A method, device, and multi-split air conditioner for oil return control.

Abstract

This invention provides a method, device, and multi-split air conditioner for oil return control. The oil return control method includes: during the operation of the multi-split air conditioner, determining whether the multi-split air conditioner meets the oil return conditions; if so, controlling the multi-split air conditioner to enter the oil return mode; determining whether a second indoor unit exists in the oil return mode; if so, controlling the opening duration of the electronic expansion valve of the second indoor unit according to its operating parameters in the oil return mode. The problem solved by this invention is that in traditional oil return methods, if the electronic expansion valve of an indoor unit in standby mode is kept open throughout the oil return operation, it will cause a large amount of liquid to return to the multi-split air conditioner system, posing a significant challenge to the reliability of the compressor and generating considerable noise that disturbs users' rest.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and more specifically, to a method, apparatus, and multi-split air conditioner for controlling oil return. Background Technology

[0002] Multi-split air conditioning units have long connecting pipes and complex installation conditions. In particular, after long-term low-frequency operation, the compressor may experience oil shortage. In this case, the usual operation is to control the multi-split air conditioning unit to enter the oil return action. Specifically, this is done by enhancing the refrigerant circulation and simultaneously controlling the opening of the electronic expansion valves of all indoor units of the multi-split air conditioning unit. The external lubricating oil is brought back to the compressor by relying on high-speed circulating refrigerant and return liquid.

[0003] However, there is at least one problem with the relevant technology: In the traditional oil return method, if the electronic expansion valve of the indoor unit in standby mode is kept open during the oil return operation of the multi-split system, a large amount of liquid will return to the multi-split system, which will greatly test the reliability of the compressor and generate a lot of noise that will affect the user's rest. Summary of the Invention

[0004] The problem solved by this invention is that in traditional oil return methods, if the electronic expansion valve of the indoor unit in standby mode is kept open during the oil return operation, a large amount of liquid will return to the multi-split system, which will greatly test the reliability of the compressor and generate a lot of noise that will affect the user's rest.

[0005] To address the aforementioned problems, this invention provides a method for controlling the oil return of a multi-split air conditioner. The multi-split air conditioner includes multiple indoor units, with the unit in operation defined as the first indoor unit and the unit in standby mode defined as the second indoor unit. The oil return control method includes: during the operation of the multi-split air conditioner, determining whether the multi-split air conditioner meets the oil return conditions; if so, controlling the multi-split air conditioner to enter the oil return mode; determining whether the multi-split air conditioner has a second indoor unit in the oil return mode; if so, controlling the opening duration of the electronic expansion valve of the second indoor unit according to its operating parameters in the oil return mode.

[0006] Compared with existing technologies, the technical effects achieved by this solution are as follows: It avoids the problem of excessive liquid return and accompanying liquid flow noise in multi-split systems after entering oil return mode, which would otherwise occur due to the electronic expansion valve of the second indoor unit remaining constantly open. By adjusting the opening duration of the electronic expansion valve according to the operating parameters of the second indoor unit, the risk of liquid slugging caused by excessive liquid return from the compressor is avoided while ensuring the reliability of oil return, and the noise problem during the oil return period of the second indoor unit is also improved.

[0007] In one embodiment of the present invention, controlling the opening duration of the electronic expansion valve of the second indoor unit according to the operating parameters of the second indoor unit in the oil return mode includes: obtaining the opening rate of the second indoor unit in the oil return cycle; and controlling the electronic expansion valve of the second indoor unit to adjust the opening duration during the oil return operation according to the opening rate.

[0008] Compared to existing technologies, the technical advantages of this solution are as follows: Based on the analysis of lubricating oil storage in multi-split air conditioning systems, the oil storage locations are mostly in the evaporator of the indoor unit or in the piping between the indoor and outdoor units. Furthermore, if the indoor units are not turned on or are rarely turned on during the oil return cycle, very little lubricating oil is stored in these locations. Therefore, it is unnecessary to open the electronic expansion valve for prolonged oil return operation in these indoor units. Thus, based on the above analysis, for the second indoor unit with a low operating rate, it is unnecessary to open its electronic expansion valve during the oil return cycle. These electronic expansion valves can be kept closed, allowing the multi-split air conditioning system to remain in oil return mode, reducing the impact on compressor reliability and mitigating noise issues.

[0009] In one embodiment of the present invention, obtaining the operating rate of the second indoor unit during the oil return cycle includes: obtaining the first operating duration of the second indoor unit during the oil return cycle; obtaining the first duration of the oil return cycle; and calculating the operating rate based on the first operating duration and the first duration.

[0010] Compared with existing technologies, the technical effect achieved by adopting this technical solution is to improve the accuracy of obtaining the start-up time of the second indoor unit in oil return mode.

[0011] In one embodiment of the present invention, the lower the activation rate, the shorter the activation time.

[0012] Compared with existing technologies, the technical effects achieved by adopting this technical solution are as follows: Specifically, the lower the opening rate, the less time the second indoor unit is open during the oil return cycle, and the less oil is stored during this period. Therefore, the electronic expansion valve needs to be opened for a shorter time, which reduces the risk of a large amount of liquid returning to the multi-split unit after entering the oil return mode due to the electronic expansion valve of the second indoor unit remaining open. In addition, it also reduces liquid flow noise and improves the user experience.

[0013] In one embodiment of the present invention, the electronic expansion valve of the second indoor unit is controlled to adjust the opening duration during the oil return operation according to the opening rate, including: when K≤a, the electronic expansion valve is controlled to maintain a second opening duration; when K>a, the electronic expansion valve is controlled to maintain a third opening duration; wherein the third opening duration is longer than the second opening duration, K is the opening rate, a is a first preset value, and 0.3<a<0.5.

[0014] Compared with existing technologies, the technical effects achieved by this solution are as follows: Specifically, the oil level in the second indoor unit is related to its opening time within the oil return cycle; the shorter the initial opening time, the less oil is stored. However, it is important to note that when understanding the relationship between oil level and the initial opening time of the second indoor unit within the oil return cycle, it is also necessary to ensure the oil return efficiency of the multi-split system. For example, if relying solely on multiple first indoor units with their electronic expansion valves constantly open is insufficient to ensure the oil return efficiency of the multi-split system, or if combining a small number of second indoor units with their electronic expansion valves open for a certain duration is also insufficient, it is not enough to only consider compressor reliability and noise reduction; a balance must be maintained between oil return efficiency, compressor reliability, and noise reduction. Therefore, 'a' here can be understood as representing the balance between oil return efficiency, compressor reliability, and noise reduction. By comparing the values ​​of K and 'a' to obtain the corresponding oil level of the second indoor unit, the opening time of the electronic expansion valve can be reasonably adjusted to meet the oil return efficiency requirements of the multi-split system.

[0015] In one embodiment of the present invention, a takes the value 0.4.

[0016] Compared with existing technologies, the technical effects achieved by adopting this technical solution are as follows: by setting a value of 0.4 and combining experimental experience, the accuracy of maintaining the balance between oil return efficiency, compressor reliability and noise reduction is further improved.

[0017] In one embodiment of the present invention, the second opening duration is t2; wherein, t2 = A × T, and b × T ≤ t2 ≤ T, A is a second preset value, T is the oil return operation duration of the second indoor unit, and b is a third preset value; and / or; the third opening duration is t3, t3 = B × T, and B is a seventh preset value.

[0018] In one embodiment of the present invention, the value of A satisfies the following formula 1; Formula 1: A = n1 × K 2 -n2×K+c; n1 is the fourth preset value, n2 is the fifth preset value, and c is the sixth preset value.

[0019] Compared with existing technologies, the technical effects achieved by adopting this technical solution are: to further ensure the rationality of obtaining the second opening time, so as to meet the effect of maintaining a balance between oil return efficiency, compressor reliability and noise reduction.

[0020] On the other hand, the present invention also provides a return oil control device for a multi-split air conditioner. The multi-split air conditioner includes multiple indoor units, and the indoor unit in operation is defined as the first indoor unit, and the indoor unit in standby mode is defined as the second indoor unit. The return oil control device includes: a first judgment module, which is used to judge whether the multi-split air conditioner meets the return oil conditions; a first control module, which is used to control whether the multi-split air conditioner enters the return oil mode according to the judgment result of the first judgment module; a second judgment module, which is used to judge whether the multi-split air conditioner has a second indoor unit in the return oil mode; and a second control module, which is used to control the opening duration of the electronic expansion valve of the second indoor unit according to the operating parameters of the second indoor unit in the return oil mode.

[0021] Compared with existing technologies, the technical effects achieved by adopting this technical solution are as follows: it can achieve the technical effects of any of the above-mentioned technical solutions, which will not be elaborated here.

[0022] In another aspect, the present invention also provides a multi-unit air conditioner, including: a controller for executing an executable program to implement the oil return control method as in any example.

[0023] Compared with existing technologies, the technical effects achieved by this technical solution are as follows: it can achieve the technical effects of any of the above-mentioned oil return control methods, which will not be elaborated here.

[0024] By adopting the technical solution of the present invention, the following technical effects can be achieved:

[0025] (1) This avoids the problem of excessive liquid return and accompanying liquid flow noise in the multi-split unit after entering the oil return mode, caused by keeping the electronic expansion valve of the second indoor unit constantly open. By adjusting the opening duration of the electronic expansion valve of the second indoor unit according to its operating parameters, the risk of liquid slugging caused by excessive liquid return from the compressor is avoided while ensuring the reliability of oil return, and the noise problem during the oil return of the second indoor unit is improved.

[0026] (2) Based on the analysis of lubricating oil storage in multi-split air conditioning systems, the oil storage locations are mostly in the evaporator of the indoor unit or in the piping between the indoor and outdoor units. Furthermore, if the indoor units are not turned on or are rarely turned on during the oil return cycle, very little lubricating oil is stored in these locations. Therefore, it is unnecessary to open the electronic expansion valve for prolonged oil return operation in these indoor units. Thus, based on the above analysis, it can be concluded that for the second indoor unit with a low operating rate, it is unnecessary to open its electronic expansion valve during the oil return cycle. These electronic expansion valves can be kept closed, thereby keeping the multi-split air conditioning system in oil return mode, reducing the impact on compressor reliability and mitigating noise issues.

[0027] (3) By comparing the size between K and a, the oil level of the corresponding second indoor unit can be obtained, so as to reasonably adjust the opening time of the electronic expansion valve to meet the oil return efficiency of the multi-split unit. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating a method for controlling the return oil of a multi-split air conditioner, as provided in an embodiment of the present invention.

[0029] Figure 2 A schematic flowchart of another oil return control method for a multi-split air conditioner provided for an embodiment of the invention.

[0030] Figure 3 This is a schematic diagram of the module connection of a return oil control device for a multi-split air conditioner, provided in an embodiment of the present invention.

[0031] Explanation of reference numerals in the attached figures:

[0032] 100 - Oil return control device; 10 - First judgment module; 20 - First control module; 30 - Second judgment module; 40 - Second control module. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Example 1:

[0035] See Figure 1 This is a flowchart illustrating a method for controlling the return oil of a multi-split air conditioning unit according to an embodiment of the present invention. Combined with... Figure 2 A multi-split air conditioning system includes multiple indoor units. For ease of understanding, these indoor units can be categorized into first indoor units and second indoor units based on their different states. Specifically, the unit in operation is the first indoor unit, and the unit in standby mode is the second indoor unit. Figure 2 Oil return control methods include, for example:

[0036] Step S1: During the operation of the multi-split unit, determine whether the multi-split unit meets the oil return conditions;

[0037] Step S21: If yes, then control the multi-unit to enter the oil return mode;

[0038] Step S22: Determine whether a second indoor unit exists in the oil return mode of the multi-split air conditioner;

[0039] Step S221, if yes, then control the opening duration of the electronic expansion valve of the second indoor unit according to the operating parameters of the second indoor unit in the oil return mode.

[0040] In a specific example, when a multi-split air conditioner is operating in cooling mode, before entering oil return mode, the second indoor unit, which is in standby mode, has its fan off and its electronic expansion valve open. During normal oil return operation, the second indoor unit remains in standby mode, meaning its fan remains off and the electronic expansion valve remains open throughout. In this situation, because the second indoor unit cannot rely on the fan to drive rapid refrigerant circulation, it can only exchange heat with the indoor environment through natural convection, resulting in poor refrigerant evaporation in the evaporator of the second indoor unit.

[0041] Furthermore, if the first indoor unit remains running before and after entering the oil return mode, the fan will continue to operate, and the internal electronic expansion valve will remain open, thus improving the refrigerant evaporation efficiency. Consequently, with both the first and second indoor units maintaining their respective open electronic expansion valves throughout the process, the multi-split system experiences significant refrigerant return accompanied by liquid flow noise.

[0042] Therefore, by incorporating the content of this technical solution, the problem of excessive liquid return and accompanying liquid flow noise in multi-split air conditioners after entering oil return mode, caused by keeping the electronic expansion valve constantly open, is avoided. By adjusting the opening duration of the electronic expansion valve of the second indoor unit according to its operating parameters, the risk of liquid slugging caused by excessive liquid return from the compressor is avoided while ensuring the reliability of oil return, and the noise problem during the oil return period of the second indoor unit is also improved.

[0043] Preferably, the opening duration of the electronic expansion valve of the second indoor unit is controlled according to the operating parameters of the second indoor unit in the oil return mode, including:

[0044] Obtain the operating rate of the second indoor unit during the oil return cycle;

[0045] The electronic expansion valve controlling the second indoor unit adjusts the opening duration during oil return operation based on the opening rate.

[0046] Specifically, the oil return cycle can be understood as the operating phase from the end of the previous oil return cycle to the start of the current oil return cycle. In other words, the oil return cycle is the time interval between two consecutive oil return cycles. Oil return operation can be understood as the process by which a multi-split air conditioner, after entering oil return mode, increases the refrigerant circulation speed or returns liquid to bring the lubricating oil outside the compressor back into the compressor.

[0047] For example, when a multi-split air conditioner enters the oil return mode, it completes one oil return cycle and then resumes oil return operation. Thus, it can be seen that the oil return cycle and the oil return operation alternate.

[0048] Furthermore, based on the analysis of the lubricating oil storage in multi-split air conditioning systems, most of the oil storage locations are in the evaporator of the indoor unit or in the piping between the indoor and outdoor units. At the same time, if the indoor unit is not turned on or is rarely turned on during the oil return cycle, the lubricating oil will rarely be stored in these locations. For these indoor units, it is unnecessary to open the electronic expansion valve for a long-term oil return operation.

[0049] Therefore, based on the above analysis, it can be concluded that for the second indoor unit with a low opening rate, it is unnecessary to open its electronic expansion valve during the oil return cycle. These electronic expansion valves can be kept closed, thereby reducing the impact on compressor reliability and mitigating noise issues when the multi-split unit is in oil return mode.

[0050] Preferably, obtaining the operating rate of the second indoor unit during the oil return cycle includes:

[0051] Obtain the first operating duration of the second indoor unit within the oil return cycle;

[0052] Obtain the first duration of the oil return cycle;

[0053] The opening rate is calculated based on the first opening duration and the first duration.

[0054] Specifically, the opening rate can be defined as the ratio of the first opening duration to the first duration. Let the opening rate be K, the first opening duration be T2, and the first duration be T1. Then, K = T2 / T1.

[0055] Preferably, a lower opening rate results in a shorter opening time. Specifically, a lower opening rate means that the second indoor unit is open for less time during the oil return cycle, resulting in less oil accumulation during this period. Therefore, the electronic expansion valve needs to be open for a shorter time, reducing the risk of the multi-split unit experiencing excessive liquid return after entering the oil return mode due to the electronic expansion valve of the second indoor unit remaining constantly open. In addition, it also reduces liquid flow noise and improves the user experience.

[0056] Preferably, the electronic expansion valve controlling the second indoor unit adjusts the opening duration during oil return operation according to the opening rate, including:

[0057] When K≤a, the electronic expansion valve is controlled to remain open for the second duration;

[0058] When K > a, the electronic expansion valve is controlled to remain open for a third time; where K is the opening rate, a is the first preset value, and 0.3 < a < 0.5.

[0059] Specifically, the oil level in the second indoor unit is related to its operating time within the oil return cycle; the shorter the initial operating time, the lower the oil level. However, it's important to note that when understanding the relationship between oil level and the initial operating time of the second indoor unit within the oil return cycle, it's crucial to ensure the oil return efficiency of the multi-split system. For example, if relying solely on multiple first indoor units with their electronic expansion valves constantly open is insufficient to guarantee the oil return efficiency of the multi-split system, or if combining a small number of second indoor units with their electronic expansion valves open for a certain duration also fails to ensure sufficient oil return efficiency, then it's not enough to only consider compressor reliability and noise reduction; a balance must be maintained between oil return efficiency, compressor reliability, and noise reduction. Therefore, 'a' here can be understood as representing the balance between oil return efficiency, compressor reliability, and noise reduction. By comparing K and 'a', the corresponding oil level of the second indoor unit can be obtained.

[0060] In a specific example, when K ≤ a, it indicates that the second indoor unit operates for a shorter time during the oil return cycle, and correspondingly, the amount of oil stored during the oil return cycle is also smaller. This allows the electronic expansion valve to open for a shorter time, i.e., a smaller second opening duration is taken. Conversely, when K > a, it indicates that the second indoor unit operates for a longer time during the oil return cycle, and correspondingly, the amount of oil stored during the oil return cycle is also larger. This allows the electronic expansion valve to open for a longer time, i.e., a larger second opening duration is taken, so that a large amount of oil stored in the second indoor unit can be delivered to the compressor, thereby ensuring the compressor's oil return efficiency and improving the compressor's service life.

[0061] Preferably, 'a' is set to 0.4. By setting 'a' to 0.4, combined with experimental experience, the accuracy of maintaining the balance between oil return efficiency, compressor reliability, and noise reduction is further improved. Thus, when K ≥ 0.4, it indicates that the second indoor unit has a large amount of oil, allowing the oil return operation to be handled directly as if the electronic expansion valve were fully open.

[0062] Preferably, the second start-up time is t2; where t2 = A × T, and b × T ≤ t2 ≤ T, A is the second preset value, T is the oil return operation duration of the second indoor unit, and b is the third preset value;

[0063] And / or, the third opening duration is greater than the second opening duration; where the third opening duration is t3, t3 = B × T, and B is the seventh preset value. B can be 1, i.e., 100%.

[0064] For example, b can take the value 0.25, which is 25%.

[0065] Preferably, the value of A satisfies the following formula 1; Formula 1: A = n1 × K 2-n2×K+c; n1 is the fourth preset value, n2 is the fifth preset value, and c is the sixth preset value. For example, n1 can be 8.8095, n2 can be -2.369, and c can be 0.4321.

[0066] Controlling the multi-split air conditioner to enter oil return mode includes:

[0067] The electronic expansion valve controlling the first indoor unit remains open in the oil return mode; wherein, the operating state includes the fan of the first indoor unit remaining on.

[0068] Determining whether a multi-split air conditioner has a second indoor unit in oil return mode includes:

[0069] If not, the electronic expansion valve of the first indoor unit will remain open in the oil return mode.

[0070] See Figure 3 This invention also provides a schematic diagram of the module connection of a multi-split air conditioner oil return control device 100. The multi-split air conditioner includes multiple indoor units, with the indoor unit in operation being defined as the first indoor unit and the indoor unit in standby mode being defined as the second indoor unit. The oil return control device 100 includes, for example, a first judgment module 10, a first control module 20, a second judgment module 30, and a second control module 40. The first judgment module 10 is used to determine whether the multi-split air conditioner meets the oil return conditions; the first control module 20 is used to control whether the multi-split air conditioner enters the oil return mode based on the judgment result of the first judgment module 10; the second judgment module 30 is used to determine whether the multi-split air conditioner has a second indoor unit in the oil return mode; and the second control module 40 is used to control the opening duration of the electronic expansion valve of the second indoor unit based on the operating parameters of the second indoor unit in the oil return mode.

[0071] This invention also provides a multi-split air conditioner, which includes a controller for executing an executable program to implement the oil return control method as described in the above embodiments.

[0072] This invention also provides a computer-readable storage medium storing a computer program. When the computer program is read and executed by a processor, it implements the oil return control method provided in the above embodiments and achieves the same technical effect. To avoid repetition, it will not be described again here. The computer-readable storage medium may be a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0073] Of course, those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by computer-controlled devices. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above method embodiments. The storage medium can be a memory, a disk, an optical disk, etc.

[0074] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0075] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0076] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the air conditioner control device and air conditioner disclosed in the embodiments, since they correspond to the air conditioner control method disclosed in the above embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0077] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for controlling oil return in a multi-split air conditioning system, wherein the multi-split air conditioning system comprises multiple indoor units, and the indoor unit in operation is defined as the first indoor unit, and the indoor unit in standby mode is defined as the second indoor unit; characterized in that, The oil return control method includes: During the operation of the multi-split unit, it is determined whether the multi-split unit meets the oil return conditions; If so, then control the multi-split unit to enter the oil return mode; Determine whether the second indoor unit exists in the oil return mode of the multi-split air conditioner; If so, the opening duration of the electronic expansion valve of the second indoor unit is controlled according to the operating parameters of the second indoor unit in the oil return mode; The step of controlling the opening duration of the electronic expansion valve of the second indoor unit according to its operating parameters in the oil return mode includes: Obtain the opening rate of the second indoor unit during the oil return cycle; The electronic expansion valve controlling the second indoor unit adjusts the opening duration during oil return operation according to the opening rate.

2. The oil return control method according to claim 1, characterized in that, The step of obtaining the operating rate of the second indoor unit during the oil return cycle includes: Obtain the first operating duration of the second indoor unit within the oil return cycle; Obtain the first duration of the oil return cycle; The opening rate is calculated based on the first opening duration and the first duration.

3. The oil return control method according to claim 1, characterized in that, The lower the activation rate, the shorter the activation duration.

4. The oil return control method according to any one of claims 1-3, characterized in that, The electronic expansion valve controlling the second indoor unit adjusts its opening duration during oil return operation according to the opening rate, including: When K≤a, the electronic expansion valve is controlled to remain open for the second duration; When K > a, the electronic expansion valve is controlled to remain open for a third duration; Wherein, the third opening duration is greater than the second opening duration, K is the opening rate, a is the first preset value, and 0.3 < a < 0.

5.

5. The oil return control method according to claim 4, characterized in that, a takes the value 0.

4.

6. The oil return control method according to claim 4, characterized in that, The second start-up duration is t2; where t2 = A × T, and b × T ≤ t2 ≤ T, A is the second preset value, T is the oil return operation duration of the second indoor unit, and b is the third preset value; And / or, the third activation duration is t3, t3 = B × T, where B is the seventh preset value.

7. The oil return control method according to claim 6, characterized in that, The value of A satisfies the following formula 1; Formula 1: A=n1×K 2 -n2×K+c; n1 is the fourth preset value, n2 is the fifth preset value, and c is the sixth preset value.

8. A return oil control device for a multi-split air conditioner, the multi-split air conditioner comprising multiple indoor units, wherein the indoor unit in operation is defined as the first indoor unit, and the indoor unit in standby mode is defined as the second indoor unit; characterized in that, The oil return control device applies the oil return control method as described in any one of claims 1-7; the oil return control device comprises: The first judgment module (10) is used to determine whether the multi-unit meets the oil return condition; The first control module (20) is used to control whether the multi-split unit enters the oil return mode according to the judgment result of the first judgment module (10); The second judgment module (30) is used to determine whether the multi-split air conditioner has the second indoor unit in the oil return mode; The second control module (40) is used to control the opening duration of the electronic expansion valve of the second indoor unit according to the operating parameters of the second indoor unit in the oil return mode.

9. A multi-split air conditioner, characterized in that, include: A controller for executing an executable program to implement the oil return control method according to any one of claims 1-7.

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