.

[0058] Among them, the outer ring temperature H of the outdoor unit refers to the temperature of the outdoor environment. The allowable temperature H 0 refers to the suitable operating temperature that the outdoor unit should maintain.

[0059] Preferably, the allowable temperature H 0 is set to 15°C.

[0060] Specifically, when the outdoor unit performs enthalpy-increasing control, the first expansion valve 8 is opened, and the opening degree O n of the first expansion valve 8 is adjusted to the first initial opening degree v 0 ; and after the compressor 1 continuously operates for the fourth preset duration, according to the first preset period, the actual superheat degree ΔL of the current outdoor unit's subcooler is obtained, and based on the actual superheat degree ΔL of the current outdoor unit's subcooler, the adjusted opening degree O (+1) of the first expansion valve 8 is calculated, and the current opening degree O n of the first expansion valve 8 is adjusted accordingly; the formula for calculating the adjusted opening degree O (+1) of the first expansion valve 8 is as follows: O (+1) = n + 1 *(ΔL - 1 ); where O n is the current opening degree of the first expansion valve 8, K 1 is the first electronic expansion valve adjustment ratio multiple, M 1 is the first target superheat degree of the subcooler. And n can be understood as the number of times the opening degree of the first expansion valve 8 is adjusted, and n + 1 can be understood as the count for the next adjustment. By adopting such a method, by obtaining the actual superheat degree ΔL of the subcooler in real time every first preset period and adjusting the opening degree O (+1) of the first expansion valve 8 according to the obtained actual superheat degree ΔL of the current outdoor unit's subcooler, the refrigerant flow rate flowing into the enthalpy-increasing branch 3 can be accurately controlled to ensure the temperature of the refrigerant entering the enthalpy-increasing branch 3.

[0061] Specifically, the actual superheat degree ΔL of the current outdoor unit's subcooler is equal to the difference between the outlet pipe temperature and the inlet pipe temperature of the current subcooler 6.

[0062] Preferably, the first initial opening degree O 0 is 50 PLS, the fourth preset duration is 1 minute, the first preset period is 40 seconds, and the first target superheat degree M 1 of the subcooler is 1°C.

[0063] Among them, the above-mentioned first target superheat degree M 1 refers to the reference value set for the superheat degree of the subcooler 6. PLS is the step unit of the valve.

[0064] Specifically, the first electronic expansion valve adjustment ratio multiple K 1The value of

[0065] When |ΔL| ≥ 4*M 1 At this time, K 1 = 3.

[0066] When 2* 1 ≤ |ΔL| < 4*M 1 At this time, K 1 = 2.5.

[0067] When M 1 ≤ |ΔL| < 2*M 1 At this time, K 1 = 1.5.

[0068] When |ΔL| < 1 At this time, K 1 = 1.

[0069] Specifically, when the outdoor unit performs enthalpy-increasing control, the control valve 10 controls the subcooling branch 7 to be in the first cut-off state and controls the enthalpy-increasing branch 3 to be in the second conduction state.

[0070] Furthermore, when the outdoor unit performs enthalpy-increasing control, the process of adjusting the first expansion valve 8 is as follows:

[0071] When the outdoor unit starts to perform enthalpy-increasing control, open the first expansion valve 8 and adjust the opening degree of the first expansion valve 8 to 50 PLS (i.e., the first initial opening degree O 0 ). After the compressor 1 continuously operates for 1 minute (i.e., the fourth preset duration), every 40 seconds (i.e., the first preset period), obtain the actual superheat degree ΔL of the outdoor unit's subcooler. According to the obtained actual superheat degree ΔL of the outdoor unit's subcooler, calculate the adjusted opening degree O (+1) of the first expansion valve 8, and make corresponding adjustments to the current opening degree O n of the first expansion valve 8.

[0072] Specifically, when the outdoor unit performs subcooling control, open the first expansion valve 8 and adjust the opening degree O n of the first expansion valve 8 to the second initial opening degree O 1 ; and after the compressor 1 continuously operates for the fifth preset duration, obtain the actual superheat degree ΔL of the outdoor unit's subcooler at the second preset period. According to the current actual superheat degree ΔL of the outdoor unit's subcooler, calculate the adjusted opening degree O (+1) of the first expansion valve 8, and make corresponding adjustments to the current opening degree O n of the first expansion valve 8; the formula for calculating the adjusted opening degree O (+1) of the first expansion valve 8 is as follows: O (+1) = n + 2 *(ΔL - 2); where, O n is the opening degree of the current first expansion valve 8, K 2 is the adjustment ratio multiple of the second electronic expansion valve, M 2 is the superheat of the second target subcooler. And n can be understood as the number of times the opening degree of the first expansion valve 8 is adjusted, and n + 1 can be understood as the count of the next adjustment. By adopting such a method, the actual subcooler superheat ΔL is obtained in real time every second preset period, and the opening degree O of the first expansion valve 8 is adjusted according to the obtained actual subcooler superheat ΔL of the current outdoor unit (+1) can accurately control the refrigerant flow rate flowing into the subcooling branch 7.

[0073] Preferably, the second initial opening degree O 1 is 80 PLS, the fifth preset duration is 1 minute, the second preset period is 40 seconds, and the second target subcooler superheat M 2 is 2°C.

[0074] Among them, the above-mentioned second target subcooler superheat M 2 refers to the reference value set for the superheat of the subcooler 6. PLS is the step unit of the valve.

[0075] Specifically, the adjustment ratio multiple K of the second electronic expansion valve 2 takes the following values:

[0076] When |ΔL| ≥ 3 * M 2 then, K 2 = 8.

[0077] When M 2 ≤ |ΔL| < 3 * M 2 then, K 2 = 4.

[0078] When |ΔL| < 2 then, K 2 = 2.

[0079] Specifically, when the outdoor unit executes subcooling control, the control valve 10 controls the subcooling branch 7 to be in the first conduction state and controls the enthalpy-increasing branch 3 to be in the second cut-off state.

[0080] Furthermore, when the outdoor unit executes subcooling control, the process of adjusting the first expansion valve 8 is as follows:

[0081] When the outdoor unit starts to execute subcooling control, open the first expansion valve 8 and adjust the opening degree of the first expansion valve 8 to 80 PLS (i.e., the second initial opening degree O 1) After the compressor 1 continuously operates for 1 minute (i.e., the fifth preset duration), every 40 seconds (i.e., the second preset period), the actual superheat degree ΔL of the outdoor unit's subcooler is obtained, and based on the obtained actual superheat degree ΔL of the outdoor unit's subcooler, the opening degree O of the adjusted first expansion valve 8 is calculated. (+1) , and the current opening degree O of the first expansion valve 8 n is adjusted accordingly.

[0082] Specifically, when the outdoor unit executes static control, the first expansion valve 8 is closed (i.e., the opening degree of the first expansion valve 8 is adjusted to 0 PLS).

[0083] In this embodiment, the control method further includes: obtaining the operating mode of the multi-split air-conditioning system; when the multi-split air-conditioning system is in the initial startup mode, judging the oil return pre-control method of the outdoor unit according to at least one of the outdoor ambient temperature, the state of the outdoor unit, the capacity demand of the outdoor unit, and the compressor state; when the multi-split air-conditioning system is in other modes except the initial startup mode, judging whether the outdoor unit executes oil return pre-control according to the change amount of the capacity demand of the compressor 1. By adopting such a control method, in the initial startup mode, the compressor can quickly judge and select the most suitable oil return pre-control method according to conditions such as the outdoor ambient temperature and the state of the outdoor unit. This helps to accelerate the speed of the compressor reaching the stable operation state, shorten the time to reach the set temperature, and improve the user experience. And in the non-initial startup mode, deciding whether to execute oil return pre-control according to the change amount of the capacity demand of the compressor can more precisely control the lubrication state of the compressor, prevent compressor wear or damage caused by poor oil circulation, and extend the service life of the compressor. In addition, dynamically adjusting the oil return control strategy according to the actual operating conditions can maintain the balance of the oil circuit and refrigerant circulation inside the outdoor unit, reduce the operation fluctuations of the outdoor unit caused by unstable oil temperature and oil pressure, improve the stability and reliability of the outdoor unit, and effectively reduce unnecessary energy consumption. At the same time, by prophylactically managing the oil return problem of the compressor and reducing the failures caused by poor lubrication, the maintenance and repair costs can be reduced in the long run, and the economy of the system can be improved.

[0084] Among them, the change amount of the capacity demand of the compressor 1 mentioned above refers to the increase or decrease amount of the actual refrigeration or heating capacity that the compressor actually needs to provide for a certain reference state.

[0085] Specifically, when the multi-connected air conditioning system is in the initial startup mode, a method for determining the oil return pre-control mode of the outdoor unit according to at least one of the outdoor ambient temperature, the status of the outdoor unit, the capacity demand of the outdoor unit, and the compressor status includes: obtaining the current outdoor ambient temperature, the status of the outdoor unit, the capacity demand of the outdoor unit, and the compressor status; when within the sixth preset time period, the outdoor ambient temperature continuously remains less than or equal to the first preset ambient temperature, and the outdoor unit is in the first power-on state, and within the seventh preset time period, the capacity demand of the outdoor unit continuously remains zero, and the compressor 1 is in the unstarted state, the outdoor unit performs forced oil return; when the outdoor unit performs forced oil return, at the first preset time before the startup of the compressor 1, the opening degree of the oil return regulating valve 20 is adjusted to the third initial opening degree, and after maintaining the eighth preset time period, the opening degree of the oil return regulating valve 20 is adjusted according to the operating condition of the compressor 1. By adopting such a control method, when within the sixth preset time period, the outdoor ambient temperature continuously remains less than or equal to the first preset ambient temperature, and the outdoor unit is in the first power-on state, and within the seventh preset time period, the capacity demand of the outdoor unit continuously remains zero, and the compressor 1 is in the unstarted state, the outdoor unit performs forced oil return to prevent the refrigerant and lubricating oil from changing after being placed for a long time and unable to return the lubricating oil to the compressor. By performing forced oil return, it is ensured that during the operation of the multi-connected air conditioning system, the lubricating oil of the compressor can effectively and timely return from the evaporator to the compressor, avoiding oil shortage lubrication of the compressor, thereby protecting the compressor and maintaining the long-term stable operation of the system. In addition, through the precise control of the oil return regulating valve 20, excessive bypass of the refrigerant under non-extreme conditions can be avoided, reducing energy waste caused by bypass, and improving the overall energy efficiency ratio of the outdoor unit. This not only improves the refrigeration or heating efficiency but also reduces the unnecessary load on the compressor 1 and extends the service life of the equipment.

[0086] Among them, the opening degree of the oil return regulating valve 20 is adjusted to the third initial opening degree, and after maintaining the eighth preset time period, the opening degree of the oil return regulating valve 20 is adjusted according to the operating condition of the compressor 1. Thus, it can be seen that during the maintenance stage, it can effectively ensure the preliminary establishment of the compressor oil path and the start of effective oil return, providing good lubrication conditions for the smooth startup and initial operation of the compressor. "Adjusting the opening degree of the oil return regulating valve 20 according to the operating condition of the compressor 1" can promptly respond to the changes in the working state of the compressor, further optimize the oil return efficiency, reduce energy consumption, and at the same time protect the compressor from wear or failure caused by poor lubrication.

[0087] Among them, the capacity demand of the above-mentioned outdoor unit refers to the refrigeration or heating capacity that the outdoor unit needs to provide to meet the indoor cooling and heating load demands during the operation of the air conditioning system. The above-mentioned forced oil return is an active and relatively strong oil return control method, which can be understood as a technical measure to strengthen the return of lubricating oil to the compressor.

[0088] Preferably, the sixth preset duration is 3 seconds, the first preset ambient temperature is -15°C, the seventh preset duration is 2 minutes, the first preset time is 5 seconds, and the eighth preset duration is 120 seconds.

[0089] Specifically, the third initial opening degree value in "adjust the opening degree of the oil return regulating valve 20 to the third initial opening degree at the first preset time before the compressor 1 starts" is equal to the product of {the operating frequency of the current compressor, the saturated condensation temperature corresponding to the condensation pressure of the current compressor, the saturated temperature corresponding to the evaporation pressure of the current compressor, the exhaust superheat degree of the current compressor} and the first initialization opening degree correction value Y 1 The product.

[0090] Among them, {the operating frequency of the current compressor, the saturated condensation temperature corresponding to the condensation pressure of the current compressor, the saturated temperature corresponding to the evaporation pressure of the current compressor, the exhaust superheat degree of the current compressor} can be understood as a function, which is a parameter jointly determined by the operating frequency of the current compressor, the saturated condensation temperature corresponding to the condensation pressure of the current compressor, the saturated temperature corresponding to the evaporation pressure of the current compressor, and the exhaust superheat degree of the current compressor. It is obtained through experiments and is a preset value in advance.

[0091] Among them, the first initialization opening degree correction value Y 1 is determined according to the system design requirements, experimental data analysis, and actual operation experience. This correction value is used to fine-tune the setting of the third initial opening degree of the oil return regulating valve 20.

[0092] Furthermore, the process of the outdoor unit performing forced oil return is as follows:

[0093] First, the conditions for performing forced oil return need to simultaneously meet the following conditions:

[0094] 1. The outdoor unit is powered on for the first time.

[0095] 2. Continuously for 3 seconds (i.e., the sixth preset duration), detect that the outdoor ambient temperature is less than or equal to -15°C (i.e., the first preset ambient temperature).

[0096] 3. Continuously for 2 minutes (i.e., the seventh preset duration), the capacity demand of the outdoor unit has been maintained in the shutdown state (i.e., the capacity demand of the outdoor unit is equal to 0).

[0097] 4. The compressor of the outdoor unit is in the unstarted state (i.e., the frequency of the compressor is equal to 0).

[0098] Secondly, when the outdoor unit performs forced oil return, 5 seconds (i.e., the first preset time) before the compressor 1 is about to start, adjust the opening degree of the oil return regulating valve 20 to the third initial opening degree. After maintaining for 120 seconds (i.e., the eighth preset duration), adjust the opening degree of the oil return regulating valve 20 according to the operating condition of the compressor 1.

[0099] Specifically, when the multi-connected air-conditioning system is in the initial startup mode, a method for judging the oil return pre-control mode of the outdoor unit according to at least one of the outdoor environmental temperature, the state of the outdoor unit, the capacity demand of the outdoor unit, and the compressor state further includes: obtaining the current outdoor environmental temperature; when the outdoor environmental temperature continuously is greater than or equal to the second preset environmental temperature within the sixth preset time period, the outdoor unit performs normal oil return pre-control; when the outdoor unit performs normal oil return, when the compressor 1 starts, the opening degree of the oil return regulating valve 20 is adjusted to the fourth initial opening degree, and after maintaining for the ninth preset time period, the opening degree of the oil return regulating valve 20 is adjusted according to the operating condition of the compressor 1; when the outdoor environmental temperature continuously is greater than the first preset environmental temperature and less than the second preset environmental temperature within the sixth preset time period, it is judged whether the outdoor unit is in the first power-on state; when the outdoor unit is in the first power-on state, the outdoor unit performs strong oil return; when the outdoor unit is not in the first power-on state, the outdoor unit performs normal oil return. By adopting such a control method, when the outdoor environmental temperature continuously is greater than or equal to the second preset environmental temperature within the sixth preset time period, the outdoor unit performs normal oil return pre-control, which can timely return the lubricating oil to the compressor, avoid the decline of lubricating performance caused by too high oil temperature, and protect the compressor from damage. Ensure that under continuous high-temperature weather, the refrigerant can continuously and effectively return to the compressor, maintain the necessary lubrication, reduce wear, and extend the life of the compressor. In addition, through the precise control of the oil return regulating valve 20, excessive bypass of the refrigerant under non-extreme conditions can be avoided, energy waste caused by bypass can be reduced, and the overall energy efficiency ratio of the outdoor unit can be improved. This not only improves the refrigeration or heating efficiency, but also reduces the unnecessary load of the compressor 1 and extends the service life of the equipment.

[0100] Among them, the above-mentioned normal oil return refers to a more gentle and continuous oil return control method. Normal oil return can naturally promote the circulation of the lubricating oil, without special intervention or additional energy consumption. Normal oil return ensures that the lubricating oil can stably and continuously return to the compressor during daily operation, maintaining the basic lubrication requirements.

[0101] Preferably, the second preset environmental temperature is -5°C, and the ninth preset time period is 10 seconds.

[0102] Specifically, the value of the fourth initial opening degree in the above-mentioned "when the compressor 1 starts, the opening degree of the oil return regulating valve 20 is adjusted to the fourth initial opening degree" is equal to the product of {the operating frequency of the current compressor, the saturation condensing temperature corresponding to the condensing pressure of the current compressor, the saturation temperature corresponding to the evaporation pressure of the current compressor, the exhaust superheat degree of the current compressor} and the second initialization opening degree correction value Y 2 and.

[0103] Among them, {the operating frequency of the current compressor, the saturation condensing temperature corresponding to the condensing pressure of the current compressor, the saturation temperature corresponding to the evaporation pressure of the current compressor, the exhaust superheat of the current compressor} can be understood as a function, which is a parameter jointly determined by the operating frequency of the current compressor, the saturation condensing temperature corresponding to the condensing pressure of the current compressor, the saturation temperature corresponding to the evaporation pressure of the current compressor, and the exhaust superheat of the current compressor. It is obtained through experiments and is a preset value in advance.

[0104] Specifically, the second initialization opening correction value Y 2 takes the value of:

[0105] When the average outdoor ambient temperature is greater than 10 and less than 60 for the tenth consecutive preset duration, Y 2 = 1.

[0106] When the average outdoor ambient temperature is greater than 5 and less than or equal to 10 for the tenth consecutive preset duration, Y 2 = 1.05.

[0107] When the average outdoor ambient temperature is greater than 0 and less than or equal to 5 for the tenth consecutive preset duration, Y 2 = 1.1.

[0108] When the average outdoor ambient temperature is greater than -5 and less than or equal to 0 for the tenth consecutive preset duration, Y 2 = 1.15.

[0109] Preferably, the tenth preset duration is 3 seconds.

[0110] Furthermore, the process for the outdoor unit to perform regular oil return is as follows:

[0111] First, the conditions for performing regular oil return need to meet the following conditions:

[0112] For 3 consecutive seconds (i.e., the sixth preset duration), it is detected that the outdoor ambient temperature is greater than or equal to -5°C (i.e., the second preset ambient temperature).

[0113] Second, when the outdoor unit performs regular oil return, when the compressor 1 starts, the opening of the oil return regulating valve 20 is adjusted to the fourth initial opening. After maintaining for 10 seconds (i.e., the eighth preset duration), the opening of the oil return regulating valve 20 is adjusted according to the operating condition of the compressor 1.

[0114] Specifically, when the multi-connected air-conditioning system is in a mode other than the initial startup mode, a method for determining whether the outdoor unit performs pre-oil return control according to the change amount of the capacity demand of the compressor 1 includes: obtaining the change amount of the capacity demand of the current compressor 1; comparing the change amount of the capacity demand of the current compressor 1 with a preset change amount, and determining whether the outdoor unit performs pre-oil return control according to the comparison result of the change amount of the capacity demand of the current compressor 1 and the preset change amount; when the change amount of the capacity demand of the current compressor 1 is greater than or equal to the preset change amount, the outdoor unit performs pre-oil return control; when the outdoor unit performs pre-oil return control, obtain the actual operating frequency that the current compressor 1 needs to execute at a third preset period; within an eleventh preset duration, adjust the opening degree of the oil return regulating valve 20 accordingly according to the actual operating frequency that the current compressor 1 needs to execute. By adopting such a control method, through the comparison between the preset change amount and the actual change amount of the capacity demand, pre-oil return control can be taken before the significant change of the compressor load, effectively preventing compressor wear or failure caused by poor lubrication, extending the service life of the compressor, and reducing the maintenance cost. And the timely oil return control ensures that the compressor can obtain appropriate lubrication under any load change, reducing the additional energy consumption caused by improper lubrication and improving the energy efficiency ratio of the system. And it helps to maintain the smoothness of the oil circuit in the system, avoiding system pressure fluctuations caused by poor oil circulation, and enhancing the stability and reliability of the system.

[0115] Preferably, the preset change amount is 20%.

[0116] Specifically, the specific process of obtaining the actual operating frequency that the current compressor 1 needs to execute at a third preset period is as follows:

[0117] At a third preset period, the main chip in the multi-connected air-conditioning system will fit and calculate the operating frequency that the compressor 1 needs to execute according to the final capacity demand of the outdoor unit, and then compare the operating frequency that the compressor 1 needs to execute, which is obtained by the main chip's fitting calculation, with the final compressor target frequency, and obtain the actual operating frequency that the compressor 1 needs to execute according to the comparison result of the operating frequency that the compressor 1 needs to execute, which is obtained by the main chip's fitting calculation, and the final compressor target frequency.

[0118] When the operating frequency that the compressor 1 needs to execute, which is obtained by the main chip's fitting calculation, is greater than or equal to the final compressor target frequency, the actual operating frequency that the compressor 1 needs to execute is equal to the final compressor target frequency.

[0119] When the operating frequency that the compressor 1 needs to execute, which is obtained by the main chip's fitting calculation, is less than the final compressor target frequency, the actual operating frequency that the compressor 1 needs to execute is equal to the operating frequency that the compressor 1 needs to execute, which is obtained by the main chip's fitting calculation.

[0120] Among them, the final capacity requirement of the outdoor unit refers to the maximum or most suitable cooling or heating power that the outdoor unit should provide in order to maintain or achieve the set indoor environmental comfort under the current outdoor environmental conditions and indoor temperature and humidity requirements. The final compressor target frequency refers to the ideal operating frequency to which the compressor should be adjusted.

[0121] Further, both the third preset period and the eleventh preset duration are determined according to the time G required for the main chip to obtain the actual operating frequency that the compressor 1 actually needs to execute to the actual frequency adjustment of the compressor based on the final capacity requirement of the outdoor unit.

[0122] Further, when the time G required for the main chip to obtain the actual operating frequency that the compressor 1 actually needs to execute to the actual frequency adjustment of the compressor based on the final capacity requirement of the outdoor unit is greater than 60 seconds, the eleventh preset duration is equal to the time G required for the main chip to obtain the actual operating frequency that the compressor 1 actually needs to execute to the actual frequency adjustment of the compressor based on the final capacity requirement of the outdoor unit. When the time G required for the main chip to obtain the actual operating frequency that the compressor 1 actually needs to execute to the actual frequency adjustment of the compressor based on the final capacity requirement of the outdoor unit is less than or equal to 60 seconds, the eleventh preset duration is equal to 60 seconds.

[0123] Further, the calculation formula for the third preset period is:

[0124] Where S represents the third preset period and A represents the variable value of the outer ring temperature.

[0125] Further, the value of the variable value A of the outer ring temperature is:

[0126] When the outdoor environmental temperature is greater than -40°C and less than -25°C, A = 5.

[0127] When the outdoor environmental temperature is greater than or equal to -25°C and less than -15°C, A = 3.

[0128] When the outdoor environmental temperature is greater than or equal to -15°C and less than 0°C, A = 0.

[0129] When the outdoor environmental temperature is greater than or equal to 0°C and less than 10°C, A = -1.

[0130] When the outdoor environmental temperature is greater than or equal to 10°C and less than 60°C, A = -2.

[0131] Further, when adjusting the operating frequency of the compressor, the saturated condensation temperature corresponding to the condensation pressure of the compressor, the saturated temperature corresponding to the evaporation pressure of the compressor, and the exhaust superheat of the compressor are not adjusted.

[0132] It should be noted that the terms "first", "second", etc. in the description, claims and the above-mentioned drawings of this application are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of this application described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0133] Optionally, the specific examples in this embodiment may refer to the examples described in the above-mentioned embodiments, and will not be elaborated here.

[0134] The serial numbers of the above-mentioned embodiments of this application are only for description and do not represent the advantages or disadvantages of the embodiments.

[0135] In the above-mentioned embodiments of this application, the descriptions of each embodiment have their own focuses. For the parts not elaborated in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0136] The above are only the preferred embodiments of this application. It should be noted that for those of ordinary skill in the art, without departing from the principle of this application, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of this application.

Claims

1. An outdoor unit for use in a multi-split system, the outdoor unit comprising: A compressor (1) and an oil-liquid separator (2), wherein the exhaust port of the compressor (1) is connected to the air inlet of the oil-liquid separator (2); characterized in that the outdoor unit further comprises: An enthalpy-increasing branch (3), the enthalpy-increasing branch (3) being respectively connected to the refrigerant outlet of the oil-liquid separator (2) and the medium-pressure chamber of the compressor (1); An oil return branch (4), the oil return branch (4) being respectively connected to the oil outlet of the oil-liquid separator (2) and the air intake of the compressor (1); A heat exchange structure (5), wherein the oil return branch (4) and the enthalpy increase branch (3) are both connected to the compressor (1) via the heat exchange structure (5); When the outdoor unit performs enthalpy increase control, the heat exchange structure (5) transfers at least part of the heat in the high-temperature oil in the oil return branch (4) to the refrigerant in the enthalpy increase branch (3).

2. The outdoor unit according to claim 1, characterized in that: The outdoor unit further comprises: A subcooler (6), the subcooler (6) comprising a first pipeline (61) and a second pipeline (62), one end of the first pipeline (61) and one end of the second pipeline (62) are both connected to the refrigerant outlet of the oil-liquid separator (2); the other end of the first pipeline (61) is connected to the indoor unit (100); A subcooling branch (7), the subcooling branch (7) being connected in parallel with the enthalpy increasing branch (3), and the ends of the subcooling branch (7) and the enthalpy increasing branch (3) being away from the compressor (1) are both connected to the end of the second pipeline (62) being away from the refrigerant outlet of the oil-liquid separator (2); A first expansion valve (8), wherein the first expansion valve (8) is located between the refrigerant outlet of the oil-liquid separator (2) and the second pipeline (62), and the refrigerant outlet of the oil-liquid separator (2) is connected to an end of the second pipeline (62) away from the enthalpy increase branch (3) through the first expansion valve (8); the first expansion valve (8) is used to adjust the refrigerant flow rate flowing into the second pipeline (62).

3. The outdoor unit according to claim 2, characterized in that: The outdoor unit further comprises: An outdoor heat exchanger (9), one end of the outdoor heat exchanger (9) being connected to the refrigerant outlet of the oil-liquid separator (2); the other end of the outdoor heat exchanger (9) being connected to an end of the first expansion valve (8) away from the second pipeline (62); the first expansion valve (8) being connected to the refrigerant outlet of the oil-liquid separator (2) through the outdoor heat exchanger (9); a control valve (10), the control valve (10) being connected to the subcooling branch (7) and the enthalpy increasing branch (3) respectively, the control valve (10) being used to control the on / off of the subcooling branch (7) or the on / off of the enthalpy increasing branch (3); When the control valve (10) controls the subcooling branch (7) to be in a first cut-off state, the control valve (10) controls the enthalpy increase branch (3) to be in a second conduction state; when the control valve (10) controls the subcooling branch (7) to be in a first conduction state, the control valve (10) controls the enthalpy increase branch (3) to be in a second cut-off state.

4. The outdoor unit according to claim 3, characterized in that: The outdoor unit further comprises: A first circulation pipeline (11) and a second expansion valve (12), wherein one end of the first circulation pipeline (11) is connected to an end of the outdoor heat exchanger (9) away from the oil-liquid separator (2), and the other end of the first circulation pipeline (11) is respectively connected to an end of the first pipeline (61) close to the oil-liquid separator (2) and an end of the second pipeline (62) close to the oil-liquid separator (2); the second expansion valve (12) is arranged on the first circulation pipeline (11); when the multi-split system is in heating mode, the second expansion valve (12) is used to adjust the flow of refrigerant flowing into the outdoor heat exchanger (9).

5. The outdoor unit according to claim 3, characterized in that: The outdoor unit further comprises: a four-way valve (13), a first port A of the four-way valve (13) being connected to the refrigerant outlet of the oil-liquid separator (2), a second port B of the four-way valve (13) being connected to an end of the outdoor heat exchanger (9) away from the subcooler (6), a third port C of the four-way valve (13) being connected to the indoor unit (100), and a fourth port D of the four-way valve (13) being connected to the subcooling branch (7).

6. The outdoor unit according to claim 2, characterized in that: The outdoor unit further comprises: a low pressure sensor (14), the low pressure sensor (14) being arranged at the air intake port of the compressor (1), the low pressure sensor (14) being used to detect evaporation pressure; and / or, A gas-liquid separator (15), wherein the inlet of the gas-liquid separator (15) is connected to an end of the subcooling branch (7) away from the subcooler (6); so the outlet of the gas-liquid separator (15) is connected to the suction port of the compressor (1).

7. The outdoor unit according to claim 2, characterized in that: The outdoor unit further comprises: a first temperature sensor (16) and a second temperature sensor (17), wherein the first temperature sensor (16) is arranged at the input end of the second pipeline (62) for detecting the temperature of the refrigerant before entering the subcooler (6); and the second temperature sensor (17) is arranged at the output end of the second pipeline (62) for detecting the temperature of the refrigerant after leaving the subcooler (6).

8. The outdoor unit according to claim 2, characterized in that: The outdoor unit further comprises: a third temperature sensor (18), the third temperature sensor (18) being arranged at the exhaust port of the compressor (1) for detecting the exhaust temperature of the compressor (1); and / or, A high-pressure sensor (19), wherein the high-pressure sensor (19) is arranged at the refrigerant outlet of the oil-liquid separator (2), and the high-pressure sensor (19) is close to the refrigerant outlet of the oil-liquid separator (2), and the high-pressure sensor (19) is used to detect the condensation pressure.

9. The outdoor unit according to claim 1, characterized in that: The oil return branch (4) is provided with an oil return regulating valve (20), and the oil return regulating valve (20) is located between the oil-liquid separator (2) and the heat exchange structure (5).

10. A multi-connected air conditioning system, characterized in that: The multi-connected air conditioning system comprises: An outdoor unit, wherein the outdoor unit is the outdoor unit according to any one of claims 1 to 9; A plurality of indoor units (100), wherein the plurality of indoor units (100) are all connected to the outdoor unit.

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