Oil return control method and device and multi-connected system

Abstract

The application provides an oil return control method and device and a multi-connected system; the method comprises the following steps: in the oil return mode of the multi-connected system, periodically acquiring the oil temperature of each outdoor unit, and calculating the average oil temperature of each period according to the oil temperatures of multiple outdoor units and the number of units; for each outdoor unit, calculating the target parameter of the outdoor unit in the current period according to the oil temperature of the outdoor unit in the current period, the average oil temperature in the current period, the displacement of the compressor in the outdoor unit, the average displacement and the last operation parameter of the outdoor unit in the last period; in the current period, controlling the compressor of each outdoor unit to operate at the corresponding target operation frequency, and controlling the electronic expansion valve to operate at the corresponding target valve opening degree, so as to return oil to the multi-connected system, thereby adjusting the operation frequency of the compressor of each outdoor unit and the opening degree of the electronic expansion valve, improving the problem of uneven oil return and improving the reliability of the multi-connected system.

Description

TECHNICAL FIELD

[0001] The present application relates to the air conditioning technical field, especially to an oil return control method and device and a multi-connected system. BACKGROUND

[0002] Currently, in the existing multi-connected system, multiple outdoor units are installed and operated in parallel. Due to different rotation operation time (when operating at low frequency, most of the oil exists in the compressor and oil separator of the operating outdoor unit, and cannot be discharged into the system, resulting in more oil storage in the outdoor unit. When rotating operation, different outdoor units or different compressors are mostly low in energy demand, i.e., operating at low frequency, and the operating outdoor unit stores oil), or different compressor displacements (at the same frequency, the small displacement compressor discharges less oil, and when operating in parallel, the small displacement outdoor unit stores oil and cannot be discharged into the system), resulting in different oil amounts in each outdoor unit. However, during the oil return process, each outdoor unit operates at the same frequency and valve opening, resulting in uneven oil return in the multi-connected system, such as oil enrichment in the small displacement compressor and oil deficiency in the large displacement compressor, thereby affecting the reliability of the multi-connected system. Therefore, how to improve the uneven oil return in the multi-connected system is a problem to be solved. SUMMARY

[0003] Therefore, the present application aims to provide an oil return control method and device and a multi-connected system to alleviate the above problems, improve the uneven oil return, and improve the reliability and operation effect of the multi-connected system.

[0004] In a first aspect, an oil return control method is provided, applied to a multi-connected system; wherein the multi-connected system includes multiple outdoor units, each outdoor unit including a compressor with a displacement and an electronic expansion valve; the method includes: when the multi-connected system meets the oil return condition, controlling the multi-connected system to enter an oil return mode, and calculating an average displacement according to the displacements of the multiple compressors and the number of the multiple outdoor units; in the oil return mode, periodically obtaining the oil temperature of each outdoor unit, and calculating the average oil temperature of each period according to the oil temperatures of the multiple outdoor units and the number of the multiple outdoor units; for each outdoor unit, calculating the target parameter of the outdoor unit in the current period according to the oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement, and the last operation parameter of the outdoor unit in the last period; wherein the target parameter includes a target operating frequency and a target valve opening, and the last operation parameter includes a last operating frequency and a last valve opening; in the current period, controlling the compressor of each outdoor unit to operate at the corresponding target operating frequency, and controlling the electronic expansion valve to operate at the corresponding target valve opening, to return oil to the multi-connected system, until the multi-connected system exits the oil return mode.

[0005] The oil return control method adjusts the compressor operating frequency and the electronic expansion valve opening degree of each outdoor unit during the oil return process based on the compressor displacement and the oil temperature, thereby controlling the oil return amount of each outdoor unit, improving the problem of uneven oil return, and improving the reliability and operation effect of the multi-split system. Meanwhile, the oil return control method can be implemented by using the existing multi-split system without affecting other functions of the multi-split system, and is convenient for popularization and implementation in practical application.

[0006] Preferably, for each outdoor unit, the step of calculating the target parameter corresponding to the current period of the outdoor unit according to the oil temperature of the outdoor unit in the current period, the average oil temperature in the current period, the displacement of the compressor in the outdoor unit, the average displacement, and the last operation parameter of the outdoor unit in the last period, comprises: if the oil temperature of the outdoor unit is not less than the average oil temperature in the current period, calculating the target operating frequency of the outdoor unit in the current period according to the last operating frequency, the average oil temperature in the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit, and the average displacement; or, if the oil temperature of the outdoor unit is less than the average oil temperature in the current period, taking the last operating frequency as the target operating frequency of the outdoor unit in the current period; if the oil temperature of the outdoor unit is not less than a preset first oil temperature threshold, taking the last valve opening degree as the target valve opening degree of the outdoor unit in the current period; or, if the oil temperature of the outdoor unit is less than the first oil temperature threshold, calculating the target valve opening degree of the outdoor unit in the current period according to the last valve opening degree, the average oil temperature in the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit, and the average displacement.

[0007] Preferably, the step of calculating the target operating frequency of the outdoor unit in the current period according to the last operating frequency, the average oil temperature in the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit, and the average displacement, comprises: for the i-th outdoor unit, calculating the target operating frequency according to the following formula:

[0008] P n = P n-1 +b*(T n / T i )*(Q / Q i )

[0009] wherein, P n represents the target operating frequency, P n-1 represents the last operating frequency, T n represents the average oil temperature, T i represents the oil temperature of the i-th outdoor unit, Q represents the average displacement, Q i represents the displacement of the compressor of the i-th outdoor unit, and b represents a first calculation coefficient, and n represents the current period.

[0010] Preferably, the step of calculating the target valve opening degree of the outdoor unit corresponding to the current period according to the last valve opening degree, the average oil temperature of the current period, the oil temperature of the outdoor unit, the displacement of the compressor of the outdoor unit and the average displacement, comprises: calculating the target valve opening degree of the i th outdoor unit according to the following formula:

[0011] V n = V n-1 - c * (T n / T i ) * (Q / Q i )

[0012] Wherein, V n represents the target valve opening degree, V n-1 represents the last valve opening degree, T n represents the average oil temperature, T i represents the oil temperature of the i th outdoor unit, Q represents the average displacement, Q i represents the displacement of the compressor of the i th outdoor unit, c represents the second calculation coefficient, and n represents the current period.

[0013] Preferably, before the step of periodically obtaining the oil temperature of each outdoor unit, the method further comprises: obtaining initial parameters when the multi-split system enters the oil return mode; wherein the initial parameters include: an initial valve opening degree and an initial oil temperature of each outdoor unit; calculating an initial average oil temperature according to the initial oil temperatures of the multiple outdoor units and the number of units; calculating an initial operating frequency corresponding to each outdoor unit according to the initial oil temperature of each outdoor unit, the initial average oil temperature, the displacement of the compressor of the outdoor unit and the average displacement; and controlling the compressor of each outdoor unit to operate at the corresponding initial operating frequency and the electronic expansion valve to operate at the initial valve opening degree.

[0014] Preferably, before the step of determining that the multi-split system meets the oil return condition, the method further comprises: determining that the multi-split system meets the oil return condition if the multi-split system has not returned oil for a first preset duration; or determining that the multi-split system meets the oil return condition if the number of outdoor units with an oil temperature not greater than a preset second oil temperature threshold reaches a preset number threshold in the multi-split system.

[0015] Preferably, the step of the multi-split system exiting the oil return mode comprises: controlling the multi-split system to exit the oil return mode if the duration of the multi-split system operating in the oil return mode reaches a second preset duration; or controlling the multi-split system to exit the oil return mode if the oil temperature of all outdoor units is not less than a preset third oil temperature threshold in the oil return mode.

[0016] In a second aspect, the embodiments of the present application further provide an oil return control device, applied to a multi-connected system; wherein the multi-connected system comprises a plurality of outdoor units, each of which comprises a compressor with a displacement and an electronic expansion valve; the device comprises: an oil return entering module, configured to control the multi-connected system to enter an oil return mode when the multi-connected system meets an oil return condition, and to calculate an average displacement according to the displacements of the plurality of compressors and the number of the plurality of outdoor units; an oil temperature obtaining module, configured to periodically obtain the oil temperature of each outdoor unit in the oil return mode, and to calculate an average oil temperature of each period according to the oil temperatures of the plurality of outdoor units and the number of the plurality of outdoor units; a parameter calculating module, configured to, for each outdoor unit, calculate a target parameter corresponding to the outdoor unit in a current period according to the oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement, and a last operation parameter of the outdoor unit in a last period; wherein the target parameter comprises a target operation frequency and a target valve opening degree, and the last operation parameter comprises a last operation frequency and a last valve opening degree; and a control operation module, configured to, in the current period, control the compressor of each outdoor unit to operate at the corresponding target operation frequency, and control the electronic expansion valve of each outdoor unit to operate at the corresponding target valve opening degree, so as to return oil to the multi-connected system until the multi-connected system exits the oil return mode.

[0017] In a third aspect, the embodiments of the present application further provide a multi-connected system, comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, and the processor executes the computer program to implement the steps of the method of the first aspect.

[0018] In a fourth aspect, the embodiments of the present application further provide a computer readable storage medium, which stores a computer program, and the computer program is run by a processor to execute the steps of the method of the first aspect.

[0019] The embodiments of the present application have the following beneficial effects:

[0020] The oil return control method, device and multi-connected system provided by the embodiment of the present application can improve the problem of uneven oil return and improve the reliability and operation effect of the multi-connected system.

[0021] Other features and advantages of the present application will be set forth in the descriptions that follow and in part will be apparent from the description or can be learned by practice of the present application. The objects and other advantages of the present application will be realized and attained by the structure particularly pointed out in the description and the drawings.

[0022] In order to make the above objectives, features and advantages of the present application more apparent, the following will describe a preferred embodiment in detail, and the accompanying drawings will be referred to, and the detailed description will be as follows. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0024] Figure 1 A structural schematic diagram of a multi-connected system provided by the embodiment of the present application;

[0025] Figure 2 A flowchart of an oil return control method provided by the embodiment of the present application;

[0026] Figure 3 A schematic diagram of an oil return control device provided by the embodiment of the present application;

[0027] Figure 4This is a schematic diagram of another multi-unit system provided in an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions 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, 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.

[0029] To facilitate understanding of this embodiment, the oil return control method provided by this invention will be described in detail below. This method is applied to a multi-split air conditioning system, which includes multiple outdoor units and multiple indoor units. The specific number of outdoor and indoor units can be set according to actual conditions.

[0030] For ease of explanation, this example uses a multi-split air conditioning system consisting of two outdoor units. Figure 1 As shown, the first and second outdoor units have the same structure. Specifically, the first outdoor unit includes, but is not limited to: a first compressor 11, a first oil separator 12, a first four-way valve 13, a first gas-liquid separator 14, a first outdoor heat exchanger 15, a first electronic expansion valve (also referred to as the first outdoor unit electronic expansion valve) 16, and a first oil return capillary tube 17. Similarly, the second outdoor unit includes, but is not limited to: a second compressor 21, a second oil separator 22, a second four-way valve 23, a second gas-liquid separator 24, a second outdoor heat exchanger 25, a second electronic expansion valve (also referred to as the second outdoor unit electronic expansion valve) 26, and a second oil return capillary tube 27. For the remaining parts of the first and second outdoor units, please refer to existing multi-split air conditioning systems. The embodiments of this invention will not be described in detail here. It should be noted that the arrows in the figure indicate the flow direction of refrigerant in the outdoor unit during the oil return process of the multi-split air conditioning system.

[0031] Each outdoor unit's compressor is also equipped with a displacement Q. Displacement Q can be understood as an inherent attribute value of the compressor, which can be determined based on the compressor model and pre-stored in the controller. In practical applications, the displacement Q of the same compressor model is a fixed value. Therefore, the displacements of the first compressor 11 and the second compressor 21 may be the same or different, depending on the compressor model.

[0032] In addition, the above-mentioned multi-split air conditioning system also includes a controller and multiple indoor units. The controller and indoor units are not shown here. In practical applications, the controller is used to execute the oil return control method of the present invention to control the oil return amount of multiple outdoor units in the multi-split air conditioning system, so that each outdoor unit is not short of oil, thereby improving the problem of uneven oil return in the multi-split air conditioning system and improving the reliability and operation effect of the multi-split air conditioning system.

[0033] Example 1

[0034] Based on the above-mentioned multi-split air conditioning system, this embodiment of the invention provides a return oil control method, such as... Figure 2 As shown, the method includes the following steps:

[0035] Step S202: When the multi-split system meets the oil return conditions, control the multi-split system to enter the oil return mode, and calculate the average displacement based on the displacement of multiple compressors and the number of outdoor units.

[0036] Specifically, during the operation of the multi-split air conditioning system, if the system meets the oil return conditions, the controller switches the system from operating mode to oil return mode, and adjusts the settings according to the displacement Q of each compressor in the multiple outdoor units. i The average displacement Q of the multi-split air conditioning system is calculated based on the number of outdoor units. The controller can identify the number of outdoor units N in the multi-split system via DIP switches, or it can pre-store the number of units N, where i represents the i-th outdoor unit, i = 1, 2, ..., N. It should be noted that the number of units N here refers to the number of outdoor units operating in the multi-split system.

[0037] The average displacement Q is calculated using the following formula: Q = 10^(∑lgQ) i / N); where Q i Let represent the displacement of the compressor in the i-th outdoor unit, where i = 1, 2, ..., N. Specifically, when calculating the average displacement Q, taking the logarithm reduces the overall value by an order of magnitude, which helps eliminate the impact of extreme values ​​on the overall system and thus improves the oil return control accuracy of the multi-split air conditioning system.

[0038] It should be noted that the average displacement Q mentioned above can be calculated when the multi-split system enters the oil return control, or it can be calculated directly based on the displacement of each compressor and the number of outdoor units in operation when the multi-split system is started, or it can be calculated after startup and before the oil return control. If all outdoor units are running, the average displacement can also be pre-stored in the controller and applied directly in subsequent operation. The specific settings can be made according to the actual situation.

[0039] Step S204, in the oil return mode, the oil temperature of each outdoor unit is periodically acquired, and the average oil temperature of each period is calculated according to the oil temperatures of the multiple outdoor units and the number of units;

[0040] Specifically, when the multi-split system enters the oil return mode, in order to ensure that each outdoor unit is not short of oil, the oil temperature of each outdoor unit is periodically acquired at a preset interval, and the preset interval is preferably 20s, that is, the oil return process of the multi-split system is adjusted every 20s. The oil temperature is acquired by a temperature acquisition sensor or a temperature sensing bag. In actual application, the temperature sensor or the oil temperature is arranged at the oil return capillary tube of each outdoor unit. For example, for the multi-split system in FIG. 1, in each period, the controller acquires the oil temperature of the first outdoor unit acquired by the temperature sensor arranged at the first oil return capillary tube 17, and the oil temperature of the second outdoor unit acquired by the temperature sensor arranged at the second oil return capillary tube 27. Figure 1

[0041] For each period, after the controller acquires the oil temperatures of the multiple outdoor units, the average oil temperature T of each period is calculated according to the oil temperatures of the multiple outdoor units and the number of units. The average oil temperature T is calculated according to the following formula: T = 10^(∑lgT i / N); wherein T i represents the oil temperature of the i-th outdoor unit, i = 1, 2, …, N. In particular, when calculating the average oil temperature T, the total value is reduced by one order of magnitude after taking the logarithm, which is beneficial to eliminate the influence of extreme values on the whole, and thus improves the control precision of the oil return of the multi-split system.

[0042] Step S206, for each outdoor unit, the target parameter corresponding to the current period of the outdoor unit is calculated according to the oil temperature of the outdoor unit in the current period, the average oil temperature in the current period, the displacement of the compressor in the outdoor unit, the average displacement, and the last operation parameter of the outdoor unit in the last period; wherein the target parameter includes: target operating frequency and target valve opening degree;

[0043] In actual operation, the operating frequency and displacement of the compressor in each outdoor unit may be the same or different. Therefore, for each outdoor unit in each period, in order to avoid uneven oil return, the operating frequency of the compressor and the valve opening degree of the electronic expansion valve of the outdoor unit need to be adjusted.

[0044] ​Specifically, for the current period, the target parameter corresponding to the current period of the outdoor unit is calculated according to the oil temperature of the outdoor unit in the current period, the average oil temperature in the current period, the displacement of the compressor in the outdoor unit, the average displacement, and the last running parameter of the outdoor unit in the last period. The target parameter includes the target running frequency of the compressor of the outdoor unit in the current period and the target valve opening of the electronic expansion valve of the outdoor unit in the current period; similarly, the last running parameter includes the last running frequency and the last valve opening; here, the last running frequency is the running frequency of the compressor of the outdoor unit in the last period, and the last valve opening is the valve opening of the electronic expansion valve of the outdoor unit in the last period.

[0045] Therefore, by differentiating the control of the running frequency of the compressor and the valve opening of the electronic expansion valve of different outdoor units, the oil return amount of each outdoor unit is adjusted to improve the problem of uneven oil return of the multi-split system, so that each outdoor unit in the multi-split system is not short of oil, thereby ensuring the reliable operation of the multi-split system.

[0046] Step S208, in the current period, the compressor of each outdoor unit is controlled to run at the corresponding target running frequency, and the electronic expansion valve is controlled to run at the corresponding target valve opening, to perform oil return on the multi-split system until the multi-split system exits the oil return mode.

[0047] Specifically, for each outdoor unit, the compressor is controlled to run at the target running frequency corresponding to the current period, and the electronic expansion valve is controlled to run at the target valve opening corresponding to the current period, so as to control the oil return amount of the outdoor unit through the joint adjustment of the compressor and the electronic expansion valve, and to improve the problem of uneven oil return through the differentiated oil return control of multiple outdoor units.

[0048] In addition, during the oil return process, if the multi-split system runs in the oil return mode for a second preset time length, such as 8 minutes, the multi-split system is controlled to exit the oil return mode; or if the oil temperature of all outdoor units is not less than a third preset oil temperature threshold, that is, the oil temperature of all outdoor units is greater than or equal to the third oil temperature threshold, the multi-split system is controlled to exit the oil return mode. The third oil temperature threshold is preferably 90°C, and can be adaptively adjusted according to actual conditions.

[0049] The oil return control method provided by the embodiment of the application adjusts the running frequency of the compressor and the opening of the electronic expansion valve during the oil return process of each outdoor unit based on the displacement of the compressor and the oil temperature, thereby controlling the oil return amount of each outdoor unit, improving the problem of uneven oil return, and improving the reliability and operation effect of the multi-split system. At the same time, the oil return control method can be implemented using the existing multi-split system without affecting other functions of the multi-split system, and is convenient for popularization and implementation in actual application.

[0050] In one implementation, the process of calculating the target parameters for each outdoor unit in the current cycle based on the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the outdoor unit in the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the operating parameters of the outdoor unit in the previous cycle includes the calculation process of the target operating frequency and the calculation process of the target valve opening; specifically, each calculation process is as follows:

[0051] (1) If the oil temperature of the outdoor unit is not less than the average oil temperature of the current cycle, the target operating frequency of the outdoor unit in the current cycle is calculated based on the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement and average displacement of the compressor in the outdoor unit; or, if the oil temperature of the outdoor unit is less than the average oil temperature of the current cycle, the previous operating frequency is used as the target operating frequency of the outdoor unit in the current cycle.

[0052] Specifically, let the average oil temperature of the current cycle be T. n For the i-th outdoor unit, if its oil temperature T i <T n Then the previous operating frequency P n-1 The target operating frequency P of the outdoor unit in the current cycle n That is, P n =P n-1 Conversely, if its oil temperature T i ≥T n The target operating frequency of the outdoor unit in the current cycle is calculated based on the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement and average displacement of the compressor in the outdoor unit.

[0053] For the i-th outdoor unit, its target operating frequency is calculated according to the following formula:

[0054] P n =P n-1 +b*(T n / T i )*(Q / Q i (1)

[0055] Among them, P n P represents the target operating frequency. n-1 T represents the previous operating frequency. n T represents the average oil temperature. i Q represents the oil temperature of the i-th outdoor unit, and Q represents the average displacement. i Let represent the displacement of the compressor of the i-th outdoor unit, b represent the first calculation coefficient, preferably 0.5, and n represent the current cycle. It should be noted that the above target frequency P... n Not exceeding the compressor's maximum operating frequency Pmax i.e. P n ≤ P max .

[0056] (2) If the oil temperature of the outdoor unit is not less than the preset first oil temperature threshold, the last valve opening degree is taken as the target valve opening degree of the outdoor unit corresponding to the current period; or, if the oil temperature of the outdoor unit is less than the first oil temperature threshold, the target valve opening degree of the outdoor unit corresponding to the current period is calculated according to the last valve opening degree, the average oil temperature of the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement.

[0057] Specifically, in the current period, let the average oil temperature of the current period be T n For the i-th outdoor unit, if its oil temperature is not less than the first oil temperature threshold D, i.e. T i ≥ D, the last valve opening degree V n-1 is taken as the target valve opening degree V n of the outdoor unit corresponding to the current period. Otherwise, if its oil temperature is less than the first oil temperature threshold D, i.e. T i < D, the target valve opening degree of the outdoor unit corresponding to the current period is calculated according to the last valve opening degree, the average oil temperature of the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement. It should be noted that the first oil temperature threshold D is related to the oil discharge characteristics of the compressor itself, the oil return mode, the length of the oil return capillary and the like, and can be determined through experiments. The embodiment of the present application preferably is 55℃.

[0058] Wherein, for the i-th outdoor unit, its target valve opening degree is calculated according to the following formula:

[0059] V n = V n-1 -c*(T n / T i )*(Q / Q i ) (2)

[0060] Wherein, V n represents the target valve opening degree, V n-1 represents the last valve opening degree, T n represents the average oil temperature, T i represents the oil temperature of the i-th outdoor unit, Q represents the average displacement, Q i represents the displacement of the compressor of the i-th outdoor unit, c represents the second calculation coefficient, preferably 0.1, and n represents the current period. It should be noted that the above target valve opening degree V n should not be less than the minimum valve opening degree Vmin of the electronic expansion valve, i.e. V n ≥ Vmin.

[0061] Therefore, by differentiating the compressor operating frequency and the electronic expansion valve valve opening degree of different outdoor units, the oil return amount of each outdoor unit is adjusted to improve the problem of uneven oil return of the multi-split system, so that each outdoor unit in the multi-split system is not short of oil.

[0062] In an embodiment, before the step of periodically acquiring the oil temperature of each outdoor unit, the method further comprises: acquiring initial parameters when the multi-split system enters the oil return mode; wherein the initial parameters include: an initial valve opening degree and an initial oil temperature of each outdoor unit; calculating an initial average oil temperature according to the initial oil temperatures of the multiple outdoor units and the number of units; calculating the initial operating frequency corresponding to each outdoor unit according to the initial oil temperature of the outdoor unit, the initial average oil temperature, the displacement of the compressor of the outdoor unit, and the average displacement; controlling the compressor of each outdoor unit to operate at the corresponding initial operating frequency, and the electronic expansion valve to operate at the initial valve opening degree.

[0063] Specifically, when the multi-split system enters the oil return mode, that is, for the first cycle of the oil return mode, the initial valve opening degree V0 and the initial oil temperature of each outdoor unit at this time are acquired, and the initial average oil temperature is calculated according to the initial oil temperatures of the multiple outdoor units and the number of units. At this time, the initial operating frequency corresponding to each outdoor unit is calculated according to the initial oil temperature of the outdoor unit, the initial average oil temperature, the displacement of the compressor of the outdoor unit, and the average displacement.

[0064] Wherein, for the i-th outdoor unit, its initial operating frequency is calculated according to the following formula:

[0065] P1=A+a*(T1 / T i0 )*(Q / Q i ) (3)

[0066] Wherein, P1 represents the initial operating frequency, T1 represents the initial average oil temperature, T i0 represents the initial oil temperature of the i-th outdoor unit, Q represents the average displacement, Q i represents the displacement of the compressor of the i-th outdoor unit, a represents a second calculation coefficient, preferably 1.3, A represents a third calculation coefficient, which is related to the oil discharge characteristics of the compressor itself, the oil return mode, the oil return capillary length, etc., and can be determined by experiment, and here it is preferably 60. It should be noted that the above initial valve opening degree V0 is related to the oil discharge characteristics of the compressor itself, the oil return mode, the oil return capillary length, etc., and can be determined by experiment, and here it is preferably 200 pls.

[0067] Therefore, when the multi-connected system enters the oil return, the compressors of each outdoor unit are controlled to operate according to the corresponding initial operating frequency, and the electronic expansion valves of all operating outdoor units are controlled to operate according to the same initial valve opening V0; and in subsequent operation, the multi-connected system oil return process is adjusted periodically every 20s, thereby avoiding the uneven oil return of the multi-connected system.

[0068] In an embodiment, before the step of determining that the multi-connected system meets the oil return condition, the method further comprises: if the multi-connected system does not return oil for a first preset time length, determining that the multi-connected system meets the oil return condition; or if the number of outdoor units with an oil temperature not greater than a second preset oil temperature threshold in the multi-connected system reaches a preset number threshold, determining that the multi-connected system meets the oil return condition.

[0069] Preferably, the first preset time length is 8h, that is, when the multi-connected system has been operating continuously for 8h without oil return, it is determined that the multi-connected system meets the oil return condition and needs to be controlled for oil return. In addition, the oil return condition of the multi-connected system can also be determined according to the oil temperature. The second preset oil temperature threshold is preferably the high-pressure temperature+C°C, where C is preferably 15; and the preset number threshold is preferably 60%, that is, when the oil temperature of 60% or more of the operating outdoor units is ≤ the high-pressure temperature+C°C, it is determined that the multi-connected system meets the oil return condition and needs to be controlled for oil return. Therefore, by using the above two methods of determining whether the multi-connected system meets the oil return condition, when the multi-connected system meets one of the two methods, it is controlled for oil return, which facilitates timely oil return of the multi-connected system, thereby ensuring the reliability of the multi-connected system.

[0070] Embodiment Two

[0071] Based on the above method embodiment, the embodiment of the application provides another oil return control method applied to a multi-connected system, which comprises the following steps:

[0072] (1) When the multi-connected system has been operating continuously for 8h without oil return or the oil temperature of 60% or more of the operating outdoor units is ≤ the high-pressure temperature+C°C, the multi-connected system is controlled to enter an oil return mode;

[0073] (2) In the oil return mode, an initial valve opening and an initial oil temperature of each outdoor unit are obtained, an initial average oil temperature is calculated according to the initial oil temperatures of the multiple outdoor units and the number of units, and an average displacement Q is calculated according to the displacements of the multiple compressors and the number of units of the multiple outdoor units;

[0074] (3) According to the initial oil temperature of each outdoor unit, the initial average oil temperature, the displacement of the compressor of the outdoor unit, and the average displacement, the initial running frequency corresponding to the outdoor unit is calculated; the compressor of each outdoor unit is controlled to run according to the corresponding initial running frequency, and the electronic expansion valve of all outdoor units is controlled to run according to the initial valve opening degree;

[0075] (4) During operation, the oil temperature of each outdoor unit is obtained every 20s, and the average oil temperature of each cycle is calculated according to the oil temperatures of multiple outdoor units and the number of units;

[0076] (5) The target running frequency of each outdoor unit in each cycle is calculated; specifically, for the current cycle, for the outdoor unit with oil temperature T i <T n , the target running frequency P n of the compressor of the outdoor unit is P n-1 ; for the outdoor unit with oil temperature T i ≥T n , the target running frequency P n of the compressor of the outdoor unit is P n-1 +b*(T n / T i )*(Q / Q i ); and for the outdoor unit with oil temperature T i ≥D, the target valve opening degree V n of the electronic expansion valve of the outdoor unit is V n-1 , and for the outdoor unit with oil temperature T i <D, the target valve opening degree V n of the electronic expansion valve of the outdoor unit is V n-1 -c*(T n / T i )*(Q / Q i ); and the compressor of each outdoor unit is controlled to run according to the target running frequency P n , and the electronic expansion valve is controlled to run according to the target valve opening degree V n ;

[0077] (6) When the time length of the oil return mode reaches 8min or the oil temperature of all outdoor units is ≥ the third oil temperature threshold, the multi-split system is controlled to exit the oil return mode.

[0078] For ease of understanding, an example is given here. The outdoor units in parallel installation and operation in the multi-split system are set to two, wherein the first compressor displacement in the first outdoor unit is 60, the second compressor displacement in the second outdoor unit is 80, when the multi-split system accumulatively runs for 8h without oil return, at this time, the oil temperature of the first outdoor unit is 55℃, the oil temperature of the second outdoor unit is 70℃, the corresponding initial average oil temperature is 62℃, the average displacement is 69, the initial running frequency corresponding to the first compressor is 62Hz, the initial running frequency corresponding to the second compressor is 61Hz, and the initial valve opening of the electronic expansion valve of the two outdoor units is 200pls.

[0079] The first compressor is controlled to run at 62Hz, the second compressor is controlled to run at 61Hz, and the electronic expansion valve of the first outdoor unit and the electronic expansion valve of the second outdoor unit are both controlled to run at 200pls. After running for a period of time, for example, 20s, at this time, the oil temperature of the first outdoor unit is 70℃, the oil temperature of the second outdoor unit is 75℃, the average oil temperature at this time is calculated to be 73℃, then the target running frequency corresponding to the first compressor is kept at 62Hz, the target running frequency corresponding to the second compressor is adjusted to 63Hz, and since the oil temperatures of the two outdoor units are both less than the first oil temperature threshold (55℃), the opening of the electronic expansion valve of the two outdoor units remains unchanged, i.e., still 200pls. The process is repeated until the oil temperatures of the two outdoor units are both greater than 90℃ and the oil return control is exited.

[0080] In summary, the oil return control method provided by the embodiment of the present application is different from the existing oil return method, by differentiating the control of the running frequency of the compressors of different outdoor units and the valve opening of the electronic expansion valve, the oil-rich problem of the small-displacement compressors in the multi-split system is prevented, the displacement of the compressor (the smaller the displacement of the compressor, the more difficult it is to discharge oil, and the more likely it is to be oil-rich, so the running frequency needs to be increased during oil return) and the oil amount of the outdoor unit (here, the oil amount is fed back through the oil temperature, the higher the oil temperature, the more oil the outdoor unit has, and the more oil needs to be discharged to the system, so the running frequency needs to be increased during oil return) are comprehensively considered for control, and are adjusted according to the displacement of the compressor and the oil amount of the system, for example, the running frequency of the small-displacement compressor is increased to increase the oil discharge rate thereof; and during the oil return process, when the oil temperature is low, the outdoor unit is short of oil, and the excess oil exists in the remaining outdoor units, at this time, the compressor of the outdoor unit keeps the last running frequency unchanged, and the running frequency of the compressor of the oil-rich outdoor unit is increased to increase the oil discharge rate thereof, so as to discharge as much excess oil as possible to the system, thereby ensuring that the outdoor unit is not short of oil, and ultimately ensuring that each outdoor unit in the multi-split system is not short of oil, thereby improving the problem of uneven oil return and improving the reliability of the multi-split system.

[0081] Embodiment three

[0082] Corresponding to the above method embodiments, the embodiments of the present application also provide an oil return control device applied to a multi-connected system; wherein the multi-connected system comprises a plurality of outdoor units, each of which comprises a compressor configured with a displacement and an electronic expansion valve. Figure 3 As shown in the figure, the device comprises an oil return entering module 31, an oil temperature obtaining module 32, a parameter calculating module 33 and a control running module 34; wherein the functions of each module are as follows:

[0083] The oil return entering module 31 is configured to control the multi-connected system to enter an oil return mode when the multi-connected system meets an oil return condition, and to calculate an average displacement according to the displacements of the plurality of compressors and the number of the plurality of outdoor units;

[0084] The oil temperature obtaining module 32 is configured to periodically obtain the oil temperature of each outdoor unit in the oil return mode, and to calculate an average oil temperature of each period according to the oil temperatures of the plurality of outdoor units and the number of the plurality of outdoor units;

[0085] The parameter calculating module 33 is configured to calculate, for each outdoor unit, a target parameter corresponding to the current period of the outdoor unit according to the oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement and a last running parameter of the outdoor unit in a last period; wherein the target parameter comprises a target running frequency and a target valve opening degree, and the last running parameter comprises a last running frequency and a last valve opening degree;

[0086] The control running module 34 is configured to control, in the current period, the compressor of each outdoor unit to run at the corresponding target running frequency and the electronic expansion valve of each outdoor unit to run at the corresponding target valve opening degree, so as to return oil to the multi-connected system until the multi-connected system exits the oil return mode.

[0087] The oil return control device provided by the embodiments of the present application adjusts the running frequency of the compressor and the opening degree of the electronic expansion valve during the oil return process of each outdoor unit based on the displacement of the compressor and the oil temperature, so as to control the oil return amount of each outdoor unit, improve the problem of uneven oil return and improve the reliability and running effect of the multi-connected system; meanwhile, the oil return control method can be implemented by using the existing multi-connected system, does not affect other functions of the multi-connected system and is convenient for popularization and implementation in actual application.

[0088] Preferably, the parameter calculation module 33 is further configured to: if the oil temperature of the outdoor unit is not less than the average oil temperature of the current cycle, calculate the target operating frequency of the outdoor unit in the current cycle based on the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement and average displacement of the compressor in the outdoor unit; or, if the oil temperature of the outdoor unit is less than the average oil temperature of the current cycle, use the previous operating frequency as the target operating frequency of the outdoor unit in the current cycle; if the oil temperature of the outdoor unit is not less than a preset first oil temperature threshold, use the previous valve opening as the target valve opening of the outdoor unit in the current cycle; or, if the oil temperature of the outdoor unit is less than the first oil temperature threshold, calculate the target valve opening of the outdoor unit in the current cycle based on the previous valve opening, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement and average displacement of the compressor in the outdoor unit.

[0089] Preferably, the above calculation of the target operating frequency of the outdoor unit in the current cycle based on the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement and average displacement of the compressor in the outdoor unit includes: For the i-th outdoor unit, its target operating frequency is calculated according to the following formula:

[0090] P n =P n-1 +b*(T n / T i )*(Q / Q i )

[0091] Among them, P n P represents the target operating frequency. n-1 T represents the previous operating frequency. n T represents the average oil temperature. i Q represents the oil temperature of the i-th outdoor unit, and Q represents the average displacement. i denoted by , b represents the displacement of the compressor of the i-th outdoor unit, b represents the first calculation coefficient, and n represents the current cycle.

[0092] Preferably, the calculation of the target valve opening of the outdoor unit in the current cycle based on the previous valve opening, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement and average displacement of the compressor in the outdoor unit includes: For the i-th outdoor unit, its target valve opening is calculated according to the following formula:

[0093] V n =V n-1 -c*(T n / T i )*(Q / Q i )

[0094] Among them, V n V represents the target valve opening. n-1 Indicates the opening degree of the previous valve, Tn represents an average oil temperature, T i represents an oil temperature of the i-th outdoor unit, Q represents an average displacement, Q i represents a displacement of the compressor of the i-th outdoor unit, c represents a second calculation coefficient, and n represents a current period.

[0095] Preferably, before the oil temperature obtaining module 32, the device further comprises: obtaining initial parameters when the multi-connected system enters the oil return mode; wherein the initial parameters include: an initial valve opening degree and an initial oil temperature of each outdoor unit; calculating an initial average oil temperature according to the initial oil temperatures of the multiple outdoor units and the number of units; calculating an initial running frequency corresponding to each outdoor unit according to the initial oil temperature of each outdoor unit, the initial average oil temperature, the displacement of the compressor of the outdoor unit, and the average displacement; and controlling the compressor of each outdoor unit to run at the corresponding initial running frequency, and controlling the electronic expansion valve to run at the initial valve opening degree.

[0096] Preferably, before the oil return entering module 31, the device further comprises: determining that the multi-connected system meets the oil return condition if the multi-connected system does not return oil for a first preset time length; or determining that the multi-connected system meets the oil return condition if the number of outdoor units with an oil temperature not greater than a preset second oil temperature threshold reaches a preset number threshold in the multi-connected system.

[0097] Preferably, the multi-connected system exits the oil return mode, comprising: controlling the multi-connected system to exit the oil return mode if the multi-connected system runs in the oil return mode for a second preset time length; or controlling the multi-connected system to exit the oil return mode if the oil temperatures of all outdoor units are not less than a preset third oil temperature threshold in the oil return mode.

[0098] The oil return control device provided by the embodiments of the present application has the same technical features as the oil return control method provided by the above embodiments, and can also solve the same technical problems and achieve the same technical effects.

[0099] The embodiments of the present application further provide a multi-connected system, comprising a processor and a memory, the memory storing machine executable instructions capable of being executed by the processor, and the processor executes the machine executable instructions to implement the above oil return control method.

[0100] Referring to Figure 4 As shown in the figure, the multi-connected system comprises a processor 100 and a memory 101, the memory 101 storing machine executable instructions capable of being executed by the processor 100, and the processor 100 executes the machine executable instructions to implement the above oil return control method.

[0101] Further, Figure 4The shown multi-connected system further comprises a bus 102 and a communication interface 103, through which the processor 100, the communication interface 103 and the memory 101 are connected.

[0102] The memory 101 can comprise a high-speed random access memory (RAM) and can further comprise a non-volatile memory, such as at least one disk memory. The communication connection between the system network element and at least one other network element is realized through at least one communication interface 103 (which can be wired or wireless), and the Internet, a wide area network, a local area network, a metropolitan area network, etc. can be used. The bus 102 can be an ISA (Industrial Standard Architecture) bus, a PCI (Peripheral Component Interconnect) bus or an EISA (Enhanced Industry Standard Architecture) bus, etc. The above-mentioned buses can be divided into address buses, data buses, control buses, etc. For the sake of representation, Figure 4 Only one bidirectional arrow is used in the figure to represent the buses, but this does not mean that there is only one bus or only one type of bus.

[0103] The processor 100 can be an integrated circuit chip with processing capability. In implementation process, each step of the above method can be completed by integrated logic circuit of hardware in the processor 100 or instruction in the form of software. The processor 100 described above can be a general processor, including a central processing unit (CPU), a network processor (NP), etc.; can also be a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component. Each method, step and logic block diagram disclosed in the embodiment of the present application can be implemented or executed. The general processor can be a microprocessor or the processor can also be any conventional processor. The steps of the method disclosed in combination with the embodiment of the present application can be directly embodied as a hardware code processor for execution, or a combination of hardware and software modules in the code processor for execution. The software module can be located in a random access memory, a flash memory, a read-only memory, a programmable read-only memory or an electrically erasable programmable memory, a register, etc. The storage medium in the art. The storage medium is located in the memory 101, and the processor 100 reads the information in the memory 101, and combines the hardware to complete the steps of the method of the above embodiment.

[0104] The embodiment also provides a machine readable storage medium, the machine readable storage medium stores machine executable instructions, when the machine executable instructions are called and executed by the processor, the machine executable instructions cause the processor to implement the above oil return control method.

[0105] The computer program product of the oil return control method, device and multi-split system provided by the embodiment includes a computer readable storage medium storing program codes, the instructions included in the program codes can be used to execute the method described in the foregoing method embodiment, and specific implementation can be referred to the method embodiment, and details are not described herein.

[0106] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system and device described above can refer to the corresponding process in the foregoing method embodiment, and details are not described herein.

[0107] In addition, in the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through intervening medium, can be internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0108] If the functions are realized in the form of software function units and sold or used as independent products, they can be stored in a nonvolatile computer readable storage medium executable by a processor. Based on this understanding, the technical solutions of the present application or the part of the prior art or the part of the technical solutions can be embodied in the form of software products. The computer software product is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disk and various program code storage media.

[0109] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0110] Finally, it should be noted that the above-described embodiments are merely specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit the present application, and the protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some technical features therein, within the technical scope disclosed by the present application. Such modifications, changes or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An oil return control method characterized by, The method is applied to a multi-connected system, wherein the multi-connected system comprises a plurality of outdoor units, each of the outdoor units comprising a compressor configured with a displacement and an electronic expansion valve; the method comprising: When the multi-connected system meets an oil return condition, controlling the multi-connected system to enter an oil return mode, and calculating an average displacement according to the displacements of the plurality of compressors and the number of units of the plurality of outdoor units; In the oil return mode, periodically acquiring an oil temperature of each of the outdoor units, and calculating an average oil temperature of each period according to the oil temperatures of the plurality of outdoor units and the number of units; For each of the outdoor units, calculating a target parameter corresponding to a current period of the outdoor unit according to an oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement, and a last operation parameter of the outdoor unit in a last period; wherein the target parameter comprises a target operation frequency and a target valve opening degree, and the last operation parameter comprises a last operation frequency and a last valve opening degree; In the current period, controlling the compressor of each of the outdoor units to operate at the corresponding target operation frequency, and controlling the electronic expansion valve of each of the outdoor units to operate at the corresponding target valve opening degree, so as to return oil to the multi-connected system until the multi-connected system exits the oil return mode.

2. The method of claim 1, wherein, The step of calculating, for each of the outdoor units, a target parameter corresponding to a current period of the outdoor unit according to an oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement, and a last operation parameter of the outdoor unit in a last period, comprises: If the oil temperature of the outdoor unit is not less than the average oil temperature of the current period, calculating the target operation frequency of the outdoor unit corresponding to the current period according to the last operation frequency, the average oil temperature of the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit, and the average displacement; or if the oil temperature of the outdoor unit is less than the average oil temperature of the current period, taking the last operation frequency as the target operation frequency of the outdoor unit corresponding to the current period; If the oil temperature of the outdoor unit is not less than a preset first oil temperature threshold, taking the last valve opening degree as the target valve opening degree of the outdoor unit corresponding to the current period; or if the oil temperature of the outdoor unit is less than the first oil temperature threshold, calculating the target valve opening degree of the outdoor unit corresponding to the current period according to the last valve opening degree, the average oil temperature of the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit, and the average displacement.

3. The method of claim 2, wherein, The step of calculating, for each of the outdoor units, a target parameter corresponding to a current period of the outdoor unit according to an oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement, and a last operation parameter of the outdoor unit in a last period, comprises: For the i th outdoor unit, the target operation frequency thereof is calculated according to the following formula: P n = P n-1 + b * (T n / T i ) * (Q / Q i ) wherein P n represents the target operating frequency, P n-1 represents the previous operating frequency, T n represents the average oil temperature, T i represents the oil temperature of the i-th outdoor unit, Q represents the average displacement, Q i represents the displacement of the compressor of the i-th outdoor unit, b represents a first calculation coefficient, and n represents the current period.

4. The method of claim 3, wherein, The step of calculating the target valve opening degree of the outdoor unit corresponding to the current period according to the last valve opening degree, the average oil temperature of the current period, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement comprises: For the i-th outdoor unit, the target valve opening degree thereof is calculated according to the following formula: V n = V n-1 -c*(T n / T i )*(Q / Q i ) wherein V n represents the target valve opening, V n-1 represents the previous valve opening, T n represents the average oil temperature, T i represents the oil temperature of the i-th outdoor unit, Q represents the average displacement, Q i represents the displacement of the compressor of the i-th outdoor unit, c represents a second calculation coefficient, and n represents the current period.

5. The method of claim 1, wherein, Before the step of periodically acquiring the oil temperature of each outdoor unit, the method further comprises: acquiring initial parameters when the multi-connected system enters the oil return mode; wherein the initial parameters comprise an initial valve opening degree and an initial oil temperature of each outdoor unit; calculating an initial average oil temperature according to the initial oil temperatures of the multiple outdoor units and the number of units; calculating an initial operating frequency corresponding to each outdoor unit according to the initial oil temperature of the outdoor unit, the initial average oil temperature, the displacement of the compressor in the outdoor unit and the average displacement; controlling the compressor of each outdoor unit to operate at the corresponding initial operating frequency and controlling the electronic expansion valve to operate at the initial valve opening degree.

6. The method of claim 1, wherein, Before the step of determining whether the multi-connected system meets the oil return condition, the method further comprises: determining that the multi-connected system meets the oil return condition if the multi-connected system does not return oil for a first preset time duration; or determining that the multi-connected system meets the oil return condition if the number of outdoor units with an oil temperature not greater than a preset second oil temperature threshold reaches a preset number threshold in the multi-connected system.

7. The method of claim 1, wherein, The step of the multi-connected system exiting the oil return mode comprises: controlling the multi-connected system to exit the oil return mode if the multi-connected system operates in the oil return mode for a second preset time duration; or controlling the multi-connected system to exit the oil return mode if the oil temperature of all the outdoor units is not less than a preset third oil temperature threshold in the oil return mode.

8. An oil return control device characterized by comprising: The device is applied to a multi-connected system; wherein the multi-connected system comprises multiple outdoor units, each of which comprises a compressor configured with a displacement and an electronic expansion valve; and the device comprises: an oil return entering module configured to control the multi-connected system to enter an oil return mode when the multi-connected system meets an oil return condition and to calculate an average displacement according to the displacements of multiple compressors and the number of units of multiple outdoor units; an oil temperature acquisition module configured to periodically acquire the oil temperature of each outdoor unit in the oil return mode and to calculate an average oil temperature of each period according to the oil temperatures of multiple outdoor units and the number of units; a parameter calculation module configured to calculate, for each outdoor unit, a target parameter corresponding to the current period of the outdoor unit according to the oil temperature of the outdoor unit in the current period, the average oil temperature of the current period, the displacement of the compressor in the outdoor unit, the average displacement and a last operating parameter of the outdoor unit in a last period; wherein the target parameter comprises a target operating frequency and a target valve opening degree, and the last operating parameter comprises a last operating frequency and a last valve opening degree. The control running module is configured to control the compressor of each outdoor unit to run at the corresponding target running frequency and the electronic expansion valve to run at the corresponding target valve opening degree in the current period, so as to perform oil return for the multi-connected air conditioning system until the multi-connected air conditioning system exits the oil return mode.

9. A multi-split system comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein, The processor implements the steps of the method of any one of claims 1-7 when executing the computer program.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, and the computer program is executed by the processor to perform the steps of the method of any one of claims 1-7.

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