Oil return control method and device and multi-split air conditioning system

Abstract

The invention provides an oil return control method and device and a multi-split air conditioning system. The method comprises the steps that in an oil return mode of the multi-split air conditioning system, the oil temperature of each outdoor unit is obtained periodically, and the average oil temperature of each period is obtained through calculation according to the oil temperatures of the outdoor units and the number of units; for each 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 a compressor in the outdoor unit, the average displacement and the previous operation parameter of the outdoor unit in the previous period, the corresponding target parameter of the outdoor unit in the current period is obtained through calculation; and in the current period, the compressor of each outdoor unit is controlled to operate according to the corresponding target operation frequency, and the electronic expansion valve is controlled to operate according to the corresponding target valve opening degree, so that oil return is conducted on the multi-split air conditioning system, and therefore the problem that oil return is not uniform is solved by adjusting the operation frequency of the compressor of each outdoor unit and the opening degree of the electronic expansion valve; and the reliability of the multi-split system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioning, and in particular to an oil return control method, a device and a multi-connected system. Background Art

[0002] At present, multiple outdoor units in the existing multi-split system are installed and operated in parallel. Due to the different durations of rotation operation (when operating at a low frequency, most of the oil is in the operating outdoor unit compressor and oil separator and cannot be discharged into the system, resulting in more oil stored in the outdoor unit. Different outdoor units or different compressors usually have lower energy requirements during rotation operation, that is, low-frequency operation, and the outdoor units in operation at this time store oil) or different compressor displacements (compressors with small displacements discharge less oil at the same frequency, and outdoor units with small displacements store oil when operating in parallel, which 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-split system, such as the compressor with a small displacement is rich in oil, and the compressor with a large displacement is short of oil, which affects the reliability of the multi-split system. Therefore, how to improve the uneven oil return in the multi-split system is an urgent problem to be solved. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide an oil return control method, device and multi-split system to alleviate the above-mentioned problems, improve the problem of uneven oil return, and improve the reliability and operation effect of the multi-split system.

[0004] In a first aspect, an embodiment of the present invention provides an oil return control method, which is applied to a multi-split system; wherein the multi-split system includes a plurality of outdoor units, each of which includes: a compressor configured with a displacement and an electronic expansion valve; the method includes: when the multi-split system meets the oil return condition, controlling the multi-split system to enter an oil return mode, and calculating an average displacement according to the displacement of a plurality of compressors and the number of units of a plurality of outdoor units; in the oil return mode, periodically obtaining the oil temperature of each outdoor unit, and calculating an average oil temperature of each cycle according to the oil temperature of the plurality of outdoor units and the number of units; for each outdoor unit, according to The target parameters corresponding to the outdoor unit in the current cycle are calculated based on the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameters of the outdoor unit in the previous cycle; wherein the target parameters include: target operating frequency and target valve opening, and the previous operating parameters include: previous operating frequency and previous valve opening; in the current cycle, the compressor of each outdoor unit is controlled to operate at the corresponding target operating frequency, and the electronic expansion valve is controlled to operate at the corresponding target valve opening, so as to return oil to the multi-split system until the multi-split system exits the oil return mode.

[0005] The above-mentioned oil return control method adjusts the compressor operating frequency and the opening of the electronic expansion valve during the oil return process of each outdoor unit based on the compressor displacement and 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 easy to promote and implement in practical applications.

[0006] Preferably, the step of calculating, for each outdoor unit, the target parameter corresponding to the outdoor unit in the current cycle according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameters of the outdoor unit in the previous cycle comprises: if the oil temperature of the outdoor unit is not less than the average oil temperature of the current cycle, calculating the target operating parameter corresponding to the outdoor unit in the current cycle according to the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement operation frequency; or, if the oil temperature of the outdoor unit is lower than the average oil temperature of the current cycle, the previous operation frequency is used as the target operation frequency corresponding to the outdoor unit in the current cycle; if the oil temperature of the outdoor unit is not lower than the preset first oil temperature threshold, the previous valve opening is used as the target valve opening corresponding to the outdoor unit in the current cycle; or, if the oil temperature of the outdoor unit is lower than the first oil temperature threshold, the target valve opening corresponding to the outdoor unit in the current cycle is calculated according to the previous valve opening, the average oil temperature of the current cycle, 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 corresponding to the outdoor unit in the current cycle according to the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement includes: for the i-th outdoor unit, calculating its target operating frequency according to the following formula:

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

[0009] Among them, P n Indicates the target operating frequency, P n-1 Indicates the last operating frequency, T n Indicates 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 the first calculation coefficient, and n represents the current cycle.

[0010] Preferably, the step of calculating the target valve opening of the outdoor unit in the current cycle according to the previous valve opening, the average oil temperature of the current cycle, 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 its target valve opening according to the following formula:

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

[0012] Among them, V n Indicates the target valve opening, V n-1 Indicates the previous valve opening, T n Indicates 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 cycle.

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

[0014] Preferably, before the above-mentioned step when the multi-split system meets the oil return condition, the method also includes: if the multi-split system continuously runs for a first preset time period without returning oil, it is determined that the multi-split system meets the oil return condition; or, if in the multi-split system, the number of outdoor units whose oil temperature is not greater than a preset second oil temperature threshold reaches a preset number threshold, it is determined that the multi-split system meets the oil return condition.

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

[0016] In a second aspect, an embodiment of the present invention further provides an oil return control device, which is applied to a multi-split system; wherein the multi-split system includes multiple outdoor units, and each outdoor unit includes: a compressor with a displacement and an electronic expansion valve; the device includes: an oil return entry module, which is used to control the multi-split system to enter an oil return mode when the multi-split system meets the oil return condition, and calculate the average displacement according to the displacement of multiple compressors and the number of units of multiple outdoor units; an oil temperature acquisition module, which is used to periodically acquire the oil temperature of each outdoor unit in the oil return mode, and calculate the average oil temperature of each cycle according to the oil temperature of multiple outdoor units and the number of units; a parameter calculation module, which is used to For each outdoor unit, the target parameters corresponding to the outdoor unit in the current cycle are calculated according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement and the previous operating parameters of the outdoor unit in the previous cycle; wherein the target parameters include: target operating frequency and target valve opening, and the previous operating parameters include: previous operating frequency and previous valve opening; a control operation module is used to control the compressor of each outdoor unit to operate according to the corresponding target operating frequency and the electronic expansion valve to operate according to the corresponding target valve opening in the current cycle, so as to return oil to the multi-split system until the multi-split system exits the oil return mode.

[0017] In a third aspect, an embodiment of the present invention further provides a multi-connection system, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method of the first aspect when executing the computer program.

[0018] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the method of the first aspect are executed.

[0019] The embodiments of the present invention bring the following beneficial effects:

[0020] An embodiment of the present invention provides an oil return control method, device and a multi-split system. When the multi-split system enters the oil return mode, the oil temperature of each outdoor unit is periodically obtained, and the average oil temperature of each cycle is calculated based on the oil temperatures of the multiple outdoor units and the number of units; for each outdoor unit, the target parameters corresponding to the outdoor unit in the current cycle are calculated based on the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement and the previous operating parameters of the outdoor unit in the previous cycle; in the current cycle, the compressor of each outdoor unit is controlled to operate according to the corresponding target operating frequency, and the electronic expansion valve is operated according to the corresponding target valve opening, so as to return oil to the multi-split system until the multi-split system exits the oil return mode. In the above control method, based on the compressor displacement and oil temperature, the compressor operating frequency and the opening of the electronic expansion valve in the oil return process of each outdoor unit are adjusted, so as to control the oil return amount of each outdoor unit, improve the problem of uneven oil return, and improve 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, with low operating difficulty, without affecting other functions of the multi-split system, and is easy to promote and implement in practical applications.

[0021] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description and the drawings.

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of the structure of a multi-connection system provided by an embodiment of the present invention;

[0025] Figure 2 A flow chart of an oil return control method provided by an embodiment of the present invention;

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

[0027] Figure 4A schematic diagram of the structure of another multi-connection system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0030] For the sake of convenience, a multi-split system including two outdoor units is used as an example. Figure 1 As shown, the first outdoor unit and the second outdoor unit 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 a first outdoor electronic expansion valve) 16 and a first oil return capillary 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 a second outdoor electronic expansion valve) 26 and a second oil return capillary 27; for the rest of the first outdoor unit and the second outdoor unit, specific reference can be made to the existing multi-split system, and the embodiments of the present invention will not be described in detail here. It should be noted that the arrows in the figure indicate the flow direction of the refrigerant in the outdoor unit during the oil return process of the multi-split system.

[0031] Among them, for each outdoor unit compressor, a displacement Q is also configured, where the displacement Q can be understood as an inherent attribute value of the compressor, which can be determined according to the model of the compressor and can be pre-stored in the controller. In practical applications, the displacement Q of the same model compressor is a fixed value. Therefore, for the first compressor 11 and the second compressor 21, their displacements may be the same or different, which is specifically determined according to the model of the compressor.

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

[0033] Embodiment 1

[0034] Based on the above multi-connected system, an embodiment of the present invention provides an oil return control method, such as Figure 2 As shown, the method comprises the following steps:

[0035] Step S202, when the multi-split system meets the oil return condition, the multi-split system is controlled to enter the oil return mode, and the average displacement is calculated according to the displacement of the multiple compressors and the number of units of the multiple outdoor units;

[0036] Specifically, during the operation of the multi-split system, if the multi-split system meets the oil return condition, the controller controls the multi-split system to switch from the operation mode to the oil return mode, and according to the displacement Q of each compressor in the multiple outdoor units, i The average displacement Q of the multi-split system is calculated by the number of units of multiple outdoor units. The controller can identify the number of units N of multiple outdoor units in the multi-split system by dialing the code, or 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 multiple outdoor units running in the multi-split system.

[0037] The average displacement Q is calculated according to the following formula: Q = 10^(∑lgQ i / N); where Q i represents the displacement of the compressor of the i-th outdoor unit, i = 1, 2, ..., N. In particular, when calculating the average displacement Q, after taking the logarithm, the overall value will drop by an order of magnitude, which is conducive to eliminating the impact of extreme values ​​on the overall, thereby improving the oil return control accuracy of the multi-split system.

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

[0039] Step S204, in the oil return mode, periodically obtain the oil temperature of each outdoor unit, and calculate the average oil temperature of each cycle according to the oil temperatures of 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 embodiment of the present invention periodically obtains the oil temperature of each outdoor unit at a preset interval. Here, the preset interval is preferably 20 seconds, that is, the oil return process of the multi-split system is adjusted every 20 seconds. The oil temperature is obtained by a temperature acquisition sensor or a temperature sensing package. In actual applications, the temperature sensor or oil temperature is set at the oil return capillary of each outdoor unit. For example, for Figure 1 In the multi-split system, in each cycle, the controller obtains the oil temperature of the first outdoor unit collected by the temperature sensor set at the first oil return capillary 17, and the oil temperature of the second outdoor unit collected by the temperature sensor set at the second oil return capillary 27.

[0041] For each cycle, after the controller obtains the oil temperatures of multiple outdoor units, it also calculates the average oil temperature T of each cycle based on the oil temperatures of multiple outdoor units and the number of units. The average oil temperature T is calculated according to the following formula: i / N); where 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, after taking the logarithm, the overall value will drop by an order of magnitude, which is conducive to eliminating the impact of extreme values ​​on the overall, thereby improving the oil return control accuracy of the multi-split system.

[0042] Step S206, for each outdoor unit, according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameters of the outdoor unit in the previous cycle, calculate the target parameters corresponding to the outdoor unit in the current cycle; wherein the target parameters include: target operating frequency and target valve opening;

[0043] In actual operation, since the operating frequency and displacement of the compressor in each outdoor unit may be the same or different, for each outdoor unit in each cycle, in order to avoid uneven oil return, it is necessary to adjust the operating frequency of the compressor and the valve opening of the electronic expansion valve of the outdoor unit.

[0044] Specifically, for the current cycle, the target parameters corresponding to the outdoor unit in the current cycle are calculated based on the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameters of the outdoor unit in the previous cycle. Among them, the target parameters include the target operating frequency of the compressor of the outdoor unit in the current cycle, and the target valve opening of the electronic expansion valve of the outdoor unit in the current cycle; similarly, the previous operating parameters include: the previous operating frequency and the previous valve opening; here, the previous operating frequency is the operating frequency of the compressor of the outdoor unit in the previous cycle, and the previous valve opening is the valve opening of the electronic expansion valve of the outdoor unit in the previous cycle.

[0045] Therefore, by differentially controlling the compressor operating frequency of different outdoor units and the valve opening of the electronic expansion valve, the return oil amount of each outdoor unit is adjusted to improve the problem of uneven oil return in 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 cycle, the compressor of each outdoor unit is controlled to operate according to the corresponding target operating frequency, and the electronic expansion valve is operated according to the corresponding target valve opening to return oil to the multi-split system until the multi-split system exits the oil return mode.

[0047] Specifically, for each outdoor unit, its compressor is controlled to operate according to the target operating frequency corresponding to the current cycle, and its electronic expansion valve is controlled to operate according to the target valve opening corresponding to the current cycle, so that the return oil amount of the outdoor unit can be controlled through the joint adjustment of the compressor and the electronic expansion valve, and then the problem of uneven oil return is improved through 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, 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 the preset third oil temperature threshold, that is, 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. The third oil temperature threshold is preferably 90°C, which can be adjusted adaptively according to actual conditions.

[0049] The oil return control method provided in the embodiment of the present invention adjusts the compressor operating frequency and the opening of the electronic expansion valve in the oil return process of each outdoor unit 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; 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 easy to promote and implement in practical applications.

[0050] In one embodiment, for each outdoor unit, the process of calculating the target parameters corresponding to the outdoor unit in the current cycle according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameters of the outdoor unit in the previous cycle includes a process of calculating the target operating frequency and a process of calculating 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 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 cycle, the previous operating frequency is used as the target operating frequency of the outdoor unit in the current cycle;

[0052] Specifically, in the current cycle, the average oil temperature of the current cycle is set to T n , for the i-th outdoor unit, if its oil temperature T i <T n , then the previous operating frequency P n-1 As the target operating frequency P of the outdoor unit corresponding to the current cycle n , that is, P n =P n-1 On the contrary, if the oil temperature T i ≥T n , the target operating frequency of the outdoor unit in the current cycle is calculated according to the previous operating frequency, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement.

[0053] Among them, 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 Indicates the target operating frequency, P n-1 Indicates the last operating frequency, T n Indicates 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 the first calculation coefficient, preferably 0.5, and n represents the current cycle. It should be noted that the above target frequency P n Not exceeding the maximum operating frequency P of the compressormax , that is, P n ≤P max .

[0056] (2) If the oil temperature of the outdoor unit is not less than a preset first oil temperature threshold, the previous valve opening is used as the target valve opening corresponding to the outdoor unit in the current cycle; or, if the oil temperature of the outdoor unit is less than the first oil temperature threshold, the target valve opening corresponding to the outdoor unit in the current cycle is calculated based on the previous valve opening, the average oil temperature of the current cycle, 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 cycle, the average oil temperature of the current cycle is set to T n For the i-th outdoor unit, if its oil temperature is not less than the first oil temperature threshold D, that is, T i ≥D, then the previous valve opening V n-1 As the target valve opening V corresponding to the current cycle of the outdoor unit n On the contrary, if the oil temperature is less than the first oil temperature threshold D, that is, T i <D, then the target valve opening corresponding to the outdoor unit in the current cycle is calculated according to the previous valve opening, the average oil temperature of the current cycle, 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 method, the length of the oil return capillary, etc., and can be determined by experiments. In the embodiment of the present invention, it is preferably 55°C.

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

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

[0060] Among them, V n Indicates the target valve opening, V n-1 Indicates the previous valve opening, T n Indicates 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 cycle. It should be noted that the above target valve opening V n It should not be lower than the minimum valve opening Vmin of the electronic expansion valve, that is, V n ≥Vmin.

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

[0062] In one embodiment, before the above-mentioned step of periodically obtaining the oil temperature of each outdoor unit, the method also includes: obtaining initial parameters when the multi-split system enters the oil return mode; wherein the initial parameters include: an initial valve opening and an initial oil temperature of each outdoor unit; calculating an initial average oil temperature based on the initial oil temperatures of multiple outdoor units and the number of units; calculating an initial operating frequency corresponding to the outdoor unit based on 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; 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.

[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 V0 and the initial oil temperature of each outdoor unit at this time are obtained, and the initial average oil temperature is calculated based on the initial oil temperatures of multiple outdoor units and the number of units. At this time, the initial operating frequency corresponding to the outdoor unit is calculated based on 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.

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

[0065] P 1 =A+a*(T 1 / T i0 )*(Q / Q i ) (3)

[0066] Among them, P 1 Indicates the initial operating frequency, T 1 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 the second calculation coefficient, preferably 1.3, A represents the third calculation coefficient, which is related to the oil discharge characteristics, oil return method, and oil return capillary length of the compressor itself, and can be determined through experiments, and is preferably 60. It should be noted that the above initial valve opening V0 is related to the oil discharge characteristics, oil return method, and oil return capillary length of the compressor itself, and can be determined through experiments, and is preferably 200 pls.

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

[0068] In one embodiment, before the above-mentioned step when the multi-split system meets the oil return condition, the method also includes: if the multi-split system continuously runs for a first preset time period without returning oil, it is determined that the multi-split system meets the oil return condition; or, if in the multi-split system, the number of outdoor units whose oil temperature is not greater than a preset second oil temperature threshold reaches a preset number threshold, it is determined that the multi-split system meets the oil return condition.

[0069] Among them, the first preset time is preferably 8h, that is, when the multi-split system starts running, if it has been running for 8 hours without oil return, it is determined that the multi-split system meets the oil return condition, and the multi-split system needs to be controlled for oil return. In addition, it is also possible to judge whether the multi-split system meets the oil return condition based on the oil temperature. The above-mentioned second oil temperature threshold is preferably the high pressure temperature + C℃, where C is preferably 15; the above-mentioned preset quantity threshold is preferably 60%, that is, when the oil temperature of more than 60% of the outdoor units in operation is ≤ high pressure temperature + C℃, it is determined that the multi-split system meets the oil return condition, and the multi-split system needs to be controlled for oil return. Therefore, through the above two methods of judging whether the multi-split system meets the oil return condition, when the multi-split system meets one of the judgment methods, the multi-split system is controlled for oil return, which is convenient for timely oil return of the multi-split system, thereby ensuring the reliability of the multi-split system.

[0070] Embodiment 2

[0071] Based on the above method embodiment, the embodiment of the present invention provides another oil return control method, which is applied to a multi-split system. The method includes the following steps:

[0072] (1) When the multi-split system has been running for 8 hours without oil return or the oil temperature of more than 60% of the outdoor units in operation is ≤ high pressure temperature + C℃, the multi-split system is controlled to enter the oil return mode;

[0073] (2) in the oil return mode, obtaining an initial valve opening and an initial oil temperature of each outdoor unit, and calculating an initial average oil temperature according to the initial oil temperatures of the multiple outdoor units and the number of units, and calculating an average displacement Q according to the displacement of the multiple compressors and the number of units of the multiple outdoor units;

[0074] (3) calculating the initial operating frequency corresponding to each outdoor unit according to the initial oil temperature, 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 according to the corresponding initial operating frequency, and controlling the electronic expansion valves of all outdoor units to operate according to the initial valve opening;

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

[0076] (5) Calculate the target operating frequency of each outdoor unit in each cycle; specifically, for the current cycle, for the oil temperature T i <T n The target operating frequency of the compressor of the outdoor unit is P n =P n-1 ; For oil temperature T i ≥T n The target operating frequency of the compressor of the outdoor unit is P n =P n-1 +b*(T n / T i )*(Q / Q i ); and, for oil temperature T i ≥D outdoor unit, the target valve opening of the electronic expansion valve is V n =V n-1 , for oil temperature T i The target valve opening degree V of the electronic expansion valve of the outdoor unit with a value less than D n =V n-1 -c*(T n / T i )*(Q / Q i ) and control the compressor of each outdoor unit to operate at the target frequency P n Operation, the electronic expansion valve opens according to the target valve opening V n run;

[0077] (6) When the oil return mode runs for 8 minutes or the oil temperatures of all outdoor units are ≥ 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. There are two outdoor units installed and running in parallel in the multi-split system, where the displacement of the first compressor in the first outdoor unit is 60, and the displacement of the second compressor in the second outdoor unit is 80. When the multi-split system has been running for 8 hours without oil return, the oil temperature of the first outdoor unit is 55°C, and the oil temperature of the second outdoor unit is 70°C. The corresponding initial average oil temperature is 62°C, the average displacement is 69, the initial operating frequency of the first compressor is 62Hz, and the initial operating frequency of the second compressor is 61Hz. The initial valve opening of the electronic expansion valves 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, such as 20s, at this time, the oil temperature of the first outdoor unit is 70℃, and 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 operating frequency corresponding to the first compressor is maintained at 62Hz, and the target operating frequency corresponding to the second compressor is adjusted to 63Hz. Moreover, since the oil temperatures of the two outdoor units are both lower than the first oil temperature threshold (55℃), the opening of the electronic expansion valves of the two outdoor units remains unchanged, that is, it is still 200pls. Repeat this process until the oil temperatures of the two outdoor units are both greater than 90℃ to exit the oil return control.

[0080] In summary, the oil return control method provided in the embodiment of the present invention is different from the existing oil return method. It prevents the small-displacement compressor in the multi-split system from being oil-rich by differentially controlling the compressor operating frequency and the valve opening of the electronic expansion valve of different outdoor units. It comprehensively considers the displacement of the compressor (the smaller the compressor displacement, the more difficult it is to discharge the oil and the more likely it is to be oil-rich, so the operating frequency needs to be increased during oil return) and the oil volume of the outdoor unit (the oil volume here is fed back through the oil temperature. The higher the oil temperature, the more oil volume the outdoor unit has, and the excess oil needs to be discharged to the system. Therefore, the operating frequency needs to be increased during oil return) to perform control, and controls the compressor according to the compressor displacement. The oil volume and system oil volume are adjusted, such as increasing the operating frequency of the small-displacement compressor to increase its oil discharge rate; and, during the oil return process, when the oil temperature is low, the outdoor unit is short of oil, and excess oil exists in the other outdoor units. At this time, the compressor of the outdoor unit maintains the previous operating frequency unchanged, and increases the operating frequency of the compressor of the oil-rich outdoor unit to improve its oil discharge rate, and discharges the excess oil into the system as much as possible, so that the oil-short outdoor unit is not short of oil, and finally all outdoor units in the multi-split system are not short of oil, which improves the problem of uneven oil return and improves the reliability of the multi-split system.

[0081] Embodiment 3

[0082] Corresponding to the above method embodiment, the embodiment of the present invention further provides an oil return control device, which is applied to a multi-split system; wherein the multi-split system includes multiple outdoor units, each of which includes: a compressor with a displacement and an electronic expansion valve. Figure 3 As shown, the device includes: an oil return entry module 31, an oil temperature acquisition module 32, a parameter calculation module 33 and a control operation module 34; wherein the functions of each module are as follows:

[0083] The oil return entry module 31 is used to control the multi-split system to enter the oil return mode when the multi-split system meets the oil return condition, and calculate the average displacement according to the displacement of multiple compressors and the number of units of multiple outdoor units;

[0084] The oil temperature acquisition module 32 is used to periodically acquire the oil temperature of each outdoor unit in the oil return mode, and calculate the average oil temperature of each cycle according to the oil temperatures of multiple outdoor units and the number of units;

[0085] The parameter calculation module 33 is used to calculate the target parameters corresponding to the outdoor unit in the current cycle for each outdoor unit according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operation parameters of the outdoor unit in the previous cycle; wherein the target parameters include: target operation frequency and target valve opening, and the previous operation parameters include: previous operation frequency and previous valve opening;

[0086] The control operation module 34 is used to control the compressor of each outdoor unit to operate according to the corresponding target operating frequency and the electronic expansion valve to operate according to the corresponding target valve opening in the current cycle to return oil to the multi-split system until the multi-split system exits the oil return mode.

[0087] The oil return control device provided in the embodiment of the present invention adjusts the compressor operating frequency and the opening of the electronic expansion valve in the oil return process of each outdoor unit 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; 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 easy to promote and implement in practical applications.

[0088] Preferably, the parameter calculation module 33 is also used for: 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 corresponding to the current cycle is calculated according to the previous operating frequency, the average oil temperature of the current cycle, 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 cycle, the previous operating frequency is used as the target operating frequency corresponding to the outdoor unit in the current cycle; if the oil temperature of the outdoor unit is not less than the preset first oil temperature threshold, the previous valve opening is used as the target valve opening corresponding to the outdoor unit in the current cycle; or, if the oil temperature of the outdoor unit is less than the first oil temperature threshold, the target valve opening corresponding to the outdoor unit in the current cycle is calculated according to the previous valve opening, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement.

[0089] Preferably, the target operating frequency corresponding to 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 of the compressor in the outdoor unit, and the average displacement, including: 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 Indicates the target operating frequency, P n-1 Indicates the last operating frequency, T n Indicates 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 the first calculation coefficient, and n represents the current cycle.

[0092] Preferably, the target valve opening corresponding to the outdoor unit in the current cycle is calculated based on the previous valve opening, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement, including: for the i-th outdoor unit, the 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 Indicates the target valve opening, V n-1 Indicates the previous valve opening, Tn Indicates 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 cycle.

[0095] Preferably, before the above-mentioned oil temperature acquisition module 32, the device also includes: acquiring initial parameters when the multi-split system enters the oil return mode; wherein the initial parameters include: initial valve opening and initial oil temperature of each outdoor unit; calculating the initial average oil temperature according to the initial oil temperatures of multiple outdoor units and the number of units; calculating the initial operating frequency corresponding to the 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; controlling the compressor of each outdoor unit to operate according to the corresponding initial operating frequency, and the electronic expansion valve to operate according to the initial valve opening.

[0096] Preferably, before the above-mentioned oil return enters the module 31, the device also includes: if the multi-split system runs continuously for a first preset time period without returning oil, it is determined that the multi-split system meets the oil return condition; or, if in the multi-split system, the number of outdoor units whose oil temperature is not greater than the preset second oil temperature threshold reaches a preset number threshold, it is determined that the multi-split system meets the oil return condition.

[0097] Preferably, the above-mentioned multi-split system exits the oil return mode, including: if the duration of the multi-split system operating in the oil return mode reaches a second preset duration, controlling the multi-split system to exit the oil return mode; or, in the oil return mode, if the oil temperatures of all outdoor units are not less than a preset third oil temperature threshold, controlling the multi-split system to exit the oil return mode.

[0098] The oil return control device provided in the embodiment of the present invention has the same technical features as the oil return control method provided in the above embodiment, so it can also solve the same technical problems and achieve the same technical effects.

[0099] An embodiment of the present invention further provides a multi-connected system, including a processor and a memory, wherein the memory stores machine executable instructions that can be executed by the processor, and the processor executes the machine executable instructions to implement the above-mentioned oil return control method.

[0100] See also Figure 4 As shown, the multi-split system includes a processor 100 and a memory 101. The memory 101 stores machine executable instructions that can be executed by the processor 100. The processor 100 executes the machine executable instructions to implement the above oil return control method.

[0101] Further, Figure 4The multi-connection system shown also includes a bus 102 and a communication interface 103 , and the processor 100 , the communication interface 103 and the memory 101 are connected via the bus 102 .

[0102] Among them, the memory 101 may include a high-speed random access memory (RAM), and may also include a non-volatile memory (non-volatile memory), such as at least one disk storage. 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, wide area network, local area network, 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 bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Figure 4 Only one bidirectional arrow is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0103] The processor 100 may be an integrated circuit chip with signal processing capabilities. In the implementation process, each step of the above method can be completed by the hardware integrated logic circuit or software instructions in the processor 100. The above processor 100 can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The methods, steps and logic block diagrams disclosed in the embodiments of the present invention can be implemented or executed. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The steps of the method disclosed in conjunction with the embodiments of the present invention can be directly embodied as a hardware decoding processor for execution, or a combination of hardware and software modules in the decoding processor for execution. The software module may be located in a storage medium mature in the art, such as 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 is located in the memory 101, and the processor 100 reads the information in the memory 101 and completes the steps of the method of the above embodiment in combination with its hardware.

[0104] This embodiment further provides a machine-readable storage medium, which stores machine-executable instructions. When the machine-executable instructions are called and executed by a processor, the machine-executable instructions prompt the processor to implement the above-mentioned oil return control method.

[0105] The oil return control method, device and computer program product of the multi-split system provided in the embodiments of the present invention include a computer-readable storage medium storing program code. The instructions included in the program code can be used to execute the methods described in the previous method embodiments. The specific implementation can be found in the method embodiments and will not be repeated here.

[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 aforementioned method embodiment, and will not be repeated here.

[0107] In addition, in the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0108] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a non-volatile computer-readable storage medium that is executable by a processor. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0109] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0110] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention is described in detail with reference to the above-described embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the above-described embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An oil return control method, characterized in that: Applied to a multi-split system; wherein the multi-split system includes a plurality of outdoor units, each of which includes: a compressor configured with a displacement and an electronic expansion valve; the method includes: When the multi-split system meets the oil return condition, the multi-split system is controlled to enter the oil return mode, and the average displacement is calculated according to the displacement of the plurality of compressors and the number of units of the plurality of outdoor units; In the oil return mode, the oil temperature of each outdoor unit is periodically obtained, and the average oil temperature of each cycle is calculated based on the oil temperatures of the plurality of outdoor units and the number of units; For each of the outdoor units, the target parameters corresponding to the outdoor unit in the current cycle are calculated according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameters of the outdoor unit in the previous cycle; wherein the target parameters include: a target operating frequency and a target valve opening, and the previous operating parameters include: a previous operating frequency and a previous valve opening; In the current cycle, the compressor of each outdoor unit is controlled to operate according to the corresponding target operating frequency, and the electronic expansion valve is controlled to operate according to the corresponding target valve opening to return oil to the multi-split system until the multi-split system exits the oil return mode.

2. The method according to claim 1, characterized in that The step of calculating, for each of the outdoor units, a target parameter corresponding to the outdoor unit in the current cycle according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement, and the previous operating parameter of the outdoor unit in the previous cycle, comprises: 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 according to the previous operating frequency, the average oil temperature of the current cycle, 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 cycle, the previous operating frequency is used 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, the previous valve opening is used as the target valve opening corresponding to the outdoor unit in the current cycle; or, if the oil temperature of the outdoor unit is less than the first oil temperature threshold, the target valve opening corresponding to the outdoor unit in the current cycle is calculated based on the previous valve opening, the average oil temperature of the current cycle, the oil temperature of the outdoor unit, the displacement of the compressor in the outdoor unit and the average displacement.

3. The method according to claim 2, characterized in that The step of calculating the target operating frequency corresponding to the outdoor unit in the current cycle according to the previous operating frequency, the average oil temperature of the current cycle, 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, its target operating frequency is calculated according to the following formula: P n =P n-1 +b*(T n / T i )*(Q / Q i ) Among them, P n represents the target operating frequency, P n-1 Indicates 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 the first calculation coefficient, and n represents the current cycle.

4. The method according to claim 3, characterized in that The step of calculating the target valve opening corresponding to the outdoor unit in the current cycle according to the previous valve opening, the average oil temperature of the current cycle, 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, its target valve opening is calculated according to the following formula: V n =V n-1 -c*(T n / T i )*(Q / Q i ) Among them, V n represents the target valve opening, V n-1 Indicates 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 the second calculation coefficient, and n represents the current cycle.

5. The method according to claim 1, characterized in that Before the step of periodically obtaining the oil temperature of each outdoor unit, the method further includes: Acquire initial parameters when the multi-split system enters the oil return mode; wherein the initial parameters include: initial valve opening and initial oil temperature of each outdoor unit; Calculate the initial average oil temperature according to the initial oil temperatures of the plurality of outdoor units and the number of units; Calculating the 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; The compressor of each outdoor unit is controlled to operate according to the corresponding initial operating frequency, and the electronic expansion valve is controlled to operate according to the initial valve opening.

6. The method according to claim 1, characterized in that Before the step of when the multi-connected system meets the oil return condition, the method further includes: If the multi-split system runs continuously for a first preset time without returning oil, it is determined that the multi-split system meets the oil return condition; or, If, in the multi-split system, the number of outdoor units whose oil temperature is not greater than the preset second oil temperature threshold reaches a preset number threshold, it is determined that the multi-split system meets the oil return condition.

7. The method according to claim 1, characterized in that The step of the multi-connected system exiting the oil return mode comprises: If the duration of the multi-split system operating in the oil return mode reaches a second preset duration, controlling the multi-split system to exit the oil return mode; or, In the oil return mode, if the oil temperatures of all the outdoor units are not less than a preset third oil temperature threshold, the multi-split system is controlled to exit the oil return mode.

8. An oil return control device, characterized in that: Applied to a multi-split system; wherein the multi-split system includes a plurality of outdoor units, each of which includes: a compressor with a displacement and an electronic expansion valve; the device includes: An oil return entry module, used for controlling the multi-split system to enter an oil return mode when the multi-split system meets the oil return condition, and calculating an average displacement according to the displacement of the plurality of compressors and the number of units of the plurality of outdoor units; An oil temperature acquisition module, used for periodically acquiring the oil temperature of each outdoor unit in the oil return mode, and calculating the average oil temperature of each cycle according to the oil temperatures of the plurality of outdoor units and the number of units; A parameter calculation module, for each of the outdoor units, according to the oil temperature of the outdoor unit in the current cycle, the average oil temperature of the current cycle, the displacement of the compressor in the outdoor unit, the average displacement and the last operating parameter of the outdoor unit in the last cycle, calculates the target parameter corresponding to the outdoor unit in the current cycle; wherein the target parameter includes: a target operating frequency and a target valve opening, and the last operating parameter includes: a last operating frequency and a last valve opening; The control operation module is used to control the compressor of each outdoor unit to operate according to the corresponding target operating frequency and the electronic expansion valve to operate according to the corresponding target valve opening in the current cycle, so as to return oil to the multi-split system until the multi-split system exits the oil return mode.

9. A multi-connection system, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

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

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