Multi-connected air conditioner capable of refrigerating and heating simultaneously and control method of multi-connected air conditioner

Abstract

The invention provides a multi-union type simultaneous refrigerating and heating air conditioner and a control method thereof, and relates to the technical field of air conditioner detained oil, the air conditioner comprises an oil return four-way valve, under general circulation, the compressor exhaust pipe side of a high-pressure air pipe is communicated with the high-pressure main air pipe connecting part side of the high-pressure air pipe, and the oil return four-way valve is communicated with the high-pressure main air pipe connecting part side of the high-pressure air pipe. The compressor air suction pipe side of the low-pressure air pipe is communicated with the low-pressure main air pipe connecting part side of the low-pressure air pipe; and under the oil return circulation, the exhaust pipe side of the compressor is communicated with the low-pressure main air pipe connecting part side, and the air suction pipe side of the compressor is connected with the high-pressure main air pipe connecting part side. According to the embodiment of the invention, insufficient oil quantity of the compressor can be prevented, the sealed oil quantity of the compressor does not need to be increased, and cooling capacity or heating capacity can be prevented from being reduced; only one four-way valve is added, a plurality of valves do not need to be controlled, complication of a circuit board of the outdoor unit controller and complication of wiring are prevented, control software of oil return operation is simplified, and time needed by manufacturing and debugging of the software is shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of retained oil in air conditioners, and in particular to a multi-connected simultaneous cooling and heating air conditioner and a control method thereof. Background Art

[0002] In a multi-split cooling and heating air conditioner, if there is a height difference between the outdoor unit and the indoor unit (hereinafter referred to as the outside-inside height difference), when the main air pipe flows upward, the oil cannot move with the refrigerant and stays in the main air pipe. If this stagnant oil does not return to the compressor and increases, the compressor will be damaged due to insufficient oil.

[0003] The existing solution is to increase the amount of oil sealed in the compressor to prevent the compressor from running out of oil. However, if the amount of oil sealed in the compressor is increased, the compressor discharge will increase and flow to the outdoor heat exchanger and indoor heat exchanger together with the refrigerant, thereby reducing the heat exchange capacity and the cooling or heating capacity.

[0004] Another existing solution is to respectively set solenoid valves on the high-pressure air pipe and the low-pressure air pipe of the outdoor unit, and set the bypass connection of the solenoid valve on the high-pressure air pipe and the low-pressure air pipe. In the oil return operation when the outdoor unit has an outside-inside drop on the upper side, the high-pressure main air pipe and the low-pressure main air pipe make the high-pressure air refrigerant flow downward. In the oil return operation when the outdoor unit has an outside-inside drop on the lower side, the high-pressure main air pipe and the low-pressure main air pipe make the low-pressure air refrigerant flow downward. Through these actions, it is possible to prevent oil from being retained in the low-pressure main air pipe or the high-pressure main air pipe, resulting in insufficient oil in the compressor. However, in the oil return operation of this method, the air refrigerant is distributed to the high-pressure main air pipe and the low-pressure main air pipe. Therefore, since the flow rate of each refrigerant slows down, in order to recover the retained oil in the main air pipe, it is necessary to extend the oil return time.

[0005] Another existing solution is to respectively set solenoid valves on the high-pressure air pipe and the low-pressure air pipe of the outdoor unit, and connect the high-pressure air pipe and the low-pressure air pipe through two bypasses provided with solenoid valves. In the case of an oil return operation with an outside-inside drop on the upper side of the outdoor unit, the low-pressure main air pipe causes the high-pressure air refrigerant to flow downward. In the case of an oil return operation with an outside-inside drop on the lower side of the outdoor unit, the high-pressure main air pipe flows the low-pressure air refrigerant downward. Through these actions, it is possible to prevent oil from being retained in the low-pressure main air pipe or the high-pressure main air pipe, resulting in insufficient oil in the compressor. However, this method requires the control of 4 solenoid valves, so the relay or wiring of the outdoor unit controller circuit board increases, the control software is also complicated, and the time required for production and debugging becomes longer. Summary of the invention

[0006] To solve the above problems, an embodiment of the present invention provides a multi-connected simultaneous cooling and heating air conditioner that can prevent insufficient oil in the compressor, including an oil return four-way valve; the compressor exhaust pipe side of the high-pressure air pipe, the high-pressure main air pipe connecting part side of the high-pressure air pipe, the compressor suction pipe side of the low-pressure air pipe and the low-pressure main air pipe connecting part side of the low-pressure air pipe are respectively connected to the respective interfaces of the oil return four-way valve; the high-pressure main air pipe connecting part is connected to the high-pressure main air pipe, and the low-pressure main air pipe connecting part is connected to the low-pressure main air pipe; under normal circulation, the The connectivity relationship of the oil return four-way valve is as follows: the compressor exhaust pipe side of the high-pressure air pipe is connected to the high-pressure main air pipe connecting part side of the high-pressure air pipe, and the compressor suction pipe side of the low-pressure air pipe is connected to the low-pressure main air pipe connecting part side of the low-pressure air pipe; under the oil return cycle, the connectivity relationship of the oil return four-way valve is as follows: the compressor exhaust pipe side of the high-pressure air pipe is connected to the low-pressure main air pipe connecting part side of the low-pressure air pipe, and the compressor suction pipe side of the low-pressure air pipe is connected to the high-pressure main air pipe connecting part side of the high-pressure air pipe.

[0007] The multi-split simultaneous cooling and heating air conditioner provided in the embodiment of the present invention can prevent the oil shortage in the compressor due to oil retention in the low-pressure main air pipe and the high-pressure main air pipe when there is an external and internal height difference on the upper or lower side of the outdoor unit, resulting in insufficient oil in the compressor; there is no need to increase the amount of oil sealed in the compressor, thereby preventing the cooling capacity or heating capacity from decreasing; only one four-way valve is added, and there is no need to control multiple valves, thereby preventing the complication of the outdoor unit controller circuit board and the complication of the wiring, and the control software for the return oil operation can also be simplified, thereby shortening the time required for software production and debugging.

[0008] Optionally, in the oil return cycle when there is an outside-inside head difference on the upper side of the outdoor unit, all high-pressure side switching valves of the conversion device are set to be closed, and all low-pressure side switching valves are set to be opened.

[0009] In the embodiment of the present invention, when the outdoor unit is at the lower side, the gas refrigerant during oil return operation is only distributed to the low-pressure main air pipe, rather than to both the high-pressure main air pipe and the low-pressure main air pipe at the same time. Therefore, the refrigerant flow rate of the main air pipe becomes faster, and the retained oil can be recovered in a short time.

[0010] Optionally, it also includes an outdoor unit four-way valve; in the oil return cycle when there is an outside-inside height difference on the upper side of the outdoor unit, the outdoor unit four-way valve operates in a heating cycle.

[0011] In the embodiment of the present invention, when the oil return four-way valve performs an oil return cycle, the outdoor unit four-way valve is correspondingly switched to a heating cycle to implement a refrigerant loop, and the oil retained in the pipeline is moved to the return compressor.

[0012] Optionally, in the oil return cycle when there is an outside-inside head difference at the lower side of the outdoor unit, all high-pressure side switching valves of the conversion device are set to open, and all low-pressure side switching valves are set to closed.

[0013] In the embodiment of the present invention, when the outdoor unit is at the lower side, the gas refrigerant during oil return operation is only distributed to the high-pressure main air pipe, rather than to both the high-pressure main air pipe and the low-pressure main air pipe at the same time. Therefore, the refrigerant flow rate of the main air pipe becomes faster, and the retained oil can be recovered in a short time.

[0014] Optionally, it also includes an outdoor unit four-way valve; in the oil return cycle when there is an outside-inside height difference at the lower side of the outdoor unit, the outdoor unit four-way valve operates in a refrigeration cycle.

[0015] In the embodiment of the present invention, when the oil return four-way valve performs an oil return cycle, the outdoor unit four-way valve is correspondingly switched to a refrigeration cycle to implement a refrigerant loop, and the oil retained in the pipeline is moved to the return compressor.

[0016] Optionally, the high-pressure main gas pipe is connected to the first port of the indoor unit through a high-pressure side switching valve; the low-pressure main gas pipe is connected to the first port of the indoor unit through a low-pressure side switching valve.

[0017] In the embodiment of the present invention, the high-pressure main air pipe and the low-pressure main air pipe are arranged between the oil return four-way valve and the indoor unit to realize the refrigerant loop and move the oil retained in the pipeline to the return compressor.

[0018] Optionally, it also includes a main liquid pipe; the main liquid pipe is connected between the indoor unit and the outdoor unit, one end of the main liquid pipe is connected to the second port of the indoor unit, and the other end is connected to the outdoor heat exchanger of the outdoor unit.

[0019] In the embodiment of the present invention, the main liquid pipe connects the outdoor unit and the indoor unit to realize a refrigerant loop, and moves the oil retained in the pipe to the return compressor.

[0020] An embodiment of the present invention provides a control method for a multi-split simultaneous cooling and heating air conditioner, which is applied to any of the multi-split simultaneous cooling and heating air conditioners described above, comprising: if an oil return operation instruction is obtained and there is an internal and external drop, the oil return four-way valve is controlled to operate in an oil return cycle; if it is determined that the outdoor unit is on the upper side, all high-pressure side switching valves of the conversion device are controlled to be closed, and all low-pressure side switching valves are controlled to be opened; if it is determined that the outdoor unit is on the lower side, all high-pressure side switching valves of the conversion device are controlled to be opened, and all low-pressure side switching valves are controlled to be closed.

[0021] Optionally, the method further includes: if it is determined that the outdoor unit is on the upper side, controlling the outdoor unit four-way valve to operate in a heating cycle; if it is determined that the outdoor unit is on the lower side, controlling the outdoor unit four-way valve to operate in a cooling cycle.

[0022] Optionally, the method further includes: if the oil return operation is completed, controlling the oil return four-way valve to operate in a normal cycle, and controlling the outdoor unit four-way valve to return to a state before the oil return operation.

[0023] The control method of the multi-split simultaneous cooling and heating air conditioner provided in the embodiment of the present invention can achieve the same technical effect as the multi-split simultaneous cooling and heating air conditioner mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure is a refrigerant circulation diagram of an existing three-tube multi-connected simultaneous cooling and heating machine.

[0025] Figure 2 This is a schematic diagram of the outdoor unit being set up on the upper side;

[0026] Figure 3 This is a schematic diagram of the outdoor unit being set up on the lower side;

[0027] Figure 4 It is the refrigerant cycle diagram of prior art 1;

[0028] Figure 5 It is a schematic diagram of the operation of the outdoor unit of the prior art 1;

[0029] Figure 6 It is a schematic diagram of the operation of the outdoor unit under the prior art 1;

[0030] Figure 7 It is the refrigerant cycle diagram of prior art 2;

[0031] Figure 8 It is a schematic diagram of the operation of the outdoor unit of the prior art 2;

[0032] Fig. 9 It is a schematic diagram of the operation of the outdoor unit under the prior art 2;

[0033] Fig.10 A refrigerant circulation diagram of a multi-connected simultaneous cooling and heating air conditioner that can prevent insufficient oil in the compressor provided by an embodiment of the present invention;

[0034] Fig.11 It is a schematic diagram of the operation of the upper side of the outdoor unit of an embodiment of the present invention;

[0035] Fig.12 It is a schematic diagram of the operation of the lower side of the outdoor unit of an embodiment of the present invention;

[0036] Fig.13 A schematic flow chart of a control method for a multi-connected simultaneous cooling and heating air conditioner provided by an embodiment of the present invention;

[0037] Fig.14 A control flow chart of oil return operation of a multi-connected simultaneous cooling and heating air conditioner provided in an embodiment of the present invention.

[0038] Description of reference numerals:

[0039] 11-Indoor unit; 12-Outdoor unit; 13-Outdoor heat exchanger; 14-Indoor heat exchanger; 15-Four-way valve; 16-Compressor; 17-Compressor exhaust pipe; 18-Low-pressure main gas pipe connection; 19-High-pressure main gas pipe connection; 20-Outdoor expansion valve; 21-Indoor expansion valve; 22-Outdoor unit low-pressure gas pipe; 23-Oil return bypass pipe; 24-Low-pressure main gas pipe; 25-High-pressure main gas pipe; 26-Low-pressure side switching valve ; 27-high-pressure side switching valve; 28-manifold box; 29-main liquid pipe; 30-low-pressure gas pipe solenoid valve; 31-low-pressure gas pipe; 32-return oil bypass solenoid valve; 33-first bypass solenoid valve; 34-second bypass solenoid valve; 35-high-pressure gas pipe solenoid valve; 36-first bypass pipe; 37-second bypass pipe; 38-compressor suction pipe; 39-high-pressure gas pipe; 101-outdoor unit four-way valve; 102-return oil four-way valve. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0041] Figure 1 The diagram shows the refrigerant circulation of an existing three-tube multi-connected simultaneous cooling and heating machine.

[0042] For example, in a multi-split simultaneous cooling and heating air conditioner that can mix and use a cooling indoor unit and a heating indoor unit, the outdoor unit and the indoor unit are connected by a high-pressure side air pipe (hereinafter referred to as a high-pressure main air pipe), a low-pressure side air pipe (hereinafter referred to as a low-pressure main air pipe), and a liquid pipe (hereinafter referred to as a main liquid pipe). Figure 1 Three-tube model shown.

[0043] In a multi-split air conditioner, when there is a height difference between the outdoor unit and the indoor unit (hereinafter referred to as the outside-inside height difference), when the main air pipe flows upward, the oil cannot move with the refrigerant and stays in the main air pipe. If the retained oil does not return to the compressor and increases, the compressor will be damaged due to insufficient oil.

[0044] However, in the main air pipe of a two-pipe cooling and heating fixed machine that connects the outdoor unit and the indoor unit with the main air pipe and the main liquid pipe, when the four-way valve is in the refrigeration cycle, the low-pressure gas refrigerant flows from the indoor unit to the outdoor unit, and when the four-way valve is in the heating cycle, the high-pressure gas refrigerant flows from the outdoor unit to the indoor unit. Therefore, even if there is a height difference between the outside and the inside, if there is a switch between cooling operation and heating operation, or a switch of the four-way valve cycle such as defrosting operation, the main air pipe will switch in the opposite direction up and down, so the retained oil will not continue to increase without returning.

[0045] like Figure 1As shown, when only the indoor unit 11 is in cooling operation, the four-way valve 15 becomes a refrigeration cycle. In addition, the low-pressure side switching valve 26 of the branch box 28 is opened, and the high-pressure side switching valve 27 is closed. Then, the high-pressure refrigerant discharged from the compressor 16 flows to the outdoor heat exchanger 13 via the four-way valve 15. And, it is condensed into liquid refrigerant by the outdoor heat exchanger 13, and flows to the indoor unit 12 through the main liquid pipe 29. In addition, the liquid refrigerant is reduced in pressure in the indoor expansion valve 21 and then becomes two-phase, and evaporates in the indoor heat exchanger 14 to perform a cooling action. The low-pressure gas refrigerant after cooling flows from the indoor unit side to the outdoor unit side via the low-pressure side switching valve 26 and the low-pressure main air pipe 24 and returns to the outdoor unit 12, and is sucked into the compressor 16 through the low-pressure air pipe 31.

[0046] exist Figure 1 Also shown are a low-pressure main air pipe connection portion 18 and a high-pressure main air pipe connection portion 19, which are used to connect a low-pressure main air pipe 24 and a high-pressure main air pipe 25, respectively.

[0047] When only the indoor unit is in heating operation, the four-way valve 15 becomes a heating cycle. In addition, the low-pressure side switching valve 26 of the branch box 28 is closed, and the high-pressure side switching valve 27 is opened. Then, the high-pressure gas refrigerant discharged from the compressor 16 flows from the outdoor unit side to the indoor unit side through the high-pressure gas pipe 39 and the high-pressure main gas pipe 25, and moves to the indoor unit 11 via the high-pressure side switching valve 27. It is then condensed by the indoor heat exchanger 14 to perform the heating action. The condensed liquid refrigerant returns to the outdoor unit 12 through the main liquid pipe 29. Then, the gas-liquid mixture is decompressed by the outdoor expansion valve 20, evaporated by the outdoor heat exchanger 20, and sucked into the compressor 16 via the four-way valve 15.

[0048] When there are both indoor units in cooling operation and indoor units in heating operation, and the cooling load is greater than the heating load, the four-way valve 15 becomes a refrigeration cycle. In addition, in the branch box 28, the low-pressure side switching valve 26 connected to the indoor unit in cooling operation is opened, and the high-pressure side switching valve 27 is closed. In addition, the low-pressure side switching valve 26 connected to the indoor unit in heating operation is closed, and the high-pressure side switching valve 27 is opened. In addition, the high-pressure gas refrigerant discharged from the compressor 16 and the high-pressure gas refrigerant flowing to the outdoor heat exchanger 13 through the four-way valve 15 are distributed to the high-pressure gas refrigerant flowing through the outdoor unit high-pressure gas pipe 39. Then, the high-pressure gas refrigerant distributed to the outdoor heat exchanger 13 through the four-way valve 15 is condensed into liquid refrigerant in the outdoor heat exchanger 13, and flows into the refrigeration indoor unit through the main liquid pipe 29. Furthermore, the liquid refrigerant is decompressed in the indoor expansion valve 21 and the gas and liquid are mixed, and then evaporated in the indoor heat exchanger 14 to perform a cooling action. The low-pressure gas refrigerant after refrigeration flows from the indoor unit side to the outdoor unit side through the low-pressure side switching valve 26 and the low-pressure main air pipe 24 and returns to the outdoor unit, and the outdoor unit is sucked into the compressor through the low-pressure air pipe 31. In addition, the high-pressure gas refrigerant distributed to the outdoor unit high-pressure air pipe 39 moves to the heating indoor unit through the high-pressure main air pipe 25. It is then condensed by the indoor heat exchanger 14 to perform heating. The condensed liquid refrigerant moves to the main liquid pipe 29, merges with the liquid refrigerant condensed in the outdoor heat exchanger 13, and flows into the refrigeration indoor unit. The above actions perform cooling and heating operations simultaneously.

[0049] There are indoor units in cooling operation and indoor units in heating operation. When the heating load is greater than the cooling load, the four-way valve 15 becomes a heating cycle. In addition, in the branch box 28, the low-pressure side switching valve 26 connected to the cooling operation indoor unit is opened, and the high-pressure side switching valve 27 is closed. In addition, the low-pressure side switching valve 26 connected to the heating operation indoor unit is closed, and the high-pressure side switching valve 27 is opened. In addition, the high-pressure gas refrigerant discharged from the compressor 16 flows from the outdoor unit side to the indoor unit side through the outdoor unit high-pressure gas pipe 39 and the high-pressure main gas pipe 25, and moves to the heating indoor unit via the high-pressure side switching valve 27. It is then condensed by the indoor heat exchanger 14 to perform heating. The condensed liquid refrigerant moves to the main liquid pipe 29 and is distributed to the liquid refrigerant flowing through the outdoor unit and the liquid refrigerant flowing through the cooling indoor unit. The liquid refrigerant distributed to the outdoor unit evaporates in the outdoor heat exchanger 13 after the outdoor expansion valve 20 reduces the pressure and the gas and liquid are mixed, and then is sucked by the compressor 16 through the four-way valve 15. In addition, the liquid refrigerant distributed to the refrigeration indoor unit is decompressed by the indoor expansion valve 21, and the gas and liquid are mixed, and then evaporated by the indoor heat exchanger 14 to perform the refrigeration action. The refrigerated low-pressure gas refrigerant flows through the low-pressure main air pipe 24 via the low-pressure side switching valve 26 and returns to the outdoor unit. After passing through the outdoor unit low-pressure air pipe 22, it merges with the low-pressure gas refrigerant via the four-way valve 15 and is sucked by the compressor 16. The above actions perform cooling and heating operations simultaneously.

[0050] As mentioned above, in a three-pipe multi-connected air conditioner with simultaneous cooling and heating, regardless of the refrigeration cycle or heating cycle of the four-way valve, the refrigerant in the high-pressure main air pipe flows from the outdoor unit side to the indoor unit side, and the refrigerant in the low-pressure main air pipe flows from the indoor unit side to the outdoor unit side. Therefore, in the case of an outside-inside height difference, the refrigerant in either the high-pressure main air pipe or the low-pressure main air pipe flows upward. For example, Figure 2 The schematic diagram of the outdoor unit being placed on the upper side is shown. When the outdoor unit is placed on the upper side, the low-pressure main air pipe faces upward, and the low-pressure main air pipe always flows upward. Figure 3 The diagram shows the outdoor unit at the bottom. When the outdoor unit is at the bottom, the high-pressure main air pipe faces upward and always flows upward. Therefore, when there is a height difference between the inside and outside, the low-pressure main air pipe retains oil when the outdoor unit is at the top, and the high-pressure main air pipe retains oil without returning when the outdoor unit is at the bottom, but it continues to increase.

[0051] In general, in order to return the oil stagnation in the main air pipe to the compressor, multi-split air conditioners operate the compressor at a high speed to accelerate the flow rate of the refrigerant in the air pipe. However, in the main air pipe flowing upward, it is difficult to return the oil even when the compressor is running at a high speed. Therefore, in a three-pipe type simultaneous cooling and heating multi-split unit with an external and internal height difference, the low-pressure main air pipe is used when the outdoor unit is on the upper side, and the high-pressure main air pipe flows upward when the outdoor unit is on the lower side, which easily causes insufficient oil in the compressor.

[0052] In order to prevent this type of compressor oil shortage, there is a method of increasing the amount of oil sealed in the compressor. However, if the amount of oil sealed in the compressor is increased, the compressor discharge volume increases and flows to the outdoor heat exchanger and indoor heat exchanger together with the refrigerant. As a result, the heat exchange capacity is reduced, and the cooling capacity or heating capacity is reduced.

[0053] Figure 4 The refrigerant circulation diagram of the prior art 1 is shown, and a high-pressure gas pipe solenoid valve 35 is provided in the high-pressure gas pipe 39 between the compressor exhaust pipe 17 and the high-pressure main gas pipe connection part 19. In addition, a low-pressure gas pipe solenoid valve 30 is provided in the low-pressure gas pipe 31 between the four-way valve 15 and the low-pressure main gas pipe connection part 18. An oil return bypass pipe 23 is provided between the high-pressure gas pipe 39 connected between the high-pressure gas pipe solenoid valve 35 and the high-pressure main gas pipe connection part 19 and the low-pressure gas pipe 31 connected between the low-pressure gas pipe solenoid valve 30 and the low-pressure main gas pipe connection part 18. In addition, an oil return bypass solenoid valve 32 is provided in the oil return bypass pipe 23.

[0054] like Figure 5In the action diagram of the outdoor unit upper side of the prior art 1 shown in the figure, when the outdoor unit 12 has an outside-inside drop on the upper side, the low-pressure main air pipe 24 has nothing to do with the four-way valve 15 circulation, flows upward, and generates retained oil. Therefore, in the oil return operation, the four-way valve 15 of the outdoor unit 12 forms a heating cycle. In addition, the high-pressure air pipe solenoid valve 35 and the return oil bypass solenoid valve 32 are opened, and the low-pressure air pipe solenoid valve 30 is closed. In addition, all the high-pressure side switching valves 27 and all the low-pressure side switching valves 26 of all the branch boxes 28 are set to open. Through these actions, the high-pressure air refrigerant flows not only to the high-pressure main air pipe 25, but also to the low-pressure main air pipe 24. In addition, since the high-pressure air refrigerant flows from the outdoor unit 12 to the indoor unit 11, the low-pressure main air pipe 24 flows from the upper side to the lower side. Therefore, the retained oil in the low-pressure main air pipe 24 will move to the indoor unit 11. Then, the oil is mixed with the condensed and liquefied refrigerant in the indoor unit 11, passes through the main liquid pipe 29, and returns to the compressor 16 via the outdoor heat exchanger 13. As a result, it is possible to prevent oil from stagnating in the low-pressure main air pipe 24 and causing the compressor to run out of oil.

[0055] like Figure 6 The action diagram of the outdoor unit of the prior art 1 shown in the figure shows that when the outdoor unit has an outside-inside drop at the bottom, the high-pressure main air pipe 25 has nothing to do with the four-way valve cycle, and the upward flow generates retained oil. Therefore, in the oil return operation, the four-way valve 15 of the outdoor unit 12 forms a refrigeration cycle. In addition, the low-pressure air pipe solenoid valve 30 and the return oil bypass solenoid valve 32 are opened, and the high-pressure air pipe solenoid valve 35 is closed. In addition, all the high-pressure side switching valves 27 and all the low-pressure side switching valves 26 of all the conversion devices are set to open. Through these actions, the low-pressure air refrigerant flows not only to the low-pressure main air pipe 24, but also to the high-pressure main air pipe 25. In addition, since the low-pressure air refrigerant flows from the indoor unit 11 to the outdoor unit 12, the high-pressure main air pipe 25 flows from the upper side to the lower side. Therefore, the retained oil in the high-pressure main air pipe 25 moves to the outdoor unit 12 and returns to the compressor 16. As a result, it is possible to prevent the oil from being retained in the high-pressure main air pipe 25 and causing insufficient oil in the compressor.

[0056] However, in the oil return operation of this method, the air refrigerant is distributed to the high-pressure main air pipe and the low-pressure main air pipe, and the refrigerant flow rate slows down. In order to recover the oil retained in the main air pipe, it is necessary to extend the oil return time.

[0057] Figure 7The refrigerant circulation diagram of the prior art 2 is shown, and a high-pressure gas pipe solenoid valve 35 is provided in the high-pressure gas pipe 39 between the compressor exhaust pipe 17 and the high-pressure main gas pipe connection part 19. A low-pressure gas pipe solenoid valve 30 is provided in the low-pressure gas pipe 31 between the four-way valve 15 and the low-pressure main gas pipe connection part 18. And a first bypass pipe 36 is provided between the high-pressure gas pipe between the high-pressure gas pipe solenoid valve 35 and the high-pressure main gas pipe connection part 19, and the low-pressure gas pipe 31 between the four-way valve 15 and the low-pressure gas pipe solenoid valve 30. In addition, a first bypass solenoid valve 33 is provided in the first bypass pipe 36. In addition, a second bypass pipe 37 is provided between the low-pressure gas pipe 31 between the low-pressure gas pipe solenoid valve 30 and the low-pressure main gas pipe connection part 18, and the high-pressure gas pipe 39 between the compressor exhaust pipe 17 and the high-pressure gas pipe solenoid valve 35. In addition, a second bypass solenoid valve 34 is provided in the second bypass pipe 37.

[0058] like Figure 8 In the action diagram of the outdoor unit upper side of the prior art 2 shown, when the outdoor unit 12 has an upper side outer and inner height difference, the low-pressure main air pipe 24 has nothing to do with the four-way valve 15 circulation, and the upward flow generates retained oil. Therefore, in the oil return operation, the four-way valve 15 of the outdoor unit 12 forms a heating cycle. In addition, all low-pressure side switching valves 26 of all branch boxes 28 are opened, and all high-pressure side switching valves 27 are closed. The second bypass solenoid valve 34 is opened, and the high-pressure air pipe solenoid valve 35, the low-pressure air pipe solenoid valve 30 and the first bypass solenoid valve 33 are closed. Through these actions, the high-pressure gas refrigerant flows downward into the low-pressure main air pipe 24, and the retained oil moves to the indoor unit 11. Then it is mixed with the condensed and liquefied refrigerant in the indoor unit 11, and returns to the compressor 16 through the main liquid pipe 29 and the outdoor heat exchanger 13. As a result, it is possible to prevent the oil from being retained in the low-pressure main air pipe 24 and causing insufficient oil in the compressor.

[0059] like Fig. 9 The action diagram of the outdoor unit of the prior art 2 shown in the figure shows that when the outdoor unit 12 has an outside-inside drop at the bottom, the high-pressure main air pipe 25 has nothing to do with the four-way valve cycle, and becomes an upward flow, resulting in retained oil. Therefore, in the oil return operation, the four-way valve 15 of the outdoor unit 12 forms a refrigeration cycle. In addition, all high-pressure side switching valves 27 of all branch boxes 28 are opened, and all low-pressure side switching valves 26 are closed. In addition, the first bypass solenoid valve 33 is opened, and the high-pressure air pipe solenoid valve 35, the low-pressure air pipe solenoid valve 30 and the second bypass solenoid valve 34 are closed. Through these actions, in the high-pressure main air pipe 25, the low-pressure air refrigerant evaporated by the indoor unit 11 flows downward, and the retained oil returns to the compressor. As a result, it is possible to prevent the oil from being retained in the high-pressure main air pipe 25, resulting in insufficient oil in the compressor.

[0060] However, this method requires the control of four solenoid valves, which increases the number of relays and wiring on the outdoor unit controller circuit board. In addition, the control software is also complicated, and the time required for production and debugging becomes longer.

[0061] An embodiment of the present invention provides a multi-connected simultaneous cooling and heating air conditioner capable of preventing insufficient oil in a compressor, wherein an oil return four-way valve is added.

[0062] Specifically, the compressor exhaust pipe side of the high-pressure air pipe, the high-pressure main air pipe connection side of the high-pressure air pipe, the compressor intake pipe side of the low-pressure air pipe and the low-pressure main air pipe connection side of the low-pressure air pipe are respectively connected to the various interfaces of the above-mentioned oil return four-way valve.

[0063] The high-pressure main gas pipe connection part is connected to the high-pressure main gas pipe, the low-pressure main gas pipe connection part is connected to the low-pressure main gas pipe, and the other sides of the high-pressure main gas pipe and the low-pressure main gas pipe are connected to the indoor unit. Specifically, the high-pressure main gas pipe can be connected to the first port of the indoor unit through the high-pressure side switching valve; the low-pressure main gas pipe can be connected to the first port of the indoor unit through the low-pressure side switching valve.

[0064] Furthermore, it can also include a main liquid pipe; the main liquid pipe is connected between the indoor unit and the outdoor unit, one end of the main liquid pipe is connected to the second port of the indoor unit, and the other end is connected to the outdoor heat exchanger of the outdoor unit, connecting the refrigerant pipeline of the indoor unit and the outdoor unit.

[0065] Under normal cycle, the connection relationship of the oil return four-way valve is as follows: the compressor exhaust pipe side of the high-pressure gas pipe is connected to the high-pressure main gas pipe connecting part side of the high-pressure gas pipe, and the compressor suction pipe side of the low-pressure gas pipe is connected to the low-pressure main gas pipe connecting part side of the low-pressure gas pipe. The normal cycle refers to the normal cooling and heating cycle of the air conditioner.

[0066] Under the oil return cycle, the connection relationship of the oil return four-way valve is as follows: the compressor exhaust pipe side of the high-pressure air pipe is connected to the low-pressure main air pipe connection side of the low-pressure air pipe, and the compressor suction pipe side of the low-pressure air pipe is connected to the high-pressure main air pipe connection side of the high-pressure air pipe. The oil return cycle refers to the oil return operation of the air conditioner, which moves the oil retained in the pipeline to the return compressor.

[0067] Optionally, in the oil return cycle when there is an outside-inside drop on the upper side of the outdoor unit, all high-pressure side switching valves of the conversion device are set to closed, and all low-pressure side switching valves are set to open. Among them, the conversion device plays a high-low pressure switching role, and the flow path of the refrigerant can be changed by opening and closing the above-mentioned high-pressure side switching valve and low-pressure side switching valve. During the oil return operation, the gas refrigerant is only distributed to the low-pressure main air pipe, rather than to the high-pressure main air pipe and the low-pressure main air pipe at the same time. Therefore, the refrigerant flow rate of the main air pipe becomes faster, and the retained oil can be recovered in a short time.

[0068] Exemplarily, the air conditioner further comprises an outdoor unit four-way valve, which is the original four-way valve and plays the role of switching cooling and heating. Optionally, in the oil return cycle when there is an outside-inside height difference on the upper side of the outdoor unit, the outdoor unit four-way valve operates in a heating cycle.

[0069] Through these actions, the high-pressure gas refrigerant flows to the low-pressure main gas pipe. Since the high-pressure gas refrigerant flows from the outdoor unit to the indoor unit, the low-pressure main gas pipe flows from the upper side to the lower side. The oil retained in the low-pressure main gas pipe moves to the indoor unit, and then mixes with the condensed and liquefied refrigerant in the indoor unit, passes through the main liquid pipe, and returns to the compressor via the outdoor heat exchanger, thereby preventing the oil from being retained in the low-pressure main gas pipe and causing the compressor to run out of oil.

[0070] Optionally, in the oil return cycle when there is an outside-inside height difference at the lower side of the outdoor unit, all high-pressure side switching valves of the conversion device are set to open, and all low-pressure side switching valves are set to close. During the oil return operation, the air refrigerant is only distributed to the high-pressure main air pipe, not to both the high-pressure main air pipe and the low-pressure main air pipe, so the refrigerant flow rate of the main air pipe becomes faster, and the retained oil can be recovered in a short time.

[0071] Exemplarily, in the oil return cycle when there is an outside-inside height difference at the lower side of the outdoor unit, the four-way valve of the outdoor unit operates in a refrigeration cycle.

[0072] Through these actions, the low-pressure air refrigerant flows to the high-pressure main air pipe. Since the low-pressure air refrigerant flows from the outdoor unit to the indoor unit, the high-pressure main air pipe flows from the upper side to the lower side. The retained oil in the high-pressure main air pipe moves to the outdoor unit and returns to the compressor, thereby preventing the oil from being retained in the high-pressure main air pipe and causing the compressor to run out of oil.

[0073] The multi-split simultaneous cooling and heating air conditioner provided in the embodiment of the present invention can prevent the oil shortage in the compressor due to oil retention in the low-pressure main air pipe and the high-pressure main air pipe when there is an external and internal height difference on the upper or lower side of the outdoor unit, resulting in insufficient oil in the compressor; there is no need to increase the amount of oil sealed in the compressor, thereby preventing the cooling capacity or heating capacity from decreasing; only one four-way valve is added, and there is no need to control multiple valves, thereby preventing the complication of the outdoor unit controller circuit board and the complication of the wiring, and the control software for the return oil operation can also be simplified, thereby shortening the time required for software production and debugging.

[0074] Fig.10 A refrigerant circulation diagram of a multi-connected simultaneous cooling and heating air conditioner capable of preventing insufficient oil in a compressor provided by an embodiment of the present invention is shown.

[0075] like Fig.10As shown, in the three-pipe multi-connected cooling and heating air conditioner, it includes an indoor unit 11, an outdoor unit 12 and a branch box 28 (i.e., the above-mentioned conversion device). The outdoor unit 12 includes a compressor 16, and the branch box 28 includes a low-pressure side switching valve 26 and a high-pressure side switching valve 27.

[0076] The compressor exhaust pipe 17 side of the high-pressure air pipe 39, the high-pressure main air pipe connection part 19 side of the high-pressure air pipe 39, the compressor suction pipe 38 side of the low-pressure air pipe 31, and the low-pressure main air pipe connection part 18 side of the low-pressure air pipe 31 are connected to the oil return four-way valve 102. The high-pressure main air pipe connection part 19 is connected to the high-pressure main air pipe 25, and the low-pressure main air pipe connection part 18 is connected to the low-pressure main air pipe 24.

[0077] The above-mentioned oil return four-way valve 102, the compressor exhaust pipe 17 of the high-pressure air pipe 39 and the high-pressure main air pipe connection part 19 of the high-pressure air pipe 39 are connected, and the compressor suction pipe 38 of the low-pressure air pipe 31 and the low-pressure main air pipe connection part 18 of the low-pressure air pipe are connected, forming a normal circulation. The compressor exhaust pipe 17 of the high-pressure air pipe 39 and the low-pressure main air pipe connection part 18 of the low-pressure air pipe 31 are connected, and the compressor suction pipe 38 of the low-pressure air pipe 31 and the high-pressure main air pipe connection part 19 of the high-pressure air pipe 39 are connected, forming an oil return circulation. In addition, in order to distinguish the four-way valve, the existing four-way valve of the outdoor unit is recorded as the outdoor unit four-way valve 101.

[0078] Fig.11 The schematic diagram of the operation of the outdoor unit disposed on the upper side of an embodiment of the present invention is shown. In the oil return operation of the outdoor unit 12 in the case of the difference between the outside and the inside on the upper side, the oil return cycle of the oil return four-way valve 102 is switched, so that the compressor exhaust pipe 17 side of the high-pressure air pipe 39 is connected to the low-pressure main air pipe connecting portion 18 side of the low-pressure air pipe 31. In addition, all high-pressure side switching valves 27 of the branch box 28 are set to be closed, and all low-pressure side switching valves 26 are set to be open. Thus, the high-pressure air pipe 39 of the outdoor unit 12 is connected to the indoor unit 11 via the low-pressure main air pipe 24. In addition, the outdoor unit four-way valve 101 performs a heating cycle. Thus, the high-pressure gas refrigerant discharged from the compressor 16 flows from the outdoor unit 12 to the indoor unit 11.

[0079] Through these actions, the high-pressure gas refrigerant flows to the low-pressure main gas pipe 24. Since the high-pressure gas refrigerant flows from the outdoor unit 12 to the indoor unit 11, the low-pressure main gas pipe 24 flows from the upper side to the lower side. Therefore, the stagnant oil in the low-pressure main gas pipe 24 moves to the indoor unit 11. Then, it is mixed with the condensed and liquefied refrigerant in the indoor unit 11, passes through the main liquid pipe 29, and returns to the compressor 16 via the outdoor heat exchanger 13. As a result, it is possible to prevent the oil from being stagnant in the low-pressure main gas pipe and causing the compressor oil shortage.

[0080] Through these actions, the high-pressure gas refrigerant flows to the low-pressure main gas pipe. Since the high-pressure gas refrigerant flows from the outdoor unit to the indoor unit, the low-pressure main gas pipe flows from the upper side to the lower side, so the retained oil in the low-pressure main gas pipe moves to the indoor unit. Then it is mixed with the condensed and liquefied refrigerant in the indoor unit, passes through the main liquid pipe, and returns to the compressor via the outdoor heat exchanger. As a result, it is possible to prevent the oil from being retained in the low-pressure main gas pipe and causing insufficient oil in the compressor.

[0081] Fig.12 The schematic diagram of the operation of the lower side of the outdoor unit of the embodiment of the present invention is shown. In the oil return operation when there is an outside-inside height difference at the lower side of the outdoor unit, the oil return cycle of the oil return four-way valve 102 is switched to connect the compressor suction pipe 38 side of the low-pressure air pipe 31 and the high-pressure main air pipe connecting part 19 side of the high-pressure air pipe 39. In addition, all the high-pressure side switching valves 27 of the branch box 28 are set to open, and all the low-pressure side switching valves 26 are set to close. Thus, the low-pressure air pipe 31 of the outdoor unit 12 is connected to the indoor unit 11 via the high-pressure main air pipe 25. In addition, the outdoor unit four-way valve 101 forms a refrigeration cycle, so that the low-pressure gas refrigerant sucked by the compressor 16 flows from the indoor unit 11 to the outdoor unit 12.

[0082] Through these actions, the low-pressure air refrigerant flows to the high-pressure main air pipe. Since the low-pressure air refrigerant flows from the outdoor unit to the indoor unit, the high-pressure main air pipe flows from the upper side to the lower side, so the retained oil in the high-pressure main air pipe moves to the outdoor unit and returns to the compressor. As a result, it is possible to prevent the oil from being retained in the high-pressure main air pipe and causing the compressor to be short of oil.

[0083] The multi-connected simultaneous cooling and heating air conditioner provided in the embodiment of the present invention has the following advantages:

[0084] 1. It can prevent the oil from being retained in the low-pressure main air pipe when there is a difference between the outside and inside of the outdoor unit on the upper side, resulting in insufficient oil in the compressor; 2. It can prevent the oil from being retained in the high-pressure main air pipe when there is a difference between the outside and inside of the outdoor unit on the lower side, resulting in insufficient oil in the compressor; 3. There is no need to increase the amount of oil sealed in the compressor, which can prevent the cooling capacity or heating capacity from decreasing; 4. The gas refrigerant during oil return operation will not be distributed to the high-pressure main air pipe and the low-pressure main air pipe, but only flows to one of the main air pipes. Therefore, the refrigerant flow rate of the main air pipe becomes faster, and the retained oil can be recovered in a short time; 5. Only one four-way valve is required, and there is no need to control multiple valves. Therefore, the complexity of the outdoor unit controller circuit board and the complexity of the wiring can be prevented, and the control software for the oil return operation can also be simplified, which can shorten the time required for software production and debugging.

[0085] Fig.13 A schematic flow chart of a control method for a multi-split simultaneous cooling and heating air conditioner provided in an embodiment of the present invention, the method is applied to the multi-split simultaneous cooling and heating air conditioner, and comprises the following steps:

[0086] S1, if the oil return operation command is obtained and there is an internal and external drop, the oil return four-way valve is controlled to operate in the above-mentioned oil return cycle.

[0087] S2: If the outdoor unit is determined to be on the upper side, all high-pressure switching valves of the conversion device are controlled to be closed and all low-pressure switching valves are controlled to be opened. If the outdoor unit is determined to be on the upper side, the outdoor unit four-way valve is controlled to operate in a heating cycle.

[0088] S3, if it is determined that the outdoor unit is on the lower side, all high-pressure side switching valves of the conversion device are controlled to open, and all low-pressure side switching valves are controlled to close. If it is determined that the outdoor unit is on the lower side, the outdoor unit four-way valve is controlled to operate in a refrigeration cycle.

[0089] Furthermore, the above method also includes:

[0090] If the oil return operation is completed, the oil return four-way valve is controlled to operate in a normal cycle, and the outdoor unit four-way valve is controlled to return to the state before the oil return operation.

[0091] The control method of a multi-split simultaneous cooling and heating air conditioner provided in an embodiment of the present invention can prevent oil from being retained in the low-pressure main air pipe and the high-pressure main air pipe, resulting in insufficient oil in the compressor when there is an outside-inside height difference on the upper or lower side of the outdoor unit.

[0092] Fig.14 A control flow chart of oil return operation of a multi-connected simultaneous cooling and heating air conditioner provided in an embodiment of the present invention comprises the following steps:

[0093] S201, according to the up-down relationship between the outdoor unit and the indoor unit, select any one of [no difference between inside and outside], [outdoor unit is set on the upper side], [outdoor unit is set on the lower side], and input it to the outdoor unit controller.

[0094] Before the air conditioner starts running, check whether the outdoor unit has an outside-inside drop on the upper side, or whether the outdoor unit has an outside-inside drop on the lower side. The user can input the information of whether there is an outside-inside drop through the wired controller or the DIP switch, and the controller of the outdoor unit stores the information.

[0095] S202, determine whether there is an instruction to start oil return operation. If yes, execute S203; if no, repeat S202.

[0096] S203, judging whether there is no gap between the inside and outside. If yes, executing S210; if no, executing S204.

[0097] S204, control the oil return four-way valve to realize oil return circulation.

[0098] S205, determine whether the outdoor unit is set at the upper side. If yes, execute S206; if no, execute S208.

[0099] S206, controlling the outdoor unit four-way valve to become a heating cycle.

[0100] S207, close the high-pressure side switching valve and open the low-pressure side switching valve.

[0101] S208, controlling the outdoor unit four-way valve to enable refrigeration cycle.

[0102] S209, open the high-pressure side switching valve and close the low-pressure side switching valve.

[0103] S210, controls the oil return four-way valve to switch to normal circulation.

[0104] S211, implement oil return operation.

[0105] S212, determine whether the oil return operation is completed. If yes, execute S213; if no, return to continue to execute S211.

[0106] S213, controlling the outdoor unit four-way valve cycle to return to the state before the oil return operation begins.

[0107] S214, controls the oil return four-way valve to switch to normal circulation.

[0108] In the three-pipe multi-connected simultaneous cooling and heating air conditioner in the embodiment of the present invention, the compressor exhaust pipe side of the high-pressure air pipe and the high-pressure main air pipe connection side of the high-pressure air pipe and the compressor suction pipe side of the low-pressure air pipe and the low-pressure main air pipe connection of the low-pressure air pipe are connected to the oil return four-way valve. The compressor exhaust pipe side of the high-pressure air pipe and the high-pressure main air pipe connection side of the high-pressure air pipe are connected, and the compressor suction pipe side of the low-pressure air pipe and the low-pressure main air pipe connection side of the low-pressure air pipe are connected for normal circulation; the compressor exhaust pipe side of the high-pressure air pipe and the low-pressure main air pipe connection side of the low-pressure air pipe are connected, and the compressor suction pipe side of the low-pressure air pipe and the high-pressure main air pipe of the high-pressure air pipe are connected, and the oil return circulation can be switched.

[0109] In the oil return operation when there is a height difference between the outside and inside of the outdoor unit, the oil return cycle of the oil return four-way valve is switched to connect the compressor exhaust pipe side of the high-pressure gas pipe with the low-pressure main gas pipe connection side of the low-pressure gas pipe. In addition, all high-pressure side switching valves of the branch box are set to closed, and all low-pressure side switching valves are set to open.

[0110] In the oil return operation when there is a height difference between the outside and inside of the outdoor unit, the oil return cycle of the oil return four-way valve is switched to connect the compressor suction pipe side of the low-pressure gas pipe and the high-pressure main gas pipe connection side of the high-pressure gas pipe. In addition, all high-pressure side switching valves of the branch box are set to open, and all low-pressure side switching valves are set to close.

[0111] The embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is read and executed by a processor, the method provided in the above embodiment is implemented, and the same technical effect can be achieved. To avoid repetition, it is not repeated here. The computer-readable storage medium is, for example, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0112] Of course, those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the control device through a computer, and the program can be stored in a computer-readable storage medium. When the program is executed, it may include the processes of the above-mentioned method embodiments, wherein the storage medium may be a memory, a disk, an optical disk, etc.

[0113] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

[0114] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0115] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0116] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A multi-connected simultaneous cooling and heating air conditioner capable of preventing compressor oil shortage, characterized in that: Including oil return four-way valve; The compressor exhaust pipe side of the high-pressure air pipe, the high-pressure main air pipe connecting portion side of the high-pressure air pipe, the compressor suction pipe side of the low-pressure air pipe and the low-pressure main air pipe connecting portion side of the low-pressure air pipe are respectively connected to the respective interfaces of the oil return four-way valve; the high-pressure main air pipe connecting portion is connected to the high-pressure main air pipe, and the low-pressure main air pipe connecting portion is connected to the low-pressure main air pipe; Under normal circulation, the communication relationship of the oil return four-way valve is as follows: the compressor exhaust pipe side of the high-pressure air pipe is connected to the high-pressure main air pipe connecting portion side of the high-pressure air pipe, and the compressor suction pipe side of the low-pressure air pipe is connected to the low-pressure main air pipe connecting portion side of the low-pressure air pipe; In the oil return cycle, the connectivity relationship of the oil return four-way valve is as follows: the compressor exhaust pipe side of the high-pressure air pipe and the low-pressure main air pipe connecting portion side of the low-pressure air pipe are connected, and the compressor intake pipe side of the low-pressure air pipe and the high-pressure main air pipe connecting portion side of the high-pressure air pipe are connected.

2. The air conditioner according to claim 1, characterized in that In the oil return cycle when there is an outside-inside head difference on the upper side of the outdoor unit, all high-pressure side switching valves of the conversion device are set to closed, and all low-pressure side switching valves are set to open.

3. The air conditioner according to claim 2, characterized in that It also includes a four-way valve for the outdoor unit; In the oil return cycle when there is an outside-inside height difference on the upper side of the outdoor unit, the outdoor unit four-way valve operates in a heating cycle.

4. The air conditioner according to claim 1, wherein: In the oil return cycle when there is a height difference between the outside and inside of the outdoor unit at the lower side, all high-pressure side switching valves of the conversion device are set to open, and all low-pressure side switching valves are set to closed.

5. The air conditioner according to claim 4, characterized in that It also includes a four-way valve for the outdoor unit; In the oil return cycle when there is an outside-inside height difference at the lower side of the outdoor unit, the outdoor unit four-way valve operates in a refrigeration cycle.

6. The air conditioner according to claim 1, wherein: The high-pressure main gas pipe is connected to the first port of the indoor unit through a high-pressure side switching valve; the low-pressure main gas pipe is connected to the first port of the indoor unit through a low-pressure side switching valve.

7. The air conditioner according to claim 6, characterized in that Also included is a main liquid pipe; The main liquid pipe is connected between the indoor unit and the outdoor unit. One end of the main liquid pipe is connected to the second port of the indoor unit, and the other end is connected to the outdoor heat exchanger of the outdoor unit.

8. A control method for a multi-connected simultaneous cooling and heating air conditioner, characterized in that: The multi-connected simultaneous cooling and heating air conditioner according to any one of claims 1 to 7 comprises: If the oil return operation command is obtained and there is an internal and external drop, the oil return four-way valve is controlled to operate in an oil return cycle; If it is determined that the outdoor unit is on the upper side, all high-pressure side switching valves of the control conversion device are closed, and all low-pressure side switching valves are opened; If it is determined that the outdoor unit is on the lower side, all high-pressure side switching valves of the control conversion device are opened, and all low-pressure side switching valves are closed.

9. The method according to claim 8, characterized in that The method further comprises: If it is determined that the outdoor unit is on the upper side, the four-way valve of the outdoor unit is controlled to operate in a heating cycle; If it is determined that the outdoor unit is on the lower side, the outdoor unit four-way valve is controlled to operate in a refrigeration cycle.

10. The method according to claim 8 or 9, characterized in that The method further comprises: When the oil return operation is completed, the oil return four-way valve is controlled to operate in a normal cycle, and the outdoor unit four-way valve is controlled to return to the state before the oil return operation.

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