Multi-connected air conditioning system and control method thereof

Abstract

The application provides a multi-connected air conditioner system and a control method thereof, the multi-connected air conditioner system comprising: a compressor, an oil separator, an oil return electronic expansion valve and an oil return capillary tube connected in sequence to form a closed loop, and further comprising: a hot gas bypass pipeline, two ends of which are respectively connected in parallel to an inlet of the oil separator and an outlet of the oil return electronic expansion valve; a hot gas bypass valve arranged in the hot gas bypass pipeline; the control method comprising the following steps: a refrigeration oil discharge step: in a shutdown state, and when there is a pressure difference between an exhaust end of the compressor and a suction end of the compressor, the oil return electronic expansion valve is controlled to be closed, and the hot gas bypass valve is controlled to be opened. According to the application, the refrigeration oil in the oil return capillary tube can overcome the frictional resistance of the refrigeration oil under the large driving force provided by the pressure difference, and is discharged from the oil return capillary tube, so that the risk of freezing of the refrigeration oil in the oil return capillary tube is reduced, the oil return performance and service life of the compressor are improved, and the normal operation of the air conditioner system is ensured, and the user experience is improved.

Description

Technical Field

[0001] This invention relates to air conditioning systems, specifically a multi-split air conditioning system and its control method. Background Technology

[0002] When a multi-split air conditioning system is first started after a long period of shutdown at low temperatures, the refrigerant oil in the oil return capillary tube freezes due to the low ambient and exhaust temperatures during the initial startup of the compressor. This also results in high frictional resistance, making it difficult for the compressor to return oil, which affects the compressor's service life and the normal operation of the multi-split air conditioning system. Summary of the Invention

[0003] To address the above problems, this invention provides a multi-split air conditioning system and its control method. When the system is stopped and there is a pressure difference between the compressor's exhaust and return ends, a hot gas bypass pipeline connects the inlet of the oil separator to the outlet of the electronic expansion valve for oil return. This allows the refrigerant oil in the oil return capillary to overcome its own frictional resistance and be discharged from the capillary under the strong impetus provided by the pressure difference. This reduces the risk of refrigerant oil freezing in the capillary, improves the compressor's oil return performance and service life, helps ensure the normal operation of the air conditioning system, and enhances the user experience.

[0004] This invention provides a control method for a multi-split air conditioning system. The multi-split air conditioning system includes: a compressor, an oil separator, an oil return electronic expansion valve, and an oil return capillary tube connected in sequence to form a closed loop; and a hot gas bypass pipeline with its two ends connected in parallel at the inlet of the oil separator and the outlet of the oil return electronic expansion valve, respectively; and a hot gas bypass valve located in the hot gas bypass pipeline. The control method includes the following steps: a refrigerant oil discharge step: in the off state, and with a pressure difference between the discharge end and the suction end of the compressor, the oil return electronic expansion valve is closed, and the hot gas bypass valve is opened.

[0005] According to this technical solution, when the compressor is stopped and there is a pressure difference between the exhaust and return ends, a hot gas bypass pipeline is used to connect the inlet of the oil separator to the outlet of the electronic expansion valve for oil return. This allows the refrigerant oil in the oil return capillary to overcome its own frictional resistance and be discharged from the oil return capillary under the strong pushing force provided by the pressure difference, and then enter the pipeline between the oil return capillary and the compressor. This reduces the risk of the refrigerant oil freezing in the oil return capillary, improves the oil return performance and service life of the compressor, helps ensure the normal operation of the air conditioning system, and enhances the user experience.

[0006] In the optional technical solution of the present invention, it further includes: a first judgment step: in the start-up state, judging whether the pressure ratio is not less than the pressure ratio threshold, or in the start-up state, whether the exhaust superheat is not less than the first superheat threshold; wherein, the pressure ratio α = (Pd + 0.1) / (Ps + 0.1), Pd is the high pressure; Ps is the low pressure; exhaust superheat Tdsh = Tp - Ts, Tp is the exhaust temperature of the compressor, and Ts is the saturation temperature corresponding to the high pressure; a first oil return step: if the pressure ratio is not less than the pressure ratio threshold or the exhaust superheat is not less than the first superheat threshold, controlling the opening of the oil return electronic expansion valve and the hot gas bypass valve.

[0007] According to this technical solution, as the pressure ratio increases, the exhaust temperature also increases, and the exhaust superheat increases. By controlling the exhaust superheat or pressure ratio within the specified range, the oil separation effect of the multi-split air conditioning system can be guaranteed. In addition, when the pressure ratio or exhaust superheat exceeds the preset value, in addition to opening the return oil electronic expansion valve, the hot gas bypass valve is also opened. Based on the return oil, the high-temperature and high-pressure gaseous refrigerant at the compressor outlet enters the return oil capillary tube, which can increase the temperature of the refrigeration oil in the capillary tube, reduce the friction coefficient of the refrigeration oil, and improve the return oil efficiency of the compressor.

[0008] In an optional technical solution of the present invention, in the first oil return step, the opening degree of the oil return electronic expansion valve is K = (Pd_target - Pd) * α + (Tdsh - Tdsh_target) * β + c; where Pd_target is the target high pressure; Tdsh_target is the target superheat; α is the high pressure correction coefficient; β is the superheat correction coefficient; and c is a constant.

[0009] According to this technical solution, the opening degree of the return oil electronic expansion valve is determined based on the pressure difference between the target pressure and the high pressure, the difference between the exhaust superheat and the target superheat, the superheat correction coefficient, and the high pressure correction coefficient. This helps to improve the control accuracy of the return oil electronic expansion valve opening and improve the accuracy of return oil control.

[0010] In an optional technical solution of the present invention, after the first oil return step, the method further includes: a second judgment step: judging whether the exhaust superheat is not less than a second superheat threshold, wherein the second superheat threshold is greater than a first superheat threshold; the second oil return step: if it is not less than, then control the return oil electronic expansion valve to remain open and the hot gas bypass valve to close; if it is less than, then return to the first oil return step.

[0011] According to the technical solution, when the exhaust superheat is greater than the second superheat threshold, that is, the normal operation of the air conditioning system can ensure the normal oil return of the compressor, the hot gas bypass valve is closed, and the high-temperature and high-pressure gaseous refrigerant discharged from the compressor directly enters the main refrigerant circulation, ensuring the refrigerant dosage in the main refrigerant circuit, which is conducive to improving the operating effect of the multi-split air conditioning system and enhancing the user experience.

[0012] In an optional technical solution of the present invention, after the second oil return step, the method further includes: a third judgment step: judging whether the exhaust superheat is not less than a third superheat threshold, wherein the third superheat threshold is greater than the second superheat threshold; and a third oil return step: if it is not less than, controlling the return oil electronic expansion valve to open to the maximum opening; if it is less than, returning to the third judgment step.

[0013] According to this technical solution, when the exhaust superheat exceeds the third superheat threshold, the opening of the return oil electronic expansion valve reaches its maximum, which can greatly improve the return oil efficiency and enhance the operating stability of the compressor.

[0014] In an optional technical solution of the present invention, before the refrigeration oil discharge step, a fourth judgment step is further included: judging whether the outdoor ambient temperature is lower than the temperature threshold; if it is lower, the refrigeration oil discharge step is performed; if it is not lower, the fourth oil return step is performed: controlling the opening of the oil return electronic expansion valve and the opening of the hot gas bypass valve.

[0015] According to this technical solution, when the outdoor ambient temperature is high, the friction coefficient of the refrigeration oil is small and the frictional resistance is low. The compressor can return oil by opening the return oil electronic expansion valve and the hot gas bypass valve.

[0016] The present invention also provides a multi-split air conditioning system, comprising: a compressor, an oil separator, an oil return electronic expansion valve, and an oil return capillary tube connected in sequence to form a closed loop; further comprising: a hot gas bypass pipeline, with its two ends respectively connected in parallel to the inlet of the oil separator and the outlet of the oil return electronic expansion valve; a hot gas bypass valve, located in the hot gas bypass pipeline; and a controller configured to perform the following step: refrigerant oil discharge: in the shutdown state, and with a pressure difference between the discharge end and the suction end of the compressor, the controller closes the oil return electronic expansion valve and opens the hot gas bypass valve.

[0017] In an optional technical solution of the present invention, the controller further performs the following steps: First judgment step: In the power-on state, determine whether the pressure ratio is not less than the pressure ratio threshold, or in the power-on state, whether the exhaust superheat is not less than the first superheat threshold; wherein, pressure ratio α = (Pd + 0.1) / (Ps + 0.1), Pd is the high pressure; Ps is the low pressure; exhaust superheat Tdsh = Tp - Ts, Tp is the exhaust temperature of the compressor, and Ts is the saturation temperature corresponding to the high pressure; First oil return step: If the pressure ratio is not less than the pressure ratio threshold or the exhaust superheat is not less than the first superheat threshold, control the opening of the oil return electronic expansion valve and the hot gas bypass valve.

[0018] In an optional technical solution of the present invention, in the first oil return step, the opening degree of the oil return electronic expansion valve is K = (Pd_target - Pd) * α + (Tdsh - Tdsh_target) * β + c; where Pd_target is the target high pressure; Tdsh_target is the target superheat; α is the high pressure correction coefficient; β is the superheat correction coefficient; and c is a constant.

[0019] In an optional technical solution of the present invention, a one-way valve is also included, which is located between the outlet of the compressor and the inlet of the oil separator to control the one-way flow of refrigerant from the compressor to the oil separator. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a multi-split air conditioning system according to an embodiment of the present invention.

[0021] Figure 2 This is a flowchart illustrating the control method of a multi-split air conditioning system according to an embodiment of the present invention.

[0022] Figure label:

[0023] Compressor 11; Oil separator 12; Electronic expansion valve for oil return 13; Oil return capillary tube 14; Hot gas bypass line 2; Hot gas bypass valve 21; Low pressure sensor 31; High pressure sensor 32; Temperature sensor 33; Check valve 4. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1 , Figure 2 As shown, this invention provides a control method for a multi-split air conditioning system. The multi-split air conditioning system includes: a compressor 11, an oil separator 12, an oil return electronic expansion valve 13, and an oil return capillary tube 14 connected in sequence to form a closed loop; it also includes: a hot gas bypass pipeline 2, with its two ends connected in parallel at the inlet of the oil separator 12 and the outlet of the oil return electronic expansion valve 13; and a hot gas bypass valve 21 located in the hot gas bypass pipeline 2. In addition, the multi-split air conditioning system also includes a four-way valve 15, an indoor heat exchanger 16, a throttle valve 17, an outdoor heat exchanger 18, and a gas-liquid separator 19. The connection relationship of the four-way valve 15, the indoor heat exchanger 16, the throttle valve 17, the outdoor heat exchanger 18, and the gas-liquid separator 19 is shown in the figure, which is a common form in the art and will not be described in detail here.

[0026] In this embodiment, the control method includes the following steps: Refrigerant oil discharge step: In the shutdown state, and with a pressure difference between the discharge end and the suction end of the compressor 11 (preferably, 3-8 minutes after the compressor 11 stops, there is a certain pressure difference between the discharge end and the suction end of the compressor 11), the return oil electronic expansion valve 13 is closed, and the hot gas bypass valve 21 is opened. By using the hot gas bypass pipeline 2 to connect the inlet of the oil separator 12 and the outlet of the return oil electronic expansion valve 13 when the compressor 11 is shut down and there is a pressure difference between the discharge end and the return gas end, the refrigerant oil in the return oil capillary tube 14 overcomes its own frictional resistance and is discharged from the return oil capillary tube 14 under the greater pushing force provided by the pressure difference, and enters the pipeline between the return oil capillary tube 14 and the compressor 11. This reduces the risk of refrigerant oil freezing in the return oil capillary tube 14, improves the oil return performance and service life of the compressor 11, helps ensure the normal operation of the air conditioning system, and enhances the user experience.

[0027] In a preferred embodiment of the present invention, the method further includes: a first judgment step: in the power-on state, determining whether the pressure ratio is not less than a pressure ratio threshold, or whether the exhaust superheat is not less than a first superheat threshold; wherein, pressure ratio α = (Pd + 0.1) / (Ps + 0.1), Pd is the high-pressure pressure in MPa, Ps is the low-pressure pressure in MPa; exhaust superheat Tdsh = Tp - Ts, Tp is the exhaust temperature of the compressor, and Ts is the saturation temperature corresponding to the high-pressure pressure; a first oil return step: if the pressure ratio is not less than the pressure ratio threshold or the exhaust superheat is not less than the first superheat threshold, controlling the opening of the oil return electronic expansion valve 13 and the hot gas bypass valve 21. Specifically, the pressure ratio threshold is 2.1, the first superheat threshold is 3°C, the standard atmospheric pressure of 0.1 MPa and the detected high-pressure pressure are the absolute high-pressure pressure; the sum of the standard atmospheric pressure of 0.1 MPa and the detected low-pressure pressure is the absolute low-pressure pressure, and the pressure ratio is the ratio of the absolute high-pressure pressure to the absolute low-pressure pressure.

[0028] By increasing the pressure ratio, the exhaust temperature and exhaust superheat are also increased. Controlling the exhaust superheat or pressure ratio within the specified range ensures the oil separation effect of the multi-split air conditioning system. Furthermore, when the pressure ratio or exhaust superheat exceeds the preset value, in addition to opening the return oil electronic expansion valve 13, the hot gas bypass valve 21 is also opened. Based on the oil return process, the high-temperature, high-pressure gaseous refrigerant from the compressor 11 outlet enters the return oil capillary tube 14, increasing the temperature of the refrigerant oil in the return oil capillary tube 14, reducing the friction coefficient of the refrigerant oil, and improving the oil return efficiency of the compressor 11. In addition, in the initial stage after the compressor 11 stops, the refrigerant oil in the return oil capillary tube 14 is discharged. The discharged refrigerant oil enters the return gas line of the compressor 11 (the line between the compressor 11 and the return oil capillary tube 14), reducing the risk of refrigerant oil freezing (because the diameter of the return gas line is larger than that of the return oil capillary tube 14, the compressor oil will not freeze in the return gas line). Furthermore, when the compressor 11 is started, by judging the exhaust superheat or pressure ratio, the hot gas bypass valve 21 and the oil return electronic expansion valve 13 are opened, so that the compressor oil in the return gas pipeline mixes with the high temperature and high pressure gaseous refrigerant at the outlet of the hot gas bypass pipeline 2 and enters the compressor 11, which improves the oil return efficiency of the compressor 11 and ensures that the oil return capillary tube 14 contains only refrigerant, with no or only a small amount of compressor oil residue, reducing the risk of compressor oil freezing in the oil return capillary tube 14 and improving the operational reliability of the air conditioning system.

[0029] Furthermore, prior to the first judgment step, a detection step is also included: detecting whether a power-on signal has been received, detecting the low-pressure pressure (which can be obtained by the low-pressure sensor 31 located between the four-way valve 15 and the gas-liquid separator 19), the high-pressure pressure (which can be obtained by the high-pressure sensor 32 located between the compressor exhaust port and the four-way valve 15), and the exhaust temperature (which can be obtained by the temperature sensor 33 at the outlet of the compressor 11), and obtaining the saturation temperature corresponding to the high-pressure pressure by looking up a table based on the high-pressure pressure; and calculating the pressure ratio based on the detected high-pressure and low-pressure, and calculating the exhaust superheat based on the difference between the exhaust temperature and the saturation temperature.

[0030] In a preferred embodiment of the present invention, in the first oil return step, the opening degree K of the oil return electronic expansion valve 13 is K = (Pd_target - Pd) * α + (Tdsh - Tdsh_target) * β + c; where Pd_target is the target high pressure; Tdsh_target is the target superheat; Pd is the high pressure; α is the high pressure correction coefficient; β is the superheat correction coefficient; and c is a constant. Determining the opening degree of the oil return electronic expansion valve 13 based on the pressure difference between the target pressure and the high pressure, the difference between the exhaust superheat and the target superheat, the superheat correction coefficient, and the high pressure correction coefficient is beneficial for improving the control accuracy of the opening degree of the oil return electronic expansion valve 13 and improving the accuracy of oil return control. In this embodiment, Pd_target = 2.8, Tdsh_target = 25℃; high pressure correction coefficient α = -17; superheat correction coefficient β = -5.7, c = 320. The high pressure, low pressure and exhaust temperature are real-time detected values. The exhaust superheat Tdsh is obtained based on the real-time difference between the exhaust temperature and the saturation temperature corresponding to the high pressure.

[0031] In a preferred embodiment of the present invention, after the first oil return step, the method further includes: a second judgment step: judging whether the exhaust superheat is not less than a second superheat threshold, wherein the second superheat threshold is greater than a first superheat threshold; a second oil return step: if it is not less than, then controlling the return oil electronic expansion valve 13 to remain open and the hot gas bypass valve 21 to close; if it is less than, then returning to the first oil return step. Specifically, the second superheat threshold is 10°C.

[0032] In this way, when the exhaust superheat is greater than the second superheat threshold, that is, the normal operation of the air conditioning system can ensure the normal oil return of the compressor 11, the hot gas bypass valve 21 is closed, and the high temperature and high pressure gaseous refrigerant discharged by the compressor 11 directly enters the refrigerant main circuit circulation, ensuring the refrigerant dosage in the main circuit, which is conducive to improving the operating effect of the multi-split air conditioning system and enhancing the user experience.

[0033] In a preferred embodiment of the present invention, after the second oil return step, the method further includes: a third judgment step: determining whether the exhaust superheat is not less than a third superheat threshold, wherein the third superheat threshold is greater than the second superheat threshold; the third oil return step: if it is not less than, controlling the return oil electronic expansion valve 13 to open to the maximum opening degree (e.g., 500P); if it is less than, returning to the third judgment step. Specifically, the third superheat threshold is 25°C.

[0034] In the above manner, when the exhaust superheat is greater than the third superheat threshold, the opening of the return oil electronic expansion valve 13 reaches its maximum, which can greatly improve the return oil efficiency and improve the operating stability of the compressor 11.

[0035] In this embodiment, by repeatedly judging the magnitude of the exhaust superheat and the specified superheat threshold and closing them, and opening or closing the return oil electronic expansion valve 13 and the hot gas bypass valve 21 accordingly, the return oil and / or the heating of the refrigeration oil by the high-temperature and high-pressure gaseous refrigerant can be adjusted according to the real-time operating conditions of the multi-split air conditioning system. This ensures the return oil effect and operational stability of the multi-split air conditioning system, while avoiding unnecessary opening of the hot gas bypass valve 21, which would result in excessive refrigerant participating in the return oil and improve the cooling or heating effect of the multi-split air conditioning system.

[0036] In a preferred embodiment of the present invention, before the refrigerant oil discharge step, a fourth judgment step is included: determining whether the outdoor ambient temperature is lower than a temperature threshold (e.g., 5°C); if it is lower, the refrigerant oil discharge step is performed; if it is not lower, the fourth oil return step is performed: controlling the opening of the oil return electronic expansion valve 13 (e.g., opening degree of 320-350P, maximum opening degree of 500P) and the hot gas bypass valve 21. When the outdoor ambient temperature is high, the friction coefficient of the refrigerant oil is small, and the frictional resistance is small. Opening the oil return electronic expansion valve 13 and the hot gas bypass valve 21 can realize the oil return of the compressor 11. In some embodiments, only the oil return electronic expansion valve 13 may be opened, without opening the hot gas bypass valve 21.

[0037] It should be noted that although the above-mentioned superheat threshold, temperature threshold, various correction parameters, target parameters, opening parameters, etc. are exemplified in this embodiment, they should not be construed as limiting this embodiment. Those skilled in the art can adjust the above-mentioned parameters or adjust the above-mentioned parameters to a certain numerical range according to the actual situation, and this embodiment does not limit them in this regard.

[0038] The present invention also provides a multi-split air conditioning system, comprising: a compressor 11, an oil separator 12, an oil return electronic expansion valve 13, and an oil return capillary tube 14 connected in sequence to form a closed loop, and further comprising: a hot gas bypass pipeline 2, with its two ends respectively connected in parallel to the inlet of the oil separator 12 and the outlet of the oil return electronic expansion valve 13; a hot gas bypass valve 21, provided in the hot gas bypass pipeline 2; and a controller (not shown in the figure), configured to perform the following step: refrigerant oil discharge: in the shutdown state, and with a pressure difference between the discharge end and the suction end of the compressor 11, the controller closes the oil return electronic expansion valve 13 and opens the hot gas bypass valve 21.

[0039] Specifically, the controller can be an integrated circuit chip with signal processing capabilities. The aforementioned controller can be a general-purpose processor, including a Central Processing Unit (CPU), or a microcontroller, microcontroller unit (MCU), complex programmable logic device (CPLD), field-programmable gate array (FPGA), application-specific integrated circuit (ASIC), embedded ARM, etc. The controller can implement or execute the methods, steps, and logic block diagrams disclosed in this embodiment. Furthermore, the controller is communicatively connected to the low-pressure sensor 31, high-pressure sensor 32, and temperature sensor 33 to receive signals sent by these sensors and perform corresponding data processing. The controller is also communicatively connected to the hot gas bypass valve 21 and the return oil electronic expansion valve 13 to control their opening and closing.

[0040] In a preferred embodiment of the present invention, the controller further performs the following step: determining, in the power-on state, the superheat range of the exhaust superheat or the pressure ratio range of the pressure ratio.

[0041] The control step controls the opening or closing of the return oil electronic expansion valve and the hot gas bypass valve based on the judgment result of the judgment step.

[0042] Specifically, the judgment steps include:

[0043] The first judgment step: In the power-on state, determine whether the pressure ratio is not less than the pressure ratio threshold, or whether the exhaust superheat is not less than the first superheat threshold; where the pressure ratio α = (Pd + 0.1) / (Ps + 0.1), and Ps is the low pressure; correspondingly, the controller executes the first oil return step: if the pressure ratio is not less than the pressure ratio threshold or the exhaust superheat is not less than the first superheat threshold, control the opening of the oil return electronic expansion valve 13 and the hot gas bypass valve 21. If the pressure ratio is less than the pressure ratio threshold or the exhaust superheat is less than the first superheat threshold, return to the detection step.

[0044] Preferably, in the first oil return step, the opening degree K of the oil return electronic expansion valve 13 is K = (Pd_target - Pd) * α + (Tdsh - Tdsh_target) * β + c; where Pd_target is the target high pressure; Tdsh_target is the target superheat; Pd is the high pressure; α is the high pressure correction coefficient; β is the superheat correction coefficient; Tdsh is the exhaust superheat, Tdsh = Tp - Ts, Ts is the saturation temperature corresponding to the high pressure; and c is a constant.

[0045] The judgment step also includes: a second judgment step: judging whether the exhaust superheat is not less than a second superheat threshold, where the second superheat threshold is greater than a first superheat threshold; correspondingly, the control step includes a second oil return step: if it is not less than, then control the oil return electronic expansion valve 13 to remain open and the hot gas bypass valve 21 to close; if it is less than, then return to the first oil return step. Specifically, the second superheat threshold is 10°C.

[0046] In this way, when the exhaust superheat is greater than the second superheat threshold, that is, the normal operation of the air conditioning system can ensure the normal oil return of the compressor 11, the hot gas bypass valve 21 is closed, and the high temperature and high pressure gaseous refrigerant discharged by the compressor 11 directly enters the refrigerant main circuit circulation, ensuring the refrigerant dosage in the main circuit, which is conducive to improving the operating effect of the multi-split air conditioning system and enhancing the user experience.

[0047] The judgment steps also include: a third judgment step: determining whether the exhaust superheat is not less than the third superheat threshold, where the third superheat threshold is greater than the second superheat threshold; correspondingly, the control steps include: a third oil return step: if not less than, controlling the oil return electronic expansion valve 13 to open to the maximum opening degree (e.g., 500P); if less than, returning to the third judgment step. Specifically, the third superheat threshold is 25℃.

[0048] In the above manner, when the exhaust superheat is greater than the third superheat threshold, the opening of the return oil electronic expansion valve 13 reaches its maximum, which can greatly improve the return oil efficiency and improve the operating stability of the compressor 11.

[0049] In a preferred embodiment of the present invention, a one-way valve 4 is further provided between the outlet of the compressor 11 and the inlet of the oil separator 12 to control the one-way flow of refrigerant from the compressor 11 to the oil separator 12.

[0050] In a preferred embodiment of the present invention, the outlet end of the oil return capillary 14 is connected to the outlet pipeline of the gas-liquid separator 19. The compressor oil at the outlet of the oil return capillary 14 mixes with the gaseous refrigerant at the outlet of the gas-liquid separator 19 and then enters the compressor 11, further reducing the risk of compressor oil freezing.

[0051] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A control method for a multi-split air conditioning system, characterized in that, The multi-split air conditioning system includes: a compressor, an oil separator, an electronic expansion valve for oil return, and an oil return capillary tube connected in sequence to form a closed loop; and also includes: A hot gas bypass pipeline is connected in parallel at both ends to the inlet of the oil separator and the outlet of the return oil electronic expansion valve; A hot gas bypass valve is installed in the hot gas bypass pipeline; A return gas line is located between the compressor and the oil return capillary tube, and the diameter of the return gas line is larger than the diameter of the oil return capillary tube. The control method includes the following steps: Fourth judgment step: Determine whether the outdoor ambient temperature is lower than the temperature threshold; if it is lower, then execute the refrigerant oil discharge step; if it is not lower, then execute the fourth oil return step: control the opening of the oil return electronic expansion valve and the opening of the hot gas bypass valve; Refrigeration oil discharge procedure: In the shutdown state, and with a pressure difference between the discharge end and the suction end of the compressor, the electronic expansion valve for oil return is closed, and the hot gas bypass valve is opened, so that the refrigeration oil is discharged from the oil return capillary to the gas return line.

2. The control method for a multi-split air conditioning system according to claim 1, characterized in that, Also includes: The first judgment step: With the unit powered on, determine whether the pressure ratio is not less than the pressure ratio threshold, or with the unit powered on, whether the exhaust superheat is not less than the first superheat threshold; wherein, The pressure ratio α = (Pd + 0.1) / (Ps + 0.1), where Pd is the high pressure and Ps is the low pressure. The exhaust superheat Tdsh = Tp - Ts, where Tp is the exhaust temperature of the compressor and Ts is the saturation temperature corresponding to the high pressure. First oil return step: If the pressure ratio is not less than the pressure ratio threshold or the exhaust superheat is not less than the first superheat threshold, control the opening of the oil return electronic expansion valve and the hot gas bypass valve.

3. The control method for a multi-split air conditioning system according to claim 2, characterized in that, In the first oil return step, the opening degree K of the oil return electronic expansion valve is K = (Pd_target - Pd) * α + (Tdsh - Tdsh_target) * β + c; where, Pd_target represents the target high voltage; Tdsh_target represents the target overheat level; α is the high-voltage correction factor; β is the superheat correction factor; c is a constant.

4. The control method for a multi-split air conditioning system according to claim 3, characterized in that, Following the first oil return step, the following is also included: Second determination step: Determine whether the exhaust superheat is not less than the second superheat threshold, wherein the second superheat threshold is greater than the first superheat threshold; Second oil return step: If it is not less than, then control the return oil electronic expansion valve to remain open and the hot gas bypass valve to close; if it is less than, then return to the first oil return step.

5. The control method for a multi-split air conditioning system according to claim 4, characterized in that, The process after the second oil return step also includes: The third judgment step: determine whether the exhaust superheat is not less than the third superheat threshold, wherein the third superheat threshold is greater than the second superheat threshold; Third oil return step: If it is not less than, then control the oil return electronic expansion valve to open to the maximum opening degree; if it is less than, then return to the third judgment step.

6. A multi-split air conditioning system, characterized in that, include: The compressor, oil separator, electronic expansion valve for oil return, and capillary tube for oil return are connected in sequence to form a closed loop, and also include: A hot gas bypass pipeline is connected in parallel at both ends to the inlet of the oil separator and the outlet of the return oil electronic expansion valve; A hot gas bypass valve is installed in the hot gas bypass pipeline; A return gas line is located between the compressor and the oil return capillary tube, and the diameter of the return gas line is larger than the diameter of the oil return capillary tube. The controller is configured to execute: Fourth judgment step: Determine whether the outdoor ambient temperature is lower than the temperature threshold; if it is lower, then execute the refrigerant oil discharge step; if it is not lower, then execute the fourth oil return step: control the opening of the oil return electronic expansion valve and the opening of the hot gas bypass valve; Refrigeration oil discharge procedure: In the shutdown state, and with a pressure difference between the discharge end and the suction end of the compressor, the electronic expansion valve for oil return is closed, and the hot gas bypass valve is opened, so that the refrigeration oil is discharged from the oil return capillary to the gas return line.

7. The multi-split air conditioning system according to claim 6, characterized in that, The controller also performs: The first judgment step: With the unit powered on, determine whether the pressure ratio is not less than the pressure ratio threshold, or with the unit powered on, whether the exhaust superheat is not less than the first superheat threshold; wherein, The pressure ratio α = (Pd + 0.1) / (Ps + 0.1), where Pd is the high pressure and Ps is the low pressure. The exhaust superheat Tdsh = Tp - Ts, where Tp is the exhaust temperature of the compressor and Ts is the saturation temperature corresponding to the high pressure. First oil return step: If the pressure ratio is not less than the pressure ratio threshold or the exhaust superheat is not less than the first superheat threshold, control the opening of the oil return electronic expansion valve and the hot gas bypass valve.

8. The multi-split air conditioning system according to claim 7, characterized in that, In the first oil return step, the opening degree K of the oil return electronic expansion valve is K = (Pd_target - Pd) * α + (Tdsh - Tdsh_target) * β + c; where, Pd_target represents the target high voltage; Tdsh_target represents the target overheat level; α is the high-voltage correction factor; β is the superheat correction factor; c is a constant.

9. The multi-split air conditioning system according to claim 6, characterized in that, It also includes a one-way valve located between the outlet of the compressor and the inlet of the oil separator to control the flow of refrigerant from the compressor to the oil separator.

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