Control method of air conditioning system and air conditioning system

Abstract

The invention relates to the technical field of air conditioning systems, and particularly provides a control method of an air conditioning system and the air conditioning system. The air conditioning system comprises an oil return pipeline and an oil separator, the oil separator is arranged on a pipeline on the exhaust side of a compressor, one end of the oil return pipeline is connected with the oil separator, the other end of the oil return pipeline is connected with a pipeline on the air suction side of the compressor, and an oil return switch valve is arranged on the oil return pipeline; the control method comprises the steps that the suction superheat degree and / or suction pressure of the compressor are / is obtained; and when the suction superheat degree is smaller than or equal to the first preset superheat degree and / or the suction pressure is smaller than or equal to the first preset pressure, an oil return switch valve is controlled to be opened. The high-low pressure bypass loop and the oil return loop are combined into one oil return pipeline, lubricating oil is accumulated to a certain amount and then returns to the air suction pipe of the compressor in a unified mode, the instantaneous oil return amount is large, and mixed high-temperature refrigerants are few. When the suction superheat degree or the suction pressure is low, the oil return switch valve is opened, the high-temperature gas enters the suction pipe, the liquid refrigerant is gasified, and the performance of the compressor is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioning systems, and particularly provides a control method for an air conditioning system and an air conditioning system. Background Art

[0002] Generally, a variable-frequency air-source heat pump unit needs to adopt an oil separator to separate the oil in the compressor exhaust and return it to the compressor. However, during the real-time oil return process of the oil separator, a part of the high-temperature exhaust gas will bypass to the suction, resulting in a loss of about 3% of the heating / cooling performance. The variable-frequency air-source heat pump unit is provided with high and low pressure bypass pipes to bypass a part of the high-temperature and high-pressure refrigerant to the suction side when the suction pressure is low, so as to increase the suction pressure and prevent the compressor from operating below the allowable pressure.

[0003] In response to the problem that high-temperature exhaust gas bypasses to the suction pipe during the oil return process, the industry generally adds a capillary tube to the oil return pipeline from the oil separator to the suction pipe to reduce the amount of refrigerant bypass. However, when this solution is applied to a variable-frequency compressor, the capillary tube specification can ensure a small amount of bypass while ensuring the oil discharge amount at the maximum oil discharge amount (at the maximum frequency), and the impact on the compressor is small. However, when the compressor operates at low frequency, the oil discharge amount decreases, and more high-temperature exhaust gas will bypass to the compressor suction pipe, resulting in a greater performance loss.

[0004] Correspondingly, the art needs a new control method for an air conditioning system to solve the problem that the existing air conditioning system is prone to refrigerant bypass during oil return, resulting in performance loss of the compressor. Summary of the Invention

[0005] The present invention aims to solve the above technical problems, that is, to solve the problem that the existing air conditioning system is prone to refrigerant bypass during oil return, resulting in performance loss of the compressor.

[0006] The present invention provides a control method for an air conditioning system. The air conditioning system includes a refrigerant circulation pipeline, on which a compressor, an indoor unit heat exchanger, and an outdoor unit heat exchanger are provided. It is characterized in that the air conditioning system further includes an oil return pipeline and an oil separator. The oil separator is arranged on the pipeline on the exhaust side of the compressor. One end of the oil return pipeline is connected to the oil separator, and the other end is connected to the pipeline on the suction side of the compressor. A return oil switch valve is arranged on the oil return pipeline. The control method includes:

[0007] Obtaining the suction superheat degree and / or suction pressure of the compressor;

[0008] When the suction superheat degree ≤ the first preset superheat degree and / or the suction pressure ≤ the first preset pressure, controlling the return oil switch valve to open.

[0009] In the preferred technical solution of the control method of the above air-conditioning system, after the step of "when the suction superheat degree ≤ the first preset superheat degree, control the oil return switch valve to open", the control method further includes:

[0010] When the suction superheat degree > the second preset superheat degree, control the oil return switch valve to close, where the first preset superheat degree ≤ the second preset superheat degree.

[0011] In the preferred technical solution of the control method of the above air-conditioning system, after the step of "when the suction pressure ≤ the first preset pressure, control the oil return switch valve to open", the control method includes:

[0012] When the suction pressure > the second preset pressure, control the oil return switch valve to close, where the first preset pressure ≤ the second preset pressure.

[0013] In the preferred technical solution of the control method of the above air-conditioning system, the step of "acquire the superheat degree of the compressor" further includes:

[0014] Acquire the suction temperature and suction pressure of the compressor;

[0015] Acquire the saturation temperature corresponding to the suction pressure;

[0016] Suction superheat degree = suction temperature - saturation temperature corresponding to the suction pressure.

[0017] In the preferred technical solution of the control method of the above air-conditioning system, an oil level sensor for detecting the lubricating oil level is provided in the oil separator; the oil level sensor is set to close when the lubricating oil level in the oil separator reaches the maximum threshold and to open when it is less than the maximum threshold; before the step of "acquire the suction superheat degree and / or suction pressure of the compressor", the control method includes:

[0018] Judge whether the oil level sensor is closed;

[0019] If the oil level sensor is closed, control the oil return switch valve to open.

[0020] In the preferred technical solution of the control method of the above air-conditioning system, after the step of "when the oil level sensor is closed, control the oil return switch valve to open", the control method further includes:

[0021] Judge whether the disconnection duration of the oil level sensor exceeds the T1 duration;

[0022] If it exceeds the T1 duration, control the oil return switch valve to close.

[0023] In the preferred technical solution of the control method of the above air-conditioning system, after the step of "controlling the oil return switch valve to open", the control method includes:

[0024] Calculate the opening duration of the oil return switch valve;

[0025] If the opening duration of the oil return switch valve is greater than the T2 duration and still the suction superheat degree ≤ the first preset superheat degree, then close the oil return switch valve and report an error to the user.

[0026] In the preferred technical solution of the control method of the above air-conditioning system, after the step of "obtaining the suction pressure of the compressor", the control method includes:

[0027] When the suction pressure > the first preset pressure, return to continue obtaining the suction pressure of the compressor.

[0028] In the preferred technical solution of the control method of the above air-conditioning system, after the step of "obtaining the suction superheat degree of the compressor", the control method includes:

[0029] When the suction superheat degree > the first preset superheat degree, return to continue obtaining the suction superheat degree of the compressor.

[0030] The present invention also provides an air-conditioning system, which includes a memory and a processor. The memory is adapted to store multiple program codes, and the program codes are adapted to be loaded and run by the processor to execute the control method of the air-conditioning system described in any of the above technical solutions.

[0031] Those skilled in the art can understand that the air-conditioning system of the present invention includes a refrigerant circulation pipeline, on which a compressor, an indoor unit heat exchanger, and an outdoor unit heat exchanger are provided. The air-conditioning system also includes an oil return pipeline and an oil separator. The oil separator is arranged on the pipeline on the exhaust side of the compressor. One end of the oil return pipeline is connected to the oil separator, and the other end is connected to the pipeline on the suction side of the compressor. An oil return switch valve is arranged on the oil return pipeline; the control method includes: obtaining the suction superheat degree and / or suction pressure of the compressor; when the suction superheat degree ≤ the first preset superheat degree and / or the suction pressure ≤ the first preset pressure, controlling the oil return switch valve to open.

[0032] In the case of adopting the above technical solution, the gaseous refrigerant discharged from the compressor contains a certain amount of compressor lubricating oil. When the gaseous refrigerant enters the oil separator, the lubricating oil in the gaseous refrigerant will remain at the bottom of the oil separator, and the gas will enter the refrigerant pipeline through the upper part. In the present invention, the high-low pressure bypass capillary and the oil return circuit are combined into an oil return pipeline. After the lubricating oil accumulates to a certain amount, it is uniformly returned to the compressor suction pipe. When returning oil, the oil return switch valve is instantaneously opened. The large amount of oil return results in less mixed high-temperature refrigerant, and the amount of oil return is not affected by the low-frequency operation of the compressor, ensuring that the high-temperature refrigerant will not affect the performance of the compressor. When one of the suction superheat and the suction pressure of the compressor is less than the preset value, the oil return switch valve is delayed to open, so that more gaseous refrigerant enters the compressor suction pipe to improve the performance of the compressor.

[0033] Specifically, when the suction superheat of the compressor decreases to less than the first preset superheat, it indicates that the refrigerant entering the compressor through the suction pipe may be mixed with liquid. The liquid refrigerant entering the compressor may cause dilution of the lubricating oil and reduce the lubrication effect. At this time, the oil return switch valve is opened to concentrate the oil return and lubricate the compressor. At the same time, as the opening time of the oil return switch valve is extended, more high-temperature gaseous refrigerant of the compressor enters the suction pipe to vaporize the liquid refrigerant in the suction pipe and prevent the liquid refrigerant from entering the compressor. When the suction pressure decreases to less than the first preset pressure, as the opening time of the oil return switch valve is extended, more high-temperature gaseous refrigerant of the compressor enters the suction pipe to increase the pressure of the suction pipe. The present invention ensures that the performance of the compressor is not affected during oil return by opening the oil return switch valve for a short time, and enables more gaseous refrigerant to enter the suction pipe by opening the oil return switch valve for a long time to improve the performance of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The preferred embodiments of the present invention will be described below with reference to the drawings, in which:

[0035] Figure 1 is the main step flow chart of the control method of the air-conditioning system of the present invention;

[0036] Figure 2 is the step flow chart of an embodiment of the control method of the air-conditioning system of the present invention;

[0037] Figure 3 is the step flow chart of another embodiment of the control method of the air-conditioning system of the present invention;

[0038] Figure 4 is the schematic diagram of the air-conditioning system of the present invention. LIST OF REFERENCE NUMERALS: 1. Compressor; 2. Oil separator; 3. Four-way valve; 4. Indoor unit heat exchanger; 5. Outdoor unit heat exchanger; 6. Gas-liquid separator; 7. Oil return pipeline; 8. Oil return switch valve. Detailed implementation manners

[0039] The preferred implementation manners of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these implementation manners are only used to explain the technical principle of the present invention and are not intended to limit the protection scope of the present invention. Those skilled in the art can adjust them as needed to adapt to specific application scenarios. For example, the control method of the air-conditioning system in this application can be used for wall-mounted air conditioners, cabinet air conditioners, central air conditioners, or multi-connected air conditioners, etc. The present invention does not impose any restrictions on the type of air conditioners, and it can also be applied to devices other than air conditioners that require defrosting..

[0040] Specifically, referring to Figure 4 , the air-conditioning system of the present invention includes an indoor unit, an outdoor unit, and a refrigerant circulation circuit provided between the indoor unit and the outdoor unit. The indoor unit includes an indoor unit heat exchanger, and the outdoor unit includes a compressor 1 and an outdoor unit heat exchanger 5. Optionally, the indoor unit heat exchanger is a finned heat exchanger, and the outdoor unit heat exchanger 5 is a water-side heat exchanger. Of course, those skilled in the art can also set the types of the indoor unit heat exchanger 4 and the outdoor unit heat exchanger 5 according to needs, and the present invention does not impose any restrictions on this.

[0041] The compressor 1, the indoor unit heat exchanger 4, and the outdoor unit heat exchanger 5 are all arranged on the refrigerant circulation circuit. The refrigerant circulates between the indoor and outdoor through the refrigerant circulation circuit to exchange heat with the indoor environment through the indoor unit, so as to meet the heat exchange needs of users. Further, the air-conditioning system further includes an oil separator 2, a four-way valve 3, and a gas-liquid separator 6 arranged on the refrigerant circulation circuit. The four-way valve 3 is arranged between the indoor unit heat exchanger 4 and the compressor 1. The oil separator 2 is connected to the exhaust side pipeline of the compressor 1, and the gas-liquid separator 6 is connected to the suction side pipeline of the compressor 1.

[0042] During use, the user can control the operation of the air conditioner by setting the temperature. Those skilled in the art can understand that the present invention does not impose any restrictions on the specific structure of the air-conditioning system. Technicians can set the specific structure of the air-conditioning system according to actual use needs, as long as the outdoor unit in the air-conditioning system has a compressor 1 and an outdoor unit heat exchanger 5; such a change in the specific application object does not deviate from the basic principle of the present invention and belongs to the protection scope of the present invention.

[0043] Further, the air-conditioning system further includes an oil return pipeline 7. One end of the oil return pipeline 7 is connected to the oil separator 2, and the other end is connected to the suction side pipeline of the compressor 1 and is located between the gas-liquid separator 6 and the compressor 1. An oil return switch valve 8 is arranged on the oil return pipeline 7. The oil return switch valve 8 is used to control the on-off of the oil return pipeline 7, so as to control the lubricating oil in the oil separator 2 to enter the suction pipe of the compressor 1 and continue to lubricate the compressor 1.

[0044] Furthermore, the air-conditioning system further includes a suction temperature sensor, a suction pressure sensor, an oil level sensor, and a controller. The suction temperature sensor can detect the temperature on the suction side of the compressor 1, and there is no restriction on the detection position of the suction side temperature. Those skilled in the art can set it according to their needs. Optionally, the suction temperature sensor is arranged on the pipeline on the suction side of the compressor 1.

[0045] The suction pressure sensor can detect the pressure on the suction side of the compressor 1. Preferably, there is no restriction on the detection position of the suction side pressure. Those skilled in the art can set it according to their needs. Optionally, the suction pressure sensor is arranged inside the pipeline on the suction side of the compressor 1.

[0046] The oil level sensor is arranged in the oil separator 2. The oil level sensor is set to be closed when the lubricating oil volume reaches the maximum threshold of the oil circuit, and is disconnected when the lubricating oil volume is below the maximum threshold.

[0047] The controller can obtain the suction temperature of the compressor, the suction pressure, and the state of the oil level sensor, and the controller can also control the opening and closing of the oil return switch valve 8, the operating state of the air-conditioning system, and control the frequency of the compressor 1, etc. Those skilled in the art can understand that the present invention does not impose any restrictions on the specific structure and model of the controller, and technicians can set the structure and model of the controller according to actual usage requirements.

[0048] Refer to Figure 1 , to solve the problem that the existing air-conditioning system is prone to refrigerant bypass during oil return, resulting in performance loss of the compressor. The control method of the air-conditioning system of the present invention includes:

[0049] Step S10: Obtain the suction superheat degree and / or the suction pressure of the compressor;

[0050] Step S20: When the suction superheat degree ≤ the first preset superheat degree and / or the suction pressure ≤ the first preset pressure, control the oil return switch valve to open;

[0051] Step S30: When the suction superheat degree > the second preset superheat degree and / or the suction pressure > the second preset pressure, control the oil return switch valve to close, where the first preset superheat degree ≤ the second preset superheat degree; the first preset pressure ≤ the second preset pressure.

[0052] The advantages of the above setting method are as follows: The gaseous refrigerant discharged by the compressor 1 contains a certain amount of compressor lubricating oil. The gaseous refrigerant enters the oil separator 2, and the lubricating oil in the gaseous refrigerant will remain at the bottom of the oil separator 2, while the gas enters the refrigerant pipeline through the upper part. In the present invention, the high and low pressure bypass capillary tube and the oil return circuit are combined into an oil return pipeline 7. After the lubricating oil accumulates to a certain amount, it is uniformly returned to the compressor suction pipe. When returning oil, the oil return switch valve 8 is instantaneously opened. The large amount of oil return results in less mixed high-temperature refrigerant, and the amount of oil return is not affected by the low-frequency operation of the compressor 1, ensuring that the high-temperature refrigerant will not affect the performance of the compressor 1. When the suction superheat of the compressor 1 decreases to less than the first preset superheat, it indicates that the refrigerant entering the compressor 1 through the suction pipe may be mixed with liquid. The liquid refrigerant entering the compressor 1 may cause dilution of the lubricating oil and reduce the lubrication effect. At this time, the oil return switch valve 8 is opened to concentrate the oil return and lubricate the compressor 1. At the same time, as the opening time of the oil return switch valve 8 is extended, more high-temperature gaseous refrigerant in the lubricating oil enters the suction pipe to vaporize the liquid refrigerant in the suction pipe and prevent the liquid refrigerant from entering the compressor 1. Alternatively, when the suction pressure decreases to less than the first preset pressure, as the opening time of the oil return switch valve 8 is extended, more high-temperature gaseous refrigerant of the compressor enters the suction pipe to increase the pressure of the suction pipe, so as to improve the performance of the compressor 1 while returning oil. In the present invention, the performance of the compressor 1 is not affected during oil return by briefly opening the oil return switch valve 8, and more gaseous refrigerant enters the suction pipe by long-term opening of the oil return switch valve 8 to improve the performance of the compressor 1.

[0053] Referring to Figure 2 , in a specific embodiment,

[0054] The control method includes:

[0055] Step S41: Determine whether the oil level sensor is closed;

[0056] Step S411: If the oil level sensor is closed, control the oil return switch valve to open;

[0057] Step S412: Determine whether the disconnection duration of the oil level sensor exceeds the duration T1;

[0058] Step S413: If it exceeds the duration T1, control the oil return switch valve to close.

[0059] When the oil level sensor is closed, it means that the oil volume in the oil separator 2 has reached the maximum threshold of the oil volume that must be returned for oil return. At this time, the oil return switch valve 8 is opened to return the lubricating oil in the oil separator 2 to the compressor 1 to prevent the compressor 1 from running without oil. However, this time should not be too long to prevent excess high-temperature refrigerant from bypassing into the suction pipe and affecting the operation of the compressor 1. Therefore, after the oil level sensor is disconnected for the duration T1, the oil return switch valve 8 is controlled to close.

[0060] Step S42: If the oil level sensor is not closed, obtain the suction superheat degree of the compressor;

[0061] Step S421: When the suction superheat degree ≤ the first preset superheat degree, control the oil return switch valve to open;

[0062] Step S422: When the suction superheat degree > the second preset superheat degree, control the oil return switch valve to close, where the first preset superheat degree ≤ the second preset superheat degree.

[0063] After the step of "obtaining the suction superheat degree of the compressor", when the suction superheat degree > the first preset superheat degree, return to continue obtaining the suction superheat degree of the compressor.

[0064] When it is detected that the suction superheat degree of the compressor 1 is low, it indicates that the refrigerant entering the compressor 1 through the suction pipe may be mixed with liquid. The liquid refrigerant entering the compressor 1 may cause the lubricating oil to be diluted and reduce the lubrication effect. At this time, opening the oil return switch valve 8 can achieve centralized oil return and lubricate the compressor. At the same time, as the opening time of the oil return switch valve 8 is longer, more high-temperature gaseous refrigerant enters the suction pipe to vaporize the liquid refrigerant in the suction pipe, preventing the liquid refrigerant from entering the compressor 1, so as to improve the lubrication effect and the performance of the compressor 1 at the same time. When the suction superheat degree is greater than the second preset superheat degree, control the oil return switch valve 8 to close to stop the oil return.

[0065] Among them, the step of "obtaining the superheat degree of the compressor" further includes:

[0066] Step: Obtain the suction temperature and suction pressure of the compressor;

[0067] Step: Obtain the saturation temperature corresponding to the suction pressure;

[0068] Step: Suction superheat degree = suction temperature - saturation temperature corresponding to the suction pressure.

[0069] The suction temperature and suction pressure are measured by a suction temperature sensor and a suction pressure sensor respectively. The saturation temperature corresponding to the suction pressure can be obtained by storing a corresponding relationship table between the suction pressure and the saturation temperature of the suction pressure in the memory, and then the suction superheat degree can be calculated. Or, it can also be obtained by storing a corresponding relationship table between the suction temperature, suction pressure and suction superheat degree in the memory. Those skilled in the art can set the acquisition method of the suction superheat degree according to needs.

[0070] Refer to Figure 3 In another embodiment, step S43: If the oil level sensor is not closed, obtain the suction pressure of the compressor;

[0071] Step S431: When the suction pressure ≤ the first preset pressure, control the oil return switch valve to open;

[0072] Step S432: When the suction pressure > the second preset pressure, control the oil return switch valve to close, where the first preset pressure ≤ the second preset pressure;

[0073] After the step of "obtaining the suction pressure of the compressor", when the suction pressure > the first preset pressure, return to continue obtaining the suction pressure of the compressor.

[0074] Detect the suction pressure of the compressor 1. When the suction pressure of the compressor 1 is low, it may exceed the operating range of the compressor 1. At this time, control the oil return switch valve 8 to open, bypass the high-pressure gas discharged by the compressor 1 to the suction pipe, increase the pressure of the refrigerant in the suction pipe, prevent the compressor 1 from being lower than the allowable operating pressure, and control the oil return switch valve 8 to close when the suction pressure is greater than the second preset pressure to stop the oil return.

[0075] It should be noted that the suction superheat and suction pressure of the compressor 1 can be obtained simultaneously or in sequence. Those skilled in the art can set them according to needs. As long as one of them is lower than the preset value, the oil return switch valve 8 is opened. The present invention does not limit the order of obtaining the suction superheat and suction pressure, and both fall within the protection scope of the present invention. For example, first obtain the suction superheat of the compressor. When the suction superheat > the first preset superheat, then obtain the suction pressure of the compressor.

[0076] Further, in a possible implementation manner, after the step of "controlling the oil return switch valve to open", the control method further includes:

[0077] Step: Calculate the opening duration of the oil return switch valve;

[0078] Step: When the opening duration of the oil return switch valve is greater than the T2 duration and still the suction superheat ≤ the first preset superheat and / or the suction pressure ≤ the first preset pressure, close the oil return switch valve and report an error to the user.

[0079] If the opening duration of the oil return switch valve 8 is greater than the T2 duration, it means that the suction superheat and suction pressure of the compressor 1 for a long time of oil return still do not reach the preset values. Then close the oil return switch valve 8 and report an error to the user, prompting the user to check whether the compressor 1 has a fault. Among them, the error message can be sent to the user through terminal devices such as mobile phones / iPads, smart speakers, etc. Of course, it can also be that the air-conditioning system generates different alarm prompt sounds through the control of the alarm device and other methods to send.

[0080] In summary, the control method of the air-conditioning system of the present invention simplifies the pipeline by combining the high- and low-pressure bypass capillary tubes and the oil return pipeline, and returns the oil uniformly after the lubricating oil in the oil separator 2 accumulates to a certain amount. When returning the oil, the instantaneous oil return volume is large and there is less mixed refrigerant gas, preventing the impact of real-time oil return on the compressor 1. When the suction superheat of the compressor is low or the suction pressure is low, the opening duration of the oil return switch valve 8 is extended to discharge more high-temperature gas into the suction pipe to vaporize the liquid refrigerant in the suction pipe, preventing the liquid refrigerant from entering the compressor 1, improving the suction superheat and suction pressure, and thus improving the performance of the compressor 1 while realizing oil return.

[0081] As described in the first paragraph of this section, the above embodiments are only used to illustrate the principle of the present invention and are not intended to limit the protection scope of the present invention. Without departing from the principle of the present invention, those skilled in the art can adjust the above structure so that the present invention can be applied to more specific application scenarios.

[0082] In addition, the present invention also provides an air-conditioning system, which includes a memory and a processor. The memory is adapted to store multiple program codes, and the program codes are adapted to be loaded and run by the processor to execute the control method of the air-conditioning system described in any one of the above embodiments.

[0083] Those skilled in the art can understand that the above air-conditioning system also includes some other well-known structures, such as a processor, a controller, a memory, etc. Among them, the memory includes but is not limited to random access memory, flash memory, read-only memory, programmable read-only memory, volatile memory, non-volatile memory, serial memory, parallel memory or registers, etc. The processor includes but is not limited to CPLD / FPGA, DSP, ARM processor, MIPS processor, etc. In order not to unnecessarily obscure the embodiments of the present disclosure, these well-known structures are not shown in the drawings.

[0084] Although the steps are described in the above order in the above embodiments, those skilled in the art can understand that in order to achieve the effects of this embodiment, different steps do not have to be executed in such an order, and they can be executed simultaneously (in parallel) or in a reversed order.

[0085] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A control method for an air conditioning system, the air conditioning system including a refrigerant circulation pipeline, and a compressor, an indoor unit heat exchanger, and an outdoor unit heat exchanger being provided on the refrigerant circulation pipeline, Characterized in that, the air conditioning system further includes an oil return pipeline and an oil separator, the oil separator being provided on the pipeline on the exhaust side of the compressor, one end of the oil return pipeline being connected to the oil separator, the other end being connected to the pipeline on the suction side of the compressor, and an oil return switch valve being provided on the oil return pipeline; the control method includes: Obtaining the suction superheat degree and / or suction pressure of the compressor; When the suction superheat degree ≤ a first preset superheat degree and / or the suction pressure ≤ a first preset pressure, controlling the oil return switch valve to open.

2. The control method for an air conditioning system according to claim 1, Characterized in that, after the step of "when the suction superheat degree ≤ a first preset superheat degree, controlling the oil return switch valve to open", the control method further includes: When the suction superheat degree > a second preset superheat degree, controlling the oil return switch valve to close, where the first preset superheat degree ≤ the second preset superheat degree.

3. The control method for an air conditioning system according to claim 1, Characterized in that, after the step of "when the suction pressure ≤ a first preset pressure, controlling the oil return switch valve to open", the control method includes: When the suction pressure > a second preset pressure, controlling the oil return switch valve to close, where the first preset pressure ≤ the second preset pressure.

4. The control method for an air conditioning system according to claim 2, Characterized in that, the step of "obtaining the superheat degree of the compressor" further includes: Obtaining the suction temperature and suction pressure of the compressor; Obtaining the saturation temperature corresponding to the suction pressure; Suction superheat degree = suction temperature - saturation temperature corresponding to the suction pressure.

5. The control method for an air conditioning system according to claim 1, Characterized in that, an oil level sensor for detecting the lubricating oil level is provided in the oil separator; the oil level sensor is configured to close when the lubricating oil level in the oil separator reaches the maximum threshold and to open when it is less than the maximum threshold; before the step of "obtaining the suction superheat degree and / or suction pressure of the compressor", the control method includes: Judging whether the oil level sensor is closed; If the oil level sensor is closed, controlling the oil return switch valve to open.

6. The control method for an air conditioning system according to claim 5, Characterized in that, after the step of "when the oil level sensor is closed, controlling the oil return switch valve to open", the control method further includes: Judging whether the disconnection duration of the oil level sensor exceeds the T1 duration; If it exceeds the T1 duration, controlling the oil return switch valve to close.

7. The control method for an air conditioning system according to claim 1, Characterized in that, after the step of "controlling the oil return switch valve to open", the control method includes: Calculating the opening duration of the oil return switch valve; If the opening duration of the oil return switch valve is greater than the T2 duration and still the suction superheat degree ≤ the first preset superheat degree, closing the oil return switch valve and reporting an error to the user.

8. The control method of the air-conditioning system according to claim 1, wherein, after the step of "obtaining the suction pressure of the compressor", the control method includes: when the suction pressure > the first preset pressure, return to continue obtaining the suction pressure of the compressor.

9. The control method of the air-conditioning system according to claim 1, wherein, after the step of "obtaining the suction superheat degree of the compressor", the control method includes: when the suction superheat degree > the first preset superheat degree, return to continue obtaining the suction superheat degree of the compressor.

10. An air-conditioning system, wherein, the air-conditioning system includes a memory and a processor, the memory is adapted to store a plurality of program codes, and the program codes are adapted to be loaded and run by the processor to execute the control method of the air-conditioning system according to any one of claims 1-9.

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